30-day unplanned readmission rate in otolaryngology patients: A population-based study in Thuringia, Germany.

PURPOSE: Analyze associations between patients' characteristics and treatment factors with 30-day unplanned readmissions in hospitalized otolaryngology patients in the German Diagnosis Related Group (D-DRG) system.
METHODS: A retrospective cohort study was performed on 15.271 otolaryngology admissions of 12.859 patients in 2015 in Thuringia, Germany. The medical records of the 1173 cases (7.6%) with readmission within 30-days were analyzed in detail.
RESULTS: The 30-day readmission was planned in 747 cases (4.9%) and was unplanned in 422 cases (2.8%). The median interval between primary and next inpatient treatment was 11 days. The principal diagnosis was the same as during the primary index treatment in 72% of the cases. The most frequent reasons for readmission were: Need for non-surgical therapy (31.2%), need for further surgery (26.3%), post-surgical complaints (16.9%), and recurrence of primary complaints (10.7%). The multivariate analysis revealed that discharge due to patient's request against medical advice was a strong independent factor with high risk for unplanned readmission (Odds Ratio [OR] = 9.62]; confidence interval [CI] = 2.69-34.48). Surgery at index admission (OR = 3.33; CI = 1.86-5.96) was the second important independent risk factor for unplanned readmission. Unplanned readmission had more frequently a non-surgical treatment at readmission than a surgical treatment (OR = 3.92; CI = 2.24-6.84) and needed more frequently further diagnostics (OR = 2.34; CI = 1.34-4.11). The following index International Classification of Diseases (ICD) categories had the highest risk for unplanned readmission: Injury, poisoning and certain other consequences of external causes, ICD: S00-T98 (OR = 66.67; CI = 15.87-333.33), symptoms, signs, abnormal findings, ill-defined causes, not otherwise classified, ICD: R00-R99 (OR = 62.5; CI = 11.76-333.33), blood forming organ diseases, ICD: D50-D90 (OR = 21.276; CI = 3.508-125), and eye/ ear diseases, ICD: H00-H95 (OR = 12.66; CI = 4.29-37.03).
CONCLUSIONS: The causes of unplanned 30-day readmission in German otolaryngology inpatients are multifactorial. Specific patient and treatment characteristics were identified to be targeted with health care interventions to decrease unplanned readmissions.

Introduction

Unplanned hospital readmissions are an outcome measure in health services research as metric for health care quality and are costly [1]. Potentially avoidable readmissions can be the consequence of an adverse event or a too early discharge of a prior hospitalization [2]. One of the most widely used tools for reimbursing inpatient health services around the world is Diagnosis-Related Groups (DRGs) [3]. The risks of early discharge in order to cut costs have been well documented ever since DRG systems were first introduced [4]. Therefore, instruments were applied to include hospital readmission rates in reimbursement decisions. In the United States, for instance, the Hospital Readmission Reduction program (HRRP), a Medicare value-based purchasing program was introduced with the aim to reduce payments to hospitals with excess readmissions [5]. In the German DRG (G-DRG) system, readmissions for the same cause within 30 days after discharge are reimbursed by the original DRG and receive no additional funds. This approach financially penalizes inappropriate early discharge (at least if it leads to readmission) [4].

These two programs as many others use a time frame within 30 days of discharge, i.e. the 30-day readmission rate as a parameter because it is said that readmissions during this time can be influenced by the quality of care received at the hospital and how well discharges were coordinated. Later readmissions may not be related to the primary (index) inpatient care. Later readmissions might be more related to the outpatient care the patient receives. Other later influencing factors might be individual health choices and behaviors, and community-level factors beyond the control of the hospital that treated the patient first.

Only a few studies, which are mainly based on the experience in a single hospital, have been performed to analyze risk factors for unplanned hospital readmission in otolaryngology patients [6-8]. A larger population-based analysis has only be performed for head and neck cancer surgery cases using the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database [9]. Population-based analyses for non-surgical otolaryngology inpatients and any data for Germany are lacking so far.

Thuringia is a territorial state in Germany with approximately 2.2 million habitants. There are only eight hospitals with departments of otolaryngology. The departments of otolaryngology have built a network primarily to improve health services research in the field of otolaryngology (for instance, [10-13]). Use of this network provided an ideal platform for a population-based analysis of the 30-day readmission rates of unselected otolaryngology inpatients treated in 2015 in Thuringia in daily practice with focus on unplanned readmissions and its predictors.

Material and methods

A standardized retrospective analysis was performed in seven Thuringian hospitals that have a department of otolaryngology (the eighth hospital did not take part). These seven hospitals cover about 90% of all inpatient otolaryngology cases in Thuringia. The institutional ethics committee (Ethics Committee of the University Hospital Jena, Germany) approved the study protocol. The ethics committee waived the requirement for informed consent for the patients with exclusive retrospective data analysis using the patients’ charts.

All otolaryngology patients with inpatient treatment in 2015 were included. Outpatients and day-care patients were excluded. The patients were identified via the hospital information systems of the seven participating hospitals. As part of the G-DRG system and according to the Section 21 Hospital Remuneration Act (Krankenhausentgeltgesetz; KHEntgG), the hospitals have to prepare standardized datasets on patients’ characteristics including Patient Clinical Complexity (PCCL) coding, International Statistical Classification Of Diseases And Related Health Problems, 10th revision, German Modification coding (ICD-10-GM), and German Operations and Procedures Key (OPS) coding. The patient ID was used to identify all patients with readmission within 30 days. These patients built the group of primary interest (readmission group). The other patients built the group of patients without 30-day readmission (no readmission group). To characterize the readmission group in more detail, and especially to identify the patients with planned versus unplanned readmission, the patients’ charts of all patients with 30-day readmission were revisited. A planned readmission was defined as a readmission that was planned during the index admission. For instance, a patient with head and neck cancer had his index admission for staging and panendoscopy. Typically, if surgery was planned for definitive treatment, the day of readmission already was scheduled before demission. All other patients without planned readmission were defined as unplanned readmissions, for instance when a patient was readmitted for a complication after surgery.

The primary aim of the subsequent evaluation was to analyze associations between patients’ characteristics and treatment factors with 30-day unplanned readmissions in hospitalized otolaryngology patients in the German Diagnosis Related Group (D-DRG) system. The G-DRG system already includes instruments to avoid early readmission, especially by sanctioning the reimbursement. We hypothesized that, nevertheless, specific otolaryngology diseases and type of treatment as well as patients’ comorbidity have influence on the risk of 30-day unplanned readmission.

Statistical analysis

Patient demographics and outcome variables were analyzed with IBM SPSS statistics software (IBM Corp, released 2017, IBM SPSS Statistics for Windows, Version 25.0. Armonk, New York). Data are presented as frequencies or mean ± standard deviation (SD) if not otherwise indicated. To compare the no readmission group with the readmission group and to compare the planned readmission subgroup with the unplanned readmission subgroup, ordinal and nominal data were compared with the chi-square test. Scaled data were compared with the non-parametric Mann-Whitney U-test. The significance level was set at p < 0.05. Factors with significant differences between groups were included in the multivariate analysis: Binary logistic regression analysis was used to determine independent factors for 30-day readmission and for unplanned readmission.

Results

Comparison of patients without and with 30-day readmission

15271 inpatient cases of 12859 different patients were registered in 2015. 12925 cases had no 30-day readmission. The remaining 2346 cases equally consisted of 1173 primary cases and the 1173 related cases of 30-day readmission. An overview about all patients is given in The localizations of the diseases and the hundred most frequent ICD codes are presented in and , respectively. The univariate comparison between patients without and with 30-day readmission is summarized in . Patients with readmission were older (p<0.001) and more frequently male (p<0.001). The primary inpatient treatment was longer in readmitted patients and these patients were treated in hospitals with higher volume (p<0.001, respectively). Patients with malignant disease had a higher risk of readmission (p<0.001). Patients with higher PCCL and higher comorbidity had a higher risk of readmission (p<0.001, respectively). Non-surgical cases had a higher risk of readmission than surgical cases (p<0.001).

According to the multivariate analysis () a patient with malignant disease had the highest risk of readmission (Odds ratio [OR] = 5.56; confidence interval [CI] = 4.35–7.14) followed by patients with high PCCL (OR = 2.05; CI = 1.65–2.54). Other relevant independent risk factors were male gender (OR = 1.20; CI = 1.01–1.41), higher number of secondary diagnoses (CI = 1.03; CI = 1.01–1.04), a non-surgical treatment (OR = 1.40; CI = 1.18–2.54), and a treatment in a hospital with higher volume (OR = 1.43; CI = 1.20–1.69).

Comparison of patients with planned and unplanned 30-day readmission

1173 cases of 30-day readmission occurred, i.e. the 30-day readmission rate was 7.6%. The 30-day readmission rate for surgical cases only was 6.5%. Reasons for 30-day readmission were in descending order: Need for non-surgical therapy (31.2%), need for further surgery (26.3%), post-surgical complaints (16.9%), recurrence of primary complaints (10.7%), other complaints (9.9%), need for further diagnostics (4.7%), and reason unknown (0.2%). The principal diagnosis was the same as during the primary treatment in 72% of the cases. 37 cases were released from the hospital during the primary treatment earlier than planned against medical advice at the patient’s request. The 30-day readmission was planned in 747 cases (4.9%) and was unplanned in 422 cases (2.8%). Primary localization of the disease of the planned and unplanned readmissions is shown in . The oral cavity and the pharynx were the localization with the highest number of planned and unplanned 30-day readmissions. The absolute number of planned readmissions was also high in descending order for the localizations larynx/thyroid, neck, ear and face. The absolute number of unplanned readmission was higher than planned readmission in descending order for the localizations ear, paranasal sinus, nose, and other localizations. The fifty most frequent ICD codes at primary index admission of planned and unplanned readmissions are shown in . The ten most frequent ICD codes for planned 30-day readmission belonged to the group of head and neck cancer codes. In contrast, only 3 ICD codes for head and neck cancer are found in the group of patients with unplanned readmission. More frequent were infectious diseases as index disease (chronic tonsillitis, rhinitis, sinusitis, peritonsillar abscess), and bleeding (mainly after oropharyngeal surgery). The interval between primary and next inpatient treatment was 12.5±8.2 days (median: 11). The treatment duration at readmission was 7.0±8.2 days.

Localization of the primary disease in patients with planned (blue) and unplanned (red) 30-day readmission.

The fifty most frequent ICD codes of patients with 30-day readmission. A: planned (blue) readmission. B: Unplanned (red) readmission.

The univariate comparison between patients with planned versus unplanned 30-day readmission is summarized in . Further surgery took place more often planned than unplanned (p<0.001), but further surgery because of postoperative complaints occurred more often unplanned (p<0.001). Recurrence of the original complaints was more frequently a reason for unplanned readmission (p<0.001). Patients with unplanned readmission were younger and more frequently female (p<0.001; respectively). The interval to planned readmission was longer than to unplanned readmission (p<0.001). The duration of the first inpatient treatment was longer if an unplanned readmission occurred (p<0.001). The PCCL and comorbidity were higher for planned readmissions (p<0.001 respectively). Unplanned readmission was more frequently seen in patients who were discharged against medical advice during the prior inpatient treatment. Primary diseases with more unplanned readmission were: Certain infectious and parasitic diseases, ICD: A00-B99, ICD: A00-B99 (p<0.001), blood forming organ diseases, ICD: D50-D90 (p = 0.002), eye/ ear diseases, ICD: H00-H95 (p<0.001), circulatory system diseases, ICD: I00-I99 (p = 0.001), respiratory system diseases, ICD: J00-J99 (p<0.001), gastrointestinal tract diseases, ICD: K00-K93 (p<0.001), symptoms, signs, abnormal findings, ill-defined causes, not otherwise classified, ICD: R00-R99 (p<0.001) and injury, poisoning and certain other consequences of external causes, ICD: S00-T98 (p<0.001). Diseases with more planned readmission were: Malignant diseases, ICD: C00-C97 (p<0.001), and benign, in-situ, uncertain neoplasm, ICD: D00-D48 (p = 0.042).

The multivariate analysis is shown in . The most important predictors for 30-day unplanned readmission were: discharge due to patient’s request against medical advice, surgical cases, and several ICD categories. Discharge due to patient’s request against medical advice was a strong independent factor with high risk for unplanned readmission (OR = 9.62; CI = 2.69–34.48). Lower number of secondary diagnoses (OR = 1.17; CI = 1.08–1.27) were other independent risk factors for unplanned compared to planned readmission. Unplanned readmission had more frequently a non-surgical treatment at readmission than a surgical treatment (OR = 3.92; CI = 2.24–6.84) and needed more frequently further diagnostics (OR = 2.34; CI = 1.34–4.11). A main diagnosis in the ICD categories Injury, poisoning and certain other consequences of external causes (predominantly trauma cases in the analyzed otolaryngology population), ICD: S00-T98 (OR = 66.67; CI = 15.87–333.33), symptoms, signs, abnormal findings, ill-defined causes, not otherwise classified (most frequently: epistaxis, dyspnea, and vertigo), ICD: R00-R99, ICD: R00-R99 (OR = 62.5; CI = 11.76–333.33), blood forming organ diseases, ICD: D50-D90 (OR = 21.276; CI = 3.508–125), and eye/ ear diseases (predominantly ear diseases in the analyzed otolaryngology population), ICD: H00-H95 (OR = 12.66; CI = 4.29–37.03) had the highest risk for unplanned readmission.

Discussion

This first and large population-based analysis revealed multifactorial predictors of planned and unplanned readmission for otolaryngology patients in German hospitals. The overall 30-day readmission rate was 7.6%. Surgical cases had a 30-day readmission rate of 6.5%. Readmission was planned in 4.9% and unplanned in 2.8% of the cases (Surgical cases alone: 2.6%). Former studies were mainly focused on surgical cases: Here, 30-day unplanned readmission rates vary from 5% to 20% [14-17]. The highest rates in otolaryngology patients are reported for head and neck cancer patients, especially following laryngectomy [15, 18, 19]. Specialty readmission rates are typically lower in surgical departments (about 10–12%) than in internal medicine (about 20%) [20, 21]. Unplanned 30-day readmission rates in general surgery reach maximally 10% in newer studies after implementation of HRRP strategies [22]. It can be concluded that the unplanned 30-day readmission rate was low compared to other otolaryngology studies and especially lower compared to other surgical disciples and much lower than reported for non-surgical disciplines.

The detected readmission predictors 1) head and neck cancer, 2) higher comorbidity, and 3) non-surgical cases have also been shown to be relevant for US-American otolaryngology patients treated following the introduction of healthcare quality programs like the National Surgical Quality Improvement Program (NSQIP) [6, 9, 14–16]. High-volume departments had also a higher overall readmission rate. This seems to be to a general association seen in many hospitals independently from a specialty [20], but the results in the literature are controversial [16]. Because not only head and neck cancer patients like in most previous studies but all kind of otolaryngology patients were included in the present study, it could be shown that also (in descending order) otoneurological diseases (mainly acute vestibular syndrome; acute hearing loss), infectious diseases (mainly erysipelas, herpes zoster), and musculoskeletal system diseases (mainly acquired outer ear deformities) had a high association (OR>3) for readmission.

Discharge against medical advice seems to be a self-explanatory risk factor, seems to be an important risk factor in countries with high amount of patients with healthcare insurance [23], and was analyzed so far only in few population-based studies in countries with DRG or comparable healthcare financing systems [24]. The ICD coding of bleeding in the airways and coagulopathies is mainly found in patients with recurrent epistaxis. Epistaxis is a well-known and a factor difficult to control to prevent unplanned readmission [25]. In contrast to planned readmission, head and neck cancer was not an independent risk factor for unplanned readmission. Nevertheless, the 2485 patients with head and neck cancer formed an important subgroup. 1016 of the patients with head and neck cancer underwent head and neck surgery. In a recent study focusing on 660 US-American patients who underwent head and neck surgery, length of stay at the index admission longer than 5 days was a strong predicator for unplanned 30-day admission [17]. On the other hand, wound infection was the most common reason for 30-day admission in the US-American study. The authors speculate that keeping the patients in the hospital longer may have prevented the unplanned readmission. However, a longer length of stay could have contributed to the infection. The mean length of stay in the US-American study was 5.6 days. This is much shorter than in the present study. The mean length of stay for the German head and neck cancer patients was 9.0 days. This may be attributed to different health practices in both countries. In the end, it may be speculated that the higher rate of planned 30-day readmission lead to less unplanned 30-day admissions in the German head and neck cancer patients. Also in contrast to a general higher readmission rate, high-volume hospitals seem not to have a higher rate of unplanned readmissions [21]. This can be confirmed for otolaryngology departments. After multivariate analysis, high-volume otolaryngology departments did not have a higher rate of unplanned readmissions.

The three most frequent single diagnoses at index diagnoses (apart from already discussed patients with epistaxis as well as head and neck cancer cases were: chronic tonsillitis (ICD: J35), unspecified disorders of nose and paranasal sinuses (ICD: J34), and chronic sinusitis (ICD: J32). 98% of the patients were surgical cases. In all but one of these unplanned readmissions, the reason was secondary bleeding or wound infection. Most of the surgical site bleeding complications occurred later than 7 days after discharge. Hence, probably most of the readmissions because of bleeding were not predictable and preventable. Unfortunately, the perioperative antibiotic treatment and the discharge antibiotics were not recorded. Discharge antibiotics were not preventive of infection and readmission in another study [17]. Furthermore, a wider use of prophylactic antibiotics can definitely be viewed critically.

The present study has several limitations and strengths. Due to the retrospective design, several parameters with possible association to unplanned readmission could not be analyzed due to a lack of sufficient data. For instance, in-hospital complications during the index admission seem to be a very strong predictor associated with 30-day readmission [6, 9, 14–16]. Furthermore, in head and neck cancer patients, cancer subsite, type of procedure, socioeconomic factors, comorbidities like coronary artery disease, chronic renal failure, or presence of a gastrostomy tube influence the risk of readmission [14, 16, 17]. A detailed analysis of cancer subsites and procedures was beyond the aim of the present more general overview on otolaryngology patients. Administrative data may not reliably describe the reason for readmission, especially when the rate of unplanned readmission should be analyzed [26]. A strength of the present study is that all charts of readmitted patients were examined individually, rather than relying on coding data alone.

Not much is known about strategies to prevent unplanned readmission in otolaryngology patients beyond HRRP or comparable policies. Prospective trials are lacking. We identified only one prospective trial, showing that perioperative education programs for patients and caregivers (pre-operative hands-on classes, booklets about the treatment journey, discharge coaching) seem to be an effective approach to reducing unplanned readmission in head and neck cancer patients [15]. Reducing care fragmentation after discharge might be another strategy, at least in head and neck cancer patients, to reduce unplanned readmissions [27]. Machine learning algorithms to predict the individual 30-day readmission probability may be at least a future option to better identify patients at risk much earlier [28].

Conclusions

The most important factors for 30-day unplanned readmission were: 1) discharge due to patient’s request against medical advice, 2) surgical cases, and 3) several ICD categories. Injury, poisoning and certain other consequences of external causes (mainly unspecified complications), symptoms, signs, abnormal findings, ill-defined causes, not otherwise classified, ICD: R00-R99 (mainly bleeding in the airways and dysphagia), blood forming organ diseases, ICD: D50-D90 (mainly coagulopathies), and eye/ ear diseases (mainly: acute vestibular syndrome, acute hearing loss) were associated with higher risk for unplanned readmission. This should allow developing concepts to reduce the rate of unplanned readmissions in the German DRG-system for safer and better otolaryngology inpatient care. Patients with the mentioned risk factors (and caregivers) should receive specific perioperative education programs addressing the related reasons that might lead to readmission. Prophylactic measures like prophylactic treatment if appropriate or a higher frequency of follow-up visits in the hand of one responsible physician might help to reduce the risk of unplanned 30-day readmission.

Overview about all patients: 16,444 inpatient cases of 12,859 patients in 2015.

(DOCX)

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Comparison of the group of patients with 30-day readmission to the group of patients without readmission.

(DOCX)

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Multivariate analysis of risk factors for 30-day readmission.

(DOCX)

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Localization of the primary disease of all patients at primary index admission.

(DOCX)

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The hundred most frequent primary ICD codes of all patients at primary index admission.

A: First 50 most frequent ICD codes. B: Second 50 most frequent ICD codes.

(DOCX)

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13 Aug 2019

PONE-D-19-21224

30-day unplanned readmission rate in otolaryngology patients: a population-based study in Thuringia, Germany

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Reviewer #1: The authors investigate a heterogeneous group of otolaryngology patients across multiple institutions in Germany. The concept to identify predictors for unplanned readmissions is important. It is a bit challenging to extrapolate further data from ICD codes, leaving the findings a bit unfocused and vague, although this is the nature of the data. Centering the discussion and elaborating on the most interesting findings, with extended discussion on impact and opportunities for quality improvement would strengthen the manuscript. Some efforts to clarify and investigate the manuscript further would be helpful in enhancing its value.

Some additional points:

1. Can authors clarify how they defined “planned” readmission, perhaps give some examples? It is unclear in the manuscript what a “planned” readmission is.

2. The authors should edit for grammar throughout the manuscript. e.g. pg. 4 lines 104-105 "have be performed" and Table I the use of "ja" and "nein".

3. Figure 2 image quality could be improved.

Reviewer #2: GENERAL COMMENTS

Rippe and colleagues provide a study of unplanned readmissions in otolaryngology patients highlighting several medical conditions and demographic factors predictive of patient readmission. The study is well justified in terms of potential clinical and economic impact. As the authors point out, existing studies in this area are limited and narrowly focused. The authors were able to obtain a large sample size, and the methodological approaches, analyses, and conclusions all seem appropriate. The study will be a welcome addition to the literature database accessed by practitioners and researchers in otolaryngology. My feedback is minimal and limited to suggestions for improved clarity.

SPECIFIC COMMENTS

Major

In its current format, Figure 2 is not useful for readers without a computer nearby to lookup ICD codes. Even these readers are burdened with the task of cross referencing the codes to the conditions, assuming they haven’t memorized them all. A brief text description would greatly facilitate understanding the main points of this figure, and can easily be added, e.g., by switching the bar graph orientation from horizontal to vertical.

Another feature that would be helpful for Figure 2 is a way to directly compare ICDs common for planned vs unplanned readmissions. For instance, the grouped bar plots in Figure 1 make it easy for readers to identify disease locations associated with planned (e.g., pharynx, larynx, neck) vs unplanned (e.g., ear, paranasal sinus, nose). There are several ways this type of comparison could be implemented in Figure 2, for instance, separate grouped or stacked bar plots ranking by planned and unplanned readmissions.

Minor

146: Please provide additional detail to disambiguate the term “multivariable analysis”. Does this imply multivariate regression? Multivariate analysis of variance?

195-197: “but re-surgery because of postoperative complaints occurred more often unplanned (p<0.001).”

It’s clear from Table 1 that Further surgery was more common for Planned readmission, and that Recurrence of primary complaints was more common for Unplanned readmission. These independent observations notwithstanding, I do not see anything supporting the statement that “re-surgery” (use presumably synonymous with further surgery) was performed specifically because of postoperative complaints.

Editorial

73: ICD -> International Classification of Diseases (ICD)

98: 30-day readmission rate as parameter -> 30-day readmission rate as a parameter

104-106: Only a few studies and mainly based on the experience in a single hospital have be performed to analyze risk factors for unplanned hospital readmission in otolaryngology patients [6-8]. -> Only a few studies, which are mainly based on the experience in a single hospital, have be performed to analyze risk factors for unplanned hospital readmission in otolaryngology patients [6-8].

113: (for instance, [10-13]. -> (for instance, [10-13].)

146: multivariable analysis -> multivariate analysis

165: Due to the multivariate analysis -> According to the multivariate analysis

172: 30day -> 30-day

195: Further surgery took place rather planned than unplanned -> Further surgery took place more often for planned than unplanned

196: re-surgery -> further surgery

197: origin complaints -> original complaints

312-313: A strength of the present study is that all charts of readmitted patients were examined individually. It was not just relied on coding data. -> A strength of the present study is that all charts of readmitted patients were examined individually, rather than relying on coding data alone.

318: a potent measure to reduce unplanned readmission -> an effective approach to reducing unplanned readmission

Reviewer #3: This exploratory study aimed to "analyze associations between patients’ characteristics and treatment factors with 30 day unplanned readmissions in hospitalized otolaryngology patients". It then proceeded to present a number of possible risk factors for readmission based on the results of the univariate and multivariate analysis. Some of the risk factors that had significant associations appear counter intuitive. For example, while older patients, those with malignant disease and those with higher co morbidity had a higher risk of readmission, they also found that non-surgical cases had a higher risk of readmission than surgical cases.

They found out that unplanned readmissions were more frequent among those who were discharged against medical advice. They then listed several ICD codes that appeared more frequently among those with unplanned readmissions. None of these were explained.

I think the authors should have first defined what is a planned and an unplanned readmission.

I think that the authors should have made clear from the start what are these associations that they planned to analyze and why. I would have appreciated an a priori explanatory framework relating the most important putative factors to the outcome (i.e. unplanned readmission) which would have guided them in the analysis. The framework would have also presented the biological or clinical rationale for focusing on these putative risk factors. Because there was no explanatory framework they could not explain the results that they obtained.

The tables need to be shortened to what are essential. For example, the p values for the ICD codes which do not appear to be clinically related to otolaryngologic outcomes may probably need to be deleted.

The discussion part repeated what was found in the results and even added information that might better have been placed in the results section.

The conclusion does not recapitulate the most important findings and how they apply to improving the quality of care for otolaryngologic patients.

**********

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Reviewer #1: No

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Reviewer #3: Yes: Dr. Jose M. Acuin

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27 Aug 2019

Rebuttal letter

PONE-D-19-21224

30-day unplanned readmission rate in otolaryngology patients: a population-based study in Thuringia, Germany

Thank you very much for the detailed reviews. Herewith, we would like to respond to all queries.

1. Editorial comments

1.1. Thank you for including your ethics statement: The Ethics Committee waived the requirement for informed consent for the patients with exclusive retrospective data analysis using the patients’ charts. Please amend your current ethics statement to include the full name of the ethics committee/institutional review board(s) that approved your specific study. Once you have amended this/these statement(s) in the Methods section of the manuscript, please add the same text to the “Ethics Statement” field of the submission form (via “Edit Submission”).

Answer 1.1) Done. We added the full name of the ethics committee and added the same text in the submission form.

1.2. In your revised cover letter, please address the following prompts: a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent. b) If there are no restrictions, please upload the minimal anonymized data set necessary to replicate your study findings as either Supporting Information files or to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. Please see http://www.bmj.com/content/340/bmj.c181.long for guidelines on how to de-identify and prepare clinical data for publication. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories. We will update your Data Availability statement on your behalf to reflect the information you provide.

Answer 1.2) Done. We added this information in the cover letter.

2. Reviewer #1

2.1 The authors investigate a heterogeneous group of otolaryngology patients across multiple institutions in Germany. The concept to identify predictors for unplanned readmissions is important. It is a bit challenging to extrapolate further data from ICD codes, leaving the findings a bit unfocused and vague, although this is the nature of the data. Centering the discussion and elaborating on the most interesting findings, with extended discussion on impact and opportunities for quality improvement would strengthen the manuscript. Some efforts to clarify and investigate the manuscript further would be helpful in enhancing its value.

Answer 2.1) We followed the suggestions of all three reviewers. The result is: We focused the text by giving more summarizing information on the figures in the Results. The description of the ICD codes makes it much easier now to understand the disease behind the codes. We deleted parts of repeated results in the Discussion. We clarified definitions and aims.

Some additional points

2.2. Can authors clarify how they defined “planned” readmission, perhaps give some examples? It is unclear in the manuscript what a “planned” readmission is.

Answer 2.2) Done. We added the following sentences at the end of the Method sections: “. A planned readmission was defined as a readmission that was planned during the index admission. These patients received an appointment for readmission at discharge from the hospital. All other readmissions were defined as unplanned readmissions.”.

2.3. The authors should edit for grammar throughout the manuscript. e.g. pg. 4 lines 104-105 "have be performed" and Table I the use of "ja" and "nein".

Answer 2.3) We checked the manuscript completely and corrected the mentioned two errors.

2.4. Figure 2 image quality could be improved.

Answer 2.4) Done. We changed the format completely, following the suggestion of reviewer #2, see answer 3.2.

3. Reviewer #2

3.1. Rippe and colleagues provide a study of unplanned readmissions in otolaryngology patients highlighting several medical conditions and demographic factors predictive of patient readmission. The study is well justified in terms of potential clinical and economic impact. As the authors point out, existing studies in this area are limited and narrowly focused. The authors were able to obtain a large sample size, and the methodological approaches, analyses, and conclusions all seem appropriate. The study will be a welcome addition to the literature database accessed by practitioners and researchers in otolaryngology. My feedback is minimal and limited to suggestions for improved clarity.

Answer 3.1) Thanks.

Major

3.2. In its current format, Figure 2 is not useful for readers without a computer nearby to lookup ICD codes. Even these readers are burdened with the task of cross referencing the codes to the conditions, assuming they haven’t memorized them all. A brief text description would greatly facilitate understanding the main points of this figure, and can easily be added, e.g., by switching the bar graph orientation from horizontal to vertical. Another feature that would be helpful for Figure 2 is a way to directly compare ICDs common for planned vs unplanned readmissions. For instance, the grouped bar plots in Figure 1 make it easy for readers to identify disease locations associated with planned (e.g., pharynx, larynx, neck) vs unplanned (e.g., ear, paranasal sinus, nose). There are several ways this type of comparison could be implemented in Figure 2, for instance, separate grouped or stacked bar plots ranking by planned and unplanned readmissions.

Answer 3.2) We re-arranged Figure 2. We switched the orientation of the bars and added text to the ICD codes

Minor

3.3. 146: Please provide additional detail to disambiguate the term “multivariable analysis”. Does this imply multivariate regression? Multivariate analysis of variance?

Answer 3.2) See also answer 3.9. This sentence is leading to the next sentence explaining what is meant by multivariate analysis. To make this clear we changed the full stop to a colon: “… in the multivariate analysis: Binary logistic regression analysis was used to determine …”.

3.4. 195-197: “but re-surgery because of postoperative complaints occurred more often unplanned (p<0.001).”

It’s clear from Table 1 that Further surgery was more common for Planned readmission, and that Recurrence of primary complaints was more common for Unplanned readmission. These independent observations notwithstanding, I do not see anything supporting the statement that “re-surgery” (use presumably synonymous with further surgery) was performed specifically because of postoperative complaints.

Answer 3.4) Yes. Further surgery is meant. We changed this. Re-surgery is misleading. See also answer 3.13.

Editorial

3.5. 73: ICD -> International Classification of Diseases (ICD)

Answer 3.5) Changed.

3.6. 98: 30-day readmission rate as parameter -> 30-day readmission rate as a parameter

Answer 3.6) Changed.

3.7. 104-106: Only a few studies and mainly based on the experience in a single hospital have be performed to analyze risk factors for unplanned hospital readmission in otolaryngology patients [6-8]. -> Only a few studies, which are mainly based on the experience in a single hospital, have be performed to analyze risk factors for unplanned hospital readmission in otolaryngology patients [6-8].

Answer 3.7) Changed.

3.8. 113: (for instance, [10-13]. -> (for instance, [10-13].)

Answer 3.8) Changed.

3.9. 146: multivariable analysis -> multivariate analysis

Answer 3.9) Changed.

3.10. 165: Due to the multivariate analysis -> According to the multivariate analysis

Answer 3.10) Changed.

3.11. 172: 30day -> 30-day

Answer 3.11) Changed.

3.12. 195: Further surgery took place rather planned than unplanned -> Further surgery took place more often for planned than unplanned

Answer 3.12) Changed.

3.13. 196: re-surgery -> further surgery

Answer 3.13) Changed.

3.14. 197: origin complaints -> original complaints

Answer 3.14) Changed.

3.15. 312-313: A strength of the present study is that all charts of readmitted patients were examined individually. It was not just relied on coding data. -> A strength of the present study is that all charts of readmitted patients were examined individually, rather than relying on coding data alone.

Answer 3.15) Changed

3.16. 318: a potent measure to reduce unplanned readmission -> an effective approach to reducing unplanned readmission

Answer 3.16) Changed.

4. Reviewer #3

4.1. This exploratory study aimed to "analyze associations between patients’ characteristics and treatment factors with 30 day unplanned readmissions in hospitalized otolaryngology patients". It then proceeded to present a number of possible risk factors for readmission based on the results of the univariate and multivariate analysis. Some of the risk factors that had significant associations appear counter intuitive. For example, while older patients, those with malignant disease and those with higher co morbidity had a higher risk of readmission, they also found that non-surgical cases had a higher risk of readmission than surgical cases.

Answer 4.1) No comment needed.

4.2. They found out that unplanned readmissions were more frequent among those who were discharged against medical advice. They then listed several ICD codes that appeared more frequently among those with unplanned readmissions. None of these were explained.

Answer 4.2) We added several sentences in the Results to make is easier to understand the diseases behind the ICD codes. Furthermore, see also answer 3.2, we re-arranged figure 2, so that the ICD codes are explained now.

4.3. I think the authors should have first defined what is a planned and an unplanned readmission.

Answer 4.3 Done. See answer 2.2.

4.4. I think that the authors should have made clear from the start what are these associations that they planned to analyze and why. I would have appreciated an a priori explanatory framework relating the most important putative factors to the outcome (i.e. unplanned readmission) which would have guided them in the analysis. The framework would have also presented the biological or clinical rationale for focusing on these putative risk factors. Because there was no explanatory framework they could not explain the results that they obtained.

Answer 4.4.) We hope that we understood the direction of this comment. We added in the Methods at the end of the final paragraph: “The primary aim of the subsequent evaluation was to analyze associations between patients’ characteristics and treatment factors with 30-day unplanned readmissions in hospitalized otolaryngology patients in the German Diagnosis Related Group (D-DRG) system. The G-DRG system already includes instruments to avoid early readmission, especially by sanctioning the reimbursement. We hypothesized that, nevertheless, specific otolaryngology diseases and type of treatment as well as patients’ comorbidity have influence on the risk of 30-day unplanned readmission.”.

4.5. The tables need to be shortened to what are essential. For example, the p values for the ICD codes which do not appear to be clinically related to otolaryngologic outcomes may probably need to be deleted.

Answer 4.5) It is policy of PLOS one (as it is nowadays for several journals) to disclose as many of the data as possible. Furthermore, we think, that it is also important for the reader to understand which factors are not important (not significant in statistical analysis). Therefore, we would not like to delete parameters from the otherwise complete tables. To make Table 1 more readable, we split table 1 into table 1A and table 1B.

4.6. The discussion part repeated what was found in the results and even added information that might better have been placed in the results section.

Answer 4.6) We shifted sentences summarizing results from the Discussion (the Discussion already was not very long) back to the Results. We tried now to reduce results in the Discussion to information needed to compare the data to other studies.

4.7. The conclusion does not recapitulate the most important findings and how they apply to improving the quality of care for otolaryngologic patients.

Answer 4.7) The Conclusion was revised. We recapitulate now the most important findings. And we present now some evident strategies to reduce unplanned readmissions-

Orlando Guntinas-Lichius

for all authors

Jena, 20-August-2019

12 Sep 2019

[EXSCINDED]

PONE-D-19-21224R1

30-day unplanned readmission rate in otolaryngology patients: a population-based study in Thuringia, Germany

PLOS ONE

Dear Prof Guntinas-Lichius,

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Academic Editor

PLOS ONE

Additional Editor Comments (if provided):

Thank you to the authors for addressing most of the reviewers comments. There are still a few outstanding items which need to be answered (see reviewer comments).

Also:

1. Please give a concrete example of "planned re-admission".

2. Please double check the tables to ensure that no labels are missing. Some rows/columns are blank.

3. Please discuss risk factors for readmission in more detail.

4. Please address how head and neck surgery patients may have affected the results. There is a paper (Dziegielewski et al 2016) that discuss this group of patients in detail. It would be worthwhile comparing results.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

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PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Overall the authors have improved the manuscript. I am still confused as to the concept of a "planned readmission" before discharge from the hospital. In what clinical scenarios would this happen? For a planned reconstruction surgery? For a second stage procedure? Can the authors provide an example of "planned readmission"? Otherwise other concerns have been addressed.

Reviewer #2: The authors have adequately addressed each of the suggested revisions. My only remaining suggestion is to add x-axis labels

to Figure 2 (e.g., "Number of cases" as in Figure 1).

Reviewer #3: Please correct all typographical errors (e.g., punctuation, capitalizatio of common nouns, etc). In the conclusions section, the authors may also want to state how the findings can be used to improve hospital discharge policies.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes: Jose M. Acuin

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org. Please note that Supporting Information files do not need this step.

23 Sep 2019

Rebuttal letter

PONE-D-19-21224

30-day unplanned readmission rate in otolaryngology patients: a population-based study in Thuringia, Germany

Thank you very much for the second round of detailed reviews. Herewith, we would like to respond to all queries.

1. Editorial comments

1.1. Please give a concrete example of "planned re-admission".

Answer 1.1. We added some sentences for definition in the Methods on page 5: “Planned readmissions were defined as readmissions that were planned and agreed during the index admission. For instance, a patient with head and neck cancer had his index admission for staging and panendoscopy. Typically, if surgery was planned for definitive treatment, the day of readmission already was scheduled before demission. All other patients without planned readmission were defined as unplanned readmissions, for instance when a patient was readmitted for a complication after surgery.”.

1.2. Please double check the tables to ensure that no labels are missing. Some rows/columns are blank.

Answer 1.2. We checked all tables and supplement tables. There is no complete blank row or columns. The blank fields in many rows/columns are correct.

1.3. Please discuss risk factors for readmission in more detail.

Answer 1.3. See also answer 1.4. Including the paper of Dziegielewski et al 2016 already helped to discuss the risk factors in more detail. Furthermore, we added a paragraph in the Discussion on page 16/17 and discussed the most frequent reasons for unplanned readmission.

1.4. Please address how head and neck surgery patients may have affected the results. There is a paper (Dziegielewski et al 2016) that discuss this group of patients in detail. It would be worthwhile comparing results.

Answer 1.4. Thank you for this hint. The article of Dziegielewski et al. 2016 is now the new reference No. 17. The Discussion contains now a part on page 16 where we discuss this study in relation to our results. And we address this study in the Discussion on page 17 where we talk about the limitations of our study.

2. Reviewer #1

2.1. Overall the authors have improved the manuscript. I am still confused as to the concept of a "planned readmission" before discharge from the hospital. In what clinical scenarios would this happen? For a planned reconstruction surgery? For a second stage procedure? Can the authors provide an example of "planned readmission"? Otherwise other concerns have been addressed.

Answer 2.1. See also Answer 1.1. We added some sentences for the definition of planned and unplanned surgery on page 5 in the Methods.

3. Reviewer #2

3.1. The authors have adequately addressed each of the suggested revisions. My only remaining suggestion is to add x-axis labels to Figure 2 (e.g., "Number of cases" as in Figure 1).

Answer 3.1. Done. The x-axis in Figure 2 has now also a labeling: “Number of cases”.

4. Reviewer #3

4.1. Please correct all typographical errors (e.g., punctuation, capitalizatio of common nouns, etc). In the conclusions section, the authors may also want to state how the findings can be used to improve hospital discharge policies

Answer 4.1. The text was checked for typographical errors again. Concerning the improvement of the hospital discharge policies, the Conclusions contain three sentences: “Patients with the mentioned risk factors (and caregivers) should receive specific perioperative education programs addressing the related reasons that might lead to readmission. Prophylactic measures like prophylactic treatment if appropriate or a higher frequency of follow-up visits in the hand of one responsible physician might help to reduce the risk of unplanned 30-day readmission.”.

Orlando Guntinas-Lichius

for all authors

Jena, 22-September-2019

Submitted filename: Second rebuttal letter v4.docx

Click here for additional data file.

8 Oct 2019

30-day unplanned readmission rate in otolaryngology patients: a population-based study in Thuringia, Germany

PONE-D-19-21224R2

Dear Dr. Guntinas-Lichius,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

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Peter Dziegielewski, MD, FRCSC

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

10 Oct 2019

PONE-D-19-21224R2

30-day unplanned readmission rate in otolaryngology patients: a population-based study in Thuringia, Germany

Dear Dr. Guntinas-Lichius:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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on behalf of

Dr. Peter Dziegielewski

Academic Editor

PLOS ONE

Table 1

Comparison of the group of patients with planned versus unplanned 30-day readmission.

Parameter	All	Plannedreadmission		Unplanned readmission		p
	N	N	%	N	%
All	1169	747	63.9	422	36.1
Gender						<0.001
Male	865	604	69.8	261	30.2
Female	304	143	47.0	161	53.0
Reason for readmission
Further surgery						<0.001
Yes	309	307	99.4	2	0.6
No	860	440	51.2	420	48.8
Recurrence of primary complaints						<0.001
Yes	124	3	2.4	121	97.6
No	1045	744	71.2	301	28.8
Non-surgical treatment						<0.001
Yes	366	362	98.9	4	1.1
No	803	385	47.9	418	52.1
Further diagnostics						<0.001
Yes	55	51	92.7	4	7.3
No	1114	696	62.5	418	37.5
Post-surgical complaints						<0.001
Yes	197	10	5.1	187	94.9
No	972	737	75.8	235	24.2
Other complaints						<0.001
Yes	118	14	11.9	104	88.1
No	1051	733	69.7	318	30.3
ICD-code at readmission
Certain infectious and parasitic diseases, ICD: A00-B99						<0.001
Yes	11	1	9.1	10	90.9
No	1158	746	64.4	412	35.6
Malignant diseases, ICD: C00-C97						<0.001
Yes	682	600	88.0	82	12.0
No	487	147	30.2	340	69.8
Benign, in-situ, uncertain neoplasm, ICD: D00-D48						0.042
Yes	28	23	82.1	5	17.9
No	1141	724	63.5	417	36.5
Blood forming organ diseases, ICD: D50-D90						0.002
Yes	11	2	18.2	9	81.8
No	1158	745	64.3	413	35.7
Endocrine and metabolic diseases, ICD: E00-E90						0.452
Yes	1	1	100.0	0	0.0
No	1168	746	63.9	422	36.1
Mental and behavioral disorder, ICD: F00-F99						0.270
Yes	3	1	33.3	2	66.7
No	1166	746	64.0	420	36.0
Nervous system diseases, ICD: G00-G99						0.118
Yes	44	33	75.0	11	25.0
No	1125	714	63.5	411	36.5
Eye/ ear diseases, ICD: H00-H95						<0.001
Yes	67	19	28.4	48	71.6
No	1102	728	66.1	374	33.9
Circulatory system diseases, ICD: I00-I99						0.001
Yes	6	0	0.0	6	100.0
No	1163	747	64.2	416	35.8
Respiratory system diseases, ICD: J00-J99						<0.001
Yes	86	32	37.2	54	62.8
No	1083	715	66.0	368	34.0
Gastrointestinal tract diseases, ICD: K00-K93						0.012
Yes	23	9	39.1	14	60.9
No	1146	738	64.4	408	35.6
Skin and subcutaneous tissue diseases, ICD: L00-L99						0.709
Yes	7	4	57.1	3	42.9
No	1162	743	63.9	419	36.1
Musculoskeletal system/connective tissue diseases, ICD: M00-M99						0.270
Yes	3	1	33.3	2	67.7
No	1166	746	64.0	420	36.0
Genitourinary system diseases, ICD: N00-N99						NA
Yes	0	0	0.0	0	0.0
No	1169	747	63.9	422	36.1
Congenital malformations and chromosomal abnormalities, ICD: Q00-Q99						0.856
Yes	5	3	60.0	2	40.0
No	1164	744	63.9	420	36.1
Symptoms, signs, abnormal findings, ill-defined causes, not otherwise classified, ICD: R00-R99						<0.001
Yes	53	4	6.3	49	93.7
No	1116	743	66.6	373	33.4
Injury, poisoning and certain other consequences of external causes, ICD: S00-T98						<0.001
Yes	136	10	7.4	126	92.6
No	1033	737	71.3	296	28.7
Factors influencing good health and other utilization of the health care system, ICD: Z00-Z99						0.132
Yes	4	4	4.7	0	95.3
No	1165	743	63.8	422	36.2
OPS-Codes, categorized
Diagnostics						<0.001
Yes	310	233	75.2	77	24.8
No	859	514	59.8	345	40.2
Imaging diagnostics						0.374
Yes	155	104	67.1	51	32.9
No	1014	643	63.4	371	36.6
Surgery						0.404
Yes	498	325	65.3	173	34.7
No	671	422	62.9	249	37.1
Drug treatment						<0.001
Yes	107	93	86.9	14	13.1
No	1062	654	61.6	408	38.4
Non-surgical treatment						<0.001
Yes	570	449	78.8	121	21.2
No	599	298	49.7	301	50.3
Adjuvant treatment						0.084
Yes	49	37	75.5	12	24.5
No	1120	710	63.4	410	36.6
Main diagnosis identical to primary main diagnosis						<0.001
Ja	824	638	75.8	204	24.2
Nein	860	109	33.3	218	66.7
PCCL at primary treatment						0.001
High (0–1)	258	187	72.5	71	27.5
Low (2–4)	661	398	60.2	263	39.8
PCCL at readmission						<0.001
High (0–1)	258	196	76.0	62	24.0
Low (2–4)	658	386	58.7	272	41.3
DRG-partition at primary treatment						0.011
Surgical	621	376	60.5	245	39.5
Medical	540	366	67.8	174	32.2
DRG-partition at readmission						<0.001
Surgical	544	430	79.0	114	21.0
Medical	466	235	50.4	231	49.6
Comorbidity						<0.001
High (≥ 4 SD)	696	484	69.5	212	30.5
Low (< 4 SD)	473	263	55.6	210	44.4
Number of inpatients						0.057
High	234	137	58.5	97	41.5
Low	935	610	65.2	325	34.8
Discharge against medical advice						0.018
	28	12	42.9	16	57.1
	1135	733	64.6	402	35.4
	Mean±SD	Mean±SD		Mean±SD
Age at primary treatment, years	58.87±17.09	61.64±13.25		53.95±21.49		<0.001
Treatment duration at primary treatment, days	5.68±5.62	5.67±6.02		5.69±4.87		0.968
Interval between primary treatment and readmission, days	12.51±8.20	13.88±7.90		10.07±8.16		<0.001
Treatment duration at readmission, days	7.01±8.17	7.73±8.79		5.76±6.76		<0.001
Secondary diagnoses, n	5.32±4.50	5.57±4.24		4.86±4.89		0.009

ICD = International Classification of Diseases; PCCL = Patient Clinical Complexity; SD = Secondary diagnoses.

Table 2

Multivariate analysis of risk factors for unplanned 30-day readmission.

Parameter	OR	95% CI	p
Age, years	0.998	0.983–1.013	0.800
Treatment duration at readmission, days	0.987	0.952–1.022	0.469
Interval between primary treatment and readmission, days	1.038	1.010–1.067	0.008
Secondary diagnoses, n	0.855	0.789–0.926	<0.001
Gender			0.546
Male	1
Female	1.169	0.704–1.942
PCCL (Primary treatment)			0.121
High (0–1)	1
Low (2–4)	1.672	0.873–3.195
PCCL (readmission)			0.312
Low (2–4)	1
High (0–1)	1.439	0.711–2.914
DRG-Partition (primary treatment)			0.386
Medical	1
Surgical	1.259	0.747–2.123
DRG-Partition (readmission)			<0.001
Surgical	1
Medical	3.916	2.243–6.836
Demission against medical advice			0.001
No	1
Yes	9.615	2.688–34.482
Comorbidity			0.101
High (≥ 4 SD)	1
Low (< 4 SD)	1.740	0.898–3.369
Main diagnosis identical			0.205
Yes	1
No	1.447	0.818–2.560
ICD-codes
Certain infectious and parasitic diseases, ICD: A00-B99			0.048
No	1
Yes	10.638	0.009–0.981
Malignant diseases, ICD: C00-C97			0.613
Yes	1
No	1.270	0.503–3.206
Benign, in-situ, uncertain neoplasm, ICD: D00-D48			0.140
No	1
Yes	3.040	0.694–13.333
Blood forming organ diseases, ICD: D50-D90			0.001
No	1
Yes	21.276	3.508–125
Eye/ ear diseases, ICD: H00-H95			<0.001
No	1
Yes	12.658	4.292–37.037
Circulatory system diseases, ICD: I00-I99			0.999
Yes	1
No	NA	NA
Respiratory system diseases, ICD: J00-J99			<0.001
No	1
Yes	5.814	2.217–15.385
Gastrointestinal tract diseases, ICD: K00-K93			0.020
No	1
Yes	4.831	1.277–18.181
Symptoms, signs, abnormal findings, ill-defined causes, not otherwise classified, ICD: R00-R99			<0.001
No	1
Yes	62.5	11.765–333.333
Injury, poisoning and certain other consequences of external causes, ICD: S00-T98			<0.001
No	1
Yes	66.667	15.873–333.333
OPS-Code, categorized
Diagnostics			0.003
Yes	1
No	2.343	1.337–4.105
Drug treatment			0.062
Yes	1
No	2.455	0.956–6.302
Surgical treatment			<0.001
No	1
Yes	3.330	1.862–5.957

OR = Odds ratio, CI = confidence interval; ICD = International Classification of Diseases; PCCL = Patient Clinical Complexity; SD = Secondary diagnoses.