Incidence and risk factors of COVID-19 associated pneumothorax.

BACKGROUND: Pneumothorax has been increasingly observed among patients with coronavirus disease-2019 (COVID-19) pneumonia, specifically in those patients who develop acute respiratory distress syndrome (ARDS). In this study, we sought to determine the incidence and potential risk factors of pneumothorax in critically ill adults with COVID-19.
METHOD: This retrospective cohort study included adult patients with laboratory-confirmed SARS-CoV-2 infection admitted to one of the adult intensive care units of a tertiary, academic teaching hospital from May 2020 through May 2021.
RESULTS: Among 334 COVID-19 cases requiring ICU admission, the incidence of pneumothorax was 10% (33 patients). Patients who experienced pneumothorax more frequently required vasopressor support (28/33 [84%] vs. 191/301 [63%] P = 0.04), were more likely to be proned (25/33 [75%] vs. 111/301 [36%], P<0.001), and the presence of pneumothorax was associated with prolonged duration of mechanical ventilation; 21 (1-97) versus 7 (1-79) days, p<0.001 as well as prolonged hospital length of stay (29 [9-133] vs. 15 [1-90] days, P<0.001), but mortality was not significantly different between groups. Importantly, when we performed a Cox proportional hazard ratio (HR) model of multivariate parameters, we found that administration of tocilizumab significantly increased the risk of developing pneumothorax (HR = 10.7; CI [3.6-32], P<0.001).
CONCLUSION: Among 334 critically ill patients with COVID-19, the incidence of pneumothorax was 10%. Presence of pneumothorax was associated with prolonged duration of mechanical ventilation and length of hospital stay. Strikingly, receipt of tocilizumab was associated with an increased risk of developing pneumothorax.

Introduction

The SARS-CoV-2 infection has caused the COVID-19 pandemic, a highly variable clinical syndrome ranging from asymptomatic carriers to acute respiratory failure and high mortality [1, 2]. Epidemiological data indicates that 6 to 10% of COVID-19 patients will develop severe respiratory symptoms and will require intensive care unit (ICU) admission, which is associated with poor outcome [3]. COVID-19 associated lung injury and respiratory failure often results in prolonged need for non-invasive or invasive oxygen therapy and is linked to an extended length of ICU stay. The underlying pathogeneses of COVID-19 induced respiratory failure include damage to the angiotensin-converting enzyme-2 (ACE2) receptor of endothelial and epithelial cells, resulting in cellular injury. Additionally, damage to lung epithelial and endothelial ACE2 receptors may result in impaired cellular repair mechanisms [4, 5]. COVID-19 pneumonia, unlike other viral pneumonias, seems to be disproportionally associated with elevated incidence of thromboembolism and pneumothorax [6, 7].

Pneumothorax impairs ventilation and oxygenation and can manifest spontaneously or due to barotrauma as a complication of mechanical ventilation that can be associated with subcutaneous emphysema and pneumomediastinum or pneumopericardium. Pneumothorax can complicate mechanical ventilation especially in patients with COVID-19 associated pneumonia, leading to a prolonged ICU stay. In a recent meta-analysis of 1,814 invasively ventilated COVID-19 patients, barotrauma occurred in one out of six patients (14.7%) and it was associated with increased mortality [8]. The incidence of pneumothorax in mechanically ventilated COVID-19 patients appear to be higher than in conventional acute respiratory distress syndrome (ARDS) or other viral pneumonias [7-9]. It appears that over time the frequency of reported incidence of pneumothorax is increasing during COVID-19 pandemic [10]. Although it is possible that new variants are contributing to higher rates of pneumothorax, the role of pharmacotherapies targeting the body’s innate defense mechanisms must be considered. Many repurposed drugs explored to treat COVID-19 modulate inflammation, some of which significantly alter the immune response, including viral clearance, host cellular responses, or cellular repair mechanisms. Besides the corticosteroids, tocilizumab (TCZ) is one of the most utilized drugs to modulate the hyper-inflammatory responses in COVID-19 infection [11, 12]. Tocilizumab is a monoclonal antibody against interleukin-6 receptors, approved to treat rheumatoid arthritis with a relatively good safety profile [13]. Despite negative results of TCZ efficacy in earlier studies in treatment of severe COVID-19 [14], the Food and Drug Administration (FDA) has recently approved the use of TCZ based on more recent clinical studies [15, 16].

As clinicians continue to treat critically ill COVID-19 patients in the ICU, it is important to understand the risk factors associated with development of pneumothorax. In this study, we sought to determine the incidence, risk factors and the clinical consequences of pneumothorax in COVID-19 patients requiring ICU admission.

Materials and methods

In this retrospective, cohort, observational single-center study, we examined the incidence of pneumothorax in patients with COVID-19 positive, who were admitted to the intensive care unit (ICU) for respiratory distress at Detroit Receiving Hospital and Harper University Hospital in Detroit Medical Center in Detroit, Michigan. After receiving approval from the Institutional Review Board at Wayne State University, patients aged ≥ 18 years old requiring ICU admission from May 2020 to February 2021, with laboratory-confirmed SARS-CoV-2 infection, diagnosed by reverse-transcriptase–polymerase-chain-reaction (RT-PCR) of nasopharyngeal specimen, were included. Demographic and clinical characteristics were obtained from electronic medical records. The diagnosis of barotrauma was established using portable chest radiograph. Patients were divided into two cohort, those with and those without pneumothorax, and were followed from admission to discharge or death. Patients with iatrogenic pneumothorax, or those requiring thoracentesis or chest tube drainage for pleural effusion; or receiving extracorporeal membrane oxygenation (ECMO) were excluded. Respiratory support, including supplemental oxygen therapy and mechanical ventilation, were applied according to the best practice of using standard lung protective ventilation strategies adopted in ARDS network trial [17]. COVID-19 specific therapies were provided per our institution guidance protocol (S1 File) including anticoagulation therapy. According to our institution protocol, all patients with COVID-19 should receive full anticoagulation therapy if D-dimer >3. Tocilizumab required approval from our Infectious Diseases service and a weight-based dose was used, consistent with the Infectious Diseases Society of America Guidelines [18]. Charlson Comorbidity Index Score and Acute Physiology and Chronic Health Evaluation (APACHE) II were calculated as previously described [19, 20].

Study is approved by human investigation committee at the Wayne State University. The committee waived the requirement for informed consent. All methods were performed in accordance with the human investigation ethical guidelines and regulations by the local IRB (protocol No = IRB-20-04-2037) at Wayne State University.

Statistical analysis

Parametric continuous variables were represented as mean with standard deviation. Nonparametric continuous samples were represented as median with interquartile range (IQR). Categorical data were presented as frequencies and percentages with inference by Pearson’s chi-square test. Statistical significance was defined by a p-value <0.05. For ventilator settings, averages of all values recorded throughout the ICU-admission were calculated for each patient. Then, the average for the entire ICU stay was calculated and used for final statistical analyses. Univariate analyses of all independent variables were performed to compare the two cohorts by using independent-samples t-test, Mann-Whitney U test for nonparametric, or Pearson’s chi-square test, as appropriate. All independent variables with p-value of less than 0.05 in the univariate analysis were enrolled into multivariate analyses. Cox proportional hazards regression model with Enter method was then performed to evaluate several co-factors simultaneously and identify the predictors of pneumothorax. Kaplan-Meier Survival curves were plotted to compare survival between two groups based on Tocilizumab therapy. Log rank test (Mantel-Cox) was used to compare the survival distributions of the two cohorts at 25 days. SPSS statistical software (Version 27, Chicago, IL) was used.

Results

Out of 349 patients admitted to the ICU with laboratory-confirmed COVID-19, 334 patients with a mean age of 61 ± 14 years, 188 (56%) males, 245(73%) African-Americans were included in the analyses. Five subjects were excluded as they developed pneumothorax as a complication of invasive procedures (3 central lines, 2 chest tube for empyema). Eleven subjects, who received ECMO were also excluded. Overall, the incidence of pneumothorax was 10% (33/334) followed by pneumomediastinum 20/334 (6%) and subcutaneous emphysema 9/334 (3%). The mean duration of ICU stay prior to pneumothorax was 15.7 days, and the mean duration of mechanical ventilation prior to barotrauma was 10.3 days. There were 27/33 (81%) patients who required chest tube insertion to treat pneumothorax. Table 1 summarizes patients’ clinical characteristics and the comparison of clinical features between the two cohorts. Most patients were admitted first to an acute care unit where medical treatment was initiated. No significant differences were seen in demographics, comorbidities, or APACHE II scores on admission between the pneumothorax and non-pneumothorax cohorts, except for human immunodeficiency virus infection (HIV), which was significantly higher in the pneumothorax cohort (p = 0.05) (Table 1). The univariate analysis performed between the pneumothorax and non-pneumothorax subgroups is shown in Table 2. Median with IQR of length of hospital stay for all 334 patients was 16 (1–133) days and median length of ICU stay was 11 days (IQR = 1–100). The pneumothorax group had a significantly longer hospital and ICU stay. During their ICU stay, 299 (89%) individuals required invasive ventilation, 28 (8%) needed non-invasive ventilation, and 7 subjects (2%) required high flow nasal cannula (HFNC). Median duration of mechanical ventilation was 8 (1–97) days. Among 334 patients, 136 (40%) subjects were placed in the prone positioning during ICU stay. Subjects in the pneumothorax cohort were more likely to require prone positioning either before or after pneumothorax (75% vs 36%; p<0.001) (Table 1). Most patients developed pneumothorax while on invasive mechanical ventilation, except two patients, who developed pneumothorax while receiving HFNC or non-invasive mechanical ventilation. There were no significant differences in ventilator parameters between two groups, except the average RR. Similarly, there were no significant differences in the initial C-reactive protein (CRP) or ferritin levels between two groups. However, there were significant differences in the COVID-19 medical management between two groups: overall 75% (251/334) of patients received glucocorticoids; 73% of non- pneumothorax group, compared to 94% of pneumothorax group, (p = 0.004). Overall, 188/334 (56%) subjects received hydroxychloroquine, 59% in the non- pneumothorax group vs. 27% in the pneumothorax group, (p<0.001). Eighty-eight (26%) patients received TCZ, 22% in the non- pneumothorax group vs. 66% in the pneumothorax group. Similarly, 8% of the non- pneumothorax compared to 24% of patients in the pneumothorax group received remdesivir. Vasopressor requirements between two groups were also significantly different (p = 0.04). Additionally, based on our institution guidance (S1 File), the pneumothorax group was more likely to receive prophylactic full anticoagulation therapy, 78% versus 58%, p = 0.01. There were no significant differences in terms of mortality or dependency on ventilator as reflected by the requirement of tracheostomy placements and long-term care facility transfer (Table 2).

Table 1

Subjects characteristics.

Characteristics	All Patients n = 334	Non- pneumothorax n = 301 (90%)	Pneumothorax n = 33 (10%)	p-value
Age, Years (mean ± SD)	61 ± 14	61 ± 14	59 ± 13	0.61
Sex, n (%)				0.47
Female	148 (44)	132 (44)	16 (49)
Male	188 (56)	169 (56)	17 (51)
Known ethnicity, n (%)				0.68
African—American	245 (73)	225 (74)	20 (60)
White/Caucasian	88 (26)	75 (25)	13(40)
Hispanic	1 (0.2)	1 (0.3)	0
BMI, kg · m-2, median(IQR)	31 (15–85)	30 (15–85)	32 (22–62)	0.49
Smoker, n (%)	80 (24)	73 (24)	7 (21)	0.43
Comorbidities, n (%)
COPD a	75 (22)	68 (22)	7 (21)	0.92
Asthma	34 (10)	31 (10)	3 (9)	0.55
Hypertension	266 (79)	239 (79)	27 (81)	0.48
Diabetes mellitus	200 (60)	177 (58)	23 (69)	0.15
Coronary artery disease	67 (20)	62 (20)	5 (15)	0.31
Chronic heart failure	68 (20)	65(21)	3 (9)	0.16
Cerebrovascular accident	49 (14)	46 (15)	3 (9)	0.25
Chronic kidney disease	56 (16)	54 (18)	2 (6)	0.06
ESRD b	43 (12)	36 (12)	7 (21)	0.11
Malignancy	45 (13)	42 (14)	3 (9)	0.31
Autoimmune disease	18 (5)	17 (5)	1 (3)	0.44
HIV c infection	4 (0.5)	2 (0.6)	2 (6)	0.05
Charlson Comorbidity Index, mean ± SD	3 ± 2	3 ± 2	2 ± 2	0.06
APACHE II d Score, mean ± SD	10 ± 5	10 ± 5	10 ± 4	0.19

a Chronic obstructive pulmonary disease,

b End stage renal disease,

c Human immunodeficiency virus,

d Acute Physiology and Chronic Health Evaluation II.

Table 2

Respiratory supports, medical managements and outcome.

Features	All Patients n = 334	Non-pneumothorax n = 301	Pneumothorax n = 33	p-value
Total length of hospital stay*, median(IQR)	16 (1–133)	15 (1–90)	29 (9–133)	<0.001
ICU length of stay*, median(IQR)	11 (1–100)	10 (1–79)	23 (3–100)	<0.001
Maximal respiratory support, n (%)
High flow nasal cannula	7 (1)	6 (2)	1	0.08
Non-invasive mechanical ventilation	28 (8)	26(7)	2(1)	0.04
Invasive mechanical ventilation	299 (89)	269 (78)	30 (94)	0.01
Duration of Invasive ventilation*, median(IQR)	8 (1–97)	7 (1–79)	21 (1–97)	<0.001
Proning, n (%)	136 (40)	111 (36)	25 (75)	<0.001
Mechanical ventilation parameters, mean ± SD
Initial respiratory rate	22 ± 7	22 ± 7	22 ± 7	0.83
Average respiratory rate	22 ± 3	22 ± 3	23 ± 4	0.04
FiO2 (%)	71 ± 20	71 ± 20	76 ± 16	0.32
Tidal volume mL/kg PBW$	5.9±2.1	6±1.8	6.2±1.9	0.6
Positive end-expiratory pressure (cm H2O)	9.5 ± 3.4	9.5 ± 3.4	9.9 ± 3.2	0.52
Peak inspiratory pressure (cm H2O)	28 ± 6	28 ± 6	30 ± 5	0.07
Plateau pressure (cm H2O)	24 ± 5	24 ± 5	25 ± 4	0.23
Laboratory values, median(IQR)
Initial C-reactive protein (mg/L)	132 (5–1800)	132 (5–1800)	139 (25–620)	0.28
Initial ferritin (ng/mL)	518 (11–7500)	517 (11–7500)	575 (20–7500)	0.64
Treatment, n (%)
Glucocorticoids	251 (75)	220 (73)	31 (94)	0.004
Hydroxychloroquine	188 (56)	179 (59)	9 (27)	<0.001
Tocilizumab	88 (26)	66(22)	22 (66)	<0.001
Remdesivir	33 (9)	25 (8)	8 (24)	0.01
Vasopressors	219 (65)	191 (63)	28 (84)	0.04
Therapeutic anticoagulant	202 (60)	176 (58)	26 (78)	0.01
Ventilator dependent, n (%)	52 (15)	42 (14)	10 (30)	0.25
Mortality, n (%)	139 (41)	129 (42)	10 (30)	0.26

*Days,

$ predicted body weight

Hazard risks for pneumothorax

To evaluate for potential risk factors for pneumothorax, we performed a Cox proportional hazard regression (HR) model and evaluated several co-factors simultaneously to identify the best model to predict the presence of pneumothorax. To build the regression model, we selected cofactors, which were significantly different (p< 0.05) in univariate analysis between the two cohorts. The hazard probability of predictors lies in the range 0 to 1. We adjusted HR based on age, gender and BMI (Table 3) As shown, the ICU length of stay [HR = 0.92; CI (0.88–0.97), p = 0.005]; and TCZ therapy [HR = 10.7; CI (3.60–32.0), p<0.001] were significantly associated with pneumothorax. Although corticosteroids showed a HR of 0.58, the p value was not significant. Fig 1A shows the cumulative hazard ratio between cohorts who received TCZ therapy and who did not. The HR curve of pneumothorax in the TCZ group was increased around day 30 of hospital stay (Fig 1A). Fig 1B shows the Kaplan–Meier Curves depicting the survival function of pneumothorax in two cohorts based on receipt of TCZ therapy.

Table 3

Hazard risk of pneumothorax.

Variable	Hazard ratio (95% CI)	p-value
ICU length of stay	0.92 (0.88–0.97)	0.005
Duration of invasive ventilation	1.003 (0.95–1.05)	0.90
Average Respiratory rate	1.01 (0.90–1.14)	0.76
Proning: yes vs. no	1.02 (0.38–2.76)	0.96
Glucocorticoids: yes vs. no	0.58 (0.10–3.35)	0.54
Hydroxychloroquine: yes vs. no	1.12 (0.40–3.14)	0.81
Tocilizumab: yes vs. no	10.7 (3.60–32.0)	<0.001
Remdesivir: yes vs. no	1.78 (0.68–4.66)	0.23
Vasopressors: yes vs. no	1.64 (0.43–6.18)	0.46
Therapeutic anticoagulant: yes vs. no	0.69 (0.25–1.92)	0.48

Fig 1

A. Cox regression curve shows cumulative hazards function of Tocilizumab in developing pneumothorax during time of admission after adjusting for significant covariates. The black curve represents patients who did not receive tocilizumab and the red dotted curve represents patients who received tocilizumab. There was a significant difference (chi square test, p<0.001) between subjects who received tocilizumab and who didn’t. B. Kaplan-Meier survival curve shows cumulative probability of survival function of pneumothorax in two cohorts of tocilizumab and non-tocilizumab with known outcome up to 25 days of hospitalization. The black curve represents patients who did not receive tocilizumab and red dotted curve depicts patients who received tocilizumab. Survival function curves of pneumothorax are statistically different between two group based on receiving tocilizumab (log rank test, p<0.001) during time of admission.

Discussion

In this study, we found an overall incidence of pneumothorax of 10% among critically ill COVID-19 patients requiring ICU admission and invasive and/or non-invasive mechanical ventilation despite following the lung protective strategy. Development of pneumothorax in COVID-19 patients was associated with poor clinical outcomes and increased length of ICU stay. Although the This data corroborates recent publications evaluating the incidence and outcomes of pneumothorax in COVID-19 patients [7, 21, 22].

For the past two decades, lung-protective ventilatory strategies have become the standard of the care in ARDS management [23]. These strategies include low TV (4–6 mL/kg predicted body weight [PBW]), to achieve the lowest possible PEEP, peak and plateau pressures (<30 cm H2O) and avoid barotrauma [17]. Our study showed that tidal volume, PEEP, and peak and plateau pressures were not significantly different between patients who developed pneumothorax and those who did not. Furthermore, it has been described that the increased work of breathing in COVID-19 patients may induce Self- Inflicted Lung Injury (PSILI) [24], which may be a potential risk factor for pneumothorax. Although, our study showed a significant difference between groups in terms of mean RR, most patients who developed pneumothorax were paralyzed at the time of pneumothorax development, therefore, the PSILI less likely to explain the development of pneumothorax.

SARS-CoV-2 utilizes ACE2 receptors to gain entry into host cells, and data suggests thatACE2 serves a protective function in the alveolar epithelial repair process [5]. The damage of ACE2 by the SARS-CoV-2 virus may contribute to increased susceptibility to lung injury, including pneumothorax. However, the reported incidence of COVID-19associated pneumothorax is steadily increasing. Thus, it is warranted to seek other potential mechanisms of pneumothorax beyond the ventilatory settings or factors related to the pathogen itself, including the contribution of pharmacological therapies on cellular injury and repair. Unlike treatment of any viral infection or classical ARDS, treatment of COVID-19 associated respiratory failure led to initiation of numerous unprecedented novel treatments. As the ongoing pandemic continues, it is important to evaluate the potential interaction of these novel treatments on outcome and complications. Thus, we investigated the risk factors of pneumothorax using multivariate analysis and cox proportional regression hazard model and found that TCZ significantly associated with a higher risk of pneumothorax in COVID-19 patients.

Severe COVID-19 disease is linked to a hyper-inflammatory state based on high fever, elevated CRP, ferritin and various serum cytokines, including IL-6, tumor necrosis factor and IL-1β and others [25, 26]. Several studies suggest that IL-6 is a key cytokine associated with severity of COVID-19 disease [25, 27]. IL-6 is produced by almost all immune cells in response to infection and tissue damage and has various pleiotropic actions including B-cell activation, neutrophil and macrophage recruitments, and increased vascular permeability [28]. Therefore, inhibition of IL-6 was proposed as a potential therapeutic target when treating patients with COVID-19. Tocilizumab (TCZ) is a humanized antibody that binds to the IL-6 receptor, inhibiting its action [29]. Based on the efficacy of TCZ in cytokine release syndrome induced by CAR T-cell therapy, and potential role of IL-6 in the pathophysiology of COVID-19 ARDS, TCZ was promoted as a repurposed drug. Initial observational studies suggested that TCZ reduced mortality in COVID-19 patients [30-32]. However, randomized trials studying the efficacy of TCZ in hospitalized patients with COVID-19 failed to show a mortality benefit [33, 34]. The study by Veiga et al., was stopped early due to excessive mortality in the TCZ group at day 15 [34]. A meta-analysis of these early studies also failed to show a 28-day mortality benefit when using TCZ with a pooled RR of death of 1.09 (95% CI, 0.80–1.49). These studies primarily included patients, not requiring invasive or non-invasive mechanical ventilation, and therefore, recruited patients had much lower risk for pneumothorax than our study subjects. In addition, these studies were performed before the RECOVERY dexamethasone study [35] was published, so that the standard of care as it relates to administration of dexamethasone was different than current practice and rates of glucocorticoid administration were generally less than 25%. Safety events were assessed in some of these studies, however, pneumothorax were either not reported [15, 31], or showed no difference between TCZ patients and control [33, 34].

COVACTA was the first randomized controlled trial released publicly and included 452 patients (294 TCZ/144 control) hospitalized with severe COVID-19 pneumonia and treated with TCZ 8 mg/kg or placebo [11]. No significant difference was found in 28-day outcomes using a 7-category ordinal scale or mortality [11]. When looking specifically at the subset of patients receiving mechanical ventilation in this study, no benefit was shown by giving TCZ [23]. There was a high rate of adverse events in both the control and TCZ groups (81.1% vs. 77.3%, respectively.) but there was no mention of pneumothorax. Most studies have focused on anaphylaxis and infection as the main safety outcomes related to TCZ. It is important to note that there is a significant heterogeneity among TCZ studies, in terms of severity of COVID-19 disease, ICU requirements, or concomitant treatments. Studies have shown mixed results in critically ill COVID-patients requiring intensive care [12, 31]. After release of the RECOVERY trial using low-dose dexamethasone, the standard of care for treating hypoxic patients with COVID-19 changed and subsequent studies assessing TCZ combined with corticosteroids began to show improved outcomes [11, 16, 36, 37]. The REMAP-CAP trial had the highest percentage of patients on non-invasive and invasive ventilation and high rates of corticosteroid use (>80%), which is similar to our study population. They showed a significant reduction in 90-day mortality and more organ support-free days, but no significant adverse events [16]. To date, no significant differences in adverse events have been reported in studies comparing TCZ to standard care, but the care in most of these studies was different, in term of administration of dexamethasone, early anti-viral treatment with remdesivir, early monoclonal antibodies and prophylactic, not therapeutic anticoagulation in critically ill patients.

Our study shows that pneumothorax occurs relatively late (median 30 and mean 16 days from admission) in the course of disease, when CRP and fever were already down trending. Therefore, we postulated that dysregulation of lung repair may be important in pneumothorax development. This raises the question whether inhibition of IL-6 results in deleterious effects related to epithelial healing and cellular repair. IL-6 plays a key role in viral clearance, as well as angiogenesis, and therefore, inhibition of IL-6 could potentially cause harm through reduced viral clearance and interruption of the innate repair processes. In patients with severe lung injury, the remodeling and repair process may be an important piece in preventing pneumothorax. In a study examining biomarkers in COVID-19, survivors of COVID-19 had higher levels of epithelial growth factor, suggesting that alveolar regeneration and repair may be key features of lung recovery. Mechanisms to repair the alveolar epithelial barrier and restore a competent monolayer are initiated immediately in response to tissue injury. Initial epithelial repair events in ALI include proliferation, spreading, and migration of ATII cells to cover the denuded alveolar basement membrane [38]. Some insights in the role of IL-6 are provided by an animal model of influenza virus using IL-6 deficient mice showing that IL-6 ameliorates ALI after infection [39]. Similar effects of IL-6 have been shown by other animal studies [40]. Tocilizumab is a potent inhibitor of IL-8 and IL-6 and inhibits angiogenesis, however to what extent it inhibits EGF in COVID-19 is not known. Additionally, it is unclear what role, if any, the combination therapies like tocilizumab and dexamethasone have on the lung repair and recovery from respiratory failure, and whether antiviral treatment with remdesivir is important to facilitate viral clearance in patients whose immune response is impaired. Pneumothorax may be one identifiable example of how these drugs may interfere with the lung repair mechanisms. To our knowledge, this is the first study to raise concern about this serious adverse event of tocilizumab therapy in COVID-19.

Our study has certain noteworthy limitations. First, our study, like any other observational study, is prone to bias due to unmeasured confounders. Second, data was obtained from critically ill patients with relatively higher comorbid conditions that may raise the possibility of selection bias. Therefore, larger studies in critically ill patients are needed to assess the utility of TCZ. Third, the fact that receiving TCZ was guided by specific indications according to our institutional guidelines may create an indication bias. Fourth, missing and misclassification of data are possible because data were manually extracted. However, cox regression analysis did not include any variable with more than 10% missing data.

Conclusions

Pneumothorax is frequent in COVID-19 and is associated with poor outcomes. In our cohort, tocilizumab therapy was associated with increased HR for pneumothorax and increased length of stay in the ICU.

Institutional guidelines for Tocilizumab and anticoagulation therapy.

List of inclusion and exclusion criteria for tocilizumab therapy in our institution.

(DOCX)

Click here for additional data file.

3 Jun 2022

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Reviewer #1: Yes

Reviewer #2: Yes

**********

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Reviewer #1: Yes

Reviewer #2: Yes

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5. 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: Dear Editor,

Dear Authors,

I read the study entitled: "Incidence and Risk Factors of COVID-19 Associated Pneumothorax with great attention". The study is an observational retrospective investigation finding the "frequency" of pneumothorax in a population largely formed by African – American people.

Finally, the authors found a 10% pneumothorax frequency and, as a secondary result, tocilizumab was associated with it.

1) INTRODUCTION:

In the introduction, the authors comment that in COVID-19, thromboembolism and pneumothorax seem to show an elevated incidence.

In my opinion, you may better talk about "frequence". Second, when you argue about pneumothorax, you should speak about barotrauma. Barotrauma can be further composed of pneumothorax and pneumomediastinum.

It seems so uncommon to not have any pneumomediastinum in your population.

Up to date, what is known in COVID-19 is that pneumothorax is less frequent than pneumomediastinum compared to traditional ARDS. However, the effect of this phenomenon is largely unknown?

See this reference: McGuinness G, Zhan C, Rosenberg N, Azour L, Wickstrom M, Mason DM, Thomas KM, Moore WH, Increased Incidence of Barotrauma in Patients with COVID-19 on Invasive Mechanical Ventilation, Radiology, vol. 297, no. 2, pp. E252-E62, Nov 2020.doi:10.1148/radiol.2020202352.

The currently published scientific literature shows that pneumothorax occurs in 1 to 3% of hospitalized COVID-19 cases, with up to 6% in patients undergoing non-invasive ventilation (NIV) and mechanical ventilation (MV). Therefore, the frequency of pneumomediastinum and pneumothorax during COVID-19 is not well defined, as the available data are limited to case collections and single reports.

In McGuinness's analysis (see ref. above), which compared complications from barotrauma in patients with acute respiratory distress syndrome (ARDS) in VAM, the frequency of pneumothorax is 9%, of pneumomediastinum 10% in COVID- 19. In comparison, in non-COVID-19 patients, it is 12% for PNX and 3% for PMS.

2) INTRODUCTION:

This sentence needs a reference if true:

"It appears that the incidence of pneumothorax is increasing over time with subsequent waves of COVID-19 infection".

Along the line, the authors use pneumothorax and barotrauma indifferently, which should be corrected.

3) METHODS:

This section should be improved and explain inclusion and exclusion criteria and why the grade of pulmonary damage was not reported as lung ultrasound or CT scan scores.

4) STATISTIC

In the statistical section, the power analysis of the first aim is missing.

5) RESULTS

"Subjects in the pneumothorax cohort were more likely to require prone positioning (75% vs 36%; p<0.001)" maybe this is the consequence, not the cause?

"(Table 1). Most patients developed pneumothorax while on invasive mechanical ventilation" however, in the two courts, there were no significant differences in ventilator parameters between the two groups, except the average RR. How do you make the diagnosis of barotrauma? Could barotrauma be present before intubation?

6) RESULTS:

"Additionally, the pneumothorax group was

more likely to receive anticoagulation therapy, 78% versus 58%, p=0.01" how do you modify therapy?

There were no significant differences in mortality. That is not easy to understand.

"Second, we investigated the risk factors of barotrauma using multivariate analysis and the Cox proportional regression hazard model and found that TCZ significantly increased the risk of pneumothorax in COVID-19 patients.

That is a secondary endpoint without power analysis, and an association does not mean that this is true.

In this court, pneumothorax occurs relatively late (median 30 days) in the course

of the disease, when CRP and fever were already down-trending sound like, in the end, the lung has lost compliance and became more susceptible to barotrauma. We have observed in COVID-19 that barotrauma in COVID-19 is an early phenomenon linked to P-SILI without a clear explanation at the moment.

Reviewer #2: Dear authors,

I enjoyed reviewing this interesting paper. The subject is interesting and the paper in well written. I have detailed some comments below.

MAJOR COMMENTS:

1. In the introduction, the authors state that "Pneumothorax occurs when alveoli become damaged and/or ruptured due to elevated peak and plateau pressures, and can manifest as spontaneous pneumothorax, subcutaneous emphysema and pneumomediastinum.". Nonetheless, this is not always true ( doi: 10.1007/s00134-004-2187-7). Moreover, during the COVID-19 pandemic there seemed to be a remarkable increase in pneumomediastinum/subcutaneous emphysema occurrence despite the use of the same protective mechanical ventilation protocol used in non- COVID ARDS patients (https://doi.org/10.1183%2F23120541.00385-2020).This sentence need therefore to be rephrased.

2. Due to what is detailed in the above comment, the term "barotrauma" should be changed throughout the manuscript and abstract, using it only when elevated airway pressure is the cause of the presence of air outside the tracheobronchial tree. In its absence, such a condition should not be referred to as barotrauma, but simply described for what it is (pneumomediastinum, subcutaneous emphysema, pneumothorax)(https://doi.org/10.1183%2F23120541.00385-2020). In your study, tidal volume, PEEP, and peak and plateau pressures were not significantly different between patients who developed pneumothorax and those who did not.

**********

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Reviewer #1: Yes: Luigi Vetrugno

Reviewer #2: No

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7 Jul 2022

Point by point response:

We sincerely appreciate all valuable comments and suggestions, which helped us to improve the quality of the article. Our responses to the Reviewers’ comment are described below in a point-to-point manner. Appropriated changes, suggested by the Reviewers, has been introduced to the manuscript (highlighted within the document).

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We added the ethics statement only in the method section as required above.

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Reviewer #1: Yes

Reviewer #2: Yes

________________________________________

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

________________________________________

4. Is the manuscript presented in an intelligible fashion and written in standard English?

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

________________________________________

5. 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: Dear Editor,

Dear Authors,

I read the study entitled: "Incidence and Risk Factors of COVID-19 Associated Pneumothorax with great attention". The study is an observational retrospective investigation finding the "frequency" of pneumothorax in a population largely formed by African – American people.

Finally, the authors found a 10% pneumothorax frequency and, as a secondary result, tocilizumab was associated with it.

1) INTRODUCTION:

In the introduction, the authors comment that in COVID-19, thromboembolism and pneumothorax seem to show an elevated incidence.

In my opinion, you may better talk about "frequence".

Reply: In principal both incidence and prevalence examine the frequency of illness or injury Incidence refers to the occurrence of new cases (frequency) of disease or injury in a population over a specified period. We used the same term used by the cited articles, which was “incidence”. In all the cited articles, incidence was checked, not prevalence. Incidence is more specific term than frequency.

Second, when you argue about pneumothorax, you should speak about barotrauma. Barotrauma can be further composed of pneumothorax and pneumomediastinum.

It seems so uncommon to not have any pneumomediastinum in your population.

Up to date, what is known in COVID-19 is that pneumothorax is less frequent than pneumomediastinum compared to traditional ARDS. However, the effect of this phenomenon is largely unknown?

See this reference: McGuinness G, Zhan C, Rosenberg N, Azour L, Wickstrom M, Mason DM, Thomas KM, Moore WH, Increased Incidence of Barotrauma in Patients with COVID-19 on Invasive Mechanical Ventilation, Radiology, vol. 297, no. 2, pp. E252-E62, Nov 2020.doi:10.1148/radiol.2020202352.

The currently published scientific literature shows that pneumothorax occurs in 1 to 3% of hospitalized COVID-19 cases, with up to 6% in patients undergoing non-invasive ventilation (NIV) and mechanical ventilation (MV). Therefore, the frequency of pneumomediastinum and pneumothorax during COVID-19 is not well defined, as the available data are limited to case collections and single reports.

In McGuinness's analysis (see ref. above), which compared complications from barotrauma in patients with acute respiratory distress syndrome (ARDS) in VAM, the frequency of pneumothorax is 9%, of pneumomediastinum 10% in COVID- 19. In comparison, in non-COVID-19 patients, it is 12% for PNX and 3% for PMS.

Reply: Pneumomediastinum and subcutaneous emphysema occurs in the presence of alveolar micro injury that mostly is associated with pneumothorax or pneumothorax that is subclinical. We agree with your point. Therefore, we further examined our data and found that the incidence of pneumomediastinum was 20/334 (6%) and subcutaneous emphysema was 9/334 (3%). We added this finding in the result section. We focused on pneumothorax in our study as we feel it is more clinically important than pneumomediastinum or subcutaneous emphysema.

Again, I agree with you that the true frequency of pneumothorax (both in COVID and ARDS) is not well documented. I am an intensivist with more than 20 years ICU experience and believe that 12% of pneumothorax is well an overestimation! Nonetheless, the discrepancies of reported frequencies for pneumomediastinum, and subcutaneous emphysema can be partially explained by the heterogeneity of the method used for diagnosis between the studies. For example, higher detection of pneumomediastinum or subcutaneous emphysema could result from increased use of chest CT in some studies. But usually in mechanically ventilated patients the pneumomediastinum and subcutaneous emphysema can evolve to pneumothorax.

2) INTRODUCTION:

This sentence needs a reference if true:

"It appears that the incidence of pneumothorax is increasing over time with subsequent waves of COVID-19 infection".

Reply. That you for your comment. We rephrase the sentence. As it is possible that in early phase of pandemic clinicians did not pay much attention to this complication. We added a reference to the above sentence: (Palumbo et al., 2021).

The referred study showed higher incidence of pneumothorax in the second wave of the pandemic compared to the first. We adjusted our manuscript to specifically mention this finding.

Along the line, the authors use pneumothorax and barotrauma indifferently, which should be corrected.

Reply. Thank you for this observation, this was corrected.

3) METHODS:

This section should be improved and explain inclusion and exclusion criteria and why the grade of pulmonary damage was not reported as lung ultrasound or CT scan scores.

Reply: We already explained in detail the inclusion and the exclusion criteria for our study sample.

Inclusion criteria included: “patients aged ≥ 18 with COVID-19 positive (with laboratory-confirmed SARS-CoV-2 infection), who were admitted to the intensive care unit (ICU) for respiratory distress at Detroit Receiving Hospital and Harper University Hospital in Detroit Medical Center in Detroit, Michigan from May 2020 to February 2021.

While Exclusion criteria are: Patients with iatrogenic pneumothorax, or those requiring thoracentesis or chest tube drainage for pleural effusion; or receiving extracorporeal membrane oxygenation (ECMO) were excluded.

We also already provided a supplemental file for our Institutional guidelines for Tocilizumab therapy including a List of inclusion and exclusion criteria for tocilizumab therapy in our institution.

Regarding the grade of pulmonary damage: unfortunately, only small number of patients had ultrasound or CT of the lung done. This is mainly due to limited resources during the pandemic.

4) STATISTIC

In the statistical section, the power analysis of the first aim is missing.

Reply: Sorry I am not clear about the question. However, our initial intention was to evaluate the frequency of pneumothorax and evaluate the effect of gender. Based on power calculation (based on G power) we needed to have 148 subjects with evenly distributed gender to have a 95% CI. However, when we analyze our data, we saw no significant differences between gender. Therefore, we analyze based on the therapy and other characteristic such as ventilation. We did not mentioned the power analysis as does not contribute.

5) RESULTS

"Subjects in the pneumothorax cohort were more likely to require prone positioning (75% vs 36%; p<0.001)" maybe this is the consequence, not the cause?

Reply: Thank you for comment. The sentence above did not establish a relationship between pneumothorax and prone and we did not mean to do that. We reporting that in the pneumothorax group, subjects required more prone position suggesting more hypoxia in pneumothorax group. We believe that pneumothorax is related to the severity of the disease not to proning. Reviewing the literature, Pneumothorax was never reported as a complication of proning (Prone Positioning of Patients with Acute Respiratory Distress Syndrome: A Systematic Review - ProQuest, n.d.). In our study, pneumothorax happened either after or before pronning (we added this to our manuscript).

"(Table 1). Most patients developed pneumothorax while on invasive mechanical ventilation" however, in the two courts, there were no significant differences in ventilator parameters between the two groups, except the average RR. How do you make the diagnosis of barotrauma? Could barotrauma be present before intubation?

Reply: The diagnosis of pneumothorax was made based on chest X-ray results (This was added to the method section). At least once daily a CXR obtained during the ICU admission, in case of hypoxia or instability and after intubation we routinely perform CXR. Therefore, it is extremely unlikely that a patient developed pneumothorax before intubation and remained undetected by the ICU team. Regarding the time of pneumothorax related to intubation, we already mentioned this in our manuscript results section “Most patients developed pneumothorax while on invasive mechanical ventilation, except two patients, who developed pneumothorax while receiving HFNC or non-invasive mechanical ventilation”.

6) RESULTS:

"Additionally, the pneumothorax group was

more likely to receive anticoagulation therapy, 78% versus 58%, p=0.01" how do you modify therapy?

Reply: We added our institution guidance for COVID-19 specific therapies as well as anticoagulation in the supplemental file (S1 file). At that time, all patients with D-dimer >3 received full anticoagulation therapy (we also added this to the method section as well as to the result section).

There were no significant differences in mortality. That is not easy to understand.

Reply: This is true! However, this is what our data showed.

"Second, we investigated the risk factors of barotrauma using multivariate analysis and the Cox proportional regression hazard model and found that TCZ significantly increased the risk of pneumothorax in COVID-19 patients.

That is a secondary endpoint without power analysis, and an association does not mean that this is true.

Reply: We totally agree, association does not mean causation. We changed the sentence to “TCZ significantly associated with higher risk of pneumothorax in COVID-19 patients”. However, there is an statically significant association between TCZ and pneumothorax. Such association was not observed in case of steroid and other drugs.

In this court, pneumothorax occurs relatively late (median 30 days) in the course

of the disease, when CRP and fever were already down-trending sound like, in the end, the lung has lost compliance and became more susceptible to barotrauma. We have observed in COVID-19 that barotrauma in COVID-19 is an early phenomenon linked to P-SILI without a clear explanation at the moment.

Reply: We think this is a great point. It is possible that the pathology of early versus late pneumothorax differs. After reviewing the literature, three studies found that barotrauma is a late complication of COVID-19 (Elsaaran et al., 2021) (Belletti et al., 2021) (Kahn et al., 2021). In these studies, the mean time to development of barotrauma was range between 10 to 18 days from intubation or admission. While other studies found that barotrauma developed early in the course of the disease (Kumar Swain et al., 2021) (Lemmers et al., 2020) (Özdemir et al., 2021). In these studies, the mean time to development of barotrauma was range between 3 to 5 days from intubation or admission. Because of late occurrence of pneumothorax, we think the wound healing process is likely affected rather than disease itself. However, our study can not determine the cause and effect.

After reviewing our data and statistics, we found that the mean duration of mechanical ventilation prior to pneumothorax development was 10.3 days and the mean duration of ICU stay prior to pneumothorax was 15.7 days. Please keep in mind that most patients were admitted from the regular floor. This adds more days into the total hospital stay. This finding was added to the result section.

Reviewer #2: Dear authors,

I enjoyed reviewing this interesting paper. The subject is interesting and the paper in well written. I have detailed some comments below.

Reply: We appreciate your comment and thank you for taking the time and effort necessary to review the manuscript.

MAJOR COMMENTS:

1. In the introduction, the authors state that "Pneumothorax occurs when alveoli become damaged and/or ruptured due to elevated peak and plateau pressures, and can manifest as spontaneous pneumothorax, subcutaneous emphysema and pneumomediastinum.". Nonetheless, this is not always true ( doi: 10.1007/s00134-004-2187-7). Moreover, during the COVID-19 pandemic there seemed to be a remarkable increase in pneumomediastinum/subcutaneous emphysema occurrence despite the use of the same protective mechanical ventilation protocol used in non- COVID ARDS patients (https://doi.org/10.1183%2F23120541.00385-2020).This sentence need therefore to be rephrased.

Reply: We agree with you. Our study also showed that PEEP, peak and plateau pressures were not significantly different between patients who developed pneumothorax and those who did not. We revised the writing.

2. Due to what is detailed in the above comment, the term "barotrauma" should be changed throughout the manuscript and abstract, using it only when elevated airway pressure is the cause of the presence of air outside the tracheobronchial tree. In its absence, such a condition should not be referred to as barotrauma, but simply described for what it is (pneumomediastinum, subcutaneous emphysema, pneumothorax)(https://doi.org/10.1183%2F23120541.00385-2020). In your study, tidal volume, PEEP, and peak and plateau pressures were not significantly different between patients who developed pneumothorax and those who did not.

Reply: We agree with you. This has been revised.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

12 Jul 2022

Incidence and Risk Factors of COVID-19 Associated Pneumothorax

PONE-D-22-10994R1

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Reviewers' comments:

28 Jul 2022

PONE-D-22-10994R1

Incidence and risk factors of COVID-19 associated pneumothorax

Dear Dr. Samavati:

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