Accuracy of estimation of total body weight by legs and head weight measuring and comparison method in the anesthetized patients.

CONTEXT: Accurate patient weight is an important factor in the emergency and operating room departments. AIMS: The aim of this study is to determine the accuracy of estimation of total body weight by legs and head weight measuring and comparison method in the anesthetized patients. SETTINGS AND
DESIGN: Education of hospitals, Mazandaran University of Medical Sciences, prospective, observational study. SUBJECTS AND METHODS: This is prospective observational study. Nursing staff were asked to estimated weight that knows about a similar person weight on the operating room and matched together, then told his/her guests. They were measured total body weight before anesthesia and then patient head and legs weight after anesthesia. The main outcome was mean weight of these methods and percent accuracy in weight estimation for each group recorded. STATISTICAL ANALYSIS: Descriptive statistically used.
RESULTS: Overall, 57.3% (243/425) of operating personnel estimations were equal with actual weight. 35.4% (150/425) of the estimations were less 10 kg than the actual weight and only 7.3 (31/425) of the estimations were above 5 kg of actual weight. The accuracy of overall estimations by operating personnel and its comparison to the accuracy of legs weight, head, and sum weight by a similar method is demonstrated.
CONCLUSIONS: Despite having no formula in the critical intensive care and anesthesia region for estimation anesthetized, for comatose patient weight. We can use this formula, but where possible, should be based on measured weight for drug dose calculation and this is not possible, combination of these formulas is suitable.

INTRODUCTION

Measurement of weight during the pre-operative and anesthesia is very important because it is dependent to drug dosing, ventilation parameters, airway control, IV problems, and fluid management.[12] Drug dosage and infusion rates in adults are usually based on body weight.[345] One of the most common methods for arriving at a dosage is weight estimation.[678] Measuring weight may be impossible, especially for critically ill-patients and emergency condition and before anesthesia.[1391011] Dosage errors can occur when medications are ordered, especially in emergency state.[121314] In the operating room, with stressful condition, patients may frequently arrive unconscious or with emergency condition and accurate weight measurement can be difficult or impossible to obtain.[41214]

An overestimation of the patients’ weight will increase the calculated dosage of esthetics drugs and may result in potentially life-threatening side-effects. An underestimation will result in a lower dosage that may not provide the patient with therapeutic concentration of the medication and may result in side-effects. Thus, inaccurate estimation of total body weight in critically state is potentially dangerous.[10111315] Therefore, accurate estimation or measurement of weight of critically ill-patients or before anesthesia is an important for optimum esthetics agents and optimum clinical care.[5131516] Previous studies showed that many methods of estimation weight, for example, staff estimation, visual estimation, self-report estimation, and pediatric patients’ weight were inaccurate.[89111617181920]

The ability of practitioners, to estimate a patient's weight accurately has not been studied in the adult anesthetized population. Patients are not routinely weighed in our anesthesia department; and before anesthesia, weights were not listed on adult patient charts so far. The purpose of this study was to derive and validate simple method leg and head weight measurements for anesthetized patients to estimate body weight among comatose or anesthetized adult patients. The sum of lower limbs and head weight is very cheap can be performed easily and adapted for use of any unconsciousness patient too.

The purpose of this study was to assess the accuracy of the sum of lower limbs and head weights to determine total body weight of anesthetized patients and to compare it with the operating nurse's estimation, using comparison method. We hypothesized that a lower limbs sum head weight or similar method estimated of weight may give a better approximation of weight than other methods.

SUBJECTS AND METHODS

This prospective observational trial study was approved by Mazandaran University of Medical Sciences ethics committee. Moreover, all patients gave informed consent. Convenience sample of 425 patients were those who underwent elective surgical procedures who were given anesthesia drugs and enrolled at educational hospitals of Mazandaran province.

Two observers measured legs and head weight (LH weight) in 425 adult patients, who were lying on operating room trolleys, after anesthesia on an operating table by pediatric digital Weighing-scale. The capacity of the weight pediatric scale is 20 kg, with weight measurements displayed in 0.01 kg increments. The digital Weighing-Scale was used as well to obtain total actual body weight measurements, with capacity of 120 kg with 0.5 kg increments for all of the patients before anesthesia.

Before weight measurement, instruments displayed reading 0 kg, the researcher then assisted each patient during pre-anesthesia to put lower limbs side by side and then head on the instrument after anesthesia. When the display indicated the patient's weight measurement as stable, the researcher recorded the amount on the collection data forms 1, 2. Data form 1 contained demographic data of patients, which contained lower and head weight that was filled by the second researcher and blinded to the first data form. Patients’ sex, age, surgical procedure, height, endotracheal tube size and actual weight and esthetics agents, which were used, were recorded.

All anesthesia was performed in the supine position. Lower extremity of the foot and head weights were measured without any cover on the operating table. The part of body and patients body weight had measurements on three occasions that one time estimated by nursing of operating room (nurses) by comparison method estimated of weight. The part and total body weight of the patients were measured 3 times. In the First time, operating room nurses were asked to guess the weight of patient with using the comparison method before anesthesia. Second time, the patients, total weight was measured by the Beurer (Art. Nr. 710.00, Beurer. Ulm. Germany) before anesthesia. A total of 16 nurses worked on the study. The third time, the lower feet and head weight were measured by Infant weighing-Scale (Sonoform) after induction of anesthesia.

The comparison method (match method) means that since the first an operation room of nurse staff with known body weight was introduced to a person to estimate a patients weight who was laying on an operating table through observing the two persons appearance and comparing them judges the patient's weight.

The patient have been lay on the operating table, then one person of the operating room worker like patient in a standing position that his/her actual weight is known were shown to the nurse of operating room and asked him/her that were used attention similar together and estimated patient weight. Nursing of operating room was blinded from actual patient weights. Data collection forms were completed and collected by an associate investigator who was blinded from actual patient weights.

Accuracy of estimating weight (error) calculated by this formula:

Accuracy = Estimated weight − actual weight/actual weight.

Scatter grams and linear regression were used to analyze the data.

The SPSS version 15 for windows statistical package was used to analyze the data. The significance level in this study was P < 0.05.

RESULTS

There were 16 staff operating nurse's estimations and 425 patients were enrolled. In this study, 1700 times estimates and measures were obtained. The result showed that 62% (264 persons) of patients undergoing general anesthesia had endotracheal intubation.

The descriptive data include demographics patient characteristics, which are shown in Table 1.

Table 1

Patient demographic

The results show that the mean weight of legs is more than head weight while anesthetic patient is at supine position. These are shown in Table 2.

Table 2

Mean weight of legs and head (kg)

Experienced staff estimates were respectively, 52%, less than 5 years. 28% between 5 years and 15 years and the other persons had over 15 years of experience. The mean experience was 10.7 ± 8 years (2-30 years).

Personnel error rate to calculate the weight of patients in comparison method to the actual weight of the patients came in Table 3.

Table 3

Error of comparison method for estimating of weights (no=425)

Each participant on average 16 times estimated patient weight, with a range of 15-32 times.

The mean weight of our patients was 64.6 ± 11.5 kg (range 32-120).

Guess the patient weight were deference between male and female staff and their difference, respectively 66.1 ± 12.1 and 63.04 ± 10.7 (P < 0.006).

Overall, 57.3% (243/425) of operating personnel estimations were close to the actual weight. 35.4% (150/425) of the estimations were less 10 kg than the actual weight and only 7.3 (31/425) of them were estimated more than 5 kg of actual weight.

The accuracy of overall estimating of each methods and relation between them with actual total body weight is demonstrated in Figures 1–3.

Figure 1

Correlation between legs weight of anesthetized patients with actual weight

Figure 3

Correlation between comparison method estimation of weight with actual patient's weight

Correlation between legs plus head weight of anesthetized patients with actual weight

The single best predictor of actual weight between LH weight measurement and the sum of weights shows in the formula in Table 4.

Table 4

Model of estimated actual weight with linear regression

DISCUSSION

We undertook this study to determine LH weight, with the comparison method in anesthetized patients for estimating actual patient weight, to see whether the correlation linear between these measures with true patient weights is positive.

Overall, the operating personnel were as a group that helped anesthesiologists in the operating room for estimating anesthetized patients with comparison methods.

We showed 63.9% of nursing operating personnel before surgery were able to report the comparison method estimate weight within ±10% actual weight.

Vilke et al., showed that ability of Emergency Medical Technician-personnel to estimate weights were within ± 50% of actual weight. They have shown that estimation of pediatric patients’ weight by parents may not be reliable under more stressful situations.[2]

Anglemyer et al. recorded that child's body weight, 51.5% were within 5% of actual weight, 73.4% were within ±20%.[10]

Although these studies were performed on pediatric patients, the results of the two studies are approximately the same.

The findings of a similar method estimation (SUM) of our study are slightly better than the result of those studies, for true weight estimation. Thus, difference of results is perhaps related to the condition of patients and different methods of weight estimation in these studies.

Critical condition, for example intensive care unit, perianesthesia especially induction of anesthesia for emergency patients, and emergency department are stressful situations, thus, estimation of weight of patients may be difficult and not reliable.

However, our study was performed in genteelly condition and 16 personnel's of nursing operating room guest of an adult patient weight, with similar patient method, may be suitable for identifying adult patient's weight.

Therefore, the result of our study, which measured LH weight by the instrument, is not affected by an emergency situation; because the patients usually to be movement and it are not simply performed except they have been coma and although this method is reliable for the total body weight estimation.

Some study reported that a visual estimation of total body weight in critically ill-patients is inaccurate or underestimated self-reported her weight.[919]

These study methods of measuring weight by asking the person to state his or her weight, are not valid and reliable. Although the accuracy of our study has the degree of error for adult weight estimation, the similar method and sum of the LH weight have good correlation with true total body patients’ weight. These methods were easily performed at critically situations.

One of the most important findings of this study was that sum of the LH weight is better than legs and head separately for estimation of actual weight.

Actual weight = 10.8 + (5.1 × legs weight) + (5.5 × head weight), r = 0/65. This result may serve as a guide to anesthesiologists and other clinicians and researchers for patients that cannot be weighted by clinical practice and research.

Martin et al. in their study have shown that a majority of paramedics estimated within 20% of the actual weight.[21]

The previous studies shown that nursing staff and doctors with varying degrees of accuracy involving both over and under estimation in patients.[378122223]

Haftel et al. reported that paramedics in the field could not use the hanging leg weight method of estimating body weight for children.[22]

Limitations

This study (comparison method) may not be reliable under more stressful situations and legs sum head weight may be not suitable for estimated total weight for awake patients because all of the patients in our study were anesthetized. Furthermore, our study founded measuring of LH weight by instrument has no effect or change during stressful condition.

CONCLUSION

Therefore, we found improved estimations by personnel of operating room using the similar method and sum of LH weight together because it seems a simple method, and good correlated with total body weight for under patients.

This studies and similar method in our study may not be reliable under more stressful situations, but our study founded measuring of LH weight by instrument has no effect or change during stressful condition. Therefore, this method with good correlation coefficient (65%) to actual adult patient weight can help and guide anesthesiologists and other clinicians or researchers.

True weight of an adult patient LH = 10.8+ (5.1 × legs weight) + (5.5 × head weight), r = 65%. Despite having no formula in the critical intensive care and anesthesia region for estimation anesthetized, comatose patient weight.

We can use sum LH weight formula or SUM and LH weight under the new formula (LH SME weight):

True weight LH SME weight = –9.3 + (2 × SUM legs + head weight) + (0.83 × Operating nurse estimation weight) r = 0/87, r2 = 75%.