Complications of percutaneous tracheostomy in obese patients

I read with interest the article by Byhahn et al. [1] and would like to offer some comments on the study. The World Health Organisation (WHO) states ‘A BMI over 25 kg.m−2 is defined as overweight, and a BMI of over 30 kg.m−2 as obese’[2]. This study may therefore have categorised as ‘obese’ patients that the WHO would consider to be non-obese. Even the average BMI in the obese group, BMI 29.1 kg.m−2, is not within the WHO's obese category. Furthermore, the average BMI of the study's obese group (29.1 kg.m−2) is not very different to that of their non-obese group (24.5 kg.m−2). In addition, I wonder whether the BMI alone is the correct measurement that should have been used in this study. Some studies on obesity and obstructive sleep apnoea appear to show that the effects of obesity on the airway are probably secondary to variation in neck circumference [3] and suggest that the obesity produces its effect via fat in the neck [4]. It would have been interesting to know whether the complications of tracheostomy were greater in those patients with a high neck circumference to height ratio. This would also be more practical to measure in ITU than body weight and BMI. The sex of the subjects in the study was not stated, and may be important in the interpretation of results as there is a greater proportion of neck fat in men than women [5]. It is not stated whether the operators had similar training and experience in the procedures. A learning curve has been described for percutaneous dilational tracheostomy [6] and variation in operator ability alone could explain the differences in the complication rates between the two groups. The choice of technique used was user-dependent and not randomised. Peri-operative complication rates vary for the different techniques used: for example, 4–12% for Ciaglia's technique and about 4% for Griggs' technique [6]. These differences could lead to difficulties with the interpretation of the results. ‘Discharge to another hospital’ was used as a marker of the end of the peri-operative period. However, some of the complications listed, such as peristomal infection, could have developed after transfer and therefore have been missed from the results. The finding that ‘the rate of intermediate complications was not significantly different’ between the two groups may not be valid. Seven major complications in six obese patients were reported, but not all the details were provided. Only five of the techniques involved were stated and only two BMI figures given. Moreover, it is not known whether the same operator did all of the procedures that resulted in complications. Some of the major complications which occurred, such as ‘accidental extubation and difficulty reintubating’ and ‘intra-operative airway loss’, could have more to do with the abilities of the person caring for the airway during the procedure than with the patients' BMIs. This study seems to have too many design problems to allow the authors to conclude that the risk for peri-operative complications with percutaneous tracheostomy is ‘high in obese patients’. Perhaps a more standardised method with one operator, or operators with similar levels of experience and training, studying convincingly obese patients should have been used. Each tracheostomy technique could also be studied in turn so that any differences in complication rates could be more reliably attributed to the patients' BMIs. We would like to thank Ms Dawson for her valuable comments. She is right that, according to the World Health Organisation, overweight is defined as a BMI > 25 kg.m−2, and obesity as a BMI > 30 kg.m−2. Unfortunately, as in many fields of medical and scientific research, there is no uniform definition of overweight and obesity. The Canadian Task Force on Preventive Health Care, for example, defines obesity as BMI > 27 kg.m−2[1], which is even stricter than the 27.5 kg.m−2 threshold used in our study. This lack of uniform definitions in medical research often leads to difficulties with data interpretation, as in the present study. We agree with Ms Dawson's suggestion not to rely on the BMI alone as a marker of obesity, but to consider also the neck circumference. However, we were not aware of the potential impact of the neck-circumference-to-height-ratio on the patient's airway, but will adopt these measurements for forthcoming studies. Regarding the four different tracheostomy techniques used, the investigators were equally experienced with each technique. We do not believe therefore that learning curves or a lack of skill had an impact on either the number and the type of complications. There were no statistically or clinically significant differences between the four techniques used in terms of complications in both groups. However, Ms Dawson is right that some complications in the late postoperative period could have been missed in patients discharged to another hospital. Nine patients (12.3%) in the obese and 77 patients (19.2%) in the control group were discharged to other hospitals. Since we usually receive feedback from secondary hospitals or rehabilitation facilities when clinically important complications occur in patients who have been transferred from our ICU while still cannulated, it is unlikely that major and intermediate postoperative complications were missed. In conclusion, we still feel that percutaneous tracheostomy in obese patients – without recommending a certain BMI threshold – should be performed after thorough risk–benefit analysis by operators who are experts in both percutaneous tracheostomy and airway management.

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