The Health and Social Care Information Centre (HSCIC) together with the NHS in the UK reported a 30% increase in bariatric surgical procedures over the past 10 years and a ten-fold increase in hospital episodes related to obesity. Obese patients in the UK account for approx. 25% of all patients admitted to the ICU³. As the prevalence of obesity increases worldwide, obese surgical patients will be a growing challenge for physicians in the OR.

Obesity, especially morbid obesity, results in reduced lung volumes, significant atelectasis in dependent lung regions and a ventilation/perfusion mismatch. At the same time oxygen consumption and the work of breathing are increased⁴. This combination means that, following the onset of apnea, arterial oxygen levels may decrease rapidly. The reason for this lies in specific changes in the anatomy and physiology of obese patients, amplifying the risks associated with general anesthesia compared to non-obese patients and making obese patients prone to perioperative complications⁴. An altered strategy to pre-oxygenation and induction for obese patients may be considered, as desaturation occurs quickly in the lung and airway management can be difficult.

The post-operative phase may hold more respiratory challenges for obese patients when compared to non-obese patients. The effects of obesity described in our whitepaper persist in the post-operative phase. Obese patients suffering from obstructive sleep apnea (OSA) or from obesity hypoventilation syndrome (OHS) may be at a higher risk of postoperative pulmonary complications (PPCs) as opiate sensitivity adds to the severity of nocturnal hypoxia⁷.

Obese patients are more likely to develop post-operative acute respiratory failure and have higher rates of pneumonia⁷. Morbidly obese patients, known to have significantly more atelectasis preoperatively compared to non-obese patients, will develop more atelectasis after extubation. In non-obese patients, atelectasis developed during operation will return to normal within 24 hours postoperatively. In morbidly obese patients, atelectasis is more likely to persist⁸. This atelectasis increases the work of breathing further as the patient then breathes at lower lung volumes. This in turn is associated with early airway closure and expiratory flow limitations resulting in the development of intrinsic PEEP (PEEPi). These factors are worsened in the supine position – a potential challenge in the recovery room⁷.

Considering these factors, obese patients should be kept in an elevated position, such as the reversed Trendelenburg position or with elevated head and torso. Elevation mitigates intra-abdominal pressure effects on the lungs which in turn improves oxygenation and lung compliance. Continuous positive airway pressure (CPAP) and non-invasive ventilation (NIV) have been demonstrated to be beneficial since they can restore and maintain lung volumes and reduce the work of breathing. Particularly in morbidly obese patients, CPAP applied immediately after extubation improved spirometry 24 hours postoperatively as compared to deferring initiation of external CPAP to the recovery room. NIV has also been demonstrated to be feasible. One study demonstrated a 16% reduction in risk for post-extubation respiratory failure by the application of NIV immediately after extubation of patients with a BMI of >35. In addition, postoperative early mobilization and respiratory physiotherapy is recommended⁷.

In summary: Obese patients not only require adapted approaches during pre-oxygenation, induction and maintenance of general anesthesia, but modified respiratory care techniques in the immediate postoperative period have also been shown to be important in preventing postoperative pulmonary complications.

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2. Ng M, Fleming T, Robinson M, et al: Global, regional, and national prevalence of overweight and obesity in children and adults during 1980-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 2014;384:766-781.
3. Health and Social Care Information Centre. The Health Survey for England - 2012 trend tables. London: Health and Social Care Information Centre, 2013 Link
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