Obesity is further classified according to fat distribution, namely, the android and gynecoid obesity (Fig. 12.2). This distinction has important clinical implications [5].

Android (or central) obesity mainly involves the upper part of the body and often implies intra-abdominal visceral fat accumulation. This type of obesity predominates in men and can lead to the metabolic syndrome, a group of risk factors known to predispose to type 2 diabetes and cardiovascular disease. Indeed, from a physiological standpoint, adipose cells should not be regarded only for its role in energy balance and storage. Abdominal fat does participate in a prothrombotic and pro-inflammatory cascade that affects fatty acid metabolism and contributes to the development of insulin resistance [6]. There are several definitions of the metabolic syndrome, but recognition is mostly based on the finding of at least three of the following five criteria: (1) glucose intolerance, (2) abdominal obesity, (3) increased blood pressure, (4) low high-density lipoprotein (HDL) levels, and (5) increased triglyceride (TG) level [7]. The metabolic syndrome may have a negative impact on outcomes after noncardiac and cardiac procedures. It increases the risk of perioperative and postoperative complications [8]. In contrast, women more often present with a gynecoid (or peripheral) obesity that involves predominantly the accumulation of fat at the thighs and hips levels. The intra-abdominal cavity being relatively spared from significant fat accumulation, they may avoid the complications associated with the metabolic syndrome. Consequently, indirect measures of central fat distribution such as the waist circumference may be better markers of obesity-related comorbidities such as coronary artery disease [9]. Also, abdominal obesity may be of importance in the postoperative period. Not surprisingly, in a large cohort of patients who underwent isolated CABG, a strong association between BMI-defined obesity and adverse postoperative events was found. More interestingly, adiposity, assessed according to WC, was associated with an increased risk of postoperative adverse events, independently of BMI. This data suggest that WC and BMI, both markers of different features of adiposity, are both associated with postoperative complications [10].

Cardiomyopathy is a common finding among the severely obese patients, and it can lead to diastolic and/or systolic heart failure [11]. A significant accumulation of body fat causes an increase in overall metabolism, blood volume, and cardiac output. The heart chambers dilate in response to a chronic volume overload, thus increasing stress on ventricular walls. The myocardium adapts to this phenomenon through hypertrophy. This eventually leads to left ventricular dysfunction and diastolic heart failure. With long-standing severe obesity, myocardial hypertrophy fails to compensate for this additional stress imposed on the ventricles. Systolic heart failure may eventually develop. This often occurs after several years of severe obesity (BMI > 50 kg/m²) [12]. It should be noted that the ventricular remodeling associated with obesity may be reversible after significant weight loss [13–15]. Because pulmonary comorbidities are frequently found in this population, right ventricular dysfunction is a common finding. Repeated hypoxic episodes lead to pulmonary hypertension and ensuing right ventricular dilatation and eventually failure [14].

Obesity impacts respiratory function in various ways. The burden on respiratory mechanics and diaphragmatic excursion will be greater if the bulk of tissue is in the upper chest and abdominal area, as seen with central obesity. Chest compliance is diminished, and reduced lung volumes confirm the presence of a restrictive syndrome. Also, the increased circulating blood volume adds to this restrictive physiology by decreasing lung compliance. The functional residual capacity (FRC) is primarily affecting lung volume. This lower FRC, especially in the supine position, often leads to lung volumes being lower than the closing capacity, causing ventilation-perfusion mismatch and hypoxemia even during normal breathing [16]. This phenomenon is increased during general anesthesia. Overall, obese subjects present an increased work of breathing, and to compensate, they tend to adopt a breathing pattern with reduced tidal volumes and higher respiratory rates. Obesity-induced bronchial hyperactivity is frequent in this population, and it can be resistant to standard asthma treatment [17]. An abundance of soft tissue in the cervical region predisposes to upper airway obstruction. Therefore, obstructive sleep apnea (OSA) affects up to 40% of obese patients [18]. Patients with severe undiagnosed OSA are particularly at risk of respiratory depression during the postoperative period, especially with the administration of opiates. The patient suffering from OSA who is not adequately managed with a continuous positive airway pressure (CPAP) could then present episodes of significant desaturation, even a few days after the procedure [19]. Moreover, the treatment of moderate to severe OSA with a CPAP reduces the risk of cardiovascular complications in the long term and should be instituted when feasible [20].

The obesity hypoventilation syndrome (Pickwickian syndrome) is characterized by daytime hypercapnia related to central hypoventilation. The physiopathology of this condition remains imprecise. It is estimated that this syndrome affects about 11% of severely obese patients suffering from OSA [21]. These patients are particularly vulnerable to postoperative respiratory complications and often present with significant right ventricular dysfunction. Of importance, waist circumference (WC) has been shown to be associated with an increased risk of postoperative atrial fibrillation, prolonged mechanical ventilation and reintubation, renal failure, and new postoperative renal replacement therapy, blood stream infection, sternal wound infections, and intensive care unit and hospital length of stay independently of BMI. These associations were independent of BMI, a marker of total adiposity in contrast to WC, which represents a marker of central obesity. These findings suggest that, besides total adiposity per se, fat mass distribution also influences clinical outcomes after isolated CABG [10].

Obese patients have a higher incidence of type 2 diabetes, chronic kidney disease, osteoarthritis, hiatal hernias and certain types of cancer. They may also develop nonalcoholic fatty liver disease, which can progress to cirrhosis. The obesity-related state of chronic inflammation and impaired fibrinolysis place patients with high BMI at risk for thromboembolic complications, especially in the perioperative period.

Some obese patients presenting for surgery are relatively healthy, and thus, the need for further cardiac evaluation should be based on the patient’s specific risk factors for cardiovascular disease and the risks associated with the surgery itself [14]. A patient’s ability to perform at least four metabolic equivalents (METs) should be reassuring that its cardiopulmonary status is adequate to undergo most low- and intermediate-risk surgeries without further testing [22]. Unfortunately, obese patients may have limited functional capacity because of weight-related issues. Also, dyspnea on exertion, non-anginal chest pain and lower limb edema are frequent complaints in this population.

Features of the metabolic syndrome should be actively sought, as it is frequently associated with coronary artery disease [7]. A preoperative electrocardiogram should be obtained if coronary artery disease is suspected based on history or risk factors. A new left bundle branch block can be a sign of occult CAD. An ECG showing right axis deviation or a right bundle branch block should raise suspicion of possible right ventricular dysfunction and pulmonary hypertension, and further investigation is appropriate [14].

An algorithm for the assessment of severely obese individuals undergoing noncardiac surgery has been published and may help in planning appropriate investigations in this population [14]. Known coexisting cardiac conditions should be stable prior to surgery and optimized if necessary.

OSA is usually diagnosed based on the apnea-hypopnea index (AHI) following a sleep study using an overnight polysomnography. Treatment with a CPAP is recommended for moderate (15–30 events/h) and severe OSA (>30 events/h) [23]. A polysomnography is a costly exam, time-consuming, and not always readily available in the perioperative setting. The “STOPBANG” questionnaire (Table 12.2) is validated in the surgical population for preoperative screening for OSA [24]. It has a high sensitivity in detecting severe OSA using a cutoff score ≥3 (100% sensitivity) but with only moderate specificity. In the obese population, using a cutoff score of four provides a better balance between sensitivity and specificity, yielding lower false-positive rates. If a patient scores 0–2 on the questionnaire, moderate or severe OSA can be confidently ruled out [25].

OSA increases the risk of perioperative complications [23]. Identifying patients at high risk for OSA before surgery will target perioperative precautions and interventions that may help reduce perioperative complications. OSA should ideally be diagnosed during the preoperative period in order to adjust a continuous positive airway pressure (CPAP) device, and this may decrease perioperative complication rates. According to the Society of Anesthesia and Sleep Medicine guidelines, when management of comorbid conditions has been optimized, patients with diagnosed, partially treated, untreated, or suspected OSA may proceed to surgery, provided that strategies for mitigation of postoperative complications are implemented [23]. The obesity hypoventilation syndrome can be suspected in patients with severe OSA and severe obesity. Elevated serum bicarbonate levels (>27 mmol/L) should raise suspicion that this condition is present. The diagnosis can be confirmed during the preoperative assessment by arterial blood gases showing a PCO₂ > 45 mmHg and a PO₂ < 70 mmHg (at room air) if there are no other pathologies to explain these findings [25].

Whether for inducing general anesthesia or for an awake intubation, the adequate positioning of the obese patient and the optimal preoxygenation are essential for a safe airway management.

The supine position is undoubtedly the worst enemy regarding the oxygen reserve in the obese patient. The weight of the abdomen compresses the functional residual capacity (FRC) and even more when the patient has a paralyzed diaphragm. The impact on FRC of different positions of the obese patient on the operating table has been evaluated [32]. Preliminary results suggest that reverse Trendelenburg and beach chair positions are superior to the decubitus position to ensure a safe apnea period [32]. Furthermore, when a preoxygenation is performed in spontaneous ventilation, the patient is often unable to overcome the restriction of lung compression due to the abdominal content. Therefore, oxygen reserve is built up via deeper lung volumes. Using a CPAP or a BiPAP can defeat this restrictive syndrome and provide efficient preoxygenation [33].

We recently showed that reverse Trendelenburg position used in association with noninvasive positive pressure preoxygenation compared with the association of beach chair position with spontaneous ventilation allowed 16% longer (42 s) safe non-hypoxic apnea time (Sat O₂ > 90%) (258 ± 42 vs. 217 s ± 17, p = 0.0053) and faster recovery to Sat O₂ = 97% (68 ± 11 vs. 88 s ± 17, p = 0.029) following ventilation when reaching Sat O₂ = 90% after tracheal intubation [34]. These results confirmed our laboratory data which demonstrated in awake obese patient the advantage of the association of reverse Trendelenburg position and noninvasive positive pressure preoxygenation to get better FRC compared to the association of beach chair or supine position with spontaneous ventilation [35] (Fig. 12.3).