Keywords

1 Introduction

The number of overweight patients undergoing major surgical procedures and subsequently admitted to the intensive care unit (ICU) is dramatically increasing [1]. Since these patients are affected by several systemic pathophysiological alterations and comorbidities (Table 3.1), their management in both the operating room and ICU may present several challenges for the clinicians.

Table 3.1 More frequent systemic pathophysiological alterations in the obese patient
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Major surgery, general anesthesia and mechanical ventilation (MV) can per se contribute to the development of lung and systemic organ failure. However, a reliable tool to assess the perioperative and ICU risk for obese patients has not been yet defined [2].

2 Perioperative Management of the Obese Patient

2.1 Preoperative Evaluation

Preoperative evaluation of obese patients should take into consideration the assessment of the patient’s baseline functional state and comorbidities as well as the complexity of surgery. The vast majority of obese patients undergoing surgery are relatively healthy and their risk is similar to that of normal weight patients [3].

However, several risk factors in obese patients have been correlated to an increased incidence of perioperative complications and mortality, including: central obesity, metabolic syndrome [1], hypertension, BMI >50 kg/m2, male sex, age >45 years, risk factors for pulmonary embolism, overlap syndrome, obesity hypoventilation syndrome (OHS) and poor compliance to continuous positive airway pressure (CPAP) [4].

Difficult intubation and mask ventilation occur more frequently in obese compared to non-obese patients, and a thorough assessment of these risks should be performed. Risk factors for difficult ventilation include increasing BMI, age above 50 years and history of snoring. The main predictors for difficult intubation are almost the same as for the non-obese patients; other specific factors include neck circumference, the severity of obstructive sleep apnea (OSA) and OHS, pre-tracheal soft tissue thickness and high BMI [5, 6].

OSA is frequently undiagnosed (and untreated) until an acute-on-chronic respiratory failure occurs, which during the perioperative period can be exacerbated by the administration of sedatives, opioids and prolonged supine position [7, 8]. Preoperative identification of high-risk patients for respiratory complications is crucial as these patients can benefit from preoperative positive airway pressure (PAP) therapy and eventually ICU admission [6, 8].

The main key points of preoperative evaluations in obese patients are summarized in Table 3.2 [3, 6]. In the case of emergency surgery, the previous described assessments are not always feasible; therefore, the preoperative risk should be evaluated mainly through a quick clinical examination, and arterial blood gas samples to assess blood gas exchanges and serum lactate [3].

Table 3.2 Preoperative evaluation in the obese patient
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2.2 Intraoperative Management

2.2.1 Regional Anesthesia

Regional anesthesia presents several advantages, especially in obese patients, including minimal airway manipulation, avoidance of cardiopulmonary depression due to anesthetic drugs, reduced opioid requirements and postoperative nausea and vomiting. Unfortunately, loco-regional procedures in obese patients are often technically challenging and may be ineffective and therefore a plan for airway management and intubation is always recommended [6].

2.2.2 General Anesthesia

Each anesthesiological step can be potentially more difficult to perform in obese patients compared to the general population (Table 3.3).

Table 3.3 Intraoperative management of the obese patient: key points
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2.2.2.1 Induction of Anesthesia

Ideal or adjusted body weight is used to calculate initial anesthetic drug doses rather than total body weight. Current kinetic models use to titrate anesthetic agents to site effect that can generate paradoxical concentrations in morbidly obese patients. Therefore, the monitoring of the depth of anesthesia and of the neuromuscular block should be always considered. Caution is required with the use of long-acting drugs, especially opioids [3].

Quick and profound episodes of desaturation are common in obese patients; therefore, prolonged pre-oxygenation in ramped position is suggested to maximize the intrapulmonary oxygen reserve and to increase the safety period of apnea between induction and intubation [2].

In morbidly obese patients or patients with severe OSA, airway obstruction, hypoxemia or acute respiratory failure (ARF), pre-induction with high-flow oxygen with nasal cannula (HFNC) or PAP therapy should be considered [8].

Intubation should always be considered potentially at risk in obese patients and devices for difficult intubation should always be easily available; in particular, videolaryngoscopes have shown to be useful also in obese patients [2].

Supraglottic devices are increasingly used as rescue ventilatory, mainly in difficult ventilation or intubation. The use of supraglottic airway devices as a first line device should be reserved only for highly selected patients undergoing short procedures, when the upper airway is accessible and tracheal intubation quickly feasible [3].

2.2.2.2 Maintenance of Anesthesia

In obese patients, no evidence is available regarding the best anesthetic strategy to use. Achieving appropriate oxygenation and carbon dioxide levels as well as the choice of the respiratory settings to apply to obese patients during surgery can be challenging because of the previously described respiratory pitfalls [2, 9].

Several ventilatory strategies have been suggested to improve the perioperative outcome of obese patients; lung protective ventilation strategy with low tidal volume (Vt) and the use of positive end expiratory pressure (PEEP) should be considered in the operating room. The use of protective Vt is warranted to avoid high plateau pressure (Pplat) and high driving pressure (Pdriv), even if this can necessitate an increase of the respiratory rate to optimize carbon dioxide levels [10].

The appropriate intraoperative level of PEEP and its effect on postoperative outcome is controversial. Many authors are focusing their research on identifying strategies to set individualized PEEP (PEEPind); however, nowadays the hypothesis that PEEPind could produce better outcomes has still to be proven. Furthermore, some authors demonstrated that PEEPind could be significantly higher compared to the routinely used PEEP during anesthesia [11], thus posing the patient at risk for PEEP-related hemodynamic effects [12]. Intraoperative recruitment maneuvers (RMs) can have an important role in atelectasis reduction [13]. It is not clear which is the most efficient RM mode in preventing pulmonary complications [14]; however, it is well known that bag squeezing presents several pitfalls that have to discourage its use in favor of RMs consisting of stepwise transient changes of ventilator settings [15].

In obese patients, there are no data suggesting the superiority in terms of outcome between the different controlled ventilation modes [14]. Pressure support ventilation might be the most beneficial ventilatory mode, as it preserves muscular tone and prevents posterior-basilar atelectasis [2], but it is not often feasible in the intraoperative settings.

2.2.2.3 Emergence from Anesthesia

During the extubation phase in obese patients, a large number of complications are described. Therefore, an extubation plan should be always put in place (Table 3.3) [16].

2.3 Postoperative Management

Obesity predisposes to several postoperative complications, mainly involving the respiratory system [17]. To decrease the risk of complications, there are several postoperative strategies that could be adopted (Table 3.3) [7, 17, 18]. Several studies encourage the use of postoperative PAP therapy in obese patients to improve postoperative outcome [4], mainly in subjects with OHS and/or OSA [2, 8]. To date, there is no evidence supporting the use of a specific patient interface device and ventilation modality in obese patients. Intolerance is reported as a PAP treatment-related complication, while anastomotic leakage does not seem to be connected to the insufflation of PAP [19]. More studies about HFNC are needed before recommending this strategy in the post-extubation phase [2].

Obese patients without major medical comorbidities are managed in the standard post-anesthesia care unit [20]. Indications to ICU admission could be: BMI ≥ 50 kg/m2, long-acting opioid treatment, OSA or OHS and/or PAP therapy requirements, need for respiratory and cardiac monitoring, difficult glycemic control, intraoperative surgical or anesthetic complications and emergency surgery [3].

3 ICU Management of the Obese Surgical Patient

Critically ill obese patients may be at higher risk for acute cardiovascular, pulmonary and renal complications in comparison to healthy-weight patients [18]. Furthermore, obesity is associated with an increased risk of morbidity and death in the general population, but a decrease in mortality has been reported by some authors in patients with septic shock and acute respiratory distress syndrome (ARDS) (obesity paradox). The actual existence and basis for this apparent paradox are still debated [21]. In Table 3.4, the complications and corresponding management of obese patients admitted to ICU post-surgery are summarized [18, 20].

Table 3.4 Main ICU complications of the obese surgical patient and suggestions for reducing the risk of complications
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4 Conclusions

Obese patients present several challenges in the perioperative period and in the ICU. Obese patients present a bundle of pathophysiologic changes, with consequent pulmonary and cardiovascular issues, which make them susceptible to several complications. Future studies are warranted to better define the optimal settings of invasive mechanical ventilation, weaning protocols, hemodynamic monitoring and other specific strategies in this cohort of patients.