Perioperative Care of the Patient with Obesity

Introduction

• Over 40% of the adult population in America is obese. Patients with obesity frequently have concurrent comorbidities such as heart disease, diabetes, and pulmonary dysfunction. The presence of these comorbidities increases the risk for anesthesia.
• A thorough preoperative evaluation allows the clinician to optimize the patient’s health prior to anesthesia to mitigate risk.

Preoperative Assessment

• Preoperative assessment of patients with obesity should be thorough and prioritize the identification of pathophysiology with anesthetic implications. The history and physical examination of the patient with obesity can be approached in a systems-based manner as outlined in Table 1.

Airway

• A critical component of the preoperative assessment of patients with obesity is a detailed airway exam. Several risk factors are associated with difficult intubation and/or mask ventilation. These airway risk factors are outlined in Table 2 and illustrated in Figure 1.

• Patients with obesity have a significantly reduced functional residual capacity (FRC), which results in rapid desaturation following induction.
• Proper positioning of patients before laryngoscopy is important. One can use the 25-degree reverse Trendelenburg position or the ramped position where the patients’ external auditory meatus is at the same level as the sternum.
• Apneic oxygenation with 15 L/minute oxygen through a nasopharyngeal airway and a standard nasal cannula can significantly increase the safe apneic duration during induction of anesthesia.¹
• Both direct laryngoscopy and video laryngoscopy can be used to facilitate endotracheal intubation. There is no conclusive evidence that video laryngoscopy is superior to direct laryngoscopy in patients with obesity.³

Monitoring and Mechanical Ventilation

• Monitoring oxygenation, ventilation, and circulation in the patient with obesity can have unique challenges.
• Atelectasis-induced hypoxemia is a risk that should be monitored intraoperatively. Patients with obesity are at an increased risk of atelectasis due to decreased total lung capacity, vital capacity, and functional residual capacity. Application of positive end-expiratory pressure (PEEP) intraoperatively minimizes atelectasis. PEEP titration can be difficult in patients with obesity, but titration of PEEP using esophageal manometry has shown to be beneficial in this population.² Use of esophageal manometry, a surrogate for pleural pressures, allows for monitoring of transpulmonary pressure, and alveoli are kept open if the transpulmonary pressure P L (i.e., the difference between airway pressure and pleural pressure) exceeds atmospheric pressure.
• Protective mechanical ventilation should be used in patients with obesity using low tidal volumes (6-8 mL/kg of ideal body weight), low to moderate levels of PEEP, and titrating the inspired oxygen fraction to achieve oxygen saturations of 92-95%.⁴
• Capnography has limitations in patients with obesity due to a greater expired CO₂/arterial CO₂ gradient than in lean subjects. Furthermore, patients with obesity have an increased production of CO₂ secondary to high oxygen consumption (VO₂). One may consider arterial blood gasses to guide ventilation settings.
• When monitoring circulation, the goal is to maintain adequate end-organ perfusion. Currently, standard noninvasive blood pressure (NIBP) is our best available routine surrogate measurement but is vulnerable to greater inaccuracy in patients with obesity compared to nonobese patients.³ In patients with obesity, forearm NIBP exhibits better measurement performance than upper arm or lower leg readings.⁵ Furthermore, NIBP measured at the wrist has the highest correlation with radial arterial catheter blood pressure measurements.⁶

Extubation and Postoperative Care

• When extubating patients with obesity, one must ensure adequate tidal volumes are being achieved, which can be facilitated by positioning the patient in the ramped position or 25-degree reverse Trendelenburg position prior to extubation.³
• If there is a concern for obstruction after extubation, use of an oral airway or nasal trumpet is advised.
• Patients with obesity have altered respiratory mechanics, which places them at an increased risk for postoperative pulmonary complications (PPC), which can range from mild (unplanned need for oxygen) to severe (acute respiratory distress syndrome or need for reintubation). PPCs are associated with increased PACU time, increased length of hospitalization, and mortality.
• Given their increased risk for PPCs, patients with obesity should be carefully monitored in the PACU, with specific attention to recurrent respiratory events, including apnea, bradypnea, pain-sedation mismatch, CO₂ retention, and oxygen desaturation. Should postoperative respiratory events persist, an inpatient admission may be warranted.⁴