Thoracic Anesthesia for Morbidly Obese Patients and Obese Patients with Obstructive Sleep Apnea

Abstract

A patient with a body mass index (BMI) >30 kg/m2 is obese, and a patient with a BMI >40 kg/m2 is by definition morbidly obese (MO). Morbid obesity is associated with many medical conditions including hypertension, type II diabetes mellitus, cardiovascular disease, obstructive sleep apnea (OSA), and obesity hypoventilation syndrome (OHS). Moderate to severe OSA, often unrecognized, is present in >50% of MO patients. All MO patients should be managed as if they have OSA using the ASA Practice Guidelines for the Perioperative Management of Patients with Obstructive Sleep Apnea. The STOP-Bang questionnaire is a validated tool widely used to screen for OSA. Anesthesiologists should also have a high index of suspicion for the presence of OHS, especially in older MO patients. Patients with OHS have an even higher risk of developing cardiovascular problems and pulmonary hypertension. A MO OSA patient using a continuous positive airway pressure (CPAP) device preoperatively should bring their equipment to the hospital to use during their postoperative recovery. Many MO patients are difficult to ventilate by mask, but the majority have no difficulty undergoing direct laryngoscopy and successful tracheal intubation. The best preoperative predictors of potential problems with direct laryngoscopy in MO patients are a high Mallampati score (III or IV) and increased neck circumference (>48 cm men, >40 cm women). A MO patient in the supine position should never be allowed to breathe without assistance. Prior to induction of anesthesia, MO patients should be positioned in the head-elevated laryngoscopy position (HELP). If the patient is hemodynamically stable, the operating room table should also be in a reverse Trendelenburg position (RTP) to maximize “safe apnea time” (SAT). Obese patients are not at increased risk for gastric aspiration, and therefore a rapid sequence induction (RSI) is usually unnecessary. In obesity, drugs are administered based on lean body weight (LBW) and ideal body weight (IBW). The single exception is succinylcholine, which is dosed on total body weight (TBW). Depressant medications should be avoided preoperatively as they can decrease ventilatory responsiveness to hypoxemia and hypercarbia and can cause airway collapse. Regional anesthetic techniques should be used whenever possible. Multimodal analgesia (local anesthetics for epidural, spinal and paravertebral analgesia, nonsteroidal anti-inflammatory agents, and alpha-2 agonists (clonidine, dexmedetomidine)) is used to reduce the amount of opioids needed for pain management. MO patients tolerate one-lung ventilation (OLV) in the lateral position, and the success rate for lung separation with either a double-lumen tube (DLT) or bronchial blocker (BB) is similar to that in nonobese patients. Although there are no clinical studies of OLV in supine MO patients, in theory a MO patient would not be expected to tolerate OLV in this position. MO patients experience significantly more atelectasis, greater decreases in FRC, and lower PaO2 values postoperatively than matched normal-weight patients. Following long-duration procedures, MO patients can develop rhabdomyolysis (RML). Symptoms include numbness, pain, and weakness, all of which can be masked by regional anesthesia techniques. A creatinine phosphokinase (CPK) serum level of >1, 000 IU/L is diagnostic for RML. Associated myoglobinuria can cause acute renal failure. RML is initially treated with aggressive IV fluid administration.