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

Abstract

Body mass index (BMI) (BMI = Weightkilograms/(Height) meters 2 ) is a measure of obesity. A patient with a BMI >30 kg/m2 is obese, and >40 kg/m2 morbidly obese (MO). Morbid obesity is associated with medical conditions including hypertension, type II diabetes, cardiac disease, and obstructive sleep apnea (OSA). Moderate to severe OSA is present in more than 50% of MO patients, and is often unrecognized. Definitive diagnosis is made by polysomnography (PSG). In the absence of PSG documentation, all MO patients should be managed as if they have OSA. The ASA Practice Guidelines for the Perioperative Management of Patients with Obstructive Sleep Apnea should be used for all MO patients, whether or not they have had a PSG diagnosis of OSA. The best preoperative predictors of potential problems with tracheal intubation in MO patients are high Mallampati (III or IV) score and increased neck circumference (>48 cm men, >40 cm women). Many MO are difficult to ventilate by face mask, but the majority have no difficulty undergoing direct laryngoscopy and tracheal intubation. Never allow a supine MO patient to breathe without assistance. A MO patient should be positioned in the head-elevated laryngoscopy position (HELP) prior to anesthetic induction. In this position, the patient’s head and upper body are ramped or “stacked” so that an imaginary horizontal line can be drawn from the sternum to the ear. If the patient is hemodynamically stable, the operating room table should also be in a reverse-Trendelenburg position (RTP) to maximize “safe apnea time.” MO patients tolerate one-lung ventilation (OLV) in the lateral position. Although there are no clinical studies of OLV in supine MO patients, in theory a MO patient would not be expected to tolerate OLV this position. A MO OSA patient using a continuous positive airway pressure (CPAP) device preoperatively should bring their equipment to the hospital for use during their postoperative recovery. Depressant medications can decrease ventilatory responsiveness to hypoxemia and hypercarbia in all MO patients, and can also cause airway collapse in OSA patients. Avoid sedative premedication and long-lasting opioids since both increase the risk of postoperative ventilatory problems. Use regional techniques when possible. For postoperative analgesia, use multimodal analgesic therapy (local anesthetics for epidural, spinal and paravertebral analgesia, nonsteroidal anti-inflammatory agents, and alpha-2 agonists (clonidine, dexmedetomidine)) to reduce the need for opioids. Following any long-duration operation check the patient’s serum for creatinine phosphokinase (CPK). A CPK level >1,000 IU/L is diagnostic for rhabdomyolysis (RML). The initial symptoms of RML (numbness, pain, weakness) can be masked, especially if epidural analgesia is being used.