Bariatric Times

MAY 2018

A peer-reviewed, evidence-based journal that promotes clinical development and metabolic insights in total bariatric patient care for the healthcare professional

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Opinion Review 9 Bariatric Times • May 2018 usually during urgent or emergent procedures involving RSI. 17 During RSI bolus, doses of induction and paralyzing drugs are given in quick succession. NAP5 reported that titration of the anesthetic induction agent until loss of consciousness is achieved would reduce awareness events. NAP5 suggested a "fundamental reassessment" of the indications for RSI. Cricoid pressure is an integral part of RSI. Applying too low a force can lead to incomplete occlusion of the esophagus, while excessive force can compress the trachea and deform the airway anatomy making tracheal intubation more difficult. 18 The incidence of failed intubations is increased when cricoid pressure is applied. 19 Cricoid pressure also decreases lower esophageal sphincter tone, and this might explain the occurrence of aspiration during RSI. 20 Cricoid pressure is difficult to perform correctly, is potentially dangerous, and probably offers no protection. OPTIMAL ANESTHETIC INDUCTION IN PATIENTS WITH OBESITY The anesthetic management of a patient with morbid obesity does differ from that of other patients. For induction, the standard supine position must be avoided since a patient with obesity lying flat will experience a marked decrease in lung volume. This will result in a marked reduction of oxygen reserves following preoxygenation. The "safe apnea period" (SAP), that is, the length of time following paralysis and apnea until the onset of hypoxemia, is very short. Unless tracheal intubation is achieved quickly and/or the duration of SAP is increased, patients with obesity can experience hypoxemia following paralysis. A patient with obesity should be placed in a "ramped" or "head-elevated laryngoscopy position" (HELP). 21 This improves the view during direct laryngoscopy so that successful tracheal intubation can be accomplished more rapidly. 22 If the patient is hemodynamically stable, the operating table should also be tilted in a reverse-Trendelenburg position to "unload" the diaphragm. This will increase lung volume and oxygen reserves, lengthening the duration of the SAP and allowing more time to intubate the trachea. Prior to induction, a patient with obesity is preoxygenated until his or her oxygen saturation (SpO 2 ) is 100 percent and end-tidal O 2 is greater than 90 perecnt. The application of some form of "apneic oxygenation" (THRIVE, nasal cannulae or buccal O 2 ) can also be applied. In RSI, bag- mask ventilation is avoided because of concerns that positive-pressure ventilation will inflate the stomach, increasing the risk of aspiration. It has been demonstrated that clinically significant gastric insufflation does not occur during normal bag-mask ventilation, even when cricoid pressure is applied. 23 The incidence of oxygen desaturation (SpO 2 < 95%) is as high as 35 percent in patients undergoing RSI without bag-mask ventilation. 24 For a patient with obesity and a markedly shortened SAP, the risk of hypoxemia could be even greater, especially if an initial attempt at tracheal intubation fails. Unlike RSI, the anesthetic induction of a patient with obesity should include positive-pressure bag-mask ventilation following paralysis and prior to intubation. 25–26 Giving fixed doses of drugs in rapid succession during RSI can lead to under-dosing and patient awareness, or over-dosing with potentially serious hemodynamic consequences. Administration of the induction agent in a patient with obesity should titrated to loss of consciousness. The initial dose should be based on lean body weight and not total body weight. Following administration of the induction agent, assessment of adequate depth of anesthesia should be performed before administering a neuromuscular blocking agent for The anesthetic management of a patient with morbid obesity does differ from that of other patients.

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