In the UK, the majority of maternal anesthesia-related deaths occurred under general anesthesia and, therefore, only 5-19% of cesarean sections are presently performed under this kind of anesthesia.[22,44]
Airway-management problems are the principal cause of maternal death under general anesthesia, including aspiration of gastric content, failed intubation, inadequate ventilation and respiratory failure. One in 280 attempted tracheal intubations in obstetrics fail, compared with one in 2230 in the general population. Although the increasing weight or BMI per se are not risk factors for difficult laryngoscopy, some authors report increased incidence of difficult or failed intubation in morbidly obese parturient (up to 33%), as well as increased difficulty in maintaining adequate mask ventilation.[47,48] The strategy recommended for airway management for the obese parturient is similar to the routine management of morbidly obese patients. Potential airway-management problems (e.g., fat face and cheeks, limited range of motion of the head, neck and jaw, small mouth with large tongue, excessive palatal and pharyngeal tissue, short large neck and high Mallampati [III or IV] score) should all be evaluated during the preoperative anesthesiologic exam. High Mallampati score and large neck circumference are the most reliable predictors of potential intubation difficulties. If a difficulty is anticipated preoperatively, an awake oral intubation with a fiber optic bronchoscope is recommended. The nasal route is not recommended because of the characteristic engorgement of nasal mucosa during pregnancy.
If potential airway problems are excluded, the steps that need to be followed to ensure successful oro-tracheal intubation should include preoxygenation, 'ramped' position (head, upper body and shoulders significantly elevated to align the pharyngeal, laryngeal and tracheal axis) and rapid sequence induction combined with cricoid pressure.[12,50] However, all the necessary aids for difficult intubation, such as a short laryngoscope handle, a variety of laryngoscope blades, special laryngoscopy equipments, equipment for cricothyroidotomy and transtracheal jet ventilation, should always be available. Moreover, a second experienced anesthesiologist should be present to assist when difficulty is anticipated.
Prevention of acid aspiration is important in every parturient, but even more so in obese patients. For elective cesarean delivery, an H2-receptor antagonist can be administered orally the night before and again on the morning of surgery along with 30 ml of nonparticulate antacid to increase gastric fluid pH and decrease gastric fluid content.
A study comparing three different preoxygenation techniques in pregnant women showed that the eight deep breaths or 3 min of tidal volume breathing with FiO2 of 100% performed better oxygenation than four deep breaths.
Succinylcholine is still the muscle relaxant of choice for intubation in the obstetric patient. Both pseudocholinesterase levels and extracellular fluid space are increased in obesity but pregnancy reduces pseudocholinesterase activity. However, relatively high doses of succinylcholine (1.0 mg/kg total bodyweight) are needed for a rapid sequence anesthetic induction.
Expert Rev of Obstet Gynecol. 2009;4(3):313-319. © 2009 Expert Reviews Ltd
Cite this: Pathophysiological and Perioperative Features of Morbidly Obese Parturients - Medscape - May 01, 2009.