Date Published: February 26, 2012
Publisher: Hindawi Publishing Corporation
Author(s): Alessia Pedoto.
Obesity is a worldwide health problem affecting 34% of the American population. As a result, more patients requiring anesthesia for thoracic surgery will be overweight or obese. Changes in static and dynamic respiratory mechanics, upper airway anatomy, as well as multiple preoperative comorbidities and altered drug metabolism, characterize obese patients and affect the anesthetic plan at multiple levels. During the preoperative evaluation, patients should be assessed to identify who is at risk for difficult ventilation and intubation, and postoperative complications. The analgesia plan should be executed starting in the preoperative area, to increase the success of extubation at the end of the case and prevent reintubation. Intraoperative ventilatory settings should be customized to the changes in respiratory mechanics for the specific patient and procedure, to minimize the risk of lung damage. Several non invasive ventilatory modalities are available to increase the success rate of extubation at the end of the case and to prevent reintubation. The goal of this review is to evaluate the physiological and anatomical changes associated with obesity and how they affect the multiple components of the anesthetic management for thoracic procedures.
Obesity is a worldwide health problem. It is estimated that 34% of the North American adult population is obese, of which 5% is morbidly obese . Thus, more patients requiring anesthesia for thoracic surgery will be overweight or obese. Anesthetic goals for thoracic procedures include a smooth induction and intubation, stable hemodynamic parameters during the intraoperative period, optimal lung isolation with adequate minute ventilation and good oxygenation,and optimal analgesia. However, being obese poses a challenge for all the above. The aim of this paper is to evaluate the physiological and anatomical changes associated with obesity and how they affect the anesthetic management for thoracic procedures.
Induction of general anesthesia causes a significant decrease in FRC, which is inversely related to the increased BMI . A low FRC, paired with increased intrapulmonary shunt, decreased chest wall and lung compliance, increased airway resistance and atelectasis predispose the obese patient to rapid desaturation on induction [19, 20]. This may be aggravated by the abnormal upper airway anatomy, especially in the presence of OSA, causing difficult mask ventilation and intubation. The supine position causes a further decrease in FRC, due to both a cephalad displacement of the diaphragm and an increase in pulmonary blood volume. Both total respiratory and chest wall compliance are decreased when supine. Ventilation and perfusion are mismatched. As a result, relative hypoxemia is quite common and may persist in the postoperative period . Patients should be placed in a semisitting position, preoxygenated for more than 5 minutes, and induced only if deemed easy to mask ventilate. If not, awake-fiberoptic intubation should be considered after topicalizing the airway with a local anesthetic. If sedation is needed, dexmedetomidine can be beneficial, as it has sedative and analgesic properties, with the lack of respiratory depression. Recruitment maneuvers, consisting of continuous positive pressure at 40 cmH20 for 40 seconds, when used immediately after induction of general anesthesia seem to be successful at reducing the degree of atelectasis and improving oxygenation in normal weight and obese subjects , especially when followed by the immediate use of PEEP [10, 20].
General anesthesia, surgery (especially high abdominal and thoracic procedures), as well as suboptimal analgesia, are all contributory factors to abnormal respiratory mechanics in the postoperative period, which may persist for several days . The resulting restrictive respiratory pattern seen in obese patients contributes to an increased work of breathing and the tendency to develop atelectasis. Therefore, weaning from the ventilator may be prolonged, increasing the rate of ICU admissions and the overall hospital length of stay . The rate of reintubation may also be higher when compared to normal weight patients. Noninvasive ventilation modalities have been developed trying to decrease the incidence of postoperative respiratory complications and avoid reintubation in the immediate postoperative period.
Obese patients have significant changes in static and dynamic respiratory mechanics, as well as multiple preoperative comorbidities, which should be considered when providing general anesthesia. The preoperative evaluation should be tailored to identify patients at risk for difficult ventilation and intubation and postoperative complications. The analgesia plan should be executed starting in the preoperative area. Intraoperative ventilatory settings should be customized to the changes in respiratory mechanics for the specific patient and procedure. Several non invasive ventilatory modalities are available to increase the success rate of extubation at the end of the case and to prevent reintubation. However, they are not free of risks and complications. A high index of suspicion for postoperative respiratory complications is necessary prior to the start of the case, as well as a thorough multidisciplinary approach to the perioperative care in order to optimize outcomes.