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| |  ASA: Obesity Associated with Hypoxaemia During Cesarean Section By Anne Jacobson Special to DG News ORLANDO, FL -- October 18, 2002 -- In obstetric patients, obesity is associated with a significant decrease in partial arterial oxygen pressure (PaO2) and increase in alveolar-arterial oxygen difference (A-aDO2) after induction and intubation. In these patients, obesity is also associated with increased risk of venous air embolism of posture change, although it has minimal effects on respiration and circulation. Shinji Kawahito, MD, of the Tokushima University School of Medicine, in Tokushima, Japan, reported his findings here October 16 at the 55th Annual Meeting of the American Society of Anesthesiologists (ASA). The influence of obesity in the decrease of PaO2 and the increase of A-aDO2 due to the change of posture was minimum. Venous air embolism occurred often, however, its effects on respiration and circulation were limited. Anaesthesia induction and tracheal intubation caused a significant decrease of PaO2 and an increase of A-aDO2 especially for obese parturients. To evaluate the effects of anesthaesia induction and change in posture from a sitting to a supine position on arterial blood gases in obese and normal obstetric patients, Dr. Kawahito studied 29 obstetric patients scheduled for cesarean section. Patients with a body mass index (BMI) greater than 30 were considered to be obese (n=16); those with BMI of 30 or less were considered normal (n=13). Preoperative pulmonary tests included measurements of vital capacity (VC), expiratory reserve volume (ERV), and closing volume (CV). During surgery, venous air embolism was monitored using transesophageal echocardiography (TEE). All patients received general anaesthaesia. Arterial blood gas analysis was performed and A-aDO2 was calculated at three points -- before anaesthaesia induction (room air; both sitting position and supine position), and after tracheal intubation (supine position, fraction of inspired oxygen [FIO2]=0.5). Compared with normal patients, VC and ERV-CV were significantly lower among obese patients. After changing position from sitting to supine, PaO2 in both groups tended to decrease. Compared with obese patients, normal patients had significantly lower PaO2 after intubation. In the normal group, PaO2 values at the three time points were 106.4, 99.5, and 217.0 mm Hg, respectively, compared with 104.9, 98.4, and 150.5 mm Hg, respectively, in the obese group. Similar changes in A-aDO2 were observed. Though venous air embolism was detected during surgery in seven patients (24 percent), its severity was mild and was not associated with oxygen desaturation, Dr. Kawahito said. Obstetric patients are likely to develop hypoxia, so that apnea for a short interval during tracheal intubation may cause severe hypoxaemia, he added. Venous air embolism is also a concern during cesarean section, especially, during repair of the uterus The influence of obesity in the decrease of PaO2 and the increase of A-aDO2 due to the change of posture was minimum. Venous air embolism often occurred, however, its effects on respiration and circulation were limited. Anaesthesia induction and tracheal intubation caused a significant decrease of PaO2 and an increase of A-aDO2 especially for obese parturients, he concluded.
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