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Anesthesia adversely affects respiratory function, particularly in morbidly obese patients. Although many studies have been performed to determine the optimal ventilatory settings in these patients, this question has not been answered. The aim of this study was to evaluate the effect of reverse Trendelenburg position (RTP) on gas exchange and respiratory mechanics in 15 obese patients undergoing biliopancreatic diversion. A standardized anesthetic regimen was used and patients were examined at standard times: 1) after tracheal intubation, 2) after laparotomy, 3) after positioning of subcostal retractors, 4) with retractors in RTP. The measurements of respiratory mechanics were repeated for a wide range of tidal volumes by using the technique of rapid occlusion during constant flow inflation. We noted a wide alveolar-arterial oxygen difference [P(A-a)O(2)] in all patients, particularly during Phase 3. When the patients were placed in RTP, P(A-a)O(2) showed a significant improvement and a return toward baseline values. As for mechanics, total respiratory system compliance was significantly higher in RTP than in the other phases. In conclusion, our data suggest that RTP is an appropriate intraoperative posture for obese subjects because it causes minimal arterial blood pressure changes and improves oxygenation.

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Background: Endoscopic parathyroidectomy and thyroidectomy were introduced into clinical practice in 1995. Concerns about the use of carbon dioxide insufflation in the neck exist owing to reports of potential adverse metabolic and hemodynamic changes. Hypothesis: Carbon dioxide insufflation in the neck may cause adverse effects on hemodynamic and blood gas levels. These adverse effects may reflect the level of pressure and duration of insufflation. Methods: Fifteen pigs, 5 per group, underwent endoscopic thyroidectomy at 10, 15, and 20 mm Hg. Partial pressure of carbon dioxide (arterial), pH, cardiac output, central venous pressure, heart rate, and mean arterial pressure (MAP) were measured at baseline, 1 and 2 hours after carbon dioxide insufflation, and 30 minutes after desufflation.

RTP and PEEP can be considered adequate ventilatory settings for morbidly obese patients, without any significant difference with regard to gas exchange improvement. However, the decrease in CO may partially counteract the beneficial effects on oxygenation of these ventilatory settings.

Background: Driving pressure (DP) represents tidal volume normalised to respiratory system compliance (C RS) and is a novel parameter to target ventilator settings. We conducted a study to determine whether C RS and DP reflect aerated lung volume and dynamic strain during general anaesthesia. Methods: Twenty non-obese patients undergoing open abdominal surgery received three PEEP levels (2, 7, or 12 cm H 2 O) in random order with constant tidal volume ventilation. Respiratory mechanics, lung volumes, and alveolar recruitment were measured to assess end-expiratory aerated volume, which was compared with the patient's individual predicted functional residual capacity in supine position (FRCp). Results: C RS was linearly related to aerated volume and DP to dynamic strain at PEEP of 2 cm H 2 O (intraoperative FRC) (r¼0.72 and r¼0.73, both P<0.001). These relationships were maintained with higher PEEP only when aerated volume did not overcome FRCp (r¼0.73, P<0.001; r¼0.54, P¼0.004), with 100 ml lung volume increases accompanied by 1.8 ml cm H 2 O À1 (95% confidence interval [1.1e2.5]) increases in C RS. When aerated volume was greater or equal to FRCp (35% of patients at PEEP 2 cm H 2 O, 55% at PEEP 7 cm H 2 O, and 75% at PEEP 12 cm H 2 O), C RS and DP were independent from aerated volume and dynamic strain, with C RS weakly but significantly inversely related to alveolar dead space fraction (r¼e0.47, P¼0.001). PEEP-induced alveolar recruitment yielded higher C RS and reduced DP only at aerated volumes below FRCp (P¼0.015 and 0.008, respectively). Conclusions: During general anaesthesia, respiratory system compliance and driving pressure reflect aerated lung volume and dynamic strain, respectively, only if aerated volume does not exceed functional residual capacity in supine position, which is a frequent event when PEEP is used in this setting.

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