Change of respiratory mechanics at different intra-abdominal pressures and position change during laparoscopic surgery

Corresponding author: Dea Ja Um, M.D., Department of Anesthesiology and Pain Medicine, Yonsei University Wonju College of Medicine, 162, Ilsan-dong, Wonju 220-701, Korea. Tel: 82-33-741-1522, Fax: 82-33-742-8198, E-mail: [email protected] This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. CC Laparoscopy results in less scar formation due to smaller incision, and less postoperative pain, facilitating earlier ambulation. These characteristics result in decreased pulmonary com plication rate and shortened admission time, leading to numerous advantages such as reduction of medical cost. As laparo scopy involves maximal increase in abdominal pressure through continuous flow of carbon dioxide gas into the abdominal cavity, numerous studies have reported the resulting hemodynamic, respiratory and endocrinologic alterations, as well as surgical complications [1]. We have compared the dynamic compliance, peak airway pressure and respiratory resistance, as the abdominal pressure and body position change during laparoscopic gynecologic surgeries. This protocol involved 50 patients who were classified as having physical status class I or II according to the American Society of Anesthesiologists, and had no underlying cardiopulmonary diseases or planned elective operations. All patients informed consent prior to being included in the study. All patients were premedicated by glycopyrrolate (0.004 mg/kg) and midazolam (0.06 mg/kg) 30 minutes prior to induction. Anesthesia was induced by intravenous thiopental sodium (5 mg/kg) and vecuronium (0.1 mg/kg). Anesthesia was maintained by volume-controlled ventilation with O2 (2 L/ min), N2O (2 L/min) and enflurane (1.5-2 vol%). Additional vecuronium (0.02 mg/kg) was administered to maintain constant muscle paralysis as needed. Tidal volume of 10 ml/ kg and respiratory rate of 14/minute was maintained with a volume anesthesia ventilator (Ohmeda, Modulus). Blood pressure, heart rate, oxygen saturation, and end-tidal carbon dioxide pressure (EtCO2) were measured continuously using patient-monitoring devices. The patients were maintained in 15 lithotomy-Trendelenburg position during operation time, and carbon dioxide was injected at the start of and during operation to achieve and maintain steady abdominal pressure at 14 mmHg for H group and 10 mmHg for L group. Dynamic compliance, peak airway pressure, and respiratory resistance were measured with VENTRAK (Novametrix Medical System Inc, USA) at 2 minutes after the beginning of mechanical ventilation (control), 3 minutes after position change (immediately before carbon dioxide insufflation) and 5 and 15 minutes after carbon dioxide insufflation. All measurements are presented as mean ±standard deviation, and Wilcoxon signed-rank test and Mann-Whitney test were performed for intraand inter-group comparison of respiratory dynamics. P values less than 0.05 were determined as statistically significant. Dynamic compliance in the H group significantly decreased from 61.3 ± 13.2 ml/cmH2O for the control to 57.7 ± 11.6 ml/ cmH2O after positional change (P < 0.05), continuing to decrease to 32.5 ± 9.2 ml/cmH2O and 30.3 ± 6.6 ml/cmH2O at 5 minutes and 15 minutes after carbon dioxide insufflation. Dynamic compliance also significantly decreased in the L group at each measurement. There was no significant difference between the H group and L group in dynamic compliance at any measurement point (Fig. 1). In the H group, the peak airway pressure did not change noticeably upon positional change compared to the control, but was significantly elevated with an increasing trend with the passage of time. In the L group, the peak airway pressure was 13.1 ± 2.1 cmH2O for the control, which