VENTILATORY EFFECTS, BLOOD-GAS CHANGES, AND OXYGEN-CONSUMPTION DURING LAPAROSCOPIC HYSTERECTOMY

We evaluated the ventilatory effects and blood gas changes of prolonged CO2-pneumoperitoneum in normoventilated patients and examined the respiratory and gas exchange consequences of head-down positioning (25-30 degrees) and CO2 insufflation into the peritoneal cavity in 20 patients without major cardiorespiratory disorders in various phases of laparoscopic hysterectomy. The patients received general anesthesia with isoflurane, fentanyl, and vecuronium, and minute ventilation (MV) was adjusted to maintain the PETCO(2) at 33-36 mm Hg throughout the entire procedure, either by increasing the tidal volume (TV) and keeping the respiratory rate (RR) at 12/min (10 patients) or by changing the RR and maintaining the TV at 8 mL/kg (10 patients). Arterial and mixed venous blood samples were collected simultaneously for blood gas analysis and for measurements of oxygen consumption, and respiratory mechanics and gases were recorded by an anesthetic gas analyzer and side stream spirometry device. Oxygen consumption decreased with anesthesia, remained stable to the end of the laparoscopy, increased soon after deflation of the pneumoperitoneum, and reached preanesthetic values during recovery. The MV requirement increased by approximately 30% after the start of CO2 insufflation, then increased somewhat further toward the end of the laparoscopy, reaching the highest level a few minutes after deflation of the intra-abdominal gas. The compliance decreased by 20% with the head-down position and by an additional 30% with the increased intraabdominal pressure. PaCO2 and mixed venous PCO2 increased with CO2 insufflation, and the arterial to end-tidal PCO2 (a-etPCO(2)) gradient increased by 1.5 mm Hg during laparoscopy. A mild metabolic acidosis developed. The MV requirement was more among patients whose RR was changed to maintain normocapnia. In conclusion, there was a small increase in the a-etPCO(2) gradient, indicating some increase in alveolar dead space during laparoscopy. Normocapnia during laparoscopy in healthy patients was achieved by maintaining the PETCO(2) at a somewhat lower level than normal, preferably by increasing the TV of controlled ventilation.