THE EFFECTS OF ELEVATED INTRAABDOMINAL PRESSURE, HYPERCARBIA, AND POSITIONING ON THE HEMODYNAMIC-RESPONSES TO LAPAROSCOPIC COLECTOMY IN PIGS

Background: This study investigated three factors postulated to be sou rces of physiological stress in laparoscopic surgery: hypercarbia, ele vated intraabdominal pressure, and the steep Trendelenburg position. O ur research was designed to define the effects of each of these potent ial stressors on hemodynamic responses observed during laparoscopic co lectomy in pigs. Methods: Twenty-four pigs were randomized into the fo llowing four groups, based on the method for obtaining surgical exposu re while a colectomy or laparoscopic-assisted colectomy was performed: Open surgery (n = 6), CO2 pneumoperitoneum (n = 6), Helium pneumoperi toneum (n = 6), and abdominal wall Lifter (n = 6). The animals were pa ralyzed with minute ventilation adjusted. All animals underwent extens ive pulmonary and hemodynamic monitoring with measurements of the foll owing parameters: RR, Vt, minute ventilation, O-2, sat, ETCO2, PVR, HR , MAP, CO, PAP, CVP, PCWP, SV, LVSWI, DO2, and VO2. The laparoscopic p igs were placed in the steep Trendelenburg position during surgery. Re sults: The effect of a CO pneumoperitoneum was to increase PaCO2 PVR a nd cause an acidemia that could not be prevented by an increase in min ute ventilation. Elevated intraabdominal pressure decreased UO. Both p neumoperitoneum groups had a fourfold increase in IVCP, a measure of i ntraabdominal pressure. Some of this increase was due to placement int o the Trendelenburg position; IVCP increased to a lesser degree in the Lifter group. The steep Trendelenburg position caused significant inc reases in PAP, CVP, and PCWP; however, a contributory effect of elevat ed intraabdominal pressure cannot be ruled out. None of these procedur es had any significant effect on the HR or MAP. There was a significan t increase in CO in the CO2 and Lifter groups; however, when CO was co ntrolled for HR effects, there was no significant effect on SV from an y of these different procedures. LVSWI, DO2, and VO2 were not affected by any of the different exposure methods. Conclusions: The effects of laparoscopic surgery and open surgery on hemodynamic responses are mi nimal, and no one method is superior to another when performed in pigs that are healthy, hydrated, and hyperventilated to keep ETCO2 <40. Ho wever, since elderly and sick patients have a lower threshold for phys iologic decompensation, we can infer that the small hemodynamic change s noted in this study might become significant factors when surgery is performed on compromised patients. The finding that an abdominal wall lifting device causes the fewest metabolic and hemodynamic effects ma kes its use an important consideration when performing laparoscopic su rgery in patients with cardiopulmonary compromise, hemodynamic instabi lity, or any preexisting renal insufficiency.