Renal and Hormonal

Urine output decreases during laparoscopy (64,65). In one study, urine output during laparoscopy was only 0.03 mL/kg/hr, compared to 1.70 mL/kg/hr immediately postoperatively, despite an average intravenous intraoperative fluid administration of 13.0 mL/kg/hr (66). In rodents, an intra-abdominal pressure less than 10 mmHg produces only mild oliguria, whereas pressures greater than 10 mmHg reduce urine output by 50% to 100% (67). Using a porcine model, McDougall et al. observed a 29% reduction of the urine output during intra-abdominal insufflation at pressures lesser than 10 mmHg, and a 65% reduction with pneumoperitoneum greater than 10 mmHg pressure (68).

The mechanisms involved in oliguria during CO2 insufflation include (i) increased renal vein resistance (with subsequent decreased renal blood flow); (ii) renal parenchymal compression; (iii) activation of hormonal factors such as the renin-angiotensin system; and (iv) increased levels of antidiuretic hormone (67,69-76).

A reduction in creatinine clearance occurs corresponding to the decreased urine output during laparoscopy. In one study on laparoscopic cholecystectomy, creatinine clearance decreased in 29 of 48 patients, with the decrease being more than 50% in eight patients (77). Creatinine clearance decreased 18% with intra-abdominal pressures less than 10 mmHg, and 53% with pressures above 10 mmHg also in the porcine model studied by McDougall et al. (68).

The kidney appears to be particularly compromised more than other organs by the combination of hypovolemia and increased intra-abdominal pressure (27).

In addition to the respiratory acidosis that usually accompanies CO2 insufflation, various investigators have reported coexisting trends toward both metabolic alkalosis (61) and metabolic acidosis (53,78). Experimentally, metabolic acidosis is noted only at gas insufflation pressures greater than 20 mmHg (68). The cause does not appear to be lactate acidosis from splanchnic hypoperfusion because there is no increase in the anion gap. Reduction in renal function due to acid retention occurring at high intra-abdomi-nal pressures is a more likely etiology (68).

Several studies have evaluated systemic stress, immunologic derangement, and inflammation associated with laparoscopy using a number of humoral and cell-mediated measures.

When compared to open surgery, laparoscopy tends to be associated with less stress, immunologic compromise, and inflammation. However, results of published studies have been markedly variable in this regard (73,79-89).

Many of the effects appear to be related to CO2 directly (84,90). Although laparoscopy appears to be beneficial in terms of less impact on nitrogen balance and energy metabolism when compared to open surgery, the clinical significance of these findings is uncertain (88,91,92).

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