The lateral position used for laparoscopic renal surgery does not have much effect on hemodynamics unless impingement on the vena cava by extreme lateral flexion reduces venous return (6). For upper abdominal laparoscopic procedures, the patient is sometimes placed in a head-up tilt (reverse Trendelenburg) position to drop bowel away from the operative field. This position decreases cardiac output (7,8), and there is inconsistent evidence that this position may improve pulmonary mechanics during laparoscopy (9-11).

The intraperitoneal approach to radical prostatectomy and other laparoscopic pelvic surgeries is facilitated by a head-down tilt (Trendelenburg) position, which tends to modestly increase cardiac output (12-15). Most, but not all, studies suggest that this position restricts diaphragmatic movement and increases ventilation-perfusion mismatch during laparoscopy (10,16,17).

Insufflation of gas elevates the intra-abdominal pressure. Increase in intra-abdominal pressure is the most prominent of the physiologic insults of laparoscopy and can have dramatic effects with only small changes.

Vascular compression by elevated intraabdominal pressure increases the systemic vascular resistance, which tends to reduce cardiac output. The magnitude of the effect of intra-abdominal pressure on systemic vascular resistance varies with the extent and duration of insufflation pressure and the volume status of the subject.

Intra-abdominal pressure directly impacts venous return, which also affects cardiac output.

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