Reduction in lung capacity and compliance, and worsening of ventilation-perfusion mismatch are the most pronounced pulmonary effects of intra-abdominal insufflation with CO2. These effects are exacerbated by the head-down tilt position for pelvic laparoscopy.

The response to these factors is a tendency toward atelectasis, hypoxemia, and hypercapnia. CO2 absorption has no direct effect on pulmonary function. The anesthesiologist's manipulation of ventilatory parameters during laparoscopy allows the body to keep pace with the excess CO2 absorbed by the peritoneal membrane.

Normal pulmonary function is adequate to eliminate the small amount of absorbed CO2. In most patients, any tendency toward an increase in PaCO2 owing to CO2 absorption and worsened lung mechanics is easily addressed by increasing minute ventilation.

Because invasive arterial-blood gas sampling is required to measure PaCO2, end-tidal CO2 [P(et)CO2] is monitored intraoperatively with capnography to estimate the PaCO2 during general anesthesia; the P(et)CO2 is 3 to 5 mmHg lower than the PaCO2. The P(a-et)CO2 gradient, equal to the difference between PaCO2 and P(et)CO2, is not significantly worsened during short laparoscopic procedures in healthy patients (39,53,61). Therefore, a sustained P(et)CO2 between 30 and 40 mmHg indicates acceptable PaCO2 in most patients. In patients with pulmonary disease, however, a PaCO2 rise causes an unpredictable P(a-et)CO2 increase (62,63). Sampling of arterial blood gases may be necessary to monitor accurately the CO2 elimination in patients with pulmonary disease.

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