Correlation of CO2 pneumoperitoneal pressures between rodents and humans

Many studies have reported on the effects of pneumoperitoneum in a rat model, using a wide range of intra-abdominal pressures. The correlation between pneumoperitoneal pressures in rodents to pressures in humans has not been established. This study evaluates changes in various physiological parameters in different pneumoperitoneum pressures in the rat model with a comparison to known data in humans.

Three groups of eight Wistar rats each were anesthetized, tracheostomized, and mechanically ventilated with fixed tidal volume and respiratory rate. After a stabilization phase, CO(2) pneumoperitoneum was established to 12, 8, and 5 mmHg in the different groups. Changes in blood pressure, heart rate, peak ventilatory pressure, and end-tidal CO(2) (ETCO(2)) were recorded throughout the experiment.

There were no significant changes in blood pressure and heart rate in all groups. No increase in ETCO(2) was demonstrated following induction of pneumoperitoneum in the 12 and 8 mmHg groups. A statistical significant increase in ETCO(2) occurred only in the 5 mmHg group (39.4 to 41.3 mmHg, p = 0.023). Ventilatory pressures increased after induction of pneumoperitoneum in all groups. The increase reached a maximal level in the 8 and 12 mmHg groups (from 3 to 12 mmHg) and was lower in the 5 mmHg group (from 3 to 7 mmHg)

The neglected increase in ETCO(2) in pressures > or =8 mmHg, in the rat correlates to high pressures in humans (above 14-20 mmHg) when CO(2) diffusion through the peritoneum declines due to pressure occlusion of peritoneal capillaries. The maximal ventilatory pressures generated in the rat in intra-abdominal pressures > or =8 mmHg correlate to pressures, which are higher than the standard working pressures in humans. Thus, pneumoperitoneal pressures >8 mmHg in the rat do not simulate routine working pressures employed in humans. A pressure of 5 mmHg is optimal in a rat model to simulate laparoscopy in humans.