Carbon dioxide (CO₂) is by far the most commonly used gas for pneumoperitoneum because it is safe and inexpensive, but it is not the perfect gas. The absorption of CO₂ causes hypercapnia and acidosis, which have to be avoided by hyperventilation.⁷ Various cardiopulmonary complications (i.e., tachycardia, cardiac arrhythmias, and pulmonary edema) and postoperative pain from peritoneal irritation are among the adverse effects of capnoperitoneum.⁷ Other gases such as helium (He), argon (Ar), nitrogen (N₂), and nitrous oxide (N₂O, or laughing gas) have been introduced as alternatives to capnoperitoneum. Helium and argon are inert gases but are less soluble than CO₂ and may increase the risk for venous gas embolism. Although helium pneumoperitoneum has been reported to decrease cardiopulmonary effects compared with capnoperitoneum, the safety of its use has not been established.⁷ N₂O is a mild anesthetic and was shown to reduce postoperative pain, but N₂O is flammable and have caused explosions associated with electrocautery during laparoscopy.⁷ Gases other than helium and N₂O have not been compared with capnoperitoneum in clinical trials in humans.

Early in the history of small animal laparoscopy, N₂O was the preferred gas for diagnostic laparoscopy,⁸ and it was noted that this gas enabled laparoscopy under local anesthesia, in contrast to CO₂, which was associated with peritoneal irritation. Capnoperitoneum in dogs leads to decreased peritoneal fluid pH,⁹ which has been suggested as one of the reasons for irritation.¹⁰ Attempts to improve removal of residual CO₂ by aspiration, abdominal compression, and other maneuvers have been demonstrated to decrease postoperative pain in humans.^11-13

Regardless of the gas used for pneumoperitoneum, the pressurized pneumoperitoneum will exert effects on physiological parameters. Increased heart rate, increased systemic vascular resistance, increased arterial and central venous pressures, and decreased pulmonary compliance have been reported in humans, dogs, and horses with pressurized pneumoperitoneum.^14-17 These effects can be severe in dogs, especially when the intraabdominal pressures exceeds 15 mm Hg.¹⁶ These negative effects are most pronounced during induction, and healthy dogs compensate well,¹⁸ but patients with cardiopulmonary compromise may not be able to compensate to the same extent.

In addition to cardiopulmonary effects, pressures of 12 to 14 mm Hg may have clinically relevant negative effects on intraabdominal organ perfusion, especially the renal flow in patients with already impaired perfusion.¹⁹ In healthy dogs, hepatic and intestinal ­perfusion changes associated with high intraabdominal pressures (15–16 mm Hg) lead to increased blood levels of hepatic enzymes and evidence of bacterial translocation.^20,21

The intracranial pressure (ICP) increases by elevations in intraabdominal pressure and by the Trendelenburg position.¹⁹ The hypercapnia associated with capnoperitoneum may further exacerbate ICP elevation. Therefore, standard or high-pressure capnoperitoneum should likely be avoided in small animals with head injury or neurological disorders.

A Cochrane systematic review evaluated the effects of low pneumoperitoneum pressure (<12 mm Hg) compared to standard pressure (12–16 mm Hg) in humans, with the main finding of decreased postoperative pain in the low-pressure group.²² Previous clinical guidelines have stated that gasless or low-pressure laparoscopy should be considered in patients with limited cardiac function and that in general, the lowest possible pressure allowing adequate exposure should be used rather than a routine pressure.¹⁹