Clinical overview
Pneumoperitoneum — the controlled insufflation of gas into the peritoneal cavity to create a working space — is the foundation on which all laparoscopic gynaecological surgery is built. Without it there is no triangulation, no view of the pelvis, no safe passage for secondary trocars. Yet the same manoeuvre that makes minimal-access surgery possible also produces the most dangerous moments in the operation. The two phases of greatest hazard in any laparoscopy are entry (creating the pneumoperitoneum and placing the primary port) and the systemic physiological burden of the carbon dioxide and raised intra-abdominal pressure that the pneumoperitoneum imposes for the duration of the case. Understanding pneumoperitoneum is therefore not a technical footnote; it is a question about gas physics, cardiorespiratory physiology, anaesthetic interaction and the prevention of catastrophic vascular and visceral injury.
For the FCOG(SA) candidate this objective sits within the technical and perioperative domain and connects directly to MIS complication prevention, Safe use of surgical instruments, Electrosurgery safety and the safe-entry literature. The discussion below works from why we choose carbon dioxide, through how the gas is delivered and monitored, to the systemic consequences and the situations — pregnancy, cardiac disease, the obese or very thin patient — where the principles must be adapted. The South African context matters: laparoscopy is increasingly available at regional and tertiary level, but insufflator quality, CO₂ supply, anaesthetic monitoring and surgeon experience vary, so a principled understanding that does not depend on a specific machine is what protects the patient.
Core knowledge
Figure F8.1 — Pneumoperitoneum physiology: raised intra-abdominal pressure + absorbed CO₂ + steep Trendelenburg, and their pressure-dependent respiratory, cardiovascular, renal and cerebral effects — use the lowest effective pressure for the shortest time.
Why carbon dioxide?
Carbon dioxide is the near-universal insufflation gas for laparoscopy, and the reasons are worth knowing precisely because they explain both its advantages and its physiological cost. CO₂ is non-combustible, which is essential when electrosurgery or laser is used inside the abdomen — oxygen or nitrous oxide would support combustion. It is highly soluble in blood (far more soluble than air, nitrogen or helium), so a small gas embolus is buffered and rapidly cleared rather than locking in the right ventricular outflow tract. It is cheap, readily available and colourless, and it is rapidly absorbed and excreted by the lungs, which speeds recovery and limits residual post-operative gas. The price of that high solubility is precisely that the body absorbs large quantities of CO₂ across the peritoneum, producing hypercarbia and a respiratory acidosis that the anaesthetist must clear — the central physiological theme of this chapter.
Alternative gases are largely of historical or niche interest. Nitrous oxide is less irritant and is explored for awake/office procedures, but it supports combustion and is avoided where energy is used. Helium and argon are inert but insoluble, which makes any embolus more dangerous; they are not standard. Room air and oxygen are obsolete and unsafe for energy-based surgery.
Pressure, volume and the working space
A pneumoperitoneum is defined by two linked variables: the intra-abdominal pressure (IAP) the insufflator maintains and the volume of gas needed to reach it. The relationship is non-linear — the relaxed abdominal wall and diaphragm are compliant up to a point, then stiffen, so the last increments of pressure buy little extra space at a steeply rising physiological cost. Standard teaching is that the working pressure for maintenance is in the region of 12–15 mmHg, with lower pressures (often around 8–12 mmHg) increasingly favoured to reduce systemic effects and post-operative pain where the view permits. These figures are widely taught surgical convention rather than a single guideline-mandated threshold, so treat the exact numbers as standard practice rather than fixed law, and titrate to the view and the patient.
A separate and safety-critical concept is the high initial intraperitoneal pressure during Veress-needle entry. When entry is by a closed (Veress) technique, the opening pressure read on the insufflator before any gas flows is the single most useful confirmation that the needle tip lies free in the peritoneal cavity rather than in the omentum, bowel, a vessel or the preperitoneal space. A low opening pressure (commonly quoted as below about 8–10 mmHg) is reassuring; a high opening pressure suggests the tip is not free. This is the "intraperitoneal pressure" safety test emphasised in the RCOG guidance on laparoscopic injuries.
Insufflator function and the gas circuit
The electronic insufflator is a feedback device. The surgeon sets a target IAP and a flow rate; the machine delivers CO₂ until the set pressure is reached, then maintains it, replacing gas lost through leaks, suction and absorption. Modern insufflators display set pressure, actual (measured) intra-abdominal pressure, gas flow rate and total volume delivered, and they alarm when measured pressure exceeds the set value (over-pressure) or when high flow indicates a major leak. Knowing these read-outs is examinable: the opening pressure confirms safe entry, a sudden high-flow state suggests a disconnection or a large leak, and a rising measured pressure that the machine cannot relieve may indicate light anaesthesia/abdominal-wall tone, a kinked tube, or the catastrophic scenario of gas tracking into the wrong plane.