3. Laparoscopy

The benefits of avoiding open surgery with substantial tissue trauma and significant postoperative pain are intuitively obvious. Increases in surgical experience and expertise now mean that the range of operations that can be performed either laparoscopically or with laparoscopic assistance encompasses major bowel resection, nephrectomy, Nissen’s fundoplication, complex bariatric surgery and major gynaecological procedures. It is now routine to perform hernia repair, cholecystectomy and appendicectomy using the same technique.

Laparoscopy. Central to laparoscopy is the creation of a pneumoperitoneum, most commonly with carbon dioxide, but rarely with other gases such as nitrous oxide, argon and helium. (Non-absorbable gases have a theoretically higher risk of causing problems such as pneumothorax and venous gas embolism.) The gas is insufflated into the peritoneal cavity at 4–6 litres min–1 to create an intra-abdominal pressure of between 10 and 20 mmHg (normal is 0–7 mmHg). Leakage through surgical ports means that a constant gas flow of 200–400 ml min–1 may be required to maintain to prevent deflation and loss of the surgical view.

CO2 absorption. There is speculation that some insufflated CO2 leads to the intraperitoneal formation of H2CO3 and increased pain due to the local acidity. Otherwise CO2 is absorbed efficiently across the peritoneum and will increase PaCO2. Modest hypercapnia has some physiological benefits in that the catecholamine release it provokes may support the circulation and promote bronchodilation. This will, however, increase myocardial oxygen demand. Significant hypercapnia will cause a respiratory acidosis and also directly depresses the myocardium.

This depends on the surgical procedure. In major gynaecology, for example, the patient will be in the head down (Trendelenberg) position in order to move abdominal contents out of the pelvis, whereas the reverse head-up position is necessary for upper abdominal procedures. Positioning may have significantly different physiological effects, as outlined in the following.

An initial autotransfusion of a few hundred ml of blood from the splanchnic circulation increases immediate circulating volume, but this is offset by the decreases in venous return secondary to raised intra-abdominal pressure compressing the inferior vena cava. Systemic vascular resistance increases as a direct result, and it also rises indirectly with catecholamine and vasopressin release and activation of the renin-angiotensin system. This may offset any decrease in cardiac output due to reduced venous return but at the expense of increasing myocardial work. The reverse Trendelenberg position risks marked venous pooling and effective hypovolaemia.

Splinting of the diaphragm further reduces FRC, and the raised abdominal pressure can increase airway resistance and reduce pulmonary compliance. In rare instances this can lead to significant shunting and oxygen desaturation, but in most cases any falls in PaO2 can be attenuated by judicious changes to the ventilation. The changes are less marked in the head-up position. Extreme and prolonged Trendelenberg positioning can be associated with facial and upper airway oedema

The rise in intra-abdominal and venous pressure may cause a concomitant rise in intracranial pressure, but the consequences are likely to be modest. Prolonged head-down tilt, however, has been associated with the development of hydrostatic cerebral oedema, although there is nothing that can be done specifically to avoid this other than to hope for a swift and accomplished surgeon.

Gastrointestinal and renal effects. Sustained intra-abdominal pressures greater than 20 mmHg create what in effect is an abdominal compartment syndrome with mesenteric and mucosal blood flow that reduces by almost half (40%). These pressures may already be high in the morbidly obese patient in whom they can be in the region of 14 mmHg. Regurgitation of gastric contents is a possible complication, although it is very unusual to actually find gastric contents in the pharynx at the end of a procedure. Renal vascular resistance is increased by high intraabdominal pressures, and so glomerular filtration rate and urine output may decline.

. A patient in prolonged lithotomy in the Trendelenberg position is at risk of lower limb compartment syndrome secondary to immobility, compression (including by graduated compression stockings) and venous congestion due to reduced femoral venous return caused by the position and by the increase in intra-abdominal pressure.

• These may be surgical and due to damage caused by the trocars, particularly at the beginning of the procedure when the gas insufflation needle is inserted blind. Otherwise the complications are related primarily to the creation of the penumoperitoneum. • The peritoneum is insensitive to direct injury but highly sensitive to stretch, which can cause profound vagal stimulation leading in the extreme case to asystole. Rapid abdominal decompression is the vital first step in retrieving this situation should it occur. • Venous gas embolism has been described; immediate discontinuation of insufflation should precede generic resuscitation. CO2 embolism is less dangerous than air and other gases because of its high solubility and rapid absorption. High gas pressures have also been known to cause pneumomediastinum and pneumothorax. These complications, or gas injection into the wrong planes may also be associated with subcutaneous emphysema.