Introduction
Laparoscopic surgeries have become the standard of care for modern practice by surgeons. The word laparoscopy means the visualization of the abdominal cavity via an endoscope. Surgeries are performed after lifting the anterior abdominal wall and creating space by inflating the abdomen with the help of gases, most commonly carbon dioxide (CO2). It has become the preferred mode of many surgeries like cholecystectomy, hysterectomy, splenectomy, bariatric procedures, and even cancer surgeries. In the 1980s, it did not show better outcomes, as often the intra-abdominal pressure (IAP) used was more than 20 mm Hg. Modern-day laparoscopic surgeries are performed at IAP between 12 and 14 mm Hg with better anesthesia techniques and advanced monitoring, leading to better outcomes.
The advantages of laparoscopy over laparotomy are as follows:
Reduction of the stress response and pain due to surgery: Laparoscopy is less invasive, and incisions are smaller and less painful.
Early wound healing: Due to the reduced stress response, plasma levels of proinflammatory cytokines like IL-6, CRP, and intraoperative glucose levels during laparoscopy are lesser than open surgery. Elevated levels of the above are associated with delayed wound healing and delayed return of gastrointestinal (GI) functions. The reduced stress response also negates the negative nitrogen balance, thus promoting wound healing.
Improved postoperative function: Patients become ambulatory early with laparoscopy than with open surgery because of the reduced pain.
Better cosmetic appearance: Smaller size of incision gives a better cosmetic appearance.
The Technique of Laparoscopy
A pneumoperitoneum (air-filled peritoneal cavity) is created by inserting a “Veress” needle either blindly or under camera vision through a small incision in the abdominal wall and connecting it to the gas insufflator. The abdomen is filled with the gas, starting with 1 to 2 L/min flow and then slowly increasing to not more than 4 to 5 L/min of flows with pressure not exceeding 15 mm Hg, after which a constant flow of 200 to 400 mL/min is maintained to perform surgeries. One has to be careful during this step as cardiac arrhythmias can occur at this step, due to a sudden stretch of the peritoneum, causing vagal stimulation. To prevent the insufflation-related bradycardia, the upper limit of IAP, especially for patients with cardiovascular disease (discussed later separately) should not exceed 15 mm Hg. The patients are placed in different positions, for example, head up (reverse Trendelenburg) during cholecystectomy and upper abdominal surgery, head down (Trendelenburg) during gynecological/pelvic surgery, etc. The implications of these positions are also important (described later).
Pathophysiological Effects of Laparoscopy
All changes are described with respect to CO2, which is used most commonly for laparoscopy.
Effect of increased IAP pressure: Raised IAP pushes the diaphragm upward, causing a reduction of functional residual capacity (FRC) by almost 30 to 50%. Lung compliance is reduced, peak, and plateau pressure increases, leading to increased work of breathing (WOB). These changes are marked in patients with chronic obstructive pulmonary disorder (COPD), obesity, and other pulmonary diseases. Raised IAP reduces venous return to the heart and increases the arteriolar resistance, all of which may reduce the cardiac output. It also decreases renal blood flow and glomerular filtration rate (GFR). The rise in IAP > 20 mm Hg may cause reduced splanchnic blood flow and acidosis. Raised IAP and peritoneal stretch, along with surgical stress, increase blood levels of catecholamines, glucose, and vasopressin.
Effect of hypercapnia: CO2 is a pulmonary vasoconstrictor and a systemic vasodilator. The combination of the above effect with its permissive effect on the sympathetic nervous system can cause a variable impact on the vasculature. PaCO2 (partial pressure of CO2) in the blood begins to rise almost immediately after pneumoperitoneum by nearly 15 to 20% of baseline levels until 20 to 30 minutes after surgery, after which it plateaus. The main mechanism of the rise in PaCO2 is absorption through the peritoneum, but hypoventilation and increased WOB in a spontaneously breathing patient may also contribute to it. Minute ventilation (MV) should be increased by 10 to 20% in order to maintain normocarbia. Although the difference between arterial and expired CO2 (PaCO2–EtCO2) remains constant for healthy individuals, it might increase in patients with cardiopulmonary disease, probably because of increased dead space and shunt. Due to raised IAP, venous return and blood flow through pulmonary vasculature are reduced, and pulmonary resistance is increased, leading to increased dead space. In obese individuals, the loss of FRC increases the amount of nonventilated alveoli at the bases (atelectasis), causing an increase in the shunt fraction. In COPD patients, this PaCO2–EtCO2 gap increases quite significantly, and hence, EtCO2 tracing becomes unreliable in predicting arterial CO2 levels in this subset of patients. A lower EtCO2 level of 35 to 40 mm Hg should be kept as a target, or PaCO2 monitoring should be done by arterial blood gas analysis. CO2 also stimulates the sympathetic nervous system, causing a rise in heart rate and blood pressure intraoperatively.
Effect on the cardiovascular system: Due to pneumoperitoneum-induced compression of the inferior vena cava (IVC), preload to the heart reduces. Intermittent positive pressure ventilation leads to a rise in intrathoracic pressure (ITP) and central venous pressure (CVP), further reducing the preload. A combination of aortic compression and sympathetic stimulation increases systemic vascular resistance (SVR). In head-elevated positions, venous pooling in lower extremities further reduces preload, while in head-down posture, preload increases. These factors reduce cardiac output, whereas stimulation of the sympathetic nervous system tends to increase it. The net effect is determined by the interplay between the above factors. In patients with fixed low cardiac output states like valvular stenosis and heart failure with reduced ejection fraction (EF), it may lead to hypotension. The rise in PaCO2 and catecholamines may lead to arrhythmias intraoperatively. During pneumo-insufflation, peritoneal stretch leads to intense vagal stimulation and bradyarrhythmias, especially in patients with higher vagal tone. Among the various cardiac indices, mean arterial pressure (MAP), CVP, and pulmonary artery occlusion pressure (PAOP) rises, and measurement of right atrial pressure (RAP) and PAOP becomes unreliable during laparoscopy.
Effect on respiratory system: Raised IAP increases ITP and pulmonary vascular resistance, and the cranial shift of diaphragm decreases FRC, causing atelectasis. Due to the reduction of pulmonary blood flow, dead space ventilation increases, and the reduction of FRC increases the shunt fraction. This induces ventilation-perfusion (V/Q) mismatch and hypoxia. These changes may be more marked in obese individuals and COPD patients. Keeping IAP below 15 mm Hg, increasing minute ventilation, and application of positive end-expiratory pressure (PEEP) may attenuate these changes. Head elevation and descent up to 10° are well-tolerated. Anesthesia induced hypoventilation in a spontaneously breathing patient may increase PaCO2 further, which needs controlled ventilation and an increase in minute ventilation.
Effect on kidney, liver, and splanchnic bed: Raised IAP decreases renal blood flow (RBF) and raises efferent arteriolar resistance, reducing the gradient of glomerular filtration. As much as a 50% reduction of RBF and GFR ensuing pneumoperitoneum, along with increased vasopressin levels, can lead to temporary oliguria. In otherwise healthy individuals, the renal function returns to normal once the CO2 washes off, and IAP becomes normal. Giving a small dose of a diuretic may also increase urine output by anti-ADH mediated activity. IAP > 20 mm Hg may reduce hepatic and GI blood flow. But clinically, these events are rare, as CO2 has a vasodilator effect.
Effect on the central nervous system (CNS) and eyes: The rise in PaCO2 leads to vasodilatation of the cerebral vessels and a rise in intracranial pressure (ICP). This vasodilator effect is noticed at PaCO2 levels from 25 up to 80 mm Hg. A transient rise in intraocular pressure (IOP) is also seen with pneumoperitoneum. This rise in ICP and IOP is worsened by steep head low positions used in pelvic surgeries. Therefore, laparoscopy is not recommended for patients with intracranial lesions with features of raised ICP.
Gases Used in Laparoscopy
The ideal gas used in laparoscopy should have no physiological effect, should be rapidly excreted, be noncombustible (as cautery used in laparoscopy cause fire), and should be highly soluble.
The most commonly used gas is CO2 as it is noncombustible, easily available, soluble in the blood (Ostwald’s blood-gas solubility constant 0.49), and easily excreted. But hypercapnia (excess CO2 in blood) can cause acidosis by combining with water, and vasodilation of all vascular beds except pulmonary vessels, where it causes vasoconstriction. CO2 also causes activation of the sympathetic nervous system. Nitrogen and air are cheap and easily available, noncombustible, and have low Ostwald’s blood-gas solubility (0.017), which might lead to an increased chance of gas embolism. Although inert gases like helium and argon are noncombustible, their cost and lesser blood solubility preclude their use, as they might expand and cause an air embolism. In addition, argon can reduce hepatic blood flow. N2O supports combustion, and despite the fact that it is soluble (0.42), it might diffuse into air bubbles and cause their expansion and embolism. The individual gases and their properties are enlisted in Table 28.1.
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