The physiologic consequences of laparoscopy can be complex and depend on the interactions among the patient's preexisting cardiopulmonary status and surgical factors such as the magnitude of IAP, degree of CO2 absorption, alteration of patient position, and type of surgical procedure.
- Cardiovascular Effects
- The changes in the cardiovascular function during laparoscopy are attributable to the mechanical and neuroendocrine effects of pneumoperitoneum and the effects of absorbed CO2 and patient positioning as well as patient factors such as cardiopulmonary status and intravascular volume (Table 43-3: Hemodynamic Effects of Minimally Invasive Surgery).
- The cardiovascular changes of laparoscopy include increase in systemic vascular resistance (SVR) and mean arterial pressure (MAP), which is caused by increased sympathetic output from CO2 absorption and a neuroendocrine response to pneumoperitoneum.
- Increased IAP may compress venous capacitance vessels, causing decrease in preload (cardiac filling volume), particularly in hypovolemic patients.
- The hemodynamic changes that occur during abdominal robotic surgery appear to be similar to those observed during laparoscopic surgery.
- Peritoneal insufflation and a steep (40-degree) head-down position during robotic-assisted prostatectomy increase SVR and MAP; other hemodynamic variables remain in acceptable limits.
- Overall, robotic surgery appears to be well tolerated in a healthy population. However, the physiologic changes in elderly patients and in patients with impaired cardiopulmonary reserve undergoing robotic prostatectomy remains unknown.
- Regional Perfusion (Splanchnic, Renal, Cerebral, and Intraocular)
- Increased IAP, systemic CO2 absorption, and changes in patient position along with the hemodynamic changes (SVR and cardiac index) influence splanchnic, renal, and cerebral blood flow during minimal-access surgery (Table 43-4: Regional Circulatory Changes During Laparoscopy).
- The direct mechanical and neuroendocrine effects of pneumoperitoneum can decrease splanchnic circulation, causing reduced total hepatic blood flow and bowel circulation. However, these effects may be counter balanced by the direct splanchnic vasodilation caused by hypercapnia.
- The mechanical compressive and neuroendocrine effects of pneumoperitoneum may account for reduction in renal blood flow, glomerular filtration, and urine output (Table 43-5: Renal Function During Laparoscopy).
- Increases in PaCO2 during steep Trendelenburg positioning can increase cerebral blood flow and intracranial pressure with implications for patients with intracranial mass lesions.
- Intraocular pressures increase significantly during robotic-assisted radical prostatectomy with steep head-down positions.
- Respiratory and Gas Exchange Effects
- Changes in pulmonary function during laparoscopy include reduction in lung volumes and pulmonary compliance secondary to cephalad displacement of the diaphragm caused by increased IAP and patient positioning (Table 43-6: Pulmonary Changes During Laparoscopy).
- Reduction in functional residual capacity (FRC) and total lung compliance results in basal atelectasis and increased airway pressures.
- The CO2 insufflated into the peritoneal cavity is absorbed and causes hypercarbia.
- The CO2 absorption reaches a plateau within 10 to 15 minutes after initiation of intraperitoneal insufflation and thus is not influenced by the duration of surgery. However, it continues to increase progressively throughout extraperitoneal CO2 insufflation.
- Although laparoscopic surgery is associated with increased CO2 absorption, the changes in arterial CO2 (PaCO2) concentrations remain clinically insignificant in healthy patients. However, in patients with severe pulmonary disease and limited elimination of CO2, the resulting rise in PaCO2 may be significant despite aggressive hyperventilation.