What are the pulmonary effects associated with laparoscopic surgery?
Many components of laparoscopic surgery adversely affect pulmonary function. The increased IAP and volume produced by the pneumoperitoneum elevate the diaphragm, decreasing lung capacities (especially functional residual capacity (FRC)), increasing pulmonary airway pressures, and decreasing pulmonary compliance. The healthy individual may remain unaffected by these conditions; however, the obese or those with pre-existing pulmonary disease may exhibit compromised pulmonary function. The increases in airway pressures are most problematic in those with bullous lung disease. At pressures >40 cm H2O, these patients are at risk for bleb rupture and pneumothorax. To adjust for these increases one must either decrease the tidal volume, inspira-tory flow rate, or liters per minute of fresh gas flow, or ask the surgeons to decrease the IAP.
The Trendelenburg position predisposes to worsening pulmonary
compliance and V/Q mismatch. The pneumo-peritoneum and shift of the abdominal
contents cephalad both increase atelectasis and increase the risk of right
mainstem endobronchial intubation. The latter occurs as a result of cephalad
movement of the carina. Conversely, the reverse Trendelenburg position is
beneficial for lung mechanics.
Desaturation is not infrequent during laparoscopy. The differential diagnosis of hypoxemia is as follows:
· Pre-existing conditions: morbid obesity, chronic obstructive pulmonary disease
· Hypoventilation: positioning, pneumoperitoneum, endotracheal tube obstruction, inadequate ventilation
· Intrapulmonary shunting: decreased FRC, endobronchial intubation, pneumothorax
· Decreased cardiac output: hemorrhage, dysrhythmias, myocardial depression
· Technical equipment failure: circuit disconnect, delivery of hypoxic gas mixture
Laparoscopic surgery can reduce postoperative pul-monary complications by avoiding the restrictive pattern of breathing that usually follows open upper abdominal surgery. Atelectasis is more common and more severe in patients who undergo open surgery. Not only are the spirometric measures of lung function preserved, but also global respiratory strength is greater 24 and 48 hours after laparoscopic surgery than after open cholecystectomy. The use of epidural anesthesia to supplement general anesthesia does not improve lung function after the open operation.