ALTERATIONS IN LUNG VOLUME AND INTRAPULMONARY GAS MIXING AFTER INGUINAL HERNIORRHAPHY IN PATIENTS WITH NORMAL LUNG FUNCTION AND IN PATIENTS WITH EMPHYSEMA

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Abstract
Determinations of lung volumes, with particular attention to functional residual capacity (FRC) and the slowly ventilated part of FRC (Vs), were carried out before and at intervals up to five days after inguinal herniorrhapy in 20 patients. Preoperatively, 8 patients had ratios of residual volume to total lung capacity (RV/TLC) of less than 0.35, and 12 patients had emphysema and defective intrapulmonary gas mixing with RV/TLC greater than 0.35. There were no significant postoperative changes in FRC and Vs in the patients with RV/TLC 0.35, FRC and Vs were significantly smaller after surgery, probably due to diffuse closure of small lung units not recognized clinically. Only one patient had unequivocal roentgenologic evidence of postoperative atelectasis and pneumonia. In the patients who had decreased FRC after surgery, there was generally a comparable decrease in the size of the "slow space" (Vs) indicating that the collapse occurred primarily in the more slowly ventilated lung areas. It seems likely that diffuse closure of lung units is quite common postoperatively, particularly in patients with defective intrapulmonary gas mixing prior to surgery. It is certainly more common than previously suspected, and this may be the initial phase of clinically evident postoperative pulmonary complications. The exact cause of the diffuse partial collapse of the slowly ventilated lung areas cannot be determined from the results of this study, but possible etiologlc factors have been discussed.

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