General anaesthesia and total hip replacement

Abstract

Decreases in arterial oxygen tension (PaO2) and increased venous admixture (Qs/Qt) occur with acrylic cement insertion. Mean decreases in PaO2 of 17.5 mm Hg occurred in this study of 41 patients. Qs/Qt increased by 7 per cent to 16.0 per cent during general anaesthesia with N2O.O2 - Halothane (4L:2L:1%) and d-tubocurarine. Assessment of pulmonary gas exchange using PaO2, A-aDO2, a-ADCO2 and acid-base studies using arterial and central venous blood samples in 16 patients suggest that both ventilation-perfusion mismatch and pulmonary arterio-venous shunts occur transiently after acrylic bone cement is used. Stable central venous oxygen tensions and normal heart sounds (Doppler), heart rhythm and stable blood pressure suggest that cardiac output changes, if any, are minimal. Patients for total hip replacement are most commonly females, obese, in their 60s and often have airway or cardiovascular disease. General anaesthesia must be conducted with particular attention to prevention of hypovolaemia by adequate rehydration and aggressive blood transfusions, prior to cement insertion into the vented femoral shaft. Inspired oxygen tension should be increased to 50 per cent prior to cement insertion. The oxygen tension may be returned to the pre-insertion value 15 minutes after cement insertion. Fumes from the polymerizing acrylic cement may cause some liver dysfunction but insufficient data is available to confirm this. © 1974 Canadian Anesthesiologists.