Choice of anaesthetic regimen influences haemodynamic response to cemented arthroplasty

Haemodynamic changes during bilateral cemented arthroplasty (BCA) were compared in dogs anaesthetized with isoflurane/ N₂O (ISOF) or diazepam/fentanyl (100 μg · kg^{? 1})/N₂O (FENT). Eight animals were anaesthetized with each regimen. After establishing monitoring and recording baseline values, BCA was performed Haemodynamic measurements included aortic blood pressure (ABP), pulmonary artery pressure (PAP), right and left atrial pressures, and cardiac output. These were recorded at 30, 60, 180 and 300 sec after BCA. Lungs were removed and examined postmortem using quantitative morphometry. Groups demonstrated similar increases in PAP (ISOF 15 ± 2 to 32 ± 7, FENT 19 ± 4 to 38 ± 13; P > 0.05 between groups, P < 0.05 vs baseline). The proportion of lung vasculature occluded by fat was not different between groups (ISOF 9.63 ± 3.38%, FENT 8.85 ± 2.20%). Stroke volume decreased similarly in both groups (P > 0.05 between groups, P < 0.05 vs baseline). However, ABP decreased within one minute of BCA in ISOF (111 ± 17 to 55 ± 27 mmHg, P < 0.05) and two of eight dogs died. All FENT dogs survived and hypotension (118 ± 20 to 102 ± 24 mmHg) was transient and less severe (P < 0.05 vs ISOF). Increased heart rate (HR) was noted in FENT following BCA (73 ± 8 to 108 ± 25 beats · min^{? 1}; P < 0.05). Baseline HR was higher in ISOF (P < 0.05) and no increase in HR was noted. Systemic vascular resistance decreased in ISOF (P < 0.05), but not FENT (P > 0.05 vs baseline, P < 0.05 vs ISOF). To assess the role of slower baseline HR in FENT (73 ± 8) versus ISOF (131 ± 5), six FENT dogs were paced (130 beats · min^{? 1}) with epicardial leads and an AV sequential pulse generator to simulate the ISOF group’s baseline HR. Haemodynamic stability was maintained in this group in spite of a more rapid baseline HR. The choice of anaesthetic regimen strongly influenced acute haemodynamic changes in response to BCA.