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Depth of Halothane Anesthesia Potentiates Citrate‐induced Ionized Hypocalcemia and Adverse Cardiovascular Events in Dogs

The purpose of this study was to determine if depth of halothane anesthesia contributed to the adverse cardiovascular effects of citrate-induced ionized hypocalcemia. Six mongrel dogs were monitored with arterial, central venous, and pulmonary artery flow-directed catheters. Measured end-tidal halothane assured a constant depth of anesthesia, while controlled ventilation and arterial blood gas analysis provided constant acid-base status. Each dog received sodium citrate (USP Fenwal) equivalent to fresh frozen plasma, 1.0 ml.kg−1.min−1, during both deep (D) and light (L) halothane anesthesia. Three dogs received the infusion during L halothane anesthesia first; after a 1-h stabilization period (2.5 h after first infusion) they received a second equivalent infusion during D halothane anesthesia. Three other dogs were studied first with D, then with L halothane. Mean expired halothane (±SEM) for group D was 1.52 ± 0.08%, for group L, 0.85 ± 0.07%. Significantly greater adverse cardiovascular effects were seen during D halothane anesthesia; four of the six dogs that received citrate during D halothane anesthesia required cessation of the infusion or suffered cardiac arrest. All six infusions during L halothane anesthesia were tolerated. In both groups, significant reductions in ionized calcium [Ca++] (P < 0.0001) and mean arterial pressure (MAP) (P < 0.005) were observed; greater reductions in both parameters occurred in group D (P < 0.0036–0.0005). In group D, but not in group L, cardiac output was depressed compared to baseline (P < 0.005). Pulmonary vascular resistance and central venous pressure were increased (P < 0.001) in group D but not in group L; pulmonary artery occlusion pressure and heart rate were increased in both groups compared to baseline (P < 0.005). The author concludes that a deeper plane of halothane anesthesia was associated with both greater myocardial depression and greater ionized hypocalcemia following citrate infusion in dogs.