Abstract 19338: Calcium Dose During Resuscitation from Asphyxial Cardiac Arrest in Developing Rats Affects Heart Rate and Blood Pressure but Not Survival

Use of calcium during resuscitation from cardiac arrest remains controversial. Current AHA guidelines, drawing on small clinical studies, only recommend calcium use in hyperkalemia, hypocalcemia, hypermagnesemia and overdose of calcium-channel blockers. Yet, a large proportion of critical care physicians, especially in pediatrics, utilize IV calcium when cardiac arrest victims are resistant to epinephrine and vasopressin. We tested the effect of two different doses of calcium chloride - 10 mg/kg and 1 mg/kg - on blood pressure, heart rate, lactate and survival in a model of pediatric asphyxial cardiac arrest and resuscitation in developing rats. Seventeen to 19 days old Long Evans rats were anesthetized with isoflurane, endotracheally intubated and mechanically ventilated. The femoral artery and external jugular vein were cannulated for blood pressure monitoring and medication administration, respectively. EKG and EEG were continuously monitored. Anesthesia was discontinued 2 min prior to arrest to minimize confounding effect of isoflurane on outcomes. Asphyxial cardiac arrest was induced by discontinuing mechanical ventilation under neuromuscular blockade. After 9.5 minutes of asphyxia, rats were resuscitated using mechanical ventilation with 100% O2, chest compressions, epinephrine, NaHCO3, and either a standard resuscitation dose of 10 mg/kg CaCl2 (n=34) or a reduced dose of 1 mg/kg (n=40). Short-term (1 hr) survival did not differ between the two groups (85% in the 10 mg/kg group vs. 87% in the 1 mg/kg group, χ2, p > 0.05). Heart rate (HR) and mean arterial pressure (MAP) were calculated from 10 second intervals at 1, 5, 15 and 25 min post-resuscitation. Post-resuscitation HR was higher in the 10 mg/kg group (two-way ANOVA, p = 0.003 for calcium dose). Post-resuscitation MAP was also higher in the 10 mg/kg group (two-way ANOVA, p = 0.004 for calcium dose). Post-resuscitation whole blood lactate was lower in the 10 mg/kg group (5.8±1.1 mMol/L) compared to the 1 mg/kg group (6.8±2.1 mMol/L) ( t -test with unequal variances, p = 0.04). We conclude that in this clinically-realistic model of asphyxial cardiac arrest, lower dose CaCl2 during resuscitation does not affect short-term survival but is associated with lower post-resuscitation cardiac output.