Hypocalcemia following resuscitation from cardiac arrest revisited

Abstract

Objective: Hypocalcemia associated with cardiac arrest has been reported. However, mechanistic hypotheses for the decrease in ionized calcium (iCa) vary and its importance unknown. The objective of this study was to assess the relationships of iCa, pH, base excess (BE), and lactate in two porcine cardiac arrest models, and to determine the effect of exogenous calcium administration on post-resuscitation hemodynamics.

Methods: Swine were instrumented and VF was induced either electrically (EVF, n=65) or spontaneously, ischemically induced (IVF) with balloon occlusion of the LAD (n=37). Animals were resuscitated after 7 min of VF. BE, iCa, and pH, were determined prearrest and at 15, 30, 60, 90, 120 min after ROSC. Lactate was also measured in 26 animals in the EVF group. Twelve EVF animals were randomized to receive 1g of CaCl(2) infused over 20 min after ROSC or normal saline.

Results: iCa, BE, and pH declined significantly over the 60 min following ROSC, regardless of VF type, with the lowest levels observed at the nadir of left ventricular stroke work post-resuscitation. Lactate was strongly correlated with BE (r=-0.89, p<0.0001) and iCa (r=-0.40, p<0.0001). In a multivariate generalized linear mixed model, iCa was 0.005 mg/dL higher for every one unit increase in BE (95% CI 0.003-0.007, p<0.0001), while controlling for type of induced VF. While there was a univariate correlation between iCa and BE, when BE was included in the regression analysis with lactate, only lactate showed a statistically significant relationship with iCa (p=0.02). Post-resuscitation CaCl(2) infusion improved post-ROSC hemodynamics when compared to saline infusion (LV stroke work control 8+/-5 gm vs 23+/-4, p=0.014, at 30 min) with no significant difference in tau between groups.

Conclusions: Ionized hypocalcemia occurs following ROSC. CaCl(2) improves post-ROSC hemodynamics suggesting that hypocalcemia may play a role in early post-resuscitation myocardial dysfunction.

Figure 1

Mean ionized calcium values both prearrest and following ventricular fibrillation (VF) in pigs. A. Electrically-induced VF (n=65). B. Ischemically-induced VF (n=37). (Error bars represent standard deviations.)

Figure 2

Mean arterial lactate levels both prearrest and following resuscitation from electrically-induced ventricular fibrillation in 26 pigs. (Error bars represent standard deviations.)

Figure 3

Effect of subject-wise deletion of each of 26 animals resuscitated from electrically-induced ventricular fibrillation upon the coefficient for the association between natural-log transformed values of arterial lactate (ln[Lactate]) and ionized calcium levels. (Range −0.053 to −0.059, all p<0.05.)

Figure 4

Comparison of mean left ventricular stroke work (LVSW) and mean arterial pressure (MAP) both prearrest and following resuscitation from ventricular fibrillation in pigs assigned to either post-resuscitation infusion of calcium (n=6) or normal saline (control, n=6). (Error bars represent standard deviations.)