Rhabdomyolysis in classical heat stroke: Description of patients from the Chicago heat wave of 1995

Purpose: To determine the incidence and significance of rhabdomyolysis in individuals that required admission to an ICU with classical heat stroke during the Chicago heat wave of 1995. Methods: A retrospective data collection and analysis of cases admitted to 9 area ICUs in the period of 7/12-7/20, 1995, the peak days of heat. To be eligible for inclusion, the patients met the following criteria: CNS alteration, hot, dry skin, body temperature of ≥40.6 C or substantial environmental or circumstantial evidence of heat exposure. A preliminary analysis of CPK and Creatinine (Cr) levels was performed on 48 patients. One patient was excluded as a statistical outlier (CPK > mean + 2 SDs). Results: Peak CPK was available in 27/47 patients with a mean of 6523 IU/L (S.E. 1624). The values ranged from 106-32,905 IU/L. The peak CPK occurred on average 2 days after admission. 50% of these patients had evidence of renal insufficiency with Cr ranging from 2.1-10.5. In those who had both peak CPK and peak Cr (22/27), there was a significant correlation between the peak CPK level and the peak Cr. (R=.71, p=<.01). Renal insufficiency resolved in all but 1 patient who died. There was no correlation between peak CPK and either peak temperature or time from last contact to presentation. Conclusions: Patients with classical heat stroke have clinically significant rhabdomyolysis with up to 1/2 developing ARI. While the elevations in Cr may be in part attributable to prerenal azotemia and hypotension, the correlation between Cr and peak CPK indicate that myoglobinuria was a factor in ARI. We considered the possibility that the CPK elevations were due to victims lying of the ground for an extended period however we did not find evidence of a correlation between the time from last contact to presentation and the peak CPK. Clinical Implications: Previous literature suggests that CPK elevations in classical heat stroke are modest (<2000 IU/L) and of no clinical significance. Our findings disagree, suggesting that patients with classical heat stroke should be considered at risk for rhabdomyolysis and ARI and that appropriate measures should be taken to avoid this sequela.