Circadian rhythm of hospital deaths: comparison between intensive care unit and non-intensive care unit

The demonstration that cardiovascular mortality follows a circadian rhythm led us to verify whether patients dying at the intensive unit care (ICU) and at the non-intensive unit care (non-ICU) follow that rhythm.

All hospital's deaths occurring between January 1, 2006 and July 31, 2010 were analyzed. The circadian pattern of the time of death was analyzed in twelve 2 hour intervals. The Chi-square test was used to compare proportions, and Student's t test or ANOVA single factor to compare continuous variables. A p-value < 0.05 was considered statistically significant.

During the study period 700 deaths occurred in the hospital, 211 (30.1%) at the ICU and 88 (12.6%) at the non-ICU. There were more deaths in the first hours of the day, between 6 am and 12 am, at the non-ICU in comparison to the ICU (38% vs. 21%; p = 0.004). In the ICU, we observed that 21% of the deaths occurred between 6 am and 12 pm, 30% between 12 pm and 6 pm, 26% between 6 pm and 12 am and 24% between 12 am and 6 am (p = 0.13), whereas, at the non-ICU, 38% of the deaths occurred between 6 am and 12 pm, 18% between 12 pm and 6 pm, 19% between 6 pm and 12 am and 25% between 12 am and 6 am (p = 0.005).

At the non-ICU, deaths occur more often in the morning period and follow a circadian rhythm, which does not occur at the ICU.