Infection rates among cooled patients post cardiac arrest

Introduction

We conducted a retrospective study looking at infection rates in patients treated with therapeutic hypothermia (TH) following cardiac arrest who were admitted to the ICU of the Bristol Royal Infirmary since May 2007. TH is recommended in all patients presenting with persistent coma following cardiac arrest. One complication of TH is the risk of infection. Hypothermia suppresses the immune system by inhibiting the release of proinflammatory cytokines and by suppressing the chemotactic migration of leukocytes and phagocytosis [1]. In patients with traumatic brain injury, TH for more than 48 hours is associated with a higher risk of infection, but not if the period of hypothermia is less than 24 hours [2]. In patients following cardiac arrest, infection is common, reported in up to 73% of patients [3].

Methods

Data were collected retrospectively, and information about ICU length of stay, whether they had a protected catheter (PC) specimen taken, whether they had any positive cultures and whether they were treated with antibiotics was extracted. Data for ICU length of stay was also obtained. Infections were defined as >10⁵ colony-forming units (cfu) grown from either PC specimens or from peripheral blood cultures.

Results

We identified 82 patients treated with TH post cardiac arrest. Nineteen (29%) had proven infection either on PC or on peripheral blood cultures. PC specimens were taken in 21 (25%) patients. Of the 21 patients who had PC specimens taken, 16 (76%) had proven infection. We also found that an increase in ICU length of stay was associated with increased infection rates, 44% in patients with a length of stay of greater than 3 days and 55% in patients with a length of stay of greater than 4 days.

Conclusions

We have shown, in our ICU, that of patients who were treated with TH following cardiac arrest, 29% had a proven infection. On PC sampling, there was a much higher rate of infection with 76% of patients with positive cultures. This suggests that the risk of infection in patients treated with therapeutic hypothermia post cardiac arrest is higher than that for patients who are cooled post traumatic brain injury.