Cardiac arrest patients have an impaired immune response, which is not influenced by induced hypothermia (Critical Care)

IntroductionInduced hypothermia is increasingly applied as a therapeutic intervention in ICUs. One of the underlying mechanisms of the beneficial effects of hypothermia is proposed to be reduction of the inflammatory response. However, a fear of reducing the inflammatory response is an increased infection risk. Therefore, we studied the effect of induced hypothermia on immune response after cardiac arrest. Methods: Prospective observational cohort study in a mixed surgical-medical ICU. Patients admitted at the ICU after surviving cardiac arrest were included and during 24 hours body temperature was strictly regulated at 33[degree sign]C or 36[degree sign]C. Blood was drawn at 3 time points: after reaching target temperature, at the end of the target temperature protocol and after rewarming to 37[degree sign]C. Plasma cytokine levels and response of blood leucocytes to stimulation with toll-like receptor (TLR) ligands lipopolysaccharide (LPS) from Gram-negative bacteria and lipoteicoic acid (LTA) from Gram-positive bacteria were measured. Also, monocyte HLA-DR expression was determined. Results: In total 20 patients were enrolled in the study. Compared to healthy controls, cardiac arrest patients kept at 36[degree sign]C (n = 9) had increased plasma cytokines levels, which was not apparent in patients kept at 33[degree sign]C (n = 11). Immune response to TLR ligands in patients after cardiac arrest was generally reduced and associated with lower HLA-DR expression. Patients kept at 33[degree sign]C had preserved ability of immune cells to respond to LPS and LTA compared to patients kept at 36[degree sign]C. These differences disappeared over time. HLA-DR expression did not differ between 33[degree sign]C and 36[degree sign]C. Conclusions: Patients after cardiac arrest have a modest systemic inflammatory response compared to healthy controls, associated with lower HLA-DR expression and attenuated immune response to Gram-negative and Gram-positive antigens, the latter indicative of an impaired immune response to bacteria. Patients with a body temperature of 33[degree sign]C did not differ from patients with a body temperature of 36[degree sign]C, suggesting induced hypothermia does not affect immune response in patients with cardiac arrest.Trail registration: ClinicalTrials.gov NCT01020916, registered November 25, 2009