Cardiac chemoreflex sensitivity in critically ill patients

Chemoreflexes are important mechanisms for regulating ventilatory and cardiovascular function. The aim of this study was to determine the meaning of autonomic dysfunction for the pathophysiology and outcome in critical ill patients. For the determination of the chemoreflex sensitivity (ChRS), the ratio of the RR interval shift and the shift of oxygen partial pressure during a 5-min inhalation of oxygen with a nose mask was formed. Pathological chemoreflex sensitivity was predefined as a ChRS below 3.0 ms/mmHg. Out of the 27 critical ill patients included into the study, 17 had a sepsis and 10 a cardiogenic shock. In these patients, chemoreflex sensitivity was significantly reduced compared with a control group (sepsis: 2.1 +/- 1.68, cardiogenic shock: 0.4 +/- 0.27, controls: 5.0 +/- 2.8 ms/mmHg; P<0.05 vs. sepsis or cardiogenic shock). There was a significant negative correlation (r=-0.6; P<0.01) between the chemoreflex sensitivity and the severity of illness described by the SOFA-score. We conclude that cardiac reflex mechanisms are changed toward increased sympathetic activity reflected by reduced chemoreflex sensitivity in critical ill patients. Moreover, there is a close negative correlation between the ChRS and the SOFA-score.