Heart rate variability parameters measured during the initial resuscitation of patients with septic shock. Nonsurvivors showed significantly impaired variability as measured by LF and the HF/LF ratio. Data presented as logarithmic transformation to control for scale and allow visual comparison. Differences between survivors and nonsurvivors were calculated using raw averages without logarithmic conversion. Time domain factors: SDNN = standard deviation of the normal R-R interval; RMSSD = root mean square of the difference of successive R-R intervals. Frequency domain factors of HRV spectrum: LF = low frequency (0.04 to 0.15 Hz); HF = high frequency (0.18 to 0.4 Hz).