Pupillometry and parasympathetic tone activity index to detect sympathetic nervous system activation during hemorrhage

International audience ; Introduction: Hemorrhage activates the sympathetic nervous system (SNS), which helps maintain tissue perfusion but may mask the presence of bleeding. Assessing SNS activation could aid detection of occult hemorrhage. Our objective was to evaluate the utility of pupillometry and Parasympathetic tone activity index (PTA) in assessing SNS activation during hemorrhagic shock.Methods: Sixteen pigs were utilized. Following anesthesia and instrumentation, massive hemorrhage was induced by withdrawal of 35 ml/kg of blood: 20 ml/kg over 20 minutes then 15 ml/kg over the next 40 minutes. Hypotension was maintained post-hemorrhage for 1.5 hours. Pupil diameter and pupillary reflexes were measured every ten minutes using a Neurolight device (IDMED, Marseille, France). PTA (MDoloris device), heart rate (HR), and mean arterial pressure (MAP) were also recorded. Measurement changes over time and associations with the blood withdrawal volume were analyzed using mixed linear models and Pearson correlations. The results are presented as effect size (regression or correlation coefficient) and 95% confidence interval of the effect size. P-value < 0.05 were considered significant.Results: During blood withdrawal, a significant decrease in MAP (-0.6 mmHg/min [-0.7; -0.6], P < 0.0001), a significant increase in HR (1 bpm/min [0.9; 1.2], P < 0.0001) and pupillary diameter (0.02 mm/min [0.01; 0.02], P < 0.0001) were observed. Several parameters significantly correlated with the volume of blood withdrawn: decrease in MAP (r = -0.67, [-0.77; -0.55], P < 0.0001), increase in HR (r = 0.66, [0.53; 0.75], P < 0.0001) and increase in pupillary diameter (r = 0.32, [0.14; 0.48], P = 0.0009). During the hypotension phase, a significant but slight change in MAP (-0.05 mmHg/min, [-0.08; -0.02], P = 0.001) and pupillary diameter (0.004 mm/min, [0.002; 0.005], P < 0.0001) were observed, but HR did not vary significantly (0.02 bpm/min, [-0.04; 0.09], P = 0.50). Large variations in PTA were observed, ...