Abstract
BackgroundThe analysis of heart rate variability (HRV) has been shown as a promising non-invasive technique for assessing the cardiac autonomic modulation in trauma. The aim of this study was to evaluate HRV during hemorrhagic shock and fluid resuscitation, comparing to traditional hemodynamic and metabolic parameters.MethodsTwenty anesthetized and mechanically ventilated pigs were submitted to hemorrhagic shock (60% of estimated blood volume) and evaluated for 60 minutes without fluid replacement. Surviving animals were treated with Ringer solution and evaluated for an additional period of 180 minutes. HRV metrics (time and frequency domain) as well as hemodynamic and metabolic parameters were evaluated in survivors and non-survivors animals.ResultsSeven of the 20 animals died during hemorrhage and initial fluid resuscitation. All animals presented an increase in time-domain HRV measures during haemorrhage and fluid resuscitation restored baseline values. Although not significantly, normalized low-frequency and LF/HF ratio decreased during early stages of haemorrhage, recovering baseline values later during hemorrhagic shock, and increased after fluid resuscitation. Non-surviving animals presented significantly lower mean arterial pressure (43±7vs57±9 mmHg, P<0.05) and cardiac index (1.7±0.2vs2.6±0.5 L/min/m2, P<0.05), and higher levels of plasma lactate (7.2±2.4vs3.7±1.4 mmol/L, P<0.05), base excess (-6.8±3.3vs-2.3±2.8 mmol/L, P<0.05) and potassium (5.3±0.6vs4.2±0.3 mmol/L, P<0.05) at 30 minutes after hemorrhagic shock compared with surviving animals.ConclusionsThe HRV increased early during hemorrhage but none of the evaluated HRV metrics was able to discriminate survivors from non-survivors during hemorrhagic shock. Moreover, metabolic and hemodynamic variables were more reliable to reflect hemorrhagic shock severity than HRV metrics.
Highlights
Hemorrhagic shock is responsible for high mortality rates in civilian injuries (34%) and combat casualties (90%)[1,2]
All animals presented an increase in time-domain heart rate variability (HRV) measures during haemorrhage and fluid resuscitation restored baseline values
Not significantly, normalized low-frequency and low frequency (LF)/high frequency (HF) ratio decreased during early stages of haemorrhage, recovering baseline values later during hemorrhagic shock, and increased after fluid resuscitation
Summary
Hemorrhagic shock is responsible for high mortality rates in civilian injuries (34%) and combat casualties (90%)[1,2]. The initial care of these patients comprehends an early assessment of hypovolemia, bleeding management and fluid resuscitation [3]. Patient monitoring by traditional vital signs as heart rate, arterial pressure and arterial oxygen saturation can be insufficient to an early and accurate diagnosis of hemorrhage severity and shock [4]. The compensatory response to traumatic hemorrhage is driven by the autonomic nervous system [5]. Studies in animal models involving direct recording of neural activity during hemorrhagic shock demonstrated an increased sympathetic activity in response to the initial blood loss. The analysis of heart rate variability (HRV) has been shown as a promising non-invasive technique for assessing the cardiac autonomic modulation in trauma. The aim of this study was to evaluate HRV during hemorrhagic shock and fluid resuscitation, comparing to traditional hemodynamic and metabolic parameters
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