Continuous multi-parameter tissue monitoring during shock and resuscitation

Introduction

Continuous assessment of tissue perfusion may allow for early detection and correction of hemorrhagic shock. We investigated continuously monitoring pH, pO₂ and pCO₂ of skeletal muscle (SM), subcutaneous tissue (SQ) and bladder wall (BW) as possible sites for following the course of hemorrhagic shock and resuscitation.

Methods

Seven anesthetized pigs (25–35 kg) underwent laparotomy, femoral vessel cannulation, cystostomy, and ureteral cannulation. Multi-parameter sensors (Diametrics Medical, MN, USA) were placed in the deltoid (SM), chest wall (SQ), femoral artery, and adjacent to the bladder mucosa (BW). Ventilation was adjusted to keep the PaCO₂ at 40–45 mmHg. Animals were rapidly bled and maintained at a MAP = 40 mmHg by withdrawing and infusing blood as needed. When a constant infusion was required to maintain a MAP = 40 mmHg (decompensation), animals were resuscitated with shed blood + 2x shed volume in LR (20 min) and observed for 2 hours. The time dependence of pH, pO₂ and pCO₂ in each tissue was analyzed using ANOVA with repeated measures and a post hoc Tukey's test for significance (^*P < 0.05, ^†P < 0.01).

Results

Average blood loss was 48 ± 11%. All tissue sites were found to respond significantly to shock and resuscitation. Both SMpH and SQpH remained significantly lower than baseline until 90 min of recovery, whereas BW returned to normal by 30 min. PCO₂ was significantly elevated at decompensation in all tissues, but returned to baseline by the end of resuscitation. Only SM and BW were found to decrease significantly at the end of decompensation, but returned to normal with resuscitation. Overall, SM afforded the greatest measurable change with the smallest relative variance at each time point.

Conclusions

Continuous multi-parameter monitoring of SM, SQ and BW potentially provide a minimally invasive method of assessing shock and resuscitation. Of the tissue sites investigated, SM provides the most sensitive means of monitoring hemorrhagic shock with the least amount of inter-subject variance.

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