Evaluation of tissue oxygen saturation with near-infrared spectroscopy during experimental acute hemorrhagic shock and resuscitation in dogs

Objective-To evaluate tissue oxygen saturation (Sto2) by use of near-infrared spectroscopy in experimental acute hemorrhagic shock and resuscitation in dogs. Animals-14 healthy adult purpose-bred Beagles. Procedures-Dogs were anesthetized with isoflurane via facemask, anesthesia was maintained with propofol and rocuronium bromide, and dogs were mechanically ventilated to maintain normocapnia. Dogs were studied under normovolemia (baseline), hypovolemia with target mean arterial blood pressure < 40 mm Hg achieved and maintained steady for 10 minutes (hypovolemia T1), then 20 minutes later (hypovolemia T2), following resuscitation with shed blood (after transfusion), and after administration of 20 mL of hetastarch/kg (hypervolemia). Conditions were executed sequentially during a single anesthetic episode, allowing stabilization between states (10 minutes). Hemoglobin concentration, mean arterial blood pressure, arterial blood gas concentrations, cardiac index, oxygen delivery indexed to body surface area, and Sto2 were monitored. Results-From baseline to hypovolemia T1, there was a significant reduction in mean +/- SD oxygen delivery index (619 ± 257 mL/min/m2 to 205 ± 76 mL/min/m2) and StO2 (94 ± 4.4% to 78 ±12.2%). Following resuscitation, Sto2 (80 ± 8.5% vs 92 ± 6.45%) and oxygen delivery index (211 ± 73 mL/min/m2 vs 717 ± 221 mL/min/m2) significantly increased, returning to baseline values. Hypervolemia had no effect on Sto2 or oxygen delivery index. A strong correlation (r = 0.97) was detected between mean oxygen delivery index and Sto2 across all time points. Conclusions and Clinical Relevance-Under the conditions of this study, there was a strong correlation between Sto2 and oxygen delivery, suggesting that Sto2 may be used to estimate oxygen delivery.