The Influence of Hypovolemia and Fluid Resuscitation During Hemorrhagic Shock on Apneic Oxygen Desaturation After Preoxygenation in a Swine Model.

BACKGROUND

Patients experiencing major bleeding often require both aggressive fluid resuscitation and rapid sequence tracheal intubation. The influence of hemorrhage-induced hypovolemia, and/or subsequent fluid resuscitation, on the time until critical oxygen desaturation is not well described. We studied the time to oxygen desaturation in a pig model of hemorrhage shock and colloid resuscitation.

METHODS

After anesthetic induction with isoflurane, 9 swine (mean ± SD = 25.3 ± 0.6 kg) were studied with the use of a stepwise hemorrhage and fluid resuscitation model with 4 sequential stages: 600 mL hemorrhage, 600 mL hydroxyethyl starch infusion, a further 600 mL hemorrhage, and a second 600 mL hydroxyethyl starch infusion. At each stage, after 5 minutes of mechanical ventilation with 100% oxygen, we induced apnea and measured the time to oxygen desaturation (oxygen saturation [SpO2] <70%). Hemodynamic and blood gas variables were recorded, and the cerebral and peripheral tissue oxygenation indices were recorded by near-infrared spectroscopy.

RESULTS

The times ± SD to SpO2 <70% at each stage were 136 ± 41 (baseline), 147 ± 41 (hemorrhage), 131 ± 38 (resuscitation), 147 ± 38 (repeat hemorrhage), and 134 ± 36 seconds (repeat resuscitation). The mean differences in times before and after hemorrhage were 11.2 (6.5 to 16.0, P = 0.0052) and 16.0 (11.0 to 21.0, P < 0.0001), respectively. PaO2 before and after apneic desaturation (at SpO2 < 70%) was not different between stages. On the basis of tissue oxygenation index findings, hypovolemia decreased oxygen consumption, and fluid resuscitation recovered this parameter.

CONCLUSIONS

In patients with acute hemorrhagic shock, a hypovolemic state increases the duration of apnea until critical oxygen desaturation. Clinicians should thus consider the relationship between fluid resuscitation and time to desaturation when performing tracheal intubation in such patients.