Bone marrow pressure and blood flow and resistance in experimental hemorrhagic shock

Effects of humeral intraosseous epinephrine in a pediatric hypovolemic cardiac arrest porcine model

Background

Aims of the study were to determine the effects of humerus intraosseous (HIO) versus intravenous (IV) administration of epinephrine in a hypovolemic, pediatric pig model. We compared concentration maximum (Cmax), time to maximum concentration (Tmax), mean concentration (MC) over time and return of spontaneous circulation (ROSC).

Methods

Pediatric pig were randomly assigned to each group (HIO (n=7); IV (n=7); cardiopulmonary resuscitation (CPR)+defibrillation (defib) (n=7) and CPR-only group (n=5)). The pig were anesthetized; 35% of the blood volume was exsanguinated. pigs were in arrest for 2 min, and then CPR was performed for 2 min. Epinephrine 0.01 mg/kg was administered 4 min postarrest by either route. Samples were collected over 5 min. After sample collection, epinephrine was administered every 4 min or until ROSC. The Cmax and MC were analyzed using high-performance liquid chromatography. Defibrillation began at 3 min postarrest and administered every 2 min or until ROSC or endpoint at 20 min after initiation of CPR.

Results

Analysis indicated that the Cmax was significantly higher in the IV versus HIO group (p=0.001). Tmax was shorter in the IV group but was not significantly different (p=0.789). The MC was significantly greater in the IV versus HIO groups at 90 and 120 s (p<0.05). The IV versus HIO had a significantly higher MC (p=0.001). χ² indicated the IV group (5 out of 7) had significantly higher rate of ROSC than the HIO group (1 out of 7) (p=0.031). One subject in the CPR+defib and no subjects in the CPR-only groups achieved ROSC.

Discussion

Based on the results of our study, the IV route is more effective than the HIO route.

Comparison of epinephrine with vasopressin on bone marrow blood flow in an animal model of hypovolemic shock and subsequent cardiac arrest

OBJECTIVE

The intraosseous route is an emergency alternative for the administration of drugs and fluids if vascular access cannot be established. However, in hemorrhagic shock or after vasopressors are given during resuscitation, bone marrow blood flow may be decreased, thus impairing absorption of intraosseously administered drugs. In this study, we evaluated the effects of vasopressin vs. high-dose epinephrine in hemorrhagic shock and cardiac arrest on bone marrow blood flow.

DESIGN

Prospective, randomized laboratory investigation that used an established porcine model for measurement of hemodynamic variables and organ blood flow.

SETTING

University hospital laboratory.

SUBJECTS

Fourteen pigs weighing 30 +/- 3 kg.

INTERVENTIONS

Radiolabeled microspheres were injected to measure bone marrow blood flow during a prearrest control period and during hypovolemic shock produced by rapid hemorrhage of 35% of the estimated blood volume. In the second part of the study, ventricular fibrillation was induced; after 4 mins of untreated cardiac arrest and 4 mins of standard cardiopulmonary resuscitation, a bolus dose of either 200 microg/kg epinephrine (n = 6) or 0.8 units/kg vasopressin (n = 6) was administered. Defibrillation was attempted 2.5 mins after drug administration, and blood flow was assessed again at 5 and 30 mins after successful resuscitation.

MEASUREMENTS AND MAIN RESULTS

Mean +/- sem bone marrow blood flow decreased significantly during induction of hemorrhagic shock from 14.4 +/- 4.1 to 3.7 +/- 1.8 mL.100 g-1.min-1 in the vasopressin group and from 18.2 +/- 4.0 to 5.2 +/- 1.0 mL.100 g-1.min-1 in the epinephrine group (p =.025 in both groups). Five minutes after return of spontaneous circulation, mean +/- sem bone marrow blood flow was 3.4 +/- 1.1 mL.100 g-1.min-1 after vasopressin and 0.1 +/- 0.03 mL.100 g-1.min-1 after epinephrine (p =.004 for vasopressin vs. epinephrine). At the same time, bone vascular resistance was significantly (p =.004) higher in the epinephrine group when compared with vasopressin (1455 +/- 392 vs. 43 +/- 19 mm Hg. mL-1.100 g.min, respectively).

CONCLUSIONS

Bone blood flow responds actively to both the physiologic stress response of hemorrhagic shock and vasopressors given during resuscitation after hypovolemic cardiac arrest. In this regard, bone marrow blood flow after successful resuscitation was nearly absent after high-dose epinephrine but was maintained after high-dose vasopressin. These findings emphasize the need for pressurized intraosseous infusion techniques, because bone marrow blood flow may not be predictable during hemorrhagic shock and drug therapy.

Effects of variation in systemic blood pressure on intraosseous pressure, PO2, and PCO2

Several regulatory mechanisms have been shown to influence the intraosseous circulation. The influence of general hypovolemia on bone circulation and possible regulatory effects were investigated by recording the intraosseous pressure and PO2 and PCO2 continuously by mass spectrometry in rabbits. Hypovolemia was induced by repeated bleedings. The intraosseous and arterial pressures were found to be linearly related. The intraosseous PO2 already decreased after the first step of bleeding and decreased more than 50% of the initial value after an average blood loss of 40 ml. The intraosseous PCO2 showed an opposite pattern. The experimental PO2 vs. arterial pressure curves were similar to curves obtained by a computer simulation that assumes the blood flow to be proportional to the intraosseous pressure.