Study Design Summary: Double-blind, placebo controlled single center trial of 100 hemorrhagic shock patients comparing vasopressin vs placebo with a primary outcome of blood product transfusion requirements.
Notes: Significant amounts of vasopressin are released during acute hemorrhage and stores diminish with time. Low levels are associated with catecholamine resistant hypotension and increased venous capacitance. Trauma patients are at increased risk of AVP (arginine vasopressin) deficiency within the first 48 hours of resuscitation as their stores diminish, it has a short half life (10-35 minutes) and the shed blood rich in AVP is replaced with AVP poor crystalloid and blood products. When given I physiologic doses (0.04 u/min) to healthy volunteers, AVP does not increase blood pressure, only does it act as a vasopressor when given to AVP deficient patients. AVP also enhances platelet function.
Trauma patients who received 6 units of blood products (pRBC, FFP, platelets) within 12 hours of arrival were enrolled in the study. Cryopreciptate was not considered a unit of blood products in this study. Some important exclusion criteria include prehospital cardiac arrest, ED thoracotomy, chronic renal insufficiency, coronary artery disease, TBI requiring neurosurgery. The AVP arm got a 4 U bolus followed by 0.04u/min infusion, the placebo arm got a similar volume of saline for the bolus and infusion. The bolus and infusions were started after the operating surgeon declared definitive hemorrhage control. The infusion was titrated (0-0.04u/min) to maintain a MAP of 65 mm Hg. Patients received blood products at the discretion of the treating physician, but both patients and health care personnel were blinded to the AVP vs placebo. If patients required pressors, all were titrated and stopped before titrating the study infusion, the study infusion was restarted first if the patient was initially weaned and then requirement MAP support, no open label AVP was permitted. The primary end point was cumulative volume of blood products transfused within the first 48 hours of enrollment. The study was powered at 50 patients per group to detect a 50% reduction in total volume of blood product requirement.
The placebo group had a higher baseline MAP (82 vs 76 mm Hg, p=0.2) at trauma bay admission, but lower mean MAP at time of enrollment (69 vs 71, p=0.38). The patients enrolled were 93% men, with 79% being penetrating trauma. The median amount of cumulative blood product transfused at 48 hours was 1.4 L in AVP group (0.5-2.6L) vs 2.9 L in placebo group (1.1-4.8L) (p=0.01). In the per protocol analysis, all forms of blood products were transfused significantly less in the AVP arm, in the intention to treat analysis, pRBC was not transfused significantly less but all other forms of blood products were. Though the study wasn’t powered for complications, the authors report no difference in the complication rate between the two groups.
Study Conclusion: Addition of low dose vasopressin to patients with hemorrhagic shock reduces blood product requirements.
Fusion Beat Bottom Line Impression: Addition of vasopressin to hemorrhagic shock resuscitation may reduce need for blood product transfusion, however for definitive answer we need a larger study. It is reasonable to reach for AVP in the next trauma patient once blood product resuscitation is underway and you have cognitive and physical bandwidth to support it.