In Response.

Abstract

We thank Maguire and Maguire1 for their interest in our review article entitled “Reversal of Vasodilatory Shock: Current Perspectives on Conventional, Rescue, and Emerging Vasoactive Agents for the Treatment of Shock.”2 We aimed to systematically and comprehensively evaluate the vasoconstrictive medications that the anesthesiologist and intensivist may encounter in the perioperative and postoperative period for the treatment of shock. We agree with Maguire and Maguire1 that high-dose hydroxocobalamin can be used as an alternative vasoconstrictor to methylene blue (MB). It utilizes a similar mechanism to MB by targeting the nitric oxide synthase (NOS) pathway, and it also binds to hydrogen sulfide (H2S) to impair H2S-mediated vasodilation.3 One advantage over MB is that hydroxocobalamin does not antagonize monoamine oxidase, and thus, there is less potential for serotonin syndrome in patients taking serotonin reuptake inhibitors. Although hydroxocobalamin has been increasingly used for the treatment of shock that is refractory to conventional vasopressors, Maguire and Maguire1 rightly point out that the use of hydroxocobalamin in this context is off-label and is not supported by robust, high-quality evidence. While hydroxocobalamin is promising because of its unique mechanism of action independent of α1, vasopressin type 1a, and angiotensin type 1 receptor agonism, there are only case reports and 2 case series of 24 and 33 patients that describe its use in the literature.4,5 One case series reported a significant improvement in hemodynamics and vasopressor dosage 30 minutes after administration, while the other found wide variability in response to hydroxocobalamin.4,5 Currently, there are 2 small, ongoing studies examining the use of hydroxocobalamin in septic shock and post cardiopulmonary bypass vasoplegia, and additional high-quality, prospective trials are necessary to examine the efficacy of this drug.6,7 Without these studies, we may not be justified in substituting or prescribing this $650–$1050 drug that is at most supported by anecdotal evidence. Jonathan H. Chow, MDDivision of Critical Care MedicineDepartment of AnesthesiologyUniversity of Maryland School of MedicineBaltimore, Maryland[email protected]Michael A. Mazzeffi, MD, MPHDivisions of Critical Care Medicine and Cardiothoracic AnesthesiologyDepartment of AnesthesiologyUniversity of Maryland School of MedicineBaltimore, MarylandKenichi A. Tanaka, MD, MScDivision of Cardiothoracic AnesthesiologyDepartment of AnesthesiologyUniversity of Maryland School of MedicineBaltimore, Maryland