CE: Tripti; ACO/310110; Total nos of Pages: 7; ACO 310110 REVIEW CURRENT OPINION Intraoperative vasoplegia: methylene blue to the rescue! Sharon L. McCartneya, Lorent Duceb, and Kamrouz Ghadimia Purpose of review To evaluate the efficacy, dosing, and safety of methylene blue (MTB) in perioperative vasoplegic syndrome (VS). Recent findings Vasoplegic syndrome is a state of persistent hypotension with elevated cardiac output, low filling pressures, and low systemic vascular resistance (SVR). It occurs in up to 25% of patients undergoing cardiac surgery with cardiopulmonary bypass, can last up to 72 h, and is associated with a high mortality rate. MTB has been found to increase SVR and decrease vasopressor requirements in vasoplegic syndrome by inhibiting nitric oxide synthase, thus limiting the generation of nitric oxide, while inhibiting activation of soluble guanylyl cyclase and preventing vasodilation. MTB has been used in postgraft reperfusion during liver transplantation and anaphylaxis in a limited number of cases. Additionally, this medication has been used in septic shock with promising results, but similar to the cardiac surgical population, the effects of MTB administration on clinical outcomes has yet to be elucidated. Summary MTB should be considered during vasoplegic syndrome in cardiac surgery with cardiopulmonary bypass and usage may be more effective in an early critical window, prior to end-organ hypoperfusion. Other perioperative scenarios of MTB use show promise, but additional studies are required to develop formative conclusions. Keywords cardiac surgery, cardiopulmonary bypass, methylene blue, nitric oxide, vasoplegia INTRODUCTION beta blockers, calcium channel blockers, amiodar- Vasoplegic syndrome involves severe hypotension one, and use of protamine [3]. Other risk factors with normal or elevated cardiac output, tachycardia include low preoperative ejection fraction, higher in patients who may reliably mount a compensatory additive European System for Cardiac Operative Risk response to hypotension, reduced cardiac filling Evaluation (EuroSCORE) value [6], increased dura- tion of cardiopulmonary bypass (CPB), and blood pressures, and decreased systemic vascular resis- & tance (SVR) [1]. Intravascular volume expansion product administration [3,5 ]. does not typically improve the hemodynamic pro- Two distinct mechanisms are responsible for the file and aside from such clinical presentation, the loss of vascular tone and include: (1) activation of exact definition of vasoplegic syndrome remains nitric oxide synthase (NOS) with dysregulation of poorly defined. Proposed definitions encompass hypotension with mean arterial pressures (MAP) less than 50 mmHg, which is secondary to low SVR and aDivisions of Cardiothoracic Anesthesia and Critical Care Medicine, Department of Anesthesiology, Duke University Medical Center, Durham, normal or supranormal cardiac output. This b prompts increased requirements for fluids and North Carolina, USA and Division of Cardiothoracic Anesthesia, Depart- ment of Anesthesiology, University of Florida, Gainesville, Florida, USA high-dose vasopressor therapy [2,3] but ultimately Correspondence to Kamrouz Ghadimi, MD, Divisions of Cardiothoracic a state of vasodilatory shock remains with lack of Anesthesia and Critical Care Medicine, Department of Anesthesiology, adequate perfusion pressure because of extremely Duke University Medical Center, Box 3094/HAFS 5691G, Durham, NC & low vascular tone [4,5 ]. 27710, USA. Tel: +1 919 681 6532; Several risk factors for vasoplegic syndrome have e-mail: [email protected] been identified, including preoperative intravenous Curr Opin Anesthesiol 2017, 30:000–000 heparin, angiotensin-converting enzyme inhibitors, DOI:10.1097/ACO.0000000000000548 0952-7907 Copyright ß 2017 Wolters Kluwer Health, Inc. All rights reserved. www.co-anesthesiology.com Copyright © 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. CE: Tripti; ACO/310110; Total nos of Pages: 7; ACO 310110 Cardiovascular anesthesia patients undergoing cardiac surgery and quickly KEY POINTS extending use to other surgical populations [8]. Methylene blue causes vasoconstriction by inhibiting inducible nitric oxide synthase and preventing subsequent activation of soluble guanylyl cyclase, in MECHANISM OF ACTION addition to directly inhibiting soluble guanylyl cyclase MTB is an odorless, water soluble, dark blue-green in smooth muscle cells. crystalline powder, which turns blue whenever Most prospective and observational studies show that mixed in solution [9] and is often used as a dye in methylene blue causes an increase in systemic blood several medical procedures. As a vasopressor, MTB pressure and decrease in vasopressor requirements impacts the NO synthetic pathway by inhibiting during vasoplegic syndrome after cardiac surgery, but inducible NOS and inhibiting the subsequent acti- improvement in morbidity and mortality have not been vation of sGC (Fig. 1) [10]. In addition, by binding to consistently demonstrated. the iron heme moiety of sGC and causing enzyme Expansion of methylene blue into other perioperative inhibition, MTB blocks accumulation of cyclic GMP uses, such as reperfusion after orthotopic liver (cGMP), competing directly with NO in its ability to transplantation and shock related to anaphylaxis or activate soluble guanylyl cyclase (Fig. 1) [10]. sepsis, show promise, but further investigation is warranted. INTRAOPERATIVE USE OF METHYLENE BLUE MTB may be used for hypotension refractory to nitric oxide (NO) synthesis and activation of vascular high-dose vasopressors and intravascular volume smooth muscle cell-soluble guanylyl cyclase (sGC) administration during the perioperative setting activation (Fig. 1) [3]. The same Brazilian group that and has been used extensively in the cardiac surgical first reported perioperative vasoplegic syndrome, uti- population. It has also been used in liver transplan- lized methylene blue (MTB) as an inhibitor of NO tation for hypotension following graft reperfusion, synthesis and described their success in six patients anaphylaxis, carcinoid syndrome, and burn injuries. [7]. In this letter to the editor, MTB was able to restore In a meta-analysis of five randomized controlled vascular tone, normalize MAP, and reduce vasopres- trials (n ¼ 174), MTB was found to modestly increase sor usage [7]. Subsequently, a few supportive random- arterial blood pressure [weighted mean difference, ized trials and retrospective observational studies 6.93 mmHg; 95% confidence interval (CI) 1.67– were published, and MTB became recognized as a 12.18; P ¼ 0.01] without an adverse effect on mor- viable option for treating vasoplegic syndrome in tality [6% (14/88)] among MTB-treated patients and FIGURE 1. Mechanism of action of methylene blue. Methylene blue inhibits nitric oxide synthase and soluble guanylyl cyclase, preventing cGMP accumulation and vasodilation within smooth muscle. cGMP, cyclic guanosine monophosphate; GTP, guanosine 5’-triphosphate; MTB, methylene blue; NO, nitric oxide; NOS, nitric oxide synthase; sGC, soluble guanylyl cyclase. 2 www.co-anesthesiology.com Volume 30 Number 00 Month 2017 Copyright © 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. CE: Tripti; ACO/310110; Total nos of Pages: 7; ACO 310110 Intraoperative vasoplegia McCartney et al. 23% (20/86) in the control group (OR 0.65; 95% Ozal et al. [20] administered MTB at 1 h prior to CI, 0.21–2.08; P ¼ 0.5) [11]. cardiac surgery in patients with risk factors for vaso- plegic syndrome, and found higher SVR (P < 0.001), less norepinephrine usage between groups (2/50 Cardiac surgery versus 41/50, P < 0.001), and reduced intravascular Vasoplegic syndrome after cardiac surgery on CPB is volume administration in patients who received thought to be largely the result of a severe inflamma- MTB (1577 versus 1749 ml, P ¼ 0.024). tory response [1,3]. During CPB, plasma proteins are Timing of MTB administration seems to effect absorbed by biomembranes, resulting in contact sys- the hemodynamic response in cardiac surgical tem activation of the extrinsic and intrinsic coagula- patients. In a retrospective study of 88 vasoplegic tion pathways, complement system activation, and patients, MTB administration resulted in higher fibrinolysis [3,12]. Activation of these pathways cre- MAP when compared with patients that did not ates secretion of cytokines that activate endothelial receive MTB (OR 1.04, 95% CI 1.01–1.07, cells and release vasoactive substances, including P ¼ 0.02). In particular, patients that underwent NO and prostacyclin [13]. Additional aspects that deep hypothermic circulatory arrest for complex may contribute to the profound inflammatory aortic repair experienced a greater hemodynamic response during cardiac surgery include reinfusion improvement after receiving MTB (23.9%, n ¼ 21; of hemolyzed cardiotomy blood that consists of other OR 4.48, 95% CI 1.54–13.06; P ¼ 0.006). [21&&]. activated substrates, and removal of the aortic cross- These findings suggest that the use of MTB as a last clamp, which may cause an ischemia-reperfusion resort agent may not be an appropriate strategy for syndrome through neutrophil activation and release the treatment of vasoplegic syndrome and earlier of reactive oxygen species [3,13]. Vasoplegic syn- use is recommended in at-risk patients. drome may occur in 5–25% of patients undergoing Controversially, MTB has been suggested for the cardiac surgery using CPB,