Best Strategy for Perioperative Angiotensin-Converting Enzyme-Inhibitor (ACE-I) and Angiotensin II Receptor Blocker (ARB) Therapy Prior to Noncardiac Surgery

INTRODUCTION

It is estimated that more than 280 million surgeries take place globally each year. More than one-third of patients presenting for surgery have hypertension and are taking either an angiotensin-converting enzyme inhibitor (ACE-I) or angiotensin receptor blocker (ARB). Since the introduction of ACE-I/ARB therapy in the early 1980s, clinicians remain uncertain as to the perioperative management of these drugs. The decision to withhold or continue therapy perioperatively has been controversial because of differing clinical recommendations, concern about increased intraoperative hypotensive events, and adverse outcomes. The current body of evidence remains inconclusive because of a paucity of well-conducted large clinical trials. This chapter presents all current relevant literature concerning the management of ACE-I/ARB therapy before noncardiac surgery.

MECHANISM OF EFFECT

ACE-I and ARB therapies are key role players in the inhibition of the renin-angiotensin-system (RAS). The RAS is integral to the function of the cardiovascular system (in particular, fluid homeostasis, blood pressure [BP] regulation, and renal excretion). Renin, the principal regulator of the RAS, is released from the juxtaglomerular cells in the kidney in response to (1) decreased renal perfusion, (2) decreased sodium sensed by the macula densa, and (3) stimulation of the sympathetic nervous system. Angiotensinogen, an α _2- globulin formed in the liver, is converted by renin to angiotensin I (ANG I), which, in turn, is converted by angiotensin-converting enzyme (ACE) in the vascular endothelium, particularly in the pulmonary system, into the active octapeptide angiotensin II (ANG II). Bradykinin, a decapeptide responsible for vasodilation and increased vascular permeability, is also hydrolyzed by ACE and may be responsible for some of the beneficial effects of ACE-I on BP control. ANG II has both renal and extrarenal effects. Constriction of the efferent arterioles in the kidney leads to an increase in tubular absorption and maintenance of the glomerular filtration rate. Extrarenal effects include vasoconstriction by the action of the potent ANG II on angiotensin 1 (AT ₁ ) receptors in vessels, cardiac myocytes, and sympathetic nervous system and fluid homeostasis by the action on aldosterone ( Fig. 13.1 ). In addition, ANG II is responsible for the release of arginine vasopressin from the posterior pituitary, aldosterone from the zona glomerulosa, and noradrenaline from the adrenal medulla. ACE-Is inhibit the conversion of ANG I to ANG II, thus limiting ANG II–mediated vasoconstriction, whereas ARB therapy competitively blocks the binding of Ang II to the AT ₁ receptor. Both therapies are fundamental to the treatment of cardiovascular and renal diseases alike and may be interchanged if the side effect profile of ACE-I (mainly cough, angioedema, and bronchospasm) is not tolerated.

The global burden of hypertension is rapidly increasing, with a staggering 50% of all men older than 45 years currently diagnosed with stage 1 hypertension (>130/80 mm Hg). Thus it is unsurprising that the increasing number of patients presenting for noncardiac surgery may be on either an ACE-I or ARB. In addition to decreasing arterial pressures, RAS blockers have antithrombotic, anti-ischemic, and anti-atherosclerotic effects. The use of ACE-I therapy in the management of left ventricular dysfunction and congestive heart failure (CHF) has reduced the occurrence of complications such as unstable angina and myocardial infarction (MI) by as much as 25%. The peripheral vasodilatation afforded by ACE blockade may further improve cardiac afterload and increase cardiac output by 15% to 40% in the presence of CHF. Such cardioprotective effects have led to the recommendation of treatment continuation on the morning of surgery in patients with systolic heart failure. Although ACE-I withdrawal in the perioperative period has no proven physiologic effects, rebound myocardial ischemia and increased mortality in the postoperative period are concerns. ^,

PERIOPERATIVE STRATEGIES FOR ACE-I/ARB MANAGEMENT

Current options for the management of perioperative ACE-Is/ARBs are either to withhold treatment 24 hours before surgery or to continue on the morning of surgery, ^, depending on which guideline is followed. A recent survey of 194 anesthetists/perioperative physicians in the United Kingdom revealed the current disparity in medication management, with 30% choosing to continue ACE-I/ARB morning of surgery and 70% choosing to omit therapy either (1) the day of surgery (72%), (2) 24 hours before surgery (16%), or (3) based on drug specific half-life (2%). Based on conflicting current international recommendations, indications for therapy initiation and type of surgery, and any expected anesthesia complications, a single answer may not fulfill the complexity of the decision-making process. Possible perioperative risks associated with treatment continuation versus withdrawal may be divided as follows:

• 1.

  Risk for hypotension associated with treatment continuation and possible associated adverse cardiac and mortality outcomes.

• 2.

  Risk for postoperative renal failure associated with treatment continuation.

• 3.

  Risk for pre/intra/postoperative hypertension associated with treatment withdrawal and associated morbidity.

EVIDENCE AND CONTROVERSIES