Optimization of Perioperative Beta-Blockade in Patients Undergoing Operation for Peripheral Vascular Disease
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Introduction
The emergence of vascular surgery as a multidisciplinary specialty in its own regard has allowed significant advances in the diagnosis, medical management and operative techniques applied to patients with peripheral occlusive and aneurysmal vascular disease. However, its increasing effectiveness in the treatment of circulatory disorders continues to be tempered by the fact that functional status and longevity after successful intervention are often determined by coronary co-morbidity.1 Indeed, the inherent cardiac stress induced by surgery may provoke ischemic events perioperatively that markedly affect overall outcome. The 30-day postoperative mortality rates for elective vascular surgery range between 2.1%2 and 8%3, while perioperative myocardial infarction (MI) rates range between 3%4 and 17%.5 Furthermore, it has been shown that long-term outcomes are also significantly affected by perioperative events, with one study showing that an episode of myocardial ischemia within 48 hours of surgery is associated with a doubling of the risk of death over the next two years.6 Pre-operative cardiac assessment and optimization of patients scheduled for elective major vascular surgery, however, permits the opportunity to favorably address both immediate and long-term cardiac risk.7
Although the benefits of perioperative b-blockade in high-risk patients undergoing major non-cardiac vascular surgery have now been clearly established by prospective cohort studies5,8,9, it remains underutilized as a cardioprotective strategy with only 40% using it routinely in clinical practice.10–12 This is somewhat surprising considering the fact that surgical stress can invoke myocardial ischemia and result in high levels of early cardiac morbidity and mortality13–15 has been a major driving factor in the development of endovascular surgical approaches. The underlying reasons for this may relate both to an under-appreciation of the positive effects of b-blockers as well as to traditional concerns over supposed contraindications. This concern leads to a lack of clarity over harm:benefit ratios on an individualized basis. This article aims to clarify and dispel some of the concerns relating to these issues. As implementation rates are not necessarily improved by anesthetic pre-assessment (despite awareness)16,17 and patients benefit from a period of pre-treatment with this medication prior to intervention, it behooves all physicians involved in the care of patients with peripheral vascular disease (PVD) to be actively aware in this regard.
Why Should Beta-Blockade be Instituted Perioperatively?
Approximately 40% of vascular surgical patients have significant ischemic episodes during their procedure, with the average duration of these events exceeding 10% of the total operative time.18 While traditional cardiac risk factors (hypertension, hypercholesterolemia, smoking and diabetes mellitus) all require redress prior to scheduling elective surgery, minimization of cardiac stress perioperatively is being increasingly recognized as an important means for avoiding cardiac ischemia and infarction. Although the effects of various medications, including a-2 antagonists, nitrates and calcium channel blockers have been proposed to reduce perioperative cardiac morbidity and mortality, perioperative cardioselective b-blockade has emerged as the most effective agent to date. Recently, Poldermans et al. have demonstrated a 91% drop in the perioperative risk of MI or death from cardiac causes in high-risk patients (i.e., those with inducible ischemia preoperatively) undergoing vascular procedure.5 The benefits due to prolonged b-blockade in this study persisted over the first two postoperative years. The results of another randomized study also support the long-term effects of b-blockade usage in the perioperative period,19 while early beneficial effects on myocardial ischemia and infarction rates as well as mortality have been endorsed by a recent meta-analysis.20 Therefore, consideration of all patients for initiation or augmentation of b-blocker therapy prior to operation should now be standard practice in vascular surgical units.
How Do b-Blockers Modulate Perioperative Risk?
Effective b-blockade provides perioperative cardioprotection by exerting both direct hemodynamic effects (i.e., controlling the tachycardia which may be provoked by general anesthesia and surgery by such stresses as endotracheal intubation and extubation21,22, perioperative pain, hypovolemia, hypothermia and hypoxia) and indirect effects on shear stress forces in circulatory flow as well on inflammatory responses affected by catecholamine release and sympathetic tone. The reduction in heart rate facilitates ventricular filling as well as diastolic perfusion time, so coronary oxygen delivery is improved while reduced contractile effort diminishes myocardial demand. The autonomic effects on flow dynamics may promote plaque stability and alter the incidence and significance of plaque rupture. Furthermore, b-blockers may augment collateral flow (although this is controversial) and act to limit arrhythmic tendencies that may be potentiated by myocardial stress. Lastly, the lipophilic quality of b-blockers may allow for their penetration through the blood-brain barrier, allowing the exertion of central nervous effects that may allow reduced amount of anesthetic agent and so promote postoperative recovery.23,24
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Got it! Thanks a lot again for heilpng me out!
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