ANESTHETIC MANAGEMENT OF PATIENTS WITH ISCHEMIC HEART DISEASE

UNDERGOING NONCARDIAC SURGERY

ByAhmed Ibrahim ; M.D.

Prof.of AnesthesiaAin Shams University

Cairo, Egypt

Regarding perioperative myocardial ischemia , two mechanisms are important:

(i) imbalance in the O2 supply /demand

(ii) coronary plaque rupture acute coronary syndrome (ACS)

The preoperative management of patients suffering from or having risk factors for ischemic heart disease (IHD) is directed toward :

(1)Determining the extent of IHD and any previous interventions (CABG, PCI)

(2)Assessing the severity and stability of the disease

(3)Reviewing medical therapy e.g. antiplatelets or anticoagulants

The first two goals are important in risk stratification

in patients at high risk, attention to these factors should be given which may lead to adaptations in surgical plan

Cardiological evaluation may influence :

•the perioperative measures taken to reduce the cardiac risk

•the type of operation and guide the choice to less invasive interventions

N.B. it will not influence the decision to perform the intervention but in some situations , as it can reliably predict perioperative cardiac complications and estimate late survival, should be taken into consideration even when deciding whether to perform an intervention or not.

Risk Stratification

•Surgical risk

•Functional capacity (exercise tolerance)

•Risk indices

•Biomarkers

•Non-invasive testing

•Angiography

Surgical risk for cardiac events

•Any operation elicits a stress response which is mediated by neuroendocrine factors tachycardia and hypertension

•Fluid shifts in the perioperative period add to the surgical stress.

•Alterations in the balance between prothrombotic and fibrinolytic factors hypercoagulability and possible coronary thrombosis

The extent of such changes is proportionate to the extent and duration of the intervention and may cause myocardial ischemia and heart failure .

Boersma et al. Am J Med 2005

Functional capacity

•is considered to be a pivotal step in pre-operative cardiac risk assessment.

•it can be estimated by the ability to perform the daily life activities

is measured in metabolic equivalents (METs):

• 1 MET = represents metabolic demand at rest, (the basal metabolic rate).• 4 METs = climbing two flights of stairs • >10 METs = strenuous sports such as swimming

•The ability to climb two flights of stairs or run for a short distance (≥ 4METs) good functional capacity

•The inability to climb two flights of stairs or run a short distance (<4 METs) poor functional capacity with an increased incidence of postoperative cardiac events

when functional capacity is poor or unknown, the presence and number of risk factors in addition to the risk of surgery will determine pre-operative risk stratification and perioperative management

Risk indices

incidence of major cardiac complications is estimated at 0.4, 0.9 , 7, and 11% in patients with an index of 0 , 1, 2, and 3 points, respectively.

Lee index (1999), the widely used cardiac risk prediction index in non-cardiac surgery.

Lee TH, Marcantonio ER, Mangione CM, et al. Circulation. 1999;100:1043-1049

All factors contribute equally to the index (1 point each)

Biomarkers focusing on :

•Myocardial ischemia and damage cardiac troponins T & I (cTnT & cTnI)

•Inflammation CRP

•LV function Brain natriuretic peptide (BNP) and N-terminal pro-BNP (NT-proBNP)

•cTnT & cTnI are the preferred markers for the diagnosis of MI (demonstrate sensitivity and tissue specificity ).Even small increases reflect clinically relevant myocardial injury with worsened cardiac prognosis and outcome.

• CRP might identify patients with an increased risk of unstable coronary plaque.

•BNP & NT-proBNP are produced in response to increases in myocardial wall stress which may occur at any stage of heart failure, independently of the presence or absence of myocardial ischemia. Their levels have prognostic value for long-term mortality and for cardiac events after major non-cardiac vascular surgery.

routine assessment of biomarkers for patients undergoing non-cardiac surgery cannot be proposed for routine use as an index of cell damage

• LV dysfunction (radionuclide ventriculography, gated single photon emission computed tomography (SPECT) ,echocardiography, MRI, or CT)

•Valve abnormalities

•Myocardial ischemia

Non-invasive testing provides information on :

Non-invasive testing for myocardial ischemia

•ECG(12-lead) may be normal or non-specific in a patient with either ischemia or infarction.

•Physiological exercise( treadmill or bicycle ) is the preferred method for detection of ischemia and provides an estimate of functional capacity.

•Pharmacological stress testing with either nuclear perfusion imaging or echocardiography is more suitable in patients with limited physical abilities.

•MRI can be used for detection of ischemia; both perfusion and wall motion can be detected during stress and at rest.

•CT can be used to detect coronary calcium and for non-invasive angiography.

Coronary angiography

is rarely indicated to assess the risk of non-cardiac surgery.

indications for pre-operative coronary angiography and revascularization are similar to angiography indications in the non-surgical setting.

The history of co-existing noncardiac disease :

•patients with ischemic heart disease are likely to have peripheral vascular disease.

•A history of syncope may reflect cerebrovascular disease,a seizure disorder, or cardiac dysrhythmias.

•Cough is often pulmonary rather than cardiac in origin.

•Chronic obstructive pulmonary disease is likely in patients with a long history of cigarette smoking.

•Diabetes mellitus often co-exists with ischemic heart disease..•Renal insufficiency (creatinine level of >2.0 mg/dL) .

•Pharmacological-β-Blockers-Statins-Nitrates-Angiotensin-converting enzyme inhibitors-Calcium channel blockers-Ivabradine-α2 Receptor agonists-Diuretics-Aspirin-Anticoagulant therapy

•Revascularization

control of ischemia before surgery, either medically or with intervention, is recommended whenever noncardiac surgery procedures can be delayed

Risk reduction strategies

β-Blockers (β.B)

•decrease myocardial oxygen consumption by reducing heart rate

•lengthening of the diastolic filling period

•decrease myocardial contractility

•redistribution of coronary blood flow to the subendocardium

•plaque stabilization

•antihypertensive

•antidysrhythmic

•Perioperative use of β.B had been shown to be efficacious in reducing cardiac morbidity and mortality in high-risk patients undergoing vascular surgery.

•However, acute administration of high-dose β-blockers is not recommended as recent trials have not shown its efficacy in reducing overall mortality in patients undergoing noncardiac surgery.If to be used for prophylactic purposes , “they should be initiated at least a week before elective surgery”.

•Currently the only class I recommendation (action that should be taken) for perioperative administration of β-blocker is to continue its use in patients who are already receiving it i.e. therapy should be continued throughout the perioperative period specially the postoperative period as inadvertent withdrawal may occur and results in rebound hypertension and tachycardia.

•Isoproterenol is the specific pharmacologic antagonist for excessive β-blocker activity. Atropine or glycopyrrolate can be used to treat excessive bradycardia caused by β-blockers .

Statins (3-Hydroxy-3-methylglutaryl co-enzyme A reductase inhibitors )

•lipid-lowering effect •Induce coronary plaque stabilization (non-lipid or pleiotropic effects) that may prevent plaque rupture and subsequent MI .

•Clinical trials have demonstrated a beneficial effect of perioperative statin use. European guidelines recommend starting therapy 1 to 4 weeks before high-risk surgery. •It is recommended that statins be continued perioperatively as their discontinuation may cause a rebound effect that may be harmful.

Nitrates

•well known to reverse myocardial ischemia. However, prophylactic use of nitroglycerin has not been shown to be efficacious in reducing perioperative morbidity and mortality.

•may pose significant hemodynamic risk (decreased preload may lead to tachycardia, and hypotension).

Calcium channel blockers

Their effect on the balance between myocardial oxygen supply and demand makes them theoretically suitable for risk reduction strategies.

Angiotensin-converting enzyme inhibitors (ACEi) :

•May have beneficial effects on postoperative outcome: blood pressure-lowering effect ,preserve organ function and may prevent events related to myocardial ischemia and LV dysfunction.

•Perioperative use of ACEi (or ARBs) carries a risk of severe hypotension under anesthesia, specially with induction and concomitant b-blocker use.Although this remains debated, many recommend withholding ACEi for 24 hours before surgery involving significant fluid shifts or blood loss.They should be resumed after surgery as soon as volume is stable.

•In patients with clinically stable LV systolic function, it seems reasonable to continue ACEi during the perioperative period under close monitoring.

•Hypotension attributable to ACEi is usually responsive to fluids or sympathomimetic drugs. If hypotension is refractory to these measures,treatment with vasopressin or one of its analogues may be required.

Ivabradine

Is a specific inhibitor of the pacemaker in the S-A node reducing heart rate independently of sympathetic activation. It does not affect blood pressure or myocardial contractility. It might be considered for patients with strict contra-indications to b-blockers.

α2 Receptor agonists

•Have analgesic, sedative, and sympatholytic effects( might reduce catecholamine surge during surgery)

•Perioperative use of α2-agonists may be considered in patients who cannot tolerate β-blockers.

Diuretics

•Frequent treatment for hypertension or heart failure.

•If for hypertension ,they can be discontinued on the day of surgery, and resumed orally when possible.

•If necessary to control heart failure, they should be continued up to the day of surgery, and resumed orally when possible.

•In heart failure, diuretics are often used at high dose.Dosage should be increased if signs of fluid retention are present or reduced if there is a risk of hypovolemia, hypotension or electrolyte disturbances (increase renal excretion of K and Mg).

Aspirin

•Aspirin should only be discontinued if the bleeding risk outweighs the potential cardiac benefit.

•In principle and based on individualized ‘risk to benefit’ assessments, there is often no need for stopping the anti-platelet treatment prior to minor surgical or endoscopic procedures in patients who are taking antiplatelet therapy.

•For patients receiving antiplatelet therapy, i.e. aspirin, clopidogrel, or both, with excessive or life-threatening perioperative bleeding, transfusion of platelets or administration of other prohemostatic agents is recommended.

Poldermans et .European Journal of Anaesthesiology 2010, 27:92–137

AnticoagulantTherapy

Interventions that can modulate triggers of perioperative myocardial injury

Revascularization•Patients who are clinically stable in the years after CABG have a diminished risk of cardiac complications after a non-cardiac surgery.

•The indications for preoperative surgical coronary revascularization are the same as those in the nonoperative setting.

•It was thought that PCI before elective noncardiac surgery could improve perioperative outcomes. However, PCI, which is now often accompanied by stenting and dual antiplatelet therapy, poses its own unique set of problems that need to be considered in patients who are scheduled to undergo elective noncardiac surgery.

“There is no value in preoperative coronary intervention in a patient with stable ischemic heart disease.”

Preoperative Management

Strategies aimed at reducing the risk of perioperative cardiac complications should involve cardiac evaluation prior to the surgical procedure, for two main reasons:

•First, patients with an anticipated low cardiac risk can be operated on safely without further delay. It is unlikely that risk reduction strategies can reduce the perioperative risk further.

•Secondly, risk reduction by pharmacological treatment is most cost-effective in patients with a suspected increased cardiac risk.

The ACC/AHA guidelines provide a multistep algorithm for determining the need for preoperative cardiac evaluation.

The principal theme of the guidelines is “An intervention is indicated or not indicated irrespective of the need for surgery ”

Clinical risk factors: (1)Major : unstable coronary syndrome, decompensated heart

failure, significant dysrhythmias, severe valvular heart disease

(2) Moderate : stable angina pectoris, previous MI identified by history or pathologic Q waves, compensated or previous heart failure, insulin-dependent diabetes mellitus, renal insufficiency.

(3) Minor : hypertension, left bundle branch block, nonspecific ST-T wave changes, history of stroke

•BMS, Bare metal stent•CABG, coronary artery bypass graft•DES,drug-eluting stent•PCI, percutaneous coronary intervention

noninvasive test =stress testing

•Incidence of myocardial reinfarction during the perioperative period is influenced by the time elapsed since the previous MI.

•Acute MI (1 to 7 days previously), recent MI (8 to 30 days previously), and unstable angina are associated with the highest risk of perioperative myocardial ischemia, MI, and cardiac death.

•It is common practice to delay elective surgery for some time(at least 30 days) following MI.

Previous MI

•Controlling hyperglycemia in patients undergoing cardiac surgery and in patients in intensive care units has been associated with improved outcomes. It is prudent to actively manage hyperglycemia with insulin. This is especially important in patients who are at high risk of cardiac injury.

•Preoperative anxiety reduction can be achieved by bothconversational and pharmacologic means. The goal of drug-induced sedation and anxiolysis is maximum sedation and/or amnesia without significant circulatory or ventilatory depression.

•The basic challenge is to prevent (optimize O2 supply/ demand) , monitor and treat myocardial ischemia if it develops.

•Hyperventilation must be avoided, because hypocapnia maycause coronary artery vasoconstriction.

•Keep the heart rate and blood pressure within 20% of the normal awake value .

Intraoperative Management

•the incidence of perioperative cardiac morbidity and mortality does not appear to be significantly different for general and regional anesthesia.

•Regional anesthesia is an acceptable technique in patientswith ischemic heart disease. However, the decrease in bloodpressure associated with epidural or spinal anesthesia mustbe controlled. Prompt treatment of hypotension that exceeds20% of the preblock blood pressure is necessary.

Anesthetic technique (regional versus general)

INDUCTION OF ANESTHESIA

•Can be accomplished with an intravenous induction drug.

•Ketamine is not a likely choice increase in heart rate and blood pressure

•Tracheal intubation is facilitated by administration of a muscle relaxant.

•Myocardial ischemia may accompany the sympathetic stimulation that results from direct laryngoscopy and endotracheal intubation.

MAINTENANCE OF ANESTHESIA

•Good analgesia

•Overall, volatile anesthetics may be beneficial in patients with IHD as they decrease myocardial O2 requirements and precondition the myocardium to tolerate ischemia, or they may be detrimental as they lead to a decrease in blood pressure with associated reduction in coronary perfusion pressure.

Controlled myocardial depression induced by a volatile anesthetic may be useful to minimize the increase in sympathetic activity likely to develop in response to intense stimulation e.g. direct laryngoscopy ,surgical stimulation

•The AHA guidelines state that “it can be beneficial to use volatile anesthetic agents during noncardiac surgery for the maintenance of general anesthesia in patients in hemodynamically stable condition at risk for myocardial ischemia”.

•Although isoflurane may decrease coronary vascular resistance, predisposing to coronary steal syndrome, there is no evidence that it increases the incidence of intraoperative myocardial ischemia.

•The use of nitrous oxide in patients with a history of coronaryartery disease has been questioned as animal and human studies showed an increase in pulmonary vascular resistance, diastolic dysfunction, and subsequent myocardial ischemia with its use.

•Opioids may be selected as the principal anesthetic in patients with severely impaired left ventricular function who may not tolerate anesthesia-induced myocardial depression. The addition of nitrous oxide, a benzodiazepine, or a low-dose volatile anesthetic may be needed.

•Muscle relaxants with minimal or no effect on heart rate and systemic blood pressure (vecuronium, rocuronium, cisatracurium) are attractive choices for patients with IHD .

•The histamine release and resulting decrease in blood pressure caused by atracurium make it less desirable.

•However, the circulatory changes produced by pancuronium may be useful in offsetting the negative inotropic and chronotropic effects of some anesthetic drugs.

•Glycopyrrolate , which has much less chronotropic effect than atropine , is preferred in these patients for reversal of neuromuscular blockade .

Perioperative monitoring

•Select methods that allow early detection of myocardial ischemia.

- Electrocardiography (ECG)

- Transesophageal echocardiography (TEE)

- Right heart catheterization

•The simplest, most cost-effective method is ECG ST changes (elevation or depression of at least 1 mm) and T-wave inversions.

•Because visual detection of ST-segment changes is unreliable, continuous automated ST trending monitors are preferred.

•In patients with known or suspected coronary artery disease, it is reasonable to assume that intraoperative ST-segment changes represent myocardial ischemia although they can be caused by other events e.g. dysrhythmias, cardiac conduction disturbances, digitalis therapy, electrolyte abnormalities, and hypothermia.

Transesophageal echocardiography

The development of “new” regional ventricular wall motion abnormalities – that occur before ECG changes - is an accepted standard for the intraoperative diagnosis of myocardial ischemia.

Right heart catheterization

•Intraoperative myocardial ischemia can manifest as an acute increase in PAWP due to changes in LV compliance and systolic performance.If only small regions of LV become ischemic, overall ventricular compliance and PAWP will remain unchanged, so the “pulmonary artery catheter is a relatively insensitive method of monitoring for myocardial ischemia”.

•Pulmonary artery catheter is more useful to guide the treatment of myocardial dysfunction e.g. fluid replacement, measure cardiac output, and SVR and thereby evaluate the effectiveness of therapy.

•Right heart catheterization is not recommended routinely for monitoring patients with intraoperative ischemia.

INTRAOPERATIVE MANAGEMENT OF MYOCARDIAL ISCHEMIAshould be instituted when there are ST-segment changes on the ECG.

•Nitroglycerin is an appropriate choice when myocardial ischemia is associated with a normal or modestly elevated blood pressure.

•Prompt treatment of changes in heart rate and/or blood pressure .

•A persistent increase in heart rate can be treated by a β-blocker such as esmolol.

•Hypotension is treated with sympathomimetic drugs to restore coronary perfusion pressure. In addition , fluid infusion can be useful.

•In an unstable hemodynamic situation, circulatory support with inotropes or an intra aortic balloon pump may be necessary.

•Plan for early postoperative cardiac catheterization.

Postoperative Management

•Again the goals : prevent ,monitor, and treat ischemia or infarction.

•Continuous ECG monitoring is useful for detecting myocardial ischemia as most adverse cardiac events occur within the first 48 hours postoperatively.

•Avoid events that increase myocardial oxygen demand e.g. hypothermia ,pain, hypoxemia, hypercarbia, sepsis, and hemorrhage

•Avoid events that decrease myocardial oxygen supply e.g. hypovolemia , hypotension and inadequate hemoglobin concentration

•Patients taking β-blockers should continue to receive these drugs throughout the perioperative period.

•Patients with IHD can become ischemic during emergence from anesthesia and/or weaning from mechanical ventilation. Early extubation is desirable whenever possible

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