What are the considerations for using isoflurane in patients with heart disease?

Isoflurane Use in Patients with Heart Disease

Isoflurane can be safely used in patients with coronary artery disease when coronary perfusion pressure is maintained, and volatile anesthetic-based regimens are recommended to facilitate early extubation in CABG patients. 1

Current Guideline Recommendations

The 2011 ACCF/AHA CABG guidelines explicitly support volatile anesthetic use in cardiac surgery patients:

• Volatile anesthetic-based regimens are useful (Class IIa) for facilitating early extubation and reducing patient recall in CABG patients. 1
• Anesthetic management should be directed toward early postoperative extubation and accelerated recovery in low- to medium-risk patients undergoing uncomplicated CABG (Class I recommendation). 1
• Despite widespread use, volatile anesthetics have not demonstrated mortality rate advantage compared to other intravenous regimens, but they remain the standard approach. 1

Evolution of Evidence on Coronary Steal Concerns

The historical concern about isoflurane causing "coronary steal" in patients with coronary artery disease has been largely refuted:

• Early studies suggested isoflurane caused coronary steal, but subsequent detailed trials disputed this and showed that when coronary perfusion pressure is maintained, isoflurane does not cause coronary steal or myocardial ischemia. 2
• Growing evidence demonstrates isoflurane has myocardial protective properties, limiting infarct size and improving functional recovery from myocardial ischemia through mechanisms mimicking ischemic preconditioning involving ATP-dependent potassium channels. 2

Hemodynamic Considerations

Blood Pressure and Vascular Effects

• Isoflurane causes dose-dependent decreases in mean arterial pressure (approximately 18% at 1.0 MAC) primarily through systemic vascular resistance reduction (approximately 21% decrease). 3
• Cardiac index typically remains stable during isoflurane administration in patients with coronary artery disease. 3
• Central venous pressure is generally not affected by isoflurane. 3

Comparative Safety Profile

• Hemodynamic stability with isoflurane is similar to sevoflurane in patients with hypertension and ischemic heart disease, with no differences in the frequency of treatment needed for hemodynamic deviations. 4
• Isoflurane demonstrates similar cardiovascular effects to desflurane, though desflurane causes significant increases in pulmonary artery pressure (24%) and pulmonary capillary wedge pressure (40%), making isoflurane preferable in this regard. 3

Critical Management Principles

Maintaining Coronary Perfusion Pressure

The key to safe isoflurane use in heart disease patients is maintaining adequate coronary perfusion pressure. 2 When perfusion pressure drops:

• Global coronary blood flow may increase during isoflurane (from 131 to 153 ml/min), but regional blood flow can decrease. 5
• The ratio of regional to global coronary blood flow may decrease, potentially causing maldistribution of coronary circulation. 5
• Some patients may develop lactate production and electrocardiographic evidence of myocardial ischemia if perfusion pressure is not maintained. 5

Nitrous Oxide Interaction

• Adding 70% nitrous oxide to isoflurane potentiates systemic and coronary hemodynamic effects, causing further reductions in blood pressure (-18%) and myocardial oxygen consumption (-31%). 6
• Nitrous oxide can worsen myocardial ischemia in patients already showing ECG and metabolic signs of impaired oxygenation during isoflurane alone. 6
• The mechanism involves decreased coronary perfusion pressure and/or redistribution of coronary blood flow by direct coronary vasodilation. 6

Practical Clinical Algorithm

For patients with coronary artery disease requiring general anesthesia:

1. Use isoflurane as part of a volatile anesthetic-based regimen (preferred over high-dose opioid techniques for most patients). 1

2. Monitor and maintain coronary perfusion pressure aggressively through:

   • Careful titration of anesthetic depth
   • Prompt treatment of hypotension with vasopressors (phenylephrine, ephedrine) when blood pressure deviates >20% from baseline 4
   • Continuous arterial blood pressure monitoring

3. Consider avoiding or using nitrous oxide cautiously given its potentiation of isoflurane's hemodynamic effects and potential to worsen ischemia. 6

4. Combine with appropriate adjuncts including opioids (in adjuvant rather than high-dose role) and ensure optimal preoperative medication management. 1

Common Pitfalls to Avoid

• Do not assume all volatile anesthetics are equivalent: While isoflurane and sevoflurane have similar hemodynamic profiles, desflurane causes significant pulmonary pressure increases that may be problematic. 3
• Do not allow excessive hypotension: The protective effects of isoflurane are negated when coronary perfusion pressure falls significantly, potentially leading to regional ischemia despite increased global coronary flow. 5
• Do not use isoflurane for procedural pain management in ICU patients with heart disease: Guidelines recommend against using inhaled volatile anesthetics for procedural pain due to very low quality evidence, resource requirements, and safety concerns outside the operating room. 1