Is it advisable to administer ketamine (anesthetic agent) before cardioversion or defibrillation in an unstable patient with a life-threatening arrhythmia?

Ketamine Before Cardioversion in Unstable Patients

Do not delay cardioversion to administer ketamine in an unstable patient with a life-threatening arrhythmia—proceed immediately to synchronized cardioversion, with sedation only if it does not delay the shock.

Immediate Management Priority

Cardioversion is preferred when the patient is unstable 1. The American Heart Association explicitly recommends proceeding immediately to synchronized cardioversion for unstable patients with symptomatic tachycardia showing rate-related cardiovascular compromise (acute altered mental status, ischemic chest discomfort, acute heart failure, hypotension, or shock) 1, 2.

• Sedation is recommended for the conscious patient before cardioversion 2, but cardioversion should not be delayed if the patient is extremely unstable 1.
• The American College of Cardiology advises against delaying cardioversion in hemodynamically unstable patients to attempt pharmacological interventions 3.

The Ketamine Paradox in Unstable Patients

While ketamine has traditionally been considered hemodynamically favorable, critical evidence reveals significant risks in unstable patients:

Cardiovascular Depression in Critically Ill Patients

• In severely ill patients, ketamine can paradoxically suppress myocardial contractility in patients whose catecholamine reserves are depleted 1.
• A landmark 1980 study demonstrated that in critically ill patients, ketamine produced decreases in ventricular contractility in 50% of patients, decreased cardiac output in 33%, and decreased mean arterial pressure in 33% 4.
• The authors concluded that preoperative stress may alter the usual physiologic responses to ketamine, and adverse effects may predominate in severely ill patients 4.

Specific Cardiovascular Risks

• Rapid administration of ketamine can cause transient bradycardia and hypotension, even at analgesic doses 5.
• Ketamine can cause new onset myocardial ischemia in approximately 10% of patients over age 50, though this was not statistically significant in one study 6.
• In prehospital use for agitation, over 30% of patients develop adverse events after ketamine, including hypoxia (15.4%), airway compromise (14.8%), and three documented cardiac arrests 7.

Clinical Algorithm for Sedation Decision

If the patient is hemodynamically unstable (hypotension, shock, acute heart failure, altered mental status):

• Proceed immediately to cardioversion without sedation 1, 2
• If sedation is absolutely necessary and will not delay cardioversion, use the lowest possible dose to minimize cardiovascular depression 1

If the patient is conscious but relatively stable:

• Establish IV access and administer sedation before cardioversion 1
• Consider ketamine cautiously, recognizing its potential for myocardial depression in catecholamine-depleted states 1
• Have airway management equipment immediately available, as 14.8% may develop airway compromise 7

Critical Pitfalls to Avoid

• Never delay cardioversion in truly unstable patients to achieve sedation—the arrhythmia itself is immediately life-threatening 1.
• Do not assume ketamine is always hemodynamically neutral—in shock states and cardiogenic shock, it can worsen cardiovascular compromise 1, 4.
• Avoid rapid IV push of ketamine—this increases the risk of bradycardia and hypotension 5.
• Be prepared for airway complications—have bag-mask ventilation and advanced airway equipment ready, as 5.5% may require bag-mask-ventilation and some may need advanced airways 7.

Special Considerations in Cardiogenic Shock

For patients with cardiogenic shock (common in cardiac arrest populations), any sedative can aggravate hemodynamic compromise, but this may be worse with propofol or dexmedetomidine 1. The general practice for patients with shock is to minimize sedative doses and have a lower threshold to avoid sedation entirely if cardioversion can be performed immediately 1.