What are the effects of ketamine on vital signs?

Effects of Ketamine on Vital Signs

Ketamine produces a dose-dependent increase in heart rate, blood pressure, and cardiac output through stimulation of the sympathetic nervous system. 1

Cardiovascular Effects

Ketamine has distinct effects on the cardiovascular system that differentiate it from many other sedative agents:

• Blood Pressure:

  • Causes elevation in systolic and diastolic blood pressure 1
  • In patients with normal shock index (<0.9), systolic blood pressure increases by approximately 16 mmHg 2
  • In patients with high shock index (≥0.9), the hypertensive response is blunted 2

• Heart Rate:

  • Increases heart rate by approximately 8-20 beats/minute 3, 4
  • The tachycardic effect is more pronounced and sustained in hemodynamically stable patients 2

• Cardiac Output:

  • Increases cardiac output through sympathetic stimulation 1

Respiratory Effects

Unlike many sedatives, ketamine has minimal effects on respiratory function:

• Respiratory Drive:

  • Does not depress airway or cardiovascular reflexes 1
  • Maintains respiratory drive at standard doses 1
  • Preserves protective airway reflexes better than benzodiazepine/opioid combinations 1

• Oxygen Saturation:

  • Rarely causes hypoxemia when used at appropriate doses 3
  • Respiratory depression may occur with overdosage or rapid administration 5

Clinical Considerations and Precautions

Hemodynamic Considerations

• Contraindications:

  • Ketamine should be avoided in patients for whom elevation in blood pressure would constitute a serious hazard 5
  • Use with caution in patients with ischemic heart disease, cerebrovascular disease, or hypertension 1

• High-Risk Patients:

  • Patients with high shock index (≥0.9) have a 26% risk of developing hypotension after ketamine administration 2
  • Hemodynamically unstable patients may have blunted hypertensive response 2

Dosing and Administration

• Standard Dosing:

  • Induction: 1-2 mg/kg IV or 4-5 mg/kg IM 5
  • Maintenance: 0.5-1 mg/kg IV as needed 5

• Onset and Duration:

  • Rapid onset of action (1 minute IV) 1
  • Short duration of effect (15-30 minutes) 1

Special Considerations

• Emergence Reactions:

  • 10-30% of adults may experience emergence reactions (floating sensations, vivid dreams, hallucinations, delirium) 1, 6
  • Combining with midazolam can reduce these reactions 1

• Monitoring Requirements:

  • Continuous monitoring of vital signs is essential during ketamine administration 5
  • Particular attention to blood pressure and heart rate changes 5

• Agitated Patients:

  • Ketamine provides faster control of agitation compared to standard medications 7
  • May require additional medications for sustained control in 62.5% of agitated patients 4

Ketamine's unique profile of cardiovascular stimulation while preserving respiratory function makes it particularly valuable in certain clinical scenarios, but requires careful patient selection and monitoring of vital signs.