Onset of Action for PCA Fentanyl
PCA fentanyl begins working within 1-2 minutes after intravenous administration. 1, 2, 3
Pharmacokinetic Profile
- Onset of action: 1-2 minutes after IV bolus 1, 2, 3
- Duration of effect: 30-60 minutes per dose 1, 2, 3
- Peak effect: Achieved rapidly due to fentanyl's high lipid solubility, allowing it to quickly reach opioid receptors 1
Standard PCA Dosing Parameters
- Initial bolus dose: 25 micrograms per patient-activated dose is typical for PCA settings 4
- Lockout interval: 10 minutes between doses 4
- Loading dose: Patients should first be made comfortable with an initial dose (typically 375 micrograms fentanyl) before starting PCA 4
Critical Clinical Considerations
Respiratory depression is the major adverse effect and may persist longer than the analgesic effect itself 1, 2, 3. This creates a dangerous mismatch where patients may feel pain relief has worn off but still have respiratory suppression.
Key Safety Points:
- The short duration of analgesia (30-60 minutes) means patients may require frequent dosing, increasing the risk of drug accumulation 2
- Continuous monitoring of oxygen saturation is essential, as hypoxemia can occur in up to 50% of patients receiving fentanyl alone 2, 3
- Have naloxone readily available: 0.2-0.4 mg IV every 2-3 minutes for reversal 2, 3
- Observe patients for at least 2 hours after naloxone administration to prevent resedation 2, 3
Important Limitation for Post-Cesarean Use
Fentanyl is not recommended for routine PCA use following Caesarean section 4. In a randomized controlled trial, significantly more patients in the fentanyl group required supplementary boluses or alterations to PCA settings compared to morphine (13/18 vs 4/19, P = 0.005), and one patient required removal from the study due to inadequate analgesia 4. While fentanyl's rapid onset is advantageous, its short duration makes it less suitable for sustained postoperative pain control compared to morphine.