Therapeutic Effects: Analgesia

Anesthesia Implications

Remifentanil should be followed by another treatment for pain postoperatively due to its short duration after discontinuation.

Bolus doses are not recommended

Remifentanil is associated with swallowing difficulty which may lead to aspiration – especially when used in patients without an ETT tube.

Very synergistic with other anesthetic agents – so may need to be reduced in the presence of propofol, isoflurane, and midazolam by up to 75%.

midazolam decreases remifentanil dose requirements by up to 50%.

Remifentanil and propofol are synergistic and together may result in severe respiratory depression.

General anesthesia: Not recommended as the sole agent because of a high incidence of apnea, muscle rigidity, and tachycardia.

Context-sensitive half time: 4 minutes (this means it takes only 4 minutes to clear 50% of the drug from the plasma after the infusion has stopped). This remains very constant (in contrast to other opioids such as fentanyl), in spite of the amount of time the infusion has been running. This point makes remifentanyl an ideal opioid to use in long cases where constant opioids are needed and wakeup time needs to be predictable.

Does not interfere with SSEPs or MEPs

Anesthesia-significant side effects:
Respiratory depression
In the absence of hypotension, can decrease cerebral blood flow.
Muscle rigidity (esp. thoracic and abdominal muscles) is common with large doses of opioid agonists are administered rapidly IV.
Opioids slow the gastrointestinal tract which can cause constipation, colic, delayed gastric emptying.
Can cause N&V due to direct stimulation of the chemoreceptor trigger zone (CTZ).

From the Pros: “Like all drugs I think Remifentanil has limited role in practice, but cases like thyroidectomy / thyroid lobectomies, carotids, and short stimulating DL laryngoscopies (esp on the population of patients I see who are sick and obese, CAD, OSA etc.) it really cuts the narcs down significantly, keeps the HR controlled, allows them to wakeup really fast with minimal residual effects…and we discharge home safely vs if we had to pump them up with a lot of narcs or beta-blockers.”

Contraindications

Contains Glycine, so it should not be used for epidural or neuraxial anesthesia.

Should not be coadministered with blood – esterases may metabolize

IV push dose

1-3 mcg/kg over 1 minute
Induction: use IDEAL body weight
Obese – use TOTAL body weight

IV infusion dose

TIVA: use IDEAL BODY WEIGHT; 0.05 – 1.0 mcg/kg/min – intubation can be done within 8 minutes. Titration should be done in 0.025 increments. Pediatric patients follow the same dosing with a slightly lower starting point (0.04 mcg/kg/min) if < 2 years old. Obese – use LEAN body weight

Epidural bolus dose: Contraindicated – contains glycine

Epidural maintenance rate: Contraindicated – contains glycine

Spinal bolus dose: Contraindicated – contains glycine

Spinal maintenance rate: Contraindicated – contains glycine

Classification: Opioid, Narcotic

Time to Onset: 1 minute

Duration: 3-10 minutes after pump is off

Metabolism: Hydrolysis by nonspecific blood and tissue esterases (similar to atracurium, cisatracurium, and etomidate); Inactive metabolite (carboxylic acid)