Fentanyl spinal administration

The availability of new routes of administration have led to increased utility and decreased opioid adverse drug reaction risk. Epidural and intrathecal administration through spinal catheters produces adequate regional analgesia at relatively low total doses compared with intravenous or oral routes. As such, spinal administration can thus minimize somnolence, nausea, vomiting, and respiratory depression associated with these medications. Other alternative routes include intranasal administration of butorphanol, and rectal and transdermal administration of fentanyl [28]. Availability of such options provides not only a decreased risk of adverse reactions, but also more comfortable measures for patients who would otherwise require continued intravenous administration, or for those who are unable to receive oral medication [28,29]. 

Direct Mg administration into the CNS intrathe-cally (IT) has been demonstrated to augment fentanyl spinal analgesia [4]. 

After epidural injection, an opioid may transfer into the cerebrospinal fluid (CSF), into the blood or bind to epidural fat, the extent depending on their lipophilicity. After epidural administration, morphine passes slowly into the CSF. Sufentanil, which is highly lipid soluble, can be detected in the plasma within 2-5 minutes after epidural injection and part of the analgesic effect of the more lipid soluble opioids may be due to a supraspinal action amplifying the direct spinal action. Epidural fentanyl and sufentanil produce a more consistent and intense analgesia than morphine, with a faster onset. Flowever, the duration is short but this can be overcome by giving them by continuous epidural infusions. 

In addition to the development of tolerance, persistent administration of opioid analgesics has been observed to increase the sensation of pain leading to a state of hyperalgesia. This phenomenon has been observed with several opioid analgesics, including morphine, fentanyl, and remifentanil. Spinal dynorphin and activation of the bradykinin receptor have emerged as important candidates for the mediation of opioid-induced hyperalgesia. 

A 26-year-old woman with a history of multiple substance abuse required emergency caesarean section at 30 weeks of gestation as a result of crack cocaine-induced placental abruption and fetal distress (251). Her admission blood pressure was 145/95 mmHg, heart rate 95/minute and respiratory rate 20/minute. The fetal heart rate was 130/minute and non-reactive, with late and variable decelerations and no response to maternal oxygen administration. Spinal block with bupivacaine, fentanyl, and morphine was performed with the patient in a sitting position. No maternal or neonatal postoperative complications were reported. 

Kuczkowski KM. Severe persistent fetal bradycardia following subarachnoid administration of fentanyl and bupiva-caine for induction of a combined spinal-epidural analgesia for labor pain. J Clin Anesth 2004 16(l) 78-9. 

Different combinations of fentanyl, bupivacaine, and clonidine were investigated in a multicenter (6 sites) trial of 78 women undergoing elective cesarean section under spinal block (30). In some cases, this appeared to imply intrathecal administration, and in others combined intrathecal and epidural administration. Patients received hyperbaric bupivacaine alone, or with 75 pg of clonidine, or with 75 pg of clonidine and 12.5 pg of fentanyl. There were no reported hemodjmamic differences between the groups, but sedation and pruritus were significantly more common in those who received fentanyl, occurring in 65% and 25% of... 

In this case the authors felt that although the initial picture looked like the effects of subdural injection of bupi-vacaine and fentanyl, the prolonged coma with high motor blockade was more reminiscent of total spinal injection. They postulated that delayed total spinal anesthesia had occurred in this patient as a result of the epidural administration of a large quantity of bupivacaine and fentanyl via a hole made in the dura during the first attempt at epidural insertion. 

Kuczkowski KM. Respiratory arrest in a parturient following intrathecal administration of fentanyl and bupivacaine as part of a combined spinal-epidural analgesia for labour. Anaesthesia 2002 57(9) 939 0. 

The more novel routes of administration of opioids, including oral, nasal, rectal, transdermal, spinal, and by patient-controlled methods, have been outlined (SEDA-17, 78). Oral transmucosal fentanyl administration, avoiding first-pass metabolism, produces analgesia and sedation in both adults and children undergoing short, painful outpatient procedures. The quality of analgesia is good, and the adverse effects are those typical of the opioids. 

Pruritus is not due to preservatives in formulations, as it occurs with non-preservative-containing opioid solutions (176). It is unlikely to be due to histamine release, as the effect occurs about 3 hours after spinal or epidural administration (154,177-179) and occurs with fentanyl, which does not cause histamine release, in contrast to morphine (180). 

Effective in the management of severe postoperative, chronic, or cancer pain. Spinal opioids can be administered by a single bolus injection into the epidural or subarachnoid space or by continuous infusion via an indwelling catheter. Dosage requirement by these routes is significantly less than with IV administration (epidural opioid doses 10-fold lower than IV doses intrathecal opioid doses 100-fold lower than IV doses). Morphine, hydromorphone, fentanyl, and sufentanil are effective when administered intrathecally. The most commonly used local anesthetic in continuous epidural infusions is bupivacaine. Fentanyl, morphine, or hydromorphone is usually combined with bupivacaine for epidural infusions. 

Depending on whether epidural administration of fentanyl is as a bolus or a continuous infusion, analgesic effects are predominantly mediated by spinal or supraspinal mechanisms, respectively. 

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