Epidural administration

Morphine may be administered orally, intravenously, or epidurally. An advantage of epidural administration is that it provides effective analgesia while minimizing the central depressant effects associated with systemic administration. The mechanism of action with the epidural route of administration involves opioid receptors on the cell bodies of first-order sensory neurons in the dorsal root ganglia as well as their axon terminals in the dorsal hom. Stimulation of these receptors inhibits release of substance P and interrupts transmission of the pain signal to the second-order sensory neuron. 

Epidural administration in cesarean section. cDental anesthesia. 

Epidural analgesic - For epidural administration as an analgesic combined with low-dose bupivacaine, usually 12.5 mg per administration, during labor and vaginal delivery. 

Although not relevent in geriatricpatients, epidural administration of clonidine is not recommended. 

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. 

Side effects and complications tend to be higher with the intrathecal than the epidural route. A common side effect is pruritus, the incidence of which is higher with intrathecal than with epidural administration. It is dose-dependent, with an incidence of about 10% after epidural morphine 5 mg. The risk of severe, distressing itching is about 1%. Pruritus may be related to cephalad spread of morphine... 

Because of their direct action on the superficial neurons of the spinal cord dorsal horn, opioids can also be used as regional analgesics by administration into the epidural or subarachnoid spaces of the spinal column. A number of studies have demonstrated that long-lasting analgesia with minimal adverse effects can be achieved by epidural administration of... 

Veterinary methods could also include intra-ruminal, mammary, thoracic, and epidural administration. 

Tolerance to glucocorticoids in this, as in some other respects, varies from individual to individual some patients tolerate 30 mg of prednisone for a long time without developing Cushing s syndrome, while others develop symptoms at 7.5 mg the doses recommended today to avoid Cushing s syndrome in most patients are usually equivalent to hydrocortisone 20 mg. Cushing s syndrome and other systemic adverse effects can occur not only from oral and injected glucocorticoids, but also from topical and intranasal treatment (115) and intrapul-monary or epidural administration (SEDA-19, 376 SEDA-20, 370 116,117). 

Central neural blockade. The anesthetic is injected within the spaces surrounding the spinal cord10 (Fig. 12-2). Specifically, the term epidural nerve blockade refers to injection of the drug into the epidural space—that is, the space between the bony vertebral column and the dura mater. A variation of epidural administration known as a caudal block is sometimes performed by injecting the local anesthetic into the lumbar epidural space via the sacral hiatus (see Fig. 12-2). Spinal nerve blockade refers to injection within the subarachnoid space— that is, the space between the arachnoid membrane and the pia mater. Spinal blockade is also referred to as intrathecal anesthesia because the drug is injected within the tissue sheaths surrounding the spinal cord (intrathecal means within a sheath see Chapter 2). 

FIGURE 12-2 Sites of epidural and spinal administration of a local anesthetic. Caudal block represents epidural administration via the sacral hiatus. (From Clark JB, Queener SF, Karb VB. Pharmacological Basis of Nursing Practice. 4th ed. St Louis C V Mosby 1993 688. Reproduced with permission.]... 

Fentanyl is primarily used alone, but sometimes it is combined with other opiates such as Licodaine, Bupiva-caine, or morphine in epidural administration or in some I Vs. However, one of the more appealing virtues of fentanyl is that, unlike other opioids, it has a very mild effect on the emetic trigger zone of the medulla. For this reason, patients have less nausea and no vomiting when fentanyl is used. With other drugs, such as morphine, this unwanted side effect can be intense. Fentanyl also does not cause the release of histamine, which makes it safer for the cardiovascular system than morphine. 

AMIODARONE ANAESTHETICS - LOCAL Risk of 1 BP Additive myocardial depression Particular care should be taken to avoid inadvertent intravenous administration during bupivacaine infiltration monitor PR, BP and ECG during epidural administration of bupivacaine... 

After epidural administration of 150 mg with adrenaline to 12 subjects, mean peak plasma concentrations of 1.1 ng/ml were reported at 0.3 hour and peak cerebrospinal fluid concentrations averaged 30 pg/ml at 0.5 hour (G. R. Wilkinson and P. C. Lund, Anesthesiology, 1970, 2,482-486). 

Disposition in the Body. Rapidly absorbed into the circulation after epidural administration. Extensively metabolised by N-dealkylation, hydrolysis, and ring hydroxylation. Desethyleti-docaine and despropyletidocaine are detectable in plasma. Less than 1% of a dose is excreted in the urine unchanged in 48 hours. 

Half-life. Plasma half-life, after intravenous administration, about 2.5 hours, increased to about 6 hours after epidural administration. 

Spinal epidural lipomatosis secondary to exogenous administration of glucocorticoids is a rare condition that has been reported almost exclusively in association with systemic treatment. However, local epidural administration has also been implicated (389). 

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. 

In some series, transient hearing loss after anesthesia with bupivacaine was found with intrathecal but not epidural administration (SEDA-13, 99) (SEDA-16, 129)(263). It has been suggested that the cause could be a reduction in CSF pressure transmitted through the cochlear aqueduct (264), a hypothesis that has been both supported and criticized (SEDA-16,129). Sensorineural hearing loss after spinal anesthesia with bupivacaine has been thought to be due to the entry of bupivacaine into the inner ear, resulting in a direct effect on its functional apparatus (265). 

Combined spinal-epidural administration achieves almost instantaneous analgesia with longer pain relief (100). This method gives a faster onset of analgesia and less motor blockade than standard epidural analgesia (101). 

The adverse effects reported with epidural administration are similar to those reported with the intrathecal route. Again, old age and respiratory disease probably dispose to respiratory depression (133). As can be predicted from pharmacokinetic considerations, delayed respiratory depression is more common with epidural morphine than with fentanyl (134). 

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