Low-dose remifentanil infusion does not impair natural killer cell function in healthy volunteers.

BACKGROUND: Mu opioid agonists suppress natural killer (NK) cell activity in animal models. Studies in human volunteers, however, have yielded conflicting results, with morphine suppressing and fentanyl increasing NK cell activity. This study evaluated the effect of a constant 8-h infusion of remifentanil on NK cell number and function in human volunteers. METHODS: After IRB approval and informed consent was obtained, 10 healthy volunteers underwent an 11 pm to 7 am infusion of saline, and at least 1 week later an infusion of 0.02-0.04 microg x kg(-1) min(-1) remifentanil. Blood was collected at 7 am for measurement of NK cell cytotoxicity using a (51)Cr release assay and measurement of NK cell number using fluorescent flow cytometry. RESULTS: Median and range of the total NK cell cytotoxicity (KU ml(-1)) was 745.0 (498.3-1483.6) on the control morning and 818.6 (238.5-1454.5) on the morning following the remifentanil infusion. Neither the number of NK cells ml(-1) (2.5 x 10(5) (1.4 x 10(5)-4.2 x 10(5)) vs 2.7 x 10(5) (1.1 x 10(5)-4.4 x 10(5))) nor the cytotoxicity per 1000 NK cells (KU 1000 NK cells(-1)) (3.0 (1.8-5.2) vs 2.9 (0.9-6.7)) changed between the control and remifentanil conditions. CONCLUSIONS: An 8-h infusion of remifentanil did not affect NK cell activity in normal volunteers. This result differs from previous findings of morphine-induced NK cell activity suppression and fentanyl-induced NK cell activity enhancement in normal volunteers.

Acute and chronic pain management in palliative care.

Every palliative care patient should have the expectation that acute and chronic pain management will be an integral part of their overall care. However, in all too many instances, the pain of cancer is often grossly under-treated. This issue is of concern because more than 80% of patients with cancer pain can find adequate relief through the use of simple pharmacological methods. It is even more troubling to note that women and minority groups have their cancer pain under-treated more frequently. Physicians with the basic skills of assessment and treatment will be able to control the symptoms in the majority of cancer pain patients. However, there are still some patients who may require other modalities to control their moderate to severe pain. A thorough understanding of all pain management options will help the gynaecological oncologist to maintain an acceptable quality of life for their patients throughout the therapeutic and palliative phases of care.

Alpha 2 agonists in regional anesthesia and analgesia.

Clonidine is a partial alpha 2 adrenergic agonist that has a variety of different actions including antihypertensive effects as well as the ability to potentiate the effects of local anesthetics. It can provide pain relief by an opioid-independent mechanism. It has been shown to result in the prolongation of the sensory blockade and a reduction in the amount or concentration of local anesthetic required to produce perioperative analgesia. Different routes for the administration of regional anesthesia, including intravenous, intrathecal and epidural ones, as well as the addition of clonidine for peripheral neural blockade, have been described. It has been also used for intra-articular administration. The latest articles describing the use of clonidine in regional anesthesia are discussed. Most authors agree that the use of clonidine for regional neural blockade in combination with a local anesthetic results in increased duration of sensory blockade with no difference in onset time. The addition of clonidine to the local anesthetic opioid mixtures seems to produce analgesia of longer duration, more rapid onset and higher quality. The higher doses of clonidine were associated with a more cephalad spread of the spinal blockade and increased sedation and hypertension. When clonidine is added to a fentanyl-bupivacaine mixture for epidural labor analgesia, it seems to provide satisfactory analgesia of a longer duration than that produced by the fentanyl-bupivacaine combination alone. Similar results were found when epidural analgesia using levobupivacaine with clonidine was used in patients undergoing total hip arthroplasty. Less clear results were seen when clonidine was used for caudal anesthesia in a pediatric patient population. The addition of clonidine to intravenous regional anesthesia resulted in prolongation of the tourniquet time and improvement of postoperative analgesia. However, the latter was found to be short-lived. In another study, the effects of clonidine used for intra-articular administration in combination with morphine were investigated. These authors found a significantly higher rate of satisfaction in the group of patients receiving clonidine plus morphine. Although several recent studies have shown certain benefits from the use of clonidine for regional anesthesia, further investigations are necessary to clarify its role.

NO catastrophes in vivo as a result of micellar catalysis.

Micellar catalysis plays a crucial role in NO metabolism because media in vivo are heterogeneous and the concentration of NO in different phases at different levels of solubility differs by degrees of magnitude. The relative volumes of the hydrophobic phases are usually small. At small volumes (which are calculated) of these phases the reaction rates of NO metabolism change. The dependence on the relative volumes is resonance-like. Not only regulation, but bifurcations and catastrophes are possible in vivo as a result of this changing due to the small change of effectiveness of micellar catalysis.

Intrathecal opioid conversions: the importance of lipophilicity.

An intrathecal opioid infusion using an implanted programmable pump is frequently used for controlling refractory pain. Morphine, which is the only opioid presently approved by the FDA for use in such pumps, occasionally fails to work or is not tolerated by the patient; therefore other opioids are considered for infusions. When switching from one drug to another, it is important to consider not only equianalgesic dose conversions, but also lipophilicity. We report on three cases that demonstrate the need to use only a fraction of the equianalgesic dose when shifting from lipophilic to nonlipophilic opioids in such infusions.