Anesthesiology
-
Subcutaneous injection of dilute formalin in the hind paw of the rat produces a biphasic nociceptive response. Initial C-fiber activity is accompanied by flinching of the paw for about 5 min (phase 1), followed by cessation of activity and resumption of flinching beginning 15 min after injection and lasting about 40 min or more (phase 2). The second phase depends on changes in dorsal horn cell function that occur shortly after the initial C-fiber discharge. It was previously shown that isoflurane, administered during phase 1, reduced phase 2 activity, but a combination of isoflurane and nitrous oxide given throughout phase 1 did not suppress spinal sensitization. The same model was used to determine the effects of several inhalation and intravenous anesthetic agents on phase 2 of the formalin test. ⋯ Volatile anesthetics or nitrous oxide significantly suppress spinal sensitization, whereas the combination of nitrous oxide plus halothane causes no suppression. Thiopental does not affect spinal sensitization, whereas propofol causes significant suppression. These results may have important implications regarding the development of postoperative pain.
-
Comparative Study
Pulsatile versus nonpulsatile flow. No difference in cerebral blood flow or metabolism during normothermic cardiopulmonary bypass in rabbits.
Although pulsatile and nonpulsatile cardiopulmonary bypass (CPB) do not differentially affect cerebral blood flow (CBF) or metabolism during hypothermia, studies suggest pulsatile CPB may result in greater CBF than nonpulsatile CPB under normothermic conditions. Consequently, nonpulsatile flow may contribute to poorer neurologic outcome observed in some studies of normothermic CPB. This study compared CBF and cerebral metabolic rate for oxygen (CMRO2) between pulsatile and nonpulsatile CPB at 37 degrees C. ⋯ During CPB in rabbits at 37 degrees C, neither CBF nor CMRO2 is affected by arterial pulsation. The absence of pulsation per se is not responsible for the small decreases in CMRO2 observed during CPB.
-
Comparative Study
Quantitative assessment of differential sensory nerve block after lidocaine spinal anesthesia.
Recent technology allows for quantitative and selective measurement of A beta, A delta, and C fiber nerve transmission. To gain further insight into the physiology of differential block after lidocaine spinal anesthesia, the function of these different fibers was quantitatively measured over time, and these measurements were correlated with regression of anesthesia to pinprick, touch, cold, and tolerance of tetanic electrical current (equivalent to surgical incision). ⋯ Differential sensory block during spinal anesthesia is due to different recovery profiles of A beta, A delta, and C fibers. Return of A beta current perception thresholds to baseline correlated with duration of surgical anesthesia as assessed with an electrical stimulation model.
-
During spinal and epidural anesthesia, local anesthetics reach concentrations in cerebrospinal fluid and spinal cord tissues at which their actions may extend beyond the classic blockade of sodium channels. This study examines the effects of several clinical and experimental local anesthetics on the binding and actions of a peptide neurotransmitter, substance P, known to be important in nociceptive transmission in the dorsal horn. ⋯ Because millimolar concentrations of local anesthetics are within the range measured in spinal cord during intrathecal and epidural procedures, these results are consistent with a direct action of local anesthetics on tachykinin-mediated neurotransmission during regional anesthesia.
-
Recent reports of major and minor neurologic sequelae after spinal anesthesia have generated concern regarding the safety of some currently used intrathecal agents. The role of glucose, if any, in neurotoxic injury associated with spinal anesthesia is not known. The current experiments sought to determine whether the presence of 7.5% glucose alters the neurotoxicity of intrathecally administered 5% lidocaine. ⋯ The presence of 7.5% glucose does not affect the potential of intrathecally administered 5% lidocaine to induce sensory impairment. These findings provide further support for the hypothesis that recent injuries after spinal anesthesia resulted from a direct neurotoxic effect of the local anesthetic.