Anesthesia and analgesia
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A response algorithm consists of a logical sequence of maneuvers to be performed in response to a specific condition. With the advent of alarm-equipped monitors that alert anesthesiologists to the presence of potentially hazardous clinical conditions, a need has arisen to develop the corresponding alarm-oriented responses expected from anesthesiologists; this problem, however, has not been satisfactorily addressed in the literature. ⋯ The three-limbed algorithm rapidly and efficiently localizes the likely cause of the low-pressure condition without compromising patient safety; in the event that the search for a cause is fruitless, a default mode of ventilation is employed. A discussion is provided of common causes (e.g., disconnections), alarm-defeating circumstances (false negatives), and potential algorithm-defeating situations (multiple faults).
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Anesthesia and analgesia · Sep 1988
The pharmacokinetics of bupivacaine when injected intra-articularly after knee arthroscopy.
Bupivacaine pharmacokinetics were determined in 11 patients receiving the drug intra-articularly after knee arthroscopy performed under general anesthesia. Forty ml 0.25% bupivacaine was given at the end of surgery and the thigh tourniquet was released 2 to 3 minutes after injection. ⋯ Results indicate that injections of 100 mg bupivacaine intra-articularly after knee arthroscopy produce peak blood concentrations within the first hour after surgery, and that these will be well below concentrations associated with toxic reactions. Peak concentrations can be minimized with shorter tourniquet inflation times and with longer intervals between injection and tourniquet release.
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Anesthesia and analgesia · Sep 1988
Randomized Controlled Trial Clinical TrialTourniquet pain during spinal anesthesia: a comparison of plain solutions of tetracaine and bupivacaine.
The incidence of tourniquet pain was evaluated in 40 patients having orthopedic surgery of the lower extremities during spinal anesthesia using 15 mg of a plain solution of either 0.5% tetracaine or 0.5% bupivacaine. The drugs were administered in a randomized fashion, and measurement of the levels of sensory anesthesia to pinprick and motor blockade as well as the occurrence of tourniquet pain were made by an independent blinded observer. The onset and maximum cephalad spread of sensory anesthesia and the onset and degree of motor block were similar in both groups of patients. ⋯ The occurrence of tourniquet pain was not related to the level of sensory anesthesia, because patients in the tetracaine group had a higher level of sensory anesthesia (mean T6) than did patients in the bupivacaine group (mean T10) at the onset of tourniquet pain. It is speculated that during spinal anesthesia both A and C fibers (mediating fast and slow pain, respectively) are initially equally inhibited. However, as the concentration of local anesthetic in the cerebrospinal fluid declines, C fibers may become unblocked earlier with tetracaine than A fibers, resulting in tourniquet pain in the presence of an otherwise satisfactory spinal anesthetic.
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Anesthesia and analgesia · Sep 1988
Epidural blood flow and regression of sensory analgesia during continuous postoperative epidural infusion of bupivacaine.
Epidural blood flow was measured in seven patients undergoing elective abdominal surgery during combined lumbar epidural and general anesthesia. After an initial dose of 20 ml plain bupivacaine 0.5%, a continuous epidural infusion of bupivacaine 0.5% (8 ml/hr) was given for 16 hours for postoperative pain relief. The epidural blood flow was measured by a local 133Xe clearance technique in which 15-35 MBq 133Xe diluted in 1 ml saline was injected through the epidural catheter on the day before surgery (no bupivacaine), 30 minutes after the initial dose of bupivacaine on the morning before surgery, and 8, 12, and 16 hours later during the continuous infusion. ⋯ In these two patients epidural blood flow remained constant after the initial increase. Flow increased further to 10.3 +/- 0.8 ml/min per 100 g tissue (P less than 0.03) in the other five patients as the level of sensory analgesia regressed postoperatively. These data suggest that changes in epidural blood flow during continuous epidural infusion of bupivacaine, and thus changes in rates of vascular absorption of bupivacaine from the epidural space, may be an important factor contributing to differences in rates of regression of sensory analgesia.
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Anesthesia and analgesia · Sep 1988
Differential effects of isoflurane/nitrous oxide on posterior tibial somatosensory evoked responses of cortical and subcortical origin.
Posterior tibial somatosensory evoked responses (SSERs) were recorded during administration of isoflurane and nitrous oxide. Responses arising from cortical and subcortical neural generators were examined to compare their relative resistance to anesthetic-related degradation. Recordings were performed in ten adults during anesthesia with 0.5 MAC isoflurane/60% N2O, 1.0 MAC isoflurane/60% N2O, and 1.5 MAC isoflurane/60% N2O. ⋯ Elimination of N2O resulted in an increase in amplitude of approximately 100% (P less than 0.04). By contrast, the amplitude of the subcortical response as recorded in vertex to linked mastoid and vertex to upper cervical spine derivations was not significantly altered by changing concentrations of isoflurane or N2O. The results suggest that subcortical SSERs may be preferable to those of cortical origin for spinal cord monitoring in situations where isoflurane and nitrous oxide, especially in varying concentrations, are the primary anesthetic agents.