Respiratory gas exchange and hemodynamics during lumbar epidural anesthesia: effects of lidocaine with and without epinephrine.

BACKGROUND AND OBJECTIVES: Epinephrine modifies the hemodynamic response to epidural local anesthetic; effects on respiratory gas exchange are not known. We hypothesized that epidural epinephrine would increase oxygen consumption and carbon dioxide production. METHODS: Twelve healthy patients (age, 22 to 46 years) undergoing surgery on the knee were randomly assigned to receive either 2% lidocaine (group L) or 2% lidocaine with epinephrine 5 microg x mL(-1) (group E), approximately 20 mL, over 10 minutes via lumbar epidural catheter. Total-body oxygen consumption (VO2) and carbon dioxide production (VCO2) were determined by indirect calorimetry; hemodynamic measurements were obtained by noninvasive thoracic electrical bioimpedance. Values of VO2, VCO2, heart rate (HR), cardiac index (CI), and mean arterial blood pressure (MAP) were determined every minute and averaged every 5 minutes for 30 minutes. Comparisons were made with analysis of variance (ANOVA) (within groups) and t-tests (between groups). Differences were considered statistically significant if P < .05. RESULTS: VO2 did not change in either group, while VCO2 increased significantly by 22% at 20 minutes in group E. Increases in HR were apparent in both groups, with significantly greater increases in group E (group L, 13%; group E, 21%). CI did not change in group L, but increased by 41% in group E. MAP decreased significantly by 11% in group E, but did not change in group L. CONCLUSIONS: The addition of epinephrine, 5 microg x mL(-1), to the epidural injection of 2% lidocaine is associated with changes not only in hemodynamics, but also in respiratory gas exchange.

Regression of sensory anesthesia during continuous epidural infusions of bupivacaine and opioid for total knee replacement.

The epidural administration of morphine and fentanyl delay the regression of sensory anesthesia in postoperative patients receiving epidural bupivacaine. This study was performed to determine any differential effects of two lipid-soluble opioids upon regression of sensory anesthesia during coadministration with epidural bupivacaine. Forty-eight patients scheduled for total knee replacement underwent lumbar epidural catheterization and received 1.5% etidocaine with 1:200,000 epinephrine to establish sensory anesthesia to approximately T6 bilaterally. Patients were randomized by the investigational pharmacy to receive either: (a) bupivacaine without opioid (control) (n = 16), or (b) bupivacaine with 1 mg/mL of meperidine (n = 16), or (c) bupivacaine with 3 micrograms/mL of fentanyl (n = 16) in a double-blind fashion. Intraoperatively, 0.5% bupivacaine +/- opioid was administered by epidural infusion at a rate of 10 mL/h. Postoperatively, the bupivacaine concentration was decreased to 0.25% (+/- the same opioid), and the infusion rate was decreased to 4 mL/h. Pinprick sensory anesthesia and verbal numerical pain score were recorded each hour after surgery by a blinded investigator. For each patient, the study was considered terminated when the cephalad level of sensory anesthesia bilaterally decreased five dermatomal segments or the pain score reached "5" (moderate pain). Patients receiving epidural infusions of bupivacaine and meperidine had a significantly slower regression of sensory anesthesia and slower development of pain. There was no difference in the rate of regression of sensory anesthesia or the development of pain among patients receiving bupivacaine alone or bupivacaine with fentanyl.

Spinal anesthetic agents.

Lidocaine, tetracaine, and bupivacaine are the local anesthetic agents most commonly employed for spinal anesthesia in the U.S. Lidocaine provides a short duration of anesthesia and is primarily useful for surgical and obstetrical procedures lasting less than one hour. Tetracaine and bupivacaine are used for procedures lasting 2 to 5 hours. Tetracaine appears to provide a somewhat longer duration of anesthesia and a more profound degree of motor block than does bupivacaine. On the other hand, compared with tetracaine, bupivacaine has been demonstrated to be associated with a decreased incidence of hypotension. In addition, bupivacaine may be better than tetracaine for use in orthopedic surgical procedures since it appears to be associated with a lower incidence of tourniquet pain. Vasoconstrictors can prolong the duration of spinal anesthesia of all three agents. However, the greatest duration is seen when vasoconstrictors are added to tetracaine solutions. Lidocaine and bupivacaine do not appear to benefit as much from the addition of vasoconstrictors. In general, the local anesthetic agents that are currently available for spinal anesthesia provide significant versatility. By carefully considering the planned surgical procedure, the surgeon's requirements, and the patient's characteristics (e.g., age, height, gravidity), and by understanding the factors that influence spinal anesthesia, the anesthesiologist can select a local anesthetic agent that will assure adequate and satisfying spinal anesthesia.

Tourniquet 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. However, the duration of sensory anesthesia was significantly longer in patients in whom tetracaine was used. The incidence of tourniquet pain was significantly greater in patients given tetracaine (60%) than in patients given bupivacaine (25%). 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.

Decreased incidence of tourniquet pain during spinal anesthesia with bupivacaine. A possible explanation.

In a previous report, the incidence of tourniquet pain was found to be 25% with bupivacaine and 60% with tetracaine (P less than 0.05) spinal anesthesia. On the other hand, tetracaine is more potent than bupivacaine in abolishing the single-compound action potential in vitro in isolated nerves. These conflicting observations may be reconciled if bupivacaine produced greater frequency-dependent conduction blockade of nerve action potentials. This hypothesis was tested in C fibers of isolated, desheathed rabbit vagus nerves. The nerves were supramaximally stimulated at frequencies of 9 or 15 Hz. After a control period, the nerves were exposed to bupivacaine (0.2 mM) or tetracaine (0.02 mM) for 30 minutes. The local anesthetics were then washed out by continuous constant-rate perfusion. The decline and recovery of the first and last action potential amplitudes of the train were measured. Bupivacaine and tetracaine produced similar depression of the first action potential of the 9-Hz and 15-Hz trains. However, bupivacaine caused a delayed recovery of the last action potential of the 15-Hz train but not of the 9-Hz train. These results show that bupivacaine produces greater frequency-dependent conduction blockade of C fibers than does tetracaine. These findings offer a possible explanation as to why spinal anesthesia with bupivacaine results in a lower incidence of tourniquet pain than tetracaine.

A clinical double-blind study of dibucaine and tetracaine in spinal anesthesia.

The effects of 0.25% dibucaine and 0.5% tetracaine used for the production of spinal anesthesia were compared in 30 healthy surgical patients. Fifteen patients were assigned to each of the two agents using a randomized, observer and patient-blinded method. Success rate, times of onset and regression of analgesia, intensity of motor blockade, and cardiovascular effects were assessed and the results were analyzed statistically. There were no differences in success rate, in latency, or in duration of action between the two spinal anesthetic agents. Tetracaine was found to be associated with a significantly greater decrease in arterial pressure and more complete motor blockade.