Anesthesia and analgesia
-
Anesthesia and analgesia · Feb 2000
Randomized Controlled Trial Clinical TrialSmall-dose dopamine increases epidural lidocaine requirements during peripheral vascular surgery in elderly patients.
We studied 20 patients over the age of 65 yr undergoing prolonged peripheral vascular surgery under continuous lidocaine epidural anesthesia, anticipating that the increased hepatic metabolism caused by small-dose IV dopamine would lower plasma lidocaine concentrations. Subjects were assigned (random, double-blinded) to receive either a placebo IV infusion or dopamine, 2 microg. kg(-1). min(-1) during and for 5 h after surgery. Five minutes after the IV infusion was started, 20 mL of 2% lidocaine was injected through the epidural catheter. One-half hour later, a continuous epidural infusion of 2% lidocaine at 10 mL/h was begun. The epidural infusion was temporarily decreased to 5 mL/h or 5 mL boluses were added to maintain a T8 analgesic level. Arterial blood samples were analyzed for plasma lidocaine concentrations regularly during and for 5 h after surgery. Plasma lidocaine concentrations increased continuously during the epidural infusion and, despite wide individual variation, were similar for the two groups throughout the observation period. During the observation period, the mean maximal plasma lidocaine concentration was 5.8 +/- 2.3 microg/mL in the control group and 5.7 +/- 1.2 microg/mL in the dopamine group. However, the mean hourly lidocaine requirement during surgery was significantly different, 242 +/- 72 mg/h for control and 312 +/- 60 mg/h for dopamine patients (P < 0.03). At the end of Hour 4, the last period when all 20 patients were still receiving the epidural lidocaine infusion, the total lidocaine requirement was significantly different, 1088 +/- 191 mg for the control group and 1228 +/- 168 mg for the dopamine group (P < 0.05). Despite very large total doses of epidural lidocaine (1650 +/- 740 mg, control patients, and 1940 +/- 400, dopamine patients) mean maximal plasma concentrations remained below 6 microg/mL, and no patient exhibited signs or symptoms of toxicity. We conclude that small-dose IV dopamine increased epidural lidocaine requirements, presumably as a consequence of increased metabolism. ⋯ We tested dopamine, a drug that increases liver metabolism of the local anesthetic lidocaine to determine if it would prevent excessively large amounts of lidocaine in the blood during prolonged epidural anesthesia in elderly patients. Dopamine did not alter the blood levels of lidocaine, but it did increase the lidocaine dose requirement to maintain adequate epidural anesthesia.
-
Anesthesia and analgesia · Feb 2000
Comparative Study Clinical TrialA pilot study of pharyngeal pulse oximetry with the laryngeal mask airway: a comparison with finger oximetry and arterial saturation measurements in healthy anesthetized patients.
We compared pharyngeal SpO(2) by using the laryngeal mask airway (LMA) to finger SpO(2) and oxygen saturation from arterial blood samples (SaO(2)). We studied 20 hemodynamically stable, well oxygenated, anesthetized patients (ASA physical status I-III, aged 18-80 yr). A single-use pediatric pulse oximeter was attached to the back plate of a size 5 LMA. Pharyngeal and finger SpO(2) (dominant index finger) and SaO(2) (nondominant radial artery) were measured with the cuff volume at 0-40 mL in the neutral position. The intracuff pressure was then set at 60 cm H(2)O in the neutral position, and readings were taken with the head-neck flexed, extended, and rotated. SaO(2) was the same as pharyngeal SpO(2) at 20 and 30 mL cuff volume, but higher than pharyngeal SpO(2) at all other cuff volumes and head-neck positions (P < 0.04). SaO(2) was always higher than finger SpO(2) (P < 0.01). Pharyngeal SpO(2) was higher than finger SpO(2) at cuff volumes 10-40 mL and in the flexed and rotated head-neck positions (all: P < 0.007), but was lower at 0 cuff volume (P < 0.0001) and similar in the extended head-neck position. There was an increase in pharyngeal SpO(2) between 0 and 10 mL cuff volume (P < 0.0001), but no changes thereafter. Pharyngeal SpO(2) was similar in the flexed, rotated and extended head-neck positions. Pharyngeal SpO(2) agrees more closely with SaO(2) (mean difference < 0.7%) than finger SpO(2) (mean difference > 1.1%) at 10-40 mL cuff volume and in head-neck flexion. The standard error of limits was identical (0.09) for both finger SpO(2) and pharyngeal SpO(2) if data at 0 cuff volume are excluded. We conclude that pharyngeal SpO(2) with the LMA is feasible and generally provides more accurate readings than finger SpO(2) in hemodynamically stable, well oxygenated, anesthetized patients. ⋯ Pharyngeal oximetry with the laryngeal mask airway is feasible and generally provides more accurate readings than finger oximetry in hemodynamically stable, well oxygenated, anesthetized patients.
-
Anesthesia and analgesia · Feb 2000
Antinociception by epidural and systemic alpha(2)-adrenoceptor agonists and their binding affinity in rat spinal cord and brain.
This study was designed primarily to relate the antinociceptive and hemodynamic effects of clinically available alpha(2)-adrenoceptor agonists to their binding affinity for alpha(2)-adrenoceptors in the spinal cord and brain. In rats with chronic indwelling epidural catheters, the percentage maximal possible effect on tail-flick latency was measured after epidural or IM dexmedetomidine (DXM), clonidine (CL), or tizanidine (TZ) administration. To examine their binding affinities, isolated spinal cord and brain membranes with an alpha(2) agonist were incubated with (3)H-UK14304, a selective alpha(2) agonist, and the radioactivity in the reaction mixtures was measured by liquid scintillation spectrometry. Epidural DXM (0.5-10 microg), CL (10-500 microg), and TZ (5-500 microg) all produced dose-dependent antinociceptive effects; the rank order of potencies was DXM > CL > TZ, the same as for their systemic administration. The antinociceptive effects were blocked by epidural yohimbine. The receptor binding affinities expressed as the concentration that inhibits 50% for spinal cord and brain, respectively, were 0.25 and 1.3 nM (DXM), 10.8 and 12.5 nM (CL), and 48.2 and 96.8 nM (TZ). The changes in arterial blood pressure and heart rate evoked by antinociceptive doses did not correlate with the rank order of antinociceptive potencies. The relative antinociceptive potencies of epidural alpha(2) agonists may depend on their binding affinities to alpha(2)-adrenoceptors in the spinal cord, but their cardiovascular effects may result from actions both inside and outside the central nervous system. ⋯ Spinal antinociception caused by the epidural administration of alpha(2) agonists is well correlated with their binding affinity to spinal alpha(2)-adrenoceptors.
-
Anesthesia and analgesia · Feb 2000
Randomized Controlled Trial Comparative Study Clinical TrialOral ketamine/midazolam is superior to intramuscular meperidine, promethazine, and chlorpromazine for pediatric cardiac catheterization.
An IM combination of meperidine, promethazine, and chlorpromazine (DPT) has been given as sedation for pediatric procedures for more than 40 years. We compared this IM combination to oral (PO) ketamine/midazolam in children having cardiac catheterization. A total of 51 children, ages 9 mo to 10 yr, were enrolled and randomized in this double-blinded study. All children received an IM injection at time zero and PO fluid 15 minutes later. We observed acceptance of medication, onset of sedation and sleep, and sedative efficacy. The cardiorespiratory changes were evaluated. Sedation was supplemented with IV propofol as required. Recovery time, parental satisfaction, and patient amnesia were assessed. Ketamine/midazolam given PO was better tolerated (P < 0.0005), had more rapid onset (P < 0.001), and provided superior sedation (P < 0.005). Respiratory rate decreased after IM DPT only. Heart rate and shortening fraction were stable. Oxygen saturation and mean blood pressure decreased minimally in both groups. Supplemental propofol was more frequently required (P < or = 0.02) and in larger doses (P < 0.05) after IM DPT. Parental satisfaction ratings were higher (P < 0.005) and amnesia was more reliably obtained (P = 0.007) with PO ketamine/midazolam. Two patients needed airway support after the PO medication, as did two other patients when PO ketamine/midazolam was supplemented with IV propofol. Although PO ketamine/midazolam provided superior sedation and amnesia compared to IM DPT, this regimen may require the supervision of an anesthesiologist for safe use. ⋯ Oral medication can be superior to IM injections for sedating children with congenital heart disease; however, the safety of all medications remains an issue.