Anesthesia and analgesia
-
Anesthesia and analgesia · Feb 2000
An analysis of drug interaction between morphine and neostigmine in rats with nerve-ligation injury.
Intrathecal neostigmine reverses mechanical allodynia in humans and animals. The efficacy of morphine in a neuropathic pain state is still controversial. This study examines the antiallodynic interaction between morphine and neostigmine in a rat model of neuropathic pain. Rats were prepared with tight ligation of left L5-6 (fifth and sixth lumbar) spinal nerves and chronic intrathecal catheter implantation. Mechanical allodynia was measured by using application of von Frey hairs to the left hindpaw. Morphine (1, 3, 10, and 30 microg) and neostigmine (0.3, 1, 3, and 10 microg) were administered intrathecally to obtain the dose-response curves and the 50% effective dose (ED(50)) for each drug. ED(50) values and fractions of the ED(50) values (1/2, 1/4, and 1/8) were administered intrathecally in an equal dose ratio to establish the ED(50). Isobolographic and fractional analyses for the drug interaction were performed. Intrathecal morphine produced a moderate antagonism of the tactile allodynia. A morphine-neostigmine combination produced a dose-dependent increase in withdrawal threshold of the lesioned hind paw with reduced side effects. Both analyses revealed a synergistic interaction after the coadministration of morphine and neostigmine. These experiments suggest that the antiallodynic action of a morphine-neostigmine combination is synergistic at the spinal level. ⋯ This study indicates that, by using both isobolographic and fractional analyses, the antiallodynic effect of intrathecal morphine and neostigmine is synergistic when coadministered intrathecally. In a rat model of neuropathic pain, the intrathecal morphine produced a moderate antagonism on touch-evoked allodynia at the spinal level.
-
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.
-
Inhaled nitric oxide (NO) is a selective pulmonary vasodilator used to treat intraoperative pulmonary hypertension and hypoxemia. In contrast to NO delivered by critical care ventilators, NO delivered by anesthesia machines can be complicated by rebreathing. We evaluated two methods of administering NO intraoperatively: via the nitrous oxide (N(2)O) flowmeter and via the INOvent (Datex-Ohmeda, Madison, WI). We hypothesized that both systems would deliver NO accurately when the fresh gas flow (FGF) rate was higher than the minute ventilation (VE). Each system was set to deliver NO to a lung model. Rebreathing of NO was obtained by decreasing FGF and by simulating partial NO uptake by the lung. At FGF > or = VE (6 L/min), both systems delivered an inspired NO concentration ([NO]) within approximately 10% of the [NO] set. At FGF < VE and complete NO uptake, the N(2)O flowmeter delivered a lower [NO] (70 and 40% of the [NO] set at 4 and 2 L/min, respectively) and the INOvent delivered a higher [NO] (10 and 23% higher than the [NO] set at 4 and 2 L/min, respectively). Decreasing the NO uptake increased the inspired [NO] similarly with both systems. At 4 L/min FGF, [NO] increased by 10%-20% with 60% uptake and by 18%-23% with 30% uptake. At 2 L/min, [NO] increased by 30%-33% with 60% uptake and by 60%-69% with 30% uptake. We conclude that intraoperative NO inhalation is accurate when administered either by the N(2)O flowmeter of an anesthesia machine or by the INOvent when FGF > or = VE. ⋯ Inhaled nitric oxide (NO) is a selective pulmonary vasodilator. In a lung model, we demonstrated that NO can be delivered accurately by a N(2)O flowmeter or by a commercial device. We provide guidelines for intraoperative NO delivery.
-
Anesthesia and analgesia · Feb 2000
Clinical TrialInterference of cerebral near-infrared oximetry in patients with icterus.
Near-infrared spectrophotometry assesses cerebral oxygen saturation (ScO(2)) based on the absorption spectra of oxygenated and deoxygenated hemoglobin and the translucency of biological tissue in the near-infrared band. In patients with icterus, however, bilirubin can potentially hinder cerebral oximetry. In 48 patients undergoing orthotopic liver transplantation, we related total plasma bilirubin to ScO(2) as determined from spectrophotometry with wavelengths of 733 and 809 nm. Before surgery, ScO(2) was 59% (15%-78%) (median with range) and bilirubin was 71 (6-619) micromol/L with a negative correlation (r = -0.72; P < 0.05). The 95% prediction interval included the lowest measurable ScO(2) of 15% at a bilirubin level of 370 micromol/L. During reperfusion of the grafted liver, the ScO(2) increased by 7% (-8% to 17%) (P < 0.05), and bilirubin did not influence this increase. In one patient, the ScO(2) remained below 15% despite a decrease in bilirubin from 619 to 125 micromol/L, suggesting that tissue pigmentation deposits also absorb light. In conclusion, bilirubin dampens the spectrophotometry-determined cerebral oxygen saturation at 733 and 809 nm. A bilirubin level of 370 micromol/L, tissue pigment deposits, or both, may render determination of cerebral oxygen saturation impossible. Even at high bilirubin values, changes in cerebral perfusion may be visible. ⋯ In 48 patients undergoing liver transplantation, the interference of icterus on cerebral oximetry by near-infrared light was investigated. Bilirubin absorbed the near-infrared light and lowered the measured cerebral oxygen saturation. Even at high bilirubin values, changes in cerebral oxygenation, as seen during reperfusion of the grafted liver, may be visible.