Anesthesia and analgesia
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Anesthesia and analgesia · Feb 1996
Randomized Controlled Trial Comparative Study Clinical TrialContinuous hypopharyngeal pH measurements in spontaneously breathing anesthetized outpatients: laryngeal mask airway versus tracheal intubation.
We measured the hypopharyngeal pH to compare the incidence of regurgitation associated with the laryngeal mask airway (LMA) and the tracheal tube (TT) in spontaneously breathing, anesthetized patients. Sixty outpatients scheduled for elective peripheral surgery with a standardized general anesthetic technique were randomly allocated to receive either a LMA (n = 28) or a TT (n = 32) for airway management. A 4-mm pH electrode was placed in the hypopharynx, and pH values were continuously collected and stored in a portable pH data logger system until the end of the operation. ⋯ The hypopharyngeal pH values in both groups were similar, ranging between 5.5 and 7.5, with median values of 5.7 and 6.2 in the LMA and TT groups, respectively. The pH in any given patient did not vary more than 1.0 unit from the initial value recorded at the start of the operation. We conclude that continuous monitoring of the hypopharyngeal pH in spontaneously breathing, anesthetized outpatients failed to detect evidence of pharyngeal regurgitation.
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Anesthesia and analgesia · Feb 1996
The influence of carbon dioxide and body position on near-infrared spectroscopic assessment of cerebral hemoglobin oxygen saturation.
Near-infrared spectroscopy may allow continuous and noninvasive monitoring of regional brain hemoglobin oxygen saturation by measuring the differential absorption of infrared light by oxyhemoglobin and deoxyhemoglobin. We have previously examined the correlation between the spectroscopic signal generated by a prototype cerebral oximeter (Invos 3100; Somanetics, Troy, MI), and global brain hemoglobin oxygen saturation calculated from arterial and jugular venous bulb oxygen saturations. Because the technology does not distinguish between arterial and venous hemoglobin saturation, changes in the proportion of cerebral arterial and venous blood volume, which may result from changes in blood flow or venous distending pressure, may confound measurements. ⋯ We found that changes in position did not influence the association between CSfO2 and CScombO2 (r2 = 0.69-0.885) during hypoxic challenge. In a second set of eight volunteers, we studied the influence of hypercapnia and hypocapnia and body position on the association between CSfO2 and CScombO2, and found that they were less well correlated (r2 = 0.366-0.976) in individual patients. Because changes in body position and Paco2 confound the relationship between CSfO2 and CScombO2, changes in CSfO2 can best be assessed if position and Paco2 are constant.
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Anesthesia and analgesia · Feb 1996
Bupivacaine plasma concentrations during continuous epidural anesthesia in infants and children.
Venous bupivacaine plasma concentrations were measured in six neonates and infants aged 4 days to 3.9 mo (mean, 2.1 mo) and 10 infants and children aged 9 mo to 6 yr (mean, 3.1 yr) after administration of an initial bolus of 0.5 mL/kg bupivacaine 0.25%, followed by a continuous infusion of local anesthetic (0.25 mL.kg-1.h-1) over a period of 4 h (first hour: bupivacaine 0.25%, then reduced to 0.125%). Plasma concentrations of local anesthetic measured at 180 min and 300 min after beginning of bupivacaine administration were significantly higher in younger infants when compared to older infants and children (180 min: 0.67 +/- 0.24 micrograms/mL [0.25-0.97] vs 0.27 +/- 0.11 micrograms/mL [0.19-0.55], P < 0.01; 300 min: 0.86 +/- 0.36 micrograms/mL [0.35-1.25] vs 0.34 +/- 0.12 micrograms/mL [0.18-0.57], P < 0.01). The results of our study show that despite applying the same dosage of epidural bupivacaine significantly higher plasma concentrations were seen after short periods of continuous infusion in infants up to 4 mo than in children older than 9 mo.
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Anesthesia and analgesia · Feb 1996
The effects of N-methyl-D-aspartate agonists and antagonists on isolated bovine cerebral arteries.
This pharmacologic study examines the direct cerebrovascular effects of N-methyl-D-aspartate (NMDA) receptor agonists and antagonists to determine whether large cerebral arteries have NMDA receptors. Bovine middle cerebral arteries were cut into rings to measure isometric tension development in vitro. Two competitive agonists, L-glutamate and NMDA, each had negligible effects on ring tension in the absence of exogenous vasoconstrictors. ⋯ Three noncompetitive antagonists (S(+)-ketamine, dizocilpine, and dextrorphan) and their steroeisomers (R(-)-ketamine, (-)MK-801, and levorphanol) each produced dose-dependent relaxation of K(+)- or U-46,619-constricted arteries; relaxation was not selective for the (+) or (-) stereoisomers. These results suggest that large cerebral arteries lack NMDA receptors mediating constriction or relaxation. All noncompetitive antagonists dilated cerebral arteries, but by mechanisms that were not stereospecific.
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Anesthesia and analgesia · Feb 1996
Repeated dural punctures increase the incidence of postdural puncture headache.
Previous studies have failed to find a significant correlation between the number of dural punctures and the incidence of postdural puncture headache (PDPH), questioning the hypothesis that leakage of cerebrospinal fluid (CSF) through the dural tear is the cause of PDPH. We hypothesized that insufficient statistical power of these studies was the cause for this unexpected finding, and re-examined whether repeated dural punctures increase the incidence of PDPH by analyzing prospectively collected data on 8034 spinal anesthetics. Uneventful spinal anesthetics, including a single subarachnoid injection of local anesthetics, occurred in 7865 (97.9%) cases, whereas failed spinal anesthetics requiring repeated dural puncture for a second subarachnoid injection of local anesthetics occurred in 165 (2.1%) cases. ⋯ We found that repeated dural punctures significantly increased the incidence of PDPH. We conclude that increased risk of PDPH is a disadvantage of performing a second subarachnoid injection of local anesthetics after a failed spinal anesthetic. Moreover, this result suggests that leakage of CSF through the dural tear is the most plausible cause of PDPH.