Anesthesia and analgesia
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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
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
Comparative StudyRelationship between end-tidal and arterial carbon dioxide with laryngeal mask airways and endotracheal tubes in children.
The laryngeal mask airway (LMA) is a useful tool for securing the airway in adults and children and may be substituted for an endotracheal tube (ETT) in selected patients undergoing general anesthesia. The correlation between end-tidal and arterial carbon dioxide during controlled ventilation via LMA has not been reported in a within-patient design in pediatric patients. After induction of general anesthesia, 22 children had a LMA placed and mechanical ventilation initiated. ⋯ Analysis of differences between PaCO2 and PETCO2 revealed a bias +/- precision of 4.0 +/- 3.42 and 4.2 +/- 3.66 with ventilation via ETT and LMA, respectively. The root mean square error was 0.85 for the ETT and 0.89 for the LMA. Our results indicate that in infants and children weighing more than 10 kg who are mechanically ventilated via the LMA PETCO2 is as accurate an indicator of PaCO2 as when ventilated via ETT.
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Anesthesia and analgesia · Feb 1996
Responses to nondepolarizing neuromuscular blockers and succinylcholine in von Recklinghausen neurofibromatosis.
Patients with type 1 neurofibromatosis (NF-1) have been reported to have prolonged responses to nondepolarizing (ND) neuromuscular blockers (NMBs). Responses to succinylcholine (SCh) have been described as increased, decreased, or normal. The purpose of this study was to assess responses to NMBs in NF-1 patients in order to determine the clinical significance of abnormal responses. ⋯ Standard milligram per kilogram doses of NMBs were used in all cases, and in none was there evidence of abnormal response. The risk of abnormal response to NMBs in individuals with NF-1 appears to be minimal. We recommend no alteration in dosing of either SCh or ND NMBs in patients with NF-1.