Effect of intravenous butorphanol infusion on the minimum alveolar concentration of isoflurane in cats

Background Individuals with spinal cord injury may undergo multiple surgical procedures; however, it is not clear how spinal cord injury affects anesthetic requirements and movement force under anesthesia during both acute and chronic stages of the injury. Methods The authors determined the isoflurane minimum alveolar concentration (MAC) necessary to block movement in response to supramaximal noxious stimulation, as well as tail-flick and hind paw withdrawal latencies, before and up to 28 days after thoracic spinal transection. Tail-flick and hind paw withdrawal latencies were measured in the awake state to test for the presence of spinal shock or hyperreflexia. The authors measured limb forces elicited by noxious mechanical stimulation of a paw or the tail at 28 days after transection. Limb force experiments were also conducted in other animals that received a reversible spinal conduction block by cooling the spinal cord at the level of the eighth thoracic vertebra. Results A large decrease in MAC (to </= 40% of pretransection values) occurred after spinal transection, with partial recovery (to approximately 60% of control) at 14-28 days after transection. Awake tail-flick and hind paw withdrawal latencies were facilitated or unchanged, whereas reflex latencies under isoflurane were depressed or absent. However, at 80-90% of MAC, noxious stimulation of the hind paw elicited ipsilateral limb withdrawals in all animals. Hind limb forces were reduced (by >/= 90%) in both chronic and acute cold-block spinal animals. Conclusions The immobilizing potency of isoflurane increases substantially after spinal transection, despite the absence of a baseline motor depression, or "spinal shock." Therefore, isoflurane MAC is determined by a spinal depressant action, possibly counteracted by a supraspinal facilitatory action. The partial recovery in MAC at later time points suggests that neuronal plasticity after spinal cord injury influences anesthetic requirements.

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Effects of Blood Glucose Changes and Physostigmine on Anesthetic Requirements of Halothane in Rats

Anesthesiology ◽

10.1097/00000542-199708000-00023 ◽

1997 ◽

Vol 87 (2) ◽

pp. 354-360 ◽

Cited By ~ 1

Author(s):

Yumiko Ishizawa ◽

Shuichiro Ohta ◽

Hiroyuki Shimonaka ◽

Shuji Dohi

Keyword(s):

Blood Glucose ◽

Blood Glucose Level ◽

Glucose Level ◽

Minimum Alveolar Concentration ◽

Severe Hypoglycemia ◽

Dependent Manner ◽

Sprague Dawley ◽

Control Value ◽

Sprague Dawley Rats ◽

Brain Acetylcholine

Background Although hyper- and hypoglycemia induce neurophysiologic changes, there have been no reports on the effects of blood glucose changes on anesthetic requirements. This study examined the effects of hyper- and hypoglycemia on the minimum alveolar concentration (MAC) of halothane in rats. In addition, based on a previous finding that the level of brain acetylcholine was reduced during mild hypoglycemia, the authors examined the influence of physostigmine on MAC during hypoglycemia. Methods In Sprague-Dawley rats, anesthesia was induced and maintained with halothane in oxygen and air. The MAC was determined by observing the response to tail clamping and tested during mild hypoglycemia (blood glucose level, 60 mg/dl) and hyperglycemia (blood glucose level, 300 and 500 mg/dl) induced by insulin and glucose infusion, respectively (experiment 1). The effects of 0.3 and 1.0 mg/kg physostigmine given intraperitoneally on MAC were examined in rats with mild and severe hypoglycemia (blood glucose level, 60 and 30 mg/dl; experiment 2). Results In experiment 1, mild hypoglycemia significantly reduced the MAC of halothane (0.76 +/- 0.03%) compared with the control value (0.92 +/- 0.04%), but hyperglycemia did not change MAC. In experiment 2, mild and severe hypoglycemia reduced MAC of halothane in a degree-dependent manner. Physostigmine (1 mg/kg) had no effect on MAC regardless of blood glucose level, but 0.3 mg/kg reduced MAC. Conclusions Hypoglycemia reduced anesthetic requirements in a degree-dependent manner, whereas hyperglycemia had no effects. Although the mechanism of hypoglycemic MAC reduction needs further investigations, physostigmine studies suggest that this may not be related to inhibition of cholinergic transmission.

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Minimum alveolar concentration for halothane in children with cerebral palsy and severe mental retardation

Anaesthesia ◽

10.1111/j.1365-2044.1997.257-az0376.x ◽

1997 ◽

Vol 52 (11) ◽

pp. 1056-1060 ◽

Cited By ~ 47

Author(s):

F. J. Frei ◽

M. H. Haemmerle ◽

R. Brunner ◽

C. Kern

Keyword(s):

Cerebral Palsy ◽

Mental Retardation ◽

Minimum Alveolar Concentration ◽

Severe Mental Retardation ◽

Children With Cerebral Palsy

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Interaction of Isoflurane and Nitrous Oxide Combinations Similar for Median Electroencephalographic Frequency and Clinical Anesthesia

Anesthesiology ◽

10.1097/00000542-199604000-00004 ◽

1996 ◽

Vol 84 (4) ◽

pp. 782-788. ◽

Cited By ~ 18

Author(s):

Heiko Ropcke ◽

Helmut Schwilden

Keyword(s):

Nitrous Oxide ◽

Minimum Alveolar Concentration ◽

Dose Range ◽

Volatile Anesthetic ◽

Oxide Concentration ◽

Anesthetic Requirement ◽

Clinical Anesthesia ◽

Sparing Effect ◽

The Relationship ◽

Nitrous Oxide Concentration

Background The volatile anesthetic sparing effect of nitrous oxide in clinical studies is less than might be expected from the additivity of minimum alveolar concentration values. Other studies identify nonadditive interactions between isoflurane and nitrous oxide. The aim of this study was to quantify the interaction of isoflurane and nitrous oxide at a constant median electroencephalographic frequency. Methods Twenty-five patients were studied during laparotomies. Nitrous oxide was randomly administered in concentrations of 0, 20, 40, 60, and 75 vol%, to ten patients for each nitrous oxide concentration. Isoflurane vaporizer settings were chosen so that the median electroencephalographic frequency was held between 2 and 3 Hz. The relationship between nitrous oxide concentrations and required isoflurane concentrations was examined with the method of isoboles. Results Nitrous oxide linearly decreased the isoflurane requirement. Addition of every 10 vol% of nitrous oxide decreases the isoflurane requirement by approximately 0.04 vol%. The total anesthetic requirement of isoflurane and nitrous oxide, expressed in terms of previously reported minimum alveolar concentration values, increased significantly with increasing nitrous oxide concentrations. Conclusions The interaction of isoflurane and nitrous oxide in the dose range 0-75 vol% on median electroencephalographic frequency is compatible with additivity. The potency of nitrous oxide as a substitute for isoflurane is less than on a minimum alveolar concentration basis. Maintaining median electroencephalographic frequency more appropriately reflects the clinical usage of isoflurane and nitrous oxide than does maintaining minimum alveolar concentration.

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