Anesthesia and analgesia
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Anesthesia and analgesia · Apr 2003
Case ReportsBispectral index-derived facial electromyography-guided fentanyl titration in the opiate-exposed patient.
A 34-yr-old man, possibly opiate tolerant, underwent the second part of a scoliosis repair. We describe a narcotic titration protocol by using facial electromyography data derived from the bispectral index monitor that resulted in a good clinical outcome.
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Anesthesia and analgesia · Apr 2003
Cerebral blood flow is not altered in sheep with Pseudomonas aeruginosa sepsis treated with norepinephrine or nitric oxide synthase inhibition.
The origin of cerebral dysfunction in patients with sepsis is still unclear. However, altered cerebral perfusion may play an important role in its pathogenesis. Using an established, chronic model of hyperdynamic ovine sepsis, we examined cerebral perfusion in 20 sheep subjected to a continuous infusion of live Pseudomonas aeruginosa. After 24 h of sepsis, the hypotensive sheep (reduction in mean arterial blood pressure by 16%; P < 0.05) received the nitric oxide synthase inhibitor N(G)-mono-methyl-L-arginine (L-NMMA; 7 mg. kg(-1). h(-1); n = 7), norepinephrine (NE; n = 7), or normal saline (control; n = 6). NE infusion was individually targeted to achieve the same increase in mean arterial blood pressure as that observed in matched sheep of the L-NMMA group. Regional perfusion was measured by using colored microspheres. Although L-NMMA caused a significant increase in systemic vascular resistance index (1167 +/- 104 versus 793 +/- 59 dyne. cm(-5). m(2); P < 0.05), it caused a change neither in cerebrovascular resistance nor in cerebral blood flow. When related to systemic blood flow, a redistribution of blood flow to the brain became obvious. The NE-associated increase in systemic blood pressure (98 +/- 5 versus 83 +/- 5; P < 0.05) was accompanied by an increase in cardiac output (7.8 +/- 0.5 versus 6.7 +/- 0.6; P < 0.05) and, hence, systemic perfusion. However, blood flow to the brain remained unaffected. Although detrimental vasoconstrictive effects of NE and L-NMMA, including cerebral hypoperfusion, are discussed, neither drug had any effect on cerebral perfusion during experimental hyperdynamic sepsis. ⋯ Cerebral dysfunction is often found in septic patients. In this regard, it is debated whether vasopressor drugs, such as norepinephrine and L(G)-mono-methyl-L-arginine, have harmful effects on the cerebral circulation. During experimental hyperdynamic sepsis, however, neither drug altered cerebral vascular resistance or cerebral blood flow.
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Anesthesia and analgesia · Apr 2003
Preservation of the cortical somatosensory-evoked potential during dexmedetomidine infusion in rats.
Successful somatosensory-evoked potential (SEP) monitoring has been performed during the administration of dexmedetomidine to patients, but a systematic investigation of the dose response of the SEP to dexmedetomidine has not been reported. In this study, we evaluated the effect of a range of dexmedetomidine doses on the cortical SEP in rats. Twelve rats were initially anesthetized with ketamine and the lungs were mechanically ventilated. Femoral arterial and venous catheters were placed. Anesthesia was maintained with constant infusions of remifentanil (5-15 microg. kg(-1). min(-1)) and vecuronium (56 microg. kg(-1). min(-1)). Dexmedetomidine was infused at 0.1, 0.25, 0.5, 1.0, and 2.0 microg. kg(-1). min(-1) in a stepwise manner with 10-min infusion periods at each step. In eight rats, an additional large-dose infusion of dexmedetomidine at 10 microg. kg(-1). min(-1) was administered for 30 min. The cortical SEPs were recorded after stimulation of the tibial nerve. At all infusion rates, there was a statistically insignificant increase in the SEP amplitude. Dexmedetomidine consistently increased the SEP latency, but these increases were not statistically significant. These data demonstrate that dexmedetomidine maintains technically adequate conditions for SEP monitoring in rats and provides support for future studies of the effect of dexmedetomidine on SEP monitoring in humans. ⋯ In rats, the administration of a wide range of infusion rates of dexmedetomidine did not significantly affect the somatosensory-evoked potential. These results suggest that dexmedetomidine might be a useful adjunctive drug in patients undergoing intraoperative somatosensory-evoked potential monitoring.
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Anesthesia and analgesia · Apr 2003
Isoflurane antagonizes the capacity of flurothyl or 1,2-dichlorohexafluorocyclobutane to impair fear conditioning to context and tone.
In animals, the conventional inhaled anesthetic, isoflurane, impairs learning fear to context and fear to tone, doing so at concentrations that produce amnesia in humans. Nonimmobilizers are inhaled compounds that do not produce immobility in response to noxious stimulation, nor do they decrease the requirement for conventional inhaled anesthetics. Like isoflurane, the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (2N) impairs learning at concentrations less than those predicted from its lipophilicity to produce anesthesia. The capacity of the nonimmobilizer di-(2,2,2,-trifluoroethyl) ether (flurothyl) to affect learning and memory has not been studied. Both nonimmobilizers can cause convulsions. We hypothesized that if isoflurane, 2N, and flurothyl act by the same mechanism to impair learning and memory, their effects should be additive. We found that isoflurane, 2N, and flurothyl (each, alone) impaired learning fear to context and fear to tone in rats, with the nonimmobilizers doing so at concentrations less than those that cause convulsions. (Fear was defined by freezing [volitional immobility] in the presence of the conditioned stimulus [context or tone].) However, the combination of isoflurane and 2N or flurothyl produced an antagonistic rather than an additive effect on learning, a finding in conflict with our hypothesis. And flurothyl was no less potent than 2N (at least no less potent relative to the concentration of each that produced convulsions) in its capacity to impair learning. We conclude that conventional inhaled anesthetics and nonimmobilizers impair learning and memory by different mechanisms. The basis for this impairment remains unknown. ⋯ Conventional inhaled anesthetics and nonimmobilizers are antagonistic in their effects on learning and memory, and this finding suggests that they impair learning and memory, at least in part, by different mechanisms.
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Anesthesia and analgesia · Apr 2003
The effects of propofol and etomidate on airway contractility in chronically hypoxic rats.
We investigated the effect of two IV anesthetics, propofol and etomidate, on airway responsiveness in a rat model of chronic hypoxia (CH) in comparison with normoxic rats. CH rats were obtained using a hypobaric chamber (14 days at a barometric pressure of 380 mm Hg). The ability of both anesthetics to relax and prevent agonist-induced contraction was assessed in isolated tracheal rings precontracted with the muscarinic agonist carbachol (CCh) and the depolarizing agent KCl. Cumulative concentrations of both compounds relaxed tracheal rings precontracted with CCh or KCl with a similar amplitude in CH and normoxic rats. In tracheal rings precontracted with CCh, the negative logarithm of anesthetics that reduced the maximal contraction by 30%, i.e., -log half-maximal inhibitory concentration, for propofol and etomidate were 4.10 +/- 0.09 and 4.12 +/- 0.15 in normoxic rats and 4.20 +/- 0.22 and 3.61 +/- 0.19 in CH rats, respectively. At a fixed concentration, propofol (3 x 10(-4) M) or etomidate (10(-4) M) also inhibited CH tracheal rings contraction in response to cumulative concentrations of CCh and KCl. However, in contrast with the equivalent relaxant effect of both anesthetics, etomidate was two-fold less effective than propofol for inhibiting the subsequent contraction to CCh and KCl. These results indicate that propofol and etomidate retain their relaxant properties in CH rat airways by acting on the pharmaco- and electromechanical coupling. ⋯ Anesthesia may cause airway constriction or bronchospasm in patients with normal or pathological airways. This study investigated the ability of propofol and etomidate to both reverse precontraction and inhibit contraction of tracheal rings isolated from chronically hypoxic rats.