Anesthesiology
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Comparative Study Clinical Trial Controlled Clinical Trial
Thermoregulatory vasoconstriction impairs active core cooling.
Many clinicians now consider hypothermia indicated during neurosurgery. Active cooling often will be required to reach target temperatures < 34 degrees C sufficiently rapidly and nearly always will be required if the target temperature is 32 degrees C. However, the efficacy even of active cooling might be impaired by thermoregulatory vasoconstriction, which reduces cutaneous heat loss and constrains metabolic heat to the core thermal compartment. The authors therefore tested the hypothesis that the efficacy of active cooling is reduced by thermoregulatory vasoconstriction. ⋯ Vasoconstriction did not produce a full core temperature "plateau," because of the extreme microenvironment provided by forced-air cooling. However, it markedly decreased the rate at which hypothermia developed. The approximately 1-h delay in reaching core temperatures of 33 degrees C and 32 degrees C could be clinically important, depending on the target temperature and the time required to reach critical portions of the operation.
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Randomized Controlled Trial Comparative Study Clinical Trial
Arterial oxygenation during one-lung ventilation. A comparison of enflurane and isoflurane.
Because maintaining arterial oxygenation (PaO2) during one-lung ventilation (OLV) can be a clinical problem, it is useful to be aware of factors that influence PaO2 in this situation and are under the control of the anesthesiologist. It is unknown whether, among the commonly used volatile anesthetic agents, one is associated with higher PaO2 levels. Clinical studies suggest that isoflurane provides superior PaO2 during OLV than does halothane. These have not been compared to enflurane. The authors studied PaO2 and hemodynamics during OLV with 1 MAC enflurane versus 1 MAC isoflurane. ⋯ During OLV, the PaO2 values with 1 MAC isoflurane were greater than those with enflurane. The dependence of PaO2 on cardiac output does not support the hypothesis that an increase in cardiac output will cause a decrease in hypoxic pulmonary vasoconstriction and a decrease in PaO2 during OLV.
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Comparative Study
Triiodothyronine increases contractility independent of beta-adrenergic receptors or stimulation of cyclic-3',5'-adenosine monophosphate.
Triiodothyronine regulates cardiac contractility; however, the mechanisms by which it produces its acute contractile effects remains unknown. We compared the acute effects of thyroid hormones (triiodothyronine [T3] and thyroxine [T4]) and of isoproterenol on the contractility of isolated rat hearts. In addition, we sought to determine whether the acute inotropic effects of thyroid hormones were mediated by beta-adrenergic receptors or by increased production of cyclic-3',5'-adenosine monophosphate (cAMP). ⋯ These results demonstrate that the acute inotropic effects of T3 are not shared by T4 and appear unrelated to beta-adrenergic receptor mechanisms or to generation of cAMP. Thus, T3 acutely stimulates cardiac contraction by mechanisms that differ from those of the more commonly used beta-adrenergic receptor agonists and phosphodiesterase inhibitors. Further studies are needed to identify the mechanisms underlying the acute contractile effects of T3 and to determine whether T3 will prove useful for increasing ventricular function in patients.
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Randomized Controlled Trial Comparative Study Clinical Trial
Does spinal anesthesia result in a more complete sympathetic block than that from epidural anesthesia?
Spinal and epidural injection of local anesthetics are used to produce sympathetic block to diagnose and treat certain chronic pain syndromes. It is not clear whether either form of regional anesthesia produces a complete sympathetic block. Spinal anesthesia using tetracaine has been reported to produce a decrease in plasma catecholamine concentrations. This has not been demonstrated for epidural anesthesia in humans with level of anesthesia below C8. One possible explanation is that spinal anesthesia results in a more complete sympathetic block than epidural anesthesia. To examine this question, a cross-over study was performed in young, healthy volunteers. ⋯ Spinal anesthesia did not result in a more complete attenuation of the sympathetic response to a CPT than did epidural anesthesia. In response to the CPT, spinal anesthesia blocked the increase in cardiac index, and epidural anesthesia resulted in a decrease in total peripheral resistance compared to the pre-anesthesia state. The differences between the techniques are not significant and are of uncertain clinical implications.
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Randomized Controlled Trial Comparative Study Clinical Trial
Cervical spine movement during laryngoscopy with the Bullard, Macintosh, and Miller laryngoscopes.
Direct laryngoscopy requires movement of the head, neck, and cervical spine. Spine movement may be limited for anatomic reasons or because of cervical spine injury. The Bullard laryngoscope, a rigid fiberoptic laryngoscope, may cause less neck flexion and head extension than conventional laryngoscopes. The purpose of this study was to compare head extension (measured externally), cervical spine extension (measured radiographically), and laryngeal view obtained with the Bullard, Macintosh, and Miller laryngoscopes. ⋯ The Bullard laryngoscope caused less head extension and cervical spine extension than conventional laryngoscopes and resulted in a better view. It may be useful in care of patients in whom cervical spine movement is limited or undesirable.