Anesthesia and analgesia
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Anesthesia and analgesia · Mar 1996
Comparative StudyIntraoperative myogenic motor evoked potentials induced by direct electrical stimulation of the exposed motor cortex under isoflurane and sevoflurane.
We monitored myogenic motor evoked potentials (MEPS) during intracranial surgery in 21 patients anesthetized with nitrous oxide in oxygen, fentanyl, and 0.75-1.5 minimum alveolar anesthetic concentration (MAC) isoflurane (n = 11) or sevoflurane (n = 10). The exposed motor cortex was stimulated with a single or train-of-five rectangular pulses at a high frequency (500 Hz), while the compound muscle action potentials (CMAPS) were recorded from the abductor pollicis brevis muscle. Neuromuscular block was monitored by recording the CMAPs from the abductor pollicis brevis muscle in response to electrical stimulation of the median nerve at the wrist (M-response). ⋯ In the remaining patient, MEP amplitudes were attenuated to approximately 10% of the baseline value and recovered after cessation of surgical manipulation. In the two patients in whom MEPs disappeared, motor paresis developed postoperatively. We conclude that 1) intraoperative myogenic MEP monitoring is feasible during isoflurane or sevoflurane anesthesia if stimulation is performed with a short train of rectangular pulses, and 2) that electromyographic monitoring of neuromuscular block is useful to assess intraoperative MEP changes under partial neuromuscular block.
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Anesthesia and analgesia · Mar 1996
Comparative Study Clinical Trial Controlled Clinical TrialCost-benefit analysis of nasal cannulae in non-tracheally intubated subjects.
We evaluated four nasal cannulae used to deliver oxygen and measure PETC02 in a non-tracheally intubated, healthy population. The effect of various oxygen flow rates on PETC02 and respiratory rate (RR), as well as the cost and relative patient comfort of the cannulae, was compared. In this controlled study, 20 healthy volunteers tested the cannulae using oxygen flow rates of 0 (breathing room air), 2, 4, and 6 L/min. ⋯ Of the nasal cannula systems evaluated in this study, the HOS system demonstrated the best cost-benefit ratio, performing well clinically while being comfortable to wear and relatively inexpensive. These conclusions are specific to a healthy population and not to patients with lung disease,those who smoke, or those having a higher ASA classification status. Our evaluation suggests that comfort and clinical performance of nasal cannulae may well depend on device design.
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Anesthesia and analgesia · Mar 1996
Comparative StudyChanges in lung and chest wall properties with abdominal insufflation of carbon dioxide are immediately reversible.
Previously we have reported that large increases in lung and chest wall elastances as well as lung resistance occur with abdominal insufflation of carbon dioxide during laparoscopic surgery. To examine whether these effects were reversible with abdominal deflation, we calculated lung and chest wall elastances and resistances from measurement of airway flow and pressure and esophageal pressure in 17 anesthetized/paralyzed patients undergoing laparoscopic surgery. Measurements were made immediately prior to abdominal insufflation and after deflation. ⋯ The change in total respiratory elastance did not correlate with abdominal insufflation time, surgical site, smoking history, or physical characteristics of the patients. There were no differences in frequency and tidal volume dependences of the elastances and resistances before and after abdominal insufflation (P > 0.5). We conclude that residual changes in respiratory mechanics caused by carbon dioxide insufflation during laparoscopic surgery are minor, and that the reported compromise of respiratory function indicated by pulmonary function tests after laparoscopy does not appear to be due to changes in passive mechanical properties of the lungs or chest wall.
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Anesthesia and analgesia · Mar 1996
Simulated clinical evaluation of conventional and newer fluid-warming devices.
The purpose of the study was to evaluate the ability of five commercially available devices utilizing a variety of heat exchange technologies to deliver normothermic (37 degrees C) fluids. Conditions of slow (6.5 mL/ min), moderate (13-25 mL/min), and rapid (gravity and pressure driven flows, roller clamp wide open) infusion were simulated. Fluid temperatures were measured using rapid response thermistors after the fluid exited the heat exchanger (T outlet) and before delivery to the patient intravenously (IV) (T distal). ⋯ With gravity and pressure driven flows, T distal of crystalloid were 39.0 and 38.9 for H1000 at 42 degrees C, 38.7 and 38.4 degrees C for FW537 at 42 degrees C, 34.7 and 28.9 degrees C for Hotline at 42 degrees C, 29.2 and 24.2 degrees C for BairHugger, and 29.7 and 24.2 degrees C for Flotem. In conclusion, only the H1000 at 42 degrees C was effective at delivering normothermic fluids at all clinically relevant flow rates. The Hotline at 42 degrees C was effective at slow and moderate flow, whereas the FW537 was effective only at rapid flow.
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The anesthetist exerts axial force on the laryngoscope handle to expose the glottis. The anesthetist must also apply a perpendicular force to balance the torque on the laryngoscope. Several studies have measured axial force during direct laryngoscopy, but none has measured torque. ⋯ Peak force and torque demonstrated stress relaxation, a viscous property of biologic tissues. Force and torque decreased monoexponentially to approximately 70% of peak values with a half-time of 4 +/- 0.3 s. The phenomenon occurred in spite of administration of muscle relaxants, and was probably due to stress relaxation of pharyngeal tissues that are passively stretched during laryngoscopy.