Anesthesia and analgesia
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Anesthesia and analgesia · Aug 1995
Comparative StudyComparison of the effects of halothane, isoflurane, and sevoflurane on atrioventricular conduction times in pentobarbital-anesthetized dogs.
It is not known how sevoflurane affects the cardiac conduction system. We compared the effects of halothane, isoflurance, and sevoflurane on specialized atrioventricular (AV) conduction times in eight pentobarbital-anesthetized dogs. AV conduction times with three inhaled anesthetics at end-tidal concentrations of 1 and 2 minimum alveolar anesthetic concentration (MAC), were measured by His-bundle electrocardiography during both sinus rhythm and right atrial pacing at a slightly higher rate than sinus one. ⋯ No significant difference in AV conduction times was observed between isoflurane and sevoflurane. Heart rate during sinus rhythm remained unchanged despite a decrease in arterial pressure with three inhaled anesthetics. The property of sevoflurane and isoflurane which does not affect the cardiac conduction system may be important in the stability of the cardiac rhythm during anesthesia with these drugs.
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Anesthesia and analgesia · Aug 1995
Case ReportsTransient neurologic deficit after spinal anesthesia: local anesthetic maldistribution with pencil point needles?
Recent reports of transient neurologic deficits have raised concern about the potential toxicity of single-dose spinal 5% lidocaine in 7.5% dextrose. Two cases of volunteers who experienced minor local sensory deficits after slow (60 s) injections of 2 mL 5% lidocaine via Whitacre needles are described. One case was a result of a double injection because of a "failed" block. ⋯ Triplicate injections were done at rapid (2 mL/10 s) and slow (2 mL/60 s) rates, with needle side ports oriented in a sacral and cephalad direction. At slow rates of injection, using 27- or 25-gauge sacrally directed Whitacre needles, injections showed evidence of maldistribution with extrapolated peak sacral lidocaine concentrations reaching 2.0%. In contrast, distribution after slow injection through sacrally directed Quincke needles was uniform.(ABSTRACT TRUNCATED AT 250 WORDS)
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Anesthesia and analgesia · Aug 1995
The effect of changing end-expiratory pressure on respiratory system mechanics in open- and closed-chest anesthetized, paralyzed patients.
The decrease in functional residual capacity (FRC) with anesthesia may cause lung volume to decrease below closing volume, thereby impairing oxygenation. Increasing end-expiratory pressure (EEP) reexpands atelectatic areas in anesthetized, ventilated patients, but its effect on pulmonary mechanics is less well understood. We studied the effect of varying EEP on the mechanical behavior of the respiratory system in patients undergoing either closed (Group 1) or open-chest (Group 2) surgical procedures. ⋯ The magnitudes of RRS and RL were similar in both groups of subjects and in each group these quantities decreased with increases in EEP. Dynamic EL responded differently to changes in EEP in subjects with open-chest and closed-chest procedures. We attribute this difference to overdistension of the remaining ventilable lung tissue at all levels of EEP in open-chest patients.
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Perioperative hypothermia usually results largely from pharmacologic inhibition of normal thermoregulatory control. Midazolam is a commonly used sedative and anesthetic adjuvant whose thermoregulatory effects are unknown. We therefore tested the hypothesis that midazolam administration impairs thermoregulatory control. ⋯ Similarly, midazolam decreased the shivering threshold: 35.9 +/- 0.3 degrees C vs 35.3 +/- 0.6 degrees C (P = 0.03). The sweating-to-vasoconstriction (interthreshold) range, therefore, increased from 0.2 +/- 0.1 degrees C to 0.7 +/- 0.3 degrees C (P = 0.002). Although statistically significant, this relatively small increase contrasts markedly with the 3-5 degrees C interthreshold ranges produced by clinical doses of volatile anesthetics, propofol, and opioids.(ABSTRACT TRUNCATED AT 250 WORDS)
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Anesthesia and analgesia · Aug 1995
Exhaled flow monitoring can detect bronchial flap-valve obstruction in a mechanical lung model.
Flap-valve obstruction to expiratory flow (V) in a major bronchus can result from inspissated secretions, blood, or foreign body. During inhalation, increasing airway caliber preserves inspired V past the obstruction; during exhalation, decreasing airway diameter causes airflow obstruction and even frank gas trapping. We reasoned that the resultant sequential, biphasic exhalation of the lungs would be best detected by measuring exhaled V versus time. ⋯ Airway P could not differentiate between bronchial and tracheal flap-valve obstruction because P decreased abruptly in both conditions. The flow-volume loop displayed less distinctive changes than the flow-time plot, in part because the flow-volume loop was data (flow) plotted against its time integral (volume), with loss of temporal data. In this mechanical lung model, we conclude that bronchial flap-valve obstruction was best detected by the flow-time plot, which could measure the sequential emptying of the lungs.