Anesthesia and analgesia
-
Anesthesia and analgesia · Jan 2001
Clinical TrialVideo imaging to assess neuromuscular blockade at the larynx.
We describe video imaging as a technique for assessing neuromuscular blockade at the larynx. We sought to determine the stability and reproducibility of this technique and to compare the effect of succinylcholine at the adductor pollicis and the larynx. Ten patients were studied. Anesthesia was induced and maintained with propofol. The recurrent laryngeal nerve was stimulated superficially and movements of the vocal cords were recorded on videotape by using a fiberoptic bronchoscope passed via a laryngeal mask airway. Neuromuscular function was recorded at the adductor pollicis by using a mechanomyograph. Twenty images of the vocal cords were examined repeatedly by one investigator and by ten independent observers. The mean difference between the two sets of observations was 0.86 degrees with a correlation coefficient (r) of 0.997. For 3 min before the administration of relaxant the coefficient of variation in the cord movement during supramaximal stimulation ranged from 1%-4% (median 2.7%). After the administration of succinylcholine 1 mg. kg(-1) the times to loss of T1 at the larynx and hand were 63 +/- 15 s and 63 +/- 12 s respectively. Times to 25% recovery were 215 +/- 36 s at the larynx and 436 +/- 74 s at the hand and times to 75% recovery were 285 +/- 55 s and 525 +/- 85 s respectively. These results indicate that video imaging may be a useful research technique for estimating neuromuscular blockade at the larynx and that the time to onset of succinylcholine at the larynx is similar to that at the hand, whereas the duration of blockade is significantly shorter at the larynx. ⋯ Assessment of neuromuscular blockade at the larynx is possible by using a video imaging technique. By using this technique, the time to onset of neuromuscular blockade at the larynx is similar to that at the hand after the administration of succinylcholine; this finding is different from previously published data obtained by using a cuff pressure measurement technique.
-
Anesthesia and analgesia · Jan 2001
Comparative StudyLow preoperative antithrombin activity causes reduced response to heparin in adult but not in infant cardiac-surgical patients.
We evaluated the interaction of preoperative antithrombin (AT) activity and intraoperative response to heparin in cardiac surgery. Heparin anticoagulation is essential during cardiopulmonary bypass (CPB). Heparin itself has no anticoagulant properties, however it causes a conformational change of the physiologic plasma inhibitor AT that converts this slow-acting serine protease inhibitor into a fast acting one. Thus, adequate AT activity is a prerequisite for sufficient heparin anticoagulation. AT activity is reduced by long-term heparin therapy. This prospective, observational study investigated 1516 consecutive cardiac-surgical patients (1304 patients >1 yr (Group A) and 212 patients < or = 1 yr (Group I)). AT activity was measured the day before surgery by a chromogenic substrate assay. The celite-activated activated clotting time (ACT) was used to guide intraoperative heparin administration. Heparin sensitivity was calculated and the postoperative blood loss and perioperative blood requirement was recorded. Infant patients had significantly less preoperative AT activity compared with older patients: 84 (33)% vs 97 (17)%, median (interquartile range) (P < 0. 05). The subgroup of patients aged <1 mo (n = 64) demonstrated a preoperative AT activity of 56 (27)% as compared with 90 (23)% in infant patients between one month and one year (n = 148). In adult patients, preoperative AT activity depended predominantly on preoperative heparin treatment: 62% of the patients with an AT activity <80% were pretreated with heparin. Five minutes after heparin but before CPB the ACT was 587 (334) s in Group A patients with AT activity > or = 80%, and 516 (232) in patients with AT activity < or = 80% (P < 0.05). The target ACT of 480 s was achieved in 70% of patients with normal AT activity in Group A compared with only 54% of patients with AT activity <80% (P < 0.05). In Group A patients with decreased AT activity, 18% demonstrated an inadequate ACT response-defined as ACT <400 s-to the first bolus injection of heparin. In Group I, preoperative AT activity did not influence the ACT response (ACT 5 min after heparin: 846 [447] s in patients with AT activity > or = 80% vs 1000 [364] s in patients with decreased AT activity). The heparin sensitivity was 2.4 (1.1) s/unit heparin/kg compared with 1.5 (0.8) s/unit heparin/KG in group A (P < 0.05). These results suggest that preoperative diminished AT activity causes reduced response to heparin in adult but not in infant patients. Infant patients demonstrate a higher heparin sensitivity despite lower preoperative AT activity. Measurement of preoperative AT activity identifies adult patients at risk of reduced sensitivity to heparin. ⋯ In patients less than one year of age, low antithrombin (AT) activity is caused by the immature coagulation system. Despite low AT activity, these young patients demonstrate a normal or increased response to heparin anticoagulation before cardiopulmonary bypass (CPB). In contrast, in patients older than one year of age and adult patients decreased preoperative AT activity is mainly caused by preoperative heparin therapy and causes insufficient response to heparin anticoagulation with a standard heparin dosage. Measurement of preoperative AT activity identifies patients at risk of inadequate anticoagulation during CPB.
-
Anesthesia and analgesia · Jan 2001
Clinical TrialThe effect of breath termination criterion on breathing patterns and the work of breathing during pressure support ventilation.
With pressure support ventilation (PSV), each PSV breath is flow-cycled, and the breath termination criterion (TC) is usually nonadjustable. When TC does not match the interaction between the patient's inspiratory-expiratory efforts to the opening and closing of the inspiratory and expiratory valves, patient-ventilator asynchrony may occur, and the work of breathing (WOB) may increase. Therefore, we studied the effect of TC on breathing patterns and WOB during PSV in eight patients with acute respiratory distress syndrome or acute lung injury. We studied five levels of TC during PSV-1%, 5%, 20%, 35%, and 45% of the peak inspiratory flow. With increasing levels of TC, the tidal volume decreased and respiratory frequency increased, along with a decrease in duty cycle. WOB markedly increased with increasing levels of TC from 0.31 +/- 0.12 J/L with TC 1% to 0.51 +/- 0.11 J/L with TC 45%. Premature termination with double breathing occurred in one patient with TC 35% and four patients with TC 45%. Delayed termination with a duty cycle of >0.5 occurred in two patients with TC 1%. In conclusion, the proper adjustment of TC improves patient-ventilator synchrony and decreases WOB during PSV. ⋯ Although termination criterion (TC) is usually nonadjustable, it influences the effectiveness of pressure support ventilation for mechanical ventilation. The proper adjustment of TC is crucial to improve patient-ventilator synchrony and decrease work of breathing. TC 5% of the peak inspiratory flow may be the optimal value for patients with acute respiratory distress syndrome or acute lung injury.
-
Anesthesia and analgesia · Jan 2001
Comparative StudyIntraoperative monitoring in neuroanesthesia: a national comparison between two surveys in Germany in 1991 and 1997. Scientific Neuroanesthesia Research Group of the German Society of Anesthesia and Intensive Care Medicine.
Two surveys initiated by the Neuroanesthesia Research Group of the German Society of Anesthesia and Intensive Care Medicine examined the practice of intraoperative monitoring during intracranial procedures in Germany in 1991 and 1997. Questionnaires were mailed to departments that were registered members of the German Society of Anesthesia and Intensive Care Medicine and that provided neuroanesthesia service on a routine basis in 1991. In 1997, the survey was repeated in the 1991 respondents. In 1991, 68 departments and in 1997, 44 departments returned completed questionnaires, indicating a response rate of 87% for 1991 and of 65% for 1997. Compared with 1991, the standards for monitoring, such as surveillance of oxygenation, ventilation, circulation, and body temperature, were universally applied in adult and pediatric patients in 1997. Overall, there was a 20% increase in neuromuscular blockade monitoring and in the use of electroencephalography and evoked potentials in 1997 compared with 1991. Further brain-specific monitoring was rarely provided in 1997. Overall, jugular venous oximetry was used in 20% and transcranial Doppler ultrasonography in 15% of responding hospitals. To detect venous air embolism in sitting patients, 75% of all responding hospitals used precordial Doppler ultrasonography in both years, whereas transesophageal echocardiography was more often used in 1997 (38%) as compared with 1991 (17%). ⋯ Standards of anesthetic monitoring were surveyed in neuroanesthesia in Germany in 1991 and 1997. Central nervous system monitoring was not the standard of practice.