Anesthesia and analgesia
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Anesthesia and analgesia · Aug 1999
Randomized Controlled Trial Comparative Study Clinical TrialSevoflurane speeds recovery of baroreflex control of heart rate after minor surgical procedures compared with isoflurane.
Volatile anesthetics attenuate arterial baroreflex functions, whereas noxious stimuli may modify baroreflex-induced circulatory responses during anesthesia. We designed the present study to compare baroreflex control of heart rate during sevoflurane and isoflurane anesthesia in young healthy surgical patients. Baroreflex sensitivity was assessed in 24 patients randomized to receive either sevoflurane (n = 12) or isoflurane (n = 12) for general anesthesia. After an 8- to 10-h fast and no premedication, measurements of RR intervals obtained from electrocardiography and systolic blood pressure (SBP) measured through a radial artery catheter were made at conscious baseline (Awake), during end-tidal sevoflurane 2% or isoflurane 1.2% plus 67% nitrous oxide before incision (Anesth), during surgery at end-tidal sevoflurane 2% or isoflurane 1.2% plus 67% nitrous oxide (Surg), and 20 min after tracheal extubation (Recov). Baroreflex responses were triggered by bolus i.v. injections of phenylephrine (100-150 micrograms) and nitroprusside (100-150 micrograms) to increase and decrease SBP by 15-30 mm Hg, respectively. The linear portions of the baroreflex curves relating RR intervals and SBP were determined to obtain baroreflex sensitivities. Baroreflex sensitivities to both pressor and depressor tests were significantly depressed during Anesth and Surg periods compared with Awake values in both anesthetic techniques. The pressor test sensitivity during the Recov period returned to the Awake value after sevoflurane (12.9 +/- 3.7 vs 11.0 +/- 8.7 ms/mm Hg [mean +/- SD]) but was still depressed after isoflurane anesthesia (13.9 +/- 8.0 vs 4.8 +/- 3.2 ms/mm Hg; P < 0.05). The depressor test sensitivities during the Recov period remained depressed after both anesthetic techniques. We conclude that both sevoflurane and isoflurane depress arterial baroreflex function during anesthesia and surgery, but the pressor test sensitivity was restored more quickly after sevoflurane than after isoflurane anesthesia. ⋯ Arterial baroreflex function is an important neural control system for maintaining cardiovascular stability. We found that baroreflex control of heart rate due to hypertensive perturbation returned to the preanesthetic level more quickly after sevoflurane than after isoflurane anesthesia.
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Anesthesia and analgesia · Aug 1999
Randomized Controlled Trial Clinical TrialThe effect of hematocrit on cerebral blood flow velocity in neonates and infants undergoing deep hypothermic cardiopulmonary bypass.
Varying degrees of hemodilution are used during deep hypothermic cardiopulmonary bypass. However, the optimal hematocrit (Hct) level to ensure adequate oxygen delivery without impairing microcirculatory flow is not known. In this prospective, randomized study, cerebral blood flow velocity in the middle cerebral artery was measured using transcranial Doppler sonography in 35 neonates and infants undergoing surgery with deep hypothermic cardiopulmonary bypass. Patients were randomized to low Hct (aiming for 20%) or high Hct (aiming for 30%) during cooling on cardiopulmonary bypass (CPB). Systolic (V(s)), mean (Vm), and diastolic (Vd) cerebral blood flow velocity, as well as pulsatility index (PI = [V(s) - Vd]/Vm) and resistance index (RI = [V(s) - Vd]/V(s)) were recorded at six time points: postinduction, at cannulation, after 10 min cooling on CPB, rewarmed to 35 degrees C on CPB, immediately off CPB, and at skin closure. Vm was significantly lower in the high Hct group compared with that in the low Hct group during cooling (P < 0.01). Postinduction, the high Hct group demonstrated significantly lower Vd immediately off CPB (P < 0.01) and significantly lower Vm and V(s) at skin closure (P < 0.001). We conclude that there is an inverse relation between hematocrit and cerebral blood flow velocity during deep hypothermic cardiopulmonary bypass in neonates and infants. ⋯ There is an inverse relation between hematocrit and cerebral blood flow velocity during deep hypothermic cardiopulmonary bypass in neonates and infants. Further studies correlating Hct and cerebral blood flow velocity with cerebral metabolic rate and neurologic outcome are necessary to determine the optimal Hct during deep hypothermic cardiopulmonary bypass.
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Anticipated technical difficulty is one factor that can influence the anesthesiologist's decision to perform neuraxial (spinal or epidural) blockade. Problems during the procedure may be associated with patient dissatisfaction, neurologic sequelae, or hematoma. We designed this study of 595 neuraxial blocks to determine whether any patient characteristics would be useful in predicting a difficult neuraxial block. Before the procedure, the following data were noted: demographic data, body habitus (normal, thin, muscular, obese), spinal landmarks (good = easily palpable spinous processes, poor = difficult to palpate spinous processes, none = unable to positively identify spinous processes), and spinal anatomy (assessed by inspection and examination as normal or deformed). We noted the technique, approach, needle type, needle gauge, etc. We also recorded whether the procedure was completed at the first (first-level success) or second spinal level and the total number of new skin punctures (attempts) necessary to complete the procedure. Of all the factors considered, the quality of landmarks best correlated with technical difficulty as measured by both first-level success and number of attempts. Abnormal spinal anatomy correlated with difficulty as measured by number of attempts. Body habitus also correlated with difficulty, but only as measured by number of attempts. There was no association between either measure of difficulty and any of the following: age, sex, spinal versus epidural, approach, needle type, needle gauge, or training level of the provider. Thoracic epidurals were less difficult than lumbar epidurals by both measures of difficulty. We conclude that body habitus does not seem to be the best predictor of technical difficulty. An examination of the patient's back for the quality of landmarks and obvious anatomical deformity better predicts the ease or difficulty of neuraxial block. Other factors seem to have little or no influence on the difficulty of neuraxial block procedures. ⋯ We studied a number of factors, including equipment, technique, and patient characteristics, that may indicate the ease or difficulty of performing neuraxial (spinal and epidural) blocks. Of these factors, only patient characteristics had significant predictive value. We found that an examination of the patient's back for the quality of landmarks and obvious anatomical deformity better predicts the ease or difficulty of neuraxial block than does body habitus.
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Anesthesia and analgesia · Aug 1999
Early outpatient preoperative anesthesia assessment: does it help to reduce operating room cancellations?
Increased understanding of the high cost associated with operating room (OR) cancellations has led to efforts by healthcare providers to decrease case cancellations on the day of surgery. To investigate whether preoperative evaluations within 24 h of surgery were associated with more frequent OR cancellations than those completed 2-30 days before surgery, we prospectively studied OR cancellations for 3 mo. Of the 529 patients in the study, 166 were seen within 24 h of surgery (standard group), and the remaining 363 patients were seen 2-30 days before surgery (early group). There were 70 OR cancellations on the day of surgery, and the largest single group of cancellations was related to administrative problems. The standard group and the early group were similar in terms of gender, age, ASA physical status, and percentage of patients undergoing major surgery. The OR cancellation rates were also comparable between groups: 13.3% for the standard group and 13.2% for the early group. These data suggest that patients can be evaluated in an outpatient preoperative evaluation clinic in a timeframe that is convenient for the patient without adversely affecting the cancellation rate on the day of surgery. ⋯ The operating room cancellation rate for outpatients evaluated 2-30 days before surgery was compared with the cancellation rate for outpatients who received their anesthesia evaluation within 24 h of surgery. Because both groups had similar rates, outpatients may be seen at a convenient time without adversely affecting operating room cancellations.
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Anesthesia and analgesia · Aug 1999
Effects of one minimum alveolar anesthetic concentration sevoflurane on cerebral metabolism, blood flow, and CO2 reactivity in cardiac patients.
We investigated the cerebral hemodynamic effects of 1 minimum alveolar anesthetic concentration (MAC) sevoflurane anesthesia in nine male patients scheduled for elective coronary bypass grafting. For measurement of cerebral blood flow (CBF), a modified Kety-Schmidt saturation technique was used with argon as an inert tracer gas. Measurements of CBF were performed before the induction of anesthesia and 30 min after induction under normocapnic, hypocapnic, and hypercapnic conditions. Compared with the awake state under normocapnic conditions, sevoflurane reduced the mean cerebral metabolic rate of oxygen by 47% and the mean cerebral metabolic rate of glucose by 39%. Concomitantly, CBF was reduced by 38%, although mean arterial pressure was kept constant. Significant changes in jugular venous oxygen saturation were absent. Hypocapnia and hypercapnia caused a 51% decrease and a 58% increase in CBF, respectively. These changes in CBF caused by variation of Paco2 indicate that cerebrovascular CO2 reactivity persists during 1 MAC sevoflurane anesthesia. ⋯ We used a modified Kety-Schmidt saturation technique to investigate the effects of 1 minimum alveolar anesthetic concentration (MAC) sevoflurane on cerebral blood flow, metabolism, and CO2 reactivity in cardiac patients. We found that the global cerebral blood flow and global cerebral metabolic rate of oxygen remained coupled and that cerebrovascular CO2 reactivity is not impaired by the administration of 1 MAC sevoflurane.