Bispectral Index values are higher during halothane vs. sevoflurane anesthesia in children, but not in infants.

BACKGROUND: Previously, we have shown in adult patients that bispectral index score (BIS) values are significantly higher during halothane anesthesia (53-61 units) as compared with those observed during equipotent concentrations of sevoflurane (39-43 units). Because halothane is frequently used in the pediatric setting, we tested the hypothesis that BIS values observed in children might also be higher during general anesthesia with halothane than with sevoflurane. METHODS: Forty-one healthy, unpremedicated pediatric patients scheduled for elective operations received either halothane or sevoflurane titrated as appropriate for surgical stimulation. RESULTS: During maintenance sevoflurane anesthesia (n=20), the mean BIS values and percent end-tidal concentrations were 44+/-14 and 2.1+/-0.6, respectively, whereas for the halothane group (n=21) the corresponding values were 61+/-7 and 1.1+/-0.4, respectively. CONCLUSION: These findings suggest that BIS values are higher during halothane vs. sevoflurane anesthesia in children, but not in infants.

Isoflurane versus fentanyl: hemodynamic effects in cancer patients treated with anthracyclines.

Cancer patients treated with anthracycline derivatives are at risk for perioperative cardiovascular decompensation. The authors studied hemodynamic performance before, during, and after laparotomy in 14 anthracycline-treated patients with ovarian carcinoma. General anesthesia was maintained with 70% N2O in O2, and patients were randomized to receive supplementation with either isoflurane, 0.59% end-tidal +/- 0.04 (mean +/- SE), or fentanyl, 2.67 micrograms/kg +/- 0.49 as a loading dose, and a total dose of 7.16 micrograms/kg +/- 0.71. The degree of hemodynamic stability relative to the baseline was assessed. There was no obvious superiority of either technique prior to the skin incision. However, during and immediately after surgery, a clearer tendency for isoflurane-N2O to result in better hemodynamic stability was found. Isoflurane-N2O demonstrated significantly smaller change scores in systemic vascular resistance (SVR) and cardiac index (CI). At the start of surgery, the isoflurane-N2O change in SVR was 228.08 dyne.sec.cm-5 compared to 479.58 for the fentanyl patients, (P = 0.002); at the end of surgery the corresponding means were -12.09 and 703.14 dyne.sec.cm-5, respectively, (P = 0.002). Isoflurane-N2O was associated with significantly greater CI stability in the early postoperative period: the isoflurane-N2O mean change was -0.081 L/min/m2, versus -0.993 for the fentanyl-N2O patients, (P = 0.005). The authors conclude that anthracycline-treated patients who do not have overt evidence of cardiomyopathy can be safely anesthetized with either anesthetic technique. However, during surgery and in the early postoperative period, an isoflurane-N2O technique appears to offer better hemodynamic stability.

EEG and memory effects of low-dose infusions of propofol.

The purpose of this study was to identify EEG changes associated with low-dose propofol infusion producing only sedative effects, and to describe the memory effects of low-dose propofol infusion. Ten healthy volunteers underwent EEG monitoring (at Fz, Cz, Pz and Oz electrode sites) before, during and after propofol 0.5 mg kg-1 i.v. bolus and 75 micrograms kg-1 min-1 as an infusion. Mean serum concentration of propofol during infusion was 0.86 (SD 0.14) micrograms ml-1. The EEG changed significantly during infusion, with increased power in the beta 1 (15-20 Hz), beta 2 (20.5-30 Hz) and delta (1-3.5 Hz) frequencies. Beta 1 and beta 2 power changes were most marked at the Fz and Cz electrodes. Subjects were sedated, but able to complete cognitive tasks. Visual analogue scales of attention and sleepiness were obtained throughout the study and demonstrated a sedative effect during propofol infusion, but were not a significant factor in memory performance or EEG changes. A verbal learning task (Rey Auditory-Verbal Learning Task) administered before, during and after infusion showed a marked reduction in short-term memory capacity and dramatically impaired free recall and recognition during infusion. Nine of 10 subjects had partial amnesia for complex visual scenes presented during infusion, recalling less than 50% of the material. Stronger cueing was required to retrieve information presented during propofol infusion, with an increase in mean retrieval time from 95.4 (41.2) s to 426.8 (83.1) s. EEG and memory effects resolved quickly after the end of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Esmolol infusion during nitroprusside-induced hypotension: impact on hemodynamics, ventricular performance, and venous admixture.

The impact of esmolol infusion on hemodynamics, ventricular performance, venous admixture, sympathoadrenal, and renin-angiotensin system responses during sodium nitroprusside (SNP)-induced hypotension was studied in 11 patients undergoing lymph node dissection during general anesthesia with 60% nitrous oxide and fentanyl. Radial arterial and thermistor-tipped pulmonary catheters were employed for hemodynamic monitoring. Arterial and mixed venous blood gas tensions, arterial plasma renin activity (PRA), and plasma catecholamine levels were measured. Derived hemodynamic parameters and venous admixture (Qs/Qt) data were obtained from standard equations. Transesophageal echocardiography (6 patients) was used to assess left ventricular performance using the relationship between end-systolic wall stress (ESWS) and velocity of circumferential shortening (VCFC). After surgical incision, arterial hypotension was induced with SNP alone. Esmolol was infused at each of the following rates in sequence: 200, 300, and 400 micrograms/kg/min. Each esmolol infusion lasted 20 minutes and the SNP dose was adjusted to maintain MAP at 55 to 60 mm Hg. The mean dose of SNP required to induce hypotension was 5.5 micrograms/kg/min +/- 0.5 SE. Compared to prehypotension values, SNP induced significant increases in Qs/Qt and reductions in PaO2, systemic vascular resistance (SVR), and stroke volume index (SVI). Esmolol infusion caused dose-dependent (highest with 400 micrograms/kg/min) reductions in the SNP requirement, heart rate (HR), SVI, Qs/Qt, and PRA, and also led to significant increases in SVR and left ventricular (LV) internal diameter in diastole as well as systole. Furthermore, esmolol infusion was associated with a dose-dependent downward and leftward shift of the ESWS versus VCFC relationship, implying diminished contractility.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of midazolam on the auditory event-related potential: measures of selective attention.

To elucidate the delayed effects of midazolam, we assessed electrophysiologic and motor responses by measuring auditory event-related potentials and a button-press reaction time response in 10 normal volunteers (aged 25-36 yr). Fifty minutes after intravenous infusion of 0.07 mg/kg of midazolam, subjects were mildly sedated, oriented, and readily responsive to verbal commands. To obtain ERPs, frequent tones (85%: 1000 Hz) and rare tones (15%: 2500 Hz) were presented at intervals of 1.5 s. Electroencephalographic signals were collected from FZ, CZ, and PZ for 1000 ms after stimulus presentation until 40 artifact-free rare-tone responses were obtained (average time, 6 min). Peak-to-peak amplitudes and latencies for N2, P3, and the subsequent negative slow wave (N3) were averaged within condition and were analyzed by repeated measures analysis of variance. After midazolam infusion, there was a 50% decrease in amplitude of P3 in response to target tones (P less than 0.006), whereas N3 latency increased by 40 ms (P less than 0.05). Event-related potential amplitudes were still significantly larger to rare (target) stimuli (P less than 0.003) after midazolam infusion. Although reaction time increased by 70 ms (P = 0.031), performance accuracy remained unchanged. Self-ratings of sleepiness and concentration show that a significant sedation effect was still present 50 min after infusion. Although routine clinical examination may be normal, full recovery from the effects of a typical intravenous dose of midazolam requires more than 50 min. The potential for adverse drug interaction, particularly with narcotics, is still present at this time.

The EEG as a monitor of midazolam amnesia: changes in power and topography as a function of amnesic state.

In order to identify EEG parameters that might be specific for identifying amnesia during midazolam infusion, we examined changes in the EEG power spectrum associated with a period of amnesia, determined by inability to recall a sequence of numbers and objects presented verbally, after intravenous midazolam 0.07 mg/kg in ten normal volunteers. Measurements were taken at baseline, during infusion immediately before and after the onset of amnesia, immediately at end of infusion, and 0.5 and 1.5 h after infusion. All subjects had onset of amnesia during infusion, were completely amnesic by the end of infusion, partially amnesic 0.5 h after infusion, and had complete recall by 1.5 h after infusion. The EEG beta power increased and alpha power decreased during amnesic periods. The beta 1/alpha power ratio was the parameter most specific for amnesia. From a baseline value of 0.20 +/- 0.05 (standard error of the mean [SEM]), it increased to 0.96 +/- 0.26 at the end of infusion and decreased to 0.61 +/- 0.15 0.5 h after infusion. By 1.5 h after infusion, all EEG parameters had returned to baseline values. Beta power changes associated with midazolam amnesia were most pronounced in the Fz and Cz lead positions, and alpha power changes were most pronounced in the Oz position. We conclude that 1) EEG power values, particularly the beta 1/alpha ratio, can identify periods of amnesia after midazolam infusion; 2) specific EEG changes and the presence of amnesia vary with the probable serum concentration of midazolam; and 3) the characteristic EEG pattern during partial or complete amnesia varies as one moves across the cerebral cortex.

Improved detection of hypotension by automated noninvasive blood pressure monitoring.

This study was undertaken to determine whether the use of automated noninvasive blood pressure monitoring altered the frequency of detection of intraoperative hypotension. We retrospectively reviewed 1,861 anesthetic records from a period in 1987, when blood pressure was obtained manually by auscultation. We compared the records from 1987 with 1,716 anesthetic records from 1989, when automated blood pressure monitors were used universally. The incidences of hypotension requiring vasopressor therapy were determined during the two periods and compared using Student's two-tailed t test. The data revealed that the incidence of detected hypotension increased from 2.4 to 5.2% with the use of automated blood pressure monitors (P less than 0.00002). We conclude that at our hospital the use of automated noninvasive blood pressure monitors increases the incidence of detection of intraoperative hypotension as compared with the use of manual blood pressure measurement.

General anesthesia prior to treatment of anterior mediastinal masses in pediatric cancer patients.

Many children with malignant diseases who present with an anterior mediastinal mass must undergo general anesthesia for tissue diagnosis or tumor resection. One hundred sixty-three pediatric patients over a period of 6 yr were admitted to Memorial Sloan-Kettering Cancer Center with a diagnosis of anterior mediastinal mass. Forty four of these patients required surgery and their records were reviewed. In recent years perioperative radiation therapy has been advocated for this patient group prior to their receiving general anesthesia. If a tissue diagnosis has not been made, preoperative radiation therapy may distort histologic findings and prevent accurate diagnosis. All patients with an anterior mediastinal mass who must receive general anesthesia in our institution do so prior to treatment with radiation or chemotherapy even in the presence of cardiovascular or respiratory symptoms. No patient died or sustained permanent injury as a result of their anesthetic or operative experience. Two patients who experienced difficulty on induction of anesthesia required tracheal intubation with a rigid bronchoscope. Two patients developed airway obstruction during anesthetic maintenance that was corrected with changes in patient position. Four patients were unable to have their tracheas extubated at the conclusion of surgery and one patient required tracheal reintubation in the immediate postoperative period. These patients were treated with radiation therapy and chemotherapy after tissue for diagnosis had been obtained. The authors conclude that in the absence of life-threatening preoperative airway obstruction and severe clinical symptoms general anesthesia may be safely induced prior to radiation therapy.

A clinical evaluation of pulse oximetry during thoracic surgery.

To evaluate the utility of pulse oximetry for monitoring oxygenation during thoracic surgery, pulse oximeter oxygen saturation (SpO2) values from the Nellcor N-100 (Nellcor Inc, Haywood, CA) and Novametrix model 500 (Medical Systems Inc, Wallingford, CT) were compared with simultaneous arterial saturation values (SaO2) in 20 patients. A total of 255 matched observations were recorded, and the data were divided for statistical analysis into preinduction of anesthesia and postinduction groups. The preinduction group showed a good correlation between SpO2 and SaO2 values, with both pulse oximeters consistently overestimating the SaO2. However, once anesthesia was induced, there was no longer any correlation for either of the pulse oximeters versus simultaneous SaO2 values, although on average, the SpO2 values were significantly higher than the corresponding SaO2 values. It was concluded that pulse oximetry is useful in following trends of oxygenation in patients with preexisting lung pathology undergoing thoracic surgery, but it cannot replace arterial blood gas sampling for the intraoperative management of respiratory function.

Anesthesia for diagnostic and therapeutic procedures in pediatric outpatients.

Appropriate sedation of pediatric oncology patients during painful diagnostic and therapeutic procedures is a recognized problem. At the Memorial Sloan-Kettering Cancer Center the pediatric oncologists and anesthesiologists have developed a cooperative program that has provided safe and effective sedation of outpatients. The experience with 100 consecutive outpatients is reported. Patients ranged from 3 months to 17 years of age. Procedures included lumbar puncture and/or intrathecal chemotherapy, multiple bone marrow aspirations, bone marrow biopsies, and removal of indwelling central vein catheters. Monitoring of patients during the procedures as well as various pharmacologic techniques to provide adequate working conditions are described.

A comparison of EEG determinants of near-awakening from isoflurane and fentanyl anesthesia. Spectral edge, median power frequency, and delta ratio.

To evaluate the efficacy of the computer-processed electro-encephalogram (EEG) for determining near-awakening from anesthesia, 14 patients were monitored during emergence from either isoflurane or fentanyl anesthesia at the termination of major surgical procedures. The raw EEG was obtained using bilateral frontomastoid electrodes. The compressed spectral array was digitized and recorded on disk in 4-s epochs using a Tractor Northern "Nomad" processor. The EEG information was displayed in four formats: 1) the frequency-power spectrum from 1-20 Hz, 2) the 95% power frequency, 3) the 50% power frequency, and 4) the ratio of power in the 8-20 Hz frequency range to the power in the 1-4 Hz frequency range (delta ratio). During emergence from isoflurane, there were obvious changes in the EEG frequency-power spectrum that occurred several minutes before patients opened their eyes in response to verbal stimuli. Although no one descriptor of EEG activity could be shown to be superior in anticipating when patients would respond by opening their eyes, awakening was always presaged by an abrupt decrease in power in the 1-4 Hz frequency range; this resulted in a marked increase in the delta ratio value. During emergence from fentanyl anesthesia, however, there was no obvious change in the overall EEG frequency-power spectrum. However, the same numeric EEG descriptors that were predictive of awakening from isoflurane also occurred during emergence from fentanyl, even though they usually occurred within 1 min of awakening. It is concluded that EEG criteria for identifying when patients will awaken from anesthesia are more reliable with isoflurane than with fentanyl.

Comparison of the Bain and the ADE systems during controlled ventilation in adults.

It has been suggested that Humphrey's ADE system may be an improvement on the Bain system. To compare their efficiencies we have studied 20 anesthetized adults who had controlled ventilation established with a circle absorber system at a VE sufficient to maintain normocapnia. Patients were then randomly allocated to either a Bain or an ADE system. Fresh gas flow was sufficient to keep PE'CO2 constant for 30 min. The other circuit was then used for an additional 30 min. The required FGF was 54 ml kg-1 min-1 for the Bain system, compared with 67 ml kg-1 min-1 for the ADE system. We conclude that, during controlled ventilation, the ADE system is 25% less efficient than the Bain system.