ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:Different anesthetic agents have different effects on cerebrovascular physiology. However, the importance of these differences In neuroanesthetic practice are unclear. In an effort to determine whether important clinical differences are present, the authors compared three anesthetic techniques in 121 adults undergoing elective surgical removal of a supratentorial, intracranial mass lesion.Methods:Patients were assigned randomly to one of three groups. In group 1 (n=40), anesthesia was induced with propofol and maintained with fentanyl (≊10 µg/kg load, 2-3 µg · kg-1· h-1infusion) and propofol (50-300 µg · kg-1· mln-1). In group 2 (n=40), anesthesia was induced with thiopental and maintained with isoflurane and nitrous oxide. Up to 2 µg/kg fentanyl was given after replacement of the bone flap. In group 3 (n=41), anesthesia was induced with thiopental and maintained with fentanyl (≊10 µg/kg load, 2-3 µg · kg-1· h1infusion), nitrous oxide, and low-dose Isoflurane, if required. Blood pressure, heart rate, expired gas concentrations, and ventilatory parameters were recorded automatically in all patients. Epidural intracranial pressure (ICP) was measuredviathe first burr hole, brain swelling was rated at the time of dural opening, and emergence was monitored closely. Preoperative computed tomography or magnetic resonance imaging scans were evaluated, and pre- and postoperative neurologic exams were performed by a neurosurgeon unaware of group assignments. Total hospital stay (days) and total hospital cost (exclusive of physician charges) also were reviewed.Results:During induction, higher heart rates were seen in isoflurane/nitrous oxide patients, whereas mean arterial pressure was ≊10 mmHg less during the maintenance phase (compared with both other groups). Otherwise, there were few intergroup hemodynamic differences. While there were no clinically important intergroup differences in mean ICP (±SD)—group 1, ICP=12 ± 7 mmHg; group 2,15 ± 12 mmHg; group 3, ICP=11 ± 8 mmHg—more isoflurane/nitrous oxide patients (nine, group 2) had an ICP £24 mmHg than in the other groups (two each). Emergence was, overall, more rapid with fentanyl/nitrous oxide. For example, the median time until the patient could be awakened by quiet verbal command, e.g., “Open your eyes,” was 5 min,versus10 min in the other groups. There were no relationships between ICP and any measurement of emergence (e.g., time to response to commands). Seven of 41 (17%) fentanyl/nitrous oxide patients vomited In the early postoperative period, compared with only 1 of 40 (2.5%) of those given propofol/fentanyl and 2 of 40 (5%) receiving isoflurane/nitrous oxide (P=0.03). There were no differences in the incidence of new postoperative deficits, total hospital stay, or cost.Conclusions:Although there are modest differences among the three tested anesthetics, short-term outcome was not affected. These results indicate that, despite their respective cerebrovascular effects, all of the anesthetic regimens used were acceptable in these patients undergoing elective surgery.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:Epidural administration of the α2-adrenergic agonist clonidine induces hypotension. Animal experiments have indicated a possible spinal mechanism through activation of α2-adrenergic receptors on sympathetic preganglionic neurons, resulting in a decrease of efferent sympathetic activity. However, the pharmacokinetic behavior of epidural clonidine, the high lipld solubility of the drug, and the apparent sedative side effects also indicate a possible supraspinal mechanism. To test this hypothesis, the effect of epidural and intramuscular clonidine on efferent sympathetic nerve activity to the leg was studied with microneurography.Methods:In 15 healthy volunteers, a lumbar epidural catheter was inserted and multlunit postganglionic sympathetic activity was recorded in a skin or muscle fascicle of the peroneal nerve before and after epidural injection of clonidine. Skin blood flow in the hand and in the foot was measured with laser Doppler flowmetry. In six additional experiments, performed at another time, clonidine was given intramuscularly.Results:After epidural injection of clonidine (3 µg/kg) the resting level of skin sympathetic activity decreased to 18 ± 5% (n=6;P<0.001), muscle sympathetic activity expressed as bursts/min to 41 ± 12% (n=7;P<0.01), and integrated muscle sympathetic activity to 41 ± 13% (n=7;P<0.01) of control values after 30 min. However, the capacity for activation of skin sympathetic activity by arousal stimuli and of muscle sympathetic activity by apnea remained. Intramuscular clonidine inhibited both skin sympathetic activity (n=3) and muscle sympathetic activity (n=3) to the same extent. Skin blood flow increased whereas blood pressure and heart rate decreased after epidural and intramuscular clonidine.Conclusions:The comparable inhibition of resting sympathetic nerve activity, paralleled by a decrease in heart rate and blood pressure after both epidural and intramuscular clonidine, indicates that epidural clonidine induces a supraspinally evoked general decrease in sympathetic outflow.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:Inhaled nitric oxide (NO), an endothellum-derlved relaxing factor, is a selective pulmonary vasodilator. The authors investigated whether the pulmonary vasodilation resulting from 20 ppm inhaled NO is related to the degree of pulmonary hypertension or affected by cardiopulmonary bypass (CPB) or the presence of intravenous nitrates.Methods:In patients undergoing cardiac surgery (n=20) or in whom the circulation was supported with a ventricular assist device (VAD; n=5), the lungs were ventilated with 80% O2and 20% N2followed by the same gas concentrations containing 20 ppm NO for 6 min.Results:Inhaled NO decreased (P<0.05) the pulmonary artery pressure from 36 ± 3 to 29 ± 2 mmHg and 32 ± 2 to 27 ± 1 mmHg, before and after CPB, respectively, and from 68 ± 12 to 55 ± 9 mmHg in patients with a VAD. Similarly, the pulmonary vascular resistance (PVR) decreased (P<0.05) from 387 ± 44 to 253 ± 26 dyne·cm·s-5and 260 ± 27 to 182 ±18 dyne·cm·s-5, before and after CPB, respectively, and from 1,085 ± 229 to 752 ± 130 dyne·cm·s-5in patients with a VAD. Central venous pressure, cardiac output, systemic hemodynamics, and blood gases did not change after inhalation of NO before or after CPB, whereas arterial oxygen tension, mixed venous hemoglobin saturation, and mean arterial pressure increased (P<0.05) in patients supported with a VAD. All hemodynamic and laboratory data returned to control 6 min after discontinuation of NO. The decrease in PVR was proportional to baseline PVR ( PVR=-0.45 PVRb+ 39.9) before CPB. The pre- and post-CPB slopes were identical despite possible damage to the endothelium resulting from CPB and the post-CPB presence of intravenous nitroglycerin (17 of 20 patients).Conclusions:This study demonstrates that 20 ppm inhaled NO is a selective pulmonary vasodilator in cardiac surgical patients before and after CPB and in patients in whom the circulation is supported with a VAD. Furthermore, NO-induced pulmonary vasodilation is proportional to PVRband does not appear to be altered by CPB, the presence of a VAD, or infusion of nitrates.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:Although propofol and alfentanil are given in combination in clinical practice, the pharmacodynamic interaction between these drugs has not been described.Methods:The pharmacodynamics of alfentanil when given as a supplement to propofol were studied in 10 ASA physical status 1 female patients (group P) undergoing lower abdominal surgery and compared to the pharmacodynamics of alfentanil when given as a supplement to nitrous oxide (group N, n=10). Anesthesia was induced by either computer-controlled infusion of propofol and alfentanll at target concentrations of 3 µg/ml and 100 ng/ml (group P) or computer-controlled infusion of 400 ng/ml alfentanll as a supplement to nitrous oxide and oxygen (ratio 2:1; group N). The target concentration of alfentanil was varied to patient responses, and the nitrous oxide and propofol concentrations were maintained constant. A sigmoid Emax model was fitted to response/no response dataversusplasma alfentanil concentrations at intubation, skin incision, and the opening of the peritoneum in both groups and for the intraabdominal part of surgery in the individual patients. In addition, the speed of recovery in both groups was determined by a deletlon-of-p's test.Results:The EC50(the concentration at which, with a 50% probability, the patients did not respond to the surgical stimuli) of alfentanil during propofol anesthesia was 92 ng/ml for intubation, 55 ng/ml for skin incision, 84 ng/ml for the opening of the peritoneum, and 66 ± 38 ng/ml (mean ± SD) for the intraabdominal part of surgery. The corresponding values during nitrous oxide anesthesia were significantly higher: 429 ng/ml for intubation, 101 ng/ml for skin incision, and 206 ± 65 ng/ml for the intraabdomlnal part of surgery (P<0.001). The speed of recovery was similar in both groups.Conclusions:The alfentanil requirements in ASA physical status 1 female patients undergoing lower abdominal surgery are less when given as a supplement to propofol (4 µg/ml) compared to 66% N2O.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:During combined epldural/isoflurane anesthesia, the core temperature triggering finger-tip vasoconstriction is ≊1° C less than that triggering redilatlon. This hysteresis suggests that thermoregulatory responses are not dependent entirely on current thermal status (state-dependence), but may be influenced also by the system's recent thermal history (direction-dependence). Once triggered, the gain and maximum response intensity of many thermoregulatory responses is nearly normal during isoflurane anesthesia. However, it remains unknown whether preserved gain and maximum response intensities are a characteristic paradigm describing thermoregulatory responses to general anesthetics. Also unknown is whether the sweating and pre-capillary vasodilation thresholds are comparably impaired by different volatile anesthetics. Accordingly, the authors tested the hypotheses that, during one minimum alveolar concentration of enflurane anesthesia: (1) there is a direction-dependent hysteresis for sweating; (2) the sweating and active vasodilation thresholds increase ≊1.2° C, as they do during one minimum alveolar concentration of isoflurane; and (3) the gain and maximum intensity of sweating are well preserved.Methods:Six female volunteers each were studied on 2 days, once during epidural anesthesia alone and once with combined enflurane (1.7%)/epldural anesthesia. On each study day, core hyperthermia was induced by cutaneous warming restricted to the legs. Warming continued until chest sweating reached maximal values; the volunteers then were cooled gradually until sweating stopped. The core temperature at which the sweating rate departed from baseline values was considered the activation threshold. Gain was expressed as the slope of the sweating rateversuscore temperature curve within the range 25-75% of the maximum sweating rate. Hysteresis was evaluated by subtracting the tympanic membrane temperature at which the sweating rate suddenly increased during warming (approximately 25% above baseline values) from that at which sweating precipitously decreased during cooling (approximately 75% of maximum values).Results:The sweating threshold was 1.4 ± 0.7° C higher during combined enflurane/epldural anesthesia than during epidural anesthesia alone. Maximum intensity was ≊700 g·m-2·h-1, and the gain 1,300 g·m-2·h-1·° C-1during each treatment. No hysteresis was detected on either study day.Conclusions:One minimum alveolar concentration of enflurane increased the sweating threshold only slightly more than previously reported for isoflurane. As in previous studies of sweating and vasoconstrlction during isoflurane anesthesia, gain and maximum response intensity were well preserved during enflurane anesthesia. An increase in the interthreshold range (temperatures not triggering thermoregulatory responses), with little change in gain and maximum response intensities, appears to be the typical effect of volatile anesthetics. Sweating during enflurane anesthesia appears to be state-dependent and little influenced by the direction of core temperature perturbations.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:Hypothermia develops rapidly during the 1st h of anesthesia and results in part from evaporative heat loss during surgical skin preparation. The authors tested the hypothesis that evaporation of skin preparation solution contributes significantly to hypothermia.Methods:Five healthy, unanesthetized volunteers were studied in a 22 ± 0.4° C environment. One thigh of each volunteer was washed for 10 min, using each of the following representative solutions: (1) water; (2) 50% ethanol in water (EtOH/H2O; similar to tincture of iodine); and (3) povidoneiodine gel. Water and EtOH/H2O each were tested at ambient temperature (cold), warmed to 40° C before application (warm), and with radiant heating of the skin, and gel only at ambient temperatures, resulting in seven study states. Heat loss and skin temperatures on the washed thighs were measured using thermal flux transducers, and values compared with the data obtained from the contralateral unwashed thighs. Change in mean body temperature (per 70 kg) due to washing was calculated by integrating measured heat loss over time and multiplying by the specific heat of human tissue. A mathematical model was developed to predict cutaneous heat loss using only skin temperature, independent of the type and temperature of skin-preparation solution or the use of radiant heating during preparation.Results:Heat loss from the unwashed thigh was ≊14 kcal/m2during radiant warming and ≊39 kcal/m2without warming. Net heat loss (increment produced by washing) was ≊30 kcal/m2with water and gel without radiant warming, but loss was larger with EtOH/H2O than with water under all study conditions. Radiant warming reduced total heat loss (increment produced by washing and environment) during both the EtOH/H2O and water trials, compared with warm or cold EtOH/H2O and water alone. The calculated decreases in mean body temperature per 70 kg ranged from -0.2 to -0.7° C/m2. The smallest decrease occurred during radiant warming and washing with water, and the largest decreases during warm or cold EtOH/H2O.Conclusions:Heat loss was significantly less with waterbased than with alcohol-based solutions. Though heating the solutions and radiant warming decreased heat loss, such loss under each tested condition, even per square meter of washed surface, was small compared to other causes of perioperative hypothermia. Consequently, the authors recommend that efforts to maintain intraoperative normothermla be directed elsewhere.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:Dexmedetomidine is a new potent and selective α2-agonist that might prove useful as a preanesthetic agentMethods:A randomized, double-blind study design was used in 192 ASA physical status 1 and 2 patients scheduled for elective abdominal hysterectomy, cholecystectomy, or intraocular surgery under general anesthesia. Intramuscular injection of 2.5 µg/kg dexmedetomidine administered 60 mln before and intravenous saline placebo 2 min before induction of anesthesia (DEXPLA group, n=64) was compared with a combination of 0.08 mg/kg intramuscular midazolam 60 min and 1.5 µg/kg intravenous fentanyl 2 mln before induction (MIDFENT group, n=64), or a combination of intramuscular dexmedetomidine and intravenous fentanyl (DEXFENT group, n=64). After thlopental induction, anesthesia was maintained with 70% N2O/O2, and fentanyl was administered according to clinical and cardiovascular criteria. Patients undergoing cholecystectomy received additional enflurane.Results:Dexmedetomidine and midazolam induced comparable preoperative sedation and anxlolysls. The DEXFENT combination blunted the increases in blood pressure and heart rate induced by tracheal intubation more efficiently when compared with the DEXPLA and MIDFENT groups, in which approximately 25 mmHg and 15 beats/min greater increases were observed. The intraoperative fentanyl requirements were greater in MIDFENT patients when compared with both dexmedetomidine groups, in which 56% (DEXFENT group) and 31% (DEXPLA group) less fentanyl, respectively, was needed. Intraoperatively, fluids or vasopressors for hypotension and glycopyrrolate for bradycardia were administered more often to patients receiving dexmedetomidine than to those who did not. Postoperatively, there were no differences in oxygen saturation, analgesic, or antlemetlc requirements, but dexmedetomidlne- induced blood pressure and heart rate reductions were still evident at the end of the 3-h follow-up period. Bradycardia as an adverse event was reported more frequently in dexmedetomidine patients (20% in the DEXPLA and 33% in the DEXFENT groups) than in MIDFENT patients (8%).Conclusions:The results suggest that pretreatmeht with a single intramuscular injection of 2.5 µg/kg dexmedetomidine is efficacious, but significantly increases the incidence of intraoperative hypotension and bradycardia in ASA physical status 1 or 2 patients.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:Preterm and ex-preterm infants are at risk for life-threatening apnea after general anesthesia. The authors attempted to define the postconceptual age beyond which apnea is less likely to occur and to identify the factors that predispose to postanesthetic apnea.Methods:Ninety-one infants younger than 60 weeks postconceptual age undergoing 101 general anesthetics were prospectively studied. All infants were admitted to the hospital for cardiorespiratory monitoring overnight. The presence of coexistent medical conditions that could influence the incidence of apnea was determined by a review of current and previous medical records and by history.Results:Of 38 procedures performed in 35 infants younger than 44 weeks postconceptual age, 10 (26.3%) procedures in 9 infants were associated with postanesthetic apnea. In eight of these, apnea did not resolve spontaneously: four infants required stimulation, and four required continuous positive airway pressure by face mask. Apnea occurred after 2 of 63 procedures performed in infants 44 weeks postconceptual age or older. Both episodes occurred in one patient who had neurologic disease. Of the remaining 61 procedures in the latter age group, 7 were associated with episodes of bradycardia (lowest heart rate was 79 beats/min) postoperatlvely without apnea. These episodes lasted up to 5 s, were not associated with apnea or cyanosis, and resolved spontaneously in all cases. All infants with postanesthetic apnea and/or bradycardia experienced their first episode within 12 h after surgery.Conclusions:Ex-preterm infants younger than 44 weeks postconceptual age are at greater risk for apnea after general anesthesia than are infants older than 44 weeks postconceptual age. Based on these results, the maximum long-run risk of postanesthetic apnea in preterm infants older than 44 weeks postconceptual age is 5% with 95% confidence.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Background:Although lung volume may be changed by certain procedures during anesthesia and mechanical ventilation, dependence of the dynamic mechanical properties of the lungs on lung volume are not clear. Based on studies in dogs, the authors hypothesized that changes in lung mechanics caused by anesthesia in healthy humans could be accounted for by immediate changes in lung volume and that lung resistance will not be decreased by positive end-expiratory airway pressure if tidal volume and respiratory frequency are in the normal ranges.Methods:Lung resistance and dynamic lung elastance were measured in six healthy, relaxed, seated subjects during sinusoidal volume oscillations at the mouth (5 mL/kg; 0.4 Hz) delivered at mean airway pressure from —9 to +25 cmH2O. Changes in lung volume from functional residual capacity were measured with inductance plethysmographic belts.Results:Decreases in mean mean airway pressure that caused decreases in lung volume from functional residual capacity comparable to those typically observed during anesthesia were associated with significant increases in both dynamic lung elastance and lung resistance. Increases in mean mean airway pressure that caused increases in lung volume from functional residual capacity did not increase lung resistance and increased dynamic lung elastance only above about 15 cmH2O.Conclusions:Increases in dynamic lung elastance and lung resistance with anesthesia can be explained by the accompanying, acute decreases in lung volume, although other factors may be involved. Increasing lung volume by increasing mean airway pressure with positive end-expiratory pressure will decrease lung resistance only if the original lung volume is low compared to awake, seated functional residual capacity.

ISSN:0003-3022    

出版商:OVID    

年代:1993

数据来源: OVID