摘要:

The influence of different vasopressors on the cerebral pressure—flow relationship during 1.0 MAC isoflurane anesthesia has been studied. Mean arterial pressure (MAP) was increased by one of three vasopressors [angiotensin II (AT), norepinephrine (NE), or phenylephrine (PE)] in three groups of New Zealand white rabbits (n = 11, 10, and 9, respectively). Regional cerebral blood flow (CBF) was measured at five intervals by the injection of radioactive microspheres at a stable 2.05% (1.0 MAC) end-tidal isoflurane concentration (baseline) and following elevation of mean arterial pressure (MAP) by 20%, 40%, 60%, and 80% above baseline MAP with either AT, NE, or PE. Baseline MAP was the same in all groups. No differences in MAP were seen between groups when MAP was elevated from 20% to 80% above baseline. Normocapnia (Pa&OV0312; 35.8–38.2 mmHg) was maintained throughout. Total cerebral blood flow (tCBF), hemispheric CBF (hCBF), and posterior fossa (cerebellum and brain stem) CBF (pCBF) were determined. Baseline tCBF, hCBF, and pCBF was similar in all groups. For each experiment a pressure—flow curve was generated by curvilinear regression analysis. Mean slopes and intercepts were derived for each group. For all regions examined, the slope of the pressure—flow curve was significantly less steep when MAP was elevated with ATversusNE or PE (P< 0.05 Tukey's studentized range test). There was no difference in slope between the NE and PE groups for any region. These results indicate that either NE and PE result in indirect cerebral vasodilation or that AT has intrinsic cerebral vasocontrictive effects during 1.0 MAC isoflurane anesthesia in the rabbit. Thus, in teh rabbit choice of vasopressor critically influences the interpretation of whether cerebrovascular autoregulation is intact during isoflurane anesthesia.

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Human and animal experiments have not consistently shown halothane to inhibit hypoxic pulmonary vasoconstriction (HPV). The authors used a canine lung lobe perfusedin situto more precisely characterize the effects of halothane on HPV. The pulmonary vasculature can be divided into inflow, middle, and outflow segments by sequentially occluding the lobar inflow and outflow of blood. The lobes were ventilated with four different gas mixtures (normoxia, hypoxia, normoxia/halothane, hypoxia/halothane) and measured inflow, outflow, and middle segment (Rm) resistances using this stopflow technique. All values are shown as means ± standard deviation. The authors found that hypoxia increased Rm from normoxia values of .006 ± .005 cmH2O&OV0312;ml−1&OV0312; min−1to .025 ± .008 cmH2O &OV0312; ml−1&OV0312; min−1(P< 0.05). During hypoxia/halothane Rm returned to .005 ± .004 cmH2O &OV0312; ml−1&OV0312; min−1. The relationship between pressure and flow (P-&OV0312;) for the lobes for each gas mixture was also determined. The slopes of the P-&OV0312; lines by linear regression were all similar. The zero-flow pressure intercepts of the P-&OV0312; lines for normoxia (3.2 ± .9 cmH2O) and hypoxia (4.4 ± 1.1 cmH2O) were significantly decreased after the administration of halothane (1.7 ± 1.0 cmH2O and 2.6 ± 1.0 cmH2O, respectively). Since the zero-flow intercept likely reflects the tone at alveolar vessel level, the authors conclude that halothane inhibits HPV by decreasing the tone in the middle vascular segment.

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Blood pressure is usually well maintained during epidural or spinal anesthesia even in the presence of extensive sympathetic blockade. The authors investigated whether hormonal systems support arterial pressure and how the circulation copes with a hypoxic challenge when activation of the sympathetic nervous system is selectively impaired by neural blockade. Accordingly, the effects of high epidural anesthesia alone and combined with hypoxia were evaluated in seven awake trained dogs. On different days, either bupivacaine 0.5% (8–12ml) or saline (placebo) were randomly injected epidurally and the effects evaluated on cardiovascular (arterial pressure, heart rate) and respiratory (blood gases, oxygen consumption) variables, as well as on hormone plasma concentrations (vasopressin, norepinephrine, epinephrine, renin) during both normoxia and hypoxia. During epidural anesthesia alone, vasopressin increased tenfold (1.7 pg/ml ± 1.0 SD to 16.8 ± 13.8,P< 0.05), norepinephrine decreased (90 pg/ml ± 31 to 61 ± 28,P< 0.05) while epinephrine and renin concentrations remained unchanged. Mean arterial and pulse pressure decreased by 13 mmHg and 23 mmHg (P< 0.05), respectively. In dogs without sympathetic blockade (saline group), hypoxemia (Pa&OV0312;: 31 ± 4 mmHg) evoked an increase in mean blood pressure by 37 mmHg ± 8 and heart rate by 50 beats per min ± 17. In contrast, in the presence of sympathetic blockade but with a similar degree of hypoxemia, blood pressure failed to increase (+1 mmHg ± 14) and heart rate rose by only 15 beats per min ± 11. These differences between groups were statistically significant (P< 0.001). Hypoxemia induced a similar hypocarbia (Pa&OV0312;: 25 mmHg) in both groups, indicating that the ventilatory response to hypoxemia was preserved after epidural blockade. During hypoxemia vasopressin concentrations increased 35-fold to 64 pg/ml ± 38 (P< 0.0001) compared to base line only during epidural anesthesia, but not after epidural saline (2 pg/ml ± 2), while other hormones showed no significant differences. The authors conclude that high epidural anesthesia in awake unsedated dogs: 1) almost completely abolishes the normal cardiovascular response to hypoxemia while promoting vasopressin secretion; 2) preserves the ventilatory response to hypoxemia; and 3) is associated with increased vasopressin concentrations, most likely to compensate for decreased cardiac filling and/or arterial blood pressure when sympathoadrenal responses are impaired. Thus, the changes in cardiovascular vital signs in response to severe hypoxemia are markedly blunted when spinal sympathetic outflow is selectively eliminated by epidural anesthesia.

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

To quantify the changes in plasma concentrations of atracurium and laudanosine induced by the lack of hepatic function and circulation, the authors studied nine domestic pigs (22–25 kg) under-going an orthotopic liver transplantation, and three control animals without surgery, using atracurium as the muscle relaxant. After intubation facilitated by isoflurane 2–3%, anesthesia was maintained with isoflurane (0.5% in oxygen) and fentanyl (4 μg &OV0312; kg−1&OV0312; hr−1). Ventilation was controlled to keep end-tidal Co2at 35–40 mmHg, body temperature maintained at 35.5–37.5° C, and arterialpH at 7.35–7.50. The right sciatic nerve was stimulated with a nerve stimulator delivering a single twitch at 0.1 Hz with 0.2-ms duration, at supramaximal stimulation. The force of the corresponding evoked isometric muscle contraction was continuously measured by a force-displacement transducer. A single iv bolus of atracurium (2 mg/kg) was given to obtain a 90–95% twitch depression, followed 5 min later by a constant-rate iv infusion of atracurium at 120 μg &OV0312; kg−1&OV0312; min−1maintained during the entire investigation. Blood samples for plasma atracurium and laudanosine concentrations were drawn every 15 min. In the control group, plasma concentrations of atracurium remained stable between 6.5–8.0 μg/ml following initial bolus injection; plasma concentrations of laudanosine increased during the first 60 min, then remained stable between 0.69–0.74 μg/ml up to the end of the study. In animals undergoing transplantation, plasma concentrations of atracurium remained stable between 10–12 μg/ml, despite a 90-min duration of liver exclusion. In contrast, plasma concentrations of laudanosine were significantly increased 45 min after the hepatic vessels were clamped (from 0.57 ± 0.03 μg/ml to 0.91 ± 0.02 μg/ml, mean ± SE,P< 0.05), increased further to peak values of 1.24 ± 0.05 μg/ml after 90 min, and remained at these elevated concentrations after restoration of circulation to the transplanted liver. The results of the present study demonstrate that in pigs plasma clearance of atracurium does not depend on hepatic function. In contrast, plasma clearance of its major metabolite laudanosine is strongly dependent on liver function.

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Descriptions of the earliest iv injections of various substances by individuals who actually witnessed the experiments in 1656 are presented. Of particular interest is an apparently overlooked account of an experiment in which opium was administered intravenously to a dog many years before 1674 as related by the physician and anatomist Thomas Willis. He does not identify the precise date nor the experimenters. However, at the time of this event Willis would have been at Oxford. There he was a very close professional associate of Christopher Wren who originated the practice of iv injection. These eyewitness accounts are worthy of note because the articles usually cited to establish Wren as the first individual to administer a drug intravenously were not written by anyone who actually observed the experiments.

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Mass spectrometers are used in ICUs and ORs to measure the concentration of medical and anesthetic gases gathered from multiple sites. This investigation was designed to determine the accuracy of a clinical system, which included 12 ICU bedside stations monitored by a medical mass spectrometer (Perkin-Elmer RMS III, Pomona, CA). Each site station was connected to the analyzing unitviatwo Teflon tubes, one permanently installed, 30-m long, and the second disposable, 2.4-m long. A gas mixture containing 95% O2and 5% CO2, alternating with room air, was delivered to a solenoid valve and from there to the connecting tubes. Gas flow-rate, delay time, rise time, and peak and through concentrations were determined for each gas at solenoid cycling frequencies of 25, 50, and 100/min. After the first set of measurements, the 30-m tubes were thoroughly cleaned and all measurements repeated. In addition, the authors also measured CO2delay and rise times when the gas was delivered to the mass spectrometer through an unused 30-m tube or a new 2.4-m tube.Gas flow-rate increased from 143 ± 1 ml/min (mean ± SD) to 238 ± 9 ml/min after the tubes were cleaned. Delay time was identical for all gases at all solenoid cycling rates but decreased significantly (P< 0.05), from 11.5 ± 0.3 to 4.8 ± 0.7 s after the ceiling tubes were cleaned. As solenoid valve rate increased, the difference between measured and actual gas concentration increased. The lowest accuracy was 63.6 ± 2.1%, for CO2at 100 cycles/min. Even after the tubes were cleaned, peak measured values of CO2concentration were only 82.9 ± 4.7% of steady-state concentration at the highest solenoid valve cycling rate. When CO2passed through the tubes connecting active beside stations to the mass spectrometer, rise time was 583 ± 14 ms. This value decreased to 453 ± 84 ms after the ceiling tubes were cleaned but remained significantly higher than when new 30-m (272 ± 3 ms) or 2.4-m (178 ± 2 ms) tubes were used.The authors conclude that gas concentration measured by mass spectrometry can be quite inaccurate when gases are sampled from remote stations, especially at respiratory rates ≥ 50/min. This problem is largely related to the obstruction caused by the progressive accumulation of particulate materials in the long gas transport tubes. These errors cannot be detected by static self-calibration routines, but require dynamic testing.

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

The Anesthesia Simulator-Recorder is a computer program that trains and evaluates anesthesiologists' management of critical incidents. The program executes on IBM compatible personal computers, combining a graphic display of the operating room with mouse-driven input and using an integrated set of physiological and pharmacological models to predict patient responses. The program records the simulated patient's vital signs and all management decisions, and produces a printed case summary. The Anesthesia Simulator-Recorder was evaluated by 44 resident and attending anesthesiologists at seven different anesthesia training centers. These anesthesiologists found the simulator easy to use with clear presentation of the case and management options. The physiological and pharmacological models produced clinically realistic predictions of patient behavior (mean score = 8.5, where 10 is highly realistic and 1 is unrealistic). The Anesthesia Simulator-Recorder was appraised as an excellent training device (mean score = 8.5, where 10 is outstanding and 1 is poor) because it provides the ability to repeatedly practice the management of critical incidents. The simulator was judged to be a good evaluation device (mean score = 6.6, where 10 is outstanding and 1 is poor). No significant differences were found in evaluations between the institution where the program was developed and other institutions, or between residents and attendings.

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0003-3022    

出版商:OVID    

年代:1990

数据来源: OVID