The use of dexmedetomidine infusion for awake craniotomy.
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Adult↗
Biomedical subjects
A Y Bekker
Publications and source records attributed to A Y Bekker.
The recovery of cognitive function after remifentanil-nitrous oxide anesthesia is faster than after an isoflurane-nitrous oxide-fentanyl combination in elderly patients.
UNLABELLED: We tested the hypothesis that remifentanil-nitrous oxide (N(2)O) anesthesia shortens postoperative emergence and recovery compared with an isoflurane-N(2)O-fentanyl combination in elderly patients undergoing spinal surgery. A total of 60 patients (>65 yr old) were randomly assigned to one of two groups for maintenance of anesthesia. After the induction with 3.6 +/- 1.2 mg/kg IV thiopental and endotracheal intubation facilitated with 1.4 +/- 0.5 mg/kg succinylcholine, patients were maintained with either 0.5%-1.5% isoflurane, 70% N(2)O, and up to 7 microg/kg fentanyl (iso/fent group) or 48 +/- 11 microg/kg remifentanil and 70% N(2)O (remi group). A mini-mental status examination was used to assess cognitive ability preoperatively, at 15, 30, and 60 min after arrival at the postanesthesia care unit and again 12-24 h postoperatively. The time from the conclusion of anesthesia to spontaneous respiration was similar in both groups. Times to eye opening (4.8 +/- 2.6 vs 2.3 +/- 1.1 min), extubation (6.8 +/- 3.8 vs 3.2 +/- 2.1 min), and verbalization (9.9 +/- 6.2 vs 3.9 +/- 2.6 min) were significantly shorter for the remi group (P < 0.05). Postoperative mini-mental status examination scores were significantly lower in the iso/fent group at 15 (16.3 +/- 5.8 vs 23. 7 +/- 3.3), 30 (20.2 +/- 5.2 vs 26.3 +/- 2.7), and 60 min (23.5 +/- 4.4 vs 27.5 +/- 2.0) (P < 0.001); however, the scores equalized after 12 h. Requirements for postoperative analgesics were similar in the two groups. More patients in the remi group were treated with antiemetics (21 vs 7, P = 0.06). Use of remifentanil-N(2)O for maintenance did not shorten the overall length of stay in the postanesthesia care unit; a stay is often related to multiple administrative issues, rather than cognitive recovery. IMPLICATIONS: Maintenance of anesthesia with remifentanil-nitrous oxide (N(2)O), compared with isoflurane-N(2)O-fentanyl, can safely shorten postoperative recovery of cognitive function in a geriatric population. Earlier recovery may facilitate postoperative neurological assessment. Use of remifentanil-N(2)O for maintenance did not shorten the overall length of stay in the postanesthesia care unit, a stay often related to multiple administrative issues, rather than cognitive recovery.
Aged↗
Computer simulation of intracranial pressure changes during induction of anesthesia: comparison of thiopental, propofol, and etomidate.
We have developed a computer model of cerebrovascular hemodynamics that interacts with a pharmacokinetic drug model. We used this model to examine the effects of various stimuli occurring during anesthesia on cerebral blood flow (CBF) and intracranial pressure (ICP). The model is a seven-compartment constant-volume system. A series of resistances and compliances relate blood and cerebrovascular fluid fluxes to pressure gradients between compartments. Variable arterial-arteriolar resistance (Ra-ar) and arteriolar-capillary resistance (Rar-c) simulate autoregulation and drug effects, respectively. Rar-c is also used to account for the effect of CO2 on the cerebral circulation. A three-compartment pharmacokinetic model predicts concentration-time profiles of intravenous induction agents. The effect-site compartment is included to account for disequilibrium between drug plasma and biophase concentrations. The simulation program is written in VisSim dynamic simulation language for an IBM-compatible personal computer. Using the model, we have predicted ICP responses during induction of anesthesia for a simulated patient with normal as well as elevated ICP. Simulation shows that the induction dose of intravenous anesthetic reduces ICP up to 30% (propofol > thiopental > etomidate). The duration of this effect is limited to less than 5 minutes by rapid drug redistribution and cerebral autoregulation. Subsequent laryngoscopy causes acute intracranial hypertension, exceeding the initial ICP. ICP elevation is more pronounced in a nonautoregulated cerebral circulation. Simulation results are in good agreement with the available experimental data. The presented model allows comparison of various drug administration schedules to control ICP.
Anesthetics, Intravenous↗
Calcium entry blockade prevents leakage of macromolecules induced by ischemia-reperfusion in skeletal muscle.
Calcium kinetics and its intracellular mobilization are important in all biological processes. We used verapamil to examine the effect of calcium entry blockade on microvascular transport of macromolecules in ischemia-reperfusion injury. The rat cremaster muscle was splayed, placed in a Lucite intravital chamber, and suffused with bicarbonate buffer. The clearance of fluorescein isothiocyanate-conjugated dextran (FITC-dextran 150) was measured as an index of microvascular transport. After determination of baseline data (clearance of FITC-dextran 150, 3.0 +/- 0.5 microliters/5 min/g), the muscle was made ischemic for 2 hours by clamping its vascular pedicle and subsequently was reperfused for 2 hours. Ischemia-reperfusion produced a marked increase in FITC-dextran clearance. After a peak of 12 +/- 2-fold increase observed in the first 15 minutes into reperfusion, FITC-dextran 150 clearance decreased in magnitude and stabilized at about sixfold above baseline. Verapamil did not change the baseline clearance values. Importantly, verapamil inhibited the ischemia-induced increase in clearance and maintained the values at or near the baseline levels. We simultaneously determined the rate of release of 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 (TXB2) into the suffusate. Verapamil decreased the baseline values of 6-keto-PGF1 alpha and increased those of TXB2. Verapamil inhibited the ischemia-reperfusion-induced increase in 6-keto-PGF1 alpha but did not alter the effect of ischemia-reperfusion on TXB2. Our main results demonstrate the effectiveness of verapamil in preventing microvascular alterations leading to increased leakage of macromolecules.
Animals↗
Analysis of microvascular permeability to macromolecules by video-image digital processing.
The dynamics of macromolecular transport across microvascular walls were studied in the hamster cheek pouch by intravital fluorescence microscopy. A graded series of fluorescein isothiocyanate-labeled dextrans (FITC-Dx) of 20,000-70,000 MW was used as macromolecular tracers. The time-dependent extravasation of FITC-Dxs was videotaped for about 2.5 hr to allow for tracer equilibration in the interstitial space. Permeation of macromolecules from individual microvessels was quantified by digital video-image processing. Histograms of the light intensity distributions for selected fields at various times were measured and used to construct integral optical density-time profiles of the extravasated fluorochromes for particular leaky sites. A nonlinear regression algorithm was employed to determine the effective microvascular permeability (P) for the macromolecules studied using a one-dimensional two-compartmental diffusion model and a step change in macromolecular concentration at the boundary. The calculated P's (X 10(-8) cm/sec) were 47.8 +/- 8.7 for FITC-Dx 20; 31.7 +/- 5.9 for FITC-Dx 40, and 17.5 +/- 4.1 for FITC-Dx 70. Our values are comparable to those obtained by whole organ techniques. The observed differences can be explained by explicit consideration of interstitial resistance in the calculations.
Algorithms↗
Dose-response relationships between platelet activating factor and permeability--surface area product of FITC-dextran 150 in the hamster cheek pouch.
Changes in vascular permeability to FITC-dextran 150 associated with topical application of platelet activating factor (PAF) in the hamster cheek pouch preparation were calculated using a mathematical model (Baxter et al., Microvasc. Res. 34:336, 1987). Least square estimates of apparent permeability-surface area product (PS) and interstitial diffusion coefficient (D) were calculated from the data and the mathematical model using a Marquart optimization algorithm. Calculated PS products varied with applied PAF concentration while the best-fit estimate of apparent D remained constant at 10.5 X 10(-10) cm2/s. Average baseline PS was 16.5 X 10(-8) ml/s. PS increased to 45.2 X 10(-8) ml/s and 52.3 X 10(-8) ml/s with application of 10(-8)M and 10(-7)M PAF, respectively. A further increase in PAF concentration to 10(-6)M decreased the calculated PS product to 30.5 X 10(-8) ml/s. PAF is a potential modulator of macromolecular permeability in the microcirculation. This is the first study which quantitates the changes in PS of FITC-dextran 150 as a function of PAF concentration.
Animals↗
Comparison of cardiotropic drug effects on haemodynamic and myocardial energetics in patients with heart failure: a computer simulation.
The purpose of our study is to compare haemodynamic responses and the ischaemic potential of commonly used inotropes (dopamine, dobutamine and milrinone) using a computer model of the cardiovascular system. Cardiotropic drugs interact with the model by changing ventricular elastance and resistance of the individual circulation. All three drugs increase cardiac index in a dose-dependent manner. Dopamine at medium and high infusion rates increases heart rate, systemic vascular resistance and arterial blood pressure. The associated increase in coronary blood flow, however, is not sufficient to account for increased oxygen demand. Both dobutamine and milrinone decrease vascular resistance and increase coronary blood flow. The more pronounced increase in heart rate associated with dobutamine, however, results in a higher ischaemic potential for this drug. Our simulation demonstrates that although all the drugs studied improve cardiac function in simulated patients with heart failure, milrinone accomplishes this at a lower energy cost. The computer simulation developed can be used to assess the complex effect of cardiotropic drugs and possibly suggest optimal drug therapy in specific clinical situations.
Cardiotonic Agents↗
Reduction of pressure in postcapillary venules induced by EPI-fluorescent illumination of FITC-dextrans.
Blue light (488nm) irradiation of intravenously injected fluorescein isothiocyanate (FITC)-Dextrans induces platelet aggregation in microvessels. The build-up of the aggregates in the microvessel lumen results in a change in microcirculatory hemodynamics. We found that lumenal pressure falls to approximately 75% of the control pressure within the first 10 seconds following the onset of irradiation. The damage, however, is not permanent and pressure returns to control level after the illumination of the microcirculatory field is discontinued. This effect can lead to erroneous conclusions in studies of microcirculatory hemodynamics and macromolecular permselectivity in preparations in which intravital fluorescence microscopy is employed. Short time irradiation (1 min. or less) of the microcirculatory field is recommended as a means of minimizing the deleterious effects of blue light irradiation.
Animals↗