Anesthesia and analgesia
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Anesthesia and analgesia · Jan 2003
Comparative StudyA comparison of lactated ringer's solution to hydroxyethyl starch 6% in a model of severe hemorrhagic shock and continuous bleeding in dogs.
In this randomized, controlled study in dogs, we examined the short-term effects of blood pressure targeted fluid resuscitation with colloids or crystalloids solutions on systemic oxygen delivery, and lactate blood concentration. Fluid resuscitation using hydroxyethyl starch (HES) 6% to a mean arterial blood pressure (MAP) of 60 mm Hg was compared with lactated Ringer's solution (LR) to a MAP of 60 or 80 mm Hg (LR60 and LR80, respectively). The model was one of withdrawal of blood to a MAP of 40 mm Hg through an arterial catheter that was then connected to a system allowing bleeding to occur throughout the study whenever MAP exceeded 40 mm Hg. Target MAP was maintained for 60 min with a continuous infusion of the designated fluid replacement. All 15 dogs (5 in each group) survived until the last measurement. Blood loss in the LR80 group (2980 +/- 503 mL) (all values mean +/- SD) was larger than in the LR60 and HES60 groups (1800 +/- 389 mL, and 1820 +/- 219 mL, respectively) (P < 0.001). Whereas 840 +/- 219 mL of HES60 was needed to maintain target MAP, 1880 +/- 425 mL of LR was needed in the LR60 group, and 4590 +/- 930 mL in the LR80 group (P < 0.001). Lactate blood concentrations were smaller and delivered O(2) higher in the HES60 group (35 +/- 17 mg/dL and 239 +/- 61 mL/min, respectively) in comparison to the LR60 group (89 +/- 18 mg/dL and 140 +/- 48 mL/min, respectively) and the LR80 group (75 +/- 23 mg/dL and 153 +/- 17 mL/min, respectively) (P = 0.02 and P = 0.026). In conclusion, fluid resuscitation during uncontrolled bleeding, to a target MAP of 60 mm Hg, using HES60 resulted in larger oxygen delivery and smaller systemic lactate A resuscitation to a target MAP of 60 or 80 mm Hg using LR. ⋯ Fluid resuscitation to a target mean arterial blood pressure of 60 mm Hg during uncontrolled bleeding resulted in larger oxygen delivery and smaller systemic lactate concentrations when hydroxyethyl starch 6% was used, in comparison to lactated Ringer's solution resuscitation to a target mean arterial blood pressure of 60 or 80 mm Hg.
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Anesthesia and analgesia · Jan 2003
Minimum alveolar anesthetic concentration of isoflurane with different xenon concentrations in Swine.
For patients requiring a fraction of inspired oxygen more than 0.3, the use of xenon (Xe) as the sole anesthetic is limited because of its large minimum alveolar anesthetic concentration (MAC) of 71%. This warrants investigating the combination of Xe with other inhaled anesthetics. We therefore investigated the influence of Xe on the MAC of isoflurane. The study was performed in 10 swine (weight, 28-35 kg) ventilated with Xe 0%, 15%, 30%, 40%, 50%, and 65% in oxygen. For each Xe concentration, various concentrations of isoflurane were administered in a step-wise design. For each combination, a supramaximal pain stimulus (claw-clamp) was applied, and the appearance of a withdrawal reaction was recorded. The isoflurane MAC was defined as the end-tidal concentration required to produce a 50% response rate. At each Xe concentration, the responses to the pain stimulus were categorized, and a logistic regression model was fitted to the results to determine isoflurane MAC. Isoflurane MAC was decreased by inhalation of Xe in a nonlinear manner from 1.92% (95% confidence interval, 1.70%-2.15%) with 0% Xe to 1.17% (95% confidence interval, 0.75%-1.59%) with 65% Xe. Although this indicates partial antagonism of the two anesthetics, a combination of Xe with isoflurane may prove valuable for patients requiring a fraction of inspired oxygen more than 0.3. ⋯ We investigated the influence of the anesthetic gas xenon on the minimum alveolar anesthetic concentration (MAC) for isoflurane (another anesthetic gas). The study was performed in 10 swine ventilated with fixed xenon and various concentrations of isoflurane. The isoflurane MAC is decreased by inhalation of xenon in a nonlinear relationship.
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Anesthesia and analgesia · Jan 2003
Validity of arterial and mixed venous oxygen saturation measurements in a canine hemorrhage model after resuscitation with varying concentrations of hemoglobin-based oxygen carrier.
In this study, we evaluated the validity of saturation measurements in mixed venous and arterial blood during posthemorrhagic anemia and resuscitation with varying levels of hemoglobin-based oxygen carrier (Hemoglobin glutamer-200 [bovine]; Oxyglobin [Hb-200]). Nineteen anesthetized, splenectomized, mixed-breed dogs were anesthetized (two were excluded from the data because they did not survive the exsanguination, supporting the validity of the model). Their pulmonary arteries were cannulated with the Abbott QVUE Oximetrix 3 catheter. An 18-gauge catheter was placed in the femoral artery, and a reusable Nellcor probe was applied to the tongue. Mixed venous and arterial samples were drawn at baseline, after 40% hemorrhage (to keep arterial pressure at 50 mm Hg), and postresuscitation with 30 mL/kg of 6% hetastarch in lactated Ringer's solution (n = 4), 10 mL/kg of Hb-200, 20 mL/kg of hetastarch (n = 6), 20 mL/kg of Hb-200, and 10 mL/kg of hetastarch (n = 7). Samples were compared with oxygen content from the LEXO2CON-K oxygen analyzer, and oxygen content was calculated for all values from the monitors. Results were compared by using analysis of variance. There was good correlation (0.97 > or = r > or = 0.92) for the measured versus calculated hemoglobin oxygen saturation values at baseline. After resuscitation, the correlation between calculated and measured values of oxygen content was significantly smaller for all tested instruments. The values of oxygen content calculated from the oxygen saturation monitor and from the oximetric pulmonary artery can deviate by as much as 20% from directly measured values. We conclude that the administration of this oxygen therapeutic may interfere with the values of some monitors. ⋯ This study evaluated oxygen saturation monitors in a canine model of acute blood loss and resuscitation with a blood substitute and found that these may interfere with the monitors' results in a dose-dependent way.
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Anesthesia and analgesia · Jan 2003
Modulation of GABA(A) receptor function by nonhalogenated alkane anesthetics: the effects on agonist enhancement, direct activation, and inhibition.
At clinically relevant concentrations, ethers, alcohols, and halogenated alkanes enhance agonist action on the gamma-aminobutyric acid(A) (GABA(A)) receptor, whereas nonhalogenated alkanes do not. Many anesthetics also directly activate and/or inhibit GABA(A) receptors, actions that may produce important behavioral effects; although, the effects of nonhalogenated alkane anesthetics on GABA(A) receptor direct activation and inhibition have not been studied. In this study, we assessed the abilities of two representative nonhalogenated alkanes, cyclopropane and butane, to enhance agonist action, directly activate, and inhibit currents mediated by expressed alpha(1)beta(2)gamma(2L) GABA(A) receptors using electrophysiological techniques. Our studies reveal that cyclopro- pane and butane enhance agonist action on the GABA(A) receptor at concentrations that exceed those required to produce anesthesia. Neither nonhalogenated alkane directly activated nor inhibited GABA(A) receptors, even at concentrations that approach their aqueous saturated solubilities. These results strongly suggest that the behavioral actions of nonhalogenated alkane anesthetics do not result from their abilities to enhance agonist actions, directly activate, or inhibit alpha(1)beta(2)gamma(2L) GABA(A) receptors and are consistent with the hypothesis that electrostatic interactions between anesthetics and their protein binding sites modulate GABA(A) receptor potency. ⋯ When normalized to either their in vivo anesthetic potencies or hydrophobicities, cyclopropane and butane are 1-1.5 orders of magnitude less potent enhancers of agonist action on alpha(1beta2gamma2L) GABA(A) receptors than isoflurane. Additionally, cyclopropane and butane fail to directly activate or inhibit receptors, even at near aqueous saturating concentrations. Thus, it is unlikely that either enhancement or inhibition of the most common GABA(A) receptor subtype in the brain accounts for the behavioral activities of cyclopropane and butane.
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Reports of anesthesia personnel shortages in 2001 led to the first comprehensive analysis of labor supply and demand for anesthesiologists since 1993. We now update this analysis and forecast, incorporating newly available data about residency composition, American Board of Anesthesiology and Certified Registered Nurse Anesthetist certification, the 2002 residency match, surgical facilities, and the US physician workforce. In addition, US residency programs were surveyed; national health care utilization and economic data were reviewed. Adjusted for the new information, our model still shows an anesthesiologist shortfall in 2002, projected to continue through 2005. We now estimate a current shortage of 1100-3800 anesthesiologists in 2002, on the basis of past service demand growth assumptions of 2%-3%, respectively. By 2005 this number is expected to be 500-3900, depending on a future service demand growth of 1.5%-2%, respectively. To avoid a surplus of anesthesiologists in 2006-2010, our model suggests that the number of graduates should level out at 1600 yearly, with a 1.5% service demand growth. To forecast the anesthesia personnel market more accurately, thereby helping supply match demand, substantially better quantification of future demand for anesthesia services is needed. If sustained growth in service demand >1.5% is likely, entry into the specialty should be encouraged beyond the current level. ⋯ With updates from training programs, surgical activity, and other sources, our previously described model estimates a continuing shortfall of 1000-3800 anesthesiologists in 2002 and 500-3900 in 2005, assuming that service demand growth is 1.5% or 2% annually. If service growth >1.5% is likely, entry into the specialty should be encouraged beyond current levels.