Anesthesia and analgesia
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Anesthesia and analgesia · Dec 1997
Pharmacokinetics and efficacy of long-term epidural ropivacaine infusion for postoperative analgesia.
The aim of this study was to evaluate the pharmacokinetics and efficacy of the new local anesthetic ropivacaine when used for epidural infusion for up to 72 h after major orthopedic surgery. Immediately after surgery, an epidural infusion of ropivacaine 2 mg/mL was begun at a rate of 6 mL/h in 11 patients. The infusion rate was then adjusted according to patient analgesic needs or side effects. Blood samples were taken during and after the infusion to determine total and unbound ropivacaine and alpha1-acid glycoprotein (AAG) concentrations. Patients were assessed regularly for sensory and motor block and pain using a visual analog scale (VAS) score (0-100 mm). Ten patients received 63-72 h of infusion. Total plasma concentrations of ropivacaine and binding protein (AAG) increased during the infusion such that free concentrations plateaued or began to fall over time. VAS values during mobilization were less than 40 mm in 93% of patients. The majority of patients had no measurable motor block once the surgical block had regressed. When epidural ropivacaine was titrated to achieve a stable sensory block, there was a low incidence of motor block, and free plasma ropivacaine levels were well below the toxic range. ⋯ The pharmacokinetics of continuous epidural infusions of ropivacaine are described in patients for up to 72 h postoperatively. Clinical efficacy and side effects are also reported. An understanding of the plasma concentrations obtained and modes of elimination during prolonged epidural infusion is important for safe, routine clinical use in postoperative analgesia.
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Anesthesia and analgesia · Dec 1997
Predicting and treating coagulopathies after cardiopulmonary bypass in children.
Coagulopathies in children after cardiopulmonary bypass (CPB) are complex. There are very limited data correlating coagulation tests with postoperative bleeding. We evaluated coagulation changes after CPB and after the administration of coagulation products to 75 children. Baseline coagulation tests were obtained and repeated after protamine administration, after transfusion of individual coagulation products, and on arrival in the intensive care unit (ICU). Regression analysis demonstrated no baseline coagulation test to predict postoperative chest tube drainage. Weight and duration of CPB were determined to be the only predictors of bleeding. Further analyses demonstrated that children <8 kg had more bleeding and required more coagulation products than children >8 kg. Postprotamine platelet count and fibrinogen level correlated independently with 24-h chest tube drainage in children <8 kg, whereas postprotamine platelet count and thrombelastographic values did so in patients weighing >8 kg. Platelet administration alone was found to restore effective hemostasis in many patients. With ongoing bleeding, cryoprecipitate improved coagulation parameters and limited blood loss. Fresh-frozen plasma administration after platelets worsened coagulation parameters and was associated with greater chest tube drainage and more coagulation product transfusions in the ICU. Objective data to guide post-CPB component therapy transfusion in children are suggested. ⋯ Children <8 kg can be expected to have more severe coagulopathies, require more coagulation product transfusions, and bleed more after cardiopulmonary bypass. Correlations between coagulation tests and postoperative chest tube drainage are defined. Platelets and, if necessary, cryoprecipitate optimally restore hemostasis. Fresh-frozen plasma offers no benefits in correcting postcardiopulmonary bypass coagulopathies in children.
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Anesthesia and analgesia · Dec 1997
Dehydration of Baralyme increases compound A resulting from sevoflurane degradation in a standard anesthetic circuit used to anesthetize swine.
In a model anesthetic circuit, dehydration of Baralyme brand carbon dioxide absorbent increases degradation of sevoflurane to CF2=C(CF3)OCH2F, a nephrotoxic vinyl ether called Compound A. In the present study, we quantified this increase using "conditioned" Baralyme in a circle absorbent system to deliver sevoflurane anesthesia to swine. Mimicking continuing oxygen delivery for 2 days after completion of an anesthetic, we directed a conditioning fresh gas flow of 5 L/min retrograde through fresh absorbent in situ in a standard absorbent system for 40 h. The conditioned absorbent was subsequently used (without mixing of the granules) in a standard anesthetic circuit to deliver sevoflurane to swine weighing 78 +/- 2 kg. The initial inflow rate of fresh gas flow was set at 10 L/min with the vaporizer at 8% to achieve the target end-tidal concentration of 3.0%-3.2% sevoflurane in approximately 20 min. The flow was later decreased to 2 L/min, and the vaporizer concentration was decreased to sustain the 3.0%-3.2% value for a total of 2 h (three pigs) or 4 h (eight pigs). Inspired Compound A increased over the first 30 +/- 60 min to a peak concentration of 357 +/- 49 ppm (mean +/- SD), slowly decreasing thereafter to 74 +/- 6 ppm at 4 h. The average concentration over 2 h was 208 +/- 25 ppm, and the average concentration over 4 h was 153 +/- 19 ppm. Pigs were killed 1 or 4 days after anesthesia. The kidneys from pigs anesthetized for both 2 h and 4 h showed mild inflammation but little or no tubular necrosis. These results suggest that dehydration of Baralyme may produce concentrations of Compound A that would have nephrotoxic effects in humans in a shorter time than would be the case with normally hydrated Baralyme. ⋯ The vapor known as Compound A can injure the kidney. Dehydration of Baralyme, a standard absorbent of carbon dioxide in inhaled anesthetic delivery systems, can cause a 5- to 10-fold increase in Compound A concentrations produced from the inhaled anesthetic, sevoflurane, given at anesthetizing concentrations in a conventional anesthetic system.
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Anesthesia and analgesia · Dec 1997
Meta AnalysisDrugs to minimize perioperative blood loss in cardiac surgery: meta-analyses using perioperative blood transfusion as the outcome. The International Study of Peri-operative Transfusion (ISPOT) Investigators.
Concern about the side effects of allogeneic red blood cell transfusion has increased interest in methods of minimizing perioperative transfusion. We performed meta-analyses of randomized trials evaluating the efficacy and safety of aprotinin, desmopressin, tranexamic acid, and epsilon-aminocaproic acid in cardiac surgery. All identified randomized trials in cardiac surgery were included in the meta-analyses. The primary outcome was the proportion of patients who received at least one perioperative allogeneic red cell transfusion. Sixty studies were included in the meta-analyses. The largest number of patients (5808) was available for the meta-analysis of aprotinin, which significantly decreased exposure to allogeneic blood (odds ratio [OR] 0.31, 95% confidence interval [CI] 0.25-0.39; P < 0.0001). The efficacy of aprotinin was not significantly different regardless of the type of surgery (primary or reoperation), aspirin use, or reported transfusion threshold. The use of aprotinin was associated with a significant decrease in the need for reoperation because of bleeding (OR 0.44, 95% CI 0.27-0.73; P = 0.001). Desmopressin was not effective, with an OR of 0.98 (95% CI 0.64-1.50; P = 0.92). Tranexamic acid significantly decreased the proportion of patients transfused (OR 0.50, 95% CI 0.34-0.76; P = 0.0009). Epsilon-aminocaproic acid did not have a statistically significant effect on the proportion of patients transfused (OR 0.20, 95% CI 0.04-1.12; P = 0.07). There were not enough patients to exclude a small but clinically important increase in myocardial infarction or other side effects for any of the medications. We conclude that aprotinin and tranexamic acid, but not desmopressin, decrease the number of patients exposed to perioperative allogeneic transfusions in association with cardiac surgery. ⋯ Aprotinin, desmopressin, tranexamic acid, and epsilon-aminocaproic acid are used in cardiac surgery in an attempt to decrease the proportion of patients requiring blood transfusion. This meta-analysis of all published randomized trials provides a good estimate of the efficacy of these medications and is useful in guiding clinical practice. We conclude that aprotinin and tranexamic acid, but not desmopressin, decrease the exposure of patients to allogeneic blood transfusion perioperatively in relationship to cardiac surgery.