Anesthesia and analgesia
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Anesthesia and analgesia · Feb 1998
Propofol and thiopental in a 1:1 volume mixture is chemically stable.
Propofol and thiopental have been used clinically in combination for induction of anesthesia. Studies suggest that this mixture has synergistic activity, recovery characteristics similar to propofol alone, and bactericidal effects on multiple organisms. It may therefore be both clinically useful and cost-effective. In this study, we examined the chemical stability of this mixture. We used high-performance liquid chromatography to quantify the concentration of both propofol and thiopental in a given sample. This technique allows the detection of loss in total drug mass and of the appearance of breakdown products resulting from drug interaction. Ten samples of a 1:1 mixture by volume were prepared and assayed at Time 0 and Days 1, 3, and 7. Half the samples were incubated at 23 degrees C and the rest were stored at 4 degrees C. Other mixtures were assayed before and after filtration at Time 0 and Days 1 and 7 after storage at 23 degrees C. The assay was able to measure accurately the quantity of drug present in the samples. There was no significant decrease in the quantities of either propofol or thiopental in the mixture over the 7-day period. We conclude that the 1:1 volume mixture of propofol and thiopental is chemically stable for 1 wk at room temperature. ⋯ A mixture of propofol and thiopental has been used to induce anesthesia. We investigated the chemical stability of this mixture using high-performance liquid chromatography and found it to be stable for at least 24 h.
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Anesthesia and analgesia · Feb 1998
Extension of sensory blockade after thoracic epidural administration of a test dose of lidocaine at three different levels.
To evaluate the relationship between the level of thoracic epidural injection and the extension of sensory blockade, we inserted radiopaque epidural catheters in 87 patients at the high (C7-T2, n = 28), mid (T3-5, n = 29) or low (T7-9, n = 30) thoracic levels. Fifteen minutes after the epidural administration of 60 mg of lidocaine, the mean (+/- SD) sensory block extension varied from 5.4 +/- 3.1 to 7.7 +/- 1.8 segments. The level of epidural puncture was a statistically significant factor in determining the cranial and caudal borders of sensory blockade (P = 0.0001, analysis of variance), but in determining for the total number of segments blocked. The number of blocked dermatomes located cranially of the puncture level increased significantly with descending injection site (P = 0.0001). We acquired chest radiographs in 61 patients to determine epidural catheter tip position. Direction of the epidural catheter tip was not a significant factor in determining the extension or borders of sensory blockade. We conclude that the extension of sensory blockade in thoracic epidural anesthesia is not influenced by the level of epidural puncture or catheter tip direction. There is, however, a more cranial spread of sensory blockade in the low thoracic region compared with the high thoracic region. ⋯ After evaluating the extension and pattern of sensory blockade in high, mid, and low thoracic epidural analgesia, the authors suggest that it is safe to use similar dosage regimens in all three regions, and that in high thoracic epidural analgesia, it is important to insert the epidural catheter at the level of the intended cranial border of blockade.
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Anesthesia and analgesia · Feb 1998
The effects of the alpha2-adrenergic agonist, dexmedetomidine, in the spinal nerve ligation model of neuropathic pain in rats.
Peripheral nerve injury may lead to neuropathic pain. Alpha2-adrenergic agonists acting in the descending inhibitory tracts of the spinal cord are effective in acute nociceptive, inflammatory, and, possibly, neuropathic pain. We studied the prevention and treatment of neuropathy with the selective alpha2-adrenergic agonist dexmedetomidine in male Sprague-Dawley rats with unilateral peripheral mononeuropathy resulting from tight ligation of the L5 and L6 spinal nerves. Rats with ligation injury developed mechanical and cold allodynia, but not heat hyperalgesia. Dexmedetomidine (120 microg/kg subcutaneously [S.C.] 30 min before the injury) did not attenuate mechanical or cold allodynia. Dexmedetomidine infusions (60 microg/d for 7 days after the injury, or 30 microg/d for 7 days started 14 days after the injury) did not attenuate mechanical or cold allodynia in the ipsilateral paw, but they increased mechanical allodynia during the latter treatment in the paw contralateral to the injury. Atipamezole (1 mg/kg S.C.) induced mechanical and cold allodynia in rats that had not developed allodynia in 14 days after the injury. In conclusion, although alpha2-adrenergic mechanisms are recognized as important in the development of neuropathic pain-like symptoms in this animal model, we found no favorable effect from systemic treatment with dexmedetomidine at tolerable doses. ⋯ We studied the prevention and treatment of nerve injury-induced pain with the alpha2-adrenergic agonist dexmedetomidine in an animal model. At tolerable doses, systemic dexmedetomidine neither prevented nor attenuated neuropathic pain behavior.
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Anesthesia and analgesia · Feb 1998
The effects of red-cell scavenging, hemodilution, and active warming on allogenic blood requirements in patients undergoing hip or knee arthroplasty.
Since 1993, we have progressively adopted three techniques to reduce transfusion requirements during major orthopedic surgery: red-cell scavenging, acute normovolemic hemodilution, and active patient warming. We retrospectively evaluated all 821 elective hip and knee arthroplasties performed in our institution beginning with July 1993. Target minimal hematocrits were guided by patient ages and cardiovascular status. The first approximately 500-mL blood loss was replaced with crystalloid at a ratio of 3 mL for each milliliter of blood loss. Additional blood loss was replaced with colloid, hemodilution blood (when available), and scavenged red cells (when available). Allogenic transfusions were then administered as necessary to maintain target hematocrits, which were prospectively defined based on the patient ages and cardiovascular health. Univariate analysis was applied initially. Significant predictors of transfusion requirement were subsequently entered into a stepwise multiple regression to account for confounding factors, including age, type of anesthesia (regional versus general) and type of surgery (primary versus hardware replacement). Postoperative hemoglobin concentrations were similar over the years of study and among the patients given each treatment. During the study period, allogenic blood requirements decreased from 1.3 +/- 1.7 U/patient to 0.6 +/- 1.4 U/patient (mean +/- SD). Both univariate and regression analyses indicated that each treatment significantly reduced transfusion requirements (P < 0.05). We conclude that red-cell scavenging, hemodilution, and active cutaneous warming each reduce allogenic blood requirements during hip and knee arthroplasties. ⋯ We retrospectively evaluated three strategies to reduce overall blood loss: red-cell scavenging, acute normovolemic hemodilution, and active patient warming. During the study period, allogenic blood requirements decreased by a factor of 2. Each treatment contributed to this reduction. We therefore conclude that each treatment reduces allogenic blood requirements during hip and knee arthroplasties.