Anesthesia and analgesia
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Anesthesia and analgesia · Oct 1997
Baralyme dehydration increases and soda lime dehydration decreases the concentration of compound A resulting from sevoflurane degradation in a standard anesthetic circuit.
Soda lime and Baralyme brand carbon dioxide absorbents degrade sevoflurane to CF2 = C(CF3)OCH2F, a potentially nephrotoxic vinyl ether called Compound A. Dehydration of these absorbents increases both the degradation of sevoflurane to Compound A and the degradation of Compound A. The balance between sevoflurane degradation and Compound A degradation determines the concentration of Compound A issuing from the absorbent (the net production of Compound A). We studied the effect of dehydration on the net production of Compound A in a simulated anesthetic circuit. Mimicking continuing oxygen delivery for 1, 2, or 3 days after completion of an anesthetic, we directed a "conditioning" fresh gas flow of 5 L/min or 10 L/min retrograde through fresh absorbent in situ in a standard absorbent system for 16, 40, and/or 64 h. The conditioned absorbent was subsequently used (without mixing of the granules) in a standard anesthetic circuit in which a 3-L rebreathing bag substituted for the lung. Metabolism was mimicked by introducing 250 mL/min carbon dioxide into the "lung," and the lung was ventilated with a minute ventilation of 10 L/ min. At the same time, we introduced sevoflurane in a fresh gas inflow of 2 L/min at a concentration sufficient to produce an inspired concentration of 3.2%. Because of increased sevoflurane destruction by the absorbent, progressively longer periods of conditioning (dehydration) and/or higher inflow rates increased the delivered (vaporizer) concentration of sevoflurane required to sustain a 3.2% concentration. Dehydration of Baralyme increased the inspired concentration of Compound A by up to sevenfold, whereas dehydration of soda lime markedly decreased the inspired concentration of Compound A. ⋯ Economical delivery of modern inhaled anesthetics requires rebreathing of exhaled gases after removal of carbon dioxide. However, carbon dioxide absorbents (Baralyme/soda lime) may degrade anesthetics to toxic substances. Baralyme dehydration increases, and soda lime dehydration decreases, degradation of the inhaled anesthetic sevoflurane to the toxic substance, Compound A.
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Anesthesia and analgesia · Oct 1997
Comparative StudyThe Yale Preoperative Anxiety Scale: how does it compare with a "gold standard"?
Evaluating the effectiveness of interventions directed toward the treatment of preoperative anxiety in children has been hindered by the absence of a statistically valid measurement tool. In a previous investigation, we developed an instrument (Yale Preoperative Anxiety Scale [YPAS]) that can be used to assess anxiety in children undergoing induction of anesthesia. The purpose of the present investigation was to modify and expand the applicability of the instrument to the preoperative holding area and to validate the modified instrument (m-YPAS) against a recognized "gold standard" (State-Trait Anxiety Inventory for Childrens [STAIC]). Videotapes of children in a preoperative holding area were analyzed by the investigators. The existing five categories of the YPAS were found to reflect most of the behaviors observed. Several items, however, were modified to describe new behaviors observed. Reliability analysis using weighted kappa statistics revealed that inter-observer agreement ranged from 0.68 to 0.86, whereas intraobserver weighted kappa ranged from 0.63 to 0.90. Concurrent validity between the YPAS and the STAIC was acceptable (P = 0.01, r = 0.79). Construct validity was high as assessed by increased m-YPAS scores from the preoperative holding area (28 +/- 8) to entering the operating room (35 +/- 12), to introduction of the anesthesia mask (43 +/- 15;F [1,36] = 0.6, P = 0.001]. Showing good to excellent observer reliability and high concurrent and construct validity, the m-YPAS proved to be an appropriate tool for assessing children's anxiety during the perioperative period. ⋯ The absence of a statistically valid measurement tool that can be applied easily in perioperative settings hinders the evaluation of interventions directed toward treatment of preoperative anxiety in children. The authors describe the development of such a tool, the modified Yale Preoperative Anxiety Scale.
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Anesthesia and analgesia · Oct 1997
Postanesthetic vasoconstriction slows peripheral-to-core transfer of cutaneous heat, thereby isolating the core thermal compartment.
Forced-air warming during anesthesia increases core temperature comparably with and without thermoregulatory vasoconstriction. In contrast, postoperative forced-air warming may be no more effective than passive insulation. Nonthermoregulatory anesthesia-induced vasodilation may thus influence heat transfer. We compared postanesthetic core rewarming rates in volunteers given cotton blankets or forced air. Additionally, we compared increases in peripheral and core heat contents in the postanesthetic period with data previously acquired during anesthesia to determine how much vasomotion alters intercompartmental heat transfer. Six men were anesthetized and cooled passively until their core temperatures reached 34 degrees C. Anesthesia was then discontinued, and shivering was prevented by giving meperidine. On one day, the volunteers were covered with warmed blankets for 2 h; on the other, volunteers were warmed with forced air. Peripheral tissue heat contents were determined from intramuscular and skin thermocouples. Predicted changes in core temperature were calculated assuming that increases in body heat content were evenly distributed. Predicted changes were thus those that would be expected if vasomotor activity did not impair peripheral-to-core transfer of applied heat. These results were compared with those obtained previously in a similar study of anesthetized volunteers. Body heat content increased 159 +/- 35 kcal (mean +/- SD) more during forced-air than during blanket warming (P < 0.001). Both peripheral and core temperatures increased significantly faster during active warming: 3.3 +/- 0.7 degrees C and 1.1 +/- 0.4 degrees C, respectively. Nonetheless, predicted core temperature increase during forced-air warming exceeded the actual temperature increase by 0.8 +/- 0.3 degree C (P < 0.001). Vasoconstriction thus isolated core tissues from heat applied to the periphery, with the result that core heat content increased 32 +/- 12 kcal less than expected after 2 h of forced-air warming (P < 0.001). In contrast, predicted and actual core temperatures differed only slightly in the anesthetized volunteers previously studied. In contrast to four previous studies, our results indicate that forced-air warming increases core temperature faster than warm blankets. Postanesthetic vasoconstriction nonetheless impeded peripheral-to-core heat transfer, with the result that core temperatures in the two groups differed less than might be expected based on systemic heat balance estimates. ⋯ Comparing intercompartmental heat flow in our previous and current studies suggests that anesthetic-induced vasodilation influences intercompartmental heat transfer and distribution of body heat more than thermoregulatory shunt vasomotion.
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Postoperative pain is a common reason for the delayed discharge and unanticipated hospital admission of out-patients. In this study, we examined the pattern of pain in ambulatory surgical patients and determined those factors that predict postoperative pain. Ten thousand eight consecutive ambulatory surgical patients were prospectively studied. Preoperative patient characteristics, intraoperative variables, and pain in the postanesthesia care unit (PACU) and the ambulatory surgical unit (ASU) and 24 h postoperatively were documented. The incidence of severe pain was 5.3% in the PACU, 1.7% in the ASU, and 5.3% 24 h postoperatively. In the PACU, younger male adults (36 +/- 13 vs 47 +/- 22 yr), ASA physical status I patients, and patients with a higher body mass index (26 +/- 5 vs 25 +/- 5 kg) had a higher incidence of severe pain. In the group with severe pain, the duration of anesthesia, the duration of stay in the PACU and the ASU, and the time to discharge was longer than in the group without severe pain. In the PACU, orthopedic patients had the highest incidence of pain (16.1%), followed by urologic (13.4%), general surgery (11.5%), and plastic surgery (10.0%) patients. In patients who had general anesthesia, the intraoperative dose of fentanyl was significantly smaller in the group with severe pain than in the group without severe pain when body mass index and duration of anesthesia were taken into consideration. Body mass index, duration of anesthesia, and certain types of surgery were significant predictors of severe pain in the PACU. This knowledge will allow us to identify those patients at risk of severe postoperative pain and manage them prophylactically. ⋯ The pattern of pain was examined in 10,008 consecutive ambulatory surgical patients. The incidence of severe pain was 5.3% in the postanesthesia care unit, 1.7% in the ambulatory surgical unit, and 5.3% 24 h postoperatively. Body mass, duration of anesthesia, and certain types of surgery were significant predictors of pain in the postanesthesia care unit. These data will allow us to better predict those patients who need intense prophylactic analgesic therapy.
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Anesthesia and analgesia · Oct 1997
Letter Case ReportsPlacement of an axillary catheter in the subpectoral space.