Anesthesia and analgesia
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Anesthesia and analgesia · Jan 2002
Bispectral index values and spectral edge frequency at different stages of physiologic sleep.
Bispectral index (BIS) and spectral edge frequency (SEF) are used as measures of depth of anesthesia and sedation. We tested whether these signals could predict physiologic sleep stages, by taking processed electroencephalogram measurements and recording full polysomnography through a night's sleep in 10 subjects being investigated for mild sleep apnea/hypopnea syndrome. Computerized polysomnograph signals were analyzed manually according to standard criteria, classifying each 30-s epoch as a specific sleep stage. The BIS and SEF values were taken at the end of each period of sleep when the same stage had lasted for at least 2 min. Before sleep, median values for BIS were 97 +/- 12.1 and for SEF 23 +/- 4.2 Hz. After sleep initiation, the median BIS values for arousal, light, slow wave, and rapid eye movement sleep were 67 +/- 20.2, 50 +/- 16.5, 42 +/- 11.2, and 48 +/- 7.1, respectively, and the median SEF values were 20 +/- 4.7, 15 +/- 3.6, 10 +/- 2.6, and 19 +/- 4.1 Hz, respectively. Although both BIS and SEF decreased with increasing sleep depth, the distribution of values at each sleep depth was considerable, with overlap between each sleep stage. Neither BIS nor SEF reliably indicated conventionally determined sleep stages. In addition, the response of the BIS was slow and patients could arouse with low BIS values, which then took some time to increase. ⋯ Although computer processing of the electroencephalogram can provide an adequate index of depth of anesthesia, the same processing cannot reliably convey depth of natural sleep. At each sleep stage, the output signal has a wide range of possible values.
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Anesthesia and analgesia · Jan 2002
Physiologic characteristics of cold perfluorocarbon-induced hypothermia during partial liquid ventilation in normal rabbits.
Because perfluorocarbon (PFC) liquid contacts closely with the alveolar capillaries during partial liquid ventilation (PLV), PLV with cold PFC may be used for the induction of hypothermia. Twenty rabbits were randomized to PFC-induced hypothermia (PH) (n = 7; core temperature 35 degrees +/- 1 degrees C), surface hypothermia (SH) (n = 7; 35 degrees +/- 1 degrees C), or normothermia (n = 6; 39 degrees +/- 1 degrees C). We induced PH by repeated in situ exchanges of 0 degrees C perfluorodecalin during PLV. At the establishment (0 min) of hypothermia in the PH group, oxygen consumption (P = 0.04) and oxygen extraction ratio (P = 0.01) decreased from normothermic condition. Metabolic (oxygen consumption, oxygen extraction ratio, serum lactate level) and hemodynamic variables (heart rate, blood pressure, cardiac output, pulmonary artery pressure) of the PH group were not different from those of the SH group at 0, 30, 60, 90, and 120 min of hypothermia. The difference in temperature between the pulmonary artery and rectum during the hypothermic period was smaller in the PH group compared with the SH group (P = 0.033). In conclusion, hypothermia may be induced during PLV by using cold PFC. This "pulmonary method" of cooling was comparable to a systemic method of cooling with regard to a few important physiologic variables, while maintaining a narrower interorgan temperature difference. ⋯ The induction of moderate hypothermia was feasible in rabbits by administrating cold perfluorocarbon liquid into the lung. Physiologic changes induced by this pulmonary cooling were comparable to those induced by systemic cooling. Our method may be regarded as a methodological advance in the field of therapeutic hypothermia.
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Anesthesia and analgesia · Jan 2002
The pharmacokinetics of epsilon-aminocaproic acid in children undergoing surgical repair of congenital heart defects.
epsilon-Aminocaproic acid (epsilonACA) is often administered to children undergoing cardiac surgery by using empiric dosing techniques. We hypothesized that children would have different pharmacokinetic variables and require a dosing scheme different from adults to maintain stable and effective serum epsilonACA concentrations. Eight patients were enrolled in our study. epsilonACA 50 mg/kg was administered three times IV: before, during, and after cardiopulmonary bypass (CPB). Nine serum samples were obtained. epsilonACA plasma concentrations were measured by using high-performance liquid chromatography, and pharmacokinetic modeling was done by using NONMEM. The best fit was seen with a two-compartment model with volume of distribution (V(1)) adjusted for weight and CPB. Compared with published results in adults, modeling suggests that weight-adjusted V(1) is larger in children than in adults before, during, and after CPB. Clearance from the central compartment (k(10)) was also greater in children than adults, and declined during CPB. Redistribution rates from the central compartment, k(12) and k(21), were greater in children and not affected by CPB. We modeled several different dosing regimens for epsilonACA based on the larger V(1), and higher redistribution and clearance variables. We conclude that, because of the developmental differences in pharmacokinetic variables of epsilonACA, when compared with adult patients, a larger initial dose and faster infusion rate as well as an addi-tional dose on CPB are needed to maintain similar concentrations. ⋯ Pharmacokinetic modeling of epsilon-aminocaproic acid in children undergoing cardiac surgery suggests that there are developmental differences in pharmacokinetic variables. Based on these data, a dosing modification in children is suggested which may better maintain serum concentrations in children when compared with adults.
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Anesthesia and analgesia · Jan 2002
Peripheral nerve blockade with long-acting local anesthetics: a survey of the Society for Ambulatory Anesthesia.
Despite the growth of ambulatory anesthesia and the renewed popularity of regional techniques, there is little current information concerning outpatient regional anesthesia practices or attitudes about discharge with an insensate extremity. We present results from a survey sent to all members of the Society for Ambulatory Anesthesia (SAMBA). The survey was mailed in January 2001 to 2373 SAMBA members, along with a self-addressed stamped return envelope. After 3 mo, 1078 surveys were returned (response rate 45%). Respondents indicated that they were most likely to perform axillary (77%), interscalene (67%), and ankle blocks (68%) on ambulatory patients. They were less likely to perform lower extremity conduction blocks in ambulatory patients (femoral blocks, 40%; all other types of blocks, <23%]. Eighty-five percent of respondents discharged patients with long-acting blocks, but this was mainly limited to three types. Of the 16% who never or rarely discharged patients with long-acting blocks, the primary reasons were concern about patient injury (49%) and the inability for patients to care for themselves (28%). Only 22% of office-based anesthesiologists would perform upper extremity blocks and only 28% would perform lower extremity blocks (P < 0.001). This survey demonstrates that use of regional anesthesia in outpatients is common but restricted to a few techniques. Discharge with an insensate upper extremity is prevalent but discharge with an insensate lower extremity is not common and remains controversial. Despite the reasoning for the reported practices, randomized data are necessary to confirm the validity of these concerns. ⋯ This survey demonstrates that use of regional anesthesia in outpatients is common but restricted to a few techniques. Discharge with an insensate upper extremity is common but discharge with an insensate lower extremity is not prevalent and remains controversial.
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Anesthesia and analgesia · Jan 2002
Combining transcutaneous blood gas measurement and pulse oximetry.
We are describing the preliminary results of tests performed in adult volunteers and in adult patients during and after general anesthesia with a miniaturized single sensor combining the continuous and non-invasive measurement of oxygen saturaiton by pulse oximetry (SpO2) and transcutaneous PCO2 (OxiCarbo sensor). The sensor is heated to 42 degrees C to arterialize the cutaneous tissue and is applied at the ear lobe with a special low-pressure clip. ⋯ The ear lobe OxiCarbog sensor detects the SpO2 change 5 to 37 sec faster than a finger sensor and the PCO2 change 9 to 48 sec faster than a transcutaneous sensor fixed at the upper arm. Further improvements versus single sensors are a higher stability of the SpO2 signal and the possibility of performing long term SpO2 and PCO2 measurement at the ear lobe.