Newborn blood levels of lidocaine and mepivacaine in the first postnatal day following maternal epidural anesthesia.
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Distribution and elimination of lidocaine and mepivacaine were studies in 114 subjects after obstetric epidural anesthesia, Epinephrine significantly lowered the concentrations of lidocaine in the mothers' circulations by about 33 per cent, and the concentrations of mepivacaine by about 22 per cent. It also significantly altered their concentrations in the newborns' circulations at delivery and in the first 4 hours after birth. More mepivacaine than lidocaine crossed the placenta. The mepivacaine concentration in the cord blood was 36 to 47 per cent higher, and the mean fetal to maternal ratio for mepivacaine without epinephrine was 0.64, in contrast to 0.52 for the equivalent lidocaine group. Of importance was the long persistance of either drug in the newborns' circulation. Detectable levels of lidocaine and mepivacaine were present until 8 and 24 hours after birth, respectively. Pharmacokinetic models revealed that the long-term rate of disappearance of lidocaine was approximately three times as fast as that of mepivacaine. Computed half-times averaged 3 hours for lidocaine and 9 hours for mepivacaine. (+info)
Cardiovascular responses to the induction of mild hypothermia in the presence of epidural anesthesia.
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BACKGROUND: The combining of epidural anesthesia with general anesthesia impairs central and peripheral thermoregulatory control and therefore is often accompanied by unintended intraoperative hypothermia. However, little is known about the cardiovascular response to hypothermia during combined epidural and general anesthesia. The authors assessed the effects of hypothermia during such combined anesthesia. METHODS: The authors randomly assigned 30 mongrel dogs anesthetized with isoflurane (1.0%) to three groups of 10: control, receiving general anesthesia alone; thoracic injection, additionally receiving thoracic epidural anesthesia; and lumbar injection, additionally receiving thoracolumbar epidural anesthesia. Core temperature was lowered from 38.5 degrees C to approximately 34 degrees C (mild hypothermia) using a femoral arteriovenous shunt in an external cool water bath. During hypothermia, the authors measured heart rate, cardiac output, and plasma catecholamine concentrations in each group. Ejection fraction was also measured using echocardiography. RESULTS: Compared with measurements during baseline conditions (general anesthesia alone with no epidural injection and no hypothermia) in the control, thoracic, and lumbar injection groups, the injections followed by hypothermia produced 17, 32, and 41% decreases in heart rate; 22, 32, and 47% reductions in cardiac output; 66, 85, and 92% decreases in the epinephrine concentrations; and 27, 44, and 85% decreases in the norepinephrine concentrations. In contrast, ejection fraction did not change in any group. CONCLUSION: Mild hypothermia during combined epidural anesthesia and general anesthesia markedly reduced cardiac output in dogs, mainly by decreasing heart rate. (+info)
Epidural lidocaine decreases sevoflurane requirement for adequate depth of anesthesia as measured by the Bispectral Index monitor.
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BACKGROUND: Epidural anesthesia potentiates sedative drug effects and decreases minimum alveolar concentration (MAC). The authors hypothesized that epidural anesthesia also decreases the general anesthetic requirements for adequate depth of anesthesia as measured by Bispectral Index (BIS). METHODS: After premedication with 0.02 mg/kg midazolam and 1 microg/kg fentanyl, 30 patients aged 20-65 yr were randomized in a double-blinded fashion to receive general anesthesia with either intravenous saline placebo or intravenous lidocaine control (1-mg/kg bolus dose; 25 microg x kg(-1) x min(-1)). A matched group was prospectively assigned to receive epidural lidocaine (15 ml; 2%) with intravenous saline placebo. All patients received 4 mg/kg thiopental and 1 mg/kg rocuronium for tracheal intubation. After 10 min of a predetermined end-tidal sevoflurane concentration, BIS was measured. The ED50 of sevoflurane for each group was determined by up-down methodology based on BIS less than 50 (MAC(BIS50)). Plasma lidocaine concentrations were measured. RESULTS: The MAC(BIS50) of sevoflurane (0.59% end tidal) was significantly decreased with lidocaine epidural anesthesia compared with general anesthesia alone (0.92%) or with intravenous lidocaine (1%; P < 0.0001). Plasma lidocaine concentrations in the intravenous lidocaine group (1.9 microg/ml) were similar to those in the epidural lidocaine group (2.0 microg/ml). CONCLUSIONS: Epidural anesthesia reduced by 34% the sevoflurane required for adequate depth of anesthesia. This effect was not a result of systemic lidocaine absorbtion, but may have been caused by deafferentation by epidural anesthesia or direct rostral spread of local anesthetic within the cerebrospinal fluid. Lower-than-expected concentrations of volatile agents may be sufficient during combined epidural-general anesthesia. (+info)
Effects of thoracic epidural anesthesia with and without autonomic nervous system blockade on cardiac monophasic action potentials and effective refractoriness in awake dogs.
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BACKGROUND: The effects of thoracic epidural anesthesia (TEA) on myocardial repolarization and arrhythmogenicity are only incompletely understood. This is primarily because of the lack of appropriate experimental models. In most of the studies performed thus far, TEA was used in anesthetized animals. Baseline anesthesia itself may have modified the effects of TEA. This study investigates right atrial and ventricular repolarization by recording monophasic action potentials after TEA in awake dogs. The authors hypothesized that an antiarrhythmic role of TEA exists, which may be related to a direct effect of TEA on myocardial repolarization. METHODS: The hypothesis was tested in an in vivo canine model, in which atrial and ventricular myocardial action potential duration and refractoriness are recorded by means of monophasic action potential catheters. RESULTS: Thoracic epidural anesthesia significantly increased ventricular monophasic action potential duration for cycle lengths shorter than 350 ms. Changes in monophasic action potential duration were paralleled by a concomitant prolongation of effective refractory period (ERP) at higher rates so that the ratio of ERP to action potential duration was unaffected. CONCLUSIONS: This model helps to study the role of TEA on ventricular repolarization and arrhythmogenicity. Because lengthening of repolarization and prolongation of refractoriness may, in some circumstances, be antiarrhythmic, TEA may be protective against generation of ventricular arrhythmias mediated, e.g., by increased sympathetic tone. The results also imply that the beneficial role of TEA might be stronger at the ventricular site as compared with the atrium. At atrial sites there was only a trend toward prolongation of repolarization even at short cycle lengths. (+info)
Pharmacokinetics of bupivacaine after continuous epidural infusion in infants with and without biliary atresia.
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BACKGROUND: Continuous epidural infusion of bupivacaine is widely practiced for postoperative pain relief in pediatric patients. However, bupivacaine may induce adverse effects in infants (convulsions or cardiac arrhythmias), likely because of decreased hepatic clearance and serum protein binding capacity. The authors wanted to examine the complex relations between age, alpha-1 acid glycoprotein (AAG) concentration, and unbound and total bupivacaine serum concentrations in infants receiving bupivacaine epidurally for 2 days. METHODS: Twenty-two infants aged 1-7 months (12 with biliary atresia and 10 with another disease) received a continuous epidural infusion of 0.375 mg x kg(-1) x h(-1) bupivacaine during 2 days (during and after surgery). Unbound and total bupivacaine concentration in serum was measured 0.5, 4, 24, and 48 h after infusion initiation. AAG concentration was measured in serum before and 2 days after surgery. In eight additional infants, the blood/plasma concentration ratio was measured in vitro at whole blood concentrations of 2 and 20 microg/ml. Bupivacaine concentration was fitted to a one-compartment model to calculate basic pharmacokinetic parameters. RESULTS: No adverse effects were observed. AAG increased markedly after surgery, and the increase was correlated to both age and preoperative AAG concentration. Two infants aged 1.8 months had unbound concentrations greater than 0.2 microg/ml. Clearance of unbound drug significantly increased with age. Because of increased drug binding, clearance of bound drug decreased both with time (from 0.5 to 48 h) and with age. Blood/plasma ratio was 0.77+/-0.08 and 0.85+/-0.24 at 2 and 20 microg/ml, respectively. CONCLUSIONS: Because of a low AAG concentration and a low intrinsic clearance, unbound bupivacaine increased to concentrations greater than 0.2 microg/ml in two infants younger than 2 months, after 2 days of infusion at a rate of 0.375 mg x kg(-1) x h(-1). The increase in AAG observed after surgery did not fully buffer this unbound fraction. Similarly, the buffer capacity of erythrocytes did not sufficiently increase at high concentration to compensate the saturation of the AAG system. Thus, we propose the use of a maximum dose of 0.25 mg x kg(-1) x h(-1) in infants younger than 4 months and a maximum of 0.3 mg x kg(-1) x h(-1) in infants older than 4 months. (+info)
Identification of high risk labours by labour nomogram.
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The labour stencil representing the expected cervimetric progress of normal labour was used in 741 consecutive spontaneous labours to identify high-risk labours which needed oxytocic stimulation. Uterine contractions were stimulated if progress extended two hours past the nomogram, which resulted in shorter labours, fewer instrumental deliveries and caesarean sections, and babies with higher Apgar scores than in those dysfunctional labours which were not stimulated. According to the protocol used 36% of primigravid and 13% of multigravid labours needed acceleration. The remaining patients did not need any oxytocic interference during the first stage. This selection of patients is important to prevent a major obstetric advance being abused and discredited at a time when the profession and public are questioning the safety of active labour. (+info)
Labor epidurals improve outcomes for babies of mothers at high risk for unscheduled cesarean section.
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CONTEXT: Epidural placement for labor in the general population of laboring women is associated with increased incidence of operative deliveries, prolongation of labor, and may be associated with an increased cesarean section rate. The risks and benefits associated with epidural placement for labor in the subpopulation of mothers at high risk for cesarean section have not been studied. OBJECTIVE: To determine if a population of mothers and babies at high risk for cesarean section will have improved outcomes with labor epidural placement. DESIGN: A decision and cost analysis examining epidural placement for labor on a population of women who are at high risk for unscheduled cesarean section and may benefit from scheduled cesarean section as determined by threshold analysis was performed. Outcomes and probabilities were determined through analysis of the Department of Defense's 1996 National Quality Management Program (NQMP) Birth Product Line data set containing more than 7000 deliveries. Outcomes were defined using variables comprised of all documented conditions that occurred during the peripartum and neonatal hospitalizations. The 1997 NQMP data set was used to validate the results. SETTING: Military Treatment Facilities throughout the United States and abroad and civilian facilities in the United States providing care to military dependents. PATIENT POPULATION: Active duty and dependent pregnant women and babies. RESULTS: About 8% of mothers in this patient population were found to be at high risk for cesarean section. The decision and cost analyses showed that babies of the high risk mothers who received epidurals for labor had better clinical outcomes (p<0.05) and the procedure was cost neutral (p=0.23). The procedure did not increase the frequency of cesarean section, and there was no effect on maternal outcomes scores. These results were confirmed by the validation study. CONCLUSIONS: There is a sizable subpopulation of women at high risk for cesarean section whose babies may have better outcomes with epidural placement with no sacrifice in maternal outcomes or costs. (+info)
Spinal cord injury caused by direct damage by local anaesthetic infiltration needle.
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We describe a case of spinal cord injury caused by direct trauma from a local anaesthetic infiltration needle. During local anaesthetic infiltration before placement of an epidural catheter, the patient suddenly rolled over onto her back, causing the infiltrating needle to advance all the way to its hub. She immediately showed signs of spinal cord injury, confirmed by MRI scan. However, her neurological status gradually improved, and on discharge she was able to walk, with a sensory deficit localized to her left foot. (+info)