Anesthesia and analgesia
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Anesthesia and analgesia · Apr 1998
Chloral hydrate sedation: the additive sedative and respiratory depressant effects of nitrous oxide.
The combination of chloral hydrate and nitrous oxide (N2O) is often used for sedation in pediatric dentistry. The purpose of this study was to determine the extent to which N2O increases the level of sedation and respiratory depression in children sedated with chloral hydrate. Thirty-two children, 1-9 yr, received chloral hydrate, 70 mg/kg (maximum 1.5 g), and then received N2O (30% and 50%). Hypoventilation (maximal PETCO2 > 45 mm Hg) occurred in 23 (77%) children during administration of chloral hydrate alone, in 29 (94%) breathing 30% N2O (P = 0.08 versus control), and in 29 (97%) breathing 50% N2O (P = 0.05 versus control). Mean PETCO2 was increased during 30% (P = 0.007) and 50% (P = 0.02) N2O administration. Using chloral hydrate alone, 8 (25%) children were not sedated, 10 (31%) were consciously sedated, and 14 (44%) were deeply sedated. Using 30% N2O, 2 children (6%) were not sedated, 0 were consciously sedated, and 29 (94%) were deeply sedated (P < 0.0001). Using 50% N2O, 1 child (3%) was not sedated, 0 were consciously sedated, 27 (94%) were deeply sedated, and 1 (3%) had no response to a painful stimulus (P < 0.0001). We conclude that the addition of 30% or 50% N2O to chloral hydrate often causes decreases in ventilation and usually results in deep, not conscious, sedation in children. ⋯ Pediatric sedation in the dental office often consists of nitrous oxide (N2O) after chloral hydrate premedication. We found that the addition of 30% or 50% N2O to chloral hydrate often causes decreases in ventilation and usually results in deep, not conscious, sedation in children.
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Anesthesia and analgesia · Apr 1998
Systemic and regional pharmacokinetics of levobupivacaine and bupivacaine enantiomers in sheep.
Commercially available bupivacaine is an equimolar mixture of R(+)- and S(-)-bupivacaine. S(-)-bupivacaine (levobupivacaine) is the subject of current clinical evaluation. We conducted partial cross-over systemic and regional pharmacokinetic studies of i.v. bupivacaine (12.5-200 mg) and levobupivacaine (6.25-200 mg) in ewes. Enantiospecific analysis of blood drug concentration-time data and of regional myocardial and brain drug mass balance data indicated that (a) there was a higher mean total body clearance of R(+)-bupivacaine than of S(-)-bupivacaine (as previously reported); (b) there were no differences in the systemic pharmacokinetics of S(-)-bupivacaine whether administered alone or as a component of bupivacaine; (c) there was no evidence of dose-dependent pharmacokinetics with either enantiomer; (d) for both enantiomers, mean calculated myocardial tissue concentrations of 1%-4% dose occurred between 3 and 5 min. Mean brain concentrations of 0.2%-1% dose occurred between 2 and 4 min after the administration of bupivacaine but between 4 and 5 min after the administration of levobupivacaine. There was no evidence that systemic toxicity induced by these local anesthetics significantly modified their pharmacokinetics, and there was no evidence of an enantiomer-enantiomer pharmacokinetic interaction for bupivacaine. ⋯ Levobupivacaine comprises 50% of commercially available bupivacaine and is being considered for use in its own right. As a part of its preclinical evaluation, this study considered whether levobupivacaine behaved kinetically in the body in the same way as when administered as a component of bupivacaine.
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Anesthesia and analgesia · Apr 1998
Bacterial colonization and infection rate of continuous epidural catheters in children.
Continuous epidural infusions are widely used for postoperative analgesia in children. We prospectively studied the incidence of bacterial colonization of caudal and lumbar epidural catheters, as well as the incidence of serious systemic and local infection, in 210 children after short-term epidural analgesia. Using aseptic technique, epidural catheters were inserted into either the lumbar or the caudal epidural space based on the preferences of the anesthesia team and/or clinical indication. The integrity of the catheter and overlying transparent dressing site was evaluated by a member of the pediatric pain service at least once a day. The catheters were aseptically removed if the patient had a fever greater than 39 degrees C, if the dressing was compromised, or when epidural analgesia was no longer required. The subcutaneous portion of the catheter was semiquantitatively cultured. Cellulitis (erythema, swelling, purulent discharge, pustule formation, or tenderness) was diagnosed by examination of the epidural insertion site. The mean (+/- SD) age of patients in the caudal catheter group (n = 170) was 3 +/- 3 yr; their mean weight was 13 +/- 11 kg. The mean (+/- SD) age of patients in the epidural catheter group (n = 40) was 11 +/- 4 yr; their mean weight was 36 +/- 23 kg. All catheters remained in place for 3 +/- 1 days (range 1-5 days). There was no serious systemic infection (meningitis, epidural abscess, or systemic sepsis). Of all epidural catheters, 35% (73 of 210) were colonized. Gram-positive colonization was similar in caudal (25%; 43 of 170) and lumbar (23%; 9 of 40) catheters. Gram-negative organisms were cultured from 16% of the caudal catheters (27 of 170) and 3% of the lumbar catheters (1 of 40). In patients treated with caudal epidural catheters, children aged >3 yr were less likely to have colonized epidural catheters than younger children. Age did not affect the probability of developing cellulitis at the insertion site. Although patients aged <3 yr with caudal catheters had a slightly greater risk of cellulitis than children aged >3 yr (14% vs 9%), this association was very weak (P = 0.33). We observed that, despite bacterial colonization of caudal and lumbar epidural catheters, serious systemic and local infection after short-term epidural analgesia did not occur in our study. ⋯ Continuous epidural infusions are widely used for postoperative analgesia in children. We found no serious systemic infections after short-term (3 days) continuous epidural analgesia in children.
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Anesthesia and analgesia · Apr 1998
Laryngeal mask airway position and the risk of gastric insufflation.
A potential risk of the laryngeal mask airway (LMA) is an incomplete mask seal causing gastric insufflation or oropharyngeal air leakage. The objective of the present study was to assess the incidence of LMA malpositions by fiberoptic laryngoscopy, and to determine their influence on gastric insufflation and oropharyngeal air leakage. One hundred eight patients were studied after the induction of anesthesia, before any surgical manipulations. After clinically satisfactory LMA placement, tidal volumes were increased stepwise until air entered the stomach, airway pressure exceeded 40 cm H2O, or air leakage from the mask seal prevented further increases in tidal volume. LMA position in relation to the laryngeal entrance was verified using a flexible bronchoscope. The overall incidence of LMA malpositions was 40% (43 of 108). Gastric air insufflation occurred in 19% (21 of 108), and in 90% (19 of 21) of these patients, the LMA was malpositioned. Oropharyngeal air leakage occurred in 42%, and was independent of LMA position. We conclude that clinically unrecognized LMA malposition is a significant risk factor for gastric air insufflation. ⋯ Routine placement of laryngeal mask airways does not require laryngoscopy. In our study, fiberoptic verification of mask position revealed suboptimal placement in 40% of cases. Such malpositioning considerably increased the risk of gastric air insufflation.
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Anesthesia and analgesia · Apr 1998
Comparative StudyAntinociceptive potentiation and attenuation of tolerance by intrathecal co-infusion of magnesium sulfate and morphine in rats.
N-methyl-D-aspartate (NMDA) antagonists, such as MK801, delay the development of morphine tolerance. Magnesium, a noncompetitive NMDA antagonist, reduces postoperative morphine requirements. The present study was designed to evaluate the effects of intrathecal co-administration of magnesium sulfate with morphine on antinociceptive potentiation, tolerance, and naloxone-induced withdrawal signs. Magnesium sulfate (40-60 microg/h) co-administration for 7 days, similar to MK801 (10 nmol/h), prevented the decline in antinociceptive response compared with morphine (20 nmol/h). Magnesium sulfate (60 microg/h) produced no antinociception, but co-infused with morphine (1 nmol/h), it resulted in potentiated antinociception compared with morphine throughout the 7-day period. Probe morphine doses after 7-day infusions demonstrated a significantly greater 50% effective dose value for morphine 1 nmol/h (109.7 nmol) compared with saline (10.9 nmol), magnesium sulfate 60 microg/h (10.9 nmol), and magnesium sulfate 60 microg/h plus morphine 1 nmol/h (11.2 nmol), which indicates that magnesium had delayed morphine tolerance. Morphine withdrawal signs after naloxone administration were not altered by the co-infusion of magnesium sulfate. Cerebrospinal fluid magnesium levels after intrathecal magnesium sulfate (60 microg/h) for 2 days increased from 17.0 +/- 1.0 microg/mL to 41.4 +/- 23.6 microg/mL, although serum levels were unchanged. This study demonstrates antinociceptive potentiation and delay in the development of morphine tolerance by the intrathecal coinfusion of magnesium sulfate and morphine in the rat. ⋯ The addition of magnesium sulfate, an N-methyl-D-aspartate antagonist, to morphine in an intrathecal infusion provided better analgesia than morphine alone in normal rats. These results suggest that intrathecal administration of magnesium sulfate may be a useful adjunct to spinal morphine analgesia.