PubMed Health⌕ Search

Biomedical subjects

M E McLeod

Publications and source records attributed to M E McLeod.

At least 19 recordsLinked to original sources
PubMed1995

Incidence of malignant hyperthermia reactions in 2,214 patients undergoing muscle biopsy.

To determine the incidence of malignant hyperthermia (MH) reactions after trigger-free anaesthesia in a large population of MH-susceptible (MHS) patients, the charts of 2,214 patients who underwent elective muscle biopsy for malignant hyperthermia were reviewed. Either general or regional anaesthesia with non-triggering drugs was used. For general anaesthesia, the trachea was intubated in the absence of muscle relaxants. The halothane/caffeine contracture test was performed on the biopsied muscle. Suspected MH reactions were identified according to their site of occurrence (in the operating room, recovery room or ward). Ninety-seven percent of patients received a general anaesthetic; 3% received a regional anaesthetic or field block. Of the 2214 patients whose muscles were biopsied, 1082 patients were biopsy-positive for MH. Five patients in whom MH reactions were diagnosed in the recovery room were all subsequently proved to be biopsy-positive for MH. Four of the five received intravenous dantrolene as part of their therapy; the fifth received only symptomatic therapy as parenteral dantrolene was not commercially available. All patients recovered completely from their reactions. We conclude that the incidence of MH reactions in biopsy-positive patients who receive a trigger-free anaesthetic for minor surgery is small (0.46%, (0.15-1.07%, 95% CI)). These reactions occur in the immediate postoperative period.

Adolescent↗
PubMed1994

End-tidal carbon dioxide measurement in infants and children during and after general anaesthesia.

We have examined the reliability of end-tidal carbon dioxide (PetCO2) monitoring as an estimate of arterial carbon dioxide tension (PaCO2) in spontaneously breathing infants and children. Forty patients were studied in the post-anaesthetic care unit; 20 < 12 kg and 20 > or = 12 kg. The PetCO2 was sampled via a 5 cm 16 gauge catheter taped below an external naris and this measurement was compared with the PaCO2 of a sample drawn from an indwelling arterial line. Twenty additional patients were studied during inhalational anaesthesia. The PetCO2 was measured both from the proximal end of the elbow connector and from a 5 cm cannula inserted through the elbow. An arterial blood gas sample was obtained simultaneously. The arterial to end-tidal (Pa-et) differences were compared between the two sites. Patients studied in the post-anaesthetic care unit showed good correlation between PetCO2 and PaCO2 regardless of weight: Pa-etCO2 of -0.6 +/- 3.6 (< 12 kg) and -1.1 +/- 2.8 mmHg (> or = 12 kg). Patients studied during mask anaesthesia showed better correlation between PetCO2 and PaCO2 when PetCO2 was sampled from the cannula: Pa-etCO2 of 3.5 +/- 4.8 mmHg (cannula), 8.6 +/- 4.5 (elbow) (P < 0.05). These results suggest that end-tidal CO2 monitoring is a useful and reliable method for assessing adequacy of ventilation in spontaneously breathing children weighing between 5.2 and 35 kg.

Anesthesia Recovery Period↗
PubMed1991

Scalp infiltration with bupivacaine in pediatric brain surgery.

To evaluate whether local anesthetic scalp infiltration blunts hemodynamic responses to craniotomy in anesthetized children (age, 2-18 yr), two concentrations of bupivacaine (0.125% and 0.25%) with vasoconstrictor (epinephrine 1:400,000) were compared with control data when a solution of vasoconstrictor alone was injected. Arterial plasma levels of bupivacaine were measured by high-pressure liquid chromatography. Statistically significant increases in mean arterial pressure and heart rate above baseline measurements occurred in the control group during the period between scalp incision and dural reflection (P less than 0.05). Both concentrations of bupivacaine prevented these increases. Mean arterial pressure and heart rate during scalp incision and scalp reflection were significantly higher in the control group than in both bupivacaine groups (P less than 0.05). Peak bupivacaine plasma levels (mean +/- SD) occurred either 5 or 10 min after infiltration and were significantly higher in the 0.25% group (0.48 +/- 0.31 microgram/mL) than the 0.125% group (0.14 +/- 0.13 microgram/mL) (P less than 0.05). These results suggest that bupivacaine infiltration blocks the hemodynamic response to craniotomy. A concentration of 0.125% bupivacaine with 1:400,000 epinephrine is as effective as 0.25% bupivacaine with 1:400,000 epinephrine at reducing the hemodynamic response to craniotomy. Because the lower concentration of bupivacaine produces lower blood levels, we recommend 0.125% bupivacaine with 1:400,000 epinephrine as a useful, safe adjunct to general anesthesia in children undergoing craniotomy.

Adolescent↗
PubMed1990

Accuracy of end-tidal PCO2 measurements using a sidestream capnometer in infants and children ventilated with the Sechrist infant ventilator.

To determine the accuracy of end-tidal PCO2 (PETCO2) measurements analyzed with a sidestream capnometer in infants and children whose lungs were ventilated with a Sechrist infant ventilator and an Ayre's t-piece, we compared PETCO2 measurements obtained from the proximal (PETCO2-p) and distal (PETCO2-d) ends of the tracheal tube to arterial PCO2 (PaCO2) in 37 healthy infants and children between 1.3 and 24.5 kg. Both PETCO2-p and PETCO2-d accurately approximated PaCO2, however, the mean (+/- SD) arterial to end-tidal PCO2 difference (delta(a-ET)PCO2) was significantly greater with proximal (1.27 +/- 1.54 mmHg) than with distal sampling (0.64 +/- 1.64 mmHg) (P less than 0.01). In the subgroup of patients who weighted less than 12 kg, the delta(a-ET)PCO2 using proximal gas sampling (1.94 +/- 1.29 mmHg) was also significantly greater than it was using distal sampling (0.74 +/- 1.31 mmHg) (P less than 0.001). We conclude that although statistically different, both proximal and distal estimates of PETCO2 provide acceptable estimates of PaCO2 in healthy infants and children who are ventilated with a Sechrist infant ventilator and an Ayre's t-piece system.

Carbon Dioxide↗
PubMed1990

End-tidal carbon dioxide measurements in critically ill neonates: a comparison of side-stream and mainstream capnometers.

To determine whether end-tidal PCO2 (PETCO2) measurements obtained with two infrared capnometers accurately approximates the arterial PCO2 (PaCO2) in critically ill neonates, simultaneous measurements of PETCO2 were obtained from the distal and proximal ends of the tracheal tube with a sidestream capnometer (Puritan Bennett/Datex--BP/D) and from the proximal end with a mainstream capnometer (Hewlett-Packard-HP) in 20 intubated neonates. Distal sidestream PETCO2 and mainstream PETCO2 correlated with the PaCO2 (r2 = 0.66 and 0.61, respectively) within the range of 26-57 mmHg PaCO2. However, proximal PETCO2 with the sidestream capnometer correlated very poorly (r2 = 0.09) with PaCO2. The slope of the least square regression line for the distal sidestream capnometer, 0.67, was significantly less than that for the mainstream capnometer, 0.78 but both were significantly greater than that for the proximal sidestream capnometer, 0.39 (P less than 0.05). The slope of the regression for the proximal sidestream capnometer did not differ significantly from horizontal. Insertion of the mainstream sensor for the HP capnometer significantly increased the transcutaneous CO2 when compared with preinsertion values. We conclude that both distal sidestream and mainstream capnometry provide accurate estimates of the PaCO2 in critically ill neonates.

Carbon Dioxide↗
PubMed1990

Anterior fontanel pressure and visual evoked potentials in neonates and infants undergoing profound hypothermic circulatory arrest.

To determine the effects of cardiopulmonary bypass with profound hypothermic circulatory arrest (PHCA) on anterior fontanel pressure (AFP) and visual evoked potentials (VEPs), 21 neonates and infants undergoing cardiopulmonary bypass (CPB) with PHCA for surgical correction of congenital heart defects were studied. Mean (+/- SD) minimum nasopharyngeal, esophageal, and rectal temperatures of 16.4 +/- 2.2, 11.2 +/- 2.7, and 17.7 +/- 1.9 degrees C, respectively, were achieved for a mean duration of PHCA of 51.6 +/- 18.7 min. AFP increased significantly above pre-CPB values for the first 21.7 +/- 8.1 min of rewarming. The duration of this increase in AFP was related logarithmically and directly to the product of the nasopharyngeal temperature (NPT) at the end of PHCA and the duration of PHCA (r2 = 0.82, P less than 0.0001). Nineteen of these patients had simultaneous monitoring of VEPs. The latency of both the N70 and P100 components of the VEPs increased as temperature decreased. The cerebral perfusion pressure was linearly and inversely related to the AFP (r2 = 0.72, P less than 0.01). The VEPs disappeared as a nasopharyngeal temperature (NPT) of 18.9 +/- 2.8 degrees C and reappeared after 21.9 +/- 8.8 min post-PHCA at an NPT of 32.8 +/- 1.4 degrees C. There was no significant difference between duration of increased AFP (20.9 +/- 8.1 min) and the duration of absence of VEPs during the post-PHCA period. The duration of increased AFP correlated linearly and directly with the duration of absence of VEPs (r2 = 0.84, P less than 0.005). These data demonstrate that transient neurophysiologic dysfunction occurs after PHCA. This dysfunction is related to the duration of elevation of the AFP and cannot be explained solely by a temperature effect.

Cardiopulmonary Bypass↗
PubMed1989

Pharmacokinetics of intravenous dantrolene in children.

To determine the pharmacokinetics of iv dantrolene and its metabolites in children, ten children 2-7 yr of age scheduled for minor elective surgery, were studied. After induction of anesthesia and tracheal intubation, dantrolene (2.4 mg/kg) was administered iv over 10.2 +/- 0.83 min. Venous blood samples (3 ml) were obtained 1, 5, 10, 20, and 30 min and 1, 2, 4, 8, 12, and 20 h after the dantrolene infusion. Whole blood concentrations of dantrolene, 5-hydroxydantrolene, and nitroreduced acetylated dantrolene were measured by high-performance liquid chromatography. The whole blood concentration of dantrolene decreased rapidly from a mean (+/- SD) of 6.03 +/- 0.93 microgram/ml 1 min after the end of the dantrolene infusion to 3.56 +/- 0.49 microgram/ml at 1 h. Between 1 and 4 h, the concentration of dantrolene either remained constant or increased slightly. Thereafter, the concentration of dantrolene decreased slowly with an elimination half-life (mean +/- SD) of 10.0 +/- 2.6 h. The mean (+/- SD) time for the concentration of dantrolene to decrease to 3.0 micrograms/ml was 6.55 +/- 2.88 h. The whole blood concentration of 5-hydroxydantrolene reached a maximum of 0.60 +/- 0.18 microgram/ml approximately 7 h after the dantrolene and decreased thereafter with an elimination half-life of 9.0 +/- 2.5 h. The concentration of nitroreduced acetylated dantrolene was below the limit for detection at all times. All children recovered without complications. Intravenous dantrolene, 2.4 mg/kg, produces safe and predictable blood concentrations in children similar to those reported in adults.

Child↗
PubMed1988

Anterior fontanelle pressure responses to tracheal intubation in the awake and anaesthetized infant.

In order to define the changes in intracranial pressure which occur during tracheal intubation in young infants, a Ladd transducer was used to monitor anterior fontanelle pressure (AFP) non-invasively in awake (group 1, n = 14) and anaesthetized (group 2, n = 10) infants during intubation of the trachea. Heart rate and systolic arterial pressure were also recorded. In quiet, undisturbed infants, AFP (mean +/- SEM) was similar in groups 1 (9.6 +/- 0.5 mm Hg) and 2 (8.7 +/- 0.8 mm Hg); with crying, AFP increased significantly in both groups. During laryngoscopy in group 1, AFP increased to 33.5 +/- 3.6 mm Hg, which was significantly greater than in the quiet infant, but did not differ significantly from measurements in the crying infant. In group 2, AFP increased significantly to 15.8 +/- 18 mm Hg during laryngoscopy. This increase was significantly less than the group 1 response. Neither heart rate nor systolic arterial pressure changed significantly in either group during laryngoscopy--when compared with measurements in the quiet state. It was concluded that AFP increases significantly during intubation and during crying in the infant. The response to intubation is only partially attenuated by the prior administration of general anaesthesia.

Anesthesia, General↗
PubMed1987

The effects of cardiopulmonary bypass and profound hypothermic circulatory arrest on anterior fontanel pressure in infants.

The Ladd transducer was used to measure anterior fontanel pressure in 23 infants undergoing cardiopulmonary bypass and profound hypothermic circulatory arrest for surgical correction of congenital heart disease. Mean (+/- SD) minimum oesophageal and rectal temperatures of 11.3 +/- 1.5 degrees C and 18.1 +/- 2.2 degrees C respectively were achieved with a mean duration of arrest of 53.4 +/- 13.9 minutes. During reperfusion cardiopulmonary bypass after circulatory arrest, mean anterior fontanel pressure (18.3 +/- 6.4 mmHg) increased above baseline pre-bypass values (10.6 +/- 2.9 mmHg) (p less than 0.005). Mean arterial blood pressure decreased significantly from pre-bypass values (57.0 +/- 11.8 mmHg) during both cooling (38.8 +/- 8.4 mmHg) and rewarming cardiopulmonary bypass (45.8 +/- 8.9 mmHg) (p less than 0.005). These changes were associated with a significant decrease in cerebral perfusion pressure during cooling (27.3 +/- 11.0 mmHg) and rewarming cardiopulmonary bypass (27.5 +/- 10.6 mmHg), compared with baseline pre-bypass values (46.5 +/- 12.3 mmHg) (p less than 0.005). The data demonstrate significant but transient decreases in cerebral perfusion pressure during cooling and rewarming bypass.

Cardiopulmonary Bypass↗
PubMed1987

End-tidal PCO2 measurements sampled at the distal and proximal ends of the endotracheal tube in infants and children.

To determine whether the site of gas sampling affects end-tidal gas measurements in pediatric patients, end-tidal PCO2 was measured continuously from the distal and proximal ends of the endotracheal tube in 60 infants and children ventilated with an Air-Shields Ventimeter and a partial rebreathing circuit. These data were compared with simultaneous arterial PCO2 measurements. In infants and children weighing greater than or equal to 12 kg, both distal and proximal end-tidal PCO2 values approximated arterial PCO2 measurements. In infants and children weighing less than 12 kg, however, only distal end-tidal PCO2 measurements approximated arterial PCO2 measurements. It is concluded that in infants and children weighing less than 12 kg, accurate end-tidal measurements can be obtained only from the distal end of the endotracheal tube.

Body Weight↗
PubMed1986

Neuromuscular blockade for rapid tracheal intubation in children: comparison of succinylcholine and pancuronium.

To compare the effectiveness of succinylcholine and pancuronium for rapid intubation in children, 49 healthy children ages two to eight years were studied. After induction of anaesthesia with thiopentone and atropine, and administration of droperidol, fentanyl, nitrous oxide, and oxygen, each child received one of the following muscle relaxants: succinylcholine 1.5 mg X kg-1 (n = 12), succinylcholine 1.0 mg X kg-1 (n = 13), pancuronium 0.15 mg X kg-1 (n = 11), or pancuronium 0.10 mg X kg-1 (n = 13). The force of thumb adduction was measured by stimulating the ulnar nerve with repetitive supramaximal single twitches (0.15 Hz). The time to 95 per cent twitch depression (mean +/- S.D.) was most rapid with succinylcholine 1.5 mg X kg-1 (40.8 +/- 3.0 seconds) and succinylcholine 1.0 mg X kg-1 (51.8 +/- 14.0 seconds), slowest with pancuronium 0.10 mg X kg-1 (150.9 +/- 38.0 seconds), and intermediate with pancuronium 0.15 mg X kg-1 (80.3 +/- 21.8 seconds) (p less than 0.005). The intubating conditions were excellent in 100% of the children who received succinylcholine 1.5 and 1.0 mg X kg-1, and pancuronium 0.15 mg X kg-1, but were excellent in only 69 per cent of those who received pancuronium 0.10 mg X kg-1. We conclude that succinylcholine 1.5 mg X kg-1 produces the most rapid onset of excellent intubating conditions in children. In children in whom succinylcholine is contra-indicated, pancuronium 0.15 mg X kg-1 provides excellent intubating conditions within 80 seconds.

Child↗
PubMed1986

Anesthesia for pediatric neurological and neuromuscular diseases.

Children with neurological and neuromuscular diseases often present anesthetic problems in the perioperative period. The anesthetic technique can play a significant role in altering the state of the brain during neurosurgical procedures through effects on the cerebral circulation and metabolism. Pre-existing neuromuscular disease may also have specific anesthetic implications such as cardiorespiratory involvement (eg, myotonia dystrophica), the potential for drug interactions (eg, myasthenia gravis) or abnormal responses to commonly used drugs (eg, malignant hyperthermia). In this review, the perioperative anesthetic considerations in a number of common neurological and neuromuscular conditions in the pediatric patient are discussed.

Anesthesia, General↗