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Biomedical subjects

G A Gregory

Publications and source records attributed to G A Gregory.

At least 73 records · Page 4Linked to original sources
PubMed1983

Anesthetic requirements for halothane in young children 0-1 month and 1-6 months of age.

In a previous study, the authors found that infants, in the first 6 months of life, required the highest minimum alveolar concentration (MAC) of any age group (1.09% halothane). Because only two neonates (0-31 days of age) were included in the original study and because profound depression of blood pressure and heart rate have been reported in neonates, the authors determined 1) whether the MAC of halothane in neonates (n = 12) differs from that in infants (1-6 months of age) (n = 12) and 2) whether the blood pressure and heart rate responses in neonates differ from those in infants at approximately 1 MAC. The authors found that the MAC of halothane in neonates, 0.87% +/- 0.03 SEM, was significantly lower (P less than 0.01) than that in infants, 1.20% +/- 0.06 SEM. With induction of anesthesia, the systolic blood pressure decreased 23% in neonates (P less than 0.05) and 34% in infants (P less than 0.005) from awake values. Similarly, the heart rate decreased 12% in neonates and 22% in infants (P less than 0.05). The incidence of hypotension (greater than 30% decrease in systolic blood pressure from awake) in neonates, 33%, was not significantly different from that in infants, 44%. The authors conclude that the MAC of halothane in neonates is 25% less than that in infants and significantly less than was thought previously. The MAC in infants is the highest of any age group. The decrease in blood pressure and the incidence of hypotension in neonates are similar to those in infants at approximately 1 MAC of halothane.

Age Factors↗
PubMed1983

Osmolarity determines the solubility of anesthetics in aqueous solutions at 37 degrees C.

The authors determined whether they could predict accurately the solubility of anesthetics in aqueous solutions at 37 degrees C, knowing the osmolarity and the pH of the solution and the solute composition. The partition coefficients of the four volatile anesthetics, isoflurane, enflurane, halothane, and methoxyflurane, were determined concurrently at 37 degrees C between air and aqueous solutions containing sodium chloride, dextrose, mannitol, or heparin. The osmolarities of these solutions ranged from 0 to 7,000 mOsm/l. The partition coefficients decreased linearly with increasing osmolarity when plotted on a semilogarithmic scale. The effect of osmolarity on the partition coefficient of the alkane anesthetic, halothane, was 20% less (P less than 0.001) than the effect of osmolarity on the partition coefficients of the three methyl-ethyl ether anesthetics, isoflurane, enflurane, and methoxyflurane. The solubility of anesthetics in aqueous solutions did not depend on either the molecular structure of the solute or the pH of the solution. The solubility of volatile anesthetics in aqueous solutions at 37 degrees C is inversely and predictably dependent on the osmolarity of the solutions.

Anesthetics↗
PubMed1983

A respiratory function jacket for measuring tidal volume and changes in FRC.

We describe a simple application of a mercury-in-rubber strain gauge in a jacket used to measure tidal volume in paralyzed, mechanically ventilated rabbits. The jacket produces a record with a straight base line. Shifts of this base line can be used to assess changes in functional residual capacity (FRC).

Animals↗
PubMed1983

Fetal anesthetic requirement (MAC) for halothane.

We asked whether the anesthetic requirement (MAC) of fetal lambs is lower than that of pregnant ewes. In five pregnant ewes anesthetized with a subarachnoid block, a fetal foot was withdrawn through a hysterotomy. The ewe then breathed 1.5% halothane and a clamp was applied to the fetal foot at 2-min intervals. We concomitantly obtained arterial blood from previously implanted catheters. When fetal movement in response to clamping the foot ceased, halothane was discontinued and the stimulus and sampling continued until the fetus began to move. Anesthesia was again resumed and continued until movement stopped. Anesthesia was then deepened and MAC was determined in the mother (stimulus--ear clamp). The fetal blood concentrations of halothane at MAC were 48 +/- 28 mg/L; they were 133 +/- 5 mg/L in the mother. This difference was highly significant (P less than 0.001). Calculated end-tidal concentrations were 0.33% and 0.69%, respectively. In two animals delivered by cesarean section, MAC increased progressively over the first 12 h of life. Progesterone levels concomitantly decreased.

Animals↗
PubMed1982

The baroresponses of preterm infants during halothane anaesthesia.

Anaesthetics depress the baroresponse of adults. If the same is true of infants, they will have difficulty maintaining their cardiac output if they become hypotensive because they are primarily rate dependent for cardiac output. The opportunity to test whether anaesthetics depress the baro-response of neonates arose while anaesthetizing preterm infants for ligation of patent ductus arteriosus. The relationship between heart rate and the systolic blood pressure (baroresponse) was examined in 53 preterm infants (1,065 +/- 205 g) receiving 0.5-1.0 per cent inspired halothane for ligation of patent ductus arteriosus. The arterial pressure was measured by indwelling catheters and strain gauges (43 patients) or a doppler device (10 patients). Heart rate was measured with skin electrodes. The relationship between heart rate and systolic pressure was examined before and after the induction of anaesthesia and before and after ligation of the ductus. Just before ligation of the ductus arteriosus the systolic blood pressure had decreased 33 per cent from awake control values without a change in heart rate. Five minutes after the ductus was ligated the arterial pressure had increased 38 per cent, again without a change in heart rate. The differences between systolic pressures was highly statistically significant in both instances (P less than 0.001). The differences between heart rate were not. These data indicate a lack of baroresponse in these preterm infants during light halothane anesthesia which may alter their ability to maintain cardiac output when hypotensive.

Anesthesia↗
PubMed1982

The effect of halothane on the baroresponse of adult and baby rabbits.

The effect of anesthesia on the baroresponse of infants is not known. Therefore, the authors studied the baroreceptor activity of adult and 10- to 14-day-old rabbits during halothane anesthesia. The arterial systolic pressure was increased 20 to 30 per cent by injecting 0.03-0.04 mg/kg of phenylephrine into the femoral or external jugular vein while recording the electrocardiogram and femoral arterial blood pressure. The slope of the R-R interval on systolic pressure (baroresponse) was determined. The studies were done in the awake, unmedicated state and at 0.5, 1.0, and 1.5 MAC halothane. Oxygen was the carrier gas. The sensitivity of the response was different in the two groups of animals. When awake, the adults' slope was greater than that of the babies. During anesthesia the slopes decreased in both groups, but the decrease was greater in the babies. At 0.5 MAC halothane, the baroresponse was reduced 80 and 54 per cent in baby and adult rabbits, respectively. Lag time (the time between the onset of the rise in systolic blood pressure and the change in R-R interval) was prolonged in both the babies and the adults. Both showed the same prolongation during anesthesia, although the percentage change in the babies was greater.

Aging↗
PubMed1982

Pharmacokinetics and pharmacodynamics of d-tubocurarine in infants, children, and adults.

The pharmacokinetics and pharmacodynamics of d-tubocurarine (dTc) were determined in neonates (0-2 months, n = 7), infants (2-12 months, n = 7), children (1-12 years, n = 9), and adults (12-30 years, n = 8) during 70% nitrous oxide, 0.58 MAC halothane anesthesia. dTc was administered by infusion, while blood for determination of plasma dTc concentrations was obtained, and the EMG of the adductor pollicis recorded. The plasma dTc concentration at which 50% depression of EMG twitch height occurs (Cpss(50)) was 0.18 +/- 0.09 micrograms/ml in neonates, and 0.27 +/- 0.06 micrograms/ml in infants, both significantly lower than the values of 0.42 +/- 0.14 and 0.53 +/- 0.14 micrograms/ml for children and adults, respectively. The steady-state distribution volume (Vdss) was 0.74 +/- 0.33 l/kg in neonates, significantly greater than the values of 0.52 +/- 0.22, 0.41 +/- 0.12, and 0.30 +/- 0.10 l/kg in infants, children, and adults, respectively. The elimination half-life (t beta 1/2) was 174 +/- 60 min in neonates, significantly longer than the values of 90 +/- 23 and 89 +/- 18 min in children and adults, respectively. Plasma clearance did not differ with age. We also determined D50, the product of Vdss and Cpss(50). D50, the quantity of drug present at steady-state to produce 50% paralysis, did not differ between groups. The authors conclude that during comparable nitrous oxide-halothane anesthesia, neonates and infants have an increased sensitivity to dTc, as determined by CPss(50). However, because of the larger Vdss in younger patients, dose size should not differ with age. In addition, because of the longer t beta 1/2 in neonates, second and subsequent doses should be required at less frequent intervals.

Adolescent↗
PubMed1981

The independent effects of hyperventilation, tolazoline, and dopamine on infants with persistent pulmonary hypertension.

We studied the separate and combined effects of hyperventilation and administration of dopamine and tolazoline in five infants with pulmonary hypertension managed with indwelling pulmonary artery catheters. In five infants the right-to-left shunt reversed during ventilator-induced respiratory alkalosis (pH greater than 7.6). Response to drugs was variable and unpredictable. One infant could be oxygenated at normal pH during combined dopamine and tolazoline infusion. Other infants showed no response to drugs, or became worse during infusion. The ratio of pulmonary artery to systemic artery pressure averaged 1.14 with standard therapy, but decreased to 0.98 following respiratory alkalosis alone, to 0.87 following drug infusions, and to 0.70 following the combination of alkalosis and drug infusion. These changes were significant by analysis of variance at P less than 0.02, P less 0.001, and P less than 0.001, respectively. Systemic oxygenation was satisfactory in all cases when the pulmonary to systemic pressure ratio was less than 1.0.

Alkalosis, Respiratory↗
PubMed1981

Colloid osmotic pressure of normal newborns and premature infants.

Colloid osmotic pressure (COP) is an important regulator of fluid movement and can now be measured simply and reliably. The authors used the 4100 Wescor Colloid Osmometer to define COP values and its relation to total protein concentration (TP) in different groups of newborns. The mean COP was 19.4 +/- 2.2 (SD) torr in 99 term infants delivered vaginally and 16.0 +/- 2.1 in 40 term infants delivered by cesarean section (p less than 0.005). The COP was lower in those born operatively without preceding labor (14.9 +/- 1.8). COP correlated well with TP (r = 0.92) in term infants. In 60 sick preterm infants with 362 determinations, COP (12.5 +/- 2.5) was different from term infants (p less than 0.001) and the correlation with TP was poor (r = 0.64). Different therapeutic modalities were found to affect COP widely. Crystalloid infusion decreased COP by 22% and surgery by 32%. The authors conclude that COP varies not only with gestational age but also with mode of delivery and experience of labor. In critically ill preterm neonates, because estimations form TP are inadequate, the only way to obtain a quantitative measure of COP is by direct measurement. Repeated measurements of COP will permit precise selection of the fluids and will warn of changes that may lead to pulmonary edema.

Asphyxia Neonatorum↗
PubMed1981

Performance of neonatal ventilators: the effects of changes in resistance and compliance.

The authors tested the ability of 6 neonatal ventilators (Baby bird, Bourns BP-200, Veriflo, Bourns LS, ServoVent, SI-75) to deliver a preset tidal volume with minimal pressures when the compliance and resistance of test lung were altered. The authors also studied the effects of gas leaks from the system and the effects of PEEP. When the ventilator cycling rates exceeded 28-43/min, gas trapping occurred despite compliances and resistance appropriate for a healthy term infant. With a normal compliance and an elevated resistance, gas trapping occurred above rates of 4-6/min. Under these same conditions (normal compliance, elevated resistance), only 24-46% of the preset tidal volume was delivered. The different ventilators caused the pressure within the test lung to exceed 5, 10, and 15 cm H2O for differing amounts of time (sec)/min.

Airway Resistance↗
PubMed1981

Fentanyl-air-oxygen anesthesia for ligation of patent ductus arteriosus in preterm infants.

In 10 premature infants (1123 +/- 263 g), fentanyl citrate (30 to 50 microgram/kg) was used in conjunction with pancuronium (0.1 mg/kg) as the sole anesthetic for transthoracic ligation of patent ductus arteriosus. Ventilation was controlled with air and oxygen in concentrations sufficient to maintain transcutaneous PO2 between 50 and 70 torr. Circulatory stability was easily maintained throughout the procedure. "Stiff chest" was avoided by the use of muscle relaxants, and the infants were awake within 1 hour after the procedure.

Air↗