Atracurium, vecuronium, and intraocular pressure in humans.

We studied 60 nonophthalmologic patients, allocated to six treatment groups, to assess the effects of atracurium and vecuronium on intraocular pressure (IOP). All patients had IOP measured while awake, using pneumotonometry. In group 1, anesthesia was induced with thiopental, 5 mg/kg, and maintained with N2O, 70% in O2, using controlled mask ventilation, for 5 min. These patients then received atracurium, 0.5 mg/kg. After 5 additional minutes of ventilation, the trachea was intubated. From 1 min after thiopental administration until 1 min after intubation, IOP was recorded every minute. Patients in groups 2, 3, and 4 were treated identically to those in group 1, except the muscle relaxant given was atracurium, 1.0 mg/kg, vecuronium, 0.1 mg/kg, or vecuronium, 0.2 mg/kg, respectively. Patients in groups 5 and 6 underwent rapid sequence induction with thiopental, 5 mg/kg, and atracurium, 1.0 mg/kg, or vecuronium, 0.2 mg/kg, respectively. IOP was measured 1 min later, followed by intubation and IOP measurements for the next 3 min. Intraocular pressure decreased significantly in groups 1, 2, 4, and 6 after thiopental and remained stable in all groups during ventilation with N2O. Neither atracurium nor vecuronium affected IOP, nor was there any correlation between IOP and degree of neuromuscular blockade. However, IOP increased significantly after intubation in all six groups. We conclude that atracurium or vecuronium alone has no adverse effects on IOP.

The heart is under the lower third of the sternum. Implications for external cardiac massage.

Current guidelines for cardiopulmonary resuscitation in children state that the heart lies under the midsternum in infancy and descends with age. To verify this statement, we studied 55 patients, aged 1 day to 19 years, including eight premature infants, during either routine chest x-ray films or right-sided heart angiography. Using a Cartesian coordinate system determined by radiopaque markers placed on the chest, and computer digitization, we located the center of each patient's cardiac silhouette and/or right ventricle. Using descriptive statistics, we found that the heart lay under the lower third of the sternum in all age groups. Analysis of variance indicated that there was no significant difference in this location between age groups. These results suggest that recommendations for external cardiac massage in infants and children may need to be revised.

Endotracheal tube leak pressure and tracheal lumen size in swine.

Endotracheal tube "leak" is often estimated in children to judge the fit of uncuffed endotracheal tubes within the trachea. Twenty-five swine were intubated with uncuffed tracheal tubes to determine whether a more sensitive measurement of leaks could be devised and whether leak pressure estimates fit between tracheal tube and trachea. We compared leak pressure measurement using a stethoscope and aneroid manometer with a technique using a microphone, pressure transducer, and recorder, and found no differences between the two methods. The tracheas were then removed and slides prepared of tracheal cross-sectional specimens. Regression analysis revealed a linear relationship between tracheal lumen size and tracheal tube size for both low leak pressure (y = -0.4 + 0.79x, r = 0.88, P less than 0.05) and high leak pressure (y = -2.9 + 0.71x, r = 0.92, P less than 0.05) groups. We conclude that leak testing with a stethoscope and aneroid manometer is sensitive and accurate, and that tracheal tube leak pressure accurately portrays fit between tube and trachea.

Lidocaine pharmacokinetics in children during general anesthesia.

In spite of the increasing use of intravenous lidocaine in the operating room, no pharmacokinetic data exist for intravenous lidocaine in children. We studied ten children, ages 0.5-3 yr, and eight adults to determine lidocaine pharmacokinetics during anesthesia with halothane, nitrous oxide, and oxygen. After induction of anesthesia, tracheal intubation, and insertion of venous and arterial catheters, lidocaine, 1 mg/kg, was infused intravenously over 30 sec. Arterial samples were drawn at 0.5, 1, 2, 4, 5, 10, 15, 30, 60, 90, and 120 min. Plasma was separated and analyzed for lidocaine, using gas chromatography. Plasma concentration vs time data were fitted to a two-compartment model. Using standard formulas, we derived the following data: Children: distribution half-life (t 1/2 alpha) 3.2 min, elimination half-life (t 1/2 beta) 58 min, volume of the central compartment (V1) 0.22 L/kg, volume of distribution (Vd area) 1.1 L/kg, and total plasma clearance (Cl) 11.1 ml X kg-1 X min-1. Adults: t 1/2 alpha 3.6 min, t 1/2 beta 43 min, V1 0.16 L/kg, Vd area 0.71 L/kg, and Cl 9.8 ml X kg-1 X min-1. No significant differences were found between children and adults for all parameters analyzed. We conclude that children older than 6 months of age distribute and eliminate intravenous lidocaine in the same manner as adults.

Anaesthetic management of a child with dermatomyositis.

A two years, ten months old male with dermatomyositis was anaesthetized with enflurane, nitrous oxide and oxygen by mask followed by intravenous succinylcholine to facilitate endotracheal intubation. The evoked thumb twitch in response to succinylcholine demonstrated an abnormal, short-lived contracture. The depression, duration and return to control of muscle twitch tension and a transient rise in serum potassium concentration followed a normal pattern.

Factors affecting leak around tracheal tubes in children.

This study determined which variables affected endotracheal tube "leak" pressures in 80 surgical patients, two weeks to 11 years of age, intubated with uncuffed tracheal tubes. We defined "leak" pressure as the inspiratory pressure needed to cause an audible escape of gas around the endotracheal tube. "Leak" pressure was measured after varying either head position, tracheal tube depth within the trachea, fresh gas flow rate, or degree of neuromuscular block. "Leak" pressure increased progressively from 16.9 +/- 1.3 cmH2O with complete patient paralysis to 30.6 +/- 1.4 cmH2O following 100 per cent recovery of neuromuscular function. Turning the head from a neutral position to one side increased "leak" pressure from 14.7 +/- 1.7 cmH2O to 24.4 +/- 2.5 cmH2O. Varying tracheal tube depth or fresh gas flow rate produced no significant change in "leak" pressure. Thus, there may be marked variability in "leak" pressure, depending on head position and degree of neuromuscular blockade. Keeping the patient fully paralyzed with the head in a neutral position provides a reliable and consistent method for measuring "leak" pressures.

Heart block after intravenous lidocaine in an infant.

A 14-day-old infant received intravenous lidocaine (2 mg X kg-1) at the conclusion of cataract surgery to prevent coughing from tracheal tube stimulation. Within 30 seconds the infant developed high-grade AV heart block and a ventricular rate of 40. Following brief resuscitation efforts, the patient had a normal cardiac rhythm, blood pressure and respiratory pattern. Intravenous lidocaine may be followed by major disturbances in cardiac rhythm and rate. Cautious titration of small doses should decrease the potential for adverse effects.