Nishan G. Goudsouzian

Life-threatening Apnea in Infants Recovering from Anesthesia

To determine whether prematurely born infants with a history of idiopathic apneic episodes are more prone than other infants to life-threatening apnea during recovery from anesthesia, the authors prospectively studied 214 infants (173 full term, 41 premature) who received anesthesia. Fifteen premature infants had a preanesthetic history of idiopathic apnea. Six of these required mechanical ventilation because of idiopathic apneic episodes during emergence from anesthesia. Two were ventilated for other reasons, and seven recovered normally. Infants ventilated for apnea were younger (postnatal age 1.6 +/- 1.2 months, mean +/- SD; conceptual age 38.6 +/- 3.0 weeks) than those who recovered normally (postnatal age 5.6 +/- 2.7 months; conceptual age 55.1 +/- 11.3 weeks) (P less than 0.01). No other premature or full-term infant was ventilated because of postoperative apneic episodes. The authors conclude that anesthetics may unmask a defect in ventilatory control of prematurely born infants younger than 41-46 weeks conceptual age who have a preanesthetic history of idiopathic apnea.

Radiologic Localization of the Laryngeal Mask Airway in Children

In the absence of data on the anatomic localization of the cuff of the laryngeal mask airway (LMA) in children, radiologic images were obtained from 50 infants and children (aged 1 month to 15 yr) undergoing diagnostic radiologic procedures during halothane and N2O:O2 anesthesia. In 46 patients, the cuff of the LMA was in the pharynx and covered the laryngeal opening. The upper (proximal) section was adjacent to the base of the tongue at the level of C1 or C2 vertebrae pushing the tongue forward and its lower (distal) end was in the inferior recesses of the hypopharynx at the levels of C4 to T1 vertebrae. The cuff of LMA at this position between the base of the tongue above the epiglottis and below the laryngeal opening, covered the laryngeal aperture, forming a low pressure seal at the entrance of the larynx. In 37 of these 46 patients, a posterior deflection of the epiglottis was noted (< 45 degrees), and in only 9, the epiglottis was in the anatomic position. In four patients, the cuff of the LMA was located in the oropharynx. No correlation was found between the size of the LMA and the position of the epiglottis with respect to end-tidal CO2, respiratory rate, or the leak pressures. The size of the LMA, its anatomic location, and the position of the epiglottis had no significant effect on the respiratory parameters of spontaneously breathing children.

Prolonged Neuromuscular Block from Mivacurium in Two Patients with Cholinesterase Deficiency

M ivacurium’s short duration of action, like the ultra-short action of succinylcholine, is due to its rapid hydrolysis by plasma cholinesterase (ChE); an inverse relationship has been found between ChE activity and the duration of action of mivacurium in phenotypically normal patients (1). Reports of prolonged paralysis from succinylcholine in the presence of ChE deficiency have been reported (2), and there has been a case report of prolonged mivacurium block in a patient with dermatomyositis and muscle weakness (3). The following two incidents of prolonged paralysis occurred during the evaluation phases of mivacurium; they were seen in separate institutions and managed with different approaches.

Intraoperative events diagnosed by expired carbon dioxide monitoring in children

Expired carbon dioxide measurements (PECO2) were used (1) to assess the adequacy of initial alveolar ventilation, and (2) to document intraoperative airway events and metabolic trends. Three hundred and thirty-one children were studied. Thirty-five intraoperative events were diagnosed by continuous PeCO2 monitoring; 20 were potentially life-threatening problems (malignant hyperthermia, circuit disconnection or leak, equipment failure, accidental extubation, endobronchial intubation, or kinked tube); only two of these were also diagnosed clinically. The duration of anaesthesia may be a factor: 3.9 hours for cases with events vs. 2.5 hours for cases without events (p < 0.002). There was a higher incidence of hypercarbia (peak expired PeCO2≥ 50) in children who were not intubated (29 per cent) compared to those who had an endotracheal tube in place (12 per cent) (p = 0.0001). Hypocarbia (peak expired PeCO2≤30) was more frequent in intubated cases (11 per cent) than in unintubated cases (three per cent) (p = 0.03). There was a high incidence of hypocarbia in infants less than one year of age (p = 0.02). We conclude: (1) lifethreatening airway problems are common during anaesthesia in paediatric patients; (2) quantitative measurement of PECO2 provides an early warning of potentially catastrophic anaesthetic mishaps; (3) the incidence of events increases with duration of anaesthesia.RésuméL’6tude du CO2 en fin dexpiration (PeCO2) a été utilisée afin d’évaluer (1) la fonction respiratoire initiate et (2) pour documenter les événemenls per-opératoires touchant les voies aériennes ainsi que les changements métaboliques. 331 enfants ont été étudiés. 35 événements per-opératoires ont été diagnostiqués par une surveillance constante de la PeCO2; 20 représentaient des problèmes mettant en danger la vie (hyperthermie maligne, disconnection de circuit, fuite, bris d’équipement, extubation accidentelle, intubation endobronchique, ou tube endotrachéal coudd); seulement deux de ces événements ont été aussi diagnostiqués cliniquement. La durée de l’anesthésie pouvait aussi être un facteur: les présentants les accidents ont duré en moyenne 3.9 heurs contre 2.5 heures pour les cas n’ayant pas présenté de problèmes (p < 0.002). Il y avait un incidence plus élevée d’hypercarbie (PECO2 ≥ 50,) chez les enfants qui n’étaient pas intubés (29 pour cent) a comparé à ceux dont le tube endotrachéal élail en place (12 pour cent) (p = 0.0001). L’hypocarbie (PeCO2 ≤ 30) était plus fréquente chez les patients intubés (11 pour cent) que chez ceux qui n’étaient pas intubés (trois pour cent) (p = 0.03). It y avait une incidence plus grande d’hypocarbie chez les enfants âgés de moins qu’un an (p = 0.02). On colclut: 1) les problemes de voies aeriennes pouvant mettre en danger la vie sont fréquents lors de I’anesthésie pédiatrique; 2) la mesure quantitative de la PeCO2 fournie un signal d’alarme précoce pour les accidents anesthésiques potentiellement catastrophiques; 3) l’incidence des accidents augmente avec le temps.

End-tidal CO2 monitoring. Its use in the diagnosis and management of malignant hyperthermia

Two cases of malignant hyperthermia are described where the earliest sign was a rise in the end-tidal CO2 concentration. This led to nearly immediate detection and adequate treatment with sodium dantrolene. These cases demonstrate the efficacy of monitoring end-expired CO2 concentrations in patients at risk from malignant hyperthermia, as well as a means for following the adequacy of treatment.

Clinical Pharmacology of Muscle Relaxants in Patients With Burns

Pathophysiologic changes accompanying burn trauma can alter the pharmacokinetics and pharmacodynamic responses to neuromuscular relaxants. Pathophysiologic changes that can potentially affect kinetics in the hypermetabolic phase of burn injury include increased hepatic blood flow, increased glomerular filtration, and increased protein binding. Except for d‐tubocurarine, the pharmacokinetics of neuromuscular relaxants relative to burn trauma have not been studied. The unbound volume of distribution, clearance, and half‐life of d‐tubocurarine were not significantly different from controls, but the plasma binding and renal elimination at 24 hours was increased in burn patients. The aberrant pharmacodynamic responses to neuromuscular relaxants in burn patients include the potential for lethal hyperkalemia with the administration of depolarizing relaxant, succinylcholine, and a 2.5‐ to 5.0‐fold increase in the dose or plasma concentration requirement for nondepolarizing relaxant, including d‐tubocurarine, metocurine, pancuronium, and atracurium. The altered pharmacodynamic responses are probably related to an increase in nicotinic acetylcholine receptor number. An alternative to succinylcholine to produce rapid‐onset neuromuscular paralysis include the administration of 3XED95 doses of pancuronium and metocurine in combination (but recovery from paralysis is prolonged). Vecuronium and atracurium have good cardiovascular stability and faster recovery times even in high dosages in healthy patients, but the pharmacokinetics and pharmacodynamics of these drugs in patients with burns have not been fully characterized.

Re-evaluation of dosage and duration of action of d-tubocurarine in the pediatric age group.

A cumulative dose-response curve for d-tubocurarine based on body weight was determined for 44 infants and children 1 day to 7 years of age during halothane, nitrous oxide and oxygen anesthesia. Depression of thumb adduction was measured. Age difference did not affect the mean dose-effect response. Infants less than 10 days old, however, showed the widest deviation of responses. When the effect of d-tubocurarine is determined by twitch response, infants and children are more resistant to d-tubocurarine and recover faster than adults from similar levels of neuromuscular depression. Monitoring of neuromuscular function by train-of-four stimulation proved as useful as it is in adults.

The Dose-Response Effects of Oral Cimetidine on Gastric pH and Volume in Children

The effects of preanesthetic oral cimetidine on gastric fluid pH and volume were studied in 97 infants and children. A dose-response curve was constructed using doses of 2.5, 5.0, 7.5, and 10 mg/kg. The ED50 of cimetidine that produces pH values higher than 2.5 was 3.0 mg/kg, and the ED95 was 7.5 mg/kg. Cimetidine exponentially reduced the volume of gastric fluid. Cimetidine was most effective between one and four hours after oral administration. In children who are at high risk of pulmonary aspiration, we recommend that oral cimetidine, 7.5 mg/kg, be given 1-3 hours preoperatively in order to protect the lungs from the accidental aspiration of acidic gastric secretions.

The use of the laryngeal mask airway in children with bronchopulmonary dysplasia.

Airway maintenance with the laryngeal mask airway (LMA) was evaluated and compared to the endotracheal (ET) tube in 27 former premature infants and children with bronchopulmonary dysplasia (BPD) during second stage open-sky vitrectomy. The children were randomly assigned to a study group and anesthetized with halothane in N2 O:O2. The airway was maintained with the LMA (n = 13) or the ET tube (n = 14). Respiratory and hemodynamic variables were recorded. Intraoperative and postoperative complications were noted. The respiratory rate and the end-tidal CO (2) were significantly higher in the LMA group as compared with the ET tube group (P < 0.01); however, the pulse rate and both systolic and diastolic blood pressures throughout the surgical procedure were lower in the LMA group (P < 0.05). The incidence of coughing, with and without desaturation, wheezing, and hoarseness in the postoperative period was higher in the ET tube group. Awakening, after discontinuation of the anesthetic (P < 0.01) was more rapid, and home discharge time (P < 0.002) was shorter in the LMA group (P < 0.0025), although our study design could not isolate the use of the LMA as the factor responsible for this. This study in patients with mild chronic lung disease demonstrated that the LMA can maintain a satisfactory airway during minor surgical procedures in children with bronchopulmonary dysplasia and result in fewer respiratory adverse effects than with the ET tube. (Anesth Analg 1995;81:310-3)

End‐tidal CO2 monitoring

Two cases of malignant hyperthermia are described where the earliest sign was a rise in the end‐tidal CO, concentration. This led to nearly immediate detection and adequate treatment with sodium dantrolene. These cases demonstrate the efficacy of monitoring end‐expired CO2 concentrations in patients at risk from malignant hyperthermia, as well as a means for following the adequacy of treatment.