Philip L. Liu

A clinical sign to predict difficult tracheal intubation; a prospective study

It has been suggested that the size of the base of the tongue is an important factor determining the degree of difficulty of direct laryngoscopy. A relatively simple grading system which involves preoperative ability to visualize the faucial pillars, soft palate and base of uvula was designed as a means of predicting the degree of difficulty in laryngeal exposure. The system was evaluated in 210 patients. The degree of difficulty in visualizing these three structures was an accurate predictor of difficulty with direct laryngoscopy (p < 0,001).RésuméIl a été suggéré que la grosseur de la base de la langue est un facteur important dans la détermination du degré de difficulté de la laryngoscopie directe. Un système relativement simple de classification impliquant la capacité pré-opératoire de visualiser les piliers du voile du palais, le voile du palais et la base de la luette a été conçu afin de prédire le degré de la difficulté d’ exposition du larynx. Ce système a été évalué chez 210 patients. On a trouvé que le degré de difficulté encourue lors de la visualisation de ces trois structures était un moyen précis pour prédire la difficulté de la laryngoscopie directe (p < 0.001).

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.

Acute cardiovascular toxicity of intravenous amide local anesthetics in anesthetized ventilated dogs.

The acute intravenous cardiovascular toxicity of five amide local anesthetic agents was studied in intact, ventilated dogs anesthetized with pentobarbital. Minimal changes in various cardiovascular functions were seen at doses of 0.3 to 3.0 mg/kg. At 10 mg/kg profound hypotension accompanied by significant decreases in cardiac output and stroke volume were observed with etidocaine and bupivacaine. At this dose lidocaine, mepivacaine, and prilocaine produced moderate signs of cardiovascular depression. Myocardial depression appeared to be primarily responsible for the profound hypotension, as minimal changes in peripheral vascular resistance occurred except as a terminal event. Pulmonary vascular resistance tended to increase before myocardial depression, suggesting a pulmonary vasoconstrictor action of the anesthetics. The cumulative lethal dose varied from appproximately 80 mg/kg for lidocaine and mepivacaine to 40 mg/kg for etidocaine and 20 mg/kg for bupivacaine. The acute cardiovascular toxicity of these agents is proportional to their comparative in vivo anesthetic potency which indicates little difference in therapeutic ratio between the various amide local anesthetics.

Comparative CNS toxicity of lidocaine, etidocaine, bupivacaine, and tetracaine in awake dogs following rapid intravenous administration

The comparative central nervous system (CNS) toxicity of serially administered intravenous doses of lidocaine, bupivacaine, etidocaine, and tetracaine was investigated in awake dogs. The mean cumulative dose required for convulsive activity was 4.0 mg/kg tetracaine, 5.0 mg/kg bupivacaine, 8.0 mg/kg etidocaine, and 22.0 mg/kg lidocaine. The cumulative convulsive dose of lidocaine was significantly greater than that of the other three agents (P < 0.01). A comparison of the in vivo anesthetic potency and the acute CNS toxicity of these various agents suggests little difference in the therapeutic ratio between less potent anesthetics such as lidocaine and more potent drugs, i.e., tetracaine, bupivacaine, and etidocaine. The relative CNS toxicity of the different agents as determined in awake dogs in this study was compared with their relative cardiovascular toxicity previously evaluated in a series of ventilated dogs anesthetized with pentobarbital. The dose of lidocaine, etidocaine, tetracaine, and bupivacaine required to produce irreversible cardiovascular depression was 3.5–6.7 times greater than that which produced convulsions. These results suggest that the CNS is the primary target organ for the toxic effects of both highly lipid-soluble and highly protein-bound local anesthetics (i.e., bupivacaine, etidocaine, and tetracaine) and less lipid-soluble and less protein-bound drugs (i.e., lidocaine) following rapid intravenous administration.

Esmolol for control of increases in heart rate and blood pressure during tracheal intubation after thiopentone and succinylcholine

Esmolol, an ultra-short-acting cardioselective betaadrenergic blocker, was investigated in a double-blind prospective protocol for its ability to control haemodynamic responses associated with tracheal intubation after thiopentone and succinylcholine. Thirty ASA physical status I patients received a 12-minute infusion of esmolol (500 µg·kg-1·min-1 for four minutes, then 300 µg·kg-1 min-1 for 8 mnutes) or saline. Five minutes after the start of the drug/placebo infusion, anaesthesia was induced with 4 mg·kg-1 thiopentone followed by succinylcholine for tracheal intubation. Prior to induction esmolol produced significant decreases in heart rate (HR) (9.3 ± 1.8 per cent) and rate-pressure product (RPP) (13.1 ± 1.8 per cent), systolic blood pressure (SAP) (4.3 ± 1.5 per cent) and mean arterial blood pressure (MAP) (1.7 ± 2.0 per cent). Increases in HR, SAP and RPP after intubation were approximately 50 per cent less in patients given esmolol compared to patients given placebo. There were highly significant differences in HR (p < 0.0001), and RPP (p < 0.0005) and significant differences in SAP (p < 0.05) when the maximal esmolol post-intubation response was compared to the maximal placebo response. Infusion of esmolol in the dose utilized in this study significantly attenuated but did not completely eliminate cardiovascular responses to intubation.RésuméL’esmolol, un bloquer bêta-adrénergique cardiosélectif de courte durée d’action a été investigué dans une étude prospective à double insu pour sa capacité de contrôler les réponses hémodynamiques associées à l’intubation trachéale après thiopentone et succinylcholine. Trente patients ASA I ont requ une perfusion de 12 minutes d’esmolol (500 µg ·kg-1· min-1 pour quatre minutes, puis 300 µg ·kg-1 pour huit minutes) ou du salin. Cinq minutes après le début de la perfusion du médicament ou du placebo, l’ anesthésie était induite avec 4 mg·kg-1 de thiopentone suivi de succinylcholine pour l’intubation trachéale. Avant l’induction l’esmolol a produit une diminution significative de la fréquence cardiaque (HR) (9.3 ± 1.8 pour cent) et du produit fréquence-pression (RPP) (13.1 ±1.8 pour cent), de la tension artérielle systolique (SAP) (4.3 ± 1.5 pour cent) et de la pression artérielle mopenne (MAP) (1.7 ± 2.0 pour cent). Après l’intubation, l’augmentation dans la fréquence cardiaque, la pression artérielle systolique et la produit fréquence-pression était approximativement 50 pour cent moindre chez les patients ayant reçu de l’esmolol que chez les patients ayant regu du placebo. Il y avait une difference hautement significative dans la frequence cardiaque (p < 0.0001) et dans le produit fréquencepression (p < 0.0005) ainsi qu’une difference significative dans la pression artérielle systolique (p < 0.05) quand la réponse maximale post-intubation à l’esmolol a été comparée à la réponse maximale au placebo. La perfusion d’esmolol aux doses utilisées dans cette étude atténue significativement mais n’élimine pas complètement les réponses cardiovasculaires à l’intubation.

Objective Evaluation of Clinical Performance and Correlation with Knowledge

In certifying competence of anesthesiologists who have finished residency training, knowledge and judgment are evaluated objectively using written and oral examinations. Clinical motor skills, however, are not routinely assessed by objective techniques. This implicitly assumes that knowledge and judgment correlate with performance of motor skills. This study was designed to evaluate whether performance of a particular motor skill correlates with performance on a knowledge test related to that skill. To do this, we developed a criterion-referenced Spinal Anesthesia Skill Test and a knowledge test using multiple-choice questions related to spinal anesthesia. Both the skill and knowledge tests were administered to 44 residents at various levels of training at five major anesthesia teaching programs. Scores on the skill test were significantly higher than in the knowledge test, suggesting that proficiency in this essential motor skill is achieved earlier in training. There was no correlation between scores on the skill test and knowledge test. There were institution-linked differences in the scores on the skill test, suggesting that teaching of motor skills is not uniform. The advantages of developing criteria of performance of motor skills is discussed.

Methohexital Plasma Concentrations in Children Following Rectal Administration

Despite the increasing use of rectal methohexital as a premedicant-induction agent in pediatric anesthesia, there are no data to confirm the assumption that low plasma methohexital concentrations are the cause of inadequate sedation of children and that high concentrations are associated with the loss of consciousness. Plasma methohexital concentrations were determined in 20 ASA Class I children, ages 2–7 yr, after the rectal administration of methohexital (25 mg/kg). Seventeen of the 20 children in this study fell asleep after receiving the drug and achieved peak plasma concentrations greater than 2 μg/ml. The maximum plasma methohexital concentration in children that did not fall asleep was less than 2 μg/ml. The mean time to the onset of sleep after drug administration was 8.3 min (at which time the mean plasma concentration was 4.4 μg/ml). The mean peak plasma concentration and the mean time to peak plasma concentration were 4.7 μg/ml and 13.9 min, respectively. Loss of consciousness after rectal administration of methohexital correlates well with the plasma concentration of the drug.

Clinical Reports Foetal monitoring in parturients undergoing surgery unrelated to pregnancy

Foetal heart rate and tocodynamic monitoring of the uterus was performed in five pregnant patients undergoing urgent or emergency surgery unrelated to their pregnancy. All received general anaesthesia with halothane or enflurane and nitrous oxide. The loss of beat-to-beat variation of the foetal heart rate was observed in all patients under general anaesthesia, and is probably normal for the anaesthetized foetus. Since continuous intraoperative monitoring of foetal heart rate in pregnant patients is technically feasible during peripheral surgery and during many intra-abdominal procedures, attempts should be made to monitor foetal heart rate in all anaesthetized parturients to assure that the anaesthetic is not causing foetal insult. Postoperative monitoring of uterine tone is useful in the diagnosis and treatment of postoperative premature labor.RésuméLa surveillance des contractions utérines par toco-dynamomètre ainsi que la surveillance du coeur fatal ont été étudiées chez cinq patientes enceintes subissant une chirurgie urgente ou semi-urgente non reliée à leur état gravide. Toutes les patientes ont regu de I’anesthésie générale avec I’halothane ou l’ enflurane avec du protoxyde d’azote. La perte du “beat-to-beat variation” du coeur foetal a été observée chez toutes les patientes subissant I’anesthésie générate, ce qui serait normal pour le foetus anesthésié. Etant donné que la surveillance intraopéra-toire du coeur foetal chez les femmes enceintes est techniquement possible lors d’une chirurgie périphérique et plusieurs procédures intraabdominales, des tentatives doivent être accomplies afin de surveiller le coeur foetal chez toutes les patientes pour être sûr que la technique anesthésique ne provoque aucune insulte foetale. La surveillance du tonus utérin en période postopératoire est utile dans le diagnostic et le traitement d’un travail prématuré postopératoire.

Acute Pulmonary Edema during Laparoscopy

Laparoscopy is a frequently performed gynecologic procedure. Despi te the stress of insufflation of several liters of carbon dioxide or nitrous oxide a n d extreme Trendelenburg position, few cardiorespiratory anesthetic complications have been reported. Unexplained cardiovascular collapse resulting i n death i n clinically healthy patients during laparoscopy is a n extremely rare but tragic occurrence. A case of acute fulminant pulmonary edema short ly after insufflation for laparoscopy in a young patient without known cardiopulmonary disease is described in this report.

Performance Evaluation: Continuous Lumbar Epidural Anesthesia Skill Test

The evaluation of skills in anesthesiology residents is usually subjective and lacks demonstrable reliability. Therefore, an objective criterion-referenced skill test for measuring performance of continuous lumbar epidural anesthesia was developed. For such a test to be useful, it is necessary to demonstrate agreement among rater-observers. Eight performances of continuous lumbar epidural anesthesia were recorded on video tape and simultaneously rated by nine anesthesiology faculty observers to determine inter-rater reliability. Inter-rater agreement was analyzed by determining coefficient kappa for each item and the entire test. Coefficient kappa for the entire test was 0.82 indicating a high degree of agreement between raters on the performance or nonperformance of various items. Development and utility of skill tests are discussed.