Stevin A. Dubin

Effect of Obesity on Safe Duration of Apnea in Anesthetized Humans

Obese patients have a decreased functional residual capacity and, hence, a reduced oxygen supply during periods of apnea. To determine whether obese patients are at greater risk of developing hypoxemia during induction of anesthesia than patients of normal weight, 24 patients undergoing elective surgical procedures were studied. Group 1 (normal) were within 20% of their ideal body weight. Group 2 (obese) were more than 20% but less than 45.5 kg over ideal body weight. Group 3 (morbidly obese) were more than 45.5 kg over ideal body weight. Patients were preoxygenated for 5 min or until expired nitrogen was <5%. After induction of anesthesia and muscle relaxation the patients were allowed to remain apneic until arterial saturation as measured by pulse oximetry reached 90%. The time taken for oxygen saturation to decrease to 90% was 364 ± 24 s in group 1, 247 ± 21 s in group 2, and 163 ± 15 s in group 3; these times are significantly different at P < 0.05 between groups. Regression analysis of the data demonstrated a significant negative linear correlation (r = −0.83) between time to desaturation and increasing obesity. These results show that obese patients are at an increased risk of developing hypoxemia when apneic.

Defibrillation energy requirements and electrical heterogeneity during total body hypothermia

ObjectiveDetermine the effects of hypothermia on defibrillation energy requirements and cardiac electrophysiology. DesignProspective randomized acute intervention trial. SettingMedical center animal laboratory. SubjectsFifteen domestic farm swine. InterventionsSwine were randomized to a hypothermia group (n = 8) or a control group (n = 7). All animals were instrumented with a transvenous defibrillation system connected to a defibrillator that delivers a biphasic-truncated waveform. Values for defibrillation energy requirements were measured at baseline (normothermia, 38–40°C) and during treatment with total body hypothermia (30°C) or no temperature change (sham). Hypothermia was induced by circulating ice-water through anterior and posterior surgical thermal blankets. Measurements and Main ResultsDefibrillation energy requirement values at 20%, 50%, and 80% were determined by using an up/down method. In the hypothermia group, defibrillation energy requirement values at baseline did not significantly change during hypothermia (defibrillation energy requirements 50% = 14 ± 2 J vs. 15 ± 2 J, respectively). Similarly, the defibrillation energy requirement values in the control group did not change from baseline to sham phase (defibrillation energy requirements 50% = 12 ± 1 J vs. 13 ± 1 J, respectively). Hypothermia profoundly affected cardiac electrophysiology, decreasing ventricular fibrillation threshold by 72%, conduction velocity by 25% (p < .01), and tissue excitability, while it prolonged ventricular repolarization and refractoriness by 7.5% to 15%, respectively (p < .05). ConclusionsTotal body cooling to 30°C was highly arrhythmogenic, although this unstable electrophysiological state did not alter ventricular defibrillation energy requirements. These data suggest that hypothermia may be used to slow metabolic processes without concern over the ability to successfully defibrillate and treat hypothermia-induced arrhythmias.

Sugarless gum chewing before surgery does not increase gastric fluid volume or acidity

Patients occasionally arrive in the operating suite chewing gum despite instructions to avoid oral intake for a specific number of hours before surgery. Some anaesthetists are hesitant to proceed with these patients fearing an increase in gastric volume and acidity. This study was undertaken to determine if gum chewing increased gastric volume and acidity. Seventy seven patients were recruited and informed consent obtained. Thirtyone patients who fasted overnight were randomly assigned either to serve as control (Group 1) or to chew sugarless gum prior to anaesthesia (Group 2). The remaining 46 patients fasted overnight but were given sugarless gum and allowed to chew it until immediately before induction of anaesthesia if they desired (Group 3). Volume and pH of gastric content were determined immediately after induction of anaesthesia and tracheal intubation. Results revealed mean values (range) of gastric volume for Group 1 — 26 ml (9–60), Group 2 — 40 ml (5–93), and Group 3 — 28 ml (4–65). Mean values for pH (range) were Group 1 — 1.8 (1.0–4.6), Group 2 — 1.6 (1.3–1.9), Group 3 — 1.7 (1.0–4.4). There was no difference between groups in terms of gastric volume or pH. In addition, there was no relationship between gastric content and the length of time from gum discard to induction or the length of time gum was chewed. In conclusion, the data suggest that induction of anaesthesia is safe and surgery does not need to be delayed if a patient arrives in the OR chewing sugarless gum.RésuméOccasionnellement des patients arrivent à la salle d’opération en mâchant de la gomme contrairement à la consigne du jeûne absolu spécifié pour un nombre d’heures avant la chirurgie. Certains anesthésistes hésitent à anesthésier ces patients parce qu’ils redoutent l’augmentation du volume et de l’acidité gastriques. Cette étude vise à déterminer si la gomme à mâcher augmente le volume et l’acidité gastriques. Soixante-dix patients consentants sont inclus dans l’étude. Trente-et-un patients sont gardés à jeun pour la nuit et répartis au hasard soit pour servir de contrôle (groupe 1) ou pour mâcher de la gomme sans sucre avant l’anesthésie (groupe 2). Les quarante-six autres restent à jeun pendant toue le nuit mais ont la permission de mâcher de la gomme sans sucre jusqu’à l’induction de l’anesthésie s’ils le désirent (groupe 3). Le volume et le pH gastriques sont mesurés immédiatement après l’induction de l’anesthésie et l’intubation de la trachée. Les résultats révèlent les valeurs moyennes de volume gastrique (étendue des valeurs) suivantes: groupe 1 — 26 (9–60); groupe 2 — 40 (5–93), et groupe 3 — 28 (4–65). Les valeurs moyennes de pH (étendue des valeurs) sont pour le groupe 1 — 1,8 (1,0–4,6), groupe 2 — 1,6 (1,3–1,9), groupe 3 — 1,7 (1,0–4,4). On ne trouve pas de différence entre les groupes au regard du volume gastrique ou du pH. De plus, il n’y a pas de relation entre le contenu gastrique et l’intervalle compris entre l’abandon de la gomme à mâcher et l’induction ou le durée du mâchement. En conclusion, ces données suggèrent que l’induction de l’anesthésie n’est pas plus dangereuse et qu’on n’a pas à retarder la chirurgie si un patient arrive en salle d’opération en mâchant de la gomme sans sucre.

Comparison of the effects of oral famotidine and ranitidine on gastric volume and pH

Aspiration of acidic gastric contents during the perioperative period has been a continuing concern to anesthesiologists since the days of Hannah Greener (1). The acidity (pH < 2.5) (2) and volume (>25 mL or 0.3 mL/kg of normal body weight) (3) of gastric contents have been suggested as factors associated with significant morbidity when aspiration does occur. With the recognition of the H, receptor and its association with gastric acid production by Ash and Scheld (4) in 1966, emphasis has been placed on producing newer and safer H,-receptor antagonists. Compounds have included burimamide, metiamide, cimetidine, and ranitidine. Both cimetidine and ranitidine, despite some untoward side effects (5), have withstood the test of time and are still currently prescribed for clinical use. The most recent drug to be introduced is famotidine, which differs structurally from previous drugs by the presence of a guanylthiazole ring. It is 3-20 times more potent than ranitidine with a 30% longer duration of action (6). The efficacy of cimetidine and ranitidine in decreasing gastric volume and increasing gastric pH and so perhaps providing prophylaxis against aspiration pneumonitis in surgical patients has been shown (7-9). The efficacy of famotidine remains to be evaluated. The purpose of this study was to compare the effectiveness of famotidine, ranitidine, and placebo in reducing gastric volume and gastric acidity in outpatients, a group with an increased risk for acid aspiration (10).

Video RIFL: a rigid flexible laryngoscope to facilitate airway management.

The video RIFL (rigid flexible laryngoscope) is an airway management adjunct designed to facilitate endotracheal intubation. It is a novel stylet-based laryngoscope that incorporates a complementary metal oxide sensor distal chip imaging system and real-time articulation tip. The device combines features desired in fiberoptic bronchoscopy as well as in video laryngoscopy. Four cases involving its use in difficult airway management are presented.