A tracheal bronchus is an aberrant, accessory or ectopic bronchus arising almost invariably from the right lateral wall of the trachea, causing hypoxaemia, atelectasis, or both, during anaesthesia. We describe two patients with a tracheal bronchus found before anaesthesia. One tracheal bronchus was found by tracheobronchoscopy and the other by chest x-ray. Because of recognition of the anomaly before operation, anaesthesia was uneventful in each patient.

We have studied the effects of i.v. bolus doses of magnesium sulphate (MgSO4) 60, 90 and 120 mg kg-1 on haemodynamic state, the coronary circulation and myocardial metabolism in nine dogs anaesthetized with pentobarbitone and fentanyl. MgSO4 produced dose-dependent decreases in arterial pressure, heart rate, left ventricular dP/dtmax and left ventricular minute work index (LVMWI) and an increase in the time constant of left ventricular isovolumic relaxation. Stroke volume increased, systemic vascular resistance decreased and cardiac output did not change significantly. MgSO4 produced decreases in coronary perfusion pressure, coronary vascular resistance and myocardial oxygen consumption (MVO2). Coronary sinus blood flow, lactate extraction ratio and the ratio of LVMWI to myocardial MVO2, that is an index of cardiac efficiency, did not change significantly. This study indicated that the depressant effect of MgSO4 on cardiac function was offset by lowering of peripheral vascular resistance, so that cardiac pump function remained effective, and the almost constant coronary sinus blood flow resulted from the decrease in coronary vascular resistance even at higher doses.

Purpose: To determine the effects of propofol on the cardiac conduction system in dogs with pharmacological autonomic blockade. Methods: In eight mongrel dogs receiving 6 mg'kg -l'hr -I propofol and vecuronium under pharmacological autonomic blockade with atropine and propranolol the infusion rates of propofol were increased from 6, (baseline), to 12, 18 and 24 mg'kg -i'hr -l at 60-min intervals. An electrophysiological study assessed sinus rate, sinus node recovery time, corrected sinus node recovery time, intraatrial conduction time, AV nodal effective refractory period, Wenckebach cycle length and AV conduction times. Electrocardiographical variables and arterial pressures were also measured. All measurements were repeated at 30 min after the beginning of each infusion of propofol. Re~uJts: Propofol did not produce direct effects on the electrophysiological or electrocardiographical variables at any infusion rates. Heart rates did not change at higher infusion rates in the presence of decreases in arterial pressures. Conclusion: Propofol did not affect the cardiac conduction system in the presence of autonomic blockade. Thus, the direct cardiac effects of propofol do not play a causative role in the genesis of propofol-associated bradyarrhythmias.Objectif: DEterminer les effets du propofol sur le syst~me de conduction du coeur chez les chiens soumis ~ un blocage nerveux autonome. M&hode : I'&ude a porte sur huit chiens communs qui ont re~ju 6 mg-kg -I-hr t de propofol et du v&uronium sous un blocage pharmacologique nerveux autonome avec de ratropine et du propranolol. La vitesse de peffusion du propofol a augment& passant de 6, au depart, ~ 12, 18 puis 24 mg-kg -~'hr -I ~ des intervalles de 60 min. Un examen Electrophysiologique a permis d'Evaluer le rythme sinusal, le temps de rEcupEration sinusale, le temps de rEcupEration sinusale corrig& le temps de conduction intra-auriculaire, la pEriode rEfractaire effective clu noeud AV, la Iongueur de la p&iode de Wenckebach et les temps de conduction AV. On a aussi mesurE les variables Electrocardiographiques et les pressions artErielles. Toutes les mesures ont EtE reprises 30 min aprEs le debut de chaque perfusion de propofol. l~.~ultats : Le propofol n'a pas eu d'effet direct sur les variables ~lectrophysiologiques ou Electrocardiographiques, r&ultat valable pour route vitesse de perfusion. Les frEquences cardiaques front pas change pendant les perfusions les plus rapides en pr&ence de baisses de pression artErielle. Conclusion: Le propofol n'a pas affect6 la conduction cardiaque en presence d'un blocage nerveux autonome. Par consequent, les effets directs du propofol sur le coeur front pas eu de r61e causal dans I'apparition des bradyarythmies qui lui Etaient associEes.

We have studied the effects of magnesium on atrioventricular (AV) conduction times and surface electrocardiogram during both sinus rhythm and atrial pacing in seven dogs anaesthetized with 1 MAC of sevoflurane. A bolus dose of magnesium sulphate (MgSO4) 30, 60 and 90 mg kg-1 significantly increased plasma magnesium concentrations from 1.3 (SEM 0.1) to 15.3 (1.3) mg dl-1. MgSO4 significantly prolonged A-H (AV nodal conduction time during sinus rhythm), St-H (intra-atrial and AV nodal conduction time during atrial pacing) and H-S (total ventricular conduction time) intervals at doses > or = 30 mg kg-1 ; H-V interval (His-Purkinje conduction time) at doses > or = 60 mg kg-1; RR and PR intervals and QRS duration at doses > or = 30 mg kg-1 in a dose-related manner during both sinus rhythm and atrial pacing. QTc interval remained unchanged during sinus rhythm. The doses of MgSO4 used did not have deleterious effects on AV conduction times and surface electrocardiogram during 1 MAC of sevoflurane anaesthesia. This finding suggests that MgSO4 in high doses was safe and may be indicated for cardiac arrhythmia and hypertension during sevoflurane anaesthesia. However, further study is required to apply these findings to clinical anaesthesia.

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