Download Update 11 - Update in Anaesthesia - WFSA

20Update in Anaesthesiasurgery.Drugs may also cause changes in cardiac rhythm eg; Halothane and nitrous oxide may cause junctionalrhythms - (these will be detailed later). Halothanehas a direct effect on the SA node and conductingsystem leading to a slowing in impulse generationand conduction and predisposes to re-entryphenomena. Catecholamines also have potenteffects on impulse conduction, so the interactionof halothane and exogenous or endogenouscatecholamines may cause ventricular arrhythmias.Ventricular ectopic beats are common. Howeverrhythm disturbances such as ventriculartachycardia or rarely ventricular fibrillation mayoccur. The presence of cardiac disease, hypoxia,acidosis, hypercarbia (raised CO 2level) orelectrolyte disturbances will increase the likelihoodof these arrhythmias. Arrhythmias occurring during halothane anaesthesiacan often be resolved by reducing theconcentration of halothane, ensuring adequateventilation thereby preventing hypercarbia,increasing the inspired oxygen concentration andproviding an adequate depth of anaesthesia forthe surgical procedure. Tachyarrhythmias in thepresence of halothane anaesthesia are uncommonif ventilation is adequate, and the use ofadrenaline infiltration for haemostasis is limitedto solutions of 1:100,000 or less and the dose inadults is not greater than 0.1mg in 10 minutes or0.3mg per hour ). Drugs increasing heart rate include ketamine,ether, atropine and pancuronium. Drugsdecreasing heart rate include opioids, betablockers and halothane.Action Plan - when faced with an abnormal rhythmon the ECG monitorAssess the vital signs - A.B.C. Check the airway is patent Check the patient is breathing adequately or isbeing ventilated correctlyListen for equal air entry into both lungsCirculation - check pulse, blood pressure, oxygensaturation. Is there haemodynamic compromise?Does the abnormal rhythm on the monitor matchthe pulse that you can feel?Consider the following: Increase the inspired oxygen concentration Reduce the inspired volatile agent concentration Ensure that ventilation is adequate to preventCO 2build up. Check end tidal CO 2where thismeasurement is availableConsider what the surgeon is doing - is this thecause of the problem? Eg: traction on theperitoneum or eye causing a vagal response. Ifso ask them to stop while you treat thearrhythmia.If the arrhythmia is causing haemodynamicinstability, rapid recognition and treatment isrequired. However, many abnormal rhythmsencountered in every day practice will respondto the above basic measures - sometimes evenbefore identification of the exact rhythmabnormality is possible.PRACTICAL INTERPRETATION ANDMANAGEMENT OF ARRHYTHMIASWhen interpreting arrhythmias a paper strip is ofteneasier to read than an ECG monitor. Where this is notpossible from the theatre monitor it may be possibleto obtain a paper trace by connecting a defibrillator,most of which have a facility for printing a rhythmstrip. The following basic points should be considered:Examining an ECG strip:1. What is the ventricular rate?2. Is the QRS complex of normal duration or widened?3. Is the QRS regular or irregular?4. Are P waves present and are they normally shaped?5. How is atrial activity related to ventricular activity?1. What is the ventricular rate? Arrhythmias maybe classified as fast or slow: Tachyarrhythmias - rate greater than100/min Bradyarrhythmias - rate less than 60/min Calculate approximate ventricular rate on apaper strip by counting the number of largesquares between each QRS complex anddividing this number into 300 which willgive the rate in beats/minute.