Download Update 11 - Update in Anaesthesia - WFSA

54Update in AnaesthesiaTeaching pointDifferent anaesthetic options during transfer to theatreand in the CT scannerThe aim of the anaesthetist is the maintenance of thepatient in a physiologically stable state so that no furtherharm to the damaged brain occurs. This means fulloxygenation with slight hypocapnia and withoutcoughing or straining (avoiding cerebral venouscongestion). As an alternative to the techniquedescribed, many centres now use a propofol infusion,2-6 mg/kg/h, by syringe pump which can be started inthe accident department and continued into theatre. Athiopentone infusion can be used, but is much moredifficult to manage because thiopentone is not rapidlymetabolised. Therefore it accumulates and can takedays to reverse.Importance of monitoringIt is easy for the brain to be damaged during this period.Unnoticed hypotension, hypoxia or coughing, whichcan occur unexpectedly and suddenly, can causeirreversible damage. Therefore close clinical monitoringof the patient is crucial.CT scannerThe CT scanner is used to confirm the diagnosis andto guide the surgeon to where the bone flap should beraised. A short emergency scan is carried out causingthe minimum of delay to the start of surgery (figure 3).CT scanning is not available in many centres, andtherefore the patient would be transferred directly totheatre by the anaesthetist for initial burr holes to becarried out in the temporal region on the side of thedilated pupil.TheatreThere is a wide range of anaesthetic drugs and hencetechniques available. Anaesthesia may be maintained withan inhalational agent - isoflurane would be the first choiceand halothane the second choice. If only ether is availablethen use ether. If available, increments of morphine,pethidine or preferably fentanyl should be used as narcoticsreduce the risk of coughing and the concentration ofinhalational agent required. Neuromuscular blockade ismaintained with non-depolarising muscle relaxants, to avoidcoughing and straining with the minimum concentration ofthe inhalational agent required. However, if no long actingmuscle relaxant is available then continue with intermittentpositive pressure ventilation using the inhalational agent tosuppress normal ventilation. In some units where propofolis available, anaesthesia can be maintained with a propofolinfusion (2-6 mg/kg/hour), oxygen enriched air, and smallincrements of narcotics. The infusion rate is adjusted toensure that the blood pressure does not fall.The circulation is monitored by observing the peripheralcirculation, pulse rate, blood pressure and urine output.Blood pressure should be monitored either invasively orfrequently with a cuff. Continuous measurement of thepatient’s blood pressure is very helpful as it allows bloodpressure changes to be treated accurately and efficiently.Do not delay surgery to insert an arterial line. Howeverthere is usually time during preparation of the patient toattempt radial artery cannulation. If this proves difficultthen a cannula can be put into the femoral artery to providemonitoring for the duration of surgery.Teaching pointHypertension in theatreA systolic blood pressure of 180 mmHg, may appearto be high for a 30 year old man, but it is vital until theclot has been removed. This is because the body hasraised the blood pressure to overcome the highintracranial pressure. Therefore do not allow the bloodpressure to fall below this level.In contrast, if the blood pressure rises to more than200 mmHg systolic, this indicates insufficient depth ofanaesthesia. Treat this with a small increase inconcentration of inhalational agent or propofol infusionrate and a further dose of narcotic until the mean arterialblood pressure falls to 140 mmHg (correspondingapproximately to a systolic arterial pressure 180mmHg).Hypotension in theatreNote that high concentrations of inhalational agentscause cerebral vasodilatation, increasing cerebral bloodvolume and thus cerebral swelling. This worsens thesituation by causing a further rise in intracranialpressure. In addition higher concentrations may causea fall in blood pressure. The combination of high ICPand low BP would severely reduce cerebral perfusionand should be treated quickly with intravenous fluids,vasopressors and a reduction in the concentration ofvolatile agent.