Download Update 11 - Update in Anaesthesia - WFSA

38Update in Anaesthesiawhichever technique is used, always test the back of thelegs (S2 and S3) to confirm that the sacral dermatomesare blocked before surgery starts.How high a regional block must extend into the thoracicdermatomes to achieve intraoperative analgesia, remainscontroversial. Recommendations from T10 to T4 havebeen made, although the method of testing the block isoften unspecified and the need for supplemental analgesicsnot mentioned. The three most commonly used methodsof assessment are:loss of temperature sensationloss of pinprick sensation loss of light touch sensation.These may differ by as much as 10 dermatomes, withtemperature sensation lost first and light touch sensationlast. Experimental data suggests that intraoperativeanalgesia is most reliably predicted by blocking light touchsensation (the hub of a needle lightly applied to the skin)to T5 (just beneath the nipples).Haemodynamic consequences of regional anaesthesiaExtensive epidural and spinal blocks cause a temporarysympathectomy which makes the patient susceptible tohypotension. In pregnant women, this is made worse bythe uterus compressing the aorta and inferior vena cava(aorto-caval occlusion). Hypotension may develop rapidly.Therefore, blood pressure should be measured at leastevery two minutes from starting a regional block untilBox 1: Recommendations for monitoring duringcaesarean sectionFor operative delivery under regional blockContinuous pulse oximetry, non invasive bloodpressure and continuous ECG during induction,maintenance and recovery.The fetal heart rate should be recorded during initiationof regional block and until abdominal skin preparationin emergency caesarean section.During general anaesthesiaContinuous inspired oxygen and end-tidal carbondioxide concentration should be monitored, as wellas pulse oximetry, non-invasive blood pressure andECG.delivery. Nausea during onset of a regional block is usuallyan indication of hypotension.Blocks above T4 cause a loss of sympathetic innervationto the heart which may be associated with bradycardiaparticularly if aorto-caval occlusion is present. Becauseof this continuous monitoring of the pulse is essential.Respiratory consequences of regional anaesthesiaPregnant women are prone to hypoxia because of areduction in functional residual capacity (FRC) of the lungsand an increased oxygen consumption. This is compoundedduring regional blocks by abdominal and intercostal muscleweakness which causes a further reduction in FRC. Pulseoximetry not only monitors the pulse but also provides acontinuous non-invasive monitor of the saturation of arterialhaemoglobin. It is simple and accurate; always use it ifyou can.When the thoracic dermatomes are blocked, patients oftencomplain of a strange sensation when breathing, usuallyas they realise that they cannot produce a forceful cough.This is normal and a result of intercostal paralysis and thepatient can be reassured. However difficulty in speakingrepresents diaphragmatic paralysis developing and needsvery careful assessment of the level of block. Furtherspread of local anaesthetic must be minimised. Ifhyperbaric local anaesthetic has been used, this can bedone by careful elevation of the head and neck. Howeverbe prepared to intubate and support these patient’sventilation.Unexpected high blocks“Total spinals” or very high blocks may follow excessivespread of a deliberate intrathecal injection of localanaesthetic or be caused by an epidural catheter that ismisplaced in the subarachnoid space. Misplaced epiduralcatheters can be detected by attempting to aspirate CSFthrough the catheter and carefully assessing the effectproduced by a test dose. An appropriate test dose willproduce detectable changes in sensory and motor functionwithin five minutes of injection if the catheter is in thesubarachnoid space and no significant effect if the catheteris in the epidural space.The spread of deliberate intrathecal injections of hyperbaric(heavy) local anaesthetics can be controlled by keepingthe upper thoracic and cervical spine elevated. As spinalblocks sometimes extend very rapidly, you must checkthe spread of the block within 4 minutes of injection andreposition the patient if necessary.