Download Update 11 - Update in Anaesthesia - WFSA

Update in Anaesthesia 9excreted the half life increases slowly with deterioratingrenal function until severe nephron loss at which point thehalf life increases sharply with further reductions in renalfunction. Dialysis can only usually replace a small part ofthe excretory capacity of the healthy kidney.Induction agents Their effect is terminated byredistribution. All of these agents are myocardialdepressants and should be administered cautiously inpatients with heart disease.Muscle relaxants Suxamethonium should be avoidedif hyperkalaemia is present.Some non-depolarising muscle relaxants depend on thekidney for elimination. Atracurium is the agent of choiceas it undergoes spontaneous Hoffman degradation at bodytemperature.Vecuronium and mivacurium are safe to use in renalfailure as only small percentages are excreted renally.Gallamine should be avoided and pancuronium,alcuronium, pipecuronium, curare and doxacuriumshould be used with caution. Potentiation of neuromuscularblockade may occur in the presence of a metabolicacidosis, hypokalaemia, hypermagnesaemia, orhypocalcaemia and with medications such asaminoglycosides. Monitor neuromuscular blockadewhenever possible.Opioids Morphine is metabolised in the liver to morphine-6-glucuronide which has about half the sedative effect ofmorphine with a markedly prolonged half life. Pethidine ispartially metabolised to norpethidine which is less analgesicand has excitatory and convulsant properties. Both ofthese metabolites may accumulate in renal failure afterrepeated doses or with infusions. Standard intraoperativeuse will not usually cause problems. When available,morphine is preferable to pethidine.Fentanyl and alfentanil can be used as normal.Benzodiazepines can be used in renal failure.Inhalational agents There is decreased elimination ofthe fluoride ions which are significant metabolites ofenflurane, sevoflurane and methoxyflurane which canworsen renal function, so these inhalational agents shouldbe avoided especially if used at low flows.Non steroidal anti inflammatory agents (NSAIDS)should be avoided as all decrease renal blood flow andmay precipitate complete renal failure.Conduct of AnaesthesiaPremedication Oral sedatives such as diazepam ortemazepam may be used. H 2antagonists or non particulateantacids (e.g. sodium citrate) should be given ifoesophageal reflux is a problem.Anaesthesia Venous access may be difficult. If futurehaemodialysis is planned it is important to preserve AVfistulas and potential fistula sites. Forearm and antecubitalveins should be avoided if possible in these patients.Full monitoring must be established prior to induction ofanaesthesia, with special attention being paid to the ECGand blood pressure. The patient should be kept welloxygenated and haemodynamically stable. Hypovolaemiaand hypotension worsen renal function therefore bloodand other fluid losses should be carefully replaced. Ifpossible the shorter acting sedative agents should be used.If spinal or epidural anaesthesia is being performed fluidpreloading should be kept to a minimum andvasoconstrictors used to maintain the blood pressure.Otherwise postoperative fluid overload may necessitatedialysis.Postoperatively Postoperative fluid balance must bemeticulous and prompt action taken to limit vomiting andreplace any fluids lost. Some patients may requirehaemodialysis for fluid overload postoperatively but thisshould be delayed if possible as the patient will have to beheparinised. Some patients may become drowsy onrelatively low doses of analgesics.Oxygen (2-3 litres/minute nasally or 3-4 litres/minute viaface mask) should be administered for 48 hours after majorabdominal or thoracic surgery and 24 hours afterintermediate surgery.PREVENTING ACUTE RENAL FAILUREPreviously healthy patients most at risk of developing acuterenal tubular necrosis are those with massive haemorrhage,multiple trauma, sepsis, extensive burns and crush injuries,especially if they already have some degree of renalimpairment. Renal failure is diagnosed when urine outputis persistently