| Before any nerve block is attempted, intravenous access for resuscitation purposes should be established. Adequate resuscitative equipment (oxygen, suction, means of intubation and appropriate emergency drugs) must be available. Epidural block should only be carried out by clinicians with the necessary knowledge and experience.There have been reports of cardiac arrest with difficult resuscitation or death during the use of bupivacaine for epidural anaesthesia in obstetrical patients. Resuscitation has been difficult or impossible despite adequate preparation and appropriate management. Cardiac arrest has occurred after convulsions resulting from systemic toxicity, presumably following inadvertent intravascular injection. Regardless of the site of injection or overdosage, inadvertent intravenous injection may give rise to toxic reactions.Injection of repeated doses of bupivacaine hydrochloride may cause significant increases in blood levels with each repeated dose due to slow accumulation of the drug. Tolerance varies with the status of the patient. Debilitated, elderly or acutely ill patients should be given reduced doses commensurate with their physical status.Only in rare cases have amide local anaesthetics been associated with allergic reactions (with anaphylactic shock developing in most severe instances). Patients allergic to estertype local anaesthetics such as procaine have not shown cross-sensitivity to amide-type agents such as bupivacaine. Since bupivacaine is metabolised in the liver, it should be used cautiously in patients with liver disease or with reduced liver blood flow. Local anaesthetics should be used with caution for epidural anaesthesia in the following situations : severe shock, hypovolaemia, dehydration, hypotension below 90mm systolic or a level less than 30% of their average systolic blood pressure, gross hypertension, marked obesity, senility, cerebral atheroma, myocardial degeneration, toxaemia and severe ischaemic heart disease, (especially with a history of recent infarction) because of the dangers of hypotension.Similar caution is required in cases of impaired cardiovascular conduction, such as patients with a fixed cardiac output (severe valvular stenosis, heart block, beta-blocking therapy), resulting in decreased ability to respond to dilatation of the vascular bed or to compensate for functional changes associated with the prolongation of A-V conduction produced by local anaesthetics.Epidural anaesthesia with any local anaesthetic can cause hypotension and bradycardia which should be anticipated and appropriate precautions taken. These may include preloading the circulation with crystalloid or colloid solution. If hypotension develops, it should be treated with posture, pressor drugs e.g. ephedrine 10 - 15mg intravenously in divided doses, intravenous infusions, atropine or glycopyrrolate in the presence of severe bradycardia, and oxygen. Severe hypotension may result from hypovolaemia due to haemorrhage or dehydration, or aorta-caval occlusion in patients with massive ascites, large abdominal tumours or late pregnancy. Marked hypotension should be avoided in patients with cardiac decompensation.Patients with hypovolaemia due to any cause may develop sudden and severe hypotension during epidural anaesthesia.Epidural anaesthesia, properly performed, is generally well tolerated by obese patients and by those with obstructive lung disease. However, patients with a splinted diaphragm which interferes with breathing, such as those with hydramnios, large ovarian or uterine tumours, pregnancy, ascites or omental obesity are at risk from hypoxia due to respiratory inadequacy and aortocaval compression due to tumour mass. Lateral tilt, oxygen and mechanical ventilation should be used when indicated. Dosage should be reduced in such patients.Patients who are breathless from any cause e.g. pleural effusion, may become hypoxic, especially if the level of anaesthesia is so high as to cause paralysis of the intercostals muscles.Septicaemia can increase the risk of intraspinal abscess formation in the post operative period.Paracervical block may have a greater adverse effect on the foetus than any other nerve blocks used in obstetrics. Due to the systemic toxicity of bupivacaine, special care should be taken when using bupivacaine for paracervical block.Small doses of local anaesthetics injected into the head and neck, including retrobulbar, dental and stellate ganglion blocks, may produce systemic toxicity due to inadvertent intraarterial injection. Clinicians who perform retrobulbar blocks should be aware that there have been reports of respiratory arrest following local anaesthetic injection. Prior to retrobulbar block, necessary equipment, drugs and personnel should be immediately available as with all other regional procedures.Solutions containing adrenaline should be used with caution in patients with hypertension, arteriosclerotic heart disease, cerebrovascular insufficiency or diabetes. | |