As with anaesthesia for all patients, the key to successful trauma anaesthesia is the adequate assessment and pre-operative resuscitation of the patient. In all but the most urgent surgery, there is sufficient time for this to be undertaken.

Preoperative assessment: all injuries should be noted. If the patient has been admitted using the trauma method outlined above, then it is unlikely that serious injuries will have been missed. When faced by patients who have not been subjected to a rigorous trauma team admission the anaesthetist should thoroughly examine the patient for head, spine, thoracic and abdominal injuries. The treatment of injuries that are life threatening or have the potential to become so must be given priority.

Continuous neurological observations will be disrupted by the administration of a general anaesthetic so that only emergency surgery should be undertaken during the period of observation. The feasibility of local or regional anaesthesia should be explored if surgery is required.

Those with thoracic injury should be investigated for the presence of fractured ribs as well as haemo- or pneumothoraces or other damage. If positive pressure ventilation is to be used then consideration must be given to prior insertion of an intra-pleural drain to prevent the development of a tension pneumothorax during anaesthesia. Possible cardiac contusion must not be overlooked. A 12 lead ECG recording may assist in detecting this in patients with chest trauma. It may present as hypotension despite adequate fluid replacement in a patient at risk. A CVP line is useful in such patients.

Starvation time prior to trauma anaesthesia is a contentious issue. In the patient undergoing immediate or early (<12 hours) operation the most important time interval is that between their last meal and injury, as after this time gastric emptying may cease. In those undergoing later surgery after a period of stabilisation and observation on the ward, the patient is often assumed to have an empty stomach if they are not in severe pain or have no other preoperative reasons to delay gastric emptying.

In addition a specific anaesthetic assessment should be performed. The appropriate investigations depend on the injuries sustained and the procedure to be undertaken. A blood crossmatch must be performed and an adequate volume of blood ordered. Premedication is usually not necessary if the patient is being kept pain free and the procedure is well explained. Preoperative antibiotics and tetanus vaccination are usually required.

Following assessment pain relief should be administered to the injured patient if surgery is going to be delayed. A variety of methods are available including nerve blocks, opioids (not in head injuries as they may mask deterioration in the patient's conscious level) or non-steroidal anti-inflammatory drugs such as aspirin or diclofenac (avoid in patients with peptic ulceration and asthmatics). Opioids are best administered slowly intravenously and titrated against effect. If they are given intramuscularly the drug may not be absorbed. Nitrous oxide (often in a 50% mixture with oxygen as "Entonox") is a useful analgesic which lasts as long as the patient breathes it. It should only be given to conscious patients who can hold the mask for themselves and must be avoided in chest injuries (risk of tension pneumothorax) and in diving accidents (risk of decompression sickness "bends"). It is a particularly useful agent to give the patient when they are about to be lifted or moved in a painful fashion.

Induction of anaesthesia: local or regional anaesthesia may be appropriate but multiple procedures in different body areas precludes it. The hypotension seen with epidural or subarachnoid blockade will be greater if the patient is hypovolaemic and this must therefore be corrected before the block is performed. Spinal or epidural anaesthesia must not be undertaken in head injured patients due to the risk of spinal CSF leakage giving rise to coning of the medulla.

General anaesthesia can be performed in the normal manner assuming the patient is adequately resuscitated and precautions are taken to prevent aspiration of stomach contents. Monitoring must be instituted prior to induction and a central venous catheter may assist in cases in whom a large blood loss is expected. Care should be taken not to move a suspected cervical spine injury during positioning of monitoring and airway manoeuvres. Depolarising neuromuscular blocking agents (suxamethonium) must be avoided in those with spinal cord damage or multiple injuries if the anaesthetic takes place more than 24 hours from the time of trauma. This is to prevent catastrophic potassium level rises which may occur in these patients for up to 6 months following the injury. Ketamine raises ICP and must be avoided in those at risk.

Thiopentone must be very carefully titrated and much smaller doses are usually needed in injured patients. Ketamine is a suitable induction agent for patients who have been, or who are hypovolaemic.

Maintenance of anaesthesia: Ventilation is controlled following the administration of a non -depolarising muscle relaxant to prevent hypercarbia as this will cause a rise in intracranial pressure. A combination of nitrous oxide (unless contraindicated - see below) and oxygen with a low concentration of an inhalational agent and opiates are suitable. Deep levels of anaesthesia with respiratory depression in the spontaneously breathing patient and coughing on the endotracheal tube cause a rise in intracranial pressure and must be avoided. Adequate attention must be paid to the prevention of hypothermia. Warmed intravenous fluids, blankets to cover the patient and a woolly hat are useful to limit heat loss. In prolonged procedures the temperature should be recorded (this can be done with an axillary thermometer) and appropriate action taken if it falls. Remember that halothane is more depressant to the cardiovascular system than ether or intermittent ketamine.

The positioning and movement of the patient must be carefully planned and supervised to prevent exacerbation of any injury. If actual or potential air filled spaces (pneumothoraces or suspected intracranial air with compound skull fracture) are present then nitrous oxide must be avoided. This is to prevent enlargement of the space due to rapid diffusion of nitrous oxide.

Blood loss can be large and in long procedures vigilance is required. The urine production must be monitored and an output of at least 1 ml/kg/hr should be maintained. The most likely cause of oliguria is hypovolaemia and intravenous fluid therapy should be titrated against urine output. Where there is difficulty about deciding how much fluid replacement is required and particularly in the presence of thoracic injuries, central venous pressure should be monitored.

In addition the patient must be observed carefully for any changes in vital signs which are unexpected and which might be the result of undiagnosed injury (for example hypotension caused by intra -abdominal bleeding may persist during an operation to stabilise a fractured femur). Good communication between surgeon and anaesthetist is vital.

(Continued...)

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