ISSN 2398-2942      

Anesthesia: in head trauma

icanis

Introduction

Aims

  • To avoid exacerbating the effects of the head injury.
  • Avoid causing secondary damage to intact nervous tissue.
  • Support vital physiological functions under the control of damaged areas of nervous tissue, may be direct effects on respiratory and cardiovascular centres.
  • Avoid causing a rise in intracranial pressure (ICP).

Preparation

Risk assessment and management

  • Priority in the management of the recently traumatized dog is given to fluid therapy to restore circulating blood volume and analgesia. (See premedication for consideration of analgesic drugs.)
  • Choice of fluids is controversial as the blood-brain barrier is likely to be damaged:
    o In hemorrhagic shock blood or colloid solutions are preferable to large volumes of crystalloid solutions.
    o Dextrose containing fluids should not be used in case hyperglycemia is produced. This has been linked with post-ischemic neurological damage.
    o Hypo-osmolar solutions, eg lactated Ringer's (Hartmann's) should not be used in animals where osmotic diuretics, eg mannitol solution, have been used as this combination can lead to a rise in ICP.
    o Iso-osmotic solutions, eg normal saline, are the preferred type of crystalloid fluid.
  • Accurate management of intravenous fluid therapy is vital, overinfusion increases ICP and exacerbates cerebral edema. Once deficits have been replaced, infusion rates of 1-2 ml/kg/hour are recommended. Monitoring of central venous blood pressure is advised.
  • Use of mannitol solutions Mannitol for osmotic diuresis to reduce ICP is also controversial:
    o Only consider after the circulating blood volume has been restored, to avoid hypotension and dehydration.
    o Where the blood-brain barrier is damaged mannitol leaking into nervous tissue may actually increase ICP.
    o Can cause vomiting and pulmonary edema.
  • In the absence of life-threatening injuries requiring immediate surgery, eg compound fractures of the cranium giving rise to air embolism, anesthesia is best postponed for 24 hours. This allows time for:
    o Cardiovascular system to stabilize. Myocardial injury, eg contusion, may not become apparant for 24 hours and predisposes to cardiac arrhythmias.
    o Endocrine system to stabilize.
    o Full extent of injuries to be assessed, eg urinary system damage not readily detected until time has elapsed for urine output to be monitored.

General clinical examination

  • Include assessment of airway patency and identify any potential problems which could interfere with endotracheal intubation.
  • Auscultation of the thorax.
  • Mucous membrane color and capillary refill time.
    Cyanotic animals are very poor anesthetic risks.

Ancillary tests

  • Radiography.
  • Hematology.
  • Biochemistry.
  • Electrolyte assay.
  • Urinalysis.
  • Other ancillary aids as indicated by other injuries or concurrent diseases, eg electrocardiography, ECG: overview ultrasonography Ultrasound: physics.
  • Animals with cranial trauma will fall into:
    o Class 3 (moderate risk)
    o Class 4 (high risk)
    o Class 5 (grave risk)
    depending on the severity of nervous tissue damage, other injuries and concurrent disease.

Specific preoperative preparation

ALWAYS preoxygenate for a minimum of 5 minutes.

  • Preoxygenation can be carried out in an oxygen chamber or tent, by mask or via a naso-pharyngeal tube. The value is much reduced if the animal struggles.
    Oxygen therapy presents a fire hazard.
  • An intravenous catheter should be placed prior to induction to ensure reliable intravenous access.
  • Have equipment ready for desensitization of the larynx and intubation ready and to hand.

Requirements

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Procedure - Premedication

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Precedure- Induction

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Procedure - Maintenance

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Procedure - Monitoring + Recovery

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Armitage-Chan E A, Wetmore L A & Chan D L (2007) Anesthetic management of the head trauma patient. J Vet Emer Crit Care 17 (1), 5-14 VetMedResource.

Other sources of information

  • Bedford P G C (1991) Small Animal Anesthesia, The Increased Risk Patient. London: Bailliere Tindall. p35-38, 43-44. ISBN 0 7020 1501 6.
  • Hall L W (1982) Relaxant drugs in small animal anesthesia. In: Proceedings of the Association of Veterinary Anesthetists of Great Britain and Ireland Supplement to 10, 144-155.

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