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

Procedure - Premedication

Precedure- Induction

Procedure - Maintenance

Procedure - Monitoring + Recovery

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.