Australasian Anaesthesia 2011 - Australian and New Zealand ...

44 Australasian Anaesthesia 2011Anaesthetic Management of Acute Spinal Cord Injury 45Figure 1. ASIA standard neurological classification of spinal cord injury chart. (American Spinal InjuryAssociation: International Standards for Neurological Classification of Spinal Cord Injury, revised 2011;Atlanta, GA. Reprinted with permission 2011.)AIRWAY MANAGEMENTEmergency or semi-elective airway management may be required during the hospital stay of the patient with knownor suspected SCI. In Australia 53% of SCI cases involves the cervical segments. The most common cervical spineinjury is located at C4–C5 level, accounting for 61% of all cervical SCI cases and 32% of all documented neurologicalinjuries. 1 Up to 10% of patients with head injury will also have a cervical SCI. As such, a high index of suspicionshould be employed during airway management of the traumatically injured patient, especially with head injury.In the normal cervical spine, direct laryngoscopy causes extension at upper cervical joints, minimal movementat C4-C7, and flexion at the cervico-thoracic junction. 3,4,5 Instability involving subaxial cervical vertebrae may actas a second site for extension during laryngoscopy, leading to iatrogenic spinal cord injury.Spinal immobilisation and Manual In Line Stabilisation (MILS) are logical choices and are recommended bycurrent ATLS guidelines as a standard for airway intervention in patients with known or suspected cervical injury. 6The goal of MILS is to apply equal opposing forces to the head and neck, limiting movement during airwayintervention. MILS reduces cervical movement better than a rigid collar during laryngoscopy, and an improved viewis obtained, owing to better mouth opening. 7,8 The incidence of neurological impairment due to endotrachealintubation when MILS is used has been reported to be extremely rare. 9 Care should also be taken with maskventilation. The minimum of jaw thrust and chin lift should be used to maintain the patient›s airway. 10,11 Cricoidpressure remains controversial however, a cadaver model of upper cervical injury showed that cricoid pressure didnot result in significant cervical movement. 12The patient presenting to theatre for operative fixation of their spine or associated injuries affords time to plansuccessful airway management. Patients with pre-existing cervical spinal pathology including spondylosis, rheumatoidarthritis, Klippel-Feil, ankylosing spondylitis, tumor, pre-existing cervical fusion and upper (vs. lower) cervical diseaseor physical obstacles such as cervical traction or halo may increase the difficulty of airway interventions. 13No single intubation technique has been proved superior to others. Patients without existing neurologicalimpairment and acceptable radiological findings can be managed with direct laryngoscopy with MILS. If the airwayis potentially difficult and the patient has an existing neurological deficit and C-spine instability, an alternative shouldbe considered. Awake intubation has not been shown to be superior to asleep intubation. 14,15,16 Videolaryngoscopesincluding the Airtraq (AT) (Prodol Ltd., Vizcaya, Spain), and Glidescope (GS)(Verathon Ltd., Bothell, USA) havebecome a viable alternate technique. Numerous studies of their use in various scenarios exist but it is difficult todraw conclusions due to the heterogeneity of the studied populations. Studies in normal subjects with either MILSor hard collar in-situ to stimulate cervical immobilisation showed that AT performed better than direct laryngoscopy(DL), but GS compared to DL yielded conflicting results. GS prolonged the intubation time for experiencedlaryngoscopists, but not for new learners. Studies looking at cervical motion suggested less movement occurredwith AT, while GS again produced equivocal results. 17Reinforced endotracheal tubes are less likely to kink during patient positioning and also prevent trachealcompression during anterior cervical procedures. The decision to extubate postoperatively is influenced by factorsincluding the extent of surgery, complications (e.g. recurrent laryngeal nerve injury), duration, prone positioning,blood loss and subsequent fluid resuscitation, and ease of intubation. The presence of a cuff leak in the spontaneouslybreathing patient has not consistently been shown to predict subsequent airway obstruction from edema. An airwayexchange catheter may facilitate emergent re-intubation in the event of obstruction from airway edema. Goodclinical judgment is necessary, and if concern remains, delayed extubation should be considered.BLOOD PRESSURE MANAGEMENTTraumatic SCI may be complicated by systemic hypotension and reduced spinal cord perfusion pressure (SCPP). 18Hypotension should be avoided to prevent the worsening of secondary neurologic injury.Spinal cord perfusion is autoregulated in a similar fashion as cerebral blood flow. 19 Systemic hypotension mayresult either from hemorrhage from associated traumatic injuries (chest, intra-abdominal, retroperitoneal, pelvic orlong bone fractures) or neurogenic shock, or a combination. Neurogenic shock is hypotension and inadequatetissue perfusion due to vasodilatation from loss of central sympathetic control. 2 0 It is more common after cervicalSCI and is usually associated with bradycardia from unopposed vagal tone. Increased blood pressure leads toimproved axonal function both in motor and somatosensory tracts of the injured spinal cord. 21,22 Current recommendedblood pressure targets include maintenance of mean arterial pressure (MAP) at 85-90mmHg and avoiding systolicblood pressure below 90mmHg for up to five days post injury. 18 These parameters should be maintained perioperativelyand will require judicious use of intravenous fluids, vasopressors and inotropes. Hypotension may also interferewith neurophysiological monitoring. A retrospective review of anterior cervical fusion cases found that intraoperativedeterioration of evoked potential monitoring was associated with hypotension in 1% of cases. 23