After ensuring scene safety, the immediate management of the patient with traumatic brain injury (TBI) in a field setting should focus on stabilizing and maintaining oxygenation and blood pressure. All head-injured patients have potential cervical injury and should be immobilized. A fundamental premise in prehospital care is to anticipate and prepare for eventualities such as vomiting, seizures, and aberrations of blood pressure or oxygenation.
15.2.1 Should Tracheal Intubation Be Performed in the Field for This Patient?
In this patient, ensuring oxygenation via a patent airway is of paramount importance. Indications for a field intubation include inadequate ventilation or oxygenation despite supplemental oxygen administration or the inability of the patient to protect the airway. A relative indication for intubation is the risk of losing the airway during transport. Transport time and type of transport, that is, ground versus aeromedical, must be taken into consideration. Studies of the outcome of prehospital intubations have yielded conflicting results1,2,3-5 and, as discussed in Chapter 14, prehospital airway management protocols are currently being further investigated. In the case presented, the patient was maintaining oxygenation and ventilation. His clinical course could not be certain, and it was reasonable for the field team to consider tracheal intubation. However, the patient had clenched teeth and was predicted to pose a difficult laryngoscopic intubation based on his short neck and cervical spine immobilization. A decision to intubate would involve the use of a rapid-sequence intubation (RSI) protocol; considering the short transport time, RSI was not indicated.
15.2.2 What Additional Considerations Are Imposed by Field Conditions?
Several other priorities in clinical care must be addressed by the field team after initial patient stabilization.
Hypotension is a critical factor associated with an increased morbidity and mortality in patients with head injuries.6,7 Blood pressure in the field should be monitored closely with the goal of avoiding hypotension (systolic BP <90 mm Hg in adults); if present, it should be corrected immediately. This patient presented with a field BP of 90/60 mm Hg. As hypotension is strongly associated with poor outcomes in TBI patients, fluid resuscitation becomes a priority. However, the field team must weigh the benefit of delaying transport from the field to secure an IV with the risk of delayed transport to a trauma center. Ideally, IV access should be attempted as the patient is expeditiously transported to the trauma center. It should be emphasized that isolated brain injury rarely accounts for hypotension in trauma patients with multisystem injury;8 rather, if present, hemorrhage must always be suspected.
18.104.22.168 Neurologic Disability: ICP and C-Spine
ICP: The GCS of seven, 10 minutes after the injury, is not predictive of the patient's clinical course or prognosis (other than the increased likelihood of C-spine injury). The patient did not have unequivocal evidence of increased intracranial pressure (ICP) since the pupils were equal and reactive and the motor response was decorticate, not decerebrate. As such there was no indication for paramedics to provide any intervention for managing elevated ICP with modalities such as intubation/hyperventilation, mannitol, or hypertonic saline.9
A potential pitfall in the management of the TBI patient is to assume that trauma is entirely responsible for altered mental status. Consideration must be given to the reversible causes of altered mental status, that is, hypoglycemia and drug toxicity, in addition to hypoxemia and hypotension.
C-spine immobilization: All patients with blunt trauma to the torso or neurological dysfunction should be suspected of having spinal cord injury until proven otherwise. Although neurologic impairment is fully manifest at the time of injury in most patients with vertebral injury,10 the implications of an unidentified spine injury are such that routine use of immobilization devices is indicated. Secondary neurological injuries are reported to occur in 10% to 30% of patients with delayed diagnosis, who are not immobilized at time of entry into care11,12 and in 2% to 10% of those who are immobilized.13 Three recent studies suggest that the probability of associated C-spine injury is at least tripled with GCS scores of 8 or less.14-16 Studies of techniques for optimal cervical immobilization have supported the use of a rigid cervical collar that incorporates the upper thorax, stabilization blocks on either side of the head, and a long spine board for transport.17,18 Spinal immobilization is not without consequence in that patients are at risk of aspirating if they seize, vomit, or lose protective airway mechanisms. In addition, collars have been consistently demonstrated to increase ICP and may worsen intracranial pressure dynamics in patients with head injury,19-23 probably by interference with cerebral venous drainage.24 With the history of TBI and GCS of 7, the presented patient was at significant risk of cervical spine trauma and required full cervical spine immobilization.
Patients with severe head injuries can experience episodes of agitation and combativeness, both of which tend to increase intracranial pressure, and can pose safety risks to both the patient and the field paramedic crew. Sedatives, such as benzodiazepines and opioid analgesics, are typically employed but, if given, the GCS score should first be determined, and the status of oxygenation and ventilation closely monitored after administration.
22.214.171.124 Transport Decisions
A priority in the early management of patients with moderate or severe brain injuries is transportation to the closest facility providing immediate access to neuroimaging and neurosurgical services. Patients with severe TBI transported to trauma centers without the availability of prompt neurosurgical care are at risk of a poor outcome.7 Acute subdural hematomas in patients with severe TBI are associated with a 90% mortality if evacuated more than 4 hours after injury, but only 30% mortality if evacuated earlier.25,26 Consequently, it is recommended that field emergency medical services (EMS) systems operate under strict ground and aeromedical trauma transport protocols. Commonly accepted criteria for transport of head-injured patients to a trauma center include severity of injury, a respiratory rate less than 10, systolic blood pressure less than 90 mm Hg, and a GCS score less than 12.
The ambulance arrived at the emergency department (ED) after a 15-minute transport. While the patient was being transferred onto the gurney in the trauma bay, it was noted that he was obese (5 ft 8 in [172 cm], 275 lb [125 kg], BMI 42.3 kg·m−2), he had blood coming out of his right ear, and his cervical collar was riding high up over his short neck. His BP was now 130/80 mm Hg, HR 110 bpm, RR 24 breaths per minute, SpO2 was 90% on a nonrebreathing facemask, and he had snoring respirations. His blood sugar was 110 mg/dL (6.1 mmol·L−1). His GCS score had decreased to 6 (2 for opened eyes to pain only, 2 for moans, and 2 for intermittent decerebrate posturing). At this point, it was noted that his right pupil was 8 mm and unreactive; his left pupil was 4 mm and reacted sluggishly. He moved all four extremities with no asymmetry. A quick airway evaluation revealed that his teeth were still clenched; he had a 6 cm thyromental span and 4 cm hypothyroid distance. There was no evidence of blunt trauma to the neck, and the cricothyroid membrane was identifiable and palpable in the midline. Two large-bore IVs were secured, blood was drawn, and sent for chemistries and type and cross match. Spun hematocrit was 45%. Portable chest and pelvis radiographs in the trauma bay were normal. Cross-table lateral x-rays of the C-spine showed good alignment and no prevertebral soft tissue swelling. A focused assessment with sonography in trauma (FAST) examination of the abdomen was performed, which showed no free fluid in the abdomen. A stat neurosurgery consult was ordered. Personnel from diagnostic imaging called, saying that they were ready to image the patient once he was stabilized. While the trauma team was deciding the best approach to securing the airway and managing the suspected increased intracranial pressure, the patient had a 30-second tonic-clonic seizure and desaturated to a SpO2 of 80%.
15.3.1 What Elements of Airway Management Must Be Considered in This Patient?
The immediate priority in this patient is reoxygenation, due to evidence suggesting that even a single episode of hypoxemia can worsen the prognosis in the patient with TBI.6,7 The patient should receive assisted bag-mask-ventilation with 100% O2. Once the SpO2 is again well above 90%, attention can be turned to formulating a plan for tracheal intubation. Unless the seizure spontaneously terminates within 1 to 2 minutes, pharmacologic intervention with lorazepam would be indicated.
From the perspective of airway management, trauma patients secured on a backboard with cervical immobilization can appear very intimidating. In fact, however, formal airway assessment may point to little anticipated difficulty (see Sections 1.6.1, 1.6.2, 1.6.3, and 1.6.4). In this patient's case, his obesity predicts an increased likelihood of difficult bag-mask-ventilation (BMV).27-29 Direct laryngoscopy may be difficult due to the patient's short neck and the cervical spine immobilization: manual in-line neck stabilization (MILNS) increases the likelihood of obtaining a poor (eg, Cormack/Lehane Grade 3) view at laryngoscopy.30 Any trismus will likely resolve with muscle relaxant administration, if these are employed. Extraglottic device insertion may be difficult, but should succeed. Finally, while obesity can make trans-tracheal access difficult, in this patient, the cricothyroid membrane was easily palpable, suggesting easy access.
15.3.2 How Are You Going to Proceed with Tracheal Intubation?
With a reasonable expectation of successful laryngoscopic intubation and the availability of a backup Plan B (eg, bag-mask-ventilation, extraglottic device use, or cricothyrotomy) should intubation fail, RSI should be used in this uncooperative patient. This plan confers the advantages of optimal intubating conditions with skeletal muscle relaxation while helping to reduce the risk of seizure activity or any laryngoscopy and intubation-induced increases in ICP, through the use of induction agents.
15.3.3 What Are Your Goals during Tracheal Intubation of the TBI Patient with C-Spine Precautions?
Our goals are to achieve tracheal intubation expeditiously while avoiding secondary neurologic injury by (1) maintaining oxygenation; (2) avoiding decreases in cerebral perfusion pressure; and (3) minimizing movement of the head and neck. Attention must also be directed toward prevention of gastric content aspiration.
15.3.4 How Are Cerebral Perfusion Pressure, Intracranial Pressure, Cerebral Blood Flow, and Autoregulation Related; What Changes TBI, and How Can We Modify These Changes?
Elevated ICP is associated with worse outcomes in traumatic brain injury. While its early recognition and management have not been conclusively linked to improved outcome, it is prudent to avoid any further increases in ICP in the brain-injured patient.
Intracranial pressure reflects the state of the contents of the fixed housing of the intracranial vault. The three normal contents of the vault are brain tissue, cerebrospinal fluid (CSF), and blood. Intracranial blood volume is directly related to cerebral blood flow. This flow is normally kept relatively constant over a wide range of blood pressures by cerebral autoregulation; as blood pressure varies, cerebral vasoconstriction or vasodilatation occurs to maintain constant blood flow, and in turn volume. However, the brain's ability to autoregulate blood flow over a range of blood pressures is impaired or lost in TBI.
A second mediator of cerebral blood flow is blood carbon dioxide tension. As blood carbon dioxide tension rises, so will cerebral blood flow, leading to increased intracranial blood volume and thereby ICP. While aggressive hyperventilation in the patient with TBI is no longer recommended in the absence of signs of brain herniation,7,31 attention should be paid throughout the airway management process to maintaining normocarbia.
Cerebral perfusion pressure (CPP) is the driving force for blood flow to the brain, and is measured by the difference between the mean arterial blood pressure (MAP) and the ICP, so that CPP = MAP − ICP. In the patient with disrupted autoregulation, decreases in MAP will decrease CPP while increases in MAP, if not accompanied by equivalent increases in ICP, may be beneficial because of the increase in driving pressure for oxygenation of brain tissue. It is generally recommended that the ICP be maintained below 20 mm Hg, MAP between 100 and 110 mm Hg,31 and CPP at or above 70 mm Hg. Hypotension leading to a decrease in CPP, even for a very brief period, is especially harmful, and along with hypoxia, has been shown to be an independent predictor of increased mortality and morbidity in patients with a TBI.6,7
15.3.5 How Does Airway Management Affect Intracranial Pressure Dynamics?
Laryngoscopy and intubation may cause an increase in ICP indirectly through an increase in blood pressure (with disrupted autoregulation) or through a direct effect on ICP. Both laryngoscopy and placement of an endotracheal tube result in afferent discharges that increase sympathetic activity and release of catecholamines, that is, the reflex sympathetic response to laryngoscopy (RSRL). A catecholamine surge may occur, especially with multiple attempts at laryngoscopy, potentially leading to increased heart rate and blood pressure. In the patient with TBI who has impaired autoregulation, such a blood pressure surge may contribute to an increase in ICP. This fact underscores the importance of using drugs to mitigate this RSRL.
15.3.6 What Effects on ICP Can Be Expected from Medications Commonly Used during Airway Management in the Emergency Department?
Pharmacologic agents used to aid in airway management must be selected with consideration of their effects on CPP. Prior to intubation, a modest fluid bolus will help maintain blood pressure, while vasopressors such as ephedrine or phenylephrine should also be immediately available to treat postintubation hypotension. Pretreatment, induction, and paralytic agents used to attenuate a rise in ICP and/or facilitate intubation in the patient with TBI have been discussed in detail in Chapter 4. It should be noted that if a longer acting muscle relaxant is used to facilitate tracheal intubation or maintain postintubation paralysis, formal monitoring for ongoing seizure activity should be instituted in this patient.
Victims of major trauma often require several interventions, including definitive airway control, before a full assessment of the cervical spine (C-spine) is possible. Without radiographic evidence of an intact C-spine, an unstable injury should be assumed and airway management undertaken accordingly.
15.4.1 What Range of Cervical Spine Movement Is Considered Within Physiologic Limits?
In order to interpret the data on the effects of airway manipulations on movement of the cervical spine, the amount of motion that would indicate spinal instability should be defined. Panjabi and White have suggested that horizontal motion (anteroposterior [A-P] displacement) of one vertebral body on another exceeding 20% of vertebral body width (or 3.5-mm in an adult, corrected for x-ray magnification); greater than 11 degrees of relative angulation of adjacent cervical vertebrae; or greater than 1.4 mm of distraction on resting lateral radiography of the subaxial cervical spine is abnormal and would indicate instability.32-34 Preexisting cervical abnormalities such as spinal stenosis could have neurologic consequences within these anatomic limits.35
15.4.2 What Effect Does Direct Laryngoscopy and Intubation Have on Movement of the Normal C-Spine?
Radiographic studies on live and cadaveric subjects with intact C-spines demonstrate that direct laryngoscopy (DL) causes considerable extension between the occiput and C2. Most extension (about 12 degrees) occurs between the occiput and C1, with slightly over half as much (approximately 7 degrees) between C1 and C2.36-47 A total of about 6 degrees of extension occurs from C2 to C5.37-40,46,47 From C5 to the cervicothoracic junction, a small amount (about 8 degrees) of flexion occurs.38-40 Actual tube passage causes slight additional superior rotation between the occiput and C1, but little other movement.36,46 There is some evidence that exposing only a minimum view during laryngoscopy (eg, seeking only a view of the posterior cartilages, but not of the cords) will reduce occiput-C2 extension.36,46,48,49
15.4.3 What Effects Do Basic Airway Maneuvers Have on Movement of a Normal C-Spine?
Several radiographic studies have looked at the effects of basic airway-opening maneuvers and bag-mask-ventilation on C-spine movement. One cadaver study performed with no applied MILNS found that chin lift and jaw thrust caused as much extension at C1 to C2 as oral laryngoscopic intubation.50 A second cadaver study, using backboard, cervical collar, and tape found that significantly more cervical spine displacement occurred with bag-mask-ventilation (BMV) than with either oral or nasal tracheal intubation.51 However, a more recent study using elective surgical subjects with their heads taped in a neutral position found BMV to cause significantly less cervical spine movement than DL at each of the occiput-C1, C1-C2, C2-C5, and C5-T1 motion segments.40 Although sometimes conflicting in their results, these studies can at least be taken as an indication that appropriate cervical spine precautions should be applied during all phases of airway management in those patients at risk of C-spine injury.
15.4.4 What Are the Effects of Basic Airway Maneuvers in Models of an Injured C-Spine?
Donaldson et al50 studied the motion that occurred during various airway maneuvers in a series of six cadavers with a surgically created unstable C1-C2 segment. With the head stabilized, they found that preintubation maneuvers (chin lift and jaw thrust) caused more narrowing of the space available for the spinal cord (SAC) than DL or blind nasal intubation. In a subsequent cadaver series, this time with an unstable C5-C6, the same investigators demonstrated a trend toward chin lift/jaw thrust causing as much movement as DL.52 Aprahamian also studied a cadaveric specimen with a posteriorly destabilized C5-C6 segment, and similarly reported that chin lift/jaw thrust caused as much or more movement at the site of injury as oral or nasal intubation.53 Brimacombe et al determined cervical spine motion for six airway management techniques in cadavers with a posteriorly destabilized third cervical (C3) vertebra. Here again, both chin lift/jaw thrust and oral intubation with DL caused significant A-P displacement of the unstable segment,54 although the movements were within the previously described physiologic limits.
While these studies on basic airway maneuvers provide reassuring evidence that DL is unlikely to cause more movement than preintubation maneuvers, they also reinforce that appropriate precautions against movement be instituted well before a tracheal intubation attempt.
15.4.5 How Effective Is Manual in-Line Neck Stabilization (MILNS) in Preventing C-Spine Motion in Normal Patients and Injury Models?
Manual in-line neck stabilization (MILNS) appears to restrain overall spinal movements occurring during DL in patients and cadaveric specimens with normal spines to within physiological levels, and has less impact on airway interventions than do other forms of immobilization.37,49,55 In injury models, Lennarson reported that MILNS did not completely eliminate movement at the injury level during intubation of a cadaver model with either posterior or complete ligamentous C4-C5 disruption; however, the movements recorded during interventions were within physiological limits.46,56 Gerling evaluated the effect of MILNS as well as cervical collar immobilization on spinal movement during direct laryngoscopy in a cadaver model with a C5-C6 transection injury. Although there was less A-P displacement measured with application of MILNS compared with collar (7.5% of vertebral body width vs 13.7%), overall the magnitude of movement was small and within physiological range. There was no difference in axial distraction or angular rotation.57 Turner studied 10 cadavers surgically destabilized at C4-C5. MILNS did not significantly change the median motion seen during DL in any of angulation, distraction, or A-P displacement at the unstable level.35
Two recent comprehensive reviews on the topic support the notion that while there may be some reduction in overall C-spine motion with MILNS, movement at individual motion segments, including sites of injury, may in fact not be significantly restrained by stabilization.58,59 As Aprahamian53 stated about collar immobilization in 1984, it may be that MILNS should simply be taken as a caution sign of a possible neck injury, and to then use gentle and precise airway maneuvers to minimize C-spine movement.59
15.4.6 How Does Applied MILNS Impact Ease of Direct Laryngoscopy?
Many trauma patients presenting to the emergency department arrive on a backboard immobilized with rigid cervical collar, sandbags, and tape. Unfortunately, any immobilization technique that restricts mouth opening will make laryngoscopy more difficult. In one study, 64% of patients immobilized with a collar, tape, and sandbags presented at Grade 3 or 4 view with DL, compared to only 22% of patients undergoing MILNS, with cervical collar removed.30 Other studies concur that direct laryngoscopy in patients stabilized with cervical collars will result in a greater than 50% incidence of Grade 3 or 4 views.57,60 Goutcher et al studied the effect of semirigid cervical collars on mouth opening in awake volunteers. Mean mouth opening of 40 mm without a collar decreased to 26 to 29 mm with cervical collar, and in a quarter of the subjects, mouth opening was reduced to 20 mm or less.61 A common pattern of practice is therefore to loosen or open the rigid collar during laryngoscopy after the application of MILNS. In general, when MILNS is substituted for a rigid cervical collar, the direct laryngoscopic view should improve, with a quoted incidence of Grade 3 or 4 views between 20%47,62-64 and 50%.65-67 Thiboutot randomized elective surgical patients to standard sniffing position or MILNS for DL. In this series, the incidence of Grade 3 or 4 views in the MILNS group exceeded 50%, and 50% of patients could not be intubated within 30 seconds, compared to 5.7% without MILNS.65 The consistent message from the literature is that MILNS application is associated with difficult direct laryngoscopy; strategies to improve laryngeal view and facilitate tracheal intubation during the application of MILNS have been reported and will be discussed subsequently.
15.4.7 Why Is Traction No Longer Used during MILNS?
Older publications make reference to using in-line traction when C-spine precautions were indicated. However, traction forces applied during MILNS may endanger the spinal cord if there is a serious ligamentous injury. Lennarson noted distraction at the site of a complete ligamentous injury when traction forces were applied for the purposes of spinal stabilization during direct laryngoscopy.56 Similarly, Kaufmann demonstrated that in-line traction applied during radiographic evaluation resulted in spinal column lengthening and distraction at the site of injury in four recently deceased patients with ligamentous disruptions.68 Bivins also studied the effect of in-line traction during orotracheal intubation in four victims of blunt traumatic arrest, who had unstable spinal injuries.69 Traction applied to reduce subluxation at the site of injury resulted in both distraction and posterior displacement at the fracture site. Current recommendations promote the use of in-line stabilization and not traction during airway interventions requiring C-spine precautions.
15.4.8 Does the Choice of Direct Laryngoscope Blade Impact the Degree of C-Spine Movement during Laryngoscopy?
A number of studies have reported cervical spine movement caused by different laryngoscope blades. Two studies in elective surgical patients found significantly less (by about 3 degrees) head extension with Miller, as compared with Macintosh blade laryngoscopy.42,70 However, other studies have failed to demonstrate a difference in motion between the two blades.51,55,71 Studies with the levering tip McCoy/CLM-type blades have also generated conflicting results: some have found significantly less C-spine movement with use of the activated blade when compared to a Macintosh48,72 while others have not.57,73
In cadaver injury models, one study showed that Miller blade laryngoscopy resulted in significantly less axial distraction (1-2 mm) at the level of a surgically created C5-C6 transection than the Macintosh, but no difference in angular rotation or A-P displacement.57 However, Aprahamian's study of a single cadaver, also with an unstable C5-C6 injury, reported no difference between Macintosh and Miller blades.53 At present, there is no evidence that Miller blade use is preferred in the patient at risk from a C-spine injury.74
15.4.9 Is Any Direct Laryngoscopy Blade Superior for Exposing the Glottis with Applied MILNS?
To date, there is no convincing evidence that either curved or straight blades are superior to the other for exposing the laryngeal inlet during direct laryngoscopy with applied MILNS. However, a number of studies suggest that laryngoscopy using the levering tip McCoy/CLM blade with the tip activated may be helpful when a poor view is obtained in the setting of MILNS. Three studies report improvement of a Grade 3 view to 2 or better in 83% (with applied MILNS);75 86% (MILNS with cricoid pressure);76 and 92% (rigid cervical collar) of cases respectively.77
15.4.10 How Do Alternatives to DL Impact Cervical Spine Movement during Tracheal Intubation?
Many of the alternatives to DL appear to cause less movement of the cervical spine during tracheal intubation. Laryngoscopy and intubation with the Bullard laryngoscope has been shown to result in significantly less C-spine movement than DL with Macintosh37,71,78 or Miller blades.71 Similarly, intubation with the Pentax airway scope (AWS) results in significantly less upper C-spine movement than DL with both attempted full44,79 and minimal view80 exposure of the cords. C-spine movement during AWS use is further reduced with prior passage of a bougie via the blade's delivery channel.81 Compared with the Macintosh blade, Airtraq-facilitated intubation appears to cause significantly less movement at some, but not all C-spine motion segments.39,41 The use of a Glidescope video laryngoscope (GVL) results in some reduction in midcervical spine movement compared with DL, but elsewhere movement is similar.40,47 Studies with the Bonfils and Shikani optical stylets have concluded that less C-spine movement occurred with the optical stylets, compared to Macintosh blade DL,38,78,82 as is the case with the Trachlight™-lighted stylet.40,83 LMA Fastrach-facilitated enabled intubation results in less upper C-spine extension than direct laryngoscopy,84,85 although mask insertion, cuff inflation, and intubation exerts significantly more pressure against C3 than other techniques, and may result in some posterior displacement of the upper cervical spine.54,86 Tracheal intubation using a flexible bronchoscope laryngoscope results in less movement of the head and neck compared to direct laryngoscopy,85 GVL,87 and LMA Fastrach54-faciliated intubation in anesthetized patients, and a comparable amount to Trachlight intubation.45 However, this information must be tempered with the appreciation that flexible bronchoscopes are expensive, can be more difficult to use, particularly in the presence of blood and secretions, and can be time-consuming in emergencies.36 Flexible bronchoscopes are generally used if an awake intubation is elected, an option that permits the advantage of postintubation neurologic reassessment. Despite the evidence that there are lesser degrees of spinal movement when tracheal intubation is facilitated by some of the alternative devices, there is no evidence that neurological outcomes are altered by their use in the patient at risk with a C-spine injury.
15.4.11 How Do Adjuncts and Alternatives to DL Compare for Successful Intubation of the Patient Undergoing MILNS?
The tracheal tube introducer (TTI) is a valuable adjunct to DL in the patient undergoing MILNS. Nolan and colleagues randomized half of 157 patients undergoing MILNS in the operating room to attempted primary visual passage of the tube, or prior passage of a TTI.63 Although the technique was quicker overall, 11 patients in the visual group required greater than 45 seconds for intubation, and there were five failures. All five failures were successfully intubated with adjunctive use of the TTI.
Other studies of the Bullard laryngoscope,37 Glidescope videolaryngoscope,64 Pentax AWS,64,88,89 and Airtraq90 or optical stylets66,91 have documented one or more of a significantly improved laryngeal visualization,63,64,88,89 better success rate,66,89,91 or lower intubation difficulty score (IDS92)64,88-90 compared to Macintosh blade DL in the patient undergoing MILNS or wearing a cervical collar.
Several series evaluating LMA Fastrach use in patients with applied rigid collars have reported intubation success rates comparable to those obtained in unrestrained elective surgical patients93-95: the one study reporting a poor success rate under these conditions had included cricoid pressure in the study protocol.96 Compared with the LMA Fastrach in a prospective study of elective surgical patients with applied MILNS, intubation with the Trachlight™ was quicker and resulted in a significantly higher success rate.97
In general, most of the alternatives to DL used in the patient undergoing MILNS cause less neck movement and sometimes enable easier visualization and/or tracheal intubation. For those with access to the devices and skill in their use, these may be a good option for such conditions, although compared to DL there are no data indicating an outcome benefit.
15.4.12 Is Cricoid Pressure Contraindicated in Patients with Potential C-Spine Injury?
Radiographic studies have generally found that cervical spine movement with application of cricoid pressure is within physiologic limits. In a study of cadavers with intact cervical spines, with 40N of cricoid pressure and radiographs for assessment, Gabbott et al found a median A-P displacement of only 0.8 mm.98 In a study of cadavers with an unstable C-spine at the C5-C6 level, Donaldson reported 0.64 mm of A-P displacement, 3.6 degrees of angulation and 1 mm of distraction with cricoid pressure application,52 and no significant movement at the injury level in a second study using cadavers with instability at the C1-C2 segment.50
The decision to apply cricoid pressure in the patient with TBI must be considered in the context of both its risk of C-spine movement and other detrimental effects. Cricoid pressure may prevent successful BMV or interfere with efforts to place or ventilate through an LMA.99 This likely results from obstruction of the airway by the applied pressure; the loss of airway patency may also shorten the time to desaturation even in the absence of ventilation.100 A recent review has suggested that cricoid pressure may also increase difficulty experienced during airway management with DL, the lightwand, and the flexible fiberoptic bronchoscope.99 Thus, although cricoid pressure appears to result in radiographic movement that is within physiologic limits,32 it may be prudent to reconsider its use in patients with known unstable lesions at or near the level of the cricoid cartilage, or in those in whom difficulty with bag-mask-ventilation or tracheal intubation has been encountered.
15.4.13 Does Administration of an Induction Agent and/or a Muscle Relaxant by Itself Have Any Effect on the C-Spine?
Historically, concern has been raised that administration of an induction agent and muscle relaxant to the patient with a C-spine injury could release any splinting of an unstable segment by adjacent muscle spasm. However, there is no readily available objective evidence for a clinically significant degree of cervical spinal movement due solely to induction agent and muscle relaxant administration.
15.4.14 How Are Extraglottic (Rescue) Ventilation Devices Impacted by C-Spine Precautions?
During insertion, the LMA Classic transiently exerts as much pressure on the upper cervical vertebrae as the LMA Fastrach.86 In a cadaver model of a destabilized C3 segment, both the LMA Fastrach™ and LMA Classic™ caused significant posterior displacement of the unstable segment, yet significantly less than that caused by Combitube™ insertion.54 Available data suggest that the Combitube™ can be difficult to insert with the neck held in-line101 and is likely to cause spinal movement.54 In comparison with the LMA Fastrach, the laryngeal tube was found to have a lower first-time insertion success rate in a series of patients with in-line stabilization and required more time to successfully establish ventilation.102 However, it must be recognized that extraglottic devices are vital rescue oxygenation tools in difficult situations, and in spite of the potential for difficult insertion or C-spine movement, the benefits of their use in reoxygenating a hypoxemic patient will often outweigh the potential risk, particularly if care is taken to minimize such movement.
15.4.15 What Effect Does Cricothyrotomy Have on C-Spine Movement?
Surgical cricothyrotomy was originally advocated as a preferred airway intervention in patients at risk for cervical spine injury (CSI), rather than orotracheal intubation, and is now deemed to be an appropriate alternative if oral or nasal routes cannot be used or are unsuccessful. Although long considered safe in the presence of a CSI, the effect on C-spine movement of surgical cricothyrotomy has not been well studied. Gerling studied cervical spine movement during open surgical cricothyrotomy in a series of 13 cadavers with a complete C5-C6 transection.103 A-P displacement was limited to 6.3% of C5 body width (1-2 mm), and axial distraction to less than 1 mm across the C5-C6 injury during the procedure. Earlier, using a similar injury model in a single cadaver, Donaldson et al reported that A-P displacement was limited to 0.9 mm during tracheotomy.52 As these movements are within physiological levels, values from both studies would likely be clinically irrelevant.
15.4.16 How Safe Is It to Intubate the Trachea of the Patient with a Potential C-Spine Injury?
There is no evidence that endotracheal intubation using direct laryngoscopy with in-line stabilization increases the risk of neurologic injury in patients with unstable cervical spine fractures.104-106 Traditionally, oral intubation using direct laryngoscopy was deemed dangerous because it was thought to cause excessive spinal movement with the potential for secondary injury.62 It was thought that such secondary injury could be avoided by the careful performance of nasotracheal intubation or cricothyrotomy. Although there were no data at that time to support this thesis and later data would seem largely to refute it, this hypothesis had achieved a sufficiently widespread acceptance as to be labeled a "therapeutic legend of emergency medicine" by Rosen.107 McLeod and Calder reviewed the use of the direct laryngoscope in patients with spinal injury or pathology.108 With the possible exception of one case,109 they concluded after review and analysis of the case reports that it was unlikely that the use of the direct laryngoscope was the cause of the myelopathies reported. The potential for aggressive direct laryngoscopy with unrestricted spinal movement to cause neurological injury in spine-injured patients has been shown in two further case reports.109,110 However, the message that these reports emphasize the need for spine stabilization in patients at risk of a C-spine injury until such injury is ruled out or definitive therapy for diagnosed CSI is implemented, and not that careful direct laryngoscopy is contraindicated.
15.4.17 Is Direct Laryngoscopy Acceptable for Intubation of the Patient with a Cervical Spine Injury?
There is clearly a difference of opinion in the literature regarding the optimal means of securing the airway by tracheal intubation in patients with cervical spine injury. Many authors have reported on the use of the direct laryngoscope in the management of patients with cervical spine injury for both elective and emergency intubations.104-106,111-116 Most of these studies are limited both by their small sample size and their retrospective nature. However, they do reveal that neurological deterioration in spine-injured patients is uncommon after airway management when appropriate care is provided, even in high-risk patients undergoing urgent tracheal intubation. These studies are not sufficient to rule out the possibility that airway management provided in isolation or as part of a more complex clinical intervention, even provided with the utmost care, may rarely result in neurological injury.
The use of a direct laryngoscope following induction of anesthesia in the patient with a head injury is deemed an appropriate practice option by the American College of Surgeons as outlined in the manual of Advanced Trauma Life Support Program (ATLS, 2004) for doctors and by experts in trauma, anesthesia, and neurosurgery105,106,108,117-126 and by the Eastern Association for the Surgery of Trauma.125 Advantages of the direct laryngoscope in this setting include its effectiveness, the ability to visualize and remove upper airway foreign bodies during use and clinician familiarity; many anesthesia practitioners are not similarly skilled with other practice options.127 Enthusiasm has been expressed by neuroanesthesia experts for the exclusive use of the flexible bronchoscope to facilitate tracheal intubation in patients with a CSI, citing this as the optimal practice option.128 However, it is worth noting that over 40% of American anesthesiologists admit that they are not comfortable using a flexible bronchoscope for airway management.127 Further, it should be recognized that significant difficulties may be experienced during the use of the bronchoscope, even by persons skilled in its use, during airway management in patients with a CSI.129 Carefully performed direct laryngoscopy with appropriate MILNS in the trauma patient at risk for a C-spine injury can be considered a pattern of practice within the standard of care.
15.4.18 Is There Anything Else that Might Make Airway Management More Difficult in the Patient with a C-Spine Injury?
A small number of case reports and case series document the association of prevertebral retropharyngeal hematomas with some injuries of the upper C-spine, particularly with a hyperextension injury, as anterior elements of the spinal column are disrupted.130-133 Such patients may present with symptoms of dysphagia and dyspnea, with the potential for difficult laryngoscopy due to anterior displacement of the laryngeal inlet.
15.5.1 What Are the Postintubation Considerations in the Head-Injured Patient?
Objective confirmation (eg, with an end-tidal CO2 monitor) of tracheal placement of the ETT is essential. Recognizing the importance of maintaining CPP, blood pressure should be reassessed after airway interventions and any unacceptable drop corrected with fluid and/or vasopressors. Pupils should be reassessed. After checking for optimal position of the tip of the ETT, the tube should be firmly fixed to the patient, as a number of transfers will occur (eg, to the diagnostic imaging department and thereafter to the ICU or operating room). However, tight ties encircling the neck should be avoided. If the patient's blood pressure permits, a slight head-up position can be achieved by placing the stretcher in the reverse Trendelenberg position. This will promote venous drainage and may reduce elevated ICP.
Mechanical ventilation in the patient with elevated ICP is based on optimizing oxygenation and avoiding ventilation mechanics (eg, positive end-expiratory pressure [PEEP] or high peak inspiratory pressure [PIP]) that would increase ICP.
Controlled hyperventilation to a Paco2 of approximately 30 mm Hg was formerly recommended for the early management of elevated ICP. It was believed that reduction in Paco2 tensions in the brain led to vasoconstriction and decreased cerebral blood flow, thereby decreasing ICP. However, a growing body of research provides evidence that routine hyperventilation results in worse outcomes in TBI patients, possibly due to alterations in regional cerebral blood flow resulting in accumulations of neurotoxic agents, for example, lactate and glutamate.134 The Brain Trauma Foundation Guidelines for the Management of Severe Traumatic Brain Injury now recommends that prophylactic hyperventilation be avoided, and that patients with severe TBI be ventilated in such a way as to target not less than the lower limits of normocapnia (Paco2 of 35-40 mm Hg).135 A similar approach seems prudent in patients with nontraumatic elevations of ICP (eg, cerebral hemorrhage). Hyperventilation to a Paco2 of 30 mm Hg should be used only when osmotic agents and CSF drainage are not effective in managing an acute rise in ICP accompanied by patient deterioration, and utilized only until signs of herniation (eg, decerebrate posturing or a fixed dilated pupil) resolve.
Unless early and frequent neurological examinations are required (eg, by a neurosurgeon to decide whether there is sufficient persisting neurological functioning to warrant an attempt at surgical evacuation of a massive subdural hematoma), long-term sedation and paralysis will permit effective, controlled mechanical ventilation and other necessary interventions. Sedation and paralysis can also help mitigate the stimulating effects of the tube in the trachea and will eliminate any possibility of the patient coughing or bucking. A full paralyzing dose of a competitive neuromuscular blocking agent, such as rocuronium 1.0 mg·kg−1, may be given, along with an initial dose of a sedative agent such as a benzodiazepine. Subsequent doses of approximately one-third of the initial dose of both agents should be given if the patient shows evidence of increased sympathetic activity or initiating motor movement. The pharmacologically paralyzed patient at risk of seizures should be monitored with EEG.
15.5.2 What Happened to This Patient?
As outlined earlier in Section 15.3, the patient's airway was fully assessed. The decision was taken to perform rapid-sequence intubation. Preparations included ensuring qualified help and requisite airway equipment were at hand, together with a briefing of the team about the Plan B approach should difficulty be encountered. An assistant was delegated to provide in-line immobilization of the C-spine, following which the front of the patient's rigid collar was removed. Denitrogenation was provided with a tightly fitting face mask, and induction medications were administered followed by application of cricoid pressure and administration of the skeletal muscle relaxant. For intubation, direct laryngoscopy was performed with a Macintosh #4 blade, with the practitioner attempting to expose only the posteriormost aspect of the laryngeal inlet. A tracheal tube introducer was then placed above the exposed arytenoid cartilages63, followed by endotracheal tube (ETT) passage over the introducer with the laryngoscope blade still in situ. Tracheal placement of the ETT was confirmed with a disposable end-tidal CO2 detector, whereupon cricoid pressure was released. The anterior aspect of the rigid cervical collar was reapplied, and MILNS was released. Vital signs were reassessed, with particular reference to the blood pressure. Decisions were then made about ongoing sedation and skeletal muscle relaxation and arrangements were made for patient transfer to the diagnostic imaging department.
Airway management of the patient with a head injury must be undertaken with an appreciation of the importance of avoiding secondary injury to both brain and C-spine. Hypoxemia and hypotension must be avoided and formal C-spine precautions must be observed. However, apart from these directives, the practitioner should take comfort in the knowledge that as long as reasonable precautions are undertaken, familiar airway interventions are within the standard of care for the patient with potential C-spine injury, including rapid-sequence intubation, bag-mask-ventilation, and intubation using careful direct laryngoscopy. To the practitioner experienced in their use, alternative intubation techniques (eg, lightwand, rigid fiberoptic laryngoscope, and flexible bronchoscope) may permit tracheal intubation with less C-spine movement, although evidence is lacking of improved clinical outcome compared to use of direct laryngoscopy with MILNS. Awake intubation of the patient with a known C-spine injury confers the opportunity to reevaluate the patient's neurologic status postintubation. Irrespective of technique chosen, airway management in this setting should not proceed before a formal airway evaluation has been performed, needed personnel have been assembled and briefed, and airway equipment for the chosen and Plan B and C approaches has been readied.