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When Is It Safe to Extubate a Newly Quadriplegic Patient? When Is Early Tracheostomy Appropriate?

Christopher N. Faber and Antonios Zikos

BRIEF ANSWER

Background

When to wean and when to perform tracheostomy are controversial topics even in the general population of patients with respiratory failure. These questions are even more difficult in the tetraplegic patient popula tion because of the paucity of data specific to this unique clinical situation. Most management decisions in tetraplegic patients are based on data from studies in the general patient population, with varying degrees of modification for the unique clinical features of this patient population.

There are no well-validated weaning criteria for tetraplegic patients. Poor cough and diaphragm mobility increase the frequency of secretion-related complications (such as atelectasis and pneumonia) in these patients. Even patients with normal diaphragm function at the time of injury, who have a lower incidence of respiratory complications, have impaired clearance of secretions that necessitates meticulous respiratory hygiene to avoid later respiratory complications. Patients with paralyzed diaphragms require more time to recover independent breathing and are more prone to develop respiratory complications. Therefore, standard weaning and extubation criteria may not apply to tetraplegic patients.

Airway control, secretion clearance, and expected duration of respiratory muscle paralysis are key factors influencing the decision for the necessity and timing of tracheostomy in tetraplegic patients. Unfortunately, these parameters are not easily quantified. Therefore, the decision for tracheostomy, like that for extubation, relies heavily on clinical judgment.

Literature Review

Respiratory complications are common in the spinal cord—injured patient and are the major cause of postinjury mortality, with pneumonia being the leading cause of respiratory death.1 These complications frequently make the use of mechanical ventilation necessary. Respiratory failure complicating tetraplegia is due not only to impairment of the diaphragm’s bellows function by the neurologic injury, but also to the added ventilatory burdens imposed by the associated injury complex, subsequent infectious complications, and the systemic inflammatory response. Risk factors for the need for mechanical ventilation include neurologic level above C5, complete cord lesions, copious secretions, pneumonia, and atelectasis (class III data).²

Weaning new quadriplegics from the ventilator is a complex process requiring optimal management of the associated injury complex followed by intensive respiratory rehabilitation. Frequently, rehabilitation of respiratory muscle function is the limiting factor in liberating spinal cord—injured patients from the ventilator. The recovery of this function may take months, even in patients who have a reasonable expectation of eventual ventilator independence.³

Respiratory Physiology in Tetraplegia

The bellows function of the lung requires inspiratory and expiratory muscles. The inspiratory muscles are the diaphragm (innervation from C3 to C5); the accessory muscles, consisting of sternocleidomastoids (accessory nerve, C1 and C2), trapezius (C1 to C4), scalene, and pectoralis (C4 to C8) muscles; and the intercostal muscles (T1 to T12). During inspiration, the diaphragm descends. The intercostal muscles elevate the sternum and move the ribs upward and outward. They also stabilize the chest wall. Maximal inspiration requires use of the accessory muscles. The expiratory muscles are the internal and external oblique muscles (T7 to T12), the transverses abdominus (T7 to L1), the rectus abdominus (T7 to L1), and the lateral intercostal muscles (T1 to T12).^4,5

Cervical spine injury below C5 results in impaired expiratory function and a weakened cough. Patients with injuries from C3 to C5 have, in addition, variably diminished inspiratory function resulting in reduced vital capacity. Patients with injuries above C3 have complete loss of inspiratory and expiratory capacity; however, using forms of glossopharyngeal breathing, they may be able to sustain short periods of spontaneous breathing.⁶

Two important concepts in the respiratory management of patients with cervical spine injury are the postural dependence of vital capacity and the late development of spasticity. In the upright position, the abdominal contents descend unrestrained by the flaccid abdominal wall. This displacement of the abdominal contents passively pulls the diaphragm downward and limits inspiratory excursion, thereby paradoxically reducing vital capacity in the upright position (class II data).⁷ This adverse postural consequence can be minimized through the use of abdominal binders when a patient is in a seated position (class II data).⁸

Lung function in the tetraplegic patient improves as flaccidity is replaced by spasticity.⁶ Increased tone in the intercostal and abdominal wall muscles stabilizes the rib cage and allows for more effective diaphragmatic function. McMichan et al⁹ demonstrated an improvement in vital capacity from 1.5 to 2.7 L and an improvement in maximal inspiratory pressure from 46 to 77 cm H₂O 18 weeks after cervical spine injury (between C4 and C8) in 22 patients (class II data). Ledsome and Sharp¹⁰ found that vital capacity nearly doubled within 5 months of cervical spine injury (class II data).

Respiratory Complications in Tetraplegia

In their review of the clinical outcomes for over 2000 patients from the National Spinal Cord Injury Database, Ragnarsson et al¹ found pulmonary complications to be the most common cause of death. The major pulmonary complications of incomplete and complete tetraplegia, respectively, were aspiration (4–11%), atelectasis (16–39%), pneumonia (12–38%), and ventilatory failure (11–37%). Patients with higher and more complete cervical spine injuries, as well as older patients, had greater risk of developing these complications. Claxton et al² found that mortality was associated with increasing age, neurologic level above C4, and Glasgow Coma Scale score ≤13 (class III data). Independent risk factors for requiring mechanical ventilation included copious secretions in the first week and pneumonia.² The need for and duration of mechanical ventilation may be related to completeness of myelopathy, severity of associated injuries, and presence of cardiopulmonary comorbidities (class III data).¹¹ Once respiratory failure occurs, it is frequently prolonged (class II data).¹²

Weaning the Tetraplegic Patient from the Ventilator

Weaning “criteria” are not defined for the tetraplegic patient. Vital capacity (10–15 mL/kg),^13,14 respiratory rate (12–20 breaths/min),14 and minute ventilation (<10 L/min)¹³ are frequently recommended weaning parameters, but these measurements have poor predictive value in general populations¹⁵ and have not been validated in tetraplegic patients. The frequency-tidal volume ratio (F:V_T), or rapid shallow breathing index, also has not been validated in tetraplegics, but it does serve as a useful indicator of readiness for extubation in the general population of intensive care unit patients (class I data for a general patient population).¹⁵ An index of 105 breaths/minute/liter or less has a positive predictive value of 0.78.

Poor cough and clearance of secretions increase the susceptibility of tetraplegic patients to respiratory complications. Unfortunately, these airway-related comorbidities are not readily quantified by the conventional weaning parameters discussed above.^16,17 Epstein¹⁶ showed that patients with favorable F:V_T who failed extubation most often failed for reasons distinct from their original respiratory process. In over half of these patients, reintubation was made necessary by an airway complication such as aspiration or obstruction (class II data). In a prospective study assessing the predictive value of weaning criteria, Vallverdu et al¹⁷ showed that patients with the highest frequency of extubation failure (35.7%) were those with neurologic disease (class II data). Although none of the patients in this study had tetraplegia, the study underscored the importance of poor cough and secretion clearance as causes of weaning failure in the neurologically impaired patient. In this study, maximal inspiratory (>70 cmH₂O) and expiratory pressures (>50 cmH₂O) were better predictors of extubation readiness in patients with neurologic disease.

There exist several approaches to weaning the tetraplegic patient from mechanical ventilation. Peterson et al¹⁸ found that progressively increasing times of spontaneous respiration was twice as effective in achieving ventilator weaning in tetraplegic patients as an approach employing gradual reductions in intermittent mandatory ventilation (IMV) support (class III data). This experience mirrored that of a large prospective, randomized, multicenter study that demonstrated that once-daily spontaneous breathing allowed liberation from mechanical ventilation three times more rapidly than IMV weaning and twice as fast as pressure support weaning (class I data for a general patient population).¹⁹ This concept of respiratory muscle training is the basis for strategies employing resistive training to achieve ventilator independence.