A Comparison of High vs. Low Tidal Volumes in Ventilator Weaning for Individuals With Cervical Spinal Cord Injuries

While respiratory failure in people with SCI is common, clinicians have not come to a
consensus on the best strategy to manage the mechanical ventilation of these individuals or
whether to manage people with SCI differently from other patients. The Consortium for
Spinal Cord Medicine has developed Clinical Practice Guidelines using protocols established
at Craig Hospital in the 1980s and 1990s, but these are based only on clinical experience
and retrospective, cohort data using historical controls.

These guidelines suggest that patients should be ventilated with tidal volumes (VT)of 20-25
cc/kg of ideal body weight (IBW). This recommended VT is at least twice as large as
conventional VT used for general medical and surgical patients requiring mechanical
ventilation. However, there is a clinical belief that people with SCI should be ventilated
at higher VT to prevent atelectasis, to decrease the risk of pneumonia, and to facilitate
weaning. This belief was fostered by a retrospective, concurrent cohort comparison study of
individuals with SCI, which found that the use of high VT on the ventilator (mean 25.3
cc/kg, PAP<40) was associated with more rapid resolution of atelectasis and more rapid
weaning from mechanical ventilation than the use of low VT (mean 15.5). Therefore, people
with SCI have been clinically managed using high VT for the past 2-3 decades without
prospective data to confirm these clinical impressions.

At the same time that these ventilator strategies evolved in the care of patients with SCI,
several clinical studies in general medical and surgical patients requiring mechanical
ventilation suggested that high VT leading to higher airway pressures could actually promote
lung injury. This occurred when higher VT increased the risk of over-distending the airways
and creating volume-related trauma.16-19 In multiple studies, VT of only 10-15 cc/kg IBW
was found to produce alveolar over-distention, stretch injury and barotrauma. This work led
to the belief that low VT of 6-8 cc/kg IBW could be helpful in protecting mechanically
ventilated individuals from ventilator-induced lung injury.

Whether these findings and recommendations apply to individuals with SCI requiring
mechanical ventilation is unclear. At least one study of mechanically ventilated
individuals without acute respiratory distress syndrome suggests that the use of low VT (6
cc/kg) increases the risk of atelectasis.

With the lack of prospective, evidence-based data regarding optimal VT for persons with a
SCI who are ventilator-dependent, clinicians may be inclined to use lower VT to prevent lung
injury, unless there is more definitive data to show that higher volumes are as safe as low
VT and that higher VT facilitate more rapid weaning from mechanical ventilation.

This is a prospective randomized, controlled study to compare outcomes between individuals
with sub-acute, ventilator-dependent tetraplegia using high (20 cc/kg) tidal volume (VT) vs.
low (10 cc/kg) VT during mechanical ventilator support. While the use of lower tidal
volumes in the general pulmonary community is more common, we and others in the SCI
rehabilitation community have used 20 cc/kg IBW tidal volumes or higher to manage and
attempt to wean individuals with SCI on mechanical ventilation. This study will address the
safety and efficacy of using higher VT in ventilator weaning. A series of objective
measures and standardized protocols are implemented to ensure equivalent pulmonary
management and weaning processes in individuals, regardless of their randomization status.

- For individuals with sub-acute ventilator-dependent tetraplegia, providing high tidal
volumes (VT = 20 cc/kg) will result in more rapid weaning from mechanical ventilation
than use of low tidal volumes (VT = 10 cc/kg) in an 8-week trial.

- For these individuals, use of high tidal volumes will result in fewer episodes of
atelectasis and ventilator acquired pneumonia (VAP) compared to use of low tidal
volumes.

- There will be no difference in the incidence of a) barotrauma or b) ARDS between those
using high tidal volumes compared to those using low tidal volumes.