Respiratory Management Following Spinal Cord Injury - 15

CLINICAL PRACTICE GUIDELINE

In addition, protocol patients were totally weaned from the ventilator in an average of 37.6 days, whereas those ventilated with lower tidal volumes were weaned in an average of 58.7 days. Peterson and colleagues found no significant difference in complication rate, and only one of the 42 patients required a chest tube (requiring a chest tube was used as an indicator of barotrauma). This chest tube was required after placement of a subclavian catheter. Based on the incidence of new pneumothorax during ventilator treatment, if the patient is treated carefully, with slowly increasing ventilator tidal volumes, there is no increased risk of pneumothorax, according to this small series of patients. In this group of patients, dead space was used to control the pCO2 level. Ordinarily, physicians use smaller ventilator tidal volumes or slower respiratory rates on the ventilator to control the pCO2 level, but doing this will cause atelectasis, or a sensation of distress in the tetraplegic patient, whereas adding dead space counteracts the hyperventilation effect of larger tidal volumes. Sometimes very large amounts of dead space will be required to keep the pCO2 at a proper level. Why the larger tidal volume group of patients weans faster is unclear. It may be that the larger tidal volumes stimulate the release of surfactant (Massaro and Massaro, 1983) and that the compliance of the lungs is thereby improved. With improved compliance, the effort necessary for the patient to ventilate the lungs spontaneously is reduced. In this group of patients, where there is hypoventilation because of the paralysis, reducing the work of ventilation will be helpful in weaning off mechanical ventilation. 12. Set the ventilator so that the patient does not override the ventilator settings.
(Scientific evidence–III/V; Grade of recommendation–C; Strength of panel opinion–Strong)

side. If the patient is allowed to trigger the ventilator, because the ventilator’s rate is set too low the stronger side may actually draw air out of the weaker side, contributing to the formation of atelectasis. If the pCO2 is kept in the range of 30–35mmHg, the oxygen level is kept over 65mmHg, and the pH is kept in the range of 7.45–7.50, the individual will have no stimulus to take a breath. If the patient does not initiate a breath or attempt to breathe between ventilator breaths, the individual will not “flail,” and thus will have less likelihood of developing atelectasis on the weaker side.

Large versus Small Tidal Volumes
Patients who are recumbent require higher breath volumes, both when breathing spontaneously or when on the ventilator, in order to keep the basal areas of the lung ventilated (Bynum et al., 1976). Patients with spinal cord injury are frequently recumbent for many days or weeks after their injury. Therefore, attention needs to be paid to deep breaths. Watt and Devine (1995) list six reasons for mechanical hyperventilation in long-term ventilatory dependence (in tetraplegic patients without a cuffed tracheostomy tube): Augmentation of speech. Prevention of atelectasis. Allowance for variations in minute ventilation without incurring hypoxemia. Prevention of a decline in static compliance. Suppression of residual respiratory muscle activity by lowering carbon dioxide tension. Prevention of patients’ sensation of having insufficient ventilation. The authors note that it is not uncommon for patients receiving positive pressure ventilation to “seek increases in their tidal volumes due to feelings of breathlessness, even in the presence of normal blood gases.” (Watt and Devine reference Estenne et al. [1983] for support of their conclusions.)

When initially ventilating a patient with tetraplegia, the ventilator tidal volume should be set higher than for other types of patients requiring ventilation. A recommended initial setting is 15 ml/kg (kg of ideal body weight, based on height). Depending on whether or not the subsequent chest radiographs show atelectasis, the ventilator tidal volumes can be increased in small increments on a daily basis to treat the atelectasis. The risk of barotrauma should be reduced if the peak airway pressure is kept under 40cm of H2O. It is preferable not to allow the tetraplegic patient to trigger the ventilator. The reason for this is that the paralysis is almost always unequal—that is, one side, including the diaphragms, may be a bit stronger than the other

Respiratory Management Following Spinal Cord Injury

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