Comparison of the Effect of Adaptive Support Ventilation with the Effect of Synchronized Intermittent Mandatory Ventilation on Respiratory Mechanics in Head Injury Patients: A Randomized Cross-over Study.

BACKGROUND

In head injury patients, it is crucial to maintain normal carbon dioxide levels, improve synchrony, and keep airway pressures and dead space ventilation to a minimum during mechanical ventilation. Adaptive support ventilation (ASV) decreases airway pressure and work of breathing by providing minute ventilation at an optimal frequency and tidal volume based on the patient's lung compliance and airway resistance.

OBJECTIVE

To compare respiratory mechanics during ASV mode with that during synchronized intermittent mandatory ventilation (SIMV) mode in head injury patients.

METHODS AND MATERIAL: Forty-six adult patients of 18-50 years of age, either sex, having sustained a head injury, being tracheostomized, and receiving mechanical ventilation, were enrolled. All the patients received both modes of ventilation in a cross-over manner: SIMV and ASV for 4 hours each; half of the patients (n = 23) initially received the former, followed by the latter, and vice versa in the remaining half (n = 23). A comparison of hemodynamics, respiratory mechanics, and arterial blood gas during both modes was done.

RESULTS

Airway pressures (peak, plateau, and mean) were higher during SIMV mode, while compliance (both dynamic and static) was better (higher) during ASV mode at almost all time points (P < 0.05). Dead space ventilation was higher during SIMV mode (P < 0.05).

CONCLUSIONS

In head injury patients, owing to better patient-ventilator synchrony with ASV mode as compared to SIMV mode, similar values of oxygenation and carbon dioxide levels were maintained at lower airway pressures, leading to better compliance.