Inadequate ventilation

If there is persistent elevation of partial pressure of carbon dioxide (PaCO₂) and continued acidosis after starting acute noninvasive ventilation:

• check inspired oxygen concentration and oxygen saturation measured by pulse oximetry (SpO₂), and reduce oxygen if necessary; ensure target SpO₂ levels are being maintained
• check circuit for leaks, including mask leaks
• check patient’s synchronisation with ventilator and adjust backup rate
• check ventilator trigger is set at maximum sensitivity
• consider increasing expiratory positive airway pressure (EPAP) to reduce the possibility of rebreathing
• observe chest expansion and, if inadequate, consider increasing inspiratory positive airway pressure (IPAP). If this is not tolerated or chest expansion is adequate, consider increasing respiratory rate or inspiratory to expiratory (I:E) ratio to increase expiratory time.

If there is persisting hypoxaemia despite improvement in PaCO₂, consider increasing EPAP (while maintaining difference of at least 6 cmH₂O between IPAP and EPAP) or increasing supplemental oxygen. Also review the need for intubation and mechanical ventilation.