Table 2.

Proposed solutions for some of the causes of patient-ventilator asynchrony

Cause	Description	Solution
Auto-triggering	It is defined as the occurrence of at least three consecutive pressurizations at a ventilator frequency[8] of >40/min not synchronized with patient respiration The trigger is too sensitive or nonrespiratory factors trigger the ventilator such as  Cardiac contractions: This may cause a small amount of air movement, and if the flow trigger is sensitive enough, this air movement can trigger the ventilator breaths. The respiratory rate may match the heart rate  Leak from the circuit or from the chest drain (e.g., a bronchopleural fistula)  Inappropriate sensitivity settings  Excessive water condensation in the ventilator circuit  Large volume of respiratory secretions Swallowing or vomiting  Peristalsis in a massive hiatus hernia or intrathoracic bowel loops  Muscle contractions due to external pacing	Remove the cause such as excessive water condensation or respiratory secretions If no treatable cause is detected, adjust the trigger to a higher setting
Double-triggering	When an insufficient level of pressure support is applied or the patient’s demand is high, the inspiratory effort may continue throughout the preset ventilator inspiratory time and result in retriggering of the ventilator after it has discontinued pressurization, which may lead to the delivery of two cycles for only one patient’s effort (double-triggering)	Adjust the expiratory flow trigger until the desired tidal volume is achieved
Large leak around the NIV mask	In order to generate the specified pressure, the ventilator continues to deliver high flow. With a large leak, inspiration can be very uncomfortable (as the ventilator delivers 70-80 L/min of gas into the patients face)[5]	Adjust the mask to minimize the leak Decreasing the level of pressure support will decrease the total inspiratory time, as the machine will cycle to expiration sooner In some ventilators, one can actually adjust the inspiratory time directly
Wasted effort	Wasted efforts can occur during inspiration when the patient tries to initiate a breath (straining to inhale against a closed inspiratory valve) Possible causes  Respiratory muscle weakness  Reduced respiratory drive  Inadequate trigger threshold setting  iPEEP: Inspiratory muscles have to overcome iPEEP and trigger sensitivity to trigger the ventilator  Inadequate level of support: The flow rate is too low and it does not meet patient demand	The use of ePEEP to approximately 80%-90% of the iPEEP can counterbalance iPEEP and as such facilitate triggering Reduce the trigger sensitivity

PEEP=Positive end-expiratory pressure, ePEEP=Extrinsic PEEP, iPEEP=Intrinsic-PEEP, NIV=Noninvasive ventilation