Question

if a ventilated patient has inspiratory effort but the ventilator doesn't respond, what can be the reasons ? how can you solve this ?

Answer 1

When the patient makes an effort to initiate a breath, and the ventilator doesn't support it, it is called triggering asynchrony.

The reasons for this triggering asynchrony are:

Ventilator related cause:

1. Malfunction of ventilator sensors
2. Inappropriate sensitivity parameter -
   1. If the ventilator-breath is pressure triggered
      1. When a patient initiates a breath, there is a negative pressure developed by the patient's airways.
      2. This negative pressure is picked up by the ventilator.
      3. The ventilator then initiates the breath.
      4. If the patient doesn't initiate enough negative pressure, the ventilator doesn't initiate a breath.
   2. If the ventilator-breath is flow triggered
      1. When the patient initiates a breath, the patient develops a flow in the airways.
      2. The ventilator senses the flow and initiates a breath.
      3. If the patient doesn't initiate enough flow the ventilator doesn't initiate the breath.
3. Prolong inspiratory time - The patient cycles off his breath before the ventilator cycle off the breath ( breath cycling is defined as the end of inspiration followed by the initiation of expiration)

Patient-related causes:

1. Respiratory muscle weakness - Chronic illness ( respiratory and non-respiratory) can lead to muscle weakness. This reduces respiratory effort.
2. Decrease neural drive - ( Due to paralysis of muscle due to drugs, toxins, neurological disease.)This reduces the neural drive for respiration and therefore, there is reduced respiratory effort.
3. Dynamic hyperinflation - Due to bronchospasm, there is a prolongation of expiratory phase of respiration. This leads to air-trapping.

These problems can be solved in the following ways:

1. Change defective sensors of the ventilator.
2. Flow triggered breath ( ventilator ) is better than pressure triggered breath. To initiate a Pressure triggered breaths from the ventilator, the patient has to develop a significant pressure. Flow triggered breaths are more patient-friendly.
3. Reduce the inspiratory time
4. Reduce the level of sedatives and neuromuscular blockade.
5. Use bronchodilator to reduce bronchospasm and extrinsic peep, to reduce the dynamic hyperinflation.