Quiz 22

You go to the bedside of an intubated patient in the ICU because the High pressure alarm is alarming. He is on Assist control mode but not on any PEEP. You close the exhaust port of the ventilator (- the outlet that lets air out into the atmosphere). You find that the pressure does not drop in the ventilator to zero.

Q1. Which of the following is true about the pressure not coming down to zero?
  1. The patient has some form of bronchospasm
  2. You should never have done this
  3. The patient is consciously trying to fool you so that you do not extubate him
  4. The patient is ready for pressure support mode
  5. None of the above

Answer is choice 1(The patient has some form of bronchospasm). Closing the exhaust port at the end of expiration is a well known maneuver to find out about Auto-Peep, a phenomenon where the body spontaneously maintains the pressure in the airway. It is associated with COPD where bronchospasm is maintained in order to keep the airway open. It can become high and stack air inside, leading to high peak and plateau pressures (whereas bronchospasm without stacking leads to increase in peak but not plateau). This can be a cause of hypotension or pneumothorax. In order to avoid stacking, more expiration time should be allowed or one could decrease the tidal volume. You can provide this extra expiration time by increasing inspiratory flow velocity and thus shortening inspiration period (allowing more time for expiration).

Q2. You sort out the above problem in the patient by increasing the velocity of the inspiration phase gases. No other changes are made. The next day the patient is tachypneic and the high pressure alarm is beeping again. You get a chest X-ray on the patient. The ET tube is in the right main bronchus.

Which of the following is compatible with the finding
  1. High peak pressure, low tidal volume
  2. High peak pressure, normal tidal volume
  3. Normal peak pressure, normal tidal volume
  4. High peak & plateau pressure, normal tidal volume
  5. High plateau pressure, low tidal volume

Answer is choice 4 (High peak & plateau pressure, normal tidal volume). The volume of lung now accepting the same tidal volume is less. This will increase both the peak and plateau pressures.
The Tidal volume in a patient who is on AC mode ventilation is at least the amount that is set. He/she will get at least the dialled in volume - although the patient may, by himself/herself take in MORE. The tidal volume can vary with pressure in patients on pressure support mode. In that, the volume will decrease as the pressure in the lung increases.