Pros and Pitfalls of Disconnecting the Ventilator During Acute Respiratory Decompensation

The several pitfalls of switching to BMV

• Loss of diagnostic information: In an acute scenario, it is critical to get diagnostic information to understand what’s causing the problem. The ventilator provides a plethora of information that may help answer this question. E.g., if the problem is sudden increase in peak airway pressure, checking the plateau pressure will guide as to whether the main load is elastic or resistive. The importance of looking at the waveforms cannot be overstated. We lose all this advantage when we switch to BMV.
• Risk of decruitment: Switching from ventilator to BVM may result in sudden derecruitment in an ARDS patient. This may be avoided by clamping the endotracheal tube during the switch. A PEEP valve should also be attached to the BVM. Note that the maximum PEEP that can be provided with a PEEP valve is typically 20 cmH2O, which may not be enough in certain cases.
• Lack of tidal volume control: The typical BVM has a volume of ~1600cc. In a crunch scenario, it is not uncommon to provide dangerously large tidal volumes. This may be of special relevance in patients with ARDS and hemodynamic lability.
• Lack of respiratory rate control: By the same token, it is common to bag too rapidly. This may cause significant auto-PEEP and its several ill-effects in a patient with high airway resistance.
• Concern for aerosolization of infectious droplets: If an expiratory filter is not deployed on the BVM, bag-mask ventilation will lead to aerosolization of infectious particles. This is point is especially relevant in the current times.

General thoughts on this issue

The knee-jerk practice of switching from ventilator to BVM is often unnecessary and potentially harmful. The incidence of actual ventilator malfunction is very rare to justify this as a routine practice. Even if the switch is made and no immediate improvement occurs, the patient should be switched back to the ventilator due to the various benefits listed above.

A sample initial approach to acute respiratory decompensation in intubated patients is as follows – 

• Take control of ventilation: sedate and/or paralyze
• If a sudden increase in peak inspiratory pressures is the chief concern and the circuit has an HME, remove the HME. It should be fine to ventilate without humidification for a few minutes.
• If there is any concern for false (auto) triggering, switch to pressure trigger.
• Look at the pressure waveform to see if there’s a problem in the expiratory limb of the circuit.

Once these steps have been performed and no device malfunction is identified, I can’t think of any reason why one would disconnect the ventilator bag manually. From here on, diagnostic information from the ventilator would help identify the actual problem. An important point worth mentioning here is that in conditions causing high peak airway pressure, the pressure alarm setting becomes very important. This is not just an alarm but once the set pressure threshold is reached, the breath is cycled off (pressure cycling) to avoid further increases in airway pressure. Hence, the pressure alarm setting may have to be liberalized (along with minimizing the delivered tidal volume) to allow continued ventilation from the mechanical ventilator.

A particular scenario where disconnection of the ventilator is considered therapeutic is a patient with critically high autoPEEP. This has been used as another reason to empirically disconnect the ventilator in respiratory emergencies. Firstly, this is certainly a potentially life saving maneuver and should be performed when critical autoPEEP is strongly suspected (more on this here). However, using this as an argument for unselected disconnection of the ventilator in all respiratory emergencies cannot be justified. A quick glance as the flow waveform would help identify patients that would benefit from this maneuver. (As an aside, setting the respiratory rate to the minimum level (e.g. 1/minute) will achieve the same effect as disconnecting the ventilator.)

Let’s discuss the case in the pre-brief. There is no evidence of device malfunction here and there is a good reason for why this patient dropped their SpO2. This patient is at high risk of derecruitment with altered positioning. Sitting or reverse trendelenburg positioning allow offloading of the chest wall in obese patients. A supine position will cause significant mass loading. Changing the position and increasing the PEEP (optionally preceded by a recruitment maneuver) would help in this scenario. As mentioned before, switching to BMV would risk further decruitment. Also, the maximum PEEP that can be provided with a BVM PEEP valve is typically 20, which may not be enough in this case.