A 64 year old lady admitted with G~de V subarachnoid hemorrhage was pronounced brain dead based on a 4 vessel cerebral angiogram. Subsequent to the angiogram, the total respiratory rate was 15/min when the ventilator rate was set at 10/min.

What are the potential causes of the discrepancy between the set ventilator 
rate and the total respiratory rate? 

What steps will you take to distinguish the cause in this case? 

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College Answer

What are the potential causes of the discrepancy between the set ventilator rate and the total respiratory rate? 

1) Auto-triggering of the. ventilator due to

- cardiogenic oscillations 
- High sensitivity settings 
- Circuit leaks 
- Water condensation in the circuit 

2) True spontaneous breath (although unlikely as there is a definitive test indicating brain death. 

b) What steps will you take to distinguish the cause in this case? 

1) Connect the patient to aT -piece circuit with a capnograph and look for 
spontaneous breathing movements and a C02 waveform.

Discussion

So, why is this braindead woman seemingly making spontaneous breathing efforts?

Note that the college does not rule out true spontaneous breaths.

  • Autotriggering:
    • Cardiac oscillation
    • Inappropriately sensitive trigger
    • Condensation pooling in the circuit
    • leaky circuit
  • Triggering by something other than the patient's brain:
    • Diaphragmatic "capture" of her pacemaker
    • External movements (eg. nursing care)

One excludes the embarrassing possibility of a breathing braindead patient by connecting her to a T-piece or by adjusting the trigger to a less sensitive setting.