Question 30

A 25-year-old female is brought into the Emergency Department with acute severe asthma. She is intubated and ventilated and transferred to the ICU.

a) Discuss your assessment and management to prevent the potential of the patient developing dynamic hyperinflation. (60% marks)

The patient becomes hypotensive.

b) Excluding worsening dynamic hyperinflation, list four likely differential diagnoses. (10% marks)

c) Outline one diagnostic investigation and one management strategy for each differential diagnosis.
(30% marks)

College answer

Not available.

Specific strategies to assess for, and to prevent dynamic hyperinflation in status asthmaticus, include:

Minimise interference from chest wall movement
- Sedation, analgesia
- Neuromuscular junction blockers
Minimise airway airflow resistance
- Bronchodilator continuous nebs +/- intravenous infusion
- Ketamine for sedation
- Heliox is an option if oxygenation is satisfactory
Maximise expiratory air flow: two schools of thought:
- Keep PEEP minimal, i.e. use ZEEP - this maximises the gradient for
- Keep some low PEEP, eg 5-8, to prevent small airways from closing during expiration, thereby worsening gas trapping
Maximise expiratory time
- Use I:E ratio with a prolonged expiratory phase, eg. 1:4, up to 1:6 or even 1:10
Monitor for dynamic hyperinflation
- Observe ventilator flow and volume waveforms: it needs to reach zero before the next breath
- Watch for pulsus paradoxus or increasing pulse pressure variation: this could be a signal that the intrinsic PEEP is increasing
- Perform serial expiratory hold manoeuvres to assess intrinsic PEEP

Different possible reasons this patient is becoming hypotensive:

Hypovolemia: bedside TTE; fluid bolus
Anaphylaxis: mast cell tryptase (though this would be a clinical diagnosis); adrenaline IM, followed by an infusion
Tension pneumothorax: CXR/bedside lung ultrasound, though again this is usually a clinical diagnosis
Tachyarrhythmia: ECG; management could consist of DC cardioversion, a calcium channel blocker or amiodarone.

Golchin, A., K. Hachey, and A. Khan. "Is There a Role of Applied PEEP (PEEPe) in Controlled Mechanically Ventilated Severe Asthma Exacerbations?." C52. CRITICAL CARE CASE REPORTS: GOOD VIBRATIONS-MECHANICAL VENTILATION FROM NIV TO ECMO. American Thoracic Society, 2018. A5270-A5270.

Smith, THOMAS C., and JOHN J. Marini. "Impact of PEEP on lung mechanics and work of breathing in severe airflow obstruction." Journal of Applied Physiology 65.4 (1988): 1488-1499.