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)

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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 (common in asthma; too breathless to eat and drink)
  • Anaphylaxis to intubation drugs
  • Tension pneumothorax
  • Tachyarrhythmia due to excessive bronchodilators
  • Effect of the sedative drugs


  • 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.


Oddo, Mauro, et al. "Management of mechanical ventilation in acute severe asthma: practical aspects." Intensive care medicine 32.4 (2006): 501-510.

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.

Kondili, Eumorfia, et al. "Pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease." Intensive care medicine 30.7 (2004): 1311-1318.