You are called to review a 29-year-old male with confirmed asthma in the Emergency Department. He has been unwell for 2 days with increasing cough, wheeze and shortness of breath. He has just been intubated.
a) Describe what ventilator settings you will initially set and give the reasons for your answer. (40% marks)
Two hours later he has become increasing difficult to ventilate. You quickly assess and exclude all other causes except severe bronchospasm.
b) Briefly outline your management of this situation. (60% marks)
a)
Ventilator settings | Rationale |
FiO2 = 1.0 |
Correct/prevent hypoxia. Adjust as indicated from SpO2 |
PEEP = 0 or <3 cmH2O |
Gas trapping obviates need for PEEP in patients with no spontaneous respiratory effort. A school of thought that PEEP splints airways open and reduces airflow obstruction |
Low Respiratory rate |
Allow enough time for expiration and prevent gas trapping with adequate minute ventilation, accepting permissive hypercapnia |
Tidal volume = 6-8 ml/kg IBW |
Adequate Vt for minute ventilation but at ‘safe’ volumes to reduce risk of VALI |
I:E = 1:4 |
Allow enough time for expiration and prevent gas trapping. Accept permissive hypercapnia |
High inspiratory flow rate |
Allow delivery of target Vt in relatively short inspiratory time. Accept high peak pressures |
Reset airway pressure alarm limits |
Peak pressures reflect airway resistance and high values are not a concern. Lung compliance in asthma is normal and so elevated plateau pressures represent gas trapping |
Ensure adequate sedation:
Muscle relaxation:
Bronchodilator therapy
Steroid therapy
Ventilation
Other strategies
Additional comments:
Common scenario and should be basic knowledge. Some candidates gave a poor explanation
for their choice of ventilator settings in part a). Candidates who failed the question had
knowledge gaps and inadequate detail in their answer.
In the revision section chapter on ventilation strategies for status asthmaticus, a detailed discussion of these strategies is available, with references. Below is a summary cut and pasted from the front of this chapter.
a)
Ventilation strategy
b) Some of the other, non-ventilator strategies for the management of status asthmaticus:
First-tier therapies with strong supporting evidence
Second-tier therapies with weak supporting evidence
Third-tier therapies without any supporting evidence
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