A 24-year-old woman with a history of brittle asthma is brought to the Emergency Department by her boyfriend. She is very short of breath and wheezy and her condition deteriorates rapidly. Following back to back nebs, hydrocortisone and IV magnesium sulphate, she is taken to resus and the intensive care team is called to review her. She is now severely hypoxic and has become confused. A decision is made to intubate the patient.
1. What are the indications for intubation in an asthmatic patient?
Intubation in asthmatic patients is rarely required, with only around 2% of asthma attacks requiring intubation and most severe cases being managed with non-invasive ventilation techniques.
Intubation in asthmatic patients is risky and associated with major mortality and morbidity. It can be, however, life saving in the crashing asthmatic. Indications for intubation in an asthmatic patient include:
- Severe hypoxia
- Altered mental state
- Failure to respond to medications/NIV
- Respiratory or cardiac arrest
2. What should the patient be given prior to intubation?
Prior to intubation the patient should be pre-oxygenated and loaded with intravenous fluids. Nasal oxygen during intubation is helpful and can buy extra time.
Intravenous fluids are very important as patients with acute asthma exacerbations can have considerable insensible losses and this can result in profound hypotension during induction and with the application of positive pressure ventilation.
3. Which drugs should ideally be used for the rapid sequence induction?
Although there is no optimal set of agents to use for rapid sequence induction (RSI), ketamine (1-2 mg/kg) is often the preferred induction agent as it has bronchodilatory properties and does not cause hypotension as a side effect. Propofol can also be used but poses a risk of hypotension.
Ketamine can also be helpful at a sub-dissociative dose (0.1 mg/kg followed by an IV infusion of 0.5 mg/kg/hour for 3 hours) to facilitate the use of non-invasive ventilation in a hypoxic/combative patient.
Rocuronium and suxamethonium are commonly used as paralytic agents. Rocuronium has the added advantage of providing a longer period of paralysis, which avoids ventilator asynchrony in the early stages of management.
4. Which ventilator settings will you choose following intubation and why?
Appropriate mechanical ventilation relies on ensuring that the patient has an adequate time period to fully expire the delivered breath and avoid hyperinflation. For this reason permissive hypercapnia is generally used and ideally the ventilator setting should be approximately as follows to facilitate this:
- Respiratory rate – 6-8 breaths/minute
- Tidal volume – 6 ml/kg
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