A 56-year-old female with idiopathic pulmonary fibrosis (IPF) is transferred to your ICU from a regional hospital having presented with an acute exacerbation and hypoxic respiratory failure. She has been intubated and ventilated, with SP02 88% on a Fi02 1.0.
Outline how you would optimise lung function in this patient. (50% marks)
Outline the barriers to weaning from mechanical ventilation in this patient. (50% marks)
a) Optimise lung function
- Look for and treat reversible features e.g. fluid overload, infection, bronchospasm, heart failure
- Diuretics / fluid limitation
- Appropriate antimicrobial treatment
- Disease modifiers – steroids, immunosuppressants, novel agents e.g. tyrosine kinase inhibitors
- Pulmonary vasodilators
- Lung protective strategies and be cautious about high PEEP as the more compliant part of the lungs may be over inflated
- Involvement of respiratory physicians
- They may know the patient
- Advice regarding prognostication
- V-V ECMO as bridge to transplantation, now being pursued in some centres
b) Outline the barriers to weaning in this patient with IPF?
- Oxygenation can be significantly impaired – set realistic goals of PaO2 / SpO2
- Compliance can be severely impaired affecting ventilator synchrony – leading to difficulties in sedation
- Spontaneous respiratory rate can be high, leading to staff wanting to increase analgesia / sedation
- Muscle strength can be poor
- Progressive disease
- Chronic malnutrition
- Weakness exacerbated by steroids
- Immunosuppression can lead to recurrent infections
- Pulmonary hypertension can lead to significant CVS dysfunction
- Patient cognition and emotional status
- Negative attitudes to a bad prognostic disease
As far as "optimise lung function" goes, there are three main domains: try to control the disease process, get some gas exchange happening and control the pulmonary hypertension.
Specific management of the disease process
- High dose corticosteroids
- Nintendanib, a a receptor blocker for multiple tyrosine kinases
- Pirfenidone, a collagen synthesis inhibitor
Manipulation of gas exchange
- Inhaled pulmonary vasodilators may improve shunt (eg. inhaled prostacycline, inhaled nitric oxide)
- Mechanical ventilation strategies are largely extrapolated from ARDS management protocols, with some notable differences.
- Use smaller tidal volumes (like ARDS), 6ml/kg
- Minimise PEEP (unlike ARDS management): Fernandez et al (2008) found that high PEEP settings failed to improve oxygenation and were associated with worse outcome.
- Avoid recruitment manoeuvres. IPF patients have minimal recruitable lung, and are vulnerable to overdistension injury.
- Tolerate hypercapnia; use high respiratory rate
- Use heavy sedation and neuromuscular junction blockers to improve tolerance of this sort of ventilation strategy
- There is no evidence to promote the use of prone ventilation
- Unless the patient is being prepared for a lung transplant, VV ECMO would be a bridge to nowhere and therefore should not be offered.
Management aimed to control pulmonary hypertension
- There is a concern that any systemically administered pulmonary vasodilators may worsen shunt.
- Sildenafil may improve pulmonary haemodynamics, and does not seem to worsen the shunt (Ghofrani et al, 2002)
- Endothilin receptor antagonists, eg. bosantan (which might also have some sort of antifibrotic properties) have some role to play in long term management (Minai et al, 2008)
- Anti-acid therapy for chronic microaspiration
- The microaspiration of gastric content is viewed as one of the potential triggers of these acute exacerbations. Thus, PPI is indicated.
- Antimicrobial therapy for any pulmonary infective complications (i.e. there may be a treatable component in all this)
Barriers to weaning:
Due to the disease process
- Impaired lung mechanics due to restrictive lung disease
- Increased work of breathing due to hypoxia and respiratory acidosis
- Concomitant right heart failure due to severe pulonary hypertension
Due to side effects of therapy
- Corticosteroid-induced myopathy
- Weakness due to prolonged use of neuromuscular junction blockers
Sequelae of prolonged ICU stay
- ICU-acquired weakness
- Residual effect of high-dose sedative medication
Hilariously, the college has included "negative attitudes to a bad prognostic disease" as one of the barriers to weaning, implying that an intensivists' natural apathetic nihilism will sabotage the process of respiratory recovery. Presumably, a vigorous and positive attitude towards IPF influences survival by virtue of generating fewer palliative care referrals.
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