• Asthma
    • 1400 deaths per year - mostly pre-hospital and preventable
    • 2 main subtypes
      • Progressive over several days, slower responders
      • Highly reactive airways, usually male & respond better
    • Pathophysiology features dynamic insufflation, and generation of PEEP(i) due to increase in resistance to gas flow, changes in elastic recoil and asynchronous respiratory muscle activity.
      • Hyperinflation may be so severe such that it is near TLC. Diaphragmatic flattening reduces efficiency of ventilation such that intercostals drive inspiration predominantly.
      • Together, there is high CO₂ production with reduced elimination
    • Large negative intrathoracic pressures and PEEP(i) can impede cardiac output
      • Lactic acidosis can occur
    • Invasive ventilation
      • High risk of complications
      • Half the life threatening complications occur around the time of intubation
      • Keep RR low and no PEEP applied. Consider breath stacking if hypotensive.
      • Sedation is mandatory and patient may need NDMBDs. Consider ketamine, I:E ratios of 1:4, pPlateau of 30cmH₂O, pH >7.2, consider trying PEEP(e), volatiles.
      • Consider novolung/ECMO
      • Bronchoscopy may have a minimal role if mucus plugging.
      • Other measures (NIV, heliox, leukotriene antagonists and monoclonal anti-IgE antibodies have no role in the management of acute life threatening asthma)
    • Mortality predictors
      • Significant comorbidities
      • Hx of near fatal asthma
      • Previous intubations
      • 2 or more asthma admissions in 1 year
      • 2 or more salbutamol inhalers used per month
      • 3 or more medications to control asthma
      • Substance abuse/psychiatric illness
      • Lower socio-economic class
      • Nocturnal awakening with asthma
      • Smokers
    • Severity of asthma
      • Near fatal asthma
        • Raised pCO₂ &/or requiring mechanical ventilation
      • Life threatening asthma
        • PEFR <33%
        • SpO₂ <92%
        • Normal pCO₂
        • Silent chest
        • Cyanosis
        • Feeble respiratory effort
        • Bradycardia
        • Dysrrhythmias
        • Hypotension
        • Confusion/coma
      • Acute severe asthma
        • PEFR 33-50% predicted
        • RR >25
        • HR >110
        • Inability to complete sentence
    • Management
      • Oxygen to maintain SpO₂ >92%
      • Salbutamol via nebuliser continuously or 10mg/hr or 5-20mcg/min IV. 100mcg IV can be given in extremis.
      • Ipratropium bromide 0.5mg neb
      • Steroids
      • Magnesium sulphate 2g over 20 mins
      • Adrenaline nebs, IV or s/c (0.5ml of 1:1000)
      • Aminophylline 5mg/kg loading over 20 mins??
    • Triad of bronchial smooth muscle contraction, airway inflammation and increased secretions
    • CEACCP
      Link:ceaccp.oxfordjournals.org/content/8/3/95.full.pdf