Dr. David Lyness
Reversible airway obstruction
TRIAD: bronchial smooth muscle contraction, airway inflammation, and increased secretions
Progressively worsening over days = usually slower reaction to treatment
Acutely worsening over a short time (highly reactive airway) = usually better reaction to initial treatment
MAY NOT APPEAR DISTRESSED OR VERY SICK
Always be wary of normocapnia and consider it in clinical context. It may be a sign of patient deterioration or exhaustion.
- Gas trapping with dynamic hyperinflation and the generation of intrinsic positive end-expiratory pressure (PEEPi).
- Increases in resistance to expiratory gas flow, rapid RR, changes in pulmonary elastic recoil, and asynchronous respiratory muscle activity.
- Impaired gas exchange, increased work of breathing with respiratory muscle fatigue, and increased risk of barotrauma.
- Hyperinflation may be so severe that lung volumes approach total lung capacity.
- Diaphragmatic flattening reduces the efficiency of ventilation as inspiration becomes primarily by intercostal muscles rather than the diaphragm.
- These factors reduce CO2 elimination while increasing production.
Eventually, production will match and then exceed rate of elimination progressing to respiratory failure when there is inadequate alveolar ventilation.
Airway closure causes mismatches in ventilation-perfusion leading to hypoxaemia.
Large negative intrathoracic pressures as well as PEEPi through its effects on right atrial filling, can impede cardiac output.
Hypercapnia and/or requiring mechanical ventilationwith raised inflation pressures
Any one of the following in a pt with severe asthma:
Normal PaCO2 (4.6 – 6.0 kPa)
Feeble respiratory effort,
Any one of:
PEF 33–50% best or predicted
Respiratory rate >25/min
Heart rate >110/min
Inability to complete sentences in one breath
OXYGENATE with High Flow O2
Salbutamol 5mg via O2 neb or 10mg continuously (hourly)
if no improvement after 15-30mins
Ensure continuous B2 agonist + ipratropium as above
Senior can consider IV B2 agonist or IV aminophylline
If in ED, bring patient to resus bay
Site a large bore cannula
Consider adrenaline (SC 0.3–0.4 ml 1:1000 every 20 min for three doses), nebulized (2–4 ml of 1% solution hourly) or, in extremis, the intravenous route (0.2–1 mg as a bolus followed by 1–20 µg/min).
Refer any patient:
Considerations in Ventilation
- Ketamine (bronchodilation) vs Propofol (or ketofol!)
Peak Expiratory Flow <50% of predictedrequires immediate attention
ABCD, Oxygen, apply monitors, ABG
ECMO - may have a role in non-reversing intubated asthmaticsHeliox - is difficult to arrange via a ventilator