Acute respiratory failure
| Headline | |
|---|---|
| Etiology | Type 1 (hypoxia only) vs Type 2 (hypercapnic) You may have one or multiple of these: - alveolar space collapse - Pleural effusion compressing lung tissue - fluid filling of alveolar spaces - pulmonary oedema - pathological loss of blood flow t- alveolar tissue - PE - shunting (from hypoxic vasoconstriction) - loss of pulmonary tissue - emphysema - ↓ gas exchange due to fluid buildup/thickening etiologies of hypercapnic respiratory failure - extrinsic - chest wall abnormalities - small airway obstruction - obstruction, secretions - COPD - pneumonia - cystic fibrosis - poor muscle function - neuromuscular disease - Myasthenia gravis e.g. - tiring - spinal cord injury - ↓ respiratory drive - opioid toxicity, drugs in overdose - CNS insult e.g. Head injury, stroke |
| Clinical presentation | tachypnoea, drowsiness |
| Pathogenesis | |
| Diagnostic investigations | ABG |
| Management | NIV - starting pressures vary but 15/3 or 10/5 → uptitrate IPAP over 10-30 mins Think tube instead: not suitable for NIV - NOT indicated in asthma or pneumonia → may need IPPV instead - confusion/agitation - impending respiratory arrest This may also be an opportune time to discuss TEP and long-term goals |
initiation of non-invasive ventilation
BTS defines threshold as pH <7.35 and PaCO2 >6.5kPa despite optimal medical therapy
BTS guidelines suggest NIV should be started within 1h of these results
Best practice points:
- optimise NIV settings before increasing fiO2
- infusions of anxiolytics - only in Level 2-3, but IV morphine/benzodiazepine can help optimise/increase tolerance for NIV
- start NIV in neuromuscular disease or chest wall disease if hypercapnic, even if pH is normal
what BTS says about ABGs
- Prior to initiation of NIV
- 1 hour after commencing NIV
- 1 hour after any change in settings
- If pH significantly improved, but not normalised, ABG should be repeated after 4 hours
- If the patient deteriorates
- At 8am if the patient is on NIV overnight
- ABG sampling should not be performed if it will not alter management