emDOCs Podcast – Episode 36: Severe Asthma and Mimics
- Aug 31st, 2021
- Brit Long
Today on the emDOCs cast with Brit Long, MD (@long_brit), we cover severe asthma and asthma mimics.
Severe Asthma and Asthma Mimics
The approach for asthma and asthma mimics is to first assess for life threats, provide emergent interventions, and then obtain history and focused exam. Rapid treatment with bronchodilator and corticosteroids is required. Non-Invasive Positive Pressure Ventilation (NIPPV) should be considered.
Once treatment and initial stabilization have been completed, focused history and exam should be conducted to evaluate for mimics. As discussed, there are many causes of wheezing, and these conditions must be considered to prevent anchoring bias. Red flags for other conditions include absence of asthma history, prior history of mild asthma, or poor response to therapy.
– Assess the ABCs.
– Administer oxygen to relieve hypoxemia. If severe exacerbation present, provide IV fluids (address secondary losses).
-Deliver a short acting beta-agonist (SABA) with ipratropium (anticholinergic).
-Give systemic corticosteroids to decrease airway inflammation. Options include prednisone, methylprednisolone, and dexamethasone.
-If patients fail to respond to inhaled therapies and steroids, next steps include parenteral beta agonist, magnesium, heliox, ketamine, and/or NIPPV.
-Epinephrine is a non-selective beta agonist that causes bronchodilation, vasoconstriction, increased cardiac contractility and increased heart rate. Dose for IM is 300-500 mcg, while IV is recommended in hypotensive patients or those who fail to respond to IM dosing. Dose is 5mcg IV and titrate to effect.
-Magnesium is effective in those with severe exacerbation by relaxing bronchial smooth muscle. In adults, start with 2g, which can be repeated twice.
-Ketamine may have bronchodilator properties. It can also assist with delayed sequence intubation.
-Heliox is an option; it can improve laminar flow of inhaled has which may allow better airflow through the constricted airways; allows better gas exchange and transport of medications to flow down to distal airways and alveoli. Evidence suggests limited utility, and if hypoxic, an adequate amount of FiO2 may not be reached.
-Non-invasive positive pressure ventilation should be considered for all patients who display: moderate to severe dyspnea or respiratory distress, hypercapnic acidosis, a respiratory rate > 25/min, accessory muscle use, or paradoxical breathing. Bilevel settings are recommended to improve ventilation.
-Intubation is an inherently dangerous intervention in asthma because it does not fix the underlying problem (bronchoconstriction) and can cause dynamic hyperinflation, and rapid acidosis if respiration is not matched during RSI or post-intubation. The decision to intubate is based on a number of factors including the patients overall appearance, work of breathing, perceived ability to maintain their effort of breathing, mental status etc. Before intuition, preoxygenate and rehydrate with IV fluids. Ketamine 1-2 mg/kg IV can be used for induction. A paralytic such as rocuronium offers the advantage of longer paralysis which avoids vent asynchrony early in management.
-Mechanical ventilation: Must ensure that the patient has an adequate time to fully expire the delivered breath and avoid hyperinflation. Permissive hypercapnia involves decreasing the RR and allowing PaCO2 to rise to supranormal levels, which avoids breath stacking. Ensure post-intubation analgesia and sedation, which will assist with vent synchrony.
- Initial Ventilator Settings
- RR: 6-10 breaths/min
- VT: 6-8 ml/kg (ideal body weight
- PEEP: 0-5 cm H2O
- FiO2: Minimum necessary to maintain O2 sat > 93%
- Inspiratory Flow Rate: (suggest 100-120 L/min)
- Check Plateau Pressures and maintain at < 30 mm Hg
- Plateau pressure reflects the pressure experienced by alveoli
- Maintaining Pplat < 30 mm Hg helps to avoid alveolar damage
- If plateau pressure is > 30 mm Hg, consider lowering the RR and VT.
Mechanical ventilation does not fix the underlying bronchoconstriction. Be sure to continue maximal medical management.
Trouble Shooting the Ventilator:
- Hemodynamic instability and hypoxia after intubation/mechanical ventilation are common and life-threatening. Rapid recognition of the underlying problem and treatment are critical.
- DOPES Mnemonic
- Displacement of the endotracheal tube (ETT)
- Direct visualization with laryngoscope preferred (US confirmation another option)
- Obstruction of the endotracheal tube
- Pass ETT suction catheter
- Pneumothorax (tension)
- Lung POCUS for lung sliding
- Empiric needle decompression or finger thoracostomy
- Equipment failure
- Disconnect the vent and deliver manual BVM breaths
- Stacked Breaths
- Forcibly exhale patient (gently push down on anterior chest wall with two hands until no further exhalation detected.
- Displacement of the endotracheal tube (ETT)
-ECMO and anesthetic gases are final options for patients who continue to decline.