OVERVIEW
Non-invasive ventilation (NIV) is widely used for severe asthma in Australasia yet remains a controversial topic
USES
- improve rate of recovery and limit drug side effects (e.g. salbutamol, aminophyline)
- to avoid intubation (improved gas exchange and avoidance of fatigue)
- pre-oxygenation and ventilatory support while preparing for intubation — can use with ketamine as part of a delayed sequence intubation (DSI) approach
- part of a post-extubation strategy to prevent reintubation
RATIONALE
Mechanical ventilation in asthma is difficult and has significant risks:
- dynamic hyperinflation
- ventilator dyssynchrony
- risk of barotrauma
- often requires neuromuscular blockers together with corticosteroids resulting in high risk of ICU-acquired weakness, and is associated with increased length of stay and mortality
NIV has numerous possible advantages (see below)
PROS AND CONS
Advantages
- decreased work of breathing on inspiration
- occurs if external PEEP is set to match iPEEP in a spontaneously breathing patient
- PEEPi would otherwise need to be overcome by increased negative pleural pressure to initiate inspiration in a in a spontaneously breathing patient
- less fatigue
- improved V/Q mismatch and gas exchange
- decreased dead space
- prevent atelectasis and maximise recruitment
- direct bronchodilation (PPV leads to increased FEV1 and PEFR in some studies)
Disadvantages
- dynamic hyperinflation if external PEPP > intrinsic PEEP
- increased risk of barotrauma
- incorrect patient selection may lead to delayed intubation (risk complications)
- usual risks of NIV
EVIDENCE
There is a lack of high-level evidence to guide practice
- no large well-designed RCTs
- A 2012 Cochrane Review found 5 trials with 206 patients but was inconclusive
- some support in observational studies, case series, and small trials
PATIENT SELECTION
Consider NIV if intubation is not imminently required and any of the following are present:
- Tachypnea RR >25/min
- Tachycardia 110/min
- Use of accessory muscles of respiration
- Hypoxia with a PF ratio <200
- Hypercapnia with PaCO2 <60 mmHg
- FEV1 <50% predicted
In general, avoid NIV if:
- decreased level of consciousness
- agitated
- vomiting
- profuse secretions
- significant haemodynamic instability
SETTINGS
Typical initial BiPAP settings:
- PEEP at 3-5 cmH20 (low)
- iPAP at 7-15 cmH20, adjust to target RR <25/min
- high inspiratory flow rate, low I:E ratio (e.g. 1:5) and prolonged expiratory time
AN APPROACH
Use non-invasive ventilation in severe asthma
- unless contra-indicated
- as part of a multi-modal approach including maximal pharmacological therapy
- as long as it does not delay intubation when indicated
Monitor these patients carefully, treat aggressively and be prepared to intubated if they deteriorate
References and Links
LITFL
- CCC — Acute Severe Asthma
- CCC — Non-invasive ventilation
Journal articles
- Agarwal R, Malhotra P, Gupta D. Failure of NIV in acute asthma: case report and a word of caution. Emerg Med J. 2006 Feb;23(2):e9. [pubmed] [article]
- Gupta D, Nath A, Agarwal R, Behera D. A prospective randomized controlled trial on the efficacy of noninvasive ventilation in severe acute asthma. Respir Care. 2010;55(5):536-43. [pubmed] [article]
- Landry A, Foran M, Koyfman A. Does Noninvasive Positive-Pressure Ventilation Improve Outcomes in Severe Asthma Exacerbations? Ann Emerg Med 2013;62(6):594-596 [pubmed]
- Lim WJ, Mohammed Akram R, Carson KV, Mysore S, Labiszewski NA, Wedzicha JA, Rowe BH, Smith BJ. Non-invasive positive pressure ventilation for treatment of respiratory failure due to severe acute exacerbations of asthma. Cochrane Database Syst Rev. 2012 Dec 12;12:CD004360. [pubmed] [article]
- Murase K, Tomii K, Chin K, Niimi A, Ishihara K, Mishima M. Non-invasive ventilation in severe asthma attack, its possibilities and problems. Panminerva Med. 2011 Jun;53(2):87-96. [pubmed] [article]
- Soroksky A, Klinowski E, Ilgyev E, Mizrachi A, Miller A, Ben Yehuda TM, Shpirer I, Leonov Y. Noninvasive positive pressure ventilation in acute asthmatic attack. Eur Respir Rev. 2010 Mar;19(115):39-45. doi: 10.1183/09059180.00006109. Review. [pubmed] [article]
- Stefan MS, Nathanson BH, Lagu T, et al. Outcomes of Noninvasive and Invasive Ventilation in Patients Hospitalized with Asthma Exacerbation. Ann Am Thorac Soc. 2016;13(7):1096-104. [pubmed] [article]
- Stefan MS, Nathanson BH, Priya A, et al. Hospitals’ Patterns of Use of Noninvasive Ventilation in Patients With Asthma Exacerbation. Chest. 2016;149(3):729-36. [pubmed] [article]

Critical Care
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