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]