You are called to review a 29-year-old male with confirmed asthma in the Emergency Department. He has been unwell for 2 days with increasing cough, wheeze and shortness of breath. He has just been intubated.
a) Describe what ventilator settings you will initially set and give the reasons for your answer. (40% marks)
Two hours later he has become increasing difficult to ventilate. You quickly assess and exclude all other causes except severe bronchospasm.
b) Briefly outline your management of this situation. (60% marks)
|FiO2 = 1.0||
Correct/prevent hypoxia. Adjust as indicated from SpO2
|PEEP = 0 or <3 cmH2O||
Gas trapping obviates need for PEEP in patients with no spontaneous respiratory effort. A school of thought that PEEP splints airways open and reduces airflow obstruction
|Low Respiratory rate||
Allow enough time for expiration and prevent gas trapping with adequate minute ventilation, accepting permissive hypercapnia
|Tidal volume = 6-8 ml/kg IBW||
Adequate Vt for minute ventilation but at ‘safe’ volumes to reduce risk of VALI
|I:E = 1:4||
Allow enough time for expiration and prevent gas trapping. Accept permissive hypercapnia
|High inspiratory flow rate||
Allow delivery of target Vt in relatively short inspiratory time. Accept high peak pressures
|Reset airway pressure alarm limits||
Peak pressures reflect airway resistance and high values are not a concern. Lung compliance in asthma is normal and so elevated plateau pressures represent gas trapping
Ensure adequate sedation:
- Ketamine +/- propofol +/- analgesia
- Preferentially use non histamine releasing analgesia – fentanyl
- Non steroid/non histamine releasing agents – ideally cisatracurium
- Regular inhaled salbutamol – MDI, nebuliser
- IV infusion salbutamol
- IV adrenaline infusion
- Anticholinergic therapy – Ipratropium bromide inhaled regularly
- Magnesium infusion – aiming for Mg 1.5-2.5 mmol/L
- Methylxanthine therapy – Aminophylline infusion
- 100 mg 6 hrly hydrocortisone (or any reasonable steroid / dose)
- Confirm ventilator settings
- Tidal volume 6-8 mL/kg
- Check plateau (rather than peak) inspiratory pressure with inspiratory pause in volume control mode and paralysed patient
- Reduce respiratory rate if possible
- Minimise PEEP
- Check for evidence of dynamic hyperinflation with expiratory hold in paralysed patient
- Permissive hypercapnia
- Inhaled volatile anaesthetic agents
- Heliox if available
- Consider ECCO2 removal / ECMO
Common scenario and should be basic knowledge. Some candidates gave a poor explanation
for their choice of ventilator settings in part a). Candidates who failed the question had
knowledge gaps and inadequate detail in their answer.
In the revision section chapter on ventilation strategies for status asthmaticus, a detailed discussion of these strategies is available, with references. Below is a summary cut and pasted from the front of this chapter.
- Use the largest tube possible.
- Use lowest FiO2 to achieve SpO2 of 90-92%
- Use a small tidal volume, 5-7ml/kg
- Use a slow respiratory rate, 10-12 breaths per minute (or even less!)
- Use a long expiratory time, with I:E ratio 1:3 or 1:4
- Increase inspiratory flow rate to maximum. .
- Reset the pressure limits (i.e. ignore high peak airway pressures). .
- Use heavy sedation.
- Use neuromuscular blockade.
- Minimise the duration of neuromuscular blockade.
- Use a volume-control mode of ventilation.
- Use minimal PEEP.
- Keep the Pplat below 25cmH2o to prevent dynamic hyperinflation.
- Titrate PEEP to work of triggering once the patient is breathing spontaneously.
b) Some of the other, non-ventilator strategies for the management of status asthmaticus:
First-tier therapies with strong supporting evidence
- Humidified oxygen titrated to SpO2 90-92%
- Nebulised beta-agonist bronchodilators
- Nebulised anticholinergic drugs
- Steroids: IV hydrocortisone or oral prednisone
Second-tier therapies with weak supporting evidence
- Intravenous beta-agonist bronchodilators for refractory bronchospasm
- Nebulised adrenaline
- Magnesium sulfate
- Helium-oxygen mixture
Third-tier therapies without any supporting evidence
- Volatile anaesthetics
- ECMO in asthma
Oh's Intensive Care manual: Chapter 35 (pp. 401) Acute severe asthma by David V Tuxen and Matthew T Naughton.
Stow, Peter J., et al. "Improved outcomes from acute severe asthma in Australian intensive care units (1996–2003)." Thorax 62.10 (2007): 842-847.
Sekiya, Kiyoshi, et al. "Clinical evaluation of severe asthma attacks requiring tracheal intubation and mechanical ventilation." Allergology International 58 (2009): 289-294.
Sandford, Andrew J., et al. "Polymorphisms in the IL4, IL4RA, and FCERIB genes and asthma severity." Journal of Allergy and Clinical Immunology 106.1 (2000): 135-140.
McFadden Jr, E. R. "Acute severe asthma." American journal of respiratory and critical care medicine 168.7 (2003): 740-759.
Bousquet, Jean, et al. "Uniform definition of asthma severity, control, and exacerbations: document presented for the World Health Organization Consultation on Severe Asthma." Journal of Allergy and Clinical Immunology126.5 (2010): 926-938.
Perrin, Kyle, et al. "Randomised controlled trial of high concentration versus titrated oxygen therapy in severe exacerbations of asthma." Thorax 66.11 (2011): 937-941.
Rodrigo, Gustavo J., et al. "Effects of Short-term 28% and 100% Oxygen on Paco2 and Peak Expiratory Flow Rate in Acute AsthmaA Randomized Trial."CHEST Journal 124.4 (2003): 1312-1317.
Sellers, W. F. S. "Inhaled and intravenous treatment in acute severe and life-threatening asthma." British journal of anaesthesia 110.2 (2013): 183-190.
Cates, C. J., E. J. Welsh, and B. H. Rowe. "Holding chambers (spacers) versus nebulisers for delivery of beta-agonist relievers in the treatment of an asthma attack." (2013).
Teoh, Laurel, et al. "Anticholinergic therapy for acute asthma in children."Cochrane Database Syst Rev 4 (2012).
Coupe, M. O., et al. "Nebulised adrenaline in acute severe asthma: comparison with salbutamol." European journal of respiratory diseases 71.4 (1987): 227-232.
Albertson, T. E., et al. "Pharmacotherapy of critical asthma syndrome: current and emerging therapies." Clinical reviews in allergy & immunology (2014): 1-24.
Powell, Colin, et al. "Magnesium sulphate in acute severe asthma in children (MAGNETIC): a randomised, placebo-controlled trial." The Lancet Respiratory Medicine 1.4 (2013): 301-308.
Shan, Zhilei, et al. "Intravenous and nebulized magnesium sulfate for treating acute asthma in adults and children: a systematic review and meta-analysis."Respiratory medicine 107.3 (2013): 321-330.
Wigmore, T., and E. Stachowski. "A review of the use of heliox in the critically ill." Critical Care and Resuscitation 8.1 (2006): 64.
Rodrigo, G., et al. "Heliox for nonintubated acute asthma patients." Cochrane Database Syst Rev 4 (2006).
Jat, Kana R., and Deepak Chawla. "Ketamine for management of acute exacerbations of asthma in children." Cochrane Database of Systematic Reviews 11 (2012).
Howton, Joseph C., et al. "Randomized, double-blind, placebo-controlled trial of intravenous ketamine in acute asthma." Annals of emergency medicine 27.2 (1996): 170-175.
Vaschetto, R., et al. "Inhalational anesthetics in acute severe asthma." Current drug targets 10.9 (2009): 826-832.
Lobaz, S., and M. Carey. "Rescue of acute refractory hypercapnia and acidosis secondary to life-threatening asthma with extracorporeal carbon dioxide removal (ECCO2R)." JICS 12.2 (2011): 140-142.
Leiba, Adi, et al. "Early administration of extracorporeal life support for near fatal asthma." IMAJ-RAMAT GAN- 5.8 (2003): 600-602.
Samaria, J. K. "Role Of Niv In Acute Respiratory Failure Due To Asthma: Effectiveness And Predictors Of Failure." Am J Respir Crit Care Med 183 (2011): A1365.
Op't Holt, Timothy B. "Additional Evidence to Support the Use of Noninvasive Ventilation in Asthma Exacerbation." Respiratory care 58.2 (2013): 380-382.
Lim, Wei Jie, et al. "Non-invasive positive pressure ventilation for treatment of respiratory failure due to severe acute exacerbations of asthma." The Cochrane Library Published Online: 12 DEC 2012
Gupta, Dheeraj, et al. "A prospective randomized controlled trial on the efficacy of noninvasive ventilation in severe acute asthma." Respiratory care 55.5 (2010): 536-543.
Williams, Trevor J., et al. "Risk factors for morbidity in mechanically ventilated patients with acute severe asthma." The American review of respiratory disease146.3 (1992): 607-615.
Lacomis, David, Thomas W. Smith, and David A. Chad. "Acute myopathy and neuropathy in status asthmaticus: case report and literature review." Muscle & nerve 16.1 (1993): 84-90.
Hermans, Greet, et al. "Clinical review: critical illness polyneuropathy and myopathy." Crit Care 12.6 (2008): 238.