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Emergency Medicine Questions (EMQs)
Miscellanea
Theme: Non-invasive positive pressure ventilation (NiPPV) in the ED
  1. Michael Davey1,2
  1. 1Emergency Department, Royal Adelaide Hospital, Adelaide, South Australia
  2. 2Division of Acute Care Medicine, University of Adelaide, South Australia
  1. Correspondence to Michael Davey, Emergency Department, Royal Adelaide Hospital, Adelaide 5000, South Australia; michael.davey{at}health.sa.gov.au

https://doi.org/10.1136/emj.2010.106088

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    Question 1

    Which of the following are true regarding the physics of bilevel positive airway pressure (BPAP) and continuous positive airway pressure (CPAP) ventilatory assistance?

    1. Gas delivery by BPAP is volume regulated.

    2. A major advantage of BPAP is the delivery of a known, constant fractional inspiratory oxygen concentration (Fio2) according to the rate of supplemental oxygen entrained.

    3. A major advantage of NiPPV devices delivering CPAP using a gas reservoir is the delivery of a known, constant Fio2 according to the rate of supplemental oxygen entrained.

    4. In BPAP, inspiratory phase pressure must be set lower than expiratory phase pressure.

    Question 2

    Which of the following are true regarding the efficacy of BPAP and CPAP?

    1. Current evidence supports the use of CPAP in acute, severe exacerbations of asthma.

    2. Current evidence supports the use of NiPPV in hypercapnic acute respiratory failure in chronic obstructive pulmonary disease (COPD).

    3. CPAP is preferred over BPAP in cardiogenic pulmonary oedema because it reduces myocardial preload and afterload.

    4. NiPPV significantly reduces mortality, need for endotracheal intubation and hospital length of stay in patients with acute hypercapnic ventilatory failure in COPD.

    Question 3

    Which of the following are true?

    1. Consideration of NiPPV in patients with neuromuscular disease should be based more on symptoms such as breathlessness than on deranged arterial blood gasses.

    2. CPAP may, paradoxically, cause suffocation.

    3. CPAP may be a useful interim measure in the early ED management of acute respiratory distress due to smoke inhalation in burns patients.

    4. The patient being edentate is associated with failure of NiPPV.

    See page 966 for answers

    EMQ Answers

    See page 903 for questions

    Answer 1

    1. False. It is pressure regulated, delivering a variable volume in order to maintain preset, cyclical pressures.

    2. False. Most BPAP machines do not use a reservoir. A constant flow of supplemental oxygen is fed into the volume of BPAP-delivered room air after it leaves the BPAP machine. As the latter volume varies with tidal volume (VT) but the added oxygen does not, the patient Fio2 will vary according to VT. This minute to minute variation in Fio2 is potentially even greater with nasal BPAP with the likelihood of periodic mouth breathing.

    3. True. In machines that use a gas reservoir, the Fio2 delivered can be fixed because the supplemental oxygen and room air enter the reservoir at set (but adjustable) rates before being delivered to the patient by the machine—that is, with any given selected flow rates of air and O2 into the reservoir all delivered volumes to the patient will be the same Fio2.

    4. False. It should be higher.

    Answer 2

    1. Possibly! But the evidence is thin and the British Thoracic Society specifically recommended: ‘Non-invasive ventilation should not be used routinely in acute asthma’.1–3

    2. True, and the evidence is robust.3–5

    3. True.6

    4. True.4

    Answer 3

    1. False. ‘There is a sub-group of patients with acute on chronic hypercapnic respiratory failure who have few symptoms despite severely deranged arterial blood gas tensions.’3

    2. True. Being a sealed system, and depending on the machine used, if delivered gas flows are less than the minute volume of the patient there is a risk of suffocation. Generally a patient will fight to remove the mask under these circumstances, but this can be difficult to distinguish from the anxiety associated with acute dyspnoea due to worsening of the underlying condition.

    3. False. If CPAP is thought necessary in such a patient it is highly likely that definitive airway management by endotracheal intubation, and longer term ventilatory support, will be required. If intubation is delayed in these cases subsequent airway oedema may make the task particularly problematic!

    4. True.3

    References

    1. ↵
      1. Gupta D,
      2. Nath A,
      3. Agarwal R,
      4. et al
      . A prospective randomised controlled trial on the efficacy of non-invasive ventilation in severe acute asthma. Respir Care 2010;55:630–7.
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    2. ↵
      1. Nowak R,
      2. Corbridge T,
      3. Brenner B
      . Noninvasive ventilation. Proc Am Thorac Soc 2009;6:367–70.
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    3. ↵
      British Thoracic Society Standards of Care Committee. Non-invasive ventilation in acute respiratory failure. Thorax 2002;57:192–211.
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    4. ↵
      1. Abramson MJ,
      2. Crockett AJ,
      3. Frith PA,
      4. et al
      . COPDX: an update of guidelines for the management of chronic obstructive pulmonary disease with a review of recent evidence. MJA 2006;184:342–5.
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    5. ↵
      1. Ram FS,
      2. Picot J,
      3. Lightowler J,
      4. et al
      . Non-invasive positive pressure ventilation for treatment of respiratory failure due to exacerbations of chronic obstructive pulmonary disease. Cochrane Database Syst Rev 2004;3:CD004104.
      OpenUrlPubMed
    6. ↵
      1. Bersten AD,
      2. Soni N
      1. Duke G,
      2. Bersten AD
      . Non-invasive ventilation. In: Bersten AD, Soni N, eds. Oh's Intensive Care Manual. 6th edn. Philadelphia, PA: Butterworth Heinemann Elsevier, 2009.

    Footnotes

    • Provenance and peer review Not commissioned; not externally peer reviewed.