Outline your approach to the use of non-invasive ventilation in the critically ill patient.

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College Answer

The discussion of the approach to the use of non-invasive ventilation should include various aspects including: indications (types of patients), contra-indications/precautions, and some discussion of the way it would be used. The use of CPAP alone (e.g. via face mask, or nasal mask) may be considered to be a form of non-invasive ventilatory support, but further discussion here is not required. There is good data to support its use in patients with exacerbations of chronic airways disease (improving symptoms, physiological endpoints, deceasing intubation rate, and even potentially decreasing hospital mortality). Less data supports its use in patients with acute asthma, pulmonary  oedema,  pneumonia,  other  causes  of  hypoxic  acute  respiratory  failure,  and  as  a technique  to  avoid  endotracheal  intubation  (where  considered  inappropriate),  or  to  facilitate weaning from invasive ventilation. Usual contraindications to the use of non-invasive ventilation include facial injury/trauma, cardiovascular instability, an inappropriate conscious state (e.g. an unconscious or uncooperative patient), an unprotected airway and excessive secretions. Non- invasive ventilation is usually delivered via a face mask (or nasal mask or helmet), using an inspiratory pressure above a level of CPAP. This inspiratory pressure may be time or flow cycled on and off. Usually the pressures (CPAP and inspiratory pressure) are started at a baseline which is well tolerated (e.g. 5 and 8), and are slowly titrated upward to achieve oxygenation, relief of dyspnoea (work of breathing) or tidal volume targets. Early improvements in oxygenation, respiratory rate and carbon dioxide/pH have been claimed to b predictors of success. An approach to weaning from the non-invasive supports should also be included.
At least one candidate misinterpreted this question to read “how you set up non-invasive ventilation”.
(Hore CT. Non-invasive positive pressure ventilation in patients with acute respiratory failure. Emerg Med (Fremantle). 2002 Sep;14(3):281-95. Lightowler JV, Wedzicha JA, Elliott MW, Ram FS. Non-invasive positive pressure ventilation to treat respiratory failure resulting from exacerbations of chronic obstructive pulmonary disease: Cochrane systematic review and meta- analysis. BMJ. 2003 Jan 25;326(7382):185 and Ram FSF, Picot J, Lightowler J, Wedzicha JA. Non- invasive positive pressure ventilation for treatment of respiratory failure due to exacerbations of chronic obstructive pulmonary disease (Cochrane Review). In: The Cochrane Library, Issue 1,
2004).

Discussion

A systematic answer should look like this:

Strong indications

  • Pulmonary oedema
  • Asthma
  • COPD
  • Lung infection in the neutropenic patient

Weak indications

  • weaning from invasive ventilation
  • prevention/avoidance of intubation

Contraindications

  • decreased level of consciousness
  • vomiting
  • facial trauma
  • hemodynamic instability, particularly poor preload states

Adjustment of NIV

  • Titrate IPAP and EPAP to work of breathing and tidal volume targets
  • Adjust inspiratory flow rate and expiratory cycle-off to increase or decrease the expiratory phase
  • Adjust delivery mechanism to suit patient needs (eg. nasal mask, full face mask or half face mask, or full helmet)

References