Noninvasive Ventilation and the critically ill

Non invasive ventilation is a method of delivering oxygen by positive pressure mask that allows the clinician to postpone or prevent invasive tracheal intubation in patients who present to the emergency department with acute respiratory failure.

There are 2 primary modalities of noninvasive ventilation:

1. Continuous positive airway pressure (CPAP)
2. Bi-level positive pressure ventilation (BiPAP)

Proper patient selection is critical in the use of NIV for ED patients. Acute exacerbations of  COPD, ACPE and asthma seem to receive the most benefit from NIV.

Traditional teaching have been once a patient failed to respond to a non-rebreather mask rapid sequence intubations was indicated. NIV has changed this approach and offers clinicians another option.

Noninvasive ventilation improves lung mechanics by improving laminar airway flow by stenting closed airways or semi-obstructed airways this decreasing atelectatic alveoli, improving pulmonary compliance, and reducing work of breathing.

Continuous positive airway pressure (CPAP):

• CPAP is a  fixed positive pressure throughout the respiratory cycle.
• CPAP appears to be more effective in reducing the need for tracheal intubation and possibly mortality in patients presenting with with acute cardiogenic pulmonary oedema (ACPE).

Bi-level positive airway pressure (BiPAP):

• BiPAP is when the ventilator delivers different levels of pressure during inspiration (IPAP) and expiration (EPAP).
• BiPAP ventilation appears to be more effective in reducing mortality and the need for tracheal intubation in patients with an acute decompensation of COPD.

CPAP:

• For patients with suspected ACPE its reasonable to set the CPAP pressure at 10cm H2O. This pressure can be adjusted up or down depending on patient comfort.
• Oxygen should be titrated based on PCO2, PaO2 and titrated to the patient SpO2 at the bedside.

BiPAP:

• For patients receiving BiPAP start with an IPAP of between 12-15cm  H2O, and and EPAP of between 4-7cm H2O.
• These pressure can be titrated up or down depending on the combination of clinical effect as well as patient comfort.
• Failure to improve oxygenation should prompt sn increase in fractional inspired oxygen and EPAP.
• Failure to improve the hypercarbia should lead to an increase in IPAP.

Take Home Points:

• Based on current evidence pressures should not exceed 25cm H2O at any point regardless of the mode of NIV being used.
• In order to maintain the pressures, it is important to achieve a good seal with the NIV mask.

Although there is no uniform indications for NIV, clinicians should be aware of the following absolute and relative contraindications.

Absolute contraindications:

• Need for urgent endotracheal intubation
• Decreased level of consciousness
• Excess respiratory secretions and risk of vomiting and aspiration
• Past facial surgery precluding mask fitting

Relative contraindications:

• Haemodynamic instability
• Severe hypoxia and/0r hypercapnia, PaO2/FiO2 ratio of <200mmHg, PaCO2> 60mmHg.
• Poor patient cooperation
• Lack of trained or experienced staff

Clinical parameters that you should monitor include:

• Patient tolerance of NIV
• Increase in secretions
• Mental status change
• Synchronous breathing with the ventilator
• Air leaks
• Respiratory rate
• Tidal volume changes in relation to respiratory rate
• Oxygen requirement in relation to pulse oximetry
• Blood gas
• Tidal volume and minute ventilation

Parameters of failure in a patient on NIV include:

• Vomiting
• Persistent coughing
• Aspiration
• Progressive respiratory distress
• Respiratory arrest
• Loss of consciousness
• Respiratory rate rising greater than 35-40
• Persistent hypoxia despite supplemental oxygenation
• Haemodynamic instability and shock
• Worsening arterial pH, PCO2, PO2, or venous pH
• Worsening PaO2/FiO2 ratio

Although a large RCT  study (3CPO) showed no difference in mortality when they compared standard oxygen therapy, CPAP and BiPAP, overall NIV has shown to reduce dyspnea scores, heart rate, acidosis and hypercapnea, and a more recent study showed NIV reduced the need for tracheal intubation in patients with ACPE.

A  study by Mehta and colleges showed that patients receiving BiPAP in ACPE had a concerning relationship with developing acute myocardial ischaemia, which had a flow on effect for the use of CPAP only in ACPE -however recent studies have found no statistical difference between CPAP and BiPAP in the developing of myocardial ischaemia.

Hypotension can occur with the use of CPAP in ACPE , generally in the patients with volume depletion/hypovolaemia, due to the reduction in preload and cardiac output.

BiPAP is the preferred NIV mode for acute exacerbations of COPD. A Cochrane systematic review looking at 14 studies on Non-invasive positive pressure ventilation for treatment of respiratory failure due to exacerbations of chronic obstructive pulmonary disease, found the following results:

1. NIV reduced mortality by 50%, decreased the need for intubation by approximately 60%, and reduced treatment failure by 52%.
2. The systematic review also demonstrated by on NIV showed a rapid improvement in pH, respiratory rate and PaCo2 with the first hour of treatment.
3. The authors concluded that with the evidence supporting it that NIV should be considered a first line therapy in COPD exacerbations.

Although we have seen excellent results from the use of NIV in COPD, the use in acute asthma remains less convincing and controversial.

• BiPAP is the mode of choice in providing NIV to the acute severe asthma patient.
• Its currently postulated that noninvasive ventilation pressures, as they are currently used, may not be sufficient to overcome this degree of obstruction and associated resistance that is manifested by the inflammation, oedema, and partial or complete obstruction of the airway that is characterised in acute severe asthma.
• There have been a few small studies looking at the use NIV in asthma patients with some promising results, however a recent Cochrane Review has stated although results look promising a large randomised control trial is need to find out NIV true effectiveness in the management of asthma.

Take home point:

• Its reasonable to consider the use of NIV in acute exacerbation of asthma. If your confronted with a severe case of asthma that looks like requiring intubation place that patient on BiPAP with continuous nebs, while you prepare to intubate. If the patient is still doing poorly once your equipment is ready – go ahead and intubate -however if you see improvement give the BiPAP a chance and wait a bit longer

Problems related to pressure:

• Sinus pain
• Gastric insufflation
• Pneumothorax

Problems related to airflow:

• Dryness
• Nasal congestion
• Eye irritation

Major complications:

• Severe hypoxaemia
• Aspiration
• Hypotension
• Mucous plugging

Other complications:

• Claustrophobia
• Air leaks from poor mask seal
• Pressure sores at the nasal bridge

Be prepared – have a protocol in partnership with your nurses/respiratory therapist for NIV is needed.

• Start NIV early in eligible patients –  it may increase chances for a good outcome.
• Reassure the patient – NIV may be frightening to an already anxious patient.
• Use sedation/analgesia with extreme care.
• Have definitive airway equipment ready in case the patient deteriorates.
• Venous blood gas pH correlates well with arterial pH and may be followed as an objective marker of improved ventilation.

• EMCrit Podcast 19 – Non-Invasive Ventilation
• BiPAP Part 1
• BiPAP Part 2
• Keenan, S. et.al. (2011). Clinical practice guidelines for the use of noninvasive positive-pressure ventilation and noninvasive continuous positive airway pressure in the acute care setting. Canadian Medical Association Journal. PMID: 21324867
• Nee, P. et.al. (2010). Critical care in the emergency department: acute respiratory failure. Emergency Medicine Journal. PMID:  21112972
• Weingart, S. (2011). Preoxygenation, Reoxygenation, and Delayed Sequence Intubation in the Emergency Department. Journal of Emergency Medicine. PMID: 20378297