NIV Flashcards
What is NIV?
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:
Continuous positive airway pressure (CPAP)
Bi-level positive pressure ventilation (BiPAP)
How does NIV work?
Improves lung mechanics by improving laminar airway flow by stenting closed airways or semi-obstructed airways.
This decreases atelectatic alveoli and improves pulmonary compliance, and reduces work of breathing.
What’s the difference between CPAP & BiPAP?
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 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.
What pressure settings should I use?
CPAP:
For patients with suspected ACPE, it’s 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.
What are the indications to NIV?
Cardiogenic pulmonary oedema
Hypercarbic respiratory failure (COPD/asthma exacerbation)
Severe metabolic acidosis with respiratory failure
What are the contraindications to NIV?
- Significant secretions - Positive pressure and the BiPAP mask impair expectoration. Sometimes, it is possible to maintain a patient on BiPAP with occasional breaks on HFNC for secretion clearance (e.g. a COPD patient with mild secretions). However, for a patient with copious secretions, BiPAP is contraindicated. In such cases, BiPAP may initially have excellent results, but eventually mucus plugging occurs with abrupt deterioration.
- Decreased LOC
- No respiratory drive
- Risk of aspiration - Aspiration may occur if the patient vomits and is unable to remove the BiPAP mask.
- Hemodynamic instability
- Facial trauma/deformity/burns - affects mask seal
- Agitated or combative patient
What clinical parameters should you monitor?
- Patient’s tolerance
- 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
What are the complications resulting from NIV?
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
List some important advantages of BiPAP compared to HFNC
Positive pressure reduces pre-load and after-load on the heart, improving heart failure (this works similar to an ACE-inhibitor – but easier to titrate and no nephrotoxicity).
BiPAP can provide a greater amount of mechanical support for breathing. This is desirable for patients with respiratory muscle weakness or obesity-hypoventilation syndrome.
For patients with small airway obstruction (e.g. COPD/asthma), BiPAP can provide mechanical support. The expiratory airway pressure (PEEP) may also help stent open airways during exhalation.
List the advantages of HFNC
- Reduction in work of breathing due to dead space washout
- Preserved ability to cough & clear secretions
- Excellent tolerance, including for extended periods of time (important for patients with interstitial lung disease who may take several days to recover)
- Improved ability to communicate with patients and assess their progress
3 main settings for NIV
FiO2 – set based on oxygen requirements, just like on the vent
PEEP/EPAP/CPAP – all the same thing, set this based on OXYGENATION needs. If the patient’s sat is low, start at 5 cm H20 and titrate up to 15-17 as needed.
PSV/IPAP – this setting is for ventilation. If your patient does not have ventilation problems, they don’t need PSV. If they do, start at 5 cm H20 and titrate to 15-17.
