Non Invasive Ventilation

Non Invasive Ventilation

Definitions:

• CPAP: applies constant pressure throughout the breathing cycle to increase functional residual capacity (FRC) by recruiting alveoli, decreasing work of breathing, and improving oxygenation.

• PEEP/EPAP: alveolar pressure before inspiratory flow begins. PEEP à decrease the amount of work required to initiate a breath and decrease atelectasis

• Bi-level: Cycled ventilation between Inspiratory Positive Airway Pressure (IPAP) and Expiratory Positive Airway Pressure/PEEP. BiPAP supports ventilation and increases oxygenation.

• Pressure Support: The difference between EPAP and IPAP is referred to as pressure support. Pressure support makes it easier to draw larger tidal volumes

BiPAP/ NIPPV/ Bi-level vs HFNC

·       Oxygenation:  Both devices can almost à  100% FiO2.  HFNC à small PEEP ~5cm, max vs much higher PEEP on NPPV

·       Work of Breathing:  HFNC may wash out the anatomic deadspace à  reduces the work of breathing.  BiPAP can higher pressures and support majority of the work of breathing.

·       Secretion clearance: Important in pneumonia to prevent mucus plugging improve clearance.  BiPAP impairs secretion clearance, whereas HFNC does not seem to.

·       Monitoring: Unable to communicate with patient effectively on BIPAP. BiPAP anxiety provoking and makes it difficult to differentiate between worsening clinical resp status vs anxiety. HFNC facilitates communication  

NIPPV/Bi-level/ BiPAP

COPD

·      Bi-level ventilation à decreases the risk of death (relative risk reduction 48%) and intubation rates (RRR 60%)

·      Number Needed to Treat (NNT) for mortality benefit = 10

·      NNT to prevent intubation = 4

·      Furthermore, when comparing patients with moderate and severe acidosis, bi-level ventilation decreased mortality, rates of intubation, and lengths of stay.

·      ** Ensure patient does not have a PTX that could tension once placed in PPV

Initial Settings:

-       IPAP 8-20 cm H2O (up to 30 cm H20)

-       EPAP 2-6 cm H2O to overcome intrinsic airway collapse

-       Begin with either high IPAP and then titrate down, or low and titrate high.

SCAPE/ CHF exacerbation

·      IPAP assists ventilation à  decreases the WOB

·      EPAP/PEEP increases the FRC by recruiting collapsed alveoli, improving oxygenation, and helping to force interstitial fluid back into the pulmonary vasculature

·      Also, increases intrathoracic pressure à decreased left ventricular (LV) end diastolic volume à decreased afterload and increased LV ejection fraction/stroke volume.

·      Common Initial Settings:

·              IPAP: 10 to 20 cm H20

·              EPAP: 5 to 10 cm H20

·              I:E ratio of IT to ET and is usually set at 1:3 or 1:4 (Inspiratory to Expiratory ratio)

·      Evidence for Bi-level ventilation in CHF exacerbations is unfortunately mostly supportive of CPAP with few trials comparing CPAP and BiPAP

·      Cochrane review looking at NIPPV in CHF exacerbations à CPAP alone has been proven to decrease intubation rates and to decrease in-hospital mortality, without the same benefit seen using bi-level ventilation

·      Lack of evidence does not mean lack of efficacy

How to assess your patients on NIV

·       Oxygenation:   good pulse oximetry waveform. ABG is rarely needed to measure oxygenation

·       Work of breathing:  The best metric is the respiratory rate.  Worsening retractions, diaphoresis, tripoding, shallow breathing, and an abdominal paradoxical breathing pattern. 

·       Mentation:  A patient who is easily arousible and mentating adequately doesn't have life-threatening hypercapnia

·       BiPAP screen:  Low tidal volumes and/or low minute ventilation àhypoventilation. But  adequate tidal volumes and minute ventilation suggest a adequate response to NIV

·       Treat the patient, not the ABG- Proven by  Brochard 1995 (RCT) investigating the use of BiPAP in COPD:  BiPAP improved mortality despite having no effect on ABG parameters after one hour à  BiPAP can be successful without any immediate effect on the ABG.

High Flow Nasal Cannula

·       Low flow: NC ~ 1-5 L/min vs NRB ~15 L/min

·       High Flow- 20-60 L/min

·       Normal Resting breathing flow ~15-30 L/min

·       Respiratory distress 60-180 L/min 

• Adult devices max out at 50-60 L/Min (max it out to start) and the dose for pediatric patient’s (based on trials) is 2L/Kg/Min

• Maximize your devices flow rate initially then wean the fi02 to maintain your oxygen saturation goal

Adult Indications: Hypoxemic Respiratory failure (mostly Pneumonia) FLORALI Trial, DNR/DNI patients , Pre-oxygenation prior to Intubation

Pediatric Indications: Bronchiolitis, Asthma, Pneumonia, Croup

Take Home Points:

·      Rule out pneumothorax (auscultation, US) prior to placing patients on NIPPV

·      Do not base clinical management solely based off of an ABG esp if patient clinically improving

·      Choose Bi-level vs HFNC based on patient’s diagnosis

·      Best Metric to assess NIV success is respiratory rate

References:

Vital, F. M. R., Ladeira, M. T. & Atallah, A. N. Non-invasive positive pressure ventilation (CPAP or bilevel NPPV) for cardiogenic pulmonary oedema. Cochrane Database Syst. Rev. CD005351 (2013). doi:10.1002/14651858.CD005351.pub3

Frank Lodeserto MD, "High Flow Nasal Cannula (HFNC) – Part 1: How It Works", REBEL EM blog, August 20, 2018. Available at:  https://rebelem.com/high-flow-nasal-cannula-hfnc-part-1-how-it-works/.

Frank Lodeserto MD, "High Flow Nasal Cannula (HFNC) – Part 2: Adult & Pediatric Indications", REBEL EM blog, August 23, 2018. Available at:  https://rebelem.com/high-flow-nasal-cannula-hfnc-part-2-adult-pediatric-indications/.

EmDocs

EMCrit