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I have completed bits of my EM training from India. Currently I am boarded with credentials from Christian Medical College, Vellore and also from the prestigious Royal College of Emergency Medicine, UK.  I am currently working in London as an A&E doctor, trying to appreciate the differences in the practise and culture of Emergency Medicine across different healthcare systems. I have always been an avid FOAMed supporter because FOAMed played an indispensable role during the days of my initial training. Through this blog, I aspire to disseminate knowledge and stay up to date with the EM literature. 

Monday, October 5, 2015

NIV: What’s the big deal about that big mask?


A patient struggling for that ‘satisfying, good, deep breath’ and failing at every attempt is not an uncommon sight in the ED. Shortness of breath/breathlessness is one of the major presentations in the EDs all around the world. The diverse etiologies and the potential complications due to long periods of breathlessness makes it a time critical symptom requiring early intervention. 
Non-invasive ventilation is one of the important modalities of managing a patient with shortness of breath when indicated. Let us review some of the important points about non-invasive ventilation.




So, what is NIV?
It’s a method of giving ventilatory support/delivering oxygen to a patient with respiratory distress using a positive pressure mask so that invasive methods like endotracheal intubation is postponed or avoided.

What are the types of NIV?
There are 2 modes of NIV: CPAP (Continuous Positive Airway Pressure) and BPAP (Bilevel Positive Airway Pressure). BPAP has IPAP and EPAP (I-Inspiratory, E-Expiratory)

Terminology:
In general,
Type 1 RF requires CPAP type of NIV.
Type 2 RF requires BPAP type of NIV.

PEEP=EPAP=CPAP i.e. they all mean the same!
So you can say in Type 1 RF(Hypoxic failure), the pressure we provide is PEEP or just EPAP or CPAP. 

For Type 2 RF (Hypercapnic), we provide IPAP as well as EPAP. IPAP is greater than EPAP, PS (Pressure Support is the difference between IPAP and EPAP). For instance if IPAP = 15 and EPAP is 10 then PS = 15-10 i.e. 5cm H2O. 

A BPAP machine can be used as a CPAP machine if you set EPAP=IPAP i.e. you deliver the same pressure during inspiration as well as expiration.

Did you just say BPAP instead of BiPAP?
Yes! If you know that ‘Xerox’ is a trademark/brand while ‘photocopy’ is the actual terminology, you got this one right as well. BiPAP and BIPAP are actually trademarked modes of Bilevel Positive Airway Pressure (BPAP). (Apple fanboys can however use the i :-P)

CPAP:

  • Found to be more useful in reducing the need for intubation and reducing the mortality in patients with acute cardiogenic pulmonary edema. 
  • A fixed positive pressure is delivered throughout the respiratory cycle without any change during inspiration or expiration. The pressure required can be set on the machine and is measured in cmH2O.  
  • Commonly used pressures range 5-15cm of H2O. (5-8cm of H2O is a reasonable starting pressure)
  • O2 can be titrated depending upon the SpO2, PaO2.

BPAP:

  • Found more effective in acute exacerbation of COPD.
  • Different pressures are used during inspiration (IPAP) and expiration (EPAP).
  • The commonly used initial settings are EPAP: 3-6 and IPAP: 8-12 with supplemental oxygen of 3-5liters/min.
  • The pressure can be adjusted depending upon the clinical condition of the patients and /or values of PaO2, PCO2 and SpO2. 
  • To treat persistent hypercapnia increase IPAP by 2cms at a time. To treat persistent hypoxia, increase IPAP and EPAP by 2cms at a time.
  • The maximum EPAP/IPAP is 25/15cmH20.
  • Many comparative studies have demonstrated no significant difference between two modes of NIV when used for either for pulmonary edema or COPD.
  • So, just in case the nurse asks you “we do not have a BPAP machine but there’s an old CPAP machine, will that be okay?” the answer should be “Yes!” irrespective of the etiology! (Most modern machines can deliver both CPAP and BPAP)

In whom do we put it on?
  • In patients with respiratory failure/respiratory distress (e.g COPD and Acute Pulmonary Edema) without any contraindications.
  • Although there’s no clear consensus regarding the indications for the use of NIV, when there are no contraindications, many patients with dyspnea may be suitable candidates for NIV. (Asthma, ARDS, Neuromuscular disease, Chest trauma, Cystic Fibrosis)
  • To facilitate extubation in patients with COPD who have failed weaning attempts.
  • ‘Do-not-intubate (DNI) patients’    
  • Obstructive Sleep Apnea (OSA) – CPAP is commonly used in the night.

Contraindications for the use of NIV:
  •    Patients who require immediate endotracheal intubation.
  •    Decreased level of consciousness.
  •    Inability to fix/position the mask due to past facial surgery.
  •    Excessive secretions, vomiting and risk of aspiration.
  •    Uncooperative patient.
  •    Lack of staff trained/experienced in operating and monitoring the device and        patient the patient on NIV.
  •    Hemodynamically unstable patient.
  •    Severe hypoxia and/or hypercapnia: PaO2/FiO2 ratio<200mmHg, PaCO2 >      60mmHg.
  •    Gastrointestinal bleeding.


How does it work?
Alveolar recruitment + increased of FiO2 à Reverse hypoxia.
Improves airflow by, Stenting of closed/obstructed airways à Decreases atelectasis or lung collapse à Improves pulmonary compliance à reduces the work of breathing.
The difference between EPAP and IPAP is called pressure support, which augments ventilation and reduces the work of breathing.
Addition of positive pressure to the thoracic compartment also reduces the preload and afterload à Improvement of patients with cardiogenic pulmonary edema.


How to monitor a patient on NIV?  What do I look for?
Once the patient is on NIV, patient has to be monitored closely.
Be prepared for the RSI in case NIV fails. Keep equipment ready and make sure they are working. Involve senior on the shift. Notify anesthesia if necessary.

Parameters to be looked for which are suggestive of NIV failure include:
  •   Intolerance to NIV: Restless and irritable, asynchronous breathing with ventilator.
  •   Increased secretions, vomiting patient.
  •   Altered mental status.
  •   Increasing dyspnea/respiratory distress despite optimum settings. (RR>35-40)
  •   Persistent hypoxia despite supplemental oxygen.
  •   Hemodynamic instability.
  •   Worsening blood gases.

Other important things to be taken care of when patient is on NIV
  • Explain the patient what NIV is and how air is delivered with pressure. Just forcing that nasty mask on patient’s face without explaining anything would make an already anxious patient more anxious and you will most probably end up with an uncooperative patient and failed NIV.
  • Make sure that the mask is of appropriate size and well fitting. An Ill-fitting mask will result in air leak and NIV will be ineffective.  – Dealing with the big mask is indeed a big deal!
  • Face Mask is proffered over nasal mask in the ED.
  • Use cotton over the nasal bridge/forehead (pressure points) to avoid pressure sores.
  • Sitting position / Head end elevation
  • Follow up with a blood gas within 30-60 minutes .
  • Have an alternative plan for NIV failure. Be prepared for Intubation.
  • Be very cautious if you have to use analgesics that are known to cause sedation.



Complications of NIV:
  •   Gastric distension
  •   Failure of NIV
  •   Aspiration (rare)
  •   Hypotension with higher pressures (infrequent)
  •   Barotrauma (rare)
  •   Pressure ulcers over the face.
  •   Oral and nasal dryness à Irritation.

Take home points:
  •   Consider NIV ASAP in eligible patients (Timing is important).
  •   EPAP=CPAP=PEEP, IPAP > EPAP and PS = IPAP-EPAP.
  •   Reassure, use an appropriately sized mask .
  •   Have a definitive plan for failed   NIV.


       Author:

      Dr. Apoorva Chandra
      Resident – Emergency Medicine 
      Apollo health city
      Hyderabad, India
      @apoorvamagic on twitter 
      Email: apoorvamagic@gmail.com



References and further reading/listening/viewing:
  1. http://www.draeger.com/sites/assets/PublishingImages/Segments/Hospital-US/A_Breath_Ahead/02_Contemporary_Clinical_Practice/NIV-FAQs.pdf
  2. http://www.ebmedicine.net/topics.php?paction=showTopic&topic_id=271
  3. http://bja.oxfordjournals.org/content/early/2013/04/04/bja.aet070.full
  4. Ventilation Literature Summaries http://lifeinthefastlane.com/ccc/ventilation-literature-summaries/
  5. EMCrit Podcast 19 – Non-Invasive Ventilation: http://emcrit.org/podcasts/niv/
  6. BiPAP part 1 on YouTube by David Gibson:  https://www.youtube.com/watch?v=UXWa1r3hEoM
  7. BiPAP part 2: https://www.youtube.com/watch?v=gewxf3FopOY
  8. British thoracic society guidelines: https://www.brit-thoracic.org.uk/guidelines-and-quality-standards/non-invasive-ventilation-(niv)/
  9. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3042478/
  10. Oxford handbook of emergency medicine: Page no. 109 (section on COPD).


2 comments:

  1. So...In order to obtain CPAP, IPAP must equal EPAP? Is this only in stand alone machines? I was under the understand that on ventilators with pressure support and PEEP options, using PEEP only establishes CPAP.

    ReplyDelete
  2. CPAP provides the same pressure during inspiration as well as expiration. This pressure is called as PEEP or EPAP. When you want to give CPAP with a BiPAP machine, YES you need to set EPAP equal to IPAP on the BiPAP machine i.e set the same pressure during inspiratory and expiratory cycle.

    When you use ventilator for NIV, you can play with PEEP (EPAP) and PS directly. And changing these two variables indirectly alters the IPAP.
    The equation is PS = IPAP - EPAP (PEEP)
    or IPAP = PS + EPAP (PEEP)
    For instance, if you set up a PS of 15 on the vent and PEEP (EPAP) of 5, you deliver an IPAP of 20.

    Hope this helps
    Thanks!

    ReplyDelete