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