HiFlow / Non Invasive Ventilation (NIV)
The basics of supplemental oxygen
- when we breath in our usual gas flow is about 30 – 45 LPM (unless in hyperdynamic state ie anxiety / APO etc)
- low flow interfaces, like normal nasal cannula and Hudson masks, rely on a mixing of room air and O2 to give percentages of oxygen, however the faster or deeper the patients breathe the more room air is entrained and the patient receives less oxygen.
- by matching or exceeding that flow we can achieve the exact level of O2 required even when the patient varies their rate and depth of breathing
Add the comfort of a less claustrophobic nasal interface than a mask and humidity to increase flow tolerance and we can safely deliver an accurate level of O2 up to 100% even in mouth breathers (although they usually do require more flow)
- the fast flow of gases through the airways causes a turbulent stream that can assist with “washout”
- washout of the upper airways of the remaining CO2 from the patients last exhalation means next breath is all humidified set level O2 rather than rebreathing that gas not able to reach the “outside”
- this may assist to a degree with CO2 retainers
The concept of HiFlow via nasal cannula effectively and reliably increasing PEEP has largely been disproved, however with a closed mouth, deep nasal inspiration and PEEP may be assisted by the high flows
- failure of HiFlow to correct gas exchange in the patient may lead to the need for NIPPV
HiFlow is ALWAYS HUMIDIFIED, lack of humidification can lead to decreased cililary function, extreme pain, dry secretions and very decreased patient benefit
Currently in most ICU there are numerous methods to blend HiFlow gases for NIV;
- blender heads – this has a dial for gaseous oxygen percentage mix and a flow meter for the flow regulation
- the Draeger V500 (among other multiuse ventilators)
- the flushing of the upper airways means entrainment of room air is absent or very low at high mixer flows.
- if the patient is receiving / requiring 40% Oxygen or greater weaning should be O2 percentage first
- at less than 40% Oxygen gradual titration of percentage and flow will begin to replicate how the patient would cope on the wards with a standard low flow circuit. Should the patient struggle increase flow to its original level and observe effect before increasing O2
- 30% Oxygen or less should be able to be weaned to standard interfaces but be aware that lack of flow means they may require higher O2 through these standard interfaces
Non Invasive Positive Pressure Ventilation (NIPPV)
Adding a pressurised oxygen blend via a mask (nasal, face or hood)
Firstly, there are patients who shouldn’t…
Prior to commencement of NIPPV patients are to be assessed for:
- capacity to protect his or her airway
- level of consciousness of a GCS greater than or equal to 9 (the occassional exception being suitable “do not intubate” semi-conscious patients with hypercapnic COPD)
- anticipated level of compliance with mask interface (claustrophobia can be a major issue)
- capacity to manage their respiratory secretions and
- potential to recover to a quality of life acceptable to the patient.
Failure to meet any one of these criteria renders the patient ineligible for NIPPV and review of alternate care or escalation of therapy should be considered
But our patient is for NIPPV and most ICUs have at least 2 methods of applying this treatment
- VISION V60 (or similar)
- Dräger V500 (or similar)
Requires O2 supply only as has it’s own air compressor
Can be used as a dry system or humidified
Documentation of IPAP pressure is INCLUSIVE of PEEP (EPAP) so EPAP 4 and IPAP 14 as in the picture means an effective pressure support of 10cmH2O (Draeger EXCLUDES PEEP A.K.A. delta PEEP)
Can tolerate higher levels of mask leak than Dräger with up to a claimed 200LPM however, we usually aim for less than 50 (Dräger 40LPM)
Single concept machine it can not supply HiFlow or invasive ventilation, purely NIPPV
Requires both O2 supply and air as has no air compressor
Can be used as a dry system or humidified
Documentation of IPAP pressure is EXCLUSIVE of PEEP (EPAP) so PEEP 4 and PRESSURE SUPPORT 14 means an effective pressure support of 14cmH2O (Vision INCLUDES PEEP/EPAP)
Can tolerate generally lower levels of mask leak than Vision
Multi concept machine can supply HiFlow, NIPPV or invasive ventilation (IPPV)
NIPPV Buzz Words
PEEP = the pressure applied to the lungs when exhaling therefor increasing amount of gas trapped in lungs (residual volume)
Also known as EPAP and CPAP
PEEP = Positive End Expiratory Pressure
EPAP = Expired Positive Airway Pressure
CPAP = Continuous Positive Airway Pressure
All give the same physiological effect
Pressure Support (PS) = the assisted flow when breathing in supplied as “dialed up” on the ventilator (assists with work of breathing and volume of breathing)
Also known as IPAP
IPAP = Inspired Positive Airway Pressure
Increases oxygenation and ventilation
Process Failure Gas
Hypoxia T1 O2
Hypercapnoea T2 CO2
Using PEEP we inflate the collapsed or under supplied alveoli (a) , this fills the alveoli causing better gas exchange through the now slightly thinner and larger alveoli wall (b), this in turn stretching the capillary vessels to gently increase flow across a larger surface area, however, if we give too much PEEP the overexpansion will risk rupture of the alveoli and blockage to blood flow by compressing the vessels during excessive stretch (c).
This will increase stress to the pulmonary system and the right heart due to increased pulmonary vascular resistance.
NIPPV increases oxygenation and ventilation (mode / effect)
- increases residual gas in lungs at exhalation (PEEP / O2)
- overcomes issues with resistance and compliance (PEEP / O2 & CO2)
- increases volumes of gas on inspiration (PEEP & PS / O2 & CO2)
- decreases work of breathing (PEEP & PS / O2 & CO2)
- increases alveoli distension (PEEP / O2)
- splints open upper airway / treats sleep apnoea (PEEP)
- decreases pulmonary pressures / oedema (PEEP)
- may help avoid need for IPPV
Decreases preload to heart
HiFLOW / NIV Nursing Care
Positioning for all ICU patients can not be understated in its importance. Sitting up in bed at a raised minimum of 300 is mandated for all ICU patients UNLESS otherwise contradicted, however the NIV / NIPPV patient is most greatly assisted by sitting out of bed.
Sitting out facilitates obvious downward diaphragmatic movement both by abdominal contents and by greater ability for thoracic and lung expansion.
The large abdomen patient may assisted by encouraging them to spread their knees to allow the “gut” to drop whether in bed or chair.
NIPPV Nursing Care
The magic numbers of PEEP 5cmH2O and PS 10cmH2O are generic levels as every machine must be set at some pressures to start. Good medical and nursing care will see those numbers increased or decreased as ordered to suit the individuals need and degree of disease process.
Most dyspnoeic patients will benefit from the application of the face mask by hand rather than strapping it straight on, at least to start, this associated with copious verbal reassurance when NIPPV / mask is commenced for the first time will help the extremely anxious patient to cope better with the situation. Remember, they are already terrified of suffocating and putting a very tight mask over their face to help supply extra pressure wont make sense to most patients. Tell them you aren’t going to leave them and make sure you don’t for at least the first 15 minutes – you have to gain and keep their trust so writing down their observations or filling other paperwork can wait.
Set a timeline while talking to the patient, encourage them and set easy goals. “OK we’ll do this for 30 minutes then we can look at having a break and a spoon of ice chips”, ask the patient “When you breath in do you feel there is enough air?” We can use this feedback to actively target and titrate the pressure up or down to make the patient as comfortable and, in turn, compliant as possible. Your patient may be doing this for quite a while and it may well be their only available option to survive this event if they are not for intubation so having their comfort and trust is paramount.
Only the trained experienced CCRNs, your seniors and T/Ls plus Medical Staff are allowed to adjust the pressure settings but you may be asked to change the oxygen percentage but do so only if told to.
Your best work will be making the patient feel safe, comfortable and secure.
The primary challenge for commencing NIPPV via a mask (otherwise known as the interface) is the mask selection. Face masks are sometimes supplied with the circuit or separately but always have options, each supplied with a “3 different sizes” template to facilitate choice of the right size to suit the individual – small, medium and large. Even if the wrong size interface is on the patient when transferred into your unit change it as soon as possible to the correct one, the patient will find it more comfortable, less noisy and that it delivers less facial pressure than a badly fitting mask.
All modern NIPPV ventilators allow for considerable leakage (generally aiming for less than 40 litres overall is a good guide) and as such mask tightness and the associated pressure areas, especially the nasal bridge, should be minimised.
Part of your care for the NIPPV / mask patient is checking the areas in contact by the mask a minimum of every 2/24. Report any signs of increased pressure IMMEDIATELY to your T/L. Once the patient develops a pressure area on the nasal bridge the mask cannot be re-applied. The appropriate nursing care of this simple interface may lead to a terminal change in your patients care if done wrongly.
If you find that leak remains an issue loosen off the straps completely and start again, over-tightening decreases patient comfort and if the patient is uncomfortable compliance with treatment will suffer.
Humidification – when?
Most often patients admitted for NIPPV will be commenced on a “dry” non-humidified breathing circuit, this poses a secondary challenge to the care nurse as the patient is exposed to high pressure perfectly dry (0% humidity) gases. This soon can overcome the patient’s abilities to adequately humidify these inhaled gases and discomfort may soon affect the benefits of their therapy.
Consequently we do the following;
- frequent mouth / nasal care as able (whilst observing for the clinical effects of the lack of NIPPV), discussing with the MO the use of ice chips but certainly using water soaked mouth probes, use of mask breaks and artificial saliva
- should the patient require NIPPV / mask for a continuous prolonged period (greater than 4 -12 hrs per your units policy) consider, in discussion with the T/L, changing to a humidified circuit as this may assist long term comfort. Noting that the added temperature and moisture of a humidified circuit can be more distressing to some patients
Even the patient who desaturates markedly MUST receive regular mouth and pressure care. Ask your T/L for assistance on how to minimise adverse effects of treatment breaks.
Can they eat on NIPPV?
Feeding the NIPPV patient is frequently overlooked but the patient without adequate nutrition can not get better, discuss with the T/L diet for your patient and how to keep them breathing well during mask breaks.
A plan of escalation should be clearly written for your patient;
- are they for intubation and what are we looking for as an indicator to trigger this regarding PaO2, PaCO2 etc?
- Ii this is a trial of NIPPV, how long for?
- periods with mask on if mandated etc.
And remember you are your patients advocate and voice, if they have had enough of the mask and seem to understand that it was their “last option” please discuss this with your T/L and the medical team. Good nursing and ICU care is about comfort, treating the individual and the knowledge it’s about quality not quantity and being able to not restrain or medicate in situations that the patient may just say no.
This is usually guided by the whole clinical team while observing for tolerance of decreased NIPPV, no great increase in W.O.B., no gross tachypnoea, stable saturations and importantly patient comfort.
Depending on the initial indication for NIPPV weaning to HiFlow may be required due to high oxygen requirements (generally above 30 – 35% O2). Always remember that sudden reduction in PEEP will increase the need for higher levels of supplemental O2 (meaning a patient receiving PEEP of 10cmH2O at 30% may require 50% O2 or greater when the oxygen rich gas is no longer under pressure)
For your and the patients safety please acknowledge that HiFlow NIV or NIPPV patients are more likely to suddenly deteriorate and require rapid intervention so ANY patient receiving HiFlow NIV or NIPPV or IPPV must have a self inflating Laerdal (or similar) resuscitation bag and MASK on hand at all times
And it’s always great to see how far we have come, as ‘back in the day’ Negative Pressure Ventilation (AKA the Iron Lung) was the long-term treatment of choice
Again very well done! Basic Oxygenation and Ventilation in the ICU covered, feel free to ask the senior staff in your ICU at any time to re-explain anything that didn’t quite get in… It is a big subject!
Oh’s Intensive Care Manual 7th Edition 2014 by Andrew Bersten, Neil Soni
Pilbeam’s Mechanical Ventilation: Physiological and Clinical Applications 6th Edition by J M Cairo
ACCCN’s Critical Care Nursing 2nd Edition 2012 by Doug Elliott, Leanne Aitken and Wendy Chaboyer