While non-invasive ventilation (NIV) is used in a variety of clinical areas, I suspect emergency patients present some of the most challenging use cases. For emergency providers, investing a little time to review the basics really can lead to big improvements for your patients, even in the short timeframe of an ED stay. Like anything in medicine, there are levels of expertise that influence patient outcomes. That being said, I am but a humble non-invasive ventilation (NIV) enthusiast working in and exclusively referencing the emergency department environment so take this with whatever pinch of salt you think it requires.
While you soak up these words, try to breath slowly and deeply – feel your muscles expand and your lungs fill with air. Think about the beginning, middle and end of your breath. Give yourself this minute to just experience your breathing while you read (you might thank me for it)
Table of Contents
It’s impossible to properly understand positive pressure ventilation (including NIV) without first reminding ourselves how our normal, unassisted physiological breathing works. As you watch breathless patients desperately suck at the air it’s easy forget, we breath with our chests first, and our heads second.
When you take a breath, your chest muscles and diaphragm expand, dragging with them the lungs that are connected to your chest wall by the Pleurae (the pleural pleura, if you will). To better understand this concept, it’s helpful to consider this plastic fish…
Most of you will be familiar with this fish (or one of its buddies – a shark or dolphin will be a suitable substitute), but it is unlikely you have paid much attention to its similarity to your own respiratory system. Bear with me for a moment, this is going somewhere. This fish has the sole purpose of filling with water that can then be sprayed out under pressure (ideally toward a sibling or unsuspecting grandparent). In simple terms, the mechanics of this fish are pretty close to the mechanics of your chest wall.
When you dunk the fish under the water and expel the contained air by squeezing the fish, you have set the scene for a perfect parallel to the human chest. When you release your grip on the fish, the plastic begins to recoil to its original position – rapidly generating negative pressure inside the fish. This low-pressure system then sucks the surrounding water into the fish’s mouth to equalise the pressure. The same thing happens when you breath in – your chest muscles expand, creating negative pressure in your lungs. This negative pressure draws in gas through your nose and mouth to equalise the pressure.
By remembering that normal physiological breathing is driven by negative pressure, we can better appreciate just how different positive pressure ventilation is from your normal unassisted breaths. In positive pressure ventilation (i.e. NIV or invasive ventilation via a tracheal tube), force is applied directly into the airways. While we’re on metaphors, if negative pressure ventilation is like the operation of the squeezy fish – positive pressure ventilation is closer to blowing up a balloon. These cues can help us to visualise the potential harms associated with positive pressure ventilation (squeezy fish can fill and empty as hard as he like but overfill that balloon and you’ll know about it).
There are some essential terms / principles that I want you to think about as your keys to understanding ventilation in general. Getting your head around these terms will not only help you to understand the process of NIV, it will also greatly improve your ability to communicate in NIVese – the complicated language used by respiratory physicians and intensivists to negotiate patterns and prescriptions for ventilation. Understanding these terms and how they interrelate will help you break away from simply being able to manipulate a ventilator to a place where you are better able to understand the ventilation strategy you are aiming to provide.
PEEP and EPAP and commonly used to denote the same thing – the amount of positive pressure measurable in the airway at the very end of a breath out (expiration phase). One of the primary uses of NIV is to increase this end expiratory pressure to achieve a handful of therapeutic outcomes. By generating some ‘back-pressure’ in the lung with PEEP/EPAP, we pressurise the alveoli. Increased pressure in these tiny air sacks can be helpful in both 1) stretching the surface area of the alveoli to improve gas exchange and 2) physically squashing unwanted fluid from inside the alveoli back into the blood vessels through the permeable alveolar walls. Despite the different naming convention, these terms should be treated as the identical twins they are – in many cases term selection just comes down to the ventilator you have available.
As the name suggests, peak inspiratory pressure is the highest recorded pressure in the vent circuit during a given respiratory cycle. When using a ventilator that uses IPAP to set an upper pressure target, the PIP may appear to be quite close to the IPAP – but they are not the same thing. PIP is the product of the selected settings being applied to the individual patient – as such it is influenced by a number of factors including airway resistance, circuit tightness and mask fit.
Similar to PEEP/EPAP, IPAP and pressure support are both used to control the same thing (i.e. the amount of additional inspiratory pressure delivered when using BIPAP) – However, the way these settings represent their goal is quite different:
- Inspiratory positive airway pressure or IPAP is the upper pressure target selected when using BIPAP. When set together, PEEP and IPAP form a ‘range’ the ventilator will cycle between on inhalation and exhalation. For each breath in the vent will drive up towards the set IPAP before returning to the lower PEEP level at the end of the breath.
- Pressure support is also used to identify an upper target, but this value denotes the amount of pressure that is supplied on top of PEEP with each breath in. Where IPAP and EPAP set a targeted floor and ceiling between which the vent can cycle, pressure support acts more like a ladder with PEEP/EPAP still acting as the floor. With every breath in the pressure climbs from the PEEP baseline up to the top of the ladder before sliding back down to the floor on the breath out.
The choice between IPAP and pressure support generally comes down to the ventilator you are using as some manufacturers preference one setting over another. Importantly you won’t find both settings together on a given ventilator mode as they ultimately control the same thing. The main functional challenge when alternating between IPAP and pressure support is the implication for BIPAP ‘Prescriptions’. A pressure range of ’14:5’ can have very different implication depending on whether we are using IPAP or pressure support. While an IPAP:EPAP vent will deliver pretty close to the suggested settings targeting a peak pressure of 14cmH2O and a PEEP of 5cmH2O, setting a pressure support of 14 would be would add 14cmH2O ON TOP of the PEEP of 5 – giving you an upper pressure target of 19cmH2O. For this reason, its essential to clarify the settings in terms of the ventilator being used to keep everyone on the same page and prevent errors. You wouldn’t be happy if I asked you to give 200 paracetamols – You are always better to confirm milligrams, than to assume kilograms.
Tidal volume is the amount of gas that flows in and out of the lung with each breath. Despite lots of literature debating the utility of various volume strategies in patients, it’s probably fair to suggest a normal tidal volume for a healthy adult human would fall in the 7-8ml/kg range. Think of gentle waves rolling in and out form a shoreline, each wave rolling in and out represents the beach’s tidal volume. Understanding tidal volume goes a long way towards understanding minute volume – which is just the volume of gas that goes in and out of the lungs over a full earth minute.
Thinking back to the squeezy fish, it might be helpful to consider the VT as the amount of water that moves into and out of the fish with a single squeeze (breath), with the MV being the total volume of water that you would empty out of the fish in 1 minute.
While TV and MV are not settings you can control when using conventional NIV, they are extremely useful measurements in determining the effectiveness of the therapy. If a full-grown adult man is producing tidal volumes of 80ml, it Is safe to assume this won’t offload much CO2. Similarly, if you witness a few single breaths clocked in at 2500ml but the MV is only 5 litres – there is probably something strange happening those 2 breaths that you need to investigate. Effectively, these volumes become the breath-to-breath measurement that is most useful in determining how well your NIV is working towards its goal.
When comparing invasive ventilation via endotracheal tube (ETT) to NIV, one of the primary differences is the interface (obviously). An ETT provides a closed circuit in which fairly strict pressure control can be achieved. In NIV, the interface is more prone to leaks – meaning pressure (and subsequently a volume of gas) is lost from the circuit with each ventilation. These leaks may occur inadvertently as gas squeezes its way out the side of the patient’s mask under pressure, or it may form an essential part of the circuit itself in systems with passive exhalation ports.
While leak is not a programable parameter, it is essential to monitor to ensure NIV is optimised. While many ventilators are designed to compensate for some degree of system leak, an excessive amount can render your attempt to ventilate the patient ineffective. As such, it is important to understand what an expected or normal level of leak is for your ventilator / circuit so you can identify when things are going wrong (n.b. some ventilators are designed to function with a certain volume of leak per breath where others may aim to compensate for all leaks with a target of zero leak – this will vary from ventilator to ventilator).
The most common response I get when explaining NIV is concern that the added pressure will make it harder to breath. And I get it, surely pressurised gas flowing into your face must make it harder to get your breath out, right? To put your mind at ease – outside of some specific clinical scenarios, breathing out is the easiest thing in the world to do. In fact, for most of us breathing out will be the last thing we ever do. So, while you can certainly make it harder to breath using a non-invasive ventilator, used in the right way, for the right patient, the effect is quite the opposite. By using positive pressure to balance alveolar recruitment with appropriate volume gas exchange, NIV can both prevent further respiratory decompensation and reverse some adverse effects of hypoventilation.
While NIV is often referred more generally, the term most accurately reflects a pair of ventilation strategies: Continuous positive airway pressure (CPAP) & Bi-level positive airway pressure (BIPAP).
As the name implies, CPAP is characterised by the continuous delivery of a set positive pressure into the airway. In this mode the ventilator will attempt to provide a consistent level of positive pressure, regardless of the phase of respiration (meaning the pressure will be the same on inhalation and exhalation). The level of continuous positive pressure is often described interchangeably as CPAP, PEEP or EPAP. This ventilation strategy is useful in optimising the internal lung surface available for gas exchange. Effectively, the ventilator partially inflates the alveoli like tiny balloons. While a patient is receiving CPAP, the mechanism of breath going in and out still relies on movement of the chest muscles to create a pressure gradient – the ventilator simply compensates to keep the pressure as close to the set level of positive pressure as possible.
Instead of providing a single level of pressure, BIPAP cycles between 2 set pressures with CPAP / PEEP being the lower pressure and a secondary pressure (IPAP or pressure support depending on your ventilator) being added above to assist during inhalation. Where CPAP provides PEEP as a continuous splinting pressure allowing the respiratory cycle to occur naturally, BIPAP provides the same splinting pressure with additional pressure support (or driving pressure) during each breath to better facilitate the movement of fresh gas into the lung.
While there is a lot of nuance in mode and setting selection / titration, the following consideration may be helpful as a general principle:
- CPAP is most useful for type 1 (hypoxic) respiratory failure as it opens the airway and maximises alveolar surface area to improve gas Exchange. Examples here may include asthma, COVID pneumonitis, pulmonary oedema, pneumonia etc.
- BIPAP is most useful in type 2 (hypercapnic) respiratory failure as it directly improves ventilation allowing old gas inside the lungs to be washed out by fresh gas with each breath. Examples here may include chronic obstructive pulmonary disease (COPD), neuromuscular disorders affecting chest wall movement etc.
From providing nocturnal support to patients with obstructive sleep apnoea through to the prevention and weaning of invasive mechanical ventilation, NIV has an enormous therapeutic range. Despite its varied uses, in the emergency department there are a handful of clinical presentations where non-invasive ventilation comes into its own. Understanding each of these situations ahead of time can help you better identify when it’s time to bring out the vent:
- Exacerbation of Type 2 Respiratory Failure in COPD – One of the most common applications of NIV in the ED is the patient with established COPD who has slipped into type 2 respiratory failure. BIPAP is commonly used here to improve the offload of CO2.
- Asthma – In the case of severe life-threatening asthma, NIV can be used to support the delivery of fresh oxygenated gas into the lungs of a patient with constricted airways. While NIV is an effective means of forcing air into the lungs, as with invasive ventilation the issue of gas trapping (where the air is unable to effectively exit the lungs causing hyperinflation and dead space ventilation) is a significant concern – always proceed with caution when ventilating asthmatics.
- Sympathetic Crashing Acute Pulmonary Edema (SCAPE) or Flash acute pulmonary oedema (APO) – This is one of the quintessential emergency presentations. Picture a patient bolt upright, gasping for air, drowning in their own lungs only to be turned around in a matter of hours thanks to some aggressive NIV and nitrates. In this instance the application of positive pressure serves to physically push fluid out of alveoli, back through the membrane wall and into the circulatory system where it can be eliminated from the body.
- Cardiogenic Pulmonary Oedema – A characteristically different case to flash APO, patients with more gradual onset cardiogenic pulmonary oedema have a similar benefit from a dose of CPAP.
- COVID Pneumonitis / Pneumonia – in patients with severe COVID or pneumonia, critical hypoxia can develop through several physiological pathways. In these patients the application of NIV (particularly CPAP) can be a useful means of improving oxygenation and avoiding intubation.
When preparing equipment to deliver NIV, there are only a handful of moving parts to consider. Depending on your own clinical context your choices may be limited. Regardless of your context, understanding the strengths and limitations of your equipment is essential to optimising your ability to deliver effective ventilation. In most situations, the equipment you will need to consider can be broken down into 3 components – the ventilator, the interface (mask) and the accessories:
All that positive pressure has to come from somewhere, and mouth to mouth is not a sustainable (or desirable) option. Enter mechanical ventilators. These devices are designed to deliver set amounts of positive pressure over a defined period in response to an identified trigger. While there are numerous different ventilators that will allow you to achieve the same parameters in terms of ventilation, not all mechanical ventilators are created equal – Particularly when considering NIV. In general, there are 3 different types of ventilators that can be used to deliver NIV:
- Bi-Level Ventilators: These use a single limbed circuit with an exhalation port (either incorporated into the circuit or the interface). They are generally purpose designed for NIV and are rarely suitable for use on intubated patients. The Phillips V60 / Vision is a popular model of bi-level ventilator.
- Critical Care Ventilators: These use separate inspiratory and expiratory limbs with an active exhalation port. These ventilators are generally designed for the delivery of invasive mechanical ventilation in critical care units; however, many are equipped with a leak compensating NIV modes. The Getinge Servo is a popular example.
- Intermediate Ventilators: These are generally designed as transport or home ventilators – More importantly for our purposes, intermediate ventilators are frequently used in emergency departments for their flexibility. These vents may have single limb circuits with passive exhalation ports as in the Philips trilogy, or dual limb circuits with active exhalation valves as in the Hamilton T1. These ventilators are commonly able to deliver a wide variety of ventilation modes covering both invasive and non-invasive ventilation scenarios.
Despite the array of ventilator options available, the best advice to optimise your efforts is to develop a solid understanding of the ventilator available to you. In most EDs this will involve getting to know 1 or 2 vents at a push. However, if you are spoilt for choice, there are some important considerations when comparing the suitability of different ventilators for NIV. In general, bi-level ventilators will be most desirable for NIV (when they are available) owing to their superior leak compensation which helps reduce episodes of asynchrony between the patient and the vent (Hess & Branson, 2012).
When considering intermediate ventilators, there is a practical difference between those with passive and active exhalation ports that may be worth considering. Ventilators with active exhalation valves will generally be stricter in the delivery of pre-set pressures where those with passive ports allow for a higher degree of autoregulation by the patient. Where a vent like the Hamilton T1 is optimised to achieve the targeted pressures with little to no leak from the system, a passively vented device like the Phillips trilogy is designed to allow for a degree of leak with every breath (as there is a big hole in the circuit that the device compensates for – to a degree). Practically, this allows the passive circuit to be slightly more comfortable for the patient as they can independently regulate the pressure more than with an active circuit. While each of these devices (and indeed most transport vents outside these examples) will be completely adequate for the delivery of NIV and invasive ventilation in most circumstances – Nuances like circuit type may drive individual devices to more strongly cater to one scenario or another.
The interface is ultimately what differentiates NIV (where an external mask is applied over the mouth / nose) from invasive ventilation (where pressure is delivered via an endotracheal tube). Accordingly, the form and fit of the mask is integral to ensuring the successful application of NIV. There are several different styles of NIV interface that each have their own idiosyncrasies – as with all such equipment, ensuring you become familiar with your gear will ensure best results.
The most frequently used mask in the ED setting is an oronasal mask which forms a seal around both the nose and mouth, attempting to completely seal the upper airway from the world outside the circuit. These masks allow for a good airway seal to be achieved in most patients with a form that is universally familiar (with a similar fit to other oronasal masks i.e., BVM, non-rebreather etc). Some common challenges associated with these masks are discomfort related to pressure on the nose and a sense of claustrophobia for the user.
Aside from oronasal masks there are several wild and wonderful NIV interfaces that are available to connect a vent to your patient. These range from nasal masks to full face masks that seal around the border of the face (Scuba style), right through to hood / helmet interfaces that were popularised through the 2020 Italian COVID surge. While many of these interfaces have important use cases, a deep dive on each would double the length of this (already quite lengthy) post.
Although their use is less routine, there are a several important peripherals that may find their way into your NIV circuit:
- Nebulisers / inhaled medication ports: Many patients requiring NIV also require bronchodilatory medications. While patients have their faces crammed into NIV masks, additional connections are required to deliver these medications via the inhaled route.
- Humidification: Delivering dry, cold pressurised gas into the airway has the effect of drying out the respiratory mucosa. This inhibits the lungs’ native ability to function and facilitate gas exchange. To combat this, NIV circuits can be adapted to incorporate warmth and humidity. This is particularly important where patients are to receive NIV for a longer period.
- Filters: Through the COVID pandemic it has been highlighted that the application of positive pressure into a patient’s airway has an ‘aerosol generating’ mechanism, meaning it causes very fine particles from with patients’ respiratory tract to be forced out into the surrounding air where it can subsequently be inhaled by an unsuspecting bystander. Naturally, this is undesirable. To mitigate this risk, viral filters can be added to the circuit between the patient’s mask and the exhalation port, capturing would be contagions before they fly into your mouth.
With your understanding of the indications and your equipment if hand, it’s time to get this show on the road (…by show I mean mask – and by road, I mean face). The undermentioned steps can be followed to establish NIV as safely and efficiently as possible:
As the decision to commence NIV is occurring, it is essential to perform a suitable baseline assessment. This should include a full set of vital signs, a comment on the patient’s level of consciousness and work of breathing, blood gas (as soon as practical) and identification of any absolute contraindications or red flags (i.e. active vomiting, unconsciousness, facial trauma etc). This assessment should be documented and will become the baseline against which progress will be measured.
As with any therapy, having informed consent from the patient is essential wherever practicable. In the case of NIV, taking the appropriate time to ensure the patient is briefed on not only the raw indications and considerations, but also what to expect when you get underway can mean the difference between success and struggle. NIV can be claustrophobic and uncomfortable but explaining the process well can mitigate the initial shock.
Where historically a decreased level of consciousness has been treated as an absolute contraindication for NIV, in critical care areas such as emergency departments there are an increasing number of exceptions to this rule. Particularly for the patient in extremis with respiratory failure, the immediate options for alternative management often carry equivalent or greater risk compared to NIV. In these cases, it may be acceptable to deliver NIV with very close supervision along with simultaneous preparation for an unsuccessful course with intubation equipment readily at hand. In some of these cases the NIV may be successful in correcting the underlying cause of the patient’s unconsciousness enough to allow for safer administration. Naturally, patient briefing is less helpful in this situation. As such, the burden of briefing should be directed to the resuscitation team supporting the patient through this period – ensuring the team has a shared mental model for the patient’s progress along with any backup plans such as intubation.
As outlined above, you have collected the correct equipment ready for the patient – now it’s time to put it all together and perform any outstanding pre-operation checks that need to be done prior to patient connection. Wherever possible, having the vent and circuit checked and ready to go at the start of the shift can help save time at this point, meaning you only need a brief final check, and you are good to go. Now get the gear to the bedside and give yourself some space.
Turn on the vent and get the mask on the patient. These first few minutes of therapy are absolutely critical to the success of NIV as it sets the tone for the patient’s whole experience. If you slap it on without a word and ratchet it down so tight the patient’s hair turns blue, this will only harm their chances of tolerating the therapy. Instead, take a breath with the patient and slow down. For these next few minutes, you are acting as the patients NIV training wheels – standing by their side supporting them and orienting them to the whole process.
At this point try simply holding the mask on the patients face rather than attaching the straps and walking away. Give this a few minutes if you can. This step can add the patient’s comfort if they are inexperienced with NIV and can ease them into the sensation of positive pressure flowing into their airway. This also allows you the opportunity to provide reassurance as well as continually assessing the patient’s tolerance during the transition to NIV. In critical cases this can be helpful in determining the need for alternative troubleshooting strategies to facilitate better tolerance.
In less critical cases, this may be a good time to consider using a ramp function (which gradually introduces pressure up to a set target over a defined number of minutes) if one is available on your ventilator.
Once the patient has settled into the groove and is relatively comfortable with the mask, secure the straps as indicated for your selected interface. Ensure the seal is stable but not overtightened. Ensure the patient is set up in a comfortable and physiologically appropriate position with any required monitoring attached. In less acute patients where you may be required to step away momentarily, ensure the patient has a ready means of contacting you (note: in all acute instances of NIV direct visual monitoring is advised until the patient stabilises).
Once your patient is able to tolerate their NIV, your task now switches to ongoing monitoring. In this phase you are continually monitoring the patient and the vent to ensure you are delivering the therapy as intended. Additionally, this phase involves collecting and processing monitoring data that will help you determine whether you are making ground – or losing it.
What to Watch (ongoing monitoring)
Patients receiving acute NIV therapy should always be a closely monitored for deterioration or complications. Delaying the identification of adverse effects can lead to both delays in achieving your therapeutic goal or significant harm to your patient. To ensure you pick up any important cues early, the following observations should be attended for all patients receiving NIV:
As with the initiation steps above, patient comfort and tolerance are essential ingredients to effective NIV. While establishing a safe and comfortable start for the patient is important, it doesn’t guarantee a trouble-free course. Continuing to talk with the patient (despite their now muffled replies) is essential to picking up early warning signs of failure. Small factors affecting patient comfort can become enormously challenging if left unmanaged. Similarly, subtle signs of agitation or distress in the patient may be your earliest indicators of a significant problem like a pneumothorax. Keep talking to you patient (even if that involves a pen and paper, crude charades etc.).
Watch those digits – Hypoxia, tachypnoea and hypotension may be critical indicators of a life-threatening pathology like a tension pneumothorax. Vitals are also a great way to ensure your therapy is tracking in the right direction. Some indicators of success may be clear like an improvement in oxygenation or reduced work of breathing, but it’s important to pay attention for some subtle syndromes as well. When counting respirations make sure you are also observing for synchrony with the vent. This is as simple as watching the patient alongside the ventilator – if the patient is struggling to trigger the vent it is possible for ventilator timed breaths to trick you into thinking the resp rate is higher than it really is. If the patient has no chest rise with a pressure wave on the vent and is gasping between ‘breaths’, this needs more investigation as you may be providing suffocation rather than ventilation.
As above, essential information can be gathered just by watching the interaction between the vent and the patient. Without a clear link between the patient’s respiratory effort and the support provided by the ventilator, any numbers displayed by the latter are likely unreliable. Where the patients’ breaths are synchronised with the vent, a number of ‘ventilator vital signs’ should be monitored to identify whether ventilation targets are being met.
- Tidal volume – Useful in establishing the volume of gas being exchanged with each breath, it should be monitored frequently to determine whether the breaths being delivered are regular or whether the volumes are all over the place suggesting potential challenges with synchrony / obstruction etc.
- Minute volume – Likely more effective that isolated tidal volume for evaluating whether sufficient gas exchange is occurring to remove excess CO2.
- Peak inspiratory pressure – Should be monitored to identify any signs of obstruction ensuring the raw numbers are interpreted alongside the visual display or pressure over time.
While real time feedback from the vent and the patient are essential cues to keep you on course, measuring blood gases is a more definitive way of determining how much ground you have covered in total (think of it like stopping on a hike to check the map). Blood gas measurements are essential in determining baseline levels that can be compared to subsequent measurements following the initiation of therapy. When NIV is used to treat type 2 respiratory failure, the most reliable way of determining whether the ventilatory support is achieving the desired outcome is to see the PCO2 fall on serial blood gas measurements. In the acute phase of NIV therapy, hourly blood gas measurements may be required to titrate vent settings. As the patient stabilises, less frequent blood gases will be required.
There is ongoing contention when deciding between arterial and venous blood gases. There is evidence to suggest there is discrepancy between PCO2 levels when measuring arterial vs venous blood. When fine tuning therapy for patients outside the immediate emergency period, the differential between sampling methods may be more pressing – However in reality, the practicalities of a venous blood gas generally outweigh the improved accuracy and venous gases are commonly used to measure and track efficacy of NIV in most emergency departments. Importantly, VBGs have a well-defined role in screening for arterial hypercapnia when using a cut-off of 45mmHg (i.e. PCO2 > 45 = hypercapnia) (Kelly, Kerr, Middleton, 2005).
Now that your patient is started on NIV and your keen eyes are observing for any sign of deterioration, it is important to know what steps you will take if such a complication was to occur. Having a systematic approach to NIV troubleshooting can save you (and you patient) in the event of sudden deterioration, and one such approach is the ‘DOPES’ method described below:
One of the major causes of patient / ventilator asynchrony is excessive or uncompensated leak from the circuit. When there is too much leak, the vent may be unable to differentiate your patients breathing from baseline noise of the leak. In these cases, the vent may trigger inspiratory cycles inappropriately causing your patient to struggle against the vent and unpicking all of your work. To prevent this, the main tool in your control is to optimise the patient / vent interface to ensure leaks are minimised and patient comfort is maximised. In most case, this will involve optimising the way the mask makes, and maintains contact with the patient – below are a few key issues to keep an eye out for:
Tightness: The most obvious reason for a leaky circuit is a loss of contact with the patients face. Sometimes this is obvious, like a strap coming loose or the patient drinking a cup of tea, but other times chasing a leak near the patient’s face can become a maddening experience that results in the mask being welded to the patients face to stop the vent alarming. One important thing to remember is that tighter isn’t always better. Where there is leak perceptible beside the patient’s mask, the impulse is to tighten the straps until the leak goes away. Importantly, an overtightened mask will often lose its intended shape and may in fact leak even more than an optimally tightened mask. Over tightened masks also introduce a number of other issues like pressure areas and alike. Where your mask has been tightened to the goldilocks point (not to loose, not to tight) and is still leaking furiously, you should A) consider whether a different sized mask would be a better fit, B) consider and control the following culprits.
Bush: With the hipster revolution of the early 21st century, beards have made a glorious and terrible resurgence. While this is great for Instagram, is spells bad news for BIPAP masks. A great big bushy beard may be aesthetically pleasing (…MAY, be), it can act like a non-compressible sieve through which pressure leaks from between mask and face (a similar proposition to bag mask ventilating a patient with a beard). Where this is a simple case of the patient being dishevelled and having not shaved for a few…months, taking a razor to the beard will be the most effective way of overcoming this issue (electric trimmers will do, this isn’t a barbershop). However, there are a number of cases where trimming a patient’s beard will be a last resort. In these cases, the application of simple occlusive dressings underneath the mask interface can be just enough additional contact to get you by (noting that leak will still likely escape underneath the dressing over time).
In some cases, barrier film wipes (such as the 3M calivon wipes) may also serve to increase mask contact if applied over the beard and beneath the mask. In cases where beard preservation is important, remember to optimise all the other aspects of your interface / ventilation however you can, and remember, there may come a point where you need to choose between beard and brain.
Floppiness: In some cases, the source of your excessive leak may be areas of loose skin underneath the mask itself. When pressure is applied into the circuit, the pressurised gas can force its way out beside the mask by pushing aside the skin at the corners of the mouth and sides of the nose. While there is little you can do to reinforce a patient’s cheeks, gentle tightening of the mask may correct this issue. However, caution should be exercised as mask overtightening may in fact worsen the leak you were trying to correct. If a tighter fit alone is not enough, consider applying a barrier wipe like calivon to the skin under the mask (this can serve to create better traction between skin and mask minimising excessive leak), or shifting down a mask size.
NIV is reliant on the movement of gas from one end of a system to the other – as anticipated, any obstruction interrupting the flow of gas from point A to point B will be seriously damaging to the desired outcome of gas exchange. Obstructions come in a variety of forms and their management is specific to the type of obstruction you are dealing with.
Mechanical upper airway obstruction: NIV doesn’t natively have any feature that protects the upper airway from obstruction (something that characterises endotracheal intubation). As such, it is important to remember that upper airway obstruction is still very bad and can kill your patient. The functional causes of airway obstructions are no different for a patient on NIV compared to any other patient – things like unconsciousness, anaphylaxis, bleeding, masses vomit etc. can still cause headaches. Importantly, the native challenges NIV poses to vocalisation and projection of audible airway sounds can mask stridor / dysphonia etc., so you need to keep your eyes and ears open.
If there is any suspicion of present or impending airway compromise, consideration should be given to endotracheal intubation and invasive ventilation. One common quick fix that can be applied to many NIV patients in the acute phase is to ensure their body is positioned and supported in a way that promotes airway opening (i.e. fowlers / lateral recumbent position, slight head extension). Pillows and bed mechanics are useful here.
Bronchospasm: A common causes of airway obstruction in patients with acute respiratory failure is bronchospasm. As with all wheezers, bronchospasm in NIV patients can be signalled by increased respiratory distress and wheeze on chest auscultation. In severe cases, lung sounds may be difficult to auscultate at all as air entry is severely restricted. Keep in mind the noises of a ventilator can easily cause confusion when auscultating a chest so exercise caution. Providing appropriate bronchodilators is the mainstay of bronchospasm management, however care should be exercised for those with positive pressure ventilation in situ as gas trapping may also become an issue (where air is forced into the lung but cannot escape effectively leading to stale oxygen depleted air occupying space in the lungs instead of fresh oxygen rich air).
Blocked pipes: While obstruction of the patient is a primary concern, this should not distract from the risk of blocked equipment. In particular, peripherals like filters have a nasty habit of clogging up with condensation, snot and or phlegm. If you are struggling for volume or pressure, always be mindful to check for signs of obstruction within the various pieces of the circuit. Where connections are effected, they can usually be hot-swapped out for new ones with relatively little fuss.
Position: Owing to their connection to the remainder of the body, lungs are susceptible to the forces of gravity. Some of these effects may be obvious and others less so. Most obviously, gravity has the tendency to drag your patient unwittingly down the bed into a dreaded crunch position where their upper airway contorts and obstructs, and the weight of the chest wall squeezes into the space required for ventilation. In the case of an interrupted airway caused by bad positioning, it is essential to correct and support optimised positioning lest the finer details of your ventilatory strategy be wasted. In most cases, a semi to high fowlers position will be a great place to start – paying attention to the mechanics of the bed to prevent further southbound sliding. An upright position also has the added benefit of taking weight off the chest wall that may otherwise limit the volume of the lung. In more extreme cases, there can be utility in adopting prone positioning as a complement to your NIV. Essentially, prone positioning allows the larger posterior portion of the lung area to expand more freely, optimising alveolar surface area and in turn ventilation. Naturally a prone position with an NIV mask on can be a challenging prospect, particularly for less oriented patients – however, it is worth noting a lateral recumbent position (which is endlessly more supportable in an ED setting) is a good surrogate for traditional proning (Caputo, Strayer & Levitan, 2020).
Pneumothorax: As with all positive pressure ventilation, pneumothorax is an ever-present risk. The application of increasing force to the internal surface of the alveoli can create conditions in which the lung perforates or ‘pops’ allowing air to accumulate in the pleural space. Not only does the collapsed lung have less functional area for gas exchange, but under continued positive pressure there is a risk that the pneumothorax may continue to expand and potentially ‘tension’ – a life threatening situation in which the pleural cavity pressure begins to compress the heart increasing the risk of cardiac arrest significantly if left untreated. Cardinal signs to look for are; increased agitation, chest pain, worsening dyspnoea, hypoxia, tachycardia / hypotension (late/bad signs). If suspected, chest auscultation, x-ray and ultrasound can lead to diagnosis which should promptly lead to management with a chest tube – especially if positive pressure ventilation is still required.
While equipment failure can certainly be a significant cause of patient deterioration, in most cases it isn’t very subtle. Thinking back to the limited number of moving parts involved in NIV, your process of elimination should involve checking each component for failure moving from the mask back towards the vent. In the first order, failures of masks, peripherals and circuits are generally fairly straightforward. The most common failures with these components will be purely mechanical (i.e. the strap broke, the tube disconnected, the filter is soaked etc.) and can often be fixed in a straightforward way (i.e. re-connecting the tube, replacing the mask etc.).
Failures involving the ventilator can be a little more complex – but only a little. In the event of catastrophic vent failure – the device may shut down or the breaths you were measuring may stop being delivered. In this case, remove the whole NIV setup and provide the patient with alternative support while the device is interrogated further (this is important – don’t muck around with the buttons while the busted machine suffocates your patient). For this reason specifically it is essential to know what backup options are available for your patient in the event of equipment failure. Naturally, this may be less critical is you are providing routine CPAP for a patient with OSA, however in the context of a patient in acute respiratory failure this can be life or death stuff.
In less overt failure, there may be a partial failure involving one or more component of the device i.e. the oxygen flow may be obstructed or internal pressure limits may be set too low restricting the supply of pressure. With most modern ventilators, these errors will effectively self-diagnose and report through the in-built alarm system. For this reason it is important to pay close attention to the alarms provided by the vent, particularly in the event of patient distress or deterioration.
One of the more challenging issues to trouble shoot in acute NIV applications is the management of patient distress or agitation leading to compromised ventilation. This can occur in 2 main ways; 1) the patient simply refuses to wear the mask, or 2) the patient wear the mask but fights the ventilator leading to dyschochrony. Both of these issues can be challenging in the case of life-threatening respiratory failure, but there are some viable solutions.
The most obvious and by far the most desirable approach is to take it back to step one and provide some much needed reassurance / education to your patient. Sometimes in the rush to get started we might miss this step and fail to help the patient settle into the sensation of NIV – sometimes they suffer baseline claustrophobia and will benefit from some additional partnership. Whatever the reason, reassurance can be endlessly helpful for distressed patients having tolerance issues with NIV in the acute setting.
More challenging is the patient who cannot tolerate NIV due to their critical condition. It is increasingly common to find patients in emergency departments who have issues tolerating NIV due to their worsening hypoxic/hypercapnic encephalopathy, which ironically will only be cured by increasing their oxygen, decreasing their CO2 etc. These patients often sit on a knifes edge between non-invasive support and intubation (with all its inherent risks). In this patient group, there is emerging evidence supporting the use of small doses of anxiolytic / dissociative medications such as ketamine to facilitate NIV compliance in the short term. The idea is that a sniff of ketamine may allow the patient to settle into the ventilation, in turn allowing them to offload some CO2, in turn increasing their chances of tolerating the vent once the medication weans. Naturally this comes with a unique set of risks associated with altered consciousness and the application of positive pressure ventilation (namely vomiting / aspiration, loss of airway patency). For this reason adequate preparation and supervision are essential for these patients. Preparation should include a full airway setup (with suction handy) to respond if the patient acutely deteriorates post sedation and needs intubation. Supervision in this case means someone will be by the patient’s side, within grasping distance of their mask for the whole time they are medicated. This allows you to closely and continuously monitor for any anticipated adverse outcomes so that they can be controlled promptly (i.e. suction vomit from the mouth before it is jettisoned into the lung).
When considering the application of sedation to facilitate NIV, it is important to understand that you are balancing risk. On one hand you accept defeat and move directly to intubation – on the other, you attempt to prevent intubation by opting for sedation facilitated NIV, knowing that intubation is a fall-back option you have prepared for. To ensure this happens as safely and smoothly as possible, a shared mental model and team inclusive preparation are essential.
Perhaps the most famous example of sedation facilitated NIV took place in 2018 when Dr Richard Harris and his team successfully anaesthetised (with ketamine) 12 Thai schoolboys and their soccer coach, before applying a full-face scuba mask (providing CPAP) and extricating them 2.6km out of an underground cave (1.1km of which were completely flooded meaning the patients and their respective rescuers were completely underwater. While this remains an extreme example, it perfectly illustrates the principle and should be referenced wherever someone performs lifesaving witchcraft involving ketamine and CPAP (Van Waart et al, 2020).
To reinforce the importance of supervision in these cases – despite being in one of the least hospitable places on the planet, the rescued boys were still receiving at least one to one care (hands on no less) for the duration of there therapy. This is the type of example we should all aim to follow – however, we are fully supportive if you choose not to wear your own Scuba mask in the resus bay.
- Van Waart H, Harris RJ, Gant N, et al. Deep anaesthesia: The Thailand cave rescue and its implications for management of the unconscious diver underwater. Diving Hyperb Med. 2020;50(2):121-129. doi:10.28920/dhm50.2.121-129
- Kelly, AM, Kerr, D, Middleton, P. Validation of venous pCO2 to screen for arterial hypercarbia in patients with chronic obstructive airways disease. J Emerg Med. 2005;28(4):377-379
- Caputo N, Strayer R, Levitan R. Early Self-Proning in Awake, Non-intubated Patients in the Emergency Department: A Single ED’s Experience during the COVID-19 Pandemic. Acad Emerg Med. April 2020. doi:10.1111/acem.13994