As cases of bronchiolitis increase in the wake of COVID we wanted to visit some of the more pragmatic aspects of care. In this post, we are going to go over high flow oxygen.
What is high flow?
Horses, like babies, are obligate nasal breathers. As they gallop around the racecourse their massive lungs can draw in around 160 litres of air every minute. This can lead to exercise-induced pulmonary haemorrhage. In fact, the ‘bleeding;’ affects 95% of racing thoroughbreds. Tired of treating with horse frusemide (actually, the same as human frusemide, but probably more expensive) Blacker and Hedman (1988) developed a device to train horses, to condition their cardiorespiratory system to the high flows they would be exposed to.
In a case of horses for courses, the thought occurred to the engineers at Fisher and Paykel that if such a device could reduce the work of breathing for a horse, it might just work for something 120 times smaller.
Is it high flow an aerosol generating procedure (AGP)?
Optiflow™️/Airvo™️/heated humidified high flow nasal cannula oxygenation is an aerosol-generating procedure and, as such, should be performed in an appropriate environment with staff wearing the appropriate level of PPE. This also impacts where the treatment is started. It makes no sense to start the patient on therapy in the paediatric emergency department only to then switch it off to transfer them to either the ward or HDU. It is far more sensible to commence treatment in the setting where it is going to be continued.
The decision to initiate high flow therapy should be made by a senior decision maker.
Why do we use high flow?
There has been a great deal of debate over the evidence base for the superiority of high flow nasal cannula oxygen therapy over standard nasal cannula oxygen in cases of moderate-to-severe bronchiolitis. Anecdotally, as staff become more comfortable setting it up and using it, high flow is started earlier. This leads to an ‘it works because I have seen it work’ mentality. Trial the patient on nasal cannula oxygen first. If they remain hypoxic with oxygen saturations less than 90% then perhaps you should start them on high flow, but this is a decision that should be placed in the context of that child’s acuity and background combined with the local system and availability of escalation personal and resource (see “Getting Started” section)
Humidification and heating (to 34°C) can reduce the damage to nasal mucosa caused by room temperature air. The increased ambient moisture in the respiratory tract can also help loosen stubborn mucus.
Standard nasal cannulae may not be able to match the higher inspiratory flow rates needed in the respiratory failure of bronchiolitis.
High flow may increase the functional residual capacity, or FRC, at the end of expiration, not due to increased PEEP, per se, but due to alveolar distension.
The increased inspired concentration of oxygen will reduce the dilution of entrained air.
There is some soft evidence (in animal models) that it can help wash out CO2 from the oropharyngeal dead space but if there are chest x-ray changes suggestive of some consolidation on the background of increased work of breathing it is probably worth starting high flow sooner rather than later.
High flow should NOT be started in patients with craniofacial abnormalities, recurrent apnoeas (consider intubation) or undrained pneumothoraces.
Getting started with high flow
We tend to base our estimate of the patient’s needs on their oxygen saturations. If they are less than X we admit, and if they are greater than Y we send them home. We need to have a degree of flexibility in our guidelines based on a number of factors including pre-morbid conditions, how well the child looks and not just a magic number. Schuh et al (2014) showed that we tend to focus on the number, not the patient. When experimenters presented clinicians with artificially raised oxygen saturations, a lot fewer children were admitted. If we are not looking at the number but instead the duration of symptoms then we should heed the data from BIDS. The Bronchiolitis in Infancy Discharge Study (BIDS) found that whether we targeted sats of 90% or 94%, the cough still persisted for about 15 days.
If the patient improves there is little role for continuous pulse oximetry monitoring. Chi et al (2020) suggest it leads to an increased length of stay for no intrinsic patient benefit as staff and parents watch the monitor waiting for the correct number to pop up. It is much better to base weaning and discharge decisions around an assessment of effort and effect of breathing.
There is still a great degree of debate ongoing surrounding the benefits of high flow oxygen therapy with Kepreotes et al (2017) showing that the duration of supplemental therapy required was no different between the high flow and standard oxygen therapy groups. The more recent PARIS trial (2018) also compared standard oxygen therapy to high flow therapy. Whilst Franklin et al (2018) suggested an NNT of 9 to prevent one escalation of care (from standard O2 to high flow) there is an alternative reading of the data. If you start a patient on humidified high flow nasal cannula oxygen at the outset, 70% of the time it will be of no benefit to the patient. The trial was really a comparison of immediate high flow to rescue high flow therapy. Read Ally Munro’s piece to dive a little deeper.
Monitoring during high flow
Once a patient requires high flow therapy it is worthwhile considering where this will take place. Should it be started in the paediatric emergency department? Can the patient be managed on the ward? Should they go to PICU? Some of these decisions may have already been made before a single patient even comes through the doors with many district general hospitals not having a PICU service. There seems to be a divide between what is acceptable practice in a tertiary centre and what is acceptable in a district general hospital. These decisions are often based on both staffing levels and staffing competence. Interestingly financial considerations may not come into it as a number of studies have shown that it is cheaper to run high flow in a ward-based environment than in a PICU/HDU (Kalburgi and Halley, 2020). As the need for supplemental oxygen therapy rises is it likely that a compromise will have to be reached. Bressan et al. (2013), in a pragmatic study involving 27 infants with moderate-to-severe bronchiolitis, recorded no adverse events when they were treated with high flow in a ward-based environment.
When patients with a common disease, such as bronchiolitis, present in numbers, it is easy to think of them as a homogenous entity. One of the big challenges is identifying the patient that has a purely respiratory compromise, and needs assistance, from children who are maybe septic or have a degree of fluid overload or myocarditis. It seems reasonable for patients who simply require mild to moderate respiratory support and have no red flags for deterioration to be managed by skilled nurses in a ward-based environment. There need to be clear track and trigger guidelines in place to support nursing staff in the event of clinical deterioration.
Tachypnoea is more of a problem than tachycardia. As the rate goes up there are more insensible losses. If you can increase the flow (and hence the volume delivered) then things tend to settle down.
All children on high flow can turn tachycardic and grumpy. It is hard to know if this is their normal unless you have seen them earlier in the admission. Likewise, tachypnoea is also very subjective. If you are unsure then this is a great opportunity for some shared decision making with the retrieval service using telehealth (or your mobile phone).
Dynamic assessment is the key. Assess, intervene, watch and wait, then reassess. Repeat as necessary.
Managing on high flow
All patients on high flow therapy should have a nasogastric tube inserted before commencement. This reduces the risk of gastric distension and subsequent diaphragmatic incursion on respiration. If the child cannot tolerate oral feeds then the NG can also be used to provide enteral nutrition.
Weaning high flow
There are two main ways to wean a patient off of high flow oxygen. We can either wean the flow down first then switch to nasal cannulae or we can wean the percentage of inspired oxygen first. Generally the older (and heavier) a child is, the faster they will get better. It’s time to refresh some of our respiratory physiology and Poiseuille’s law. Smaller airways are more likely to get gunked up with snot and mucus. This creates turbulent flow. This, in turn, leads to increased work of breathing. The same amount of mucus in a larger away contributes much less and so there is more laminar flow and reduced work of breathing.
The RCPCH National guidance for the management of children with bronchiolitis and lower respiratory tract infections during COVID-19 map out a rapid weaning plan. Essentially, there are two options.
Weaning the flow
Wean the flow rate down to 1l/kg then switch to standard nasal cannulae
Weaning the oxygen
Once on a FiO2 of 0.3 (30%) oxygen (regardless of flow rate flow) switch to standard nasal cannulae.
Deteriorating on high flow
Some children are more likely to fail high flow therapy than others, becoming either hypoxic or apnoeic. See the table below for some key risk factors.
The smaller, younger patient still has an immature breathing system. If Optiflow™️ is started at the right time the overwhelming majority get better – and go home. There will always, however, those that do not get better with CPAP. Flipping the switch from CPAP to BiPAP will offer more respiratory support. It can feel uncomfortable doing this if you have not done it before. Most PICU outreach services can provide training on how to swap modes. This may be enough to stave off the need for intubation, critical care retrieval and the subsequent filling of limited paediatric ICU beds.
There may be times when transportation to a tertiary centre is required to provide ongoing care. This can be a real challenge when a patient is on high flow oxygen. Early discussions with the retrieval service can prevent delays down the track. We tend to think of a retrieval service in isolation, dealing with the patient in front of us. It is important to recognise that it is not just a simple matter of popping along in an ambulance and picking up a child and taking them down the road. Each case, or mission, can take eight hours, on average. Longer journeys of up to eighteen hours are not unheard of.
Moving the patient from a safe, warm building to another safe, warm building via a rattling metal box on wheels is not without risk. One also needs to consider the profound impact on the family of moving their child away from their home hospital to somewhere many hours away from where they may have no psycho-social support. Better training and better resources will improve family-centred care.
Many ambulances only have a two-pin plug, rather than a mains plug, and so need a converter. These cost a few pounds but require PAT testing to make sure they are medically safe. Not all transport services have access and so the Optiflow™️ device cannot be plugged in.
An 18-month-old toddler with bronchiolitis weighs approximately 10kg in weight. At 2l/kg/minute they will go through 20 litres of oxygen a minute. A standard ambulance holds 2 D size (1600L) cylinders. The smaller C-size handheld cylinders hold just 450L. Either should be more than enough for a single trip by road, even if you are driving from West Cornwall Hospital to Caithness General Hospital.
If you don’t have high flow, then what?
Healthcare is beset with the challenge of managing with finite resources. Whilst we might be able to cope with a few cases of bronchiolitis in any given year it is possible that demand for high flow outstrips availability. There are devices available that can, for very little cost, converts the dry oxygen from the wall to humidified (but not warmed) oxygen. When a baby is bunged up with copious secretions that will cause them to plug off their airways humidification of their supplemental oxygen is key. Even at higher flow rates (2l/kg/min), it is better to humidify the oxygen.
High flow vs low flow vs headbox – Ian Sinha looks at the evidence
We did a quick and dirty analysis looking at 8 studies (2122 infants)
In hypoxic infants, using high flow instead of low flow made no difference in terms of length of stay, the need for ICU admission or the need for mechanical ventilation. We can say this with a moderate to high degree of certainty though this is impaired by the lack of blinding, and differences in ICU admissions between the studies.
226/969 (23.3%) of infants randomised to low flow ‘failed’ and required escalation of therapy. It does not appear that high flow modifies the disease process.
There is no evidence, apart from one small study, comparing high flow to headbox oxygen so meaningful comparisons and conclusions cannot be inferred.
Low flow oxygen is sufficient in around 75% of infants. If care needs to be escalated because of hypoxemia then they are not at risk of worse outcomes than if they have been commenced on HFNC oxygen at the outset.
If there is a shortage of high flow delivery devices then humidify the standard wall oxygen.
The Bottom line
Unless a child is critically hypoxic or apnoeic start them on nasal cannula O2 if their saturations are less than 90%.
High flow oxygen is safe for use in the ward environment in appropriate, low-risk patients
Upskilling staff to flick the switch to BiPAP may lessen the need for higher level care thus reducing the PICU workload
Talk to your retrieval service early, they may be able to guide you in order to optimise therapy
Blackmer RH, Hedman JW. (1988). Method and apparatus for pulmonary and cardiovascular conditioning of racehorses and competition animals. US4722334A.
Bressan, S., Balzani, M., Krauss, B., Pettenazzo, A., Zanconato, S. and Baraldi, E., 2013. High-flow nasal cannula oxygen for bronchiolitis in a pediatric ward: a pilot study. European Journal of Pediatrics, 172(12), pp.1649-1656.
Chi KW, Coon ER, Destino L, Schroeder AR. Parental perspectives on continuous pulse oximetry use in bronchiolitis hospitalizations. Pediatrics. 2020 Aug 1;146(2)
Clayton, J.A., McKee, B., Slain, K.N., Rotta, A.T. and Shein, S.L., 2019. Outcomes of children with bronchiolitis treated with high-flow nasal cannula or noninvasive positive pressure ventilation. Pediatric Critical Care Medicine| Society of Critical Care Medicine, 20(2), pp.128-135.
Cunningham, S., Rodriguez, A., Adams, T., Boyd, K.A., Butcher, I., Enderby, B., MacLean, M., McCormick, J., Paton, J.Y., Wee, F. and Thomas, H., 2015. Oxygen saturation targets in infants with bronchiolitis (BIDS): a double-blind, randomised, equivalence trial. The Lancet, 386(9998), pp.1041
Durand, P., Guiddir, T., Kyheng, C., Blanc, F., Vignaud, O., Epaud, R., Dugelay, F., Breant, I., Badier, I., Degas-Bussière, V. and Phan, F., 2020. A Randomised Trial of High-Flow Nasal Cannula in Infants with Moderate Bronchiolitis. European Respiratory Journal.
Franklin, D., Babl, F.E., Schlapbach, L.J., Oakley, E., Craig, S., Neutze, J., Furyk, J., Fraser, J.F., Jones, M., Whitty, J.A. and Dalziel, S.R., 2018. A randomized trial of high-flow oxygen therapy in infants with bronchiolitis. New England Journal of Medicine, 378(12), pp.1121-1131.
Franklin, D., Babl, F.E., Gibbons, K., Pham, T.M., Hasan, N., Schlapbach, L.J., Oakley, E., Craig, S., Furyk, J., Neutze, J. and Moloney, S., 2019. Nasal high flow in room air for hypoxemic bronchiolitis infants. Frontiers in Pediatrics, 7, p.426.
Hodgson, K.A., Davis, P.G. and Owen, L.S., 2019. Nasal high flow therapy for neonates: current evidence and future directions. Journal of Paediatrics and Child Health, 55(3), pp.285-290.
Hosheh, O., Edwards, C.T. and Ramnarayan, P., 2020. A nationwide survey on the use of heated humidified high flow oxygen therapy on the paediatric wards in the UK: current practice and research priorities. BMC Pediatrics, 20(1), pp.1-9.
Jackson, T., Deibert, D., Wyatt, G., Durand-Moreau, Q., Adisesh, A., Khunti, K., Khunti, S., Smith, S., Chan, X.H.S., Ross, L. and Roberts, N., 2020. Classification of aerosol-generating procedures: a rapid systematic review. BMJ open respiratory research, 7(1), p.e000730.
Kalburgi, S. and Halley, T., 2020. High-flow nasal cannula use outside of the ICU setting. Pediatrics, 146(5).
Kawaguchi, A., Garros, D., Joffe, A., DeCaen, A., Thomas, N.J., Schibler, A., Pons-Odena, M., Udani, S., Takeuchi, M., Junior, J.C. and Ramnarayan, P., 2020. Variation in Practice Related to the Use of High Flow Nasal Cannula in Critically Ill Children. Pediatric Critical Care Medicine, 21(5), pp.e228-e
Leyenaar, J.K. and Ralston, S.L., 2020. Widespread adoption of low-value therapy: the case of bronchiolitis and high-flow oxygen. Pediatrics, 146(5).
Lin, J., Zhang, Y., Xiong, L., Liu, S., Gong, C. and Dai, J., 2019. High-flow nasal cannula therapy for children with bronchiolitis: a systematic review and meta-analysis. Archives of Disease in Childhood, 104(6), pp.564-576.
Lutman, D. and Petros, A.J., 2006. How many oxygen cylinders do you need to take on transport? A nomogram for cylinder size and duration. Emergency Medicine Journal, 23(9), pp.703-704.
Masarweh, K., Gur, M., Leiba, R., Bar-Yoseph, R., Toukan, Y., Nir, V., Gut, G., Ben-David, Y., Hakim, F. and Bentur, L., 2020. Factors predicting length of stay in bronchiolitis. Respiratory medicine, 161, p.105824.
Mayfield, S., Bogossian, F., O’Malley, L. and Schibler, A., 2014. High‐flow nasal cannula oxygen therapy for infants with bronchiolitis: Pilot study. Journal of Paediatrics and Child Health, 50(5), pp.373-378.
Milési, C., Essouri, S., Pouyau, R., Liet, J.M., Afanetti, M., Portefaix, A., Baleine, J., Durand, S., Combes, C., Douillard, A. and Cambonie, G., 2017. High flow nasal cannula (HFNC) versus nasal continuous positive airway pressure (nCPAP) for the initial respiratory management of acute viral bronchiolitis in young infants: a multicenter randomized controlled trial (TRAMONTANE study). Intensive Care Medicine, 43(2), pp.209-216.
Moreel, L. and Proesmans, M., 2020. High flow nasal cannula as respiratory support in treating infant bronchiolitis: a systematic review. European Journal of Pediatrics, pp.1-8.
O’Brien, S., Borland, M.L., Cotterell, E., Armstrong, D., Babl, F., Bauert, P., Brabyn, C., Garside, L., Haskell, L., Levitt, D. and McKay, N., 2019. Australasian bronchiolitis guideline. Journal of Paediatrics and Child Health, 55(1), pp.42
O’Brien, S., Craig, S., Babl, F.E., Borland, M.L., Oakley, E., Dalziel, S.R. and Paediatric Research in Emergency Departments International Collaborative (PREDICT) Network, Australasia, 2019. ‘Rational use of high‐flow therapy in infants with bronchiolitis. What do the latest trials tell us?’A Paediatric Research in Emergency Departments International Collaborative perspective. Journal of Paediatrics and Child Health, 55(7), pp.746-752.
Principi T, Coates AL, Parkin PC, Stephens D, DaSilva Z, Schuh S. Effect of Oxygen Desaturations on Subsequent Medical Visits in Infants Discharged From the Emergency Department With Bronchiolitis. JAMA Pediatrics 2016;170(6):602-8.
Ralston, S.L., 2020. High-flow nasal cannula therapy for pediatric patients with bronchiolitis: time to put the horse back in the barn. JAMA Pediatrics, 174(7), pp.635-636.
Ramnarayan, P. and Schibler, A., 2017. Glass half empty or half full? The story of high-flow nasal cannula therapy in critically ill children.
Ramnarayan, P., Lister, P., Dominguez, T., Habibi, P., Edmonds, N., Canter, R.R., Wulff, J., Harrison, D.A., Mouncey, P.M., Peters, M.J. and United Kingdom Paediatric Intensive Care Society Study Group, 2018. FIRST-line support for Assistance in Breathing in Children (FIRST-ABC): a multicentre pilot randomised controlled trial of high-flow nasal cannula therapy versus continuous positive airway pressure in paediatric critical care. Critical Care, 22(1), p.144.
Schuh S, Freedman S, Coates A, et al. Effect of Oximetry on Hospitalization in Bronchiolitis: A Randomized Clinical Trial. JAMA. 2014;312(7):712–718. doi:10.1001/jama.2014.8637
Slain KN, Martinez-Schlurmann N, Shein SL, et al: Nutrition and high- flow nasal cannula respiratory support in children with bronchiolitis. Hosp Pediatr 2017; 7:256–262
Spentzas, T., Minarik, M., Patters, A.B., Vinson, B. and Stidham, G., 2009. Children with respiratory distress treated with high-flow nasal cannula. Journal of Intensive Care Medicine, 24(5), pp.323-328.
Vahlkvist, S., Jürgensen, L., La Cour, A., Markoew, S., Petersen, T.H. and Kofoed, P.E., 2020. High flow nasal cannula and continuous positive airway pressure therapy in treatment of viral bronchiolitis: a randomized clinical trial. European Journal of Pediatrics, 179(3), pp.513-518.
Weiler, T., Kamerkar, A., Hotz, J., Ross, P.A., Newth, C.J. and Khemani, R.G., 2017. The relationship between high flow nasal cannula flow rate and effort of breathing in children. The Journal of Pediatrics, 189, pp.66-71.