Non-invasive BiPAP can be a successful ventilation strategy for status asthmaticus, removing the need for intubation and the complications associated with this.
A 6-year-old known asthmatic presents to ED with a two-day history of cough and coryza, worsening wheeze and work of breathing over the last day. He is usually managed with beclomethasone twice daily and salbutamol as needed.
On arrival, he had an oxygen saturation of 88% in air and significantly increased work of breathing. His respiratory rate was 36 breaths per minute, and his heart rate was 144.
He was started on nasal cannula oxygen at 2L/min and managed as per the severe asthma pathway with burst therapy salbutamol and ipratropium bromide followed by hourly salbutamol nebulisers.
He receives a dose of oral prednisolone and IV magnesium sulphate.
As he continues to have a poor response to treatment, he is started on an aminophylline infusion at 1mg/kg/hour.
His blood gas shows a respiratory acidosis with a pCO2 of 7.5kPa (increased from 5kPa at the time of cannulation). A chest X-ray is hyper-inflated, with no focal consolidation and no pneumothorax.
Despite these therapies, he is starting to look tired. The feel that he needs more ventilatory support given the rising CO2. He is referred to the regional paediatric retrieval service and the local adult intensive care team come to review the child.
Would you trial NIV in this patient?
What is status asthmaticus?
Status asthmaticus is acute severe or life-threatening asthma not responding to bronchodilator therapies
British Thoracic Society asthma definitions
– Acute severe asthma
– Can’t complete sentences in one breath or too breathless to talk or feed
– SpO2 < 92%
– Peak flow 33-50% best or predicted
– Heart rate >140 in children aged 1 – 5 OR >125 in children over 5
– Respiratory rate >40 in children aged 1 – 5 OR >30 in children aged over 5
What are the signs of life-threatening asthma?
Management of acute asthma*
*as per BTS guidelines
Acute asthma is managed in a stepwise fashion using the following guidelines.
Oxygen to achieve saturations 94-98%
Inhaled short-acting B2 agonist
Addition of ipratropium bromide
Steroids – oral/intravenous
IV magnesium sulphate
IV aminophylline
IV salbutamol
Patients who respond poorly to these treatments require PICU admission for ventilatory support. Intubation, however, can be a significant challenge in these patients. Over half of the morbidity and mortality in status asthmaticus occurs during or immediately after intubation; therefore, other ventilation strategies should be considered.
High flow nasal cannula (HFNC), although increasingly used for respiratory distress, does not have a role in the management of status asthmaticus. Evidence (although limited) suggests using HFNC can delay the initiation of NIV and result in longer intensive care and hospital stays.
How does bi-level positive pressure ventilation work?
The aim of NIV is to reduce work of breathing and muscle fatigue. The recommended mode is bi-level positive pressure ventilation (BiPAP).
The inspiratory positive airway pressure (IPAP) is a higher level of pressure delivered when the patient inhales. It helps to open the airways and make it easier for air to enter the lungs thus reducing muscle fatigue.
The positive end-expiratory pressure (PEEP) is a lower level of pressure maintained during exhalation. It assists in keeping the airways open, preventing them from collapsing, and making it easier for the patient to breathe out.
Increasing PEEP is thought to cause bronchodilation by providing direct mechanical stimulus as well as secondary stimulation through pulmonary stretch receptors coupled with activation of the non-cholinergic parasympathetic pathway. This, in turn, inhibits the bronchoconstriction cholinergic pathway.
When should you consider NIV?
Consider NIV in those who have not responded to standard medical treatment AND who have one or more of the following:
-Tachypnoea (persistent)
– Tachycardia
-Use of accessory respiratory muscles
– S/F (SpO2/FiO2) ratio <235
– Hypercapnia
The ICEMANSS mnemonic can help:
| I | Indication | Status asthmaticus |
| C | Contraindications | GCS < 9, vomiting, facial trauma, peri-arrest, haemodynamic instability, P/F ratio <100, pneumothorax |
| E | Equipment | Full facemask or oronasal (depending on tolerance/fit)Ventilator, circuit, humidifier |
| M | Mode | BiPAP. Start low and increase for the comfort/tolerance of the patient and talk to the patient throughout the process. |
| A | Analysis of success | Leaks, synchrony, clinical condition, gases, P/F or S/F ratio |
| N | Next steps | Sedation – To reduce agitation and poor cooperation can consider ketamine +/- low dose benzodiazepine or dexmedetomidine. Escalation – Intubation De-escalation strategies: NIV pressures weaned and then to low flow or air depending on the patient. |
| b | Settings | FiO2 targeted to an SpO2>92% The inspiratory and expiratory pressures can be titrated using clinical signs and blood gases. PIP may vary according to flow waves and tidal volume, but as a guide, 10 – 18- PEEP 6-10 – will again vary according to flow waves. Tidal volumes of approximately 6-9ml/kg Note – a short inspiratory time may improve success due to longer expiration time in severe obstruction |
| S | Side effects and risks: | Barotrauma/pneumothorax (often already present status asthmatics). Intolerance, interface pressure injuries, vomiting, aspiration, and subcutaneous emphysema. |
What is auto-PEEP?
Auto-PEEP occurs when there is incomplete lung emptying before the start of the next breath. This results in air trapping and a buildup of pressure at the end of expiration that is not part of the set ventilator PEEP. Essentially, it’s unintentional, extra PEEP added on top of the ventilator’s set PEEP.
Auto-PEEP can be broken down into dynamic auto-PEEP and non-dynamic auto-PEEP.
The following table is representative of intubated patients; however, the non-dynamic auto-PEEP is relevant to asthmatic patients on BiPAP.
Dynamic auto-PEEP is often seen in mechanically ventilated asthmatic patients and sometimes requires disconnection of the endotracheal tube and manual decompression of the chest.
Non-dynamic auto-PEEP may be due to secretions. These act as a uni-directional valve and can occur in non-intubated asthmatic patients.
In some cases, a temporary increase in PEEP (Positive End-Expiratory Pressure) is used to open up the airways, particularly if a mucous plug is contributing to auto-PEEP. By elevating the PEEP, the airway around the mucous plug can open sufficiently, allowing the plug to dislodge, subsequently reducing the overall PEEP. This change is often observable in the flow curves on the ventilator.
As the airway obstruction resolves and gas trapping improves, the PEEP can be gradually decreased.
What is the evidence for NIV in status asthmaticus
Although there is some evidence for the use of NIV in status asthmaticus, there are few randomised control trials.
In 2015, Silva et al. reviewed the two published randomised control trials. They concluded that using NIV in paediatric status asthmaticus was safe and efficacious for those not responding to conventional treatment. However, both RCTs were unblinded and had a small number of participants.
A Cochrane review published around the same time found insufficient evidence to support or reject the use of NIV in paediatric status asthmaticus and recommended that further large RCTs were needed.
A more recent meta-analysis involving 10 RCTs found the addition of NIV to conventional asthma treatment beneficial. However, these studies did not focus on children unresponsive to conventional treatment.
There are, however, several observational studies that support the use of NIV in paediatric status asthmaticus. They have found improved clinical symptoms and evidence of improved gas exchange following initiation of NIV in children with acute asthma.
Your young patient spent 48 hours on BiPAP in PICU, the initial 24 hours on low-dose dexmetomidine infusion and then no sedation.
The BiPAP was weaned to nasal prongs after 48 hours, and they were stepped down to the ward with long-term respiratory follow-up.
Take-homes
BiPAP can be considered as an alternative to intubation in children with status asthmaticus
Careful patient selection is crucial.
Sedation may be required to aid compliance.
Be prepared for intubation in case of treatment failure.
About PICSTAR
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If you would like to join PICSTAR and get involved in projects, have ideas you would like to propose or get advice/mentorship via PCCS-SG, don’t hesitate to contact us at picstar.network@gmail.com. See their website for more: https://pccsociety.uk/research/picstar/
References
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Beers SL, Abramo TJ, Bracken A, Wiebe RA. Bilevel positive airway pressure in the treatment of status asthmaticus in pediatrics. The American journal of emergency medicine. 2007 Jan 1;25(1):6-9.
Dai J, Wang L, Wang F, Wang L, Wen Q. Noninvasive positive-pressure ventilation for children with acute asthma: a meta-analysis of randomized controlled trials. Frontiers in Pediatrics. 2023 Apr 28;11:1167506.
Korang SK, Feinberg J, Wetterslev J, Jakobsen JC. Non‐invasive positive pressure ventilation for acute asthma in children. Cochrane Database of Systematic Reviews. 2016(9).
Mayordomo‐Colunga J, Medina A, Rey C, Concha A, Menéndez S, Arcos ML, Vivanco‐Allende A. Non‐invasive ventilation in pediatric status asthmaticus: a prospective observational study. Pediatric pulmonology. 2011 Oct;46(10):949-55.
Morley SL. Non-invasive ventilation in paediatric critical care. Paediatric respiratory reviews. 2016 Sep 1;20:24-31.
Rampersad N, Wilkins B, Egan JR. Outcomes of paediatric critical care asthma patients. Journal of Paediatrics and Child Health. 2018 Jun;54(6):633-7.
Scotland HI. BTS/SIGN British guideline on the management of asthma. A national clinical guideline. Available at: https://www. brit-thoracic. org. uk/document-library/clinical-information/asthma/btssign-asthma-guideline-2019. Accessed November 2023.
Silva, P.D.S. and Barreto, S.S.M., 2015. Noninvasive ventilation in status asthmaticus in children: levels of evidence. Revista Brasileira de terapia intensiva, 27, pp.390-396.
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Villanueva A, Orive J, Cusco M, Blokpoel R, Odena, MRimensberger P. Handbook of Paediatric and Neonatal Mechanical Ventilation. 2nd edition. Tesela Ediciones 2021
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Correct – typo being changed.
This is a typo, and meant to read <235. Thanks for pointing this out Sebastian, will amend.
Claire
“S/F (SpO2/FiO2) ratio >235”
Is it correct ? Or do you mean <235 ?