COVID-19: high-flow nasal cannula ‘valuable’ alternative to ventilation
By NIÉMAH DAVIDS.
The use of high-flow nasal cannula (HFNC) oxygen therapy has proven to be a low-resource alternative to mechanical ventilation in “selected patients” with severe COVID-19 pneumonia, said UCT’s Associate Professor Greg Calligaro.
Calligaro is a research coordinator at the Centre for Lung Infection and Immunity (CLII) at the UCT Lung Institute and a consultant pulmonologist at the Respiratory Clinic at Groote Schuur Hospital (GSH).
Speaking to UCT News after a busy night shift in the COVID-19 ward at GSH, one of the Western Cape’s most impacted COVID-19 hospitals, Calligaro said HFNC is a valuable and feasible alternative to mechanical ventilation that is being used more and more on critically ill COVID-19 patients at GSH.
According to Calligaro, clinicians use HFNC on conscious, cooperative patients whose oxygen saturation levels are low despite using a conventional oxygen face mask. To date roughly 45% of patients at GSH who would otherwise have required mechanical ventilation due to severe COVID-19 have successfully been treated using HFNC. This has also alleviated the pressure on the hospital’s overburdened intensive care unit (ICU).
“The rapidly evolving nature of the COVID-19 pandemic has required an agile response.”
“The rapidly evolving nature of the COVID-19 pandemic has required an agile response. By embracing and upscaling this intervention, we have witnessed some encouraging results. It has also considerably relieved the pressure on ICU beds at our hospital,” he said.
But HFNC is not a replacement for ICU care, Calligaro stressed.
“HFNC is an option for patients who are deteriorating or not improving on conventional oxygen therapy and supportive care, but who do not appear to be in imminent danger of collapse,” he said.
“Many of these very sick patients will still need to be escalated to mechanical ventilation anyway.”
The HFNC need-to-knows
HFNC is an oxygen-delivery technique that supplies high concentrations of warm, humidified oxygen to a conscious patient in respiratory distress with low blood oxygen levels.
The device comprises a flow generator that provides gas flow rates of up to 60 litres a minute (oxygen flow is measured in litres), as well as an oxygen–air blender and a humidifier that saturates the gas mixture. Its light nasal interface is comfortable and enables self-care, which means patients can eat and drink easily.
This treatment method provides patients with reliable levels of oxygen and helps to decrease their breathing work. For patients with respiratory failure, it’s considered to be a more a comfortable and less invasive alternative to intubation and mechanical ventilation (when the patient is sedated, a breathing tube is inserted into the windpipe, and breathing is supported by a ventilator in the ICU).
Prior to the COVID-19 pandemic, the use of HFNC helped to avoid the need for intubation and mechanical ventilation. More recently, it has proven to be useful in patients with COVID-19 pneumonia.
Important to note
HFNC should always be combined with awake self-proning – placing patients on their stomachs to redistribute oxygenated blood to different parts of the lungs.
While the use of HFNC in tandem with self-proning has proven useful, it’s “certainly not foolproof” as a treatment option for COVID-19. While the combined treatment method effectively treats low oxygen levels in patients with severe COVID-19, it has no effect on the virus itself.
The use of HFNC at GSH has been a “huge team effort”. The method has been adopted by many healthcare workers, who have fast become experts in managing large numbers of patients in “profound respiratory failure” in an unconventional setting.
According to clinicians, HFNC’s high flow rates may generate droplets and aerosols containing viral particles derived from respiratory secretions from infected patients. This could potentially pose a risk to other patients and healthcare workers. However, subsequent studies have found that this risk is in fact “overstated” and that this treatment technique is safer than conventional oxygen face masks.
“Unlike mechanical ventilation, HFNC can easily be implemented and managed by non-ICU specialists outside of an ICU setting.”
The oxygen consumption of an HFNC machine has also been questioned. Its high-flow oxygen capability exceeds requirements for general wards (4–5 litres a minute), as well as for the ICU and ventilated patients (30 litres a minute). Concern that GSH would be unable to keep up with the increasing demand of constant flow and pressure to HFNC supply points was a huge concern. Therefore, upscaling the use of this treatment method required input from medical engineers to increase oxygen infrastructure at the hospital as the demand for HFNC increased.
Unlike mechanical ventilation, HFNC can easily be implemented and managed by non-ICU specialists outside of an ICU setting and does not require intensive nursing and monitoring. While on HFNC, patients also don’t need to be sedated and the treatment method is considered “more comfortable” than a “tight-fitting” oxygen mask.
“We continue to witness the benefits of HFNC on our patients. It has also helped us to lower our overall intubation rates, which means we’re using less ICU resources and so saving on costs. This has been very encouraging given the current context,” Calligaro concluded.
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