CME INDIA Presentation by Dr N K Singh, Admin, CME INDIA.

Needless to say, LMWH, Steroids and High Flow Oxygen Therapy have changed the scenario. Out of juke box, LMWH and steroids have become almost undisputable to save life in COVID ICU.

Let us have some look at HFNC therapy – Is it changing the scenario further?

Why High Flow oxygen?

• Low-flow devices such as nasal cannulas, nonrebreathing masks, and bag valve masks can provide up to 15 L/min and 100% FiO₂.
• During times of respiratory distress, flows reach >100 L/min resulting in entrainment of much larger volumes of room air and resultant reduction in delivered FiO₂.
• But we want to Minimise oxygen dilution and Wash out dead space air.
• In COVID hypoxia becomes critical. The usual oxygen therapy can not overcome the air entrainment and dilution of the supplied oxygen. Typically, respiratory rate increases in hypoxia, further diluting the oxygen.
• The conventional teaching of 4% increase in inspired oxygen concentration per litre of oxygen through nasal cannula does not hold true in COVID ICU.
• Now here comes the increasing role of high flow system. It provides a very high flow to meet all of the airflow demand decreasing the oxygen dilution and gives a stable inspired oxygen concentration.
• The prime clinical benefit of HFNC is its efficiency in delivering supplemental oxygen. It delivers flow-dependent FiO₂. The greater the increase in flow, the more the FiO₂ is augmented.
• HFNC washes carbon dioxide (CO₂) out of the upper airways, thereby reducing the anatomical dead space. Subsequently, the work of breathing is improved and respiratory rate lowered by reduction in anatomic dead space.
• It also renders several other benefits including improved mucociliary function, thereby facilitating secretion clearance, decreased risk of atelectasis, and improved ventilation/perfusion ratio and oxygenation. Thus, flows as high as 60 L/min are tolerated by patients.

Makes Life Much liveable in ICU

• The humidified, warm air is more comforting to the patient.
• It preventing airway inflammation.
• It is more acceptable to patients than NIV with tight-fitting mask.
• The high flow of the system also creates some PEEP and increases end expiratory lung volumes.
• It decreases cardiac preload.
• Patients can continue to eat and drink during the application of HFNC.

How is it started in adults?

• Start with flow 60 L/min.
• Temperature 37 degrees.
• FiO2 to achieve SpO2 92-96% (lower as desired for COPD).
• Continue monitoring for respiratory function and need for escalation/step down of therapy.

Is HFNC a validated therapy?

• Remember the mad rush about ventilators in the beginning of the pandemic. Now this got downregulated by emerging use of HFNC by frontline workers. Even NIV role got in dispute.
• SCCM (Society for critical care medicine) and CDC now includes HFNC in the management strategy of COVID patients. SCCM has given a weak recommendation till now.
• HFNC is to be considered if patient is not maintaining oxygen saturation with supplemental oxygen therapy.
• Oxygen therapy by HFNC has been found to reduce the need for intubation. Need for intubation should be assessed after 1 to 2 hours of oxygen therapy by HFNC.

Is HFNC better then NIV?

• HFNC may be better than non-invasive ventilation (NIV).
• Positive pressure NIV may delay intubation and produce injurious large transpulmonary pressures and high tidal volume.
• Both HFNC and NIV should not be used in patients with COVID-19 who are having multi-organ disorder syndrome, abnormal mental status or haemodynamic instability.
• Newer data suggests HFNC can be used in the presence of mild to moderate non-worsening hypercapnia.

Precautions:

• Some studies have found low risk of aerosol spread.
• It is advisable to use HFNC in negative pressure environment in isolation rooms.
• The patient using HFNC should wear a surgical mask.
• All health care workers use appropriate PPE.
• HFNC should be used in a setting where expertise for performing endotracheal intubation exists.

CME INDIA Learning Points:

• HFNC is a respiratory support system that has become prominent in the treatment of respiratory failure.
• Now it has been suggested that HFNC provides high concentrations of oxygen to the patients, who cannot reach with conventional devices.
• HFNC can reduce the requiring of intubation in patients with COVID-19, and it can decrease the length of intensive care unit stay, and complications related to mechanical ventilation.
• HFNC can in achieving apneic oxygenation in patients during airway management.
• The use of high-flow oxygen cannulas can produce aerosols. So, HFNC treatment should be carried out in a negative pressure room; when it is not possible, devices should be undertaken in a single room.

CME INDIA Tail Piece:

Quick Take-Home message by Dr Atri Gangopadhyay, Pulmonologist, Ranchi about goals…

• Oxygenation – adequate oxygenation kills the free radical cascade of inflammation
• Indication would be any patient with a detected hypoxia.
• Another indication is after the worst is over, i.e. weaning from non-invasive ventilation.
• Post COVID damaged lungs with hypoxia could be another indication
• When not to give- TACHYPNEA, because increased respiratory rate would cause muscle fatigue and progress to respiratory failure.

Quick take Home message by Dr Akash kumar Singh,Internist,Baroda,Gujrat

One of the most convenient methods to deliver high flow oxygen after the NRBM delivery of oxygen has failed to meet the patients needs of oxygen, the HNFC is the bridge to BIPAP (much more convenient that BIPAP for the patient) 2 types of HNFC devices are available. One that has both the oxygen flow (upto 100 litres per minute) and FiO2 mode. This is feasible in the Fisher Paykel device the prices of which have shot up 3 times during the COVID19 epidemic (Now costing close to 4.5 lakhs) Another device which is indigenously manufactured has only the oxygen flow mode (upto 100 litres) but you can not adjust FiO2. This device is also very useful and costs less than 1.5 lakhs. However if there is air hunger, then the patient would need a bipap only. However in COVID19 patients, the air hunger is not a prominent feature, and HNFC does a job equivalent to BIPAP with much more convenience to patient as it is almost akin to oxygen delivery via nasal prongs

Re-visiting the article:

HFNC advantages compared to conventional oxygen therapy

• Ability to deliver O2 at up to 60 LPMs at nearly 100% FiO2. This is huge compared to regular Nasal Cannula (1-6 LPMs, maxing out at 45% FiO2) and NRB (10-15 LPMs, ~ 95% FiO2). The oxygen is humidified. It’s comfortable to use. Unlike having a big honking mask blowing into y face, we get a smooth flow.
• Provides a small amount of CPAP (2-6 cm H2O). This mechanically splints open the nasopharynx, preventing supraglottic collapse and decreasing nasopharyngeal resistance. Reduces work of breathing by assisting in dead-space washout.

Input Reference:

1. https://doi.org/10.5578/tt.69807
2. Indian J Respir Care 2020; 9:134-40

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