OXYGEN THERAPY IN COVID-19 INFECTION

What will I Learn?

Learning Objectives

By the end of this lesson you would learn about..

Is This Lesson For Me ?

If you are carrying out any of the following responsibilities, then this lesson is for you

• Indications of oxygen therapy

• Oxygenation Targets

• Types of Oxygen Devices

• Ventilation strategies

• Non invasive

• Invasive

• Complications associated with Oxygen therapy in COVID-19

• Specialists/Medical Doctors

• Nurses

• Allied and Healthcare Professionals

Indications – Acute Hypoxemia

Etiology

• Pneumonia

• Aspiration Event

• Airway obstruction

• Pulmonary Edema

• COPD Exacerbation

• Pulmonary Embolism

• Pneumothorax

Physiology

• Ventilation/Perfusion Mismatch

• Diffusion Impairment

• Right to left Shunt

• Low FiO2

• Hypoventilation

Indications – Dyspnea

Sudden lung problem – Heart Condition – MI Infection/Pneumonia/ or Heart Failure

Chronic lung disease

Covid-19

Flare up of chronic lung disease – Infection

Anaemia

Oxygen Targets

Moderate cases

• Target SpO2: 92-96% (88-92% in patients with COPD)

Severe cases

• Target SpO2 ≥ 90% in non-pregnant adults • SpO2 ≥ 92- 96% in pregnant patients

Oxygen Delivery Devices

1. Nasal Cannula

2. Simple Face Masks

3. Partial Re-breather face masks

4. Non Re-breather face masks

5. Venturi Masks

6. High Flow Nasal Cannula

7. Non- Invasive Ventilation

8. Invasive Ventilation

1. Nasal Cannula

• Also called as Nasal Prongs

• Stable patients with minimal requirement of oxygen (RR not more than 20-22/min)

• Well tolerated; do not interfere with eating/ speaking

• Delivery of constant airflow to nasopharynx and oropharynx

• Acts as a reservoir of 50 ml capacity

• Gas flow produces Bernoulli’s effect in posterior pharynx

• FiO2 Room Air: 21%

• Roughly FiO2=20 +4 x O2 in LPM

• Max up to 0.4 FiO2 and flow up to 6 LPM

• Higher flow rate dries the nasal mucosa and increases chances of infection.

• For a respiratory rate of 30-35 per minute, FiO2 decreases by 20-30% per minute

2. Simple Face Masks

• A light weight plastic mask

• Oxygen inlet at the base and holes at the

sides for exhalation

• Adds 100-200 ml to the capacity of reservoir

• Delivers oxygen at flow rates of 6-10 LPM

• 6 LPM is the minimum flow rate needed to clear the exhaled gas from the mask

• FiO2 decreases with increasing ventilatory demand

• To be removed during eating and drinking etc.

3. Partial Re-breather Face Masks

• Reservoir capacity increases with a bag

• No valve between the mask and the reservoir

• First 1/3 of expiratory gas (which has not participated in gas exchange) is exhaled back into the reservoir

• Next 2/3 is exhaled out via the side ports

• The next breath therefore has a higher FiO2 of

oxygen.

• Deliver FiO2 of 0.6-0.8 at flow rates 6-10 LPM

• Collapse of bag can increase the work of breathing

4. Non Re-breather Face Masks

• Similar to Partial re-breather masks except that the connection between mask and reservoir also one way valve

• Theoretically, these can deliver 100 percent oxygen; Practically 0.6-0.8 only

• Set flow rate: 6 – 15 L/min

• These partial Re-breather or Non Re-breather masks do not decrease the work of breathing significantly

6. High flow Nasal Cannula (HFNC) (1/2)

• Generate high flow oxygen at 40-60 LPM FiO2 up to 100% can be delivered

• Use extrapolated from non-COVID hypoxemic respiratory failure

• Advantages-

▪ Small pliable nasal prongs

▪ Warming and humidification of secretions

▪ Continuous positive airway pressure (CPAP) effect

▪ Allows patient to eat/speak

▪ Some patients not settled by HFNO may need NIV or even vice versa

• Relieves discomfort of air hunger

6. High flow Nasal Cannula (HFNC) – Uses (2/2)

Flow rate is usually set first (range 5-60 L/min); typical initial rates include 20-35 L/min

FiO2 is set next to achieve desired target saturation (range 21 to 100%)

Two parameters need to be set: Flow rate and FiO2

Flow rate is increased in increments of 5 to 10 L/min (if the respiratory rate, Oxygenation fails to improve, or breathing remains labored)

Flow rate should be maximized (if needed) in an attempt to keep the FiO2 ≤60%

Switch to conventional low-flow nasal cannula system once the flow rate reaches ≤20 L/minute and FiO2 ≤50 percent

NON INVASIVE VENTILATION (NIV)

Non Invasive Ventilation (NIV)

• • • •

Indication: Hypoxemia refractory to non ventilatory O2 devices

Prevents the need for intubation Reduces the work of breathing Bridge to intubation Contraindications-

▪ Inability to protect airway

▪ Excess secretions ▪ Vomiting

Persistent worsening or failure to improve – indications for intubation

Non Invasive Ventilation (NIV) – Helmet

Advantages –

▪ ▪ ▪

Minimal risk of exhaled air dispersion Lower chances of leakage

Effective lowering of work of breathing (due to maintenance of PEEP)

Helmet NIV reduces mortality and decreases the need for intubation in non-COVID 19 hypoxemic respiratory failure.

Non Invasive Ventilation: Interfaces

• Mask

 Nasal

 Oronasal

 Total face • Pillows

• Mouth piece • Helmet

Choice of Interface based on: Advantages/Disadvantages

Does NIV Help/Harm COVID-19 Patients?

Additionally, non invasive ventilation may cause harm to patients through two different mechanisms, leading to worsening patient outcomes:

1. The lack of ability to control tidal volumes 2. The possible delay in intubation and mechanical ventilation

The use of NIV in patients with ARDS has a failure rate of 50%.

NIV: Contraindications

• Uncooperative or extremely anxious patient • Reduced consciousness

• Inability to protect airway

• Unstable cardio-respiratory status

• Trauma or burns involving the face

• Facial, esophageal, or gastric surgery

• Pneumothorax with broncho-pleural fistula

INTUBATION AND MECHANICAL VENTILATION

Should Severe COVID-19 Patients Be Intubated ?

Concept of Mechanical Ventilation

Mechanical ventilation is a useful modality for patients who are unable to sustain the level of ventilation necessary to maintain the gas exchange functions-oxygenation and carbon dioxide elimination.

Mechanical ventilation is a technique in which energy is supplied in a predetermined way to augment or replace the patient’s muscles in performing the work of breathing.

Switching: NIV to Invasive Ventilation?

• Increasing-

 Drowsiness

 Work of breathing

 Oxygen requirement

• Hemodynamic instability

• Vomiting and risk of aspiration

• Progressing radiographic severity

• Falling respiratory system compliance (≤ 40 mL/cm H2O).

• Increasing need of positive end- expiratory pressure (≥ 10 cm H2O ) to maintain oxygenation.

• Increasing minute ventilation (≥ 10 L/min).

Ventilation Need In COVID-19 – When?

Possible Clinical Indications for ET Intubation

• Impending airway obstruction

• Signs of unsustainable work of breathing

• Refractory hypoxemia

• Hypercapnia or acidemia

• Encephalopathy or inadequate airway protection

Additional Considerations

• Does illness trajectory predict deterioration?

• Are difficulties in endotracheal intubation

anticipated?

• Is there hemodynamic instability?

• Will intubating now improve the safety of a

planned procedure or transportation?

• Will intubating now improve infection control

and staff safely?

Berlin, D.A. et al 2020. Severe Covid-19. New England Journal of Medicine 383, 2451–2460

VENTILATOR MANAGEMENT- SEVERE COVID-19/ARDS

Ventilator Management

Unclear whether COVID-19 is associated with a distinct form of ARDS that would benefit from a new strategy of mechanical ventilation.

Strategy aims to prevent ventilator-induced lung injury by avoiding- Alveolar overdistention

 Hyperoxia

Cyclical alveolar collapse

ARDS & Invasive Mechanical Ventilation

• Inflammatory, non-cardiogenic pulmonary oedema • Berlin definition: Mild, moderate and severe

• Alveolar recruitment manoeuvres

• Increased PEEP • Prone position:

Reduction of overinflated lung Promotes alveolar recruitment Reduces VQ mismatch

IMV in ARDS –

Reduction in elastance & increased compliance

Lung Protective Ventilation

Berlin, D.A., Gulick, R.M., Martinez, F.J., 2020. Severe Covid-19. New England Journal of Medicine 383, 2451–2460

Mechanical Ventilation: Pitfalls and Problems

Potential detrimental effects associated with PPV

 Reduced venous return and afterload

 Hypotension & reduced cardiac output

 Barotrauma

 Ventilator-induced lung injury

 Air trapping

 May increase dead space (compression of capillaries’)

Rescue Therapy – Severe COVID-19

Prone positioning during mechanical ventilation :

 Refractory hypoxemia (Pao2:Fio2 of <150 mm Hg during respiration and Fio2 of 0.6 despite appropriate PEEP).

 Randomized trials involving intubated patients with ARDS placing the patient in the prone position for 16 hours per day has improved oxygenation and reduced mortality.

Guérin C et al. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med 2013; 368: 2159-68.

Conclusion

 Medical Oxygen may be treated as equivalent to a drug.

 Use of Oxygen should be judicious.

 Devices should be selected based on the need of the patient.  Each device has its limitations.

 Mechanical ventilation can be a double-edged sword.  Intubating everyone early can be disastrous.

 Ventilation strategy needs to be individualized.

THANKS!

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