CME INDIA Presentation by Dr Chandrakant Tarke, MD, DNB, DM, EDRM, MNAMS, Consultant Pulmonary, Critical Care and Sleep Medicine. Hyderabad.

How to identify Oxygen toxicity? Whether excess use of oxygen precipitates pulmonary fibrosis? These days such questions haunt us frequently. Dr Chandrakant Tarke MD, DNB, DM, EDRM, MNAMS, Consultant Pulmonary, Critical Care and Sleep Medicine. Hyderabad, gives crystal clear answers.

Oxygen toxicity is very important topic, often neglected.

• It’s not uncommon to see critical care experts targeting 99-100% SpO2 or above 100 PaO2 while managing respiratory failure, which is totally wrong.
• Oxygen is a treatment for hypoxaemia not for breathlessness. Oxygen is a drug and should be prescribed with a target saturation range.
• The recommended oxygen target saturation range in patients not at risk of type II respiratory failure is 94–98%. The recommended oxygen target saturation range in patients at risk of type II respiratory failure (COPD, OSA, OSAH, Neuromuscular diseases) is 88–92%.
• PaO2 of 60 corresponds to 90% SpO2. In most cases of ARDS, this target is enough to prevent tissue hypoxia. (only few exceptions such as cardiopulmonary resuscitation (CPR), pneumothorax where ICD not kept or CO poisoning more SpO2 or PaO2 target is required). Traditionally, oxygen is given in acute MI. Oxygen should be used carefully here as these patients are at risk of reperfusion injury, where ROS plays important role and contributes to infarct size.
• Excess oxygen leads to formation of ROS (reactive oxygen species), free radicals, which causes lung injury, absorption atelectasis, tracheobronchitis, ARDS, fibrosis, and death.
• High oxygen flow from ventilators changes microbiota, makes lungs vulnerable to damage. High oxygen supplementation can cause CO2 narcosis, retrolental fibroplasia, raised ICT, vision impairment, convulsions, unconscious and death.

Can excess oxygen cause lung Fibrosis?

Answer: YES

• The phases of lung oxygen toxicity are initiation, inflammation, proliferation, and fibrosis.
• Clinically it’s difficult to differentiate from ARDS or Barotrauma or Volutrauma or VILI (ventilation induced lung injury) i.e. secondary ARDS.
• Oxygen toxicity is important cause of ARDS/lung fibrosis…can suspect in a ARDS patient who deteriorates (after excluding new sepsis/pulmonary embolism/pneumothorax etc.) after initial improvement.
• My observations, patients who received NIV with FiO2 less than 60% had better outcome than patient who received HFNC (where we used more than 50 liter oxygen).

What FiO2 is safe on ventilator to prevent oxygen toxicity?

Answer: less than 60%

• The World Health Organisation (WHO) recommends an oxygen therapy during resuscitation of COVID-19 patients to achieve an SpO2 of 94% or more, and 90% or more when stable (non-pregnant patients).
• The Surviving Sepsis Campaign (SSC) recommends a conservative oxygenation strategy for COVID-19 patients targeting an SpO2 no higher than 96%.
• Both are based on a systematic review and metanalysis from 2018, investigating the association with mortality and higher versus lower oxygenation strategies in critically ill patients in general.

Oxygen toxicity risk increases if

1. FiO2 more than 100% given longer than 12 hrs.
2. FiO2 more than 80% given longer than 24 hrs.
3. FiO2 more than 60% given longer than 36 hrs.

CME INDIA Learning Points

• Oxygen is drug with adverse effects.
• Liberal use of supplementary oxygen may increase the number of serious adverse events including death. 
• Oxygen is a double edged sword. We should use it judiciously.

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