12th January 2024

Background

Respiratory failure is defined as abnormalities of oxygenation or ventilation (CO2 elimination) leading to respiratory dysfunction severe enough to threaten the function of vital organs.

Respiratory failure is one of the most common reasons for ICU admission, resulting in up to ≥ 75% of ICU patients requiring mechanical ventilation during their stay.

Types and Pathophysiology

Respiratory failure is generally categorised into two types depending on the underlying pathophysiology and subsequent arterial blood gas picture.

Type 1 Respiratory Failure

When blood flows through a diseased part of the lung (e.g. asthma, pneumonia) with impaired ventilation, it results in hypoxic and CO2-rich blood entering pulmonary veins. Increased ventilation of neighbouring regions of normal lung can increase CO2 excretion but cannot augment oxygen uptake as the haemoglobin flowing through these normal regions is already fully saturated.

Hence, blood coming from normal and under-ventilated areas results in hypoxia with normocapnia, leading to Type 1 respiratory failure.

Type 2 Respiratory Failure

This happens when there is not sufficient normal lung left to correct PaCO2, leading to severe ventilation – perfusion mismatch. Seen in conditions that cause generalised reduction in total ventilation, including diseases of the lung as well as neuromuscular disorders.

Interpreting blood gas abnormalities in Respiratory Failure 

Table 1: Blood gas interpretation in respiratory failure

Ralston, S. H., Penman, I. D., Strachan, M. W. J., & Hobson, R. (Eds.). (2018). Davidson’s Principles and Practice of Medicine (23rd ed.). Elsevier Health Sciences

Aetiology

Acute Respiratory Failure may occur in a variety of pulmonary and non-pulmonary disorders. A few selected causes are mentioned here:

Table 2: Various causes of respiratory failure

Chesnutt A.N., & Chesnutt M.S., & Prendergast N.T., & Prendergast T.J. (2021). Acute respiratory failure. Papadakis M.A., & McPhee S.J., & Rabow M.W.(Eds.), Current Medical Diagnosis & Treatment 2021. McGraw Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=2957&sectionid=249370465

References

• Chesnutt A.N., & Chesnutt M.S., & Prendergast N.T., & Prendergast T.J. (2021). Acute respiratory failure. Papadakis M.A., & McPhee S.J., & Rabow M.W.(Eds.), Current Medical Diagnosis & Treatment 2021. McGraw Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=2957&sectionid=249370465
• Kress J.P., & Hall J.B. (2018). Approach to the patient with critical illness. Jameson J, & Fauci A.S., & Kasper D.L., & Hauser S.L., & Longo D.L., & Loscalzo J(Eds.), Harrison’s Principles of Internal Medicine, 20e. McGraw Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=2129&sectionid=188731384
• Ralston, S. H., Penman, I. D., Strachan, M. W. J., & Hobson, R. (Eds.). (2018). Davidson’s Principles and Practice of Medicine (23rd ed.). Elsevier Health Sciences.
• Fitzpatrick M.E., & Prendergast N.T., & Rivera-Lebron B (2022). Acute respiratory failure. Papadakis M.A., & McPhee S.J., & Rabow M.W., & McQuaid K.R.(Eds.), Current Medical Diagnosis & Treatment 2022. McGraw Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=3081&sectionid=25896008