# Hypercapnia Effects on Lung Function

## TL;DR

This paper reviews how high CO2 levels (hypercapnia) negatively affect lung function by disrupting key biological processes.

## Contribution

The paper provides a comprehensive review of CO2's role as a signaling molecule that harms lung function.

## Key findings

- Hypercapnia disrupts alveolar fluid clearance and ion transport.
- Elevated CO2 levels impair alveolar repair and mitochondrial function.
- Hypercapnia suppresses innate immunity and increases airway contractility.

## Abstract

The biological effects of hypercapnia on the lungs have been controversial. Earlier publications suggesting that hypercapnia was beneficial for mechanically ventilated patients with acute lung injury led to the clinical paradigm of “permissive hypercapnia”. However, more recent studies have challenged this paradigm by reporting that hypercapnia activates signaling pathways with deleterious effects. This review focuses on the effects of elevated CO2 as a signaling molecule, highlighting the pathways and processes contributing to the detrimental effects of hypercapnia on the alveolar epithelium, the airways and immune system.

CO2 is a signaling molecule that disrupts alveolar fluid clearance and ion transport, impairs alveolar repair, and promotes mitochondrial and endoplasmic reticulum dysfunction. It suppresses innate immunity, host defense, and inflammation, while increasing airway contractility.