Design and Development of a Compact, Portable Nondispersive Infrared (NDIR)-Based Capnography Device for Real-Time End-Tidal Carbon Dioxide (CO₂) Monitoring

Measuring carbon dioxide (CO₂) in exhaled breath provides critical insight into both ventilation and metabolism. Changes in CO₂ levels can indicate hypoventilation, airway obstruction, circulatory compromise, or metabolic imbalance, allowing the early detection of respiratory distress and other life-threatening conditions. Capnography provides continuous, non-invasive monitoring of respiratory status and metabolic function through the measurement of end-tidal CO₂ (ETCO₂). This work focuses on developing a low-cost, portable, battery-powered capnograph that enables accurate, continuous CO₂ monitoring with minimal discomfort during daily activities. This study presents the design of a portable, battery-powered capnograph for non-invasive monitoring, featuring high measurement precision and a lightweight form factor. The device integrates a rechargeable power system and a Bluetooth wireless interface to enable seamless data transmission to healthcare providers. Signal acquisition and CO₂ concentration estimation are processed in real time using an embedded microcontroller. The prototype successfully performs real-time CO₂ monitoring and wireless data transmission. Based on projected power consumption, the system enables a continuous runtime of up to approximately 22 hours on a 2000 mAh lithium battery, depending on usage conditions. Expected sensing performance follows the SprintIR-6S specifications, supporting measurements up to 20% CO₂ concentration within specified accuracy limits. The compact, portable design supports reliable continuous monitoring and may enhance the early detection of respiratory deterioration in both clinical and emergency settings. By enabling the rapid recognition of changes in ventilatory status, such a system has the potential to improve patient outcomes and expand access to timely respiratory care.