13.12: Assessment of Diffusion and Perfusion

13.12: Assessment of Diffusion and Perfusion

Understanding and evaluating diffusion and perfusion is critical in assessing a patient's respiratory and circulatory health. These processes play key roles in maintaining the body's internal environment, ensuring that tissues receive adequate oxygen while waste products are efficiently removed.

The Role of Diffusion in Respiration

Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. In the respiratory system, this principle facilitates the exchange of gases in the lungs. Oxygen is transferred from the alveoli, the tiny air sacs in the lungs, into the bloodstream and carried to the tissues. Conversely, carbon dioxide, a waste product of cellular metabolism, moves from the blood into the alveoli to be exhaled. The efficiency of this gas exchange process is vital for maintaining healthy cellular function and is a primary focus in respiratory assessments.

Understanding Perfusion in Respiration

Perfusion involves blood circulation through tissues and organs, essential for delivering oxygen and nutrients. In the respiratory system, perfusion is necessary to deliver oxygen-rich blood to all body parts and carry carbon dioxide-laden blood back to the lungs for exhalation.

Measuring Oxygen Saturation

Oxygen saturation represents the proportion of hemoglobin in red blood cells completely saturated with oxygen. Normal arterial oxygen saturation levels (SaO₂) typically range from 95% to 100%. There are two primary methods used to measure oxygen saturation:

• • Arterial Blood Gas (ABG) Analysis: This test directly measures oxygen saturation from an arterial blood sample, providing detailed information about oxygen levels, carbon dioxide, and blood pH. It is the gold standard for accurately assessing the patient's gas exchange efficiency.
• • Pulse Oximetry: This non-invasive method estimates oxygen saturation (SpO₂) by analyzing how oxygenated blood absorbs light versus deoxygenated blood. A sensor is attached to the patient's finger, toe, or earlobe. Although less accurate than ABG analysis, this is a convenient and common tool in both clinical and home settings.

Capnography in Respiratory Monitoring

Capnography is vital in respiratory monitoring and useful in assessing a patient's ventilation status. It provides real-time feedback on the patient's respiratory status by measuring the concentration of carbon dioxide (CO₂) in exhaled air, through numerical data and waveform analysis. The end-tidal CO2 (EtCO₂) is the maximum carbon dioxide concentration at the end of an exhalation and is the key metric in capnography. Normal EtCO₂ values are typically between 35 and 45 mmHg.

The waveform produced in capnography helps identify shifts in respiratory status, making it especially useful during procedures like CPR and mechanical ventilation for patients.