What observable effect indicates that drainage may be CSF?

The halo effect on gauze is a specific observation that indicates the presence of cerebrospinal fluid (CSF) in drainage. This phenomenon occurs when CSF leaks and is mixed with blood, causing a characteristic "halo" or ring of clear fluid that surrounds a central area of blood on the gauze. The clear fluid is CSF, while the blood is typically the result of an injury or trauma.

This distinction is important in a clinical context, as it helps healthcare providers identify potential cerebrospinal fluid leaks, which can lead to serious complications if not addressed. In contrast, the presence of a green tint, unusual odor, or simply blood alone does not provide the same clear diagnostic indication that a halo effect does. A green tint might suggest infection or other fluid characteristics, while unusual odors may indicate contamination but are not definitive for CSF identification. Blood presence alone can arise from various sources, and without the specific halo effect, it lacks the clarity necessary for diagnosing CSF drainage.