Capnography is monitoring the partial pressure of?

Appeared in: AIIMS BBSR SNO - 2019

Explanation

Capnography is the non-invasive measurement of the partial pressure of carbon dioxide (CO₂) in exhaled breath over time.
The image shows a capnogram, the graphical representation of CO₂ levels, with an End-Tidal CO₂ (EtCO₂) of 38 mmHg, which is the key measurement at the end of expiration.
This monitoring is crucial for assessing ventilation, confirming endotracheal tube placement, and monitoring respiratory status during anesthesia and critical care.

Option A: Carbon monoxide is a toxic gas. Its levels are measured by a CO-oximeter, typically in cases of suspected poisoning, not with standard capnography.
Option B: While nitrogen is the most abundant gas in the air we breathe, it is not the gas measured by capnography for assessing ventilation.
Option C: Oxygen levels are monitored using pulse oximetry (measuring SpO₂, the saturation of hemoglobin with oxygen) or through arterial blood gas (ABG) analysis (measuring PaO₂).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Capnography and End-Tidal CO₂ Monitoring as background academic context rather than a clinical decision trigger.
Capnography is the gold standard for confirming correct placement of an endotracheal tube in the trachea, as the presence of a consistent EtCO₂ waveform indicates gas exchange is occurring in the lungs.
A sudden drop in EtCO₂ to zero can indicate esophageal intubation, ventilator disconnection, or cardiac arrest, requiring immediate intervention.
In Indian healthcare settings, particularly in emergency departments and ICUs, capnography is increasingly used for procedural sedation and monitoring critically ill patients, improving patient safety.

How to Approach the Question

First, analyze the question's core term: 'Capnography'.
Recall or deduce the function of capnography in respiratory monitoring. The 'capno-' prefix relates to carbon dioxide.
Examine the provided image. Identify the labels 'EtCO2' and the waveform. 'CO2' is the chemical formula for carbon dioxide, and 'Et' stands for End-Tidal, meaning at the end of expiration.
This visual evidence directly confirms that capnography measures carbon dioxide during expiration.
Evaluate the options. 'Carbon dioxide during expiration' aligns perfectly with the definition of capnography and the visual data.
Eliminate the other options: Oxygen is measured by pulse oximetry, and carbon monoxide and nitrogen are not standardly measured by capnography for ventilation assessment.

Concept Tested & Keywords

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E6 Nursing Fundamentals Taylor p. 720-722

E6 Nursing Fundamentals Potter Perry 12e Part 3 p. 24-26

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