Certified Respiratory Therapist Practice Exam

In smoke inhalation cases, what is the most appropriate method to monitor a patient's oxygenation?

1. Pulse oximetry

2. ABG analysis

3. CO-oximetry

4. A-a gradient calculation

The correct answer is: CO-oximetry

In cases of smoke inhalation, monitoring a patient's oxygenation is critical for proper assessment and management. CO-oximetry is particularly valuable in this context because it provides a comprehensive analysis of hemoglobin species in the blood, including oxyhemoglobin, carboxyhemoglobin (which may rise due to carbon monoxide inhalation), and methemoglobin. Smoke inhalation often leads to exposure to carbon monoxide, which binds to hemoglobin with high affinity, reducing the blood’s oxygen-carrying capacity. CO-oximetry is specifically designed to distinguish between these different forms of hemoglobin and ascertain the level of carbon monoxide in the blood, which is essential for evaluating the patient's oxygenation status accurately. While pulse oximetry is useful for determining peripheral oxygen saturation, it cannot differentiate between oxyhemoglobin and carboxyhemoglobin. Consequently, it may present a falsely elevated reading in cases of carbon monoxide exposure. Arterial blood gas (ABG) analysis provides important information about oxygen and carbon dioxide levels and acid-base balance, but it does not provide specific values for carboxyhemoglobin or methemoglobin levels. A-a gradient calculation assesses the difference between the alveolar and arterial oxygen, but it does not directly inform about