Questions: All of the following may cause sinus tachycardia, except: hypovolemia. pain. carotid massage. hypoxemia. fever.

The answer is the third one: carotid massage.

Explanation for each option:

1. Hypovolemia: This condition involves a decreased volume of blood in the body, which can lead to sinus tachycardia as the heart compensates by increasing the heart rate to maintain adequate blood flow and blood pressure.

2. Pain: Pain can stimulate the sympathetic nervous system, leading to an increased heart rate, which is a characteristic of sinus tachycardia.

3. Carotid massage: This is a technique used to stimulate the vagus nerve, which can actually slow down the heart rate. It is often used as a treatment for certain types of tachycardia, not a cause of it.

4. Hypoxemia: Low levels of oxygen in the blood can cause the heart to beat faster to increase oxygen delivery to tissues, resulting in sinus tachycardia.

5. Fever: An increase in body temperature can lead to an increased heart rate as the body works to dissipate heat, which can cause sinus tachycardia.

In summary, carotid massage is the exception as it is used to decrease heart rate, not increase it.