What device is commonly used to monitor a patient's cardiac rhythm during surgery?

The electrocardiogram (ECG) monitor is the primary device used to continuously assess a patient's cardiac rhythm during surgery. This device tracks the electrical activity of the heart, providing real-time information on heart rate and rhythm, which is crucial for detecting any irregularities or complications that may arise during the procedure. Monitoring the ECG allows the surgical team to respond promptly to changes in the patient's heart function, ensuring optimal patient safety.

The other options have distinct purposes that don't specifically relate to monitoring cardiac rhythm. The pulse oximeter is used to measure oxygen saturation in the blood, which is vital for assessing respiratory function. The blood pressure cuff measures blood pressure, providing important information about the patient's circulatory status, but it does not provide direct insights into cardiac rhythm. A thermometer is used to monitor body temperature, which is essential for managing a patient's overall physiological status but again does not relate to heart rhythm monitoring. Each device is important in its own right, but only the ECG monitor specifically tracks cardiac electrical activity.