<p><strong>BACKGROUND: </strong>Customizing monitor alarm settings to individual patients can reduce alarm fatigue in intensive care units (ICUs), but has not been widely studied.</p>

<p><strong>OBJECTIVES: </strong>To understand ICU nurses' approaches to customization of electrocardiographic (ECG) monitor alarms.</p>

<p><strong>METHODS: </strong>A convergent mixed methods study was conducted in 3 ICUs in 1 hospital. Data on the type and frequency of ECG alarm customization were collected from patient monitors (n=298). Nurses' customization clinical reasoning was explored through semi-structured interviews (n=27).</p>

<p><strong>RESULTS: </strong>Of the 298 patients, 58.7% had ≥1 alarm(s) customized. Heart rate limits, irregular heart rate, and atrial fibrillation were the most commonly customized alarms. Interviews revealed that customization practices varied widely and were influenced by factors including clinical expertise, lack of customization education, and negative experiences.</p>

<p><strong>CONCLUSION: </strong>Alarm customization is nuanced and requires adequate support to develop safe and effective practices. The challenges identified can inform development of strategies to improve alarm customization.</p>