The Rapid Emergency Medicine Score (REMS) calculator evaluates a patient's risk of in-hospital mortality by considering several clinical parameters. This tool requires input regarding patient age, mean arterial pressure, heart rate, respiratory rate, peripheral oxygen saturation, and Glasgow Coma Scale. Each input category has predefined scoring levels to convert these clinical observations into a numerical score reflective of mortality risk.

The calculator uses the following scoring system:

- Age in years: "< 45" = 0, "45-54" = 2, "55-64" = 3, "65-74" = 5, "> 74" = 6
- Mean arterial pressure in mmHg: "> 159" = 4, "130-159" = 3, "110-129" = 2, "70-109" = 0, "50-69" = 2, "<= 49" = 4
- Heart rate in beats per minute: "> 179" = 4, "140-179" = 3, "110-139" = 2, "70-109" = 0, "55-69" = 2, "40-54" = 3, "<= 39" = 4
- Respiratory rate in breaths per minute: "> 49" = 4, "35-49" = 3, "25-34" = 1, "12-24" = 0, "10-11" = 1, "6-9" = 2, "<= 5" = 4
- Peripheral oxygen saturation: "< 75%" = 4, "75-85%" = 3, "86-89%" = 1, "> 89%" = 0
- Glasgow Coma Scale: "< 5" = 4, "5-7" = 3, "8-10" = 2, "11-13" = 1, "> 13" = 0

Each key within the patient's inputs is mapped to its corresponding value from these scales, and these values are summed to produce a total score representing the patient's REMS score. This score can range from 0 to 26, and it directly correlates to the estimated risk of in-hospital mortality:

- Score 0-3: 0% risk
- Score 4-5: 1% risk
- Score 6-9: 3% risk
- Score 10-11: 4% risk
- Score 12-13: 10% risk
- Score 14-15: 17% risk
- Score 16-17: 38% risk
- Score 18-19: 75% risk
- Score 20-21: 56% risk
- Score 22-23: 66% risk
- Score 24-26: 100% risk

The Rapid Emergency Medicine Score (REMS) is a clinical calculator used in the field of emergency medicine. It is designed to predict the mortality of patients in the emergency department. The REMS is applicable to a broad range of patients presenting to the emergency department, regardless of their specific condition or disease. 

The clinical utility of the REMS lies in its ability to assist clinicians in risk stratification, helping to identify patients who may require more intensive monitoring or intervention. It can also be used to guide resource allocation within the emergency department, and to facilitate communication about patient risk between healthcare providers.

The REMS is calculated based on six parameters: age, heart rate, systolic blood pressure, oxygen saturation, respiratory rate, and level of consciousness. Each parameter is assigned a score, and the total REMS is the sum of these scores.

There are no specific exclusion criteria for the use of the REMS. However, it should be noted that the REMS is a predictive tool and not a diagnostic tool. It should be used in conjunction with clinical judgment and not as a substitute for it.