Modeled heart rates for patients from a single age group (8-12 years). Each distribution represents a separate patient. Distributions are obtained by sampling 1000 points from a lognormal distribution parameterized by the observed mean and standard deviation of heart rate over the patient’s first 24 hours of monitoring. (A) The dashed vertical lines represent the 5th and 95th percentiles of heart rate observed for patients in this age group, the alarm thresholds as suggested by our previous study. The shaded regions are those that would trigger alarms. We see that the left-most distribution is almost entirely outside these alarm thresholds, so most of heart rate measurements from this patient would trigger a low heart rate alarm. We also see that the heart rate distribution from one of the patients is so narrow that very few heart rate measurements would trigger an alarm. The variation in vital signs among patients of the same group illustrates the weakness of alarm thresholds that are optimized for groups of patients and demonstrates the need for personalized alarm thresholds. (B) The heart rate values that would trigger an alarm if the observed 1st and 99th percentiles of heart rate are used as alarm thresholds. The shaded regions are those that would trigger alarms. Many fewer alarms would sound under this model, and alarms would be triggered for different thresholds for each patient.

Comparison of actual 1st and 99th percentiles of vital sign data observed over the first 24 hours of monitoring with the expected percentiles calculated using a lognormal model characterized by the observed mean and variance for the vital sign of interest. (A) 1st percentile of heart rate, R² = 0.929. (B) 99th percentile of heart rate, R² = 0.857. (C) 1st percentile of respiratory rate, R² = 0.933. (D) 99th percentile of respiratory rate, R² = 0.749.

Comparison of the 1st and 99th percentiles of heart rate and respiratory rate, as observed over the first 24 hours of monitoring, with the 1st and 99th percentiles calculated using our method. We propose these calculated percentiles as the personalized and adapted thresholds. (A) Comparison of the observed 1st percentile of heart rate with the calculated 1st percentile. (B) Comparison of the observed 99th percentile of heart rate with the calculated 99th percentile. (C) Comparison of the observed 1st percentile of respiratory rate with the calculated 1st percentile. (D) Comparison of the observed 99th percentile of respiratory rate with the calculated 99th percentile.

Comparison of physician-selected alarm thresholds with the personalized and adapted thresholds we derive. Comparison with the age-based thresholds from our previous study are also shown as an indication of current practice. (A) Comparison of physician-selected thresholds for low heart rate with the proposed personalized and adapted thresholds. (B) Comparison of physician-selected thresholds for high heart rate with the proposed personalized and adapted thresholds. (C) Comparison of physician-selected thresholds for low respiratory rate with the proposed personalized and adapted thresholds. (D) Comparison of physician-selected thresholds for high respiratory rate with the proposed personalized and adapted thresholds.

Number of alarms that would have sounded using the different sets of proposed thresholds. Note that only alarms that were actually historically triggered are part of this analysis. The dashed lines show the total number of alarms that were triggered. The alarms making up this analysis span a 3.5-year period.