Resolution of acute pain following discharge from the emergency department: the acute pain trajectory

Abstract

We demonstrate and evaluate a method for modeling acute pain resolution in individual patients over 6 days following an emergency department visit for an acutely painful condition. Five hundred and thirteen patients presenting with acutely painful conditions provided 11-point numerical ratings of pain intensity at discharge from an emergency department and daily thereafter for a total of 6 days. Latent growth curve modeling with a linear fit yielded measures of initial pain intensity (intercept) and rate of pain resolution (slope) for each individual patient. The linear fits provided good approximations of individual pain trajectories. The average patient had intercept of 6.57 with a slope of -.61. On Day 4, 54.6% of patients reported a pain level equal to or greater than 4. Classification of individual patients by slope revealed that 79% of the sample had the expected negative slope for acute pain resolution while 21% had flat or positive slopes, indicating lack of pain resolution or worsening of pain over time following discharge. The standard errors of measurement for the acute pain trajectories were markedly smaller than those for conventional pain ratings, indicating that the trajectory approach to pain measurement improves measurement precision.

Perspective: The acute pain trajectory provides more information than conventional pain measurement and increases measurement precision. It provides a means of determining the efficacy of acute pain management in the emergency department. The rate of pain resolution is a potentially valuable outcome measure for controlled clinical trials.

Figure 1

Mean pain report (± standard error) by day. The line depicts the mean linear acute pain trajectory for the entire patient sample.

Figure 2

Histogram of the individual patient slopes for the entire sample. The dashed line indicates a slope of zero, or no change over six days. Negative slope values represent rate of acute pain resolution.

Figure 3

Mean acute pain trajectories in three subgroups. The upper panel displays the mean acute pain trajectory for the subgroup of patients with negative slopes who eventually resolved their pain. The middle panel shows the mean acute pain trajectory for those patients whose pain worsened after ED discharge. The bottom panel provides the mean acute pain trajectory for the patients whose pain stayed the same for six days after discharged from the ED.

Figure 4

Three individual cases representing the sample subgroups. The dots indicate each patient’s pain rating on each day, and the line depicts the linear fit, or acute pain trajectory, for each case. These cases demonstrate that acute pain trajectories are meaningful at the individual level. Visual presentation of the individual trajectory allows a clinician to determine whether a patient is resolving his or her pain over days, the intensity of the pain, and rate of change in pain over days.