4.1.1 Visual Analogue Scale
The visual analogue scale (VAS) was first described by Hayes and
colleagues100 as an instrument to quantify pain
intensity. It features a linear scale ranging from ”no pain” to ”worst
pain ever”, and the individual marks the intensity of their pain on a
100 mm line. This scale has been commonly used in various populations
(e.g., children101, patients with chronic non-cancer
pain102, individuals with juvenile idiopathic
arthritis103). In patients with OUD, several studies
have utilized the VAS to assess pain104-106. Notably,
similar VAS tools have been used to measure other opioid-related
clinical phenomena, such as opioid craving and
withdrawal107, 108.
Several studies have examined the use of the VAS to assess pain in
patients with OUD undergoing opioid switching or taper. For example,
Muriel and colleagues conducted an observational study in 138 patients
with OUD and co-occurring chronic pain undergoing a 6-month opioid
taper104. They examined whether CYP2D6 (an enzyme
involved in opioid metabolism) phenotypes (poor vs. extensive vs.
ultrarapid metabolizers) affected the severity of opioid withdrawal
symptoms and pain using VAS and the Opioid Withdrawal Scale (OWS). In
the context of significant opioid tapering, CYP2D6 ultrarapid
metabolizers demonstrated more severe opioid withdrawal symptoms and
higher VAS pain scores compared to extensive and poor metabolizers. This
suggests that the VAS may be used to quantify the severity of chronic
pain experienced during opioid tapering104.
Veldman and colleagues conducted an observational study examining the
effects of switching 43 persons with OUD and co-occurring chronic pain
from full μ-opioid receptor agonists to
buprenorphine-naloxone106. Using the VAS, pain levels
were measured at baseline, while on full agonists, and again two months
after switching to buprenorphine-naloxone. Change scores indicated that
patients showed a significant reduction in pain scores on the VAS
following the transition; further, they also demonstrated increased
pressure and electrical pain thresholds and tolerance, suggesting
reduced hyperalgesia106.
Taken together, these studies demonstrate that the VAS appears to be an
acceptable and valid method for evaluating pain severity in populations
with co-occurring OUD and chronic pain. Notably, the unidimensional
nature of the VAS pain assessment portends significant limitations in
elucidating the multifaceted experience of chronic pain in persons with
OUD.
In an additional adjacent study, Nielsen and colleagues also employed
the VAS to measure perceived pain severity in a randomized trial
comparing ketamine to placebo for acute postoperative pain in 147
patients with chronic pain patients with a history of daily opioid
use105. Evaluating VAS scores, the investigators found
that ketamine reduced the need for opioids during the 24 hours after
surgery compared to placebo. A follow-up pain assessment conducted six
months post-surgery continued to show that patients treated with
ketamine had greater improvements in pain relief as measured by the VAS
compared to those who received the placebo105. Of
note, it is unclear if these patients actually met diagnostic criteria
for OUD, so caution is suggested in generalizing these findings to this
population.