This study validated the efficacy of the proposed OPS against the widely used NRS in patients undergoing elective planned abdominal surgery and presented the OPS as an effective tool for objectively demonstrating the need for analgesia in patients with mild-to-moderate pain.
The analgesia provided by APS using PCA pumps was effective, as reflected by the observed values for the mean, median, and mode of the pain scores (NRS and OPS).
The R Value was 0.578, which indicates a high degree of correlation. The R
2 value was 0.33, which is indicative of the total variation in the OPS and explained by the independent variable NRS. The P value (< 0.05) shows that the regression model statistically significantly predicts the outcome variable, i.e. the OPS, and is a good fit for the data. The derived regression equation is OPS = 3.735 - 0.334 × NRS (for every one unit of change in the NRS, the OPS decreases by 0.334). When the NRS is zero, the OPS is thus predicted to be 4 ( Table 3).
The NRS uses an 11-point pain scale for measuring pain intensity (0 = no pain and 10 = worst possible pain) (
Figure 1). The NRS is easy and can even be conducted without the aid of any physical scale ( 2). However, it requires some abstract thinking by the patient, which may be difficult and confusing and only show the changes based on the increase or decrease in scores without defining the meaningfulness of the change in scores. Moreover, it may be difficult to interpret the clinical importance of these changes by a point or two from baseline. While using the NRS, the patient could possibly be worried about the score correctly communicating the need for analgesia. The OPS, on the other hand, assigns the task of rating the pain to the physician without leaving any possibility of observer bias. The same NRS scores in different patients and in the same patient at different points of time could mean different degrees of pain, while each OPS score signifies a similar degree of pain and the need for analgesia and therefore is good to use as a protocol for APS services ( 2, 6).
Children epitomize the limitation imposed by the pain scales, as their ability to understand, quantitate, and communicate is limited. Verghese ST and Hannallah RS (
7) reported on their use of an objective pain scale at their hospital. Their score uses a combination of observations for the assessment of pain in children up to 3 years of age and also for nonverbal children. A score is assigned to each observation. The score for each observation is then added to arrive at a pain score for the child. Adults undergoing surgery are no different when it comes to quantitating and communicate their pain and the need for analgesia. This limitation is overcome by the proposed OPS.
The simultaneous assessment of pain at rest and during movement is desirable, but this may not always be done due to want of time. The OPS enables the simultaneous assessment of pain at rest and during movement without the need for a repeat evaluation, which is necessary in the NRS. The assessment of the efficacy of pain-relieving measures is also inherent to the proposed four-point OPS, such that if a patient who had pain on vital capacity breathing with an OPS of 2, upon subsequent assessment has an OPS of 3, this would mean that the analgesic measure instituted was effective.
The two scores, the NRS and the OPS, agree across the range of pain. (R = 0.578, R2 = 0.334; P < 0.05) Their agreement is evident from the graphs showing the most common and the highest OPS values for the observed NRS values (
Figures 2 and 4). There is no ambiguity between the NRS and the OPS for severe pain, but there were instances of disagreement between the two scores when the NRS was ≤ 5 and was indicative of mild or moderate pain, but OPS scores of 1 or 2 were seen and were indicative of severe pain requiring Level 2 rescue analgesia ( Figure 3).
There were 17 occasions when the NRS was 2 and the OPS was either 1 or 2, while on 7 occasions the NRS was 1 and the OPS was again either 1 or 2 (
Table 4). On these 24 occasions, analgesia supplementation was increased from Level 1 to Level 2. On one occasion, the NRS was 6 while the OPS was 3, and analgesic supplementation was downgraded from Level 2 to Level 1 on the basis of the OPS. These discrepancies could possibly be attributed to patient-related factors and could have led to ineffective analgesia supplementation or the overuse of opioids ( 2).
The difference in the number of decisions favoring the OPS over the NPS for the level of analgesia supplementation (OPS = 25 vs. NRS = 0) was statistically significant. The 24 disagreements between the NRS and OPS where increased need for analgesia was suggested by OPS and not NRS, occurred in 8 out of 93 patients. One patient out of every 11 therefore could have been left in pain if only the NRS would have been used and had OPS not been referred to for analgesia intervention.
There were 17 other instances when the NRS was 5 with a potential for observer bias in favor of Level 2 analgesic supplementation, had analgesic intervention not been determined by protocol. On these 17 occasions, the corresponding OPS was always 3, thus leaving no potential for observer bias (
Table 4). Unnecessary opioid medication could therefore be avoided.
The study has successfully highlighted the need for better interpretation of the mild and moderate pain scores on the NRS. The findings also suggest that the OPS is a good stand-alone tool to scale pain and to ascertain the need for analgesia and is a good tool to refer to when the NRS is indicative of mild or moderate pain.