Clinical Prediction Model and External Validation of Chronic Postsurgical Pain in Elders

Pain intensity was assessed using a numerical rating scale (NRS) from 0 to 10, with zero representing no pain and 10 representing worst imaginable pain. The worst pain intensity was then categorized into two groups: no or mild pain (NRS from 0 to 3) and moderate to severe pain (NRS from 4 to 10).

It measured pain location in the body; pain intensity on an 11-point numerical rating scale (NRS; 0 represents "no pain" and 10 the "worst pain imaginable"); analgesic intake; perception of analgesic relief; and pain interference with daily life on an 11-point NRS (0 "does not interfere and 10"completely interferes") indistinct dimensions (general activity, mood, walking, work, relations with others, sleep, and enjoyment of life). Higher scores represent higher levels of pain interference.

The PCS consists of 13 items, and each item is answered with a numeric value between 0 and 4; 0 corresponding to "not at all", and four corresponded to "all the time". Higher scores indicate a higher level of pain catastrophizing, the Chinese version of the PCS has demonstrated a good reliability and validity (Cronbach's alpha was 0.87 and the ICC was 0.97)

The trajectory of HRQoL is the vector of Utility values measured with EuroQol five-dimensional questionnaire(EQ-5D-5L)taken over 3 months(days 1, 3, 7, 30, 90；Day 0 is the day of surgery). The EQ-5D-5L measures health on five domains (mobility, self-care, usual activities, pain discomfort, and anxiety-depression), and the scores will be combined using Chinese general population weights to generate a single utility or index score. Utility values for the EQ-5D range from 1.00 to -0.391, where a score of 0 and 1 are regarded as equivalent to death and 'perfect health', respectively, and a score < 0 is considered as health state that is 'worse than death'.

Comprised by 2 subscales used to measure anxiety and depression through 7 items each. Subscale scores range from 0 to 21 and result from the sum of each item (Likert scale ranging from 0 to 3). Higher scores correspond to higher levels of anxiety and depression.

Frailty was assessed within 30 days prior to surgery using the FRAIL Scale assessment. The FRAIL Scale assessment is a validated 5-item scale comprising components from the Cardiovascular Health Frailty Index and Rockwood Scale.The five components measured include fatigue, resistance, ambulation, illness and loss of weight. The scale was dichotomized into two frailty categories based on prior literature on pain and frailty.16 Patients were classified as frail if they scored 3 or more on the 5-point scale and not frail if they scored below 3 .

Complications within 30 days after surgery will be classified using Clavien-Dindo Classification of Surgical Complications, ranging from Grade I(Any deviation from the normal postoperative course without the need for pharmacological treatment or surgical, endoscopic and radiological interventions) to Grade V(death of a patient).

The duration when patients stay in hospital after surgery.