Prediction of postoperative pain using path analysis in older patients

Abstract

Purpose

Effective postoperative pain management is important for older surgical patients because pain affects perioperative outcomes. A prospective cohort study was conducted to describe the direct and indirect effects of patient risk factors and pain treatment in explaining levels of postoperative pain in older surgical patients.

Methods

We studied patients who were 65 years of age or older and were scheduled for major noncardiac surgery with a postoperative hospital stay of at least 2 days. The numeric rating scale (0 = no pain, 10 = worst possible pain) was used to measure pain levels before surgery and once daily for 2 days after surgery. Path analysis was performed to examine the association between predictive variables and postoperative pain levels.

Results

Three hundred fifty patients were studied. We found that preoperative pain level, use of preoperative opioids, female gender, higher ASA physical status, and postoperative pain control methods were the strongest predictors of postoperative pain as measured on the first day after surgery. Younger age, greater preoperative symptoms of depression, and lower cognitive function also contributed to higher postoperative pain levels. Pain levels on the second day after surgery were strongly predicted by preoperative pain level, use of preoperative opioids, surgical risk, and pain and opioid dose on postoperative day 1. However, younger age, female gender, higher ASA physical status, greater preoperative symptoms of depression, lower cognitive function, and postoperative pain control methods indirectly contributed to pain levels on the second day after surgery.

Conclusion

Although preoperative pain and use of preoperative opioids have the strongest effects on postoperative pain, clinicians should be aware that other factors such as age, gender, surgical risk, preoperative cognitive impairment, and depression also contribute to reported postoperative pain. Based on significant statistical correlations, these study results can contribute to more effective postoperative care for those patients having the risk factors studied here. Preoperative treatment/intervention based in part on factors such as preoperative pain, use of preoperative opioids, and depression may improve postoperative pain management.

Appendices

Appendix 1

High-risk surgery

• 1. Aortic vascular surgery

• 2. Peripheral vascular surgery

• 3. Prolonged procedures associated with large fluid shifts or blood loss (any intraabdominal procedures such as bowel resection, which is 6 h in duration, other than appendectomy; any procedures with blood loss >1,000 ml; radical cystectomy with ileal loop) are high risk.

Intermediate-risk surgery

• 1. Carotid endarterectomy

• 2. Head and neck surgery (ear–nose–throat surgery)

• 3. Intraperitoneal and intrathoracic surgeries (total pneumonectomy is high risk; lobectomy and partial lung resection are intermediate risk)

• 4. Prostate surgery (TURP and radical prostatectomy except when the latter involves large blood loss as defined previously)

• 5. Orthopedic surgery

• 6. One- to two-level laminectomies (multiple levels with spinal fusion with blood loss >1,000 ml are high risk)

• 7. Craniotomies with blood loss <1,000 ml, parotidectomy, radical neck dissection, and parathyroidectomy.

Low-risk surgery

• 1. Breast surgery

• 2. Plastic surgery

• 3. Any “superficial” surgeries, including voice prosthesis; inguinal hernia; endoscopic surgeries.

Appendix 2

Standardized direct and indirect effects on pain and opioid dose

Effect	Direct	Indirect	Total
Pre-op pain
Gender (female)	0.129*		0.129*
Use of pre-op opioids	0.262***		0.262***
Pre-op TICS over 30	−0.097+		−0.097+
Geriatric Depression Scale	0.110*		0.110*
Pain on POD1
Pre-op pain	0.206***		0.206***
Age over 80	−0.111*		−0.111*
High ASA PS	0.144**		0.144**
Gender (female)	0.138**	0.027*	0.165***
Geriatric Depression Scale		0.023+	0.023+
Use of pre-op opioids	0.212***	0.054**	0.266***
IV-PCA analgesia	0.125**		0.125*
Pre-op TICS over 30		−0.020+	−0.020+
Pain on POD2
Pre-op pain	0.260***	0.085***	0.345***
Pain on POD1	0.389***	0.026*	0.415***
Opioid dose on POD1	0.139**		0.139**
Age over 80		−0.046*	−0.046*
Gender (female)		0.102***	0.102***
High ASA PS		0.060**	0.060**
Geriatric Depression Scale		0.038*	0.038*
Use of pre-op opioids		0.179***	0.179***
IV-PCA analgesia		0.097***	0.097***
Pre-op TICS over 30		−0.034+	−0.034+
High surgical risk	0.124**		0.124**
Opioid dose on POD1
Pre-op pain		0.038**	0.038**
Pain on POD1	0.185***		0.185***
Age over 80		−0.021*	−0.021*
Gender (female)		0.030**	0.030**
High ASA PS		0.027*	0.027*
Geriatric Depression Scale		0.004+	0.004+
Use of pre-op opioids		0.049**	0.049**
IV-PCA analgesia	0.327***	0.023*	0.350***
Pre-op TICS over 30		−0.004	−0.004
Opioid dose on POD2
Opioid dose on POD1	0.518***	0.020*	0.538***
Pre-op pain		0.070***	0.070***
Pain on POD1		0.156***	0.156***
Pain on POD2	0.145**		0.145**
Age over 80		−0.017*	−0.017*
Gender (female)		0.031**	0.031**
High ASA PS	0.108*	0.022*	0.130**
Geriatric Depression Scale		0.008+	0.008+
Use of pre-op opioids		0.051***	0.051***
IV-PCA analgesia		0.196***	0.196***
Pre-op TICS over 30		−0.007+	−0.007+
High surgical risk		0.018*	0.018*

1. Geriatric Depression Scale, opioid dose on POD1, and opioid dose on POD2 were log transformed
2. ASA PS American Society of Anesthesiologists Physical Status Classification, NRS numeric rating scale, IV-PCA intravenous patient-controlled analgesia, POD postoperative day, Pre-op preoperative, SD standard deviation, TICS telephone interview of cognitive status
3. *** P < 0.001, ** P < 0.01, * P < 0.05, ⁺  P < 0.10