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Abstract

Background:

Pain occurring in the post-anaesthesia care unit (PACU) is common, distressing to patients and remains a management challenge for staff. This study aims to identify the factors affecting pain severity and delay in discharge of patients from the PACU.

Methods:

Data from 590 consecutive postoperative patients in the PACU was collected over one month in 2012 at the Singapore General Hospital. Patient demographics, surgical, intraoperative anaesthetic and recovery data were collected. The primary outcome measured was postoperative pain score and secondary outcome was a delay in discharge. Univariate and multivariate logistic regression were performed to determine preoperative and intraoperative variables that may be associated with pain and delayed discharge.

Results:

The majority (67.6%) of patients reported no to mild pain while 32.3% reported moderate to severe pain; 65.4% of patients had delayed discharge and 28.3% of these were a result of uncontrolled pain. Factors associated with moderate to severe postoperative pain included younger age, same day admissions, duration of operation >2 h, abdominal, upper limb and spine surgeries and use of general anaesthesia. Factors associated with delay in discharge included higher body mass index, abdominal, spine and superficial surgeries, use of general anaesthesia, moderate to severe pain score and use of nurse controlled analgesia.

Conclusions:

This study identifies predictive factors for postoperative pain and delay in discharge from the PACU. Knowledge of these factors may help in better clinical judgment for postoperative pain management and can lead to quality improvement measures for patient management and work flow in the PACU.

Keywords

Retrospective cohort audit pain post-anaesthesia care unit delay in discharge

Introduction

The Singapore General Hospital (SGH) has over 8700 surgeries performed per year (as of 2012). Despite standard interventions, postoperative pain in the post-anaesthesia care unit (PACU) remains common. It is distressing to patients and staff alike and prolongs PACU stay and increases costs.

There have been many advances in the understanding of postoperative pain management in the last 40 years, with a large number publications on the topic including practice guidelines from the American Society of Anesthesiologists (ASA)^1–3 and Procedure Specific Postoperative Pain Management (PROSPECT) Group.^4–7 A number of large audits have also been carried out to provide data on postoperative pain management.^8–10

A study by Aubrun et al. on 342 patients showed that 42% had severe pain in the PACU.¹¹ They found that factors associated with severe pain included a higher intraoperative dose of sufentanil, the use of general anaesthesia and preoperative treatment with analgesics. Another more recent abstract showed that 49.6% of the patients had severe pain in the PACU.¹² The study found that younger, females, those with a lower ASA status and those who had general anaesthesia and abdominal and orthopaedic procedures were more likely to have severe pain in the PACU. Locally, there is no updated data on the incidence of postoperative pain in the PACU.

Studies have shown that severe postoperative pain is associated with a delay in discharge from the PACU.^13,14 This audit evaluates the incidence of severe postoperative pain in our centre and aims to identify the factors affecting pain severity as well as delay in discharge.

Methods

After obtaining Institutional Review Board approval (2012/250/D), data from 590 postoperative patients aged 21 years and above in the PACU was collected in February–March 2012 at SGH. Data was manually collected by the doctor in charge of patient care in the PACU for the main operating theatre complex of the SGH during office hours (08:30 to 17:00 hours) in the period stipulated.

All patients above the age of 21 years who arrived in the PACU in the main operating theatre complex postoperatively were included in the study, while exclusion criteria included patients operated outside of the main operating complex (e.g. ambulatory centre, endoscopy suites) and patients who bypassed the PACU postoperatively (e.g. directly to intensive care units (ICUs)).

The type of data collected was divided into patient data, surgical data, intraoperative anaesthetic data and postoperative recovery data. Patient data included age, admission type (ambulatory surgery admission or same day admission or inpatient), weight, height, drug allergies, ASA status, presence of obstructive sleep apnoea, drug dependence, presence of chronic pain and type of preoperative analgesia given if any.

Surgical data included operation type, specialty, duration of surgery, whether surgery was open or minimally invasive, operation site and whether local anaesthesia was given.

Intraoperative anaesthetic data included the type of anaesthesia given, morphine and fentanyl dose used and the use of remifentanil, dexmedetomidine, ketamine, nitrous or any other analgesia.

Postoperative recovery data included maximum pain score recorded, patient controlled analgesia (PCA) morphine dose if PCA was used, whether a continuous epidural or nerve block infusion was used and any top-up doses given, whether nurse initiated analgesia protocol was used, rescue morphine and fentanyl doses, any oral analgesics used, time of admission and discharge as well as reason for delay.

The primary outcome measured was the maximum postoperative pain score in PACU. Pain score was documented using numerical rating scale (NRS) 0–10. When the patient was unable to quantify using the NRS, the categorical verbal descriptor scale was used and converted to numeric scores on charting. The postoperative pain scores (1–10) were dichotomized into two categories: presence of no to mild pain (pain scores: 0–3) and presence of moderate to severe pain (pain scores: 4–10).

The secondary outcome measured was a delay in discharge from the PACU defined as longer than 30 minutes. A delay in discharge defined as longer than 30 minutes’ stay in the PACU has been the local practice adopted in the department in SGH.

Morphine doses used intraoperatively were categorized to 0–0.1 mg/kg dose used, 0.11–0.2 mg/kg used and > 0.2 mg/kg used. Fentanyl doses were categorized to 0–2 µg/kg dose used, 2.1–3 µg/kg used and >3 µg/kg used.

Statistical analysis

We used binomial logistic regression for the univariable and multivariable analyses, as pain severity and delay in discharge were categorical variables. Preoperative and intraoperative variables were analysed to look for association with pain in the PACU; preoperative, intraoperative and postoperative variables were analysed to look for association with a delay in discharge from PACU. Significant factors from the univariable analyses and factors a priori were included in the multivariable analyses; p values were two sided and values less than 0.05 were considered significant. Statistical analyses were conducted with IBM SPSS version 16.0

Sample size calculation

In our literature search, the incidence of severe pain ranged from 25% to 42%.^11,15 We therefore decided to use the mean of that range (33.5%) to calculate the sample size. We had nine covariates and based on the work of Peduzzi et al.¹⁶ we used his formula N = 10 × 9 / 0.335 = 269 to determine the minimum sample size needed

Results

Patient characteristics

Table 1 summarizes the characteristics of our patients in the audit. The majority of patients (67.6%) reported no to mild pain while 32.3% reported moderate to severe pain. The majority of patients were female (61.4%), with a mean age of 54 years. Most underwent same day admissions (53.9%), open surgery (70.8%), had no preoperative analgesia (96.6%) and were given general anaesthesia (81.4%); 65.4% of patients had delayed discharge from PACU, 28.9% of these being as a result of uncontrolled pain.

Table 1.

Patient Characteristics.

Characteristic	No.	%
No. of patients	590	100
Gender
Male	228	38.6
Female	362	61.4
Age, mean (SD)	53.6 (15.7)
Admission type
ASC	44	7.5
SDA	318	53.9
Inpatient	228	38.6
Weight, mean (SD)	65.9 (15.9)
BMI, mean (SD)Drug allergy	25.7 (5.72)
No	468	79.3
Paracetamol	5	0.8
NSAID	25	4.2
Opioids	5	0.8
Non-analgesia	87	14.7
ASA
ASA 1	113	19.2
ASA 2	326	55.3
ASA 3 and 4	151	25.6
OSA
No	568	96.3
Yes	22	3.7
Drug dependence
No	589	99.8
Yes	1	0.2
Chronic pain
No	588	99.7
Yes	2	0.3
Preop. analgesia
No	570	96.6
Paracetamol	9	1.5
NSAID	6	1.0
Opioids	5	0.8
Speciality
GS	142	24.1
Ortho.	204	34.6
Hand	13	2.2
O&G	85	14.4
ENT	41	6.9
Colorectal	34	5.8
Dental	7	1.2
Cardiothoracic	14	2.4
Plastics	43	7.3
Others	7	1.2
Duration
<1 h	271	45.9
1–2 h	207	35.1
>2 h	112	19.0
Operation type
Open	418	70.8
MIS	172	29.2
Operation site
Head and neck	92	15.6
Thorax	22	3.7
Abdo.	98	16.6
Gynae.	76	12.9
Lower limbs	177	30.0
Upper limbs	45	7.6
Spine	33	5.6
Superficial	47	8.0
LA by surgeon
No	528	89.5
Yes	62	10.5
Anaesthesia
GA	480	81.4
Others	110	18.6
Morphine, mean (SD)
Morphine dose, mg	1.5 (2.93)
Morphine, mean (SD)
Morphine dose, mg/kg	0.083 (0.074)
Fentanyl, mean (SD)
Fetanyl dose, µg	60.5 (52.32)
Fentanyl, mean (SD)
Fentanyl dose, µg/kg	0.93 (0.85)
Remifentanil
No	543	92.0
Yes	47	8.0
Dexmedetomidine
No	588	99.7
Yes	2	0.3
Ketamine
No	581	98.5
Yes	9	1.5
Nitrous
No	564	95.6
Yes	26	4.4
Other analgesia
No	582	98.6
Yes	8	1.4
Pain
No to mild pain	399	67.6
Moderate to severe pain	191	32.3
Delay in discharge from PACU
No	204	34.6
Yes	386	65.4
Delay in discharge reason
No delay	204	34.6
Delay due to pain	170	28.9
Delay due to other reasons	216	36.6

ASC: ambulatory surgery; SDA: same day admission; BMI: body mass index; NSAID: non-steroidal anti-inflammatory drug; GS: ; ASA: American Society of Anesthesiologists; OSA: ; GA: general anaesthesia; Preop.: preoperative; Ortho.: orthopaedic; O&G: obstetrics and gynaecology; ENT: ear, nose, throat; MIS: minimally invasive surgery; Abdo.: abdomen; Gynae.: gynaecological; LA: ; PACU: post-anaesthesia care unit ; ASC: ambulatory surgery centre; GS: General Surgery; OSA: Obstructive Sleep Apnoea; LA: Local Anaesthetic.

Factors associated with pain severity

A summary of factors associated with moderate to severe postoperative pain is shown in Table 2. From the multivariable logistic regression, older patients were less likely to report moderate to severe pain postoperatively (p < 0.001). Patients scheduled for surgery on the same day of admission were 2.46 times more likely to have moderate to severe pain (p = 0.048). Surgeries with >2 h duration were 2.33 times more likely (p = 0.003), those who underwent abdomen surgeries were 4.46 times more likely (p < 0.001), upper limb surgeries were 4.03 times more likely (p = 0.003) and spine surgeries were 2.65 times more likely (p = 0.039) to report moderate to severe pain postoperatively. The use of general anaesthetics compared with regional techniques had 15.4 times increased likelihood of having moderate to severe postoperative pain (p < 0.001).

Table 2.

Factors associated with Pain Severity.

Characteristic	% who reported moderate to severe pain	Unadjusted univariable model			Adjusted multivariable model
	% who reported moderate to severe pain	OR	95% CI	p value	OR	95% CI	p value
Gender
Male	33.3	Ref			Ref
Female	31.8	0.93	0.65–1.33	0.690	1.31	0.80–2.13	0.278
Age, mean	53.6	0.97	0.96–0.98	<0.001	0.96	0.94–0.97	<0.001
Admission type				0.104
ASC	18.2	Ref.^a			Ref.
SDA	32.7	2.19	0.98–4.87	0.056	2.46	1.01–6.01	0.048
Inpatient	34.6	2.39	1.06–5.38	0.036	1.91	0.73–5.03	0.189
Weight, mean	65.9	1.01	1.00–1.02	0.020	1.01	0.998–1.03	0.080
ASA				0.161
1	30.1	Ref.			Ref.
2	35.9	1.3	0.82–2.06	0.264	1.75	0.98–3.12	0.057
3 and 4	26.5	0.84	0.89–1.44	0.520	1.72	0.82–3.62	0.153
Duration				0.012
<1 h	27.3	Ref.			Ref.
1–2 h	29.5	1.11	0.75–1.66	0.603	1.20	0.74–1.94	0.455
>2 h	50.0	2.66	–	<0.001	2.33	1.32–4.12	0.003
Operation type
Open	33.7	Ref.			Ref.
MIS	29.1	0.81	0.55–1.19	0.272	0.67	0.42–1.08	0.096
Operation site				0.001
Head and neck	28.3	Ref.			Ref.
Thorax	36.4	1.45	0.54–3.87	0.457	2.89	0.96–8.72	0.059
Abdo.	45.9	2.16	1.18–3.94	0.013	4.46	2.17–9.17	<0.001
Gynae.	38.2	1.57	0.82–2.99	0.175	2.02	0.94–4.33	0.070
Lower limbs	21.5	0.694	0.39–1.24	0.216	1.87	0.93–3.75	0.079
Upper limbs	42.2	1.86	0.88–3.90	0.104	4.03	1.62–10.03	0.003
Spine	45.5	2.11	0.93–4.81	0.740	2.65	1.05–6.68	0.039
Superficial	23.4	0.78	0.34–1.75	0.540	0.98	0.39–2.46	0.962
Anaesthesia
Spinal + others	4.1	Ref.			Ref.
GA	37.9	14.2	5.14–39.3	<0.001	15.4	4.82–49.1	<0.001

All references were coded as 0 and subsequently in consecutive running order numbers.

OR; odds ratio; CI: confidence interval; ASC: ambulatory surgery; SDA: same day admission; ASA: American Society of Anesthesiologists; MIS: minimally invasive surgery; Abdo.: abdomen; Gynae.: gynaecological; GA: general anaesthesia.

Subgroup analysis for pain severity in abdominal surgeries with or without regional anaesthesia

Of interest, only 15.3% of patients who had abdominal surgery had regional anaesthesia. Of patients who had abdominal surgeries without regional anaesthesia 52.4% had moderate to severe pain compared with 13.3% of patients who had abdominal surgeries with regional anaesthesia.

Out of the patients who had spinals, 85.5% had lower limb surgeries, 81.6% had orthopaedic procedures and 82.4% were obese (defined as having a body mass index (BMI) > 30 kg/m²).

Factors associated with delay in discharge

A summary of factors associated with a delay in discharge from the PACU is shown in Table 3. Higher BMI was associated with a delay in discharge from the PACU (overall p = 0.024). Patients who had abdominal surgeries were 2.18 times more likely (p = 0.049), spine surgeries 3.88 times more likely (p = 0.038) and superficial surgeries 2.73 times more likely (p = 0.037) to have a delay in discharge from PACU. Patients who had general anaesthesia were 4.41 times more likely (p < 0.001) and patients who had moderate to severe pain score were 10.4 times more likely (p < 0.001) to have a delay in discharge from the PACU. Patients who had nurse initiated analgesia in the PACU had a 3.86 times increased likelihood of delay in discharge (p = 0.017).

Table 3.

Factors associated with delay in discharge.

Characteristic	% delay in discharge	Unadjusted univariable model			Adjusted multivariable model
	% delay in discharge	OR	95% CI	p value	OR	95% CI	p value
BMI				0.024
<18.5	50.0	Ref.^a			Ref.
18.6–25	66.0	1.94	0.90–4.16	0.089	3.54	1.36–9.18	0.009
25.1–30	70.2	2.36	1.06–5.22	0.035	4.28	1.58–11.59	0.004
>30.1	69.1	2.24	0.97–5.19	0.059	4.83	1.69–13.86	0.003
Operation site				0.069
Head and neck	64.1	Ref			Ref
Thorax	72.7	1.49	0.53–4.18	0.45	1.34	0.41–4.32	0.630
Abdo.	77.6	1.93	1.02–3.66	0.043	2.18	1.00–4.73	0.049
Gynae.	64.5	1.02	0.54–1.91	0.96	0.97	0.46–2.07	0.943
Lower limbs	55.4	0.69	0.41–1.17	0.17	1.69	0.84–3.40	0.140
Upper limbs	62.2	0.92	0.44–1.93	0.83	0.80	0.30–2.15	0.659
Spine	78.8	2.08	0.81–5.30	0.13	3.88	1.08–13.98	0.038
Superficial	72.3	1.46	0.68–3.15	0.33	2.73	1.06–7.00	0.037
Anaesthesia
Spinal + others	29.9	Ref			Ref
GA	72.3	6.16	3.82–9.92	<0.001	4.41	2.34–8.28	<0.001
Pain score
No to mild	52.1	Ref			Ref
Moderate to severe	93.2	12.58	6.93–22.8	<0.001	10.4	5.08–21.3	<0.001
Nurse controlled analgesia
No	62.0	Ref			Ref
Yes	92.5	7.62	3.01–19.3	<0.001	3.86	1.27–11.71	0.017

All references were coded as 0 and subsequently in consecutive running order numbers.

OR; odds ratio; CI: confidence interval; BMI: body mass index; Abdo.: abdomen; Gynae.: gynaecological; GA: general anaesthesia.

Pain severity associated with delay in discharge from the PACU

Patients who had moderate to severe pain were 10.2 times more likely to have a delayed discharge compared with those who had no pain (p < 0.001), as shown in Table 4.

Table 4.

Pain severity associated with delay in discharge from PACU.

Characteristic	OR	95% CI	p value
Pain severity
No pain	Ref.
Mild pain	1.16	0.69–1.95	0.580
Moderate to severe pain	10.2	4.97–20.9	<0.001

Adjusted for gender, age, admission type, weight, ASA status, duration of operation, operation type, operation site and anaesthesia used.

OR: odds ratio; CI: confidence interval; Ref.: reference; ASA: American Society of Anesthesiologists.

Discussion

Our study showed that 32.3% of our patients reported moderate to severe postoperative pain. Patients having a delay in discharge from the PACU numbered 65.4% and 28.3% of these were as a result of uncontrolled pain. The factors associated with moderate to severe postoperative pain include younger age; duration of surgery >2 h; site of surgery being abdominal, upper limb and spine; and the use of general anaesthesia. The factors associated with a delay in discharge from the PACU include higher BMI; site of surgery being abdominal, spine and superficial; use of general anaesthesia; use of nurse controlled analgesia and moderate to severe pain scores.

There are numerous factors that affect postoperative pain.^10,17 The association of younger age group and operative site (abdominal or orthopaedic surgeries) with more severe postoperative pain is in concordance with previous studies.^18,19 The use of regional techniques lowering incidence of postoperative pain is also in agreement with previous work.^11,20,21There have been conflicting findings regarding the association of gender and postoperative pain. Our study did not find any significance in this association and this was found similarly in a previous study.²² Prolonged surgical duration is associated with greater surgical stress to the body and likely greater tissue trauma. This was significantly associated with postoperative pain, which is in congruence with a previous study.²²

Same day admissions appear to be a significant factor associated with increased pain severity postoperatively as compared with day surgery cases. Patients with higher pain scores are likely to be admitted rather than sent home as a day surgical patient. The use of pre-emptive analgesia and multi-modal analgesia techniques has been shown to provide good postoperative pain control.²³ However, in our study data there was a large percentage of documented ‘no analgesia’ given preoperatively (96.6%). Our study focus was not designed to look at pre-emptive analgesia or multi-modal analgesia techniques affecting postoperative pain. Instead we focused on overall intraoperative factors that may affect postoperative pain. The cut off points for moderate to severe pain in the NRS ranged from 4 to 6 in non-cancer pain in a previous review article.²⁴ We chose to use pain scores > 4 as our cut-off for moderate to severe pain.

For the secondary outcome measure of factors affecting a delay in discharge from the PACU, a delay in discharge was defined as more than a 30 min stay in the PACU. Literature on the definition of a delay in discharge is varied, with a range from 30 min to 2 h.^25–28 Our choice of 30 min as the cut-off is based on our institutional practice and different from previous studies.^29–31 Nurse initiated analgesia was set up in our institution to reduce delay in patients with pain in PACU receiving analgesia. Patients with higher pain scores and needing nurse initiated analgesia are significantly associated with a delay in discharge from the PACU.

We acknowledge several limitations to this study. First, there was no data collected on the ethnicity of patients despite the large varied population characteristic in our centre. Ethnicity has been shown to be a predictive factor in postoperative pain in previous studies.^32,33 The data collected over the one-month period may represent seasonal presentation of certain case types although this may have minimal effect on the results due to the high caseload in our centre. Second, the data collection over the period stipulated was carried out by different doctors in charge in the PACU on different days. Although the data collected is standardized, there is possibility of observer and reporting bias as different interviewers may influence patient reports on pain score. Third, patients with more severe pathology and long duration of surgery tend towards postoperative direct ICU admission, bypassing the PACU and excluded from the data in this study. Our study focuses on postoperative pain in the PACU and excludes postoperative pain presenting outside of the PACU (e.g. patients who are directly admitted to the ICU or patients in ambulatory centres). For the secondary outcome of delay in discharge, our study did not address non-clinical issues that may affect delay in discharge from the PACU, such as inadequate manpower, resources or beds or inefficiency in patient transfer processes. Patients may have been required to wait for bed availability even when they were fit for discharge from the PACU.

This study opens up further areas of improvement for postoperative pain management and managing reasons for delay in discharge from the PACU. The results allow us to target our efforts in any interventions or quality improvements for patient care in the PACU. Further study into non-clinical factors affecting delay in discharge could also be conducted.

Footnotes

Declaration of conflicting interests

The authors declare that there is no conflict of interest.

Funding

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

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Factors affecting postoperative pain and delay in discharge from the post-anaesthesia care unit: A descriptive correlational study

Abstract

Background:

Methods:

Results:

Conclusions:

Keywords

Introduction

Methods

Statistical analysis

Sample size calculation

Results

Patient characteristics

Factors associated with pain severity

Subgroup analysis for pain severity in abdominal surgeries with or without regional anaesthesia

Factors associated with delay in discharge

Pain severity associated with delay in discharge from the PACU

Discussion

Footnotes

Declaration of conflicting interests

Funding

References