The length of stay in the post-anaesthesia care unit correlates with pain intensity, nausea and vomiting on arrival

Today, post-anaesthesia care units (PACUs) are a standard and integral part of daily anaesthesia practice in most developed countries. Their main purpose is to safely recover patients from surgical and interventional procedures with concomitant anaesthesia. Through structured and tight clinical observation combined with continuous patient monitoring, discomfort and complications can be identified and treated early, thereby reducing adverse outcomes and increasing efficacy [1]. Several practice guidelines for post-anaesthesia care are available and have been recently updated, such as those from the European Board of Anaesthesiology and the American Society of Anesthesiologists [2],[3].

The benefit of a PACU service with respect to early detection of postoperative complications is beyond dispute. From a patient perspective, however, prevention and optimal management of pain, nausea and vomiting are of utmost importance as well. Therefore, the degree of pain, quantity of pain relief over time and the presence of postoperative nausea and vomiting (PONV) are being used as popular quality indicators for anaesthesia and postoperative care in PACU audits [2],[4].

The first aim of the present study was to prospectively measure pain and PONV at two defined time points: on arrival to our PACU and before discharge to the ward. As a quality management project, we wanted to specifically monitor these indicators and to compare our results to published reports. The second aim of the study was to determine if pain and PONV on arrival correlate with the length of stay in our PACU. It is important to early identify patients at risk for unplanned, prolonged PACU stay for optimal perioperative efficiency [5]. If the PACU becomes congested by these patients, the outflow of patients from the PACU to the ward is stopped and the unit cannot receive any further patients from the operating room (OR).

After approval from the local ethic committee (Kantonale Ethik Kommission, 8090 Zurich, Switzerland: KEK-StV-Nr. 47/12), which waived the requirement for informed consent, the anaesthesia quality management project was established. Data were prospectively collected in the PACU of the Triemli City Hospital Zurich, Switzerland during a time period of 30 months.

A total of 16,309 patients were cared for in the PACU during a time period of 30 months. This collective represents 41% of all patients that underwent anaesthesia in this time period. The data of 12,179 patients were available for statistical analysis. Sets of data (4,130) had to be excluded because our questions related to pain and PONV could not be answered reliably. These patients had language difficulties or suffered from concomitant neurologic/psychiatric diseases. Patient characteristics and case related data are presented in Table 1.

On admittance to the PACU, 73% of patients were free of pain (NRS 0), 23% of patients had minor pain (NRS 1–4) and 4% of patients suffered from severe pain (NRS 5–10). Before discharge, 87% of patients were pain free, 13% of patients had minor pain and only 0.1% patients suffered from major pain. There was a significant difference in the presence of pain (NRS 1–10) on admission between regular PACU (24%) and more complex IMC (38%) patients (Figure 1). Incidence of postoperative pain for different subgroups is presented in Table 2. Risk factors for increased postoperative pain (on admittance) determined by multivariate analysis were female gender; higher ASA classification; general, cardiac and orthopaedic surgery and prolonged case duration. Furthermore, the performance of general anaesthesia without the combination of regional anaesthesia was an independent risk factor. By contrast, old age, ophthalmologic procedures or ENT surgery were predictive for lower pain scores (Table 3).

PONV was observed in 257 patients on admittance to the PACU, whereas 21 patients were vomiting. Until discharge to the ward, 224 of these 257 patients were free of symptoms and 103 patients (0.8%) developed new nausea (data not shown). Therefore at the time of discharge, a total of 135 patients had nausea but none suffered from vomiting (Figure 2). A total of 360 patients (3%) had PONV during the recovery period. Subgroup analysis showed a significant reduction of postoperative nausea and vomiting during the PACU stay for all patient groups except for those undergoing spine surgery and patients with higher ASA classification (Table 4). Patients with major pain levels (NRS 5–10) on admittance had a higher incidence of postoperative nausea (5.3%) and vomiting (1.3%) compared to patients with lower pain levels (NRS 0–4; nausea 2.2%, vomiting 0.2%, p <0.05). Risk factors for nausea in the multiple linear regression analysis were female gender, monitored anaesthesia care and performance of regional anaesthesia. By contrast, reduced nausea occurred in older patients and a patient undergoing ophthalmologic procedures. The only independent risk factors for postoperative vomiting were female gender and postoperative pain (Table 3).

Duration of PACU stay was longer in a woman compared to a man and PACU stay became longer with increasing age, ASA classification and anaesthesia time (Table 1). Levels of pain and presence of PONV on admittance correlated with the length of stay: for example, patients with no pain or no PONV stayed for 5.3 ± 5.5 or 5.7 ± 5.9 h, whereas patients with severe pain (NRS 5–10) or nausea/vomiting stayed significantly longer (9.0 ± 7.3 or 7.4 ± 7.5/10.0 ± 8.9 h; Figure 3). Risk factors for prolonged stay, as determined by multiple regression analysis, are shown in Table 3.

In the present PACU quality audit, the majority of the studied 12,179 patients had good pain control (73% and 87% of patients were pain free on arrival and on discharge to the ward, respectively) and the incidence of PONV was 3% overall. In more complex IMC patients, pain scores were higher on arrival but dropped to similar levels on discharge compared to regular PACU patients. The levels of pain and presence of PONV on arrival correlated with the length of stay in the PACU. Thereby, pain- or PONV-free patients stayed almost half of the time in the PACU compared to patients with severe pain or vomiting on arrival.

The incidence of early postoperative pain in our study (Figure 1, Table 2) is only half or even less of commonly cited postoperative pain levels in the literature [13]-[15]. Several reasons may explain this difference: our patients were asked about their postoperative pain during their PACU stay with a simple numeric rating scale only, whereas the other studies performed more complex telephone or written surveys several weeks and months after the surgical procedures and asked for global postoperative pain experience. The results are therefore not comparable since two different things were measured.

Prompt and appropriate management of pain initiated in a PACU environment and continued on a regular ward may have a positive impact on patient satisfaction and perception of pain according to results of studies on the implementation of PACU-based pain services [16],[17]. Our data are in accordance with these recommendations and show that pain relief was effective in our PACU resulting in a significant reduction of postoperative pain from admittance to discharge (Figure 1). Multivariate analysis revealed a variety of risk factors for increased postoperative pain (Table 3). Our data agree with previously published large trials, where younger age and type of surgery (e.g. major general, orthopaedic and cardiac surgery under general anaesthesia) were predictors for postoperative pain [13],[18],[19]. Concerning female gender as a predictor for increased postoperative pain, studies report conflicting results, however [19]. Patients at risk for increased postoperative pain may have a clear benefit from postoperative care in a PACU. On the other hand, patients undergoing surgery under regional anaesthesia may initially present in a pain free state. Nevertheless, PACU pain management can still be appropriate for these patients, e.g. to adjust continuous regional anaesthesia or to initiate and titrate systemic intravenous analgesia.

The incidence of PONV revealed in this study was much lower than the 25%–30% found in the literature (Figure 2, Table 4) [11]. This might be explained by the fact that preoperatively a systematic risk assessment was done for PONV in all patients and regional anaesthesia favoured whenever possible. According to the present study, the care in our PACU was able to significantly reduce postoperative nausea. A reduction of approximately 50% was observed in the total patient population as well as in the majority of the subgroups. Postoperative nausea was completely controlled during the PACU stay for all patients. The fact that women are especially prone to PONV has been demonstrated repeatedly [10] and is again supported by our data. Female patients obviously benefit from a post-anaesthesia care service.

An increased incidence of PONV was observed in patients with higher pain scores on PACU admittance. This finding may be explained by a higher use of opioids in order to control postoperative pain. Only recently, a study evaluating the relationship between postoperative opioid administration and PONV has been published and a logarithmic dose-effect relationship could be established [20]. In the present study, we did not record the individual doses and dosing intervals of opioids. However, we could show that postoperative pain is an independent predictor for PONV (Table 3). Based on these findings, profound intraoperative and early postoperative analgesia should be promoted to minimise deliberate use of postoperative opioids. This goal may be achieved by an increased use of multimodal analgesia techniques, including regional anaesthesia or combined anaesthetic techniques [21],[22].

A limitation of the present investigation is the heterogeneity of the studied patient population with regard to the surgical specialities and the intraoperative anaesthetic technique. On the other side, by representing daily clinical reality, this heterogeneity could also be interpreted as strength. Additionally, our pain scores were not compared to preoperative values and both pain and PONV were just measured in the PACU period. To get more detailed information and to increase validity, it would be interesting for future studies to compare pain levels to baseline levels before and to add a follow-up on pain and PONV experience several weeks after their PACU stay.

We conclude that the majority of PACU patients had good pain control, both on admittance and before discharge and that the overall incidence of PONV was low. Managing patients in the PACU could achieve a significant reduction of pain and PONV. The level of pain and presence of PONV on admittance to the PACU correlate with and act as predictors for increased length of PACU stay.