In this retrospective study, we found that off-hours anesthesia was associated with higher intraoperative CRBC and FFP in both the unmatched cohort and the propensity score–matched cohort. The intraoperative dosage of sufentanil was higher in the off-hours group before PSM, although not in the propensity score–matched analysis. Before PSM, postoperative LOS and total LOS was longer in the off-hours group, while there was no statistical difference after PSM. Some postoperative adverse outcomes, including in-hospital mortality, ICU admission, hypotension, pulmonary infection, and hyoxemia, also happened more often in the off-hours group in the unmatched analysis, although not after PSM.
The anesthesia method, which have been added into propensity score matching as a covariate, is a main embodiment of the anesthetist's decision and judgment. It is worth noticing that in the off-hours group, the anesthetist was more likely to choose GA (63.8% vs. 18.0%), rather than CSEA (13.8% versus 29.8%) or pure PNB (3.4% versus 18.7%) to finish the hip surgery. Considering that current studies support the superiority of spinal anesthesia (Chen et al., 2019, Neuman et al., 2012) or PNB (Guay et al., 2017, Min et al., 2020) over GA for the prognosis of hip surgery patients, this phenomenon might be an important factor for worse postoperative outcomes of patients in the off-hours group before PSM. It is also explicable a phenomenon that off-hours working might affect the decision and judgment of the anesthetist. It is found that, at night, fatigue may cause worse task performance and mood of anesthetists (Cao et al., 2008). Also, after night-shift sleep deprivation, anesthetists present longer reaction time and greater reliance on avoidance as a coping strategy, which have a potential negative impact on patients (Saadat et al., 2017). Besides, from another perspective, during off-hours, the spare resources of anesthesia were insufficient and the time of preoperative preparation was limited, as a consequence, GA became to be the most applicable choice for the anesthetist. Therefore, we reasoned that anesthesia starting at off-hours may negatively affect the decision and judgment of the anesthetist during hip surgery, thus leading to the occurrence of the perioperative adverse outcomes.
It is consistent that the intraoperative CRBC and FFP were higher in the off-hours group before and after PSM. Ren et al. had similar finding that patients undergoing liver transplantation in the night group had more requirement of intraoperative RBC suspension (Ren et al., 2019), while their finding that the intraoperative blood loss was also more in the night group cannot be reproduced in our analysis. It remained to be further studied why the intraoperative CRBC and FFP was higher in the off-hours group even if the intraoperative blood loss or the urine volume had no difference in the propensity score–matched cohort. Even worse, although the intraoperative CRBC and FFP were higher in the off-hours group, the ratio of postoperative renal dysfunction and hyoxemia tended to be higher in the off-hours group after PSM. These findings might reflect that, during off-hours anesthesia, (1) the patient's intraoperative status might have been “mis-assessed” by the anesthetist, and (2) the clinical measures taken by the anesthetist might not be “sufficient” to improve the patient's fluid loss or hypoxia. These findings further support that the decision and judgment of anesthetist could be greatly impaired during off-hours anesthesia.
In general, anesthesia starting at off-hours may negatively affect anesthesia method choosing and intraoperative anesthesia management. Instead of discussing the direct influence of off-hours anesthesia on the prognosis of patient undergoing hip surgery, we are supposed to pay more attention to the adverse effects of off-hours anesthesia on the anesthetist, which may not only indirectly lead to poor prognosis of the hip surgery patient, but also affect the physical and mental health of the anesthetist.
Strengths and Limitations
As a retrospective study, although we have used PSM to minimize the baseline differences between two groups, some bias still could not be avoided. For example, due to information bias or recall bias, the incidence of some postoperative complications documented in our study was lower than in some previous prospective studies, which may bring errors to our results. The incidence of postoperative delirium is about 20 to 45% among elderly surgery patients, varied by the surgery type (Daiello et al., 2019, Inouye et al., 2014, Rudolph and Marcantonio, 2011). And it is reviewed that hip fracture has the highest incidence of postoperative delirium, about 35 to 65% (Rudolph and Marcantonio, 2011), which is much higher than that in our study. The incidence of postoperative delirium is also greatly influenced by the method used for delirium assessment, with daily mental status testing and application of a validated diagnostic algorithm the most efficient (Rudolph and Marcantonio, 2011). However, delirium is frequently missed by nurses as well as physicians (Inouye et al., 2001, Ozsaban and Acaroglu, 2016), which makes it almost impossible to be daily tested. Since we had only recorded the occurrence of postoperative delirium according to the clinical medical records, there might be a large error in the incidence of postoperative delirium.
In addition, due to the small sample size in this study, the proportion of some postoperative outcomes in the off-hours group may increase when the sample size is enlarged, and accordingly, the differences between two groups may become statistical.
Furthermore, we adopted a relatively arbitrary either-or grouping (Cortegiani et al., 2019, van Zaane et al., 2015), although we had the grouping pattern improved. The grouping in this study is not only according to the time of anesthesia induction but also depending on the end time of anesthesia. However, a step further, the prognosis of patients could also differ from different times of the day (Hajdu et al., 2021, Wright et al., 2006). It needs further study about the effects on patients undergoing hip surgery at different times of the day, by creating narrower segmentations of times when grouping.