To date, there is no accepted definition of APH. Therefore, the reported incidence of APH depends on the criteria used and the type of surgery. In the present study, we found that the incidence of APH was 30.1%.

There are many factors that cause APH in patients, but no consensus has emerged. In the present study, analysis confirmed that age is one of the most important factors in the occurrence of APH in patients. One study showed that the prevalence of hypertension increases from 8% in those aged 18 to 39 years to 65% in those aged 60 years and older [5]. In this study, there were 258 patients (21.9%) over the age of 65 years, of whom 97 patients had APH, and the incidence of APH in the elderly was as high as 37.6%. On the one hand, aging is seen as a major factor, since cardiovascular function in the elderly gradually declines with increasing age and disease progression. On the other hand, 137 (53.1%) of the elderly in this study had a history of hypertension. On May 6, 2020, the International Society of Hypertension (ISH) published its own global hypertension practice guidelines, dividing hypertensive patients into three categories [6]. Among them, high-risk patients have a very low tolerance for stress responses to various adverse stimuli. In elderly patients with primary hypertension, arterial pressure acts extraordinarily long in response to stimuli that cause vasoconstriction, such as pain and hypoxemia. Then, a sudden and severe rise in blood pressure may occur during recovery from anesthesia [7, 8], which is in good agreement with the present results.

The results of this study showed that the use of propofol in PACU was significantly associated with the occurrence of APH. In 2017, an online survey initiated by The German Society of Anesthesiologists showed that experienced anesthesiologists tend to use propofol to treat restlessness during the recovery period [9]. Kim et al. suggested that propofol can prevent or alleviate restlessness [10]. In fact, in our study center, anesthesiologists tend first to use propofol to control patients’ restlessness symptoms quickly, avoid adverse effects caused by restlessness, and then comprehensively analyze the patient’s condition and provide other corresponding and appropriate treatments. Therefore, in this study, we believe that adding propofol during the recovery period implies the development of restlessness. Since restlessness can be a stimulus for hypertension [11], patients who received additional propofol were more likely to develop APH. We suggest that restlessness be addressed promptly to reduce the incidence of APH.

It can be seen that patients with higher baseline blood pressure were less likely to develop APH, but this result may be related to the definition of APH in this study. The study noted that patients with intraoperative hypertension were more likely to develop APH than patients without intraoperative hypertension, which seems reasonable. Intraoperative hypertension often indicates that the patient was in a state of sympathetic agitation, elevated catecholamine levels, or volume overload during surgery. If these conditions are not addressed and corrected in a timely manner, patients are often more likely to develop hypertension postoperatively.

This study found that compared with male patients, APH was more likely to occur in female patients. With increasing age, the degree of increase in sympathetic nerve activity that causes vasoconstriction is higher in women than in men [12]. This sex difference may be related to estrogen activity levels. Among the 576 female patients included in this study, about 337(59%) patients were older than 50 years old, and the proportion of women with menopause was larger. Postmenopausal women experience changes in estrogen levels and are prone to emotional agitation, resulting in increased excitability of sympathetic nervous system and changes in endocrine function, thus easily leading to abnormal increase in blood pressure [13].

In this study, the role of dexmedetomidine on APH was examined and found to have a certain protective effect. A subgroup analysis of the dexmedetomidine-treated (Dex group) and non-treated (non-Dex group) groups was performed.The results showed that the incidence of APH was statistically lower in the Dex group (Additional file 1). Studies have demonstrated that perioperative infusion of dexmedetomidine results in lower blood pressure during anesthesia recovery [14, 15]. It has been reported in the literature that intraoperative ues of dexmedetomidine reduces the stress response of patients during tracheal intubation and extubation [16], and Turan et al. [17] found that the use of dexmedetomidine in neurosurgical procedures improved the quality of extubation, stabilized patient hemodynamics during extubation. They were consistent with the results obtained in the present study.

In the sensitivity analysis, a stepwise logistic regression was performed using the model excluding the baseline blood pressure. The results were compared with the primary analysis. The results did not change significantly, suggesting that our results are fairly robust (Additional file 2).

This study is a retrospective study and has unavoidable limitations. This study has some flaws in the process of extracting clinical information for patients in recovery. Data collection is every 5 min, which may result in missing important data, and the inclusion of relevant risk factors in the PACU is not sufficient. For patients whose blood pressure was controlled with oral antihypertensive drugs over a long period of time, it was not possible to collect relevant information because the type and method of medication were not recorded in detail in the medical record system. Therefore, it remains necessary to conduct a prospective study in the later stages of the disease to record detailed clinical information on patients’ baseline data and recovery periods in order to improve the predictive model.

In conclusion, the risk of acute postoperative hypertension was found to be increased with age ≥ 65 years, female patients, restlessness during recovery and intraoperative hypertension. Intraoperative use of dexmedetomidine was protective factors for APH. These findings may have implications for postoperative blood pressure management in patients admitted to the PACU.