HI during surgical resection of pheochromocytomais is still a big concern for surgeons and anesthesiologists, since it has been proven to be associated with morbidity [8, 9]. However, there was still no agreement on the definition of intraoperative HI according to the studies. Bruynzeel and Brunaud indicated that intraoperative SBP above 160 mmHg was a risk factor for HI [2, 8] and Aksakal et al. revealed that HI was associated with the requirement of cardioactive or vasoactive drugs administration [10]. Integrating those findings, Pisarska-Adamczyk et al. defined HI as an occurrence of both intraoperative episodes of SBP above 160 mmHg and requirement of vasoactive drug administration [7]. In our study, based on this definition, the hemodynamic parameters including the highest intraoperative BP, incidence of extreme hypertensive episodes, the highest HR and the range of BP fluctuation were significantly higher in the HI group, indicating it could objectively reflect the intraoperative hemodynamic status. The incidence of intraoperative HI was 61.8% in our series, which was higher than previous reports [7, 10]. However, considering the heterogeneity of HI definition, operating techniques, tumour size and perioperative patient management, it is difficult to compare the results among different studies.

Nowadays LA is the gold standard of surgical treatment for adrenal tumours. For pheochromocytoma, there has been debate in the literature whether the formation of pneumoperitoneum could lead to a massive release of catecholamines, resulting in hypertension and tachycardia [11]. However, several recent studies have demonstrated that LA is equally safe as open surgery and does not increase the risk of HI [12, 13]. Therefore, LA gradually became the first choice for resection of pheochromocytoma, especially for small to medium-sized tumour. As LA became more technologically mature, its indication was extended to large tumours [14]. In the present study, the maximal diameter of the tumours was 110 mm for both transperitoneal and retroperitoneal approaches. To our knowledge, only few studies specially focused on LA and its predictors for intraoperative HI, and moreover, the tumour was confined to medium size [7].

Similar to the results of the previous studies [3, 10], we demonstrated that tumour size was an independent risk factor for intraoperative HI. Larger tumours have a tendency to secrete higher levels of catecholamines and as a result to increase the incidence and duration of intraoperative hypertensive episodes [2, 15, 16]. In addition, larger tumours required increased manipulation during tumour dissection and resection, resulting in high catecholamine release and significant hemodynamic fluctuation [17].

Some underlying diseases can impair the cardiovascular function, which may in turn influence intraoperative hemodynamic parameters. Pisarska-Adamczyk et al. [7] and Bai et al. [18] demonstrated that presence of diabetes mellitus and coronary artery disease were independent risk factors for HI, respectively. In the present study, however, we did not prove a causal link between patients’ comorbidities and HI. The incidence of diabetes mellitus in the HI and non-HI group was comparable. Although coronary artery disease was significantly more common in the HI group, it was not proven to be associated with the development of HI in the multivariate logistic regression analysis.

Our study showed that previous hypertension history was an independent risk factor for intraoperative HI. As is known, a proportion of patients with pheochromocytoma are normotensive. Normotension is seen mostly in patients with relatively small amounts of catecholamines in circulation. On the other hand, sustained and paroxysmal hypertension strongly correlates with high levels of plasma norepinephrine and epinephrine, respectively [19]. Increased plasma level of catecholamine and/or metabolites has been confirmed to be associated with intraoperative HI [20]. That may explain why patients with previous hypertension history were more prone to intraoperative HI. Furthermore, hypertensive patients have higher arterial stiffness compared to normotensive ones, so these patients may be relatively susceptible to hypertension episodes.

With respect to LA for pheochromocytoma, only a few studies have evaluated the effects of surgical approach on the occurrence of HI with conflicting results. Vorselaars et al. showed that retroperitoneal approach carried greater risk of intraoperative hypotension than transperitoneal approach [9]. On the contrary, Ban et al. found retroperitoneal approach provided favorable intraoperative hemodynamic parameters compared with transperitoneal approach [21]. In their opinion, the anatomical benefits of retroperitoneal approach enables minimum manipulation of the tumour and early control of the adrenal vein, which reduces excessive catecholamine secretion. However, when performing retroperitoneal LA, we found it was sometimes difficult to access the adrenal vein underneath larger tumours. Moreover, the right kidney often blocks the way to control the adrenal vein, making early ligation of the adrenal vein more difficult. On the other hand, when performing transperitoneal LA, we initially placed an aspirator between the adrenal gland and vena cava or left renal vein to retract the tumour. In this way, attachments along the border of the glands and near the adrenal vein could be clearly exposed and divided. This technique allows the surgeons to isolate and control the adrenal vein at the early stage of surgery via transperitoneal approach. In the present study, we found surgical approach had no significant impact on intraoperative HI. This was consistent with the findings of a recent meta-analysis by Jiang et al. [22], which demonstrated no significant difference between transperitoneal and retroperitoneal approaches in the incidence of hemodynamic crisis, though some advantages for retroperitoneal approach including shorter operative time and less blood loss were reported.

Numerous other risk factors for HI were reported in the literature, including plasma or urinary level of catecholamine, BMI, clinical symptoms and et al. [3, 9, 23, 24]. Possible reasons for this variability might be a lack of standardized perioperative anaesthesiological and surgical management. In addition, discrepancies could arise from different HI definitions. Among the possible risk factors, plasma or urinary level of catecholamine has been most frequently reported [24]. Unfortunately, we did not routinely test that before the year of 2020 in our center. Thus, preoperative levels of catecholamine were not evaluated in the current study.

This study has limitations typical of a single center study. A relatively limited number of patients were included, mainly due to the rare occurrence of pheochromocytoma. Second, this is a retrospective study, and selection bias was not avoidable. Another important limitation of the study seems to be the choice of the definition of HI. The multitude of definitions presented by various authors makes it difficult to compare the results.