Intraoperative hypotension and postoperative pneumonia in patients after selective intracranial tumor resection: a retrospective cohort study

Introduction

Annually, an estimated five million patients globally undergo neurosurgery (Dewan et al., 2018). As one of the most prevalent complications following neurosurgery, postoperative pneumonia prolongs hospitalization and increases the risk of postoperative mortality (Chastre & Fagon, 2002; Dasenbrock et al., 2015; Kazaure et al., 2014; Warren et al., 2003). Previous research has identified several patient-specific and surgery-related factors that are closely associated with the occurrence of postoperative pneumonia, such as preoperative anemia, hypoalbuminemia, tumor types, American Society of Anesthesiologists classification (ASA), chronic obstructive pulmonary disease (COPD), smoking history, surgery duration, and mechanical ventilation (Chughtai et al., 2017; Garibaldi et al., 1981; Hooda et al., 2019; Ryan et al., 2013; Shin et al., 2020; Turan et al., 2011). However, these factors are often difficult to optimize before surgery.

Recent studies observed that intraoperative hypotension increased postoperative cardiovascular complications and mortality (Gregory et al., 2021; Huang et al., 2020; Kouz et al., 2020; Lizano-Diez et al., 2022). At the same time, intraoperative hypotension also elevated the risk of postoperative infections (Ishikawa et al., 2014; Tassoudis et al., 2011; Yamamoto et al., 2007; Zhang et al., 2021). There is limited research investigating the association between intraoperative hypotension and postoperative pneumonia in patients undergoing neurosurgery. As intraoperative hypotension could be aggressively addressed during surgery, clarifying the relationship between intraoperative hypotension and postoperative pneumonia may help to develop evidence-based intraoperative blood pressure management strategies to improve patient outcomes.

Intracranial tumor resection is one of the most common neurosurgeries. The present single-center retrospective study aimed to explore the association between intraoperative hypotension and postoperative pneumonia in adult patients undergoing intracranial tumor resection.

Materials and Methods

Results

A total of 341 patients underwent elective intracranial tumor resection between between January 1, 2018, and December 31, 2022. After data review, 85 patients were excluded from the study, including 73 who were admitted to the intensive care unit during hospitalization and 12 who required reoperation during the initial hospitalization. Consequently, 256 patients were included and considered for the final analysis (Fig. 1).

Of the 256 patients included in the analysis, 43 (16.8%, 95% CI [12.3%–21.3%]) experienced postoperative pneumonia. Table 1 presents the comparison of baseline parameters between patients with postoperative pneumonia and patients without pneumonia. Compared with patients without postoperative pneumonia, patients with postoperative pneumonia were more likely to have a history of preoperative smoking.

Table 2 presents the comparison of perioperative parameters between patients with postoperative pneumonia and patients without pneumonia. Patients with postoperative pneumonia experienced longer durations of intraoperative hypotension, surgery, and controlled ventilation in comparison to patients without postoperative pneumonia.

Discussion

In this single-center retrospective study, we observed a a history of preoperative smoking and intraoperative MAP < 55 mm Hg were independently associated with an increased risk of postoperative pneumonia in patients undergoing resection of intracranial tumors. Among the two identified risk factors, intraoperative hypotension might be one that can be actively addressed during surgery. Therefore, aggressive correction of hypotension during intracranial tumor surgery may play a crucial role in reducing the risk of postoperative pulmonary pneumonia in patients.

Intraoperative hypotension is common during general anesthesia (Sessler et al., 2019). If the blood pressure falls below the critical threshold required for adequate perfusion of vital organs, it may result in ischemic injuries (Meng, 2021). Several observational studies have shown that intraoperative hypotension is associated with postoperative complications, including acute kidney injury, myocardial injury after noncardiac surgery, and dysfunction of other vital organs (Ruetzler, Khanna & Sessler, 2020; Shaw et al., 2022; Wijnberge et al., 2021). Even one minute of intraoperative MAP < 55 mmHg significantly increased the risk of postoperative cardiovascular complications (Gregory et al., 2021). However, research is scarce exploring the relationship between intraoperative hypotension and postoperative pneumonia in patients undergoing intracranial tumor resection.

Several studies have observed an association between intraoperative hypotension and postoperative infection. Zhang et al. (2021) retrospectively explored risk factors for postoperative infection in 880 patients who underwent gastrectomy for gastric cancer. Their results indicated that intraoperative SAP < 90 mmHg for > 10 min was associated with a higher incidence of postoperative infection (Zhang et al., 2021). Other studies also observed that intraoperative SAP < 80 mmHg increased postoperative wound infection in patients after major abdominal surgery (Babazade et al., 2016; Yamamoto et al., 2007). Although the exact mechanism behind the association of intraoperative hypotension with postoperative infections is currently unclear, it is speculated that the reduced tissue defense capabilities due to insufficient tissue perfusion because of hypotension may increase the risk of infection.

Currently, there is limited research on the relationship between intraoperative hypotension and postoperative pneumonia. We hypothesize that intraoperative hypotension may increase the risk of postoperative pneumonia through several potential mechanisms in the present study. Firstly, inadequate tissue perfusion during hypotension can lead to insufficient blood flow to vital organs such as the lungs, impairing oxygenation and increasing susceptibility to pulmonary infections. Secondly, ischemia-reperfusion injury caused by hypotension and subsequent blood pressure recovery may trigger inflammatory responses and oxidative stress, further damaging lung tissue. Additionally, hypotension and surgical stress can suppress immune function, weakening the body’s defense against pathogens. Hypotension may also impair respiratory defense mechanisms by causing ischemia of the respiratory mucosa, disrupting ciliary movement and mucus clearance. Furthermore, prolonged recovery due to hypotension may increase the need for bed rest and mechanical ventilation, both of which are risk factors for pneumonia. Lastly, hypotension may induce systemic inflammatory response syndrome (SIRS), releasing inflammatory cytokines that further harm lung tissue. Therefore, intraoperative hypotension may indirectly elevate the risk of postoperative pneumonia through these interconnected pathways.

Relative definitions of intraoperative hypotension are widely applied in clinical practice (Bijker et al., 2007). In previous studies, the relationship between the definition of relative intraoperative hypotension and postoperative outcomes remained unclear. In a retrospective cohort study that included 18,756 surgical patients, Monk and colleagues observed that intraoperative MAP decreased > 50% from the preoperative level that lasted more than 5 min elevating the risk of mortality within 30 days after surgery, while intraoperative MAP decreased less than 50% from the preoperative level did not increase the risk of 30-day mortality (Monk et al., 2015). Gregory et al. (2021) retrospectively analyzed 621,482 intraoperative records. Their results suggested that intraoperative MAP decreased > 40% from baseline was not associated with major adverse cardiac or cerebrovascular events (Gregory et al., 2021). We observed that intraoperative MAP decreased > 30% from the preoperative baseline was not associated with postoperative pneumonia. Because of the paucity of studies on intraoperative hypotension and postoperative pneumonia, more research is needed to explore whether the use of a relative definition of intraoperative hypotension helps to improve patient prognosis.

At the same time, this study cannot confirm that hypotension is inherently harmful. Most current observations suggesting the detrimental effects of intraoperative hypotension are derived from retrospective studies (D’Amico et al., 2023; D’Amico & Landoni, 2024). Prospective randomized controlled trials and meta-analyses have failed to establish intraoperative hypotension as a direct cause of postoperative adverse complications. On the contrary, in certain patient populations, those in the hypotension group may even benefit. Additionally, intraoperative blood pressure may not accurately reflect tissue perfusion. Continuous infusion of catecholamines, while increasing blood pressure, can cause microcirculatory vasoconstriction, leading to inadequate tissue perfusion (D’Amico et al., 2025b). Therefore, during surgery, ensuring adequate blood supply to vital organs should not rely solely on maintaining blood pressure above a single threshold. Instead, it is essential to individualize the hypotension threshold based on the patient’s specific condition, optimize cardiac function, and adjust fluid balance to ensure adequate perfusion of vital organs (D’Amico & Landoni, 2024).

This study has several limitations. Firstly, since we collected only adult patients who underwent surgery for intracranial tumors in a single center and returned directly to the ward, the representativeness of this study is limited. The positive association between intraoperative hypotension and postoperative pneumonia observed in this study requires a larger population to be examined. Secondly, due to the retrospective nature of the present study, other confounders that were not routinely recorded may confound our results. Perioperative lung-protective ventilation strategies such as intraoperative pulmonary resuscitation maneuvers are not routinely documented in the anesthesia information system. Furthermore, our anesthesia information system did not capture values of positive end-expiratory pressure (PEEP). Therefore, this study cannot exclude whether using pulmonary reanimation maneuvers or PEEP would have interfered with our results. Thirdly, details of preventive strategies for postoperative pneumonia that applied before and after surgery in surgical wards, such as deep-breathing exercises, were not routinely documented in our institution. In the present study, we cannot exclude the effect of undocumented preventive strategies on our results. Future studies are needed to collect more complete postoperative data on postoperative pneumonia to clarify the etiology of postoperative pneumonia. Fourly, in this study, we did not explore the association of vasopressors or inotropic agents to postoperative pneumonia. The choice of medication to correct hypotension for each patient was determined by the attending anesthesiologist based on the patient’s condition at the time. The medications used included norepinephrine, phenylephrine, ephedrine, dopamine, and others. Therefore, this study cannot use a uniform vasopressor or inotropic agent to analyze whether they are associated with postoperative pneumonia. Future prospective studies need to standardize the strategy for correcting intraoperative hypotension to investigate whether vasopressors or inotropic agents are related to postoperative pneumonia. Fifth, there are numerous methods available to quantify intraoperative hypotension, such as single-event duration, cumulative duration, area under the curve (AUC), time-weight average (TWA), among others. However, there is still insufficient evidence to determine which method of quantifying intraoperative hypotension best reflects the impact of intraoperative hypotension on postoperative complications. Wesselink et al. (2018) summarized recent clinical evidence on the relationship between intraoperative hypotension and postoperative complications. They observed that any exposure to MAP < 55 mmHg increased the risk of postoperative cardiovascular complications. Therefore, we selected whether patients experienced MAP < 55 mmHg during surgery to explore the relationship between hypotension and postoperative pneumonia in neurosurgical patients. Finally, in this retrospective study, the observed association between intraoperative hypotension and postoperative pneumonia cannot establish a causal relationship between the two, primarily due to factors such as confounding variables, unclear temporal sequence, selection bias, measurement errors, and the inability to determine biological mechanisms (D’Amico et al., 2025a). Retrospective studies can only suggest a potential correlation but cannot confirm a causal link. To establish causality, prospective studies or randomized controlled trials are typically required for further validation.

Conclusions

Intraoperative MAP < 55 mmHg was associated with postoperative pneumonia in patients undergoing intracranial tumor resection. Our findings may provide clinically relevant information in designing prospective studies to evaluate possible etiology of postoperative pneumonia and could shed insights on intraoperative blood pressure management in neurosurgeries.

Supplemental Information