Using the anesthesia database of 3512 patients at Beijing Tongren hospital, the postoperative PE was prevalent in 0.85%(95%CI = 0.56–1.14). The main finding of this study is that the intraoperative cumulative duration of hypotension, oliguria, and operation time > 4 h were significant risk factors for postoperative PE in patients underwent radical resection with head and neck cancers.
Many assessment models have been used to evaluate the risk of thrombotic disease in patients, such as the Roger score , Padua score , and Caprini scale , which quantitatively layer the risk in order to guide preoperative thromboprophylaxis. But the efficacy and accuracy of these models are still controversial . We compared the Caprini scale and Charlson comorbidity index, the mean Caprini scale and was 6.5 in the PE group and 6.4 in the C group, all patients were at high risk of thromboembolism, but there were no significant differences was founded between the two groups. Therefore, we suspected that some other factors may also affect the occurrence of postoperative PE. In our study, we investigated some factors such as blood pressure control and fluid therapy, aiming to find some controllable factors to improve the prognosis of patients.
In general anesthesia, a 20% reduction in normal blood pressure is considered acceptable, generally. Excessive blood pressure reduction beyond that should be avoided. Intraoperative hypotension is often considered to be related to the occurrence of postoperative adverse events [18,19,20,21]. Due to the special location of the cancer, dysphagia and dietary problems often occur in patients with head and neck cancers. These patients usually have somewhat nutritional problems, preoperative dehydration, and hypovolemia are not uncommon . Surgical resection of head and neck cancers results in a large trauma but is not associated with high blood loss. Using the amount of blood loss as a reference for fluid infusion, it usually leads to insufficient intake. In addition to the vasodilation effect of anesthesia, all these factors may lead to severe hypovolemia and insufficient blood perfusion in important organs during operation, which can even last until after the operation. Few studies have paid attention to the relationship between intraoperative fluid management and postoperative PE. Insufficient blood volume may lead to slow blood flow and increase blood viscosity, which may be risk factors for thrombosis. We did not find a difference in absolute or percentage blood pressure change between the PE group and the control group. However, the cumulative duration of intraoperative hypotension was significantly different between the two groups, whether absolute or relative, and the ROC curve analysis showed that the cumulative duration of hypotension (MBP decrease> 20%) had an optimal cut-off value of 1.46 h. This suggests that short-term intraoperative hypotension is not enough to lead to hemodynamic changes that may cause thrombosis, but when the cumulative time of hypotension during the perioperative period is too long it will lead to hypoperfusion, which will in turn lead to hypoxic-ischemic damage of important organs and increase the probability of complications, including thrombus complications. Mechanism of hypotension leading to thrombosis is unclear, one research has shown that orthostatic hypotension had a moderately increased risk of VTE, which may be due to changes in posture leading to vasodilation and lower extremity venous stasis, this results in a decrease in venous return to the heart or a decrease in cardiac output . We suspect that intraoperative hypotension, which associates with vasodilation or low cardiac output induced by anesthesia may have a similar effect on thrombosis. Under anesthesia, physiological compensatory mechanisms such as the neurohumoral effects, the skeletal muscle pump, or neurovascular compensation may be impaired, possibly will produce a more serious consequence. Also, hypoxic-ischemic damage may lead to vascular endothelial injury and causes the blood to be hypercoagulable. Triple low state, a combination of hypotension, low bispectral index, and low minimum alveolar concentration of volatile anesthesia, was considered to increases hospital stay and perioperative mortality . In a recent study, Kertai failed to found the association between cumulative duration of triple low state and perioperative complications or mortality . This might be interpreted as avoiding hypotension do not have any benefit for patients, however, Kertai’s study defined hypotension as mean arterial pressure < 75 mmHg, which is not severe hypotension in clinical practice. So, the duration of hypotension is still a matter we need special care in perioperative management.
Urine output is also a commonly monitored indicator to reflect tissue perfusion during surgery. Many studies have shown the relationship between fluid infusion and postoperative complications of head and neck surgery [26,27,28], but few have paid attention to urine output. We found that urine output in the PE group was significantly lower than that in the control group. Corresponding, the incidence of oliguria was significantly higher in the PE group. This phenomenon may be related to the long cumulative duration of intraoperative hypotension, renal perfusion was partly affected. In multivariable conditional regression analysis, urine output was not associated with postoperative PE, but the P value was very close to the threshold. This may be due to the recall bias of the retrospective study, the limited sample size, and other reasons. We believe that intraoperative fluid management to ensure adequate urine output is still an important factor affecting the prognosis of thrombotic complications. Elaborate goal-directed fluid therapy will be a trend for future studies and may have potential benefits for these patients. Oliguria is a risk factor in multivariable conditional regression analysis, however, due to the large 95%CI range of its OR value, its credibility was reduced. The internationally accepted standard for oliguria is< 0.5 ml·kg− 1·h− 1, based on which there is a significant difference between the two groups. The ROC curve analysis showed that the urine output had an optimal cut-off value of 1.775 ml·kg− 1·h− 1, this may be associated with hypercoagulability and a higher requirement for fluid load in patients with malignant tumors. Due to its low sensitivity and specificity, it is not accurate to use the urine output as an independent indicator for predicting the PE after general anesthesia, postoperative PE may be the result of multiple factors.
Factors such as a high ASA grade, high BMI, smoking history, and operation time may be related to postoperative PE in this study, but these factors are uncontrollable in the short term, it is difficult to adopt active measures based on them to reduce the risk of postoperative PE. Other factors, including age, gender, tumor type, which have been identified as the risk factors for pulmonary embolism and have been included in the commonly used risk assessment system, were used as a matching condition to eliminate effects of their influence on the results.
We also assessed the outcome of patients, due to the close monitoring after the operation, most pulmonary embolism was found and treated in time, and there was no difference in mortality between the two groups. But this kind of complication increases the patient’s hospitalization time and expense, increases the use of medical resources, avoids the occurrence can economize the medical resources and reduces the medical burden.
The current study has some limitations. First, the single center, retrospective nature of the design and the relatively small number of patients with PE significantly limit the interpretation of the data. Accordingly, there is the potential for recall or selection bias, such as inaccurate blood pressure records. Second, patients with subclinical PE were not identified, and only symptomatic patients were investigated by imaging. Therefore, it is possible that our study underestimated the true PE incidence. In addition, we did not adjust for other confounding factors such as operation time, history of smoking, or surgical confounders, because the number of remaining cases after adjustment is too small to make accurate statistical analysis. We cannot rule out the possibility that the between-group differences may be due, at least in part, to the differences in the confounding factors, and only revealed a phenomenon that hypotension may be associated with PE. A postulate that hypotension and hypoperfusion are perhaps causal for PE cannot be determined with a case-control study, the relationship between the risk factors and conclusions is exploratory, further prospective or randomized controlled studies are needed to confirm this phenomenon and clarify its mechanism.