Intraoperative arterial pressure management: knowns and unknowns

Impact of norepinephrine versus phenylephrine on brain circulation, organ blood flow and tissue oxygenation in anaesthetised patients with brain tumours: study protocol for a randomised controlled trial

INTRODUCTION

Vasopressor support is often preferred as an efficient and convenient way to raise the blood pressure during surgery and intensive care therapy. However, the optimal vasopressor for ensuring organ blood flow and tissue oxygen delivery during surgery remains undetermined. This study aims to assess the impact of norepinephrine versus phenylephrine on cerebral and non-cerebral organ perfusion and oxygenation during anaesthesia in neurosurgical patients with brain tumours. The study also explores the impact of the vasopressor agents on the distribution of cardiac output between various organs.

METHODS AND ANALYSIS

This is an investigator-initiated, double-blinded, randomised clinical trial including 32 patients scheduled for supratentorial brain tumour surgery. The patients are randomised to receive a phenylephrine or norepinephrine infusion during preoperative positron emission tomography (PET) examinations and the following neurosurgical procedure. PET measurements of blood flow and oxygen metabolism in the brain and other organs are performed on the awake subject during anaesthesia, following a 10% and 20% gradual increase in blood pressure from the baseline value. The primary endpoint is the between-group difference in cerebral blood flow. Secondary endpoints include detection of ischaemic brain lesions possibly associated with vasopressor treatment, changes in cerebral oxygen metabolism, non-cerebral organ blood flow and oxygen metabolism, cardiac output, regional cerebral oxygen saturation, autoregulation and distribution of cardiac output between organs.

ETHICS AND DISSEMINATION

This study was approved by the Danish National Medical Ethics Committee (20 May 2022; 2203674). Results will be disseminated via peer-reviewed publication and presentation at international conferences.

TRIAL REGISTRATION NUMBER

EudraCT no: 2021-006168-26.

CLINICALTRIALS

gov: NCT06083948.

Hip Fracture Intervention Study for Prevention of Hypotension Trial: a Pilot Randomized Controlled Trial

BACKGROUND

Hypotension during anesthesia for surgery for hip fracture is common and associated with myocardial injury, stroke, acute kidney injury, and delirium. We hypothesized that maintaining intraoperative blood pressure close to patients' preoperative values would reduce these complications compared to usual care.

METHODS

A pilot feasibility patient- and assessor-blinded parallel group randomized controlled trial. People with unilateral hip fracture aged ≥70 years with capacity to give consent before surgery were eligible. Participants were allocated at random before surgery to either tight blood pressure control (systolic blood pressure ≥80% preoperative baseline and mean arterial blood pressure ≥75 mm Hg) or usual care. Feasibility outcomes were protocol adherence, primary outcome data completeness, and recruitment rate. The composite primary outcome was myocardial injury, stroke, acute kidney injury or delirium within 7 days of surgery.

RESULTS

Seventy-six participants were enrolled, and 12 withdrew before randomization. Sixty-four participants were randomized, 30 were allocated to control, and 34 to intervention. There was no crossover, all 64 participants received their allocated treatment, primary outcome was known for all participants. The composite primary outcome occurred in 14 of 30 participants in the control group compared with 23 of 34 participants in the intervention group (P = .09), relative risk 1.45 (95% confidence interval [CI], 0.93-2.27).

CONCLUSIONS

A randomized controlled trial of tight intraoperative blood pressure control compared to usual care to reduce major postoperative complications after fractured neck of femur surgery is possible. However, the data would suggest a large sample size would be required for a definitive trial.

Intraoperative Hypotension Prediction: Current Methods, Controversies, and Research Outlook

Intraoperative hypotension prediction has been increasingly emphasized due to its potential clinical value in reducing organ injury and the broad availability of large-scale patient datasets and powerful machine learning tools. Hypotension prediction methods can mitigate low blood pressure exposure time. However, they have yet to be convincingly demonstrated to improve objective outcomes; furthermore, they have recently become controversial. This review presents the current state of intraoperative hypotension prediction and makes recommendations on future research. We begin by overviewing the current hypotension prediction methods, which generally rely on the prevailing mean arterial pressure as one of the important input variables and typically show good sensitivity and specificity but low positive predictive value in forecasting near-term acute hypotensive events. We make specific suggestions on improving the definition of acute hypotensive events and evaluating hypotension prediction methods, along with general proposals on extending the methods to predict reduced blood flow and treatment effects. We present a start of a risk-benefit analysis of hypotension prediction methods in clinical practice. We conclude by coalescing this analysis with the current evidence to offer an outlook on prediction methods for intraoperative hypotension. A shift in research toward tailoring hypotension prediction methods to individual patients and pursuing methods to predict appropriate treatment in response to hypotension appear most promising to improve outcomes.

Use of 400 µg/mL Peripheral Phenylephrine Infusions During Anesthesia: A Safety Initiative

During a general anesthetic case, a patient was administered a 400 µg/mL infusion of phenylephrine as opposed to the 40 µg/mL solution typically used in most operating rooms. The patient experienced iatrogenic hypertension, which resolved once the cause was discovered and the phenylephrine was discontinued. A root cause analysis was performed, with multiple factors contributing to the error. The Department of Pharmacy advocated switching to one concentration of phenylephrine hospital-wide. After performing a literature review regarding the safety of using 400 µg/mL phenylephrine peripherally, the decision was made to switch the operating room to this concentration of phenylephrine. The switch has been successful, with only one known medication error and no adverse events occurring since implementation. This quality improvement initiative demonstrates that 400 µg/mL phenylephrine can be used as an infusion in the operating room, which has potential implications for patient safety and efficiency. This safety initiative may serve as an example for other operating rooms.

Association between Transient-Continuous Hypotension during Mechanical Thrombectomy for Acute Ischemic Stroke and Final Infarct Volume in Patients with Proximal Anterior Circulation Large Vessel Occlusion

Background/Objectives: Periprocedural blood pressure changes in stroke patients with a large vessel occlusion are a known modifiable risk factor of unfavorable treatment outcomes. We aimed to evaluate the association between pre-revascularization hypotension and the final infarct volume. Methods: In our retrospective analysis, we included 214 consecutive stroke patients with an anterior circulation large vessel occlusion that underwent mechanical thrombectomy under general anesthesia. Noninvasively obtained blood pressure values prior to symptomatic vessel recanalization were analyzed as a predictor of post-treatment infarct size. Linear logistic regression models adjusted for predefined factors were used to investigate the association between blood pressure parameters and the final infarct volume. Results: In our cohort, higher baseline systolic blood pressure (aβ = 8.32, 95% CI 0.93-15.7, p = 0.027), its maximal absolute drop (aβ = 6.98, 95% CI 0.42-13.55, p = 0.037), and >40% mean arterial pressure decrease (aβ = 41.77, CI 95% 1.93-81.61, p = 0.040) were independently associated with higher infarct volumes. Similarly, continuous hypotension measured as intraprocedural cumulative time spent below either 100 mmHg (aβ = 3.50 per 5 min, 95% CI 1.49-5.50, p = 0.001) or 90 mmHg mean arterial pressure (aβ = 2.91 per 5 min, 95% CI 0.74-5.10, p = 0.010) was independently associated with a larger ischemia size. In the subgroup analysis of 151 patients with an M1 middle cerebral artery occlusion, two additional factors were independently associated with a larger ischemia size: systolic blood pressure maximal relative drop and >40% drop from pretreatment value (aβ = 1.36 per 1% lower than baseline, 95% CI 0.04-2.67, p = 0.043, and aβ = 43.01, 95% CI 2.89-83.1, p = 0.036, respectively). No associations between hemodynamic parameters and post-treatment infarct size were observed in the cohort of intracranial internal carotid artery occlusion. Conclusions: In patients with ischemic stroke due to a proximal middle cerebral artery occlusion, higher pre-thrombectomy treatment systolic blood pressure is associated with a larger final infarct size. In patients treated under general anesthesia, hypotension prior to the M1 portion of middle cerebral artery recanalization is independently correlated with the post-treatment infarct volume. In this group, every 5 min spent below the mean arterial pressure threshold of 100 mmHg is associated with a 4 mL increase in ischemia volume on a post-treatment NCCT. No associations between blood pressure and final infarct volume were present in the subgroup of patients with an intracranial internal carotid artery occlusion.

Incorporating intraoperative blood pressure time-series variables to assist in prediction of acute kidney injury after type a acute aortic dissection repair: an interpretable machine learning model

BACKGROUND

Acute kidney injury (AKI) is a common and serious complication after the repair of Type A acute aortic dissection (TA-AAD). However, previous models have failed to account for the impact of blood pressure fluctuations on predictive performance. This study aims to develop machine learning (ML) models combined with intraoperative medicine and blood pressure time-series data to improve the accuracy of early prediction for postoperative AKI risk.

METHODS

Indicators reflecting the duration and depth of hypotension were obtained by analyzing continuous mean arterial pressure (MAP) monitored intraoperatively with multiple thresholds (<65, 60, 55, 50) set in the study. The predictive features were selected by logistic regression and the least absolute shrinkage and selection operator (LASSO), and 4 ML models were built based on the above features. The performance of the models was evaluated by area under receiver operating characteristic curve (AUROC), calibration curve and decision curve analysis (DCA). Shapley additive interpretation (SHAP) was used to explain the prediction models.

RESULTS

Among the indicators reflecting intraoperative hypotension, 65 mmHg showed a statistically superior difference to other thresholds in patients with or without AKI (p < .001). Among 4 models, the extreme gradient boosting (XGBoost) model demonstrated the highest AUROC: 0.800 (95% 0.683-0.917) and sensitivity: 0.717 in the testing set and was verified the best-performing model. The SHAP summary plot indicated that intraoperative urine output, cumulative time of mean arterial pressure lower than 65 mmHg outside cardiopulmonary bypass (OUT_CPB_MAP_65 time), autologous blood transfusion, and smoking were the top 4 features that contributed to the prediction model.

CONCLUSION

With the introduction of intraoperative blood pressure time-series variables, we have developed an interpretable XGBoost model that successfully achieve high accuracy in predicting the risk of AKI after TA-AAD repair, which might aid in the perioperative management of high-risk patients, particularly for intraoperative hemodynamic regulation.