Effect of Intraoperative Arterial Hypotension on the Risk of Perioperative Stroke After Noncardiac Surgery: A Retrospective Multicenter Cohort Study

The association between intraoperative low driving pressure ventilation and perioperative healthcare-associated costs: A retrospective multicenter cohort study

STUDY OBJECTIVE

A low dynamic driving pressure during mechanical ventilation for general anesthesia has been associated with a lower risk of postoperative respiratory complications (PRC), a key driver of healthcare costs. It is, however, unclear whether maintaining low driving pressure is clinically relevant to measure and contain costs. We hypothesized that a lower dynamic driving pressure is associated with lower costs.

DESIGN

Multicenter retrospective cohort study.

SETTING

Two academic healthcare networks in New York and Massachusetts, USA.

PATIENTS

46,715 adult surgical patients undergoing general anesthesia for non-ambulatory (inpatient and same-day admission) surgery between 2016 and 2021.

INTERVENTIONS

The primary exposure was the median intraoperative dynamic driving pressure.

MEASUREMENTS

The primary outcome was direct perioperative healthcare-associated costs, which were matched with data from the Healthcare Cost and Utilization Project-National Inpatient Sample (HCUP-NIS) to report absolute differences in total costs in United States Dollars (US$). We assessed effect modification by patients' baseline risk of PRC (score for prediction of postoperative respiratory complications [SPORC] ≥ 7) and effect mediation by rates of PRC (including post-extubation saturation < 90%, re-intubation or non-invasive ventilation within 7 days) and other major complications.

MAIN RESULTS

The median intraoperative dynamic driving pressure was 17.2cmH2O (IQR 14.0-21.3cmH2O). In adjusted analyses, every 5cmH2O reduction in dynamic driving pressure was associated with a decrease of -0.7% in direct perioperative healthcare-associated costs (95%CI -1.3 to -0.1%; p = 0.020). When a dynamic driving pressure below 15cmH2O was maintained, -US$340 lower total perioperative healthcare-associated costs were observed (95%CI -US$546 to -US$132; p = 0.001). This association was limited to patients at high baseline risk of PRC (n = 4059; -US$1755;97.5%CI -US$2495 to -US$986; p < 0.001), where lower risks of PRC and other major complications mediated 10.7% and 7.2% of this association (p < 0.001 and p = 0.015, respectively).

CONCLUSIONS

Intraoperative mechanical ventilation targeting low dynamic driving pressures could be a relevant measure to reduce perioperative healthcare-associated costs in high-risk patients.

The Use of the Perfusion Index to Predict Post-Induction Hypotension in Patients Undergoing General Anesthesia: A Systematic Review and Meta-Analysis

Post-induction hypotension (PIH) is a common and potentially serious complication of general anesthesia. This meta-analysis (Prospero registration number: CRD42024566321) aimed to evaluate the predictive efficacy of the perfusion index (PI) for PIH in patients undergoing general anesthesia. A comprehensive literature search was performed using multiple electronic databases (Google Scholar, EMBASE, Cochrane Library, and MEDLINE). Studies involving adult patients undergoing general anesthesia, with the PI measured before anesthesia induction and reporting PIH incidence, were included. The primary outcome was the diagnostic accuracy of the PI in predicting the probability of PIH. The secondary outcome was the pooled PIH incidence. Eight studies with 678 patients were included. The pooled incidence of PIH was 44.8% (95% confidence interval [CI]: 29.9%-60.8%). The combined sensitivity and specificity of the PI for predicting PIH were 0.84 (95% CI: 0.65-0.94) and 0.82 (95% CI: 0.70-0.90), respectively. The summary receiver operating characteristic (sROC) analysis revealed an area under curve of 0.89 (95% CI: 0.86-0.92). The Deek's funnel plot asymmetry test indicated no significant publication bias. The PI demonstrates high predictive efficacy for PIH in patients undergoing general anesthesia, indicating that it can be a valuable tool for identifying those at risk of PIH.

Predictive ability of hypotension prediction index and machine learning methods in intraoperative hypotension: a systematic review and meta-analysis

INTRODUCTION

Intraoperative Hypotension (IOH) poses a substantial risk during surgical procedures. The integration of Artificial Intelligence (AI) in predicting IOH holds promise for enhancing detection capabilities, providing an opportunity to improve patient outcomes. This systematic review and meta analysis explores the intersection of AI and IOH prediction, addressing the crucial need for effective monitoring in surgical settings.

METHOD

A search of Pubmed, Scopus, Web of Science, and Embase was conducted. Screening involved two-phase assessments by independent reviewers, ensuring adherence to predefined PICOS criteria. Included studies focused on AI models predicting IOH in any type of surgery. Due to the high number of studies evaluating the hypotension prediction index (HPI), we conducted two sets of meta-analyses: one involving the HPI studies and one including non-HPI studies. In the HPI studies the following outcomes were analyzed: cumulative duration of IOH per patient, time weighted average of mean arterial pressure < 65 (TWA-MAP < 65), area under the threshold of mean arterial pressure (AUT-MAP), and area under the receiver operating characteristics curve (AUROC). In the non-HPI studies, we examined the pooled AUROC of all AI models other than HPI.

RESULTS

43 studies were included in this review. Studies showed significant reduction in IOH duration, TWA-MAP < 65 mmHg, and AUT-MAP < 65 mmHg in groups where HPI was used. AUROC for HPI algorithms demonstrated strong predictive performance (AUROC = 0.89, 95CI). Non-HPI models had a pooled AUROC of 0.79 (95CI: 0.74, 0.83).

CONCLUSION

HPI demonstrated excellent ability to predict hypotensive episodes and hence reduce the duration of hypotension. Other AI models, particularly those based on deep learning methods, also indicated a great ability to predict IOH, while their capacity to reduce IOH-related indices such as duration remains unclear.

Postoperative haemoglobin and anaemia-associated ischaemic events after major noncardiac surgery: A sex-stratified cohort study

STUDY OBJECTIVE

To determine the sex-specific associations between postoperative haemoglobin and mortality or complications reflecting ischaemia or inadequate oxygen supply after major noncardiac surgery.

DESIGN

A retrospective cohort study with prospective validation.

SETTING

A large university hospital health system in China.

PATIENTS

Men and women undergoing elective major noncardiac surgery.

INTERVENTIONS AND MEASUREMENTS

The primary exposure was nadir haemoglobin within 48 h after surgery. The outcome of interest was a composite of postoperative mortality or ischaemic events including myocardial injury, acute kidney injury and stroke within hospitalisation.

MAIN RESULTS

The study included 26,049 patients (15,757 men and 10,292 women). Low postoperative haemoglobin was a strong predictor of the composite outcome in both sexes, with the risk progressively increasing as the nadir haemoglobin concentration dropped below 130 g l-1 in men and 120 g l-1 in women (adjusted odds ratio [OR] 1.43, 95% CI 1.37-1.50 in men, and OR 1.45, 95% CI 1.35-1.55 in women, per 10 g l-1 decrease in postoperative nadir haemoglobin). Above these sex-specific thresholds, the change of nadir haemoglobin was no longer associated with odds of the composite outcome in either men or women. There was no significant interaction between patient sex and the association between postoperative haemoglobin and the composite outcome (Pinteraction = 0.673). Validation in an external prospective cohort (n = 2120) with systematic postoperative troponin and creatinine measurement confirmed our findings.

CONCLUSIONS

Postoperative haemoglobin levels following major noncardiac surgery were nonlinearly associated with ischaemic complications or mortality, without any clinically important interaction with patient sex.

Intraoperative intensive blood pressure management strategy and the outcome of patients who had an acute ischaemic stroke undergoing endovascular treatment under general anaesthesia: study protocol for a prospective randomised controlled trial

BackgroundEndovascular thrombectomy is the recommended treatment for acute ischaemic stroke, but the optimal blood pressure management strategy during the procedure under general anaesthesia remains controversial. In this study protocol, we propose an intraoperative intensive blood pressure range (110-140 mm Hg systolic blood pressure) based on a retrospective analysis and extensive literature review. By comparing the outcomes of patients who had an acute ischaemic stroke undergoing mechanical thrombectomy under general anaesthesia with standard blood pressure management (140-180 mm Hg systolic blood pressure) versus intensive blood pressure management, we aim to determine the impact of intraoperative intensive blood pressure management strategy on patient prognosis.

METHODS AND ANALYSIS

The study is a double-blinded, randomised, controlled study, with patients randomised into either the standard blood pressure management group or the intensive blood pressure management group. The primary endpoint of the study will be the sequential analysis of modified Rankin Scale scores at 90 days after mechanical thrombectomy.

ETHICS AND DISSEMINATION

The study has been approved by the ethics committee of Shanghai Changhai Hospital with an approval number CHEC2023-015. The results of the study will be published in peer-reviewed international journals.

TRIAL REGISTRATION NUMBER

ChiCTR2300070764.

Incidence and risk factors of peri-operative stroke in major non-cardiovascular, non-neurologic surgery-A retrospective register-based cohort study

BACKGROUND

Peri-operative stroke is a rare but serious surgical complication. Both overt and covert stroke, occurring in approximately 0.1% and 7% of cases, respectively, are associated with significant long-term effects and increased morbidity.

METHODS

Retrospective register data for patients >18 years old, presenting for major non-cardiovascular, non-neurosurgical and non-ambulatory surgical procedures at 23 hospitals in Sweden between 2007 and 2014 was collected and linked with various quality registers. The primary outcome was stroke within 30 days from surgery. Using multivariable logistic regression, significant independent risk factors influencing the primary outcome were identified and their adjusted odds ratios (ORs) were calculated. Mortality was assessed, along with the composite score of days alive and at home within 30 days after surgery (DAH 30).

RESULTS

In total, 318,017 patients were included, with 687 (0.22%) suffering a stroke within 30 days of surgery. The strongest significant risk factors included: increasing ASA-class (OR [95% confidence interval, CI]: 2.23 [1.53-3.36], 3.91 [2.68-5.93] and 7.82 [5.03-12.5] for ASA 2, 3 and 4, respectively) and age (OR [95% CI]: 4.47 [2.21-10.3], 9.9 [5.15-22.1], 16.3 [8.48-36.5] and 21 [10.6-48.1], for age 45-59, 60-74, 75-89 and >90, respectively), along with non-elective procedures, male gender and a history of cerebrovascular disease (OR [95%]: 2.72 [2.25-3.27]). Mortality was increased and DAH 30 was reduced in patients suffering a stroke.

CONCLUSIONS

Increasing ASA-class and age was clearly associated with an increased risk of peri-operative stroke, which in turn was associated with increased mortality and poorer outcome. Detailed pre-operative risk stratification and individualised peri-operative management could potentially improve patient-centred outcomes and, in turn, have positive implications for public health.

Intraoperative Use of Phenylephrine versus Ephedrine and Postoperative Delirium: A Multicenter Retrospective Cohort Study

BACKGROUND

The treatment of intraoperative hypotension with phenylephrine may impair cerebral perfusion through vasoconstriction, which has been linked to postoperative delirium. The hypothesis was that intraoperative administration of phenylephrine, compared to ephedrine, is associated with higher odds of postoperative delirium.

METHODS

A total of 103,094 hospitalized adults undergoing general anesthesia for noncardiac, non-neurosurgical procedures between 2008 and 2020 at two tertiary academic healthcare networks in Massachusetts were included in this multicenter hospital registry study. The primary exposure was the administration of phenylephrine versus ephedrine during surgery, and the primary outcome was postoperative delirium within 7 days. Multivariable logistic regression analyses adjusted for a priori defined confounding variables including patient demographics, comorbidities, and procedural factors including magnitude of intraoperative hypotension were applied.

RESULTS

Between the two healthcare networks, 78,982 (76.6%) patients received phenylephrine, and 24,112 (23.4%) patients received ephedrine during surgery; 770 patients (0.8%) developed delirium within 7 days. The median (interquartile range) total intraoperative dose of phenylephrine was 1.0 (0.2 to 3.3) mg and 10.0 (10.0 to 20.0) mg for ephedrine. In adjusted analyses, the administration of phenylephrine, compared to ephedrine, was associated with higher odds of developing postoperative delirium within 7 days (adjusted odds ratio, 1.35; 95% CI, 1.06 to 1.71; and adjusted absolute risk difference, 0.2%; 95% CI, 0.1 to 0.3%; P = 0.015). A keyword and manual chart review-based approach in a subset of 45,465 patients further validated these findings (delirium incidence, 3.2%; adjusted odds ratio, 1.88; 95% CI, 1.49 to 2.37; P < 0.001). Fractional polynomial regression analysis further indicated a dose-dependent effect of phenylephrine (adjusted coefficient, 0.08; 95% CI, 0.02 to 0.14; P = 0.013, per each μg/kg increase in the cumulative phenylephrine dose).

CONCLUSIONS

The administration of phenylephrine compared to ephedrine during general anesthesia was associated with higher odds of developing postoperative delirium. Based on these data, clinical trials are warranted to determine whether favoring ephedrine over phenylephrine for treatment of intraoperative hypotension can reduce delirium after surgery.

EDITOR’S PERSPECTIVE

Differences in the Incidence of Hypotension and Hypertension between Sexes during Non-Cardiac Surgery: A Systematic Review and Meta-Analysis

Background: Major determinants of blood pressure (BP) include sex and age. In youth, females have lower BP than males, yet in advanced age, more pronounced BP increases result in higher average BPs in females over 65. This hypothesis-generating study explored whether age-related BP divergence impacts the incidence of sex-specific intraoperative hypotension (IOH) or hypertension. Methods: We systematically searched PubMed and Embase databases for studies reporting intraoperative BP in males and females in non-cardiac surgery. We analyzed between-sex differences in the incidence of IOH and intraoperative hypertension (primary endpoint). Results: Among 793 identified studies, 14 were included in this meta-analysis, comprising 1,110,636 patients (56% female). While sex was not associated with IOH overall (females: OR 1.10, 95%CI [0.98-1.23], I2 = 99%), a subset of studies with an average age ≥65 years showed increased exposure to IOH in females (OR 1.17, 95%CI [1.01-1.35], I2 = 94%). One study reported sex-specific differences in intraoperative hypertension, with a higher incidence in females (31% vs. 28%). Conclusions: While sex-specific reporting on intraoperative BP was limited, IOH did not differ between sexes. However, an exploratory subgroup analysis offers the hypothesis that females of advanced age may face an increased risk of IOH, warranting further investigation.

ABO blood types may affect transient neurological events after surgical revascularization in patients with moyamoya disease: a retrospective single center study

BACKGROUND

Moyamoya disease (MMD) is a cerebrovascular disease with unknown cause. Patients with MMD disease usually experience transient neurological events (TNEs) after revascularization surgery. This retrospective single-center study was aimed to explore the risk factors of postoperative TNEs after surgical revascularization in patients with MMD.

METHODS

We selected 324 patients who underwent surgical revascularization between January 2017 and September 2022 in our center. The perioperative characteristics of the patients were recorded and the outcome was TNEs after surgery. An analysis of risk factors contributing to postoperative TNEs by using logistic regression model.

RESULTS

Three hundred twelve patients were enrolled, and the incidence of postoperative TNEs was 34% in our study. Males were more likely to suffer from postoperative TNEs (OR = 2.344, p = 0.002). Preoperative ischemic presentation (OR = 1.849, p = 0.048) and intraoperative hypotension (OR = 2.332, p = 0.002) were associated with postoperative TNEs. Compared to patients with blood type O, patients with blood type A (OR = 2.325, p = 0.028), B (OR = 2.239, p = 0.027) and AB (OR = 2.938, p = 0.019) had a significantly higher incidence of postoperative TNEs. A risk prediction model for postoperative TNEs was established, and the established risk prediction area under the receiver operating characteristic curve (ROC) of the model was 0.741.

CONCLUSIONS

Males, preoperative ischemic presentation and intraoperative hypotension were associated with postoperative TNEs. We also found a possible link between postoperative TNEs and ABO blood types after surgical revascularization for moyamoya patients.

Prevention of perioperative stroke in patients undergoing non-cardiac surgery

About 300 million adults undergo non-cardiac surgery annually. Although, in this setting, the incidence of perioperative stroke is low, the absolute number of patients experiencing a stroke is substantial. Furthermore, most patients with this complication will die or end up with severe disability. Covert brain infarctions are more frequent than overt strokes and are associated with postoperative delirium, cognitive decline, and cerebrovascular events at 1 year after surgery. Evidence shows that traditional stroke risk factors including older age, hypertension, and atrial fibrillation are also associated with perioperative stroke; previous stroke is the strongest risk factor for perioperative stroke. Increasing evidence also suggests the pathogenic role of perioperative events, such as hypotension, new atrial fibrillation, paradoxical embolism, and bleeding. Clinicians involved in perioperative care should be aware of this evidence on prevention strategies to improve patient outcomes after non-cardiac surgery.

Intraoperative Hypotension and Postoperative Stroke in Older Patients Who Had Brain Tumor Resections: A Retrospective Cohort Analysis

BACKGROUND

At some level, intraoperative hypotension causes strokes. Elderly neurosurgical patients are presumably at especially high risk. We tested the primary hypothesis that intraoperative hypotension is associated with postoperative stroke in older patients undergoing brain tumor resection.

METHODS

Patients >65 years old who had elective craniotomy for tumor resections were included. The primary exposure was the area under the threshold of intraoperative hypotension. The primary outcome was newly diagnosed ischemic stroke within 30 days, confirmed by scheduled brain imaging.

RESULTS

Among 724 eligible patients, 98 (13.5%) had strokes within 30 days after surgery, 86% of which were clinically silent. Curves of lowest mean arterial pressure versus stroke incidence suggested a threshold at 75 mm Hg. Area under the threshold of mean arterial pressure below 75 mm Hg was therefore incorporated into multivariable modeling. There was no association of area below 75 mm Hg and stroke (adjusted odds ratio, 1.00; 95% confidence interval, 1.00-1.00). The adjusted odds ratio for area below 75 mm Hg between 1 and 148 mm Hg × minutes was 1.21 (95% confidence interval, 0.23-6.23). When the area below 75 mm Hg exceeded 1117 mm Hg × minutes, the association remained insignificant. In contrast, malignant tumor and history of previous stroke or myocardial ischemia were associated with strokes.

CONCLUSIONS

Postoperative strokes were common in older patients who underwent brain tumor resection, with about 14% having ischemic cerebrovascular events within 30 days, of which 86% were clinically silent. Malignant brain tumors and previous ischemic vascular events were associated with postoperative strokes, but area under 75 mm Hg was not.

Association of intraoperative hypotension and severe postoperative complications during non-cardiac surgery in adult patients: A systematic review and meta-analysis

Background

Intraoperative hypotension (IOH) is a common side effect of non-cardiac surgery that might induce poor postoperative outcomes. The relationship between the IOH and severe postoperative complications is still unclear. Thus, we summarized the existing literature to evaluate whether IOH contributes to developing severe postoperative complications during non-cardiac surgery.

Methods

We conducted a comprehensive search of PubMed, Embase, Cochrane Library, Web of Science, and the CBM from inception to 15 September 2022. The primary outcomes were 30-day mortality, acute kidney injury (AKI), major adverse cardiac events (myocardial injury or myocardial infarction), postoperative cognitive dysfunction (POCD), and postoperative delirium (POD). Secondary outcomes included surgical-site infection (SSI), stroke, and 1-year mortality.

Results

72 studies (3 randomized; 69 non-randomized) were included in this study. Low-quality evidence showed IOH resulted in an increased risk of 30-day mortality (OR, 1.85; 95% CI, 1.30-2.64; P < .001), AKI (OR, 2.69; 95% CI, 2.15-3.37; P < .001), and stroke (OR, 1.33; 95% CI, 1.21-1.46; P < .001) after non-cardiac surgery than non-IOH. Very low-quality evidence showed IOH was associated with a higher risk of myocardial injury (OR, 2.00; 95% CI, 1.17-3.43; P = .01), myocardial infarction (OR, 2.11; 95% CI, 1.41-3.16; P < .001), and POD (OR, 2.27; 95% CI, 1.53-3.38; P < .001). Very low-quality evidence showed IOH have a similar incidence of POCD (OR, 2.82; 95% CI, 0.83-9.50; P = .10) and 1-year-mortality (OR, 1.66; 95% CI, 0.65-4.20; P = .29) compared with non-IOH in non-cardiac surgery.

Conclusion

Our results suggest IOH was associated with an increased risk of severe postoperative complications after non-cardiac surgery than non-IOH. IOH is a potentially avoidable hazard that should be closely monitored during non-cardiac surgery.

Risk Factors for Cerebral Infarction After Microsurgical Clipping of Hunt-Hess Grade 0-2 Single Intracranial Aneurysm: A Retrospective Study

OBJECTIVE

The study aimed to explore risk factors for cerebral infarction after microsurgical clipping in patients with Hunt-Hess grade 0-2 single intracranial aneurysms.

METHODS

A total of 137 patients with Hunt-Hess grade 0-2 single intracranial aneurysms treated with microsurgical clipping between March 2017 and December 2020 were retrospectively enrolled. Patients were divided into 2 groups on the basis of the occurrence of cerebral infarction after surgery.

RESULTS

Of 137 enrolled patients, 14 (10.22%) showed cerebral infarction symptoms after surgery. Univariate analysis indicated that ruptured aneurysm status, aneurysm rupture during surgery, history of transient ischemic attack (TIA)/stroke, aneurysm size ≥7 mm, temporary clipping, intraoperative systolic hypotension (IOH), and occurrences of intraoperative motor-evoked potentials change were significantly related to postoperative cerebral infarction (PCI). However, using multivariate regression, only history of TIA/stroke (odds ratio = 0.124; 95% confidence interval [CI] = 0.021-0.748, P = 0.023) and IOH (odds ratio = 0.032; 95% CI = 0.005-0.210, P < 0.001) were independent predictors for PCI. Receiver operating characteristic curve analysis showed that the critical duration of temporary clipping and IOH that minimized the risk of PCI was 5.5 minutes and 7.5 minutes, respectively.

CONCLUSIONS

Our study identified history of TIA/stroke and IOH as independent risk factors for cerebral infarction after microsurgical clipping.

Complications of Vascular Disease

Vascular diseases and their sequelae increase perioperative risk for noncardiac surgical patients. In this review, the authors discuss vascular diseases, their epidemiology and pathophysiology, risk stratification, and management strategies to reduce adverse perioperative outcomes.

Carbon Dioxide, Blood Pressure, and Perioperative Stroke: A Retrospective Case-Control Study

BACKGROUND

The relationship between intraoperative physiology and postoperative stroke is incompletely understood. Preliminary data suggest that either hypo- or hypercapnia coupled with reduced cerebrovascular inflow (e.g., due to hypotension) can lead to ischemia. This study tested the hypothesis that the combination of intraoperative hypotension and either hypo- or hypercarbia is associated with postoperative ischemic stroke.

METHODS

We conducted a retrospective, case-control study via the Multicenter Perioperative Outcomes Group. Noncardiac, nonintracranial, and nonmajor vascular surgical cases (18 yr or older) were extracted from five major academic centers between January 2004 and December 2015. Ischemic stroke cases were identified via manual chart review and matched to controls (1:4). Time and reduction below key mean arterial blood pressure thresholds (less than 55 mmHg, less than 60 mmHg, less than 65 mmHg) and outside of specific end-tidal carbon dioxide thresholds (30 mmHg or less, 35 mmHg or less, 45 mmHg or greater) were calculated based on total area under the curve. The association between stroke and total area under the curve values was then tested while adjusting for relevant confounders.

RESULTS

In total, 1,244,881 cases were analyzed. Among the cases that screened positive for stroke (n = 1,702), 126 were confirmed and successfully matched with 500 corresponding controls. Total area under the curve was significantly associated with stroke for all thresholds tested, with the strongest combination observed with mean arterial pressure less than 55 mmHg (adjusted odds ratio per 10 mmHg-min, 1.17 [95% CI, 1.10 to 1.23], P < 0.0001) and end-tidal carbon dioxide 45 mmHg or greater (adjusted odds ratio per 10 mmHg-min, 1.11 [95% CI, 1.10 to 1.11], P < 0.0001). There was no interaction effect observed between blood pressure and carbon dioxide.

CONCLUSIONS

Intraoperative hypotension and carbon dioxide dysregulation may each independently increase postoperative stroke risk.

EDITOR’S PERSPECTIVE

Association Between Intraoperative Arterial Hypotension and Postoperative Delirium After Noncardiac Surgery: A Retrospective Multicenter Cohort Study

BACKGROUND

It is unclear whether intraoperative arterial hypotension is associated with postoperative delirium. We hypothesized that intraoperative hypotension within a range frequently observed in clinical practice is associated with increased odds of delirium after surgery.

METHODS

Adult noncardiac surgical patients undergoing general anesthesia at 2 academic medical centers between 2005 and 2017 were included in this retrospective cohort study. The primary exposure was intraoperative hypotension, defined as the cumulative duration of an intraoperative mean arterial pressure (MAP) <55 mm Hg, categorized into and short (<15 minutes; median [interquartile range {IQR}], 2 [1-4] minutes) and prolonged (≥15 minutes; median [IQR], 21 [17-31] minutes) durations of intraoperative hypotension. The primary outcome was a new diagnosis of delirium within 30 days after surgery. In secondary analyses, we assessed the association between a MAP decrease of >30% from baseline and postoperative delirium. Multivariable logistic regression adjusted for patient- and procedure-related factors, including demographics, comorbidities, and markers of procedural severity, was used.

RESULTS

Among 316,717 included surgical patients, 2183 (0.7%) were diagnosed with delirium within 30 days after surgery; 41.7% and 2.6% of patients had a MAP <55 mm Hg for a short and a prolonged duration, respectively. A MAP <55 mm Hg was associated with postoperative delirium compared to no hypotension (short duration of MAP <55 mm Hg: adjusted odds ratio [ORadj], 1.22; 95% confidence interval [CI], 1.11-1.33; P < .001 and prolonged duration of MAP <55 mm Hg: ORadj, 1.57; 95% CI, 1.27-1.94; P < .001). Compared to a short duration of a MAP <55 mm Hg, a prolonged duration of a MAP <55 mm Hg was associated with greater odds of postoperative delirium (ORadj, 1.29; 95% CI, 1.05-1.58; P = .016). The association between intraoperative hypotension and postoperative delirium was duration-dependent (ORadj for every 10 cumulative minutes of MAP <55 mm Hg: 1.06; 95% CI, 1.02-1.09; P =.001) and magnified in patients who underwent surgeries of longer duration (P for interaction = .046; MAP <55 mm Hg versus no MAP <55 mm Hg in patients undergoing surgery of >3 hours: ORadj, 1.40; 95% CI, 1.23-1.61; P < .001). A MAP decrease of >30% from baseline was not associated with postoperative delirium compared to no hypotension, also when additionally adjusted for the cumulative duration of a MAP <55 mm Hg (short duration of MAP decrease >30%: ORadj, 1.13; 95% CI, 0.91-1.40; P = .262 and prolonged duration of MAP decrease >30%: ORadj, 1.19; 95% CI, 0.95-1.49; P = .141).

CONCLUSIONS

In patients undergoing noncardiac surgery, a MAP <55 mm Hg was associated with a duration-dependent increase in odds of postoperative delirium. This association was magnified in patients who underwent surgery of long duration.

The association of nitrous oxide on length of stay in the postanesthesia care unit: a retrospective observational study

PURPOSE

To assess whether intraoperative use of nitrous oxide (N₂O) as an adjunct to general anesthesia is associated with a shorter length of stay in the postanesthesia care unit (PACU).

METHODS

We analyzed data from adult patients who underwent non-cardiothoracic surgery under general anesthesia between May 2008 and December 2018. We assessed the association between intraoperative low- and high-dose N₂O and PACU length of stay.

RESULTS

A total of 148,284 patients were included in the primary analysis. After adjusting for a priori defined confounders, a high dose of N₂O significantly decreased PACU length of stay, with a calculated difference of -9.1 min (95% confidence interval [CI], -10.5 to -7.7; P < 0.001). Patients who received high-dose N₂O had a lower incidence of both short- and prolonged-duration of intraoperative hypotension (adjusted odds ratio [aOR], 0.85; 95% CI, 0.83 to 0.88; P < 0.001 and aOR, 0.76; 95% CI, 0.73 to 0.80; P < 0.001, respectively) and received a lower total intraoperative vasopressor dose (-0.04 mg of norepinephrine equivalents; 95% CI, -0.06 to -0.01; P = 0.01). The effect of high-dose N₂O on PACU length of stay was modified by surgical complexity (adjusted absolute difference: -26.1 min; 95% CI, -29.2 to -23.1; P < 0.001; P for interaction < 0.001), and most pronounced in patients who underwent complex surgery and received intraoperative antiemetic therapy (adjusted absolute difference: -38.9 min; 95% CI, -43.1 to -34.6; P < 0.001; P for interaction < 0.001).

CONCLUSIONS

Nitrous oxide was dose-dependently associated with a decreased PACU length of stay. The effect was clinically relevant (> 30 min difference) in patients who underwent complex surgical procedures and received intraoperative antiemetic therapy.