Implementation of closed-loop-assisted intra-operative goal-directed fluid therapy during major abdominal surgery: A case-control study with propensity matching

Assisted Fluid Management and Sublingual Microvascular Flow During High-Risk Abdominal Surgery: A Randomized Controlled Trial

BACKGROUND

Implementation of goal-directed fluid therapy (GDFT) protocols remains low. Protocol compliance among anesthesiologists tends to be suboptimal owing to the high workload and the attention required for implementation. The assisted fluid management (AFM) system is a novel decision support tool designed to help clinicians apply GDFT protocols. This system predicts fluid responsiveness better than anesthesia practitioners do and achieves higher stroke volume (SV) and cardiac index values during surgery. We tested the hypothesis that an AFM-guided GDFT strategy would also be associated with better sublingual microvascular flow compared to a standard GDFT strategy.

METHODS

This bicenter, parallel, 2-arm, prospective, randomized controlled, patient and assessor-blinded, superiority study considered for inclusion all consecutive patients undergoing high-risk abdominal surgery who required an arterial catheter and uncalibrated SV monitoring. Patients having standard GDFT received manual titration of fluid challenges to optimize SV while patients having an AFM-guided GDFT strategy received fluid challenges based on recommendations from the AFM software. In all patients, fluid challenges were standardized and titrated per 250 mL and vasopressors were administered to maintain a mean arterial pressure >70 mm Hg. The primary outcome (average of each patient's intraoperative microvascular flow index (MFI) across 4 intraoperative time points) was analyzed using a Mann-Whitney U test and the treatment effect was estimated with a median difference between groups with a 95% confidence interval estimated using the bootstrap percentile method (with 1000 replications). Secondary outcomes included SV, cardiac index, total amount of fluid, other microcirculatory variables, and postoperative lactate.

RESULTS

A total of 86 patients were enrolled over a 7-month period. The primary outcome was significantly higher in patients with AFM (median [Q1-Q3]: 2.89 [2.84-2.94]) versus those having standard GDFT (2.59 [2.38-2.78] points, median difference 0.30; 95% confidence interval [CI], 0.19-0.49; P < .001). Cardiac index and SVI were higher (3.2 ± 0.5 vs 2.7 ± 0.7 l.min-1.m-2; P = .001 and 42 [35-47] vs 36 [32-43] mL.m-2; P = .018) and arterial lactate concentration was lower at the end of the surgery in patients having AFM-guided GDFT (2.1 [1.5-3.1] vs 2.9 [2.1-3.9] mmol.L-1; P = .026) than patients having standard GDFT strategy. Patients having AFM received a higher fluid volume but 3 times less norepinephrine than those receiving standard GDFT (P < .001).

CONCLUSIONS

Use of an AFM-guided GDFT strategy resulted in higher sublingual microvascular flow during surgery compared to use of a standard GDFT strategy. Future trials are necessary to make conclusive recommendations that will change clinical practice.

Closed-loop anesthesia: foundations and applications in contemporary perioperative medicine

A closed-loop automatically controls a variable using the principle of feedback. Automation within anesthesia typically aims to improve the stability of a controlled variable and reduce workload associated with simple repetitive tasks. This approach attempts to limit errors due to distractions or fatigue while simultaneously increasing compliance to evidence based perioperative protocols. The ultimate goal is to use these advantages over manual care to improve patient outcome. For more than twenty years, clinical studies in anesthesia have demonstrated the superiority of closed-loop systems compared to manual control for stabilizing a single variable, reducing practitioner workload, and safely administering therapies. This research has focused on various closed-loops that coupled inputs and outputs such as the processed electroencephalogram with propofol, blood pressure with vasopressors, and dynamic predictors of fluid responsiveness with fluid therapy. Recently, multiple simultaneous independent closed-loop systems have been tested in practice and one study has demonstrated a clinical benefit on postoperative cognitive dysfunction. Despite their advantages, these tools still require that a well-trained practitioner maintains situation awareness, understands how closed-loop systems react to each variable, and is ready to retake control if the closed-loop systems fail. In the future, multiple input multiple output closed-loop systems will control anesthetic, fluid and vasopressor titration and may perhaps integrate other key systems, such as the anesthesia machine. Human supervision will nonetheless always be indispensable as situation awareness, communication, and prediction of events remain irreplaceable human factors.

Perioperative Fluid and Vasopressor Therapy in 2050: From Experimental Medicine to Personalization Through Automation

Intravenous (IV) fluids and vasopressor agents are key components of hemodynamic management. Since their introduction, their use in the perioperative setting has continued to evolve, and we are now on the brink of automated administration. IV fluid therapy was first described in Scotland during the 1832 cholera epidemic, when pioneers in medicine saved critically ill patients dying from hypovolemic shock. However, widespread use of IV fluids only began in the 20th century. Epinephrine was discovered and purified in the United States at the end of the 19th century, but its short half-life limited its implementation into patient care. Advances in venous access, including the introduction of the central venous catheter, and the ability to administer continuous infusions of fluids and vasopressors rather than just boluses, facilitated the use of fluids and adrenergic agents. With the advent of advanced hemodynamic monitoring, most notably the pulmonary artery catheter, the role of fluids and vasopressors in the maintenance of tissue oxygenation through adequate cardiac output and perfusion pressure became more clearly established, and hemodynamic goals could be established to better titrate fluid and vasopressor therapy. Less invasive hemodynamic monitoring techniques, using echography, pulse contour analysis, and heart-lung interactions, have facilitated hemodynamic monitoring at the bedside. Most recently, advances have been made in closed-loop fluid and vasopressor therapy, which apply computer assistance to interpret hemodynamic variables and therapy. Development and increased use of artificial intelligence will likely represent a major step toward fully automated hemodynamic management in the perioperative environment in the near future. In this narrative review, we discuss the key events in experimental medicine that have led to the current status of fluid and vasopressor therapies and describe the potential benefits that future automation has to offer.

Impact of fluid and haemodynamic management in cytoreductive surgery with hyperthermic intraperitoneal chemotherapy on postoperative outcomes - A systematic review

Background and Aims

Cytoreduction surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC) is an extensive surgery associated with significant fluid shift and blood loss. The haemodynamic management and fluid therapy protocol may impact postoperative outcomes. This systematic review was conducted to find the effect of haemodynamic monitoring and perioperative fluid therapy in CRS-HIPEC on postoperative outcomes.

Methods

We searched PubMed, Scopus and Google Scholar. All studies published between 2010 and 2022 involving CRS-HIPEC surgeries that compared the effect of fluid therapy and haemodynamic monitoring on postoperative outcomes were included. Keywords for database searches included a combination of Medical Subject Headings terms and plain text related to the CRS-HIPEC procedure. The risk of bias and the certainty assessment were done by Risk of Bias-2 and the methodological index for non-randomised studies.

Results

The review included 16 published studies out of 388 articles. The studies were heterogeneous concerning the design type and parameter measures. The studies with goal-directed fluid therapy protocol had a duration of intensive care unit (ICU) stay that varied from 1 to 20 days, while mortality varied from 0% to 9.5%. The choice of fluid, crystalloid versus colloid, remains inconclusive. The studies that compared crystalloids and colloids for perioperative fluid management did not show a difference in clinical outcomes.

Conclusion

The interpretation of the available literature is challenging because the definitions of various fluid regimens and haemodynamic goals are not uniform among studies. An individualised approach to perioperative fluid therapy and a justified dynamic index cut-off for haemodynamic monitoring seem reasonable for CRS-HIPEC procedures.

Goal-directed fluid management associates with fewer postoperative fluid collections in pancreatoduodenectomy patients

BACKGROUND

The association between perioperative fluid management and complications in pancreatoduodenectomy patients remains controversial. We explored the association between fluid management and radiological signs of complications.

METHODS

We examined pancreatoduodenectomy patients operated between July 2014 and December 2015 (n = 125) and between January 2017 and June 2018 (n = 124). The first cohort received intraoperative fluid management according to a goal-directed strategy and the second cohort was treated conventionally. We analyzed fluid administration, edema visible in computed tomography (CT) scans seven days postoperatively, and radiological signs of complications occurring up to 30 days. We performed multivariable logistic regression analyses to identify risk factors for fluid collections.

RESULTS

No statistically significant difference in postoperative edema via CT scans emerged between the fluid management groups. However, the intraperitoneal space expanded in patients with severe Clavien-Dindo complications compared with patients experiencing mild or no complications (19.1% (IQR 10.4-40.5) vs 2.5% (IQR -7.9-16.6), p = 0.004). Fluid collections were less frequent in the goal-directed group than in the conventional fluid management group (16.8% vs 34.7%, p = 0.001). Risk factors for fluid collections included main pancreatic duct size ≤3 mm, less intraoperative fluid volume accompanying conventional fluid management, a lower postoperative urine output, and postoperative congestive heart failure. The goal-directed group received more intraoperative fluids than the conventional fluid management group and postoperative urine output was higher in the goal-directed group on postoperative days 1-3.

CONCLUSIONS

Optimization of intraoperative fluid management through target-controlled strategies and early diuresis were associated with a lower frequency of fluid collections in postoperative CT.

Arterial Lactate Concentration at the End of Liver Transplantation is Independently Associated With One-Year Mortality

BACKGROUND

Liver transplant patients who develop hyperlactatemia are at increased risk of postoperative morbidity and short-term mortality, but there are few data on longer-term outcomes. We therefore investigated if arterial lactate concentration obtained immediately after surgery, at the time of admission to the intensive care unit (ICU), was associated with 1-year mortality.

METHODS

In this retrospective cohort study, all patients who underwent liver transplant surgery from a deceased donor between September 2013 and December 2019 were screened for inclusion. Patients who underwent combined transplantation surgery and those with a history of previous liver transplantation (ie, redo surgery) were not included. Logistic regression modeling included univariate and multivariate analyses. Receiver operating characteristic curves and areas under the curves were calculated. Lactate thresholds and association with outcome were analyzed for specificity, sensitivity, and Youden's index.

RESULTS

Of 226 patients included, 18.4% died within 1 year of liver transplantation. Immediate postoperative lactate concentration was independently associated with 1-year mortality with an adjusted odds ratio of 1.35 (95% CI 1.16-1.59; P < .001) per mmol/L increase in lactate and an area under the curve of 0.80 (95% CI 0.72-0.87; P < .001). A lactate concentration of 2.25 mmol/L (cutoff determined using Youden's index) was associated with increased 1-year mortality with a sensitivity of 0.71 and a specificity of 0.72.

CONCLUSIONS

Increased arterial lactate concentration on admission to the intensive care unit immediately after orthotopic liver transplantation is independently associated with increased 1-year mortality.

Optimal Perioperative Fluid Therapy Associates with Fewer Complications After Pancreaticoduodenectomy

BACKGROUND

Optimal fluid management in pancreaticoduodenectomy patients remains contested. We aimed to examine the association between perioperative fluid administration and postoperative complications.

METHODS

We studied 168 pancreaticoduodenectomy patients operated in 2015 (n = 93) or 2017 (n = 75) at Helsinki University Hospital. In 2015, patients received intraoperative fluids following a goal-directed approach and, in 2017, according to anesthesiologist's clinical practice (conventional fluid management). We analyzed the differences in perioperative fluid administration between the groups, specifically examining the occurrence of severe complications (Clavien-Dindo ≥ III), pancreatic fistulas, cardiovascular complications, and the length of hospital stay.

RESULTS

The goal-directed group received more intraoperative fluids than the conventional fluid management group (12.0 ml/kg/h vs. 8.3 ml/kg/h, p < 0.001). Urine output (770 ml vs. 575 ml, p = 0.004) and intraoperative fluid balance (9.4 ml/kg/h vs. 6.3 ml/kg/h, p < 0.001) were higher in the goal-directed group than in the conventional fluid management group. Severe surgical complications (19.4% vs. 38.7%, p = 0.009) as well as clinically relevant pancreatic fistulas (1.1% vs. 10.7%, p = 0.011) occurred more frequently in patients receiving conventional fluid management. Moreover, the conventional fluid management group experienced longer hospital stays (9.0 vs. 11.5 days, p = 0.02). Lower intraoperative fluid volume accompanying conventional fluid management was associated with a higher risk of severe postoperative complications compared with higher volume in the goal-directed group (odds ratio 2.58 (95% confidence interval 1.04-6.42), p = 0.041).

CONCLUSIONS

The goal-directed group experienced severe complications less frequently. Our findings indicate that optimizing the intraoperative fluid administration benefits patients, while adopting a too-restrictive approach represents an inferior choice.

Closed-Loop Controlled Fluid Administration Systems: A Comprehensive Scoping Review

Physiological Closed-Loop Controlled systems continue to take a growing part in clinical practice, offering possibilities of providing more accurate, goal-directed care while reducing clinicians’ cognitive and task load. These systems also provide a standardized approach for the clinical management of the patient, leading to a reduction in care variability across multiple dimensions. For fluid management and administration, the advantages of closed-loop technology are clear, especially in conditions that require precise care to improve outcomes, such as peri-operative care, trauma, and acute burn care. Controller design varies from simplistic to complex designs, based on detailed physiological models and adaptive properties that account for inter-patient and intra-patient variability; their maturity level ranges from theoretical models tested in silico to commercially available, FDA-approved products. This comprehensive scoping review was conducted in order to assess the current technological landscape of this field, describe the systems currently available or under development, and suggest further advancements that may unfold in the coming years. Ten distinct systems were identified and discussed.

Impact of conventional vs. goal-directed fluid therapy on urethral tissue perfusion in patients undergoing liver surgery: A pilot randomised controlled trial

BACKGROUND

Although fluid administration is a key strategy to optimise haemodynamic status and tissue perfusion, optimal fluid administration during liver surgery remains controversial.

OBJECTIVE

To test the hypothesis that a goal-directed fluid therapy (GDFT) strategy, when compared with a conventional fluid strategy, would better optimise systemic blood flow and lead to improved urethral tissue perfusion (a new variable to assess peripheral blood flow), without increasing blood loss.

DESIGN

Single-centre prospective randomised controlled superiority study.

SETTING

Erasme Hospital.

PATIENTS

Patients undergoing liver surgery.

INTERVENTION

Forty patients were randomised into two groups: all received a basal crystalloid infusion (maximum 2 ml kg-1 h-1). In the conventional fluid group, the goal was to maintain central venous pressure (CVP) as low as possible during the dissection phase by giving minimal additional fluid, while in the posttransection phase, anaesthetists were free to compensate for any presumed fluid deficit. In the GDFT group, patients received in addition to the basal infusion, multiple minifluid challenges of crystalloid to maintain stroke volume (SV) variation less than 13%. Noradrenaline infusion was titrated to keep mean arterial pressure more than 65 mmHg in all patients.

MAIN OUTCOME MEASURE

The mean intra-operative urethral perfusion index.

RESULTS

The mean urethral perfusion index was significantly higher in the GDFT group than in the conventional fluid group (8.70 [5.72 to 13.10] vs. 6.05 [4.95 to 8.75], P = 0.046). SV index (ml m-2) and cardiac index (l min-1 m-2) were higher in the GDFT group (48 ± 9 vs. 33 ± 7 and 3.5 ± 0.7 vs. 2.4 ± 0.4, respectively; P < 0.001). Although CVP was higher in the GDFT group (9.3 ± 2.5 vs. 6.5 ± 2.9 mmHg; P = 0.003), intra-operative blood loss was not significantly different in the two groups.

CONCLUSION

In patients undergoing liver surgery, a GDFT strategy resulted in a higher mean urethral perfusion index than did a conventional fluid strategy and did not increase blood loss despite higher CVP.

TRIAL REGISTRATION

NCT04092608.

Artificial intelligence and anesthesia: A narrative review

Rapid advances in Artificial Intelligence (AI) have led to diagnostic, therapeutic, and intervention-based applications in the field of medicine. Today, there is a deep chasm between AI-based research articles and their translation to clinical anesthesia, which needs to be addressed. Machine learning (ML), the most widely applied arm of AI in medicine, confers the ability to analyze large volumes of data, find associations, and predict outcomes with ongoing learning by the computer. It involves algorithm creation, testing and analyses with the ability to perform cognitive functions including association between variables, pattern recognition, and prediction of outcomes. AI-supported closed loops have been designed for pharmacological maintenance of anesthesia and hemodynamic management. Mechanical robots can perform dexterity and skill-based tasks such as intubation and regional blocks with precision, whereas clinical-decision support systems in crisis situations may augment the role of the clinician. The possibilities are boundless, yet widespread adoption of AI is still far from the ground reality. Patient-related “Big Data” collection, validation, transfer, and testing are under ethical scrutiny. For this narrative review, we conducted a PubMed search in 2020-21 and retrieved articles related to AI and anesthesia. After careful consideration of the content, we prepared the review to highlight the growing importance of AI in anesthesia. Awareness and understanding of the basics of AI are the first steps to be undertaken by clinicians. In this narrative review, we have discussed salient features of ongoing AI research related to anesthesia and perioperative care.

Machine Learning, Deep Learning, and Closed Loop Devices-Anesthesia Delivery

With the tremendous volume of data captured during surgeries and procedures, critical care, and pain management, the field of anesthesiology is uniquely suited for the application of machine learning, neural networks, and closed loop technologies. In the past several years, this area has expanded immensely in both interest and clinical applications. This article provides an overview of the basic tenets of machine learning, neural networks, and closed loop devices, with emphasis on the clinical applications of these technologies.

Computer-assisted Individualized Hemodynamic Management Reduces Intraoperative Hypotension in Intermediate- and High-risk Surgery: A Randomized Controlled Trial

BACKGROUND

Individualized hemodynamic management during surgery relies on accurate titration of vasopressors and fluids. In this context, computer systems have been developed to assist anesthesia providers in delivering these interventions. This study tested the hypothesis that computer-assisted individualized hemodynamic management could reduce intraoperative hypotension in patients undergoing intermediate- to high-risk surgery.

METHODS

This single-center, parallel, two-arm, prospective randomized controlled single blinded superiority study included 38 patients undergoing abdominal or orthopedic surgery. All included patients had a radial arterial catheter inserted after anesthesia induction and connected to an uncalibrated pulse contour monitoring device. In the manually adjusted goal-directed therapy group (N = 19), the individualized hemodynamic management consisted of manual titration of norepinephrine infusion to maintain mean arterial pressure within 10% of the patient's baseline value, and mini-fluid challenges to maximize the stroke volume index. In the computer-assisted group (N = 19), the same approach was applied using a closed-loop system for norepinephrine adjustments and a decision-support system for the infusion of mini-fluid challenges (100 ml). The primary outcome was intraoperative hypotension defined as the percentage of intraoperative case time patients spent with a mean arterial pressure of less than 90% of the patient's baseline value, measured during the preoperative screening. Secondary outcome was the incidence of minor postoperative complications.

RESULTS

All patients were included in the analysis. Intraoperative hypotension was 1.2% [0.4 to 2.0%] (median [25th to 75th] percentiles) in the computer-assisted group compared to 21.5% [14.5 to 31.8%] in the manually adjusted goal-directed therapy group (difference, -21.1 [95% CI, -15.9 to -27.6%]; P < 0.001). The incidence of minor postoperative complications was not different between groups (42 vs. 58%; P = 0.330). Mean stroke volume index and cardiac index were both significantly higher in the computer-assisted group than in the manually adjusted goal-directed therapy group (P < 0.001).

CONCLUSIONS

In patients having intermediate- to high-risk surgery, computer-assisted individualized hemodynamic management significantly reduces intraoperative hypotension compared to a manually controlled goal-directed approach.

EDITOR’S PERSPECTIVE

Effect of dexmedetomidine on Nociception Level Index-guided remifentanil antinociception: A randomised controlled trial

BACKGROUND

The effect of dexmedetomidine on Nociception Level Index-guided (Medasense, Israel) antinociception to reduce intra-operative opioid requirements has not been previously investigated.

OBJECTIVE

We aimed to determine if low-dose dexmedetomidine would reduce remifentanil requirements during Nociception Level Index-guided antinociception without increasing complications associated with dexmedetomidine.

DESIGN

Double-blind randomised controlled trial.

SETTING

Two university teaching hospitals in Brussels, Belgium.

PATIENTS

American Society of Anesthesiologists 1 and 2 patients (n = 58) undergoing maxillofacial or cervicofacial surgery under propofol--remifentanil target-controlled infusion anaesthesia.

INTERVENTIONS

A 30 min infusion of dexmedetomidine, or equal volume of 0.9% NaCl, was infused at 1.2 μg kg-1 h-1 immediately preceding induction and then decreased to 0.6 μg kg-1 h-1 until 30 min before ending surgery. Nociception Level Index and frontal electroencephalogram guided the remifentanil and propofol infusions, respectively.

MAIN OUTCOMES

The primary outcome was the remifentanil requirement. Other outcomes included the propofol requirement, cardiovascular status and postoperative outcome.

RESULTS

Mean ± SD remifentanil (3.96 ± 1.95 vs. 4.42 ± 2.04 ng ml-1; P = 0.0024) and propofol (2.78 ± 1.36 vs. 3.06 ± 1.29 μg ml-1; P = 0.0046) TCI effect site concentrations were lower in the dexmedetomidine group at 30 min postincision and remained lower throughout surgery. When remifentanil (0.133 ± 0.085 vs. 0.198 ± 0.086 μg kg-1 min-1; P = 0.0074) and propofol (5.7 ± 2.72 vs. 7.4 ± 2.80 mg kg-1 h-1; P = 0.0228) requirements are represented as infusion rates, this effect became statistically significant at 2 h postincision.

CONCLUSION

In ASA 1 and 2 patients receiving Nociception Level Index-guided antinociception, dexmedetomidine decreases intra-operative remifentanil requirements. Combined frontal electroencephalogram and Nociception Level Index monitoring can measure dexmedetomidine's hypnotic and opioid-sparing effects during remifentanil-propofol target-controlled infusion anaesthesia.

TRIAL REGISTRATIONS

Clinicaltrials.gov: NCT03912740, EudraCT: 2018-004512-22.

Automated closed-loop versus manually controlled norepinephrine infusion in patients undergoing intermediate- to high-risk abdominal surgery: a randomised controlled trial

BACKGROUND

Hypotension occurs frequently during surgery and may be associated with adverse complications. Vasopressor titration is frequently used to correct hypotension, but requires considerable time and attention, potentially reducing the time available for other clinical duties. To overcome this issue, we have developed a closed-loop vasopressor (CLV) controller to help correct hypotension more efficiently. The aim of this randomised controlled study was to evaluate whether the CLV controller was superior to traditional vasopressor management at minimising hypotension in patients undergoing abdominal surgery.

METHODS

Thirty patients scheduled for elective intermediate-to high-risk abdominal surgery were randomised into two groups. In the CLV group, hypotension was corrected automatically via the CLV controller system, which adjusted the rate of a norepinephrine infusion according to MAP values recorded using an advanced haemodynamic device. In the control group, management of hypotension consisted of standard, manual adjustment of the norepinephrine infusion. The primary outcome was the percentage of time that a patient was hypotensive, defined as MAP <90% of their baseline value, during surgery.

RESULTS

The percentage of time patients were hypotensive during surgery was 10 times less in the CVL group than in the control group (1.6 [0.9-2.3]% vs 15.4 [9.9-24.3]%; difference: 13 [95% confidence interval: 9-19]; P<0.0001). The CVL group also spent much less time with MAP <65 mm Hg (0.2 [0.0-0.4]% vs 4.5 [1.1-7.9]%; P<0.0001).

CONCLUSIONS

In patients undergoing intermediate- to high-risk surgery under general anaesthesia, computer-assisted adjustment of norepinephrine infusion significantly decreases the incidence of hypotension compared with manual control.

CLINICAL TRIAL REGISTRATION

NCT04089644.

Hydroxyethyl starch for perioperative goal-directed fluid therapy in 2020: a narrative review

BACKGROUND

Perioperative fluid management - including the type, dose, and timing of administration -directly affects patient outcome after major surgery. The objective of fluid administration is to optimize intravascular fluid status to maintain adequate tissue perfusion. There is continuing controversy around the perioperative use of crystalloid versus colloid fluids. Unfortunately, the importance of fluid volume, which significantly influences the benefit-to-risk ratio of each chosen solution, has often been overlooked in this debate.

MAIN TEXT

The volume of fluid administered during the perioperative period can influence the incidence and severity of postoperative complications. Regrettably, there is still huge variability in fluid administration practices, both intra-and inter-individual, among clinicians. Goal-directed fluid therapy (GDFT), aimed at optimizing flow-related variables, has been demonstrated to have some clinical benefit and has been recommended by multiple professional societies. However, this approach has failed to achieve widespread adoption. A closed-loop fluid administration system designed to assist anesthesia providers in consistently applying GDFT strategies has recently been developed and tested. Such an approach may change the crystalloid versus colloid debate. Because colloid solutions have a more profound effect on intravascular volume and longer plasma persistence, their use in this more "controlled" context could be associated with a lower fluid balance, and potentially improved patient outcome. Additionally, most studies that have assessed the impact of a GDFT strategy on the outcome of high-risk surgical patients have used hydroxyethyl starch (HES) solutions in their protocols. Some of these studies have demonstrated beneficial effects, while none of them has reported severe complications.

CONCLUSIONS

The type and volume of fluid used for perioperative management need to be individualized according to the patient's hemodynamic status and clinical condition. The amount of fluid given should be guided by well-defined physiologic targets. Compliance with a predefined hemodynamic protocol may be optimized by using a computerized system. The type of fluid should also be individualized, as should any drug therapy, with careful consideration of timing and dose. It is our perspective that HES solutions remain a valid option for fluid therapy in the perioperative context because of their effects on blood volume and their reasonable benefit/risk profile.

Anesthetic Management Using Multiple Closed-loop Systems and Delayed Neurocognitive Recovery: A Randomized Controlled Trial

BACKGROUND

Cognitive changes after anesthesia and surgery represent a significant public health concern. We tested the hypothesis that, in patients 60 yr or older scheduled for noncardiac surgery, automated management of anesthetic depth, cardiac blood flow, and protective lung ventilation using three independent controllers would outperform manual control of these variables. Additionally, as a result of the improved management, patients in the automated group would experience less postoperative neurocognitive impairment compared to patients having standard, manually adjusted anesthesia.

METHODS

In this single-center, patient-and-evaluator-blinded, two-arm, parallel, randomized controlled, superiority study, 90 patients having noncardiac surgery under general anesthesia were randomly assigned to one of two groups. In the control group, anesthesia management was performed manually while in the closed-loop group, the titration of anesthesia, analgesia, fluids, and ventilation was performed by three independent controllers. The primary outcome was a change in a cognition score (the 30-item Montreal Cognitive Assessment) from preoperative values to those measures 1 week postsurgery. Secondary outcomes included a battery of neurocognitive tests completed at both 1 week and 3 months postsurgery as well as 30-day postsurgical outcomes.

RESULTS

Forty-three controls and 44 closed-loop patients were assessed for the primary outcome. There was a difference in the cognition score compared to baseline in the control group versus the closed-loop group 1 week postsurgery (-1 [-2 to 0] vs. 0 [-1 to 1]; difference 1 [95% CI, 0 to 3], P = 0.033). Patients in the closed-loop group spent less time during surgery with a Bispectral Index less than 40, had less end-tidal hypocapnia, and had a lower fluid balance compared to the control group.

CONCLUSIONS

Automated anesthetic management using the combination of three controllers outperforms manual control and may have an impact on delayed neurocognitive recovery. However, given the study design, it is not possible to determine the relative contribution of each controller on the cognition score.

Feasibility of closed-loop titration of norepinephrine infusion in patients undergoing moderate- and high-risk surgery

BACKGROUND

Vasopressor agents are used to prevent intraoperative hypotension and ensure adequate perfusion. Vasopressors are usually administered as intermittent boluses or manually adjusted infusions, but this practice requires considerable time and attention. We have developed a closed-loop vasopressor (CLV) controller to correct hypotension more efficiently. Here, we conducted a proof-of-concept study to assess the feasibility and performance of CLV control in surgical patients.

METHODS

Twenty patients scheduled for elective surgical procedures were included in this study. The goal of the CLV system was to maintain MAP within 5 mm Hg of the target MAP by automatically adjusting the rate of a norepinephrine infusion using MAP values recorded continuously from an arterial catheter. The primary outcome was the percentage of time that patients were hypotensive, as defined by a MAP of 5 mm Hg below the chosen target. Secondary outcomes included the total dose of norepinephrine, percentage of time with hypertension (MAP>5 mm Hg of the chosen target), raw percentage "time in target" and Varvel performance criteria.

RESULTS

The 20 subjects (median age: 64 years [52-71]; male (35%)) underwent elective surgery lasting 154 min [124-233]. CLV control maintained MAP within ±5 mm Hg of the target for 91.6% (85.6-93.3) of the intraoperative period. Subjects were hypotensive for 2.6% of the intraoperative period (range, 0-8.4%). Additional performance criteria for the controller included mean absolute performance error of 2.9 (0.8) and mean predictive error of 0.5 (1.0). No subjects experienced major complications.

CONCLUSIONS

In this proof of concept study, CLV control minimised perioperative hypotension in subjects undergoing moderate- or high-risk surgery. Further studies to demonstrate efficacy are warranted.

TRIAL REGISTRY NUMBER

NCT03515161 (ClinicalTrials.gov).

Evaluation of Fluid Resuscitation Control Algorithms via a Hardware-in-the-Loop Test Bed

OBJECTIVE

This paper presents a hardware-in-the-loop (HIL) testing platform for evaluating the performance of fluid resuscitation control algorithms. The proposed platform is a cyber-physical system that integrates physical devices with computational models and computer-based algorithms.

METHODS

The HIL test bed is evaluated against in silico and in vivo data to ensure the hemodynamic variables are appropriately predicted in the proposed platform. The test bed is then used to investigate the performance of two fluid resuscitation control algorithms: a decision table (rule-based) and a proportional-integral-derivative (PID) controller.

RESULTS

The statistical evaluation of test bed indicates that similar results are observed in the HIL test bed, in silico implementation, and the in vivo data, verifying that the HIL test bed can adequately predict the hemodynamic responses. Comparison of the two fluid resuscitation controllers reveals that both controllers stabilized hemodynamic variables over time and had similar speed to efficiently achieve the target level of the hemodynamic endpoint. However, the accuracy of the PID controller was higher than the rule-based for the scenarios tested in the HIL platform.

CONCLUSION

The results demonstrate the potential of the HIL test bed for realistic testing of physiologic controllers by incorporating physical devices with computational models of physiology and disturbances.

SIGNIFICANCE

This type of testing enables relatively fast evaluation of physiologic closed-loop control systems to aid in iterative design processes and offers complementary means to existing techniques (e.g., in silico, in vivo, and clinical studies) for testing of such systems against a wide range of disturbances and scenarios.

Closed-loop hemodynamic management

As the operating room and intensive care settings become increasingly complex, the required vigilance practitioners must dedicate to a wide array of clinical systems has increased concordantly. The resulting shortage of available attention to these various clinical tasks creates a vacuum for the introduction of systems that can administer well-established goal-directed therapies without significant provider feedback. Recently, there has been an explosion of academic exploration into creating such automated systems, with a strong specific focus on hemodynamic control. Within this field, the largest focus has been on goal-directed fluid therapy as systems automating vasopressor administration have only recently become viable options. Our goal in this review article is to summarize the validity of the relevant goal-directed hemodynamic systems and explore the expanding role of automation within these systems.

Pleth variability index versus pulse pressure variation for intraoperative goal-directed fluid therapy in patients undergoing low-to-moderate risk abdominal surgery: a randomized controlled trial

Background

Goal-directed fluid therapy (GDFT) based on dynamic indicators of fluid responsiveness has been shown to decrease postoperative complications and hospital length of stay (LOS) in patients undergoing major abdominal surgery. The usefulness of this approach still needs to be clarified in low-to-moderate risk abdominal surgery. Both pulse-pressure variation (PPV) and pleth variability index (PVI) can be used to guide GDFT strategies. The objective of this prospective randomized controlled trial was to determine if the use of PVI guided GDFT, when compared to PPV guided GDFT, would lead to similar hospital LOS in patients undergoing low-to-moderate risk surgery. Secondary outcomes included amount of fluid administered and incidence of postoperative complications.

Methods

Patients were randomized into either PVI or PPV guided GDFT groups. Both received a baseline 2 ml kg^− 1 h^− 1 Lactated Ringer infusion. Additional fluid boluses consisted of 250 mL of colloid that was infused over a 10 min period if PVI was > 15% or PPV was > 13% for at least five minutes. The primary outcome was to determine if hospital LOS, which was defined as the number of days from surgery up to the day the surgeon authorized hospital discharge, was equivalent between the two groups.

Results

A total of 76 patients were included and they were randomized into two groups of 38 patients. Baseline characteristics were similar in both groups. Both PVI and PPV guided GDFT strategies were equivalent for the primary outcome of LOS (median [interquartile range]) (days) 2.5 [2.0–3.3] vs. 3.0 [2.0–5.0], p = 0.230, respectively. Fluids infused, postoperative complications, and all other outcomes were not different between groups.

Conclusion

In patients undergoing low-to-moderate risk abdominal surgery, PVI seems to guide GDFT similarly to PPV in regards to hospital LOS, amount of fluid, and incidence of postoperative complications. However, in low-risk patients undergoing these surgical procedures optimizing stroke volume may have limited impact on outcome.

Trial registration

ClinicalTrials.gov Identifier: NCT02908256, September 2016, retrospectively registered.

Electronic supplementary material

The online version of this article (10.1186/s12871-019-0707-9) contains supplementary material, which is available to authorized users.

Monitoring of pulse pressure variation using a new smartphone application (Capstesia) versus stroke volume variation using an uncalibrated pulse wave analysis monitor: a clinical decision making study during major abdominal surgery

Pulse pressure variation (PPV) and stroke volume variation (SVV) can be used to assess fluid status in the operating room but usually require dedicated advanced hemodynamic monitors. Recently, a smartphone application (Capstesia™), which automatically calculates PPV from a picture of the invasive arterial pressure waveform from any monitor screen (PPV_CAP), has been developed. The purpose of this study was to compare PPV_CAP with SVV from an uncalibrated pulse wave analysis monitor (SVV_PC). In 40 patients undergoing major abdominal surgery, we compared PPV_CAP with SVV_PC at post-induction, pre-incision, post-incision, end of surgery, and during every hypotensive episode (mean arterial pressure < 65 mmHg). We classified PPV_CAP and SVV_PC into three categories reflecting the thresholds used for the decision to administer fluids: no fluid administration (PPV and SVV < 9%), gray zone (PPV and SVV 9-13%), and fluid administration (PPV and SVV > 13%). The agreement between SVV_PC and PPV_CAP for these three categories was measured by the number of concordant paired measurements divided by the total number of paired measurements and Cohen's kappa coefficient. In the 549 pairs of PPV-SVV data obtained, the overall agreement of PPV_CAP with SVV_PC was 79%, and the kappa coefficient was moderate (0.55). The highest agreement and kappa coefficient value were observed after the induction of anesthesia before surgical incision. PPV_CAP and SVV_PC would have resulted in completely opposite clinical decisions regarding fluid administration in 1% of the cases. In this clinical decision making study in patients undergoing major abdominal surgery, we observed a moderate agreement between PPV_CAP and SVV_PC with regard to categories used to guide fluid administration. Trial Registration: Clinical Trials.gov (NCT03137901).