Haemodynamic monitoring in the peri-operative period: the past, the present and the future

Machine Learning-Based Cardiac Output Estimation Using Photoplethysmography in Off-Pump Coronary Artery Bypass Surgery

Background/Objectives: Hemodynamic monitoring is crucial for managing critically ill patients and those undergoing major surgeries. Cardiac output (CO) is an essential marker for diagnosing hemodynamic deterioration and guiding interventions. The gold standard thermodilution method for measuring CO is invasive, prompting a search for non-invasive alternatives. This pilot study aimed to develop a non-invasive algorithm for classifying the cardiac index (CI) into low and non-low categories using finger photoplethysmography (PPG) and a machine learning model. Methods: PPG and continuous thermodilution CO data were collected from patients undergoing off-pump coronary artery bypass graft surgery. The dataset underwent preprocessing, and features were extracted and selected using the Relief algorithm. A CatBoost machine learning model was trained and evaluated using a validation and testing phase approach. Results: The developed model achieved an accuracy of 89.42% in the validation phase and 87.57% in the testing phase. Performance was balanced across low and non-low CO categories, demonstrating robust classification capabilities. Conclusions: This study demonstrates the potential of machine learning and non-invasive PPG for accurate CO classification. The proposed method could enhance patient safety and comfort in critical care and surgical settings by providing a non-invasive alternative to traditional invasive CO monitoring techniques. Further research is needed to validate these findings in larger, diverse patient populations and clinical scenarios.

Goal-directed therapy guided by the FloTrac sensor in major surgery: a systematic review and meta-analysis

OBJECTIVE

To provide insights into the potential benefits of goal-directed therapy guided by FloTrac in reducing postoperative complications and improving outcomes.

METHODS

We performed a systematic review and meta-analysis of randomized controlled trials to evaluate goal-directed therapy guided by FloTrac in major surgery, comparing goal-directed therapy with usual care or invasive monitoring in cardiac and noncardiac surgery subgroups. The quality of the articles and evidence were evaluated with a risk of bias tool and GRADE.

RESULTS

We included 29 randomized controlled trials with 3,468 patients. Goal-directed therapy significantly reduced the duration of hospital stay (mean difference -1.43 days; 95%CI 2.07 to -0.79; I2 81%), intensive care unit stay (mean difference -0.77 days; 95%CI -1.18 to -0.36; I2 93%), and mechanical ventilation (mean difference -2.48 hours, 95%CI -4.10 to -0.86, I2 63%). There was no statistically significant difference in mortality, myocardial infarction, acute kidney injury or hypotension, but goal-directed therapy significantly reduced the risk of heart failure or pulmonary edema (RR 0.46; 95%CI 0.23 - 0.92; I2 0%).

CONCLUSION

Goal-directed therapy guided by the FloTrac sensor improved clinical outcomes and shortened the length of stay in the hospital and intensive care unit in patients undergoing major surgery. Further research can validate these results using specific protocols and better understand the potential benefits of FloTrac beyond these outcomes.

The Impact of Individualized Hemodynamic Management on Intraoperative Fluid Balance and Hemodynamic Interventions during Spine Surgery in the Prone Position: A Prospective Randomized Trial

Background and Objectives: The effect of individualized hemodynamic management on the intraoperative use of fluids and other hemodynamic interventions in patients undergoing spinal surgery in the prone position is controversial. This study aimed to evaluate how the use of individualized hemodynamic management based on extended continuous non-invasive hemodynamic monitoring modifies intraoperative hemodynamic interventions compared to conventional hemodynamic monitoring with intermittent non-invasive blood pressure measurements. Methods: Fifty adult patients (American Society of Anesthesiologists physical status I−III) who underwent spinal procedures in the prone position and were then managed with a restrictive fluid strategy were prospectively randomized into intervention and control groups. In the intervention group, individualized hemodynamic management followed a goal-directed protocol based on continuously non-invasively measured blood pressure, heart rate, cardiac output, systemic vascular resistance, and stroke volume variation. In the control group, patients were monitored using intermittent non-invasive blood pressure monitoring, and the choice of hemodynamic intervention was left to the discretion of the attending anesthesiologist. Results: In the intervention group, more hypotensive episodes (3 (2−4) vs. 1 (0−2), p = 0.0001), higher intraoperative dose of ephedrine (0 (0−10) vs. 0 (0−0) mg, p = 0.0008), and more positive fluid balance (680 (510−937) vs. 270 (196−377) ml, p < 0.0001) were recorded. Intraoperative norepinephrine dose and postoperative outcomes did not differ between the groups. Conclusions: Individualized hemodynamic management based on data from extended non-invasive hemodynamic monitoring significantly modified intraoperative hemodynamic management and was associated with a higher number of hemodynamic interventions and a more positive fluid balance.

[Targeted hemodynamic monitoring in the operating theatre: what for and by what means?]

Goal directed hemodynamic monitoring and the balance in goal directed therapy between adequate fluid/volume therapy and the application of vasoactive or inotropic drugs are the basic elements of modern perioperative therapy.Surgical procedures should be accompanied by as few side effects and complications as possible. Nevertheless, the number of postoperative complications remains surprisingly high, despite of the modern surgical procedures. Anticipation of potential complications in the perioperative period and their rapid treatment build a core competence of anesthesiological action. Thus, it is clear that anesthesia plays a central role in this balancing act.This article aims to provide an overview of the application of the currently available perioperative goal directed hemodynamic monitoring. The current possibilities are discussed by using a case example and an outlook on the future of hemodynamic monitoring is given.

Assessment of fluid unresponsiveness guided by lung ultrasound in abdominal surgery: a prospective cohort study

A fluid challenge can generate an infraclinical interstitial syndrome that may be detected by the appearance of B-lines by lung ultrasound. Our objective was to evaluate the appearance of B-lines as a diagnostic marker of preload unresponsiveness and postoperative complications in the operating theater. We conducted a prospective, bicentric, observational study. Adult patients undergoing abdominal surgery were included. Stroke volume (SV) was determined before and after a fluid challenge with 250 mL crystalloids (Delta-SV) using esophageal Doppler monitoring. Responders were defined by an increase of Delta-SV > 10% after fluid challenge. B-lines were collected at four bilateral predefined zones (right and left anterior and lateral). Delta-B-line was defined as the number of newly appearing B-lines after a fluid challenge. Postoperative pulmonary complications were prospectively recorded according to European guidelines. In total, 197 patients were analyzed. After a first fluid challenge, 67% of patients were responders and 33% were non-responders. Delta-B-line was significantly higher in non-responders than responders [4 (2–7) vs 1 (0–3), p < 0.0001]. Delta-B-line was able to diagnose fluid non-responders with an area under the curve of 0.74 (95% CI 0.67–0.80, p < 0.0001). The best threshold was two B-lines with a sensitivity of 80% and a specificity of 57%. The final Delta-B-line could predict postoperative pulmonary complications with an area under the curve of 0.74 (95% CI 0.67–0.80, p = 0.0004). Delta-B-line of two or more detected in four lung ultrasound zones can be considered to be a marker of preload unresponsiveness after a fluid challenge in abdominal surgery.

The objectives and procedures of the study were registered at Clinicaltrials.gov (NCT03502460; Principal investigator: Stéphane BAR, date of registration: April 18, 2018).

Perioperative Management of Polytrauma Patients with Severe Traumatic Brain Injury Undergoing Emergency Extracranial Surgery: A Narrative Review

Managing the acute phase after a severe traumatic brain injury (TBI) with polytrauma represents a challenging situation for every trauma team member. A worldwide variability in the management of these complex patients has been reported in recent studies. Moreover, limited evidence regarding this topic is available, mainly due to the lack of well-designed studies. Anesthesiologists, as trauma team members, should be familiar with all the issues related to the management of these patients. In this narrative review, we summarize the available evidence in this setting, focusing on perioperative brain protection, cardiorespiratory optimization, and preservation of the coagulative function. An overview on simultaneous multisystem surgery (SMS) is also presented.

Is there still a role for the oesophageal Doppler in cardiac output monitoring?

The oesophageal Doppler monitor received early endorsement as an effective emerging medical technology, although numerous alternatives have since been widely adopted. This article examines the evidence supporting the continued use of the oesophageal Doppler.

Impact of Goal Directed Therapy in Head and Neck Oncological Surgery with Microsurgical Reconstruction: Free Flap Viability and Complications

Simple Summary

Based on the proven benefits of goal directed therapy (GDT) in the perioperative management of different surgical procedures and in high-risk patients, we hypothesised that this approach would also be beneficial in microvascular free flap reconstruction in head and neck cancer. In this study, we investigated whether GDT would directly benefit flap viability in addition to improving morbidity and mortality. As this reconstructive technique is gradually being introduced in more specialist fields, particularly radical oncological surgery, the benefits of GDT in this context could be extended to numerous procedures.

Abstract

(1) Background: Surgical outcomes in free flap reconstruction of head and neck defects in cancer patients have improved steadily in recent years; however, correct anaesthesia management is also important. The aim of this study has been to show whether goal directed therapy can improve flap viability and morbidity and mortality in surgical patients. (2) Methods: we performed an observational case control study to analyse the impact of introducing a semi invasive device (Flo Trac^®) during anaesthesia management to optimize fluid management. Patients were divided into two groups: one received goal directed therapy (GDT group) and the other conventional fluid management (CFM group). Our objective was to compare surgical outcomes, complications, fluid management, and length of stay between groups. (3) Results: We recruited 140 patients. There were no differences between groups in terms of demographic data. Statistically significant differences were observed in colloid infusion (GDT 53.1% vs. CFM 74.1%, p = 0.023) and also in intraoperative and postoperative infusion of crystalloids (CFM 5.72 (4.2, 6.98) vs. GDT 3.04 (2.29, 4.11), p < 0.001), which reached statistical significance. Vasopressor infusion in the operating room (CFM 25.5% vs. GDT 74.5%, p < 0.001) and during the first postoperative 24h (CFM 40.6% vs. GDT 75%, p > 0.001) also differed. Differences were also found in length of stay in the intensive care unit (hours: CFM 58.5 (40, 110) vs. GDT 40.5 (36, 64.5), p = 0.005) and in the hospital (days: CFM 15.5 (12, 26) vs. GDT 12 (10, 19), p = 0.009). We found differences in free flap necrosis rate (CMF 37.1% vs. GDT 13.6%, p = 0.003). One-year survival did not differ between groups (CFM 95.6% vs. GDT 86.8%, p = 0.08). (4) Conclusions: Goal directed therapy in oncological head and neck surgery improves outcomes in free flap reconstruction and also reduces length of stay in the hospital and intensive care unit, with their corresponding costs. It also appears to reduce morbidity, although these differences were not significant. Our results have shown that optimizing intraoperative fluid therapy improves postoperative morbidity and mortality.

Indwelling catheters increase altered mental status and urinary tract infection risk: A retrospective Cohort Study

Background

Although indwelling urinary catheters (IUCs) are used intraoperatively and may cause complications (e.g., delirium), only few robust studies have investigated the association between intraoperative IUC use and complications. We hypothesized that IUC use might increase the postoperative incidence of altered mental status and/or urinary catheter infection.

Materials and methods

In this retrospective single-center cohort study, we analyzed the data of adult patients undergoing surgery at our facility between January 2013 and December 2018. The primary endpoint was altered mental status and/or incidence of urinary catheter infections. The patients were divided into IUC and control groups. A multivariable logistic regression model was used to identify the predictors of postoperative complications, and a multivariable Cox proportional hazards regression model was used to analyze hospital discharge in unmatched and inverse propensity-weighted patients.

Results

Of the 14,284 patients that were reviewed, we analyzed 5112 patients (control group, 44.0%; IUC group, 56.0%). Almost all procedures comprised less invasive surgeries. The prevalence of postoperative altered mental status and postoperative urinary catheter infection were 3.56% and 0.04%, respectively. After inverse propensity weighting, all baseline characteristics were similar between the two groups. However, patients with IUCs had a higher risk of postoperative complications (adjusted odds ratio, 1.97; 95% confidence interval [CI], 1.50-2.59) and prolonged hospital stays (hazard ratio, 0.84; 95% CI, 0.80-0.89).

Conclusion

In patients undergoing less invasive surgery, IUCs may be associated with a relatively high risk of altered mental status or urinary catheter infection. These data may facilitate preoperative discussions regarding the perioperative use of IUCs.

[Enhanced recovery after surgery (ERAS): less is more : What must be considered from an anesthesiological perspective?]

BACKGROUND

Enhanced recovery after surgery (ERAS) is a multidisciplinary treatment model with the aim of guaranteeing a reduction of postoperative complications by the maintenance or early restoration of the patient-specific homoeostasis. From the anesthesiologist's perspective in all three areas of the perioperative phases there are important aspects that need to be addressed in the sense of a holistic treatment concept in order to achieve the highest possible benefit for the patient.

OBJECTIVE

In the perioperative period there is a bundle of anesthesiological measures, which make the ERAS concept into what it is now. At this point the focus is on the preoperative preparation and optimization of the patient and on the intraoperative and postoperative fluid management.

MATERIAL AND METHODS

A selective literature search was carried out in the Medline and Cochrane Library databases including consideration of national and international guidelines.

RESULTS

From an anesthesiological perspective there are relevant aspects in all three pillars of the perioperative phase, the adherence of which will improve the outcome of the patient: a comprehensive risk evaluation in the preoperative period and the avoidance of any sedative drugs; intraoperative individualized fluid management in the sense of a target-oriented optimization; early postoperative enteral nutrition and the avoidance of intravenous fluid administration, whenever justifiable.

CONCLUSION

Implementing the ERAS concept in the daily clinical routine in combination with maintaining a high compliance with the protocols is a demanding interdisciplinary challenge that urgently needs to be continued.

Perioperative anaesthetic management of patients with or at risk of acute distress respiratory syndrome undergoing emergency surgery

Patients undergoing emergency surgery may present with the acute respiratory distress syndrome (ARDS) or develop this syndrome postoperatively. The incidence of ARDS in the postoperative period is relatively low, but the impact of ARDS on patient outcomes and healthcare costs is relevant Aakre et.al (Mayo Clin Proc 89:181-9, 2014).The development of ARDS as a postoperative pulmonary complication (PPC) is associated with prolonged hospitalisation, longer duration of mechanical ventilation, increased intensive care unit length of stay and high morbidity and mortality Ball et.al (Curr Opin Crit Care 22:379-85, 2016). In order to mitigate the risk of ARDS after surgery, the anaesthetic management and protective mechanical ventilation strategies play an important role. In particular, a careful integration of general anaesthesia with neuraxial or locoregional techniques might promote faster recovery and reduce opioid consumption. In addition, the use of low tidal volume, minimising plateau pressure and titrating a low-moderate PEEP level based on the patient's need can improve outcome and reduce intraoperative adverse events. Moreover, perioperative management of ARDS patients includes specific anaesthesia and ventilator settings, hemodynamic monitoring, moderately restrictive fluid administration and pain control.The aim of this review is to provide an overview and evidence- and opinion-based recommendations concerning the management of patients at risk of and with ARDS who undergo emergency surgical procedures.

Application of standardized hemodynamic protocols within enhanced recovery after surgery programs to improve outcomes associated with anastomotic leak and conduit necrosis in patients undergoing esophagectomy

Esophagectomy for cancer is associated with high risk for postoperative morbidity. The most serious regularly encountered complication is anastomotic leak and the most feared individual complication is conduit necrosis. Both of these complications affect the length of stay, mortality, quality of life, and survival for patients undergoing esophageal resection. The maintenance of conduit viability is of primary importance in the perioperative care of patients following esophageal resection. It has been shown that restrictive fluid management may be associated with improved postoperative outcomes in abdominal and other types of surgery, but many factors can affect the incidence of anastomotic leak and the viability of the gastric conduit. We have performed a comprehensive review with the aim to give an overview of the available evidence for the use of standardized hemodynamic protocols (SHPs) for esophagectomy and review the hemodynamic protocol, which has been applied within a standardized clinical pathway (SCP) at the Department of Thoracic surgery at the Virginia Mason Medical Center between 2004-2018 where the anastomotic leak rate over the period has been 5.2% and the incidence of conduit necrosis requiring surgical management is zero. The literature review demonstrates that there are few high quality studies that provide scientific evidence for the use of a SHP. The evidence indicates that the use of goal-directed hemodynamic monitoring might be associated with a reduced risk for postoperative complications, shortened length of stay, and decreased need for intensive care unit stay. We propose that the routine application of a SHP can provide a uniform infrastructure to optimize conduit perfusion and decrease the incidence of anastomotic leak.

A pilot study evaluating adaptive closed-loop fluid resuscitation during states of absolute and relative hypovolemia in dogs

OBJECTIVE

To evaluate and determine the performance of a partially automated as well as a fully automated closed-loop fluid resuscitation system during states of absolute and relative hypovolemia.

DESIGN

Prospective experimental trial.

SETTING

Research laboratory.

ANIMALS

Five adult Beagle dogs.

METHODS

Isoflurane anesthetized mechanically ventilated dogs were subjected to absolute hypovolemia (controlled: 2 trials; uncontrolled: 3 trials), relative hypovolemia (2 trials), and the combination of relative and absolute controlled hypovolemia (2 trials). Controlled and uncontrolled hypovolemia were produced by withdrawing blood from the carotid or femoral artery. Relative hypovolemia was produced by increasing the isoflurane concentration (1 trial) or by infusion of intravenous sodium nitroprusside (1 trial). Relative hypovolemia combined with controlled absolute hypovolemia was produced by increasing the isoflurane concentration (1 trial) and infusion of IV sodium nitroprusside (1 trial). Hemodynamic parameters including stroke volume variation (SVV) were continuously monitored and recorded in all dogs. A proprietary closed-loop fluid administration system based on fluid distribution and compartmental dynamical systems administered a continuous infusion of lactated Ringers solution in order to restore and maintain SVV to a predetermined target value.

MEASUREMENTS AND MAIN RESULTS

A total of 9 experiments were performed on 5 dogs. Hemodynamic parameters deteriorated and SVV increased during controlled or uncontrolled hypovolemia, relative hypovolemia, and during relative hypovolemia combined with controlled hypovolemia. Stroke volume variation was restored to baseline values during closed-loop fluid infusion.

CONCLUSIONS

Closed-loop fluid administration based on IV fluid distribution and compartmental dynamical systems can be used to provide goal directed fluid therapy during absolute or relative hypovolemia in mechanically ventilated isoflurane anesthetized dogs.

Accuracy, Precision, and Trending of 4 Pulse Wave Analysis Techniques in the Postoperative Period

OBJECTIVE

The aim of this study was to analyze the accuracy, precision, and trending ability of the following 4 pulse wave analysis devices to measure continuous cardiac output: PiCCO₂ ([PCCO]; Pulsion Medical System, Munich, Germany); LiDCO_Rapid ([LCCO]; LiDCO Ltd, London, UK); FloTrac/Vigileo ([FCCO]; Edwards Lifesciences, Irvine, CA); and Nexfin ([NCCO]; BMEYE, Amsterdam, The Netherlands).

DESIGN

Prospective, observational clinical study.

SETTING

Intensive care unit of a single-center, teaching hospital.

PARTICIPANTS

The study comprised 22 adult patients after elective coronary artery bypass surgery.

INTERVENTIONS

Three measurement cycles were performed in all patient durings their immediate postoperative intensive care stay before and after fluid loading. Hemodynamic measurements were performed 5 minutes before and immediately after the administration of 500 mL colloidal fluid over 20 minutes.

MEASUREMENTS AND MAIN RESULTS

PCCO, LCCO, FCCO, and NCCO were assessed and compared with cardiac output derived from intermittent transpulmonary thermodilution (ICO). One hundred thirty-two matched sets of data were available for analysis. Bland-Altman analysis using linear mixed effects models with random effects for patient and trial revealed a mean bias ±2 standard deviation (%error) of -0.86 ± 1.41 L/min (34.9%) for PCCO-ICO, -0.26 ± 2.81 L/min (46.3%) for LCCO-ICO, -0.28 ± 2.39 L/min (43.7%) for FCCO-ICO, and -0.93 ± 2.25 L/min (34.6%) for NCCO-ICO. Bland-Altman plots without adjustment for repeated measurements and replicates yielded considerably larger limits of agreement. Trend analysis for all techniques did not meet criteria for acceptable performance.

CONCLUSIONS

All 4 tested devices using pulse wave analysis for measuring cardiac output failed to meet current criteria for meaningful and adequate accuracy, precision, and trending ability in cardiac output monitoring.

Monitoring of cardiac output and lung ventilation by Electrical Impedance Tomography in a porcine model of acute lung injury

Adequate medical treatment of the Acute Respiratory Distress Syndrome is still challenging since patient-individual aspects have to be taken into account. Lung protective ventilation and hemodynamic stability have always been two of the most crucial aims of intensive care therapy. For both aspects, a continuous - preferably non-invasive - monitoring is desirable that is available at the bedside. Unfortunately, there is no technique clinically established yet, that provides both measurement of cardiac stroke volume and ventilation dynamics in real-time. Electrical Impedance Tomography (EIT) is a promising technique to close this gap. The aim of the study was to investigate if stroke volume can be estimated by a self-developed software using EIT-based image analysis. In addition, two EIT-derived parameters, namely Global Inhomogeneity Index (GII) and Impedance Ratio (IR), were calculated to evaluate homogeneity of air distribution. Experimental acute lung injury (ALI) was provoked in seven female pigs (German Landrace) by lipopolysaccharide (LPS). All animals suffered from experimental ALI 3 to 4 hours after LPS infusion. At defined time points, respiratory and hemodynamic parameters, blood gas analyses and EIT-recordings were performed. Eight hours after ALI, animals were euthanized. Stroke volume, derived from pulmonary artery catheter (PAC), decreased continuously up to four hours after ALI. Then, stroke volume increased slightly. Stroke volume, derived from the self-developed tool, showed the same characteristics (p=0.047, r = 0.365). In addition to the GII and IR individually, both classified scores showed a high correlation with the Horowitz Index, defined as p_aO₂/FiO₂. To conclude, EIT-derived measures enabled a reliable estimation of cardiac stroke volume and regional distribution of ventilation.