Neuropsychologic impairment after coronary bypass surgery: effect of gaseous microemboli during perfusionist interventions

Hypobaric type oxygenators - physics and physiology

Brain injury is still a serious complication after cardiac surgery. Gaseous microemboli (GME) are known to contribute to both short and longer-term brain injury after cardiac surgery. Hypobaric and novel dual-chamber oxygenators use the physical behaviors and properties of gases to reduce GME. The aim of this review was to present the basic physics of the gases, the mechanism in which the hypobaric and dual-chamber oxygenators reduce GME, their technical performance, the preclinical studies, and future directions. The gas laws are reviewed as an aid to understanding the mechanisms of action of oxygenators. Hypobaric-type oxygenators employ a high oxygen, no nitrogen environment creating a steep concentration gradient of nitrogen out of the blood and into the oxygenator, reducing the risk of GMEs forming. Adequately powered clinical studies have never been carried out with a hypobaric or dual-chamber oxygenator. These are required before such technology can be recommended for widespread clinical use.

[History of anti-embolic protection in cardiac surgery]

The review is devoted to history of anti-embolic protection system, in particular protection against cerebral embolism, in cardiac surgery and endovascular surgery. Cerebral embolism is a common and dangerous complication in cardiovascular surgery, leading to disability of patients and significantly impairing treatment outcomes. Prevention of embolic complications is an urgent task in correction of heart valve disease in cardiac and endovascular surgery.

Carbon dioxide flushing versus saline flushing of thoracic aortic stents (INTERCEPTevar): protocol for a multicentre pilot randomised controlled trial

INTRODUCTION

Thoracic endovascular aortic repair (TEVAR) carries a 3%-6.1% stroke risk, including risk of 'silent' cerebral infarction (SCI). Stent-grafts are manufactured in room air and retain air. Instructions for use recommend saline flushing to 'de-air' the system prior to insertion, but substantial amounts of air are released when deploying them, potentially leading to downstream neuronal injury and SCI. Carbon dioxide (CO2) is more dense and more soluble in blood than air, without risk of bubble formation, so could be used in addition to saline to de-air stents. This pilot trial aims to assess the feasibility of a full-scale randomised controlled trial (RCT) investigating the neuroprotective benefit against SCI with the use of CO2-flushed aortic stent-grafts.

METHODS AND ANALYSIS

This is a multicentre pilot RCT, which is taking place in vascular centres in the UK, USA and New Zealand. Patients identified for TEVAR will be enrolled after informed written consent. 120 participants will be randomised (1:1) to TEVAR-CO2 or TEVAR-saline, stratified according to TEVAR landing zone. Participants will undergo preoperative neurocognitive tests and quality of life assessments, which will be repeated at 6 weeks, or first outpatient appointment, and 6 months. Inpatient neurological testing will be performed within 48 hours of return to level 1 care for clinical stroke or delirium. Diffusion-weighted MRI will be undertaken within 72 hours postoperatively (1-7 days) and at 6 months to look for evidence and persistence of SCI. Feasibility will be assessed via measures of recruitment and retention, informing the design of a full-scale trial.

ETHICS AND DISSEMINATION

The study coordination centre has obtained approval from the London Fulham Research Ethics Committee (19/LO/0836) and Southern Health and Disability Ethics Committee (NZ) and UK's Health Regulator Authority (HRA). The study has received ethical approval for recruitment in the UK (Fulham REC, 19/LO/0836), New Zealand (21/STH/192) and the USA (IRB 019-264, Ref 378630). Consent for entering into the study will be taken using standardised consent forms by the local study team, led by a local PI. The results of the trial will be submitted for publication in an open access journal.

TRIAL REGISTRATION NUMBER

NCT03886675.

Microvascular dysfunction following cardiopulmonary bypass plays a central role in postoperative organ dysfunction

Despite significant advances in surgical technique and strategies for tissue/organ protection, cardiac surgery involving cardiopulmonary bypass is a profound stressor on the human body and is associated with numerous intraoperative and postoperative collateral effects across different tissues and organ systems. Of note, cardiopulmonary bypass has been shown to induce significant alterations in microvascular reactivity. This involves altered myogenic tone, altered microvascular responsiveness to many endogenous vasoactive agonists, and generalized endothelial dysfunction across multiple vascular beds. This review begins with a survey of in vitro studies that examine the cellular mechanisms of microvascular dysfunction following cardiac surgery involving cardiopulmonary bypass, with a focus on endothelial activation, weakened barrier integrity, altered cell surface receptor expression, and changes in the balance between vasoconstrictive and vasodilatory mediators. Microvascular dysfunction in turn influences postoperative organ dysfunction in complex, poorly understood ways. Hence the second part of this review will highlight in vivo studies examining the effects of cardiac surgery on critical organ systems, notably the heart, brain, renal system, and skin/peripheral tissue vasculature. Clinical implications and possible areas for intervention will be discussed throughout the review.

Continuous field flooding versus final one-shot CO2 insufflation in minimally invasive mitral valve repair

Background

Insufflation of carbon dioxide (CO₂) into the operative field to prevent cerebral or myocardial damage by air embolism is a well known strategy in open-heart surgery. However, here is no general consensus on the best delivery approach.

Methods

From January 2018 to November 2021, we retrospectively collected data of one hundred consecutive patients undergoing minimally invasive mitral valve repair (MIMVR). Of these, fifty patients were insufflated with continuous CO₂ 1 min before opening the left atrium and ended after its closure, and fifty patients were insufflated with one shot CO₂ 10 min before the start of left atrium closure. The primary outcome of the study was the incidence of transient post-operative cognitive disorder, in particular agitation and delirium at discontinuation of anesthesia, mechanical ventilation (MV) duration and intensive care unit (ICU) length of stay.

Results

In all patients that received continuous field flooding CO₂, correction of ventilation for hypercapnia during cardiopulmonary bypass (CPB) was applied with an increase of mean sweep gas air (2.5 L) and monitoring of VCO₂ changes. One patient vs. 9 patients of control group reported agitation at discontinuation of anesthesia (p = 0.022). MV duration was 14 ± 3 h vs. 27 ± 4 h (p = 0.016) and ICU length of stay was 33 ± 4 h vs. 42 ± 5 h (p = 0.029). A significant difference was found in the median number of total micro-emboli recorded from release of cross-clamp until 20 min after end of CPB (154 in the continuous CO₂ group vs. 261 in the one-shot CO₂ control group; p < 0.001). Total micro-emboli from the first 15 min after the release of cross-clamp was 113 in the continuous CO₂ group vs. 310 in the control group (p < 0.001). In the continuous CO₂ group, the median number of detectable micro-emboli after CPB fell to zero 9 ± 5 min after CPB vs. 19 ± 3 min in the control group (p = 0.85).

Conclusion

Continuous field flooding insufflation of CO₂ in MIMVR is associated with a lower incidence of micro-emboli and of agitation at discontinuation of anesthesia, along with improved MV duration and ICU length of stay.

Warm humidified CO2 insufflation improves pericardial integrity for cardiac surgery: a randomized control study

BACKGROUND

Flooding the surgical field with dry cold CO<inf>2</inf> during open-chamber cardiac surgery has been used to mitigate air entrainment into the systemic circulation. However, exposing epithelial surfaces to cold, dry gas causes tissue desiccation. This randomized controlled study was designed to investigate whether the use of humidified warm CO<inf>2</inf> insufflation into the cardiac cavity could reduce pericardial tissue damage and the incidence of micro-emboli when compared to dry cold CO<inf>2</inf> insufflation.

METHODS

Forty adult patients requiring elective open-chamber cardiac surgery were randomized to have either dry cold CO<inf>2</inf> insufflation via a standard catheter or humidified warm CO<inf>2</inf> insufflation via the HumiGard device (Fisher & Paykel Healthcare, Panmure, Auckland, New Zealand). The primary endpoint was biopsied pericardial tissue damage, assessed using electron microscopy. We assessed the percentage of microvilli and mesothelial damage, using a damage severity score (DSS) system. We compared the proportion of patients who had less damage, defined as DSS<2. Secondary endpoints included the severity of micro-emboli, by visual assessment of bubble load on transesophageal echocardiogram; lowest near infrared spectroscopy; total de-airing time; highest cardio-pulmonary bypass sweep speed; hospital length of stay and complications.

RESULTS

A higher proportion of patients in the humidified warm CO<inf>2</inf> group displayed conserved microvilli (47% vs. 11%, P=0.03) and preserved mesothelium (42% vs. 5%, P=0.02) compared to the control group. There were no differences in the secondary outcomes.

CONCLUSIONS

Humidified warm CO<inf>2</inf> insufflation significantly reduced pericardial epithelial damage when compared to dry cold CO<inf>2</inf> insufflation in open-chamber cardiac surgery. Further studies are warranted to investigate its potential clinical benefits.

Clinical Evaluation of Micro-Embolic Activity with Unexpected Predisposing Factors and Performance of Horizon AF PLUS during Cardiopulmonary Bypass

Background: During Cardiopulmonary Bypass (CPB) gaseous micro-emboli (GMEs) decrease the quality of the blood flow and the capillary oxygen delivery, increasing the incidence of postoperative neurocognitive disorders (POCD) following cardiac surgery. In these circumstances, the use of an efficient device, could be crucial for the removal and reduction of micro-embolic activity. Methods: From February 2022 to March 2022, we prospectively collected data from 40 consecutive patients undergoing conventional and minimally invasive cardiac surgery that used the Horizon AF PLUS (Eurosets, Medolla, Italy). We collected, during the CPB's time, the incidence of unexpected predisposing factors for micro-embolic activity reported in the literature with the GMEs count and their diameter through the GAMPT BCC 300 (Germany). Results: The group of patients without unexpected predisposing factors for micro-embolic activity (55%) reported a GME volume of 0.59 ± 0.1 (μL) in the arterial line (p-value 0.67). In both groups were no reported performance deficit during the procedures for oxygenation and CO2 removal. Conclusions: Our clinical analysis showed that Horizon AF PLUS is an effective and safe device without iatrogenic perioperative complications, for the reduction of micro embolic activity during CPBs procedures, with high efficiency in terms of oxygenating performance and thermal exchange.

An Update on Postoperative Cognitive Dysfunction Following Cardiac Surgery

Postoperative cognitive dysfunction is extremely prevalent following cardiac surgery. The increasing patient age and comorbidity profile increases their susceptibility to cognitive impairment. The underlying pathophysiological mechanisms leading to cognitive impairment are not clearly elucidated. Using the contemporary literature (2015-present), this narrative review has three aims. Firstly, to provide an overview of postoperative cognitive impairment. Secondly, to analyse the predominant pathophysiological mechanisms leading to cognitive dysfunction following cardiac surgery such as inflammation, cerebral hypoperfusion, cerebral microemboli, glycaemic control and anaesthesia induced neurotoxicity. Lastly, to assess the current therapeutic strategies of interest to address these pathophysiological mechanisms, including the administration of dexamethasone, the prevention of prolonged cerebral desaturations and the monitoring of cerebral perfusion using near-infrared spectroscopy, surgical management strategies to reduce the neurological effects of microemboli, intraoperative glycaemic control strategies, the effect of volatile vs. intravenous anaesthesia, and the efficacy of dexmedetomidine.

Role of Transcranial Doppler in Cardiac Surgery Patients

Abstract

Purpose of Review

This review discusses applications of transcranial Doppler (TCD) in cardiac surgery, its efficacy in preventing adverse events such as postoperative cognitive decline and stroke, and its impact on clinical outcomes in these patients.

Recent Findings

TCD alone and in combination with other neuromonitoring modalities has attracted attention as a potential monitoring tool in cardiac surgery patients. TCD allows not only the detection of microemboli and measurement of cerebral blood flow velocity in cerebral arteries but also the assessment of cerebral autoregulation.

Summary

Neuromonitoring is critically important in cardiac surgery as surgical and anesthetic interventions as well as several other factors may increase the risk of cerebral embolization (gaseous and particulate) and cerebral perfusion anomalies, which may lead to adverse neurological events. As an experimental tool, TCD has revealed a possible association of poor neurological outcome with intraoperative cerebral emboli and impaired cerebral perfusion. However, to date, there is no evidence that routine use of transcranial Doppler can improve neurological outcome after cardiac surgery.

Elimination of CO2 insufflation-induced hypercapnia in open heart surgery using an additional venous reservoir

 

OBJECTIVES

Carbon dioxide (CO2) gas insufflation is used for continuous de-airing during open heart surgery. The aim was to evaluate if an additional separate venous reservoir eliminates CO2 insufflation-induced hypercapnia and keeps sweep gas flow of the oxygenator constant.

METHODS

A separate reservoir was used during cardiopulmonary bypass in addition to a standard venous reservoir. The additional reservoir received drained blood and CO2 gas continuously via a suction drain (1 l/min) and handheld suction devices from the surgical wound. CO2 gas was insufflated via a gas diffuser in the open wound at 10 l/min. In a cross-over design for each patient, gas and blood were either continuously drained from the additional to the standard venous reservoir or not. CO2 pressure in arterial blood (PaCO2) was measured after adjustment of sweep gas flow as necessary and after steady state of PaCO2 was observed. Mean values for each setup (median 4 times) for each patient were analysed with Wilcoxon rank-sum test.

RESULTS

Ten adult patients undergoing open aortic valve replacement were included. Median PaCO2 did not differ between setups (5.41; 5.29-5.57, interquartile range vs 5.41; 5.24-5.58, P = 0.92), whereas sweep gas flow (l/min) was lower (2.58; 2.50-3.16 vs 4.42; 4.0-5.40, P = 0.002) when CO2 gas was not drained from the additional to the standard reservoir.

CONCLUSIONS

An additional venous reservoir for the evacuation of blood from the open surgical wound eliminates CO2 insufflation-induced hypercapnia in open heart surgery keeping PaCO2 and sweep gas flow constant. This prevents possible CO2-induced hyperperfusion of the brain and decreases the risk of cerebral particulate embolization during CO2 insufflation for de-airing in open heart surgery.

CLINICAL TRIAL REGISTRATION

NCT04202575.

IRB APPROVAL DAT AND NUMBER

2018-07-13 and 2018/1091-31.

The Performance of the Current Risk Prediction Scoring Systems in Patients Undergoing Anaortic Off-pump Coronary Artery Bypass Grafting

BACKGROUND

This study aimed to evaluate the performance of the Society of Thoracic Surgeons (STS) risk model and European System for Cardiac Operative Risk Evaluation (EuroSCORE) II for patients undergoing anaortic off-pump coronary artery bypass grafting (OPCAB).

METHODS

From January 2010 to June 2017, 1,048 patients (isolated anaortic OPCAB: 1,043, on-pump conversion:5) undergoing isolated anaortic OPCAB were enrolled. The STS risk score and EuroSCORE II were calculated with dedicated online software. Calibration of the models were performed by the risk-adjusted event ratio that was defined as observed events divided by expected events (O/E ratio) and Hosmer-Lemeshow test. The discrimination powers were evaluated by the area under the receiver operating characteristic curve (AUC).

RESULTS

Operative mortality occurred in 10 patients (0.95%). The predicted mortality rates by the EuroSCORE II and STS risk model were 2.58 ± 4.15% and 1.72 ± 2.92%, respectively. The O/E ratio of the EuroSCORE II was 0.370 with significant overprediction of operative mortality (confidence interval [CI], 0.157-0.652; P = 0.003). The STS score also overpredicted the operative mortality (O/E ratio, 0.556) with marginal significance (CI, 0.266-1.023; P = 0.052). Permanent stroke occurred in 6 patients (0.53%). The predicted permanent stroke occurrence rate was 1.73 ± 1.48%. The O/E ratio was 0.332 with significant overprediction of permanent stroke (CI, 0.121-0.722; P = 0.011). Regarding discrimination power for the STS risk model, the operative mortality was excellent (AUC, 0.876) and permanent stroke was acceptable (AUC, 0.740). The EuroSCORE II showed good discrimination power (AUC, 0.784). There was a significant difference in discrimination power for mortality between STS and EuroSCORE II risk models (P = 0.007).

CONCLUSION

Preexisting risk predicting scoring systems, STS risk model and EuroSCORE II, overpredict the risk of mortality and stroke rate for anaortic OPCAB. These findings suggest the possibility that anaortic OPCAB can lower the operative mortality and occurrence of postoperative stroke than conventional coronary artery bypass grafting.

Robotic-assisted cardiac surgery without aortic cross-clamping: A safe alternative approach

BACKGROUND AND AIM

Attempting to place an aortic cross-clamp may complicate surgery and postoperative outcomes in patients who have mediastinal adhesions or in those with extensive aortic calcification. Although right-sided cardiac surgery via thoracotomy is not a new technique in these patients, robotic-assisted intracardiac repair without cross-clamping was not reported in a large group of patients previously. In this study, the safety of robotic-assisted cardiac surgery without aortic cross-clamping was examined.

METHODS

From January 2010 to March 2020, 304 patients underwent robotic-assisted cardiac surgery in our center and in 25 of these patients (8.2%) with a mean age of 65.5 ± 20 years myocardial protection was succeeded with moderate hypothermic ventricular fibrillatory arrest. Severe pericardial adhesions or existence of highly calcified ascending aorta were the indications for fibrillatory arrest during robotic assistant surgery.

RESULTS

Most patients were in New York Heart Association Class ≥II (88.0%) and the mean logistic Euroscore value was 18.5 ± 22.3. The type of operations were mitral/tricuspid valve repair/replacement, cryoablation, atrial septal defect closure, and pericardiectomy. Cardiopulmonary bypass times were 141.5 ± 47 (minimum 77-maximum 252) min. There was no case of conversion to open thoracotomy or sternotomy. Hemiparesis was observed in one patient. Two patients with 78.2 and 81.9 Euroscore values had mesenteric ischemia and multiorgan failure, respectively, and died at postoperative period.

CONCLUSIONS

Robotic-assisted cardiac surgery without cross-clamping may provide reasonable outcomes in patients with severe aortic calcification or mediastinal adhesions undergoing intracardiac repair. These acceptable outcomes may encourage surgeons to perform this approach in appropriate group of patients.

Bubbles Moving in Blood Flow in a Microchannel Network: The Effect on the Local Hematocrit

Air inside of blood vessels is a phenomenon known as gas embolism. During the past years, studies have been performed to assess the influence of air bubbles in microcirculation. In this study, we investigated the flow of bubbles in a microchannel network with several bifurcations, mimicking part of a capillary system. Thus, two working fluids were used, composed by sheep red blood cells (RBCs) suspended in a Dextran 40 solution with different hematocrits (5% and 10%). The experiments were carried out in a polydimethylsiloxane (PDMS) microchannel network fabricated by a soft lithography. A high-speed video microscopy system was used to obtain the results for a blood flow rate of 10 µL/min. This system enables the visualization of bubble formation and flow along the network. The results showed that the passage of air bubbles strongly influences the cell's local concentration, since a higher concentration of cells was observed upstream of the bubble, whereas a lower local hematocrit was visualized at the region downstream of the bubble. In bifurcations, bubbles may split asymmetrically, leading to an uneven distribution of RBCs between the outflow branches.

Is hospitalisation a risk factor for cognitive decline in the elderly?

PURPOSE OF REVIEW

Cognitive decline is frequently reported after hospitalisation in the contexts of surgery, delirium and critical care. The question not adequately addressed is whether all types of acute hospitalisations increase the risk of cognitive decline. As acute hospitalisations are common in the elderly, who are also vulnerable to cognitive decline, this possible association is of significant concern.

RECENT FINDINGS

This review summarises cognitive outcomes from recent observational studies investigating acute hospitalisation (emergent and elective) in older age adults. Studies were identified from searching Medline, Embase and PsycINFO databases and citations lists. The highest incidence of cognitive decline has been reported following critical care admissions and admissions complicated by delirium, although all types of acute hospitalisations are implicated. Age is the most consistent risk factor for cognitive decline. Several etiological and therapeutic aspects are being investigated, particularly the measurement of inflammatory biomarkers and treatment with anti-inflammatory medications.

SUMMARY

Acute hospitalisation for any reason appears to increase the risk of cognitive decline in older adults, but the cause remains elusive. Future research must clarify the nature and modifiers of posthospitalisation cognitive change, a priority in the face of an ageing population.

Pumping O2 with no N2: An Overview of Hollow Fiber Membrane Oxygenators with Integrated Arterial Filters

The advancement of cardiac surgery benefits from the continual technological progress of cardiopulmonary bypass (CPB). Every improvement in the CPB technology requires further clinical and laboratory tests to prove its safety and effectiveness before it can be widely used in clinical practice. In order to reduce the priming volume and eliminate a separate arterial filter in the CPB circuit, several manufacturers developed novel hollow-fiber membrane oxygenators with integrated arterial filters (IAF). Clinical and experimental studies demonstrated that an oxygenator with IAF could reduce total priming volume, blood donor exposure and gaseous microemboli delivery to the patient. It can be easily set up and managed, simplifying the CPB circuit without sacrificing safety. An oxygenator with IAF is expected to be more beneficial to the patients with low body weight and when using a minimized extracorporeal circulation system. The aim of this review manuscript was to discuss briefly the concept of integration, the current oxygenators with IAF, and the in-vitro / in-vivo performance of the oxygenators with IAF.

Carbon dioxide de-airing in minimal invasive cardiac surgery, a new effective device

BACKGROUND

Arterial air embolism during open heart surgery may cause postoperative complications including cerebral injury, myocardial dysfunction, and dysrhythmias. Despite standard de-airing techniques during surgery large amounts of arterial air emboli may still occur, especially during weaning from cardiopulmonary bypass. To prevent this insufflation of carbon dioxide in the wound cavity has been used since the 1950s. The aim of this study was to assess a new mini-diffuser for efficient carbon dioxide de-airing of a minimal invasive cardiothoracic wound cavity model. Up until now no device has been evaluated for this purpose.

METHODS

A new insufflation device, a mini-diffuser, was tested. A thin plastic tube was used as control. The end of the mini-diffuser or the control, respectively, was positioned in a minimal invasive thoracic wound model. Remaining air content was measured during steady state and during intermittent suction with a rough suction device at different carbon dioxide flow rates. Measurements were also carried out in the open surgical wound during minimal invasive aortic surgery in six patients.

RESULTS

The air content was below 1% 4 cm below the surface of the open wound model during continuous carbon dioxide inflow of 2-10 L/min with the mini diffuser. In comparison, carbon dioxide insufflation via the open-ended tube resulted in a mean air content between 10 and 75%. The mean air content of the wound model remained below 1% at a carbon dioxide flow rate of 3-5 L/min during intermittent application of a suction device with a suction rate of 15 L/min. In 6 patients undergoing minimal invasive aortic valve replacement air content in the open surgical wound remained below 1% at a continuous carbon dioxide flow rate of 5 and 8 L/min via the mini-diffuser, respectively.

CONCLUSIONS

The mini diffuser was effective for carbon dioxide de-airing, i.e. < 1% remaining air, of a minimal invasive cardiothoracic wound cavity model with and without intermittent rough suction as well as in patients undergoing minimal invasive aortic valve surgery.

Retrospective Analysis of Air Handling by Contemporary Oxygenators in the Setting of Cardiac Surgery

Purpose: Cardiac surgery with the use of extracorporeal circulation is associated with a significant risk for gaseous microemboli (GME) despite excellent surgical techniques and highest operative standards. GME are associated with postoperative neurocognitive dysfunction and negative clinical outcome. This study determines whether oxygenator design has influence on perioperative outcome after cardiac surgery.

Methods: Three different oxygenator models with integrated arterial filter (HiliteAF 7000, Fusion Affinity, and Synthesis) were retrospectively evaluated in 55 patients undergoing elective cardiac surgery with the use of extracorporeal circulation. The two-channel ultrasound bubble counter BCC200 was used to detect GME in real time.

Results: All three oxygenators differ in terms of structural specifications and have different rates of number and volume GME reduction. The Fusion Affinity had the lowest arterial GME volume (1.81 µL ± 0.23 µL), which was statistically significant compared to the Synthesis (3.37 µL ± 0.71 µL, p = 0.014). However, the Synthesis had lower absolute numbers at the venous GME count (31771 µL ± 6579 µL) versus the Fusion Affinity (49304 µL ± 8196 µL). However, with regard to clinical outcome after cardiac surgery (duration of invasive and non-invasive mechanical ventilation, incidence of delirium, stroke, acute renal failure, or new myocardial infarction), we found no differences between groups.

Conclusion: Despite significant differences in the design specifications, all oxygenators eliminated relevant GME volumes safely.

Microbubble moving in blood flow in microchannels: effect on the cell-free layer and cell local concentration

Gas embolisms can hinder blood flow and lead to occlusion of the vessels and ischemia. Bubbles in microvessels circulate as tubular bubbles (Taylor bubbles) and can be trapped, blocking the normal flow of blood. To understand how Taylor bubbles flow in microcirculation, in particular, how bubbles disturb the blood flow at the scale of blood cells, experiments were performed in microchannels at a low Capillary number. Bubbles moving with a stream of in vitro blood were filmed with the help of a high-speed camera. Cell-free layers (CFLs) were observed downstream of the bubble, near the microchannel walls and along the centerline, and their thicknesses were quantified. Upstream to the bubble, the cell concentration is higher and CFLs are less clear. While just upstream of the bubble the maximum RBC concentration happens at positions closest to the wall, downstream the maximum is in an intermediate region between the centerline and the wall. Bubbles within microchannels promote complex spatio-temporal variations of the CFL thickness along the microchannel with significant relevance for local rheology and transport processes. The phenomenon is explained by the flow pattern characteristic of low Capillary number flows. Spatio-temporal variations of blood rheology may have an important role in bubble trapping and dislodging.

Vascular air embolism: A silent hazard to patient safety

PURPOSE

To narratively review published information on prevention, detection, pathophysiology, and appropriate treatment of vascular air embolism (VAE).

MATERIALS AND METHODS

MEDLINE, SCOPUS, Cochrane Central Register and Google Scholar databases were searched for data published through October 2016. The Manufacturer and User Facility Device Experience (MAUDE) database was queried for "air embolism" reports (years 2011-2016).

RESULTS

VAE may be introduced through disruption in the integrity of the venous circulation that occurs during insertion, maintenance, or removal of intravenous or central venous catheters. VAE impacts pulmonary circulation, respiratory and cardiac function, systemic inflammation and coagulation, often with serious or fatal consequences. When VAE enters arterial circulation, air emboli affect cerebral blood flow and the central nervous system. New medical devices remove air from intravenous infusions. Early recognition and treatment reduce the clinical sequelae of VAE. An organized team approach to treatment including clinical simulation can facilitate preparedness for VAE. The MAUDE database included 416 injuries and 95 fatalities from VAE. Data from the American Society of Anesthesiologists Closed Claims Project showed 100% of claims for VAE resulted in a median payment of $325,000.

CONCLUSIONS

VAE is an important and underappreciated complication of surgery, anesthesia and medical procedures.

Delirium after cardiac surgery: A pilot study from a single tertiary referral center

BACKGROUND

Advances in cardiac surgery has shifted paradigm of management to perioperative psychological illnesses. Delirium is a state of altered consciousness with easy distraction of thoughts. The pathophysiology of this complication is not clear, but identification of risk factors is important for positive postoperative outcomes. The goal of the present study was to prospectively identify the incidence, motoric subtypes, and risk factors associated with development of delirium in cardiac surgical patients admitted to postoperative cardiac intensive care, using a validated delirium monitoring instrument.

MATERIALS AND METHODS

This is a prospective, observational study. This study included 120 patients of age 18-80 years, admitted to undergo cardiac surgery after applying inclusion and exclusion criteria. Specific preoperative, intraoperative, and postoperative data for possible risk factors were obtained. Once in a day, assessment of delirium was done. Continuous variables were measured as mean ± standard deviation, whereas categorical variables were described as proportions. Differences between groups were analyzed using Student's t-test, Mann-Whitney U-test, or Chi-square test. Variables with a P < 0.1 were then used to develop a predictive model using stepwise logistic regression with bootstrapping.

RESULTS

Delirium was seen in 17.5% patients. The majority of cases were of hypoactive delirium type (85.72%). Multiple risk factors were found to be associated with delirium, and when logistic regression with bootstrapping applied to these risk factors, five independent variables were detected. History of hypertension (relative risk [RR] =6.7857, P = 0.0003), carotid artery disease (RR = 4.5000, P < 0.0001) in the form of stroke or hemorrhage, noninvasive ventilation (NIV) use (RR = 5.0446, P < 0.0001), Intensive Care Unit (ICU) stay more than 10 days (RR = 3.1630, P = 0.0021), and poor postoperative pain control (RR = 2.4958, P = 0.0063) was associated with postcardiac surgical delirium.

CONCLUSIONS

Patients who developed delirium had systemic disease in the form of hypertension and cerebrovascular disease. Delirium was seen in patients who had higher postoperative pain scores, longer ICU stay, and NIV use. This study can be used to develop a predictive tool for diagnosing postcardiac surgical delirium.

Aortic Arch Atheroma: Stroke Reduction in Cardiac Surgical Patients

Cardiac surgery is increasingly performed on elderly patients with extensive coronary artery abnormalities who have impaired left ventricular function, decreased physiologic reserve, and multiple comorbid conditions. Considerable numbers of these patients develop perioperative neurologic complications ranging from subtle cognitive dysfunction to more evident postoperative confusion, delirium, and, less commonly, clinically apparent stroke. Magnetic resonance imaging studies have elucidated that a considerable number of patients have new ischemic brain infarcts, particularly after conventional coronary artery bypass graft surgery. Mechanisms of cerebral injury during and after cardiac surgery are discussed. Intraoperative transesophageal echocardiography and epiaortic scanning for detection of atheromatous disease of the proximal thoracic aorta is paramount in identifying patients at high risk from neurologic injury. It is important to recognize that our efforts to minimize neurologic injury should not be limited to the intraoperative period. Particular efforts should be directed to temperature management, glycemia control, and pharmacologic neuroprotection extending into the postoperative period. Preoperative magnetic resonance angiography may be of value for screening patients with significant atheroma of the proximal thoracic aorta. It is likely that for patients with no significant atheromatous disease, conventional coronary artery revascularization is the most effective long-term strategy, whereas patients with atheromatous thoracic aorta may be better managed with beating heart surgery, hybrid techniques, or medical therapy alone. Patient stratification based on the aortic atheromatic burden should be addressed in future trials designed to tailor treatment strategies to improve long-term outcomes of coronary heart disease and reduce the risks of perioperative neurologic injury.

Bubbles and bypass: an update

Bubbles in the bloodstream are not a normal condition -yet they remain a fact of cardiopulmonary bypass (CPB), having been extensively studied and documented since its inception some 50 years ago. While detectable levels of gaseous microemboli (GME) have decreased significantly in recent years and gross air embolism has been nearly eliminated due to increased awareness of etiologies and technological advances, methods of use of current perfusion systems continue to elicit concerns over how best to totally eliminate GME during open-heart procedures. A few studies have correlated adverse neurocognitive manifestations associated with excessive quantities of GME.

Newer techniques currently in vogue, such as vacuum-assisted venous drainage, low-prime perfusion circuits, and carbon dioxide flooding of the operative field, have, in some instances, exacerbated the problem of gas embolism or engendered secondary complications in the safe conduct of CPB. Doppler monitoring (circuit or transcranial) primarily remains a research tool to detect GME emanating from the circuit or passing into the patients’ cerebral vasculature. Newer developments not yet widely available, such as multiple-frequency harmonics, may finally provide a tool to distinguish particulate microemboli from GME and further delineate the clinical significance of GME.

Cognitive Dysfunction After Cardiac Surgery: Revisiting Etiology

Cognitive dysfunction remains a frequent complication of cardiac surgery. Despite many years of research, few preventive strategies and no definitive therapeutic options exist for the management of this troublesome clinical problem. This shortcoming may be secondary to an incomplete understanding of the pathophysiology and etiology of cognitive loss after cardiac surgery; a better understanding of the etiology is essential to finding new therapies. The etiology of cognitive dysfunction after cardiac surgery is multifactorial and includes cerebral microembolization, global cerebral hypoperfusion, systemic and cerebral inflammation, cerebral temperature perturbations, cerebral edema, and possible blood-brain barrier dysfunction, all superimposed on genetic differences in patients that may make them more susceptible to injury or unable to repair from injury once it has occurred. This review expands on these potential etiologies in detailing the evidence for their existence.

Reducing Cerebral Emboli During Cardiopulmonary Bypass

Neurologic injury is a common complication of cardiac surgery and is associated with significant morbidity, mortality, and resource utilization. The incidence varies widely according to the definition used, patient age, and complexity of surgery. The manifestations of neurologic injury are broad, ranging from subtle neurocognitive dysfunction to frank stroke. An increasing amount of evidence points to cerebral embolization during cardiopulmonary bypass (CPB) as the principal etiologic factor of these neurologic complications. Cerebral emboli may be composed of atherosclerotic debris, calcium, air, fat, platelet thrombi, or CPB tubing. Advancements in perfusion technology, CPB techniques and surgical strategies may lead to a reduction in neurologic injury during cardiac surgery. In the current paper, we discuss the pathophysiology of neurologic injury after cardiac surgery and methods of reducing cerebral embolization. Reducing emboli and neurologic injury during CPB requires a multidisciplinary approach that includes several simple diagnostic and therapeutic strategies. Reducing cerebral emboli should be a major goal for future research in the fields of cardiac anesthesia, surgery and perfusion.

Clinical evaluation of the air-handling properties of contemporary oxygenators with integrated arterial filter

Gaseous microemboli (GME) may originate from the extracorporeal circuit and enter the arterial circulation of the patient. GME are thought to contribute to cerebral deficit and to adverse outcome after cardiac surgery. The arterial filter is a specially designed component for removing both gaseous and solid microemboli. Integration of an arterial filter with an oxygenator is a contemporary concept, reducing both prime volume and foreign surface area. This study aims to determine the air-handling properties of four contemporary oxygenator devices with an integrated arterial filter. Two oxygenator devices, the Capiox FX25 and the Fusion, showed significant increased volume of GME reduction rates (95.03 ± 3.13% and 95.74 ± 2.69%, respectively) compared with both the Quadrox-IF (85.23 ± 5.84%) and the Inspire 6F M (84.41 ± 12.93%). Notably, both the Quadrox-IF and the Inspire 6F M as well as the Capiox FX 25 and the Fusion showed very similar characteristics in volume and number reduction rates and in detailed distribution properties. The Capiox FX25 and the Fusion devices showed significantly increased number and volume reduction rates compared with the Quadrox-IF and the Inspire 6F M devices. Despite the large differences in design of all four devices, our study results suggest that the oxygenator devices can be subdivided into two groups based on their fibre design, which results in screen filter (Quadrox-IF and Inspire 6F M) and depth filter (Capiox FX25 and Fusion) properties. Depth filter properties, as present in the Capiox FX25 and Fusion devices, reduced fractionation of air and may ameliorate GME removal.

The dynamic bubble trap reduces microbubbles in extracorporeal circulation and high intensity transient signals in the middle cerebral artery: a case report

Microemboli during extracorporeal circulation (ECC) might be a reason for postoperative neuropsychological dysfunction. This case report shows that reduction of microbubbles in the arterial line, as well as high intensity transient signals (HITS) in the middle cerebral artery (MCA), could be accomplished by use of a dynamic bubble trap (DBT) during routine coronary artery bypass graft (CABG) surgery in a 63-year-old male. The DBT was placed after the arterial filter, an ultrasound Doppler device was used for detection of microemboli before and after the DBT. HITS were measured by a transcranial ultrasound Doppler in both MCAs. For first 32 min of ECC, the DBT was excluded; 54 916 microbubbles and 507 HITS were counted. In the next 30 min, blood flow was directed through the DBT. This led to a significant reduction of microbubbles from 55 888 to 18 237; accordingly, only 120 HITS were registered. A DBT, integrated in ECC for routine CABG, effectively reduces air bubbles, thus protecting the cerebrovascular system from micro-embolization, as demonstrated by lower HITS counts.

Effect of perfusionist technique on cerebral embolization during cardiopulmonary bypass

Objective: To determine the association between high-intensity transient signals (HITS) and perfusionist interventions, purging techniques, pump flows and venous reservoir blood volume levels during cardiopulmonary bypass.

Methods: Transcranial Doppler was used to detect HITS in the middle cerebral artery during the period of aortic crossclamping in patients undergoing coronary artery bypass grafting. Perfusionist-related interventions were recorded and included blood sampling (including the number of times that the oxygenator sampling manifold was purged), drug bolus injections and infusions (vasopressors, crystalloid and mannitol). Pump flows and venous reservoir volume levels were also documented.

Results: There were 534 interventions in 90 patients [median number of interventions per patient: 6 (quartiles: 4, 8)]. The median total HITS count from all interventions was 17 (5, 37). This represented 38% of the total HITS counts during aortic crossclamping. Factors contributing to differences in the HITS count included type of intervention ( p<0.0001) and perfusionist (p=0.0012). Blood sampling ( p<0.001) and drug bolus injections (p=0.06) had higher HITS counts per patient than infusions. Repetitive purging significantly increased HITS counts (r=0.74; p<0.001). Purging perfusionists (purging: 1 - 10 times) had higher HITS counts per patient [5 HITS (1, 15) than nonpurgers [0 HITS (0, 1) p<0.0001]. HITS counts were significantly correlated with reservoir volumes (r=-0.20, p=0.017) and pump flow rates (r=0.21, p=0.008). Reservoir volume levels ≤ 800 mL were associated with higher HITS counts per intervention [11 HITS (2, 27)] during blood sampling compared with higher volume levels [3 HITS (1, 10), p=0.001].

Conclusions: Cerebral emboli associated with perfusionist interventions can be minimized by not purging the sampling manifold, using continuous infusions rather than bolus injections, and maintaining high blood-volume levels (>800 mL) in the venous reservoir.

Use of a dynamic bubble trap in the arterial line reduces microbubbles during cardiopulmonary bypass and microembolic signals in the middle cerebral artery

Neurological complications remain an important cause of morbidity and mortality of patients following cardiopulmonary bypass (CPB). Microemboli, as well as cerebral hypoperfusion, are the main postulated mechanisms. This study demonstrates that the insertion of a dynamic bubble trap (DBT) into the curcuit reduces microbubbles in the arterial line and microembolic signals (MES) in the middle cerebral arteries (MCAs).

We investigated 12 patients during coronary artery bypass grafting (CABG). The DBT was inserted between the arterial filter and the arterial cannula. For detection of microemboli before and after the DBT, a special ultrasound Doppler device was used. MES were detected by transcranial Doppler monitoring in both MCAs of the patients. Microbubbles and MES were counted during bypass. These data were compared to 12 patients who were operated in a previous period without the use of a DBT. There were no significant differences in both groups with respect to gender, age, crossclamp and bypass time and number of anastomoses. In the group without a DBT in the circuit, a mean of 6311 microbubbles per operation could be observed distal to the arterial filter, corresponding to 282 MES. After inclusion of a DBT, we could register, in the second group, 8496 microemboli proximal and 2915 distal of the DBT, corresponding to 89 MES per operation. The reduction rate of microbubbles in the tubing was 65.7%, corresponding to a reduction in MES of about 86.2%. We conclude that the insertion of a DBT in the arterial line of CPB circuit protects the cerebrovascular system from microembolic events, as demonstrated by lower MES counts.

Comparison of conventional extracorporeal circulation and minimal extracorporeal circulation with respect to microbubbles and microembolic signals

The intention of minimal extracorporeal circulation (MECC) is to reduce priming volume and minimize contact of blood with polymers and air in a closed system. In contrast to conventional extracorporeal circulation (ECC), a venous reservoir is missing. Thus, air trapping is limited and avoidance of bubble embolism is a major concern. This study investigates microbubbles (MBB) number and size in the venous and arterial lines of ECC and MECC compared to the number of microembolic signals (MES) in the right and left middle cerebral artery (MCA).

Twenty patients undergoing coronary surgery were operated either with conventional ECC (cardiotomy reservoir, Rotaflow pump, Quadrox oxygenator, Quart filter) or MECC (Quart filter, Rotaflow pump, Quadrox oxygenator). Number and size of MBB were monitored in the venous and arterial lines with an ultrasound Doppler system. MES in right and left MCAs were measured by transcranial Doppler (TCD) monitoring. Patients undergoing MECC had additional sealing of the venous cannula by a ligature at the site of its insertion into the right atrium.

There were no significant differences between groups with respect to age, X-clamping, bypass time and number of distal anastomoses. The number of MES and MBB in the arterial line was comparable between the groups. On the venous side, MECC-perfusion shows a significantly lower number of MBB. This could be explained with the additional sealing of the venous cannula. Furthermore, our data indicate that the MBB-volume reaching the pump will also appear in the arterial outflow and into the patient’s MCA. For this reason, the avoidance of air contamination is a major concern for surgeons, anaesthesiologists and perfusionists.

Intraoperative Embolization and Cognitive Decline After Cardiac Surgery

Since the advent of cardiac surgery, complications have existed in many forms. Recent work has focused on the safety of current cardiac surgery with particular emphasis on cognitive outcomes. Cardiopulmonary bypass has improved the safety of operative practice; however, increasing concern surrounds the measurable and immeasurable impact embolization has on the brain. New ischemic lesions have been associated with distant emboli, which intraoperatively enter the cardiovascular system. This has prompted better characterization of the nature of emboli manifesting as cognitive impairment postoperatively. The difficulty in attributing causation relates to the subclinical damage that does not necessarily manifest as clinical stroke. Transcranial Doppler has become an important tool in documenting cerebral emboli during surgery. The purpose of this systematic review is to focus on the current literature to improve our understanding of the impact embolization has on the brain. We also aim to investigate which cardiac interventions hold the greatest burden of embolic load and how previous literature has investigated the impact of emboli on cognition by monitoring emboli during specific cardiac interventions. Significant intraoperative factors such as the cardiopulmonary bypass machine and surgical interventions have been highlighted to summarize the current literature associating cerebral embolization with these factors and postoperative cognitive outcomes. The findings of this review report that the current literature is divided as to whether the impact of embolization during cardiac surgery has any adverse impact on cognition. This review highlights that the ultimate goal of improving cognitive safety will involve further careful consideration of multifactorial events.

Carbon dioxide insufflation and neurocognitive outcome of open heart surgery

Aim

Neurocognitive dysfunction continues to be the bane of open heart surgery despite vast improvements in surgical, anesthetic, and postoperative management. This observational cohort study was carried out to evaluate the efficacy of intraoperative CO2 insufflation by the field flooding technique in reducing postoperative neurocognitive dysfunction.

Methods

Three hundred randomly selected patients undergoing open heart surgery were observed: 150 (group A) were exposed to CO2 insufflation, and the other 150 (group B) were not exposed to CO2. Anesthetic, cardiopulmonary bypass, and myocardial protection techniques were standardized and similar in both groups. Neurocognitive function tests were performed preoperatively, 1 week postoperatively, and after 1 month.

Results

The analysis revealed that neurocognitive dysfunction occurred in 8 of 150 patients in group A (incidence p1 = 0.053) and 27 of 150 in group B (incidence p2 = 0.18). The relative risk of neurocognitive dysfunction was 0.30 ( p = 0.001, 95% confidence interval 0.14–0.63), implying that CO2 insufflation is protective against neurocognitive dysfunction. The risk difference was 0.13 ( p2– p1); this implies that 13% of patients can be prevented from developing neurocognitive dysfunction if exposed to CO2.

Conclusion

This study confirms the known advantage of the relatively underutilized practice of CO2 insufflation. We recommend that CO2 insufflation be performed in all open heart surgery cases to bring down the incidence of neurocognitive dysfunction. This technique is simple to use without any major paraphernalia or additional cost.

A novel software program for detection of potential air emboli during cardiac surgery

Background

Risks associated with air emboli introduced during cardiac surgery have been highlighted by reports of postoperative neuropsychological dysfunction, myocardial dysfunction, and mortality. Presently, there are no standard effective methods for quantifying potential emboli in the bloodstream during cardiac surgery. Our objective was to develop software that can automatically detect and quantify air bubbles within the ascending aorta and/or cardiac chambers during cardiac surgery in real time.

Findings

We created a software algorithm (“Detection of Emboli using Transesophageal Echocardiography for Counting, Total volume, and Size estimation”, or DETECTS™) to identify and measure potential emboli present during cardiac surgery using two-dimensional ultrasound. An in vitro experiment was used to validate the accuracy of DETECTS™ at identifying and measuring air emboli. An experimental rig was built to correlate the ultrasound images to high definition camera images of air bubbles created in water by an automatic bubbler system. There was a correlation between true bubble size and the size reported by DETECTS™ in our in vitro experiment (r = 0.76). We also tested DETECTS™ using TEE images obtained during cardiac surgery, and provide visualization of the software interface.

Conclusions

While monitoring the heart during cardiac surgery using existing ultrasound technology and DETECTS™, the operative team can obtain real-time data on the number and volume of potential air emboli. This system will potentially allow de-airing techniques to be evaluated and improved upon. This could lead to reduced air in the cardiac chambers after cardiopulmonary bypass, possibly reducing the risk of neurological dysfunction following cardiac surgery.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-7120-13-3) contains supplementary material, which is available to authorized users.

In vitro air removal characteristics of two neonatal cardiopulmonary bypass systems: filtration may lead to fractionation of bubbles

Introduction of gaseous microemboli (GME) into the arterial line of a pediatric cardiopulmonary bypass (CPB) circuit may lead to cognitive decline and adverse outcomes of the pediatric patient.Arterial filters are incorporated into CPB circuits as a safeguard for gross air and to reduce GME. Recently, arterial filters were integrated in two neonatal oxygenators to reduce volume and foreign surface area. In this study a clinical CPB scenario was simulated. The oxygenators, the corresponding venous reservoirs and the complete CPB circuits were compared regarding air removal and bubble size distribution after the introduction of an air bolus or GME. During a GME challenge, the Capiox FX05 oxygenator removed a significantly higher volume of GME than the QUADROX-i Neonatal oxygenator (97% vs. 86%). Detailed air removal characteristics showed that more GME in the range of 20-50 µm were leaving the devices than were entering. This phenomenon seems to be more present in the Capiox FX05. The circuits were also challenged with an air bolus. Each individual component tested removed 99.9%, which resulted in an air volume reduction of 99.99% by either complete CBP circuit. Overall, we conclude that both CPB systems were very adequate in removing GME and gross air. The air removal properties of both systems are considered safe and reliable. Detailed GME distribution data show that the Capiox FX05 showed more small GME (<50 µm) due to fractionation of larger GME when compared to the QUADROX-i Neonatal. We may conclude that filtration may lead to fractionation.

Cognitive dysfunction after on-pump operations: neuropsychological characteristics and optimal core battery of tests

Postoperative cognitive dysfunction (POCD) is a mild form of perioperative ischemic brain injury, which emerges as memory decline, decreased attention, and decreased concentration during several months, or even years, after surgery. Here we present results of our three neuropsychological studies, which overall included 145 patients after on-pump operations. We found that the auditory memory span test (digit span) was more effective as a tool for registration of POCD, in comparison with the word-list learning and story-learning tests. Nonverbal memory or visuoconstruction tests were sensitive to POCD in patients after intraoperative opening of cardiac chambers with increased cerebral air embolism. Psychomotor speed tests (digit symbol, or TMT A) registered POCD, which was characteristic for elderly atherosclerotic patients. Finally, we observed that there were significant effects of the order of position of a test on the performance on this test. For example, the postoperative performance on the core tests (digit span and digit symbol) showed minimal impairment when either of these tests was administered at the beginning of testing. Overall, our data shows that the selection of tests, and the order of which these tests are administered, may considerably influence the results of studies of POCD.

Cerebrovascular Complications Related to Atrial Fibrillation Ablation and Strategies for Periprocedural Stroke Prevention

Transcatheter treatment of atrial fibrillation (AF) is a complex intervention performed in patients who are at inherently increased risk of a thromboembolic complication, including stroke. It is therefore not surprising that cerebrovascular accidents have been among the most feared complications since the inception of AF ablation. While improvements have been made to limit the incidence of thromboembolic events during catheter ablation of AF, the optimal strategy to minimize such complications has yet to be determined. It is hoped that larger trials using periprocedural anticoagulation strategies can be undertaken to definitively address these important concerns.

Cognitive performance after carotid angioplasty and stenting with brain protection devices

OBJECTIVE

Neuropsychological outcomes after carotid endarterectomy (CEA) have been investigated extensively. However, cognitive impacts of carotid angioplasty and stenting (CAS), an emerging alternative to CEA, have not been studied. This study is aimed at investigating pattern and degree of cognitive changes after CAS among patients with high-grade carotid stenosis.

PATIENTS AND METHODS

Fifty-four patients with high-grade carotid artery stenosis and received elective CAS were followed. Sixty-six patients with similar medical conditions requiring carotid angiography (CAG) were enrolled as controls. Cognitive functions among patients in both groups were evaluated at baseline and follow-ups utilizing a battery of neuropsychometric tests. Results were analysed by inter-group and within-group comparisons.

RESULTS

There were no statistically significant differences between CAS and CAG patients regarding demographic characteristics, risk factors for stroke and baseline cognitive performance (p>0.05). CAS patients performed significantly better than CAG patients in Rey auditory verbal learning tests (RAVLT) at week 1 (41.2 +/- 5.2 versus 37.4 +/- 4.0, p<0.001) and week 12 follow-ups (43.3 +/- 7.7 versus 37.3 +/- 4.5, p<0.001). Comparison of z score also indicated CAS patients improved significantly more than CAG patients in RAVLT at both weeks 1 (1.08 +/- 1.29 versus 0.25 +/- 0.99, p<0.001) and 12 follow-ups (1.62 +/- 1.95 versus 0.05 +/- 1.02, p<0.001).

CONCLUSION

CAS patients demonstrated improvement in verbal memory after procedures. Correction of cerebral hypoperfusion and reduction of artery-to-artery embolization after CAS are postulated responsible for the cognitive improvement.

Preexisting depressive symptoms are associated with long-term cognitive decline in patients after cardiac surgery

OBJECTIVE

To examine whether preoperative psychological dysfunctions rather than intraoperative factors may differentially predict short- and long-term postoperative cognitive decline (POCD) in patients after cardiac surgery.

METHOD

Forty-two patients completed a psychological evaluation, including the Trail Making Test Part A and B (TMT-A/B), the memory with 10/30-s interference, the phonemic verbal fluency and the Center for Epidemiological Studies of Depression (CES-D) scale for cognitive functions and depressive symptoms, respectively, before surgery, at discharge and at 18-month follow-up.

RESULTS

Ten (24%) and 11 (26%) patients showed POCD at discharge and at 18-month follow-up, respectively. The duration of cardiopulmonary bypass significantly predicted short-term POCD [odds ratio (OR)=1.04, P<.05], whereas preoperative psychological factors were unrelated to cognitive decline at discharge. Conversely, long-term cognitive decline after cardiac surgery was significantly predicted by preoperative scores in the CES-D (OR=1.26, P<.03) but not by intraoperative variables (all Ps >.23).

CONCLUSIONS

Our findings showed that preexisting depressive symptoms rather than perioperative risk factors are associated with cognitive decline 18 months after cardiac surgery. This study suggests that a preoperative psychological evaluation of depressive symptoms is essential to anticipate which patients are likely to show long-term cognitive decline after cardiac surgery.

Pre-existing cerebral infarcts as a risk factor for delirium after coronary artery bypass graft surgery

OBJECTIVES

Delirium is a common and critical clinical syndrome in older patients. We examined whether abnormalities in the brain that could be assessed by magnetic resonance imaging predisposed patients to develop delirium after coronary artery bypass graft surgery. We also analysed the association between delirium and cognitive dysfunction after coronary artery bypass graft surgery.

METHODS

Data were collected prospectively on 153 patients aged 60 years or older who consecutively underwent elective isolated coronary artery bypass graft surgery. All patients were assessed for prior cerebral infarctions and craniocervical artery stenosis by magnetic resonance imaging (MRI) and angiography of their brains. Atherosclerosis of the ascending aorta was examined by epiaortic ultrasound at the time of surgery. Individual cognitive status was measured using four tests in all the patients before surgery and on the seventh postoperative day. A single psychiatrist diagnosed delirium using the Diagnostic and Statistical Manual of Mental Disorders 4th edition IV criteria.

RESULTS

Postoperative delirium occurred in 16 patients (10.5%). Compared with patients who did not develop postoperative delirium, delirious patients had significantly higher rates of peripheral artery disease, preoperative decline in global cognitive function and pre-existing multiple cerebral infarctions on MRI. In addition, 9 (56%) of the delirious patients suffered postoperative cognitive dysfunction. Stepwise logistic regression analysis found significant independent predictors of postoperative delirium to be preoperative cerebral infarcts on MRI (odds ratio [OR], 2.26; 95% confidence interval [CI] 1.10-4.78), preoperative decline in global cognitive function (OR 4.54; 95% CI 1.21-16.51) and atherosclerosis of the ascending aorta (OR 2.44; 95% CI 1.03-5.62).

CONCLUSIONS

Our findings suggested that postoperative delirium was associated with pre-existing multiple cerebral infarctions on MRI, preoperative decline in global cognitive function and ascending aortic atherosclerosis in elderly patients undergoing coronary artery bypass graft surgery and increased risk of postoperative cognitive dysfunction.

Brain emboli distribution and differentiation during cardiopulmonary bypass

OBJECTIVE

Cardiopulmonary bypass (CPB) is a lifesaving practice in cardiac surgery, but its use frequently is associated with cerebral injury and neurocognitive dysfunctions. Despite the involvement of numerous factors, microembolism occurring during CPB seems to be one of the main mechanisms leading to such alterations. The aim of the present study was to characterize the occurrence of cerebral microembolism with reference to microembolic amount, nature, and distribution in different combinations of cardiac procedures and CPB on the microembolic load.

DESIGN

A retrospective observational clinical study.

SETTING

A single-center regional hospital.

PARTICIPANTS

Fifty-five patients undergoing elective cardiac surgery with CPB.

INTERVENTIONS

Bilateral detection of the patients' middle cerebral arteries using a multifrequency transcranial Doppler.

MEASUREMENTS AND MAIN RESULTS

Patients were divided into 3 groups depending on the CPB circuit used (open, open with vacuum, or closed). There was a significant difference between the number of solid and gaseous microemboli (p<0.001), with the solid lower than the gaseous ones. The number of solid microemboli was affected by group (p< 0.05), CPB phase (p<0.001), and laterality (p<0.01). The number of gaseous microemboli was affected only by group (p<0.05) and CPB phase (p<0.001). Generally, the length of CPB phase did not affect the number of microemboli.

CONCLUSIONS

Surgical procedures combined with CPB circuits, but not the CPB phase length, affected the occurrence, nature, and laterality of microemboli.

Hypovolemia in extracorporeal life support can lead to arterial gaseous microemboli

Next to severely decreased pump flow, hypovolemia in extracorporeal life support (ELS) can result in subatmospheric venous line pressure. Such pressure may lead to degassing and resultant gaseous microemboli (GME), with potential changes in neurological clinical outcome. CME activity resulting from degassing was investigated in relation to subatmospheric venous line pressure, partial oxygen pressure (pO2 ), and hematocrit in a model of a centrifugal pump-based circuit for long-term ELS. Additionally, a device that provides instantaneous volume buffer capacity during hypovolemia was evaluated in relation to GME appearance. An exponential relationship was found between decreasing venous line pressure and GME downstream of the centrifugal pump (P = 0.001). Arterial bubble activity appeared at subatmospheric venous line pressures of -200 mm Hg and less. A rising (pO2 ) increased formation of GME (P = 0.05). A rise in hematocrit, in contrast, did not affect embolic activity (P = 0.22). With simulated hypovolemia, volume buffer capacity added to the venous line dampened fluctuations of venous line pressure by approximately 40%, but a significant reduction in GME formation could not be found (P = 0.22). Moreover, the device enabled a 14% higher support flow. With ELS flow being related to patient volume status, hypovolemia can diminish support. A coherent decrease of venous line pressure triggers degassing of blood-dissolved gases and causes arterial GME, which can become massive during persistent conditions of limited venous return. Incorporation of a volume buffer capacity device into the extracorporeal support circuit enables a higher and more stable support flow in critically low patient filling.

Preliminary evidence for reduced preoperative cerebral blood flow velocity as a risk factor for cognitive decline three months after cardiac surgery: an extension study

This extension study investigated the association between preoperative cerebral blood flow (CBF) velocity and postoperative cognitive decline (POCD) at a three-month follow-up in patients who underwent cardiac surgery. Continuous transcranial Doppler ultrasound on both middle cerebral arteries (MCAs) was used preoperatively in 31 right-handed cardiac surgery patients at rest. Each patient performed a neuropsychological evaluation to assess cognitive performance before surgery, at discharge and at three-month follow-up. Patients with POCD at the three-month follow-up had a marginally significantly lower preoperative CBF velocity in the left MCA than patients without POCD. Moreover, the group with POCD had a significantly lower CBF velocity in the left than in the right MCA, whereas no difference between the left and right CBF velocity was found in the group without POCD. These preliminary findings suggest that reduced preoperative CBF velocity in the left MCA may represent an independent risk factor for cognitive decline in patients three months after surgery.