When do cerebral emboli appear during open heart operations? A transcranial Doppler study

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.

Combined Treatment With Carotid Endoarterectomy and Coronary Artery Bypass Grafting: A Single-Institutional Experience in 222 Patients

INTRODUCTION

Carotid atherosclerotic disease is a known independent risk factor of post operative stroke after coronary artery bypass grafting (CABG). The best management of concomitant coronary artery disease and carotid artery disease remains debated. Current strategies include simultaneous carotid endoarterectomy (CEA) and CABG, staged CEA followed by CABG, staged CABG followed by CEA, staged transfemoral carotid artery stenting (TF-CAS) followed by CABG, simultaneous TF-CAS and CABG and transcarotid artery stenting.

METHODS

We report our experience based on a cohort of 222 patients undergoing combined CEA and CABG surgery who come to our observation from 2004 to 2020. All patients with >70% carotid stenosis and severe multivessel or common truncal coronary artery disease underwent combined CEA and CABG surgery at our instituion. 30% of patients had previously remote neurological symptoms or a cerebral CT-scan with ischemic lesions. Patients with carotid stenosis >70%, either asymptomatic or symptomatic, underwent CT-scan without contrast media to assess ischemic brain injury, and in some cases, if necessary, CT-angiography of the neck and intracranial vessels.

RESULTS

The overall perioperative mortality rate was 4.1% (9/222 patients). Two patients (.9%) had periprocedural ipsilateral transient ischemic attack (TIA) which completely resolved by the second postoperative day. Two patients (.9%) had an ipsilateral stroke, while 7 patients (3.2%) had a stroke of the controlateral brain hemisphere. Two patients (.9%) patients were affected by periprocedural coma caused by cerebral hypoperfusion due to perioperative heart failure. There were no statistically significant differences between patients in Extracorporeal Circulation (ECC) and Off-pump patients in the onset of perioperative stroke.

CONCLUSION

Our experience reported that combined surgical treatment of CEA and CABG, possibly Off-Pump, is a feasible treatment procedure, able to minimize the risk of post-operative stroke and cognitive deficits.

Renal and Cerebral Hypoxia and Inflammation During Cardiopulmonary Bypass

Cardiac surgery-associated acute kidney injury and brain injury remain common despite ongoing efforts to improve both the equipment and procedures deployed during cardiopulmonary bypass (CPB). The pathophysiology of injury of the kidney and brain during CPB is not completely understood. Nevertheless, renal (particularly in the medulla) and cerebral hypoxia and inflammation likely play critical roles. Multiple practical factors, including depth and mode of anesthesia, hemodilution, pump flow, and arterial pressure can influence oxygenation of the brain and kidney during CPB. Critically, these factors may have differential effects on these two vital organs. Systemic inflammatory pathways are activated during CPB through activation of the complement system, coagulation pathways, leukocytes, and the release of inflammatory cytokines. Local inflammation in the brain and kidney may be aggravated by ischemia (and thus hypoxia) and reperfusion (and thus oxidative stress) and activation of resident and infiltrating inflammatory cells. Various strategies, including manipulating perfusion conditions and administration of pharmacotherapies, could potentially be deployed to avoid or attenuate hypoxia and inflammation during CPB. Regarding manipulating perfusion conditions, based on experimental and clinical data, increasing standard pump flow and arterial pressure during CPB appears to offer the best hope to avoid hypoxia and injury, at least in the kidney. Pharmacological approaches, including use of anti-inflammatory agents such as dexmedetomidine and erythropoietin, have shown promise in preclinical models but have not been adequately tested in human trials. However, evidence for beneficial effects of corticosteroids on renal and neurological outcomes is lacking. © 2021 American Physiological Society. Compr Physiol 11:1-36, 2021.

Risk of Ischemic Stroke in Transcatheter Aortic Valve Implantation Versus Surgical Aortic Valve Replacement in Patients With Prior Stroke

It has not been well studied whether transcatheter aortic valve implantation (TAVI) or surgical aortic valve replacement (SAVR) have lower risk of ischemic stroke (IS) in those with prior history of IS. From the Nationwide Readmission Database from October 2015 to November 2017, TAVI and SAVR above age 50 were identified with the International Classification of Diseases, Tenth Revision, Clinical Modification/Procedure Coding System codes. Transapical TAVI and SAVR with concomitant bypass, mitral, or tricuspid surgery were excluded. The primary outcome was in-hospital IS. A total of 92,435 TAVI (13,292 with prior stroke) and 68,651 SAVR (5,365 with prior stroke) were identified. In-hospital IS was significantly lower in TAVI compared with SAVR (3.7% vs 8.0%, adjusted odds ratio 0.65, 95% confidence interval 0.47 to 0.89, p <0.01) with prior stroke whereas it was similar between TAVI and SAVR (1.7% vs 2.1%, adjusted odds ratio 0.97, 95% confidence interval 0.78 to 1.19, p = 0.75) in those without prior stroke (P _interaction < 0.001). In-hospital mortality, acute kidney injury, and bleeding were lower in TAVI compared with SAVR in patients with and without prior stroke (P _interaction > 0.05 for all). This analysis of a national claims database showed that TAVI was associated with a lower risk of in-hospital IS compared with SAVR among patients with prior stroke.

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.

Temperature management on cardiopulmonary bypass: Is it standardised across Great Britain and Ireland?

Temperature management is an essential element of cardiopulmonary bypass (CPB), as indicated in the Guide to Good Practice in Clinical Perfusion, 'The safe conduct of CPB requires the clinical perfusionist to measure and control. . . blood temperature. . . during the period of bypass'. To review current practice, we have conducted a research survey into the management of temperature on CPB. Surveys were distributed to each centre in Great Britain and the Republic of Ireland, investigating numerous temperature management practices, to elucidate current practice and assess if recent research into temperature management marry routine clinical practice. Our results demonstrate that nasopharyngeal temperature is the most common (52%) temperature site used across the many centres, which correlates with previous research as a routine site for cerebral temperature management. The arterial outlet of the oxygenator temperature was used in 33% of centres, however, all centres lacked the knowledge to maintain this temperature below 37°C. There was significant variation between all centres, especially regarding rewarming times (20-40 minutes), demonstrating a lack of uniformity among perfusion centres. Interestingly, most centres have been using the same protocol that has been in place over the previous 10 years.To conclude, the practice of temperature management is changing with the awareness of new research. Lower target temperatures are recommended for rewarming, ensuring a lower temperature gradient and a longer mean rewarming time.

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.

Outcomes in 937 Intermediate-Risk Patients Undergoing Surgical Aortic Valve Replacement in PARTNER-2A

BACKGROUND

The Placement of Aortic Transcatheter Valves 2A (PARTNER-2A) randomized trial compared outcomes of transfemoral transcatheter and surgical aortic valve replacement (SAVR) in intermediate-risk patients with severe aortic stenosis. The purpose of the present study was to perform an in-depth analysis of outcomes after SAVR in the PARTNER-2A trial.

METHODS

From January 2012 to January 2014, 937 patients underwent SAVR at 57 centers. Mean age was 82 ± 6.7 years and 55% were men. Less-invasive operations were performed in 140 patients (15%) and concomitant procedures in 198 patients (21%). Major outcomes and echocardiograms were adjudicated by an independent events committee. Follow-up was 94% complete to 2 years.

RESULTS

Operative mortality was 4.1% (n = 38, Society of Thoracic Surgeons predicted risk of mortality: 5.2% ± 2.3%), observed to expected ratio (O/E) was 0.8, and in-hospital stroke was 5.4% (n = 51), twice expected. Aortic clamp and bypass times were 75 ± 30 minutes and 104 ± 46 minutes, respectively. Patients having severe prosthesis-patient mismatch (n = 260, 33%) had similar survival to patients without (p > 0.9), as did patients undergoing less-invasive SAVR (p = 0.3). Risk factors for death included cachexia (p = 0.004), tricuspid regurgitation (p = 0.01), coronary artery disease (p = 0.02), preoperative atrial fibrillation (p = 0.001), higher white blood cell count (p < 0.0001), and lower hemoglobin (p = 0.0002).

CONCLUSIONS

In this adjudicated prospective study, SAVR in intermediate-risk patients had excellent results at 2 years. However, there were more in-hospital strokes than expected, most likely attributable to mandatory neurologic assessment after the procedure. No pronounced structural valve deterioration was found during 2-year follow-up. Continued long-term surveillance remains important.

Carbon dioxide field flooding versus mechanical de-airing during open-heart surgery: a prospective randomized controlled trial

Removal of intracardiac air during valvular surgery should be accomplished in the most effective manner. We conducted a prospective randomized controlled trial to compare mechanical de-airing and carbon dioxide (CO2) field flooding in 18 patients undergoing elective valvular surgery. Transoesophageal echocardiography was used to record intracardiac bubbles, and this was assessed postoperatively by two independent echocardio-graphers blinded to treatment group. Both assessors graded the bubble count higher in the mechanical de-airing group compared with the CO2 flooding group, and there was good agreement between assessors. CO2 field flooding is more effective than mechanical de-airing in removing intracardiac bubbles following valvular surgery.

Retrograde Cerebral Perfusion for Treatment of Air Embolism after Valve Surgery

Air embolism occurred after termination of cardiopulmonary bypass in a 22-year-old man undergoing aortic valve replacement for rheumatic aortic insufficiency. Normothermic retrograde cerebral perfusion was instituted for 5 min at a flow rate of 300–500 mL·min−1, maintaining internal jugular vein pressure < 25 mmHg. The aortic cannula was declamped intermittently for 5–10 seconds. Mean arterial pressure was kept at 60–70 mmHg. The patient recovered without any neurological deficit.

Incidence and causes of silent and symptomatic stroke following surgical and transcatheter aortic valve replacement: a comprehensive review

Stroke associated with aortic valve replacement in calcific aortic stenosis, either via transcatheter implantation (TAVR) or via surgical replacement (SAVR), is one of the most devastating complications. However, data concerning the clinical impact and incidence of clinical and silent stroke complicating SAVR and TAVR are varying. This comprehensive review of the literature explores the genuine incidence of neurological events after these procedures. Additionally, potential factors responsible for the discrepancies in stroke rates in the current literature are analysed and a lack of uniform neurological definitions and standardized neurological assessments revealed. Current stroke rates after TAVR show a decline from 7 to 1.7-4.8% in recent studies. Randomized studies comparing TAVR with SAVR yielded initially a significantly higher stroke rate after TAVR procedures as opposed to SAVR. Recently published data showed opposite results with strokes being higher following SAVR. Current data concerning stroke after surgical valve replacement report significantly higher rates of clinical strokes (17%) than previously mentioned in the literature (≤4.9%). Silent cerebral lesions were detected in 68-93% after TAVR and 38-54% after SAVR. A broader application of cerebral protection devices may help to reduce embolic cerebral 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.

AKI associated with cardiac surgery

Approximately 18% of patients undergoing cardiac surgery experience AKI (on the basis of modern standardized definitions of AKI), and approximately 2%-6% will require hemodialysis. The development of AKI after cardiac surgery portends poor short- and long-term prognoses, with those developing RIFLE failure or AKI Network stage III having an almost 2-fold increase in the risk of death. AKI is caused by a variety of factors, including nephrotoxins, hypoxia, mechanical trauma, inflammation, cardiopulmonary bypass, and hemodynamic instability, and it may be affected by the clinician's choice of fluids and vasoactive agents as well as the transfusion strategy used. The risk of AKI may be ameliorated by avoidance of nephrotoxins, achievement of adequate glucose control preoperatively, and use of goal-directed therapy hemodynamic strategies. Remote ischemic preconditioning is an exciting future strategy, but more work is needed before widespread implementation. Unfortunately, there are no pharmacologic agents known to reduce the risk of AKI or treat established AKI.

Evaluation of effect of continuous positive airway pressure during cardiopulmonary bypass on cardiac de-airing after open heart surgery in randomized clinical trial

BACKGROUND

Cardiac and pulmonary veins de-airing are of the most important steps during open heart surgery. This study evaluates the effect of continuous positive airway pressure (CPAP) on air trapping in pulmonary veins and on quality of de-airing procedure.

MATERIALS AND METHODS

This randomized prospective double blind clinical trial conducted on 40 patients. In the control group: During cardiopulmonary bypass (CPB), the ventilator was turned off and adjustable pressure limit (APL) valve was placed in SPONT position. In CPAP group: During CPB, after turning the ventilator off, the flow of oxygen flow was maintained at the rate of 0.5 L/min and the APL valve was placed in MAN position on 20 mbar. During cardiopulmonary bypass (CPB) weaning, the patients were observed for air bubbles in left atrium by using transesophageal echocardiography.

RESULTS

The mean de-airing time after the start of mechanical ventilation in CPAP group (n = 20) was significantly lower than the control group (n = 20) (P = 0.0001). The mean time of the left atrium air bubbles occupation as mild (P = 0.004), moderate (P = 0.0001) and severe (P = 0.015) grading was significantly lower in CPAP group.

CONCLUSIONS

By CPAP at 20 mbar during CPB in open heart surgery, de-airing process can be down in better quality and in significantly shorter time.

Incidence, predictors, origin and prevention of early and late neurological events after transcatheter aortic valve implantation (TAVI): a comprehensive review of current data

Transcatheter aortic valve implantation (TAVI) is a novel treatment option for patients with severe, symptomatic aortic valve stenosis considered inoperable or at high risk for surgical aortic valve replacement. Despite rapid adoption of this technology into clinical application, however, recent randomized controlled clinical trials have raised safety concerns regarding an increased risk of neurological events with TAVI compared to both medical treatment and conventional, surgical aortic valve replacement. Moreover, neuro-imaging studies have revealed an even higher incidence of new, albeit clinically silent cerebral lesions as a surrogate for procedural embolization. In this article, we review currently available data on the incidence, timing, predictors, prognostic implications and potential mechanisms of neurological events after TAVI.

Trends in aortic clamp use during coronary artery bypass surgery: effect of aortic clamping strategies on neurologic outcomes

OBJECTIVE

The purpose of the present study was to determine the effect of different clamping strategies during coronary artery bypass grafting on the incidence of postoperative stroke.

METHODS

In the present case-control study, all patients at Emory hospitals from 2002 to 2009 with postoperative stroke after isolated coronary artery bypass grafting (n = 141) were matched 1:4 to a contemporaneous cohort of patients without postoperative stroke (n = 565). The patients were matched according to the Society of Thoracic Surgeons' predicted risk of postoperative stroke score, which is based on 26 variables. The patients who received on-pump and off-pump coronary artery bypass grafting were matched separately. Multiple logistic regression analysis with adjusted odds ratios was performed to identify the operative variables associated with postoperative stroke.

RESULTS

Among the on-pump cohort, the single crossclamp technique was associated with a decreased risk of stroke compared with the double clamp (crossclamp plus partial clamp) technique (odds ratio, 0.385; P = .044). Within the on-pump cohort, no significant difference was seen in the incidence of stroke according to clamp use. Epiaortic ultrasound of the ascending aorta increased from 45.3% in 2002 to 89.4% in 2009. From 2002 to 2009, clamp use decreased from 97.7% of cases to 72.7%.

CONCLUSIONS

During on-pump coronary artery bypass grafting, the use of a single crossclamp compared with the double clamp technique decreased the risk of postoperative stroke. The use of any aortic clamp decreased and epiaortic ultrasound use increased from 2002 to 2009, indicating a change in the operative technique and surgeon awareness of the potential complications associated with manipulation of the aorta.

Off-pump coronary artery bypass grafting--the current state

The optimal strategy for coronary revascularization remains controversial. Currently, most surgical revascularizations are performed with the use of cardiopulmonary bypass (ONCAB), yet over the past 20 years off-pump coronary artery bypass grafting (OPCAB) has been increasingly used because of the increased awareness of the deleterious effects of cardiopulmonary bypass (CPB) and aortic manipulation. Small, prospective, randomized controlled trials have lacked sufficient sample size to demonstrate differences in early and long-term outcomes. Larger observational studies that are better powered to statistically compare outcomes have shown more favorable in-hospital outcomes and equivalent long-term outcomes with OPCAB and ONCAB. The benefits of OPCAB techniques may be more apparent for patients at high risk for complications associated with CPB and aortic manipulation. Recent studies have demonstrated improved outcomes in higher-risk patients undergoing OPCAB, as well as improved neurological outcomes. The purpose of this review is to outline the recent literature comparing OPCAB with ONCAB, and to demonstrate efficacy of OPCAB as a useful technique for coronary revascularization.

Generation, detection and prevention of gaseous microemboli during cardiopulmonary bypass procedure

Neuropsychological injury after cardiopulmonary bypass (CPB) is one of the most serious and costly complications arising from the procedure. Gaseous microemboli (GME) have long been implicated as one of the principal causes. There are two major sources of GME: surgical and manual manipulation of the heart and arteries; and the components of the extracorporeal circuit, including the type of pump, different perfusion modes, the design of the oxygenator and reservoir, and the use of vacuum assisted venous drainage (VAVD), all of which have a great impact on the delivery of existing GME to the patients. Transcranial cranial Doppler (TCD) has been used for more than two decades to assess and monitor the quality of extracorporeal perfusion with regard to the blood flow velocity of the middle cerebral arteries (MCA) and emboli detection, contributing to the achievement of better perfusion results. The Emboli Detection and Classification (EDAC) Quantifier has been able to detect and track microemboli in CPB circuits up to 1,000 microemboli per second at flow rates ranging from 0.2 L/min to 6.0 L/min. The deleterious effects of GME are multiple, including damage to the cerebral vascular endothelium, disruption of the blood-brain barrier, complement activation, leukocyte aggregation, increased platelet adherence, and fibrin deposition in the micro-vasculature. Improvements in perfusion equipment and in perfusion and surgical techniques have led to a dramatic reduction in the occurrence of GME during cardiac surgery. Although the clinical relevance of cerebral air embolization in causing neurological damage is unclear, every single person involved in perfusion and surgical technology should be aware of the risk of embolization and strictly regulate clinical behavior. Related research should also be done to improve the design of circuit components and clinical practice with a view to eliminating air bubbles during CPB procedure.

The effect of carbon dioxide insufflation on cognitive function during cardiac surgery

The use of carbon dioxide (CO(2)) insufflation into the pericardial well has become widespread, and in some units routine. The rationale behind this practice is the fact that CO(2) is more soluble than air leading to fewer gaseous microemboli entering the bloodstream and being transferred to the brain or heart. However, the evidence that this reduces postoperative neurocognitive decline is scant. Although CO(2) insufflation is generally a safe procedure there are case reports of significant complications. The aim of this systematic review is to analyze the current evidence for this practice.

Hyperbaric Oxygen Therapy in the Treatment of Post Cardiac Surgical Strokes – a Case Series and Review of the Literature

Strokes remain an uncommon but significant complication of cardiac surgery. Cerebral air embolism is the likely aetiology in the majority of cases. Hyperbaric oxygen therapy is the recognised treatment for cerebral air embolism associated with compressed air (SCUBA) diving accidents and is therefore also the standard of care for iatrogenic causes of air embolism. It follows that there is a logic in treating post-cardiac surgical stroke patients with hyperbaric oxygen.

The aim of this retrospective review was to examine the outcomes of 12 such patients treated in the Christchurch Hospital hyperbaric unit and to appraise the evidence base for the use of hyperbaric oxygen therapy in this setting.

Despite delays of up to 48 hours following surgery before the institution of hyperbaric oxygen therapy, 10 of the 12 patients made a full neurological recovery or were left with mild residual symptoms, with nine returning to their previous level of care. One patient remained hemiplegic and there was one early neurological death.

There is a paucity of prospective data in this area, but based on sound pathophysiological principles and clinical experience, we believe that patients suffering a stroke following open cardiac surgery should be considered for hyperbaric oxygen therapy.

Does CO 2 flushing of the empty CPB circuit decrease the number of gaseous emboli in the prime?

Twenty (20) CPB-circuits were randomized to a CO2 group or a control group. In the CO 2 group, each circuit was flushed with CO2 (10L/min) at the top of the venous reservoir for 5 minutes, after which priming fluid was added without interruption of the CO2 inflow. Control group circuits were not flushed and contained air. A perfusionist, blinded to the study, started the pump (5L/min), ventilated the oxygenator (3L O2/min), and knocked on the oxygenator 20 times during the first and 14th minutes. Arterial line microemboli counts were registered with a Doppler for 15 minutes. In both groups, the median number of microemboli was highest during the first minute, 380.5 (288.75/422.25, 25th/75th percentile) counts in the control group versus 264.5 (171.75/422.25) counts in the CO 2 group (p=0.01). Throughout the experiment, the median microembolic count minute by minute in the CO2 group remained lower (p≤ 0 .004) than in the control group. Knocking on the reservoir (14th minute) increased the microemboli counts in both groups (p<0.01). The median values during the 15th minute were 15.5 and 0.5 in the control and the CO2 groups, respectively, which were 9% (15.5/173) and 0.5% (0.5/87), respectively, of the values registered after 14 minutes. In conclusion, CO 2 flushing of the empty circuit decreases the number of gaseous emboli in the prime compared with a conventional circuit that contains air before being primed with fluid. Knocking of the oxygenator releases gaseous emboli and the duration of re-circulating the circuit with prime influences the number of microemboli.

Temporal pattern of strokes after on-pump and off-pump coronary artery bypass graft surgery

BACKGROUND

The incidence of strokes has not decreased after coronary artery bypass graft surgery (CABG). The purpose of this study is to identify incidence, risk factors, and temporal pattern of strokes after on-pump and off-pump CABG.

METHODS

We analyzed 2,516 consecutive patients who underwent first elective isolated CABG. The primary endpoint was strokes within 30 days. The temporal onset of the deficits was classified by consensus as either an "early stroke," which is present just after emergence from anesthesia, or a "delayed stroke," which is present after first awaking from surgery without a neurologic deficit.

RESULTS

More than half of strokes (29 of 46; 63%) were delayed strokes. Patients undergoing off-pump CABG had significantly lower risk of early stroke (0.1% versus 1.1%, p = 0.0009), whereas the incidence of delayed strokes was not different significantly (0.9% versus 1.4%, p = 0.3484) between patients undergoing on-pump and off-pump CABG. In multivariate analyses, undergoing off-pump CABG was an independent protective factor for all strokes (relative risk 0.29, 95% confidence interval: 0.14 to 0.56, p = 0.0005) and early strokes (relative risk 0.05, 95% confidence interval: 0.003 to 0.24, p < 0.0001), but it was not an independent protective factor for delayed strokes (relative risk 0.54, 95% confidence interval: 0.24 to 1.17, p = 0.1210).

CONCLUSIONS

Undergoing off-pump CABG reduces the incidence of perioperative stroke mainly by minimizing early strokes; however, the risk of delayed strokes is not different between patients undergoing on-pump and off-pump CABG.

Cardiac surgery as a cause of acute kidney injury: pathogenesis and potential therapies

Cardiopulmonary bypass surgery occurs in nearly 1 million patients per year. Acute kidney injury requiring dialysis can occur in up to 1% of these patients. The development of acute kidney injury is associated with substantial morbidity and mortality independent of all other factors, and many patients are left dependent on dialysis therapies. The pathogenesis of acute kidney injury involves multiple pathways. Hemodynamic, inflammatory, and nephrotoxic factors are involved and overlap each other in leading to kidney injury. Clinical studies have identified risk factors for acute kidney injury that can be used to effectively determine the risk of acute kidney injury in patients undergoing bypass surgery. These high-risk patients can then be targeted for renal protective strategies. Thus far, no single strategy has conclusively demonstrated its ability to prevent renal injury post-bypass surgery. Novel anti-inflammatory agents are in development and offer hope as potential therapies.

Behavior of gaseous microemboli in extracorporeal circuits: air versus CO2

BACKGROUND

Open heart surgery is associated with serious risk of cerebral and peripheral organ dysfunction, attributed in part to air microbubbles generated in or not eliminated from the extracorporeal circuit (ECC). Venous air leakage leads to increased arterial bubble load. CO2 replacing air in cardiac chambers show faster resorption times, reducing possible cerebral or peripheral organ damage after heart valve interventions. In two models of ECC the effect of air entering closed circuits was demonstrated and compared to the effect of CO2 entry.

METHODS

Fragmentation and dissolution of gas (0.5 mL) was evaluated in an in vitro model of ECC, using ultrasonic bubble detection. Air leakage (10 mL) in the venous line of the ECC was simulated and compared to the effect of the same quantity of CO2 entering the circuit. Both models used whole blood priming and physiological conditions, verified with blood gas analyses.

RESULTS

Fragmentation and dissolution of gas bubbles injected into a closed ECC could be demonstrated, complete resorption of CO2 bubbles was observed earlier than complete resorption of room air (5.0+/-0.6 vs. 14.4+/-5.9 min, p=0.0009). CO2 entering the venous line lead to 40% less arterial bubble load as compared to the same amount of room air entering the circuit (2099+/-991 vs. 3555+/-632, p=0.005).

CONCLUSIONS

Current ECC systems fail to eliminate gas entering the circuit, leading rather to microbubble dispersion. CO2 is much faster resorbed within the circuit than room air. In open heart surgery as valvular operations, CO2 insufflation into the operative field is protective, as we have demonstrated in our models.

Reduction in Air Bubble Size Using Perfluorocarbons During Cardiopulmonary Bypass in the Rat

BACKGROUND

Perfluorocarbon (PFC) emulsions are artificial oxygen-carrying compounds with a high solubility for gases that have experimentally been shown to ameliorate cerebral air embolism. Cerebral air embolism has been associated with adverse cerebral outcomes after cardiac surgery using cardiopulmonary bypass (CPB). We designed this study to test whether PFC emulsions could reduce the volume of bubbles within the CPB circuit.

METHODS

Male Sprague-Dawley rats undergoing 60 min of normothermic nonpulsatile CPB were randomized to one of the three groups. The PFC group (n = 10) received 60% O(2)/36% N(2)/4% CO(2) via the membrane oxygenator and 2.7 g/kg (4.5 mL/kg) of PFC into the venous reservoir; the control group (n = 10) received the same gas mixture and 4.5 mL/kg of saline; the N(2)O group (n = 6) was exposed to 36% N(2)O/60% O(2)/4% CO(2) and received 4.5 mL/kg of saline. After 10 min and 35 min of CPB, 400 microL of air was injected into a bubble chamber in the CPB circuit. After 20 min, the bubble was removed for volumetric analysis.

RESULTS

Compared with baseline, the bubble decreased 13% +/- 5% in size in the PFC group and increased 46% +/- 9% in the nitrous oxide group, both of these changes significantly different from the control group (P < 0.0001).

CONCLUSION

The results suggest that PFC administration may be useful in reducing the volume of gaseous bubbles present during CPB.

Acute kidney injury associated with cardiac surgery

Acute renal failure (ARF) occurs in up to 30% of patients who undergo cardiac surgery, with dialysis being required in approximately 1% of all patients. The development of ARF is associated with substantial morbidity and mortality independent of all other factors. The pathogenesis of ARF involves multiple pathways. Hemodynamic, inflammatory, and nephrotoxic factors are involved and overlap each other in leading to kidney injury. Clinical studies have identified risk factors for ARF that can be used to determine effectively the risk for ARF in patients who undergo bypass surgery. These high-risk patients then can be targeted for renal protective strategies. Thus far, no single strategy has demonstrated conclusively its ability to prevent renal injury after bypass surgery. Several compounds such as atrial natriuretic peptide and N-acetylcysteine have shown promise, but large-scale trials are needed.

Relation between neurocognitive impairment, embolic load, and cerebrovascular reactivity following on- and off-pump coronary artery bypass grafting

OBJECTIVES

To evaluate the effect of on-pump and off-pump coronary artery bypass grafting (CABG) on postoperative cognitive impairment and cerebrovascular reactivity, with attention for the perioperative high-intensity transient signals (HITS).

DESIGN

A prospective comparative study.

SETTING

Urban university hospital.

PATIENTS

Candidates for cardiac surgery.

METHODS

Measurement of HITS as a reflection of embolic load was performed in 50 patients (on-pump CABG, n = 32; off-pump CABG, n = 18). To measure cognitively induced cerebrovascular reactivity, cerebral blood flow velocity (BFV) was measured preoperatively in 66 patients, early postoperatively (after 6 days) in 63 patients, and late postoperatively (after 6 months) in 44 patients during five cognitive tasks. In the same session, seven standardized neuropsychological tests were administered.

RESULTS

A higher embolic load was found in the on-pump group (p < 0.01). In the on-pump group, aortic cannulation was the most important HITS-prone surgical maneuver. Repeated-measures multivariate analysis of variance (using surgical technique as between-subjects factor and significant differences between both groups as covariates) on the group data revealed no significant differences in neuropsychological performance and BFV immediately after surgery or at 6 months after surgery, compared with preoperative performance. No main effect of surgery was found for neuropsychological performance and BFV. No significant correlations were found between the number of HITS and the degree of postoperative neuropsychological impairment. Individual comparisons revealed that 60% (59.4% in the on-pump group; 61.1% in the off-pump group) of the patients undergoing CABG showed evidence of cognitive impairment soon after surgery. In 24.2%, the cognitive sequelae persisted at 6 months follow-up (31.8% in the on-pump group; 9.1% in the off-pump group). The cognitive impairment index (sum of impaired neuropsychological tests) showed a significant difference after 6 months between both surgery groups with fewer neurocognitive tests that remained impaired in the off-pump group.

CONCLUSIONS

In off-pump surgery, significantly fewer HITS were observed. On an individual level, more favorable results in neuropsychological test performance were demonstrated in the off-pump group after 6 months. The number of HITS showed no correlation with degrees of early and late postoperative neuropsychological impairment.

Transcranial Doppler emboli count predicts rise in creatinine after coronary artery bypass graft surgery

OBJECTIVE

To examine the correlation between transcranial Doppler ultrasonography-detected emboli during coronary artery bypass graft surgery with cardiopulmonary bypass and renal dysfunction as determined by the postoperative change in creatinine.

DESIGN

Retrospective review of data from the anesthesia and cardiothoracic surgery databases.

SETTING

Tertiary care university hospital.

PARTICIPANTS

Two hundred eighty-six patients undergoing coronary artery bypass graft surgery.

INTERVENTIONS

Transcranial Doppler ultrasonography of the right middle cerebral artery was performed after induction of general anesthesia through completion of the operation. Doppler signals were recorded and emboli counts determined using an automated counting system.

MEASUREMENTS AND MAIN RESULTS

Renal dysfunction was assessed as the change in creatinine from the preoperative value to the maximum postoperative value (Delta-Cr). There was a significant (p = 0.0003) univariate correlation between postoperative change in creatinine and total number of Doppler-detected emboli. The effect of total number of emboli remained significant (p = 0.0038) in the multivariable analysis after adjustment for covariables (age, sex, number of grafts, left ventricular ejection fraction, hypertension, history of congestive heart failure, diabetes, cardiopulmonary bypass time, preoperative creatinine, and maximum postoperative creatinine).

CONCLUSIONS

Increased numbers of Doppler-detected emboli during coronary artery bypass graft surgery are associated with postoperative renal dysfunction.

The Impact of Aortic Manipulation on Neurologic Outcomes After Coronary Artery Bypass Surgery: A Risk-Adjusted Study

BACKGROUND

Cerebral embolization of atherosclerotic plaque debris caused by aortic manipulation during conventional coronary artery bypass grafting (CABG) is a major mechanism of postoperative cerebrovascular accidents (CVA). Off-pump CABG (OPCABG) reduces stroke rates by minimizing aortic manipulation. Consequently, the effect of different levels of aortic manipulation on neurologic outcomes after CABG surgery was examined.

METHODS

From January 1998 to June 2002, 7,272 patients underwent isolated CABG surgery through three levels of aortic manipulation: full plus tangential (side-biting) aortic clamp application (on-pump surgery; n = 4,269), only tangential aortic clamp application (OPCABG surgery; n = 2,527) or an "aortic no-touch" technique (OPCABG surgery; n = 476). A risk-adjusted logistic regression analysis was performed to establish the likelihood of postoperative stroke with each technique. Preoperative risk factors for stroke from the literature, and those found significant in a univariable model were used.

RESULTS

A significant association for postoperative stroke correspondingly increasing with the extent of aortic manipulation was demonstrated by the univariable analysis (CVA incidence respectively increasing from 0.8% to 1.6% to a maximum of 2.2%, p < 0.01). In the logistic regression model, patients who had a full and a tangential aortic clamp applied were 1.8 times more likely to have a stroke versus those without any aortic manipulation (95% confidence interval: 1.15 to 2.74, p < 0.01) and 1.7 times more likely to develop a postoperative stroke than those with only a tangential aortic clamp applied (95% confidence interval: 1.11 to 2.48, p < 0.01).

CONCLUSIONS

Aortic manipulation during CABG is a contributing mechanism for postoperative stroke. The incidence of postoperative stroke increases with increased levels of aortic manipulation.

Selective antegrade cerebral perfusion attenuates brain metabolic deficit in aortic arch surgery: a prospective randomized trial

BACKGROUND

Aortic arch surgery has a high incidence of brain injury. This may in part be caused by a cerebral metabolic deficit observed after hypothermic circulatory arrest (HCA). We hypothesized that selective antegrade cerebral perfusion (SACP) would attenuate this phenomenon.

METHODS AND RESULTS

In a prospective randomized trial, 42 adult patients were allocated to either HCA (22) or SACP. HCA occurred at a nasopharyngeal temperature of 15 degrees C and SACP at a corporeal temperature of 25 degrees C with cerebral perfusion at 15 degrees C. Paired arterial and jugular venous samples were taken before and after arrest. Continuous transcranial Doppler monitoring of middle cerebral artery velocity (MCAV) was performed. Neuropsychometric testing was performed preoperatively and at 6 and 12 weeks postoperatively. There were 3 hospital deaths (7.1%), 2 strokes (4.8%), and 6 episodes of transient neurological deficit (14.3%). From before to after arrest, jugular bulb pO2 changed by -21.67 mm Hg (26.4) in the HCA group versus +2.27 mm Hg (18.8) in the SACP group (P=0.007). Oxygen extraction changed by +1.7 mL/dL (1.3) in the HCA group versus -1 mL/dL (2.4) in the SACP group (P<0.001). MCAV increased by 6.25 cm/s (9.1) in the HCA group and 19.2 cm/s (10.1) in the SACP group (P=0.001). Incidence of neuropsychometric deficit at 6 weeks was 6/12 (50%) in HCA patients and 8/10 (80%) in SACP patients (P=0.2), and at 12 weeks was 6/16 (38%) in HCA patients and 4/11 (36%) in SACP patients (P=1).

CONCLUSIONS

SACP attenuates the metabolic changes seen after HCA. Further studies are required to assess optimal perfusion conditions and clinical outcome.

Elimination of microbubbles from the extracorporeal circuit: dynamic bubble trap versus arterial filter

BACKGROUND

Open heart surgery is associated with important risk of cerebral and peripheral organ dysfunction, attributed in part to microbubbles generated in or not eliminated from the ECC. For elimination of microbubbles, a dynamic bubble trap (DBT) was developed for the arterial line of ECCs.

METHODS

Bubble eliminating properties of an arterial filter were evaluated in four CABG patients and compared to the performance of the DBT in four patients. One patient received both devices.

RESULTS

Elimination of bubbles between 40-120 microm was significantly higher with the DBT (88% vs. 57% with arterial filter, p=0.034). Reduction of bubbles below 40 microm was equivalent in both groups. The combination of both devices was most effective (94% for bubbles >40 microm).

CONCLUSION

Arterial filter and DBT are equally effective in elimination of smaller gas bubbles. However, bigger bubbles possibly causing cerebral and peripheral organ damage are eliminated to a greater degree by the DBT.

Effect of CO2 insufflation on the number and behavior of air microemboli in open-heart surgery: a randomized clinical trial

BACKGROUND

The risks that the presence of air microemboli implies in open-heart surgery have recently been emphasized by reports that their number is correlated with the degree of postoperative neuropsychological disorder. Therefore, we studied the effect of CO2 insufflation into the cardiothoracic wound on the incidence and behavior of microemboli in the heart and ascending aorta.

METHODS AND RESULTS

Twenty patients undergoing single-valve surgery were randomly divided into 2 groups. Ten patients were insufflated with CO2 via a gas diffuser, and 10 were not. Microemboli were ascertained by intraoperative transesophageal echocardiography (TEE) and recorded on videotape from the moment that the aortic cross-clamp was released until 20 minutes after end of cardiopulmonary bypass (CPB). The surgeon performed standard de-airing maneuvers without being aware of TEE findings. Postoperatively, a blinded assessor determined the maximal number of gas emboli during each consecutive minute in the left atrium, left ventricle, and ascending aorta. The 2 groups did not differ in the usual clinical parameters. The median number of microemboli registered during the whole study period was 161 in the CO2 group versus 723 in the control group (P<0.001). Corresponding numbers for the left atrium were 69 versus 340 (P<0.001), left ventricle 68 versus 254 (P<0.001), and ascending aorta 56 versus 185 (P<0.001). In the CO2 group, the median number of detectable microemboli after CPB fell to zero 7 minutes after CPB versus 19 minutes in the control group (P<0.001).

CONCLUSIONS

Insufflation of CO2 into the thoracic wound markedly decreases the incidence of microemboli.

Improved cerebral protection through replacement of residual intracavital air by carbon dioxide: a porcine model using diffusion-weighted magnetic resonance imaging

BACKGROUND

Major risk of central or peripheral organ damage is attributed to air embolism from incompletely de-aired cardiac chambers after cardiac operations. Replacement of air by carbon dioxide insufflation into the thoracic cavity is widely used. Diffusion-weighted magnetic resonance imaging of the brain detects ischemia within minutes after onset. The reversibility of ischemia in cerebral tissue after massive gaseous emboli has not yet been described.

METHODS

After selective catheterization of a common carotid artery in 15 pigs, boli of 1 mL/kg body weight of air (n = 5) or carbon dioxide (n = 5, "low dose") were applied. Five pigs received 2 mL/kg body weight of carbon dioxide ("high dose"). Diffusion-weighted magnetic resonance imaging of the brain was performed 2, 5, 10, 15, and 25 minutes after embolization.

RESULTS

All animals of the "air" group showed important circulatory reactions leading to death of 2 animals. In the whole group, diffusion-weighted magnetic resonance imaging revealed irreversible hyperintense signals in both hemispheres. In the low-dose group, no change in signal intensity was observed in 2 pigs, and 3 others showed reversible changes in signal intensity, without important circulatory reactions. In 3 animals of the high-dose group, hyperintense signals were reversible, but 2 others presented with bilateral, irreversible signals in diffusion-weighted magnetic resonance imaging, accompanied by minor circulatory reactions.

CONCLUSION

In contrast to the dramatic effect of air emboli, identical quantities of carbon dioxide injected into cerebral arteries of the pigs were not associated with major clinical symptoms. The early reversibility of ischemic reactions visualized in diffusion-weighted magnetic resonance imaging encourages the use of carbon dioxide insufflation as a protective method in cardiac surgery.

The dynamic air bubble trap reduces cerebral microembolism during cardiopulmonary bypass

OBJECTIVE

Neuropsychologic disorders are common after coronary artery bypass operations. Air microbubbles are identified as a contributing factor. A dynamic bubble trap might reduce the number of gaseous microemboli.

METHODS

A total of 50 patients undergoing coronary artery bypass operation were recruited for this study. In 26 patients a dynamic bubble trap was placed between the arterial filter and the aortic cannula (group 1), and in 24 patients a placebo dynamic bubble trap was used (group 2). The number of high-intensity transient signals within the proximal middle cerebral artery was continuously measured on both sides during bypass, which was separated into 4 periods: phase 1, start of bypass until aortic clamping; phase 2, aortic clamping until rewarming; phase 3, rewarming until clamp removal; and phase 4, clamp removal until end of bypass. S100 beta values were measured before, immediately after, and 6 and 48 hours after the operation and before hospital discharge.

RESULTS

The bubble elimination rate during bypass was 77% in group 1 and 28% in group 2 (P <.0001). The number of high-intensity signals was lower in group 1 during phase 1 (5.8 +/- 7.3 vs 16 +/- 15.4, P <.05 vs group 2) and phase 2 (6.9 +/- 7.3 vs 24.2 +/- 27.3, P <.05 vs group 2) but not during phases 3 and 4. Serum S100 beta values were equally increased in both groups immediately after the operation. Group 2 patients had higher S100 beta values 6 hours after the operation and significantly higher S100 beta values 48 hours after the operation (0.06 +/- 0.14 vs 0.18 +/- 0.24, P =.0133 vs group 2). Age and S100 beta values were correlated in group 2 but not in group 1.

CONCLUSION

Gaseous microemboli can be removed with a dynamic bubble trap. Subclinical cerebral injury detectable by increases of S100 beta disappears earlier after surgical intervention.