Cognitive Dysfunction After Cardiac Surgery: Revisiting Etiology

Most High-Intensity Transient Signals Are Not Associated With Specific Surgical Maneuvers

Background:

Mortality after congenital heart defect surgery has dropped dramatically in the last few decades. Current research on long-term outcomes has focused on preventing secondary neurological sequelae, for which embolic burden is suspected. In children, little is known of the correlation between specific surgical maneuvers and embolic burden. Transcranial Doppler ultrasound is highly useful for detecting emboli but has not been widely used with infants and children.

Methods:

Bilateral middle cerebral artery blood flow was continuously monitored from sternal incision to chest closure in 20 infants undergoing congenital heart defect repair or palliative surgery. Embolus counts for specific maneuvers were recorded using widely accepted criteria for identifying emboli via high-intensity transient signals (HITS).

Results:

An average of only 13% of all HITS detected during an operation were correlated with any of the surgical maneuvers of interest. The highest mean number of HITS associated with a specific maneuver occurred during cross-clamp removal. Cross-clamp placement also had elevated HITS counts that significantly differed from other maneuvers.

Conclusions:

In this study of infants undergoing cardiac surgery with cardiopulmonary bypass, the great majority of HITS detected are not definitively associated with a specific subset of surgical maneuvers. Among the measured maneuvers, removal of the aortic cross-clamp was associated with the greatest occurrence of HITS. Future recommended research efforts include identifying and confirming other sources for emboli and longitudinal outcome studies to determine if limiting embolic burden affects long-term neurological outcomes.

Carotid artery blood flow velocities during open-heart surgery and its association with delirium: A prospective, observational pilot study

The aim of this prospective observational single-centre pilot study was to evaluate the association between alterations in carotid artery blood flow velocities during cardiac surgery and postoperative delirium.Carotid artery blood flow velocity was determined perioperatively at 5 different timepoints by duplex sonography in 36 adult cardiac surgical patients. Delirium was assessed using the Confusion Assessment Method for the ICU and the Intensive Care Delirium Screening Checklist. Additionally, blood flow velocities in the middle cerebral arteries, differences in regional cerebral tissue oxygenation and quantity and quality of microemboli were measured.Delirium was detected in 7 of 36 patients. After cardiopulmonary bypass carotid artery blood flow velocities increased by +23 cm/second (95% confidence interval (CI) 9-36 cm/second) in non-delirious patients compared to preoperative values (P = .002), but not in delirious patients (+3 cm/second [95% CI -25 to 32 cm/second], P = .5781). Middle cerebral artery blood flow velocities were higher at aortic de-cannulation in non-delirious patients (29 cm/second [inter-quartile range (IQR), 24-36 cm/second] vs 12 cm/second [IQR, 10-19 cm/second]; P = .017). Furthermore, brain tissue oxygenation was higher in non-delirious patients during surgery.Our results suggest that higher cerebral blood flow velocities after aortic de-clamping and probably also improved brain oxygenation might be beneficial to prevent postoperative delirium.

Effects of methylprednisolone on blood-brain barrier and cerebral inflammation in cardiac surgery-a randomized trial

BACKGROUND

Cognitive dysfunction is a frequent complication to open-heart surgery. Cerebral inflammation caused by blood-brain barrier (BBB) dysfunction due to a systemic inflammatory response is considered a possible etiology. The effects of the glucocorticoid, methylprednisolone, on cerebrospinal fluid (CSF) markers of BBB function, neuroinflammation, and brain injury in patients undergoing cardiac surgery with cardiopulmonary bypass were studied.

METHODS

In this prospective, randomized, blinded study, 30 patients scheduled for elective surgical aortic valve replacement were randomized to methylprednisolone 15 mg/kg (n = 15) or placebo (n = 15) as a bolus dose administered after induction of anesthesia. CSF and blood samples were obtained the day before and 24 h after surgery for assessment of systemic and brain inflammation (interleukin-6, interleukin-8, tumor necrosis factor-alpha), axonal injury (total-tau, neurofilament light chain protein), neuronal injury (neuron-specific enolase), astroglial injury (S-100B, glial fibrillary acidic protein), and the BBB integrity (CSF/serum albumin ratio).

RESULTS

In the control group, there was a 54-fold and 17-fold increase in serum interleukin-6 and interleukin-8, respectively. This systemic activation of the inflammatory cytokines was clearly attenuated by methylprednisolone (p < 0.001). The increase of the CSF levels of the astroglial markers was not affected. A postoperative BBB dysfunction was seen in both groups as the CSF/serum albumin ratio increased from 6.4 ± 8.0 to 8.0 in the placebo group (p < 0.01) and from 5.6 ± 2.3 to 7.2 in the methylprednisolone group (p < 0.01) with no difference between groups (p = 0.98). In the CSF, methylprednisolone attenuated the interleukin-6 release (p < 0.001), which could be explained by the fall in systemic interleukin-6, and the serum to CSF gradient of IL-6 seen both at baseline and after surgery. In the CSF, methylprednisolone enhanced the interleukin-8 release (p < 0.001) but did not affect postoperative changes in CSF levels of tumor necrosis factor alpha. Serum levels of S-100B and neuron-specific enolase increased in both groups with no difference between groups. CSF levels of total tau, neurofilament light chain protein, and neuron-specific enolase were not affected in any of the groups.

CONCLUSIONS

Preventive treatment with high-dose methylprednisolone attenuated the systemic inflammatory response to open-heart surgery with cardiopulmonary bypass, but did not prevent or attenuate the increase in BBB permeability or the neuroinflammatory response.

TRIAL REGISTRATION

Clinical Trials, Identifier: NCT01755338 , registered 24 December 2012.

Cerebral blood flow measured by positron emission tomography during normothermic cardiopulmonary bypass: an experimental porcine study

BACKGROUND

Mean arterial blood pressure (MAP) and/or pump flow during normothermic cardiopulmonary bypass (CPB) are the most important factors of cerebral perfusion. The aim of this study was to explore the influence of CPB blood flow on cerebral blood flow (CBF) measured by dynamic positron emission tomography (PET) using ¹⁵O-labelled water with no pharmacological interventions to maintain the MAP.

METHODS

Eight pigs (69-71 kg) were connected to normothermic CPB. After 60 minutes (min) with a CPB pump flow of 60 mL/kg/min, the pigs were changed to either 35 mL/kg/min or 47.5 mL/kg/min for 60 min and, thereafter, all the pigs returned to 60 mL/kg/min for another 60 min. The MAP was measured continuously and the CBF was measured by positron emission tomography (PET) during spontaneous circulation and at each CPB pump flow after 30 min of steady state.

RESULTS

Two pigs were excluded due to complications. CBF increased from spontaneous circulation to a CPB pump flow of 60 mL/kg/min. A reduction in CPB pump flow to 47.5 mL/kg/min (n=3) resulted in only minor changes in CBF while a reduction to 35 mL/kg/min (n=3) caused a pronounced change (correlation coefficient (R²) 0.56). A return of CPB pump flow to 60 mL/kg/min was followed by an increase in CBF, except in the one pig with the lowest CBF during low flow (R²=0.44). CBF and MAP were not correlated (R²=0.20).

CONCLUSION

In this experimental porcine study, a relationship was observed between pump flow and CBF under normothermic low-flow CPB. The effect of low pump flow on MAP showed substantial variations, with no correlation between CBF and MAP.

Quantification of Postmembrane Gaseous Microembolization During Venoarterial Extracorporeal Membrane Oxygenation

Prolonged use of venoarterial extracorporeal membrane oxygenation (VA ECMO) may be complicated by end-organ dysfunction. Although gaseous microemboli (GME) are thought to damage end organs during cardiopulmonary bypass, patient exposures to GME have not been well characterized during VA ECMO. We therefore performed an observational study of GME in adult VA ECMO patients, with correlation to clinical events during routine patient care. After institutional review board (IRB) approval, we used two Doppler probes to detect GME noninvasively in extracorporeal membrane oxygenation (ECMO) circuits on four patients for 15 hours total while also recording patient care events. We then conducted in vitro trials to compare Doppler signals with gold-standard measurements using an Emboli Detection and Classification EDAC quantifier (Luna Innnovations, Inc. Roanoke, VA) (Terumo Cardiovascular, Ann Arbor, MI) during simulated clinical interventions. Correlations between Doppler and EDAC data were used to estimate GME counts and volumes represented by clinical Doppler data. A total of 503 groups of Doppler peaks representing GME showers were observed, including 194 statistically larger showers during patient care activities containing 92% of total Doppler peaks. Intravenous injections accounted for an estimated 68% of GME and 88% of GME volume, whereas care involving movement accounted for an estimated 6% of GME and 3% of volume. Overall estimated embolic rates of 24,000 GME totaling 4 μl/hr rivals reported GME rates during cardiopulmonary bypass. Numerous GME are present in the postmembrane circuit during VA ECMO, raising concern for effects on microcirculation and organ dysfunction. Strategies to detect and minimize GME may be warranted to limit embolic exposures experienced by VA ECMO patients.

Melatonin pretreatment prevents isoflurane-induced cognitive dysfunction by modulating sleep-wake rhythm in mice

BACKGROUND

Sleep plays an important role in memory processing. However, its role in anesthesia-induced cognitive dysfunction was not revealed. Our study sought to investigate the connection between the cognition decline and sleep-wake rhythm disorders after long-term isoflurane anesthesia in mice. Also, we examined the effect of exogenous melatonin pretreatment on both cognitive function and circadian rhythm. Furthermore, we discussed whether NR2B (N-methyl-D-aspartate receptor 2B subunit)-CREB (cAMP-response element binding protein) signaling pathway was involved in this course.

METHODS

2-month-old male C57/BL-6J mice were submitted to long-term anesthesia using 1% isoflurane from CT (Circadian Time) 14 to CT20. Melatonin pretreatment were conducted before anesthesia for 7 Days. Intellicage for mice and Mini-Mitter were applied to monitor spatial memory and gross motor activity which can reflect cognition and sleep-wake rhythm. Messenger RNA and protein expression of right hippocampus NR2B and CREB were examined by RT-PCR and Western blot.

RESULTS

6h isoflurane anesthesia led to impaired spatial memory from Day 3 to Day 10 in mice accompanied by the disruption of sleep-wake rhythm. Meanwhile, the hippocampus CREB and NR2B expression declined in step. Melatonin pretreatment ameliorated disturbed sleep-wake cycle, improved isoflurane-induced cognitive dysfunction, and reversed the down-regulation of CREB and NR2B expression.

CONCLUSIONS

Our data demonstrate that sleep-wake rhythm is involved in the isoflurane-induced cognition impairment and pretreatment of melatonin has a positive effect on circadian normalization and cognition reversal. Also, NR2B-CREB signaling pathway has a critical role in this process. This study provides us a new strategy for anesthesia-induced cognitive dysfunction therapy.

Evaluation of olfactory memory after coronary artery bypass grafting

Introduction

This study determined whether coronary artery bypass grafting (CABG) surgery has any effect on olfactory function, employing the Brief Smell Identification Test (B-SIT).

Material and methods

All the participants were informed preoperatively about the B-SIT test and the mode of its application. The test was performed by each patient preoperatively (d0) as well as 1 (d1) and 3 (d3) days following the surgery. C-reactive protein (CRP) levels were recorded at the same time as the smell test.

Results

This prospective study included 45 patients. The mean age was 67 ± 7.55, and the group was 29% male. The mean durations of cross clamping and cardiopulmonary bypass were 54 ± 32 min and 62.5 ± 37.0 min, respectively. Eleven different odors were tested. Significant differences were observed for several odors: leather between d0 and d3, pine between d0 and d3, onion between d0 and d1, onion between d0 and d3, and soap between d0 and d1. The postoperative CRP levels were significantly higher than the preoperative levels. The correlation analysis determined that the postoperative CRP levels were negatively correlated with the B-SIT score (r = –0.48, p = 0.001).

Conclusions

Our findings suggest that patients after CABG are prone to develop olfactory dysfunction in the early postoperative period and that olfactory dysfunction is associated with postoperative CRP levels.

Effect of slow versus rapid rewarming on jugular bulb oxygen saturation in adult patients undergoing open heart surgery

BACKGROUND

A debate has appeared in the recent literature about the optimum rewarming strategy (slow vs. rapid) for the best brain function. This study was designed to compare the effect of slow versus rapid rewarming on jugular bulb oxygen saturation (SjO2) in adult patients undergoing open heart surgery.

MATERIALS AND METHODS

A total of 80 patients undergoing valve and adult congenital heart surgery were randomly allocated equally to rapid rewarming group 0.5 (0.136)°C/min and slow rewarming group 0.219 (0.055)°C/min in jugular bulb sampling was taken before, during and after surgery. Surgery was done at cardiopulmonary bypass (CPB) temperature of 28-30°C and rewarming was performed at the end of the surgical procedure.

RESULTS

CPB time, rewarming period were significantly longer in the slow rewarming group. Significant difference was observed in the number of the desaturated patients (SjO2 ≤ 50%) between the two groups; 14 (35%) in rapid rewarming versus 6 (15%) in the slow rewarming group; P = 0.035 by Fisher's exact test.

CONCLUSIONS

Slow rewarming could reduce the incidence of SjO2 desaturation during rewarming in adult patients undergoing open heart surgery.

Elimination of gaseous microemboli from cardiopulmonary bypass using hypobaric oxygenation

BACKGROUND

Numerous gaseous microemboli (GME) are delivered into the arterial circulation during cardiopulmonary bypass (CPB). These emboli damage end organs through multiple mechanisms that are thought to contribute to neurocognitive deficits after cardiac surgery. Here, we use hypobaric oxygenation to reduce dissolved gases in blood and greatly reduce GME delivery during CPB.

METHODS

Variable subatmospheric pressures were applied to 100% oxygen sweep gas in standard hollow fiber microporous membrane oxygenators to oxygenate and denitrogenate blood. GME were quantified using ultrasound while air embolism from the surgical field was simulated experimentally. We assessed end-organ tissues in swine postoperatively using light microscopy.

RESULTS

Variable sweep gas pressures allowed reliable oxygenation independent of carbon dioxide removal while denitrogenating arterial blood. Hypobaric oxygenation produced dose-dependent reductions of Doppler signals produced by bolus and continuous GME loads in vitro. Swine were maintained using hypobaric oxygenation for 4 hours on CPB with no apparent adverse events. Compared with current practice standards of oxygen/air sweep gas, hypobaric oxygenation reduced GME volumes exiting the oxygenator (by 80%), exiting the arterial filter (95%), and arriving at the aortic cannula (∼100%), indicating progressive reabsorption of emboli throughout the CPB circuit in vivo. Analysis of brain tissue suggested decreased microvascular injury under hypobaric conditions.

CONCLUSIONS

Hypobaric oxygenation is an effective, low-cost, common sense approach that capitalizes on the simple physical makeup of GME to achieve their near-total elimination during CPB. This technique holds great potential for limiting end-organ damage and improving outcomes in a variety of patients undergoing extracorporeal circulation.

Review of transcranial Doppler ultrasound to detect microemboli during orthopedic surgery

Transcranial Doppler ultrasonography has been used to detect microemboli in the middle cerebral artery during orthopedic surgery. We conducted a comprehensive systematic literature review of transcranial Doppler ultrasonography in orthopedic surgery to evaluate its status in this setting. Fourteen studies were selected for qualitative analysis. The highest number of patients studied was 45; emboli were detected in all studies, occurring in 20%-100% of patients. Most embolic counts were below 10, but some high counts were noted. No study reported all the technical parameters of the transcranial Doppler ultrasonography. All studies assessed neurologic status, and 6 studies evaluated cognitive function postoperatively. No study identified an association between postoperative cognitive function and embolic count. Six studies sought the presence of right-to-left shunts.

Open-heart surgery increases cerebrospinal fluid levels of Alzheimer-associated amyloid β

BACKGROUND

Neurocognitive dysfunction occurs frequently after open-heart surgery. It has been suggested that cognitive decline after cardiac surgery with cardiopulmonary bypass (CPB) could be a functional consequence of Alzheimer's disease (AD)-like neuropathological changes. The aim of the present study was to evaluate the cerebrospinal fluid (CSF) levels of amyloid β peptide (Aβ(1-42) ) and soluble fragments of amyloid precursor protein (sAPP) as well as the cerebral inflammatory response to open-heart surgery.

METHODS

Ten patients undergoing aortic valve replacement with CPB were included. CSF was obtained the day before and 24 h after surgery for assessment of CSF levels of Aβ(1-42) α-cleaved sAPP and β-cleaved sAPP (sAPP-β). Furthermore, CSF and serum levels of the inflammatory cytokines: tumour necrosis factor alpha (TNF-α), interleukin-6 (IL-6) and interleukin-8 (IL-8) were also assessed.

RESULTS

Cardiac surgery with CPB increased CSF levels of Aβ(1-42) from 447 ± 92 to 641 ± 83 ng/l (P = 0.011), while CSF levels of sAPP-β decreased from 276 ± 35 to 192 ± 21 ng/ml (P = 0.031). CSF levels of TNF-α increased from ≤ 0.60 to 0.79 ± 0.26 ng/l (P = 0.043), IL-6 from 1.89 ± 0.53 to 22.8 ± 6.9 ng/l (P = 0.003) and IL-8 from 39.8 ± 7.8 to 139 ± 18.3 ng/l (P < 0.001).

CONCLUSIONS

Cardiac surgery with CPB causes a profound cerebral inflammatory response, which was accompanied by increased post-operative CSF levels of the AD biomarker Aβ(1-42) . We hypothesize that these changes may be relevant to Alzheimer-associated amyloid build-up in the brain and cognitive dysfunction after cardiac surgery with CPB.

Magnesium reduces matrix metalloproteinase-9, but not glial fibrillary acidic protein, in cardiac surgery patients

Magnesium (Mg) is one of the most important ions in the brain. Its supplementation decreases intracellular disorders and improves final outcomes following traumatic brain injury. Aim: The aim of the study was to analyze the effects of magnesium supplementation on arteriovenous differences in plasma magnesium concentration in brain circulation (a–vMg), plasma matrix metalloproteinase-9 (MMP-9) and glial fibrillary acidic protein (GFAP) concentrations in cardiac surgery patients. Methods: A total of 92 adult patients were enrolled. Patients were allocated into three groups: A, receiving 6.66 mg of MgSO4 per min intravenously; B, receiving 10 mg of MgSO4; and C, receiving 13.33 mg of MgSO4. Results: In all groups, GFAP and MMP-9 increased after extracorporeal circulation and immediately after surgery. Sequentially higher concentrations of MMP-9 and a–vMg were noted in groups A, B and C. Plasma GFAP concentrations were similar in all groups. Conclusion: Magnesium supplementation reduces plasma MMP-9 and a-vMg in brain circulation but does not affect plasma GFAP.

Postoperative cognitive deficit after cardiopulmonary bypass with preserved cerebral oxygenation: a prospective observational pilot study

Background

Neurologic deficits after cardiac surgery are common complications. Aim of this prospective observational pilot study was to investigate the incidence of postoperative cognitive deficit (POCD) after cardiac surgery, provided that relevant decrease of cerebral oxygen saturation (cSO2) is avoided during cardiopulmonary bypass.

Methods

cSO2 was measured by near infrared spectroscopy in 35 patients during cardiopulmonary bypass. cSO2 was kept above 80% of baseline and above 55% during anesthesia including cardiopulmonary bypass. POCD was tested by trail making test, digit symbol substitution test, Ray's auditorial verbal learning test, digit span test and verbal fluency test the day before and 5 days after surgery. POCD was defined as a decline in test performance that exceeded - 20% from baseline in two tests or more. Correlation of POCD with lowest cSO2 and cSO2 - threshold were determined explorative.

Results

POCD was observed in 43% of patients. Lowest cSO2 during cardiopulmonary bypass was significantly correlated with POCD (p = 0.015, r2 = 0.44, without Bonferroni correction). A threshold of 65% for cSO2 was able to predict POCD with a sensitivity of 86.7% and a specificity of 65.0% (p = 0.03, without Bonferroni correction).

Conclusions

Despite a relevant decrease of cerebral oxygen saturation was avoided in our pilot study during cardiopulmonary bypass, incidence of POCD was comparable to that reported in patients without monitoring. A higher threshold for cSO2 may be needed to reduce the incidence of POCD.

Independent association between preoperative cognitive status and discharge location after cardiac surgery

BACKGROUND

Among cardiac surgery patients, those with impaired cognitive status before surgery may have longer postoperative stays than do patients with normal status and may require additional care upon discharge.

OBJECTIVES

To determine if preoperative scores on a screening measure for cognitive status (the Clock-in-the-Box), were associated with postoperative length of stay and discharge to a location other than home in patients who had cardiac surgery.

METHODS

A total of 181 consecutive patients scheduled for cardiac surgery at a single site were administered the Clock-in-the-Box as part of the preoperative evaluation. Scores on the Clock-in-the-Box tool, demographic and operative information, postoperative length of stay, and discharge location were collected retrospectively from medical records.

RESULTS

The mean age of the patients was 68.1 years (SD, 0.7), and 99% were men. Mean postoperative length of stay was 10.5 days (SD, 8.2), and 35 patients (19%) were discharged to a facility. Scores on the Clock-in-the-Box assessment were not associated with postoperative length of stay. Increasing age, living alone before surgery, and duration of cardiopulmonary bypass were associated with discharge to a facility and were used as covariates in adjusted analyses. After adjustment, better preoperative cognitive status reduced the risk of being discharged to a facility (adjusted relative risk, 0.93; 95% confidence interval, 0.89-0.98) after cardiac surgery.

CONCLUSIONS

Cognitive screening before cardiac surgery can identify patients with impaired cognitive status who are less likely than patients with normal cognitive status to return home after cardiac surgery.

Minocycline may be useful to prevent/treat postoperative cognitive decline in elderly patients

Postoperative cognitive dysfunction (POCD) is reported to occur frequently after all types especially cardiac surgery in elderly patients. It can be short-term or long-term and some cases even develop into Alzheimer's disease (AD). Although multi-risk factors associated with POCD have been identified, the etiology and pathophysiological mechanisms of this surgical complication remain elusive. Therefore, developing strategies for preventing or treating POCD is still challenging. However, increasing evidence suggests that central and systemic inflammation triggered by surgery likely plays a fundamental role in POCD developing and progression. Minocycline, a tetracycline derivative with anti-inflammatory properties, has been shown to be effective in treating neuroinflammatory related conditions or neurodegenerative diseases such as AD, Parkinson's disease, Huntington's disease. Considering that inflammation may be a potential factor of POCD and minocycline is effective in improving cognitive dysfunction induced by inflammation, we hypothesize that minocycline may be useful to treat/prevent the POCD development after surgery in elderly patients.

Aortic atheroma and adverse cerebral outcome: risk, diagnosis, and management options

Aortic atheromatous disease is a common finding in the patient presenting for cardiac surgery. Adverse neurologic outcome has been closely linked to the extent of aortic atherosclerosis. In order to optimize perioperative outcomes, the location and severity of disease needs accurate characterization using multimodal techniques. Although various preoperative radiographic techniques have variably identified patients with significant atheroma, intraoperative echocardiographic imaging has proven most useful in localizing and characterizing the degree of aortic atheroma. Epiaortic assessment of the ascending aorta has been utilized in guiding surgical modifications and interventions aimed at reducing the risk of neurologic injury. Although no particular technique has been definitely studied, avoidance of the identifiable atheromatous aortic region has been a main feature of the various modifications employed to optimize neurologic outcome after cardiac surgery.

Animal models of cardiopulmonary bypass: development, applications, and impact

Neurologic and neurocognitive complications after cardiac surgery have been reported repeatedly. To better understand its etiology and design protective strategies, small animal models have been developed. This study describes the development of a survival rat cardiopulmonary bypass (CPB) model, along with the introduction of an appropriately sized oxygenator. This model led the way for even more complicated models with CPB, facilitating full cardiac arrest with anterograde cardioplegia administration, air embolization, and deep hypothermic circulatory arrest. In addition, the results of several of those rat CPB studies are summarized and their preclinical relevance is pointed out.

Size of left cardiac chambers correlates with cerebral microembolic load in open heart operations

Background. Microemboli are a widely recognized etiological factor of cerebral complications in cardiac surgery patients. The present study was aimed to determine if size of left cardiac chambers relates to cerebral microembolic load in open heart operations. Methods. Thirty patients participated in the study. Echocardiography was performed in 2-3 days before surgery. A transcranial Doppler system was used for registering intraoperative microemboli. Results. Preoperative left atrium and left ventricular end-systolic and end-diastolic sizes significantly correlated with intraoperative microembolic load (rs = 0.48, 0.57 and 0.53, Ps < .01, resp.). The associations between left ventricular diameters and number of cerebral microemboli remained significant when cardiopulmonary bypass time was included as a covariate into the analysis. Conclusions. The present results demonstrate that increased size of left heart chambers is an influential risk factor for elevated cerebral microembolic load during open heart operations. Mini-invasive surgery and carbon dioxide insufflation into wound cavity may be considered as neuroprotective approaches in patients with high risk of cerebral microembolism.

Pathophysiological aspects of cardiotomy suction usage

Cardiotomy suction is used for preservation of autologous blood during on-pump cardiac surgery at present. Controversially, the exclusion of cardiotomy suction in some types of operations (coronary artery bypass surgery) is not necessarily associated with an increased transfusion requirement. On the other hand, the use of cardiotomy suction causes an amplification of systemic inflammatory response and a resulting coagulopathy, as well as exacerbation of the microembolic load and hemolysis. This leads to a tendency towards increased blood loss, transfusion requirement and organ dysfunction. On the basis of these facts, it is appropriate to reconsider routine use of cardiotomy suction in on-pump coronary artery surgery.

Microbubbles detection during cardiopulmonary bypass with transoesophageal echocardiography: a case report

INTRODUCTION

Microembolic signals are usually detected with transcranial doppler during cardiac surgery.This report focuses on suggesting the transesophageal echocardiography as a different diagnostic approach to detect microemboli during cardiopulmonary bypass.

CASE PRESENTATION

A 58 year old male patient, caucasian race, was operated on video assisted minimally invasive mitral valve repair using right minithoracotomy approach. His past medical history included an uncontrolled hypertension, dyslipidemia, insulin dependent diabetes mellitus, carotid arteries stenosis. The extracorporeal circulation was performed with femoral-femoral artery and venous approach. Negative pressure for vacuum assist venous drainage was applied in order to facilitate venous blood return. The patient had a brain monitoring with bilateral transcranial doppler of middle cerebral arteries and a double channels electroencephalogram. A three dimensional transesophageal echocardiography to evaluate the mitral valve repair was performed.During the cardiopulmonary bypass a significant microembolic activity was detected in the middle cerebral arteries spectrum velocities due to gas embolism from venous return. Simultaneous recording of microbubbles was also observed on the descending thoracic aorta transesophageal echo views.

CONCLUSION

During the aortic cross-clamping time the transesophageal echocardiography can be useful as an alternative method to assess the amount of gas embolism coming from cardiopulmonary bypass. These informations can promote immediate interaction between perfusionist, surgeon and anesthesiologist to perform adequate manoeuvres in order to reduce the microembolism during extracorporeal circulation.

Neuroprotection during cardiac surgery

Cardiac surgery continues to be associated with significant adverse cerebral outcomes, ranging from stroke to cognitive decline. The underlying mechanism of the associated cerebral injury is incompletely understood but is believed to be primarily caused by cerebral embolism and hypoperfusion, exacerbated by ischemia/reperfusion injury. Extensive research has been undertaken in an attempt to minimize the incidence of perioperative cerebral injury, and both pharmacological and nonpharmacological strategies have been investigated. Although many agents demonstrated promise in preclinical studies, there is currently insufficient evidence from clinical trials to recommend the routine administration of any pharmacological agents for neuroprotection during cardiac surgery. The nonpharmacological strategies that can be recommended on the basis of evidence include transesophageal echocardiography and epiaortic ultrasound-guided assessment of the atheromatous ascending aorta with appropriate modification of cannulation, clamping or anastomotic technique and optimal temperature management. Large-scale randomized controlled trials are still required to address further the issues of optimal pH management, glycemic control, blood pressure management and hematocrit during cardiopulmonary bypass. Past, present and future directions in the field of neuroprotection in cardiac surgery will be discussed.

The effect of limited rewarming and postoperative hypothermia on cognitive function in a rat cardiopulmonary bypass model

BACKGROUND

Clinical studies have failed to demonstrate significant benefits of hypothermia for the prevention of postoperative cognitive dysfunction (POCD) after cardiopulmonary bypass (CPB). One explanation for this might be that potentially injurious cerebral hyperthermia occurs during rewarming at the end of CPB, off-setting the protective benefits of hypothermia. In this study, we investigated the relative influence of CPB temperature, rewarming strategies, and postoperative temperature in a rat CPB model.

METHODS

Four groups of male Sprague-Dawley rats were surgically prepared and subjected to 90 min of CPB. Group A was normothermic (37.5 degrees C) during and after CPB. Group B underwent hypothermic (32 degrees C) CPB, followed by rewarming to 37.5 degrees C at the end of bypass. Group C had hypothermic (32 degrees C) CPB, followed by limited rewarming to 35 degrees C. Group D had normothermic CPB with hypothermia (35 degrees C) induced only postoperatively. Groups were compared for POCD determined by the performance in the Morris water maze on postoperative days 3-9. Histologic analysis of the brains (CA1 and CA3 hippocampal regions) was also performed.

RESULTS

Hypothermia induced only during (group B versus group A) or after CPB (group D versus group A) conferred no significant POCD benefit. Hypothermia when induced during CPB and continued into the postoperative period resulted in a significant improvement in water maze performance versus all other temperature regimens (group C versus group A, P = 0.044; group C versus group B, P = 0.011; group C versus group D, P = 0.012). No histological differences among groups were demonstrated.

CONCLUSIONS

The combination of hypothermic (32 degrees C) CPB coupled with limited rewarming and prolonged postoperative hypothermia (35 degrees C) decreased POCD after CPB in rats.

Intraoperative hyperglycemia and cognitive decline after CABG

BACKGROUND

Neurocognitive dysfunction (NCD) continues to occur in a significant number of patients after cardiac procedures. The factors influencing its incidence and severity are not completely known. We hypothesized that hyperglycemia, which is known to exacerbate other forms of cerebral injury, may exacerbate NCD after cardiac operations.

METHODS

A total of 525 patients having on-pump coronary artery bypass graft (CABG) procedures underwent cognitive testing at baseline and 6 weeks postoperatively. Multivariable linear regression was used to determine the relationship between NCD and intraoperative hyperglycemia (glucose > or = 200 mg/dL). Diabetic and nondiabetic patients were analyzed separately to eliminate a possible confounding effects between diabetes and hyperglycemia.

RESULTS

In the nondiabetic patients, even after controlling for age, years of education, and baseline cognitive function, hyperglycemia was associated with a decrease in cognitive function at 6 weeks (p = 0.0351). Hyperglycemia had no effect on cognitive function in diabetic patients, however.

CONCLUSIONS

These findings suggest that in nondiabetic patients undergoing CABG operations, intraoperative hyperglycemia is associated with an increased risk of NCD.

Neuroprotection during cardiac surgery

Cerebral injury following cardiac surgery continues to be a significant source of morbidity and mortality after cardiac surgery. A spectrum of injuries ranging from subtle neurocognitive dysfunction to fatal strokes are caused by a complex series of multifactorial mechanisms. Protecting the brain from these injuries has focused on intervening on each of the various etiologic factors. Although numerous studies have focused on a pharmacologic solution, more success has been found with nonpharmacologic strategies, including optimal temperature management and reducing emboli generation.

Cardiopulmonary bypass and long-term neurocognitive dysfunction in the rat

Neurologic and neurocognitive complications after cardiac surgery with cardiopulmonary bypass (CPB) have been reported repeatedly. To better understand its etiology and design protective strategies, an appropriate animal model may prove useful. Although impaired short-term neurocognitive function has been recently demonstrated after CPB in rats, the demonstration of persistent long-term neurocognitive changes would be more relevant from a clinical perspective. We hypothesized that CPB results in long-term impairment of neurocognitive performance in rats. Male rats were exposed to either 60 min of normothermic non-pulsatile CPB, using a roller-pump and a neonatal membrane oxygenator, or to cannulation only (sham animals). Long-term neurocognitive function was assessed at 4 to 7 weeks after CPB (Can test), and again after 12 weeks (Morris water maze) in both operated groups and in a non-operated control group, followed by histologic evaluation of the hippocampus. In separate groups of CPB and sham animals, we also measured TNF-alpha and IL-6 in plasma. There were no significant differences in long-term neurocognitive performance or histological outcome between the three groups. Cytokine patterns were also similar in both operated groups. We conclude that CPB did not appear to cause long-term neurocognitive dysfunction in this model of CPB in young healthy rats. The lack of long-term deficits may be due to the absence of clinically important etiologic factors such as atheromatous and gaseous embolization in this model. Similar cytokine patterns in both operated groups suggest that surgical trauma rather than exposure of blood to extra-corporeal circuit was probably responsible for the inflammatory response.

Cardiothoracic Anesthesia, Respiration and Airway

PURPOSE

Cerebral hyperthermia during rewarming from hypothermic cardiopulmonary bypass (CPB) commonly occurs and has been associated with postoperative neurocognitive dysfunction. Increased awareness of this has likely led to changes in rewarming strategies, including the reduction of rewarming rates and lowering of target rewarming temperatures. As a result, we hypothesized that the maximum temperature reached during cardiac surgery has decreased at our institution over time.

METHODS

We retrospectively reviewed the maximum intraoperative nasopharyngeal (NP) temperature in 6,334 patients having undergone cardiac surgery utilizing hypothermic CPB from January 1993 to June 2000. The incidence of cerebral hyperthermia (defined by a NP temperature > 38 degrees C) was examined over time using Chi-square testing and the relationship between maximum temperature and date of surgery was studied using linear regression.

RESULTS

Maximum temperature decreased over time (P < 0.0001; r2 = 0.40) having the greatest reduction from January 1993 to December 1996 (0.34 degrees C temperature drop per year), while from January 1997 to June 2000, it continued to decrease, but at a slower rate (0.10 degrees C per yr; P < 0.0001). The incidence of cerebral hyperthermia decreased over time with 83% of the first 10% of patients and 3% of the latter 10% of patients during the study period having a maximum temperature > 38 degrees C (P < 0.0001).

CONCLUSION

The incidence of cerebral hyperthermia has decreased at our institution suggesting that a change in temperature management has occurred at our institution from January 1993 to June 2000 thereby outlining a temporal evolution in temperature management during CPB.