The role of CPB management in neurobehavioral outcomes after cardiac surgery

Microemboli and Neurologic Dysfunction After Cardiovascular Surgery

Several recent studies have shown that cardiac surgery poses significant risks for negative neurologic and neu ropsychological outcome. Death and major stroke have become uncommon consequences of cardiac surgery, but more than two-thirds of the patients show evidence of neuropsychological dysfunction postoperatively.

The mechanisms contributing to postcardiopulmonary bypass neuropsychological deficits are uncertain, and potentially there are many possible causative factors that may play a significant role in perioperative neuro logic injury. However, two major interrelated factors, hypoperfusion and emboli, are suggested as probable culprits. Perfusion is important because the level of global and focal cerebral blood flow during periods of high embolic risk will determine the amount of brain embolization as well as the localization of the lesions. Ultrasonically detected macroemboli have been re ported to be the best predictor of neurobehavioral outcome. Microemboli found in autopsy specimens may also be important predictors of negative outcome. The relationship between microemboli and changes in brain function, as detected by magnetic resonance spectroscopy, may provide further insight into the prob ability of the clinical expression of a neurobehavioral dysfunction after cardiac surgery.

The incidence and severity of neuropsychological defi cits after cardiac surgery appear to be related to the delivery of macroemboli. The composition of the embo lus may be the most important determinant of the level and volume of focal injury, but the time of occurrence (ie, rewarming) of macroemboli during cardiopulmo nary bypass may also be important in determining the effect of emboli on neuropsychological outcome. How ever, the key variable in the manifestation of neurobe havioral dysfunction remains the location of the lesion site.

Assessment of dynamic cerebral autoregulation and cerebral carbon dioxide reactivity during normothermic cardiopulmonary bypass

Despite increased risk of neurological complications after cardiac surgery, monitoring of cerebral hemodynamics during cardiopulmonary bypass (CPB) is still not a common practice. Therefore, a technique to evaluate dynamic cerebral autoregulation and cerebral carbon dioxide reactivity (CO2R) during normothermic nonpulsatile CPB is presented. The technique uses continuous recording of invasive arterial blood pressure, middle cerebral artery blood flow velocity, absolute cerebral tissue oxygenation, in-line arterial carbon dioxide levels, and pump flow measurement in 37 adult male patients undergoing elective CPB. Cerebral autoregulation is estimated by transfer function analysis and the autoregulation index, based on the response to blood pressure variation induced by cyclic 6/min changes of indexed pump flow from 2.0 to 2.4 up to 2.8 L/min/m(2). CO2R was calculated from recordings of both cerebral blood flow velocity and cerebral tissue oxygenation. Cerebral autoregulation and CO2R were estimated at hypocapnia, normocapnia, and hypercapnia. CO2R was preserved during CPB, but significantly lower for hypocapnia compared with hypercapnia (p < 0.01). Conversely, cerebral autoregulation parameters such as gain, phase, and autoregulation index were significantly higher (p < 0.01) during hypocapnia compared with both normocapnia and hypercapnia. Assessing cerebral autoregulation and CO2R during CPB, by cyclic alteration of pump flow, showed an impaired cerebral autoregulation during hypercapnia.

Off-pump coronary revascularization: A potential benefit for female patients?

Coronary artery disease is one of the leading causes of illness for both men and women. However, women are 3 times more likely to die for coronary artery disease as they are of breast cancer. There are an increasing prevalence of coronary artery disease in women and thus facing the need for surgical revascularization. It has long being accepted that women carry a high risk of coronary surgery than men. Many investigators have suggested that female itself is predictive of poor outcome after on pump coronary surgery. We thought to search the litlature to investigate whether women who undergo off-pump surgery receive any benefits compared with women undergoing on-pump surgery.

Dementia and depression with ischemic heart disease: a population-based longitudinal study comparing interventional approaches to medical management

BACKGROUND

We compared the proportion of ischemic heart disease (IHD) patients newly diagnosed with dementia and depression across three treatment groups: percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) and medical management alone (IHD-medical).

METHODS AND FINDINGS

De-identified, individual-level administrative records of health service use for the population of Manitoba, Canada (approximately 1.1 million) were examined. From April 1, 1993 to March 31, 1998, patients were identified with a diagnosis of IHD (ICD-9-CM codes). Index events of CABG or PCI were identified from April 1, 1998 to March 31, 2003. Outcomes were depression or dementia after the index event. Patients were followed forward to March 31, 2006 or until censored. Proportional hazards regression analysis was undertaken. Independent variables examined were age, sex, diabetes, hypertension and income quintile, medical management alone for IHD, or intervention by PCI or CABG. Age, sex, diabetes, and presence of hypertension were all strongly associated with the diagnosis of depression and dementia. There was no association with income quintile. Dementia was less frequent with PCI compared to medical management; (HR = 0.65; p = 0.017). CABG did not provide the same protective effect compared to medical management (HR = 0.90; p = 0.372). New diagnosis depression was more frequent with interventional approaches: PCI (n = 626; hazard ratio = 1.25; p = 0.028) and CABG (n = 1124, HR = 1.32; p = 0.0001) than non-interventional patients (n = 34,508). Subsequent CABG was nearly 16-fold higher (p<0.0001) and subsequent PCI was 22-fold higher (p<0.0001) for PCI-managed than CABG-managed patients.

CONCLUSIONS

Patients managed with PCI had the lowest likelihood of dementia-only 65% of the risk for medical management alone. Both interventional approaches were associated with a higher risk of new diagnosed depression compared to medical management. Long-term myocardial revascularization was superior with CABG. These findings suggest that PCI may confer a long-term protective effect from dementia. The mechanism(s) of dementia protection requires elucidation.

Adrenomedullin blood concentrations in infants subjected to cardiopulmonary bypass: correlation with monitoring parameters and prediction of poor neurological outcome

BACKGROUND

Brain injury is a major adverse event after cardiac surgery, especially when extracorporeal circuits are used. We evaluated whether cardiopulmonary bypass (CPB) affects cerebrovascular resistance and plasma concentrations of adrenomedullin (AM), a vasoactive peptide regulating cerebral blood flow.

METHODS

We evaluated 50 infants (age <1 year) with congenital heart defects, matched according to a 2-year follow-up; 40 infants had no overt neurological injury, and 10 had brain damage. Blood samples were taken before surgery, during surgery before CPB, at the end of CPB, at the end of surgery, and at 12 h after surgery. Neurological outcome was evaluated before surgery, on postoperative day 7, and 2 years after surgery. We measured AM concentrations and used Doppler velocimetry to measure middle cerebral artery (MCA) pulsatility index (PI).

RESULTS

The highest MCA PI values and lowest AM concentrations occurred at the end of CPB and of the surgical procedure. Infants who developed abnormal neurologic sequelae had significantly (P <0.001 for both) higher MCA PI values and lower AM concentrations than patients with normal neurologic outcome at the end of CPB and after surgery. As single markers for predicting neurological abnormalities, AM (cutoff: 17.4 ng/L) achieved a sensitivity of 100% and a specificity of 73.0% and MCA PI (cutoff value: 1.8) a sensitivity of 100% and a specificity of 56.8%.

CONCLUSIONS

AM concentrations and MCA PI patterns change during CPB, mainly in infants with brain damage, and may be useful for early identification of infants at risk for brain damage.

[Multi-value regulatory systems for extracorporeal circulation]

Extracorporeal perfusion is the standard technique in cardiac surgery. It is controlled by perfusionists on the basis of their clinical experience and on the available data collected pre- and intra-operatively. But in spite of intensive monitoring postoperative complications occur. An appropriate control of the heart-lung machine (HLM) using an "autopilot" might improve the quality of heart-surgery and decrease postoperative complications. Hence, a mathematical model of a human circulatory system has been developed which provides much more information about haemodynamics, blood gases and acid-base status than standard monitoring. It has been implemented on a system which is capable of integrating measured data as input parameters in real-time in the simulation. Now, soft- and hardware control concepts based on the human circulatory system have to be developed which are able to control the HLM.

Observer design for haemodynamics in patients undergoing cardiac surgery

During extracorporeal circulation, many important circulatory parameters are unknown, being inaccessible for measuring probes, as e.g. the perfusion of the brain. An observer system, which estimates such patient variables continuously throughout the operation, can extend the information basis for the decisions of the perfusionist regarding the control of the heart-lung machine and thus contribute to adjust this operation procedure to the actual patient situation. The observer design is based on a mathematical model of the human circulatory system. Beside the classical Luenberger observer design, a rule-based approach has been tested, which is also based on the structure of a Luenberger observer, however instead of an observer matrix a correction algorithm has been used in the feedback loop. A prototype of this system for animal experimental and clinical evaluation has been realised.

Neurological and neuropsychological examination and outcome after use of an intra-aortic filter device during cardiac surgery

Cerebral embolization of particles after cardiac surgery is frequently associated with neurological deficits. Aortic crossclamp manipulation seems to be the most significant cause of emboli release during cardiac surgery. The goal of this study was to demonstrate whether the use of an intra-aortic filter device has an effect on the magnet resonance imaging (MRI) and functional neurological outcome. Twenty-four patients undergoing cardiosurgical procedures using cardiopulmonary bypass (CPB) were selected: coronary artery bypass graft (CABG) surgery (n = 17), aortic valve replacement (AVR) surgery (n = 4) or combined procedures (n = 3). Patients were evaluated by diffusion weighted MRI of the brain, neurological examination and neuropsychological assessment regarding alertness as well as divided and selective attention before and five to seven days after surgery. The patients were divided into two groups. In group I, 12 patients received a filter through a modified 24 F arterial cannula immediately before the aortic crossclamp was released. Filters remained in the aorta until CPB was discontinued. Intraoperatively, bilateral middle cerebral artery transcranial Doppler (TCD) was monitored at baseline, at the beginning of CPB, at a timepoint when the aorta was crossclamped, when the filter was inserted and while the crossclamp was switched to partial clamping until the CPB was discontinued. TCD was used for detection of microembolic signals (MES). The captured material in the filter was examined histologically. Twelve patients served as controls without aortic filtration (group II). The MRI of the brain did not show any diffusion alterations in either group before or after surgery. No patient developed a focal neurological deficit or stroke. Intraoperative quantitative MES detection revealed a four to tenfold increase in patients of group I compared with group II (5-6 versus 0.5-1 MES/min) during the filter dwell time. There was no consistent pattern regarding the neurobehavioural sequelae. Filters showed arteriosclerotic debris in 75% of the patients. The use of the intra-aortic filter device did not show a positive effect on neurological, neuroradiographical and neuropsychological outcomes. The increase of the MES rate in group I patients may be due to microbubbles generated as microcavitations by the filter or the aortic filter cannula. The intra-aortic filter was able to capture atheromatous material in 75% of the patients.

S100B blood levels correlate with rewarming time and cerebral Doppler in pediatric open heart surgery

BACKGROUND

Brain hyperthermia, accompanying the rewarming phase of cardiopulmonary bypass (CPB), has been involved in the genesis of postoperative brain damage. Blood S100B levels are emerging as a marker of brain distress, and could offer a reliable monitoring tool at different times during and after open heart surgery.

METHODS

Thirty-two patients undergoing repair of congenital heart disease with CPB and deep hypothermic circulatory arrest (DHCA) were monitored by S100B blood levels and middle cerebral artery Doppler velocimetry pulsatility index (MCA PI) before, during, and after surgical procedure at five predetermined time-points.

RESULTS

Both S100B and MCA PI significantly increased, MCA PI values exhibiting a peak at the end of surgery time-point (p > 0.05), while S100B blood levels were increased at the end of CPB (p < 0.05). Multivariate analysis, with S100B levels measured at the end of CPB as dependent variable, showed a positive significant correlation with MCA PI (p = 0.04), with the CPB and the rewarming duration (p = 0.03 and p = 0.009, respectively).

CONCLUSIONS

The present results show a significant correlation between a biochemical marker of brain damage and an index of increased cerebrovascular resistance, with higher levels during the rewarming CPB phase in pediatric open heart surgery.

Alterations to haemostasis following cardiopulmonary bypass and the relationship of these changes to neurocognitive morbidity

Cardiopulmonary bypass (CPB) is routinely utilized to provide circulatory support during cardiac surgical procedures. The morbidity of CPB has been significantly reduced since its introduction 50 years ago; however, cerebral injury remains a potentially serious consequence of otherwise successful surgery. The risk of stroke postoperatively is approximately 1-5%. Incidence rates for neurocognitive deficit, however, vary markedly depending on the detection method, although typically it is reported in at least 50% of patients. The aetiology of this cerebral injury remains open to debate, although evidence shows that ischaemia secondary to microembolism may be the principal factor. Emboli originate from bubbles of air, atheroemboli released on aortic manipulation and thromboemboli generated as a result of haemostatic activation. Significant generation of thrombin occurs during CPB resulting in fibrin formation, although the trigger of this activation is not fully understood. Rather than originating from contact activation as previously thought, the primary trigger may be via the activated factor VII/tissue factor pathway of coagulation, with an additional role of contact activation in amplification of coagulation as well as the fibrinolytic response to CPB. Haemostatic activation is inhibited with systemic heparin therapy. The relationship between haemostatic activation and emboli formation during CPB is not known. Interventions to reduce cerebral injury in the context of cardiac surgery depend, in large part, on the minimization of emboli. This review investigates cerebral injury after cardiac surgery and evidence showing that microembolism is the principal causative agent. Fibrin emboli are postulated to be an important source of cerebral embolism. The mechanism of haemostatic activation during CPB is therefore also discussed.

The combination of lamotrigine and mild hypothermia prevents ischemia-induced increase in hippocampal glutamate

The excessive release of glutamate during cerebral ischemia may play an important role in subsequent neuronal injury. Both lamotrigine and hypothermia have independently been shown to attenuate the release of glutamate. In this study, the authors sought to determine whether these effects were additive. Thirty-five New Zealand White rabbits were randomized to one of six groups: a normothermic control group; a lamotrigine-treated group; two hypothermic groups at 33 degreesC or 34.5 degreesC; or two groups treated with both hypothermia at 33 degreesC or 34.5 degreesC plus lamotrigine. Animals were anesthetized before implanting microdialysis probes in the hippocampus. Esophageal temperature was maintained at 38 degreesC in the control and lamotrigine groups, while the temperatures of animals in the hypothermia and hypothermia-plus-lamotrigine groups were cooled to 33 degreesC or 34.5 degreesC. Two 10 minute periods of global cerebral ischemia were produced by inflating a neck tourniquet. Levels of glutamate in the microdialysate were then determined using high-performance liquid chromatography. Extracellular glutamate concentrations increased only slightly from baseline during the first ischemic period. Glutamate levels during the second ischemic episode in the hypothermia-plus-lamotrigine group (34.5 degreesC) were significantly lower than those in the hypothermia group alone (34.5 degreesC), lamotrigine, or control groups (P < .01). The fact that mild hypothermia (34.5 degreesC) plus lamotrigine (20 mg/kg) together were more effective in inhibiting extracellular glutamate accumulation than hypothermia (34.5 degreesC) or lamotrigine (20 mg/kg) alone, suggests the potential for increased neuroprotection by the addition of lamotrigine to mild hypothermia.

Platelet PlA2 polymorphism enhances risk of neurocognitive decline after cardiopulmonary bypass. Multicenter Study of Perioperative Ischemia (McSPI) Research Group

BACKGROUND

Neurocognitive decline, often produced by atherosclerotic plaque embolization, remains a frequent complication of cardiopulmonary bypass. Plaque fragments may initiate local thrombosis, which, in turn, aggravates the embolic insult. Prothrombotic genetic factors may exacerbate this process. We investigated whether the PlA2 polymorphism of platelet GPIIIa, a prothrombotic risk factor in other cardiovascular settings, is associated with early neurocognitive decline after cardiopulmonary bypass.

METHODS

Neurocognitive changes were evaluated by the Mini-Mental State Examination administered preoperatively and on postoperative day 4 and the PlA genotype determined in 70 patients undergoing cardiopulmonary bypass.

RESULTS

Forty-nine patients were PlA1/A1, and 21 were PlA1/A2 or PlA2/A2. Fifty-two patients (74%) demonstrated post-cardiopulmonary bypass neurocognitive decline, of which 34 were PlA1/A1 and 18 were PlA1/A2 or PlA2/A2 Multivariate analysis revealed that the PlA2 genotype and baseline Mini-Mental State Examination were significantly associated with greater neurocognitive decline (decreased Mini-Mental State Examination scores, p = 0.036 and 0.024, respectively).

CONCLUSIONS

This study demonstrates a link between the PlA2 allele of platelet GPIIIa and more severe neurocognitive decline after cardiopulmonary bypass. Although the mechanism is unknown, it could represent exacerbation of platelet-dependent thrombotic processes associated with plaque embolism.

Early natural course of transient encephalopathy after coronary artery bypass grafting

OBJECTIVE

A decline of neuropsychological performance is an unwanted side effect of coronary artery bypass grafting (CABG) with extracorporeal circulation. There is little data on the neuropsychological changes during the first 2 wks after CABG.

DESIGN, SETTING, PATIENTS

In this prospective observational study at our university medical center, a group of 67 patients who underwent routine CABG was selected for absence of comorbidity (such as carotid stenosis, previous stroke, dementia, and advanced general medical disorders) and examined. In this selected group of patients, no focal deficit was seen throughout the study. A total of 20 hospitalized patients with different types of peripheral neuropathy and free from drugs interfering with cognition served as a control group for the practice effects of the neuropsychological testing.

MEASUREMENTS AND MAIN RESULTS

Seven standard tests covering different neuropsychological domains were used as a composite battery. Examinations took place before surgery and serially at days 3, 6, and 9 after CABG; general neurologic examination was done every day, including the first postoperative day. We observed a definite decline in all tests at day 3 (p < .01) and progressive recovery thereafter up to or even beyond preoperative values within 9 days (p < .01). Transient depression as indicated by self-rated scores occurred in some patients.

CONCLUSION

We observed a uniform, but transient, deterioration in performance on a battery of frequently repeated standardized neuropsychological tests early after CABG. Our data on the early natural course may help to better evaluate treatment efforts aimed at preventing or reducing after-surgery neuropsychological alterations.

Particulate emboli capture by an intra-aortic filter device during cardiac surgery

OBJECTIVE

Particulate embolization is associated with neurologic morbidity after cardiac surgery. Crossclamp manipulation has been identified as the single most significant cause of particulate emboli release during cardiac surgery. A new intra-aortic filtration method has been assessed with regard to its safety and its ability to capture particulate emboli before they enter the central circulation.

METHODS

Patients undergoing cardiac surgery with cardiopulmonary bypass through standard median sternotomy were selected for emboli management by means of intra-aortic filtration. A novel intra-aortic filter device was inserted through a modified 24F arterial cannula immediately before releasing the crossclamp in 77 patients. Filters remained in the aorta until cardiopulmonary bypass was discontinued and the heart was fully ejecting. The procedure was assessed for facility, safety, and effect on routine cardiopulmonary bypass operation and function.

RESULTS

The insertion and removal of the intra-aortic filter were safe, easy, and uneventful in most patients. Patient hemodynamics and bypass flow rates remained normal throughout the filter dwell period. No strokes or gross neurologic defects were noted. Electron microscopic analysis of 12 filters revealed an insignificant degree of platelet adhesion on filter surfaces. Histology samples (n = 44) were examined, and 66% (n = 29) showed evidence of atheromatous material, 36% (n = 16) with platelet-fibrin, 25% (n = 11) with true thrombus and/or blood clot, 7% (n = 3) with normal vessel wall, and 2% (n = 1) with aggregates of cholesterol or grumous portion of atheromatous plaque.

CONCLUSION

The intra-aortic filter can be safely deployed and captures particulate emboli, the predominant origin of which is atheromatous. The beneficial effects of this device on neurologic outcomes have yet to be determined.

Evaluation of self-reported failures in cognitive function after cardiac and noncardiac surgery

Long-term cognitive deficits after cardiac surgical procedures involving cardiopulmonary bypass have been well documented. The occurrence of prolonged cognitive changes after noncardiac surgery has not, however, been clearly established. Using the Cognitive Failures Questionnaire, which permits self-assessment of cognitive impairment, we studied 50 patients before and 2 months after coronary bypass surgery and major vascular surgical procedures. Pre-operative test scores did not differ between groups. Postoperatively, 24 cardiac surgical patients and 22 vascular surgical patients completed the questionnaire. Both groups reported significantly more cognitive failures occurring after surgery than in the pre-operative period. This suggests that there are factors other than the exposure to cardiopulmonary bypass during cardiac surgery that affect self-assessed, long-term postoperative cognitive sequelae.

Bilateral cerebral emboli monitoring during extracorporeal circulation

Microembolism generated during extracorporeal circulation is thought to be responsible for stroke and neuropsychological deficits. Before one can investigate the pathogenetic role in more detail, reproducible and reliable quantitative methods need to be developed. In several previous studies, microemboli detection was performed unilaterally. We questioned if this reflects the bihemispheric embolic load. In 42 patients undergoing coronary artery bypass grafting, bilateral embolus detection was performed during extracorporeal circulation. The side-to-side correlation of microembolus counts was strong (0.91), but there was a significant difference in number (p < 0.01) comparing left and right emboli. The side of higher embolus counts cannot be predicted in the individual because either side may show higher counts. Doubling the unilateral count may deviate from the bilateral count by as much as 51% in the individual patient. The total embolic load to the brain during extracorporeal circulation cannot be precisely predicted from unilateral transcranial insonation alone.

Effect of aortic cannula characteristics and blood velocity on transcranial doppler-detected microemboli during cardiopulmonary bypass

OBJECTIVES

Cerebral microemboli are responsible to a large extent for the neuropsychiatric deficits after cardiac surgery. Differences in cannula size during cardiopulmonary bypass (CPB) will result in different velocities of blood exiting the aortic cannula. This study determined whether the number of transcranial Doppler (TCD)-detected emboli in the middle cerebral artery (MCA) during CPB correlated with blood speed or the direction of flow as determined by the shape of the aortic cannula.

DESIGN

Patients were studied prospectively for evidence of TCD-detected emboli. If patients met the inclusion criteria, the choice of cannula was determined by surgical preference.

SETTING

All studies were conducted at a single tertiary care academic cardiac surgery hospital by a single observer.

PARTICIPANTS

Thirty-two patients undergoing first-time elective aortocoronary bypass surgery who were free of neurologic dysfunction or peripheral vascular disease and weighed 60 to 85 kg were studied. Patients who had other concurrent cardiac operations or who were in cardiogenic shock were excluded.

INTERVENTIONS

Three aortic cannula types for elective aortocoronary bypass surgery were used: 24F curved (n = 19), 24F straight (n = 6), and 22F straight (n = 7), with internal diameters (IDs) of 7.2, 6.6, and 5.9 mm, respectively. TCD-detected emboli were identified in the MCA.

MEASUREMENTS AND MAIN RESULTS

The rate of TCD-detected emboli (0.02 to 11.4 emboli per minute) was not related to the velocity of blood (46 to 77 cm/s) and was not affected by the choice of either a straight or curved aortic cannula.

CONCLUSIONS

The choice of a straight or curved aortic cannula or of a 24F versus 22F cannula may not be important with respect to the number of cerebral microemboli.

The arterial to end-tidal carbon dioxide gradient increases with uncorrected but not with temperature-corrected PaCO2 determination during mild to moderate hypothermia

End-tidal carbon dioxide (PETCO2) monitoring is recommended as a basic standard of care and is helpful in adjusting mechanical ventilation. Gas solubility changes with temperature, which might affect the PaCO2 and thereby the gradient between PaCO2 and PETCO2 (PA-ETCO2) under hypothermic conditions. We investigated whether the PA-ETCO2 changes during mild to moderate hypothermia (36 degrees C-32 degrees C) using PaCO2 measured at 37 degrees C (uncorrected PaCO2) and PaCO2 corrected to actual body temperature. We preoperatively investigated 19 patients. After anesthesia had been induced, controlled ventilation was established to maintain normocarbia using constant uncorrected PaCO2 to adjust ventilation (alpha-stat acid-base regimen). Body core temperature was reduced without surgical intervention to 32 degrees C by surface cooling. Continuous PETCO2 was monitored with a mainstream PETCO2 module. The PA-ETCO2 was calculated using the uncorrected and corrected PaCO2 values. During body temperature reduction from 36 degrees C to 32 degrees C, the gradient between PETCO2 and uncorrected PaCO2 increased 2.5-fold, from 4.1 +/- 3.7 to 10.4 +/- 3.8 mm Hg (P < 0.002). The PA-ETCO2 remained unchanged when the corrected PaCO2 was used for the calculation. We conclude that when the alpha-stat acid-base regimen is used to adjust ventilation, the PA-ETCO2 calculated with the uncorrected PaCO2 increases and should be added to the differential diagnosis of widened PA-ETCO2. In contrast, when the corrected PaCO2 is used for the calculation of the PA-ETCO2, the PA-ETCO2 remains unaltered during hypothermia.

IMPLICATIONS

We investigated the impact of induced hypothermia (36 degrees C-32 degrees C) on the gradient between PaCO2 and PETCO2 (PA-ETCO2). The PA-ETCO2 increased 2.5-fold when CO2 determinations were not temperature-corrected. Hypothermia should be added to the differential diagnosis of an increased PA-ETCO2 when the alpha-stat acid-base regimen is used.

Alterations of neuropsychological function and cerebral glucose metabolism after cardiac surgery are not related only to intraoperative microembolic events

BACKGROUND AND PURPOSE

High-intensity transient signals (HITS) during cardiac surgery are capable of causing encephalopathy and cognitive deficits. This study was undertaken to determine whether intraoperative HITS cause alterations of neuropsychological function (NPF) and/or cerebral glucose metabolism (CMRGlc), even in a low-risk patient group, and whether induced changes are interrelated.

METHODS

Eighteen patients without signs of cerebrovascular disease underwent elective coronary artery bypass grafting (CABG), and two of these additionally underwent valve replacement in normothermia. Intraoperatively, HITS were recorded by means of transcranial Doppler ultrasonography (TCD). Perioperatively, NPF and CMRGlc were assessed using a standardized complex test battery and positron emission tomography with 18F-2-fluoro-2-deoxy-D-glucose (FDG-PET), respectively.

RESULTS

Intraoperatively, the number of HITS ranged from 90 to 1710 per patient and hemisphere, more on the right side than on the left (P<.05). HITS occurred primarily during cardiopulmonary bypass (71.3%) and, to a lesser extent, during aortic manipulation (22.2%). Changes in global and regional CMRGlc between first (one day preoperatively) and second (8 to 12 days postoperatively) FDG-PET scans were mild. No correlations were found between the number of HITS, age of patient, duration of cardiac ischemia or cardiopulmonary bypass and the changes in CMRGlc. In patients with recorded HITS and a postoperative decrease of regional CMRGlc (n=11), the maximal decrease of rCMR Glc in each hemisphere below the individual global change of CMRGlc correlated with the number of HITS (r= -0.46, P<.05). Limitations in NPF occurred 8 to 12 days postoperatively, resolved within 3 months, and were not found to be correlated to the absolute number of HITS or changes in CMRGlc.

CONCLUSIONS

HITS during cardiac surgery can cause alterations of both NPF and CMRGlc, even in a low-risk patient group. However, the number of HITS and changes in NPF and CMRGlc are not necessarily interrelated, which indicates that (1) the location of brain damage related to HITS is more important for the development of NPF than is the absolute number of HITS, and (2) factors in addition to HITS might contribute to surgery-related brain damage.

What is the best perfusion temperature for coronary revascularization?

BACKGROUND

[corrected] A National Institutes of Health-funded clinical trial of patients undergoing coronary artery bypass randomized perfusate and myocardial preservation to cold, tepid, or warm temperatures. The goal of the trial was to evaluate neurologic function before and after operation (4 days and 1 month after operation) and to measure hematologic data for fibrinolytic potential.

METHODS

The three groups comprised 116 patients who completed neurologic evaluation by means of the Mathew scale out of 130 entered into the trial (37 cold group, 50 tepid, and 43 warm). Twenty-five patients had complete hematologic studies done. All three groups were comparable before operation. The myocardial preservation protocol used blood cardioplegic solution at cold (8 degrees to 10 degrees C), tepid (32 degrees C), or warm (37 degrees C) temperature and the systemic perfusate temperature during cardiopulmonary bypass was 20 degrees (cold), 32 degrees C (tepid), or 37 degrees (warm).

RESULTS

Patients in the cold group had a longer duration of intubation and postoperative hospitalization and a slightly but significantly higher peak postoperative creatine kinase MB level than patients in the warm group. There were no deaths. There was deterioration in Mathew scale findings in all three groups, and no distinction could be made between groups. However, a significantly higher number in the cold group had an abnormal postoperative neurologic examination result that prompted computed tomographic scanning (18.9% cold, 2% tepid, 9.3% warm). A cerebrovascular accident was documented by computed tomographic scanning in 8.1%, 0%, and 4.7% of patients in the cold, tepid, and warm groups, respectively (not significant). Hematologic data documented significantly increased fibrinolytic potential in the warm group.

CONCLUSIONS

Perfusion temperature is a factor in recovery from cardiopulmonary bypass. Cold has more adverse neurologic sequelae that prompt computed tomographic scanning whereas warm has more activation of fibrinolytic potential. Tepid is the best temperature for optimizing recovery from cardiopulmonary bypass.

Normothermic Cardiopulmonary Bypass

Normothermic cardiopuhnonary bypass avoids the detrimental systemic effects of hypothermia. It is a safe and effective technique of systemic perfusion during cardiopulmonaiy bypass. Myocardial preservation is not compromised when electromechanical quiescence is maintained. Cerebral protection is comparable to that of systemic hypothermia. Low vascular resistance is common and easily treated with higher perfusion flows or vasopressors during bypass and facilitates weaning from bypass. Duration of cardiopulmonary bypass is significantly shortened by the absence of systemic cooling and rewarming phases. Clinical outcomes of patients undergoing cardiac, surgery with normothermic bypass compare favorably with those receiving moderate hypothermia.