Normothermic cardiopulmonary bypass is beneficial for cognitive brain function after coronary artery bypass grafting--a prospective randomized trial

Delirium after Cardiac Surgery-A Narrative Review

Postoperative delirium (POD) after cardiac surgery is a well-known phenomenon which carries a higher risk of morbidity and mortality. Multiple patient-specific risk factors and pathophysiologic mechanisms have been identified and therapies have been proposed to mitigate risk of delirium development postoperatively. Notably, cardiac surgery frequently involves the use of an intraoperative cardiopulmonary bypass (CPB), which may contribute to the mechanisms responsible for POD. Despite our greater understanding of these causative factors, a substantial reduction in the incidence of POD remains high among cardiac surgical patients. Multiple therapeutic interventions have been implemented intraoperatively and postoperatively, many with conflicting results. This review article will highlight the incidence and impact of POD in cardiac surgical patients. It will describe some of the primary risk factors associated with POD, as well as anesthetic management and therapies postoperatively that may help to reduce delirium.

Mild hypothermia versus normothermia in patients undergoing cardiac surgery

Objective

Temperature during cardiopulmonary bypass (CPB) for cardiac surgery has been controversial. The aim of the current study is to compare the outcomes for patients with mild hypothermia versus normothermic CPB temperatures.

Methods

All patients who underwent cardiac surgery with CPB and temperatures ≥32°C from 2011 to 2018 were included, which consisted of mild hypothermia (32°C-35°C) and normothermia (>35°C) cohorts. Propensity matching (1:1) was performed for risk adjustment. Primary outcomes included operative and long-term survival. Secondary outcomes included postoperative complications.

Results

A total of 6525 patients comprised 2 cohorts: mild hypothermia (32°C-35°C; n = 3148) versus normothermia (>35°C; n = 3377). Following adjustment for surgeon preference, there were 1601 propensity-matched patients who had similar baseline characteristics (standard mean difference, ≤0.10), including CPB time, crossclamp time, and intra-aortic balloon pump placement. Kaplan-Meier analysis showed no difference in long-term survival (82.6% vs 81.6%; P = .81). Over a median follow-up of 4.4 years, there were no differences in overall mortality (18.1% vs 18.1%; P = 1.1) or readmission (50.3% vs 48.3%; P = .2). Acute renal failure (3.7% vs 2.4%; P = .03) and intensive care unit hours (46.5 vs 45.1; P = .04) were significantly higher with hypothermia. There was no difference between cohorts for postoperative stroke (2.0% vs 2.0%; P = 1.0), reoperation (5.9% vs 6.0%; P = .9), or operative intra-aortic balloon pump placement (1.7% vs 1.8%; P = .9).

Conclusions

Patients with mild hypothermia during CPB had increased postoperative renal failure and length of intensive care unit stay. Although there was no difference in long-term survival, mild hypothermia does not appear to offer patients appreciable benefits, compared with normothermia.

Current approach to diagnosis and treatment of delirium after cardiac surgery

Delirium after cardiac surgery remains a common occurrence that results in significant short- and long-term morbidity and mortality. It continues to be underdiagnosed given its complex presentation and multifactorial etiology; however, its prevalence is increasing given the aging cardiac surgical population. This review highlights the perioperative risk factors, tools to assist in diagnosing delirium, and current pharmacological and nonpharmacological therapy options.

Risk Factors Associated with Cognitive Decline after Cardiac Surgery: A Systematic Review

Modern day cardiac surgery evolved upon the advent of cardiopulmonary bypass machines (CPB) in the 1950s. Following this development, cardiac surgery in recent years has improved significantly. Despite such advances and the introduction of new technologies, neurological sequelae after cardiac surgery still exist. Ischaemic stroke, delirium, and cognitive impairment cause significant morbidity and mortality and unfortunately remain common complications. Postoperative cognitive decline (POCD) is believed to be associated with the presence of new ischaemic lesions originating from emboli entering the cerebral circulation during surgery. Cardiopulmonary bypass was thought to be the reason of POCD, but randomised controlled trials comparing with off-pump surgery show contradictory results. Attention has now turned to the growing evidence that perioperative risk factors, as well as patient-related risk factors, play an important role in early and late POCD. Clearly, identifying the mechanism of POCD is challenging. The purpose of this systematic review is to discuss the literature that has investigated patient and perioperative risk factors to better understand the magnitude of the risk factors associated with POCD after cardiac surgery.

Postoperative Critical Care of the Adult Cardiac Surgical Patient. Part I: Routine Postoperative Care

OBJECTIVES

Cardiac surgery, including coronary artery bypass, cardiac valve, and aortic procedures, is among the most common surgical procedures performed in the United States. Successful outcomes after cardiac surgery depend on optimum postoperative critical care. The cardiac intensivist must have a comprehensive understanding of cardiopulmonary physiology and the sequelae of cardiopulmonary bypass. In this concise review, targeted at intensivists and surgeons, we discuss the routine management of the postoperative cardiac surgical patient.

DATA SOURCE AND SYNTHESIS

Narrative review of relevant English-language peer-reviewed medical literature.

CONCLUSIONS

Critical care of the cardiac surgical patient is a complex and dynamic endeavor. Adequate fluid resuscitation, appropriate inotropic support, attention to rewarming, and ventilator management are key components. Patient safety is enhanced by experienced personnel, a structured handover between the operating room and ICU teams, and appropriate transfusion strategies.

Therapeutic hypothermia and the risk of infection: a systematic review and meta-analysis

OBJECTIVE

Observational studies suggest that infections are a common complication of therapeutic hypothermia. We performed a systematic review and meta-analysis of randomized trials to examine the risk of infections in patients treated with hypothermia.

DATA SOURCES

PubMed, Embase, and the Cochrane Central Register of Controlled Trials were systematically searched for eligible studies up to October 1, 2012.

STUDY SELECTION

We included randomized controlled clinical trials of therapeutic hypothermia induced in adults for any indication, which reported the prevalence of infection in each treatment group.

DATA EXTRACTION

For each study, we collected information about the baseline characteristics of patients, cooling strategy, and infections.

DATA SYNTHESIS

Twenty-three studies were identified, which included 2,820 patients, of whom 1,398 (49.6%) were randomized to hypothermia. Data from another 31 randomized trials, involving 4,004 patients, could not be included because the occurrence of infection was not reported with sufficient detail or not at all. The risk of bias in the included studies was high because information on the method of randomization and definitions of infections lacked in most cases, and assessment of infections was not blinded. In patients treated with hypothermia, the prevalence of all infections was not increased (rate ratio, 1.21 [95% CI, 0.95-1.54]), but there was an increased risk of pneumonia and sepsis (risk ratios, 1.44 [95% CI, 1.10-1.90]; 1.80 [95% CI, 1.04-3.10], respectively).

CONCLUSION

The available evidence, subject to its limitations, strongly suggests an association between therapeutic hypothermia and the risk of pneumonia and sepsis, whereas no increase in the overall risk of infection was observed. All future randomized trials of hypothermia should report on this important complication.

Hypothermic versus normothermic cardiopulmonary bypass in patients with valvular heart disease

OBJECTIVE

The aim of this study was to test the hypothesis that normothermic cardiopulmonary bypass (CPB) is as effective as hypothermic CPB in terms of cardiac protection (cTnI level) and outcome in patients with valvular heart disease.

DESIGN

Prospective randomized study.

SETTING

A tertiary cardiothoracic referral center.

PARTICIPANTS

140 patients who had valvular heart disease, with/without coronary artery disease, surgically treated under CPB.

INTERVENTIONS

The patients were allocated randomly to undergo either hypothermic (temperature [T], 31 °C-32 °C) or normothermic CPB (T>36 °C).

MEASUREMENTS AND MAIN RESULTS

The primary endpoint was the dynamics of troponin I. The secondary endpoints were ventilation time, the need for inotropic support, intensive care unit (ICU) and hospital stay durations, complications, and mortality. There were no significant intergroup differences in dynamics of troponin I. Ventilation time was significantly lower in the hypothermic group (6 (5-9) and 8 (5-12); p = 0.01).

CONCLUSIONS

Normothermic CPB in patients with valvular heart disease was as effective as hypothermic perfusion in terms of myocardial protection after the surgery assessed by cTnI release. The short ventilation duration in patients who underwent hypothermic CPB needs to be confirmed in a future investigation.

Normothermic cardiopulmonary bypass increases cerebral tissue oxygenation during combined valve surgery: a single-centre, randomized trial

OBJECTIVES

In cardiac surgery, the choice of temperature regimen during cardiopulmonary bypass (CPB) remains a subject of debate. Hypothermia reduces tissue metabolic demands, but may impair the autoregulation of cerebral blood flow and contribute to neurological morbidity. The aim of this study was to evaluate the effect of two different temperature regimens during CPB on the systemic oxygen transport and the cerebral oxygenation during surgical correction of acquired heart diseases.

METHODS

In a prospective study, we randomized 40 adult patients with combined valvular disorders requiring surgical correction of two or more valves into two groups: (i) a normothermic (NMTH) group (n = 20), in which the body core temperature was maintained at 36.6°C during CPB and (ii) a hypothermic (HPTH) group (n = 20), in which the body was cooled to a core temperature of 32°C maintained throughout the period of CPB. The systemic oxygen transport and the cerebral oxygen saturation (SctO2) were assessed by means of a PiCCO2 haemodynamic monitor and a cerebral oximeter, respectively. All the patients received standard perioperative monitoring. We assessed haemodynamic and oxygen transport parameters, the duration of mechanical ventilation and the length of the ICU and the hospital stays.

RESULTS

During CPB, central venous oxygen saturation was significantly higher in the HPTH group but SctO2 was increased in the NMTH group (P < 0.05). Cardiac index, systemic oxygen delivery and consumption increased postoperatively in both groups. However, oxygen delivery and consumption were significantly higher in the NMTH group (P < 0.05). The duration of respiratory support and the length of ICU and hospital stays did not differ between the groups.

CONCLUSIONS

During combined valve surgery, normothermic CPB provides lower central venous oxygen saturation, but increases cerebral tissue oxygenation when compared with the hypothermic regimen.

Cognitive P300-evoked potentials in school-age children after surgical or transcatheter intervention for ventricular septal defect

BACKGROUND

Some studies have suggested that neurological development may be adversely affected in children with severe coronary heart disease who have undergone long periods of deep hypothermic cardiopulmonary bypass (CPB). Reports of cognitive function in VSD patients in whom surgical repair required only a relatively brief period of CPB are rare. Also, CPB is unnecessary for VSD patients undergoing transcatheter closure. The aim of this study was to assess the cognitive function in patients with ventricular septal defect.

METHODS

A total of 29 patients treated with surgery, and 35 treated with transcatheter closure and their age- and sex-matched best friends completed the cognitive P300 auditory-evoked potentials test and the intelligence test.

RESULTS

The patients and their best friends had normal intelligence quotient; however, the patients had longer P300 peak latencies in cranial frontal lobe and cranial vertex leads (329.2 ± 24.8 and 335.1 ± 20.0 ms) than the healthy controls did (319.1 ± 20.6 and 313 ± 18.2 ms) (P < 0.05). Patients who underwent surgery had longer P300 peak latency in the cranial frontal lobe and cranial vertex leads than did those with transcatheter closure and controls. When cardiopulmonary bypass and aortic clamping were used, the duration was associated with P300 peak latency for patients (P < 0.05).

CONCLUSION

VSD patients, especially those undergoing surgery, showed poor cognitive function, which may be associated with duration of cardiopulmonary bypass or aortic-clamping.

Autotransfusion system or integrated automatic suction device in minimized extracorporeal circulation: influence on coagulation and inflammatory response

OBJECTIVE

To measure surrogate markers of coagulation activation as well as of the systemic inflammatory response in patients undergoing primary elective coronary artery bypass grafting (CABG) using either the so-called Smart suction device or a continuous autotransfusion system (C.A.T.S.®).

METHODS

Fifty-eight patients being operated with a miniaturized circuit (minimal extracorporeal circuit, MECC) were prospectively randomized to using a so-called Smart suction device or a routine continuous autotransfusion system (C.A.T.S.®) for collection of mediastinal shed blood. The coagulation response was measured by thrombin-antithrombin complex (TAT) and D-dimer. The inflammatory response was measured by Interleukin 6 (IL-6) and complement factor 3a (C3a) at three different time points, before surgery, 2h after surgery, as well as 18 h after surgery.

RESULTS

No serious adverse cardiovascular event was observed. Serum levels of TAT significantly differed between both groups 2h after surgery (Smart suction 16.12 ± 13.51 μg l⁻¹ vs C.A.T.S® 9.83 ± 7.81 μg l⁻¹, p = 0.040) and returned to baseline values after 18 h in both groups. Serum levels of D-dimer showed a corresponding pattern with a peak 2h after surgery (Smart suction 1115 ± 1231 ng ml⁻¹ vs C.A.T.S.® 507 ± 604 ng ml⁻¹, p = 0.025). IL-6 levels also significantly differed between both groups 2h after surgery (Smart suction 186 ± 306 pg ml⁻¹ vs C.A.T.S.® 82 ± 71 pg ml⁻¹, p = 0.072). No significant changes in serum levels of C3a over time could be observed.

CONCLUSIONS

Despite no differences in the clinical course of patients with either Smart suction or C.A.T.S.® being observed, surrogate markers of coagulation and inflammation seem to be less pronounced in patients where cardiotomy blood is not being directly reinfused. As such, C.A.T.S.® should be preferred in routine CABG, as long as no extensive volume substitution is anticipated.

Totally normothermic aortic arch replacement without circulatory arrest

BACKGROUND

Various techniques have been proposed for cerebral protection during the surgical treatment of complex aortic disease. The authors propose a revisited strategy of normothermic replacement of the aortic arch to avoid limitations and complications of profound hypothermic circulatory arrest.

MATERIALS AND METHODS

From April 2000 to May 2006, 19 patients with an aneurysm of the aortic arch and 10 patients with an acute (7) or a chronic (3) aortic dissection underwent a totally normothermic, complete replacement of the aortic arch using three pumps: One pump ensured antegrade cerebral perfusion, at a flow rate adapted to obtain a pressure of 70 mmHg in the right radial artery, and required a selective cannulation of the supra-aortic vessels. A second pump ensured body perfusion at a flow rate adapted to obtain a pressure of 55 mmHg in the left femoral artery and was situated between the right femoral artery and the right atrium. A special balloon aortic occlusion catheter was placed in the descending thoracic aorta. A third pump ensured intermittent normothermic myocardial perfusion via the coronary venous sinus. The arch reconstruction was performed with no time limit.

RESULTS

There were two operative, in-hospital (6.8%) mortalities. All others patients were rapidly extubated, except one, with no neurological sequelae, and postoperative course was uneventful, without coagulopathy or hepato-renal impairment.

CONCLUSIONS

In the light of these results, a normothermic procedure is possible for arch surgery and may ensure a more physiological autoregulation of cerebral blood flow while maintaining body perfusion without high vascular resistances.

Cognitive brain function after hypothermic circulatory arrest assessed by cognitive P300 evoked potentials

BACKGROUND

The role of hypothermic circulatory arrest (HCA) in cardiovascular surgery is controversial and assumed to result in neurocognitive dysfunction that is not always detected by standard clinical observation. We assessed cognitive P300 visual evoked potentials (P300) in patients undergoing either HCA or coronary artery bypass grafting (CABG) to elucidate whether HCA was associated with postoperative cognitive decline.

METHODS

Thirteen patients undergoing either aortic arch replacement (n=4) or pulmonary thromboendarterectomy (n=9) using HCA (mean: 28+/-11 min, 22+/-2 degrees C) were studied. They were compared to 13 patients undergoing on-pump CABG. P300s were measured 1 day before and 1 week after the operation. We assessed an area under the curve (AUC) between 280 and 600 ms and center of this area [Ct (time), Cv (voltage)]. The ratio of these parameters acquired by target (TG) and non-target (NTG) stimulus (TG/NTG) was calculated to assess concentration on TG stimulus and defined as concentration index (CI: CI(AUC), CI(Ct), and CI(Cv)).

RESULTS

There was no significant difference in preoperative characteristics between groups. There were neither strokes nor hospital deaths. Preoperatively, the HCA group could not concentrate on target stimulus as well as the control group in frontal leads (CI(AUC) and CI(Cv) were lower in HCA group than in control group). However, the HCA group could concentrate on target stimulus better than the control group postoperatively because postoperative CI(AUC) (pre-operation: 1.1+/-0.5 to post-operation: 1.7+/-0.4, P=.02) and CI(Cv) (1.1+/-0.4 to 1.6+/-0.4, P=.01) were significantly improved in the HCA group, whereas these were significantly impaired in the control group (CI(AUC): 1.6+/-0.6 to 1.3+/-0.4, P=.03, CI(Cv): 1.5+/-0.5 to 1.2+/-0.3, P<.01). Postoperative CI(Ct) in the HCA group were significantly impaired in all leads. The duration of HCA did not correlate with any values of postoperative P300. No specific trends were observed in either preoperative or postoperative P300 values between patients with or without postoperative temporary neurological dysfunction (one in each group). Postoperative improvement of CI(AUC) and CI(Cv) in Fz lead were found in 85 and 69% in the HCA group and 23 and 23% in the control group, respectively (CI(AUC): P<.01, CI(Cv): P<.05).

CONCLUSIONS

P300 detected no significant neurocognitive impairment due to the relatively brief period of HCA (approximately 28 min).

Opening the Cardiac Chambers Does Not Make Any Difference in P300 Measurement

OBJECTIVE

Cognitive brain dysfunction after open heart surgery is a serious complication caused by cardiopulmonary bypass (CPB). The presence of gaseous and/or particulate emboli in the CPB circuit and cerebral hypoperfusion may be the causes of neurologic problems after cardiac operations.

METHODS

In this prospective study we examined 42 consecutive cardiac surgery patients (24 mitral valve replacement [MVR] and 18 coronary artery bypass grafting [CABG] patients). In addition to determination of clinical measurements, cognitive brain function was measured objectively by P300 auditory-evoked potentials before operation, at day 7, and at 4-month follow-up. Electroencephalographic evaluations were also performed.

RESULTS

In preoperative measures there was no difference between the groups (peak latencies in the MVR group were 324 +/- 8 milliseconds; CABG group, 318 +/- 6 milliseconds; P > .05). At day 7, cognitive P300 auditory-evoked potentials were significantly impaired (prolonged) in both groups compared to preoperative values (MVR group, 347 +/- 7 milliseconds; CABG group, 342 +/- 7 milliseconds; P < .05). P300 measurements almost returned to normal at 4-month follow-up (MVR group, 331 +/- 6 milliseconds; CABG group, 319 +/- 8 milliseconds; P > .05 compared to preoperative values). One week and 4 months after surgery no difference between the 2 groups could be found (P > .05).

CONCLUSION

Postoperative patients had prolonged P300 values according to the preoperative measurements and we have not found any difference between the groups whether cardiac chambers were opened or not.

Use of P300 Cognitive Evoked Potentials in the Diagnosis of Impairments of Higher Mental Functions after Cardiac Surgery in Conditions of Cardiopulmonary Bypass

A total of 40 patients with ischemic heart disease undergoing aortocoronary shunting surgery in conditions of cardiopulmonary bypass were studied. Parameters of the P300 cognitive evoked potentials were studied before surgery and 7-9 days after surgery. Neurological and neuropsychological assessments were also performed. The most significant parameters of the P300 potential were found to be the latencies of the P3 and N2 components, increases in which showed positive correlations with the extent of the developing cognitive deficit. Evidence supporting the neuroprotective effects of Trasylol given during surgery was obtained. Patients given Trasylol showed less marked cognitive deficit and smaller changes in P300 parameters. Analysis of the P300 cognitive evoked potential can be recommended for detecting early cognitive dysfunction and assessing the efficacy of neuroprotective therapy in patients undergoing surgery with cardiopulmonary bypass.

Cardiopulmonary bypass temperature and brain function

A debate has emerged in recently published studies about the optimum cardiopulmonary bypass temperature for good neurological outcome - warm vs. cold, i.e. normothermic vs. hypothermic. Although many comparative studies have been performed, the results of these studies are inconclusive and are difficult to interpret. Brain function has been studied in terms of neurological and neuropsychological outcome, protein S100beta levels as a marker of brain damage, and cerebral oxygenation using jugular bulb oximetry and near-infrared spectroscopy. The studies produce no conclusive proof of the superiority of warm or cold cardiopulmonary bypass. However, it appears that any degree of bypass hypothermia (< 35 degrees C) may protect the brain. On the other hand, even a slight increase in bypass temperature to > 37 degrees C may cause marked brain injury.

Pulmonary artery blood temperature at admission to the intensive care unit is predictive of outcome after on-pump coronary artery bypass surgery

OBJECTIVE

To evaluate whether pulmonary artery blood (PA) temperature on admission to the intensive care unit (ICU) is predictive of postoperative outcome after isolated on-pump coronary artery bypass grafting (CABG).

DESIGN

A retrospective study on 1639 patients who underwent isolated on-pump CABG in whom PA temperature at admission to the ICU was available for review.

RESULTS

Thirty-three patients (2.0%) died during the in-hospital stay and 87 patients (5.3%) developed low cardiac output syndrome. PA temperature at admission to the ICU was significantly associated with an increased risk of overall postoperative death (p = 0.002), cardiac death (p = 0.03), and low cardiac output syndrome (p < 0.0001), and was significantly correlated with prolonged length of ICU stay (p < 0.0001) and postoperative bleeding (p = 0.001). Patients with high PA temperature had significantly more severe comorbidities, and longer aortic cross-clamping and cardiopulmonary bypass time. The receiver operating characteristic curve showed that PA temperature at admission to the ICU in predicting postoperative death had an area under the curve of 0.660 (p = 0.002) and its best cut-off value was 36.4 degrees C (sensitivity: 63.6%, specificity: 65.2%). When the PA temperature at admission to the ICU was > or = 36.4 degrees C, the postoperative mortality and low cardiac output syndrome rates were 3.6 and 8.3%, whereas they were 1.1 and 3.7% when the PA temperature at admission to the ICU was < 36.4 degrees C (p = 0.001, p < 0.0001), respectively.

CONCLUSION

Patients having a PA temperature > or =36.4 degrees C at admission to the ICU after CABG seem to be at higher risk of poor postoperative outcome.

Totally normothermic aortic arch replacement without circulatory arrest

The authors propose a new strategy of normothermic perfusion for replacement of the aortic arch to avoid the complications of profound hypothermic circulatory arrest. Six patients underwent complete replacement of the aortic arch under normothermia using two pumps for the body (one for the brain and the thoracoabdominal aortic branches) and one for the heart. The surgical procedure was performed with no time limit. There were no operative or late deaths. No patients had neurologic deficit and all were rapidly extubated with uneventful postoperative courses. The method preserves autoregulation of cerebral blood flow and maintains body perfusion without high vascular resistances.

Neurocognitive deficit following aortic valve replacement with biological/mechanical prosthesis

OBJECTIVE

The aim of this study was to objectively measure neurocognitive deficit following aortic valve replacement with a mechanical or biological prosthesis.

MATERIALS AND METHODS

In this prospective, contemporary study we followed 82 consecutive patients undergoing isolated aortic valve replacement with either a mechanical (n=29, mean age=52+/-7 years) or a biological (n=53, mean age=68+/-10 years) valve prosthesis. Neurocognitive function was measured by means of objective P300 auditory evoked potentials (peak latencies, ms) and two standard psychometric tests (Trailmaking Test A, Mini Mental State Examination) before the operation, 7 days and 4 months after the operation, respectively.

RESULTS

Since P300 peak latencies increase with age, preoperative P300 measures are lower in patients receiving mechanical valves (360+/-35 ms, mean 52 years) as compared to patients receiving biological valves (381+/-34 ms, 68 years, P=0.0001). Seven days after surgery, P300 peak latencies were prolonged (-worsened) in both groups as compared to preoperative values (mechanical valves: 384+/-36 ms; P=0.0001 and biological valves: 409+/-39 ms; P=0.0001). Although on a different level (-age-related), this development was comparable within both groups (P=0.800). Four months after surgery, P300 peak latencies normalized in the mechanical valve group (372+/-27 ms, P=0.857 versus preoperative), while in contrast in the biological valve group they remained prolonged (417+/-37 ms, P=0.0001). We found no difference within patients receiving different types of biological or mechanical aortic valves.

CONCLUSION

Postoperative neurocognitive damage is not reversible in (-elderly) patients with biological aortic valve replacement, while in contrast postoperative neurocognitive damage is reversible in (-younger) patients with mechanical valve replacement. For this contrary development, age seems to be most important, whereas damage related to type of valve prosthesis may be overestimated.

Cognitive deficit after aortic valve replacement

BACKGROUND

Impairment of cognitive brain function after coronary artery bypass grafting (CABG) is well known. In contrast the potential neurocognitive damage related to aortic valve replacement (AVR) is uncertain.

METHODS

In this contemporary case-matched control study we followed 30 patients (mean age 70 years) receiving isolated AVR with a biological prosthesis. A cohort of sex-and age-matched patients (n = 30, mean age 70 years) receiving CABG with cardiopulmonary bypass served as controls. Cognitive brain function was measured by means of auditory evoked P300 potentials (peak latencies, ms) before the operation and 7 days and 4 months after the operation. Additionally, two standard psychometric tests (Mini-Mental State Examination and the Trailmaking Test A) were performed.

RESULTS

In preoperative measures there was no difference between patients undergoing AVR and patients undergoing CABG (AVR 378 +/- 37 ms, CABG 374 +/- 32 ms, p = 0.629). One week after surgery P300 peak latencies were prolonged (impaired) in both groups compared with preoperative values (AVR 405 +/- 43 ms, p = 0.001; CABG 398 +/- 44 ms, p = 0.004). At this point of follow-up there was no difference between the groups (p = 0.607). Finally, 4 months after surgery P300 auditory evoked potentials returned to normal in the CABG group (380 +/- 24 ms, p = 0.940) while in contrast in the valve group they continued to become prolonged (worsened) compared with preoperative values (410 +/- 47 ms, p = 0.005). At this time of follow-up P300 peak latencies were prolonged in AVR patients as compared with CABG patients (p = 0.032). The Trailmaking Test A and Mini-Mental State Examination failed to discriminate any difference.

CONCLUSIONS

Four-month impairment of cognitive brain function is more pronounced in patients undergoing biological AVR as compared with age-matched control patients undergoing CABG. Further studies are needed to clarify the potential pathologic mechanisms causing an ongoing cognitive impairment in patients with biological aortic valve prostheses.

Neuroprotection during cardiac surgery: strategies to reduce cognitive decline

Although the population receiving cardiac surgery is older and therefore more prone to cognitive deterioration, these difficulties have declined over the last ten years. It is likely that the multiple changes introduced to cardiac surgery over time have had a cumulative benefit in protecting the brain. The most likely causes of cognitive difficulties are microemboli delivered to the brain during surgery, altered cerebral perfusion and an inflammatory response. The interventions that have been implemented can be divided into those which have attempted to reduce the potential causes of damage and those aimed at reducing the impact by attempting to protect the brain. The evidence for three main types of intervention (equipment, techniques and drugs) is reviewed in this paper. Although many interventions are available only a few have shown a clear benefit. Progress in the future will require larger studies to address this multifactorial problem.

Prolonged mild hypothermia after experimental hypothermic circulatory arrest in a chronic porcine model

OBJECTIVES

We sought to evaluate the potential efficacy of prolonged mild hypothermia after hypothermic circulatory arrest.

METHODS

Twenty pigs, after a 75-minute period of hypothermic circulatory arrest, were randomly assigned to be rewarmed to 37 degrees C (normothermia group) or to 32 degrees C and kept at that temperature for 14 hours from the start of rewarming (hypothermia group).

RESULTS

The 7-day survival was 30% in the hypothermia group and 70% in the normothermia group (P =.08). The hypothermia group had poorer postoperative behavioral scores than the normothermia group. Prolonged hypothermia was associated with lower oxygen extraction and consumption rates and higher mixed venous oxygen saturation levels during the first hours after hypothermic circulatory arrest. Decreased cardiac index, lower pH, and higher partial pressure of carbon dioxide were observed in the hypothermia group. There was a trend for beneficial effect of prolonged hypothermia in terms of lower brain lactate levels until the 4-hour interval and of intracranial pressure until the 10-hour interval. Postoperatively, total leukocyte and neutrophil counts were lower, and creatine kinase BB was significantly increased in the hypothermia group. At extubation, the hypothermia group had higher oxygen extraction rates and lower brain tissue oxygen tension.

CONCLUSIONS

A 14-hour period of mild hypothermia after 75-minute hypothermic circulatory arrest seems to be associated with poor outcome. However, the results of this study suggest that mild hypothermia may preserve its efficacy when it is used for no longer than 4 hours, but the potentials of a shorter period of postoperative mild hypothermia still require further investigation.