Pathophysiological Basis of CNS Injury in Cardiac Surgical Patients: Detection and Prevention

Cerebral oximetry and preventing neurological complication post-cardiac surgery: a systematic review

OBJECTIVES

This systematic review aims to provide an up-to-date summary of the current literature examining the relationship between intraoperative regional cerebral oxygen saturation and neurological complications after cardiac surgery.

METHODS

Observational and interventional studies investigating the link between regional cerebral oxygen saturation and postoperative delirium, cognitive dysfunction and stroke were included. After database searching and study screening, study characteristics and major findings were extracted.

RESULTS

Twenty-seven studies were identified. Of the observational studies (n = 17), 8 reported that regional cerebral oxygen desaturations were significantly associated with neurological complications after cardiac surgery. Of the interventional studies (n = 10), 3 provided evidence for monitoring cerebral oximetry during cardiac surgery as a means of reducing incidence of postoperative cognitive dysfunction or stroke. There was significant heterogeneity in the tools and rigor used to diagnose neurological complications.

CONCLUSIONS

Studies to date show an inconsistent relationship between regional cerebral oxygen saturation and neurological outcomes after cardiac surgery, and lack of clear benefit of targeting cerebral oximetry to minimize neurological complications. Standardized assessments, definitions of impairment and desaturation thresholds will help determine the benefits of cerebral oximetry monitoring during cardiac surgery.

180 ml and less: Cardiopulmonary bypass techniques to minimize hemodilution for neonates and small infants

Objective. To determine the efficacy of decreasing cardiopulmonary bypass (CPB) prime volume for neonates and small infants by using low prime oxygenators, small diameter polyvinyl chloride (PVC) tubing and removing the arterial line filter (ALF) in an effort to reduce intraoperative exposure to multiple units of packed red blood cells (PRBC). Methods. Two retrospective database studies comparing neonatal CPB prime volume were undertaken: Study 1 — A CPB circuit consisting of a 1/8 inch arterial line, a 3/16 inch venous line and a low prime oxygenator with 172 ml total circuit prime ( n = 74) was compared to a circuit with a 3/16 inch arterial line, a 1/4 inch venous line and a higher prime oxygenator with a 350 ml total circuit prime ( n = 74). Study 2 — The 172 ml circuit ( n = 389) was compared to a circuit that included an ALF and had a total circuit prime volume of 218 ml ( n = 389). Results. Study 1— of the 74 neonates and small infants whose CPB prime volume was 350 ml, 19 were exposed to two or more intraoperative exogenous PRBC units while only 3 neonates and small infants in the 172 ml prime group ( n = 74) received two or more units ( p = 0.0002). Study 2 — of the 389 neonates and small infants where an ALF was used (prime volume 218 ml), 54 were exposed to two or more exogenous PRBC units while only 36 of the 389 patients where an ALF was not used (prime volume 172 ml) received two or more units of intraoperative PRBCs ( p = 0.0436). Conclusion. Decreasing the neonatal and small infant extracorporeal circuit prime volume by as little as 46 ml resulted in significantly fewer multiple exposures to exogenous PRBC units. Perfusion (2007) 22, 327—331.

Insulin binding to the cardiopulmonary bypass biomaterials

Hyperglycemia associated with cardiopulmonary bypass (CPB) is an independent predictor of morbidity and mortality. One suggested cause of hyperglycemia during CPB is a decline of serum insulin concentrations. Since plasma C-proteins are not reduced during CPB — suggesting that pancreatic insulin secretion is not affected — the reduction of insulin concentrations is hypothesized to be due to the binding of the insulin protein to the CPB biomaterials. The hypothesis of this study is that insulin binds to the CPB polyvinyl chloride (PVC) tubing and that selected bio-coatings inhibit this process. Human insulin was diluted to a physiologic concentration of 30 μU/mL in saline and exposed to four types of sterile PVC tubing, namely: uncoated, Terumo X-coated, Medtronic Carmeda, and Cobe SMARxT for 30 minutes at 37°C. Insulin concentrations were determined with ELISA. The recovered insulin concentrations were found to be 9.3 ± 0.6 μU/mL in the uncoated (control), 17.7 ± 1.9 μU/mL in the X-coating, 17.9 ± 1.1 μU/mL in the Carmeda, and 14.28 ± 0.17 μU/mL in the SMARxT coated tubing. These data support the hypothesis that the insulin binding to the PVC tubing can be reduced by 48% and up to 35% with X-coating and Carmeda, and SMARxT coating, respectively. Therefore, the use of coated CPB systems is justified to reduce CPB-associated hyperglycemia. Perfusion (2007) 22, 207—210.

Elevated Stroke Risk Associated With Femoral Artery Cannulation During Mitral Valve Surgery

Minimally invasive mitral valve (MV) surgery, often requiring femoral artery (FA) cannulation, is increasingly being adopted. There is concern about increased stroke rates associated with minimally invasive MV surgery. This study aims to examine whether FA cannulation is independently associated with increased stroke rates in minimally invasive MV procedures. MV procedures from January 2004 to June 2012 were reviewed using our institutional Society of Thoracic Surgeons database. We included 384 patients after the exclusion of patients with emergency procedures, with infective endocarditis, who underwent other concomitant procedures, who were older than 60 years, and with nonstandard aortic clamping (endoballoon or no clamp). Patients were divided into 2 groups: those who underwent aortic cannulation (n = 327) and those who underwent femoral cannulation (n = 57). Risk adjustments through multivariable regression were used to identify independent predictors for various outcomes. Adjustments were made for cardiopulmonary bypass and aortic clamp times. Preoperatively, the femoral cannulation group had less baseline cerebrovascular disease (P = 0.032), heart failure (P = 0.028), and atrial fibrillation (P = 0.012). Other baseline characteristics were similar. The aortic cannulation group had shorter cardiopulmonary bypass (P < 0.001) and clamp times (P < 0.001). There were more repairs done in the FA cannulation group as opposed to replacements. Risk-adjusted outcomes showed a higher incidence of permanent stroke in the femoral cannulation group (P = 0.032). Other outcomes were not significantly different. In conclusion, FA cannulation may be associated with increased stroke rates in isolated MV surgery. Antegrade arterial cannulation (direct aortic or axillary cannulation) may be preferable in minimally invasive MV procedures. Randomized trial data are needed.

Intraoperative echocardiography in valvular heart disease: an evidence-based appraisal

Intraoperative (IO) transesophageal echocardiography (TEE) is widely used for assessing the results of valvular heart disease (VHD) surgery. Epiaortic ultrasonography (EAU) has been recommended for prevention of perioperative strokes. To what extent does high-quality evidence justify the widespread use of these imaging modalities? In March 2009, we searched MEDLINE (PubMed and OVID interfaces) and EMBASE for studies published in English using database-specific controlled vocabulary describing the concepts of IOTEE, cardiac surgery, VHD, and EAU. We found no randomized trials or studies with control groups assessing the impact of IOTEE in VHD surgery. Pooled analysis of 8 observational studies including 15,540 patients showed an average incidence of 11% for prebypass surgical changes and 4% for second pump runs, suggesting that patients undergoing VHD surgery may benefit significantly from IOTEE, particularly from postcardiopulmonary bypass IOTEE in aortic repair and mitral repair and replacement, but less so in isolated aortic replacement. Further available indirect evidence was satisfactory in the test accuracy and surgical quality control aspects, with low complication rates for IOTEE. The data supporting EAU included 12,687 patients in 2 prospective randomized studies and 4 nonrandomized, controlled studies, producing inconsistent outcome-related results. Despite low-quality scientific evidence supporting IOTEE in VHD surgery, we conclude that indirect evidence supporting its use is satisfactory and suggests that IOTEE may offer considerable benefit in valvular repairs and mitral replacements. The value of IOTEE in isolated aortic valve replacement remains less clear. Evidence supporting EAU is scientifically more robust but conflicting. These findings have important clinical policy and research implications.

Lower perfusion pressure during hypothermic cardiopulmonary bypass is associated with decreased cerebral blood flow and impaired memory performance 6 months postoperatively

OBJECTIVES

We undertook to determine the influence of perfusion pressure during hypothermic cardiopulmonary bypass (CPB) on cerebral blood flow (CBF) and cognitive memory outcome at 6 months postoperatively.

METHODS

Nineteen patients who underwent hypothermic nonpulsatile CPB for elective coronary artery bypass (CAB) surgery were evaluated by (133)Xe measurement of the CBF and by the Incidental Memory Assessment for evaluating cognitive memory (IMTscore), both at baseline before the operation (T(1)) and again at 5 to 6 months postoperatively (T(2)).

RESULTS

Overall, the mean CBF fell significantly from 39 +/- 5 mL.(100 g)(-1).min(-1) at T(1) to 33 +/- 3 mL.(100 g)(-1).min(-1) at T(2) (P < .001). The decrease in CBF from T(1) to T(2) (DeltaCBF(2-1)) correlated with a significant reduction in the IMTscore from T1 to T2 (DeltaIMTscore(2-1)) (P < .001) and with a mean arterial pressure during CPB (MAPCPB) of <60 mm Hg (P = .05). Cluster analysis of DeltaCBF(2-1) and DeltaIMTscore(2-1) demonstrated that the patients with the greatest decrease in CBF showed the greatest decrease in IMTscore, whereas cluster analysis of DeltaCBF(2-1) and MAPCPB indicated that patients with a perfusion pressure maintained at a mean of <60 mm Hg during CPB were prone to a greater decrease in later postoperative CBF.

CONCLUSION

This study demonstrated that a MAPCPB of <60 mm Hg during CPB was associated with a significant decrease in CBF 6 months after CAB surgery and with an associated decrease in memory performance.

Epiaortic scanning modifies planned intraoperative surgical management but not cerebral embolic load during coronary artery bypass surgery

BACKGROUND

Patients with aortic atheroma are at increased risk for neurological injury after coronary artery bypass graft (CABG) surgery. We sought to determine the role of epiaortic ultrasound scanning for reducing cerebral embolic load, and whether its use leads to changes of planned intraoperative surgical management in patients undergoing CABG surgery.

METHODS

Patients >70-yr-of-age scheduled for CABG surgery were prospectively randomized to either an epiaortic scanning (EAS) group (aortic manipulation guided by epiaortic ultrasound) or a control group (manual aortic palpation without EAS). All patients received a comprehensive transesophageal echocardiographic examination. Transcranial Doppler (TCD) was used to monitor the middle cerebral arteries for emboli continuously from 2 min before aortic cannulation to 2 min after aortic decannulation. Neurological assessment was performed with the National Institute of Health stroke scale before surgery and at hospital discharge. The NEECHAM confusion scale was used for assessment and monitoring of patient global cognitive function on each day after surgery until hospital discharge.

RESULTS

Intraoperative surgical management was changed in 16 of 55 (29%) patients in the EAS group and in 7 of 58 (12%) patients in the control group (P = 0.025). These changes included adjustments of the ascending aorta cannulation site for cardiopulmonary bypass (CPB), the avoidance of aortic cross-clamping by using ventricular fibrillatory arrest during surgery, or by conversion to off-pump surgery. During surgery, 7 of 58 (12%) patients in the control group crossed over to the EAS group based on the results of manual aortic palpation. The median [range] TCD detected cerebral embolic count did not differ between the EAS and control groups during aortic manipulations (EAS, 11.5 [1-516] vs control, 22.0 [1-160], P = 0.91) or during CPB (EAS, 42.0 [4-516] vs control, 63.0 [5-758], P = 0.46). The NEECHAM confusion scores and National Institute of Health stroke scale scores were similar between the two groups.

CONCLUSIONS

These results show that the use of EAS led to modifications in intraoperative surgical management in almost one-third of patients undergoing CABG surgery. The use of EAS did not lead to a reduced number of TCD-detected cerebral emboli before or during CPB.