Preservation of pancreatic beta cell function with pulsatile cardiopulmonary bypass

Acute Response of Human Aortic Endothelial Cells to Loss of Pulsatility as Seen during Cardiopulmonary Bypass

Cardiopulmonary bypass (CPB) results in short-term (3-5 h) exposure to flow with diminished pulsatility often referred to as "continuous flow". It is unclear if short-term exposure to continuous flow influences endothelial function, particularly, changes in levels of pro-inflammatory and pro-angiogenic cytokines. In this study, we used the endothelial cell culture model (ECCM) to evaluate if short-term (≤5 h) reduction in pulsatility alters levels of pro-inflammatory/pro-angiogenic cytokine levels. Human aortic endothelial cells (HAECs) cultured within the ECCM provide a simple model to evaluate endothelial cell function in the absence of confounding factors. HAECs were maintained under normal pulsatile flow for 24 h and then subjected to continuous flow (diminished pulsatile pressure and flow) as observed during CPB for 5 h. The ECCM replicated pulsatility and flow morphologies associated with normal hemodynamic status and CPB as seen with clinically used roller pumps. Levels of angiopoietin-2 (ANG-2), vascular endothelial growth factor-A (VEGF-A), and hepatocyte growth factor were lower in the continuous flow group in comparison to the pulsatile flow group whereas the levels of endothelin-1 (ET-1), granulocyte colony stimulating factor, interleukin-8 (IL-8) and placental growth factor were higher in the continuous flow group in comparison to the pulsatile flow group. Immunolabelling of HAECs subjected to continuous flow showed a decrease in expression of ANG-2 and VEGF-A surface receptors, tyrosine protein kinase-2 and Fms-related receptor tyrosine kinase-1, respectively. Given that the 5 h exposure to continuous flow is insufficient for transcriptional regulation, it is likely that pro-inflammatory/pro-angiogenic signaling observed was due to signaling molecules stored in Weible-Palade bodies (ET-1, IL-8, ANG-2) and via HAEC binding/uptake of soluble factors in media. These results suggest that even short-term exposure to continuous flow can potentially activate pro-inflammatory/pro-angiogenic signaling in cultured HAECs and pulsatile flow may be a successful strategy in reducing the undesirable sequalae following continuous flow CPB.

Strategies to Protect the Brain During Cardiac Surgery

Despite significant advances in cardiopulmonary by pass (CPB) technology, surgical techniques, and anes thetic management, central nervous system (CNS) com plications remain a common and costly problem after CPB. Stroke is often considered a rare and unprevent able complication of cardiac surgery. Recent studies have shown that through the use of echocardiography and historical risk stratification strategies, we can de fine which patients are at substantially greater risk for CNS injury. Through enhanced understanding of the etiology of stroke and perioperative factors, which are associated with potential for neuroprotection or injury extension, there now exists a greater potential than ever to substantially reduce neurological injury associ ated with cardiac surgery. Strategies and theories of stratifying patients at risk and secondarily reducing that risk are described, as well as consideration for early postoperative assessment to allow treatment when events occur.

Comparison of TIVA and Desflurane Added to a Subanaesthetic Dose of Propofol in Patients Undergoing Coronary Artery Bypass Surgery: Evaluation of Haemodynamic and Stress Hormone Changes

Introduction. Increased levels of stress hormones are associated with mortality in patients undergoing coronary artery bypass grafting (CABG). Aim. To compare total intravenous anaesthesia (TIVA) and desflurane added to a subanaesthetic dose of propofol. Material and Methods. Fifty patients were enrolled in this study. Fentanyl (3-5 mcg/kg/h) was started in both groups. Patients were divided into two groups. The PD group (n = 25) received 1 minimum alveolar concentration (MAC) desflurane anaesthesia in addition to propofol infusion (2-3 mg/kg/h), while P group (n = 25) received propofol infusion (5-6 mg/kg/h) only. Biochemical data, cortisol, and insulin levels were measured preoperatively (T0), after initiation of CPB but before cross-clamping the aorta (T1), after removal of the cross-clamp (T2), and at the 24th postoperative hour (T3). Results. Systolic, diastolic, and mean arterial pressure levels were significantly higher in PD group than those in P group in T1 and T2 measurements (p ≤ 0.05). CK-MB showed a significant decrease in group P (p ≤ 0.05). When we compared both groups, cortisol levels were significantly higher in PD group than P group (p ≤ 0.05). Conclusion. Stress and haemodynamic responses were better controlled using TIVA than desflurane inhalation added to a subanaesthetic dose of propofol in patients undergoing CABG.

Effects on the Endocrine System of Pulsatile and Nonpulsatile Perfusion in Heart Surgery

The effects of cardiopulmonary bypass on the endocrine system were investigated in 10 patients who had pulsatile perfusion and in another 10 who had nonpulsatile perfusion during coronary bypass or valve replacement surgery. Measurements were made of thyroid-stimulating hormone, free and total triiodothyronine, free and total tetraiodothyronine, adrenocorticotropic hormone, cortisol, aldosterone, growth hormone, insulin, and glucose at 5 fixed time intervals up to 24 hours postoperatively. In the perfusion period, free and total triiodothyronine levels were less depressed in the pulsatile group. The mean level of growth hormone was significantly higher in the pulsatile group after 60 minutes of perfusion. The mean levels of insulin and glucose were significantly lower in the pulsatile group after 60 minutes of perfusion. Other changes were not statistically significant. We concluded that pulsatile perfusion was of benefit in stabilizing glucose and some hormone levels.

Continuous and Pulsatile Pediatric Ventricular Assist Device Hemodynamics with a Viscoelastic Blood Model

To investigate the effects of pulsatile and continuous pediatric ventricular assist (PVAD) flow and pediatric blood viscoelasticity on hemodynamics in a pediatric aortic graft model. Hemodynamic parameters of pulsatility, along with velocity and wall shear stress (WSS), are analyzed and compared between Newtonian and viscoelastic blood models at a range of physiological pediatric hematocrits using computational fluid dynamics. Both pulsatile and continuous PVAD flow lead to a decrease in pulsatility (surplus hemodynamic energy, ergs/cm(3)) compared to healthy aortic flow but with continuous PVAD pulsatility up to 2.4 times lower than pulsatile PVAD pulsatility at each aortic outlet. Significant differences are also seen between the two flow modes in velocity and WSS. The higher velocity jet during systole with pulsatile flow leads to higher WSSs at the anastomotic toe and at the aortic branch bifurcations. The lower velocity but continuous flow jet leads to a much different flow field and higher WSSs into diastole. Under a range of physiological pediatric hematocrit (20-60%), both velocity and WSS can vary significantly with the higher hematocrit blood model generally leading to higher peak WSSs but also lower WSSs in regions of flow separation. The large decrease in pulsatility seen from continuous PVAD flow could lead to complications in pediatric vascular development while the high WSSs during peak systole from pulsatile PVAD flow could lead to blood damage. Both flow modes lead to similar regions prone to intimal hyperplasia resulting from low time-averaged WSS and high oscillatory shear index.

Effect of pulsatile perfusion during cardiopulmonary bypass in terms of radial artery sphygmogram

OBJECTIVE

To investigate a quantitative method for using radial artery pulse waveforms to assess the effect of pulsatile flow during cardiopulmonary bypass (CPB).

METHODS

A total of 34 adults with heart disease who underwent open-heart surgery between April 2010 and January 2011 were randomized into a pulsatile perfusion group (n = 17) and a non-pulsatile perfusion group (n = 17). Radial arterial pulse waveforms of pulsatile and non-pulsatile perfusion patients were observed and compared before and during CDB.

RESULTS

No pulse waveform could be detected at patients' radial artery in both groups when the aorta was cross-clamped. Pulse waveforms could be detected at pulsatile perfusion patients' radial artery, but could not be detected at non-pulsatile perfusion patients' radial artery during CPB. Additionally, patients' pulse waveforms during pulsatile perfusion were lower than those before the operation.

CONCLUSION

Our findings indicate that radial artery sphygmogram can be used as a valid indicator to evaluate the effectiveness of pulsatile perfusion during CPB.

Pathophysiology of Cardiopulmonary Bypass

The techniques and equipment of cardiopulmonary bypass (CPB) have evolved over the past 60 years, and numerous numbers of cardiac surgical procedures are conducted around the world using CPB. Despite more widespread applications of percutaneous coronary and valvular interventions, the need for cardiac surgery using CPB remains the standard approach for certain cardiac pathologies because some patients are ineligible for percutaneous procedures, or such procedures are unsuccessful in some. The ageing patient population for cardiac surgery poses a number of clinical challenges, including anemia, decreased cardiopulmonary reserve, chronic antithrombotic therapy, neurocognitive dysfunction, and renal insufficiency. The use of CPB is associated with inductions of systemic inflammatory responses involving both cellular and humoral interactions. Inflammatory pathways are complex and redundant, and thus, the reactions can be profoundly amplified to produce a multiorgan dysfunction that can manifest as capillary leak syndrome, coagulopathy, respiratory failure, myocardial dysfunction, renal insufficiency, and neurocognitive decline. In this review, pathophysiological aspects of CPB are considered from a practical point of view, and preventive strategies for hemodilutional anemia, coagulopathy, inflammation, metabolic derangement, and neurocognitive and renal dysfunction are discussed.

Acute and chronic consequences of non-pulsatile blood flow pattern in long-term total artificial heart experiment

Vessel pulsation is presumably a key physiological function for the optimal supply of peripheral tissues and vital organs by oxygen and nutrients. The absence of pulsatility might impair the peripheral perfusion stability and trigger microvascular dysfunction of vital organs. The main purpose of this study was to investigate the influence of non-pulsatile flow on the microcirculation in experimental goat with implanted undulation pump total artificial heart (UPTAH). A microscopic system (Keyence, Japan) for the direct observation of the microcirculation of bulbar conjunctiva was used. Following the acute flow pattern change (from pulsatile to non-pulsatile one), the number of perfused capillaries decreased significantly (from 34.7+/-6.3 to 19.7+/-4.1 number of capillaries/mm; P<0.05). The velocity of erythrocytes dropped (from 526+/-83 to 132+/-41mum/s; P<0.05). The velocity of erythrocytes and capillary density were only partly recovered, when the pulsatile flow mode was restored. Histopathological analysis after 33 days of pumping in non-pulsatile mode revealed the presence of chronic venostasis, tissue edema, hemorrhages, hypoxia and ischemic necroses in the tissue samples from liver, kidneys and lung. These findings could be regarded as a direct effect of the chronic non-pulsatile pumping mode and inadequate blood supply. We conclude that the presence of pulsatile flow should be considered as a vital condition for a successful long-term survival after total artificial heart implantation.

Effects of Propofol and Midazolam on Lipids, Glucose, and Plasma Osmolality during and in the Early Postoperative Period Following Coronary Artery Bypass Graft Surgery: A Randomized Trial

It is not clear how levels of serum lipids and glucose and plasma osmolality change during propofol infusion in the pre- and postoperative period of coronary artery bypass graft surgery (CABG). This prospective, randomized, controlled trial evaluated changes in these parameters during propofol or midazolam infusion during and in the early postoperative period following surgery. Twenty patients undergoing CABG were randomized preoperatively into two groups: 10 patients received propofol (induction 1.5 mg/kg, maintenance 1.5 mg kg(-1) h(-1)) and 10 patients received midazolam (induction 0.5 mg/kg, maintenance 0.1 mg kg(-1) h(-1)). Both groups also received fentanyl (induction 20 mug/kg, maintenance 10 microg kg(-1)). Serum lipids, glucose, and plasma osmolality were measured preinduction, precardiopulmonary bypass, at the end of cardiopulmonary bypass, at the end of surgery, and 4 and 24 h postoperatively. In the propofol group, we observed a significant increase in triglycerides and very low-density lipoprotein levels 4 h postoperatively. In the midazolam group, we observed a significant decrease in low-density lipoprotein, cholesterol at the end of cardiopulmonary bypass, end of surgery, and 4 and 24 h postoperatively and significant increase in osmolality at the end of cardiovascular bypass. Changes in glucose levels did not differ significantly different between the two groups. In patients with normal serum lipids, glucose, and plasma osmolality undergoing CABG, propofol infusion for maintenance anesthesia is not associated with dangerous changes in serum lipids, glucose, and plasma osmolality compared with midazolam. A propofol infusion technique for maintenance of anesthesia for cardiac surgery where serum lipids and glucose may be of concern could be recommended as an alternative to midazolam.

An Evaluation of the Benefits of Pulsatile versus Nonpulsatile Perfusion during Cardiopulmonary Bypass Procedures in Pediatric and Adult Cardiac Patients

The controversy over the benefits of pulsatile and nonpulsatile flow during cardiopulmonary bypass procedures continues. The objective of this investigation was to review the literature in order to clarify the truths and dispel the myths regarding the mode of perfusion used during open-heart surgery in pediatric and adult patients. The Google and Medline databases were used to search all of the literature on pulsatile vs. nonpulsatile perfusion published between 1952 and 2006. We found 194 articles related to this topic in the literature. Based on our literature search, we determined that pulsatile flow significantly improved blood flow of the vital organs including brain, heart, liver, and pancreas; reduced the systemic inflammatory response syndrome; and decreased the incidence of postoperative deaths in pediatric and adult patients. We also found evidence that pulsatile flow significantly improved vital organ recovery in several types of animal models when compared with nonpulsatile perfusion. Several investigators have also shown that pulsatile flow generates more hemodynamic energy, which maintains better microcirculation compared with nonpulsatile flow. These results clearly suggest that pulsatile flow is superior to nonpulsatile flow during and after open-heart surgery in pediatric and adult patients.

Splanchnic Organ Injury During Coronary Surgery With or Without Cardiopulmonary Bypass: A Randomized, Controlled Trial

BACKGROUND

We investigated the efficacy of coronary surgery with or without cardiopulmonary bypass in protecting the function of the small intestine, liver, and pancreas.

METHODS

Patients were randomized to off-pump coronary artery bypass grafting (OPCAB) or coronary artery bypass grafting with cardiopulmonary bypass (CABG-CPB). Small intestine function was assessed by differential four sugars (O = methyl-D-glucose, D-xylose, L-rhamnose, and lactulose) permeability and absorption tests. Liver function was assessed by monoethylglycinexylidide/lidocaine ratios and by serial measurements of transaminases (aspartate transaminase and alanine-amino transferase), bilirubin, and alkaline phosphatase. Pancreatic function was assessed by serial measurements of insulin/glucagon ratio, amylase, and glucose. Forty patients were recruited (20 per group).

RESULTS

Permeability and absorption were more impaired in the OPCAB group immediately after surgery, but returned to baseline levels in both groups by postoperative day 5 (interaction of surgery type and time; p = 0.05 and p = 0.02, respectively). Monoethylglycinexylidide/lidocaine ratios were not different in the two groups. Aspartate transaminase and alanine-amino transferase levels were higher in the CABG-CPB group for the first postoperative day, but levels converged by day 3 (interaction of surgery type and time; p < 0.0001 and p = 0.04, respectively). The bilirubin level for the OPCAB group overshot the CABG-CPB group at 36 hours before returning to a similar level 60 hours postoperatively. Amylase levels were higher in the CABG-CPB group than in the OPCAB group (1.17 times; p = 0.03); other markers of pancreatic function showed no differences between the groups.

CONCLUSIONS

Early small intestine function is worse with OPCAB; all functions recover to similar levels in both groups by day 5. Conversely, pancreatic function is worse with the CABG-CPB group than with the OPCAB group. Hepatic metabolic function does not differ by type of surgery to the end of the operation. Postoperative hepatocellular injury was worse with the CABG-CPB group.

The effects of pulsatile versus non-pulsatile extracorporeal circulation on the pattern of coronary artery blood flow during cardiac arrest

BACKGROUND

In sudden cardiac arrest, the effective maintenance of coronary artery blood flow is of paramount importance for myocardial preservation as well as cardiac recovery and patient survival. The purpose of this study was to directly compare the effects of pulsatile versus non-pulsatile circulation to coronary artery flow and myocardial preservation in a cardiac arrest condition.

METHODS

A cardiopulmonary bypass circuit was constructed in a ventricular fibrillation model using fourteen Yorkshire swine weighing 25-35 kg each. The animals were randomly assigned to group I (n=7, non-pulsatile centrifugal pump) or group II (n=7, pulsatile T-PLS pump). Extracorporeal circulation was maintained for two hours at a pump flow of 2 L/min. The left anterior descending coronary artery flow was measured with an ultrasonic coronary artery flow measurement system at baseline (before bypass) and at every 20 minutes after bypass. Serologic parameters were collected simultaneously at baseline, 1 hour, and 2 hours after bypass in the systemic arterial and coronary sinus venous blood. The Mann-Whitney U test of STATISTICA 6.0 was used to determine intergroup significances using a p value of <0.05.

RESULTS

The resistance index of the coronary artery was lower in group II and the difference was significant at 40 min, 80 min, 100 min and 120 min (p<0.05). The mean velocity of the coronary artery was higher in group II throughout the study, and the difference was significant from 20 min after starting the pump (p<0.05). The coronary artery blood flow was higher in group II throughout the study, and the difference was significant from 40 min to 120 min (p<0.05) except at 80 min. Serologic parameters showed no differences between the groups at 1 hour and 2 hours after bypass in the systemic and coronary sinus blood (p=NS).

CONCLUSION

In the cardiac arrest condition, pulsatile extracorporeal circulation provides more blood flow, higher flow velocity and less resistance to coronary artery than non-pulsatile circulation.

Gatifloxacin as a Possible Cause of Serious Postoperative Hypoglycemia

The case we present describes an episode of serious postoperative hypoglycemia after cardiopulmonary bypass for a relatively minor cardiac procedure. A fluoroquinolone antibiotic had been administered, and we believe that this strongly contributed to this event. Fluoroquinolone antibiotics have a recognized propensity to alter glucose homeostasis.

Intraoperative glucose control in diabetic and nondiabetic patients during cardiac surgery

OBJECTIVE

The purpose of this study was to evaluate intraoperative glucose control.

DESIGN

Prospective unblinded study.

SETTING

Tertiary care center.

PARTICIPANTS

Diabetic (n = 17) and nondiabetic (n = 23) patients undergoing elective cardiac surgery.

INTERVENTIONS

Diabetics received a modified insulin regimen consisting of a fixed rate infusion of regular insulin, 10 U/m2/h, and a variable infusion of D10W, adjusted to maintain glucose between 101 to 140 mg/dL.

MEASUREMENTS AND MAIN RESULTS

Baseline glucose was higher in diabetics versus nondiabetics (mean +/- standard error of the mean: 203 +/- 27 v 117 +/- 3 mg/dL, p < 0.005). After baseline, insulin levels were increased in diabetics to 410 to 568 microU/mL. Corresponding insulin levels in nondiabetics were 12 to 40 microU/mL. Compared with baseline, glucose was decreased by 10% +/- 29% in diabetics during hypothermic cardiopulmonary bypass and increased by 21% +/- 30% in nondiabetics (p < 0.005). After discontinuation of bypass, glucose was lower in diabetics (137 +/- 12 mg/dL) versus nondiabetics (162 +/- 8 mg/dL, p < 0.005). Nine diabetics had adequate intraoperative glycemic control during hypothermic bypass (glucose 123 +/- 8 mg/dL, insulin 550 +/- 68 microU/mL, glucose infusion rate 1.87 +/- 0.29 mg/kg/min), 6 approached adequate control near the end of surgery (glucose 147 +/- 8 mg/dL, insulin 483 +/- 86 microU/mL, glucose infusion rate 0.35 +/- 0.05 mg/kg/min), and 2 never achieved control. Diabetics with elevated initial glucose >300 mg/dL did not achieve adequate glycemic control. Four diabetics (3 with renal failure) required injection of 50% dextrose after bypass for hypoglycemia.

CONCLUSION

Adequate glycemic control can be achieved in most diabetics during cardiac surgery using a modified insulin clamp technique provided initial glucose is <300 mg/dL.

Hyperglycemia during normothermic cardiopulmonary bypass: the role of the kidney

BACKGROUND

Hyperglycemia commonly occurs during cardiopulmonary bypass. We studied the quantitative impact of glucose input and its renal excretion on hyperglycemia during cardiopulmonary bypass.

METHODS

The quantity of glucose infused and metabolite and hormone concentrations in plasma, as well as oxygen consumption, carbon dioxide production, and renal glucose excretion, were determined before, during, and after cardiopulmonary bypass in 8 patients.

RESULTS

Hyperglycemia (14 to 29 mmol/L) was accompanied by an increase in plasma insulin levels. The degree of hyperglycemia was directly related to the amount of glucose infused. The rate of oxygen consumption did not decrease and the rate of urea appearance (gluconeogenesis) did not rise. Despite a very high filtered load of glucose, there was very little glucosuria, indicating a markedly enhanced renal absorption of glucose.

CONCLUSIONS

Hormonal and metabolic factors permit the development of hyperglycemia during cardiopulmonary bypass but its severity depends on the quantity of glucose infused and, what appears to be a new finding, a markedly enhanced renal reabsorption of filtered glucose. Thus the kidney plays an important role in the development of severe hyperglycemia during cardiopulmonary bypass.

Hyperglycemia during hypothermic cardiopulmonary bypass does not alter postbypass vascular endothelial responses in dogs

BACKGROUND

Hyperglycemia during hypothermic cardiopulmonary bypass (CPB) may alter intrinsic vasomotion by reducing endothelial-dependent vasorelaxation. Using a canine model of hypothermic CPB, this study tested whether hyperglycemia altered the vasodilator response to acetylcholine (ACh) and the vasoconstrictor response to phenylephrine (Phe).

METHODS

In 20 anesthetized dogs, the left femoral arteries were excised and placed in gassed (95% O2-5% CO2) cold Krebs's solution. The animals were randomized into two groups undergoing 120 minutes of 28 degrees C CPB using membrane oxygenators. A hyperglycemic group (n = 10) received a continuous infusion of 50% dextrose to maintain blood glucose level greater than 500 mg/dL; a normoglycemic group (n = 10) received 0.9% saline. After rewarming and discontinuing CPB, the right femoral arteries were excised. Vessel rings were placed in a suffusion bath, and changes in isometric tension were measured. Dose-response relationships (ACh: 10(-9) to 10(-6)M; Phe: 3 x 10(-8) to 10(-4)M) and -log ED50 sensitivity to ACh and Phe before and after CPB were compared.

RESULTS

Serum glucose during hypothermic CPB was significantly greater in glucose-treated dogs (525 +/- 9 mg/dL) than controls (109 +/- 5 mg/dL; p < 0.05). After CPB, -log ED50 values for ACh changed from 7.7 +/- 0.1 to 7.5 +/- 0.2 (p < 0.05) in normoglycemic dogs and from 7.8 +/- 0.1 to 7.6 +/- 0.1 (p < 0.05) in hyperglycemic animals, indicating similar and significant rightward shifts of the dose-response relationship to ACh after CPB in both groups. Neither hyperglycemia nor CPB altered the vasoconstrictor response to Phe.

CONCLUSIONS

The reduction in ACh-mediated vasorelaxation after CPB did not differ between hyperglycemic and normoglycemic animals, indicating that hyperglycemia does not contribute to impaired vasorelaxation after CPB. Because Phe-induced vasoconstriction was unaffected, hyperglycemia during hypothermic CPB does not appear to increase the potential for postbypass vasospasm.

Release of vasoactive substances during cardiopulmonary bypass

Cardiopulmonary bypass is associated with bleeding and thrombotic complications, massive fluid shifts, and cellular and hormonal defense reactions that are collectively termed "the whole body inflammatory response." A host of vasoactive substances are produced, released or altered during cardiopulmonary bypass. These hormones, autacoids, and cytokines react with specific receptor proteins distributed throughout the body, and mediate the vascular smooth muscle and endothelial cell contractions that are responsible for much of the morbidity associated with open heart operations. This essay briefly reviews the actions, sources, and perturbations of the approximately 25 vasoactive substances known or believed to be altered by cardiopulmonary bypass, and provides an introductory reference list.