Splanchnic oxygen transport, hepatic function and gastrointestinal barrier after normothermic cardiopulmonary bypass

Risk factors of gastrointestinal bleeding after cardiopulmonary bypass in children: a retrospective study

Background

During cardiac surgery that involved cardiopulmonary bypass (CPB) procedure, gastrointestinal (GI) system was known to be vulnerable to complications such as GI bleeding. Our study aimed to determine the incidence and risk factors associated with GI bleeding in children who received CPB as part of cardiac surgery.

Methods

This retrospective study enrolled patients aged <18 years who underwent cardiac surgery with CPB from 2013 to 2019 at Shanghai Children's Medical Center. The primary outcome was the incidence of postoperative GI bleeding in children, and the associated risk factors with postoperative GI bleeding episodes were evaluated.

Results

A total of 21,893 children who underwent cardiac surgery with CPB from 2013 to 2019 were included in this study. For age distribution, 636 (2.9%) were neonates, 10,984 (50.2%) were infants, and 10,273 (46.9%) were children. Among the 410 (1.9%) patients with GI bleeding, 345 (84.2%) survived to hospital discharge. Incidence of GI bleeding in neonates, infants and children were 22.6% (144/636), 2.0% (217/10,984) and 0.5% (49/10,273), respectively. The neonates (22.6%) group was associated with highest risk of GI bleeding. Patients with GI bleeding showed longer length of hospital stays (25.8 ± 15.9 vs. 12.5 ± 8.9, P < 0.001) and higher mortality (15.9% vs. 1.8%, P < 0.001). Multivariate logistic regression analysis showed that age, weight, complicated surgery, operation time, use of extracorporeal membrane oxygenation (ECMO), low cardiac output syndrome (LCOS), hepatic injury, artery lactate level, and postoperative platelet counts were significantly associated with increased risk of GI bleeding in children with congenital heart disease (CHD) pediatric patients that underwent CPB procedure during cardiac surgery.

Conclusion

The study results suggest that young age, low weight, long operation time, complicated surgery, use of ECMO, LCOS, hepatic injury, high arterial lactate level, and low postoperative platelet counts are independently associated with GI bleeding after CPB in children.

Does severe hyperlactatemia during cardiopulmonary bypass predict a worse outcome?

INTRODUCTION

The aim of the current study was to evaluate the impact of increased blood lactate levels during cardiopulmonary bypass (CPB) on immediate results in patients who underwent open heart surgery.

MATERIALS AND METHODS

We performed a retrospective single-center study on 1290 patients. Adult cardiac surgical patients who underwent valve surgery, coronary artery bypass graft, combined procedure, adult congenital anomalies and aortic surgery were enrolled. Patients with associated comorbidities such as liver dysfunction, hemodynamic instability before surgery were excluded. Arterial blood lactate concentration was measured immediately after weaning from CPB and evaluated together with clinical data and outcomes including in hospital mortality. Patients were classified into 3 groups according to their peak arterial lactate level: group I [normal lactatemia, lactate ˂ 2 mmol/l (n = 749)], group II [mild hyperlactatemia, lactate 2-5 mmol/l (n = 489)], group III [severe hyperlactatemia, lactate ˃ 5 mmol/l (n = 52)].

RESULTS

When comparing outcomes across the 3 groups, severe hyperlactatemia was correlated with worse outcomes including higher in-hospital mortality, low output cardiac syndrome, postoperative renal insufficiency, myocardial infarction, red blood cell transfusion (RBC) transfusion, prolonged mechanical ventilation and longer intensive care unit (ICU) stay hours.

CONCLUSION

Blood lactate level above 5 mmol/l and more during CPB is associated with higher in-hospital mortality rate and postoperative complications. More attention must be given to correct the common abnormalities conditions inherent of CPB in order to conduct adequate tissue perfusion and reduce the risk of hyperlactatemia.

Perioperative intraperitoneal metabolic markers in patients undergoing cardiac surgery with cardiopulmonary bypass: an exploratory pilot study

Background:

Cardiopulmonary bypass and postoperative cardiac dysfunction cause splanchnic hypoperfusion resulting in intra-abdominal anaerobic metabolism and risk for gastrointestinal complications. The intra-abdominal metabolism can be monitored by intraperitoneal measurement of relevant metabolites using microdialysis. The aim of this study was to investigate the intraperitoneal metabolism using microdialysis during and after cardiopulmonary bypass at 34°C.

Methods:

In six patients undergoing elective coronary artery bypass grafting or aortic valve replacement under cardiopulmonary bypass, microdialysis was used to measure intraperitoneal and subcutaneous glucose, lactate, pyruvate, glycerol and glutamate concentrations, intraoperatively and up to 36 hours postoperatively. Arterial and central venous blood gases were analysed as were haemodynamics and the development of complications.

Results:

All patients had an ordinary perioperative course and did not develop gastrointestinal complications. The arterial, intraperitoneal and subcutaneous lactate concentrations changed during the perioperative course with differences between compartments. The highest median (interquartile range) concentration was recorded in the intraperitoneal compartment at 1 hour after the end of cardiopulmonary bypass (2.1 (1.9–2.5) mM compared to 1.3 (1.2–1.7) mM and 1.5 (1.0–2.2) mM in the arterial and subcutaneous compartments, respectively). In parallel with the peak increase in lactate concentration, the intraperitoneal lactate/pyruvate ratio was elevated to 33.4 (12.9–54.1).

Conclusion:

In cardiac surgery, intraperitoneal microdialysis detected changes in the abdominal metabolic state, which were more pronounced than could be shown by arterial blood gas analysis. Despite an uneventful perioperative course, patients undergoing low-risk surgery under cardiopulmonary bypass might be subjected to a limited and subclinical intra-abdominal anaerobic state.

Increased Small Intestinal Permeability during Severe Acute Exacerbations of COPD

BACKGROUND

Disturbances of intestinal integrity, manifested by increased gastro-intestinal (GI) permeability, have been found in chronic obstructive pulmonary disease (COPD) patients during physical activity, often associated with intermittent hypoxic periods. Evidence about extrapulmonary organ disturbances, especially of the GI tract, during hospitalised acute exacerbation of COPD (AE-COPD) with hypoxaemic respiratory failure (RF) is lacking.

OBJECTIVE

The aim was to assess changes in GI permeability in patients with AE-COPD and during recovery 4 weeks later.

METHODS

All patients admitted to our hospital with AE-COPD accompanied by hypoxaemia at admission (PaO2 <8.7 kPa or O2 saturation <93%) were screened between October 2013 and February 2014. Patients with a history of GI or renal disease, chronic heart failure, or use of non-steroidal anti-inflammatory drugs in the 48 h before the test were excluded. GI permeability was assessed by evaluating urinary excretion ratios of the orally ingested sugars lactulose/L-rhamnose (L/R ratio), sucrose/L-rhamnose (Su/R ratio) and sucralose/erythritol (S/E ratio).

RESULTS

Seventeen patients with severe to very severe COPD completed the study. L/R ratio (×103) at admission of AE-COPD was significantly higher than in the recovery condition (40.9 [29.4-49.6] vs. 27.3 [19.5-47.7], p = 0.039), indicating increased small intestinal permeability. There were no significant differences in the individual sugar levels in urine nor in the 0- to 5-h urinary S/E and Su/R ratios between the 2 visits.

CONCLUSION

This is the first study showing increased GI permeability during hospitalised AE-COPD accompanied by hypoxaemic RF. Therefore, GI integrity in COPD patients is an attractive target for future research and for the development of interventions to alleviate the consequences of AE-COPD.

Lactate Elevation During and After Major Cardiac Surgery in Adults: A Review of Etiology, Prognostic Value, and Management

Elevated lactate is a common occurrence after cardiac surgery. This review summarizes the literature on the complex etiology of lactate elevation during and after cardiac surgery, including considerations of oxygen delivery, oxygen utilization, increased metabolism, lactate clearance, medications and fluids, and postoperative complications. Second, the association between lactate and a variety of outcomes are described, and the prognostic role of lactate is critically assessed. Despite the fact that elevated lactate is strongly associated with many important outcomes, including postoperative complications, length of stay, and mortality, little is known about the optimal management of postoperative patients with lactate elevations. This review ends with an assessment of the limited literature on this subject.

Cardiopulmonary Bypass-Induced Inflammatory Response: Pathophysiology and Treatment

OBJECTIVES

The objectives of this review are to discuss the pathophysiology of the pro-inflammatory response to the cardiopulmonary bypass circuit, the impact of ischemia reperfusion injury on post-operative organ function, the compensatory anti-inflammatory response and the evidence for immune-modulatory strategies and their impact on outcomes.

DATA SOURCE

MEDLINE, PubMed.

CONCLUSION

Innovations such as the development of more biocompatible surfaces and miniaturized circuits, as well as the increasing expertise of surgeons, anesthesiologists and perfusionists has transformed cardiac surgery and the use of cardiopulmonary bypass into a relatively routine procedure with favorable outcomes. Despite these refinements, the attendant inflammatory response to bypass, ischemia reperfusion injury and the compensatory anti-inflammatory response contribute to post-operative morbidity and mortality. Additional studies are needed to further delineate the impact of immunomodulatory strategies on outcomes.

Liver Function Tests Following Open Cardiac Surgery

Introduction: The cardiopulmonary bypass may have multiple systemic effects on the body organs as liver. This prospective study was planned to explore further the incidence and significance of this change.

Methods: Two hundred patients with coronary artery bypass grafting (CABG), were randomly selected for the study. Total and indirect bilirubin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase were measured preoperatively and at 24, 48 and 72 hours, following coronary artery bypass grafting. Postoperative value of the liver function tests with respect to hypothermia or hypotension were compared by one way analysis of variance for repeated measure and compared with t test. Patient’s characteristics with bilirubin value (≤1.5 mg or >1.5 mg) were compared with t test.

Results: A significant increase of total bilirubin, aspartate aminotransferase, and alkaline phosphatase were noted in the third postoperative day. Significant relation was seen between hypotension and alkaline phosphatase, and aspartate aminotransferase change but hypothermia had not affected alanine aminotransferase, total bilirubin and indirect bilirubin change. Pump time, alanine aminotransferase in third postoperative day and direct bilirubin in first and second day of postoperative period had significant relation with pre and post-operative bilirubin change.

Conclusion: Transient but not permanent alterations of hepatic enzymes after coronary artery bypass grafting presumably attributed to the decreased hepatic flow, hypoxia, or pump-induced inflammation.

Abdominal Problems in Children with Congenital Cardiovascular Abnormalities

BACKGROUND

Congenital cardiovascular abnormality is an important cause of morbidity and mortality in childhood. Both the type of congenital cardiovascular abnormality and cardiopulmonary bypass are responsible for gastrointestinal system problems.

AIMS

Intra-abdominal problems, such as paralytic ileus, necrotizing enterocolitis, and intestinal perforation, are common in patients who have been operated or who are being followed for congenital cardiovascular abnormalities. Besides the primary congenital cardiovascular abnormalities, ischemia secondary to cardiac catheterization or surgery contributes to the incidence of these problems.

STUDY DESIGN

Cross-sectional study.

METHODS

In this study, we aimed to screen the intra-abdominal problems seen in patients with congenital cardiovascular abnormalities who had undergone surgical or angiographical intervention(s). Patients with congenital cardiovascular abnormalities who had been treated medically or surgically between 2000 and 2014 were analyzed retrospectively in terms of intra-abdominal problems. The patients' demographic data, type of congenital cardiovascular abnormalities, the intervention applied (surgical, angiographic), the incidence of intra-abdominal problem(s), the interventions applied for the intra-abdominal problems, and the results were evaluated.

RESULTS

Fourteen (Group I) of the 76 patients with congenital cardiovascular abnormalities diagnosis were operated due to intra-abdominal problems, and 62 (Group II) were followed-up clinically for intra-abdominal problems. In Group I (10 boys and 4 girls), 11 patients were aged between 0 and 12 months, and three patients were older than 12 months. Group II included 52 patients aged between 0 and 12 months and 10 patients older than 12 months. Cardiovascular surgical interventions had been applied to six patients in Group I and 40 patients in Group II. The most frequent intra-abdominal problems were necrotizing enterocolitis and intestinal perforation in Group I, and paralytic ileus in Group II. Seven of the Group I patients and 22 of the Group II patients died. The patients who died in both groups had more than three congenital cardiovascular abnormalities in the same patient, and 80% of these patients had been operated for congenital cardiovascular abnormalities.

CONCLUSION

The gastrointestinal system is involved in important complications experienced by patients with congenital cardiovascular abnormalities. The mortality rate was higher in operated patients due to gastrointestinal complications. Gastrointestinal complications are more frequent in patients with cyanotic anomalies. The presence of more than one congenital cardiovascular abnormality in a patient increased the mortality rate.

Analysis of the effect of renal replacement therapy: in the prolonged extracorporeal membrane oxygenation patients

Background

This paper aimed to verify the effects of renal replacement therapy on changing the levels of serum creatinine for different veno-arterial and veno-venous configurations in prolonged extracorporeal membrane oxygenation (ECMO) patients.

Methods

The subjects were chosen 71 patients who had undergone more than 1,440 minutes (24 hours) of the therapy from among 117 patients who had undergone ECMO insertion between January 2008 and December 2012. The patients were separated into the veno-arterial configuration group I (51 patients) and the veno-venous configuration group II (20 patients). The difference in the level of serum creatinine (ΔCr) between before or just after ECMO insertion (Cr_I) and the level when the pump time was between 2,880 and 4,320 minutes (Cr_F) was checked (ΔCr=Cr_F−Cr_I), and the average ΔCr for each group was compared using a Student t-test at the confidence interval (CI) of 95%.

Results

The change in the level of serum creatinine was an increase of 0.341 mg/dL (σ=0.9202) for group I and a decrease of 0.120 mg/dL (σ=1.5292) for group II. The change was significantly high for group I (p=0.011, CI=95%). Meanwhile, within group I, when renal replacement therapy was not done, there was a significant increase in the level of serum creatinine (p=0.009, CI=95%).

Conclusion

For ECMO insertion patients whose pump time was more than 1,440 minutes, there was a significant change in the level of serum creatinine when renal replacement therapy was not done, for the veno-arterial configuration of group I.

Smooth muscle contractile diversity in the control of regional circulations

Each regional circulation has unique requirements for blood flow and thus unique mechanisms by which it is regulated. In this review we consider the role of smooth muscle contractile diversity in determining the unique properties of selected regional circulations and its potential influence on drug targeting in disease. Functionally smooth muscle diversity can be dichotomized into fast versus slow contractile gene programs, giving rise to phasic versus tonic smooth muscle phenotypes, respectively. Large conduit vessel smooth muscle is of the tonic phenotype; in contrast, there is great smooth muscle contractile diversity in the other parts of the vascular system. In the renal circulation, afferent and efferent arterioles are arranged in series and determine glomerular filtration rate. The afferent arteriole has features of phasic smooth muscle, whereas the efferent arteriole has features of tonic smooth muscle. In the splanchnic circulation, the portal vein and hepatic artery are arranged in parallel and supply blood for detoxification and metabolism to the liver. Unique features of this circulation include the hepatic-arterial buffer response to regulate blood flow and the phasic contractile properties of the portal vein. Unique features of the pulmonary circulation include the low vascular resistance and hypoxic pulmonary vasoconstriction, the latter attribute inherent to the smooth muscle cells but the mechanism uncertain. We consider how these unique properties may allow for selective drug targeting of regional circulations for therapeutic benefit and point out gaps in our knowledge and areas in need of further investigation.

The interpretation of perioperative lactate abnormalities in patients undergoing cardiac surgery

Hyperlactataemia and lactic acidosis are commonly encountered during and after cardiac surgery. Perioperative lactate production increases in the myocardium, skeletal muscle, lungs and in the splanchnic circulation during cardiopulmonary bypass. Hyperlactataemia has a bimodal distribution in the perioperative period. An early increase in lactate levels, arising intraoperatively or soon after intensive care unit admission, is a familiar and concerning finding for most clinicians. It is highly suggestive of tissue ischaemia and is associated with a prolonged intensive care unit stay, a prolonged requirement for respiratory and cardiovascular support and increased postoperative mortality. Its presence should prompt a thorough search for potential causes of tissue hypoxia. In contrast, late-onset hyperlactataemia, a less well recognised complication, occurs 4 to 24 hours after completion of surgery and is typically associated with preserved cardiac output and oxygen delivery. Risk factors for late-onset hyperlactataemia include hyperglycaemia, long cardiopulmonary bypass time and elevated endogenous catecholamines. Although patients with this complication may have a longer duration of ventilation and intensive care unit length of stay than those with normolactataemia, an association with increased mortality has not been demonstrated. The discovery of late-onset hyperlactataemia should not delay the postoperative progress of an otherwise stable patient following cardiac surgery.

Nutrition intervention in the critically ill cardiothoracic patient

Despite acute myocardial infarction and cardiac surgery accounting for 2 of the most common reasons patients are admitted to the intensive care unit, little attention and investigation have been directed specifically for these patients. This patient population therefore deserves special attention as they are often malnourished but require emergent interventions, making nutrition intervention challenging. This article reviews current medical interventions implemented in critically ill cardiothoracic patients and discusses evidence-based nutrition therapy, including enteral and parenteral feeding, glycemic control, and antioxidant provision.

Central venous saturation is not an alternative to mixed venous saturation during cardiopulmonary bypass in coronary artery surgery patients

BACKGROUND

To evaluate the correlation and agreement between central venous saturation (ScvO(2)) and mixed venous saturation (SvO(2)) during cardiopulmonary bypass.

METHODS

Twenty-two consecutive patients scheduled for coronary artery surgery were prospectively included. Paired measurements of ScvO(2) and SvO(2) were performed 5 minutes after aortic cross-clamping, after each cardioplegia dose and after de-clamping of the aortic cross-clamp. ScvO(2) and SvO(2) were measured, respectively, by a fibreoptic catheter in the superior vena cava and on blood samples from the venous return line of the extracorporeal circuit, using a blood gas analyser

RESULTS

Ninety-five paired measurements of venous saturation were obtained. Correlation between the measurements was associated with an r = 0.55. The mean bias was 2.2 [Limits of agreement: -13.6%, +18%]. Changes in oxygen saturation over time showed an r = 0.4 and a mean bias of 0.2 [Limits of agreement: -17.9%, +18.3%]. Multivariate analysis identified the oxygen consumption index as the only factor explaining this variability.

CONCLUSIONS

Although mean biases between the measurements were low, limits of agreement were too large to provide a clinically acceptable estimation of SvO(2) by ScvO(2) in these conditions. Variations in regional oxygen consumption seem to be the main factor worsening the relationship.

Minimized and conventional cardiopulmonary bypass damage intestinal mucosal integrity

OBJECTIVES

Previous studies have suggested that gastrointestinal integrity is compromised after cardiopulmonary bypass (CPB). We compared the effects of prolonged minimized (MCPB) and conventional CPB (CCPB) on intestinal mucosal integrity by determining mucosal damage, epithelial cell proliferation rate and distribution of tight junction proteins in a porcine model.

DESIGN

Fourteen animals were randomly assigned to undergo 240 minutes of mild hypothermic MCPB or CCPB. Ileal and colonic biopsies were obtained prior and at the end of CPB. Mucosal damage was determined under light microscopic evaluation. Immunohistochemistry was used to investigate epithelial expression of Ki-67 as a measure of cell proliferation rate and claudin-1, 2, 3, 4, 5, and 7 as elements of tight junctions.

RESULTS

In colonic biopsies, independent of the circuit type used, moderate mucosal damage was observed as indicated by focal epithelial damage, increased epithelial cell proliferation and decreased expression of tight junction protein claudin-4.

CONCLUSIONS

Colonic mucosal damage was observed similarly in MCPB and CCPB. Based on these results, the effects of MCPB on intestinal mucosal stability are similar to those of CCPB.

Perioperative indocyanine green clearance is predictive for prolonged intensive care unit stay after coronary artery bypass grafting--an observational study

Introduction

During cardiac surgery with cardiopulmonary bypass (CPB) haemodilution occurs. Hepatic dysfunction after CPB is a rare, but serious, complication. Clinical data have validated the plasma-disappearance rate of indocyanine green (PDR ICG) as a marker of hepatic function and perfusion. Primary objective of this analysis was to investigate the impact of haemodilutional anaemia on hepatic function and perfusion by the time course of PDR ICG and liver enzymes in elective CABG surgery. Secondary objective was to define predictors of prolonged ICU treatment like decreased PDR ICG after surgery.

Methods

60 Patients were subjected to normothermic CPB with predefined levels of haemodilution anaemia (haemotacrit (Hct) of 25% versus 20% during CPB). Hepatic function and perfusion was assessed by PDR ICG, plasma levels of aspartate aminotransferase (ASAT) and α-GST. Prolonged ICU treatment was defined as treatment ≥ 48 hours.

Results

Logistic regression analysis showed that all postoperative measurements of PDR ICG (P < 0.01), and the late postoperative ASAT (P < 0.01) measurement were independent risk factors for prolonged ICU treatment. The predictive capacity for prolonged ICU treatment was best of the PDR ICG one hour after admission to the ICU. Furthermore, the time course of PDR ICG as well as ASAT and α-GST did not differ between groups of haemodilutional anaemia.

Conclusions

Our study provides evidence that impaired PDR ICG as a marker of hepatic dysfunction and hypoperfusion may be a valid marker of prolonged ICU treatment. Additionally this study provides evidence that haemodilutional anaemia to a Hct of 20% does not impair hepatic function and perfusion.

Trial registration

[ISRCTN35655335]

The effect of fenoldopam and dopexamine on hepatic blood flow and hepatic function following coronary artery bypass grafting with hypothermic cardiopulmonary bypass

BACKGROUND

Hypothermic cardiopulmonary bypass is associated with low perfusion state causing a mismatch between demand and supply to various organs such as gut, kidneys and brain. The consequences are thought to be responsible for postoperative complications like systemic inflammatory response, renal failure, neurological injury, etc. Pharmacological agents like dopamine, dopexamine and dobutamine have been used in an attempt to reduce hypoperfusion and hence complications. Fenoldopam, a dopamine analog (DA-1 receptor agonist), has recently been shown to be specific reno-splanchnic vasodilator in animal studies. We studied the haemodynamic effects of fenoldopam and its effect on hepatic blood flow (HBF) during and after cardiopulmonary bypass and compared these with dopexamine.

METHODS

Ethics committee approval was obtained. Forty-two consecutive patients with good/moderate left ventricular function undergoing either elective/urgent coronary artery bypass grafting were included in the study. Patients were randomised to receive either fenoldopam (0.2 microg/kgmin) (F; n=14) or dopexamine (2.0 microg/kgmin) (Dx; n=14) normal saline (NS; n=14) continuously after induction of anaesthesia for 24h following completion of surgery. HBF was measured using the Indocyanine green dye disappearance rate method, before, during and after cardiopulmonary bypass. Data were collected pre-, intra- and postoperatively. Serum liver enzymes were measured during the perioperative period. Repeated measures ANOVA test was used to compare timed samples in both groups.

RESULTS

The study groups were comparable in pre- and intraoperative variables. In the fenoldopam and dopexamine groups there was a significant increase in heart rate 15 min following the commencement of the infusion (NS:F:DX::-2.0+/-7.8 beats/min:13.6+/-8.1 beats/min (p=0.007):18.36+/-20.2 beats/min (p=0.004)). However the change in mean arterial blood pressure was similar (NS:F:DX::-12.7+/-14.9:-4.0+/-23.1 (p=0.699):-2.6+/-22.3) (p=0.235). Cardiac index increased and systemic vascular resistance decreased (requiring noradrenaline infusion) in the fenoldopam group, however this did not reach statistical significance. Hepatic blood flow reduced during CPB and returned to near preoperative levels in all three groups with no statistical difference between groups.

CONCLUSIONS

Fenoldopam infusion induced transient tachycardia, with no augmentation of hepatic blood flow whereas dopexamine induced tachycardia and did not augment hepatic blood flow. Fenoldopam and dopexamine may have hepato-protective effect.

Clinical relevance of measuring colonic permeability

BACKGROUND

Gastroduodenal and small intestinal permeability are increased in patients with Crohn's disease (CD) and intensive care patients. The relevance of colonic permeability has not yet been adequately investigated. The aim of this study was to investigate the clinical value of sucralose excretion as indicator for colonic permeability in these patient groups.

DESIGN

After oral administration of four sugars and subsequent analysis of urinary excretion, gastroduodenal and intestinal permeability were calculated from saccharose excretion and lactulose/mannitol (L/M) ratio over 5 h, and sucralose excretion from 5 to 26 h in 100 healthy controls, 29 CD and 35 patients after coronary surgery (CABG).

RESULTS

In controls, sucralose excretion was highly variable (0.67+/-0.92%) and not related to small intestinal permeability. In CD and CABG, L/M ratio was increased (0.054+/-0.060; 0.323+/-0.253 vs. 0.018+/-0.001 in controls). Sucralose excretion was increased in 77% of CABG but only in 7% of CD. There was an association between gastroduodenal and intestinal permeability in CD and CABG (r=0.72, and r=0.51), but sucralose excretion was not related to either one of these two parameters. Other than a weak association between sucralose and length of stay in intensive care in CABG patients (P=0.099), sucralose excretion was not related to clinical outcome.

CONCLUSIONS

The proposed cut-off for normal sucralose excretion is 2.11%, but its high variability and lack of association to gastrointestinal permeability or clinical outcome leave it open, if it can provide information beyond established permeability tests.

Clinical relevance of pharmacokinetics and pharmacodynamics in cardiac critical care patients

Pharmacokinetics is a discipline aimed at predicting the best dosage and dosing regimen for each single drug in order to ensure and maintain therapeutically effective concentrations at the action sites. In cardiac critical care patients, various pathophysiological conditions may significantly alter the pharmacokinetic behaviour of drugs. Gastrointestinal drug absorption may be erratic and unpredictable in the early postoperative period, and so patients may be unresponsive to oral therapy; thus the intravenous route should be preferred for life-saving drugs whenever feasible. Variations in the extracellular fluid content as a response to the trauma of surgery and the fluid load or significant drug loss through thoracic drainages may significantly lower plasma concentrations of extracellularly distributed hydrophilic antimicrobials (beta-lactams, aminoglycosides and glycopeptides). Drug metabolism may be altered by the systemic inflammatory response and/or multiple organ failure and/or drug-drug pharmacokinetic interactions that can potentially occur during polytherapy, especially in immunosuppressed cardiac transplant patients. Instability of renal function may promote significant changes in body fluid concentrations of renally eliminated drugs, even in a brief period of hours. Finally, the application of extracorporeal circulation by means of cardiopulmonary bypass may significantly alter the disposition of several drugs during the operation because of acute haemodilution, hypoalbuminaemia, hypothermia and/or adsorption to the bypass equipment. Accordingly, to avoid either overexposure and the consequent increased risk of toxicity or underexposure and the consequent risk of therapeutic failure in critically ill cardiac patients, the dosing regimens of several drugs are expected to be significantly different from those suggested for clinically stable patients. Additionally, therapeutic drug monitoring may be helpful in the management of drug therapy and should be routinely used to guide individualized dose adjustments for (i) immunosuppressants whenever cytochrome P450 3A4 isoenzyme inhibitors (e.g. macrolide antibacterials, azole antifungals) or inducers (e.g. rifampicin [rifampin]) are added to or withdrawn from the regimen; and (ii) glycopeptide and aminoglycoside antibacterials whenever haemodynamically active agents (such as dopamine, dobutamine and furosemide [frusemide]) are added to or withdrawn from the regimen, and also whenever significant changes of haemodynamics and/or of renal function occur.

Review of ECMO (extra corporeal membrane oxygenation) support in critically ill adult patients

Mechanical circulatory support has evolved markedly over recent years. ECMO (extra corporeal membrane oxygenation) is instituted for the management of life threatening pulmonary or cardiac failure (or both), when no other form of treatment has been or is likely to be successful. Most commonly, it is instituted in an emergency or urgent situation after failure of other treatment modalities. It is used as temporary support, usually awaiting recovery of organs, or can be used as a bridge to a more permanent device or cardiac transplantation. ECMO can be deployed in a veno-arterial configuration (either peripheral or central cannulation) for the treatment of cardiogenic shock. This is usually seen post-cardiotomy, post-heart transplant and in severe cardiac failure due to almost any other cause (e.g. cardiomyopathy, myocarditis, acute coronary syndrome with cardiogenic shock). Veno-venous ECMO is used for respiratory failure and usually involves peripheral cannulation using the femoral veins+/-internal jugular vein if required. The indications for veno-venous ECMO are respiratory failure, most commonly due to adult respiratory distress syndrome (ARDS), pneumonia, trauma or primary graft failure following lung transplantation. ECMO is also used for neonatal and paediatric respiratory support. Its use in premature neonates is the mainstay of treatment for immature lungs and insufficient surfactant. In this review, the technical aspects of ECMO cannulation, maintenance and weaning are outlined. Complication rates and outcomes are reviewed and our experience at The Epworth Hospital is summarized.

Reactive hyperemia in the human liver

We tested whether hepatic blood flow is altered following central hypovolemia caused by simulated orthostatic stress. After 30 min of supine rest, hemodynamic, plasma density, and indocyanine green (ICG) clearance responses were determined during and after release of a 15-min 40 mmHg lower body negative pressure (LBNP) stimulus. Plasma density shifts and the time course of plasma ICG concentration were used to assess intravascular volume and hepatic perfusion changes. Plasma volume decreased during LBNP (-10%) as did cardiac output (-15%), whereas heart rate (+14%) and peripheral resistance (+17%) increased, as expected. On the basis of ICG elimination, hepatic perfusion decreased from 1.67 +/- 0.32 (pre-LBNP control) to 1.29 +/- 0.26 l/min (-22%) during LBNP. Immediately after LBNP release, we found hepatic perfusion 25% above control levels (to 2.08 +/- 0.48 l/min, P = 0.0001). Hepatic vascular conductance after LBNP was also significantly higher than during pre-LBNP control (21.4 +/- 5.4 vs. 17.1 +/- 3.1 ml.min(-1).mmHg(-1), P < 0.0001). This indicates autoregulatory vasodilatation in response to relative ischemia during a stimulus that has cardiovascular effects similar to normal orthostasis. We present evidence for physiological post-LBNP reactive hyperemia in the human liver. Further studies are needed to quantify the intensity of this response in relation to stimulus duration and magnitude, and clarify its mechanism.

Gastrointestinal perfusion in septic shock

Septic shock is characterised by vasodilation, myocardial depression and impaired microcirculatory blood flow, resulting in redistribution of regional blood flow. Animal and human studies have shown that gastrointestinal mucosal blood flow is impaired in septic shock. This is consistent with abnormalities found in many other microcirculatory vascular beds. Gastrointestinal mucosal microcirculatory perfusion deficits have been associated with gut injury and a decrease in gut barrier function, possibly causing augmentation of systemic inflammation and distant organ dysfunction. A range of techniques have been developed and used to quantify these gastrointestinal perfusion abnormalities. The following techniques have been used to study gastrointestinal perfusion in humans: tonometry, laser Doppler flowmetry, reflectance spectrophotometry, near-infrared spectroscopy, orthogonal polarisation spectral imaging, indocyanine green clearance, hepatic vein catheterisation and measurements of plasma D-lactate. Although these methods share the ability to predict outcome in septic shock patients, it is important to emphasise that the measurement results are not interchangeable. Different techniques measure different elements of gastrointestinal perfusion. Gastric tonometry is currently the most widely used technique because of its non-invasiveness and ease of use. Despite all the recent advances, the usefulness of gastrointestinal perfusion parameters in clinical decision-making is still limited. Treatment strategies specifically aimed at improving gastrointestinal perfuision have failed to actually correct mucosal perfusion abnormalities and hence not shown to improve important clinical endpoints. Current and future treatment strategies for septic shock should be tested for their effects on gastrointestinal perfusion; to further clarify its exact role in patient management, and to prevent therapies detrimental to gastrointestinal perfusion being implemented.

Altered intestinal function in patients with chronic heart failure

OBJECTIVES

We evaluated morphology and function of the gut in patients with chronic heart failure (CHF).

BACKGROUND

Intestinal translocation of bacterial endotoxin may contribute to the inflammatory state observed in patients with CHF. The morphology and function of the gut may be abnormal.

METHODS

We studied 22 patients with CHF (age 67 +/- 2 years, left ventricular ejection fraction [LVEF] 31 +/- 1%, New York Heart Association functional class 2.3 +/- 0.1, peak VO2 15.0 +/- 1.0 ml/kg/min) and 22 control subjects (62 +/- 1 years, LVEF 68 +/- 2%, peak VO2 24.7 +/- 1.3 ml/kg/min). Bowel wall thickness was assessed by transcutaneous sonography, small intestinal permeability by the lactulose-mannitol test, passive carrier-mediated transport by D-xylose test, large intestinal permeability by sucralose test (5- and 26-h urine collection, high-performance liquid chromatography), and mucosal bacterial biofilm by fluorescence in situ hybridization in biopsies taken during sigmoidoscopy.

RESULTS

Chronic heart failure patients, compared with control patients, showed increased bowel wall thickness in the terminal ileum (1.48 +/- 0.16 mm vs. 1.04 +/- 0.08 mm), ascending colon (2.32 +/- 0.18 mm vs. 1.31 +/- 0.14 mm), transverse colon (2.19 +/- 0.20 vs. 1.27 +/- 0.08 mm), descending colon (2.59 +/- 0.18 mm vs. 1.43 +/- 0.13 mm), and sigmoid (2.97 +/- 0.27 mm vs. 1.64 +/- 0.14 mm) (all p < 0.01). Chronic heart failure patients had a 35% increase of small intestinal permeability (lactulose/mannitol ratio: 0.023 +/- 0.001 vs. 0.017 +/- 0.001, p = 0.006), a 210% increase of large intestinal permeability (sucralose excretion: 0.62 +/- 0.17% vs. 0.20 +/- 0.06%, p = 0.03), and a 29% decrease of D-xylose absorption, indicating bowel ischemia (26.7 +/- 3.0% vs. 37.4 +/- 1.4%, p = 0.003). Higher concentrations of adherent bacteria were found within mucus of CHF patients compared with control subjects (p = 0.007).

CONCLUSIONS

Chronic heart failure is a multisystem disorder in which intestinal morphology, permeability, and absorption are modified. Increased intestinal permeability and an augmented bacterial biofilm may contribute to the origin of both chronic inflammation and malnutrition.

Agreement of central venous saturation and mixed venous saturation in cardiac surgery patients

OBJECTIVE

Comparison of the bias and the limits of agreement (LOA; 2 SD) of the central venous saturation (S(cv)O(2)) before, during and after coronary artery bypass graft surgery with a simultaneous measurement of the mixed venous saturation (S(v)O(2)).

DESIGN AND SETTING

Prospective controlled study in a university hospital department of anaesthesiology.

PATIENTS

60 patients with coronary artery bypass surgery, 300 paired measurements of S(v)O(2) and S(cv)O(2).

MEASUREMENTS AND RESULTS

S(cv)O(2) and S(v)O(2) were analysed after induction of anaesthesia 15 min after cardiopulmonary bypass and 1, 6 and 18 h after admission to the intensive care unit. Regression analysis for the pooled measurements of S(cv)O(2) and S(v)O(2) showed a correlation R (2) = 0.52. After induction of anaesthesia 15 min after weaning from cardiopulmonary bypass and 6 h after admission to the intensive care unit the correlation coefficient was R (2) = 0.46, on admission to the intensive care unit it was R (2) = 0.42, and at 18 h it was R (2) = 0.38. Bland-Altman analysis for the measurements of S(cv)O(2) and S(v)O(2) showed a mean bias and LOA of 0.3% and -11.9 to +12.4%. In patients with a low S(cv)O(2) there was a trend to overestimate the S(v)O(2) by using the S(cv)O(2). The only factor that influenced the DeltaS(v)O(2) - S(cv)O(2) was the oxygen extraction rate (R (2) = 0.16). In patients with S(cv)O(2) below 70% this association was more pronounced (R (2) = 0.60).

CONCLUSIONS

Our findings demonstrate that oxygen extraction rate is the major factor in the difference between S(v)O(2) and S(cv)O(2). Under certain circumstances S(cv)O(2) differed substantially from S(v)O(2). Therefore in selected patients both parameters should be monitored to exclude general or focal hypoperfusion.

Barrier function of the gut and multiple organ dysfunction after cardiac surgery

We studied the influence of sequential involvement of the gastrointestinal (GI) tract on the development of multiple organ dysfunction (MOD) after cardiopulmonary bypass (CPB). One hundred and forty-six patients undergoing elective cardiac surgery were included in this prospective observational study. Standardized oral inert-sugar tests (sucrose, lactulose, mannitol, sucralose) were performed before and after CPB in different patients. Enzyme-linked immunosorbent assay of plasma levels of endotoxin core antibodies (EndoCAb) were performed peri-operatively. The functional mucosal surface was calculated from the amount of mannitol absorbed from the GI tract. Lower urine concentrations of absorbed mannitol were observed pre-operatively in patients developing MOD. In binary logistic regression this was an independent parameter. Decreased plasma concentrations of EndoCAb after surgery were seen in every patient, but were more significant in patients developing MOD. A reduced pre-operative functional mucosal surface may predict the early occurrence of MOD after surgery.

Measurements of Optical Pathlength Using Phase-Resolved Spectroscopy in Patients Undergoing Cardiopulmonary Bypass

BACKGROUND

Near infrared spectroscopy (NIRS) has been used during cardiac surgery to monitor cerebral oxygenation although the validity of this technique has yet to be established. Although optical pathlength included in the algorithm for calculating NIRS values is supposed to be constant, recent evidence has suggested that optical pathlength could be affected by acute hemodilution in animals. We conducted the present study to investigate whether optical pathlength changes during cardiopulmonary bypass (CPB), and whether these changes affect NIRS values in adult patients.

METHODS

Nine patients undergoing elective cardiac surgery with CPB were enrolled in this study. Optical pathlength and cerebral NIRS values (oxyhemoglobin [DeltaO(2)Hb] and tissue oxygen index) were measured by phase-resolved spectroscopy and NIRO 100, respectively. Optical pathlength, hemoglobin concentration, and NIRS values were measured at the following points: 1) after the induction of anesthesia, 2) 10 min after the start of CPB, 3) 60 min after the start of CPB, and 4) 1 h after CPB. The associations between optical pathlength and other variables were analyzed by Pearson correlation coefficients and multiple regression analysis.

RESULTS

Optical pathlength significantly increased starting at 27.7-30.8 cm at 10 min, and 31.3 cm at 60 min after the start of CPB (P < 0.0001). Hemoglobin concentrations significantly decreased (from 11.2 to 7.1 g/dL at 10 min and 7.7 g/dL at 60 min P < 0.0001). There was a significant correlation (r = 0.55, P < 0.001) between percentage changes in pathlength and hemoglobin concentration. Multiple regression analysis showed that optical pathlength was a significant determinant of DeltaO2Hb.

CONCLUSION

The results indicate that optical pathlength can change during CPB and its changes may affect DeltaO2Hb.

Arterio-venous gradients of free energy change for assessment of systemic and splanchnic perfusion in cardiac surgery patients

Objective: Adequacy of organ perfusion depends on sufficient oxygen supply in relation to the metabolic needs. The aim of this study was to evaluate the relationship between gradients of free energy change, and the more commonly used parameter for the evaluation of the adequacy of organ perfusion, such as oxygen-extraction in patients undergoing valve replacement surgery using normothermic cardiopulmonary bypass (CPB).

Methods: In 43 cardiac patients, arterial, mixed venous, and hepato-venous blood samples were taken synchronously after induction of anaesthesia (preCPB), during CPB, and 2 and 7 h after admission to the intensive care unit (ICU+2, ICU+7). Blood gas analysis, cardiac output, and hepato-splanchnic blood flow were measured. Free energy change gradients between mixed venous and arterial (-ΔΔG(v-a)) and hepato-venous and arterial (-ΔΔG(hv-a)) compartments were calculated.

Measurements and results: Cardiac index (CI) increased from 1.9 (0.7) to 2.8 (1.3) L/min/m (median, inter-quartile range) (p =0.001), and hepato-splanchnic blood flow index (HBFI) from 0.6 (0.22) to 0.8 (0.53) L/min/m (p =0.001). Despite increasing flow, systemic oxygen extraction increased after CPB from 24 (10)% to 35 (10)% at ICU+2 (p =0.002), and splanchnic oxygen extraction increased during CPB from 37 (19)% to 52 (14)% (p =0.001), and remained high thereafter. After CPB, high splanchnic and systemic gradients of free energy change gradients were associated with high splanchnic and systemic oxygen extraction, respectively (p =0.001, 0.033, respectively).

Conclusion: Gradients of free energy change may be helpful in characterising adequacy of perfusion in cardiac surgery patients independently from measurements or calculations of data from oxygen transport.

Clonidine attenuated early proinflammatory response in T-cell subsets after cardiac surgery

T-cells play a central role in the immune response to injury. Cardiac surgery is associated with significant risk of systemic inflammatory response syndrome and subsequent unbalanced induction of proinflammatory cytokines. As clonidine has immunomodulating properties via reducing sympathetic activity, this study involved the analysis of T-cell function in the early postoperative period in patients undergoing coronary artery bypass graft surgery. Forty patients undergoing cardiac surgery were randomly allocated to one of the following groups: clonidine group (n = 20) [clonidine 1 microg kg(-1) h(-1)] and placebo group (n = 20). Study medication was started after induction of anesthesia and maintained until 6 h after surgery. Blood samples to determine Th1 and Th2 cells and cytotoxic lymphocytes (Tc1 and Tc2 cells) were drawn preoperatively, on admission to the intensive care unit, 6 and 12 h postoperatively as well as on the morning of days 1 and 2 after surgery. In the clonidine group significantly lower levels of Th1/Th2 ratios as well as Tc1/Tc2 ratios were found 6 h postoperatively compared to the placebo group (P < 0.05). Clonidine changed the ratio of T-lymphocyte subpopulations in peripheral blood in favor of a proinflammatory response, which might be favorable for maintaining immune balance after surgery.

Pulsatile Versus Nonpulsatile Cardiopulmonary Bypass Flow: An Evidence-Based Approach

OBJECTIVE

To derive evidence-based recommendations for the use of pulsatile perfusion (PP) technique for the reduction of mortality and nonfatal complications after elective coronary artery bypass grafting surgery (CABG).

OUTCOMES

Incidence of total mortality, myocardial infarction (MI), stroke, and renal failure during hospital stay.

EVIDENCE

Medline, Embase, and the Cochrane controlled trial register (CCTR) on the Cochrane library were searched from the earliest achievable date of each database to March 2005. No language restrictions were applied. Retrieved reprints were evaluated according to a priori inclusion criteria, and those included were critically appraised using established internal validity criteria. BENEFITS AND HARMS: Only one fair quality randomized controlled trial demonstrated the beneficial effect of PP in reducing the incidence of total mortality and MI. No studies demonstrated the beneficial effect of PP in reducing the incidence of stoke or renal failure. One randomized controlled trial demonstrated that PP was associated with increased hemolysis compared to nonpulsatile (NP) perfusion.

CONCLUSION

The evidence is conflicting and therefore does not support making recommendation for or against routinely providing the PP to reduce the incidence of mortality or MI. The evidence is insufficient to recommend for or against routinely providing the pulsatile profusion to reduce the incidence of stroke or renal failure.

Gastrointestinal failure in intensive care: a retrospective clinical study in three different intensive care units in Germany and Estonia

Background

While gastrointestinal problems are common in ICU patients with multiple organ failure, gastrointestinal failure has not been given the consideration other organ systems receive. The aim of this study was to evaluate the incidence of gastrointestinal failure (GIF), to identify its risk factors, and to determine its association with ICU mortality.

Methods

A retrospective analysis of adult patients (n = 2588) admitted to three different ICUs (two ICUs at the university hospital Charité-Universitätsmedizin Berlin, Germany and one at Tartu University Clinics, Estonia) during the year 2002 was performed.

Data recorded in a computerized database were used in Berlin. In Tartu, the data documented in the patients' charts was retrospectively transferred into a similar database. GIF was defined as documented gastrointestinal problems (food intolerance, gastrointestinal haemorrhage, and/or ileus) in the patient data at any period of their ICU stay. ICU mortality, length of stay, and duration of mechanical ventilation were assessed as outcome parameters.

Results

GIF was identified in 252 patients (9.7% of all patients). Only 20% of GIF patients were identifiable at admission. GIF was related to significantly higher mortality (43.7% vs. 5.3% in patients without GIF), as well as prolonged length of ICU stay (10 vs. 2 days) and mechanical ventilation (8 vs. 1 day), p < 0.001, respectively. Patients' profile (emergency surgical or medical), APACHE II and SOFA scores and the use of catecholamines at admission were identified as independent risk factors for the development of GIF. Development of GIF during ICU stay was an independent predictor for death.

Conclusion

Gastrointestinal failure represents a relevant clinical problem accompanied by an increased mortality, longer ICU stay and mechanical ventilation.

Gastric intramucosal perfusion during descending aortic repair under femoro-femoral bypass

The changes in gastric mucosal perfusion during distal aortic perfusion with femoro-femoral bypass (F-F bypass) were assessed by air-automated gastric tonometry. A prospective study was performed in six patients who underwent descending aortic surgery for aortic aneurysm under F-F bypass with mild hypothermia (34 degrees C). Gastric intramucosal pH (pHi) and PaCO2-PgCO2 gap (PCO2 gap) were measured. Data are presented as means and standard deviations and analyzed by using one-way analysis of variance followed by Scheffe test. Perioperative variables of hepatorenal functions are also evaluated. The PCO2 gap significantly increased during F-F bypass (3.0 +/- 2.1 mm Hg at control, 14.2 +/- 5.5 mm Hg during F-F bypass; p = 0.004), indicating abnormal gastric mucosal perfusion during F-F bypass. Significantly low pHi was found at weaning from F-F bypass (7.35 +/- 0.05 at control, 7.21 +/- 0.10 at weaning; p = 0.009), which might be related to progressing systemic metabolic acidosis. No impairment of hepatorenal functions was observed after the surgery. Distal perfusion with F-F bypass during descending aortic surgery could impair the gastric mucosal perfusion, but may have little effect on postoperative visceral dysfunction.

Small-dose epoprostenol decreases systemic oxygen consumption and splanchnic oxygen extraction during normothermic cardiopulmonary bypass

Normothermic, nonpulsatile cardiopulmonary bypass (CPB) impairs systemic and splanchnic oxygen transport and increases gastrointestinal permeability. It is an important therapeutic goal to avoid splanchnic dysoxia during CPB. Small-dose prostacyclin therapy improves splanchnic oxygen transport and microcirculation in septic patients. In this study, we sought to determine if during cardiac surgery, the prostacyclin analog epoprostenol improves the balance of systemic and splanchnic oxygen transport. Eighteen patients undergoing cardiac valve replacement were randomized to receive either epoprostenol (3 ng x kg(-1) x min(-1)) or placebo during, and for 1 hour after, surgery. Systemic and splanchnic oxygen delivery, consumption, and extraction and arterial, mixed venous, and hepato-venous lactate concentrations were measured before, during, and after CPB. Gastrointestinal permeability was measured 1 day before and 1 day after surgery using the triple sugar permeability test. During CPB, the epoprostenol group had decreased systemic oxygen consumption and splanchnic oxygen extraction (P = 0.024). These effects were not present 1 hour after the end of epoprostenol infusion. The study was not adequately powered to determine whether epoprostenol altered the trend towards increased lactate metabolism and increased postoperative gastrointestinal permeability, nor could we demonstrate any differences between groups in clinically relevant end-points. In conclusion, these findings suggest that during normothermic CPB, small-dose epoprostenol therapy may reduce systemic oxygen consumption and splanchnic oxygen extraction.