A study of size-selective renal elimination using a novel human model

The recently discovered selective glomerular hypofiltration syndromes have increased interest in the actual elimination of molecules in the human kidney. In the present study, a novel human model was introduced to directly measure the single-pass renal elimination of molecules of increasing size. Plasma concentrations of urea, creatinine, C-peptide, insulin, pro-BNP, β2-microglobulin, cystatin C, troponin-T, orosomucoid, albumin, and IgG were analysed in arterial and renal venous blood from 45 patients undergoing Transcatheter Aortic Valve Implantation (TAVI). The renal elimination ratio (RER) was calculated as the arteriovenous concentration difference divided by the arterial concentration. Estimated glomerular filtration rate (eGFR) was calculated by the CKD-EPI equations for both creatinine and cystatin C. Creatinine (0.11 kDa) showed the highest RER (21.0 ± 6.3%). With increasing molecular size, the RER gradually decreased, where the RER of cystatin C (13 kDa) was 14.4 ± 5.3% and troponin-T (36 kDa) was 11.3 ± 4.6%. The renal elimination threshold was found between 36 and 44 kDa as the RER of orosomucoid (44 kDa) was -0.2 ± 4.7%. The RER of creatinine and cystatin C showed a significant and moderate positive linear relationship with eGFR (r = 0.48 and 0.40). In conclusion, a novel human model was employed to demonstrate a decline in renal elimination with increasing molecular size. Moreover, RERs of creatinine and cystatin C were found to correlate with eGFR, suggesting the potential of this model to study selective glomerular hypofiltration syndromes.

Interleukin-10: A Potential Pre-Cannulation Marker for Development of Acute Kidney Injury in Patients Receiving Veno-Arterial Extracorporeal Membrane Oxygenation

INTRODUCTION

Acute kidney injury (AKI) in patients treated with veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is associated with high mortality. The objective of this study was to investigate whether cytokine levels before the initiation of ECMO treatment could predict AKI. We also aimed to investigate the impact of AKI on 30-day and 1-year mortality.

METHODS

Serum cytokine levels were analyzed in 100 consecutive VA-ECMO-treated patients at pre-cannulation, at 48 h post-cannulation, and at 8 days. Clinical data to establish the incidence and outcome of AKI after the start of ECMO was retrieved from the local ECMO registry.

SETTING

The study was conducted at tertiary care, university hospital. Participants included 100 patients treated with VA-ECMO.

INTERVENTIONS

The blood samples for cytokine analysis were collected before VA-ECMO treatment, at 48 h after VA-ECMO treatment was started, and at 8 days.

RESULTS

Pre-cannulation serum IL-10 levels were significantly higher in patients who developed AKI (212 [38.9, 620.7]) versus those who did not (49.0 [11.9, 102.2]; p = 0.007), and the development of AKI can be predicted by pre-cannulation IL-10 levels (p = 0.025, OR = 1.2 [1.02-1.32]). The development of AKI during ECMO treatment is associated with increased 30-day mortality (p = 0.049) compared to patients who did not develop AKI and had a pre-cannulation estimated glomerular filtration rate ≥ 45 mL/min. The 1-year survival rate for patients with AKI who survived the first 30 days of ECMO treatment is comparable to that of patients without AKI.

CONCLUSION

Increased pre-cannulation IL-10 levels are associated with the development of AKI during VA-ECMO support. AKI is associated with increased 30-day mortality compared to patients with no AKI and better renal function. However, patients with AKI who survive the first 30 days have a 1-year survival rate similar to those without AKI.

Carbon dioxide flooding to reduce postoperative neurological injury following surgery for acute type A aortic dissection: a prospective, randomised, blinded, controlled clinical trial, CARTA study protocol - objectives and design

INTRODUCTION

Neurological complications after surgery for acute type A aortic dissection (ATAAD) increase patient morbidity and mortality. Carbon dioxide flooding is commonly used in open-heart surgery to reduce the risk of air embolism and neurological impairment, but it has not been evaluated in the setting of ATAAD surgery. This report describes the objectives and design of the CARTA trial, investigating whether carbon dioxide flooding reduces neurological injury following surgery for ATAAD.

METHODS AND ANALYSIS

The CARTA trial is a single-centre, prospective, randomised, blinded, controlled clinical trial of ATAAD surgery with carbon dioxide flooding of the surgical field. Eighty consecutive patients undergoing repair of ATAAD, and who do not have previous neurological injuries or ongoing neurological symptoms, will be randomised (1:1) to either receive carbon dioxide flooding of the surgical field or not. Routine repair will be performed regardless of the intervention. The primary endpoints are size and number of ischaemic lesions on brain MRI performed after surgery. Secondary endpoints are clinical neurological deficit according to the National Institutes of Health Stroke Scale, level of consciousness using the Glasgow Coma Scale motor score, brain injury markers in blood after surgery, neurological function according to the modified Rankin Scale and postoperative recovery 3 months after surgery.

ETHICS AND DISSEMINATION

Ethical approval has been granted by Swedish Ethical Review Agency for this study. Results will be disseminated through peer-reviewed media.

TRIAL REGISTRATION NUMBER

NCT04962646.

Reduced renal elimination of larger molecules is a strong predictor for mortality

Renal dysfunction is a major risk factor for premature death and has been studied extensively. A new renal syndrome, shrunken pore syndrome (SPS), confers higher mortality in all studied populations. SPS is a condition in which cystatin C-based estimation of glomerular filtration rate (eGFR_{cystatin C}) is ≥ 60% than creatinine-based estimation of glomerular filtration rate (eGFR_creatinine). We aimed to study the impact of SPS on mortality in a cohort of patients with follow up of up to 10 years. This was a retrospective single centre cohort study. We enrolled 3993 consecutive patients undergoing elective cardiac surgery. Outcome was evaluated using Kaplan Meier analysis and multivariable Cox regression. 1-, 5- and 10-year survival for patients with SPS was 90%, 59% and 45%, and without SPS 98%, 88% and 80% (p < 0.001). SPS was found to be an independent predictor for mortality with an HR of 1.96 (95% CI 1.63-2.36). SPS negatively affected survival regardless of pre-operative renal function. SPS is an independent predictor for mortality after elective cardiac surgery, equal to or greater than risk factors such as diabetes, impaired left ventricular function or renal dysfunction. SPS affected mortality even in patients with normal eGFR.Clinical registration number: ClinicalTrials.gov, ID NCT04141072.

Effect of Cyclosporine on Cytokine Production in Elective Coronary Artery Bypass Grafting: A Sub-Analysis of the CiPRICS (Cyclosporine to Protect Renal Function in Cardiac Surgery) Study

OBJECTIVES

The augmented inflammatory response to cardiac surgery is a recognized cause of postoperative acute kidney injury. The present study aimed to investigate the effects of preoperative cyclosporine treatment on cytokine production and delineate factors associated with postoperative kidney impairment.

DESIGN

A randomized, double-blind, placebo-controlled, single-center study.

SETTING

At a tertiary care, university hospital.

PARTICIPANTS

Patients eligible for elective coronary artery bypass grafting surgery; 67 patients were enrolled.

INTERVENTIONS

Patients were randomized to receive 2.5 mg/kg cyclosporine or placebo before surgery. Cytokine levels were measured after the induction of anesthesia and 4 hours after the end of cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

Tissue-aggressive (interleukin [IL]-1β, macrophage inflammatory protein [MIP]-1β, granulocyte colony-stimulating factor [G-CSF], IL-6, IL-8, IL-17, MCP-1), as well tissue-lenient (IL-4) cytokines, were significantly elevated in response to surgery. Changes in cytokine levels were not affected by cyclosporine pretreatment.

CONCLUSIONS

Elective coronary artery bypass grafting surgery with cardiopulmonary bypass triggers cytokine activation. This activation was not impacted by preoperative cyclosporine treatment.

Lung transplant after 6 months on ECMO support for SARS-CoV-2-induced ARDS complicated by severe antibody-mediated rejection

There have been a few reports of successful lung transplantation (LTx) in patients with SARS-CoV-2-induced acute respiratory distress syndrome (ARDS); however, all reports were with rather short follow-up. Here we present a 62-year-old man without prior lung diseases. Following SARS-CoV-2-induced ARDS and 6 months of extracorporeal membrane oxygenation, he underwent LTx. 3 months post-transplantation he developed acute hypoxia requiring emergency intubation. Chest imaging showed acute rejection, and de novo DQ8-DSA was discovered. He was treated with a high dose of corticosteroids and plasmapheresis and was extubated 4 days later, yet the de novo DQ8-DSA remained. After sessions of plasmapheresis and rituximab, the levels of de novo DQ8-DSA remained unchanged. Nine months post-transplantation the patient died of respiratory failure. We herein discuss the decision to transplant, the transplantation itself and the postoperative course with severe antibody-mediated rejection. In addition, we evaluated the histological changes of the explanted lungs and compared these with end-stage idiopathic pulmonary fibrosis tissue, where both similarities and differences are seen. With the current case experience, one might consider close monitoring regarding DSA, and gives further support that LTx should only be considered for very carefully selected patients.

Monitoring lung injury with particle flow rate in LPS- and COVID-19-induced ARDS

In severe acute respiratory distress syndrome (ARDS), extracorporeal membrane oxygenation (ECMO) is a life-prolonging treatment, especially among COVID-19 patients. Evaluation of lung injury progression is challenging with current techniques. Diagnostic imaging or invasive diagnostics are risky given the difficulties of intra-hospital transportation, contraindication of biopsies, and the potential for the spread of infections, such as in COVID-19 patients. We have recently shown that particle flow rate (PFR) from exhaled breath could be a noninvasive, early detection method for ARDS during mechanical ventilation. We hypothesized that PFR could also measure the progress of lung injury during ECMO treatment. Lipopolysaccharide (LPS) was thus used to induce ARDS in pigs under mechanical ventilation. Eight were connected to ECMO, whereas seven animals were not. In addition, six animals received sham treatment with saline. Four human patients with ECMO and ARDS were also monitored. In the pigs, as lung injury ensued, the PFR dramatically increased and a particular spike followed the establishment of ECMO in the LPS-treated animals. PFR remained elevated in all animals with no signs of lung recovery. In the human patients, in the two that recovered, PFR decreased. In the two whose lung function deteriorated while on ECMO, there was increased PFR with no sign of recovery in lung function. The present results indicate that real-time monitoring of PFR may be a new, complementary approach in the clinic for measurement of the extent of lung injury and recovery over time in ECMO patients with ARDS.

Ciclosporin to Protect Renal function In Cardiac Surgery (CiPRICS): a study protocol for a double-blind, randomised, placebo-controlled, proof-of-concept study

INTRODUCTION

Acute kidney injury (AKI) after cardiac surgery is common and results in increased morbidity and mortality. One possible mechanism for AKI is ischaemia-reperfusion injury caused by the extracorporeal circulation (ECC), resulting in an opening of the mitochondrial permeability transition pore (mPTP) in the kidneys, which can lead to cell injury or cell death. Ciclosporin may block the opening of mPTP if administered before the ischaemia-reperfusion injury. We hypothesised that ciclosporin given before the start of ECC in cardiac surgery can decrease the degree of AKI.

METHODS AND ANALYSIS

Ciclosporin to Protect Renal function In Cardiac Surgery (CiPRICS) study is an investigator-initiated double-blind, randomised, placebo-controlled, parallel design, single-centre study performed at a tertiary university hospital. The primary objective is to assess the safety and efficacy of ciclosporin to limit the degree of AKI in patients undergoing coronary artery bypass grafting surgery. We aim to evaluate 150 patients with a preoperative estimated glomerular filtration rate of 15-90 mL/min/1.73 m². Study patients are randomised in a 1:1 ratio to receive study drug 2.5 mg/kg ciclosporin or placebo as an intravenous injection after anaesthesia induction but before start of surgery. The primary end point consists of relative P-cystatin C changes from the preoperative day to postoperative day 3. The primary variable will be tested using an analysis of covariance method. Secondary end points include evaluation of P-creatinine and biomarkers of kidney, heart and brain injury.

ETHICS AND DISSEMINATION

The trial is conducted in compliance with the current version of the Declaration of Helsinki and the International Council for Harmonisation (ICH) Good Clinical Practice guidelines E6 (R1) and was approved by the Regional Ethical Review Board, Lund and the Swedish Medical Products Agency (MPA). Written and oral informed consent is obtained before enrolment into the study.

TRIAL REGISTRATION NUMBER

NCT02397213; Pre-results.

The predictive value of s-cystatin C for mortality after coronary artery bypass surgery

OBJECTIVES

To evaluate serum creatinine (s-creatinine) and serum cystatin C (s-cystatin C) levels and estimated glomerular filtration rate (eGFR) at different time points as predictors for mortality in patients undergoing coronary artery bypass grafting (CABG).

METHODS

A total of 1638 patients undergoing elective CABG were studied prospectively over a median follow-up of 3.5 years (range, 2.0-5.0 years). Renal function was assessed by a comparison of s-creatinine, s-cystatin C values measured preoperatively and at the lowest postoperative level of renal function. The eGFR was estimated by different formulas: Modification of Diet in Renal Disease, the 2009 Chronic Kidney Disease Epidemiology (CDK-EPI) for s-creatinine, the 2012 CKD-EPI formula for s-cystatin C, the 2012 CKD-EPI formula for s-cystatin C and s-creatinine in combination, and the Caucasian Asian, Pediatric, and Adult subjects formula for s-cystatin C. Cox proportional hazards model analysis and C-statistics were used to evaluate independent predictors of mortality and to assess the predictive ability of the different renal function measures.

RESULTS

The 30-day mortality was 0.8%. Overall survival was 96.1% ± 0.4% at 2 years and 90.0% ± 1.2% at 5 years. Preoperative s-cystatin C showed greater predictive power than s-creatinine for overall mortality (area under the curve, 0.794 vs 0.653). Preoperative s-cystatin C (hazard ratio [HR], 1.65; 95% confidence interval [CI], 1.36-1.99) and eGFR based on s-cystatin C (HR, 0.96; 95% CI, 0.95-0.98), were both independent predictors of mortality. The unadjusted HR for mortality comparing the lowest preoperative cystatin C quintile (Q1) with Q4-Q5 were as follows: Q1 versus Q5, HR, 2.0; 95% CI, 1.6-2.5 (P < .001); Q1 versus Q4, HR, 1.6; 95% CI, 1.2-2.2 (P = .005).

CONCLUSIONS

The s-cystatin C level and s-cystatin C-based eGFR measured preoperatively are strong predictors for mortality after elective CABG.

Incidence, dynamics, and prognostic value of acute kidney injury for death after cardiac surgery

OBJECTIVE

This study relates long-term mortality after cardiac surgery to different methods of measuring postoperative renal function, classified according to the Risk, Injury, Failure, Loss, and End-stage (RIFLE) criteria. The dynamics of acute kidney injury during hospital stay were studied by comparing renal function preoperatively, at its poorest measurement, and at discharge.

METHODS

A total of 5746 patients undergoing coronary artery bypass grafting were studied in a Cox analysis, over a median follow-up time of 6.0 years (range, 2.5-9.5 years). Renal function was determined using the highest and discharge levels of plasma creatinine by Cockroft-Gault and Modification of Diet in Renal Disease formulae. Acute kidney injury was classified according to the RIFLE criteria. Renal recovery was studied in a 2-dimensional matrix, and the impact of renal function at different time points was related to survival.

RESULTS

Although the p-creatinine classified most patients in the nonacute kidney injury and Risk class; the Cockroft-Gault and Modification of Diet in Renal Disease formulae classified more patients in Injury and Failure classes; and higher Risk, Injury, and Failure classes were associated with increased long-term mortality. The effect of renal recovery on long-term survival was only in part associated with improved outcome. In addition, the poorest renal function was a stronger predictor of mortality compared with preoperative and discharge levels.

CONCLUSIONS

Classification using RIFLE criteria seems to be useful because it detects patients with renal impairment that affects long-term survival. The Modification of Diet in Renal Disease method seems to be the most robust method when predicting outcome, and the poorest renal function was the best predictor of outcome. Renal recovery was generally associated with better outcome.

Risks associated with the transfusion of various blood products in aortic valve replacement

BACKGROUND

Patients undergoing cardiac operations often require transfusions of red blood cells, plasma, and platelets. From a statistical point of view, there is a significant collinearity between the components, but they differ in indications for use and composition. This study explores the relationship between the transfusion of different blood components and long-term mortality in patients undergoing aortic valve replacement alone or combined with revascularization.

METHODS

A retrospective single-center study was performed including 1,311 patients undergoing aortic valve replacement. Patients who received more than 7 units of red blood cells, those who died early (7 days), and emergency cases were excluded. Patients were monitored for up to 9.5 years. A broad selection of potential risk factors were analyzed using Cox proportional hazards regression, where transfusion of red blood cells, plasma, and platelets were forced to remain in the model.

RESULTS

The transfusion of red blood cells was not associated with decreased long-term survival (hazard ratio [HR], 1.01; p = 0.520) nor was the transfusion of platelets (HR, 0.946; p = 0.124); however, the transfusion of plasma was (HR, 1.041; p < 0.001). All HRs are per unit of blood product transfused. No increased risk was found for patients undergoing a combined procedure.

CONCLUSIONS

No significant risk for long-term mortality was associated with transfusion of red blood cells during the study period. However, the transfusion of plasma was associated with increased mortality.

Blood transfusion after cardiac surgery: is it the patient or the transfusion that carries the risk?

BACKGROUND

The transfusion of red blood cells (RBCs) after cardiac surgery has been associated with increased long-term mortality. This study reexamines this hypothesis by including pre-operative hemoglobin (Hb) levels and renal function in the analysis.

METHODS

A retrospective single-center study was performed including 5261 coronary artery bypass grafting (CABG) patients in a Cox proportional hazard survival analysis. Patients with more than eight RBC transfusions, early death (7 days), and emergent cases were excluded. Patients were followed for 7.5 years. Previously known risk factors were entered into the analysis together with pre-operative Hb and estimated glomerular filtration rate (eGFR). In addition, subgroups were formed based on the patients' pre-operative renal function and Hb levels.

RESULTS

When classical risk factors were entered into the analysis, transfusion of RBCs was associated with reduced long-term survival. When pre-operative eGFR and Hb was entered into the analysis, however, transfusion of RBCs did not affect survival significantly. In the subgroups, transfusion of RBCs did not have any effect on long-term survival.

CONCLUSIONS

When pre-operative Hb levels and renal function are taken into account, moderate transfusions of RBC after CABG surgery do not seem to be associated with reduced long-term survival.

Evaluation of cystatin C with iohexol clearance in cardiac surgery

BACKGROUND

Post-operative renal dysfunction after cardiac surgery is not uncommon and can lead to adverse outcome. The ability to accurately monitor renal function is therefore important. Cystatin C is known to be a sensitive marker of the glomerular filtration rate (GFR), but it has not been fully evaluated in cardiac surgery. Iohexol clearance is considered a reliable reference method for the determination of GFR. The aim of this study is to, for the first time, evaluate the diagnostic accuracy of plasma cystatin C compared with iohexol clearance in cardiac surgery.

METHODS

Twenty-one patients scheduled for elective coronary artery bypass grafting were prospectively enrolled in the study. Before surgery and on the second post-operative day, an iohexol clearance was performed. Plasma cystatin C, plasma creatinine and plasma C-reactive protein were determined before surgery and on the first, second, third and fifth post-operative day. Estimated creatinine and cystatin C clearances were determined.

RESULTS

Post-operative cystatin C and 1/cystatin C correlated strongly to iohexol clearance (r=-0.90 and 0.86) and so did creatinine and 1/creatinine (r=-0.83 and 0.78). Estimated creatinine clearance differed from iohexol clearance (P<0.01), whereas estimated cystatin C clearance did not differ from iohexol clearance (P=0.81). No correlation was found between C-reactive protein and cystatin C.

CONCLUSION

This study indicates that clearance estimations based on cystatin C are more accurate compared with estimations based on creatinine in determining GFR in cardiac surgery. Cystatin C has, in this study population, a stronger correlation to iohexol clearance than creatinine.

The influence of age on the distribution of morphine and morphine-3-glucuronide across the blood-brain barrier in sheep

BACKGROUND AND PURPOSE

The effect of age on the distribution of morphine and morphine-3-glucuronide (M3G) across the blood-brain barrier (BBB) was studied in a sheep model utilizing intracerebral microdialysis. The effect of neonatal asphyxia on brain drug distribution was also studied.

EXPERIMENTAL APPROACH

Microdialysis probes were inserted into the cortex, striatum and blood of 11 lambs (127 gestation days) and six ewes. Morphine, 1 mg x kg(-1), was intravenously administered as a 10 min constant infusion. Microdialysis and blood samples were collected for up to 360 min and analysed using liquid chromatography-tandem mass spectrometry. The half-life, clearance, volume of distribution, unbound drug brain : blood distribution ratio (K(p,uu)) and unbound drug volume of distribution in brain (V(u,brain)) were estimated.

KEY RESULTS

Morphine K(p,uu) was 1.19 and 1.89 for the sheep and premature lambs, respectively, indicating that active influx into the brain decreases with age. Induced asphyxia did not affect transport of morphine or M3G across the BBB. Morphine V(u,brain) measurements were higher in sheep than in premature lambs. The M3G K(p,uu) values were 0.27 and 0.17 in sheep and premature lambs, indicating a net efflux from the brain in both groups.

CONCLUSIONS AND IMPLICATIONS

The morphine K(p,uu) was above unity, indicating active transport into the brain; influx was significantly higher in premature lambs than in adult sheep. These results in sheep differ from those in humans, rats, mice and pigs where a net efflux of morphine from the brain is observed.

Blood-brain barrier transport of morphine in patients with severe brain trauma

AIMS

In experimental studies, morphine pharmacokinetics is different in the brain compared with other tissues due to the properties of the blood-brain barrier, including action of efflux pumps. It was hypothesized in this clinical study that active efflux of morphine occurs also in human brain, and that brain injury would alter cerebral morphine pharmacokinetics.

METHODS

Patients with traumatic brain injury, equipped with one to three microdialysis catheters in the brain and one in abdominal subcutaneous fat for metabolic monitoring, were studied. The cerebral catheter locations were classified as 'better' and 'worse' brain tissue, referring to the degree of injury. Morphine (10 mg) was infused intravenously over a 10-min period in seven patients in the intensive care setting. Tissue and plasma morphine concentrations were obtained during the subsequent 3-h period with microdialysis and regular blood sampling.

RESULTS

The area under the concentration-time curve (AUC) ratio of unbound morphine in brain tissue to plasma was 0.64 (95% confidence interval 0.40, 0.87) in 'better' brain tissue (P < 0.05 vs. the subcutaneous fat/plasma ratio), 0.78 (0.49, 1.07) in 'worse' brain tissue and 1.00 (0.86, 1.13) in subcutaneous fat. The terminal half-life and T(max) were longer in the brain vs. plasma and fat, respectively. The relative recovery for morphine was higher in 'better' than in 'worse' brain tissue. The T(max) value tended to be shorter in 'worse' brain tissue.

CONCLUSIONS

The unbound AUC ratio below unity in the 'better' human brain tissue demonstrates an active efflux of morphine across the blood-brain barrier. The 'worse' brain tissue shows a decrease in relative recovery for morphine and in some cases also an increase in permeability for morphine over the blood-brain barrier.

Altered brain exposure of morphine in experimental meningitis studied with microdialysis

BACKGROUND

During pathologic conditions such as meningitis and traumatic brain injury the function of the blood-brain barrier (BBB) is disturbed. In the present study we examined the cerebral pharmacokinetic pattern of morphine in the intact brain and during experimentally induced meningitis using a pig model. Secondly, the use of intracerebral microdialysis as a potential tool for monitoring damage in the BBB by studying the pharmacokinetics of morphine is addressed.

METHODS

Six pigs were studied under general anaesthesia. One occipital and two frontal microdialysis probes and one pressure transducer were inserted into the brain tissue. Another probe was placed into the jugularis interna. Morphine 1 mg kg(-1) was administered as a 10-min infusion, and morphine concentrations were then measured for 3 h. Meningitis was subsequently induced by injecting lipopoly-saccharide into the cisterna magna. When meningitis was established, the morphine experiment was repeated.

RESULTS

The unbound area under the concentration-time curve (AUCu) ratio of morphine in brain to blood was 0.47 (0.19) during the control period, and 0.95 (0.20) (P < 0.001) during meningitis. The increase in the brain/blood AUCu ratio during meningitis implies decreased active efflux and increased passive diffusion of morphine over the BBB. The half-life of morphine in brain was longer than in blood during both periods, and was unaffected by meningitis.

CONCLUSION

This study demonstrates that the morphine exposure to the brain is significantly increased during meningitis as compared with the control situation.

Correlation between blood glucose concentration and glucose concentration in subcutaneous adipose tissue evaluated with microdialysis during intensive care

BACKGROUND

Hyper- as well as hypoglycemia may be detrimental for brain energy metabolism and even a moderate increase in blood glucose concentration can affect outcome adversely. During physiological conditions, glucose concentration obtained from microdialysis of subcutaneous adipose tissue adequately reflects plasma glucose concentration. This study examines whether this correlation is also obtained during intensive care in patients with severe injuries.

METHODS

The study included 62 patients with severe traumatic brain injuries. All patients received one 30 mm microdialysis catheter (CMA 60, CMA Microdialysis) inserted into periumbilical subcutaneous adipose tissue. The probe was perfused (0.3 microl/min) with a Ringer solution from a microinfusion pump and analyzed for glucose, lactate, and glycerol. The study included 2.434 simultaneous analyses of glucose concentration in arterial blood and subcutaneous adipose tissue.

RESULTS

The correlation coefficient for glucose concentration in blood and interstitial fluid was 0.743 for the whole material. The correlation was relatively poor for 1-6 h after insertion of the probes. During this period, a continuous increase in the subcutaneous level of glucose and decreases in lactate and glycerol were noted.

CONCLUSIONS

The correlation between blood glucose concentration and glucose concentration in subcutaneous adipose tissue was not as good during intensive care as in normal humans. The poor correlation during the first 6 h probably reflects a stress reaction (and possibly local vasoconstriction). Microdialysis of subcutaneous adipose tissue permits frequent bedside analyses of the biochemical composition of the extracellular fluid and may be of value during routine intensive care provided the methodological limitations are recognized.

Experimental pancreatitis causes acute perturbation of energy metabolism in the intestinal wall

INTRODUCTION

The systemic inflammatory response syndrome (SIRS) may be initiated by a number of underlying conditions such as acute pancreatitis. The association between the local inflammatory reaction, the systemic response, and potential concomitant dysfunction of remote organs is not quite clear.

AIM

To evaluate whether severe acute pancreatitis in the rat affects energy metabolism in the pancreas and whether the focal inflammation also causes biochemical deterioration in remote organs such as the liver and intestine.

METHODOLOGY

With the patient under general anesthesia, microdialysis probes were inserted in the pancreas, liver, and small intestine. Two groups of eight rats each were studied: the sham (control) group and the pancreatitis group. Acute pancreatitis was induced by intraductal injection of 5% sodium taurodeoxycholate, and the animals were studied for 3 hours thereafter. The microdialysis fluid was analyzed for glucose, lactate, and pyruvate.

RESULTS

In the pancreatitis group we found significant increases in glucose concentration in the pancreas and lactate levels in the pancreas and intestinal wall, and the lactate/pyruvate ratio was significantly higher in the intestine than in the sham group.

CONCLUSION

Induction of severe acute pancreatitis results in immediate metabolic alterations in the pancreas. In the intestinal wall a severe perturbation of energy metabolism is observed after only 1 hour. This implies a rapid onset of metabolic disturbances, not only in the local, challenged organ (pancreas) but also in remote organs.

Local metabolic changes in subcutaneous adipose tissue during intravenous and epidural analgesia

BACKGROUND

This clinical study aimed at investigating the impact of postoperative thoracic epidural analgesia on extracellular glycerol concentration and glucose metabolism in subcutaneous adipose tissue, using the microdialysis technique. The sympathetic nervous activity, which can be attenuated by epidural anesthesia, influences lipolysis and the release of glycerol.

METHODS

Fourteen patients who underwent major abdominal or thoraco-abdominal surgery were studied postoperatively over 3 days. For postoperative analgesia the patients were prospectively randomized to receive either thoracic epidural analgesia with a bupivacaine/morphine infusion (EPI-group, n=6) or a continuous i.v. infusion of morphine (MO-group, n=8). The concentration of glycerol, glucose and lactate in the abdominal and deltoid subcutaneous adipose tissue were measured using a microdialysis technique.

RESULTS

The abdominal glycerol levels were equal in both groups. In the deltoid region of the EPI-group, glycerol concentrations started to increase on Day 2, and reached significantly higher levels on Day 3 compared with the MO-group. The glucose and lactate levels showed no differences between groups in the two regions.

CONCLUSION

The uniform glycerol levels in abdominal subcutaneous adipose tissue in conjunction with the difference in glycerol levels in the deltoid area indicate that the local lipolysis is different in the two study groups. This might be explained by a regional metabolic influence of thoracic epidural analgesia, possibly via the sympathetic nervous system.

Increased blood-brain barrier permeability of morphine in a patient with severe brain lesions as determined by microdialysis

Intracerebral microdialysis was utilised to obtain information regarding how morphine is transported across the blood-brain barrier (BBB). In a patient with a severe brain injury, we measured simultaneously unbound extracellular fluid (ECF) concentrations of morphine in human brain and in subcutaneous fat tissue, which were compared to morphine levels in arterial blood. This report shows an increase in morphine levels near the trauma site in the brain compared to uninjured brain tissue. The half-life of morphine in uninjured and injured brain tissue of 178 min and 169 min, respectively, were comparable but were longer than in blood (64 min) and adipose tissue (63 min). This indicates that morphine is retained in brain tissue for a longer time than what could be expected from the blood concentration-time profile. These results show the potential of the microdialysis technique in providing new information regarding the pharmacokinetics of drug in the human brain close to the trauma site and in macroscopically intact tissue.