Apparent heterogeneity of regional blood flow and metabolic changes within splanchnic tissues during experimental endotoxin shock

The impact of endotoxin on jejunal tissue oxygenation

OBJECTIVE

We examined the effects of systemic ETX on jejunal mucoal microcirculatory parameters in anesthetized pigs.

METHODS

Jejunal mucosal tissue PO₂ was measured employing Clark-type surface oxygen electrodes. Oxygen saturation of jejunal microvascular hemoglobin was determined by tissue reflectance spectrophotometry. Jejunal microcirculatory blood flow was assessed by laser Doppler flowmetry. Microvascular conductance and rhythmical oscillation of the tissue PO₂ were calculated. Systemic hemodynamic variables, mesenteric venous and systemic acid base and blood gas variables, and lactate measurements were recorded. Measurements were taken at BL and after Escherichia coli LPS administration in 20 minutes intervals for 110 minutes.

RESULTS

ETX infusion led to a significant (P<.05) decrease of PO₂ muc (from 24±4 to 8±4 mm Hg) and microvascular HbO₂ (from 41±13 to 24±12%). Microcirculatory conductivity increased in ETX animals, microvascular blood flow remained unchanged (PU; from 228±45 to 232±58). ETX induced an increase in oscillation frequency of mucosal tissue oxygenation.

CONCLUSIONS

Endotoxinemia resulted in a significant depression of mucosal tissue oxygenation despite a constant microcirculatory blood flow. This impairment of tissue oxygenation resulted in an increase in the vasomotion pattern in a futile attempt to counteract the undersupply of oxygen to the jejunal tissue.

Validation of intraluminal and intraperitoneal microdialysis in ischemic small intestine

BACKGROUND

We sought to define the sensitivity and specificity of intraperitoneal (IP) and intraluminal (IL) microdialysate metabolites in depicting ex vivo small intestinal total ischemia during GI-tract surgery. We hypothesized that IL as opposed to IP microdialysis detects small intestinal ischemia with higher sensitivity and specificity.

METHODS

IL and IP microdialysate lactate, pyruvate, glucose and glycerol were analysed from small intestine of pancreaticoduodenectomy patients before and after occluding the mesenteric vasculature and routine resection of a segment of small intestine. Ex vivo time sequences of microdialysate metabolites were described and ROC analyses after 0-30, 31-60, 61-90 and 91-120 minutes after the onset ischemia were calculated.

RESULTS

IL lactate to pyruvate ratio (L/P ratio) indicated ischemia after 31-60 minutes with 0.954 ROC AUC (threshold: 109) in contrast to IP L/P (ROC AUC of 0.938 after 61-90 minutes, threshold: 18). At 31-60 minutes IL glycerol concentration indicated ischemia with 0.903 ROC AUCs (thresholds: 69 μmol/l). IP glycerol was only moderately indicative for ischemia after 91-120 minutes with 0,791 ROC AUCs (threshold 122 μmol/l). After 31-60 minutes IL and IP lactate to glucose ratios (L/G ratio) indicated ischemia with 0.956 and 0,942 ROC AUCs (thresholds: 48,9 and 0.95), respectively.

CONCLUSIONS

The results support the hypothesis that intraluminal application of microdialysis and metabolic parameters from the small intestinal lumen indicate onset of ischemia earlier than intraperioneal microdialysis with higher sensitivity and specificity.

Moderate intra-abdominal hypertension is associated with an increased lactate-pyruvate ratio in the rectus abdominis muscle tissue: a pilot study during laparoscopic surgery

Background

The development of intra-abdominal hypertension [IAH] in critically ill patients admitted to the ICU is an independent predictor of mortality. In an attempt to find an early, clinically relevant metabolic signal of modest IAH, we investigated abdominal wall metabolite concentrations in a small group of patients undergoing laparoscopic surgery. We hypothesized that elevated intra-abdominal pressure [IAP] due to pneumoperitoneum leads to an increased lactate/pyruvate [L/P] ratio in the rectus abdominis muscle [RAM], indicating anaerobic metabolism.

Method

Six patients scheduled for elective laparoscopic gastric fundoplication were studied. Two hours before surgery, a microdialysis catheter (CMA 60, CMA Small Systems AB, Solna, Sweden) was inserted into the RAM under local anaesthesia. Catheter placement was confirmed by ultrasound. The microdialysis perfusion rate was set at 0.3 μL/min. Dialysate was collected hourly prior to pneumoperitoneum, during pneumoperitoneum, and for 2 h after pneumoperitoneum resolution. IAP was maintained at 12 to 13 mmHg during the surgery. The glucose, glycerol, pyruvate and lactate contents of the dialysate were measured.

Results

The median (interquartile range) L/P ratio was 10.3 (7.1 to 15.5) mmol/L at baseline. One hour of pneumoperitoneum increased the L/P ratio to 16.0 (13.6 to 35.3) mmol/L (p = 0.03). The median pneumoperitoneum duration was 86 (77 to 111) min. The L/P ratio at 2 h post-pneumoperitoneum was not different from that at baseline (p = 1.0). No changes in glycerol or glucose levels were observed.

Conclusions

IAH of 12 to 13 mmHg, even for a relatively short duration, is associated with metabolic changes in the abdominal wall muscle tissue of patients undergoing laparoscopic surgery. We suggest that tissue hypoperfusion occurs even during a modest increase in IAP, and intramuscular metabolic monitoring could therefore serve as an early warning sign of deteriorating tissue perfusion.

Hepatic arterial infusion with tumor necrosis factor-α induces early hepatic hyperperfusion

BACKGROUND

Hepatic arterial infusion (HAI) has been developed for high-dose regional chemotherapy of unresectable liver metastases or primary liver malignancies. While it is well known that high concentrations of tumor necrosis factor (TNF)-α damage tumor blood perfusion, there is no information on whether autochthonous liver perfusion is affected by HAI with TNF-α. Therefore, we investigated the effects of HAI with TNF-α on hepatic macro- and microvascular perfusion.

METHODS

Swabian Hall pigs were randomized into three groups. HAI was performed with either 20 or 40 µg/kg body weight TNF-α (n = 6 each group). Saline-treated animals served as controls (n = 6). Analyses during a 2-hour post-HAI observation period included systemic hemodynamics, portal venous and hepatic arterial blood flow, portal venous pressure, and the blood flow in the hepatic microcirculation.

RESULTS

HAI with TNF-α caused a slight decrease of mean arterial blood pressure (p < 0.001), which was compensated by a moderate increase of heart rate (p < 0.001). No further systemic side effects of TNF-α were observed. HAI with TNF-α further caused a slight but not significant decrease of portal venous blood flow (p = 0.737) in both experimental groups, paralleled by an increase of hepatic arterial blood flow (p = 0.023, 20 µg/kg; p = 0.034, 40 µg/kg) resulting in an overall hepatic hyperperfusion. The hepatic hyperperfusion after HAI with 20 µg/kg TNF-α was more pronounced and associated with a 40% decrease of the blood flow in the hepatic microcirculation (p = 0.009). HAI with 40 µg/kg TNF-α was only associated with a temporary and moderate total hepatic hyperperfusion and did not affect the blood flow in the hepatic microcirculation.

CONCLUSION

HAI with TNF-α causes a decrease of portal venous flow; however, this is overcompensated by an increased hepatic arterial blood flow, resulting in a total hepatic hyperperfusion. Moderate total hepatic hyperperfusion does not affect the blood flow in the hepatic microcirculation, while a persistent and more pronounced hyperperfusion may cause hepatic microcirculatory disturbances.

Luminal lactate in acute pancreatitis--validation and relation to disease severity

Background

Increased rectal luminal lactate concentration may be associated with the severity of the septic shock and high dose of vasopressors. It suggests hypoperfusion of the gut mucosa. This is potentially associated with bacterial translocation from the gut leading to local and systemic inflammation. In acute pancreatitis (AP) bacterial translocation is considered as the key event leading to infection of necrotic pancreatic tissue and high severity of illness.

Methods

We used rectal luminal equilibration dialysis for the measurement of gut luminal lactate in 30 consecutive patients admitted to hospital due to acute pancreatitis to test the hypothesis that a single measurement of rectal luminal lactate predicts the severity of acute pancreatitis, the length of hospital stay, the need of intensive care and ultimately, mortality. We also tested the physiological validity of luminal lactate concentration by comparing it to luminal partial tension of oxygen. Additionally, a comparison between two different L-lactate analyzers was performed.

Results

High rectal luminal lactate was associated with low mucosal partial tension of oxygen (R = 0.57, p = 0.005) thereby indicating the physiological validity of the method. Rectal luminal lactate at the hospital admission was not associated with the first day or the highest SOFA score, CRP level, hospital length of stay, length of stay in intensive care or mortality. In this cohort of unselected consecutive patients with acute pancreatitis we observed a tendency of increased rectal lactate in the severe cases. Low precision and high bias was observed between two lactate analyzers.

Conclusions

The association between rectal luminal lactate and oxygen tension indicates that luminal lactate is a marker mucosal anaerobiosis. Comparison between two different analyzers showed poor, non-constant precision over the range of lactate concentrations. Rectal luminal lactate concentration at the time of hospital admission did not predict the severity of pancreatitis.

Splanchnic vasoregulation after major abdominal surgery in pigs

BACKGROUND

Unrecognized reduction of blood supply to intestinal organs is associated with significant postoperative morbidity in abdominal surgery. The aim of this study was to determine whether--in the absence of hypovolemia--intestinal hypoperfusion as a result of blood flow redistribution occurs after abdominal surgery.

METHODS

Standardized operative trauma was induced in 14 healthy pigs. Systemic, regional, and local blood flow, intestinal and gastric intraluminal-to-end-tidal pCO(2) gradients representing mucosal perfusion, and oxygen transport variables were measured for 10 postoperative hours. Normovolemia was maintained using continuous infusion of Ringer's lactate and additional boluses of colloids in response to blood pressure, pulmonary wedge pressure, and urinary output.

RESULTS

Postoperative blood flow was significantly increased in the celiac trunk (76% increase [percentage of baseline flow], p = 0.003) and the hepatic (136% increase, p = 0.002) and splenic (36% increase, p = 0.025) arteries. Blood flow was significantly decreased in the mesenteric artery (25% decrease, p = 0.007) and portal vein (13% decrease, p = 0.028). Carotid and renal artery blood flow remained unchanged.

CONCLUSIONS

Maintenance of normovolemia is insufficient to protect from intestinal hypoperfusion after abdominal surgery. Postoperative redistribution of cardiac output results in decreased intestinal and increased hepatic and splenic arterial blood flow.

Effects of levosimendan on indocyanine green plasma disappearance rate and the gastric mucosal-arterial pCO2 gradient in abdominal aortic aneurysm surgery

BACKGROUND

Levosimendan has a dual mechanism of action: it improves myocardial contractility and causes vasodilatation without increasing myocardial oxygen demand. In a laboratory setting, it selectively increases gastric mucosal oxygenation in particular and splanchnic perfusion in general. The aim of our study was to describe the effects of levosimendan on systemic and splanchnic circulation during and after abdominal aortic surgery.

METHODS

Twenty abdominal aortic aneurysm surgery patients were randomized to receive either levosimendan (n=10) or placebo (n=10) in a double-blinded manner. Both the mode of anaesthesia and the surgical procedures were performed according to the local guidelines. Automatic gas tonometry was used to measure the gastric mucosal partial pressure of carbon dioxide. Systemic indocyanine green clearance plasma disappearance rate (ICG-PDR) was used to estimate the total splanchnic blood flow.

RESULTS

The immediate post-operative recovery was uneventful in the two groups with a comparable, overnight length of stay in the intensive care unit. Cumulative doses of additional vasoactive drugs were comparable between the groups, with a tendency towards a higher cumulative dose of noradrenaline in the levosimendan group. After aortic clamping, the cardiac index was higher [4(3.8-4.7) l/min/m(2) vs. 2.6(2.3-3.6) l/min/m(2); P<0.05] and the gastric mucosal-arterial pCO(2) gradient was lower in levosimendan-treated patients [0.9(0.6-1.2) kPa vs. 1.7(1.2-2.1) kPa; (P<0.05)]. However, the total splanchnic blood flow, estimated by ICG-PDR, was comparable [29(21-29)% vs. 20(19-25)%; NS]. Organ dysfunction scores (sequential organ dysfunction assessment) were similar between the groups on the fifth post-operative day.

CONCLUSION

Levosimendan favours gastric perfusion but appears not to have a major effect on total splanchnic perfusion in patients undergoing an elective aortic aneurysm operation.

The immediate and sustained effects of volume challenge on regional blood flows in pigs

BACKGROUND

The postoperative assessment of volume status is not straightforward because of concomitant changes in intravascular volume and vascular tone. Hypovolemia and blood flow redistribution may compromise the perfusion of the intraabdominal organs. We investigated the effects of a volume challenge in different intra- and extraabdominal vascular beds.

METHODS

Twelve pigs were studied 6 h after major intraabdominal surgery under general anesthesia when clinically normovolemic. Volume challenges consisted of 200 mL rapidly infused 6% hydroxyethyl starch. Systemic (continuous thermodilution) and regional (ultrasound Doppler) flows in carotid, renal, celiac trunk, hepatic, and superior mesenteric arteries and the portal vein were continuously measured. The acute and sustained effects of the challenge were compared with baseline.

RESULTS

Volume challenge produced a sustained increase of 22% +/- 15% in cardiac output (P < 0.001). Blood flow increased by 10% +/- 9% in the renal artery, by 22% +/- 15% in the carotid artery, by 26% +/- 15% in the superior mesenteric artery, and by 31% +/- 20% in the portal vein (all P < 0.001). Blood flow increases in the celiac trunk (8% +/- 13%) and the hepatic artery (7% +/- 19%) were not significant. Increases in regional blood flow occurred early and were sustained. Mean arterial and central venous blood pressures increased early and decreased later (all P < 0.05).

CONCLUSIONS

A volume challenge in clinically euvolemic postoperative animals was associated with a sustained increase in blood flow to all vascular beds, although the increase in the celiac trunk and the hepatic artery was very modest and did not reach statistical significance. Whether improved postoperative organ perfusion is accompanied by a lower complication rate should be evaluated in further studies.

Effects of endotoxaemia on markers of permeability, metabolism and inflammation in the large bowel of healthy subjects

BACKGROUND

Increased permeability and increased luminal concentrations of L-lactate have previously been shown in the large bowel in septic patients. To advance these observations, a human model of colorectal barrier failure in sepsis is desirable. Therefore, we assessed the effects of endotoxaemia on markers of permeability, metabolism and inflammation in the large bowel in healthy subjects.

METHODS

Twelve healthy male subjects received intravenous endotoxin (2 ng/kg body weight) or saline in a paired cross-over design. Colorectal permeability was assessed after 3, 6, 9 and 12 h by the systemic recovery of luminally instilled (99m)Tc-diethylenetriaminepentaacetate. Luminal concentrations of L-lactate were assessed by equilibrium dialysis. Mucosal biopsies from the large bowel were sampled after 6 and 12 h, and the apoptotic ratio of the epithelium was assessed by terminal deoxynucleotidyl transferase-mediated desoxyuridinetriphosphate nick end-labelling (TUNEL) assay and the expression of inducible nitric oxide synthase (iNOS) mRNA by reverse transcriptase-polymerase chain reaction.

RESULTS

Systemic effects of endotoxaemia were observed, including fever, tachycardia and strongly increased plasma values of tumour necrosis factor-alpha. By contrast, the colorectal permeability, luminal lactate concentrations, mucosal infiltration of inflammatory cells, epithelial apoptotic ratio and expression of iNOS were all unaffected by endotoxin.

CONCLUSIONS

No effect of a single intravenous dose of endotoxin was observed on markers of large bowel permeability, metabolism and inflammation in healthy subjects. This suggests that this part of the gut is relatively resistant to the systemic inflammation induced by experimental endotoxaemia in humans.

Oscillation frequency of skin microvascular blood flow is associated with mortality in critically ill patients

BACKGROUND

Microcirculatory dysfunction has been hypothesized to play a key role in the pathophysiology of multiple organ failure and, consequently, patient outcome. The objective of this study was to investigate the differences in reactive hyperemia response and oscillation frequency in surviving and non-surviving patients with multiple organ dysfunction syndrome.

METHODS

Twenty-nine patients (15 survivors; 14 non-survivors) with two or more organ failures were eligible for study entry. All patients were hemodynamically stabilized, and demographic and clinical data were recorded. A laser Doppler flowmeter was used to measure the cutaneous microcirculatory response. Reactive hyperemia and oscillatory changes in the Doppler signal were measured during 3 min before and after a 5-min period of forearm ischemia.

RESULTS

Non-survivors demonstrated a significantly higher multiple organ dysfunction score when compared with survivors (P= 0.004). Norepinephrine administration was higher in non-survivors (P= 0.018). Non-survivors had higher arterial lactate levels (P= 0.046), decreased arterial pH levels (P= 0.001) and decreased arterial Po(2) values (P= 0.013) when compared with survivors. A higher oscillation frequency of the skin microvasculature at rest (P= 0.033) and after an ischemic stimulus (P= 0.009) was observed in non-survivors. The flow motion frequency observed in reactive hyperemia was associated with the severity of multiple organ dysfunction (P= 0.009) and, although not statistically significant, with the arterial lactate concentration (P= 0.052).

CONCLUSION

Increased skin microvascular oscillation frequency at rest and in the hyperemic state after an ischemic stimulus is associated with increased mortality in patients suffering from multiple organ dysfunction. The underlying mechanism could be a response of the skin microvasculature to an impaired oxygen utilization of the skin tissue.

Luminal concentrations of L- and D-lactate in the rectum may relate to severity of disease and outcome in septic patients

INTRODUCTION

Little is known about the condition of the large bowel in patients with sepsis. We have previously demonstrated increased concentrations of L-lactate in the rectal lumen in patients with abdominal septic shock. The present study was undertaken to assess the concentrations of L- and D-lactate in rectal lumen and plasma in septic patients including the possible relation to site of infection, severity of disease, and outcome.

METHODS

An intensive care unit observational study was conducted at two university hospitals, and 23 septic patients and 11 healthy subjects were enrolled. Participants were subjected to rectal equilibrium dialysis, and concentrations of L- and D-lactate in dialysates and plasma were analysed by spectrophotometry.

RESULTS

Luminal concentrations of L-lactate in rectum were related to the sequential organ failure assessment scores (R2 = 0.27, P = 0.01) and were higher in non-survivors compared to survivors and healthy subjects (mean [range] 5.0 [0.9 to 11.8] versus 2.2 [0.4 to 4.9] and 0.5 [0 to 1.6] mmol/l, respectively, P < 0.0001), with a positive linear trend (R2 = 0.53, P < 0.0001). Also, luminal concentrations of D-lactate were increased in non-survivors compared to survivors and healthy subjects (1.1 [0.3 to 2.5] versus 0.3 [0 to 1.2] and 0.1 [0 to 0.8] mmol/l, respectively, P = 0.01), with a positive linear trend (R2 = 0.14, P = 0.04). Luminal concentrations of L- and D-lactate were unaffected by the site of infection. Plasma concentrations of L-lactate were also increased in non-survivors compared to survivors (3.8 [1.7 to 7.0] versus 1.5 [0 to 3.6] mmol/l, P < 0.01). In contrast, plasma concentrations of D-lactate were equally raised in non-survivors (0.4 [0.1 to 0.7] mmol/l) and survivors (0.3 [0.1 to 0.6] mmol/l) compared with healthy subjects (0.03 [0 to 0.13] mmol/l).

CONCLUSION

In patients with severe sepsis and septic shock, luminal concentrations of L- and D-lactate in the rectum were related to severity of disease and outcome.

Rectal lactate levels in endoluminal microdialysate during routine coronary surgery

The aim of this prospective study was to determine the feasibility of intestinal endoluminal microdialysis as a new method for clinical monitoring of the adequacy of splanchnic perfusion in the large bowel. A microdialysis catheter for continuous lactate, glycerol, glucose and pyruvate measurements attached to a tonometric catheter was placed into the lumen of the recto-sigmoid junction prior to surgery in 13 patients undergoing elective cardiac surgery with cardiopulmonary bypass (CPB). Lactate was also measured in blood and muscle. CPB was associated with a 10-fold increase in luminal lactate from 0.16 (0.01) to 1.67 (0.38) mmol x l(-1) (p < 0.001). Muscular lactate increased from baseline levels 1.20 (0.21) to 1.77 (0.36) mmol x l(-1) during CPB (p = 0.01), but the muscular lactate-pyruvate ratio remained unchanged. Arterial lactate increased only slightly from 0.9 (0.05) to 1.1 (0.06) mmol x l(-1) (p = 0.027) during CPB. Increased lactate concentrations in the large bowel during CPB are suggestive of local lactate production consistent with impaired oxygen delivery. Intestinal endoluminal microdialysis is a potential clinically applicable method for monitoring intestinal metabolism. Combined with tonometry, microdialysis provides the opportunity to monitor both circulation and metabolism in the rectal mucosa.

Dopexamine and norepinephrine versus epinephrine on gastric perfusion in patients with septic shock: a randomized study [NCT00134212]

Introduction

Microcirculatory blood flow, and notably gut perfusion, is important in the development of multiple organ failure in septic shock. We compared the effects of dopexamine and norepinephrine (noradrenaline) with those of epinephrine (adrenaline) on gastric mucosal blood flow (GMBF) in patients with septic shock. The effects of these drugs on oxidative stress were also assessed.

Methods

This was a prospective randomized study performed in a surgical intensive care unit among adults fulfilling usual criteria for septic shock. Systemic and pulmonary hemodynamics, GMBF (laser-Doppler) and malondialdehyde were assessed just before catecholamine infusion (T₀), as soon as mean arterial pressure (MAP) reached 70 to 80 mmHg (T₁), and 2 hours (T₂) and 6 hours (T₃) after T₁. Drugs were titrated from 0.2 μg kg^-1 min^-1 with 0.2 μg kg^-1 min^-1 increments every 3 minutes for epinephrine and norepinephrine, and from 0.5 μg kg^-1 min^-1 with 0.5 μg kg^-1 min^-1 increments every 3 minutes for dopexamine.

Results

Twenty-two patients were included (10 receiving epinephrine, 12 receiving dopexamine–norepinephrine). There was no significant difference between groups on MAP at T₀, T₁, T₂, and T₃. Heart rate and cardiac output increased significantly more with epinephrine than with dopexamine–norepinephrine, whereas. GMBF increased significantly more with dopexamine–norepinephrine than with epinephrine between T₁ and T₃ (median values 106, 137, 133, and 165 versus 76, 91, 90, and 125 units of relative flux at T₀, T₁, T₂ and T₃, respectively). Malondialdehyde similarly increased in both groups between T₁ and T₃.

Conclusion

In septic shock, at doses that induced the same effect on MAP, dopexamine–norepinephrine enhanced GMBF more than epinephrine did. No difference was observed on oxidative stress.

Microdialysis of the bowel: the possibility of monitoring intestinal ischemia

Assessment of the intestinal circulation in a clinical setting still presents a significant diagnostic challenge. In patients suspected of having intestinal ischemia pre- or postoperatively, there is no clinically relevant marker which can determine whether the bowel is suffering from lack of oxygen or not. Microdialysis is a microinvasive technique that makes it possible to continuously detect tissue-specific metabolic changes. Recently, it has been demonstrated that intestinal ischemia can be detected and monitored continuously by the use of a microdialysis catheter placed in the proximity of the ischemic bowel. This review summarizes the clinical dilemma of intestinal ischemia and the latest experimental results using the microdialysis technique to detect critical perfusion in the small intestine. The possibility of using microdialysis in a clinical setting is outlined with the perspective of using it as a pre- or postoperative monitoring tool in relevant patients.

Decreasing gut wall glucose as an early marker of impaired intestinal perfusion

OBJECTIVE

The aim of this study was to assess the microcirculatory and metabolic consequences of reduced mesenteric blood flow.

DESIGN

Prospective, controlled animal study.

SETTING

The surgical research unit of a university hospital.

SUBJECTS

A total of 13 anesthetized and mechanically ventilated pigs.

INTERVENTIONS

Pigs were subjected to stepwise mesenteric blood flow reduction (15% in each step, n = 8) or served as controls (n = 5). Superior mesenteric arterial blood flow was measured with ultrasonic transit time flowmetry, and mucosal and muscularis microcirculatory perfusion in the small bowel were each measured with three laser Doppler flow probes. Small-bowel intramucosal Pco2 was measured by tonometry, and glucose, lactate (L), and pyruvate (P) were measured by microdialysis.

MEASUREMENTS AND MAIN RESULTS

In control animals, superior mesenteric arterial blood flow, mucosal microcirculatory blood flow, intramucosal Pco2, and the lactate/pyruvate ratio remained unchanged. In both groups, mucosal blood flow was better preserved than muscularis blood flow. During stepwise mesenteric blood flow reduction, heterogeneous microcirculatory blood flow remained a prominent feature (coefficient of variation, approximately 45%). A 30% flow reduction from baseline was associated with a decrease in microdialysis glucose concentration from 2.37 (2.10-2.70) mmol/L to 0.57 (0.22-1.60) mmol/L (p < .05). After 75% flow reduction, the microdialysis lactate/pyruvate ratio increased from 8.6 (8.0-14.1) to 27.6 (15.5-37.4, p < .05), and arterial-intramucosal Pco2 gradients increased from 1.3 (0.4-3.5) kPa to 10.8 (8.0-16.0) kPa (p < .05).

CONCLUSIONS

Blood flow redistribution and heterogeneous microcirculatory perfusion can explain apparently maintained regional oxidative metabolism during mesenteric hypoperfusion, despite local signs of anaerobic metabolism. Early decreasing glucose concentrations suggest that substrate supply may become crucial before oxygen consumption decreases.

Regional microvascular function and vascular reactivity in patients with different degrees of multiple organ dysfunction syndrome

The pathophysiology of multiple organ dysfunction syndrome (MODS) is believed to be related to that of microcirculatory dysfunction. We hypothesized that the severity of MODS is determined by measuring regional variables of microvascular function and vascular reactivity in critically ill patients. Therefore, we compared (a) reactive hyperemia response in the forearm using transcutaneous Po2/Pco2 electrodes and laser Doppler velocimetry, (b) microvascular permeability assessed by strain-gauge plethysmography in legs, and (c) variables derived from gastric tonometry in hemodynamically stable patients with moderate (n = 15) and severe (n = 15) MODS. There were no differences in systemic oxygen delivery, consumption, and oxygen extraction ratio between the groups. Mortality was 20% in patients with moderate MODS and 60% in patients with severe MODS (P = 0.025). Patients with a high MODS score had significantly larger arterial lactate concentrations (3.81 +/- 2.7 mmol/L) than patients with moderate MODS (1.66 +/- 0.82 mmol/L; P = 0.006). No significant differences in gastric pHi, gastric regional-to-arterial Pco2 difference, capillary filtration coefficient, isovolumetric venous pressure, and skin reactive hyperemia response were observed between patients with moderate and severe MODS. Once MODS is established, regional variables of microvascular function and vascular reactivity measured in this study do not reflect severity of organ dysfunction.

Gut luminal microdialysis of glycerol as a marker of intestinal ischemic injury and recovery

OBJECTIVE

To evaluate microdialysis as a method to assess different degrees of intestinal damage and recovery during ischemia and reperfusion; to evaluate information obtained from microdialysis catheters in the peritoneum, the gut wall, and the gut lumen.

DESIGN

Randomized, controlled animal experiment.

SETTING

University laboratory animal center.

SUBJECTS

Twenty-seven domestic pigs.

INTERVENTIONS

The superior mesenteric artery was cross-clamped for 60 mins (n = 14) or 120 mins (n = 10) followed by 2 or 4 hrs of reperfusion. Three pigs served as controls.

MEASUREMENTS AND MAIN RESULTS

Intestinal mucosal integrity was assessed by morphometry, adenosine triphosphate in the gut wall, and permeability of C-polyethylene glycol. Lactate, glycerol, pyruvate, and glucose were measured by microdialysis. Changes in adenosine triphosphate, permeability, or lactate did not correlate to different extents of intestinal damage caused by 60 or 120 mins of ischemia. During the reperfusion period, pigs with 60 mins of intestinal ischemia showed a faster recovery of these variables than pigs with 120 mins of intestinal ischemia. Glycerol increased with increasing duration of the ischemic insult. After 60 mins of intestinal ischemia, glycerol in the gut lumen decreased toward baseline but remained high after 120 mins of intestinal ischemia. There was a good correlation between gut luminal glycerol and recovery of mucosal damage throughout the reperfusion period. In the peritoneal cavity, both glycerol and lactate decreased to baseline relatively shortly after onset of reperfusion independent of the duration of intestinal ischemia.

CONCLUSIONS

Microdialysis of glycerol provides information about the extent and severity of intestinal damage after ischemia and about the ensuing recovery. The gut lumen is to be preferred as a site for placement of microdialysis catheters.

Lactic acidosis: from sour milk to septic shock

Lactic acidosis is frequently encountered in the intensive care unit. It occurs when there is an imbalance between production and clearance of lactate. Although lactic acidosis is often associated with a high anion gap and is generally defined as a lactate level >5 mmol/L and a serum pH <7.35, the presence of hypoalbuminemia may mask the anion gap and concomitant alkalosis may raise the pH. The causes of lactic acidosis are traditionally divided into impaired tissue oxygenation (Type A) and disorders in which tissue oxygenation is maintained (Type B). Lactate level is often used as a prognostic indicator and may be predictive of a favorable outcome if it normalizes within 48 hours. The routine measurement of serum lactate, however, should not determine therapeutic interventions. Unfortunately, treatment options remain limited and should be aimed at discontinuation of any offending drugs, treatment of the underlying pathology, and maintenance of organ perfusion. The mainstay of therapy of lactic acidosis remains prevention.

Oxygen extraction in pigs subjected to low-dose infusion of endotoxin after major abdominal surgery

BACKGROUND

Sepsis may impair O(2) extraction due to blood flow redistribution or decreased utilization of the available oxygen.

METHODS

We assessed the effect of endotoxemia on systemic and regional O(2) extraction and lactate handling in pigs, randomized to receive either endotoxin (0.4 microg kg(-1) h(-1); n = 10) or saline infusion (controls; n = 9) for 12 h.

RESULTS

High baseline regional and systemic O(2) extraction in the endotoxin group (median 56%, range 45-77%) and in the controls (67%, 49-72%) was maintained until the end of the experiment (endotoxin group: 60%, 50-71%; controls: 60%, 50-74%) despite hypotension and a decrease in stroke volume in endotoxic animals. Hepatic lactate exchange decreased during endotoxemia from 14 micromol kg(-1) min(-1) (range 10-28 micromol kg(-1) min(-1)) to 10 (range 3-15) micromol kg(-1) min(-1); P < 0.01), but remained stable in the controls, with 13 micromol min(-1) (4-18 micromol min(-1)) at baseline and 7 micromol min(-1) (3-17 micromol min(-1)) after 12 h of saline infusion.

CONCLUSIONS

The high and sustained oxygen consumption and oxygen extraction in this endotoxemic model speak against any major impairment of hepatosplanchnic or systemic oxygen extraction and oxidative metabolism. The reduced hepatic lactate exchange despite an unchanged hepatic lactate influx suggests altered metabolic activities independent of oxygen consumption.

Epinephrine induces tissue perfusion deficit in porcine endotoxin shock: evaluation by regional CO(2) content gradients and lactate-to-pyruvate ratios

Epinephrine is widely used as a vasoconstrictor or inotrope in shock, although it may typically induce or augment lactic acidosis. Ongoing debate addresses the question of whether hyperlactatemia per se is a sign of tissue perfusion deficit or aerobic glycolysis. We wanted to test the hypothesis that epinephrine has selective detrimental effects on visceral perfusion and metabolism. We performed rigorous regional venous blood gas analyses as well as intraperitoneal microdialysis. We used a mathematical model to calculate regional arteriovenous CO(2) content gradients and estimated the magnitude of the Haldane effect in a porcine model of prolonged hypotensive shock induced by endotoxin infusion (mean arterial blood pressure < 60 mmHg). Subsequently, vasopressors (epinephrine or norepinephrine) were administered and adjusted to maintain systemic mean arterial pressure > 70 mmHg for 4 h. Epinephrine caused systemic hyperlactatemia and acidosis. Importantly, both systemic and regional venous lactate-to-pyruvate ratios increased. Epinephrine was associated with decreasing portal blood flow despite apparently maintained total splanchnic blood flow. Epinephrine increased gastric venous-to-arterial Pco(2) gradients and CO(2) content gradients with decreasing magnitude of the Haldane effect, and the regional gastric respiratory quotient remained higher after epinephrine as opposed to norepinephrine infusion. In addition, epinephrine induced intraperitoneal lactate and glycerol release. We did not observe these adverse hemodynamic or metabolic changes related to norepinephrine with the same arterial pressure goal. We conclude that high CO(2) content gradients with decreasing magnitude of the Haldane effect pinpoint the most pronounced perfusion deficiency to the gastric wall when epinephrine, as opposed to norepinephrine, is used in experimental endotoxin shock.

Lingual, splanchnic, and systemic hemodynamic and carbon dioxide tension changes during endotoxic shock and resuscitation

Sublingual and intestinal mucosal blood flow and Pco2 were studied in a canine model of endotoxin-induced circulatory shock and resuscitation. Sublingual Pco2 (PsCO2) was measured by using a novel fluorescent optrode-based technique and compared with lingual measurements obtained by using a Stowe-Severinghaus electrode [lingual Pco2 (PlCO2)]. Endotoxin caused parallel changes in cardiac output, and in portal, intestinal mucosal, and sublingual blood flow (Q̇s). Different blood flow patterns were observed during resuscitation: intestinal mucosal blood flow returned to near baseline levels postfluid resuscitation and decreased by 21% after vasopressor resuscitation, whereas Q̇s rose to twice that of the preshock level and was maintained throughout the resuscitation period. Electrochemical and fluorescent Pco2 measurements showed similar changes throughout the experiments. The shock-induced increases in PsCO2 and PlCO2 were nearly reversed after fluid resuscitation, despite persistent systemic arterial hypotension. Vasopressor administration induced a rebound of PsCO2 and PlCO2 to shock levels, despite higher cardiac output and Q̇s, possibly due to blood flow redistribution and shunting. Changes in PlCO2 and PsCO2 paralleled gastric and intestinal Pco2 changes during shock but not during resuscitation. We found that the lingual, splanchnic, and systemic circulations follow a similar pattern of blood flow variations in response to endotoxin shock, although discrepancies were observed during resuscitation. Restoration of systemic, splanchnic, and lingual perfusion can be accompanied by persistent tissue hypercarbia, mainly lingual and intestinal, more so when a vasopressor agent is used to normalize systemic hemodynamic variables.

Terlipressin increased the concentration of L-lactate in the rectal lumen in a patient with septic shock

Terlipressin--a long-acting analogue of vasopressin--has been described to restore blood pressure in patients with catecholamine-resistant septic shock without obvious complications. We administered low-dose terlipressin (a single i.v.-bolus of 0.5 mg) to a patient with severe, hyperdynamic septic shock requiring high dosage of noradrenalin. After terlipressin the dose of noradrenalin could be reduced by 2/3 to obtain the same blood pressure. Two hours after terlipressin, the cardiac index had decreased from 6.2 to 3.3 l min(-1) m(-2) and the concentration of L-lactate in the rectal lumen, as assessed by equilibrium dialysis, increased from 3.6 to 7.2 mmol l(-1). In contrast, the systemic concentration of L-lactate was unaffected around 2.8 mmol l(-1). After 8 h the effect of terlipressin started to decline, and after an additional 12 h the systemic haemodynamics, dose of noradrenalin and concentrations of rectal and systemic L-lactate were the same as prior to the administration of terlipressin. As a strong vasopressor, terlipressin may have further impaired the metabolic dysfunction in the rectal mucosa either directly via vasoconstriction of mucosal vessels or through decreased cardiac output in this patient with noradrenalin-treated septic shock.

Dobutamine compensates deleterious hemodynamic and metabolic effects of vasopressin in the splanchnic region in endotoxin shock

BACKGROUND

Vasopressin is a potent vasopressor in septic shock, but it may impair splanchnic perfusion. We compared the effects of vasopressin alone and in combination with dobutamine on systemic and splanchnic circulation and metabolism in porcine endotoxin shock.

METHODS

Twelve pigs were randomized to receive either vasopressin (VASO, n = 6) or vasopressin in combination with dobutamine (DOBU, n = 6) during endotoxin shock (E. coli endotoxin infusion). Endotoxin infusion rate was increased to induce hypotension after which vasoactive drugs were started. We aimed to keep systemic mean arterial pressure (MAP) >70 mmHg by vasopressin; the goal of dobutamine infusion was to prevent decrease in cardiac output often associated with vasopressin infusion. Regional blood flows, oxygen delivery and consumption, arterial and regional lactate concentrations were measured.

RESULTS

Mean arterial pressure >70 mmHg was achieved in both the VASO and DOBU groups. After the primary decrease of cardiac output by vasopressin, systemic blood flow remained stable in vasopressin-treated animals. However, vasopressin as a monotherapy decreased portal venous blood flow. This was prevented by dobutamine. Vasopressin also induced splanchnic lactate release and arterial hyperlactatemia, which were not observed when dobutamine was combined with vasopressin.

CONCLUSION

Dobutamine prevents adverse hemodynamic and metabolic effects of vasopressin in septic shock.

Splanchnic metabolism in acute liver failure and sepsis

PURPOSE OF REVIEW

A number of papers have suggested that the splanchnic circulation and oxidative metabolism are compromised in critical illness. This review discusses this hypothesis and outlines the recent advances in the understanding of splanchnic metabolism with special focus on acute liver failure and hyperdynamic sepsis.

RECENT FINDINGS

Splanchnic blood flow, oxygen delivery, and consumption are increased in both acute liver failure and sepsis. The capability of the liver to extract oxygen, even under extreme conditions, renders the liver less prone to hypoxia. A common feature of acute liver failure and sepsis is a hypermetabolic state with enhanced glycolysis and production of lactate and pyruvate. Human studies on other features of intermediary metabolism are sparse, but there are indications that several intermediary processes are severely compromised in patients with acute liver failure, whereas these processes are maintained in sepsis.

SUMMARY

There is increasing evidence that both acute liver failure and sepsis are accompanied by a hypermetabolic state in the hepatosplanchnic area, characterized by enhanced glycolysis and hyperlactatemia. This should not be rigorously interpreted as an indication of hypoxia. In fact, clinically important splanchnic hypoxia may be a relatively uncommon phenomenon in such patients.

Bench-to-bedside review: microdialysis in intensive care medicine

Microdialysis is a technique used to measure the concentrations of various compounds in the extracellular fluid of an organ or in a body fluid. It is a form of metabolic monitoring that provides real-time, continuous information on pathophysiological processes in target organs. It was introduced in the early 1970s, mainly to measure concentrations of neurotransmitters in animal experiments and clinical settings. Using commercial equipment it is now possible to conduct analyses at the bedside by collecting interstitial fluid for measurement of carbohydrate and lipid metabolites. Important research has been reported in the field of neurosurgery in recent decades, but use of metabolic monitoring in critical care medicine is not yet routine. The present review provides an overview of findings from clinical studies using microdialysis in critical care medicine, focusing on possible indications for clinical biochemical monitoring. An important message from the review is that sequential and tissue-specific metabolic monitoring, in vivo, is now available.

SPLANCHNIC METABOLISM DURING GUT ISCHEMIA AND SHORT-TERM ENDOTOXIN AND HEMORRHAGIC SHOCK AS EVALUATED BY INTRAVASAL MICRODIALYSIS

The splanchnic area is of considerable interest in different types of shock. To characterize the metabolic changes in the splanchnic region in response to different types of shock we used a model where shock-induced metabolic changes in the splanchnic region were studied by the use of intravasal microdialysis. 23 anesthetized domestic pigs were randomized into four groups: Group I, serving as controls (n = 5); Group II, mesenteric ischemia for 180 followed by 120 min of reperfusion (n = 5); Group III, endotoxin shock for 5 h (n = 5); and Group IV, hemorrhagic shock for 180 min followed by re-transfusion of shed blood (n = 8). Microdialysis catheters were placed in the left femoral artery, portal vein and a small ileal mesenteric vein. Samples of the perfusate were continuously collected in micro-vials and analyzed for glucose, lactate, pyruvate and glycerol. In gut ischemia and endotoxin shock the outflow-pattern of lactate, lactate/pyruvate ratio and glucose in the mesenteric vein differed significantly from controls and hemorrhage whereas an increase in glycerol was only noted in the ischemic group. The most prominent differences were detected in lactate/pyruvate ratio, a marker of tissue ischemia with the most pronounced changes during mesenteric ischemia/reperfusion. During endotoxin shock increases in microdialysate metabolites were only noted in the splanchnic region suggesting a specific vulnerability in the region. Studying the lactate/pyruvate ratio may provide additional information when interpreting increased blood lactate levels. In addition glycerol may prove to be a useful marker of splanchnic ischemia. Intravasal microdialysis represents a potentially useful method for monitoring regional metabolic events.

Dopexamine reverses colonic but not gastric mucosal perfusion defects in lethal endotoxin shock

BACKGROUND

Whilst dopexamine appears to increase overall splanchnic blood flow in postoperative and septic patients, the effects on gastric mucosal perfusion are controversial and based on concomitantly increasing mucosal to arterial PCO(2) gradients (PdCO(2)). We hypothesized that dopexamine alters splanchnic blood flow distribution and metabolism during experimental endotoxin shock and modifies the inflammatory response induced by endotoxin.

METHODS

In an experiment with anaesthetized normovolaemic, normoventilated pigs, 21 animals were randomized into: (i). subacute lethal endotoxin shock for 14 h (n=7 at baseline); (ii). endotoxin shock with dopexamine infusion (aiming to exceed baseline cardiac output, n=7); or (iii). controls (n=7). Regional blood flow and metabolism were monitored.

RESULTS

Endotoxin produced a hypodynamic phase followed by a normo/hyperdynamic, hypotensive phase. Despite increasing systemic blood flow in response to dopexamine, proportional splanchnic blood flow decreased during the hypodynamic phase. Dopexamine gradually decreased fractional coeliac trunk flow, while fractional superior mesenteric arterial flow increased. Dopexamine induced early arterial hyperlactataemia and augmented the gastric PdCO(2) gradient while colonic luminal lactate release and colonic PdCO(2) gradient were reversed. Dopexamine did not modify the inflammatory response as evaluated by arterial IL-1beta and IL-6 concentrations.

CONCLUSIONS

Dopexamine protects colonic, but not gastric mucosal epithelium in experimental endotoxin shock. This may be related to redistribution of blood flow within the splanchnic circulation.