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.

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.

Therapeutic hypothermia after cardiac arrest - cerebral perfusion and metabolism during upper and lower threshold normocapnia.

BACKGROUND: During cardiac arrest and after successful resuscitation a continuum of ischaemia-reperfusion injury develops. Mild hypothermia exerts protective effects in the postresuscitation phase but also alters CO2 production and solubility, which may lead to deleterious effects if overlooked when adjusting the ventilation of the resuscitated patient. Using a multimodality approach, the effects of different carbaemic states on cerebral perfusion and metabolism were evaluated during therapeutic hypothermia. METHODS: Eight comatose survivors of prehospital cardiac arrest were cooled to 33°C for 24 h and underwent a 60 min phase of interventional lower threshold normocapnia according to temperature non-corrected pCO2 (4.2 kPa) and higher threshold normocapnia according to corrected pCO2 (6.0 kPa) in a random order. Prior to, during and after each phase, cerebral perfusion and metabolites via a microdialysis catheter were measured. RESULTS: During upper-threshold pCO2, an increase in middle cerebral artery mean flow velocity (MFV) and jugular bulb oxygen saturation (jSvO2) were observed with a concomitant decrease in cerebral lactate concentration. Lower threshold normocapnia was associated with a decrease in MFV in most patients. In all patients jSvO2 decreased but no change in cerebral lactate was observed. In seven patients jSvO2 decreased below 55%. These changes were not reflected to intracranial pressure or cerebral oximetry. CONCLUSIONS: During induced hypothermia, lower threshold normocapnia was associated with decreased cerebral perfusion/oxygenation but not reflected to interstitial metabolites. Upper threshold pCO2 increased cerebral perfusion and reduced cerebral lactate. Vigilance over the ventilatory and CO2 analysis regimen is mandatory during mild hypothermia.