Effects of a dobutamine-induced increase in splanchnic blood flow on hepatic metabolic activity in patients with septic shock

Norepinephrine and nomega-monomethyl-L-arginine in porcine septic shock: effects on hepatic O2 exchange and energy balance

We compared the effects of norepinephrine (NOR; n = 11) and the nonselective nitric oxide synthase inhibitor Nomega-monomethyl-L-arginine (L-NMMA; n = 11) on hepatic blood flow (Q liv), O2 exchange, and energy metabolism over 24 h of hyperdynamic, normotensive porcine endotoxic shock. Endotoxin (ETX; n = 8) caused a continuous fall in mean arterial pressure (MAP) despite a sustained 50% increase in cardiac output (Q) achieved by adequate fluid resuscitation. NOR maintained MAP at preshock levels owing to a further rise in Q, while the comparable hemodynamic stabilization during L-NMMA infusion resulted from systemic vasoconstriction, increasing the systemic vascular resistance (SVR) about 30% from shock level after 6 h of treatment concomitant with a reduction in Q to preshock values. Whereas NOR also increased Q liv and, hence, hepatic O2 delivery (hDO2), but did not affect hepatic O2 uptake (hVO2), L-NMMA influenced neither Q liv nor hDO2 and hVO2. Mean capillary hemoglobin O2 saturation (HbScO2) on the liver surface as well as HbScO2 frequency distributions, which mirror microcirculatory O2 availability, remained unchanged as well. Neither treatment influenced the ETX-induced derangements of cellular energy metabolism reflected by the progressive decrease in hepatic lactate uptake rate and increased hepatic venous lactate/pyruvate ratios. ETX nearly doubled the endogenous glucose production (EGP) rate, which was further increased with NOR, whereas L-NMMA nearly restored EGP to preshock levels. Nevertheless, despite the different mechanisms in maintaining blood pressure neither treatment influenced ETX-induced liver dysfunction.

Impact of exogenous beta-adrenergic receptor stimulation on hepatosplanchnic oxygen kinetics and metabolic activity in septic shock

OBJECTIVE

To investigate the impact of exogenous beta-adrenergic receptor stimulation on splanchnic blood flow, oxygen kinetics, glucose-precursor flux, and liver metabolism in septic shock.

DESIGN

Prospective trial.

SETTING

University hospital intensive care unit.

PATIENTS

Six patients with hyperdynamic (cardiac index >4.0 L/min/m2) septic shock, all requiring norepinephrine to maintain blood pressure >65 mm Hg.

INTERVENTIONS

We compared norepinephrine and phenylephrine titrated to achieve similar systemic hemodynamics and gas exchange. Splanchnic hemodynamics, oxygen kinetics, and metabolic parameters were measured before, during, and after replacing norepinephrine with phenylephrine.

MEASUREMENTS AND MAIN RESULTS

Splanchnic blood flow and oxygen kinetics were derived from the steady-state indocyanine-green clearance based on hepatic dye extraction and arterial and hepatic venous blood gases. Endogenous glucose production rate was derived from the plasma appearance rate of stable-isotope-labeled glucose using a primed-constant infusion. Splanchnic lactate, alanine (high-performance liquid chromatography) uptake, and hepatic monoethylglycinexylidide (MEGX) (fluorescence polarization immunoassay) formation rates were calculated from splanchnic blood flow and arterial-hepatic venous concentration differences. Replacing norepinephrine with phenylephrine induced no change in systemic hemodynamics or gas exchange. While splanchnic oxygen consumption and alanine uptake rate remained unaffected, splanchnic blood flow, oxygen delivery, and lactate uptake rate were significantly decreased. Glucose production rate also decreased significantly. A return to norepinephrine restored splanchnic blood flow, oxygen delivery, and lactate uptake rate to baseline values, while glucose production rate remained depressed. Hepatic MEGX formation rate was not influenced during the investigation.

CONCLUSIONS

Exogenous beta-adrenergic receptor stimulation determines splanchnic blood flow, oxygen delivery, and glucose precursor flux but not splanchnic oxygen utilization in septic shock. Gluconeogenesis is not directly affiliated to hepatosplanchnic oxygen kinetics. The different response of glucose and MEGX production rates, metabolic pathways of the periportal and perivenous region, may document intrahepatic heterogeneity associated with hepatocellular metabolic compartmentation.

Effect of increased cardiac output on liver blood flow, oxygen exchange and metabolic rate during longterm endotoxin-induced shock in pigs

We investigated hepatic blood flow, O2 exchange and metabolism in porcine endotoxic shock (Control, n = 8; Endotoxin, n = 10) with administration of hydroxyethylstarch to maintain arterial pressure (MAP)>60 mmHg. Before and 12, 18 and 24 h after starting continuous i.v. endotoxin we measured portal venous and hepatic arterial blood flow, intracapillary haemoglobin O2 saturation (Hb-O2%) of the liver surface and arterial, portal and hepatic venous lactate, pyruvate, glycerol and alanine concentrations. Glucose production rate was derived from the plasma isotope enrichment during infusion of [6,6-2H2]-glucose. Despite a sustained 50% increase in cardiac output endotoxin caused a progressive, significant fall in MAP. Liver blood flow significantly increased, but endotoxin affected neither hepatic O2 delivery and uptake nor mean intracapillary Hb-O2% and Hb-O2% frequency distributions. Endotoxin nearly doubled endogenous glucose production rate while hepatic lactate, alanine and glycerol uptake rates progressively decreased significantly. The lactate uptake rate even became negative (P<0.05 vs Control). Endotoxin caused portal and hepatic venous pH to fall significantly concomitant with significantly increased arterial, portal and hepatic venous lactate/pyruvate ratios. During endotoxic shock increased cardiac output achieved by colloid infusion maintained elevated liver blood flow and thereby macro- and microcirculatory O2 supply. Glucose production rate nearly doubled with complete dissociation of hepatic uptake of glucogenic precursors and glucose release. Despite well-preserved capillary oxygenation increased lactate/pyruvate ratios reflecting impaired cytosolic redox state suggested deranged liver energy balance, possibly due to the O2 requirements of gluconeogenesis.

Does hepato-splanchnic VO2/DO2 dependency exist in critically ill septic patients?

Since the gradient between the mixed venous and hepatic vein oxygen saturation (DSO2) is often increased in septic patients, we suspected these patients may have an imbalance between oxygen supply and demand in the hepato-splanchnic area. In 42 septic patients, hepato-splanchnic blood flow was determined by the indocyanine green clearance method with hepatic vein catheterization. The relationships between hepato-splanchnic oxygen delivery (DO2spla) and consumption (VO2spla) were analyzed during an increase in blood flow induced by a dobutamine infusion at doses up to 10 microg/kg x min. In 14 patients, positive end-expiratory pressure (PEEP) was also increased up to 20 cm H2O. The patients were separated according to their DSO2 (Group I: DSO2 < 10%, n = 13; and Group II: DSO2 > 10%, n = 29). Although DO2spla increased similarly in both groups, VO2spla only increased in Group II (from 45+/-22 to 59+/-39 ml/min x M2, p < 0.01). The slope of the VO2spla/DO2spla relationship was higher in Group II than in Group I (31.2+/-16.7 versus 10.4+/-5.1%, p < 0.001) and was similar during dobutamine and PEEP (21.9+/-14.2 versus 21.9+/-14.0%, p = NS). In conclusion, VO2spla increased only in septic patients with an increased DSO2 indicating splanchnic dysoxia. The similar slope observed with dobutamine and PEEP suggests that a thermogenic effect was unlikely.

The effect of dobutamine on distal colon ischaemia in the pig

OBJECTIVE

To test the hypotheses that dobutamine increases intestinal blood flow, it reduces mucosal acidosis and it prevents mucosal injury in an experimental porcine model of distal colonic ischaemia. And the hypothesis that mannitol prevents reperfusion injury.

DESIGN

Randomised animal experiment.

SETTING

University Hospital, Department of Experimental Research.

MATERIALS

Twenty-four pigs.

INTERVENTIONS

Twenty-one pigs were subjected to 7 h of controlled non-occlusive intestinal ischaemia of the distal colon, consisting of an occlusion of the inferior mesenteric artery (IMA) and a constriction of the superior mesenteric artery (SMA). At 3.5 h six pigs were treated with dobutamine, six with mannitol (0.18 g/kgBW), six with dobutamine and mannitol and three served as controls. Three non-ischaemic pigs were treated with dobutamine.

MEASUREMENTS AND RESULTS

All animals were haemodynamically stable throughout the experiment. There was no difference in any variable between the animals treated with mannitol and those not treated. The ischaemic dobutamine-treated animals increased their cardiac output (CO) by 14% compared to baseline and by 59% compared to controls. The median final dosage of dobutamine was 13.2 micrograms/kg per min (range 8.6-25.8). The blood flow in the restricted SMA, the intramucosal pH of the colonic mucosa (pHi) and the degree of histological mucosal injury were identical in animals treated with dobutamine and controls. The pH gap (pHa-pHi) correlated well (r = 0.97) with the PCO2 gap (aPCO2-intestinal PCO2). The non-ischaemic animals treated with dobutamine increased CO by 37% and blood flow of the SMA by 16%.

CONCLUSIONS

Dobutamine increased CO but did not ameliorate or deteriorate colonic ischaemia in this experimental model. The PCO2 gap correlated well with the pH gap.