Redistribution of intestinal microcirculatory oxygenation during acute hemodilution in pigs

Acute normovolemic hemodilution (ANH) compromizes intestinal microcirculatory oxygenation; however, the underlying mechanisms are incompletely understood. We hypothesized that contributors herein include redistribution of oxygen away from the intestines and shunting of oxygen within the intestines. The latter may be due to the impaired ability of erythrocytes to off-load oxygen within the microcirculation, thus yielding low tissue/plasma PO2 but elevated microcirculatory hemoglobin oxygen (HbO(2)) saturations. Alternatively, oxygen shunting may also be due to reduced erythrocyte deformability, hindering the ability of erythrocytes to enter capillaries. Anesthetized pigs underwent ANH ( 20, 40, 60, and 90 ml/kg hydroxyethyl starch; ANH group: n = 10; controls: n = 5). We measured systemic and mesenteric perfusion. Microvascular intestinal oxygenation was measured independently by remission spectrophotometry [ microcirculatory HbO(2) saturation (muHbO(2))] and palladium-porphyrin phosphorescence quenching [ microcirculatory oxygen pressure in plasma/tissue (muPO(2))]. Microcirculatory oxygen shunting was assessed as the disparity between mucosal and mesenteric venous HbO(2) saturation (HbO(2)-gap). Erythrocyte deformability was measured as shear stress-induced cell elongation (LORCA difractometer). ANH reduced hemoglobin concentration from 8.1 to 2.2 g/dl. Relative mesenteric perfusion decreased ( decreased mesenteric/systemic perfusion fraction). A paralleled reduction occurred in mucosal muHbO(2) (68 +/- 2 to 41 +/- 3%) and muPO(2) (28 +/- 1 to 17 +/- 1 Torr). Thus the proposed constellation indicative for oxygen off-load deficits ( sustained muHbO(2) at decreased muPO(2)) did not develop. A twofold increase in the HbO(2)-gap indicated increasing intestinal microcirculatory oxygen shunting. Significant impairment in erythrocyte deformability developed during ANH. We conclude that reduced intestinal oxygenation during ANH is, in addition to redistribution of oxygen delivery away from the intestines, associated with oxygen shunting within the intestines. This shunting appears to be not primarily caused by oxygen off-load deficit but rather by oxygen/erythrocytes bypassing capillaries, wherein a potential contributor is impaired erythrocyte deformabilit

Pharmacologic Interventions to Improve Splanchnic Oxygenation During Ventilation with Positive End-Expiratory Pressure

Mechanical ventilation with positive end-expiratory pressure (PEEP) is an indispensable tool in the management of respiratory failure to preserve or improve lung function and systemic oxygenation. However, PEEP per se may also, as has been shown in experimental animals, impair regional microcirculation and oxygenation. The latter effects have received attention of late because of possible systemic sequelae such as multiple system organ failure (MSOF) in case of the splanchnic region. In this review, we examine the impact of pharmacologic interventions to improve splanchnic mucosal oxygen saturation depressed by mechanical ventilation with PEEP in a canine model of compromised cardiac function. Although much remains to be elucidated about the mechanisms of action, the primary way to improve splanchnic oxygenation seems to be a vasodilatory action of the drugs

Effekt von Noradrenalin und Adrenalin auf die mikrovaskuläre Hämoglobin-Oxygenation der gastralen Mukosa unter Anästhesie mit Sevofluran oder Propofol

Background: Adequate gastrointestinal mucosa oxygenation appears important for the prevention and therapy of sepsis and multiorgan failure [1] . Adrenaline (ADR) and norepinephrine (NOR) become perioperative hemodynamic stabilization. However, the effects are unclear of ADR and NOR on the microvascular hemoglobin oxygenation of the gastric mucosa (μHbO2). Here, the effects of ADR and NOR could depend on the used anesthetic. We therefore examined the effects of ADR and NOR under sevoflurane (SEVO) or propofol (PROPO) anesthesia on the regional μHbO2 and the systemic O2 transport (DO2). Material & Methods: Chronically instrumented dogs (24 experiments, 27-35kg; approved by the Animal Protection Commission) were repeatedly anesthetized (randomized with SEVO or PROPO), ventilated, and were randomized to NOR or ADR (0 / 0.05 / 0.1 / 0.2 μg / kg / min). The μHbO2 were measured (spectrophotometry) and the DO2 [2] .  Statistics: Data are given as mean ± sem, ANOVA, Fisher PLSD; P <0.05. Results: Under SEVO, NOR significantly increased the μHbO2 from 55 ± 1 to 67 ± 2% and also the DO2 (from 12 ± 1 to 20 ± 2 ml / kg / min). In contrast to ADR could not increase the μHbO2 (57 ± 1 vs. 57 ± 2%), despite the more pronounced increase in DO2 (from 12 ± 1 to 27 ± 3 ml / kg / min). In contrast to these significant and contrasting effects under SEVO, was achieved under PROPO none of the catecholamines significantly alter the μHbO2: both ADR and NOR (in all dosages) stably maintained the μHbO2 at the initial level (ADR: 58 ± 2 vs. 58 ± 3%; NOR: 56 ± 2 vs. 57 ± 3%). However, as under SEVO, doubled ADR also under PROPO the DO2 (from 16 ± 1 to 33 ± 2 ml / kg / min), whereas again, NOR changed the DO2 only slightly (from 16 ± 1 to 19 ± 1 ml / kg / min). Conclusions:  The regional effects (μHbO2) of NOR and ADR are depending on the anesthetic used, i. SEVO or PROPO. Here increases NOR, but not ADR, the μHbO2 under SEVO, where both are catecholamines do not increase the μHbO2 under PROPO. If our data can be transferred to the clinical situation, NOR appears (depending on the anesthetic, for example), gastric mucosal oxygenation to maintain or even to increase. R eferences:   [1] LA Schwarte, M Stevens, C Ince. JL Vincent (ed.) Yearbook of Intensive Careand Emergency Medicine 2006; 627-40 [2] LA Schwarte, O Picker, SR Bornstein et al. Crit Care Med. 2005; 33: 135-4