Hypercapnic Acidosis Preserves Gastric Mucosal Microvascular Oxygen Saturation in a Canine Model of Hemorrhage

Local Mucosal CO2 but Not O2 Insufflation Improves Gastric and Oral Microcirculatory Oxygenation in a Canine Model of Mild Hemorrhagic Shock

Introduction

Acute hemorrhage results in perfusion deficit and regional hypoxia. Since failure of intestinal integrity seem to be the linking element between hemorrhage, delayed multi organ failure, and mortality, it is crucial to maintain intestinal microcirculation in acute hemorrhage. During critical bleeding physicians increase FiO₂ to raise total blood oxygen content. Likewise, a systemic hypercapnia was reported to maintain microvascular oxygenation (μHbO₂). Both, O₂ and CO₂, may have adverse effects when applied systemically that might be prevented by local application. Therefore, we investigated the effects of local hyperoxia and hypercapnia on the gastric and oral microcirculation.

Methods

Six female foxhounds were anaesthetized, randomized into eight groups and tested in a cross-over design. The dogs received a local CO₂-, O₂-, or N₂-administration to their oral and gastric mucosa. Hemorrhagic shock was induced through a withdrawal of 20% of estimated blood volume followed by retransfusion 60 min later. In control groups no shock was induced. Reflectance spectrophotometry and laser Doppler were performed at the gastric and oral surface. Oral microcirculation was visualized by incident dark field imaging. Systemic hemodynamic parameters were recorded continuously. Statistics were performed using a two-way-ANOVA for repeated measurements and post hoc analysis was conducted by Bonferroni testing (p < 0.05).

Results

The gastric μHbO₂ decreased from 76 ± 3% to 38 ± 4% during hemorrhage in normocapnic animals. Local hypercapnia ameliorated the decrease of μHbO₂ from 78 ± 4% to 51 ± 8%. Similarly, the oral μHbO₂ decreased from 81 ± 1% to 36 ± 4% under hemorrhagic conditions and was diminished by local hypercapnia (54 ± 4%). The oral microvascular flow quality but not the total microvascular blood flow was significantly improved by local hypercapnia. Local O₂-application failed to change microvascular oxygenation, perfusion or flow quality. Neither CO₂ nor O₂ changed microcirculatory parameters and macrocirculatory hemodynamics under physiological conditions.

Discussion

Local hypercapnia improved microvascular oxygenation and was associated with a continuous blood flow in hypercapnic individuals undergoing hemorrhagic shock. Local O₂ application did not change microvascular oxygenation, perfusion and blood flow profiles in hemorrhage. Local gas application and change of microcirculation has no side effects on macrocirculatory parameters.

Regional hypothermia improves gastric microcirculatory oxygenation during hemorrhage in dogs

Mild systemic hypothermia increases gastric mucosal oxygenation (μHbO₂) during hemorrhagic shock in dogs. In the context of critical blood loss hypothermia might be fatal due to adverse side effects. Selective regional hypothermia might overcome these limitations. The aim of our study was to analyze the effects of regional gastric and oral mucosal hypothermia on μHbO₂ and perfusion (μflow). In a cross-over study six anesthetized dogs were subjected to local oral and gastric mucosal hypothermia (34°C), or maintenance of local normothermia during normovolemia and hemorrhage (-20% blood volume). Macro- and microcirculatory variables were recorded continuously. During normovolemia, local hypothermia increased gastric microcirculatory flow (μflow) without affecting oxygenation (μHbO₂) or oral microcirculation. During mild hemorrhagic shock gastric μHbO₂ decreased from 72±2% to 38±3% in the normothermic group. This was attenuated by local hypothermia, where μHbO₂ was reduced from 74±3% to 52±4%. Local perfusion, oral microcirculation and macrocirculatory variables were not affected. Selective local hypothermia improves gastric μHbO₂ during hemorrhagic shock without relevant side effects. In contrast to systemic hypothermia, regional mucosal hypothermia did not affect perfusion and oxygen supply during hemorrhage. Thus, the increased μHbO₂ during local hypothermia rather indicates reduced mucosal oxygen demand.

Local gastric RAAS inhibition improves gastric microvascular perfusion in dogs

During circulatory shock, gastrointestinal microcirculation is impaired, especially via activation of the renin-angiotensin-aldosterone system. Therefore, inhibition of the renin-angiotensin-aldosterone system might be beneficial in maintaining splanchnic microcirculation. The aim of this study was to analyze whether locally applied losartan influences gastric mucosal perfusion (µflow, µvelo) and oxygenation (µHbO2) without systemic hemodynamic changes. In repetitive experiments six anesthetized dogs received 30 mg losartan topically on the oral and gastric mucosa during normovolemia and hemorrhage (-20% blood volume). Microcirculatory variables were measured with reflectance spectrometry, laser Doppler flowmetry and incident dark field imaging. Transpulmonary thermodilution and pulse contour analysis were used to measure systemic hemodynamic variables. Gastric barrier function was assessed via differential absorption of inert sugars. During normovolemia, losartan increased gastric µflow from 99 ± 6 aU to 147 ± 17 aU and µvelo from 17 ± 1 aU to 19 ± 1 aU. During hemorrhage, losartan did not improve µflow. µvelo decreased from 17 ± 1 aU to 14 ± 1 aU in the control group. Application of losartan did not significantly alter µvelo (16 ± 1 aU) compared to the control group and to baseline levels (17 ± 1 aU). No effects of topical losartan on macrohemodynamic variables or microcirculatory oxygenation were detected. Gastric microcirculatory perfusion is at least partly regulated by local angiotensin receptors. Topical application of losartan improves local perfusion via vasodilation without significant effects on systemic hemodynamics. During mild hemorrhage losartan had minor effects on regional perfusion, probably because of a pronounced upstream vasoconstriction.

Carbon Monoxide-Releasing Molecule Enhances Coagulation and Decreases Fibrinolysis in Normal Canine Plasma

The dog is an important companion animal and also purpose-bred for research studies. Coagulopathies in dogs are common, although the availability of blood products for therapy is inconsistent throughout the profession. A pro-coagulant therapeutic that is readily available and easily stored would be useful for the treatment of coagulopathies. Tricarbonyldichlororuthenium (II) dimer [Carbon monoxide-releasing molecule-2 (CORM-2)] acts as a prothrombotic agent in plasma by increasing the velocity of clot formation and clot strength, and by decreasing the clot's vulnerability to fibrinolysis. We sought to test CORM-2's effect on coagulation and fibrinolysis in vitro in canine plasma using thromboelastography. Measures of the rate of clot formation and clot strength in plasma without CORM-2 were highly correlated with fibrinogen concentration. We found that CORM-2 significantly enhanced the rate of clot formation and clot strength and significantly reduced the rate of fibrinolysis and the clot lysis time. The per cent change in rate of clot formation and clot strength was not significantly correlated with fibrinogen concentration, indicating that CORM-2's pro-coagulant effect is not dependent on fibrinogen concentration. This study corroborates studies in other species that show that CORM-2 is pro-coagulant in plasma, and lays the groundwork for developing CORM-2 as a therapeutic agent for canine coagulopathies. Future studies will evaluate the effect of CORM-2 on whole blood both in vitro and in vivo.

Melatonin pretreatment improves gastric mucosal blood flow and maintains intestinal barrier function during hemorrhagic shock in dogs

OBJECTIVE

Melatonin improves hepatic perfusion after hemorrhagic shock and may reduce stress-induced gastric lesions. This study was designed to investigate whether pretreatment with melatonin may influence gastric mucosal microcirculatory perfusion (μflow), oxygenation (μHbO₂ ), or intestinal barrier function during physiological and hemorrhagic conditions in dogs.

METHODS

In a randomized crossover study, five anesthetized foxhounds received melatonin 100 μg kg^-1 or vehicle (ethanol 5%) intravenously in the absence or presence of hemorrhagic shock (60 minutes, -20% blood volume). Systemic hemodynamic variables, gastric mucosal perfusion, and oxygenation were recorded continuously; intestinal barrier function was assessed intermittently via xylose absorption.

RESULTS

During hemorrhagic shock, melatonin significantly attenuated the decrease in μflow, compared with vehicle (-19±9 vs -43±10 aU, P<.05), without influence on μHbO₂ . A significant increase in xylose absorption was detected during hemorrhage in vehicle-treated dogs, compared with sham-operated animals (13±2 vs 8±1 relative amounts, P<.05); this was absent in melatonin-treated animals (6±1 relative amounts). Melatonin did not influence macrocirculation.

CONCLUSIONS

Melatonin improves regional blood flow suggesting improved oxygen delivery in gastric mucosa during hemorrhagic shock. This could provide a mechanism for the observed protection of intestinal barrier function in dogs.

Hypercapnia: clinical relevance and mechanisms of action

PURPOSE OF REVIEW

Multiple clinical and laboratory studies have been conducted to illustrate the effects of hypercapnia in a range of injuries, and to understand the mechanisms underlying these effects. The aim of this review is to highlight and interpret information obtained from these recent reports and discuss how they may inform the clinical context.

RECENT FINDINGS

In the last decade, several important articles have addressed key elements of how carbon dioxide interacts in critical illness states. Among them the most important insights relate to how hypercapnia affects critical illness and include the effects and mechanisms of carbon dioxide in pulmonary hypertension, infection, inflammation, diaphragm dysfunction, and cerebral ischemia. In addition, we discuss molecular insights that apply to multiple aspects of critical illness.

SUMMARY

Experiments involving hypercapnia have covered a wide range of illness models with varying degrees of success. It is becoming evident that deliberate hypercapnia in the clinical setting should seldom be used, except wherever necessitated to avoid ventilator-associated lung injury. A more complete understanding of the molecular mechanisms must be established.

Predictors of mortality and prehospital monitoring limitations in blunt trauma patients

This study aimed at determining predictors of in-hospital mortality and prehospital monitoring limitations in severely injured intubated blunt trauma patients. We retrospectively reviewed patients' charts. Prehospital vital signs, Injury Severity Score (ISS), initial Glasgow Coma Scale (GCS), Revised Trauma Score (RTS), arterial blood gases, and lactate were compared in two study groups: survivors (n = 40) and nonsurvivors (n = 30). There were no significant differences in prehospital vital signs between compared groups. Nonsurvivors were older (P = 0.006), with lower initial GCS (P < 0.001) and higher ISS (P < 0.001), along with higher lactate (P < 0.001) and larger base deficit (BD; P = 0.006), whereas RTS (P = 0.001) was lower in nonsurvivors. For predicting mortality, area under the curve (AUC) was calculated: for lactate 0.82 (P < 0.001), for ISS 0.82 (P < 0.001), and for BD 0.69 (P = 0.006). Lactate level of 3.4 mmol/L or more was 82% sensitive and 75% specific for predicting in-hospital death. In a multivariate logistic regression model, ISS (P = 0.037), GCS (P = 0.033), and age (P = 0.002) were found to be independent predictors of in-hospital mortality. The AUC for regression model was 0.93 (P < 0.001). Increased levels of lactate and BD on admission indicate more severe occult hypoperfusion in nonsurvivors whereas vital signs did not differ between the groups.

Hypothermia improves oral and gastric mucosal microvascular oxygenation during hemorrhagic shock in dogs

Hypothermia is known to improve tissue function in different organs during physiological and pathological conditions. The aim of this study was to evaluate the effects of hypothermia on oral and gastric mucosal microvascular oxygenation (μHbO₂) and perfusion (μflow) under physiological and hemorrhagic conditions. Five dogs were repeatedly anesthetized. All animals underwent each experimental protocol (randomized cross-over design): hypothermia (34°C), hypothermia during hemorrhage, normothermia, and normothermia during hemorrhage. Microcirculatory and hemodynamic variables were recorded. Systemic (DO₂) and oral mucosal (μDO₂) oxygen delivery were calculated. Hypothermia increased oral μHbO₂ with no effect on gastric μHbO₂. Hemorrhage reduced oral and gastric μHbO₂ during normothermia (−36 ± 4% and −27 ± 7%); however, this effect was attenuated during additional hypothermia (−15 ± 5% and −11 ± 5%). The improved μHbO₂ might be based on an attenuated reduction in μflow during hemorrhage and additional hypothermia (−51 ± 21 aU) compared to hemorrhage and normothermia (−106 ± 19 aU). μDO₂ was accordingly attenuated under hypothermia during hemorrhage whereas DO₂ did not change. Thus, in this study hypothermia alone improves oral μHbO₂ and attenuates the effects of hemorrhage on oral and gastric μHbO₂. This effect seems to be mediated by an increased μDO₂ on the basis of increased μflow.

Hypercapnia counteracts captopril-induced depression of gastric mucosal oxygenation

Hypercapnia (HC) increases systemic oxygen delivery (DO2) and gastric mucosal oxygenation. However, it activates the renin-angiotensin-aldosterone system (RAAS), which conversely reduces mesenteric perfusion. The aims of this study were to evaluate the effect of RAAS inhibition during normocapnia and HC on oral and gastric mucosal oxygenation (μHbO2) and to assess the effect of blood pressure under these circumstances. Five dogs were repeatedly anesthetized to study the effects of ACE inhibition (ACE-I; 5 mg/kg captopril, followed by 0.25 mg/kg per h) on μHbO2 (reflectance spectrophotometry) and hemodynamic variables during normocapnia (end-tidal CO2=35 mmHg) and HC (end-expiratory carbon dioxide (etCO2)=70 mmHg). In the control group, the dogs were subjected to HC alone. To exclude the effects of reduced blood pressure, in one group, blood pressure was maintained at baseline values via titrated phenylephrine (PHE) infusion during HC and additional captopril infusion. ACE-I strongly reduced gastric μHbO2 from 72±2 to 65±2% and mean arterial pressure (MAP) from 64±2 to 48±4 mmHg, while DO2 remained unchanged. This effect was counteracted in the presence of HC, which increased gastric μHbO2 from 73±3 to 79±6% and DO2 from 15±2 to 22±4 ml/kg per min during ACE-I without differences during HC alone. However, MAP decreased similar to that observed during ACE-I alone from 66±3 to 47±5 mmHg, while left ventricular contractility (dPmax) increased from 492±63 to 758±119 mmHg/s. Titrated infusion of PHE had no additional effects on μHbO2. In summary, our data suggest that RAAS inhibition reduces gastric mucosal oxygenation in healthy dogs. HC not only abolishes this effect, but also increases μHbO2, DO2, and dPmax. The increase in μHbO2 during ACE-I under HC is in accordance with our results independent of blood pressure.

Vasopressin V(1A) receptors mediate the increase in gastric mucosal oxygenation during hypercapnia

Hypercapnia (HC) improves systemic oxygen delivery (DO₂) and microvascular hemoglobin oxygenation of the mucosa (μHbO₂). Simultaneously, HC increases plasma levels of vasopressin. Although vasopressin is generally regarded a potent vasoconstrictor particularly in the splanchnic region, its effects on splanchnic microcirculation during HC is unclear. The aim of this study was to evaluate the role of endogenous vasopressin on gastric mucosal oxygenation and hemodynamic variables during physiological (normocapnia) and hypercapnic conditions. Five dogs were repeatedly anesthetized to study the effect of vasopressin V(1A) receptor blockade ([Pmp¹,Tyr(Me)²]-Arg⁸-Vasopressin, 35  μg/kg) on hemodynamic variables and μHbO₂ during normocapnia or HC (end-tidal CO₂ 70  mmHg). In a control group, animals were subjected to HC alone. μHbO₂ was measured by reflectance spectrophotometry, systemic DO₂ was calculated from intermittent blood gas analysis, and cardiac output was measured by transpulmonary thermodilution. Data are presented as mean±s.e.m. for n=5 animals. During HC alone, DO₂ increased from 12±1 to 16±1 ml/kg per min and μHbO₂ from 70±4 to 80±2%. By contrast, additional vasopressin V(1A) receptor blockade abolished the increase in μHbO₂ (80±2 vs. 69±2%) without altering the increase in DO₂ (16±1 vs. 19±2  ml/kg per min). Vasopressin V1A receptor blockade (VB) during normocapnia neither affected DO₂ (13±1 vs. 14±1  ml/kg per min) nor μHbO₂ (75±3 vs. 71±5%). Vasopressin V(1A) receptor blockade abolished the increase in μHbO₂ during HC independent of DO₂. Thus, in contrast to its generally vasoconstrictive properties, the vasopressin V1A receptors seem to mediate the increase in gastric microcirculatory mucosal oxygenation induced by acute HC.

Hypocapnia as a poor prognostic factor in aneurysmal subarachnoid hemorrhage

In this editorial, the issues of hypocapnia and its relation to symptomatic vasospasm, prognosis, and outcome among patients with aneurysmal subarachnoid hemorrhage is discussed. Potential directions for future studies are provided.

Hyperpressure intraperitoneal fluid administration for control of bleeding after liver injury

BACKGROUND

Acute hemorrhage is the principal cause of death in trauma patients, with most fatalities occurring during the pre-hospital phase. Recently, intra-abdominal insufflation by carbon dioxide has been shown to drastically reduce bleeding in vascular and splanchnic hemorrhagic animal models simulating the pre-hospital phase. Here, we propose that using dialysate fluid for increasing intra-abdominal pressure is at least as effective as gas with some potential advantages.

MATERIALS AND METHODS

A novel method of inducing liver trauma was used in 24 White New Zealand rabbits randomized into three groups: intra-abdominal carbon dioxide insufflation (GAS) with 15 cm H(2)O pressure; intra-abdominal infusion of type III dialysate solution (DIAL) with the same pressure; no change in intra-abdominal pressure (CTRL). All groups received intravenous resuscitation when their mean arterial pressure was below 30 mmHg. Physiologic parameters were recorded during 20 min of bleeding.

RESULTS

Red blood cell (RBC) volume loss in the DIAL and GAS was 45% and 48% lower than that in the CTRL, respectively (P < 0.0005). Similar trends were observed for losses in RBC count and hemoglobin (Hb). Final mean arterial pressure, arterial RBC, Hb, and hematocrit were higher in the DIAL and GAS than in the CTRL; glucose concentration in the DIAL group was significantly higher than that in the GAS and CTRL groups. No intravenous fluid therapy was needed in the DIAL group.

CONCLUSIONS

Hyperpressure intraperitoneal dialysate administration successfully reduced bleeding after severe liver injury in rabbits. This method can potentially be used as an adjunct to increase patient survival during pre-hospital cares.