Occlusive mesenteric ischemia and its effects on jejunal intramucosal pH, mesenteric oxygen consumption and oxygen tensions from surfaces of the jejunum in anesthetized pigs

Objective: To investigate the effects of superior mesenteric artery (SMA) flow reduction on the jejunal intramucosal pH (pH_i) and to compare these effects with corresponding changes of mesenteric oxygen transport variables and oxygen tensions on the surfaces of the jejunal serosa and mucosa. Design: Prospective, randomized, controlled, experimental study. Setting: Animal research laboratory. Subjects: 20 domestic pigs. Interventions: Mechanical flow reduction in the SMA. The animals were randomized to have an SMA flow of 0%, 25%, 38%, 50% or 100% (control). Measurements and main results: Measurements (baseline, ischemia, reperfusion) consisted of hemodynamic and oxygen transport variables, SMA blood flow, mesenteric oxygen transport variables, pH_i and oxygen tensions of the jejunal serosa and mucosa. Flow reduction in the SMA resulted in a significant decrease of pH_i indicating ischemia earlier than mesenteric oxygen transport variables. The relationship between mesenteric oxygen delivery (DO_2ms) and pH_i during acute ischemia is best described by a sigmoid curve. There was a linear correlation between the changes of the jejunal surface oxygen tensions and pH_i due to SMA flow reduction. Conclusion: The sigmoid relationship between pH_i and DO_2ms indicated that pH_i is a sensitive parameter for detecting ischemia at 50% of the baseline oxygen delivery and that below 25% there was no further decrease of pH_i. In contrast, mesenteric and whole body oxygen transport parameters were not indicative of impaired mucosal oxygen supply. Received: 11 March 1996 Accepted: 4 October 1996     

Dobutamine reverses the vasopressin-associated impairment in cardiac index and systemic oxygen supply in ovine endotoxemia

Introduction

Arginine vasopressin (AVP) is increasingly used to treat sepsis-related vasodilation and to decrease catecholamine requirements. However, AVP infusion may be associated with a marked decrease in systemic blood flow and oxygen transport. The purpose of the present study was to evaluate whether dobutamine may be titrated to reverse the AVP-related decrease in cardiac index (CI) and systemic oxygen delivery index (DO₂I) in an established model of ovine endotoxemia.

Methods

Twenty-four adult ewes were chronically instrumented to determine cardiopulmonary hemodynamics and global oxygen transport. All ewes received a continuous endotoxin infusion that contributed to a hypotensive-hyperdynamic circulation and death of five sheep. After 16 hours of endotoxemia, the surviving ewes (n = 19; weight 35.6 ± 1.5 kg (mean ± SEM)) were randomized to receive either AVP (0.04 Umin^-1) and dobutamine (n = 8) or the vehicle (normal saline; n = 6) and compared with a third group treated with AVP infusion alone (n = 5). Dobutamine infusion was started at an initial rate of 2 μg kg^-1min^-1 and was increased to 5 and 10 μg kg^-1 min^-1 after 30 and 60 minutes, respectively.

Results

AVP infusion increased mean arterial pressure (MAP) and systemic vascular resistance index at the expense of a markedly decreased CI (4.1 ± 0.5 versus 8.2 ± 0.3 l min^-1 m^-2), DO₂I (577 ± 68 versus 1,150 ± 50 ml min^-1 m^-2) and mixed-venous oxygen saturation (S_vO₂; 54.5 ± 1.8% versus 69.4 ± 1.0%; all p < 0.001 versus control). Dobutamine dose-dependently reversed the decrease in CI (8.8 ± 0.7 l min^-1 m^-2 versus 4.4 ± 0.5 l min^-1 m^-2), DO₂I (1323 ± 102 versus 633 ± 61 ml min^-1 m^-2) and S_vO₂ (72.2 ± 1.7% versus 56.5 ± 2.0%, all p < 0.001 at dobutamine 10 μg kg^-1 min^-1 versus AVP group) and further increased MAP.

Conclusion

This study provides evidence that dobutamine is a useful agent for reversing the AVP-associated impairment in systemic blood flow and global oxygen transport.     

The effects of balloon filling into the inferior vena cava on the VO2/DO2 Relationship

We explored the effects of balloon filling into the inferior vena cave as a relatively simple and atraumatic method to study the relationship between oxygen uptake (VO₂) and oxygen supply (DO₂) during an acute reduction in blood flow. Via a femoral vein, a Foley catheter was inserted with its balloon placed above the renal veins and filled with fluid for 40 minutes. A fluid challenge with saline was performed before and during the balloon filling. In nine control dogs, the critical DO₂ (D0_2crit) below which VO₂ started to decline was found at 18.5 mL/kg/min. In nine dogs receiving endotoxin as a bolus of 0.5 mg/kg followed by an infusion of 0.02 mg/kg/min, the D0_2crit was found at 18.4 mL/kg/min. In seven dogs, increasing doses of endotoxin did not influence D0_2crit. In two dogs, prolonged balloon filling demonstrated the stability and also the reversibility, of the model. As the DO_2crit is much higher on this model than in other studies using acute hemorrhage, six dogs were submitted first to balloon filling and second to hemorrhage. The DO_2crit was 14.6 mL/kg/min during balloon filling but only 9.0 mL/kg/min during hemorrhage (P < .01). These differences in extraction capabilities are probably due to blood flow redistribution in the present model. Thus, balloon filling in the inferior vena cave represents a relatively atraumatic and reversible model to study the effects of an acute reduction in blood flow on the VO₂/DO₂ relationship. However, the DO_2crit is significantly higher in this balloon-filling model than in hemorrhaggc models. In the present study, effects of endotoxin on the tissues' extraction capabilities could not be demonstrated. In view of the probable effects of balloon filling on the distribution of blood flow, this model might not be suitable to study global changes in VO₂/DO₂ relationships.     

Red blood cell transfusion compared with gelatin solution and no infusion after cardiac surgery: effect on microvascular perfusion,vascular density,hemoglobin, and oxygen saturation

BACKGROUND: After cardiac surgery, red blood cell (RBC) transfusion may improve systemic hemodynamics and thereby microvascular blood flow and O₂ delivery (DO₂). STUDY DESIGN AND METHODS: In a nonrandomized prospective observational study on post–cardiac surgery patients, systemic hemodynamics and microvascular blood flow, vascular density (sidestream dark‐field imaging), hemoglobin (Hb) content, and saturation (reflectance spectrophotometry) were measured before and 1 hour after start of transfusion of 1 to 2 units of leukoreduced RBCs (270 ± 203 mL), 500 mL of gelatin solution, or control (no infusion), when patients were considered clinically hypovolemic with (RBC group, n = 12) or without (gelatin group, n = 14) anemia (Hb < 10 g/dL) or not (n = 13), respectively. RESULTS: Systemic Hb was lower and increased in the RBC transfusion but not in gelatin and control groups. There were no differences in changes in systemic DO₂, O₂ uptake, and extraction between groups. RBC transfusion, compared with gelatin or control, increased medium‐sized vascular density, Hb content, and saturation in the microcirculation, while blood flow remained unchanged. Changes of microvascular Hb and saturation paralleled changes in systemic Hb. CONCLUSION: The data argue in favor of efficacy of RBC transfusion after cardiac surgery. RBC transfusion increases systemic Hb and this in turn increases medium‐sized vascular density and DO₂ in the sublingual microcirculation, independently of systemic hemodynamics and volume status.     

Effects of chronic anemic hypoxia on skeletal muscle mass, protein degradation, and oxygen utilization

We evaluated the effects of 6 months of anemic hypoxia (mean hemoglobin 7.0 ± .9 g/dL) in six dogs on muscle mass, protein degradation, and oxidative performance at rest and during exercise. Anemia reduced systemic oxygen delivery (DO₂) by 56% relative to controls, but oxygen uptake (VO₂) Was unchanged and similar to controls. Anemic animals demonstrated significant weight loss (16% relative to controls) and a reduction in skeletal muscle mass (84% of control, P < .05). This reduction in muscle mass was due to decreased muscle synthesis, as evidenced by reduction of the ratio of urinary 3-methylhistidine to creatinine, an index of skeletal muscle protein degradation. In resting skeletal muscle, VO₂ was independent of DO₂. During stimulated contraction, evidence for both supply dependence and diffusion limitation of VO₂ was observed. Thus, resting systemic and skeletal muscle VO₂ is maintained during chronic anemic hypoxia by increasing O₂ extraction, and VO₂ is independent of DO₂. However, supply dependence and diffusion limitation of VO₂, together with reduced skeletal muscle mass, may limit oxidative performance of exercising skeletal muscle.     

Evaluation of oxygen uptake and delivery in critically ill patients: A statistical reappraisal

Objective The evaluation of oxygen consumption (VO₂) and oxygen delivery (DO₂) has gained increasing importance in the monitoring of critically ill patients. They can be obtained from either direct measurements or by indirect calculations based on the Fick principle. However the choice between these two approaches remains controversial. The aim of the study was to investigate whether these 2 methods provide similar results, and if not, to define the best one in terms of reproducibility. Design Oxygen delivery and oxygen consumption were prospectively analyzed in 171 consecutive critically ill patients. Metabolic data were obtained simultaneously. Setting The study was completed in the intensive care unit as part of the management of the patients studied. Patients A first “group” of 279 evaluations was carried out in 73 consecutive critically ill patients. The results were subsequently validated by 423 observations performed in the 98 following patients. Interventions Before and during each evaluation, the patients were kept in stable hemodynamic and metabolic conditions. All were mechanically ventilated. Measurements and results VO₂ was evaluated by calculation (Fick principle) and direct measurement using indirect calorimetry. Cardiac output was both measured by the thermodilution technique and calculated (Fick principle) and the data were used for the evaluation of the directly measured and indirectly calculated DO₂. For both VO₂ and DO₂ the agreement between direct and indirect evaluations was not satisfactory. Differences as great as 55 ml/min·m² and 267 ml/min·m² between simultaneously measured and calculated VO₂ and DO₂ respectively may be expected. Finally, the indirect calculated methods were less reproducible than the measured ones. These observations resulted mainly from the cumulative effects of the random errors in the metabolic data entering into the calculation of VO₂ and DO₂. Conclusions Our data suggested that the indirect calculation (Fick equation) and the direct measurement (indirect calorimetry, thermodilution) of both VO₂ and DO₂ did not provide similar results. Direct measurements are more reproducible methods and must be preferred.     

Non-invasive cardiac output and oxygen delivery measurement in an infant with critical anemia

Objective

To assess the combination of a non-invasive blood oxygen content (CaO₂) monitor and a non-invasive cardiac output (CO) monitor to continuously measure oxygen delivery (DO₂; DO₂ = CaO₂ × CO).

Methods

DO₂ was assessed during blood transfusions in an infant with acute hemolytic anemia following admission (~48 h). CaO₂ was measured by Pulse Co-Oximetry, which also provides estimates of hemoglobin (Hgb) concentration and percent oxygen saturation. CO was measured by Electrical Velocimetry, which also provides an estimate of stroke volume (SV). Lactate levels, an indirect measure of adequate DO₂, were assessed during the initial 8 h following admission.

Results

Incremental blood transfusions during the first 36 h increased Hgb from 2.7 to 9.5 g/dL during which time heart rate (HR) normalized from 156 to 115 beats/min. Lactate levels decreased from 20 to 0.8 mmol/L in the first 7 h. Non-invasive Hgb and CaO₂ measurements were well correlated with invasive Hgb and CaO₂ measures (r ² = 0.88; P = 0.019; r ² = 0.86; P = 0.0074, respectively). CO decreased from 2.47 ± 0.06 to 1.28 ± 0.02 L/min and SV decreased from 15.9 ± 0.4 to 11.1 ± 0.2 mL/beat. Mean arterial blood pressure was stable throughout the admission with systemic vascular resistance increasing from 407.6 ± 15.2 to 887.7 ± 30.1 dynes-s/cm⁵. DO₂ was estimated to increase from 120.2 ± 18.9 to 182.4 ± 5.6 mL O₂/min.

Conclusions

Non-invasive contin- uous CO and CaO₂ monitors are shown in this single case to provide continuous DO₂ measurement. The ability to assess DO₂ may improve hemodynamic monitoring during goal directed therapies.     

Effects of fenoldopam on systemic and splanchnic haemodynamics and oxygen delivery/consumption relationship during hyperdynamic ovine endotoxaemia

Objective: To evaluate the use of a selective dopamine-1 agonist (fenoldopam) to provide selective splanchnic vasodilatation during sustained hypotensive endotoxaemia in sheep. Design: Randomised, controlled, experimental study. Setting: Animal research laboratory. Subjects: 12 adult instrumented, midazolam-sedated sheep. Interventions: The animals were randomised to receive a 20-min continuous infusion of dopamine (10 μg · kg^{− 1}· min^{− 1}), fenoldopam (10 μg · kg⁻¹· min^{− 1}) and noradrenaline (1 μg · kg^{− 1}· min^{− 1}) under control conditions and 12 h after endotoxaemia was induced by a continuous infusion of Escherichia coli endotoxin producing a stable hyperdynamic state simulating human septic shock. This drug dosage was selected to produce a 25–30 % increase in cardiac output by all three drugs during control conditions. Measurements and results: Systemic and splanchnic haemodynamic data were continuously obtained and systemic and splanchnic oxygen delivery (DO₂) and consumption (VO₂) were calculated. Hyperdynamic hypotensive endotoxaemia did not modify the splanchnic and renal reduction in DO₂ and the vasoconstrictive reactivity to noradrenaline observed during control conditions. In contrast, endotoxaemia abolished the fenoldopam and dopamine-induced increase in splanchnic DO₂ (especially in the coeliac trunk) observed during control conditions. Conclusions: During sustained hyperdynamic endotoxaemia, the dopaminergic-induced selective increase in coeliac trunk blood flow is abolished, most probably because of an already maximally vasodilated splanchnic circulation which prevented dopamine or fenoldopam to vasodilate this area further. Contrary to common belief, selective dopamine-1 agonist administration under these conditions may therefore not be beneficial to the splanchnic organs, though it improves whole body DO₂ and VO₂. Received: 22 May 1997 Accepted: 13 January 1998     

Splanchnic blood flow is greater in septic shock treated with norepinephrine than in severe sepsis

Objective To assess global and splanchnic blood flow and oxygen transport in patients with sepsis with and without norepinephrine treatment.Design Prospective, clinical study.Setting University hospital intensive care unit.Patients A convenience sample of 15 septic shock patients treated with norepinephrine and 13 patients with severe sepsis who did not receive norepinephrine.Measurements and main results There were no differences between the two groups in global haemodynamics and oxygen transport. Splanchnic blood flow and oxygen delivery (splanchnic DO₂ 303±43 ml/min per m²) and consumption (splanchnic VO₂ 100±13 ml/min per m²) were much higher in the septic shock group compared with the severe sepsis group (splanchnic DO₂ 175±19 ml/min per m², splanchnic VO₂ 61±6 ml/min per m²). Gastric mucosal pH was subnormal in both groups (septic shock 7.29±0.02, severe sepsis 7.25±0.02) with no significant difference. No significant differences between groups were detected in lactate values.Conclusion These data confirm a redistribution of blood flow to the splanchnic region in sepsis that is even more pronounced in patients with septic shock requiring norepinephrine. However, subnormal gastric mucosal pH suggested inadequate oxygenation in part of the splanchnic region due to factors other than splanchnic hypoperfusion. Progress in this area will depend on techniques that address not only total splanchnic blood flow, but also inter-organ flow distribution, intra-organ distribution, and other microcirculatory or metabolic malfunctions.     

Effects of environmental hypothermia on hemodynamics and oxygen dynamics in a conscious swine model of hemorrhagic shock

BACKGROUND:

Hypothermia is associated with poor outcome in trauma patients; however, hemorrhagic shock (HS) model with anesthetized swine was different from that of clinical reality. To identify the effects of environmental hypothermia on HS, we investigated hemodynamics and oxygen dynamics in an unanesthetized swine model of HS under simulating hypothermia environment.

METHODS:

Totally 16 Bama pigs were randomly divided into ambient temperature group (group A) and low temperature group (group B), 8 pigs in each group. Venous blood (30 mL/kg) was continuously withdrawn for more than 15 minutes in conscious swine to establish a hemorrhagic shock model. Pulmonary arterial temperature (Tp), heart rate (HR), mean arterial pressure (MAP), pulmonary arterial pressure (PAP), pulmonary arterial wedge pressure (PAWP), central venous pressure (CVP), cardiac output (CO), hemoglobin (Hb), saturation of mixed venous blood (SvO₂) and blood gas analysis were recorded at the baseline and different hemorrhagic shock time (HST). The whole body oxygen delivery indices, DO₂I and VO₂I, and the O₂ extraction ratio (O₂ER) were calculated.

RESULTS:

Core body temperature in group A decreased slightly after the hemorrhagic shock model was established, and environmental hypothermia decreased in core body temperature. The mortality rate was significantly higher in group B (50%) than in group A (0%). DO₂I and VO₂I decreased significantly after hemorrhage. No difference was found in hemodynamics, DO₂I and VO₂I between group A and group B, but the difference in pH, lactic acid and O₂ER was significant between the two groups.

CONCLUSION:

Environmental hypothermia aggravated the disorder of oxygen metabolism after hemorrhagic shock, which was associated with poor prognosis.KEY WORDS: Hemorrhagic shock, Environmental hypothermia, Hemodynamics, Oxygen dynamics     

My paper 20 years later: effects of dobutamine on the VO2/DO2 relationship

Introduction

Oxygen uptake (VO₂) is independent of oxygen delivery (DO₂) over a wide range of values, because O₂ extraction can readily adapt to changes in DO₂. However, VO₂ can become DO₂-dependent in acute circulatory failure.

Methods

Various methods of evaluating the presence of VO₂/DO₂ dependency were conducted, but criticized because of potential problems with mathematical coupling of data. Some 20 years ago, we proposed using a dobutamine test and showed similar relationships using direct and indirect measurements. Since these studies on the systemic VO₂/DO₂ relationship, investigators have also explored regional alterations.

Conclusion

The relationship between VO₂ and DO₂ remains an important concept. Abnormal global VO₂/DO₂ dependency does not exist in stable, critically ill patients, but can exist in circulatory shock of all etiologies. It can also occur regionally in septic patients, and microcirculatory alterations may contribute. Patient management should be titrated individually with careful assessment to identify those who will benefit from increased DO₂.     

Impact of emergency intubation on central venous oxygen saturation in critically ill patients: a multicenter observational study

Introduction  

Central venous oxygen saturation (ScvO₂) has emerged as an important resuscitation goal for critically ill patients. Nevertheless, growing concerns about its limitations as a perfusion parameter have been expressed recently, including the uncommon finding of low ScvO₂ values in patients in the intensive care unit (ICU). Emergency intubation may induce strong and eventually divergent effects on the physiologic determinants of oxygen transport (DO₂) and oxygen consumption (VO₂) and, thus, on ScvO₂. Therefore, we conducted a study to determine the impact of emergency intubation on ScvO₂.     

Arteriovenous pH and partial pressure of carbon dioxide detect critical oxygen delivery during progressive hemorrhage in dogs

Arteriovenous (AV) pH and PCO₂ gradients increase as flow decreases and might potentially detect “dysoxia,” ie, inadequate tissue O₂ delivery (DO₂). However, expanding AV pH and PCO₂ gradients previously have been attributed to respiratory acidosis lie, pH that decreases only in proportion to increasing CO₂, an expected consequence of flow that is decreased but not necessarily inadequate). We studied AV pH and Pco₂ during O₂ supply independence, wherein O₂ consumption (VO₂) does not vary with DO₂, and O₂ supply dependence, a pathologic condition wherein VO₂ and DO₂ co-vary, in 14 dogs during graded progressive hemorrhage. Critical DO₂ (DO₂c), estimated by dual line regression, was 7.04 ± 0.30 mL/ kg min (SE). Arteriovenous pH and AV Pco₂ also varied with 1502 in a biphasic fashion, with inflections occurring at very similar DO₂ values (8.71 and 6.84 mL/kg min, respectively). Arteriovenous pH increased in proportion to expanding AV PCO₂ during O₂ supply independence, consistent with a “respiratory” etiology of AV pH in this region. During O₂ supply dependence, however, the response of AV pH to AV Pco₂ was greater, such that the linear regression of O₂ supply dependent AV pH versus AV Pco₂ was significantly different from the O₂ supply independent regression (P < .001). Our data support the hypothesis that rapidly expanding AV pH and AV Pco₂ represent metabolic acidosis and that these parameters may potentially be used to detect dysoxia.     

Optimal oxygen delivery in critically ill patients

Standard hemodynamic support in septic shock is to increase pulmonary capillary wedge pressure to above 15 mmHg by volume replacement and to give inotropic support if the mean arterial pressure (MAP) is not adequate. In an attempt to decrease mortality in critically ill patients, oxygen delivery (DO₂) was increased by switching inotropic support from dobutamine alone or in combination with norepinephrine to dopamine alone, or by adding dopexamine, prostacyclin, or hypertonic saline to the treatment. DO₂ increased significantly in all patients, but the increase in DO₂ was accompanied by only a 10% increase in oxygen consumption (VO₂). The increase in VO₂ was similar in survivors and nonsurvivors and in patients with and without septic shock. The results indicate that if adequate volume and inotropic support is provided for critically ill patients, the detectable oxygen debt is small and has little effect on patient outcome. When DO₂ is adequate, factors other than a tissue oxygen deficit seem to determine patient outcome.     

The concept of a critical oxygen delivery

In healthy tissues, decreases in oxygen delivery (QO_n) do not lower oxygen consumption (VO₂) because tissue O₂ extraction increases proportionately. When delivery is reduced below a critical threshold, VO₂ falls because tissue extraction exceeds a critical threshold, and cannot compensate for the reduction in delivery. In the adult respiratory distress syndrome and perhaps in septicemia, tissue extraction capacity is impaired, leading to O₂ supply dependency despite normal or increased overall delivery. This pathologic supply dependency could be caused by a loss in autoregulatory capacity, by disrupted blood flow distribution secondary to peripheral microembolization, or to other factors interfering with efficient tissue distribution of QO₂ with respect to VO₂. Alternatively, the increased VO₂ may be consumed in biochemical pathways not associated with ATP production, or in the production of oxygen radicals or hydrogen peroxide. To the extent this abnormal dependence of VO₂ on QO₂ reflects tissue hypoxia, clinical interventions which decrease systemic delivery should be evaluated with regard to possible deleterious effects on organ system function.     

Matching total body oxygen consumption and delivery: a crucial objective?

The strength of the rationale for incorporating total body oxygen consumption (VO₂) and delivery (DO₂) into our decision making strategies contrasts with the absence of demonstrated benefits of bedside calculations in clinical practice. This situation mandates a careful reappraisal of the theoretical limitations of bedside calculations of DO₂ and VO₂, including a re-evaluation of the clinical situations in which these calculations are valid. Three levels of complexity can be distinguished when analysing a patients hemodynamic status: 1) simple cases where investigations can be limited to clinical monitoring, including lactate changes over time; 2) intermediate situations requiring invasive investigations in which continuous monitoring of VO₂-related variables such as cardiac output and mixed venous oxygen saturation often provide enough information to guide clinical decision; and 3) complex situations where assessment of VO₂ and VO₂/DO₂ analysis might be recommended. Although studies that support such recommendations are limited they are based on a widely accepted physiological model. VO₂ and DO₂ analysis is also limited by theoretical and technical difficulties. In this article, we discuss the validity of these limitations in the bedside assessment of VO₂ and DO₂, and review data supporting the use of VO₂/DO₂ analysis in the clinical evaluation of complex cases.     

The compensatory reserve: potential for accurate individualized goal-directed whole blood resuscitation

Hemorrhagic shock can be mitigated by timely and accurate resuscitation designed to restore adequate delivery of oxygen (DO₂). Current doctrine of using systolic blood pressure (SBP) as a guide for resuscitation can be associated with increased morbidity. The compensatory reserve measurement (CRM) is a novel vital sign based on the recognition that the sum of all mechanisms that contribute to the compensatory response to hemorrhage reside in features of the arterial pulse waveform. CRM can be assessed continuously and non-invasively in real time. Compared to standard vital signs, CRM provides an early, as well as more sensitive and specific, indicator of patient hemorrhagic status since the activation of compensatory mechanisms occurs immediately at the onset of blood loss. Recent data obtained from our laboratory experiments on non-human primates have demonstrated that CRM is linearly related to DO₂ during controlled progressive hemorrhage and subsequent whole blood resuscitation. We used this relationship to determine that the time of hemodynamic decompensation (i.e., CRM = 0%) is defined by a critical DO₂ at approximately 5.3 mL O₂∙kg⁻¹∙min⁻¹. We also demonstrated that a target CRM of 35% during whole blood resuscitation only required replacement of 40% of the total blood volume loss to adequately sustain a DO₂ more than 50% (i.e., 8.1 mL O₂∙kg⁻¹∙min⁻¹) above critical DO₂ (i.e., threshold for decompensated shock) while maintaining hypotensive resuscitation (i.e., SBP at ~90 mmHg). Consistent with our hypothesis, specific values of CRM can be used to accurately maintain DO₂ thresholds above critical DO₂, avoiding the onset of hemorrhagic shock with whole blood resuscitation.     

Haemodynamic changes and skeletal muscle oxygen tension during complete blood exchange with ultrapurified polymerized bovine haemoglobin

Objective: The study investigates the effect of continuous blood exchange with ultrapurified, polymerized bovine haemoglobin (UPBH) in comparison to hetastarch on haemodynamics, oxygen transport and skeletal muscle oxygen tension in a canine model. Design: Sixteen anaesthetized beagle dogs underwent haemodilution with lactated Ringer's to a starting haematocrit of 20 % followed by progressive blood exchange with 6 % hetastarch 200,000/0.5 (HES, group 1) or UPBH (haemoglobin 13 ± 1 g · dl⁻¹, molecular weight (MW) 32–500,000, group 2) to haematocrit target levels of 15 %, 10 % and 5 % or less. Measurements and results: Besides haemodynamics, skeletal muscle tissue oxygen tension (tPO₂) was measured using a polarographic needle probe. In HES-treated animals, heart rate, cardiac output and blood flow were higher while systemic vascular resistance, systemic and regional arterio-venous oxygen difference (avDO₂) and oxygen extraction ratios were lower when compared to the UPBH group. In spite of a higher final haematocrit of 5 % in group 1, in comparison to group 2 with 2 %, final muscular oxygen uptake (4.7 ± 4 vs 10.1 ± 2 ml · min⁻¹) and mean tPO₂ (11.8 ± 2.3 vs 51.1 ± 2.9 mm Hg) were lower in group 1 than in group 2. While tPO₂ histograms were continuously shifted to lower oxygen tensions during progressive haemodilution with HES, UPBH-exchanged animals showed tPO₂ histograms shifted to higher values than baseline. Conclusion: In spite of vasoconstriction, UPBH provided more haemodynamic stability and enhanced skeletal muscle tPO₂ during progressive blood exchange when compared to HES. Received: 30 December 1996 Accepted: 16 June 1997     

O2 delivery and CO2 production during cardiopulmonary bypass as determinants of acute kidney injury: time for a goal-directed perfusion management?

Introduction  

Acute kidney injury (AKI) is common after cardiac operations. There are different risk factors or determinants of AKI, and some are related to cardiopulmonary bypass (CPB). In this study, we explored the association between metabolic parameters (oxygen delivery (DO₂) and carbon dioxide production (VCO₂)) during CPB with postoperative AKI.     

The influence of different levels of PEEP on peripheral tissue perfusion measured by subcutaneous and transcutaneous oxygen tension

Objective To compare subcutaneous (PscO₂) and transcutaneous (PtcO₂) oxygen tension measurements in relation to hemodynamic variables at different levels of PEEP, and to evaluate the usefulness of these measurements as monitors of peripheral tissue perfusion.Design Prospective trial.Setting Intensive care unit in a university hospital.Patients Seven patients with gastric cancer who where undergoing total gastrectomy.Interventions Silicone catheter was placed in the upper arm and transcutaneous oxygen monitor was placed on the upper part of the chest. A pulmonary artery catheter was placed in the right pulmonary artery.Measurements and results PscO₂ and PtcO₂ together with hemodynamic variables were measured at different levels of PEEP. Progressive increase of PEEP reduced cardiac index (CI) (p<0.05) with a concomitant decrease of PscO₂ (p<0.05) and oxygen delivery (DO₂) (p<0.05). Changes in PtcO₂ parallelled changes in arterial oxygen tension (PaO₂), but no correlation was found between PtcO₂, CI and DO₂.Conclusion PscO₂ is a sensitive indicator of subcutaneous tissue perfusion, which can be used to identify the PEEP level, with optimum peripheral perfusion. PscO₂ seems to be a more reliable indicafor of tissue perfusion than PtcO₂.This study was supported by Tore Nilsons Fund for Medical Research. Lundgrens Stiftelse, Medical Faculty, University of Lund and by the Swedish Medical Research Council Projecr no. B88-17x-00640-24B