Use of tissue oxygen tension measurements during resuscitation from hemorrhagic shock

Cremaster muscle perfusion, oxygenation, and heterogeneity revealed by a new automated acquisition system in a rodent model of prolonged hemorrhagic shock

Local blood flow/oxygen partial pressure (Po₂) distributions and flow-Po₂ relationships are physiologically relevant. They affect the pathophysiology and treatment of conditions like hemorrhagic shock (HS), but direct noninvasive measures of flow, Po₂, and their heterogeneity during prolonged HS are infrequently presented. To fill this void, we report the first quantitative evaluation of flow-Po₂ relationships and heterogeneities in normovolemia and during several hours of HS using noninvasive, unbiased, automated acquisition. Anesthetized rats were subjected to tracheostomy, arterial/venous catheterizations, cremaster muscle exteriorization, hemorrhage (40% total blood volume), and laparotomy. Control animals equally instrumented were not subjected to hemorrhage/laparotomy. Every 0.5 h for 4.5 h, noninvasive laser speckle contrast imaging and phosphorescence quenching were employed for nearly 7,000 flow/Po₂ measurements in muscles from eight animals, using an automated system. Precise alignment of 16 muscle areas allowed overlapping between flow and oxygenation measurements to evaluate spatial heterogeneity, and repeated measurements were used to estimate temporal heterogeneity. Systemic physiological parameters and blood chemistry were simultaneously assessed by blood samplings replaced with crystalloids. Hemodilution was associated with local hypoxia, but increased flow prevented major oxygen delivery decline. Adding laparotomy and prolonged HS resulted in hypoxia, ischemia, decreased tissue oxygen delivery, and logarithmic flow/Po₂ relationships in most regions. Flow and Po₂ spatial heterogeneities were higher than their respective temporal heterogeneities, although this did not change significantly over the studied period. This quantitative framework establishes a basis for evaluating therapies aimed at restoring muscle homeostasis, positively impacting outcomes of civilian and military trauma/HS victims.NEW & NOTEWORTHY This is the first study on flow-Po₂ relationships during normovolemia, hemodilution, and prolonged hemorrhagic shock using noninvasive methods in multiple skeletal muscle areas of monitored animals. Automated flow/Po₂ measurements revealed temporal/spatial heterogeneities, hypoxia, ischemia, and decreased tissue oxygen delivery after trauma/severe hemorrhage. Hemodilution was associated with local hypoxia, but hyperemia prevented a major decline in oxygen delivery. This framework provides a quantitative basis for testing therapeutics that positively impacts muscle homeostasis and outcomes of trauma/hemorrhagic shock victims.

Automated noninvasive evaluation of blood flow and oxygenation in rats integrated with systemic physiological monitoring

BACKGROUND

Many studies evaluating blood flow and oxygen partial pressure (PO2) do not directly measure both parameters, are confined to few locations/microvessels, and depend on investigator's selection of measuring sites. Moreover, clinically/physiologically relevant systemic parameters are not simultaneously recorded. We implemented an automated system for prolonged blood flow/PO2 acquisition in large areas while collecting relevant systemic information.

METHODS

In anesthetized animals, cardiorespiratory parameters were continuously recorded. Other data were collected at baseline and hourly after 4 hours of hemorrhagic shock. A cremaster muscle was spread over a pedestal fixed to a motorized stage. One 2-dimensional tissue scan allowed 16 noninvasive PO2 measurements using oxygen-dependent phosphorescence quenching and fiber optics. Blood flow was estimated using laser speckle contrast imaging in the same areas used for PO2 measurements. At each timepoint, blood was sampled for extensive biochemistry/coagulation profile.

RESULTS

The system was used successfully by different operators. A set of flow/PO2 measurements was completed in less than 90 seconds. Muscle flow and PO2 correlated with some but not several systemic parameters, emphasizing the importance of performing both local and systemic evaluations.

CONCLUSION

System advantages include integration between local and over 40 systemic parameters, unbiased data collection/analysis, improved performance/sampled area, easy expansion, implementation and maintenance, no customized programming, and simplified training. Combining this system with trauma/prolonged HS models will enhance our ability to investigate tissue stability and select better resuscitation strategies to improve outcomes and survival.

LEVEL OF EVIDENCE

Diagnostic test, level V.

Bedside monitoring of patients with shock using a portable spatially-resolved near-infrared spectroscopy

Clinical monitoring of shock mainly depends on blood-oxygen-indices obtained from invasive blood sample tests. The central internal jugular central vein oxygenation level (ScvO2) has been considered as a gold standard indicator for shock prediction. We developed a noninvasive spatially-resolved near-infrared spectroscopy (SR-NIRS) to measure tissue blood oxygen saturation (StO2) surrounding the region of taking blood sample for the ScvO2 test in 25 patients with shock. StO2 values were found to be highly correlated (r = 0.84, p < 0.001) with ScvO2 levels and the concordance coefficient of 0.80 is high. The results suggest the potential of noninvasive SR-NIRS for bedside shock monitoring.

Critical care issues in the early management of severe trauma

Violent trauma and road traffic injuries kill more than 2.5 million people in the world every year, for a combined mortality of 48 deaths per 100,000 population per year. Most trauma deaths occur at the scene or in the first hour after trauma, with a proportion from 34% to 50% occurring in hospitals. Preventability of trauma deaths has been reported as high as 76% and as low as 1% in mature trauma systems. Critical care errors may occur in a half of hospital trauma deaths, in most of the cases contributing to the death. The most common critical care errors are related to airway and respiratory management, fluid resuscitation, neurotrauma diagnosis and support, and delayed diagnosis of critical lesions. A systematic approach to the trauma patient in the critical care unit would avoid errors and preventable deaths.

Continuous Muscle Tissue Oxygenation in Critically Injured Patients: A Prospective Observational Study

BACKGROUND

Despite normalization of vital signs, critically injured patients may remain in a state of occult underresuscitation that sets the stage for sepsis, organ failure, and death. A continuous, sensitive, and accurate measure of resuscitation after injury remains elusive.

METHODS

In this pilot study, we evaluated the ability of two continuous measures of peripheral tissue oxygenation in their ability to detect hypoperfusion: the Licox polarographic tissue oxygen monitor (PmO2) and the InSpectra near-infrared spectrometer (StO2). We hypothesized that deltoid muscle tissue oxygenation measurements could detect patients in "occult shock" who are at increased risk for post-injury complications. The study was designed to (1) define values for PmO2 and StO2 in patients who by all standard measures appeared to be clinically resuscitated; (2) evaluate the relationship between PmO2, StO2 and other physiologic variables including mean arterial pressure (MAP), lactate and base deficit (BD); and (3) examine the relationship between early low tissue oxygen values and the subsequent development of infections and organ dysfunction. Licox probes were inserted into the deltoid muscle of critically injured patients after initial surgical and radiologic interventions, and transcutaneous StO2 monitors were applied over the same muscle bed. PmO2, StO2, and standard physiologic data were collected continuously using a multimodal bioinformatics system.

RESULTS

Twenty-eight critically injured patients were enrolled in this study at admission to the intensive care unit (ICU). For patients who appeared to be well resuscitated (defined as MAP > or = 70 mm Hg, heart rate [HR] < or = 110 bpm, BD > or = -2, and partial pressure of arterial oxygen (PaO2) = 80 and 150 mm Hg), the mean PmO2 was 34 +/- 11 mm Hg and StO2 was 63 +/- 27%. There was a strong relationship between PmO2 and BD (p < 0.001) but no significant relationship between StO2 and BD. The relationship between PmO2 and StO2 was weak but statistically significant. Early low values of both PmO2 and StO2 identified patients at risk for infectious complications or multiple organ failure (MOF). In patients who were well resuscitated by standard continuous parameters (HR and MAP), low PmO2 during the first 24 hours after admission (PmO2 < or = 25 for at least 2 hours) was strongly associated with the development of infectious complications (Odds Ratio = 16.5, 95% CI 1.49 to 183, p = 0.02).

CONCLUSIONS

PmO2 is a responsive, reliable and continuous monitor of changes in base deficit. Initial low values for either PmO2 or StO2 were associated with post-injury complications. PmO2 monitoring may be useful in identifying patients in the state of occult underresuscitation who remain at risk for developing infection and MOF.

Tissue oxygen saturation during colorectal surgery measured by near-infrared spectroscopy: pilot study to predict anastomotic complications

INTRODUCTION

We investigated the relation between tissue oxygen saturation measured by near-infrared spectroscopy (NIRS) and anastomotic complications associated with colorectal surgery.

METHODS

A series of 20 patients with colorectal cancer underwent radical surgery with enteric anastomosis. Measurements of tissue oxygen saturation (StO2) were performed at both the proximal and distal portions of the anastomotic site; in cases of anterior resection, we measured StO2 only in the proximal portion.

RESULTS

Two anastomotic complications (one leakage, one stenosis) occurred in the 20 cases. The StO2 in patients with anastomotic complications was 58.0%, and that in patients without complications was 71.0%. Altogether, 18 patients had StO2 values > 66%, and none of them had anastomotic complications. In contrast, 2 patients had StO2 values < 60%, and both had anastomotic complications.

CONCLUSIONS

The StO2 of the anastomotic site can be safely and reliably measured by NIRS during colorectal surgery. Low StO2 on both sides of the anastomosis may indicate an increased risk of anastomotic complications. Further study is needed to determine the cutoff value for StO2 required to prevent serious complications.

Tumor necrosis factor receptor deficiency exacerbated Adriamycin-induced cardiomyocytes apoptosis: an insight into the Fas connection

Cardiomyopathy is a major dose-limiting factor for applications of Adriamycin, a potent chemotherapeutic agent. The present study tested the hypothesis that increased tumor necrosis factor (TNF)-alpha signaling via its receptors protects against Adriamycin-induced cardiac injury. We used mice in which both TNF receptor I and II have been selectively inactivated (DKO) with wild-type mice as controls. Morphometric studies of cardiac tissue following Adriamycin treatment revealed greater ultrastructural damage in cardiomyocyte mitochondria from DKO mice. Biochemical studies of cardiac tissues showed cytochrome c release and the increase in proapoptotic protein levels, suggesting that lack of TNF-alpha receptor I and II exacerbates Adriamycin-induced cardiac injury. The protective role of TNF receptor I and II was directly confirmed in isolated primary cardiomyocytes. Interestingly, following Adriamycin treatment, the levels of Fas decreased in the wild-type mice. In contrast, DKO mice had an increase in Fas levels and its downstream target, mitochondrial truncated Bid. These results suggested that TNF-alpha receptors play a critical role in cardioprotection by suppression of the mitochondrial-mediated associated cell death pathway.

Assessment and treatment of perfusion abnormalities in the emergency patient

Many patients presented to the emergency veterinarian are suffering from global or local tissue hypoperfusion. Global or systemic hypoperfusion can occur secondary to a reduction in the effective circulating intravascular volume (hypovolemic shock) or reduced ability of the heart to pump blood around the body secondary to reduced cardiac function (cardiogenic shock),obstruction to blood flow (obstructive shock), or maldistribution of the circulating intravascular volume (distributive shock). Initial assessment involving physical examination supplemented by measurement of hemodynamic and metabolic parameters allows the clinician to recognize and treat patients with severe global hypoperfusion. Use of techniques like sublingual capnometry and measurement of central venous oxygen saturation may aid recognition and evaluation of early hypoperfusion. Treatment decisions are made based on an assessment of the severity of the hypoperfusion and its probable underlying cause. Early effective treatment of hypoperfusion is likely to lead to a better outcome for the patient.

Molecular diagnostics of injury and repair responses in critical illness: what is the future of "monitoring" in the intensive care unit?

OBJECTIVE

To identify potential future means of monitoring injury and repair in critical illness.

DESIGN

Review of the literature.

RESULTS

Critically ill patients are monitored extensively and intensively by such means as hemodynamics, laboratory values, and radiologic studies. In general, however, the goal of monitoring has been to measure the degree of injury and to prevent further injury, rather than to measure repair. Measures of repair have been limited to phenotypic end points such as return of organ function, as measured by blood chemistry. In this article, I examine how it may be possible in the future to monitor the progress of repair using genomic and proteomic biomarkers. These types of monitors would enable clinicians to control the healing environment using real time, rapid biomarkers, and sophisticated techniques to target therapy to the patient's current inflammatory state, taking into account the genetic makeup of the patient and his or her likely response to a given drug.

CONCLUSIONS

The rapidly evolving sciences of genomics, proteomics, computational biology, and complex system theory can be used a) to model critical illness; b) to model adaptive and maladaptive responses to critical illness; c) to tailor treatments to create an ideal inflammatory environment for repair and regeneration, taking into account the individual genetic contribution; and d) to monitor the progress of repair. The major obstacles to reaching these goals are technological, and experience suggests that they will be overcome.

Diagnosis and monitoring of hemorrhagic shock during the initial resuscitation of multiple trauma patients: a review

The initial management of the multiple trauma victim requires evaluation for potential hemorrhage and ongoing monitoring to assess the efficacy of resuscitation and avoid complications related to hemorrhagic shock. A variety of strategies exist to assess circulatory status, including hemodynamic monitoring, tissue perfusion measurement, and use of serum markers of metabolism. We review available technologies used to assess fluid status and tissue perfusion in patients with blood loss or hemorrhagic shock, discuss how these methods can be used effectively and efficiently during initial trauma resuscitation to guide therapy and disposition, and suggest directions for future research to improve outcomes by providing more appropriate and timely care and avoiding unnecessary complications.

Tissue oxygen monitoring during hemorrhagic shock and resuscitation: a comparison of lactated Ringer's solution, hypertonic saline dextran, and HBOC-201

BACKGROUND

The ideal resuscitation fluid for the trauma patient would be readily available to prehospital personnel, universally compatible, effective when given in small volumes, and capable of reversing tissue hypoxia in critical organ beds. Recently developed hemoglobin-based oxygen-carrying solutions possess many of these properties, but their ability to restore tissue oxygen after hemorrhagic shock has not been established. We postulated that a small-volume resuscitation with HBOC-201 (Biopure) would be more effective than either lactated Ringer's (LR) solution or hypertonic saline dextran (HSD) in restoring baseline tissue oxygen tension levels in selected tissue beds after hemorrhagic shock. We further hypothesized that changes in tissue oxygen tension measurements in the deltoid muscle would reflect the changes seen in the liver and could thus be used as a monitor of splanchnic resuscitation.

METHODS

This study was a prospective, blinded, randomized resuscitation protocol using anesthetized swine (n = 30), and was modeled to approximate an urban prehospital clinical time course. After instrumentation and splenectomy, polarographic tissue oxygen probes were placed into the liver (liver PO2) and deltoid muscle (muscle PO2) for continuous tissue oxygen monitoring. Swine were hemorrhaged to a mean arterial pressure (MAP) of 40 mm Hg over 20 minutes, shock was maintained for another 20 minutes, and then 100% oxygen was administered. Animals were then randomized to receive one of three solutions: LR (12 mL/kg), HSD (4 mL/kg), or HBOC-201 (6 mL/kg). Physiologic variables were monitored continuously during all phases of the experiment and for 2 hours postresuscitation.

RESULTS

At a MAP of 40 mm Hg, tissue PO2 was 20 mm Hg or less in both the liver and muscle beds. There were no significant differences in measured liver or muscle PO2 values after resuscitation with any of the three solutions in this model of hemorrhagic shock. When comparing the hemodynamic effects of resuscitation, the cardiac output was increased from shock values in all three animal groups with resuscitation, but was significantly higher in the animals resuscitated with HSD. Similarly, MAP was increased by all solutions during resuscitation, but remained significantly below baseline except in the group of animals receiving HBOC-201 (p < 0.01). HBOC-201 was most effective in both restoring and sustaining MAP and systolic blood pressure. There was excellent correlation between liver and deltoid muscle tissue oxygen values (r = 0.8, p < 0.0001).

CONCLUSION

HBOC-201 can be administered safely in small doses and compared favorably to resuscitation with HSD and LR solution in this prehospital model of hemorrhagic shock. HBOC-201 is significantly more effective than HSD and LR solution in restoring MAP and systolic blood pressure to normal values. Deltoid muscle PO2 reflects liver PO2 and thus may serve as an index of the adequacy of resuscitation in critical tissue beds.

EPR spectroscopy and imaging of oxygen: applications to the gastrointestinal tract

EPR imaging has emerged as an important tool for noninvasive three-dimensional (3D) spatial mapping of free radicals in biological tissues. Spectral-spatial EPR imaging enables mapping of the spectral information at each spatial position, and, from the observed linewidth, the localized tissue oxygenation can be mapped. We report the application of EPR imaging techniques enabling 3D spatial and spectral-spatial EPR imaging of small animals. This instrumentation, along with the use of a biocompatible charcoal oximetry-probe suspension, enabled 3D spatial imaging of the gastrointestinal (GI) tract, along with mapping of oxygenation in living mice. By using this technique, the oxygen tension was mapped at different levels of the GI tract from the stomach to the rectum. The results clearly show the presence of a marked oxygen gradient from the proximal to the distal GI tract, which decreases after respiratory arrest. This technique for in vivo mapping of oxygenation is a promising method, enabling the noninvasive imaging of oxygen within the normal GI tract. This method should be useful in determining the alterations in oxygenation associated with disease.

The effects of anisodamine and dobutamine on gut mucosal blood flow during gut ischemia/reperfusion

AIM: To determine if anisodamine is able to augment mucosal perfusion during gut I/R ischemia-reperfusion.

METHODS: A jejunal sac was formed in Sprague Dawley rat. A Laser Doppler probe and a tonometer were inserted into the sac which was filled with saline. The superior mesenteric artery was occluded (SMAO) for 60 minutes followed by 90 minutes of reperfusion. At the end of 60 minutes of SMAO, either 0.2 mg/kg of anisodmine or dobutamine was injected into the jejunal sac. Laser Doppler mucosal blood flow and regional PCO₂ (PrCO₂) measurements were made.

RESULTS: Mucosal blood flow was significantly increased at 30, 60 and 90 minutes of reperfusion (R₃₀, R₆₀, R₉₀) when intraluminal anisodamine or dobutamine was present compared to intraluminal saline only (44 ± 3.3% or 48 ± 4.1% vs 37 ± 2.6% at R₃₀, 57 ± 5.0% or 56 ± 4.7% vs 45 ± 2.7% at R₆₀, 64 ± 3.3% or 56 ± 4.2% vs 48 ± 3.4% at R₉₀, respectively P < 0.05). Blood flow changes were also reflected by lowering of jejunal PrCO₂ measurements after intraluminal anisodamine or dobutamine compared with that of the saline controls (41 ± 3.1 mmHg or 44 ± 3.0 mmHg vs 49 ± 3.7 mmHg at R₃₀, 38 ± 3.7 mmHg or 40 ± 2.1 mmHg vs 47 ± 3.8 mmHg at R₆₀, 34 ± 2.1 mmHg or 39 ± 3.0 mmHg vs 46 ± 3.4 mmHg at R₉₀, respectively, P < 0.05). Most interesting finding was that there were significantly higher mucosal blood flow and lower jejunal PrCO₂ in anisodamine group than those in dobutamine group at 90 minutes of reperfusion (64 ± 3.3% vs 56 ± 4.2% for blood flow or 34 ± 2.1 mmHg vs 39 ± 3.0 mmHg for PrCO₂, respectively, P < 0.05), suggesting that anisodamine had a more lasting effect on mucosal perfusion than dobutamine.

CONCLUSION: Intraluminal anisodamine and dobutamine can augment mucosal blood flow during gut I/R and alleviate mucosal acidosis. The results provided benificial effects on the treatment of splanchnic hypoperfusion following traumatic or burn shock.

Alterations in tissue oxygen consumption and extraction after trauma and hemorrhagic shock

OBJECTIVES

Although trauma and hemorrhage are associated with tissue hypoperfusion and hypoxemia, changes in oxygen delivery (DO2), oxygen consumption VO2), and oxygen extraction at the organ level in a small animal (such as the rat) model of trauma and hemorrhage have not been examined. Therefore, the objectives of this study were to determine whether blood flow, DO2, VO2, and oxygen extraction ratio in various organs are differentially altered after trauma-hemorrhagic shock and acute resuscitation in the rat.

DESIGN

Prospective, randomized animal study.

SETTING

A university research laboratory.

SUBJECTS

Male Sprague-Dawley rats (n = 6-7 animals/group) weighing 275-325 g.

INTERVENTIONS

Male rats underwent laparotomy (i.e., soft tissue trauma) and were bled to and maintained at a blood pressure of 40 mm Hg until 40% of shed blood volume was returned in the form of lactated Ringer's solution. They were then resuscitated with four times the volume of shed blood with lactated Ringer's solution for 60 mins. At 1.5 hrs postresuscitation, cardiac output and blood flow were determined by using strontium-85 microspheres. Blood samples (0.15 mL each) were collected from the femoral artery and vein and the hepatic, portal, and renal veins to determine total hemoglobin and oxygen content. Systemic and regional DO2, VO2, and oxygen extraction ratio were then calculated.

MEASUREMENTS AND MAIN RESULTS

Both the systemic hemoglobin and systemic arterial oxygen content in hemorrhaged animals at 1.5 hrs postresuscitation were >50% lower as compared with sham-operated controls. Cardiac output and blood flow in the liver, small intestine, and kidneys decreased significantly, but blood flow in the brain and heart remained unaltered after hemorrhage and resuscitation. Systemic DO2 and VO2 were 73% and 54% lower, respectively, than controls at 1.5 hrs after resuscitation. Similarly, regional DO2 and VO2 in the liver, small intestine, and kidneys decreased significantly under such conditions. In addition, the liver had the most severe reduction in VO2 (76%) among the tested organs. However, the oxygen extraction ratio in the liver of sham animals was the highest (72%) and remained unchanged after hemorrhage and resuscitation.

CONCLUSION

Because the liver experienced the most severe reduction in VO2 associated with an unchanged oxygen extraction capacity, this organ appears to be more vulnerable to hypoxic insult after hemorrhagic shock.

The potential for myocardial imaging with hypoxia markers

Direct "hot spot" imaging of myocardial tissue hypoxia is potentially of great clinical importance because available noninvasive approaches for the detection of myocardial ischemia have generally been based on the detection of flow heterogeneity or identification of regional alterations of myocardial metabolism. These existing approaches provide only an indirect assessment of regional myocardial ischemia, and may be affected by either sympathetic activation or substrate availability. The assessment of tissue oxygenation with hypoxic compounds may be the best indicator of the balance of flow and oxygen consumption. These compounds may provide a means of identifying dysfunctional chronically ischemic but viable "hibernating" myocardium and find a critical place in the assessment of angiogenesis. Nitroimidazole compounds hold promise for positive imaging of hypoxia in the heart. However, refinement of these compounds is needed to improve target specificity. The potential of technetium-99m (Tc99m) complexes derived from removal of the nitroimidazole moiety from a nitroimidazole-containing ligand is interesting and warrants further investigation. Experimental studies support the possibility of identifying myocardial hypoxia with the positron-emitting compound F18-fluoromisonidazole noninvasively. The potential of a Tc99m labeled nitroimidazole for positive imaging of myocardial ischemia is tremendous because single-photon imaging is more widely available. The true clinical potential of these nitroimidazole compounds can only be defined with future experimental and clinical studies. Ideally, these studies should include comparisons of tracer uptake with independent measures of regional ischemia or measures of oxygen tension, potentially using magnetic resonance imaging.

Noninvasive measurement of anatomic structure and intraluminal oxygenation in the gastrointestinal tract of living mice with spatial and spectral EPR imaging

EPR imaging has emerged as an important tool for noninvasive three-dimensional (3D) spatial mapping of free radicals in biological tissues. Spectral-spatial EPR imaging enables mapping of the spectral information at each spatial position, and, from the observed line width, the localized tissue oxygenation can be mapped. We report the development of EPR imaging instrumentation enabling 3D spatial and spectral-spatial EPR imaging of small animals. This instrumentation, along with the use of a biocompatible charcoal oximetry-probe suspension, enabled 3D spatial imaging of the gastrointestinal (GI) tract, along with mapping of oxygenation in living mice. By using these techniques, the oxygen tension was mapped at different levels of the GI tract from the stomach to the rectum. The results clearly show the presence of a marked oxygen gradient from the proximal to the distal GI tract, which decreases after respiratory arrest. This technique for in vivo mapping of oxygenation is a promising method, enabling the noninvasive imaging of oxygen within the normal GI tract. This method should be useful in determining the alterations in oxygenation associated with disease.