Tissue hemoglobin O2 saturation during resuscitation of traumatic shock monitored using near infrared spectrometry

Low tissue oxygen saturation at the end of early goal-directed therapy is associated with worse outcome in critically ill patients

Introduction

The prognostic value of continuous monitoring of tissue oxygen saturation (StO₂) during early goal-directed therapy of critically ill patients has not been investigated. We conducted this prospective study to test the hypothesis that the persistence of low StO₂ levels following intensive care admission is related to adverse outcome.

Methods

We followed 22 critically ill patients admitted with increased lactate levels (>3 mmol/l). Near-infrared spectroscopy (NIRS) was used to measure the thenar eminence StO₂ and the rate of StO₂ increase (R_incStO₂) after a vascular occlusion test. NIRS dynamic measurements were recorded at intensive care admission and each 2-hour interval during 8 hours of resuscitation. All repeated StO₂ measurements were further compared with Sequential Organ Failure Assessment (SOFA), Acute Physiology and Chronic Health Evaluation (APACHE) II and hemodynamic physiological variables: heart rate (HR), mean arterial pressure (MAP), central venous oxygen saturation (ScvO₂) and parameters of peripheral circulation (physical examination and peripheral flow index (PFI)).

Results

Twelve patients were admitted with low StO₂ levels (StO₂ <70%). The mean scores for SOFA and APACHE II scores were significantly higher in patients who persisted with low StO₂ levels (n = 10) than in those who exhibited normal StO₂ levels (n = 12) at 8 hours after the resuscitation period (P < 0.05; median (interquartile range): SOFA, 8 (7 to 11) vs. 5 (3 to 8); APACHE II, 32(24 to 33) vs. 19 (15 to 25)). There was no significant relationship between StO₂ and mean global hemodynamic variables (HR, P = 0.26; MAP, P = 0.51; ScvO₂, P = 0.11). However, there was a strong association between StO₂ with clinical abnormalities of peripheral perfusion (P = 0.004), PFI (P = 0.005) and R_incStO₂ (P = 0.002). The persistence of low StO₂ values was associated with a low percentage of lactate decrease (P < 0.05; median (interquartile range): 33% (12 to 43%) vs. 43% (30 to 54%)).

Conclusions

We found that patients who consistently exhibited low StO₂ levels following an initial resuscitation had significantly worse organ failure than did patients with normal StO₂ values, and found that StO₂ changes had no relationship with global hemodynamic variables.

Monitoring trauma and intensive care unit resuscitation with tissue hemoglobin oxygen saturation

INTRODUCTION

The purpose of the present review is to review our experience with near-infrared spectroscopy (NIRS) monitoring in shock resuscitation and predicting clinical outcomes.

METHODS

The management of critically ill patients with goal-oriented intensive care unit (ICU) resuscitation continues to evolve as our understanding of the appropriate physiologic targets improves. It is now recognized that resuscitation to achieve supranormal indices is not beneficial in all patients and may precipitate abdominal compartment syndrome.

RESULTS

Over the years, ICU technology has provided physicians with specific physiologic parameters to guide shock resuscitation. Throughout this time, the tissue hemoglobin oxygen saturation (StO2) monitor has emerged as a non-invasive means to obtain reliable physiologic parameters to guide clinicians' resuscitative efforts. StO2 monitors have been shown to aid in early identification of nonresponders and to predict outcomes in hemorrhagic shock and ICU resuscitation. These data have also been used to better understand and refine existing resuscitation protocols. More recently, use of NIRS technology to guide resuscitation in septic shock has been shown to predict outcomes in high-risk patients.

CONCLUSIONS

StO2 is an important tool in identifying high-risk patients in septic and hemorrhagic shock. It is a non-invasive means of obtaining vital information regarding outcome and adequacy of resuscitation.

Tissue oxygenation monitoring in the field: a new EMS vital sign

BACKGROUND

A tissue hemoglobin oxygen saturation (STO2) monitor was created to assess the perfusion status of a peripheral muscle bed using near infrared light to directly measure oxygen saturation in the microcirculation. Hypoperfusion has been noted when the STO2 is <75%. The use of this technology has not been tested in the prehospital setting. This pilot study was performed to assess the technology's ease of use in the field and to correlate STO2 readings with patient outcomes.

METHODS

Hospital-based transport vehicles were equipped with STO2 monitors and personnel were asked to evaluate the functionality of the technology. Initial, average, and minimal STO2 values were collected and compared with data of the trauma registry.

RESULTS

Forty five of 55 surveys were returned with 100% reporting ease of use and no reports of interference with monitors or avionics. Monitoring length averaged 16.9 minutes +/- 6.9 minutes. Forty-one patients had complete data sets and five deaths were reported for a mortality rate of 12%. STO2 endpoints revealed and increased risk of death for every 10% decrease in STO2.

CONCLUSION

The STO2 monitor can easily be used in the prehospital environment. In addition, initial recordings were significantly different between survivors and nonsurvivors with every 10% decrease in STO2 increasing mortality threefold. This monitor seems to give the prehospital provider a noninvasive tool for assessment of hypoperfusion in the field and may allow for earlier resuscitative efforts to commence.

Transfusion of aged packed red blood cells results in decreased tissue oxygenation in critically injured trauma patients

BACKGROUND

Blood transfusion is a common event in the treatment of injured patients. The effect of red blood cell transfusion on tissue oxygenation is unclear. The transfusion of older blood has been shown to be detrimental in retrospective studies. This study aims to study the effect of the age of the blood transfused on the tissue oxygenation using near infrared spectroscopy.

METHODS

Thirty-two critically injured trauma patients for whom a blood transfusion had been ordered were recruited. Each patient had a transcutaneous probe placed on the thenar eminence. The probe was placed 1 hour before the transfusion and left in place until 4 hours after transfusion. Tissue oxygen saturation (Sto2) was recorded every 2 minutes. The Sto2 area under the curve (AUC) over time periods was calculated. A control group (n = 16), not transfused, was recruited. The transfusion group was divided into two groups by blood age. One group received blood less than 21 days old, (new blood, n = 15) and the other received blood 21 days old or greater (old blood, n = 17). The data were analyzed for significance with Kendall's W and Wilcoxon's signed rank test (p < 0.05).

RESULTS

Baseline characteristics such were not significantly different between groups. The baseline AUC did not differ between groups. The old blood group demonstrated a significant decline in Sto2 comparing its baseline period to its transfusion period (p < 0.05). There was no similar decline in the control group or the new blood group. The posttransfusion period AUC for the old blood group was also lower versus baseline (p = 0.06). There was a moderate correlation between increasing age of blood and decrease in oxygenation (r = 0.5).

CONCLUSIONS

There was a decrease in peripheral tissue oxygenation in patients receiving older red blood cells. There was no oxygenation decrease in patients receiving blood less than 21 days. This indicates that factors in stored blood may influence the peripheral vasculature and oxygen delivery.

Computerized clinical decision support for traumatic shock resuscitation

PURPOSE OF REVIEW

To review what we learned through implementation of computerized decision support for ICU resuscitation of major torso trauma patients who arrive in shock.

RECENT FINDINGS

Overall, these patients respond well to preload-directed goal-orientated ICU resuscitation; however, the subset of patients destined to develop abdominal compartment syndrome do not respond well. In fact, this strategy precipitates the full-blown syndrome that is a new iatrogenic variant of multiple organ failure. The clinical trajectory of abdominal compartment syndrome starts early after emergency department admission and its course is fairly well defined by the time patients reach the ICU. It occurs in patients who arrive with severe bleeding that is not readily controlled. These patients require a very different emergency department management strategy. Hemorrhage control is paramount. Alternative massive transfusion protocols should be used with an emphasis on hemostasis and avoidance of excessive isotonic crystalloids. Finally, near-infrared spectroscopy that measures tissue hemoglobin saturation in skeletal muscle (StO2) is good at identifying high-risk patients. A falling StO2 in the setting of ongoing resuscitation is a harbinger of death from early exsanguination and multiple organ failure.

SUMMARY

Fundamental changes are needed in the care of trauma patients who arrive in shock and require a massive transfusion.

Thenar oxygen saturation measured by near infrared spectroscopy as a noninvasive predictor of low central venous oxygen saturation in septic patients

OBJECTIVE

To validate thenar oxygen saturation (StO(2)) measured by near-infrared spectroscopy (NIRS) as a noninvasive estimation of central venous saturation (ScvO(2)) in septic patients.

DESIGN

Prospective observational study.

SETTING

A 26-bed medical-surgical intensive care unit at a university-affiliated hospital.

PATIENTS

Patients consecutively admitted to the ICU in the early phase of severe sepsis and septic shock, after normalization of blood pressure with fluids and/or vasoactive drugs.

MEASUREMENTS

We recorded demographic data, severity score, hemodynamic data, and blood lactate, as well as ScvO(2), and StO(2) measured simultaneously on inclusion. Patients were divided into two groups according to ScvO(2) values: group A, with ScvO(2) < 70%, and group B, with ScvO(2) > or = 70%.

RESULTS

Forty patients were studied. StO(2) was significantly lower in group A than in group B (74.7 +/- 13.0 vs. 83.3 +/- 6.2, P 0.018). No differences in age, severity score, hemodynamics, vasoactive drugs, or lactate were found between groups. Simultaneously measured ScvO(2) and StO(2) showed a significant Pearson correlation (r = 0.39, P 0.017). For a StO(2) value of 75%, sensitivity was 0.44, specificity 0.93, positive predictive value 0.92, and negative predictive value 0.52 for detecting ScvO(2) values lower than 70%.

CONCLUSIONS

StO(2) correlates with ScvO(2) in normotensive patients with severe sepsis or septic shock. We propose a StO(2) cut-off value of 75% as a specific, rapid, noninvasive first step for detecting patients with low ScvO(2) values. Further studies are necessary to analyze the role of noninvasive StO(2) measurement in future resuscitation algorithms.

Muscle StO2 in critically ill patients

PURPOSE OF REVIEW

Tissue hypoperfusion is a common pathophysiologic process leading to multiple-organ dysfunction and death. An important goal of hemodynamic monitoring is the early detection of inadequate tissue perfusion and oxygenation. The use of simple, noninvasive monitoring techniques has the advantage of facilitating earlier initiation of therapy. Near-infrared spectroscopy has emerged in recent years as a tool for monitoring peripheral oxygenation (StO2) in various tissues, including muscle. Here, we review our current knowledge about the applicability, usefulness, and limitations of near-infrared spectroscopy as a technique to evaluate muscle oxygenation in acutely ill patients.

RECENT FINDINGS

StO2 may be an appropriate measure for early resuscitation of critically ill patients, especially in those with low cardiac output states or after severe trauma. Its usefulness in sepsis is less well established. However, by inducing an occlusion stress, a variety of dynamic variables can be measured to assess local metabolic demand and microvascular reactivity. Several recent studies have shown that profound alterations of these near-infrared-spectroscopy-derived dynamic variables are frequent in patients with severe sepsis and these alterations are associated with a poor outcome.

SUMMARY

Near-infrared spectroscopy provides a noninvasive measure of muscle oxygen metabolism and microvascular dysfunction in critically ill patients. It may be useful to guide the management of critically ill patients.

Preoperative resuscitation of the trauma patient

PURPOSE OF REVIEW

The traditional approach to trauma patients with presumed internal hemorrhage has been immediate, aggressive intravenous fluid resuscitation. Recent experimental and clinical data, however, suggest a more discriminating approach that first considers concurrent head injury, hemodynamic stability and the presence of potentially uncontrollable hemorrhage (e.g. deep truncal injury) versus a controllable source (e.g. distal extremity wound) as well as the use of new techniques to inhibit bleeding and better ways to monitor the patient's condition.

RECENT FINDINGS

Evolving data suggest that while aggressive fluid infusions could be used for patients with isolated extremity, thermal or head injury, they should be limited in conditions with potentially uncontrollable internal hemorrhage, and particularly in patients with penetrating truncal injury being transported immediately to a trauma center. Likewise, the minute volume of positive pressure ventilatory support should be limited with potential severe hemorrhage due to the secondary reductions in venous return. For trauma patients with severe bleeding there is growing evidence for the increased use of plasma and factor VIIa, as well as tourniquets, intraosseus devices and evolving monitoring techniques.

SUMMARY

Owing to the growing societal threat of trauma, further research, including studies already under way, will be critical to delineate the timing and technique of infusing advantageous resuscitative fluids such as hypertonic saline and hemoglobin-based oxygen carriers as well as the use of hemostatic agents and special blood products.

Oxygen saturation determined from deep muscle, not thenar tissue, is an early indicator of central hypovolemia in humans

OBJECTIVE

To compare the responses of noninvasively measured tissue oxygen saturation (StO2) and calculated muscle oxygen tension (PmO2) to standard hemodynamic variables for early detection of imminent hemodynamic instability during progressive central hypovolemia in humans.

DESIGN

Prospective study.

SETTING

Research laboratory.

SUBJECTS

Sixteen healthy human volunteers.

INTERVENTIONS

Progressive lower body negative pressure (LBNP) to onset of cardiovascular collapse.

MEASUREMENTS AND MAIN RESULTS

Noninvasive measurements of blood pressures, heart rate, and stroke volume were obtained during progressive LBNP with simultaneous assessments of StO2, PmO2, and muscle oxygen saturation (SmO2). Forearm SmO2 and PmO2 were determined with a novel near infrared spectroscopic measurement device (UMMS) and compared with thenar StO2 measured by a commercial device (HT). All values were normalized to the duration of LBNP exposure required for cardiovascular collapse in each subject (i.e., LBNP maximum). Stroke volume was significantly decreased at 25% of LBNP maximum, whereas blood pressure was a late indicator of imminent cardiovascular collapse. PmO2 (UMMS) was significantly decreased at 50% of maximum LBNP while SmO2 (UMMS) decreased at 75% of maximum LBNP. Thenar StO2 (HT) showed no statistical change throughout the entire LBNP protocol.

CONCLUSIONS

Spectroscopic assessment of forearm muscle PO2 and SmO2 provides noninvasive and continuous measures that are early indicators of impending cardiovascular collapse resulting from progressive reductions in central blood volume.

Thresholded area over the curve of spectrometric tissue oxygen saturation as an indicator of volume resuscitability in porcine hemorrhagic shock

BACKGROUND

A rapid, reliable, and noninvasive functional measure of responsiveness to resuscitation in posttraumatic hemorrhagic shock could prove useful in guiding therapy, especially under circumstances such as the battlefield and civilian mass casualties. Tissue oxygen saturation (Sto2) is a promising candidate for this application. We therefore explored the value of peripheral muscle Sto2 in predicting systemic responsiveness to colloid volume resuscitation in a porcine model of hemorrhagic shock.

METHODS

Fourteen isoflurane-anesthetized piglets were subjected to a standardized hemorrhage protocol that maintained mean arterial pressure (MAP) between 30 and 40 mm Hg. Asanguineous resuscitation with a volume of Hextend equal to the total volume bled was initiated when compensation was exhausted (MAP <30 mm Hg). We recorded continuous MAP and Sto2 values, and calculated the contiguous area over the Sto2 curve yet below a given threshold of Sto2 (TAOC) as a function of this threshold before the selected timepoint for timepoints up to 30 minutes before resuscitation.

RESULTS

Hemorrhage resulted in significant fluctuations of MAP and high interindividual variability of disease dynamics and outcome: 4 nonsurvivors and 10 survivors at 2 hours postresuscitation. Sto2 measurements reflected hemodynamic conditions in most animals, with a pronounced drop preceding final decompensation in 7 of 14 animals. TAOC discriminated three of four nonresuscitable (nonsurvivor) animals from the survivors, with group differences reaching significance even for the earliest examined timepoint (30 minutes before resuscitation), depending on the choice of TAOC threshold.

CONCLUSIONS

Sto2 may serve as a marker of decompensation, whereas TAOC, a physiologically motivated correlate of perfusion debt and cumulative hypoperfusion injury, may be a useful early indicator of responsiveness to volume resuscitation in hemorrhagic shock.

The Correlation of Near-Infrared Spectroscopy with Changes in Oxygen Delivery in a Controlled Model of Altered Perfusion

Alterations in regional tissue perfusion may precede global indications of shock. This study compared regional tissue oxygenation saturation (StO2) using near-infrared spectroscopy with standard hemodynamic and biochemical variables in 40 patients undergoing cardiopulmonary bypass (CPB). Mean arterial pressure, cardiac output, oxygen delivery, arterial blood gases, and lactate were recorded at specific intervals during surgery. Data were organized by stage of procedure, and the relationship of StO2 to established parameters was investigated. With initiation of CPB, StO2 declined by 12.9 per cent (standard deviation ± 14.75%) with a delayed increase in lactate from 0.9 (interquartile range [IQR], 0.6–1.5) mmol/L to 2.3 (IQR, 1.8–2.5) mmol/L. The minimum StO2 value preceded the maximum lactate level by an average time of 93.9 (standard deviation ± 86.3) minutes. Additionally, a decrease in StO2 corresponded with an increase in base deficit of 4.84 (standard deviation ± 2.37) mEq/L over the same period. Calculated oxygen delivery decreased from a baseline value of 754 (IQR, 560–950) mL/min to 472 (IQR, 396–600) mL/min with initiation and maintenance of CPB. For patients undergoing CPB, StO2 is a reliable, noninvasive monitor of perfusion, which correlates well with oxygen delivery and identifies perfusion deficits earlier than lactate or base deficit.

Fluid management of the trauma patient

Hemodynamic instability in the trauma patient is most commonly secondary to blood loss and the accumulation of fluid in injured tissue. The etiologies of shock unrelated to hypovolemia must also be investigated. The treatment of hypovolemia in patients with non-cerebral trauma should begin with Ringer's lactate solution. Normal saline (0.9% sodium chloride) is appropriate for patients with head injury, alkalosis, or hyponatremia, but in large volumes may lead to metabolic acidosis. The role of colloids, hypertonic saline, and hemoglobin solutions in trauma resuscitation is unclear at the present time. Base deficit and lactate levels are useful as predictors of morbidity and mortality and can be used to guide resuscitation.

Skeletal muscle oxygen saturation does not estimate mixed venous oxygen saturation in patients with severe left heart failure and additional severe sepsis or septic shock

INTRODUCTION

Low cardiac output states such as left heart failure are characterized by preserved oxygen extraction ratio, which is in contrast to severe sepsis. Near infrared spectroscopy (NIRS) allows noninvasive estimation of skeletal muscle tissue oxygenation (StO2). The aim of the study was to determine the relationship between StO2 and mixed venous oxygen saturation (SvO2) in patients with severe left heart failure with or without additional severe sepsis or septic shock.

METHODS

Sixty-five patients with severe left heart failure due to primary heart disease were divided into two groups: groups A (n = 24) and B (n = 41) included patients without and with additional severe sepsis/septic shock, respectively. Thenar muscle StO2 was measured using NIRS in the patients and in 15 healthy volunteers.

RESULTS

StO2 was lower in group A than in group B and in healthy volunteers (58 +/- 13%, 90 +/- 7% and 84 +/- 4%, respectively; P < 0.001). StO2 was higher in group B than in healthy volunteers (P = 0.02). In group A StO2 correlated with SvO2 (r = 0.689, P = 0.002), although StO2 overestimated SvO2 (bias -2.3%, precision 4.6%). In group A changes in StO2 correlated with changes in SvO2 (r = 0.836, P < 0.001; DeltaSvO2 = 0.84 x DeltaStO2 - 0.67). In group B important differences between these variables were observed. Plasma lactate concentrations correlated negatively with StO2 values only in group A (r = -0.522, P = 0.009; lactate = -0.104 x StO2 + 10.25).

CONCLUSION

Skeletal muscle StO2 does not estimate SvO2 in patients with severe left heart failure and additional severe sepsis or septic shock. However, in patients with severe left heart failure without additional severe sepsis or septic shock, StO2 values could be used to provide rapid, noninvasive estimation of SvO2; furthermore, the trend in StO2 may be considered a surrogate for the trend in SvO2.

Feasibility of Using Near-Infrared Spectroscopy to Diagnose Testicular Torsion: An Experimental Study in Sheep

STUDY OBJECTIVE

To assess whether near-infrared spectroscopy can detect testicular hypoxia in a sheep model of testicular torsion within 6 hours of experimental torsion.

METHODS

This was a randomized, controlled, nonblinded study. Trans-scrotal, near-infrared, spectroscopy-derived testicular tissue saturation of oxygen values were obtained from the posterior hemiscrota of 6 anesthetized sheep at baseline and every 15 minutes for 6 hours after either experimental-side, 720-degree, unilateral, medial testicular torsion and orchidopexy or control-side sham procedure with orchidopexy and then for 75 minutes after reduction of torsion and pexy. Color Doppler ultrasonography was performed every 30 minutes to confirm loss of vascular flow on the experimental side, return of flow after torsion reduction, and preserved flow on the control side.

RESULTS

Near infrared spectroscopy detected a prompt, sustained reduction in testicular tissue saturation of oxygen after experimental torsion. Further, it documented a rapid return of these values to pretorsion levels after reduction of torsion. Experimental-side testicular tissue saturation of oxygen fell from a median value of 59% (interquartile range [IQR] 57% to 69%) at baseline to 14% (IQR 11% to 29%) at 2.5 hours of torsion, and postreduction values were approximately 70%. Control-side testicular tissue saturation of oxygen values increased from a median value of 67% (IQR 59% to 68%) at baseline to 77% (IQR 77% to 94%) at 2.5 hours and remained at approximately 80% for the entire protocol. The difference in median testicular tissue saturation of oxygen between experimental and control sides, using the Friedman test, was found to be significant (P=.017).

CONCLUSION

This study demonstrates the feasibility, in a sheep model, of using near-infrared spectroscopy for the noninvasive diagnosis of testicular torsion and for quantification of reperfusion after torsion reduction. The applicability of these findings, from an animal model using complete torsion, to the clinical setting remains to be established.

Measurement of acid-base resuscitation endpoints: lactate, base deficit, bicarbonate or what?

PURPOSE OF REVIEW

Inadequate oxygen delivery to the tissues frequently results in significant metabolic acidosis. The resultant cellular and organ dysfunction can increase morbidity, mortality and hospital stay. Early diagnosis of shock can lead to early resuscitation efforts that can prevent ongoing tissue injury. This review focuses on the metabolic, hemodynamic and regional perfusion endpoints utilized in the diagnosis of metabolic acidosis resulting from shock. Resuscitation strategies aimed at supranormal oxygen delivery will be discussed.

RECENT FINDINGS

Serum pH, lactate, base deficit and bicarbonate have all been extensively studied as clinical markers of metabolic acidosis in shock. While their trend helps guide resuscitation, no single marker or specific value can be utilized to guide resuscitation for all patients. Hemodynamic parameters and regional tissue endpoints are designed to identify compensated shock before it progresses to uncompensated shock. Resuscitation strategies initiated in the early phases of shock can reduce complications and death. Efforts to resuscitate patients to supranormal oxygen delivery endpoints have demonstrated mixed success, with several notable complications.

SUMMARY

Despite the large number of endpoints available to the clinician, none are universally applicable and none have independently demonstrated improved survival when guiding resuscitation. Patients who respond well to initial resuscitation efforts demonstrate a survival advantage over nonresponders.

Tissue oxygen saturation predicts the development of organ dysfunction during traumatic shock resuscitation

BACKGROUND

Near-infrared spectroscopy (NIRS) can continuously and noninvasively monitor tissue oxygen saturation (StO2) in muscle and may be an indicator of shock severity. Our purpose was to evaluate how well StO2 predicted outcome in high-risk torso trauma patients presenting in shock.

METHODS

The primary outcome in this prospective study was multiple organ dysfunction syndrome (MODS). StO2 data were obtained upon hospital arrival and for 24 hours along with other known predictors of hypoperfusion and clinical outcomes. Clinicians were blinded to StO2 measurements.

RESULTS

Seven Level I trauma centers enrolled 383 patients, 50 of whom developed MODS. Minimum StO2 performed similarly to maximum base deficit (BD) in discrimination of MODS patients. The sensitivity for both measures (StO2 cutoff = 75%; BD cutoff = 6 mEq/L) was 78%, the specificity was 34% to 39%, the positive predictive value was 18% to 20% and the negative predictive value was 88% to 91%. StO2 and BD were also comparable in predicting death.

CONCLUSIONS

NIRS-derived muscle StO2 measurements perform similarly to BD in identifying poor perfusion and predicting the development of MODS or death after severe torso trauma, yet have the additional advantages of being continuous and noninvasive.

Noninvasive cerebral oximeter as a surrogate for mixed venous saturation in children

We evaluated the relationship between regional cerebral oxygen saturation (rSO(2)) measured by near-infrared spectroscopy (NIRS) cerebral oximeter with superior vena cava (SVC), inferior vena cava (IVC), right atrium (RA), and pulmonary artery (PA) saturation measured on room air and 100% inspired oxygen administered via a non-rebreather mask (NRB) in children. Twenty nine pediatric post-orthotopic heart transplant patients undergoing an annual myocardial biopsy were studied. We found a statistically significant correlation between rSO(2) and SVC saturations at room air and 100% inspired oxygen concentration via NRB (r = 0.67, p = 0.0002 on room air; r = 0.44, p = 0.02 on NRB), RA saturation (r = 0.56, p = 0.002; r = 0.56, p = 0.002), and PA saturation (r = 0.67, p < 0.001; r = 0.4, p = 0.03). A significant correlation also existed between rSO(2) and measured cardiac index (r = 0.45, p = 0.01) and hemoglobin levels (r = 0.41, p = 0.02). The concordance correlations were fair to moderate. Bias and precision of rSO(2) compared to PA saturations on room air were -0.8 and 13.9%, and they were 2.1 and 15.6% on NRB. A stepwise linear regression analysis showed that rSO(2) saturations were the best predictor of PA saturations on both room air (p = 0.0001) and NRB (p = 0.012). In children with biventricular anatomy, rSO(2) readings do correlate with mixed venous saturation.

Repetitive Ischemia–Reperfusion Injury: A Plausible Mechanism for Documented Clinical Burn-Depth Progression After Thermal Injury

Our previous studies confirmed the phenomenon of burn depth progression despite adequate Parkland formula resuscitation [Kim et al. J Burn Care Rehabil 2001;22960:406-6]. Repetitive ischemia-reperfusion injury (I-R) is a plausible explanation and is suggested by the concomitant swings we have observed in serum base deficit (BD) during resuscitation from burn shock. We chose to explore whether laser Doppler imaging (LDI) evidence of burn depth progression mirrored cycles of I-R (episodic swings in continuously measured BD). Positive findings would support the hypothesis that repetitive episodes of I-R is a factor in burn depth progression despite apparently adequate resuscitation. A total of 14 patients with severe life-threatening burns (median 51% TBSA) underwent continuous BD monitoring using a Paratrend 7 (Malvern PA) during 48 hours of resuscitation. Fluid needs were estimated using the Parkland formula, then were titrated to urine output. The slopes of BD changes were then analyzed. Worsening of BD greater than 0.2 mmol/l/min was noted, and a proportion derived relative to pooled data on 5-minute intervals. In four of the patients, LDI scans were performed on six representative areas sequentially every 4 hours. The analysis of median flux in these LDI images provided real-time determination of burn depth progression. Eight patients eventually died. Only four patients achieved a normal BD within 12 hours of monitoring despite exceeding the Parkland formula estimate and meeting urinary output parameters. Our analysis also showed cyclical peaks and valleys in the BD curve (P < .001), suggesting repetitive I-R insults. All increases in BD preceded changes that could be detected in vital signs or urine output. Finally, LDI confirmed that the burn depths continued to progress despite apparently adequate resuscitation, and also showed that there are similar peaks and valleys in the perfusion of the wounds (P < .0001), which mimic the changes in the BD curve. Responses to fluid resuscitation do not follow a linear pattern in the case of massive burns. These results in repetitive periods of tissue hypoperfusion evidenced by BD alterations and may contribute to progressive deepening of the burn wound.

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.

End expiratory oxygen concentrations to predict central venous oxygen saturation: an observational pilot study

BACKGROUND

A non-invasive surrogate measurement for central venous oxygen saturation (ScVO2) would be useful in the ED for assessing therapeutic interventions in critically ill patients. We hypothesized that either linear or nonlinear mathematical manipulation of the partial pressure of oxygen in breath at end expiration (EtO2) would accurately predict ScVO2.

METHODS

Prospective observational study of a convenience sample of hemodialysis patients age > 17 years with existing upper extremity central venous catheters were enrolled. Using a portable respiratory device, we collected both tidal breathing and end expiratory oxygen and carbon dioxide concentrations, volume and flow on each patient. Simultaneous ScVO2 measurements were obtained via blood samples collected from the hemodialysis catheter. Two models were used to predict ScVO2: 1) Best-fit multivariate linear regression equation incorporating all respiratory variables; 2) MathCAD to model the decay curve of EtO2 versus expiratory volume using the least squares method to estimate the pO2 that would occur at <20% of total lung capacity.

RESULTS

From 21 patients, the correlation between EtO2 and measured ScVO2 yielded R2 = 0.11. The best fit multivariate equation included EtCO2 and EtO2 and when solved for ScVO2, the equation yielded a mean absolute difference from the measured ScVO2 of 8 +/- 6% (range -18 to +17%). The predicted ScVO2 value was within 10% of the actual value for 57% of the patients. Modeling of the EtO2 curve did not accurately predict ScVO2 at any lung volume.

CONCLUSION

We found no significant correlation between EtO2 and ScVO2. A linear equation incorporating EtCO2 and EtO2 had at best modest predictive accuracy for ScVO2.

Continuous renal replacement therapy in patients following traumatic injury

In critically injured patients, the incidence of acute renal failure has been reported to occur in as many as 31% of patients. The use of CRRT modalities for patients following traumatic injuries is becoming more common, albeit slowly, and this therapy may impact upon long-term recovery of renal function and mortality. Historical studies investigating the early use of intermittent dialysis reported significant improvement in survival in patients who were dialyzed earlier and more vigorously than in control subjects. Early trauma patients also showed improved survival following war injuries when dialyzed prophylactically. Although there is a growing acceptance in favor of earlier renal replacement therapy, the published consensus and the practice in many centers has been to dialyze/filter relatively ill rather than relatively healthy patients. The R Adams Cowley Shock Trauma Center (STC) in Baltimore, Maryland, USA, admits over 8,000 trauma patients each year. Within the STC, a program of continuous renal replacement therapy was established in the early 1980's. We review both historical and current literature on the use of renal replacement therapies after traumatic injury, and suggest some future areas of investigation and indications for these modalities.

Review of the pathophysiology and acute management of haemorrhage in pelvic fracture

Mortality following pelvic fractures has declined dramatically as better methods of controlling haemorrhage, such as angioembolisation to control arterial bleeding, have been introduced. But about 10% of patients still die, despite these advances. To save these patients, the key questions in managing pelvic fractures are: which patients are at highest risk for a life-threatening bleed, in these patients, what is the exact anatomical source of the bleeding and what is the best way to stop it? There is wide consensus that bleeding is most likely to occur with unstable fractures. However, it remains difficult to predict which fractures will actually cause excessive bleeding. Current treatment protocols rely on angiographic embolisation and external fixation, either alone or in combination. Direct pelvic packing is gaining in popularity, but, ultimately, the ideal treatment method remains unclear. The purpose of this review is to examine our current understanding of the pathophysiology and management of bleeding pelvic fractures.

Hyperspectral imaging: a new approach to the diagnosis of hemorrhagic shock

BACKGROUND

Skin color changes and mottling are frequently described signs of hemorrhagic shock (HEM). Based on this, we developed a noninvasive, noncontact hyperspectral imaging system (HSI), which quantifies and depicts the surface tissue saturation of oxygen (SHSIO2) for each pixel in a region of interest (ROI). Our purpose was to assess HSI in a porcine HEM model. We hypothesized that HEM would cause decreases in SHSIO2 of the skin.

METHODS

The HyperMed HSI system employs a spectral separator to vary the wavelength of light admitted to a digital camera. During image acquisition, a "hypercube" of images, each at a separate wavelength, is generated (at 5-nm intervals, from 500 to 600 nm). Then, the visible light spectrum for each pixel in the hypercube is compared by linear regression to standard spectra for oxyhemoglobin (OxyHb) and deoxyhemoglobin (DeoxyHb). The resulting fit coefficients for OxyHb and DeoxyHb are used to calculate SHSIO2 values for each pixel in the ROI. The mean values for OxyHb, DeoxyHb, and SHSIO2 across the ROI are calculated. Grayscale SHSIO2 pictures of the ROI are also generated, in which the brightness of each pixel is proportional to its value. Seventeen pigs, 36.4 +/- 0.11 kg, underwent standard preparation, and were maintained on ketamine and isoflurane. Normothermia was maintained (37 degrees C to 39 degrees C). The hemorrhage group (HEM, n = 9) underwent three blood withdrawals, each 10 mL/kg, with 15 minutes between withdrawals. After the third withdrawal, animals were resuscitated with lactated Ringer's and then shed blood. The control group (CTRL, n = 8) received intravenous fluids at 100 mL/h. HSI images were obtained of the inner hindlimb throughout.

RESULTS

All HEM animals showed linear decreases in both mean SHSIO2 and OxyHb values with blood loss, which were reversed by resuscitation. These changes were evident on the grayscale SHSIO2 pictures, but not to the naked eye, and paralleled those of invasively obtained arterial base excess and mixed venous oxygen saturation.

CONCLUSIONS

HSI is a promising noninvasive and noncontact tool for quantifying changes in skin oxygenation during HEM and resuscitation.

Resonance Raman spectroscopy: a new technology for tissue oxygenation monitoring

OBJECTIVE

To evaluate resonance Raman spectroscopy for the detection of changes in sublingual mucosal hemoglobin oxygen saturation (Smo2) in response to hemorrhage and resuscitation, and to compare Smo2 with other indicators of tissue oxygenation including central venous oxygen saturation (Scvo2), lactate, base excess, and shed blood volume.

DESIGN

Prospective single group pilot study.

SETTING

University laboratory.

SUBJECTS

Five Sprague-Dawley rats.

INTERVENTIONS

Animals were anesthetized and instrumented for measurement of arterial and central venous blood gases. Raman spectroscopy was performed using a krypton ion laser providing excitation at 406.7 nm (5 mW). A 1-mm2 region of the sublingual tongue surface was chosen for investigation. Animals were subjected to stepwise hemorrhage until approximately 50% of the blood volume was removed. At each hemorrhage and resuscitation interval, Raman spectroscopy was performed and corresponding arterial and central venous blood gas and lactate measurements were made. Smo2 was calculated as the ratio of the oxygenated heme spectral peak height to the sum of the oxy- and deoxyhemoglobin spectral peak heights. Raman spectroscopy-derived Smo2 measurements were compared with Scvo2 as well as with other indicators of oxygenation.

MEASUREMENTS AND MAIN RESULTS

The mean difference between Smo2 and Scvo2 for all paired measurements was 5.8+/-11.7 absolute saturation points. Smo2 was significantly (p<.0001) correlated with Scvo2 (r=.80), lactate (r=-.78), base excess (r=.80), and shed blood volume (r=-.75). Smo2 and Scvo2 showed similar levels of precision for predicting elevated lactate and base deficit.

CONCLUSIONS

These studies demonstrate the ability of Raman spectroscopy to noninvasively track microvascular hemoglobin oxygenation in tissue and favorably correlate with other important indicators of tissue oxygenation such as Scvo2, lactate, base deficit, and shed blood volume. The technique shows promise as a method to noninvasively monitor tissue oxygenation.

The efficacy of B-type natriuretic peptide for early identification of blood loss in traumatic injury

BACKGROUND

Because B-type natriuretic peptide (BNP) secretion has a direct linear correlation with intravascular volume status, it was assessed as an initial marker for blood loss (BL) in polytrauma patients.

METHODS

Hemodynamically unstable trauma patients between 18 and 45 years had serial BNP levels and hemoglobin (Hgb) levels obtained on admission, at 8 and 24 hours, and every morning during resuscitation.

RESULTS

The 14 patients were categorized into 2 groups based on the 24-hour trend in Hgb levels: clinically significant blood loss (Hgb decrease >3 g/dL) or no clinical blood loss (Hgb decrease <3 g/dL). On admission, the 5 patients in the no blood loss group had normal BNP levels, whereas the 9 patients in the BL group had below-normal BNP levels. Because patients in the BL category were resuscitated, their BNP levels normalized.

CONCLUSIONS

BNP levels below normal are indicative of intravascular volume loss in traumatically injured patients.

Monitoring oxygen delivery in the critically ill

An accurate assessment of regional tissue oxygen delivery (DO(2)) may help the intensivist to attenuate end-organ damage in critically ill patients. Transport of oxygen from the ambient air to the mitochondria occurs by convection and diffusion, and is tightly regulated by neural and humoral factors. This article reviews the basic principles of DO(2) and the abnormal oxygen supply-demand relationship seen in patients with shock. It also discusses approaches to monitoring DO(2), including clinical symptoms/signs, acid-base status, and gas exchange, which provide global assessment, as well as gastric tonometry, which may reflect regional DO(2). Some new experimental methods, such as near-infrared spectroscopy and positron emission tomography, are still in development but may in the future provide useful clinical devices for quantifying the adequacy of regional tissue oxygenation in critically ill patients.

Near infrared spectroscopy for evaluation of the trauma patient: a technology review

Clinicians now realize the limitations of the physical examination in detecting compensated shock states, the severity of uncompensated states, and in determining the adequacy of resuscitation in order to prevent subsequent post-traumatic multisystem organ failure and death. A renewed interest has developed in interrogating the state of oxygen transport at the end-organ level in the trauma patient. Although used as a research tool and now clinically to monitor cerebral oxygenation during complex cardiovascular and neurosurgery, near infrared absorption spectroscopy (NIRS) is being more aggressively investigated and now marketed clinically as a noninvasive means to assess tissue oxygenation in the trauma patient at the end organ level. This paper will describe the principles of NIRS and the basis for its proposed use in the trauma patient to assess tissue oxygenation. This includes its known limitations, current controversies, and what will be needed in the future to make this technology a part of the initial and ongoing assessment of the trauma patient. The ultimate goal of such techniques is to prevent misassessment of patients and inadequate resuscitation, which are believed to be major initiators in the development of multisystem organ failure and death.

Evaluation of tissue saturation as a noninvasive measure of mixed venous saturation in children

BACKGROUND

Mixed venous saturation (S & OV0456;o2) is an important measurement that helps guide the care of critically ill patients. Invasive S & OV0456;o2 assessment in infants and children is often avoided because of the inherent risks. A noninvasive tissue saturation (S to 2) monitor has recently been developed that uses near-infrared spectroscopy to measure oxyhemoglobin saturation in muscle. In adult and animal studies, S to 2 correlated with oxygen delivery and S & OV0456;o2. There has been no evaluation in pediatric patients.

OBJECTIVE

To evaluate tissue saturation as a noninvasive measure of mixed venous saturation in children.

DESIGN

A prospective observational study.

SETTING

Catheterization laboratory in a tertiary care children's medical center.

PATIENTS

We studied 98 children (49 without intracardiac mixing and 49 with intracardiac mixing) <or=12 yrs of age who underwent cardiac catheterization. Under general anesthesia, we compared S to 2 measured over the deltoid muscle with superior vena cava saturation in both groups and S to 2 with pulmonary artery saturation in patients without intracardiac mixing. Paired measurements were analyzed for bias, precision, and correlation via Bland-Altman plot and linear regression.

RESULTS

No meaningful correlation was found between S to 2 and superior vena cava saturation or pulmonary artery saturation. Bland-Altman analyses of S to 2 with superior vena cava saturation yielded bias values of -6.67 +/- 37.33% in patients with intracardiac mixing and -0.82 +/- 41.31% in patients without mixing. Bland-Altman analysis of S to 2 with pulmonary artery saturation yielded a bias of 3.61 +/- 41.32% in patients without mixing. Differences between noninvasive and invasive measurements were greatest in smaller children.

CONCLUSION

Noninvasive tissue saturation over the deltoid does not correlate with S & OV0456;o2 in children. It is possible that more precise probe spacing, coupled with optimal muscle-mass location, could result in more accurate measures in future investigations.

Prehospital hemoglobin-based oxygen carrier resuscitation attenuates postinjury acute lung injury

BACKGROUND

Crystalloid infusion has been the standard prehospital fluid resuscitation in the United States for the past 35 years, but the emergence of a safe and effective hemoglobin-based oxygen carrier (HBOC) may change that practice. The purpose of this in vivo study is to simulate an existing multicenter prehospital trial of HBOC versus crystalloid to determine the effects in a controlled 2-event construct of postinjury multiple organ failure.

METHODS

Rats underwent hemorrhagic shock (30 mm Hg x 45 min) and were resuscitated over 2 hours in a clinically relevant design: 2 x volume of shed blood (SB) using normal saline (NS) in the first 30 minutes; 1/2 volume of SB in the next 30 minutes; another 2 x SB volume with NS over the remaining 60 minutes. Study groups represented alternative fluid strategies during the first hour of resuscitation: (1) Inhospital SB (standard resuscitation), (2) Inhospital HBOC, (3) Prehospital SB, and (4) Prehospital HBOC. Global physiologic response was assessed via tissue oxygenation (near infrared spectroscopy) and arterial base deficit, and pulmonary response, via lung polymorphonuclear neutrophil accumulation and vascular permeability.

RESULTS

Prehospital HBOC resuscitation provided the most efficient recovery of tissue oxygenation and correction of base deficit, had the greatest reduction in pulmonary polymorphonuclear neutrophil accumulation, and abrogated acute lung injury. Prehospital SB and Inhospital HBOC regimens afforded intermediate lung protection, compared with standard resuscitation.

CONCLUSIONS

The findings in this controlled in vivo study suggest prehospital HBOC resuscitation improves the recovery from postshock oxygen debt and reduces postinjury organ dysfunction.

Noninvasive monitoring of peripheral perfusion

BACKGROUND

Early hemodynamic assessment of global parameters in critically ill patients fails to provide adequate information on tissue perfusion. It requires invasive monitoring and may represent a late intervention initiated mainly in the intensive care unit. Noninvasive monitoring of peripheral perfusion can be a complementary approach that allows very early application throughout the hospital. In addition, as peripheral tissues are sensitive to alterations in perfusion, monitoring of the periphery could be an early marker of tissue hypoperfusion. This review discusses noninvasive methods for monitoring perfusion in peripheral tissues based on clinical signs, body temperature gradient, optical monitoring, transcutaneous oximetry, and sublingual capnometry.

DISCUSSION

Clinical signs of poor peripheral perfusion consist of a cold, pale, clammy, and mottled skin, associated with an increase in capillary refill time. The temperature gradients peripheral-to-ambient, central-to-peripheral and forearm-to-fingertip skin are validated methods to estimate dynamic variations in skin blood flow. Commonly used optical methods for peripheral monitoring are perfusion index, near-infrared spectroscopy, laser Doppler flowmetry and orthogonal polarization spectroscopy. Continuous noninvasive transcutaneous measurement of oxygen and carbon dioxide tensions can be used to estimate cutaneous blood flow. Sublingual capnometry is a noninvasive alternative for gastric tonometry.

Targeted resuscitation strategies after injury

PURPOSE OF REVIEW

The management of the traumatically injured patient has evolved during the past half century despite continually high morbidity and mortality rates. The management of the trauma victim requires timely intervention and damage control in an attempt to maintain normal hemodynamic parameters and adequate systemic perfusion. There is a fine balance between oxygen delivery and consumption, and when this is perturbed, oxygen debt may ensue. The presence of ongoing oxygen debt is rather deleterious, resulting in an inflammatory cascade that can lead to multisystem organ dysfunction. The rapid identification and restoration of oxygen debt are central to the resuscitation of the critically ill patient, be it the result of sepsis or trauma.

RECENT FINDINGS

Resuscitation end points have evolved that allow the physician to more rapidly identify a perturbation between oxygen delivery and consumption. Moreover, end points allow uniformity in gauging the adequacy of resuscitation: preventing under- and overresuscitation and serving as a basis to compare outcome measures in resuscitation trials. Recent technologic advances have allowed a greater wealth of clinical data that can be obtained via less invasive means. Examples of this include esophageal Doppler monitoring, sublingual capnography, orthogonal polarization spectral imaging, and lithium dilution cardiac output determinations. These devices can be used in concert with more traditional resuscitation end points (ie, lactate and base deficit) to maximize oxygen delivery and correct tissue dysoxia. In addition, the management of hemorrhagic shock is continuing to evolve and challenge the dogmatic practices of normotensive resuscitation.

SUMMARY

This review addresses (1) resuscitation end points to optimize cardiac function, (2) resuscitation end points to assess the microcirculation, (3) recent developments in the management of hypotensive hemorrhagic shock, and (4) the translation of early goal-directed therapy from septic shock to use in trauma. Past findings are reflected on and direction for future investigation and clinical practice based on recent clinical advances is provided.

Non-PET functional imaging techniques: optical

The strong and steady development of diffuse optical spectroscopy and tomography as new biomedical optics technologies promises to bring these optical techniques into clinical practice. This article provides a brief review of the light-tissue interaction, the instrumentation, and the theory relevant to this field. This is followed by a survey of the three main applications: brain imaging, muscle imaging, and breast imaging. Lastly, the future outlook of the technology is presented, highlighting the new promises based on recent breakthroughs.

Bladder Mucosa pH and Pco2 as a Minimally Invasive Monitor of Hemorrhagic Shock and Resuscitation

BACKGROUND

Continuous monitoring of pH, Pco2, and Po2 using fiberoptic sensor technology has been proposed recently as a clinical monitor of the severity of shock and impaired tissue perfusion. Surrogates of gut tissue perfusion such as gastric tonometry, although cumbersome, have been used to indirectly quantify the degree of gut ischemia. The purpose of this study was to demonstrate the feasibility of monitoring bladder mucosa (BM) and to compare urinary bladder mucosa and proximal jejunum mucosa interstitial pH and Pco2 during hemorrhagic shock and resuscitation.

METHODS

Eleven male miniature swine (25-35 kg) (control, n = 4; shock, n = 7) underwent jejunal tonometry and cystostomy. A multisensor probe was placed adjacent to the BM. Urine was diverted. Normocarbia was maintained. Animals were hemorrhaged and kept at a mean arterial pressure of 40 mm Hg. When a constant infusion was required to maintain the mean arterial pressure at 40 mm Hg (decompensation), animals were resuscitated with shed blood plus two times the shed volume in lactated Ringer's solution (20 minutes) and observed for 2 hours.

RESULTS

During decompensation, BM pH values decreased significantly from 7.33 +/- 0.08 to 7.01 +/- 0.2 (p < 0.01) and recovered to 7.11 +/- 0.19 at 120 minutes after completion of resuscitation. During decompensation, BM Pco2 values increased significantly compared with baseline (from 49 +/- 6 mm Hg to 71 +/- 19 mm Hg, p < 0.05) and returned to baseline with resuscitation. Jejunum mucosa and BM interstitial Pco2 correlated throughout shock and resuscitation (r = 0.49). Bland-Altman analysis demonstrated significant differences between jejunum mucosa (intramucosal pH) and BM interstitial pH.

CONCLUSION

Shock-induced changes in the Pco2 of the BM are comparable to tonometric changes in the gut. These data suggest that continuous fiberoptic multisensor probe monitoring of the BM could potentially provide a minimally invasive method for the assessment of impaired tissue perfusion of the splanchnic circulation during shock and resuscitation.

The next generation in shock resuscitation

Resuscitation of the severely injured patient who presents in shock has improved greatly, following focused wartime experience and insight from laboratory and clinical studies. Further benefit is probable from technologies that are being brought into clinical use, especially hypertonic saline dextran, haemoglobin-based oxygen carriers, less invasive early monitors, and medical informatics. These technologies could improve the potential of prehospital and early hospital care to pre-empt or more rapidly reverse hypoxaemia, hypovolaemia, and onset of shock. Damage control surgery and definitive interventional radiology will probably combine with more real-time detection and intervention for hypothermia, coagulopathy, and acidosis, to avoid extreme pathophysiology and the "bloody vicious cycle". Although now widely practised as standard of care in the USA and Europe, shock resuscitation strategies involving haemoglobin replacement and fluid volume loading to regain tissue perfusion and oxygenation vary between trauma centres. One of the difficulties is the scarcity of published evidence for or against seemingly basic intervention strategies, such as early or large-volume fluid loading. Standardised protocols for resuscitation, representing the best and most current knowledge of the clinical process, could be devised and widely implemented as interactive computerised applications among trauma centres in the USA and Europe. Prevention of injury is preferable and feasible, but early care of the severely injured patient and modulation of exaggerated systemic inflammatory response due to transfusion and other complications of traditional strategies will probably provide the next generation of improvements in shock resuscitation.

Phosphomonoesters Predict Early Mortality in Porcine Hemorrhagic Shock

BACKGROUND

Hemodynamic, laboratory, and tissue energetics were measured in a porcine model of hemorrhagic shock to evaluate variables as predictors of early mortality from shock. We hypothesized that elevated phosphomonoesters would predict early mortality in hemorrhagic shock.

METHODS

Pigs (n = 36) were subjected to 35% hemorrhage for 90 minutes in a 1.5-T nuclear magnetic resonance (NMR) magnet. Measurements included base deficit (BD); lactate; oxygen consumption/delivery; near-infrared spectroscopy of liver, stomach, and skeletal muscle tissue oxyhemoglobin saturation; and NMR spectroscopic measurements of high-energy phosphates of liver and skeletal muscle. Variables were compared between nonsurvivors and survivors to resuscitation after 90-minute measurements.

RESULTS

Ninety-minute mortality was 25%. Muscle phosphomonoesters (PMEs) and oxygen consumption differed significantly between survivors and nonsurvivors at baseline. Regression analysis identified baseline muscle PME levels, baseline BD, and 30-minute BD as early predictors of mortality before resuscitation (r2 = 0.304).

CONCLUSION

Baseline elevation in muscle PME levels predicts mortality in an animal model of severe hemorrhagic shock.

Serum bicarbonate concentration correlates with arterial base deficit in critically ill patients

BACKGROUND

Base deficit (BD) and lactate concentration have been established as endpoints of resuscitation (EOR) in critically ill patients. However, obtaining these data has traditionally required an arterial blood gas (ABG) sample. We hypothesized that the more easily available serum bicarbonate (SB) concentration could approximate BD and potentially serve as a useful EOR of critically ill or septic patients. We evaluated retrospectively the correlation of SB with BD in a cohort of surgical intensive care unit patients.

MATERIALS AND METHODS

Clinical data from April 1996 through April 1998 were recorded in a computerized application from 1,712 critically ill adult patients. The data were downloaded daily and imported into a relational database for storage and analysis. A subset of paired SB and ABG samples obtained simultaneously was analyzed by linear regression to determine the correlation coefficients (r) and coefficient of determinations (r(2)) for the respective analyses.

RESULTS

A total of 26,690 BD and 16,737 SB determinations were available in the database. Of these, 5,301 BD and SB samples were drawn simultaneously on the same patient. The correlation coefficient for these data pairs was 0.91, and the coefficient of determination was 0.83. The base deficit was predicted by the equation: BD = 22.43 - (0.9522 x SB) (p < 0.0001).

CONCLUSION

In this large data set, there was a close inverse correlation between SB and BD in critically ill or septic patients. The predictive equation explains 83% of the variability for BD values. A prospective study comparing SB to BD and lactate could confirm SB as a useful marker of resuscitation.

Goal-oriented shock resuscitation for major torso trauma: what are we learning?

Shock resuscitation is an obligatory intervention for severely injured patients who present in shock. During the past 15 years, with widespread acceptance of "damage control" surgery and early triage to the intensive care unit (ICU) to optimize resuscitation, the lives of many major trauma victims have been saved, and much has been learned about shock resuscitation. Due largely to the work of Shoemaker et al., a resuscitation strategy based on a standardized process using O(2) delivery index (DO(2)I) as an endpoint and physiologic performance goal for interventions has been developed, studied, and refined for resuscitation of shock caused by major trauma. DO(2)I >or=600 mL O(2)/min-m2 is the only resuscitation endpoint variable that has been tested in prospective randomized trials (PRTs) of trauma patient outcome. These PRTs are limited, and their results are not conclusive. Results from other investigators, including our group, using similar process and endpoints, are indicating similar performance and outcomes. We believe that DO(2)I is a useful endpoint because it integrates three important variables, ie, hemoglobin concentration [Hb], arterial hemoglobin O(2) saturation, and cardiac output. We have found DO(2)I >or=500 mL O(2)/min-m2 to be an endpoint with more general applicability, but we believe that the standardized process is more important than the specific endpoint. To standardize our process, we have developed a computerized decision support tool for shock resuscitation. This technology has provided novel data collection and has permitted refinement of the bedside process. Our data analysis indicates that the next challenge will be to develop a similar pre ICU resuscitation process that will use less invasive monitors and different endpoints. Identification of the high-risk resuscitation nonresponders early in the resuscitation process will be needed to redirect their clinical trajectories. As an endpoint for interventions for goal-directed resuscitation in the critically injured trauma patient, systemic O(2) delivery is the current state of the art and the basis for near future development of clinical processes for resuscitation of shock due to major trauma.