Elevated arterial base deficit in trauma patients: a marker of impaired oxygen utilization

Sublingual Capnometry for Rapid Determination of the Severity of Hemorrhagic Shock

BACKGROUND

Sublingual capnometry (SLCO2) is a rapid, minimally invasive bedside test of focal tissue perfusion. We hypothesized that SLCO2 could diagnose hemorrhagic shock and monitor adequacy of resuscitation. We compared the ability of SLCO2, serum lactate (LAC), and base deficit (BD) to predict outcome in hypotensive trauma patients.

METHODS

Prospective, observational trial at two Level I trauma centers was performed. Inclusion criteria were blunt or penetrating trauma patients, age > or =16 years, with hypotension (systolic blood pressure < or =90 mm Hg). SLCO2, LAC, and BD were measured in each patient at admission, at the end of active hemorrhage, and at 6, 24, and 48 hours. Data are reported as means (+/-SD).

RESULTS

A total of 86 patients were enrolled: mean age 35 (+/-17) years, 80% male, 51% blunt trauma, Injury Severity Score score 20 (+/-14). Twenty patients died. SLCO2 at admission was 52.4 (+/-13.3) in survivors versus 87.9 (+/-35.6) in nonsurvivors (p < 0.001). Receiver operating characteristic (ROC) curves showed that SLCO2, LAC, and BD were all good predictors of mortality. The area under each ROC curve was as follows: SLCO2 (0.82; 95% CI 0.70-0.96; p < 0.001), LAC (0.80; 95% CI 0.69-0.91; p < 0.001), BD (0.87; 95% CI 0.77-0.98; p < 0.001). There was no significant difference (p > 0.05) in the areas under the three curves.

CONCLUSIONS

SLCO2 predicted survival in hypotensive trauma patients. It had equivalent diagnostic ability to LAC and BD. This rapid test may supplement standard, more invasive measures of hemorrhagic shock.

A Pilot Study on Early Versus Delayed Hypertonic Saline Dextran Resuscitation in a Porcine Model of Near-Lethal Liver Injury: Early Hemodynamic Response and Short-Term Survival

BACKGROUND

We studied the effects of early versus delayed fluid resuscitation on hemodynamic response and short-term survival in a porcine model of severe hepatic injury associated with hemorrhagic shock.

MATERIALS AND METHODS

Eighteen anesthetized swine were randomized after standardized liver injury into two groups: early resuscitation (ER, n = 9) and delayed resuscitation (DR, n = 9). The ER and DR groups were resuscitated with hypertonic saline dextran (HSD) 20 min and 40 min after the injury, respectively. Mean arterial pressure (MAP), cardiac output (CO), and arterial blood gases were measured in addition to vascular blood flow rates in the aorta, hepatic artery and portal vein. The duration of follow-up was 100 min.

RESULTS

MAP decreased from 112 +/- 4 to 23 +/- 2 mmHg (P < 0.05) during 20 min after the injury. Bolus infusion of HSD significantly elevated MAP, CO, and flow rates in the aorta, portal vein and common hepatic artery in both groups. Portal vein flow remained relatively high during the shock. Intra-abdominal bleeding (ER, 701 +/- 42 mL; DR 757 +/- 78 mL) and the mortality rate (ER 44%; DR 33%) did not differ between the groups 100 min after injury (P > 0.05). Aortic flow, portal vein flow, common hepatic artery flow, MAP, CO, PaO(2), PaCO(2), base deficit, pH, hemoglobin measurements, and the volume of blood shed into the intraperitoneal cavity did not affect survival in the Cox regression analysis.

CONCLUSIONS

Early versus delayed fluid infusion with HSD resulted in a comparable hemodynamic response and survival 100 min after injury. No rebleeding was observed.

Effect of normal saline infusion on the diagnostic utility of base deficit in identifying major injury in trauma patients

BACKGROUND

Base deficit (BD) is a reliable marker of metabolic acidosis and is useful in gauging hemorrhage after trauma. Resuscitation with chloride-rich solutions such as normal saline (NS) can cause a dilutional acidosis, possibly confounding the interpretation of BD.

OBJECTIVES

To test the diagnostic utility of BD in distinguishing minor from major injury after administration of NS.

METHODS

This was a prospective observational study at a Level 1 trauma center. The authors enrolled patients with significant mechanism of injury and measured BD at triage (BD-0) and at four hours after triage (BD-4). Major injury was defined by any of the following: injury severity score of > or =15, drop in hematocrit of > or = 10 points, or the patient requiring a blood transfusion. Patients were divided into a low-volume (NS < 2L) and a high-volume (NS 2L) group. Data were reported as mean (+/-SD). Student's t- and Wilcoxon tests were used to compare data. Receiver operating characteristic (ROC) curves tested the utility of BD-4 in differentiating minor from major injury in the study groups.

RESULTS

Four hundred eighty-nine trauma patients (mean age, 36 [+/-18] yr) were enrolled; 82% were male, and 34% had penetrating injury. Major-(20%) compared with minor-(80%) injury patients were significantly (p = 0.0001) more acidotic (BD-0 mean difference: -3.3 mmol/L; 95% confidence interval [CI] = -2.5 to -4.2). The high-volume group (n = 174) received 3,342 (+/-1,821) mL, and the low-volume group (n = 315) received 621 (+/-509) mL of NS. Areas under the ROC curves for the high-volume (0.63; 95% CI = 0.52 to 0.74) and low-volume (0.73; 95% CI = 0.60 to 0.86) groups were not significantly different from each other.

CONCLUSIONS

Base deficit was able to distinguish minor from major injury after four hours of resuscitation, irrespective of the volume of NS infused.

Gut-lymph hypothesis of systemic inflammatory response syndrome/multiple-organ dysfunction syndrome: validating studies in a porcine model

BACKGROUND

Trauma-hemorrhagic shock (T/HS) mesenteric lymph from rats has multiple biological properties and appears to cause organ injury via the activation of neutrophils and endothelial cells. As the next step in testing the potential clinical relevance of these rodent studies, we utilized a swine T/HS model to determine whether the intestinal lymph results observed in the rodent could be replicated in swine. A porcine model was chosen because the pig and human cardiovascular and gastrointestinal physiology are similar.

METHODS

Male pigs were subjected to T/HS and a major intestinal lymph duct was cannulated. Hemorrhagic shock (mean arterial pressure, 40 mm Hg) was performed by withdrawing blood, for 3 hours or until the base deficit reached -5. Animals were then resuscitated in two stages to mimic the prehospital and hospital phases of resuscitation. Mesenteric lymph was collected hourly throughout the experiment and its biological activity was tested on neutrophils (respiratory burst) and endothelial cells (monolayer permeability and cytotoxicity).

RESULTS

T/HS lymph but not trauma-sham shock lymph (T/SS) increased neutrophil activation as reflected by an augmented respiratory burst. Likewise T/HS lymph collected at all time points up to 5 hours postshock significantly increased endothelial cell permeability by twofold or greater (p < 0.05), whereas T/HS lymph produced during the first 2 hours postshock was cytotoxic for endothelial cells (viability 70%, p < 0.05 vs. preshock). In contrast, T/SS lymph had no effect on the endothelial cells.

CONCLUSION

This large animal model validates rodent studies showing that the shock-injured gut releases biologically active factors into the mesenteric lymph and these factors activate neutrophils and injure endothelial cells.

Reduced Heart Rate Variability: An Indicator of Cardiac Uncoupling and Diminished Physiologic Reserve in 1,425 Trauma Patients

BACKGROUND

Measurements of a patient's physiologic reserve (age, injury severity, admission lactic acidosis, transfusion requirements, and coagulopathy) reflect robustness of response to surgical insult. We have previously shown that cardiac uncoupling (reduced heart rate variability, HRV) in the first 24 hours after injury correlates with mortality and autonomic nervous system failure. We hypothesized: Deteriorating physiologic reserve correlates with reduced HRV and cardiac uncoupling.

METHODS

There were 1,425 trauma ICU patients that satisfied the inclusion criteria. Differences in mortality across categorical measurements of the domains of physiologic reserve were assessed using the chi test. The relationship of cardiac uncoupling and physiologic reserve was examined using multivariate logistic regression models for various levels of cardiac uncoupling (>0 through 28% reduced HRV in the first 24 hours).

RESULTS

Of these, 797 (55.9%) patients exhibited cardiac uncoupling. Deteriorating measures of physiologic reserve reflected increased risk of death. Measures of acidosis (admission lactate, time to lactate normalization, and lactate deterioration over the first 24 hours), coagulopathy, age, and injury severity contributed significantly to the risk of cardiac uncoupling (area under receiver operator curve, ROC=0.73). The association between deteriorating reserve and cardiac uncoupling increases with the threshold for uncoupling (ROC=0.78).

CONCLUSIONS

Reduced heart rate variability is a new biomarker reflecting the loss of command and control of the heart (cardiac uncoupling). Risk of cardiac uncoupling increases significantly as a patient's physiologic reserve deteriorates and physiologic exhaustion approaches. Cardiac uncoupling provides a noninvasive, overall measure of a patient's clinical trajectory over the first 24 hours of ICU stay.

Serum bicarbonate may replace the arterial base deficit in the trauma intensive care unit

OBJECTIVE

Arterial base deficit (BD) is a commonly used marker of injury severity and endpoint of resuscitation but requires an arterial puncture and blood gas analysis. Serum bicarbonate (HCO3) is routinely obtained as part of the chemistry panel on most admissions. We hypothesized that serum HCO3 strongly correlates with arterial BD and provides equivalent predictive information.

METHODS

All trauma ICU admissions from 1996 to 2004 with simultaneously obtained serum chemistry panels and arterial blood gases were identified. Correlation between BD and HCO3 was analyzed by using linear regression, and predictive abilities for acidoses and mortality were compared using the area under the respective receiver operating characteristic curve (AUC). Separate analyses were done for the entire dataset and the subset of ICU admission laboratory values.

RESULTS

We identified 3,102 patients with 50,311 matched pairs of laboratory data. Serum HCO3 showed a significant linear correlation with BD for all laboratory sets (r = 0.85, P < .01) and admission laboratory values only (r = 0.80, P < .01). Serum HCO3 reliably predicted the presence of significant metabolic acidoses (BD >5), with an AUC of 0.96 (P < .01), which clearly outperformed pH (AUC = 0.83), anion gap (AUC = 0.7), and lactate (AUC = 0.73). The mean admission BD among survivors was 2.5 versus 5.2 for nonsurvivors (P < .01), and the mean HCO3 was 17.7 versus 19.8 (P < .01). The admission HCO3 identified nonsurvivors as accurately as BD (AUCs of 0.66 and 0.68) and more accurately than either pH (AUC = 0.53) or anion gap (AUC = 0.6).

CONCLUSION

Serum HCO3 measurement shows a strong linear correlation and similar predictive ability compared with the arterial BD. Serum HCO3 may be safely and accurately substituted for arterial BD measurement in critically injured patients.

Induction and detection of disturbed homeostasis in cardiopulmonary bypass

During cardiopulmonary bypass (CPB) haemodynamic alterations, haemostasis and the inflammatory response are the main causes of homeostatic disruption. Even with CPB procedures of short duration, the homeostasis of a patient is disrupted and, in many cases, requires intensive postoperative treatment to re-establish the physiological state of the patient. Although mortality is low, disruption of homeostasis may contribute to increased morbidity, particularly in high-risk patients. Over the past decades, considerable technical improvements in CPB equipment have been made to prevent the development of the systemic inflammatory response syndrome (SIRS). Despite all these improvements, only the inflammatory response, to some extent, has been reduced. The microcirculation is still impaired, as measured by tissue degradation products of various organs, indicating that CPB may still be considered as an unphysiological procedure. The question is, therefore, whether we can detect the pathophysiological consequences of CPB in each individual patient with valid bedside markers, and whether we can relate this to determinant factors in the CPB procedure in order to assist the perfusionist in improving the adequacy of CPB. The use of these markers could play a pivotal role in decision making by providing an immediate feedback on the determinant quality of perfusion. Therefore, we suggest validating the proposed markers in a nomogram to optimize not only the CPB procedure, but also the patient's safety.

Diagnosis of Acid-Base Derangements and Mortality Prediction in the Trauma Intensive Care Unit: The Physiochemical Approach

BACKGROUND

Conventional measures such as anion gap and base deficit can be inadequate for defining and managing complex acid-base derangements. Physiochemical analysis is an alternative approach based on the principles of electroneutrality and conservation of mass, and may be more accurate for defining the presence and type of acidosis and unmeasured anions.

METHODS

We retrospectively analyzed 2,152 sets of laboratory data from 427 trauma patients admitted to the intensive care unit. All data sets included simultaneous measurements of an arterial blood gas with base deficit (BD), serum electrolytes, albumin, lactate, and a calculated anion gap (AG). Physiochemical analysis was used to calculate the corrected anion gap (AGcorr), the apparent strong ion difference, the effective strong ion difference, the strong ion gap (SIG), and the base deficit corrected for unmeasured anions (BDua). Statistical analysis comparing AG and BD to the physiochemical measures was performed on all data and the subset of admission laboratory data only (n = 427).

RESULTS

Unmeasured anions as defined by an elevated SIG were present in 92% of patients (mean SIG, 5.9 +/- 3.3), whereas hyperlactatemia and hyperchloremia were present in only 18% and 21%, respectively. The physiochemical approach yielded a different clinical interpretation of the acid-base status than the conventional approach in 597 (28%) of the data sets. Lactate level was more strongly correlated with the physiochemical measures of SIG (r = 0.48) and AGcorr (r = 0.47) than with the conventional measures of AG (r = 0.24) and BD (r = 0.36, p < 0.01 for all). Both admission BD and BDua were significantly elevated in nonsurvivors, and logistic regression analysis for prediction of mortality revealed an area under the curve of 0.70 for BDua (p < 0.01) versus 0.65 for BD (p < 0.01). AGcorr and SIG did not differentiate survivors from nonsurvivors in the group as a whole. However, analysis of patients with a normal admission lactate level (n = 322) demonstrated a significant difference between survivors and nonsurvivors in SIG (7 vs. 5, p = 0.009), BDua (-4.2 vs. -2.0, p = 0.004), and AGcorr (21 vs. 19, p = 0.04), whereas the conventional measures of BD and AG showed no significant discriminatory ability.

CONCLUSION

Unmeasured anions are the most common component of metabolic acidosis in trauma intensive care unit patients. The physiochemical approach can significantly alter the acid-base diagnosis compared with conventional measures. The SIG, AGcorr, and BDua may be particularly helpful in predicting acid-base derangements and mortality in patients with normal serum lactate levels.

Diagnostic measures to evaluate oxygenation in critically ill adults: implications and limitations

Accurate assessment and treatment of disturbances in oxygenation are crucial to optimal outcomes in critically ill patients. Oxygenation is dependent upon adequate pulmonary gas exchange, oxygen delivery, and oxygen consumption. Each of these physiologic processes may vary independently in response to pathophysiologic conditions and therapeutic interventions. The author reviews diagnostic measures available to evaluate pulmonary gas exchange, oxygen delivery, and oxygen consumption in critically ill patients. Currently available tools and their potential value as well as key methodological limitations are addressed. Failure on behalf of clinicians to fully appreciate these limitations can lead to misdiagnoses and inappropriate treatment. The aim of this article is to help advanced practice nurses more fully understand the implications and limitations of these diagnostic measures to ensure accurate assessment and treatment of disturbances in oxygenation.

Methods of monitoring shock

Intensive monitoring is a crucial component of the management of shock. However, there is little consensus about optimal strategies for monitoring. Although the pulmonary artery catheter has been widely used, conflicting data exist about the utility of this device. A variety of other techniques have been developed in hopes of providing clinically useful information about myocardial function, intravascular volume, and indices of organ function. In addition, there is evolving evidence that targeting and monitoring certain physiological goals may be most important early in the course of shock. In this chapter, we examine many of the available monitoring techniques and the evidence supporting their use.

Correction of base deficits in deceased organ donors: Effects on immediate renal allograft function

Fluid status in the brain-dead donor is often difficult to assess. We hypothesized that using base deficit as a measure of tissue perfusion will facilitate fluid management in these donors, thereby improving renal allograft function. Consecutive donors over a 12-month period were prospectively studied. In Group I, resuscitation was based on maintaining normal blood pressure and urine output. In Group II, additional parameters of resuscitation included the correction of base deficit. Immediate renal allograft function was examined in the 48 recipients. Delayed graft function occurred in 48% of Group I, and in 19% of Group II recipients. Creatinine clearance on day 7, calculated by the Cockroft-Gault formula, was 29 +/- 6 mL/min in Group I versus 41 +/- 8 mL/min in Group II. We conclude that correcting base deficit is an extremely useful approach to expedite organ recovery and potentially improve function of transplanted kidneys.

Admission lactate level and the APACHE II score are the most useful predictors of prognosis following torso trauma

BACKGROUND

Markers of dysoxic metabolism and scoring systems for triage have been widely used in critically injured patients. However, so far, no model is sufficiently reliable to predict the outcome in trauma victims. The purposes of the present study, therefore, were to determine whether a correlation exits between the main trauma scoring systems and the markers of dysoxic metabolism. Moreover, to assess if any of the admission parameters can be used to indicate outcome.

METHODS

Sixty-four patients were included in this study. Admission data, including arterial lactate level, base deficit (BD), pH, revised trauma score (RTS), injury severity score (ISS), shock index (SI), and Acute Physiology and Chronic Health Evaluation (APACHE II), were collected and analysed by logistic regression analysis. Degree of association between continuous variables were calculated by either Pearson's or Spearman's correlation coefficient, where applicable. The dependence of lactate on two or more other variables was evaluated by multiple linear regression analysis.

RESULTS

Logistic regression analysis showed that the fatal outcome following major torso trauma was principally associated with the APACHE II score and lactate. The specificity and the sensitivity of this logistic regression model was 94.6 and 79.2%, respectively. According to standardised linear regression coefficients, BD was the best single predictor of lactate, and APACHE II added a small amount of predictive power. The proportion of total variation in lactate level explained by base deficit, APACHE II and age is R2=85.2%.

CONCLUSION

APACHE II score and the arterial lactate level are the most important determinants of clinical outcome in critically injured patients. A correlation exits between lactate and APACHE II and between lactate and base deficit.

Diagnostic Utility of Sublingual Pco2 for Detecting Hemorrhage in Penetrating Trauma Patients

BACKGROUND

Hemorrhage results in early compromise of splanchnic circulation. Studies have shown that sublingual Pco2 (SLCO2) correlates with gut perfusion. We tested SLCO2's ability to detect hemorrhage. We compared SLCO2 with arterial base deficit (BD) and lactate (LAC).

METHODS

This was a prospective study of patients with penetrating torso trauma. SLCO2 was measured at triage. Blood loss was defined as none (group 1), minimal to moderate (<1,500 mL) (group 2), or severe (>/=1,500 mL) (group 3). Data were reported as mean (95% confidence interval) and compared by analysis of variance. Receiver operating characteristic curves compared diagnostic performance between SLCO2, BD, and LAC.

RESULTS

One hundred eight patients were enrolled. There was a significant difference (p < 0.001) in SLCO2 between all blood loss groups: group 1, 46.9 mm Hg (44.9-49.0 mm Hg); group 2, 53.5 mm Hg (50.8-56.2 mm Hg); and group 3, 66.0 mm Hg (53.1-78.9 mm Hg). There were no significant (p > 0.05) differences for receiver operating characteristic curves between SLCO2, BD, or LAC.

CONCLUSION

SLCO2 differentiated blood loss groups. SLCO2 may be useful in triage of penetrating trauma patients.

Evaluation of Initial Base Deficit as a Prognosticator of Outcome in the Pediatric Trauma Population

Although the utility of the base deficit as an indicator of hypoperfusion and physiologic derangement in adults is well established, its value in the assessment of children is not as clear. The purpose of this study was to evaluate this tool with regard to injury severity, infectious morbidity, and outcome in a pediatric trauma population. A retrospective review of a 6-year period of the database of our level 1 pediatric trauma center was performed. One hundred seventeen severely injured children requiring mechanical ventilation were identified. Initial base deficit, Injury Severity Score, time to correction of this abnormality, ventilator days, infectious morbidity, and mortality were obtained and compared. Of the 117 patients included in this study, 30 patients were identified with an initial BD of less than or equal to -8 mEq/L and were placed into group 1. Group 2 consisted of the remaining 87 patients who presented with a base deficit (BD) of greater than -8 mEq/L. An admission base deficit of -8 mEq/L or less corresponded to a probability of mortality of 23 per cent as opposed to only 6 per cent with a BD greater than -8. Patients in group 1 remained on mechanical ventilation 9.4 ± 8.1 days, whereas patients in group 2 remained ventilated 6.5 ± 6.4 days; an increase of nearly 145 per cent. Likewise, the number of infectious complications rose 26 per cent with a worsening initial base deficit from 17 per cent of group 2 patients to 43 per cent of group 1 patients. We conclude that a high initial base deficit in injured children predicts a higher incidence of infectious complications and a less favorable outcome. This readily available laboratory study can identify those children most at risk of potentially preventable complications.

Different cardiorespiratory responses to hemorrhage and hyperoxia in normotensive (WKY) and spontaneously hypertensive (SHR) rats

OBJECTIVE

To compare the cardiorespiratory responses underlying the beneficial effects of hyperoxia during blood loss between normotensive (WKY) and hypertensive (SHR) rats.

METHODS

Experiments were carried out in anesthetized animals with both carotid bifurcations either innervated or denervated. The effects of breathing 60% O2 in N2 were studied either in combination with non-hypotensive hemorrhage or during hemorrhagic hypotension.

RESULTS

In normoxia arterial pressure fell more in SHR than in WKY for a given blood loss. During hyperoxia, nerve-intact rats showed initial suppression of ventilation, but bifurcation-denervated rats a powerful enhancement. In all groups, hyperoxia increased the overall tone of venous capacitance vessels.

CONCLUSIONS

The greater blood loss in SHR than in WKY when bleeding down to a given arterial pressure results from a stronger constriction of venous capacitance vessels. Hyperoxia improves the ability of the cardiorespiratory system to resist the effects of hemorrhage by increasing the overall venous tone, thus supporting cardiac filling, and in some cases also by increasing alveolar ventilation, probably secondary to improved cerebral oxygenation. The beneficial effects of hyperoxia were: (i) not prevented by carotid denervation, and thus were presumably direct tissue effects of oxygen, (ii) strikingly weaker in SHR than in normotensive (WKY) rats.

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.

Resolution and outcome of acute circulatory failure does not correlate with hemodynamics

INTRODUCTION

Hemodynamic goals in the treatment of acute circulatory failure (ACF) are controversial. In critical care, organ failures can be assessed using Sequential Organ Failure Assessment and its refinement, total maximal Sequential Organ Failure Assessment (TMS). We studied the associations between resolution of ACF and hemodynamics in the early (< 24 hours) phase of intensive care unit care and their relation to TMS and mortality.

PATIENTS AND METHODS

Eighty-three patients with ACF (defined as arterial lactate > 2 mmol/l and/or base deficit > 4) who had pulmonary artery catheters and stayed for longer than 24 hours in the intensive care unit were included. Hemodynamics, oxygen transport, vasoactive drugs and TMS scores were recorded. Normalisation of hyperlactatemia and metabolic acidosis in less than 24 hours after admission was defined as a positive response to hemodynamic resuscitation.

RESULTS

Fifty-two patients responded to resuscitation. Nonresponders had higher mortality than responders (52% versus 33%, P = 0.044). Hospital mortality was highest (63%) among nonresponders who received vasoactive drugs. The TMS scores of nonresponders (median [interquartile range], 12 9-16) were higher than the scores of responders (10 7-12, P = 0.019). Late accumulation of TMS scores was associated with increasing mortality, and if the TMS score increase occurred > 5 days after admission then the mortality was 77%. Responders had higher mean arterial pressure at 24 hours, but it was no different between survivors and nonsurvivors. No other hemodynamic and oxygen transport variables were associated with the success of resuscitation or with mortality.

CONCLUSIONS

Except for the mean arterial pressure at 24 hours, invasively derived hemodynamic and oxygen transport variables are not associated with the response to resuscitation or with mortality. Positive response to resuscitation in ACF is associated with less severe organ failures as judged by TMS scores. Late accumulation of the TMS score predicts poor outcome.

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Serum lactate and base deficit as predictors of mortality and morbidity

OBJECTIVES

To determine whether lactate levels and base deficits in critically ill surgical intensive care unit (SICU) patients correlate and whether either measure is a significant indicator of mortality and morbidity.

METHODS

A review was made of 137 SICU patients who had serial lactate and blood gas measurements. Patients were stratified by absolute lactate and base deficit values as well as time to lactate clearance.

RESULTS

Initial and 24-hour lactate level was significantly elevated in nonsurvivors versus survivors (P = 0.002). Initial base deficit was not significantly different; 24-hour base deficit did achieve statistical significance (P = 0.02). Subgroup analysis among trauma patients (n = 36) and major abdominal surgery (n = 101) confirmed the significant correlation between lactate levels and survival. There was poor correlation between initial and 24-hour lactate and base deficit among all patients (r = -0.3 and -0.5). Mortality if lactate normalized within 24 hours was 10%, compared with 24% for >48 hours and 67% if lactate failed to normalize. Physical status at discharge was related to initial lactate (P = 0.05), as well as to lactate clearance time (P = 0.01).

CONCLUSIONS

Elevated initial and 24-hour lactate levels are significantly correlated with mortality and appear to be superior to corresponding base deficit levels. Lactate clearance time may be used to predict mortality and is associated with outcome at discharge. Initial base deficit is a poor predictor of mortality and did not correlate with lactate levels except in trauma nonsurvivors. In addition to being used as an endpoint for resuscitation, lactate may be predictive of certain morbidities and patient outcome at discharge.

Triage scoring systems, severity of illness measures, and mortality prediction models in pediatric trauma

Trauma triage scores, severity of illness measures, and mortality prediction models quantitate severity of injury and stratify patients according to a specified outcome. Triage scoring systems are typically used to assist prehospital personnel determine which patients require trauma center care, but they are not recommended as the sole determinant of triage. Severity of illness measures and mortality prediction models are used in clinical and health services research for risk-adjusted outcomes analyses and institutional benchmarking. As clinicians and researchers, it is imperative that we be knowledgeable of the methodologies and applications of these scoring and risk prediction systems to ensure their quality and appropriate utilization.

Acute Respiratory Distress Syndrome in Blunt Trauma: Identification of Independent Risk Factors

Acute respiratory distress syndrome (ARDS) is a major contributor to morbidity and mortality in trauma patients. Although many injuries and conditions are believed to be associated with ARDS independent risk factors in trauma patients and their relative importance in development of the syndrome are undefined. The aim of this project is to identify independent risk factors for the development of ARDS in blunt trauma patients and to examine the contributions of each factor to ARDS development. Patients with ARDS were identified from the registry of a Level I trauma center over a 4.5-year period. Records were reviewed for demographics, injury characteristics, transfusion requirements, and hospital course. Variables examined included age >65 years, Injury Severity Score (ISS) >25, hypotension on admission (systolic blood pressure <90), significant metabolic acidosis (base deficit <-5.0), severe brain injury as shown by a Glasgow Coma Scale score (GCS) <8 on admission, 24-hour transfusion requirement >10 units packed red blood cells, pulmonary contusion (PC), femur fracture, and major infection (pneumonia, empyema, or intraabdominal abscess). Both univariate and stepwise logistic regression were used to identify independent risk factors, and receiver operating characteristic curve (ROC) analysis was used to determine the relative contribution of each risk factor. A total of 4397 patients having sustained blunt trauma were admitted to the intensive care unit and survived >24 hours between October 1995 and May 2000. Of these patients 200 (4.5%) developed ARDS. All studied variables were significantly associated with ARDS in univariate analyses. Stepwise logistic regression, however, demonstrated age >65 years, ISS >25, hypotension on admission, 24-hour transfusion requirement >10 units, and pulmonary contusion as independent risk factors, whereas admission metabolic acidosis, femur fracture, infection, and severe brain injury were not. Using a model based on the logistic regression equation derived yields better than 80 per cent discrimination in ARDS patients. The risk factors providing the greatest contribution to ARDS development were ISS >25 (ROC area 0.72) and PC (ROC area 0.68) followed by large transfusion requirement (ROC area 0.56), admission hypotension (ROC area 0.57), and age >65 (ROC area 0.54). Independent risk factors for ARDS in blunt trauma include ISS >25, PC, age >65 years, hypotension on admission, and 24-hour transfusion requirement >10 units but not admission metabolic acidosis, femur fracture, infection, or severe brain injury. Assessment of these variables allows accurate estimate of risk in the majority of cases, and the most potent contributors to the predictive value of the model are ISS >25 and PC. Improvement in understanding of which patients are actually at risk may allow for advances in treatment as well as prevention in the future.

Improving ventricular-arterial coupling during resuscitation from shock: effects on cardiovascular function and systemic perfusion

BACKGROUND

Efficacy of circulation depends on interactions between the heart and the vascular system. Ventricular-arterial coupling (VAC) has been described as an important determinant of cardiovascular function during resuscitation from shock. However, no prospective studies examining VAC and systemic perfusion have been performed. VAC is measured by the ratio of afterload (aortic input impedance [E ]) to contractility (end-systolic elastance [E ]). Lowering E /E is associated with better VAC and improved myocardial work efficiency. Our hypothesis was that optimizing VAC during resuscitation results in improved myocardial work efficiency while simultaneously improving systemic perfusion.

METHODS

This was a prospective study in a consecutive series of critically injured patients. Hemodynamic variables, including E, E, and myocardial work efficiency were evaluated by constructing ventricular pressure-volume loops at the bedside during resuscitation. After pulmonary artery catheterization and adequate fluid resuscitation, left ventricular power output and E /E were optimized with inotropic agents and/or afterload reduction. Efficiency was calculated as stroke work/total left ventricular energy expenditure. Tissue perfusion was estimated by calculating base deficit clearance per hour.

RESULTS

Twenty-three patients were studied over a 9-month period. Fifteen patients required inotropic support or afterload reduction. Improvements were seen in E /E (from 1.0 +/- 0.4 to 0.6 +/- 0.2 mm Hg/mL/m, p = 0.0004), and left ventricular power output (from 280 +/- 77 to 350 +/- 81 L/min/m. mm Hg, p = 0.003) with resuscitation. A concomitant improvement in myocardial efficiency (from 70% +/- 8.0% to 77% +/- 5.0%, p = 0.0001) and base deficit clearance (from 0.1 +/- 0.4 to -0.2 +/- 0.1 mEq/L/h, p = 0.006) was seen.

CONCLUSION

Improved ventricular-arterial coupling during resuscitation is associated with improved myocardial efficiency and systemic tissue perfusion. Perfusion can be improved at lower energy cost to the heart by focusing on thermodynamic principles during resuscitation.

Impact of alcohol intoxication on hemodynamic, metabolic, and cytokine responses to hemorrhagic shock

BACKGROUND

Alcohol intoxication is associated with a high incidence of traumatic injury, particularly in the young healthy population. The impact of alcohol intoxication on the immediate pathophysiologic response to injury has not been closely examined. We hypothesized that acute alcohol intoxication would aggravate the immediate outcome from hemorrhagic shock by impairing homeostatic counterregulation to blood loss.

METHODS

Chronically catheterized male Sprague-Dawley rats were randomized to receive an intragastric infusion of ethyl alcohol (1.75 g/kg followed by 250-300 mg/kg/h) or isocaloric dextrose (3-mL bolus + 0.375 mL/h) for 15 hours. Before initiating fixed-pressure hemorrhage followed by fluid resuscitation, an additional intragastric bolus of ethyl alcohol (1.75 g/kg) was administered. Hemodynamic, metabolic, cytokine, and acid-base parameters were assessed during the hemorrhage period and at completion of resuscitation. Lungs were obtained for cytokine determinations.

RESULTS

Basal mean arterial pressure was significantly lower in alcohol-intoxicated (blood-alcohol concentration, 135 +/- 12 mg/dL) animals than in controls during baseline (20%) and after the initial fluid resuscitation period (30%). Hemorrhage decreased arterial HCO3 and Pco2, and increased Po2 without significant alteration in arterial blood pH. Alcohol intoxication blunted the decrease in Pco2 and increase in Po2 and decreased blood pH during baseline and throughout the course of the hemorrhage period. Hemorrhage produced marked and progressive elevations in plasma glucose and lactate levels in controls, and this was inhibited by alcohol intoxication. Hemorrhage elevated plasma tumor necrosis factor-alpha (TNF-alpha) (686 +/- 252 pg/mL) and interleukin (IL)-10 (178 +/- 25 pg/mL), and did not alter IL-6 and IL-1 levels. Alcohol blunted the hemorrhage-induced rise in plasma TNF-alpha (142 +/- 48 pg/mL) and enhanced the hemorrhage-induced increase in IL-10 (678 +/- 187 pg/mL). Hemorrhage produced a two- to threefold increase in lung content of TNF-alpha, IL-1alpha, and IL-6 without significantly altering lung IL-10. Alcohol exacerbated the hemorrhage-induced increase in lung TNF-alpha, and did not alter the IL-1alpha, IL-6, and IL-10 lung responses.

CONCLUSION

These results indicate marked alterations in the hemodynamic and metabolic responses to hemorrhagic shock by alcohol intoxication. Furthermore, our findings suggest that alcohol modulates the early proinflammatory responses to hemorrhagic shock. Taken together, these alterations in metabolic and inflammatory responses to hemorrhage are likely to impair immediate outcome and predispose to tissue injury.

End points of resuscitation: choosing the right parameters to monitor

Determining when resuscitation is complete can be challenging, as tissue hypoperfusion can persist despite normal vital signs. This article discusses the limitations of traditional parameters used as resuscitation guidelines and describes new technologies that aid in assessing resuscitation efforts, including advances in hemodynamic monitoring and methods for obtaining global and organ-specific indexes.

Admission base deficit in pediatric trauma: a study using the National Trauma Data Bank

BACKGROUND

The base deficit, an important indicator of physiologic derangement after severe injury in adults, has not been specifically examined in the pediatric trauma population. The purpose of this study was to assess the ability of the admission base deficit to predict injury severity and outcome in the pediatric trauma population.

METHODS

The study group included all patients in the National Trauma Data Bank over a 2-year period aged 0 to 12 years with a base deficit (0 to -30 mEq/L) recorded from the emergency department. Age, presence of a severe closed head injury, and base deficit were analyzed with respect to mortality and other indicators of injury severity.

RESULTS

A total of 515 patients constituted the study group. Base deficit less than -4 mEq/L (p < 0.001) and the presence of a closed head injury (odds ratio, 3.8; p < 0.05) were predictors of mortality. For the group, an admission base deficit of -8 mEq/L corresponded to a probability of mortality of 25%. Significant correlations were found between base deficit and emergency department systolic blood pressure, Injury Severity Score, and Revised Trauma Score. There was no relationship between age and mortality.

CONCLUSION

In injured children, the admission base deficit reflects injury severity and predicts mortality. The probability of mortality increases precipitously in children with a base deficit less than -8 mEq/L, and should alert the clinician to the presence of potentially lethal injuries or uncompensated shock.

The effect of pregnancy on the response to blood loss in a rat model

STUDY OBJECTIVES

A commonly held belief is that the blunted hemodynamic response to hemorrhage observed in pregnant women is secondary to expanded blood volume. In addition to increased blood volume, pregnancy is also a vasodilated state. Vasodilatation may have deleterious effects on the response to hemorrhage by inhibiting central blood shunting after blood loss. How these conflicting variables of increased blood volume and vasodilatation integrate into a whole body model of maternal hemorrhagic shock has yet to be studied in a controlled experiment. We tested the null hypothesis that there would be no difference in the hemodynamic and metabolic responses to hemorrhage between pregnant (PRG) and non-pregnant (NPRG) rats.

METHODS

Twenty-four adult female Sprague-Dawley rats (12 PRG and 12 NPRG) were anesthetized with Althesin via the intraperitoneal route. Femoral arteries were cannulated by cut-down. Twelve (six PRG and six NPRG) rats underwent controlled catheter hemorrhage of 25% of their total blood volume. Twelve rats (six PRG and six NPRG) served as non-hemorrhage controls. Mean arterial pressure (MAP) and base excess (BE) were measured pre-hemorrhage and then every 15 min post-hemorrhage for the next 90 min. Data were reported as mean+/-standard error of the mean (S.E.M.) over the 90-min post-hemorrhage observation period. Group comparisons were analyzed by ANOVA with repeated values post-hoc by Bonferroni. Statistical significance was defined by an alpha=0.05.

RESULTS

PRG and NPRG rats were evenly matched for MAP (P=0.788) and BE (P=0.146) pre-hemorrhage. Post-hemorrhage there were no mortalities in either group. Post-hemorrhage both the PRG and NPRG groups experienced significant (P=0.011) drops in systolic and diastolic blood pressures as compared to their non-hemorrhage controls. Post-hemorrhage there was no significant (P=0.43) difference in MAP between the PRG (89+/-2 mmHg) and NPRG (80+/-2 mmHg) rats. BE also dropped significantly within both PRG (P=0.004) and NPRG (P=0.001) groups post-hemorrhage. No significant (P=0.672) difference was noted in BE between PRG and NPRG groups post-hemorrhage -6.1+/-0.3 mEq/l and -6.9+/-0.4 mEq/l, respectively.

CONCLUSION

After a controlled hemorrhage of 25% of total blood volume we found no significant differences in MAP and BE between pregnant and non-pregnant rats. Pregnancy does not affect the response to hemorrhage.

Trauma critical care

The surgical approach to the most injured patients has changed in recent years. Many patients arrive in the intensive care unit with problems that in the past would have been definitively addressed in the operating room, or led to the patient's demise due to continued attempts to complete all surgical procedures, despite deteriorating physiology. As a result, the triad of hypothermia, acidosis, and coagulopathy, along with the frequent complication of abdominal compartment syndrome, are critical factors that require correction in the intensive care unit. Prompt correction is necessary not only to allow expeditious completion of required surgical procedures, but because this triad, unless interrupted, invariably leads to death during resuscitation.

Resuscitative effects of polynitroxylated alphaalpha-cross-linked hemoglobin following severe hemorrhage in the rat

alphaalpha-Cross-linked hemoglobin (alphaalphaHb) is an example of a hemoglobin-based oxygen carrier (HBOC) with significant cardiovascular activity. This may compromise the safety and efficacy of this HBOC by causing systemic hypertension and reducing blood flow to some organs. The present work is based on the hypothesis that incorporating antioxidant activity into an HBOC in the form of a covalently attached nitroxide may prevent these effects. We have tested this hypothesis by adding antioxidant activity to alphaalphaHb with 2,2,6,6-tetramethyl-piperidinyl-1-oxyl (Tempo) to create polynitroxylated alphaalphaHb (PN-alphaalphaHb). The new compound PN-alphaalphaHb acts as an antioxidant in our in vitro and in vivo assays. In this study urethane-anesthetized rats were hemorrhaged to a mean arterial pressure (MAP) of 35-40 mmHg and maintained for 30 min. Animals were resuscitated with solutions of (1) 10% PN-alphaalphaHb (43 mmHg), (2) 10% alphaalphaHb (43 mmHg), (3) 7.5% albumin (43 mmHg), (4) 300% Ringers lactate (RL), and (5) 0. 9% normal saline equal to the shed blood volume (SBV). Hemodynamics and regional blood circulation was measured at baseline, following hemorrhage, and at 30 and 60 min postresuscitation using a radioactive microsphere technique. Base deficit (BD) was measured at baseline, following hemorrhage, and at 60 min following resuscitative fluid infusion. Finally survival was determined as the time following resuscitation until secession of heart rhythm. Saline and 300% RL resuscitation did not improve BD, systemic hemodynamics, or regional blood circulation. PN-alphaalphaHb, alphaalphaHb, and albumin significantly improved these parameters, however, only PN-alphaalphaHb and alphaalphaHb improved survival. PN-alphaalphaHb was found to be less hypertensive than alphaalphaHb due to blunted increases in both cardiac output and systemic vascular resistance. This study demonstrates that, by using alphaalphaHb as a scaffold for polynitroxylation, improvement in vasoactivity and resuscitative efficacy may be possible. In conclusion, the addition of antioxidant activity in the form of polynitroxylation of a low molecular weight Hb (alphaalphaHb) may create a safe and efficacious resuscitative fluid.

Application of base deficit in resuscitation of trauma patients

Clinical measures, such as blood pressure or urine output, have been the traditional methods used to assess tissue perfusion in trauma patients with hypovolemia. Hypoperfusion of tissues results in increased levels of lactate and carbonic acids. Base deficit is a clinical measure of metabolic acidosis that normalizes rapidly with adequate resuscitation and hemorrhage control, and it can be used to monitor the initial care of a patient with trauma. The method used to measure base deficit is discussed, along with its clinical uses and limitations. A case study is used to correlate changes in base deficit with other clinical parameters.

Maintaining survivors' values of left ventricular power output during shock resuscitation: a prospective pilot study

OBJECTIVE

Maintaining left ventricular power output (LVP) > 320 mm Hg x L/min/m2 during resuscitation has been retrospectively associated with faster resolution of acidosis and survival after posttraumatic shock. The purpose of this prospective study was to evaluate the effects of maintaining LVP above this threshold during resuscitation on base deficit clearance, organ failure, and survival.

METHODS

This was a study of a consecutive series of critically injured patients (PWR) monitored with a pulmonary artery catheter during initial resuscitation. LVP, calculated as cardiac index-(mean arterial pressure-central venous pressure), was maintained >320 mm Hg x L/min/m2 via a predefined protocol by using ventricular pressure-volume diagrams. Outcome was assessed by base deficit clearance (<6 mEq/L) in <24 hours, lowest base deficit in the first 24 hours after admission (24-hr base deficit), organ dysfunctions/patient, and survival. Results were compared with 39 control patients (OXY) with identical enrollment criteria from a previous prospective study who were resuscitated based on oxygen transport criteria.

RESULTS

Twenty patients were studied over a 6-month period. Mean LVP during resuscitation in the PWR group was 360 +/- 100 mm Hg x L/min/m2. Admission base deficit was similar between the two groups (PWR 11 +/- 4.2 vs. OXY 11 +/- 5.8 mEq/L;p = 0.66). More PWR patients cleared base deficit in < 24 hours than OXY patients (16 of 20 vs. 17 of 39, p = 0.009, Fisher's exact test), and the PWR patients had a significantly lower 24-hr base deficit (3.9 +/- 3.7 vs. 7.1 +/- 4.6 mEq/L, p = 0.01). Organ dysfunction rate was lower in the PWR group (2.1 +/- 1.5 vs. 3.2 +/- 1.4 organ dysfunctions/patient, p = 0.007). Survival in the PWR group was 15 of 20, versus 21 of 39 in the OXY group (p = 0.10).

CONCLUSION

Prospectively maintaining LVP above 320 mm Hg x L/min/m2 during resuscitation is an achievable goal. It is associated with improved base deficit clearance and a lower rate of organ dysfunction after resuscitation from traumatic shock.

The effect of hypertension on the response to blood loss in a rodent model

OBJECTIVE

Hypertensive patients having higher baseline peripheral resistance and sympathetic tone than normotensive patients may have aberrant responses to hemorrhage. In an attempt to further characterize this clinical observation, the authors compared the hemodynamic and metabolic responses to hemorrhage between spontaneously hypertensive rats (SHR) and normotensive rats (NTR).

METHODS

Twenty adult rats (10 NTR and 10 SHR) were anesthetized with althesin via the intraperitoneal route. Femoral arteries were cannulated by cutdown. Twelve (6 SHR and 6 NTR) rats underwent controlled catheter hemorrhage of 25% of their total blood volumes. Eight rats (4 SHR and 4 NTR) served as nonhemorrhage controls. Mean arterial pressure (MAP) and base excess (BE) were measured prehemorrhage and then every 15 minutes for the next 120 minutes. Data were reported as mean +/- standard error of the mean (SEM). Group comparisons were analyzed by ANOVA with repeated values post-hoc by Bonferroni. Statistical significance was defined by an alpha = 0.05.

RESULTS

Immediately after hemorrhage, the SHR group experienced a significantly (p < 0.001) greater drop in MAP of 70 +/- 4% in the SHR vs 40 +/- 6% in the NTR. Blood pressure in the NTR returned to control values 15 minutes after hemorrhage, but the SHR remained relatively hypotensive for the entire length of the experiment. Base excess in the SHR decreased significantly (p < 0.004) by 8.2 +/- 2 mmol/L from control values, as compared with no changes in BE for the NTR.

CONCLUSIONS

The authors observed significant differences in the response to hemorrhage between hypertensive and normotensive rats. Hypertensive rats experienced a more profound hemorrhagic shock insult than normotensives for the same degree of blood loss.