Cardiac preload, splanchnic perfusion, and their relationship during resuscitation in trauma patients

Cardiovascular implications of abdominal compartment syndrome

Cardiovascular dysfunction and failure are commonly encountered in the patient with intra-abdominal hypertension or abdominal compartment syndrome. Accurate assessment and optimization of preload, contractility, and afterload, in conjunction with appropriate goal-directed resuscitation and abdominal decompression when indicated, are essential to restoring end-organ perfusion and maximizing patient survival. The validity of traditional hemodynamic resuscitation endpoints, such as pulmonary artery occlusion pressure and central venous pressure, must be reconsidered in the patient with intra-abdominal hypertension as these pressure-based estimates of intravascular volume have significant limitations in patients with elevated intra-abdominal pressure. If such limitations are not recognized, misinterpretation of the patient's cardiac status is likely, resulting in inappropriate and potentially detrimental therapy. Appropriate fluid administration is mandatory as under-resuscitation leads to organ failure and over-resuscitation the development of secondary abdominal compartment syndrome, both of which are associated with increased morbidity and mortality. Volumetric monitoring techniques have been proven to be superior to traditional intra-cardiac filling pressures in directing the appropriate resuscitation of this patient population. Calculation of the "abdominal perfusion pressure", defined as mean arterial pressure minus intra-abdominal pressure, has been shown to be a beneficial resuscitation endpoint as it assesses not only the severity of the patient's intra-abdominal hypertension, but also the adequacy of abdominal blood flow. Application of a goal-directed resuscitation strategy, including abdominal decompression when indicated, improves cardiac function, reverses end-organ failure, and minimizes intra-abdominal hypertension-related patient morbidity and mortality.

Comparison of hemodynamic measurements from invasive and noninvasive monitoring during early resuscitation

BACKGROUND

Measurements obtained from the insertion of a pulmonary artery catheter (PAC) in critically ill and/or injured patients have traditionally assisted with resuscitation efforts. However, with the recent utilization of ultrasound in the intensive care unit setting, transthoracic echocardiography (TTE) has gained popularity. The purpose of this study is to compare serial PAC and TTE measurements and document levels of serum biomarkers during resuscitation.

METHODS

Over a 25-month period, critically ill and/or injured patients admitted to a Level I adult trauma center were enrolled in this 48-hour intensive care unit study. Serial PAC and TTE measurements were obtained every 12 hours (total = 5 points/patient). Serial levels of lactate, Δ base, troponin-1, and B-type natriuretic peptide were obtained. Pearson correlation coefficient and intraclass correlation (ICC) assessed relationship and agreement, respectively, between PAC and TTE measures of cardiac output (CO) and stroke volume (SV). Analysis of variance with post hoc pairwise determined differences over time.

RESULTS

Of the 29 patients, 69% were male, with a mean age of 47.4 years ± 19.5 years and 79.3% survival. Of these, 25 of 29 were trauma with a mean Injury Severity Score of 23.5 ± 10.7. CO from PAC and TTE was significantly related (Pearson correlations, 0.57-0.64) and agreed with moderate strength (ICC, 0.66-0.70). SV from PAC and TTE was significantly related (Pearson correlations, 0.40-0.58) and agreed at a weaker level (ICC, 0.41-0.62). Tricuspid regurgitation was noted in 80% and mitral regurgitation in 50% to 60% of patients.

CONCLUSION

Measurements of CO and SV were moderately strong in correlation and agreement which may suggest PAC measurements overestimate actual values. The significance of tricuspid regurgitation and mitral regurgitation during early resuscitation is unknown.

Global and right ventricular end-diastolic volumes correlate better with preload after correction for ejection fraction

BACKGROUND

Volumetric monitoring with right ventricular end-diastolic volume indexed (RVEDVi) and global end-diastolic volume indexed (GEDVi) is increasingly being suggested as a superior preload indicator compared with the filling pressures central venous pressure (CVP) or the pulmonary capillary wedge pressure (PCWP). However, static monitoring of these volumetric parameters has not consistently been shown to be able to predict changes in cardiac index (CI). The aim of this study was to evaluate whether a correction of RVEDVi and GEDVi with a measure of the individual contractile reserve, assessed by right ventricular ejection fraction (RVEF) and global ejection fraction, improves the ability of RVEDVi and GEDVi to monitor changes in preload over time in critically ill patients.

METHODS

Hemodynamic measurements, both by pulmonary artery and by transcardiopulmonary thermodilution, were performed in 11 mechanically ventilated medical ICU patients. Correction of volumes was achieved by normalization to EF deviation from normal EF values in an exponential fashion. Data before and after fluid administration were obtained in eight patients, while data before and after diuretics were obtained in seven patients.

RESULTS

No correlation was found between the change in cardiac filling pressures (DeltaCVP, DeltaPCWP) and DeltaCI (R(2) 0.01 and 0.00, respectively). Further, no correlation was found between DeltaRVEDVi or DeltaGEDVi and DeltaCI (R(2) 0.10 and 0.13, respectively). In contrast, a significant correlation was found between DeltaRVEDVi corrected to RVEF (DeltacRVEDVi) and DeltaCI (R(2) 0.64), as well as between DeltacGEDVi and DeltaCI (R(2) 0.59). An increase in the net fluid balance with +844 + or - 495 ml/m(2) resulted in a significant increase in CI of 0.5 + or - 0.3 l/min/m(2); however, only DeltacRVEDVi (R(2) 0.58) and DeltacGEDVi (R(2) 0.36) correlated significantly with DeltaCI. Administration of diuretics resulting in a net fluid balance of -942 + or - 658 ml/m(2) caused a significant decrease in CI with 0.7 + or - 0.5 l/min/m(2); however, only DeltacRVEDVi (R(2) 0.80) and DeltacGEDVi (R(2) 0.61) correlated significantly with DeltaCI.

CONCLUSION

Correction of volumetric preload parameters by measures of ejection fraction improved the ability of these parameters to assess changes in preload over time in this heterogeneous group of critically ill patients.

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.

Monitoring global volume-related hemodynamic or regional variables after initial resuscitation: What is a better predictor of outcome in critically ill septic patients?

OBJECTIVE

Regional variables of organ dysfunction are thought to be better monitoring variables than global pressure-related hemodynamic variables. Whether a difference exists between regional and global volume-related variables in critically ill patients after resuscitation is unknown.

DESIGN

Prospective diagnostic test evaluation.

SETTING

University-affiliated mixed intensive care unit.

PATIENTS

Twenty-eight critically ill patients.

INTERVENTIONS

Using standardized resuscitation, hemodynamic optimization was targeted at mean arterial pressure, heart rate, occlusion pressure, cardiac output, systemic vascular resistance, and urine output. Primary outcome variable was in-hospital mortality.

MEASUREMENTS AND MAIN RESULTS

During resuscitation, global volume-related hemodynamic variables were measured simultaneously and compared with regional variables. At admission no variable was superior as a predictor of outcome. During resuscitation, significant changes were seen in mean arterial pressure, central venous pressure, oxygen delivery, systemic vascular resistance, total blood volume, right heart and ventricle end-diastolic volume, right ventricle ejection fraction, right and left stroke work index, intramucosal carbon dioxide pressure, gastric mucosal pH, mucosal-end tidal Pco2 gap, indocyanine green blood clearance, indocyanine green plasma clearance, and plasma disappearance rate. Multivariate analysis identified lactate, gastric mucosal pH, mucosal-end tidal Pco2 gap, mucosal-arterial Pco2 gap, indocyanine green plasma clearance, and plasma disappearance rate of dye as nondependent predictors of outcome. Patients who subsequently died had a significantly lower gastric mucosal pH, higher intramucosal carbon dioxide pressure and mucosal-end tidal Pco2 gap, and lower indocyanine green blood clearance, indocyanine green plasma clearance, plasma disappearance rate, and right ventricular end-diastolic volume index, of which gastric mucosal pH, mucosal-end tidal Pco2 gap, and indocyanine green blood clearance were the most important predictors of outcome.

CONCLUSIONS

Initial resuscitation of critically ill patients with shock does not require monitoring of regional variables. After stabilization, however, regional variables are the best predictors of outcome.

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.

PRELOAD OPTIMIZATION USING “STARLING CURVE” GENERATION DURING SHOCK RESUSCITATION: CAN IT BE DONE?

Preload-directed resuscitation is the standard of care in U.S. trauma centers. As part of our standardized protocol for traumatic shock resuscitation, patients who do not respond to initial interventions of hemoglobin replacement and fluid volume loading have optimal preload determined using a standardized algorithm to generate a "Starling curve." We retrospectively analyzed data from 147 consecutive resuscitation protocol patients during the 24 months ending August 2002. Fifty (34%) of these patients required preload optimization, of which the optimization algorithm was completed in 36 (72%). The average age of those who required preload optimization was 44 +/- 3 years vs. 34 +/- 1 years for patients who did not. Execution of the algorithm caused PCWP to increase from 18 +/- 1 mmHg to a maximum of 25 +/- 2 mmHg and CI to increase from 3.2 +/- 0.1 L/min m(-2) to 4.5 +/- 0.4 L/min m(-2). Algorithm logic determined PCWP = 24 +/- 2 to be optimal preload at the maximum CI = 4.8 +/- 0.4, and as the volume loading threshold for the remaining time of the resuscitation process. Starling curve preload optimization was begun 6.5 +/- 0.8 h after start of the resuscitation protocol and required 36 +/- 5 min and 4 +/- 0.4 fluid boluses (1.6 +/- 0.2 L). Comparison of early response of those patients who required preload optimization and those who did not indicated hemodynamic compromise apparent in the 1st 4 h of standardized resuscitation. We conclude that preload optimization using sequential fluid bolus and PCWP-CI measurement to generate a Starling curve is feasible during ICU shock resuscitation, but that there is the disadvantage that increasing and maintaining high PCWP may contribute to problematic tissue edema.

Trends in burn resuscitation: shifting the focus from fluids to adequate endpoint monitoring, edema control, and adjuvant therapies

Bum shock is a complex process involving a series of intertwined physiologic responses to injury that require more rigorous intervention than simply a change in fluid tonicity, fluid composition, or fluid resuscitation volume. Controversy ensues over monitoring techniques and resuscitation goals, in part because the identification of true markers of perfusion is clouded by intradependence of endpoints on other metabolic processes. The persistence of cellular hypoperfusion in patients who have been deemed adequately resuscitated by global indices supports the growing realization that failure of conventional endpoint-monitoring strategies to detect compensated bum shock can lead to significant organ injury from SIRS or MODS. Current endpoints should be interpreted in the aggregate, because none have yet been demonstrated to reflect tissue perfusion status independently and accurately. Numerous technologically advanced endpoints to predict patient outcome, which may be useful in determining futility of treatment or end-of-life decisions, are now available. Still lack-ing, however, is a reliable tool proven to improve outcome that can guide bum shock resuscitation therapies successfully. Exciting new research in tissue oxygenation and perfusion has revealed that damaging mediator cascades and irreversible microvascular changes may preclude complete resolution of bum shock solely through restoration of oxygen delivery. Because bum patients now frequently survive the early resuscitation phase. the focus should be on controlling derangements in oxygen use and correcting occult hypoperfusion to reduce later adverse patient outcomes from SIRS, sepsis, and MODS. Bum-specific research on resuscitation endpoints and monitoring strategies lags behind research in other patient populations. Present standards and monitoring guidelines for bum shock resuscitation should be critically evaluated and based on true, scientifically validated data rather than on observational studies or personal beliefs. Thus the continuing challenge for clinicians and researchers:burn centers must collaborate to perform large, multi-center studies to evaluate critically and to prove resuscitation endpoints and therapies. Future technologies targeted at microcirculatory perfusion and cellular oxygenation offer an exciting promise for less invasive, easily accessible, more accurate endpoints and treatments for bum shock resuscitation.

Pediatric trauma: beyond the brain

In pediatric trauma care, many long-held tenets of management have been revised. This article reviews the latest advances in pediatric trauma care, particularly in the areas of resuscitation and management of thoracic and abdominal injuries. The final topic is a discussion of what the intensivist and surgeon must know when caring for the pediatric victim of terrorist attacks.

Regional carbon dioxide monitoring: a different look at tissue perfusion

Adequate tissue oxygenation is one of the main therapeutic goals for the critically ill patient. Until recently, the perfusion status of the critically ill and injured has been assessed by global indices such as blood pressure, heart rate, and urine output. However, these global parameters are inadequate in that they fail to demonstrate the actual perfusion status of a patient. Research has shown the splanchnic region to be a pivotal organ bed in response to shock. Because this region shows early signs of hypoperfusion and hypoxia, its monitoring provides for more effective and complete resuscitation. To that end, gastric tonometry offers a noninvasive means by which early symptoms of low flow can be determined, allowing for optimization of tissue perfusion and patient outcome. The most proximal segment of the gastrointestinal tract offers promising information regarding tissue perfusion with the use of sublingual capnography.

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

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

Monitoring right ventricular volumes: a paradigm shift

The resuscitation of critically ill patients frequently requires the administration of fluids for the purpose of increasing cardiac output and oxygen delivery to the tissues. The assessment of the patient's preload status during this process is vital. Traditionally, preload assessment has been through the use of right atrial pressure and pulmonary artery occlusion pressure, which are often referred to as the "filling pressures." The use of these filling pressures is based upon the assumption that ventricular compliance does not change. In recent years studies have demonstrated a poor correlation between these pressures and cardiac output. More recently, the ability to measure right ventricular end-diastolic volume (RVEDV) at the bedside using a modified pulmonary artery catheter became available. Initially the measurement was obtained using intermittent bolus measurements. Today, near continuous measurements of RVEDV are available. The shift from using pressure measurements for the purpose of assessing preload to the new paradigm of using right ventricular volumetric measurements is challenging. The purpose of this article is to review pertinent anatomy of the right ventricle and the interdependence of the ventricular chambers. The volumetric parameters are presented followed by a discussion of research supporting the use of the volumetric parameters in lieu of pressure measurements for preload assessment in a variety of patient populations. The technology providing continuous RVEDV measurements is presented followed by a discussion of a case study demonstrating the value of continuous measurements. Specific implications for the advanced practice nurse are addressed.

Flow-rate measurements and models for colloid and crystalloid flows in central and peripheral venous line infusion systems

The resuscitation fluids, including crystalloids and colloids, were tested in an experimental module with 16-gauge central and peripheral catheters. Infusion pressures were ranged from the gravity driving 10 kPa (75 mmHg) to the pressurized driving 50 kPa (375 mmHg). The experiment results were correlated to obtain the empirical friction factors and the loss factors for the components commonly used in a fluid resuscitation system. The modified Bernoulli equation with the correlated friction factors and loss factors for the components were used to evaluate the pressure and flow relationship in the fluid resuscitation system with peripheral and central catheters. Fair agreements were observed from the comparison of the predictions of the total driving pressure and test results from water, crystalloid and colloid solutions. The modified Bernoulli equation is, therefore, applicable to evaluate the pressure-flow relationship for efficient fluid resuscitations. The coefficients of flow (F) and the square of flow (F2) for the binominal model are varied with the changes of geometry and size of the infusion components, fluid properties and the units of parameters. These coefficients for the fluids and catheters tested in this study were also listed for reference.

MEGX disposition in critically-ill trauma patients: subsequent assessments during the first week following trauma

The objective of this study was to evaluate MEGX disposition as a surrogate marker in assessing the influence that injury may exert on liver function during the first week after the traumatic event in young vs. elderly patients. The MEGX exposure over time was assessed at 0.25, 0.5, 1, 2, 4 and 6 h after the intravenous administration of a 1 mg/kg lidocaine test dose in 12 young and 7 elderly trauma patients on days 1, 4 and 7 after a severe injury (Apache II score > 10). MEGX plasma concentration-time profiles were consistently different on day 1 in the elderly vs. young, consistent with a statistically significant lower rate of both lidocaine clearance and MEGX formation, and with a considerably longer MEGX elimination in the elderly than in the young. This suggests an impairment of liver blood flow as a result of splanchnic vasoconstriction occurring mainly in elderly trauma patients. A significant improvement in MEGX disposition occurred on days 4 and 7 vs. the day of trauma in most elderly, whereas minor changes were observed in the young. Multiple factors may account for these major changes in the elderly: the more severe status, the major sensitivity to the pathophysiologic changes induced by trauma, and also at least partially the ageing processes. Although referring to a limited number of observations, our findings on MEGX disposition suggest that liver function may be affected by the severity of injury, even if the influence of age should not be underestimated in these patients.

Resuscitation in the pediatric trauma population: admission base deficit remains an important prognostic indicator

BACKGROUND

Base deficit (BD), as an endpoint for trauma resuscitation, has been extensively studied in the adult trauma patient but not in the pediatric population. We proposed that admission BD would correlate with outcomes after trauma in a pediatric population.

METHODS

This study was a retrospective review of all patients admitted to the pediatric intensive care unit in an adult trauma center with pediatric commitment in whom an admission BD was available, over the 5-year period ending June 2001.

RESULTS

A total of 65 patients formed the study population. Overall mortality was 20%. Patients who died were younger (6 +/- 5 vs. 9 +/- 5 years; p = 0.009), had lower Glasgow Coma Scale scores at admission (7 +/- 5 vs. 10 +/- 5; p < 0.0001), had higher Injury Severity Scores (24 +/- 14 vs. 14 +/- 9; p < 0.0001), and had lower Pediatric Trauma Scores (7 +/- 4 vs. 10 +/- 2; p < 0.0001). No patient with a BD less negative than -5 died, whereas 13 of 37 patients with a BD of -5 or higher died (37%) (p < 0.0001). Of the 13 patients who died, 8 never cleared their BD and died within 33 +/- 18 hours of admission. Failure to clear BD was associated with 100% mortality. Five patients who normalized their BD died of isolated closed head injuries (time to death, 37 +/- 18 hours; p = not significant). All surviving patients normalized their BD within 43 +/- 41 hours of admission. Seventy-five percent of patients who survived (39 of 52) had a normal BD within 48 hours of admission.

CONCLUSION

Admission BD in the pediatric trauma patient is a strong indicator of posttraumatic shock. An admission BD of < or = -5 is predictive of severe injury and of poor outcome, with a 37% mortality in this series. Failure to clear BD is an extremely poor prognostic indicator.

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.

Determining optimal cardiac preload during resuscitation using measurements of ventricular compliance

BACKGROUND

While the right ventricular end-diastolic volume index (RVEDVI) has been shown to be a better indicator of preload than cardiac filling pressures, optimal values during resuscitation from trauma are unknown. This study examines right ventricular stiffness as a guide to optimal values of RVEDVI.

METHODS

Prospective study of 19 critically injured patients monitored with a volumetric pulmonary artery catheter during resuscitation. Per resuscitation protocol, the target RVEDVI was > or = 120 mL/m2. Sequential fluid boluses of 500 to 1000 mL were administered to obtain at least four values of RVEDVI and right ventricular end-diastolic pressure (estimated by central venous pressure [CVP]). For each patient, nonlinear regression was used to construct the ventricular compliance curve based on the equation, CVP = aek(RVEDVI), where k is the coefficient of chamber stiffness.

RESULTS

Overall, the derived compliance curves had excellent fit with the theoretical equation (mean R2, 0.95 +/- 0.04). Mean k was 0.043 +/- 0.012 (range, 0.029-0.067). For each patient, mean RVEDVI during resuscitation was significantly correlated with k (R2 = 0.75, p < 10-5) indicating that chamber stiffness, measured during initial fluid administration, may be used to determine RVEDVI during the ensuing resuscitation.

CONCLUSION

In critically injured patients, bedside assessment of right ventricular compliance is possible and may help determine optimal values of RVEDVI during resuscitation.

Start with a subjective assessment of skin temperature to identify hypoperfusion in intensive care unit patients

OBJECTIVE

To determine whether physical examination alone or in combination with biochemical markers can accurately diagnose hypoperfusion.

METHODS

Data from 264 consecutive surgical intensive care unit patients were collected by two intensivists and included extremity temperature, vital signs, arterial lactate, arterial blood gases, hemoglobin, and pulmonary artery catheter values with derived indices. Days of data were divided into data collected from patients with cool extremities (cool skin temperature [CST] group) versus warm extremities (warm skin temperature [WST] group). Values are means +/- SD. Comparisons between groups were made by two-tailed unpaired t test; significance was assumed for p < or = 0.05.

RESULTS

There were 328 days of observations in the CST group versus 439 in the WST group. There were no differences (p > 0.05) between CST and WST data with regard to heart rate (107 +/- 14 vs. 99 +/- 19 beats/min), systolic blood pressure (118 +/- 24 vs. 127 +/- 28 mm Hg), diastolic blood pressure (57 +/- 14 vs. 62 +/- 15 mm Hg), pulmonary artery occlusion pressure (14 +/- 6 vs. 16 +/- 5 mm Hg), Fio2 (0.48 +/- 0.7 vs. 0.45 +/- 0.2), hemoglobin (8.8 +/- 1.6 vs. 9.3 +/- 1.3 g/dL), Pco2 (44.3 +/- 11.8 vs. 40.7 +/- 9.2 mm Hg), or Po2 (96.4 +/- 12.6 vs. 103.8 +/- 22.2 mm Hg). However, cardiac output (5.3 +/- 2.2 vs. 8.2 +/- 2.6 L/min), cardiac index (2.9 +/- 1.2 vs. 4.3 +/- 1.2 L/min/m2), pH (7.32 +/- 0.2 vs. 7.39 +/- 0.07), TCO2 (19.5 +/- 3.1 vs. 25.1 +/- 4.8 mEq/L), and Svo2 (60.2 +/- 4.4% vs. 68.2 +/- 7.8%) were all significantly lower (p < 0.05) in CST patients compared with WST patients. By comparison, lactate (4.7 +/- 1.5 vs. 2.2 +/- 1.6 mmol/L, p < 0.05) was significantly elevated in patients with cool extremities.

CONCLUSION

Combining physical examination with serum bicarbonate and arterial lactate identifies patients with hypoperfusion as defined by low Svo2 and cardiac index. Hypoperfusion may occur despite supranormal cardiac indices. Patients with cool extremities and elevated lactate levels may benefit from a pulmonary artery catheter to guide but not initiate therapy.

Systemic hemodynamics, gastric intramucosal PCO2 changes, and outcome in critically ill burn patients

OBJECTIVES

To define the hemodynamic and gastric intramucosal PCO2 (PiCO2) changes during the first 48 hrs after burn trauma and to analyze their relationship with outcome.

DESIGN

Prospective, observational study in a cohort of consecutively admitted critically ill burn patients.

SETTING

Intensive care burn unit in a university hospital.

PATIENTS

Forty-two patients with burns covering >20% of body surface area or inhalation injury.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients were monitored with an oximetric pulmonary arterial catheter and a gastric tonometer to measure PiCO2. The difference between arterial and gastric mucosal PCO2 (P[i-a]CO2) was considered indicative of gastric mucosal hypoxia. Hemodynamic and PiCO2 measurements were performed during the first 48 hrs after admission. Patients suffered burns covering 36.1% +/- 14.3% (mean +/- SD) and 45.3% +/- 21.9% of body surface area (survivors and nonsurvivors, respectively). All patients were successfully resuscitated by conventional standards. Nonsurvivors (n = 16) died a median of 17 days after admission. In univariate analysis, the presence of shock during the resuscitation phase, age, mixed venous pH, P[i-a]CO2, right atrial pressure, pulmonary arterial pressure, pulmonary arterial occlusion pressure, cardiac index, systemic and pulmonary vascular resistance, left ventricular stroke work index, mixed venous oxygen saturation, and systemic oxygen delivery, consumption, and extraction ratio, measured over the first 12 hrs after admission, were significantly (p < .05) different between survivors and nonsurvivors. These differences disappeared after 12 hrs after admission. Multivariate analysis identified age, percentage body surface area burned, and oxygen delivery index (6 hrs after admission) as factors independently associated with a poor outcome. P[i-a]CO2 (12 hrs after admission) was significantly greater in patients with than in those without inhalation injury (17 +/- 13 torr [2.26 +/- 1.73 kPa] vs. 6 +/- 10 torr [0.79 +/- 1.33 kPa]; p = .005). Patients with a P[i-a]CO2 difference (6 hrs after admission) > or =10 torr (1.33 kPa) had a mortality rate of 56% vs. 25% of those patients with <10 torr (p = .044).

CONCLUSIONS

Our data indicate that there are hemodynamic and biochemical changes that occur early after burn trauma that are associated with prognosis after an apparently successful resuscitation. Particularly, a hemodynamic profile characterized by systemic acidosis, low systemic blood flow, and systemic and pulmonary vasoconstriction early after trauma is associated with a poor outcome. Additionally, intestinal mucosal acidosis occurs after burn trauma, is influenced by inhalation injury, and is a variable related to outcome.

A critical assessment of endpoints of shock resuscitation

Modern hemodynamic therapy is not only the recognition and treatment of hypotension but also the avoidance and treatment of shock in its broadest sense. The major issues include the recognition of hypoperfusion of the body as a whole or its individual tissues and organ systems and the determination of the best endpoints for the treatment of shock. Even if all of the commonly used clinical indicators of shock are "normal," shock on a cellular, tissue, or organ basis may still be present. Whether "organ-specific" assessments, such as gastric tonometry or tissue oxygen tension measurement, are the ultimate answer to this problem remains to be seen. The determination of adequate intravascular volume (preload) continues to present major difficulties in the care of critically ill or injured patients. Although PCWP is frequently helpful, it is not a gold standard. A bedside ultrasonic technique, such as esophageal Doppler sonography, may replace the Swan-Ganz catheter technique in many patients.

Oxygen consumption in the early postinjury period: use of continuous, on-line indirect calorimetry

OBJECTIVE

To determine the patterns of oxygen consumption (Vo2) using indirect calorimetry (IC) for the first 24 hrs after serious blunt traumatic injury.

DESIGN

Prospective, observational study.

SETTING

Surgical intensive care unit of a Level 1 trauma center.

PATIENTS

Sixty-six mechanically ventilated patients with blunt traumatic injury and Injury Severity Score >15.

INTERVENTIONS

IC for 24 hrs postinjury. Patients were resuscitated to standard parameters of perfusion.

MEASUREMENTS AND MAIN RESULTS

Mean patient age was 50.1+/-18.7 yrs with a mean Injury Severity Score 30.7+/-11.3). Mean Vo2 for all patients for the 24-hr study period was 168.5+/-29.5 mL/min/m2. The level of Vo2 was not related to Injury Severity Score, the number or combination of organ systems injured, or to the use of vasoactive agents. Patients >65 yrs of age had significantly lower Vo2 (P = .0038) compared with patients < or =50 yrs. Vo2 did not change over time after resuscitation to normal parameters of perfusion. Mean Vo2 was 156.5+/-63.2 mL/min/m2 in patients who developed multiple organ dysfunction, and 172.4+/-33.3 mL/min/m2 in those who did not develop multiple organ dysfunction (p = .16).

CONCLUSIONS

Seriously injured patients are hypermetabolic in the early postinjury period. The level of Vo2 is unrelated to injury severity or number of organ systems involved. Elderly patients can be expected to have lower levels of Vo2. Vo2 does not change significantly in response to resuscitation to normal parameters of perfusion. Vo2 measured by IC did not predict the development of multiple organ dysfunction.

Pulmonary artery catheterization and esophageal doppler monitoring in the ICU

The clinical assessment of cardiac performance and ventricular preload is notoriously unreliable in critically ill patients. Consequently, a number of technologies have been developed to provide the clinician with indexes of cardiovascular function to assist in therapeutic decision making. Foremost among these is the pulmonary artery catheter (PAC). Indeed, the PAC has largely shaped the practice of modern critical care. Yet, the information provided by the PAC is largely misunderstood, and its efficacy is never proven. Recently, continuous esophageal Doppler monitoring has emerged as an alternative to pulmonary artery catheterization. This paper evaluates the clinical utility of the PAC and esophageal Doppler monitoring in assessing the hemodynamic status of ICU patients.

Decreased alpha-adrenergic response in the intestinal microcirculation after "two-hit" hemorrhage/resuscitation and bacteremia

BACKGROUND

The two-hit theory of multiple organ dysfunction syndrome proposes that an initial insult primes the host for an altered response to subsequent stimuli. We have previously documented enhanced dilator tone in the small intestine after a two-hit insult; however, the effects on vasoconstrictor function are unknown. We postulated that prior hemorrhage and resuscitation followed by bacteremia would alter microvascular responsiveness to alpha-adrenergic stimulation.

METHODS

Male Sprague-Dawley rats underwent fixed-volume hemorrhage with resuscitation (H/R) or sham procedure (Sham). At 24 or 72 h, in vivo videomicroscopy of the small intestine was performed (inflow A1 and premucosal A3 arterioles). Constrictor function was assessed by topical application of norepinephrine (NE; 10(-8)-10(-6) M) before and 1 h after intravenous Escherichia coli or saline.

RESULTS

Sham, 24 or 72 h H/R, and E. coli alone produced no significant changes in A1 or A3 response to NE. Sequential H/R + E. coli resulted in decreased constrictor response in both A1 (72 h H/R + E. coli-38% from baseline vs Sham - 54%, P < 0.05) and A3 arterioles (-8% vs -51%, P < 0.05) at high doses of NE (10(-6) M).

CONCLUSIONS

Prior H/R primes the intestinal microvasculature for an altered response during a subsequent stress and these effects persist for up to 72 h following H/R. Sequential insults in this two-hit model caused marked hyporesponsiveness to NE. These alterations in control of microvascular tone might contribute to the hemodynamic compromise of sepsis, impair mucosal blood flow, and contribute to the development of MODS.

Effect of gastric feeding on intragastric P(CO2) tonometry in healthy volunteers

PURPOSE

The tonometric detection of a high intragastric regional P(CO2) (PrCO2) reflecting an elevated intramucosal P(CO2) can be helpful to diagnose mucosal ischemia, if acid secretion is suppressed to avoid intragastric CO2 production through buffering of acid by bicarbonate in the stomach. It is recommended to perform tonometry in the fasting state, but this may hamper feeding of the critically ill. On the other hand, postfeeding tonometry could serve as a diagnostic stress test because feeding increases mucosal blood flow demand, provided that the meal itself does not hamper diffusion of CO2 from mucosa to tonometer balloon and does not generate intragastric CO2, independently from intramucosal P(CO2). We therefore studied the effect of a standard meal on intragastric PrCO2 tonometry in healthy volunteers with suppression of meal-stimulated gastric acid secretion and, presumably, with an adequate mucosal blood flow reserve.

MATERIAL AND METHODS

The gastric juice pH and tonometric PrCO2 were measured in 14 human volunteers, after gastric acid secretion suppression by either ranitidine (100-mg bolus, followed by 25 mg/h i.v., n = 7) or by ranitidine plus pirenzepine (10-mg bolus, followed by 3 mg/h i.v., n=7) to suppress any residual meal-stimulated gastric acid secretion, before and at 30-minute intervals until 120 minutes after oral ingestion of a standard liquid test meal (Pulmocare [Abbott, the Netherlands]; 500 mL, 750 kcal, P(CO2) 5 mm Hg, pH 7.50).

RESULTS

The gastric juice pH, which was >4.0 in all individuals throughout the study, and the PrCO2 did not depend on the regimen for gastric acid secretion suppression, and therefore the data were pooled. The PrCO2 (median [range]) after feeding was 69% (56% to 170%) of baseline (42 [37-51] mm Hg) from 0 to 30 minutes (P < .001), 85% (72% to 167%) of baseline from 30 to 60 (P < .05), 97% (57% to 193%) from 60 to 90 minutes, and 112% (97% to 189%) of baseline from 90 to 120 minutes with a rise above baseline in 10 of 14 patients. In vitro, the liquid test meal generated CO2 after adding bicarbonate but not after hydrochloric acid.

CONCLUSION

We recommend intragastric tonometry to be performed in the fasting state and discourage tonometry after feeding as a stress test, because a single test meal changes tonometric PrCO2 in a time-dependent manner until 2 hours after gastric feeding of healthy volunteers. The fall in PrCO2 directly after feeding can be attributed to dilution, whereas a rise above baseline in some patients may have been caused, as supported by CO2 production after adding bicarbonate to the test meal in vitro, by CO2 production through buffering of meal-derived acid by gastric bicarbonate, in the absence of stimulated gastric acid secretion by feeding.

Preload assessment in patients with an open abdomen

BACKGROUND

Intra-abdominal hypertension and abdominal compartment syndrome cause significant morbidity and mortality in surgical and trauma patients. Maintenance of intravascular preload and use of open abdomen techniques are essential. The accuracy of pulmonary artery occlusion pressure (PAOP) and central venous pressure (CVP) in patients with intra-abdominal hypertension has been questioned.

METHODS

Twenty surgical and trauma patients with intra-abdominal hypertension requiring open abdominal decompression were monitored using volumetric thermodilution pulmonary artery catheters. Hemodynamic, oxygenation, inspiratory, and intravesicular pressure measurements were collected prospectively. PAOP, CVP, and right ventricular end-diastolic volume index (RVEDVI) were compared as estimates of preload status.

RESULTS

Multiple regression analysis demonstrated that cardiac index correlated significantly better with RVEDVI (r = 0.69) than with PAOP (r = -0.27) or CVP (r = -0.28) during resuscitation after open abdominal decompression (p < 0.0001).

CONCLUSION

RVEDVI is superior to PAOP and CVP as an estimate of preload status in patients with an open abdomen.

Right ventricular end-diastolic volume index as a predictor of preload status in patients on positive end-expiratory pressure

OBJECTIVE

To evaluate the clinical utility of right ventricular end-diastolic volume index (RVEDVI) and pulmonary artery occlusion pressure (PAOP) as measures of preload status in patients with acute respiratory failure receiving treatment with positive end-expiratory pressure.

DESIGN

Prospective, cohort study.

SETTING

Surgical intensive care unit in a Level I trauma center/university hospital.

PATIENTS

Sixty-four critically ill surgical patients with acute respiratory failure.

INTERVENTIONS

All patients were treated for acute respiratory failure with titrated levels of positive end-expiratory pressure (PEEP) with the goal of increasing arterial oxygen saturation to > or =0.92, reducing FIO2 to <0.5, and reducing intrapulmonary shunt to < or =0.2. Serial determinations of RVEDVI, PAOP, and cardiac index (CI) were recorded.

MEASUREMENTS AND MAIN RESULTS

Two hundred-fifty sets of hemodynamic variables were measured in 64 patients. The level of PEEP ranged from 5 to 50 cm H2O (mean 12+/-9 [SD] cm H2O). At all levels of PEEP, CI correlated significantly better with RVEDVI than with PAOP. At levels of PEEP > or =15 cm H2O, CI was inversely correlated with PAOP, but remained positively correlated with RVEDVI.

CONCLUSIONS

CI correlates significantly better with RVEDVI than PAOP at all levels of PEEP up to 50 cm H2O. RVEDVI is a more reliable predictor of volume depletion and preload recruitable increases in CI, especially in patients receiving higher levels of PEEP where PAOP is difficult to interpret.

Threshold values of intramucosal pH and mucosal-arterial CO2 gap during shock resuscitation

BACKGROUND

The gastric intramucosal pH (pHi) and gastric mucosal-arterial CO2 gap (GAP) estimate visceral perfusion and predict outcome. Threshold values of these variables for use during resuscitation, however, remain poorly defined. The purpose of this study was to develop clinically derived cutoffs for both pHi and GAP for predicting death and multiple organ failure (MOF) in trauma patients.

METHODS

This was a cohort study of 114 consecutive trauma patients who had pHi determined at 24 hours after intensive care unit admission. The corresponding GAP for each of these values of pHi was obtained through chart review. Receiver operating characteristic curves were constructed for both pHi and GAP with respect to death and MOF. These curves were used to determine the value of each variable that maximized the sum of sensitivity and specificity in predicting outcome. chi2 tests and odds ratios were used to determine if significant differences in outcome occurred above and below these cutoff values.

RESULTS

Of 114 patients who had pHi determined at 24 hours after admission, 108 had corresponding GAP values available. The values of pHi and GAP that maximized sensitivity and specificity were 7.25 and 18 mm Hg, respectively. The odds ratio for pHi versus death was 4.6 and for pHi versus MOF was 4.3. The odds ratios for GAP versus death and MOF were 2.9 and 3.3, respectively.

CONCLUSION

In trauma patients, the ability to predict death and MOF is maximized at values of pHi less than 7.25 and GAP greater than 18 mm Hg. These values represent clinically derived cutoffs that should be useful for evaluating the adequacy of intestinal perfusion during resuscitation.

Hypocapnia does not alter hepatic blood flow or oxygen consumption in patients with head injury

OBJECTIVE

To evaluate the effects of hypocapnia on the systemic and hepatic circulations and oxygenation values in patients with head injury.

DESIGN

Open-label, prospective study.

SETTING

University hospital, department of anesthesiology and intensive care unit.

PATIENTS

Eleven mechanically ventilated patients with isolated head trauma and stable hemodynamic status.

INTERVENTIONS

At the beginning of the study, each patient presented with normocapnic ventilation. Mechanical hyperventilation was then adjusted to obtain stable hypocapnia over an interval of 24 hrs. Cardiac output and other systemic hemodynamic parameters were measured, using a pulmonary artery catheter. Hepatic parameters were measured via a catheter inserted into the hepatic vein. Total hepatic blood flow was determined by the Fick principle using a continuous infusion of indocyanine green. Arterial and hepatic venous blood gases were sampled to determine systemic and hepatic-splanchnic oxygenation. Measurements were done at the end of the four phases: a) 30 mins of normocapnia (N); b) 30 mins of hypocapnia (H0); c) 3 hrs of hypocapnia (H3); and d) 24 hrs of hypocapnia (H24). Intracranial pressure and cerebral perfusion pressure were hourly monitored throughout the study.

MEASUREMENTS AND MAIN RESULTS

There were no significant changes in systemic hemodynamic parameters. The hepatic blood flow index did not differ from normocapnia (N 1.8 +/- 0.4 L/min/m2) to hypocapnia (H0 1.6 +/- 0.3 L/min/m2; H3 1.7 +/- 0.4 L/min/m2; H24 1.7 +/- 0.4 L/min/m2). The ratio of hepatic blood flow index to cardiac index remained stable throughout the study. Hypocapnia did not affect hepatic-splanchnic oxygen delivery and consumption.

CONCLUSIONS

Hypocapnic hyperventilation does not alter hepatic hemodynamic parameters in patients with head injury. This result may be related to the lack of changes in cardiac output or in the hepatic vasoreactivity. Moreover, hypocapnia does not modify hepatic-splanchnic oxygenation. Thus, in case of intracranial hypertension, hypocapnia might be used without undesirable effect on the hepatic-splanchnic perfusion.

Effects of abdominal decompression on cardiopulmonary function and visceral perfusion in patients with intra-abdominal hypertension

OBJECTIVE

Increased intra-abdominal pressure (IAP) compromises cardiopulmonary function and visceral perfusion. Our goal was to characterize acute changes in these subsystems associated with operative abdominal decompression.

PATIENT POPULATION

A series of 11 consecutive injured patients monitored with a pulmonary artery catheter and nasogastric tonometer in whom operative decompression was performed. Indications for decompression included oliguria or progressive acidosis despite aggressive resuscitation in the presence of elevated IAP (>25 mm Hg).

MAIN OUTCOME MEASURES

Studied hemodynamic variables included pulmonary artery occlusion pressure (PAOP), right ventricular end-diastolic volume index (RVEDVI), and cardiac index (CI). Pulmonary variables included shunt fraction (Qs/Qt) and dynamic compliance (Cdyn). Visceral perfusion was assessed using hourly urine output 4 hours before and after decompression (UOP) and gastric intramucosal pH (pHi). Mean values before and after decompression were compared using the paired t test. Linear regression and Fisher's z transformation were used to evaluate the relationships between RVEDVI, PAOP, CI, and IAP. IAP was transduced via bladder pressures. Significance was defined as p < 0.05. Data are expressed as means+/-SD.

RESULTS

IAP decreased with decompression (49+/-11 to 19+/-6.8 mm Hg; p < 0.0001). RVEDVI improved independent of CI and correlated better (p < 0.01) with CI (r =0.49, p=0.04) than PAOP did (r=-0.36, p=0.09). PAOP correlated significantly with IAP (r=0.45, p=0.04). Decompression resulted in significant improvements in Qs/Qt, Cdyn, UOP, and pHi.

CONCLUSION

Abdominal decompression in patients with increased IAP improves preload, pulmonary function, and visceral perfusion. Elevated IAP has important effects on PAOP, which makes the PAOP an unreliable index of preload in these patients.

Randomized, prospective comparison of increased preload versus inotropes in the resuscitation of trauma patients: effects on cardiopulmonary function and visceral perfusion

OBJECTIVE

To evaluate the effects of maintaining increased levels of preload on cardiopulmonary function and visceral perfusion during resuscitation.

METHODS

Randomized, prospective study of 39 consecutive trauma patients with a low right ventricular ejection fraction (<40%) admitted to a university Level I trauma center during a 10-month period. Patients were randomized to one of two groups: increased preload (PL), or normal preload with inotropes (INO). The PL group received fluid administration to maintain a target right ventricular end-diastolic volume index (RVEDVI) > or = 120 mL/m2 during resuscitation. The INO group had inotropes added according to a prospectively determined protocol and was maintained at a RVEDVI of 90 to 100 mL/m2. Systemic perfusion was assessed using oxygen transport and acid-base parameters, and pulmonary function was evaluated with PaO2/FiO2 ratio, dynamic compliance, ventilator days, and incidence of adult respiratory distress syndrome. Gut perfusion was assessed by measuring gastric intramucosal pH (pHi). Data are expressed as means +/- SD.

RESULTS

The mean RVEDVI was significantly higher in the PL group (n = 19) than in the INO group (n = 20) during resuscitation (119+/-18 vs. 103+/-22 mL/m2, p = 0.01). There was no difference in oxygen delivery, mixed venous oxygen saturation, lactate, PaO2/FiO2 ratio, dynamic compliance, or ventilator days between the groups. The incidence of adult respiratory distress syndrome was not significantly different (PL 31% vs. INO 50%, p > 0.1). In the patients who had pHi measured sequentially during resuscitation (PL = 13, INO = 17), the final pHi was significantly higher in the PL group (7.31+/-0.1 vs. 7.16+/-0.2, p = 0.03).

CONCLUSION

Patients resuscitated at higher levels of preload have significantly better visceral perfusion than those resuscitated at normal preload with addition of inotropes. This higher preload does not adversely affect pulmonary function.