Outcome prediction of emergency patients by noninvasive hemodynamic monitoring

Use of an Artificial Intelligence Device for Evaluating Blood Loss in Complex Major Orthopaedic Surgery Procedures

BACKGROUND

An artificial intelligence algorithm that analyzes the pulse oximeter waveform in the fingertip can be used to determine the compensatory reserve index (CRI) in trauma patients. This measurement shows the remaining cardiovascular capacity and is known to be more specific and sensitive in detecting blood loss than are routine vital signs. We hypothesized that the CRI measurement could predict loss of reserve cardiovascular capacity in patients undergoing major orthopaedic surgery, and therefore could help in their management.

METHODS

A total of 304 patients undergoing lower extremity arthroplasty consented to participate in waveform monitoring. Pulse oximeter waveforms were sensed with a fingertip probe and processed with a tablet computer that remained with the patient during surgery and recovery in the hospital. The CRI, systolic blood pressure, and heart rate were evaluated throughout the postoperative period.

RESULTS

The CRI measurement identified a group of patients who were significantly more likely to require transfusions and emergency medical care (P = .000021). Patients who had morbid obesity were especially likely to have low CRI results and a high percentage of clinical events. A CRI of 0.40 or more was evaluated retrospectively as the criterion for withholding transfusion in 54 patients, but that group had a significantly higher incidence of transfusion later in treatment than did the cohort as a whole. The systolic blood pressure and heart rate were not useful in predicting the need for transfusion until late in treatment.

CONCLUSIONS

This study suggests that the CRI measurement can identify patients at risk for transfusion and the need for urgent medical care and may aid in the management of blood loss and transfusion in major orthopedic surgery.

Physiology of Human Hemorrhage and Compensation

Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.

Unmasking the Hypovolemic Shock Continuum: The Compensatory Reserve

Hypovolemic shock exists as a spectrum, with its early stages characterized by subtle pathophysiologic tissue insults and its late stages defined by multi-system organ dysfunction. The importance of timely detection of shock is well known, as early interventions improve mortality, while delays render these same interventions ineffective. However, detection is limited by the monitors, parameters, and vital signs that are traditionally used in the intensive care unit (ICU). Many parameters change minimally during the early stages, and when they finally become abnormal, hypovolemic shock has already occurred. The compensatory reserve (CR) is a parameter that represents a new paradigm for assessing physiologic status, as it comprises the sum total of compensatory mechanisms that maintain adequate perfusion to vital organs during hypovolemia. When these mechanisms are overwhelmed, hemodynamic instability and circulatory collapse will follow. Previous studies involving CR measurements demonstrated their utility in detecting central blood volume loss before hemodynamic parameters and vital signs changed. Measurements of the CR have also been used in clinical studies involving patients with traumatic injuries or bleeding, and the results from these studies have been promising. Moreover, these measurements can be made at the bedside, and they provide a real-time assessment of hemodynamic stability. Given the need for rapid diagnostics when treating critically ill patients, CR measurements would complement parameters that are currently being used. Consequently, the purpose of this article is to introduce a conceptual framework where the CR represents a new approach to monitoring critically ill patients. Within this framework, we present evidence to support the notion that the use of the CR could potentially improve the outcomes of ICU patients by alerting intensivists to impending hypovolemic shock before its onset.

Non-invasive cardiac output monitoring device "ICON" in trauma patients: a feasibility study

PURPOSE

Assessment of hemodynamics is crucial for the evaluation of major trauma patients. Cardiac output (CO) monitoring provides additional information and may improve volume resuscitation. The goal of this prospective pilot study was to evaluate the feasibility of a new non-invasive CO monitoring (NICOM) device in the emergency department (ED).

METHODS

Single-center prospective observational pilot study including 20 trauma patients admitted to a level 1 trauma center. CO was continuously monitored for 60 min after ED admission using the new NICOM device ICON^®. This device measures changes of the thoracic bioimpedance to calculate CO. Conventional vital signs were recorded simultaneously. Feasibility, safety, reliability, user-friendliness, and impact of the device on standard ED procedures were assessed.

RESULTS

Thirteen (65%) patients were male, median age was 57.5 (IQR 25), and median ISS was 10.5 (IQR 14.8). Median CO over time was 9.8 l/min (IQR 4.6). No adverse effects were recorded. The device proved to be user-friendly with no negative impact on routine ED care. In four patients, detachment of electrodes was observed, and in four patients, the CO recording was temporary discontinued. Short-term changes of the CO were observed 44 times after the placement of electrodes and during patient transfers.

CONCLUSIONS

Non-invasive CO monitoring proved to be feasible and safe for the initial hemodynamic evaluation of trauma patients. Problems with the NICOM device were detachment of electrodes and temporary signal loss. Due to the small sample size and relatively low injury burden of the patients included in this study, further prospective investigation is warranted.

The Compensatory Reserve For Early and Accurate Prediction Of Hemodynamic Compromise: A Review of the Underlying Physiology

Shock is deadly and unpredictable if it is not recognized and treated in early stages of hemorrhage. Unfortunately, measurements of standard vital signs that are displayed on current medical monitors fail to provide accurate or early indicators of shock because of physiological mechanisms that effectively compensate for blood loss. As a result of new insights provided by the latest research on the physiology of shock using human experimental models of controlled hemorrhage, it is now recognized that measurement of the body's reserve to compensate for reduced circulating blood volume is the single most important indicator for early and accurate assessment of shock. We have called this function the "compensatory reserve," which can be accurately assessed by real-time measurements of changes in the features of the arterial waveform. In this paper, the physiology underlying the development and evaluation of a new noninvasive technology that allows for real-time measurement of the compensatory reserve will be reviewed, with its clinical implications for earlier and more accurate prediction of shock.

Perfusion indices revisited

Monitoring of tissue perfusion is an essential step in the management of acute circulatory failure. The presence of cellular dysfunction has been a basic component of shock definition even in the absence of hypotension. Monitoring of tissue perfusion includes biomarkers of global tissue perfusion and measures for assessment of perfusion in non-vital organs. The presence of poor tissue perfusion in a shocked patient is usually associated with worse outcome. Persistently impaired perfusion despite adequate resuscitation is also associated with worse outcome. Thus, normalization of some perfusion indices has become one of the resuscitation targets in patients with septic shock. Although the collective evidence shows the clear relation between impaired peripheral perfusion and mortality, the use of different perfusion indices as a resuscitation target needs more research.

Non-invasive hemodynamic monitoring in trauma patients

BACKGROUND

The assessment of hemodynamic status is a crucial task in the initial evaluation of trauma patients. However, blood pressure and heart rate are often misleading, as multiple variables may impact these conventional parameters. More reliable methods such as pulmonary artery thermodilution for cardiac output measuring would be necessary, but its applicability in the Emergency Department is questionable due to their invasive nature. Non-invasive cardiac output monitoring devices may be a feasible alternative.

METHODS

A systematic literature review was conducted. Only studies that explicitly investigated non-invasive hemodynamic monitoring devices in trauma patients were considered.

RESULTS

A total of 7 studies were identified as suitable and were included into this review. These studies evaluated in a total of 1,197 trauma patients the accuracy of non-invasive hemodynamic monitoring devices by comparing measurements to pulmonary artery thermodilution, which is the gold standard for cardiac output measuring. The correlation coefficients r between the two methods ranged from 0.79 to 0.92. Bias and precision analysis ranged from -0.02 +/- 0.78 l/min/m(2) to -0.14 +/- 0.73 l/min/m(2). Additionally, data on practicality, limitations and clinical impact of the devices were collected.

CONCLUSION

The accuracy of non-invasive cardiac output monitoring devices in trauma patients is broadly satisfactory. As the devices can be applied very early in the shock room or even preclinically, hemodynamic shock may be recognized much earlier and therapeutic interventions could be applied more rapidly and more adequately. The devices can be used in the daily routine of a busy ED, as they are non-invasive and easy to master.

Model-based prediction of autoregulatory exhaustion in response to lower-body negative pressure-induced shock

BACKGROUND

We assessed the ability of a normalized autonomic nervous system (ANS) stress measure defined as an increase in the percentage of pulse rate from a baseline homeostasis state to identify corresponding changes in circulating blood volume to quantitatively recognize hypovolemia and predict subsequent autoregulatory exhaustion. Autoregulatory exhaustion is defined as the point where decreased circulatory volume exceeds the compensatory mechanism capacity to maintain flow and pressure. We derived frequency-based measures of pulse rate and pulse strength using a reflective pulse oximeter waveform of a photoplethysmograph placed on the forehead.

METHODS

This study was performed at the Penn State Heart and Vascular Institute, Hershey, Pennsylvania, in June 2010. Ten healthy subjects (5 each male and female) were placed supine in a lower-body negative-pressure chamber to induce central volume loss. Systolic blood pressure was continuously measured, and a value of less than 90 mm Hg defined autoregulatory exhaustion. Derived measures of circulating blood volume were compared with echocardiographic measures to access photoplethysmograph-derived circulatory volume measure relative to traditional cardiac hemodynamics.

RESULTS

All 10 subjects produced consistent patterns of response characterized as a progressively increasing ANS stress in response to increasing lower-body negative pressure. Three subjects exhibited autoregulatory exhaustion, and ANS stress increased markedly on the step before displaying hypotension in these subjects but not the others.

CONCLUSION

Results demonstrate the potential to use model-based measures to serve as a definitive presymptom predictive tool to recognize an impending hypovolemic condition, making this approach suitable for chronic care or for the management of hemodialysis patient where resting baseline measures can be obtained.

Nutrition and the open abdomen

Adequate nutrition support is critical in the management of patients with an open abdomen. Despite the literature supporting its use in trauma patients, provider concerns and clinical controversies remain regarding the early administration and long-term sequelae of enteral nutrition (EN) therapy in these patients. The purpose of this article is to review the clinical concepts behind the use of the open abdomen, as well as examine the altered nutrition requirements associated with the maintenance of a temporary laparostomy. The rationale for early EN is described, as well as the pros and cons surrounding the use of supplemental parenteral nutrition in those patients unable to meet nutrition goals enterally in a reasonable time frame. Finally, an open abdomen nutrition support algorithm is provided as part of the critical care plan in these patients who represent the sickest of surgical patients.

Latest developments in peri-operative monitoring of the high-risk major surgery patient

Peri-operative monitoring technology has made great strides in the last 20 years with the introduction of minimally invasive devices to measure inter alia stroke volume, cardiac output, depth of anaesthesia and cerebral and tissue oxygen monitoring. Despite these technological advances, peri-operative management of the high risk major surgery patient has remained virtually unchanged. The vast majority of patients undergo a pre-operative assessment which is neither designed to quantify functional capacity nor predict outcome. Anaesthetists then usually monitor these patients using the same technology (e.g. pulse oximetry (SpO2), invasive systemic BP and CVP, end tidal carbon dioxide (etCO2) and anaesthetic agent monitoring) that was available in the early 1980s. Conventional intra-operative management can result in occult low levels of blood flow and oxygen delivery that lead to complications that only occur days or weeks following surgery and give false re-assurance to the anaesthetist that he or she is doing a "good job". Post-operative management then often takes place in an environment with reduced levels of both monitoring equipment and staff expertise. It is perhaps not surprising that outcome still remains poor in high-risk patients.(1) In this review, we will briefly describe the role of peri-operative optimization, some of the available monitors and indicate how their combined use might be beneficial in managing the high-risk surgical patient. We believe that although there is now evidence to suggest that the use of individual new monitors (such as assessment of fluid status, depth of anaesthesia, tissue oxygenation and blood flow) can influence outcome, it will only be their combination that will radically improve the peri-operative management and outcome of high-risk surgical patients. It is a matter of some urgency that large scale, prospective and collaborative studies be designed, funded and executed to prove or disprove this hypothesis.

Early identification of shock in critically ill patients

Emergency providers must be experts in the resuscitation and stabilization of critically ill patients, and the rapid recognition of shock is crucial to allow aggressive targeted intervention and reduce morbidity and mortality. This article reviews the physiologic definition of shock, the importance of early intervention, and the clinical and diagnostic signs that emergency department providers can use to identify patients in shock.

Noninvasive monitoring of the autonomic nervous system and hemodynamics of patients with blunt and penetrating trauma

BACKGROUND

To describe early effects of sympathetic (SNS) and parasympathetic nervous system (PSNS) activities measured by heart rate (HR) and respiratory rate variabilities simultaneously with noninvasive hemodynamic patterns in patients with blunt and penetrating trauma.

METHODS

Descriptive study of 168 monitored trauma patients in a level I university-run trauma service. We studied HR and respiratory rate variability by spectral analysis as a measure of autonomic nervous system (ANS) activity in severe blunt and penetrating injuries beginning shortly after their admission to the emergency department. The low frequency area is the area under the HR spectral analysis curve within the frequency range of 0.04 Hz to 0.10 Hz. This area primarily reflects the tone of the SNS as mediated by the vagus nerve. The respiratory frequency area, sometimes referred to as the high frequency area, is a 0.12 Hz-wide frequency range centered around the fundamental respiratory frequency defined by the peak mode of the respiratory activity power spectrum. It is indicative of vagal outflow reflecting PSNS activity. The low frequency area/respiratory frequency area, or L/R ratio, reflects the balance of the SNS and the PSNS. ANS was studied simultaneously with noninvasive hemodynamic patterns after blunt and penetrating thoracic or abdominal injury beginning shortly after admission. We measured cardiac index by bioimpedance, HR, and mean arterial pressure (MAP) to evaluate cardiac function, pulse oximetry (SapO2) to reflect changes in respiratory function, and transcutaneous oxygen indexed to fractional inspired oxygen (PtcO2/FIO2) to reflect tissue perfusion.

RESULTS

ANS activity markedly increased especially in the nonsurvivors at 12 hours to 24 hours after admission. Compared with survivors, the nonsurvivors had lower MAP, CI, and PtcO2/FIO2 values associated with increased ANS activity.

CONCLUSIONS

In the nonsurvivors, low flow, low MAP, and reduced tissue perfusion were associated with pronounced increases in PSNS and lesser increases in SNS activity. In the survivors, higher CI, MAP, and PtcO2/FIO2 values were associated with lesser increases in both PSNS and SNS activities.

Using transcutaneous oxygen pressure measurements as selection criteria for activated protein C use

BACKGROUND

Limited resources and the expense of Activated Protein C (APC) (drotrecogin alfa) may contribute to the reluctance to utilize this drug in sepsis. Employing the PROWESS criteria resulted in absolute reduction in 28-day mortality of 6.1%, representing a relative risk reduction of 19.4%. Additional patient categorization and selection may lead to less frequent drug use with the same survival advantage. We used transcutaneous partial pressure of oxygen (PtcO2) as an indicator of microcirculatory perfusion to identify which septic patients may benefit from APC.

METHODS

Nineteen patients consecutively admitted with severe sepsis or septic shock that fulfilled the PROWESS criteria for APC treatment. APC was administered to patients with the PROWESS selection criteria, only if the PtcO2 information demonstrated tissue ischemia.

RESULTS

Nineteen patients met the PROWESS criteria. Ten patients demonstrated poor tissue perfusion using PtcO2 monitors and received APC. Nine patients had adequate tissue perfusion and did not receive APC. There were no differences in age, gender, APACHE II scores, lactate levels, or organ failure between the two groups. The 10 patients who received APC had a mortality of 3 of 10 (30%). The survivors of this group uniformly converted to PtcO2 values consistent with survival within 12 hours to 24 hours of drug administration. The nine patients who did not receive APC had a mortality of 2 of 9 (22%), not statistically significant from those who received the drug (p = 0.89).

CONCLUSION

Withholding APC did not result in an increase in mortality from severe sepsis in those patients who demonstrated adequate PtcO2 values. The transcutaneous oxygen measurement may be a useful adjuvant in addition to the other selection criteria for better identification of patients who may benefit from APC.

Assessment of moderate to severe abdominal blood loss using peripheral to central blood oxygen saturation

PURPOSE

There are various definitions and monitoring modalities for hemodynamic status. Each of them has its own advantages and shortcomings. A new hemodynamic index is proposed in this study. This index can be calculated by placing the measured hemoglobin saturation in a formula. Blood samples for this measurement are taken from arterial, antecubital and central venous blood.

MATERIAL AND METHODS

We calculated this index in three different groups undergoing laparatomy. The control group consisted of patients who underwent elective surgery. The case group with acute internal abdominal bleeding was divided into two groups. Those with more than 20 ml/kg of blood in their abdominal cavity were designated as the severe case group, while those bleeding less were categorized as moderate. Blood samples were taken from ten patients in each group in stable and unstable conditions.

RESULTS

This index differed significantly between dissimilar hemodynamic conditions. The pre-anesthesia value of this index in the control group showed a mean +/- SD of 8.5 +/- 3.2 vs. 1.6 +/- 0.4 in the moderate case group vs. 0.7 +/- 0.08 in the case group with severe hemodynamic changes (p < .001). The index approximated to the control values as the circumstances improved. After compensation for volume loss, pre-extubation values were not significantly different. These were 9.6 +/- 2 in the control group vs. 8 +/- 2 in the case group with moderate hemodynamic change vs. 8 +/- 1.8 in the severe case group. The likelihood ratio of bleeding increased as this index decreased.

CONCLUSION

As the hemodynamic condition deteriorates, this index decreases significantly. This index is an accurate indicator for predicting hemodynamic changes compared to some other modalities. Further investigations are needed into the prognostic and therapeutic advantages of this index.

Comparison of cardiac output measurements between NICO and the pulmonary artery catheter during repeat surgery for total hip replacement

OBJECTIVE

The aim of this study was to compare cardiac output measurements of the non-invasive cardiac output and the pulmonary artery catheter during repeat surgery for hip replacement.

METHODS

In this prospective observational study, patients undergoing repeat hip surgery who needed a pulmonary artery catheter were included. A standard protocol was followed for induction, endotracheal intubation and maintenance of anaesthesia (sufentanil, etomidate, sevoflurane, cisatracurium). After endotracheal intubation, the non-invasive cardiac output was connected and a pulmonary artery catheter was inserted. Data were collected every 3 min until patients were extubated.

RESULTS

Ten patients were included and 2455 points of comparison recorded. Cardiac output from the pulmonary artery catheter varied from 1.7 to 8.9 L min(-1) (mean 4.1 L min(-1)) and the non-invasive cardiac output (using averaging mode) from 1.7 to 8.0 L min(-1) (mean 3.7 L min(-1)). There was a significant correlation between them (P < 0.01; bias 0.3 L min(-1); limits of agreement +1.9 and -2.5 L min(-1)), although these differed between patients.

CONCLUSION

The perioperative bias was small and the non-invasive cardiac output slightly underestimated cardiac output intraoperatively compared to the pulmonary artery catheter. The bias was smaller when mean cardiac output was below 3 L min(-1). Core temperature between 34.4 degrees C and 37.6 degrees C had no influence on the differences.

Effects of age and obesity on hemodynamics, tissue oxygenation, and outcome after trauma

OBJECTIVE

The aims of this study are (1) to describe the early time course of hemodynamic and tissue perfusion/oxygenation patterns in the elderly and in obese patients who survive and those who die after trauma; and (2) to evaluate postinjury hemodynamic patterns for use as guides for resuscitation and subsequent treatment.

METHODS

We noninvasively monitored 625 trauma patients upon arrival in the emergency department to assess the temporal hemodynamic patterns associated with age and obesity. Cardiac index (CI), mean arterial pressure, and heart rate were monitored to assess cardiac function, pulse oximetry (Sapo2) to reflect changes in pulmonary function and transcutaneous oxygen (PtcO2), carbon dioxide (PtcCO2), and oxygen delivery (DO2) to reflect tissue perfusion. We evaluated these hemodynamic data after they were stratified by the patient age and body mass index.

RESULTS

When all trauma patients were considered together, the predominant findings were high CI, transient hypotension, tachycardia, normal pulmonary function, and reduced tissue oxygenation. The elderly and, to a lesser extent the obese, had lower flow and tissue perfusion. The survivors had higher CI and better tissue oxygenation than did the nonsurvivors of each category.

CONCLUSIONS

Elderly and obese nonsurvivors of severe injury had low CI with reduced tissue oxygenation associated with organ failures and death. The study suggests that survivors' CIs and tissue oxygenation may be used as markers of circulatory deterioration and shock as well as resuscitation.

Noninvasive cardiac output monitoring

PURPOSE OF REVIEW

In an effort to provide high-quality intensive care without increasing morbidity and possibly decreasing mortality, noninvasive means of monitoring hemodynamics have been developed. Recently, commercially available monitoring techniques have been afforded the intensivist for just this purpose. This review will discuss the various means available, their limitations and recent literature describing their clinical use in comparison with pulmonary artery catheterization.

RECENT FINDINGS

Each method has been tested clinically, some more so than others. The general consensus is that each method correlates well with pulmonary artery catheterization. Each method, however, has limitations. Users must be familiar with the limitations and aware of which method is most appropriate for their patients. In general, the derived data provided by the noninvasive methods parallel those of pulmonary artery catheterization, with the exclusion of some commonly used variables (i.e. mixed venous oxygen, wedge pressure). Some novel variables derived from the new techniques can provide analogous information to that gathered from the pulmonary artery catheter.

SUMMARY

In summary, the methods commercially available today to measure hemodynamics in a noninvasive fashion offer good correlation to the traditional data derived from pulmonary artery catheterization. Pulmonary artery catheterization is considered, by most, to be the standard by which to compare other methods and will most likely remain so. This is due to a long history of reliance and clinical familiarity with its use. Additional clinical studies will need to be performed in a heterogeneous population of patients (trauma, burn, sepsis etc.) to enable better determination of reliability and limitations in various clinical scenarios. Overcoming the clinician's personal preference to rely on traditional pressure-derived data will also be a large obstacle to overcome.

Hemodynamic patterns preceding circulatory deterioration and death after trauma

OBJECTIVE

To describe the sequence of hemodynamic changes associated with sudden circulatory deterioration compared with those of terminal patients to identify the earliest signs warning of shock and death.

METHODS

This is a prospective observational study of 89 patients with thermodilution cardiac index and continuous noninvasive hemodynamic monitoring who had episodes of circulatory deterioration. These data were compared with the data of a second group of 24 patients in their terminal stage just before death.

RESULTS

The earliest indications of impending collapse were decreased cardiac index, and tissue perfusion reflected by decreased transcutaneous O2 tension (PtcO2). This was followed by reduced blood pressure, tachycardia, reduced arterial hemoglobin saturation, and increased transcutaneous CO2 tension (PtcCO2). This pattern of changes was more pronounced in the nonsurvivors and was seen in exaggerated form in terminal patients.

CONCLUSION

Sequential hemodynamic patterns revealed reduced blood flow and poor tissue perfusion as the earliest warning signs in both circulatory deterioration and death. These were followed by reduced mean arterial pressure, tachycardia, and low values of pulse oximetry. Adequate blood flow and even distribution of flow are needed for tissue perfusion.

A mathematical program to predict survival and to support initial therapeutic decisions for trauma patients with long-bone and pelvic fractures

AIM

To test a mathematical program to monitor early haemodynamic patterns of patients with fractures, predict survival and support initial therapeutic decisions.

METHODS

A mathematical search and display program based on non-invasive haemodynamic monitoring was used to study 430 consecutively monitored patients with fractures during the first 48 h after admission to the emergency department of an inner city public hospital. We studied four types of fractures: simple extremity fractures, long-bone fractures, pelvic fractures and fractures incidental to severe trauma. The program continuously displayed haemodynamic patterns and predicted survival probability (SP), which was evaluated by the actual outcome at hospital discharge. The program also assessed the effectiveness of therapies according to haemodynamic responses.

RESULTS

The cardiac index, heart rate, mean arterial pressure, arterial saturation and transcutaneous oxygen tensions at the initial resuscitation were significantly higher in survivors than in non-survivors. After the first 48 h, the haemodynamic patterns were more influenced by fever, sepsis, complications and organ failures. The calculated survival probability averaged 81%+/-18% in the first 48 h for survivors and 72%+/-20% for non-survivors.

CONCLUSION

Early continuous non-invasive haemodynamic monitoring using the proposed information system is helpful in predicting outcome and guiding therapy for patients with fractures.

Cardiac output measurements in off-pump coronary surgery: comparison between NICO and the Swan-Ganz catheter

BACKGROUND

The aim of this prospective study was to compare continuous cardiac output measurements of the non-invasive cardiac output system (NICO) with the pulmonary artery catheter during off-pump coronary bypass surgery.

METHODS

Twenty-two patients enrolled for off-pump coronary surgery received both a pulmonary artery catheter and a non-invasive cardiac output system for measurement of cardiac output. Data were compared by the Bland-Altman method to calculate the degree of agreement and to analyse if a significant difference existed between the two methods of cardiac output measurements.

RESULTS

Perioperatively, the non-invasive cardiac output underestimated cardiac output, but postoperatively overestimated it. The limits of agreement were larger during surgery compared to the postoperative period (-3.1; +2.5 vs. -1.4; +2.2 L min(-1)). Perioperatively, cardiac output measured with the pulmonary artery catheter varied from 0.5 to 7.5 L min(-1) (mean 3.6 L min(-1)) and with the non-invasive cardiac output from 0.5 to 8.4 L min(-1) (mean 3.9 L min(-1)). Postoperatively, these were 2.5-7.7 L min(-1) (mean 4.5 L min(-1)) and 2.3-8.4 L min(-1) (mean 4.9 L min(-1)), respectively.

CONCLUSION

During off-pump cardiac surgery, the non-invasive cardiac output reliably measures cardiac output and does it more rapidly than a pulmonary artery catheter and may be more useful in order to detect rapid haemodynamic changes.

Transcutaneous pressure of oxygen: a noninvasive and early detector of peripheral shock and outcome

A noninvasive tool to recognize early shock would improve outcome by providing prompt recognition of tissue ischemia and precise resuscitation endpoint. The skin is the first tissue bed to vasoconstrict in shock states. Studies have demonstrated that transcutaneous partial pressure of oxygen (PtCO2) increases with higher FiO2 in nonshock states as arterial pressure of oxygen (PaO2) increases, but in shock situations, PtCO2 mirrors changes in cardiac output and oxygen delivery with minimum response to increasing FiO2 and PaO2. This study examined the relationship of hemodynamic variables and the degree of PtCO2 response to FiO2 of 1.0 (identified as the "oxygen challenge test") to mortality and organ failure. This prospective observational study examined 38 patients requiring at least 24 h of cardiac output monitoring for shock resuscitation in the Surgical Intensive Care Unit. Patients were resuscitated to the standard protocol of blood pressure, urine output, oxygen delivery (DO2), and mixed venous O2 (SvO2). Seventy-nine percent of the patients (30/38) with a mean age of 59 +/- 21 years had septic shock or severe sepsis with a 26% mortality (10/38). Measurements included hemodynamic variables, PtCO2, and outcome (mortality and organ failure). In this study, the ability of PtCO2 value to increase by 21 mmHg on a FiO2 of 1.0, at 24 h of resuscitation, divided survivors from nonsurvivors, P <.001. The PtCO2 response to FiO2 may provide an additional noninvasive method of detecting early shock as well as a specific endpoint of resuscitation.

Hemodynamic Patterns of Blunt and Penetrating Injuries

BACKGROUND

The aims of this prospective observational study were to describe early hemodynamic patterns of blunt and penetrating truncal injury and to evaluate outcomes prediction using noninvasive hemodynamic monitoring with a mathematical model tested against actual in-hospital outcomes. The hypothesis was that traumatic shock is a circulatory disorder that can be monitored by noninvasive hemodynamic parameters that reflect cardiac, pulmonary, and tissue perfusion functions.

STUDY DESIGN

The cardiac index (CI), heart rate (HR), mean arterial pressure (MAP), pulse oximetry (SapO(2)), transcutaneous oxygen tension indexed to FiO(2) (PtcO(2)/FiO(2)), and carbon dioxide (PtcCO(2)) tensions were monitored beginning shortly after emergency department admission in 657 emergency patients with severe blunt and penetrating chest, abdominal, and extremity trauma. Of these, 113 patients had associated head injury, and these patients also were analyzed separately. A search and display mathematical model, with a decision support program, was based on continuous online, real-time, noninvasive hemodynamic monitoring.

RESULTS

There were similar patterns in the blunt and penetrating injuries; the cardiac index, mean arterial pressure, pulse oximetry, transcutaneous oxygen tension indexed to FiO(2), and survival probability values of the survivors were significantly higher (p < 0.01) than the corresponding values of those who died, although heart rate and carbon dioxide tension were higher in the nonsurvivors during the first 24 hours after their emergency department admission. These patterns occurred more rapidly in patients with penetrating injuries. After initial resuscitation in the emergency department, results were correlated with actual outcomes at hospital discharge and found to be 88% correct.

CONCLUSIONS

Early noninvasive hemodynamic monitoring with a computerized information system provided a feasible pattern recognition program for outcomes prediction and therapeutic decision support.

Evaluation of invasive and noninvasive hemodynamic monitoring in trauma patients

OBJECTIVES

The aim of this study was to compare a recently developed and improved noninvasive hemodynamic monitoring system with the conventional invasive monitoring by pulmonary artery catheterization (PAC) in acute emergency trauma patients.

METHODS

In a large, university-run, inner city public hospital, we monitored 993 trauma patients noninvasively; 262 of these were simultaneously monitored with both noninvasive hemodynamic and invasive PAC monitoring. The noninvasive monitoring was begun shortly after admission to the emergency department and the invasive PAC monitoring was started in the operating room, or as soon as the patient arrived in the intensive care unit. Noninvasive monitoring included cardiac index (CI) by the IQ or Physio Flow bioimpedance device, together with mean arterial blood pressure, heart rate, pulse oximetry (SapO2), transcutaneous oxygen (PtcO2), and carbon dioxide (PtcCO2) tensions. We compared CI by simultaneous measurements with both invasive and noninvasive methods 907 times in 262 patients.

RESULTS

The CI by thermodilution (CItd) correlated well with simultaneous measurements with the bioimpedance (CIbi), r2 = 0.915, r2 = 0.84, p < 0.001. The bias and precision of simultaneous measurements was -0.070 +/- 0.47 L/min/m2; agreement was considered satisfactory. In the initial resuscitation period of both monitoring systems, the CI, mean arterial blood pressure, SapO2, and tissue perfusion (reflected by invasive DO2 and VO2, and by noninvasive PtcO2/FiO2 ratio) were higher in survivors than in nonsurvivors, whereas heart rate values were higher in the nonsurvivors. We concluded that noninvasive hemodynamic monitoring provided a feasible, safe, inexpensive, accurate, continuous, on-line real-time graphic displays that are equivalent to the essential features of invasive pulmonary artery catheter monitoring.

Interrater reliability of cardiac output measurements by transcutaneous Doppler ultrasound: implications for noninvasive hemodynamic monitoring in the ED

INTRODUCTION

Hemodynamic monitoring is an important aspect of caring for the critically ill patients boarding in the emergency department (ED). The purpose of this study is to investigate the interrater agreement of noninvasive cardiac output measurements using transcutaneous Doppler ultrasound technique.

METHODS

This is a prospective observational cohort study performed in a 32-bed adult ED of an academic tertiary center with approximately 65000 annual patient visits. Patients were enrolled after verbal consent over a 7-month period. The raters were ED personnel involved in patient care. Paired measurements of cardiac index (CI) and stroke volume index (SVI) were obtained from a transcutaneous Doppler ultrasound cardiac output monitor.

RESULTS

A convenience sample of 107 (50 women and 57 men) patients with a median age of 49 (32, 62) years was enrolled. One hundred two paired measurements were performed in 91 patients in whom adequate Doppler ultrasound signals were obtainable. The raters included 35 emergency medicine attending physicians, 31 emergency medicine residents, 80 medical students, 47 nurses, and 11 emergency medical technicians. Cardiac index range was 0.6 to 5.3 L/min per square meter, and SVI range was 7.7 to 63.0 mL/m(2). The correlation of CI measurements between 2 raters was good (r(2) = 0.87; 95% confidence interval, 0.86-1.00; P < .001). Likewise, SVI measurements between 2 raters also showed acceptable correlation (r(2) = 0.84; 95% confidence interval, 0.81-0.96; P < .001). Interrater reliability was strong for CI (kappa = 0.83 with 92.2% agreement) and SVI measurements (kappa = 0.72 with 88.2% agreement). Most patients had an interrater difference below 10% in CI and SVI measurements.

CONCLUSIONS

Emergency department personnel, regardless of their role in patient care, are able to obtain reliable cardiac output measurements in ED patients over a wide range of CI and SVI. Transcutaneous Doppler ultrasound technique may be an alternative to traditional invasive hemodynamic monitoring of critically ill patients presenting to the ED.

Available ventilation monitoring methods during pre-hospital cardiopulmonary resuscitation

High quality cardiopulmonary resuscitation (CPR) in the pre-hospital setting has been associated with improved survival rates during cardiopulmonary arrest (CPA). Recent documentation of hyperventilation associated deterioration in hemodynamics during CPR, suggests that guided or controlled ventilation strategies may contribute to improved hemodynamics and increased survival. This article briefly reviews the mechanical methods, advantages, and disadvantages of the available ventilation monitoring methods currently available for clinical use, with an emphasis on pre-hospital implementation. We recommend that more objective measurement of ventilation during CPR be performed, with emphasis on a strategy for measuring both attempted ventilation frequency (f) and delivered tidal volume (VT). The use of improved thoracic impedance pneumography and capnography are appealing for such monitoring because of the widespread availability, but modifications to existing software and clinical data compared to a clinical standard would be required before general acceptance is possible. Other methods listed may offer advantages over these in select circumstances.

Stochastic model for outcome prediction in acute illness

The aims were to apply a stochastic model to predict outcome early in acute emergencies and to evaluate the effectiveness of various therapies in a consecutively monitored series of severely injured patients with noninvasive hemodynamic monitoring. The survival probabilities were calculated beginning shortly after admission to the emergency department (ED) and at subsequent intervals during their hospitalization. Cardiac function was evaluated by cardiac output (CI), heart rate (HR), and mean arterial blood pressure (MAP), pulmonary function by pulse oximetry (SapO(2)), and tissue perfusion function by transcutaneous oxygen indexed to FiO(2),(PtcO(2)/FiO(2)), and carbon dioxide (PtcCO(2)) tension. The survival probability (SP) of survivors averaged 81.5+/-1.1% (SEM) and for nonsurvivors 57.7+/-2.3% (p<0.001) in the first 24-hour period of resuscitation and subsequent management. The CI, SapO(2),PtcO(2)/FiO(2) and MAP were significantly higher in survivors than in nonsurvivors during the initial resuscitation, while HR and PtcCO(2) tensions were higher in the nonsurvivors. Predictions made during the initial resuscitation period in the first 24-hours after admission were compared with the actual outcome at hospital discharge, which were usually several weeks later; misclassifications were 9.6% (16/167). The therapeutic decision support system objectively evaluated the responses of alternative therapies based on responses of patients with similar clinical-hemodynamic states.

Survival, Hemodynamics, and Tissue Oxygenation after Head Trauma

BACKGROUND

The aims of this study were to describe the early time course of hemodynamic and tissue perfusion and oxygenation patterns in survivors and nonsurvivors after head injury; to suggest physiologic mechanisms responsible for the observed patterns; and to evaluate postinjury parameters that might be useful for treatment. The hypothesis was that reduced hemodynamics and tissue oxygenation and reduced arterial oxygen saturation affect outcomes.

STUDY DESIGN

Sixty patients with head trauma were noninvasively monitored on arrival in the emergency department to assess the temporal hemodynamic patterns associated with head injury; patients who were brain dead were excluded because they have very different hemodynamic patterns. Cardiac index, mean arterial pressure, and heart rate were monitored to assess cardiac function, pulse oximetry to reflect changes in pulmonary function, and transcutaneous oxygen and carbon dioxide to reflect tissue perfusion function. Patients were stratified by inhospital survival outcomes, the Glasgow Coma Scale, and the presence or absence of associated somatic injuries.

RESULTS

When all head injured patients were considered together, the predominant findings were high cardiac index, hypertension, mild tachycardia, normal pulmonary function, and reduced tissue oxygenation. The subset of survivors and those with high Glasgow Coma Scale had greater than normal cardiac index responses (4.02 +/- 0.01 (SEM) L/min/m2, p < 0.01 versus normal) and better tissue oxygenation (217 +/- 2 mmHg PtcO2/FiO2) than nonsurvivors (70 +/- 3 mmHg, p < 0.01) and those with low Glasgow Coma Scale (160 +/- 2, p < 0.05). Patterns of patients with associated somatic injuries were similar to those with isolated head injury.

CONCLUSIONS

The study suggested that survivors' cardiac index, tissue oxygenation, and arterial oxygen saturation may be considered as markers of resuscitation. Nonsurvivors of head injury had normal blood flow with reduced tissue oxygenation that might have contributed to unfavorable outcomes.

Outcome Prediction by a Mathematical Model Based on Noninvasive Hemodynamic Monitoring

BACKGROUND

The aims are to apply a mathematical search and display model based on noninvasive hemodynamic monitoring, to predict outcome early in a consecutively monitored series of 661 severely injured patients.

METHODS

A prospective observational study by a previously designed protocol in a Level I trauma service in a university-run inner city public hospital was conducted. The survival probabilities were calculated at the initial resuscitation on admission and at subsequent intervals during their hospitalization beginning shortly after admission to the emergency department. Cardiac function was evaluated by cardiac output (CI), heart rate (HR), and mean arterial blood pressure (MAP), pulmonary function by pulse oximetry (SapO2), and tissue perfusion function by transcutaneous oxygen indexed to FiO2, (PtcO2/FiO2), and carbon dioxide (PtcCO2) tension.

RESULTS

The survival probability (SP) averaged 89 +/- 0.4% for survivors and 75.7 +/- 1.6% (p < 0.001) for nonsurvivors in the first 24-hour period of resuscitation. The CI, MAP, SapO2, PtcO2, and PtcO2/FiO2 were significantly higher in survivors than in nonsurvivors in initial resuscitation, whereas HR and PtcCO2 were higher in nonsurvivors.

CONCLUSIONS

During the initial resuscitation period, misclassifications were 102 of 661 or 15%. The SP provided early objective criteria to evaluate hospital outcome and to track changes throughout the hospital course based on a large database of patients with similar clinical-hemodynamic states.

Continuous noninvasive monitoring of cardiac performance and tissue perfusion in pediatric trauma patients

PURPOSE

The aim of this study was to assess the accuracy of a continuous survival probability prediction using noninvasive measures of cardiac performance and tissue perfusion in severely injured pediatric patients.

METHODS

Review of all patients entered into a prospective noninvasive monitoring protocol. Cardiac index (CI) was measured using a thoracic bioimpedance device and tissue perfusion was assessed by transcutaneous carbon dioxide (Ptcco(2)) tension and oxygen tension indexed to the fraction of inspired oxygen (Ptco(2)/Fio(2)). Survival probability (SP) was continuously calculated using a stochastic analysis program.

RESULTS

There were 45 patients with a total of 953 data sets. The mean age was 11 years (range, 1-16 years) with a mean Injury Severity Score of 24 (+/-16). There was no difference between survivors (n = 32) and nonsurvivors (n = 13) at study entry for heart rate, blood pressure, CI, or pulse oximetry (all P > .05). However, survivors demonstrated higher Ptcco(2) (45 vs 35), higher Ptco(2)/Fio(2) (236 vs 156), and higher predicted SP (89% vs 62%) compared with nonsurvivors at study entry and throughout the monitoring period (all P < .01). For the entire data set, the strongest independent predictors of survival were Ptco(2)/Fio(2) and SP. The area under the receiver operating characteristic curve for mortality prediction was 0.83 for SP and 0.71 for Ptco(2)/Fio(2), compared with 0.6 for heart rate, 0.51 for blood pressure, and 0.53 for CI. Similar hemodynamic patterns were observed for all injury patterns with the exception of those with severe brain injury.

CONCLUSIONS

Thoracic bioimpedance and transcutaneous monitoring give critical real-time hemodynamic and tissue perfusion data that can provide early identification of pathologic flow patterns and accurately predict survival.

A hemoglobin-based oxygen carrier, bovine polymerized hemoglobin (HBOC-201) versus hetastarch (HEX) in a moderate severity hemorrhagic shock swine model with delayed evacuation

OBJECTIVE

To evaluate the efficacy of HBOC-201 for resuscitation of hemorrhagic shock in a swine model incorporating soft tissue injury and delayed evacuation.

METHODS

A muscle crush injury and 40% estimated blood volume controlled hemorrhage was completed in 24 Yucatan mini-pigs. Pigs were untreated or resuscitated with HBOC-201 or 6% hetastarch (HEX) at 20 min. Invasive hemodynamics and clinical variables were monitored for 4 h (pre-hospital phase) and subsequent fluid infusions were administered for severe hypotension or tachycardia. Animals were recovered from anesthesia and monitored non-invasively to 72 h (hospital phase).

RESULTS

100% (8/8) of HBOC-201-, 88% (7/8) of HEX-, and 63% (5/8) of non-resuscitated pigs, survived to 72 h (p=0.27). Mean arterial pressure, mean pulmonary arterial pressure and systemic vascular resistance index were higher in HBOC-201 pigs. By 90 min, cardiac index was restored to baseline in the HBOC-201 group and was 1.4-fold greater than baseline in the HEX group. HBOC-201 pigs had lower fluid requirements than HEX pigs (18.8+/-1.8 and 29.9+/-1.1 ml/kg, p<0.001) in the pre-hospital phase and required fewer blood transfusions (1.3+/-1.3 and 9.4+/-0.6 ml/kg, respectively, p<0.001) in the hospital phase. Urine output and blood creatinine were comparable in HBOC-201 and HEX pigs. Tissue oxygenation levels were highest in the HBOC-201 group.

CONCLUSIONS

As HBOC-201 restored hemodynamics and tissue oxygenation and decreased fluid requirements, in comparison with HEX, HBOC-201 was at least as efficacious and possibly a superior resuscitative fluid in a military-relevant delayed evacuation hemorrhagic shock swine model.

Mathematical program for outcome prediction and therapeutic support for trauma beginning within 1 hr of admission: a preliminary report

OBJECTIVES

The aims were a) to noninvasively monitor acute emergency trauma patients beginning within 1 hr after admission to the emergency department; b) to prospectively predict outcome; and c) to evaluate the relative effectiveness of various modes of therapy.

DESIGN

Prospective outcome prediction study using a mathematical search and display model based on noninvasive hemodynamic monitoring.

SETTING

A level I trauma service in a large university-run inner-city public hospital.

PATIENTS

We studied 185 consecutively noninvasively monitored emergency patients.

INTERVENTIONS

We noninvasively monitored cardiac index, mean arterial blood pressure, heart rate, pulse oximetry, and transcutaneous oxygen and carbon dioxide tensions beginning within 1-hr after emergency admission.

MEASUREMENTS AND MAIN RESULTS

The cardiac index, pulse oximetry, transcutaneous oxygen tension, transcutaneous carbon dioxide tension, and mean arterial blood pressure were higher in survivors than in nonsurvivors in the initial resuscitation period and at the hemodynamic nadir. Heart rate and transcutaneous carbon dioxide tension were higher in the nonsurvivors. The calculated survival probability in the first hour observation period of survivors averaged 85 +/- 14% vs. 69 +/- 16% for nonsurvivors (p = .0001). Misclassifications of the series as a whole were 11.3%; after excluding brain death from severe head injury, there were 6.4% misclassifications. A decision support system evaluated the effects of various therapies based on responses of patients with similar clinical-hemodynamic states.

CONCLUSION

Noninvasive hemodynamic monitoring and an information system provided a feasible approach to predict outcome early and to evaluate prospectively the efficacy of various therapies.

Stroke volume equation for impedance cardiography

The study's goal was to determine if cardiac output (CO), obtained by impedance cardiography (ICG), would be improved by a new equation N, implementing a square root transformation for dZ/dtmax/Z0, and a variable magnitude, mass-based volume conductor Vc. Pulmonary artery catheterisation was performed on 106 cardiac surgery patients pre-operatively. Post-operatively, thermodilution cardiac output (TDCO) was simultaneously compared with ICG CO. dZ/dtmax/Z0 and Z0 were obtained from a proprietary bioimpedance device. The impedance variables, in addition to left ventricular ejection time TLVE and patient height and weight, were input using four stroke volume (SV) equations: Kubicek (K), Sramek (S), Sramek-Bernstein (SB), and a new equation N. CO was calculated as SV x heart rate. Data are presented as mean +/- SD. One way repeated measures of ANOVA followed by the Tukey test were used for inter-group comparisons. Bland-Altman methods were used to assess bias, precision and limits of agreement. P< 0.05 was considered statistically significant. CO implementing N (6.06 +/- 1.48 l min(-1)) was not different from TDCO (5.97 +/- 1.41 l min(-1)). By contrast, CO calculated using K (3.70 +/- 1.53 l min(-1)), S (4.16 +/- 1.83 l min(-1)) and SB (4.37 +/- 1.82 l min(-1)) was significantly less than TDCO. Bland-Altman analysis showed poor agreement between TDCO and K, S and SB, but not between TDCO and N. Compared with TDCO, equation N, using a square-root transformation for dZ/dtmax/Z0, and a mass-based Vc, was superior to existing transthoracic impedance techniques for SV and CO determination.

Transthoracic electrical bioimpedance: a means of filling the void?

OBJECTIVES

To examine the published evidence regarding the use of transthoracic electric bioimpedance (TEB) for the non-invasive monitoring of cardiac output in the ED.

METHOD

Databases of the medical literature, relevant textbooks and the Internet were searched for articles regarding TEB. Criteria for inclusion were drawn up prior to examination of the articles and included adherence to guidelines for comparing methods of clinical measurement.

RESULTS

Results are discussed under the following headings: technological capability, diagnostic accuracy, limitations, range of possible uses, therapeutic impact, impact on health care providers, patient outcome and future directions.

CONCLUSION

TEB is a technique for the non-invasive monitoring of cardiac output whose ease of use, continuous data acquisition and versatility suggest it may have a role to play in the care of patients in our EDs.

A Stochastic Control Program to Predict Outcome and to Support Therapeutic Decisions: A Preliminery Report

BACKGROUND AND OBJECTIVES

Early noninvasive hemodynamic monitoring with an outcome predictor and a therapeutic decision support system may be useful to identify and correct hemodynamic deficiencies in emergency patients. The first aim was to apply a stochastic (probability) search and display model to predict outcome as early as possible. The second aim was to explore the usefulness of a therapeutic decision support system to evaluate the relative effectiveness of various therapies.

METHODS

A stochastic control and display program based on noninvasive hemodynamic monitoring was applied in 100 consecutive critically ill patients admitted to the emergency department of an inner city public hospital. The program continuously displayed the noninvasive hemodynamic data and the patient's predicted survival probability (SP) that was based on the patient's diagnosis, covariates, and hemodynamic data. The accuracy of the SP at the initial resuscitation on admission to the emergency department (ED) was evaluated by the actual outcome at hospital discharge. The therapeutic decision support program evaluated the relative effectiveness of various therapies on based on their hemodynamic and SP responses and outcome of patients with similar clinical-hemodynamic states.

RESULTS

The cardiac index, mean arterial pressure, arterial saturation, transcutaneous oxygen and carbon dioxide tensions were appreciably higher in survivors than in nonsurvivors in the initial resuscitation. Heart rate was higher in the nonsurvivors. The calculated Survival Probability (SP) of survivors averaged 81 +/- 1.4% in the first 24-hour observation period. It was 58 +/- 2.2% for nonsurvivors during this period. Misclassifications were 10/100 or 10%.

Is Noninvasive Hemodynamic Monitoring Appropriate for the Elderly Critically Injured Patient?

BACKGROUND

Noninvasive hemodynamic monitoring in critically ill patients using bioimpedance technology has been shown to be a reliable alternative to invasive thermodilution techniques. However, there have been some concerns that the bioimpedance method may be unreliable in elderly patients with an atherosclerotic and rigid thoracic aorta. The purpose of the present study was to evaluate the effect of age on the reliability of noninvasive bioimpedance technology in measuring cardiac index.

METHODS

This is a retrospective analysis of prospectively collected data in critically injured patients admitted to the surgical intensive care unit. All patients had simultaneous measurement using thermodilution cardiac index (TDCI) and bioimpedance cardiac index (BICI). The population was divided into three age groups (<55 years, 55-70 years, and >70 years). The correlation between TDCI and BICI was calculated for each age group.

RESULTS

There were 1,138 simultaneous measurements of TDCI and BICI in 285 patients. The BICI correlated well with TDCI in all three age groups (r = 0.82 for group <55 years, r = 0.87 for group 55-70 years, and r = 0.80 for group >70 years).

CONCLUSION

Noninvasive cardiac index monitoring in elderly patients is reliable and correlates well with standard thermodilution techniques.

Differences in mortality on the basis of laboratory parameters in an unselected population at the Emergency Department

The objective of this study was to relate multiple laboratory results of initial blood gas analysis in patients visiting the emergency department to mortality. A total of 1806 adult patients visiting the emergency department for any reason, who underwent blood gas analysis, were included in this study. The results of nine laboratory parameters (ionised calcium, potassium, sodium, glucose, lactate, pH, pCO

Lower body negative pressure as a model to study progression to acute hemorrhagic shock in humans

Hemorrhage is a leading cause of death in both civilian and battlefield trauma. Survival rates increase when victims requiring immediate intervention are correctly identified in a mass-casualty situation, but methods of prioritizing casualties based on current triage algorithms are severely limited. Development of effective procedures to predict the magnitude of hemorrhage and the likelihood for progression to hemorrhagic shock must necessarily be based on carefully controlled human experimentation, but controlled study of severe hemorrhage in humans is not possible. It may be possible to simulate hemorrhage, as many of the physiological compensations to acute hemorrhage can be mimicked in the laboratory by applying negative pressure to the lower extremities. Lower body negative pressure (LBNP) sequesters blood from the thorax into dependent regions of the pelvis and legs, effectively decreasing central blood volume in a similar fashion as acute hemorrhage. In this review, we compare physiological responses to hemorrhage and LBNP with particular emphasis on cardiovascular compensations that both share in common. Through evaluation of animal and human data, we present evidence that supports the hypothesis that LBNP, and resulting volume sequestration, is an effective technique to study physiological responses and mechanisms associated with acute hemorrhage in humans. Such experiments could lead to clinical algorithms that identify bleeding victims who will likely progress to hemorrhagic shock and require lifesaving intervention(s).

A Hemoglobin Based Oxygen Carrier, Bovine Polymerized Hemoglobin (HBOC-201) versus Hetastarch (HEX) in an Uncontrolled Liver Injury Hemorrhagic Shock Swine Model with Delayed Evacuation

BACKGROUND

As HBOC-201 improves outcome in animals with hemorrhagic shock (HS), we compared HBOC-201 and HEX (used by U.S. military special operations forces) in a swine model of delayed evacuation and uncontrolled HS.

METHODS

Twenty-four Yucatan pigs underwent a grade III liver injury and were resuscitated with HBOC-201, HEX, or no fluid (NON). Additional infusions were given for hypotension or tachycardia. After 4 hours, the liver was repaired; IV fluids and blood transfusions were administered. Pigs were monitored for 72 hours.

RESULTS

Survival was 7/8, 1/8, and 1/8 in HBOC-201-, HEX-, and NON-resuscitated pigs, respectively. Compared with HEX, HBOC-201 pigs had higher systemic and pulmonary artery pressures and had comparable cardiac outputs, but were less tachycardic. Transcutaneous tissue oxygenation was restored more rapidly in HBOC-201 pigs, there was a trend to lower lactic acid, and base deficit was less. HBOC-201 pigs had lower fluid requirements, higher urine output, and lower blood loss than HEX pigs.

CONCLUSIONS

Despite evidence of vasoactivity, HBOC-201 more effectively stabilized tissue oxygenation, reversed anaerobic metabolism, decreased bleeding, and increased survival in comparison with HEX. If confirmed in clinical trials, these data suggest that for the resuscitation of combat casualties with delayed evacuation and uncontrolled HS due to solid organ injury, HBOC-201 is a superior low-volume resuscitative fluid.