A critical assessment of endpoints of shock resuscitation

Central Hypovolemia Detection During Environmental Stress-A Role for Artificial Intelligence?

The first step to exercise is preceded by the required assumption of the upright body position, which itself involves physical activity. The gravitational displacement of blood from the chest to the lower parts of the body elicits a fall in central blood volume (CBV), which corresponds to the fraction of thoracic blood volume directly available to the left ventricle. The reduction in CBV and stroke volume (SV) in response to postural stress, post-exercise, or to blood loss results in reduced left ventricular filling, which may manifest as orthostatic intolerance. When termination of exercise removes the leg muscle pump function, CBV is no longer maintained. The resulting imbalance between a reduced cardiac output (CO) and a still enhanced peripheral vascular conductance may provoke post-exercise hypotension (PEH). Instruments that quantify CBV are not readily available and to express which magnitude of the CBV in a healthy subject should remains difficult. In the physiological laboratory, the CBV can be modified by making use of postural stressors, such as lower body "negative" or sub-atmospheric pressure (LBNP) or passive head-up tilt (HUT), while quantifying relevant biomedical parameters of blood flow and oxygenation. Several approaches, such as wearable sensors and advanced machine-learning techniques, have been followed in an attempt to improve methodologies for better prediction of outcomes and to guide treatment in civil patients and on the battlefield. In the recent decade, efforts have been made to develop algorithms and apply artificial intelligence (AI) in the field of hemodynamic monitoring. Advances in quantifying and monitoring CBV during environmental stress from exercise to hemorrhage and understanding the analogy between postural stress and central hypovolemia during anesthesia offer great relevance for healthy subjects and clinical populations.

The assessment of circulating volume using inferior vena cava collapse index and carotid Doppler velocity time integral in healthy volunteers: a pilot study

BACKGROUND

Assessment of circulating volume and the requirement for fluid replacement are fundamental to resuscitation but remain largely empirical. Passive leg raise (PLR) may determine fluid responders while avoiding potential fluid overload. We hypothesised that inferior vena cava collapse index (IVCCI) and carotid artery blood flow would change predictably in response to PLR, potentially providing a non-invasive tool to assess circulating volume and identifying fluid responsive patients.

METHODS

We conducted a prospective proof of concept pilot study on fasted healthy volunteers. One operator measured IVC diameter during quiet respiration and sniff, and carotid artery flow. Stroke volume (SV) was also measured using suprasternal Doppler. Our primary endpoint was change in IVCCI after PLR. We also studied changes in IVCCI after "sniff", and correlation between carotid artery flow and SV.

RESULTS

Passive leg raise was associated with significant reduction in the mean inferior vena cava collapsibility index from 0.24 to 0.17 (p < 0.01). Mean stroke volume increased from 56.0 to 69.2 mL (p < 0.01). There was no significant change in common carotid artery blood flow. Changes in physiology consequent upon passive leg raise normalised rapidly.

DISCUSSION

Passive leg raise is associated with a decrease of IVCCI and increase in stroke volume. However, the wide range of values observed suggests that factors other than circulating volume predominate in determining the proportion of collapse with respiration.

CONCLUSION

In contrast to other studies, we did not find that carotid blood flow increased with passive leg raise. Rapid normalisation of post-PLR physiology may account for this.

Trauma hemostasis and oxygenation research position paper on remote damage control resuscitation: definitions, current practice, and knowledge gaps

The Trauma Hemostasis and Oxygenation Research Network held its third annual Remote Damage Control Resuscitation Symposium in June 2013 in Bergen, Norway. The Trauma Hemostasis and Oxygenation Research Network is a multidisciplinary group of investigators with a common interest in improving outcomes and safety in patients with severe traumatic injury. The network's mission is to reduce the risk of morbidity and mortality from traumatic hemorrhagic shock, in the prehospital phase of resuscitation through research, education, and training. The concept of remote damage control resuscitation is in its infancy, and there is a significant amount of work that needs to be done to improve outcomes for patients with life-threatening bleeding secondary to injury. The prehospital phase of resuscitation is critical in these patients. If shock and coagulopathy can be rapidly identified and minimized before hospital admission, this will very likely reduce morbidity and mortality. This position statement begins to standardize the terms used, provides an acceptable range of therapeutic options, and identifies the major knowledge gaps in the field.

Trauma and aggressive homeostasis management

Homeostasis refers to the capacity of the human body to maintain a stable constant state by means of continuous dynamic equilibrium adjustments controlled by a medley of interconnected regulatory mechanisms. Patients who sustain tissue injury, such as trauma or surgery, undergo a well-understood reproducible metabolic and neuroendocrine stress response. This review discusses 3 issues that concern homeostasis in the acute care of trauma patients directly related to the stress response: hyperglycemia, lactic acidosis, and hypothermia. There is significant reason to question the "conventional wisdom" relating to current approaches to restoring homeostasis in critically ill and trauma patients.

Applications of minimally invasive cardiac output monitors

Because of the increasing age of the population, critical care and emergency medicine physicians have seen an increased number of critically ill patients over the last decade. Moreover, the trend of hospital closures in the United States t imposes a burden of increased efficiency. Hence, the identification of devices that facilitate accurate but rapid assessments of hemodynamic parameters without the added burden of invasiveness becomes tantamount. The purpose of this review is to understand the applications and limitations of these new technologies.

Therapeutic Effects of Intravenous Infusion of Hyperoxygenated Solution on Acute Haemorrhagic Shock in Rabbits

Tissue anoxia is the main mechanism of the shock reaction. Here, the effect of hyperoxygenated solution (HOS) on acute haemorrhagic shock was studied in rabbits. At 60 min after shock, rabbits were infused intravenously with hyperoxygenated solution at 10 (HOS1 group) or 20 ml/kg (HOS2 group) or with Ringer's solution at 10 ml/kg (RS group). Compared with values before shock, values after shock were lower for mean arterial pressure (MAP), more negative for base excess (BE) and higher for blood lactate (BL) and blood viscosity. After infusion, MAP declined more slowly in the HOS1 and HOS2 groups than in the RS group. At 30 and 60 min after infusion, arterial partial pressure of oxygen (PaO2) and oxygen saturation (SaO2) were higher and BE was less negative in the HOS1 and HOS2 groups than in the RS group, BL was lower in the HOS1 and HOS2 groups than in the RS group, and PaO2 and SaO2 were higher in the HOS2 group than in the HOS1 group. It was concluded that HOS infusion can rectify changes in vital signs more effectively than Ringer's solution after acute haemorrhagic shock in rabbits.

1H-NMR-based metabolic signatures of clinical outcomes in trauma patients--beyond lactate and base deficit

The determination of reliable biomarkers capable to predict clinical outcome of a trauma patient remains essential toward better therapeutic management of the patient in the intensive care unit. Assessment of global metabolic profiling using quantitative nuclear magnetic resonance (NMR)-based metabolomics offers an attractive modern methodology for fast and comprehensive determination of multiple circulating metabolites and for establishing metabolic phenotype of survivors versus nonsurvivors. Multivariate data analysis on 43 quantitative metabolic parameters identified three lipid metabolites, triacylglycerol, glycerol heads of phospholipids, and monounsaturated fatty acids, as being the most discriminative markers to separate survivors versus nonsurvivors at the time of admission. Glucose and glutamate were intermediate predictors, followed by lactate and hydroxybutyrate as two low-weight predictors. Ultimately, cellular and subcellular failure in nonsurviving trauma patients results in multiple systemic biochemical effects and in changes in circulating metabolites in the blood that are characteristic for decreased lipid synthesis and urea cycle activity in the liver, and for increased hyperglycemia, lactic, and ketoacidosis.

The role of pre-hospital blood gas analysis in trauma resuscitation

Background

To assess, whether arterial blood gas measurements during trauma patient's pre-hospital shock resuscitation yield useful information on haemodynamic response to fluid resuscitation by comparing haemodynamic and blood gas variables in patients undergoing two different fluid resuscitation regimens.

Methods

In a prospective randomised study of 37 trauma patients at risk for severe hypovolaemia, arterial blood gas values were analyzed at the accident site and on admission to hospital. Patients were randomised to receive either conventional fluid therapy or 300 ml of hypertonic saline. The groups were compared for demographic, injury severity, physiological and outcome variables.

Results

37 patients were included. Mean (SD) Revised Trauma Score (RTS) was 7.3427 (0.98) and Injury Severity Score (ISS) 15.1 (11.7). Seventeen (46%) patients received hypertonic fluid resuscitation and 20 (54%) received conventional fluid therapy, with no significant differences between the groups concerning demographic data or outcome. Base excess (BE) values decreased significantly more within the hypertonic saline (HS) group compared to the conventional fluid therapy group (mean BE difference -2.1 mmol/l vs. -0.5 mmol/l, p = 0.003). The pH values on admission were significantly lower within the HS group (mean 7.31 vs. 7.40, p = 0.000). Haemoglobin levels were in both groups lower on admission compared with accident site. Lactate levels on admission did not differ significantly between the groups.

Conclusion

Pre-hospital use of small-volume resuscitation led to significantly greater decrease of BE and pH values. A portable blood gas analyzer was found to be a useful tool in pre-hospital monitoring for trauma resuscitation.

Central venous pressure versus pulmonary artery catheter-directed shock resuscitation

Previously, we developed a protocol for shock resuscitation of severe trauma patients to reverse shock and regain hemodynamic stability during the first 24 intensive care unit (ICU) hours. Key hemodynamic measurements of cardiac output and preload were obtained using a pulmonary artery catheter (PAC). As an alternative, we developed a protocol that used central venous pressure (CVP) to guide decision making for interventions to regain hemodynamic stability [mean arterial pressure (MAP) >or= 65 mmHg and heart rate (HR) <or= 130 bpm]. Either protocol was available and required for traumatic shock resuscitation using bedside computerized clinical decision support to standardize decision making, and PAC was available if CVP-directed resuscitation was inadequate. We hypothesized that patients would be appropriately assigned to either protocol by trauma surgeon assessment of hemodynamic stability upon ICU admission. High-risk patients admitted to a level-1 trauma center ICU underwent resuscitation. Criteria were 1) major torso trauma, 2) base deficit (BD) >or= 6 mEq/L or systolic blood pressure < 90 mmHg, 3) transfusion of >or= 1 unit packed red blood cells (PRBC), or >or= age 65 years with two of three criteria. Patients with brain injury were excluded. Data were recorded prospectively. In 24 months ending July 31, 2006, of 193 patients, 114 (59%) were assigned CVP- directed resuscitation, and 79 (41%) were assigned PAC-directed resuscitation. A subgroup of 11 (10%) initially assigned CVP was reassigned PAC-directed resuscitation (7 +/- 2 h after start) due to hemodynamic instability. Crystalloid fluid and PRBC resuscitation volumes for PAC (8 +/- 1 L lactated Ringer's [LR], 5 +/- 0.4 units PRBC) were > CVP (5 +/- 0.4 L LR, 3 +/- 0.3 units PRBC) and similar to CVP - PAC protocol subgroup patients (9 +/- 2 L LR, 5 +/- 1 units PRBC). Intensive care unit (ICU) stay and survival rate for PAC (18 +/- 2 days, 75%) were similar to CVP - PAC (17 +/- 4 days, 73%) and worse than CVP protocol subgroup patients (9 +/- 1 days, 98%). Traumatic shock resuscitation is feasible using CVP as a primary hemodynamic monitor as part of a protocol that includes explicit definition of hemodynamic instability and where PAC monitoring is readily available. Computerized decision support provides a technique to implement complex protocol care processes and analyze patient response.

Identification of complex metabolic states in critically injured patients using bioinformatic cluster analysis

Introduction

Advances in technology have made extensive monitoring of patient physiology the standard of care in intensive care units (ICUs). While many systems exist to compile these data, there has been no systematic multivariate analysis and categorization across patient physiological data. The sheer volume and complexity of these data make pattern recognition or identification of patient state difficult. Hierarchical cluster analysis allows visualization of high dimensional data and enables pattern recognition and identification of physiologic patient states. We hypothesized that processing of multivariate data using hierarchical clustering techniques would allow identification of otherwise hidden patient physiologic patterns that would be predictive of outcome.

Methods

Multivariate physiologic and ventilator data were collected continuously using a multimodal bioinformatics system in the surgical ICU at San Francisco General Hospital. These data were incorporated with non-continuous data and stored on a server in the ICU. A hierarchical clustering algorithm grouped each minute of data into 1 of 10 clusters. Clusters were correlated with outcome measures including incidence of infection, multiple organ failure (MOF), and mortality.

Results

We identified 10 clusters, which we defined as distinct patient states. While patients transitioned between states, they spent significant amounts of time in each. Clusters were enriched for our outcome measures: 2 of the 10 states were enriched for infection, 6 of 10 were enriched for MOF, and 3 of 10 were enriched for death. Further analysis of correlations between pairs of variables within each cluster reveals significant differences in physiology between clusters.

Conclusions

Here we show for the first time the feasibility of clustering physiological measurements to identify clinically relevant patient states after trauma. These results demonstrate that hierarchical clustering techniques can be useful for visualizing complex multivariate data and may provide new insights for the care of critically injured patients.

Abdominal compartment syndrome: a concise clinical review

OBJECTIVE

There has been an increased awareness of the presence and clinical importance of abdominal compartment syndrome. It is now appreciated that elevations of abdominal pressure occur in a wide variety of critically ill patients. Full-blown abdominal compartment syndrome is a clinical syndrome characterized by progressive intra-abdominal organ dysfunction resulting from elevated intra-abdominal pressure. This review provides a current, clinically focused approach to the diagnosis and management of abdominal compartment syndrome, with a particular emphasis on intensive care.

METHODS

Source data were obtained from a PubMed search of the medical literature, with an emphasis on the time period after 2000. PubMed "related articles" search strategies were likewise employed frequently. Additional information was derived from the Web site of the World Society of the Abdominal Compartment Syndrome (http://www.wsacs.org).

SUMMARY AND CONCLUSIONS

The detrimental impact of elevated intra-abdominal pressure, progressing to abdominal compartment syndrome, is recognized in both surgical and medical intensive care units. The recent international abdominal compartment syndrome consensus conference has helped to define, characterize, and raise awareness of abdominal compartment syndrome. Because of the frequency of this condition, routine measurement of intra-abdominal pressure should be performed in high-risk patients in the intensive care unit. Evidence-based interventions can be used to minimize the risk of developing elevated intra-abdominal pressure and to aggressively treat intra-abdominal hypertension when identified. Surgical decompression remains the gold standard for rapid, definitive treatment of fully developed abdominal compartment syndrome, but nonsurgical measures can often effectively affect lesser degrees of intra-abdominal hypertension and abdominal compartment syndrome.

Hemoglobin drops within minutes of injuries and predicts need for an intervention to stop hemorrhage

BACKGROUND

Hemoglobin (Hgb) levels obtained shortly after injury may not detect occult bleeding in trauma patients because of the time needed for plasma levels to equilibrate, or may be confounded by crystalloid-related hemodilution. We hypothesized that Hgb levels measured within minutes of arrival can identify trauma patients who are actively bleeding.

METHODS

A retrospective study of 404 consecutive patients was undertaken at an urban Level I trauma center, which included 39 patients who required emergent surgical or radiologic intervention to control bleeding. All 404 patients underwent point-of-care Hgb measurements within 30 minutes of emergency department (ED) arrival. Hgb levels were correlated with physiologic signs of hemorrhage(blood pressure, heart rate, base deficit, pH, and resuscitation volume), and the need for emergent interventions to stop hemorrhage.

RESULTS

Early Hgb levels were significantly lower in patients who required emergent interventions to stop hemorrhage (mean +/- SD: 12 +/- 2 gm/dL vs. 13 +/- 2 gm/dL, p < 0.001). Lower Hgb levels were associated with increasing heart rate, decreasing blood pressure, decreasing pH, worsening base deficit, and increasing transfusion requirements. Hgb < or =10 gm/dL was associated with a greater than three-fold increase in the need for emergent interventions to stop bleeding (odds ratio 3.14, 95% confidence interval 1.18-8.35, p < 0.03), and correctly identified the need for intervention in 87% of patients.

CONCLUSION

Hemorrhage in trauma patients is associated with an early decrease in Hgb level. Hgb < or =10 gm/dL in the first 30 minutes of patient arrival will correctly identify presence or absence of significant bleeding in almost 9 of 10 trauma patients.

Fluid management of the trauma patient

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

Trauma and aggressive homeostasis management

Three important issues concerning homeostasis in the acute care of trauma patients that are related directly to the stress response are hyperglycemia, lactic acidosis, and hypothermia. Recently, there has been a resurgence of interest in investigating the effects of aggressive thermal and glucose concentration and volume resuscitation on outcomes in critically ill and trauma patients. Significant reason exists to question the "conventional wisdom" relating to current approaches to restoring homeostasis in this patient population.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Monitoring 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.

The Role of Transesophageal Echocardiography in Optimizing Resuscitation in Acutely Injured Patients

BACKGROUND

The goal of resuscitation is to correct the mismatch between oxygen delivery and that of cellular demands. The pulmonary artery catheter (PAC) is frequently used to gauge the adequacy of resuscitation and guide therapy based on ventricular filling pressures. Transesophageal echocardiography (TEE) has emerged as a potential tool in assessing adequacy of acute hemodynamic resuscitation. The purpose of this study was to evaluate the role of TEE in assessing preload during ongoing volume resuscitation in trauma patients.

METHODS

A retrospective review was conducted of acutely injured patients undergoing TEE during resuscitation from hemorrhagic shock from January 2002 to 2004 at a Level I trauma center. The indication for TEE was persistent hemodynamic instability in the absence of ongoing surgical hemorrhage. Variables included hemodynamic and PAC parameters, pre-TEE resuscitation volume, and vasopressor requirements. The impact of TEE findings on therapeutic decisions was evaluated.

RESULTS

Twenty-five patients underwent TEE, 18 (72%) had an indwelling PAC with a mean pulmonary artery occlusion pressure of 19.3 mm Hg (range, 12-29 mm Hg) and mean cardiac index of 2.9 L/min/m2 (range, 1.6-4.6 L/min/m2). Twelve patients (48%) were receiving inotropes and/or vasopressors for hypotension at the time of TEE. Resuscitation volume within 6 hours before TEE included a mean of 6.5 L of crystalloid and 12.2 units of blood products (packed red blood cells, fresh frozen plasma, and platelets). TEE revealed left ventricular hypovolemia in 13 patients (52%) and altered therapy in 16 patients (64%), including additional volume (n = 13), addition of an inotrope (n = 4), and addition of a vasodilator (n = 1) in one patient with ventricular overdistention. Comparison of the abnormal and normal TEE groups revealed that only cardiac index was significantly different (2.6 L/min/m2 in the abnormal group vs. 3.9 L/min/m2 in the normal group; p = 0.005). Significant mitral valve regurgitation leading to valve replacement was identified in one patient. No clinically relevant pericardial effusion was identified.

CONCLUSION

TEE altered resuscitation management in almost two thirds of patients. Many patients with "acceptable" pulmonary artery occlusion pressure parameters may in fact have inadequate left ventricular filling. In addition, TEE offers the advantage of direct assessment of cardiac valve competency, myocardial wall contractility, and pericardial fluid.

Can near-infrared spectroscopy identify the severity of shock in trauma patients?

BACKGROUND

Our recent experimental study showed that peripheral muscle tissue oxygen saturation (StO2), determined noninvasively by near-infrared spectroscopy (NIRS), was more reliable than systemic hemodynamics or invasive oxygenation variables as an index of traumatic shock. The purpose of this study was to establish the normal range of thenar muscle StO2 in humans and the relationship between shock state and StO2 in trauma patients.

METHODS

This was a prospective, nonrandomized, observational, descriptive study in normal human volunteers (n = 707) and patients admitted to the resuscitation area of our Level I trauma center (n = 150). To establish a normal StO2 range, an NIRS probe was applied to the thenar eminence of volunteers (normals). Subsequently, in a group of trauma patients, an NIRS probe was applied to the thenar eminence and data were collected and stored for offline analysis. StO2 monitoring was performed continuously and noninvasively, and values were recorded at 2-minute intervals. Five moribund trauma patients were excluded. Members of our trauma faculty, blinded to StO2 values, classified each patient into one of four groups (no shock, mild shock, moderate shock, and severe shock) using conventional physiologic parameters.

RESULTS

Mean +/- SD thenar StO2 values for each group were as follows: normals, 87 +/- 6% (n = 707); no shock, 83 +/- 10% (n = 85); mild shock, 83 +/- 10% (n = 19); moderate shock, 80 +/- 12% (n = 14); and severe shock, 45 +/- 26% (n = 14). The thenar StO2 values clearly discriminated the normals or no shock patients and the patients with severe shock (p < 0.05).

CONCLUSION

Decreased thenar muscle tissue oxygen saturation reflects the presence of severe hypoperfusion and near-infrared spectroscopy may be a novel method for rapidly and noninvasively assessing changes in tissue dysoxia.

Assessment and treatment of perfusion abnormalities in the emergency patient

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Assessment of Fluids and Electrolytes

Bedside evaluation of a patient's intravascular volume status is challenging, even for the seasoned practitioner. There is no single diagnostic test to determine whether a patient is hypovolemic, hypervolemic, or euvolemic. Often, underlying or concomitant disease states, medications, and other therapeutics can make available data difficult to interpret. Therefore, a combination of clinical evaluation, laboratory studies, and other diagnostics are required to make a clinical judgment regarding volume status. Patients who demonstrate alterations in their volume status are likely to have electrolyte abnormalities as well, and assessment of serum electrolyte values and potential therapeutic interventions is a vital piece in caring for critically ill patients.

Noninvasive muscle oxygenation to guide fluid resuscitation after traumatic shock

BACKGROUND

Three different protocols tested the hypothesis that hind limb muscle tissue O(2) saturation (StO(2)), measured noninvasively with near-infrared spectroscopy (NIRS), is as reliable as invasive systemic oxygenation indices to guide fluid resuscitation.

METHODS

In series 1, swine (n=30) were hemorrhaged, then received either no fluid, a fixed volume of colloid (15 mL/kg), or shed blood plus lactated Ringer's (LR) titrated to MAP >60 mm Hg. In series 2, swine (n=16) received a penetrating femur injury, a 47% to 55% hemorrhage to determine a median lethal dose (LD(50)) then shed blood plus LR titrated to MAP >60 mm Hg. In series 3, swine (n=5) received the femur injury plus LD(50) hemorrhage, and were resuscitated with LR titrated to StO(2) >50%.

RESULTS

In series 1, StO(2) tracked mixed venous O(2) saturation (SvO(2)), but discriminated between 3 survivor groups better than SvO(2), arterial lactate, or arterial base excess. In series 2, StO(2) tracked SvO(2) but discriminated between 2 survivor groups better than SvO(2), arterial lactate, or arterial base excess. In series 3, animals survived to extubation when resuscitated to an StO(2) target.

CONCLUSIONS

Noninvasive muscle StO(2) determined by NIRS was more reliable than invasive oxygenation variables as an index of shock. Because muscle StO(2) can be easily monitored in emergency situations, it may represent an improved method to gauge the severity of shock or the adequacy of fluid resuscitation after trauma.

Fluid resuscitation and blood replacement in patients with polytrauma

Hemorrhage is the most common cause of shock in patients with polytrauma, leading to cellular hypoxia and death. A large body of experimental and clinical research has greatly expanded our knowledge of cellular mechanisms and clinical outcomes in resuscitation of patients with hypovolemic shock. However, the fundamental principles of fluid resuscitation have not changed during the past few decades. Aggressive resuscitation to correct tissue hypoperfusion within 24 hours of injury is associated with improved clinical outcomes. Initial volume expanders of choice are crystalloid solutions, with blood and blood products used for patients who are hemodynamically unstable, patients with Class III and Class IV hemorrhage, and patients with ongoing uncontrolled sources of bleeding. The incidence of immunologic and infectious complications associated with blood transfusions in resuscitation of patients with polytrauma has not been shown to be any higher than in other clinical settings. Massive resuscitations, however, are associated with specific complications such as hypothermia, coagulopathy, and abdominal compartment syndrome. Novel blood substitutes, hypertonic saline, and minimally invasive hemodynamic monitoring techniques have the potential of optimizing fluid resuscitation in patients with polytrauma. Additional research using standardized animal models and randomized clinical trials is needed.

Gastric tonometry: the role of mucosal pH measurement in the management of trauma

Effective management of hemorrhagic shock depends on titration of therapies against reliable resuscitation end points. Conventional clinical and laboratory indexes of shock are often slow to respond to progressive circulatory compromise. GI mucosal ischemia resulting from redistribution of blood flow may, however, precede uncompensated shock and may compound the initial hemorrhagic insult by touching off cascades of inflammatory responses. Trauma patients with evidence of subclinical GI ischemia have been shown to have poor outcomes. Gastric tonometry, by detecting the presence of gastric intramucosal acidosis as a proxy of splanchnic hypoperfusion, may facilitate more timely and rational shock resuscitation. This article reviews the development and validation of gastric tonometry and summarizes the clinical studies that have used this modality to guide the management of shock in trauma patients.

Pathophysiologic characteristics of hypovolemic shock

In the late 1800s, while caring for a trauma victim, Warren characterized shock as "a momentary pause in the act of death." A great deal about shock has been discovered since this first description. Dorland's Medical Dictionary defines shock as a condition of profound hemodynamic and metabolic disturbance characterized by failure of the circulatory system to maintain adequate perfusion of vital organs. Shock is now being defined at the cellular level as the inadequate delivery of nutrients to the cells of the body. Because oxygen is the only nutrient that cells cannot store in any appreciable quantity, shock is also equivalent to inadequate oxygen delivery (DO2). Although there are many types of shock, this article concentrates on the pathophysiologic characteristics of hypovolemic shock.