Measurement of extravascular lung water using the single indicator method in patients: research and potential clinical value

Incidence of Acute Pulmonary Edema Before and After the Systematic Use of Ultrasound B-Lines

INTRODUCTION

Acute pulmonary edema (APE) due to fluid overload is considered the most feared complication in hemodialysis patients. Various diagnostic tests have been proposed to assess the fluid status in patients with end-stage kidney failure (ESKF); among these, lung ultrasound (measuring the number of B-lines) is emerging as a promising tool to identify pulmonary congestion in this patient population.

METHODS

We compared the incidence of APE before and after the implementation of lung ultrasound as a routine practice in our unit. The pre (from 1 January 2007 to 31 December 2008)- and post (from 1 January 2017 to 31 December 2018)-B-line implementation periods included 98 and 108 hemodialysis patients, respectively. By accurately reviewing their electronic medical records, all episodes of APE were collected. The 10-year interval between the two periods was specifically chosen to ensure no overlap between patients of the two cohorts whereas the single-center design was adopted to minimize the influence of center effect on the study results.

RESULTS

APE episodes occurred more frequently in patients from the pre-B-line implementation group (18/98, i.e., 18.4%) compared with those from the post B-line implementation group (6/108, i.e., 5.5%) (p = 0.004). An analysis based on repeated APE events showed that the incidence rate of APE was significantly higher during the pre-implementation period (2.0 APE episodes per 100 person-months, 95% CI: 1.4-2.7) than during the post-implementation period (0.3 APE episodes per 100 person-months, 95% CI: 0.1-0.7), with an incidence rate ratio (post- versus pre-) of 0.17 (95% CI: 0.07-0.40; p < 0.001). The odds of experiencing APE episodes were 74% lower (odds ratio: 0.26, 95% CI: 0.10-0.69) in patients from the post B-line implementation period compared with those from the pre-implementation period. Notably, adjusting for potential confounders did not affect the strength of this association, which remained statistically significant (p ≤ 0.030). Finally, dominance analysis indicated that the implementation of B-lines was the primary factor explaining the difference in APE episodes between the two periods, followed by dialysis duration and intra-dialysis weight gain.

CONCLUSIONS

The systematic use of lung ultrasound (a simple, easy-to-learn, rapid and non-invasive method, easily performed at the patient's bed) in everyday clinical practice was associated with a drastic reduction in episodes of APE in hemodialysis patients. Further observational and interventional studies are needed to confirm these results.

Studying the Pulmonary Endothelium in Health and Disease: An Official American Thoracic Society Workshop Report

Lung endothelium resides at the interface between the circulation and the underlying tissue, where it senses biochemical and mechanical properties of both the blood as it flows through the vascular circuit and the vessel wall. The endothelium performs the bidirectional signaling between the blood and tissue compartments that is necessary to maintain homeostasis while physically separating both, facilitating a tightly regulated exchange of water, solutes, cells, and signals. Disruption in endothelial function contributes to vascular disease, which can manifest in discrete vascular locations along the artery-to-capillary-to-vein axis. Although our understanding of mechanisms that contribute to endothelial cell injury and repair in acute and chronic vascular disease have advanced, pathophysiological mechanisms that underlie site-specific vascular disease remain incompletely understood. In an effort to improve the translatability of mechanistic studies of the endothelium, the American Thoracic Society convened a workshop to optimize rigor, reproducibility, and translation of discovery to advance our understanding of endothelial cell function in health and disease.

Update on the Features and Measurements of Experimental Acute Lung Injury in Animals: An Official American Thoracic Society Workshop Report

Advancements in methods, technology, and our understanding of the pathobiology of lung injury have created the need to update the definition of experimental acute lung injury (ALI). We queried 50 participants with expertise in ALI and acute respiratory distress syndrome using a Delphi method composed of a series of electronic surveys and a virtual workshop. We propose that ALI presents as a "multidimensional entity" characterized by four "domains" that reflect the key pathophysiologic features and underlying biology of human acute respiratory distress syndrome. These domains are 1) histological evidence of tissue injury, 2) alteration of the alveolar-capillary barrier, 3) presence of an inflammatory response, and 4) physiologic dysfunction. For each domain, we present "relevant measurements," defined as those proposed by at least 30% of respondents. We propose that experimental ALI encompasses a continuum of models ranging from those focusing on gaining specific mechanistic insights to those primarily concerned with preclinical testing of novel therapeutics or interventions. We suggest that mechanistic studies may justifiably focus on a single domain of lung injury, but models must document alterations of at least three of the four domains to qualify as "experimental ALI." Finally, we propose that a time criterion defining "acute" in ALI remains relevant, but the actual time may vary based on the specific model and the aspect of injury being modeled. The continuum concept of ALI increases the flexibility and applicability of the definition to multiple models while increasing the likelihood of translating preclinical findings to critically ill patients.

Transpulmonary thermodilution in patients treated with veno-venous extracorporeal membrane oxygenation

BACKGROUND

We tested the effect of different blood flow levels in the extracorporeal circuit on the measurements of cardiac stroke volume (SV), global end-diastolic volume index (GEDVI) and extravascular lung water index derived from transpulmonary thermodilution (TPTD) in 20 patients with severe acute respiratory distress syndrome (ARDS) treated with veno-venous extracorporeal membrane oxygenation (ECMO).

METHODS

Comparative SV measurements with transesophageal echocardiography and TPTD were performed at least 5 times during the treatment of the patients. The data were interpreted with a Bland-Altman analysis corrected for repeated measurements. The interchangeability between both measurement modalities was calculated and the effects of extracorporeal blood flow on SV measurements with TPTD was analysed with a linear mixed effect model. GEDVI and EVLWI measurements were performed immediately before the termination of the ECMO therapy at a blood flow of 6 l/min, 4 l/min and 2 l/min and after the disconnection of the circuit in 7 patients.

RESULTS

170 pairs of comparative SV measurements were analysed. Average difference between the two modalities (bias) was 0.28 ml with an upper level of agreement of 40 ml and a lower level of agreement of -39 ml within a 95% confidence interval and an overall interchangeability rate between TPTD and Echo of 64%. ECMO blood flow did not influence the mean bias between Echo and TPTD (0.03 ml per l/min of ECMO blood flow; p = 0.992; CI - 6.74 to 6.81). GEDVI measurement was not significantly influenced by the blood flow in the ECMO circuit, whereas EVLWI differed at a blood flow of 6 l/min compared to no ECMO flow (25.9 ± 10.1 vs. 11.0 ± 4.2 ml/kg, p = 0.0035).

CONCLUSIONS

Irrespectively of an established ECMO therapy, comparative SV measurements with Echo and TPTD are not interchangeable. Such caveats also apply to the interpretation of EVLWI, especially with a high blood flow in the extracorporeal circulation. In such situations, the clinician should rely on other methods of evaluation of the amount of lung oedema with the haemodynamic situation, vasopressor support and cumulative fluid balance in mind.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00021050). Registered 03/30/2020 https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00017237.

Aortic volume determines global end-diastolic volume measured by transpulmonary thermodilution

Background

Global end-diastolic volume (GEDV) measured by transpulmonary thermodilution is regarded as indicator of cardiac preload. A bolus of cold saline injected in a central vein travels through the heart and lung, but also the aorta until detection in a femoral artery. While it is well accepted that injection in the inferior vena cava results in higher values, the impact of the aortic volume on GEDV is unknown. In this study, we hypothesized that a larger aortic volume directly translates to a numerically higher GEDV measurement.

Methods

We retrospectively analyzed data from 88 critically ill patients with thermodilution monitoring and who did require a contrast-enhanced thoraco-abdominal computed tomography scan. Aortic volumes derived from imaging were compared with GEDV measurements in temporal proximity.

Results

Median aortic volume was 194 ml (interquartile range 147 to 249 ml). Per milliliter increase of the aortic volume, we found a GEDV increase by 3.0 ml (95% CI 2.0 to 4.1 ml, p < 0.001). In case a femoral central venous line was used for saline bolus injection, GEDV raised additionally by 2.1 ml (95% CI 0.5 to 3.7 ml, p = 0.01) per ml volume of the vena cava inferior. Aortic volume explained 59.3% of the variance of thermodilution-derived GEDV. When aortic volume was included in multivariate regression, GEDV variance was unaffected by sex, age, body height, and weight.

Conclusions

Our results suggest that the aortic volume is a substantial confounding variable for GEDV measurements performed with transpulmonary thermodilution. As the aorta is anatomically located after the heart, GEDV should not be considered to reflect cardiac preload. Guiding volume management by raw or indexed reference ranges of GEDV may be misleading.

Short-term effects of low-volume resuscitation with hypertonic saline and hydroxyethylstarch in an experimental model of lung contusion and haemorrhagic shock

OBJECTIVES

This study aimed to assess the short-term respiratory tolerance and haemodynamic efficiency of low-volume resuscitation with hypertonic saline and hydroxyethylstarch (HS/HES) in a pig model of lung contusion and controlled haemorrhagic shock. We hypothesised that a low-volume of HS/HES after haemorrhagic shock did not impact contused lungs in terms of extravascular lung water 3hours after trauma.

METHODS

A lung contusion resulting from blunt chest trauma was induced in 28 anaesthetised female pigs with five bolt-shots to the right thoracic cage, followed by haemorrhagic shock and fluid resuscitation. Pigs were randomly allocated into two groups: fluid resuscitation by 4ml/kg of HS/HES, or fluid resuscitation by 10ml/kg of normal saline (NS). Monitoring was based on transpulmonary thermodilution and a pulmonary artery catheter. After 3h, animals were euthanized to measure extravascular lung water (EVLW) by gravimetry.

RESULTS

Blunt chest trauma was followed by a transient collapse and hypoxaemia in both groups. Post-mortem gravimetric assessment demonstrated a significant difference between EVLW in the NS-group (8.1±0.7ml/kg) and in the HS/HES-group (6.2±0.6ml/kg, P=0.038). Based on a pathological EVLW threshold of > 7ml/kg, results indicated that only the NS-group experienced moderate pulmonary oedema, contrary to the HS/HES-group. After haemorrhagic shock, HS/HES infusion enabled the restoration of effective mean arterial pressure and cardiac index. Intrapulmonary shunting increased transiently after fluid resuscitation but there was no significant impairment of oxygenation.

CONCLUSION

In this pig model of lung contusion, the short-term assessment of fluid resuscitation after haemorrhagic shock with 4ml/kg of HS/HES showed that pulmonary oedema was avoided compared to fluid resuscitation with 10ml/kg of NS.

Electrical impedance tomography (EIT) for quantification of pulmonary edema in acute lung injury

Background

Assessment of pulmonary edema is a key factor in monitoring and guidance of therapy in critically ill patients. To date, methods available at the bedside for estimating the physiologic correlate of pulmonary edema, extravascular lung water, often are unreliable or require invasive measurements. The aim of the present study was to develop a novel approach to reliably assess extravascular lung water by making use of the functional imaging capabilities of electrical impedance tomography.

Methods

Thirty domestic pigs were anesthetized and randomized to three different groups. Group 1 was a sham group with no lung injury. Group 2 had acute lung injury induced by saline lavage. Group 3 had vascular lung injury induced by intravenous injection of oleic acid. A novel, noninvasive technique using changes in thoracic electrical impedance with lateral body rotation was used to measure a new metric, the lung water ratio_EIT, which reflects total extravascular lung water. The lung water ratio_EIT was compared with postmortem gravimetric lung water analysis and transcardiopulmonary thermodilution measurements.

Results

A significant correlation was found between extravascular lung water as measured by postmortem gravimetric analysis and electrical impedance tomography (r = 0.80; p < 0.05). Significant changes after lung injury were found in groups 2 and 3 in extravascular lung water derived from transcardiopulmonary thermodilution as well as in measurements derived by lung water ratio_EIT.

Conclusions

Extravascular lung water could be determined noninvasively by assessing characteristic changes observed on electrical impedance tomograms during lateral body rotation. The novel lung water ratio_EIT holds promise to become a noninvasive bedside measure of pulmonary edema.

Thermal Dynamics in Newborn and Juvenile Models Cooled by Total Liquid Ventilation

BACKGROUND

Total liquid ventilation (TLV) consists in filling the lungs with a perfluorocarbon (PFC) and using a liquid ventilator to ensure a tidal volume of oxygenated, CO 2 -free and temperature-controlled PFC. Having a much higher thermal capacity than air, liquid PFCs assume that the filled lungs become an efficient heat exchanger with pulmonary circulation.

OBJECTIVE

The objective of the present study was the development and validation of a parametric lumped thermal model of a subject in TLV.

METHODS

The lungs were modeled as one compartment in which the control volume varied as a function of the tidal volume. The heat transfer in the body was modeled as seven parallel compartments representing organs and tissues. The thermal model of the lungs and body was validated with two groups of lambs of different ages and weights (newborn and juvenile) undergoing an ultrafast mild therapeutic hypothermia induction by TLV.

RESULTS

The model error on all animals yielded a small mean error of -0.1 ±0.4  (°)C for the femoral artery and 0.0 ±0.1   (°)C for the pulmonary artery.

CONCLUSION

The resulting experimental validation attests that the model provided an accurate estimation of the systemic arterial temperature and the venous return temperature.

SIGNIFICANCE

This comprehensive thermal model of the lungs and body has the advantage of closely modeling the rapid thermal dynamics in TLV. The model can explain how the time to achieve mild hypothermia between newborn and juvenile lambs remained similar despite of highly different physiological and ventilatory parameters. The strength of the model is its strong relationship with the physiological parameters of the subjects, which suggests its suitability for projection to humans.

Midterm effects of fluid resuscitation strategies in an experimental model of lung contusion and hemorrhagic shock

BACKGROUND

This study compared three different fluid resuscitation strategies in terms of respiratory tolerance and hemodynamic efficacy in a pig model of blunt chest trauma with lung contusion and controlled hemorrhagic shock. We hypothesized that the choice of fluid resuscitation strategy (type and amount of fluids) may impact differently contused lungs in terms of extravascular lung water (EVLW) 20 h after trauma.

METHODS

Anesthetized female pigs (n = 5/group) received five bolt shots to the right thoracic cage and allowed to hemorrhage for 30 min, with 25 to 30 mL/kg of blood loss. Pigs were randomly assigned to resuscitation groups that maintained a minimum mean arterial blood pressure of 70 mmHg with one of three methods: normal saline (NS), unrestricted normal saline; NOREPI, low-volume normal saline with norepinephrine; or HS-HES, hypertonic saline with hydroxyethyl starch. Control pigs were anesthetized, but received no injury or treatment. After 20 h, animals were killed to measure EVLW by gravimetry.

RESULTS

Fluid loading was significantly different in each group. All three treatment groups had higher EVLW than controls. Moderate, bilateral pulmonary edema was observed in the NS and HS-HES groups. The three treatment groups showed similar reductions in oxygenation. Static pulmonary compliance was diminished in the NS and HS-HES groups, but compliance was similar in NOREPI and control groups. The NOREPI group had pathological lactate levels.

CONCLUSIONS

This study demonstrated the impact of fluid resuscitation on contused lungs. Twenty hours after the trauma, all three resuscitation approaches showed modest clinical consequences, with moderate lung edema and reduced compliance in response to the infused volume.

The evaluation and management of thermal injuries: 2014 update

Burns are among the most common injuries presenting to the emergency department. While burns, especially large ones, may be associated with significant morbidity and mortality, most are minor and can be managed by emergency practitioners and discharged home with close follow-up. In contrast, patients with large burns require aggressive management of their airway, breathing and circulation in order to reduce mortality and morbidity. While early endotracheal intubation of patients with actual or impending airway compromise and aggressive fluid resuscitation have been emphasized, it appears that the pendulum may have swung a bit too far towards the extreme. The current review will briefly cover the epidemiology, pathogenesis and diagnosis of burn injuries with greater emphasis on airway and fluid management. We will also discuss the local management of the burn wound, which is all that is required for most burn patients in the emergency department.

The effect of high-frequency oscillatory ventilation combined with tracheal gas insufflation on extravascular lung water in patients with acute respiratory distress syndrome: a randomized, crossover, physiologic study

PURPOSE

High-frequency oscillation combined with tracheal gas insufflation (HFO-TGI) improves oxygenation in patients with acute respiratory distress syndrome (ARDS). There are limited physiologic data regarding the effects of HFO-TGI on hemodynamics and pulmonary edema during ARDS. The aim of this study was to investigate the effect of HFO-TGI on extravascular lung water (EVLW).

MATERIALS AND METHODS

We conducted a prospective, randomized, crossover study. Consecutive eligible patients with ARDS received sessions of conventional mechanical ventilation with recruitment maneuvers (RMs), followed by HFO-TGI with RMs, or vice versa. Each ventilatory technique was administered for 8 hours. The order of administration was randomly assigned. Arterial/central venous blood gas analysis and measurement of hemodynamic parameters and EVLW were performed at baseline and after each 8-hour period using the single-indicator thermodilution technique.

RESULTS

Twelve patients received 32 sessions. Pao2/fraction of inspired oxygen and respiratory system compliance were higher (P<.001 for both), whereas extravascular lung water index to predicted body weight and oxygenation index were lower (P=.021 and .029, respectively) in HFO-TGI compared with conventional mechanical ventilation. There was a significant correlation between Pao2/fraction of inspired oxygen improvement and extravascular lung water index drop during HFO-TGI (Rs=-0.452, P=.009).

CONCLUSIONS

High-frequency oscillation combined with tracheal gas insufflation improves gas exchange and lung mechanics in ARDS and potentially attenuates EVLW accumulation.

Comparison of quantitative computed tomography analysis and single-indicator thermodilution to measure pulmonary edema in patients with acute respiratory distress syndrome

Objective

To compare quantitative computed tomography (CT) analysis and single-indicator thermodilution to measure pulmonary edema in patients with acute respiratory distress syndrome (ARDS).

Method

Ten patients with ARDS were included. All underwent spiral CT of the thorax for estimating gas content of lung (GV_CT), tissue volume of lung (TV_CT), tissue volume index (TVI), mean radiographic attenuation (CTmean) for the whole lung and gas-to-tissue ratio (g/t). Pulmonary thermal volume (PTV) and extravascular lung water index (ELWI) were determined by the PiCCO plus system. CT or single-indicator thermodilution variables were correlated with respiratory system compliance (Crs), PaO₂/FiO₂, and Acute Physiology And Chronic Health EvaluationII (APACHE II) and Sequential Organ Failure Assessment (SOFA) scores.

Results

1) TV_CT and PTV were positively correlated (r =0.8878; P = 0.0006; equation of regression line: PTV = 1.0793 × TV_CT + 179.8) as were TVI and ELWI (r =0.9459; P < 0.0001; equation of regression line: ELWI = 1.4506 × TVI-8.7792). The bias between TV_CT and PTV as well as TVI and ELWI was -277 ± 217 and 0.62 ± 4.56, respectively. 2) ELWI and CT distribution of lung-tissue compartments were not correlated. 3) CT or single-indicator thermodilution variables were not correlated with Crs, PaO2/FiO2 or APACHE II or SOFA score.

Conclusion

Quantitative CT analysis and single-indicator thermodilution showed good agreement in measuring pulmonary edema.

Clinical review: the role of ultrasound in estimating extra-vascular lung water

The estimation of extra-vascular lung water (EVLW) is an essential component in the assessment of critically ill patients. EVLW is independently associated with mortality and its manipulation has been shown to improve outcome. Accurate assessment of lung water is possible with CT and MR imaging but these are impractical for real-time measurement in sick patients and have been superseded by single thermal dilution techniques. While useful, single thermo-dilution requires repeated calibration and is prone to error, suggesting a need for other monitoring methods. Traditionally the lung was not thought amenable to ultrasound examination owing to the high acoustic impedance of air; however, the identification of artefacts in diseased lung has led to increased use of ultrasound as a point of care investigation for both diagnosis and to monitor response to interventions. Following the initial description of B-lines in association with increased lung water, accumulating evidence has shown that they are a useful and responsive measure of the presence and dynamic changes in EVLW. Animal models have confirmed a correlation with lung gravimetry and the utility of B-lines has been demonstrated in many clinical situations and correlated against other established measures of EVLW. With increasing availability and expertise the role of ultrasound in estimating EVLW should be embedded in clinical practice and incorporated into clinical algorithms to aid decision making. This review looks at the evidence for ultrasound as a valid, easy to use, non-invasive point of care investigation to assess EVLW.

The role for invasive monitoring in acute lung injury

Because acute lung injury (ALI) may arise from diverse and heterogeneous clinical insults, monitoring strategies for patients with ALI are heterogeneous as well. This review divides the monitoring strategies for ALI into three distinct phases. The "at-risk phase" is the period in which patients are at risk for ALI, and interventions may be applied to minimize or eliminate this risk. The "ALI phase" is the period during which ALI has occurred and requires attentive clinical management. The "resolution phase" is the period defined by resolution of ALI and successful discontinuation of mechanical ventilation. These phases are arbitrary, but they provide a useful framework for discussing the temporal changes in patient condition and monitoring goals in ALI.Invasive hemodynamic monitoring has specific roles in each phase of therapy for patients with ALI: pre-ALI, peri-ALI, and post-ALI. The primary goals are to optimize fluid resuscitation to prevent organ dysfunction, including ALI, and if ALI occurs to additional optimize fluid balance vis-à-vis the lung. By judicious application of invasive hemodynamic monitoring, particularly in its more modern iterations, clinicians can optimize the ebb and flow phases common to critically ill patients. This is vitally important given our current and growing understanding of the relationship between fluid balance and important clinical outcomes, multiple organ dysfunction syndrome, and mortality.

Comparison of thermodilution measured extravascular lung water with chest radiographic assessment of pulmonary oedema in patients with acute lung injury

Background

Acute lung injury and the acute respiratory distress syndrome (ALI/ARDS) are characterized by pulmonary oedema, measured as extravascular lung water (EVLW). The chest radiograph (CXR) can potentially estimate the quantity of lung oedema while the transpulmonary thermodilution method measures the amount of EVLW. This study was designed to determine whether EVLW as estimated by a CXR score predicts EVLW measured by the thermodilution method and whether changes in EVLW by either approach predict mortality in ALI/ARDS.

Methods

Clinical data were collected within 48 hours of ALI/ARDS diagnosis and daily up to 14 days on 59 patients with ALI/ARDS. Two clinicians scored each CXR for the degree of pulmonary oedema, using a validated method. EVLW indexed to body weight was measured using the single indicator transpulmonary thermodilution technique.

Results

The CXR score had a modest, positive correlation with the EVLWI measurements (r = 0.35, p < 0.001). There was a 1.6 ml/kg increase in EVLWI per 10-point increase in the CXR score (p < 0.001, 95% confidence interval 0.92-2.35). The sensitivity of a high CXR score for predicting a high EVLWI was 93%; similarly the negative predictive value was high at 94%; the specificity (51%) and positive predictive value (50%) were lower. The CXR scores did not predict mortality but the EVLW thermodilution did predict mortality.

Conclusion

EVLW measured by CXR was modestly correlated with thermodilution measured EVLW. Unlike CXR findings, transpulmonary thermodilution EVLWI measurements over time predicted mortality in patients with ALI/ARDS.

How to perform indexing of extravascular lung water: a validation study

BACKGROUND

Extravascular lung water is a quantitative marker of the amount of fluid in the thoracic cavity besides the vasculature. Indexing to both predicted and actual body weight have been proposed to compare different individuals and provide a uniform range of normal.

OBJECTIVE

We explored extravascular lung water measured by single-indicator transpulmonary thermodilution in a large cohort of patients without cardiopulmonary instability, in order to evaluate current and alternative indexing methods.

DESIGN

Prospective, observational.

SETTING

Neurosurgical ICU in a tertiary referral academic teaching hospital.

PATIENTS

One hundred and one consecutive patients requiring elective brain tumor surgery and postoperative ICU surveillance.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Indexed to predicted body weight, females had a mean extravascular lung water of 9.1 (SD=3.1, range: 5-23) mL/kg and males of 8.0 (SD=2.0, range: 4-19) mL/kg (p<0.001). Values indexed to predicted body weight were inversely correlated with the patient's height (p<0.001). Indexed to the traditionally used actual body weight, data showed a significant relationship to weight (p<0.001) and gender (p<0.05). In contrast, indexing to body height presented a method without dependencies on height, weight, or gender, yielding a uniform 95% confidence interval of 218-430 mL/m. Extravascular lung water increased with positive perioperative fluid balance (p=0.04).

CONCLUSIONS

Using either predicted or actual body weight for indexing extravascular lung water does not lead to independence of height, weight, and gender of the patient. Specifying a fixed range of normal or a uniform upper threshold for all patients is misleading for either method, despite widespread use. Our data suggest that indexing extravascular lung water to height is superior to weight-based methods. As we are not aware of any abnormal hemodynamic profile for brain tumor patients, we propose our findings to be a close approximation to normal values.

Correlation of thermodilution-derived extravascular lung water and ventilation/perfusion-compartments in a porcine model

PURPOSE

This study examines the correlation between the transpulmonary thermodilution derived extravascular lung water content (EVLW) and the ventilation/perfusion-distribution ([Formula: see text]) measured by multiple inert gas elimination (MIGET) in a porcine model.

METHODS

[Formula: see text] measured by micropore membrane inlet mass spectrometry-MIGET (MMIMS-MIGET) and EVLW were simultaneously measured in twelve pigs in the heathy state, with impaired gas exchange from repetitive lung lavage and after 3 h of ventilation. The relationship between [Formula: see text] compartments and EVLW was analysed by linear correlation and regression.

RESULTS

Considerable increases in EVLW and [Formula: see text] mismatching were induced through the lavage procedure. Significant correlations between the EVLW and the [Formula: see text] fractions representing pulmonary shunt and low [Formula: see text] were found. Perfusion to the normal [Formula: see text] regions was inversely correlated to the EVLW.

CONCLUSIONS

Increased EVLW is associated with increased low [Formula: see text] and shunt, but not equal to pulmonary shunt alone. Beneath true shunt EVLW can also be associated with low [Formula: see text] regions.

Clinical review: Respiratory monitoring in the ICU - a consensus of 16

Monitoring plays an important role in the current management of patients with acute respiratory failure but sometimes lacks definition regarding which 'signals' and 'derived variables' should be prioritized as well as specifics related to timing (continuous versus intermittent) and modality (static versus dynamic). Many new techniques of respiratory monitoring have been made available for clinical use recently, but their place is not always well defined. Appropriate use of available monitoring techniques and correct interpretation of the data provided can help improve our understanding of the disease processes involved and the effects of clinical interventions. In this consensus paper, we provide an overview of the important parameters that can and should be monitored in the critically ill patient with respiratory failure and discuss how the data provided can impact on clinical management.

Technological advancements in the care of the trauma patient

INTRODUTION

Medical technology has benefited many types of patients, but trauma care has arguably benefited more from technologic development than almost any other field.

METHODS

A literature review to identify key technological advances in the care of trauma patients was performed.

RESULTS

The advances in trauma care are in great measure due to the integration of many different systems. Medical technology impacts care in the field at the site of the trauma, in the transport to trauma facilities, and care at the trauma center itself. Once at the hospital, technology has impacted care in the trauma bay, intensive care units, the operating room, and in postoperative and long-term care settings. The integration of advancements, however, needs to be examined in a careful systematic fashion to insure that patients will actually derive benefit.

Volume-limited versus pressure-limited hemodynamic management in septic and nonseptic shock

OBJECTIVES

To evaluate the effect of hemodynamic management guided by upper limits of cardiac filling volumes or pressures on durations of mechanical ventilation and lengths of stay in critically ill patients with shock.

DESIGN

Prospective, randomized, clinical trial.

SETTING

Mixed intensive care unit of a large teaching hospital and mixed intensive care unit of a tertiary care, academic medical center.

PATIENTS

A total 120 septic (n = 72) and nonseptic (n = 48) shock patients, randomized (after stratification) to transpulmonary thermodilution (n = 60) or pulmonary artery catheter (n = 60) between February 2007 and July 2009.

INTERVENTIONS

Hemodynamic management was guided by algorithms including upper limits for fluid resuscitation of extravascular lung water (<10 mL/kg) and global end-diastolic volume index (<850 mL/m) in the transpulmonary thermodilution group and pulmonary artery occlusion pressure (<18-20 mm Hg) in the pulmonary artery catheter group for 72 hrs after enrollment.

MEASUREMENTS AND MAIN RESULTS

Primary outcomes were ventilator-free days and lengths of stay in the intensive care unit and the hospital. Secondary outcomes included organ failures and mortality. Cardiac comorbidity was more frequent in nonseptic than in septic shock. Ventilator-free days, lengths of stay, organ failures, and 28-day mortality (overall 33.3%) were similar between monitoring groups. Transpulmonary thermodilution (vs. pulmonary artery catheter) monitoring was associated with more days on mechanical ventilation and longer intensive care unit and hospital lengths of stay in nonseptic (p = .001) but not in septic shock. In both conditions, fewer patients met the upper limit of volume than of pressure criteria at baseline and transpulmonary thermodilution (vs. pulmonary artery catheter) monitoring was associated with a more positive fluid balance at 24 hrs.

CONCLUSIONS

Hemodynamic management guided by transpulmonary thermodilution vs. pulmonary artery catheter in shock did not affect ventilator-free days, lengths of stay, organ failures, and mortality of critically ill patients. Use of the a transpulmonary thermodilution algorithm resulted in more days on mechanical ventilation and intensive care unit length of stay compared with the pulmonary artery catheter algorithm in nonseptic shock but not in septic shock. This may relate to cardiac comorbidity and a more positive fluid balance with use of transpulmonary thermodilution in nonseptic shock.

Extravascular lung water in acute respiratory distress syndrome: potential clinical value, assumptions and limitations

Extravascular lung water has been proposed as a marker of disease severity, response to treatment and mortality in patients with acute respiratory distress syndrome. Here, we discuss its potential value and limitations in clinical practice.

Comparison of chest radiograph scoring to lung weight as a quantitative index of pulmonary edema in organ donors

Quantification of the degree of pulmonary edema in organ donors is useful for assessing the clinical severity of pulmonary edema, determining response to therapy, and as an endpoint for therapeutic trials. Currently, there is no accurate non-invasive method for assessing the degree of pulmonary edema. We tested the performance of a four-quadrant chest radiographic scoring system compared to quantification of pulmonary edema by excised lung weight in 84 donors whose lungs were not used for transplantation. Chest radiographs were taken 3.6 ± 3.0 h prior to organ procurement and were scored by two of the authors. Lungs were excised without perfusion and individually weighed. The chest radiographic scoring system had good performance: correlation between total radiographic score and total lung weight of 0.61, p < 0.001. Performance of the scoring system was improved when chest radiographs with atelectasis were excluded (r = 0.79, p < 0.001). The area under the receiver operator characteristic curve for the detection of moderate pulmonary edema (total lung weight >1000 g) was 0.80. This chest radiographic scoring system may potentially be used to assess the clinical severity of pulmonary edema and may be useful as part of the evaluation of donors for suitability for lung transplantation.

Perioperative pulmonary complications

PURPOSE OF REVIEW

This article reviews current concepts in perioperative pulmonary management.

RECENT FINDINGS

Preoperative risk assessment tools for perioperative pulmonary complications (POPCs) are evolving for both children and adults. Intraoperative management strategies have a demonstrable effect on outcomes. Late POPCs may be preceded by clinical signs.

SUMMARY

POPCs are common and lead to significant resource utilization. Optimal POPC risk mitigation must span all phases of surgical care. Preoperative assessment may identify patients at risk and effectively lower their risk by identifying targeted interventions. Intra-operative strategies impact postoperative outcome. POPCs continue to be a concern for several days postoperatively. We review the current literature on this broad subject with a focus on implementable interventions for the clinician.

Advanced hemodynamic monitoring in critically ill children

Circulatory shock is an important cause of pediatric morbidity and mortality and requires early recognition and prompt institution of adequate treatment protocols. Unfortunately, the hemodynamic status of the critically ill child is poorly reflected by physical examination, heart rate, blood pressure, or laboratory blood tests. Advanced hemodynamic monitoring consists, among others, of measuring cardiac output, predicting fluid responsiveness, calculating systemic oxygen delivery in relation to oxygen demand, and quantifying (pulmonary) edema. We discuss here the potential value of these hemodynamic monitoring technologies in relation to pediatric physiology.

Effect of fluid balance on alveolar-arterial oxygen gradient in mechanically ventilated patients

BACKGROUND

Fluid balance affects outcome in critically ill patients. We studied the effect of fluid balance on oxygen exchange by assessing alveolar-arterial oxygen gradient (PA-a O2) in mechanically ventilated patients. Our primary objective was to evaluate the difference in PA-aO2 and the secondary goal was to evaluate the differences in age and mortality rate.

MATERIALS AND METHODS

This retrospective observational study was performed on patients who were admitted to medical and surgical ICUs of Sari Imam Hospital, Mazandaran University of Medical Sciences, from 2003 to 2009. Daily fluid balance was calculated by input minus output. Thirty patients with continuous positive fluid balance (PFB) and 30 subjects with continuous negative fluid balance (NFB) during 4 consecutive days were enrolled in this study. PA-a O2 was calculated in these two groups.

RESULTS

The mean (±SD) age was 48.9±21.2 yrs. in PFB group (19 males and 11 females) and 37.1±15.7 yrs. in NFB group (25 males and 5 females) which showed a statistically significant difference in age between the two groups (p = 0.017). The 24h, 48h, and 96h fluid balances were 1226(cc)±881, 1311(cc)±751, and 957(cc)±661 in PFB group and -1122(cc)±692, -920(cc)±394, and -1164(cc)±695 in NFB group, respectively. The mean differences (±SD) of PA-a O2 in 24h, 48h, and 96h versus the same value in the admission day were 11.3±39.2, 1.69±51.1, and -1.50±64 in PFB subjects and -21.8±60.8, -27.8±84.9, and -19.3±68.7 in NFB patients. The difference was statistically significant only in the first day of admission (p = 0.015). However, no difference was detected in overall mean oxygen gradient during 96h among the two groups. Mortality rate was significantly higher in PFB patients (P < 0.0001).

CONCLUSION

Positive fluid balance had no significant effect on PA-a O2 but can be used as a predictor of mortality.

Validation of a new transpulmonary thermodilution system to assess global end-diastolic volume and extravascular lung water

INTRODUCTION

A new system has been developed to assess global end-diastolic volume (GEDV), a volumetric marker of cardiac preload, and extravascular lung water (EVLW) from a transpulmonary thermodilution curve. Our goal was to compare this new system with the system currently in clinical use.

METHODS

Eleven anesthetized and mechanically ventilated pigs were instrumented with a central venous catheter and a right (PulsioCath; Pulsion, Munich, Germany) and a left (VolumeView™; Edwards Lifesciences, Irvine, CA, USA) thermistor-tipped femoral arterial catheter. The right femoral catheter was used to measure GEDV and EVLW using the PiCCO(2)™ (Pulsion) method (GEDV(1) and EVLW(1), respectively). The left femoral catheter was used to measure the same parameters using the new VolumeView™ (Edwards Lifesciences) method (GEDV(2) and EVLW(2), respectively). Measurements were made during inotropic stimulation (dobutamine), during hypovolemia (bleeding), during hypervolemia (fluid overload), and after inducing acute lung injury (intravenous oleic acid).

RESULTS

One hundred and thirty-seven paired measurements were analyzed. GEDV(1) and GEDV(2) ranged from 701 to 1,629 ml and from 774 to 1,645 ml, respectively. GEDV(1) and GEDV(2) were closely correlated (r(2) = 0.79), with mean bias of -11 ± 80 ml and percentage error of 14%. EVLW(1) and EVLW(2) ranged from 507 to 2,379 ml and from 495 to 2,222 ml, respectively. EVLW(1) and EVLW(2) were closely correlated (r(2) = 0.97), with mean bias of -5 ± 72 ml and percentage error of 15%.

CONCLUSIONS

In animals, and over a very wide range of values, a good agreement was found between the new VolumeView™ system and the PiCCO™ system to assess GEDV and EVLW.

Assessing the quantity of pulmonary edema in critically ill children

Measuring extravascular lung water may be useful for predicting outcome in adults with acute lung injury. The present commentary briefly reviews the potential role and limitations of extravascular lung water measurement in critically ill children.

Extravascular lung water index measurement in critically ill children does not correlate with a chest x-ray score of pulmonary edema

INTRODUCTION

Extravascular lung water index (EVLWI) can be measured at the bedside using the transpulmonary thermodilution technique (TPTD). The goal of this study was to compare EVLWI values with a chest x-ray score of pulmonary edema and markers of oxygenation in critically ill children.

METHODS

This was a prospective observational study in a pediatric intensive care unit of a university hospital. We included 27 critically ill children with an indication for advanced invasive hemodynamic monitoring. No specific interventions for the purpose of the study were carried out. Measurements included EVLWI and other relevant hemodynamic variables. Blood gas analysis, ventilator parameters, chest x-ray and TPTD measurements were obtained within a three-hour time frame. Two radiologists assessed the chest x-ray and determined a score for pulmonary edema.

RESULTS

A total of 103 measurements from 24 patients were eligible for final analysis. Mean age was two years (range: two months to eight years). Median cardiac index was 4.00 (range: 1.65 to 10.85) l/min/m2. Median EVLWI was 16 (range: 6 to 31) ml/kg. The weighted kappa between the chest x-ray scores of the two radiologists was 0.53. There was no significant correlation between EVLWI or chest x-ray score and the number of ventilator days, severity of illness or markers of oxygenation. There was no correlation between EVLWI and the chest x-ray score. EVLWI was significantly correlated with age and length (r2 of 0.47 and 0.67 respectively).

CONCLUSIONS

The extravascular lung water index in critically ill children does not correlate with a chest x-ray score of pulmonary edema, nor with markers of oxygenation.