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 Table of Contents  
Year : 2018  |  Volume : 2  |  Issue : 4  |  Page : 237-241

Extravascular lung water measurement in critically ill patients

1 Department of Anesthesiology, Center of Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg Eppendorf, Martinistr, Hamburg, Germany
2 Anesthesiology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Date of Submission20-Jun-2018
Date of Decision21-Jul-2018
Date of Acceptance24-Jul-2018
Date of Web Publication11-Dec-2018

Correspondence Address:
Dr. Seyed Mohammadreza Hashemian
Anesthesiology Research Center, Shahid Beheshti University of Medical Sciences, Tehran
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/bbrj.bbrj_77_18

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In intensive care patients, due to increase in hydrostatic pressure and hyperpermeability state, pulmonary edema occurs. In this review, we discussed about definition and amount of extravascular lung water index (EVLWI) which relates to an increasing pulmonary capillary hydrostatic pressure or increasing capillary permeability. EVLWI-to-intrathoracic blood volume ratio is useful in determining the cause of pulmonary edema. EVLWI can be helpful in approximation of the amount of fluid overload and capillary leak in acute inflammatory injury. This is identified as a prognostic marker that is related to respiratory function and mortality in patients with acute respiratory distress syndrome and sepsis. Usage of EVLWI for determining of pulmonary edema in children would be beneficial.

Keywords: Acute respiratory distress syndrome, critically ill patients, extravascular lung water, pulmonary edema

How to cite this article:
Khosravi PM, Reuter D, Kassiri N, Hashemian SM. Extravascular lung water measurement in critically ill patients. Biomed Biotechnol Res J 2018;2:237-41

How to cite this URL:
Khosravi PM, Reuter D, Kassiri N, Hashemian SM. Extravascular lung water measurement in critically ill patients. Biomed Biotechnol Res J [serial online] 2018 [cited 2022 Aug 14];2:237-41. Available from: https://www.bmbtrj.org/text.asp?2018/2/4/237/247245

  Introduction Top

A lot of critical conditions can be associated with the assemblage of lung water resulting in pulmonary edema. During systemic inflammation and sepsis, acute respiratory distress syndrome (ARDS), multiple trauma with severe blood loss, burns, pancreatitis, ischemia-reperfusion damage, and other conditions, the discharge of pro-inflammatory agents may increase pulmonary microvascular permeability and pressure, therefore, cause to fluid gathering in the lungs.[1],[2],[3],[4],[5],[6],[7],[8],[9],[10] In contrast to hyperpermeability occurrences, increase in hydrostatic pressure in pulmonary circulation, during cardiac failure, is the main mechanism for edema. However, enhance in extravascular lung water index (EVLWI) is a common sign in both noncardiogenic and cardiogenic sources of airway edema.[1] Recent analytic studies have demonstrated that EVLWI relates to the hardness of lung injury and has a prognostic advantage, particularly in sepsis and ARDS. Several categories of both pediatric and adults critically ill patients including anyone who has noncardiogenic or cardiogenic airway edema, extensive fluid shifts, and serious alternations in microvascular permeability have been shown to benefit from monitoring EVLWI.

  Definition Top

In 1896, the elements which affect fluid transfer across semipermeable membranes such as capillaries were illustrated as Starling forces.[11] The finding was based on mesh movement of fluids between sections associated to capillary and interstitial oncotic pressures, capillary and interstitial hydrostatic pressures, and coefficients of capillary permeability [Figure 1]. If the starling forces are unbalanced, of fluid may be gathered within the extravascular region and pulmonary edema happens. This is related to an increasing capillary permeability or pulmonary capillary hydrostatic pressure.
Figure 1: A schematic representation of Starling forces based on net movement of fluids between compartments in relation to capillary and interstitial oncotic pressures, capillary and interstitial hydrostatic pressures, and coefficients of capillary permeability

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  Measurement Top

Double-indicator technique was bedside method which is used to measure EVLW. This approach needs the synchronal injection of an intravascular dye marker, which remains in the intravascular region and a diffusible (cold saline) indicator, which will be dispensed through the thorax. EVLW calculates according to differences in the dilution curves.[12] The change in the mean transit time multiplied by the cardiac output explained the extravascular thermal distribution volume, that is, intrathoracic thermal volume through cold saline – intrathoracic blood volume (ITBV) through dye dilution = EVLW. This method needs length time and has not been generally utilized. The single-indicator approach utilizes a thermal marker, cold saline, to compute EVLW. In this method, cold saline is injected using a central venous catheter. On a femoral arterial catheter, there is the thermistor tip that calculates the downstream alternation in heat in the abdominal aorta. Sakka et al. quantified the association between the ITBV and the global end-diastolic volume (GEDV). GEDV is a complete volume in the end of diastole within four cavities of the heart.[13] The equation is ITBV = 1.25 × GEDV - 28.4 mL. In other studies, it has been confirmed that there is a similar correlation between ITBV and GEDV.[14],[15] The EVLW represents both interstitial and alveolar fluid. The gravimetric approach, the gold standard examines for EVLW, compares the accuracy of this technique.[16],[17]

  Extravascular Lung Water and Acute Respiratory Distress Syndrome Top

Although ARDS has been recognized as an acute, diffuse inflammatory lung damage resulting in enhanced pulmonary vascular permeability, loss of airway tissue, and increased lung weight, none of the proposed signs assessed the indication of ARDS, enhance in airway microvascular permeability.[18] Both American-European Consensus Conference definition and the Berlin definition may involve a wide range of respiratory deficiency without an addition in pulmonary microvascular permeability.

Diagnosis of ARDS would be more realistic using more precise physiological indicators. EVLW is one probable marker and is associated to lung function and death in patients with sepsis. Increased EVLW suggests further diagnostic value for airway damage. Increased EVLW enhances the probability of death [Figure 2].
Figure 2: EVLW and PVPI measurements in ARDS. EVLW: Extravascular lung water, PVPI: Pulmonary vascular permeability index, ARDS: Acute respiratory distress syndrome

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According to Berlin definition, different levels of ARDS including mild, moderate, and severe ARDS have been defined on the basis of the degree of hypoxemia. Progress from one level to another proposes increase in fatality. An assessment of both EVLW and pulmonary blood volume can be determined through the transpulmonary thermodilution technique. The ratio of these two criteria is defined as the pulmonary vascular permeability index (PVPI). This ratio shows the degree of airway microvascular permeability,[19] which is pathognomonic for ARDS [Figure 2]. A number of studies propose that the ratio of EVLW-to-ITBV can be helpful to identify the cause of pulmonary edema.[20],[21],[22] For pulmonary edema, a big EVLW/ITBV ratio may suggest an enhanced permeability as the cause, and a small ratio can support hydrostatic origin. Recently, Kushimoto et al.[23] published a multicenter cohort study that illustrated PVPI to be a useful diagnostic criterion to identify ARDS in pulmonary edema. They concluded that the severity classes of ARDS defined by the Berlin definition may be related to increased EVLW and pulmonary microvascular permeability in participants who comply the Berlin definition of ARDS with EVLWI >10 mL/kg.

The consolidation of airway tissue and generation of atelectasis is a main part in the pathogenesis of ARDS.[24] The increase of the extravascular fluid volume may lead to pressing in the alveoli and airways. The alveolar recruitment maneuver (RM) may enlarge and continue compressed lung tissue through periodic short-acting enhancement in the pulmonary pressure. In intensive care patients, RM may increase the oxygenation ratio (PaO2/FiO2) by 29%–50% of ARDS patients.[25],[26],[27]

In a prospective report, 17 adult participants with ARDS were studied and it was seen that in ARDS patients, the reaction to a RM can be associated to the intensity of airway edema. In patients with increased EVLWI, the RM is less useful.[28]

Enhanced EVLW has been determined as a powerful indicator of death in ARDS. In a retrospective study on 373 patients, Sakka et al. represented that EVLW was higher in no survivor patients in comparison to survivor patients (median: 14.3 mL/kg vs. 10.2 mL/kg, resp., P < 0.0001).[29] The study also determined a dose efficient with morbidity lowest in the group with EVLW <7mL/kg (<30%), intermediate in the groups <7–14mL/kg (40%) and 15–20 mL/kg (60%), and highest in the group with EVLW >20 mL/kg (80% mortality). Survivors were discriminated from no survivors by threshold of 15 mL/kg (P = 0.002). Another study for 33 medical Intensive Care Unit (ICU) patients presented that the rate of in-hospital survival for participants with very severe sepsis, and a high EVLW (>10 ml/kg) was lower than those with a low EVLW (<10 ml/kg) (15% vs. 67.7%, respectively, P < 0.001).[30]

In a report, authors compared protocol - (EVLW-) guided treatment to usual hemodynamic management (pulmonary artery wedge pressure guided) in 48 intensive care patients.[12] The investigation showed a lower time on mechanical ventilation, lower mortality, well tolerated, and safe method for ARDS patients. In a follow-up study, Mitchell et al. enrolled 101 patients that compared the EVLW- and wedge pressure-guided strategies.[31] The EVLW group had a lower positive fluid balance, less ventilator days, and a lower hospital stay.

  Extravascular Lung Water and Acute Inflammatory Injury Top

In acute inflammatory injury, a cascade of pro-inflammatory mediators leads to capillary leak, microcirculatory dysfunction, and distributive shock. In the initial stage of shock, progressive and goal-directed fluid treatment can be helpful, but following over resuscitation enhances microvascular hydrostatic pressure and may cause to interstitial fluid collecting. This fluid overload is separately related to organ dysfunction, intra-abdominal hypertension, and weaker result. Contrarily, clinical outcomes and even increasing fluid elimination were recovered by a conservative fluid technique.[28]

Lungs are mostly exposed to the pro-inflammatory cascade and obtaining the total cardiac output, so they are important sight into dynamic microcirculatory alternations at the time of systemic inflammation. Bedside estimation of EVLWI provides the measurement of the extent of fluid overload and capillary leak.

In an observational investigation, 123 mechanically ventilated patients with extended hemodynamic monitoring were studied, and it was revealed that there is an essential relation between capillary leak index, EVLWI kinetics, intra-abdominal pressure, and fluid balance in mechanically ventilated patients, related to organ dysfunction and weak prognosis.[31]

  Extravascular Lung Water Index Calculation in Critically Ill Children Top

In adults, EVLWI measurement associates with hardness of illness and shows pulmonary edema. In adults, an EVLWI between 3 and 7 mL/kg is reported normal. Levels above 10 mL/kg are related to clinical pulmonary edema. Moreover, fluid overload is associated with weak outcome in children, and it may be useful to utilize the EVLWI estimation for detection of pulmonary edema and as a criterion for managing treatment. The existence and amount of pulmonary edema in children are typically detected with the bedside chest X-ray. Severity of pulmonary edema reveals by oxygenation criteria such as PaO2/FiO2(P/F ratio) and A-a gradient.[32],[33] Results of a prospective observational study involved 27 critically ill children with an indication for advanced invasive hemodynamic monitoring revealed that EVLWI measurements do not associate with a chest X-ray score of airway edema. Neither chest X-ray score nor the lung water index of pulmonary edema associated with signs of hardness of disease, oxygenation, or pediatric ICU length of stay in a general population of critically ill children. Besides, results showed that in children, EVLW is conversely associated to age.[32],[33]

  Extravascular Lung Water in Sepsis Top

Severe sepsis defined as systemic inflammatory response syndrome in the present of pathologic infection and acute organ dysfunction. Sepsis is related to high death rate in intensive care patients. Respiratory failure and ARDS are the most common complication of sepsis.[34] During sepsis, under induction of infectious agents, inflammatory products such as neutrophil elastase, protease, nitric oxide, and collagenase A, B released. This is result to increase in capillary permeability.[35] On the other hand, alveolar injury due to inflammatory reactions causes capillary endothelium and alveolar epithelium destruction which is associated with accumulation of fluid in alveolar and interstitial space.[36] Monitoring of EVLW may be beneficial in both pediatric and adult critically ill patients. Therefore, EVLWI can be used as a prognostic indicator for patients with severe sepsis.

  The Prognostic Value of Extravascular Lung Water Top

It is shown that EVLWI has prognostic value in intensive care patients. High level of EVLW index is related to severity of respiratory function and mortality due to ARDS, severe sepsis, septic shock, and burned patients.[37]

EVLWI has correlation to the severity of lung injury; therefore, increased EVLWI suggests the diagnostic value and increasing mortality rate for lung injury.[38] Patients with high level of EVLW experience severe illness with higher lung damage score and less surveillance in ICU.[39]

  Conclusion Top

A large number of critical conditions can appear with the accumulation of lung water and progress of pulmonary edema. Both cardiogenic and noncardiogenic origin of edema increase EVLWI. Recent clinical studies have shown that EVLWI is an oracle who determines ARDS severity. Moreover, it may be a suitable predictor for morbidity and organ default. These relations need validation through extra clinical investigation and critical care exercise. EVLWI has another miracle on determining pediatric pulmonary edema. However, still, additional investigations are required before lung water can be utilized in pediatric clinical guidelines.

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