Extravascular Lung Water in Critical Care - Recent Advances and Clinical Applications
Authors: Mathieu Jozwiak, Jean-Louis Teboul, Xavier Monnet
DOI / Source: https://doi.org/10.1186/s13613-015-0081-9
Date: 06 November 2015
Reading level: Intermediate
Why This Matters for Freedivers
Freedivers sometimes run into lung issues like SIPE/immersion pulmonary edema or “lung squeeze,” where extra fluid in the lungs can reduce oxygen levels and breathing comfort. This paper explains what “extravascular lung water” actually means, why it’s dangerous (it worsens gas exchange and stiffens the lungs), and how clinicians think about whether lung fluid is coming from “pressure overload” or from a leaky lung barrier—ideas that map well to understanding post-dive cough, low SpO₂, and recovery decisions.
Synopsis
When people say “fluid in the lungs,” they’re usually describing a real physiological problem: extra water collecting in the lung tissue and air spaces, making it harder to exchange oxygen and carbon dioxide. This review breaks that concept down into a measurable quantity called extravascular lung water (EVLW)—the water in the lungs outside the blood vessels. It explains how EVLW rises in two main ways: (1) increased pressure in lung capillaries pushing fluid outward (classic hydrostatic pulmonary edema), and (2) increased permeability (a “leakier” alveolocapillary barrier), which is the hallmark of ARDS. In real life, these can overlap.
A big part of the paper is about measurement. Chest X-rays and listening with a stethoscope can suggest edema, but they’re not great for quantifying it. The most practical bedside method described is transpulmonary thermodilution, which estimates EVLW by tracking how a cold saline bolus travels through the chest circulation. The authors summarize validation work (including comparisons with older double-indicator methods and post-mortem “true” measurements) and explain why EVLW should be indexed to predicted body weight (EVLWI), not actual weight, to make comparisons meaningful.
The review also introduces PVPI (pulmonary vascular permeability index)—a derived index meant to reflect how “leaky” the lung barrier is. Clinically, EVLWI and PVPI can help guide fluid decisions: if EVLWI is already high, adding more fluid risks worsening lung edema; if PVPI is high, fluid is more likely to leak into the lungs. The paper is very practical about how these numbers can support safer resuscitation in septic shock and ARDS, and how trending EVLWI over time can help predict outcomes and guide “de-escalation” (fluid removal) once the patient is stable.
Abstract
Extravascular lung water (EVLW) is the amount of fluid that is accumulated in the interstitial and alveolar spaces. In lung oedema, EVLW increases either because of increased lung permeability or because of increased hydrostatic pressure in the pulmonary capillaries, or both. Increased EVLW is always potentially life-threatening, mainly because it impairs gas exchange and reduces lung compliance. The only technique that provides an easy measurement of EVLW at the bedside is transpulmonary thermodilution. The validation of EVLW measurements by thermodilution was based on studies showing reasonable correlations with gravimetry or thermo-dye dilution in experimental and clinical studies. EVLW should be indexed to predicted body weight. This indexation reduces the proportion of ARDS patients for whom EVLW is in the normal range. Compared to non-indexed EVLW, indexed EVLW (EVLWI) is better correlated with the lung injury score and the oxygenation and it is a better predictor of mortality of patients with acute lung injury or acute respiratory distress syndrome (ARDS). Transpulmonary thermodilution also provides the pulmonary vascular permeability index (PVPI), which is an indirect reflection of the integrity of the alveolocapillary barrier. As clinical applications, EVLWI and PVPI may be useful to guide fluid management of patients at risk of fluid overload, as during septic shock and ARDS. High EVLWI and PVPI values predict mortality in several categories of critically ill patients, especially during ARDS. Thus, fluid administration should be limited when EVLWI is already high. Whatever the value of EVLWI, PVPI may indicate that fluid administration is particularly at risk of aggravating lung oedema. In the acute phase of haemodynamic resuscitation during septic shock and ARDS, high EVLWI and PVPI values may warn of the risk of fluid overload and prevent excessive volume expansion. At the post-resuscitation phase, they may prompt initiation of fluid removal thereby achieving a negative fluid balance.