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ARDS Advanced Monitoring

Challenge:
Optimize treatment of acute respiratory distress syndrome (ARDS)

The life of the critically ill patient depends on the right decision for the next therapeutic step. With ARDS this becomes even more critical because the injured lung has an increased lung permeability resulting in pulmonary edema. The need for an early clear picture of the patient’s hemodynamic status in order to apply appropriate therapy is essential.  The speed of therapy influences outcome.

How can fluid status be measured?

The last 2 decades have witnessed the introduction and evolution of the transpulmonary thermodilution (TPTD) technique for measuring EVLW and PVPI. (tagami)  This gives two new tools extravascular lung water index (EVLI) and pulmonary vascular permeability index (PVPI). EVLWI and PVPI may be used as criteria indicating the risk of fluid administration. [1]

Extravascular lung water is an accumulation of fluid in the interstitium of the lung tissue and / or the alveoli.

Pulmonary vascular permeability index (PVPI) is an indirect reflection of the integrity of the alveolo-capillary barrier.

The accuracy of transpulmonary thermodilution for the quantification of pulmonary edema has been confirmed in several experimental and clinical studies (kuzkov, tagami, katzenelson)

Ref. [2] [3] [4]

Can we quantify pulmonary edema?

Examples of chest X-rays that do not reflect the level of pulmonary edema.

Pulmonary edema

The usual clinical approach to assess pulmonary edema is the evaluation of a chest x-ray. This is very challenging as the chest x-ray is a density measurement, influenced by all compartments in the chest like bones, muscles, tissue layers, blood, blood vessels, air, tissue edema, plural effusion and possibly also pulmonary edema. Thus, in clinical studies it was demonstrated that chest x-ray evaluation for pulmonary edema is very inaccurate when comparing it to the direct quantification by transpulmonary thermodilution (Brown, Saugel, Lemson).

How can this be of a clinicial benefit?

The need to identify and quantify pulmonary edema in complex syndromes such as ARDS can influence outcomes.  Regardless of the cause, this ELWI accumulation impairs respiratory gas exchange, resulting in respiratory distress. Newer tools such as EVLWI and PVPI can be used to establish the existence, evaluate the severity and identify the nature of ARDS.[5]

Accurate and objective diagnoses can be made for ARDS patients using EVLW and PVPI.[5] PVPI more than 3 with EVLW > 10 ml/kg represents increased permeability pulmonary edema, or ARDS.[5]

What does this all mean?

In the context of ARDS, some small studies suggest that management based on protocols including EVLWI measurements is safe, leads to a lower cumulative fluid balance, improves ICU mortality, and reduces the duration of mechanical ventilation and of ICU stay.[6]

 
ARDS is progressive with an early treatment window that can be exploited.  EVLW and PVPI measurement will open the door to future ARDS clinical practice and research, and have potential to be included in the future ARDS definition.

All references

  1. 1. Felbinger TW et al. Comparison of pulmonary arterial thermodilution and arterial pulse contour analysis: evaluation of a new algorithm. J Clin Anesth 2002;14(4): 296-301

  2. 2. Kuzkov VV et al. Extravascular lung water after pneumonectomy and one-lung ventilation in sheep. Crit Care Med 2007; 35(6): 1550-1559

  3. 3. Tagami T et al. Validation of extravascular lung water measurement by single transpulmonary thermodilution: human autopsy study. Crit Care 2010; 14(5): R162

  4. 4. Katzenelson R et al. Accuracy of transpulmonary thermodilution versus gravimetric measurement of extravascular lung water. Crit Care Med 2004; 32(7): 1550-1554

  5. 5. Zollner C et al. Beat-to-beat measurement of cardiac output by intravascular pulse contour analysis: a prospective criterion standard study in patients after cardiac surgery. J Cardiothorac Vasc Anesth 2000;14(2): 125-129

  6. 6. Rauch H et al. Pulse contour analysis versus thermodilution in cardiac surgery patients. Acta Anaesthesiol Scand 2002;46(4): 424-429

  7. 7. Extravascular lung water measurements in acute respiratory distress syndrome: why, how, and when? Current Opinion in Critical Care: June 2018 - Volume 24 - Issue 3 - p 209–215

  8. 8. ICU management based on PiCCO parameters reduces duration of mechanical ventilation and ICU length of stay in patients with severe thoracic trauma and acute respiratory distress syndrome Ann Intensive Care. 2016; 6: 113.

  9. 9. Extravascular lung water in critical care: recent advances and clinical applications
    Annals of Intensive Care20155:38

  10. 10. Extravascular lung water and pulmonary vascular permeability index as markers predictive of postoperative acute respiratory distress syndrome: a prospective cohort investigation