What is transpulmonary thermodilution?

From the Guidelines

Transpulmonary thermodilution is a valuable technique in critical care settings for assessing cardiovascular function and guiding fluid management, particularly in patients with shock, acute respiratory distress syndrome, or severe sepsis, as it provides comprehensive hemodynamic data with less invasiveness compared to pulmonary artery catheters 1.

Key Principles of Transpulmonary Thermodilution

• The technique involves injecting a cold saline solution into a central vein and measuring temperature changes as the solution passes through the heart, lungs, and arterial system using a thermistor-tipped catheter placed in a large artery.
• It provides important hemodynamic parameters including cardiac output, global end-diastolic volume, extravascular lung water, and pulmonary vascular permeability index.
• The underlying principle relies on the Stewart-Hamilton equation, where the area under the thermodilution curve correlates with cardiac output.

Clinical Applications

• Transpulmonary thermodilution is particularly useful in managing patients with complex hemodynamic conditions, allowing clinicians to distinguish between different types of shock and optimize fluid therapy.
• It is beneficial in patients with acute respiratory distress syndrome (ARDS) for evaluating extravascular lung water and the pulmonary vascular permeability index, which helps in assessing the risk of fluid overload 1.
• Maintenance of euvolemia, which can be guided by transpulmonary thermodilution, is crucial in preventing delayed cerebral ischemia (DCI) and improving functional outcomes after subarachnoid hemorrhage, as evidenced by recent guidelines 1.

Considerations for Use

• While transpulmonary thermodilution offers comprehensive hemodynamic data, its interpretation requires careful consideration of the patient's clinical context for optimal decision-making.
• The technique is less invasive than pulmonary artery catheterization but still requires precise placement of the catheter and careful calibration for accurate measurements.
• Recent studies and guidelines support the use of transpulmonary thermodilution in specific clinical scenarios, highlighting its potential to improve patient outcomes by guiding fluid management and hemodynamic support 1.

From the Research

Transpulmonary Thermodilution Overview

• Transpulmonary thermodilution (TPTD) is a technique that provides a full haemodynamic assessment through cardiac output and other indices 2, 3, 4.
• It is an invasive but well-tolerated, multiparametric, advanced cardiopulmonary monitoring technique, allowing a comprehensive assessment of cardiopulmonary condition 3.
• TPTD devices invasively measure not only cardiac output but also several other haemodynamic variables estimating cardiac preload, cardiac preload, systolic function, the lung oedema and systolic function, the lung oedema and the pulmonary permeability 2.

Clinical Applications

• The greatest advantage of TPTD is to measure extravascular lung water and pulmonary permeability, which may be useful to diagnose acute respiratory distress syndrome and manage fluid therapy in various critical diseases 2, 4.
• TPTD provides several indices that may help in making decisions during the therapeutic management of haemodynamically unstable patients 2, 3.
• It allows a rapid detection of left ventricular systolic failure and provides a full cardiovascular evaluation that allows one to answer many questions regarding haemodynamic management 4.

Technical Aspects

• The technique involves the analysis of the thermodilution curve recorded at the tip of an arterial catheter after the injection of a cold bolus in the venous circulation 4, 5.
• TPTD provides continuous and real-time monitoring of cardiac output when coupled with pulse contour analysis, which is not possible with the pulmonary artery catheter 4, 5.
• The reproducibility of TPTD measurements is high, with an overall reproducibility of 6.1 ± 2.0 % in adult studies and 3.9 ± 2.9 % in pediatric studies 6.

Limitations and Side-Effects

• The technique has potential limits and side-effects, which are discussed in the literature 2, 3.
• TPTD does not allow the distinct estimation of right and left cardiac function and does not provide a full evaluation of the cardiac structure and function 4.
• However, it is easier and faster to perform than echocardiography and provides unique advantages in estimating extravascular lung water and pulmonary vascular permeability 4.