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Precision of the transpulmonary thermodilution measurements
Xavier Monnet1, Romain Persichini, Mariem Ktari
1AP-HP, Hôpitaux Universitaires Paris-Sud, Service de Réanimation Médicale, Le Kremlin-Bicêtre F-94270, France. xavier.monnet@bct.aphp.fr
Insights
For accurate cardiac index (CI), indexed global end-diastolic volume (GEDVi), and indexed extravascular lung water (EVLWi) measurements using transpulmonary thermodilution, at least three cold bolus injections are recommended. This ensures acceptable precision and clinical relevance for patient monitoring.
Area of Science:
- Critical care medicine
- Cardiovascular physiology
- Hemodynamic monitoring
Background:
- Transpulmonary thermodilution is a key method for assessing hemodynamic parameters.
- Optimizing the precision of cardiac index (CI), indexed global end-diastolic volume (GEDVi), and indexed extravascular lung water (EVLWi) measurements is crucial for patient management.
- The optimal number of cold bolus injections for reliable measurements is not definitively established.
Purpose of the Study:
- To determine the minimum number of cold bolus injections required for acceptable precision in transpulmonary thermodilution measurements.
- To evaluate the precision and least significant change for CI, GEDVi, and EVLWi based on varying numbers of injections.
Main Methods:
- A prospective study involving 91 hemodynamically stable patients monitored with a PiCCO2 device.
- Five successive cold saline (15 mL, 6 °C) bolus injections were administered to each patient.
- Measurements of CI, GEDVi, and EVLWi were recorded after each injection, and data were analyzed for precision and least significant change.
Main Results:
- Averaging three bolus injections resulted in precision below 10% for CI, GEDVi, and EVLWi (8%).
- With three injections, the least significant change for these parameters was below 15% (12%), considered clinically relevant.
- Averaging two injections yielded a precision of 8-10% and a least significant change of 14%, potentially limiting clinical interpretation.
Conclusions:
- At least three cold bolus injections are recommended for transpulmonary thermodilution to achieve acceptable precision in measuring CI, GEDVi, and EVLWi.
- This number of injections ensures that the measured changes are clinically relevant and statistically significant.
- Optimizing injection protocols enhances the reliability of hemodynamic monitoring in critically ill patients.
Introduction:
We wanted to determine the number of cold bolus injections that are necessary for achieving an acceptable level of precision for measuring cardiac index (CI), indexed global end-diastolic volume (GEDVi) and indexed extravascular lung water (EVLWi) by transpulmonary thermodilution.
Methods:
We included 91 hemodynamically stable patients (age 59 (25% to 75% interquartile range: 39 to 79) years, simplified acute physiologic score (SAPS)II 59 (53 to 65), 56% under norepinephrine) who were monitored by a PiCCO2 device. We performed five successive cold saline (15 mL, 6 °C) injections and recorded the measurements of CI, GEDVi and EVLWi.
Results:
Considering five boluses, the coefficient of variation (CV, calculated as standard deviation divided by the mean of the five measurements) was 7 (5 to 11)%, 7 (5 to 12)% and 7 (6 to 12)% for CI, GEDVi and EVLWi, respectively. If the results of two bolus injections were averaged, the precision (2 × CV/√ number of boluses) was 10 (7 to 15)%, 10 (7 to 17)% and 8 (7 to 14)% for CI, GEDVi and EVLWi, respectively. If the results of three bolus injections were averaged, the precision dropped below 10%, that is, the cut-off that is generally considered as acceptable (8 (6 to 12)%, 8 (6 to 14)% and 8 (7 to 14)% for CI, GEDVi and EVLWi, respectively). If two injections were performed, the least significant change, that is, the minimal change in value that could be trusted to be significant, was 14 (10 to 21)%, 14 (10 to 24)% and 14 (11 to 23)% for CI, GEDVi and EVLWi, respectively. If three injections were performed, the least significant change was 12 (8 to 17)%, 12 (8 to 19)% and 12 (9 to 19)% for CI, GEDVi and EVLWi, respectively, that is, below the 15% cut-off that is usually considered as clinically relevant.
Conclusions:
These results support the injection of at least three cold boluses for obtaining an acceptable precision when transpulmonary thermodilution is used for measuring CI, GEDVi and EVLWi.
