Precision of the transpulmonary thermodilution measurements
Monnet et al. Critical Care
Precision of the transpulmonary thermodilution measurements
Xavier Monnet 0 1
Romain Persichini 0 1
Mariem Ktari 0 1
Mathieu Jozwiak 0 1
Christian Richard 0 1
Jean-Louis Teboul 0 1
0 Univ Paris-Sud, Faculte de medecine Paris-Sud , EA 4046, Le Kremlin-Bicetre, F-94270 France
1 AP-HP, Hopitaux Universitaires Paris-Sud, service de reanimation medicale, Le Kremlin-Bicetre , F-94270 France
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, 6C) 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.
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Introduction
Transpulmonary thermodilution (TPTD) is increasingly
used in the clinical area [1], but its precision for
measuring CI and the number of cold boluses that must be
replicated is a matter of debate. Indeed, a recent study
concluded that calculating the mean of two TPTD
measurements was enough for reaching an acceptable level
of precision [2] but it included a limited number of
patients. Additionally, for another transpulmonary
dilution technique using the lithium and not the cold
dilution, it has been recently shown that at least three
dilution measurements were required for reaching an
* Correspondence:
1AP-HP, Hpitaux Universitaires Paris-Sud, service de ranimation mdicale,
Le Kremlin-Bictre, F-94270 France
Full list of author information is available at the end of the article
acceptable precision. In addition to CI, TPTD also
allows estimating the global end-diastolic volume
(GEDV, that is, the volume of the cardiac cavities at
end-diastole) and the extravascular lung water (EVLW,
that is, the volume of the pulmonary edema) [3]. The
precision of EVLW measurement derived from TPTD
has been reported by some studies [2,4-6], but again,
the number of cold injectates that is needed for
obtaining an acceptable reproducibility of the measurements
remains to be determined. As for GEDV, its precision
has been investigated in one study only [2].
Thus, we attempted to answer the important practical
question to know the number of thermal injections that
must be performed for assessing CI, GEDV and EVLW
with an acceptable precision. In particular, we evaluated
the number of thermodilution measurements that must
be replicated for detecting changes in CI, GEDV and
EVLW 15% with an acceptable confidence. We also
analyzed the factors influencing the precision of the
measurements.
collected. No thermodilution curve was rejected from
analysis. Treatments were kept unchanged and patients
were not mobilized during the study period. All
measurements were performed by the same operator (RP).
Materials and methods
Patients
This prospective study was conducted in the 15-bed
intensive care unit of a university hospital. As approved
by the Institutional Review Board of our institution,
patients were included according to an emergency
procedure. A deferred informed consent was asked from
the patients surrogate as soon as possible. As he/she
recovered consciousness, a deferred informed consent
was asked from the patient. If the patient or his/her
next of kin refused to consent, the patients data were
not entered into analysis.
Patients were included if they had a fem (...truncated)