Transient stop-flow arm arterial-venous equilibrium pressure measurement: determination of precision of the technique.
Transient stop-flow arm arterial-venous equilibrium pressure (Pmsf-arm) is a validated technique for measuring the mean systemic filling pressure (Pmsf). Pmsf is a functional measure of the effective intravascular volume status. This study aims to assess the precision of the Pmsf-arm measurement. Pmsf-arm was measured by inflating a pneumatic tourniquet around the upper arm 50 mmHg above systolic pressure for 60 s, four times consecutively, with an interval of 5 min. Arterial (Pa) and venous pressure (Pv) were recorded every 10 s. Pa-Pv difference was calculated to determine the stop-flow time. The coefficient error (CE) was determined and used to derive the least significant change (LSC) in Pmsf-arm that this technique could reliably detect. The rANOVA test was used to compare repeated measurements of the four determinations of Pmsf-arm. 80 measurements of Pmsf-arm were studied in 20 patients. Pa and Pv equalised after 60 s of inflation (Pa-Pv difference 0 ± 0.01 mmHg). There were no significant differences of Pmsf-arm values among determinations. For a single measurement, the CE was 5 % (±2 %) and the LSC was 14 % (±5 %). Averaging two, three and four measurements the CE improves to 4 % (±1 %), 3 % (±1 %) and 3 % (±1 %) respectively, and the LSC was reduced to 10 % (±4 %), 8 % (±3 %) and 7 % (±3 %) respectively. One measurement of Pmsf-arm can reliably detect changes on Pmsf-arm of 14 %. The precision of Pmsf-arm technique improves when averaging two or three measurements.
Intensive Care Directorate, St George's University Hospitals NHS Foundation Trust and St George's University of London, Blackshaw road, Tooting, London, SW17 0QT, UK. hollmann.aya@nhs.net.
Hollmann D
HD
Aya
Intensive Care Directorate, St George's University Hospitals NHS Foundation Trust and St George's University of London, Blackshaw road, Tooting, London, SW17 0QT, UK. andrewrhodes@nhs.net.
Andrew
A
Rhodes
Intensive Care Directorate, St George's University Hospitals NHS Foundation Trust and St George's University of London, Blackshaw road, Tooting, London, SW17 0QT, UK. snick@doctors.org.uk.
Nick
N
Fletcher
Intensive Care Directorate, St George's University Hospitals NHS Foundation Trust and St George's University of London, Blackshaw road, Tooting, London, SW17 0QT, UK. Michael.Grounds@stgeorges.nhs.uk.
R Michael
RM
Grounds
Intensive Care Directorate, St George's University Hospitals NHS Foundation Trust and St George's University of London, Blackshaw road, Tooting, London, SW17 0QT, UK. m.cecconi@nhs.net.
Maurizio
M
Cecconi
D001810:Blood Volume / Q000502:physiology*; D001811:Blood Volume Determination / Q000379:methods*; D001916:Brachial Artery / Q000502:physiology*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
Intravascular volume; Least significant change; Mean systemic filling pressure; Precision