Relationship between central venous pressure and bioimpedance vector analysis in critically ill patients

Objective: To assess the relationship between central venous pressure value s and bioelectrical impedance vector analysis (BIVA), which may be used as complementary methods in the bedside monitoring of fluid status, Design: Cross-sectional evaluation of a consecutive sample. Setting: Intensive care unit of a university hospital. Patients: One hundred and twenty-one consecutive Caucasian, adult patients of either gender, for whom routine central venous pressure measurements wer e available. Interventions: None. Measurements and Main Results: Central venous pressure values and impedance vector components (i.e., resistance and reactance) were determined simulta neously, Total body water predictions were obtained from regression equatio ns according to either conventional bioimpedance analysis or anthropometry (Watson and Hume formulas). Variability of total body water predictions was unacceptable for clinical purposes. Central venous pressure values signifi cantly and inversely correlated with individual impedance vector components (r(2) = .28 and r(2) = .27 with resistance and reactance, respectively), a nd with both vector components together (R-2 = .31), Patients were classifi ed in three groups according to their central venous pressure value: low (0 to 3 mm tig); medium (4 to 12 mm Hg); and high (13 to 20 mm Hg), Three BIV A patterns were considered: vectors within the target (reference) 75% toler ance ellipse (normal tissue hydration); long vectors out of the upper pole of the target (dehydration); and short vectors out of the lower pole of the target (fluid overload). The agreement between BIVA and central venous pre ssure indications was goad in the high central venous pressure group (93% s hort vectors), moderate in the medium central venous pressure group (35% no rmal vectors), and poor in low central venous pressure group (10% long vect ors), Conclusions: Central venous pressure values correlated with direct impedanc e measurements more than with total body water predictions. Whereas central venous pressure values >12 mm Hg were associated with shorter impedance ve ctors in 93% of patients, indicating fluid overload, central venous pressur e values <3 mm Hg were associated with long impedance vectors in only 10% o f patients, indicating tissue dehydration. The combined evaluation of inten sive care unit patients by BIVA and central venous pressure may he useful i n therapy planning, particularly in those with low central venous pressure in whom reduced, preserved, or increased tissue fluid content can be detect ed by BIVA.