title: Prospective evaluation of intravascular volume status in critically ill patients: does inferior vena cava collapsibility correlate with central venous pressure?
abstract: BACKGROUND
  In search of a standardized noninvasive assessment of intravascular volume status, we prospectively compared the sonographic inferior vena cava collapsibility index (IVC-CI) and central venous pressures (CVPs). Our goals included the determination of CVP behavior across clinically relevant IVC-CI ranges, examination of unitary behavior of IVC-CI with changes in CVP, and estimation of the effect of positive end-expiratory pressure (PEEP) on the IVC-CI/CVP relationship.
  
  
  METHODS
  Prospective, observational study was performed in surgical/medical intensive care unit patients between October 2009 and July 2013. Patients underwent repeated sonographic evaluations of IVC-CI. Demographics, illness severity, ventilatory support, CVP, and patient positioning were recorded. Correlations were made between CVP groupings (<7, 7-12, 12-18, 19+) and IVC-CI ranges (<25, 25-49, 50-74, 75+). Comparison of CVP (2-unit quanta) and IVC-CI (5-unit quanta) was performed, followed by assessment of per-unit ΔIVC-CI/ΔCVP behavior as well as examination of the effect of PEEP on the IVC-CI/CVP relationship.
  
  
  RESULTS
  We analyzed 320 IVC-CI/CVP measurement pairs from 79 patients (mean [SD] age, 55.8 [16.8] years; 64.6% male; mean [SD] Acute Physiology and Chronic Health Evaluation II, 11.7 [6.21]). Continuous data for IVC-CI/CVP correlated poorly (R = 0.177, p < 0.01) and were inversely proportional, with CVP less than 7 noted in approximately 10% of the patients for IVC-CIs less than 25% and CVP less than 7 observed in approximately 85% of patients for IVC-CIs greater than or equal to 75%. Median ΔIVC-CI per unit CVP was 3.25%. Most measurements (361 of 320) were collected in mechanically ventilated patients (mean [SD] PEEP, 7.76 [4.11] cm H2O). PEEP-related CVP increase was approximately 2 mm Hg to 2.5 mm Hg for IVC-CIs greater than 60% and approximately 3 mm Hg to 3.5 mm Hg for IVC-CIs less than 30%. PEEP also resulted in lower IVC-CIs at low CVPs, which reversed with increasing CVPs. When IVC-CI was examined across increasing PEEP ranges, we noted an inverse relationship between the two variables, but this failed to reach statistical significance.
  
  
  CONCLUSIONS
  IVC-CI and CVP correlate inversely, with each 1 mm Hg of CVP corresponding to 3.3% median ΔIVC-CI. Low IVC-CI (<25%) is consistent with euvolemia/hypervolemia, while IVC-CI greater than 75% suggests intravascular volume depletion. The presence of PEEP results in 2 mm Hg to 3.5 mm Hg of CVP increase across the IVC-CI spectrum and lower collapsibility at low CVPs. Although IVC-CI decreased with increasing degrees of PEEP, this failed to reach statistical significance. While this study represents a step forward in the area of intravascular volume estimation using IVC-CI, our findings must be applied with caution owing to some methodologic limitations.
  
  
  METHODS
  Diagnostic study, level III. Prognostic study, level III.
authors.affiliation: From the Division of Trauma, Critical Care, and Burn (S.P.A.S., D.S.E., D.C.E., C.N., D.E.L., C.H.C.), Department of Surgery, Department of Emergency Medicine (E.J.A.,CTB., D.P.B.), and Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine (N.A.A.), Department of Internal Medicine, The Ohio State University College of Medicine; Department of Anesthesiology (A.N.S.), The Ohio State College of Medicine; and OPUS 12 Foundation Multi-Center Trials Group (S.P.A.S., D.C.E., D.E.L., C.H.C., S.C.G., D.P.B.), Columbus, Ohio; Department of Anaesthesiology and Critical Care (J.M.B., S.V.), Jubilee Mission Medical College and Research Institute, Thrissur, Kerala; and Department of Emergency Medicine (S.C.G.), Global Hospital Group, Mumbai, India.
authors.forename: Stanislaw P A
authors.initials: SP
authors.lastname: Stawicki
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Adkins
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Eiferman
authors.forename: David C
authors.initials: DC
authors.lastname: Evans
authors.forename: Naeem A
authors.initials: NA
authors.lastname: Ali
authors.forename: Chinedu
authors.initials: C
authors.lastname: Njoku
authors.forename: David E
authors.initials: DE
authors.lastname: Lindsey
authors.forename: Charles H
authors.initials: CH
authors.lastname: Cook
authors.forename: Jayaraj M
authors.initials: JM
authors.lastname: Balakrishnan
authors.forename: Sebastian
authors.initials: S
authors.lastname: Valiaveedan
authors.forename: Sagar C
authors.initials: SC
authors.lastname: Galwankar
authors.forename: Creagh T
authors.initials: CT
authors.lastname: Boulger
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Springer
authors.forename: David P
authors.initials: DP
authors.lastname: Bahner
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001810:Blood Volume / Q000502:physiology*; D002496:Central Venous Pressure / Q000502:physiology*; D016638:Critical Illness; D004548:Elasticity; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011446:Prospective Studies; D014682:Vena Cava, Inferior / Q000503:physiopathology*