Article Summary
1. Why is this topic important? Bedside sonographic
Central venous pressure (CVP) is a key physiologic estimate of preload, which in turn helps define the intravascular fluid status. It is a particularly important parameter to measure in critically ill and injured patients who may require fluid resuscitation. Unfortunately, measurement of the CVP requires invasive central venous catheters that can be difficult or time-consuming to insert and are associated with complications. A non-invasive means of inferring the CVP would provide clinicians with an acceptable alternative. Gosink was among the first to fully describe a relationship between the imaged diameter of the inferior vena cava (IVC) and CVP (1). Since then, ultrasonography has emerged as a reliable means to measure internal body structures, including the vena cava. Previous studies have shown various correlations between CVP or right atrial pressure and measurements of the IVC 2, 3, 4, 5, 6, 7.
There is considerable emergency and critical care relevance to non-invasive measurements of CVP. Care of emergency patients often requires resuscitation without the benefit of invasive monitoring. Ultrasound is a tool that potentially could provide a rapid and non-invasive means of gauging preload and the need for fluid resuscitation. Because ultrasound machines are relatively light and portable, and many clinicians are trained in their use (e.g., emergency physicians, anesthesiologists, intensivists, and surgeons), the ability to non-invasively measure CVPs could extend patient monitoring capabilities to a variety of settings where direct measurements of the CVP are unavailable or impractical.
This study examined the correlation between CVP and the IVC diameter as measured by a bedside ultrasonographic technique. In particular, this study evaluated several single-view images obtained at various abdominal locations using easily identified external and internal landmarks. The study used a focused bedside ultrasound examination that is simple to perform. In essence, images and measurements were made in real time and did not require elaborate or time-consuming procedures such as multiple views or complicated measurement techniques (e.g., review of cine images), the need for special equipment (e.g., transesophageal probes), or formal studies (e.g., echocardiography) that usually require a dedicated technician and specialist interpretation (8).
The study was a prospective, cross-sectional observation that utilized a one-time assessment of IVC diameter to determine any correlation with CVP. Our primary hypothesis was that a single view technique using bedside ultrasound measurement of the diameter of the IVC correlates to simultaneously measured CVP in a variety of critical patients. Our secondary objectives included determining which combination of anatomic parameters (probe location and orientation) would demonstrate the highest
Four operators enrolled 72 subjects with a mean age of 67.2 years (range 21–94 years), 37 (51%) male, over a period of 9 months. Seven subjects were excluded for tricuspid valvulopathy but had similar demographics to the subject population; there were no other exclusions. An analysis was conducted on 65 subjects, and it showed the leading primary diagnoses were: respiratory failure including pneumonia and congestive heart failure, 12 (18%); sepsis, 11 (17%); pancreatitis, 3 (5%); renal failure,
Central venous pressure monitoring is a mainstay of estimating vascular fluid status and cardiac preload in critically ill and injured patients 10, 11. It is the preferred method in the ED and in other situations when a pulmonary artery catheter is not practical (12). Recent criticisms of using CVP to estimate fluid responsiveness notwithstanding, CVP measurements remain the standard of care in shock management (13). The advent of goal-directed therapy in sepsis and permissive-hypotension
The subxiphoid view was the most readily viewed of the three anatomic locations for obtaining adequate views of the IVC; however, the suprailiac view produced superior correlations to the CVP when compared to the subxiphoid and midpoint views. Longitudinal views generally outperformed transverse views at all levels except the suprailiac. Use of a single simple ultrasound measure of the IVC transverse diameter in end-inspiration yields weak correlation with the CVP. 1. Why is this topic important? Bedside sonographicArticle Summary
The authors thank John Ward, phd and Cristy Landt, ms for their biostatistical support.
The inferior vena cava (IVC) respiratory collapse index has been widely used to assess intravascular volume (Nagdev et al. 2010) and is regarded as an indicator of responsiveness to fluid therapy (Feissel et al. 2004). However, the IVC was difficult to visualize in more than 10% of cases in previous studies (Brennan et al. 2006; Nagdev et al. 2010; De Lorenzo et al. 2012). In contrast, the internal jugular vein (IJV) is relatively easy to visualize because of its close proximity to the body surface.
This may explain why we found a distinct increase in IVC wall stiffness when the central volume was higher in our volunteers. Several other studies present inconsistent results regarding the correlation of CVP and caval geometry (i.e., diameter and collapsibility) (Ciozda et al. 2016; Lorenzo et al. 2012; Stawicki et al. 2009). Therefore, the question remains whether an increasing wall stiffness is directly associated with increasing CVP.
In the ED, ultrasound is used as a rapid and non-invasive method for determination of preliminary diagnoses and guiding the initial therapy.4 In the evaluation of IVCD, the subxiphoid view is the most reliably assessed, and the suprailiac view produces superior correlations with CVP.5 An image of the suprailiac IVC is not obtainable in more than half of cases because of body habitus or bowel gas.5
The opinions or assertions are those of the author and do not necessarily reflect those of the Army Medical Department or the Department of Defense.
This study was funded by a grant from the US Army Telemedicine and Advanced Technology Center, Fort Detrick, MD, with limited support from Sonosite, Inc., Bothell, WA.