Assessing volume status in critically ill and injured patients is of paramount importance to the provider and patient. However, volume status can be very difficult to assess and is often dynamic. Studies such as that by Rivers et al. have shown that early aggressive fluid resuscitation directly impacts sepsis outcomes.1 Yet studies such as the SOAP trials noted that positive fluid balance was among the strongest prognostic factors for mortality.2 There are various methods by which to assess fluid status. Bedside ultrasound assessment of volume status has become an important tool for the clinician because it is noninvasive, not harmful, and, most importantly, repeatable for reassessment. Pulmonary artery catheters for pulmonary wedge pressure have been shown to provide no added benefit to patient care, with the added burden of increased cost.3–6 The use of central venous pressure (CVP) as a single marker has come under much scrutiny since Marik et al. described a poor relationship between CVP and blood volume in a systematic review in 2008 and again in 2012.7,8 This chapter will review these methods for using bedside ultrasound for evaluation including inferior vena cava (IVC) ultrasound, cardiac ultrasound, superior vena cava (SVC) ultrasound, and pleural ultrasound.
To read more about CVP, pulmonary artery occlusion pressure (PAOP), and other methods of hemodynamic monitoring, please refer to Chapter 15 (hemodynamic and perfusion monitoring).
Hypoperfusion and volume overload are associated with increased morbidity and mortality in critically ill patients. Volume status is integral to resuscitation efforts. Indications for assessment include cases of volume depletion (evaluating for presence and extent of hemorrhagic shock or dehydration), volume overload (as in cases of decompensated cardiac failure), and serial monitoring for response to fluid therapy in cases of sepsis or to direct resuscitation (fluids versus adding inotropic medications). Traditional methods for intravascular volume status assessment are invasive and associated significant complications. Ultrasound is a painless, nonirradiating, noninvasive imaging tool that can be used repeatedly at the bedside and avoid complications associated with invasive monitoring, including arterial puncture, venous thrombus, and infection.
A quick and safe bedside maneuver to establish fluid responsiveness is the passive leg raise (PLR). PLR has been widely used as an endogenous fluid bolus. With the patient in a stretcher, the head is reclined to supine with the legs raised 45 degrees, passively. This results in a 150–500 cc bolus, depending on the patient's volume reserve. Duus et al. suggest that it is more reliable than fluid challenge.9 In various studies, PLR has been shown to increase PAOP, end diastolic left ventricular dimensions, and CVP. Since this is a reversible process once the legs are brought back to the supine position, opportunity for untoward harm from a bolus is minimized.10 This information can be used to direct resuscitation efforts in the critically ill patient.