Chapter 56
Intravascular Volume Status

Ali S. Raja¹ and Christopher R. Carpenter²

¹ Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA

² Department of Emergency Medicine, Washington University School of Medicine, St. Louis, MO, USA

Background

This chapter focuses on the assessment of volume status in adults because the literature on children is vast and not always applicable to older populations.¹ Volume management decisions are frequently encountered in the emergency department (ED) in patients with trauma or other bleeding states, hot weather, congestive heart failure, sepsis, gastrointestinal, and other conditions. The optimal fluid management strategy is not always clear and can carry increased morbidity and mortality with either over‐ or under‐volume resuscitation of patients.^2,3 When encountering a hemodynamically unstable patient, it is not always obvious whether the volume issue is one of preload, afterload, cardiac contractility, or none of these. Consequently, only about one‐half of hemodynamically unstable, critically ill patients respond to fluid boluses.⁴

The terminology for volume deficiency conditions can also be confusing. Whereas volume depletion refers to extracellular space sodium losses, dehydration is the loss of intracellular water that increases plasma sodium levels and osmolality.⁵ Clinicians and investigators tend to lump these volume state descriptors together as evidenced by the accepted criterion standard of either an elevated serum urea nitrogen‐to‐creatinine ratio (which measures volume depletion) or an elevated serum sodium or osmolality (which measures dehydration). Hypernatremia occurs predominantly in geriatric adults with intravascular volume depletion and is associated with a 40% mortality rate. Hypernatremia‐related deaths are associated with the type and rate of fluid administration as well as the duration of hypotension.^4,6 In this chapter, we will use the term hypovolemia to denote the constellation of dehydration and volume depletion.

Physical exam findings for dehydration or volume depletion include assessing postural vital signs (orthostatics), skin turgor, mucous membrane dryness, capillary refill, urine output, and neurological status. One caveat for orthostatic vital signs is that clinicians should wait at least 2 minutes before measuring supine vital signs, and 1 minute after standing before measuring upright vital signs. Sitting vital signs are far less accurate than standing ones. Also, counting the pulse for 30 seconds is more accurate than for 15 seconds.⁷ Capillary refill time is assessed by gently pressing the fingernail of the patient’s middle finger while it is positioned at the same level as the heart for 5 seconds before releasing and noting the time required for the nailbed’s normal color to return (normally 3 seconds for adults and 4 seconds for the elderly). Skin turgor describes the skin’s ability to return to its normal position after being pinched between the examiner’s fingers and is a function of elastin‐related recoil. No studies on normal recoil times have been identified, but skin turgor decreases (i.e., there is a greater time to return to normal skin position) with age as elastin levels are reduced.

Investigators have evaluated the diagnostic accuracy of postural vital signs following acute blood loss in healthy volunteers following experimental phlebotomy, but with the exception of young otherwise healthy patients with hemorrhage, these lab trials are not applicable to the usual course of events, associated illness or injury, or patient populations routinely evaluated in ED settings.⁵ In summary, these studies suggest that a postural pulse change from lying to standing of ≥30 or severe postural dizziness has 97% sensitivity and 98% specificity for a large blood loss, whereas postural hypotension (>20 mmHg systolic decrease) or supine tachycardia or hypotension are insensitive tests.⁵

Clinical question

In adult patients presenting to the ED with vomiting, diarrhea, or decreased oral intake, what is the diagnostic accuracy of the physical examination for hypovolemia?

Three ED‐based studies have reported the diagnostic test characteristics for physical exam (Table 56.1).^8–10 Schriger et al. evaluated 32 ED patients with suspected hypovolemia (and frank hypotension or abnormal orthostatic vital signs, mean age 44 years) and 47 volunteer blood donors to assess capillary refill, excluding those on cardiovascular medications. The criterion standard for hypovolemia in the “suspected hypovolemia” subset was not clearly stated in their manuscript. The likelihood ratios for “abnormal capillary refill time” reported in Table 56.1 are in reference to the age‐ and sex‐specific upper limits of normal for capillary refill.⁸ Gross et al. evaluated 55 patients older than 60 years presenting to one of two academic EDs with suspected dehydration to assess 38 signs and symptoms. As their criterion standard, they used a nonvalidated Physician Dehydration Rating Scale that relied upon gestalt, vital signs, serum sodium, osmolality, and urea creatinine.⁹ Johnson et al