08 Assessment of volume status and fluid responsiveness in the emergency department

include paroxysmal nocturnal dyspnea
and orthopnea whereas dyspnea on exertion
is the most sensitive anamnestic hint.
During physical examination, jugular venous
distention and abdominojugular reflux
may secure the diagnosis of heart
failure (however, these signs have very
low sensitivity). Among the more sensitive
findings, lower extremity edema and
rales on lung auscultation may provide evidence
for hypervolemia and heart failure.
In cardiac patients, the synopsis of
clinical findings can be used to assign the
patient to a Killip class that was initially
proposed for risk stratification in patients
with myocardial infarction [13].
Taken together, we consider the clinical
examination as an immediately available
and cost-effective means to evaluate
a patient’s volume status early after his arrival
in the ED, which can help to guide
the initial resuscitation therapy. However,
clinical studies revealed significant limitations
of clinical signs and symptoms in
the assessment of a patient’s volume status
[8, 10, 14, 15].
Laboratory parameters
Blood urea nitrogen/
creatinine ratio
Volume depletion induces a neurohumeral
response which enhances the reabsorption
of sodium and water in the proximal
tubule. Since urea reabsorption occurs
passively in this very part of the nephron,
volume depletion also causes an increase
in urea reabsorption. The blood urea nitrogen
(BUN)/serum creatinine ratio is
approximately 10:1 in normal subjects but
may be substantially elevated in hypovolemic
states [16]. In a state called “prerenal
azotemia,” true volume depletion or
decreased effective arterial blood volume
(EABV) go along with BUN/creatinine ratios
of 20:1 and higher. Decreased EABV
volume may occur in edematous disorders
such as cardiac failure, liver cirrhosis,
and more rarely nephrotic syndrome
[17]. Although there are quite a few confounding
conditions such as intake of steroid
medication or upper gastrointestinal
bleeding, the BUN/creatinine ratio remains
an easily obtainable tool for volume
status assessment. We would like to point
out that mere creatinine levels are poor indicators
of kidney function in the elderly,
and the use of formulas to estimate glomerular
filtration rate is strongly suggested
in this patient group [18].
Urinary sodium and fractional
excretion of urea
Urinalysis is often performed in the ED
during the evaluation of common symptoms
such as fever or abdominal discomfort.
A “spot urine” sample may also aid in
evaluating volume status. The aforementioned
neurohumeral response to volume
depletion or decreased EABV induces the
kidneys to retain sodium and subsequently
water in order to (re-)expand the extracellular
fluid compartment. Chung and
colleagues were able to demonstrate that
in contrast to clinical assessment by two
experienced nephrologists the spot urinary
sodium concentration was highly
sensitive to distinguish between hypovolemic
and euvolemic patients with hyponatremia
[15]. In their study, a spot urinary
sodium concentration of less than
30 mmol/L was 100 % specific and 80 %
sensitive to detect patients with hyponatremia
who had elevated plasma renin and
norepinephrine concentrations, responded
to infusion of isotonic saline, and were
thus deemed to be hypovolemic.
However, when hypovolemia occurs
due to an overzealous use of loop and thiazide
diuretics, low urinary sodium concentrations
lose their sensitivity to detect
volume depletion. As sodium and water
are reabsorbed in the proximal tubulus,
the fractional excretion of urea (FE UN )
remains unaffected. In patients with renal
hypoperfusion, a FE UN of ≤ 35 % was
found to be indicative of kidney injury
due to hypovolemia or decreased EABV
even after administration of diuretic therapy
(sensitivity and specificity of 90 and
96 %, respectively [19]). However, these
results were challenged by another study
in which the diagnostic accuracy of FE UN
was explored prospectively. Pépin et al.
demonstrated that FE UN performed rather
poorly, irrespective of whether diuretics
had been administered or not [20].
In summary, a urinary spot sodium of
less than 30 mmol/L is very specific and
moderately sensitive to detect hypovolemia.
After diuretic therapy, a FE UN of
≤ 35 % may still be able to support the diagnosis
of hypovolemia, although reports
on its diagnostic accuracy are contradictive.
Blood lactate
Screening for hypotension alone might
miss patients at risk for circulatory failure
[21]. Elevated serum lactate levels indicate
ongoing tissue hypoxia and are associated
with a worse prognosis in acutely
ill patients [22], independent of age,
blood pressure, or other comorbidities
[23]. Therefore, we advocate a liberal use
of sequential [24] lactate measurements
in the ED while being aware of potential
confounders such as biguanide or antiretroviral
medications and liver disease.
Bedside ultrasound
Bedside ultrasound may provide valuable
information on circulatory function that
cannot be obtained by clinical assessment.
It may detect the presence of pericardial
and pleural effusions or ascites, which
may give important diagnostic clues both
for patients suspected to have decreased
EABV and patients with fluid loss to the
abdominal or thoracic compartment (e.g.,
pancreatitis). Furthermore, the diameter
of the inferior vena cava (IVC) can be used
to estimate right cardiac function and central
venous pressure (CVP). According to
current guidelines, a low right atrial pressure
(0–5 mmHg) can be inferred from
an IVC diameter of ≤ 2.1 cm that collapses
> 50 % with a sniff. On the contrary,
an IVC diameter > 2.1 cm without a collapse
of 50 % with a sniff suggests a high
right atrial pressure (10–20 mmHg). Values
found in between are considered indeterminate
and an intermediate pressure is
then assumed [25].
The IVC diameter is not affected by
the neurohumeral stress response but will
adapt to changes in CVP such as volume
depletion or fluid resuscitation [26, 27].
In particular, the expiratory IVC (IVCe)
diameter correlated well with complete
blood volume, as determined by I131-labeled
albumin dilution, in patients with
iatrogenic volume depletion, that is hemodialysis
[28]. Although ultrasonographic
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