The purpose of hemodynamic monitoring is to identify cardiovascular insufficiency
and to ensure optimal treatment of the unstable critically ill.
Hemodynamic monitoring serves a diagnostic, therapeutic, and resuscitation
target role. Although vital signs help assess the adequacy of tissue
perfusion, they are a late indicator of tissue ischemia.1 Analysis
of hemodynamic variables beyond traditional vital signs allows the
clinician to differentiate various causes of hemodynamic instability
and intervene appropriately.
Hemodynamic monitoring changes therapeutic decisions in up to
58% of patients and can unmask underlying cardiovascular
compromise, allowing for early intervention.2–5 In
this chapter, we discuss techniques applicable in the ED setting:
blood pressure monitoring, central venous pressure (CVP) monitoring,
cardiac output (CO) monitoring, and oxygenation and organ perfusion
monitoring (Table 34-1).
Table 34-1 Hemodynamic Variables
Obtainable in the ED |Favorite Table|Download (.pdf)
Table 34-1 Hemodynamic Variables
Obtainable in the ED
|Hemodynamic Variable||Method of Measurement|
|Hemoglobin oxygen saturation, %||Pulse oximetry, arterial blood gas|
|Heart rate, beats/minute||Physical examination, pulse oximetry, electrocardiography|
|Blood pressure, mm Hg||Sphygmomanometry, oscillometry, intra-arterial catheterization|
|Central venous pressure, mm Hg||Jugular venous pulsation, US, central venous catheterization|
|Cardiac output, L/minute||Thoracic bioimpedance or bioreactance, esophageal Doppler
US, transcutaneous Doppler US, pulse contour analysis, lithium dilution,
transpulmonary (arterial) thermodilution, pulmonary artery thermodilution|
|Central venous oxygen saturation, %||Central venous catheterization for intermittent venous blood
sampling or continuous measurement|
|Lactate, mmol/L||Arterial, venous, or capillary sampling|
|Tissue oxygen saturation, %||Near-infrared spectroscopy|
Direct measurement of blood pressure was first performed by Stephen Hales
in 1714, when he inserted a brass pipe in the left carotid artery
of a living horse tied down on its back. The blood rose 8 ft 3 in.
in the pipe above the level of the heart.6 In modern
medicine, arterial blood pressure has been the crucial element of
the clinical vital signs. Blood pressure is the
force exerted by the circulating blood through a blood vessel. The pressure
difference (ΔP) between two points in the vessel
is governed by Ohm’s law: ΔP = Q × R,
where Q is blood flow and R is
resistance to flow. The clinical application of Ohm’s law
states that the arterial pressure is determined by the CO (or blood
flow in liters per minute) and total peripheral resistance (TPR),
which means mean arterial pressure (MAP) = CO × TPR.
In evaluating blood pressure as a hemodynamic indicator of organ
perfusion, the contribution by TPR (the impediment to flow) must
be taken into account in relation to CO, which is the measure of
effective blood flow to the tissue. Although the more common measure
of resistance is systemic vascular resistance, TPR provides a better
physiologic measure of impediment to flow. Systemic
vascular resistance is calculated as the ratio of total flow (CO)
to the pressure difference between MAP and right atrial pressure.
Right atrial pressure is not the ...