Hemodynamics Flashcards
Ohm’s law: P = Q x R
Q is blood flow and R is resistance to flow.
The International Consensus Conference recommends a target MAP of:
______ mm Hg in uncontrolled hemorrhage due to trauma
______ mm Hg for traumatic brain injury
______ mm Hg for other forms of shock.
The International Consensus Conference recommends a target
MAP of 40 mm Hg in uncontrolled hemorrhage due to trauma
MAP of 90 mm Hg for traumatic brain injury, and
MAP >65 mm Hg for other forms of shock.
MAP
CO (cardiac output in L/minute) x TPR (total peripheral resistance)
Why is measurement of arterial pressure important in shock/trauma patients?
Hypotension is always pathologic and reflects a failure of normal circulatory homeostatic mechanisms, whereas normotension does not equate to cardiovascular stability.
What may cause hypotension in the following patients?
1) Cardiogenic/hemorrhagic shock?
2) Spinal cord trauma or septic shock?
3) Otherwise normal patient?
Hypotension can occur because of
1) a profoundly low CO in the setting of preserved vasomotor tone, as in severe cardiogenic or hemorrhagic shock
2) because of a primary loss of vasomotor tone independent of CO, as in spinal cord trauma and septic shock.
3) Hypotension in an otherwise normal patient reflects a failure of carotid and aortic arch baroreceptor responses.
How is MAP calculated?
Mean arterial blood pressure=
Diastolic blood pressure + [pulse pressure/3]
In an emergency, palpation of the following pulses:
1) radial
2) femoral
3) carotid
Can provide estimated minimum systolic pressures of what?
Radial: 80 mm Hg
Femoral: 70 mm Hg
Carotid: 60 mm Hg
Uses for arterial cath in the ED
1) Guides management of vasodilator or vasopressor drug to maintain optimal target mean arterial pressure and avoid hypotension
2) Provides access port for the repetitive sampling of arterial blood in patients
3) Allows monitoring of cardiovascular deterioration in patients at risk for cardiovascular instability
4) Allows calculation of pulse pressure variation and cardiac output via pulse contour analysis
5) Useful applications of arterial catheterization in the diagnosis of cardiovascular insufficiency
6) Differentiate cardiac tamponade (pulsus paradoxus) from respiration-induced swings in systolic pressure
7) Tamponade reduces the pulse pressure but keeps diastolic pressure constant.
8) Respiration reduces systolic and diastolic pressure equally, such that the pulse pressure is constant.
9) Differentiate hypovolemia from cardiac dysfunction as the cause of hemodynamic instability
10) Systolic pressure decreases after a positive pressure breath as compared to an apneic baseline during hypovolemia.
11) Systolic pressure increases during positive pressure inspiration when left ventricular contractility is reduced.
Potential risks for arterial catheterization
Permanent ischemia Temporary occlusion Sepsis Local infection Pseudoaneurysm Hematoma Bleeding
Organ perfusion pressure becomes compromised at a MAP below ________ or a cardiac index below __________.
Organ perfusion pressure becomes compromised as MAP decreases below 60 mm Hg and/or cardiac index (CO/body surface area) decreases below 2.0 L/minute/m2.
CVP (central venous pressure) is…
The back pressure to systemic venous return.
What does jugular vein distention indicate?
A pulsation >4.5 cm vertically above the sternal angle when the patient is sitting at 45 degrees indicates a CVP of >9.5 cm H2 O
When assessing CVP via ultrasound, what finding indicates increased CVP?
If the jugular vein is distended and larger than the adjacent common carotid artery when viewed in the transverse plane with the patient in a semi-upright position, the CVP is >10 cm H2O
When assessing CVP via ultrasound, what finding indicates decreased CVP?
A nearly completely collapsed internal jugular vein on the transverse view in the supine position indicates a very low CVP.
Describe the use of plethysmography in measuring CVP
Forearm volume is measured with mercury-in-silastic strain gauge plethysmography. Place a pressure cuff on the same arm with the strain gauge, in the same manner and position as a standard noninvasive blood pressure cuff. Inflate the cuff over 5 seconds to a value estimated to be higher than CVP but lower than diastolic blood pressure (about 40 mm Hg), and maintain this pressure for 1 minute. At this pressure, blood continues to flow into the forearm, but not out of the arm, allowing the arm to swell. The pressure cuff is then rapidly deflated. CVP is then determined by the cuff pressure at which the forearm volume decreases with the maximum slope during cuff deflation.
