Chapter 153 Hypovolemic Shock

Question 1

How does the body maintain adequate blood pressure in the compensatory state of hypovolemic shock?

Answer 1

• Baroreceptors in the aortic arch and carotid arteries activate neural pathways –>increase in sympathetic tone
• Adrenal medulla release epi and norepi
• The coronary and cerebral arterioles dilate in response to beta-2 adrenergic receptors
• Decreased Renal perfusion stimulates renin-angiotensin-aldosterone system

Question 2

What is the critical oxygen delivery point?

Answer 2

When oxygen delivery decreases below the level needed for oxygen consumption and anaerobic metabolism predominates

Question 3

What signals stimulate the RAAS?

Answer 3

Decreased stretch in the afferent arteriole and decreased chloride delivery to the macula densa

Question 4

What leads to the decompensatory state of shock?

Answer 4

• Decreased sensitivity of adrenergic receptors to catecholamines and exhaustion of ADH stores.
• Ischemic tissues release substances that cause local vasodilation
• Progressive intracellular acidosis in myocardium leads to ultimate failure and conduction disturbances –>resulting in progressive hypotension/bradycardia and death

Question 5

What are the perfusion parameters?

Answer 5

mentation, HR, pulse quality, mucous membrane color, CRT, extremity temperature

Question 6

What is the shock index?

Answer 6

A triage tool used by some to simplify detection of shock - calculated from the heart rate divided by the systolic BP.

Question 7

What causes a normal variation in pulse pressure during the respiratory cycle?

Answer 7

Increased right atrial pressure (primarily)

Decreased venous return during inspiration

Question 8

Why is the pulse pressure increased with hypovolemia?

Answer 8

There is greater collapsibility of the vena cava, greater right atrial compliance and greate sensitivity of the ventricles to preload changes when operating on the steep portion of the Frank-Starling curve.

Question 9

A pulse pressure variation greater than what percentage is consistent with hypovolemia?

Answer 9

10-15%

Question 10

How could one estimate pulse pressure without direct BP monitoring?

Answer 10

pulse oximeter plethysmograph

Question 11

What ECG changes are seen with hypovolemia?

Answer 11

Decreased R wave amplitude

Lack of R-R interval variation with increased sympathetic tone in early hypovolemia

Question 12

When dealing with blood gas analysis and hypovolemic shock, what sort of blood samples should be used?

Answer 12

Mixed venous blood samples or central venous blood (peripheral tissues are affected by the compensatory response)

Question 13

How can one assess for hypovolemia with TFAST?

Answer 13

• Short axis of ventricles can assess diastolic filling and contractility
• CVC size can be estiamted on DH view where vena cava crosses diaphragm. You would see decreased diameter and dynamic collapse during inspiration
• Decreased left ventricular end-diastolic volume, cardiac index and mitral valve E-wave velocity

Question 14

What is NIRS monitoring?

Answer 14

Near infra-red spectroscopy
Measures oxygenated and deoxygenated Hb and myoglobin in tissues
Can predict the need for blood transfusions in traumatized humans that appear hemodynamically stable