Oxygen Delivery and Shock
Baroreceptors
Shock: Definition
syndrome characterized by decreased tissue perfusion and impaired cellular metabolism
which results in an imbalance between supply of and demand for O2 and nutrients
impacts all body systems:
Normal Physiology: Regulation of BP
Decrease in BP > decrease in diameter of vessels > decreased flow through the vessel resulting in the inability to keep the vessel open
Renin-Angiotensin System
when low volume shock (hypovolemic or cardiogenic shock) occurs, this compensatory mechanism is to vasoconstrict
Angiotensin 1 converts to angiotensin 2 which causes 3 things to be released:
Together they increase CO and maintain BP and pull blood to core of body to perfuse heart/lungs/brain
Shock: Pathophysiology
Shock begins with cardiovascular system failure
Alteration in at least one of four components:
Stress Hormones
adrenaline
cortisol (glucose secretions)
Classifications of Shock
Low blood flow:
cardiogenic shock
hypovolemic shock
-absolute hypovolemia: external loss of whole blood or loss of other body fluids
-relative hypovolemia: pooling of blood or fluids, fluid shifts (third spacing, volume is not gone from pt, it’s not in vasculature where it belongs), internal bleeding, massive vasodilation
Maldistribution (distributive) Shock:
Stages of Shock
Pre-shock:
Shock:
End-organ dysfunction:
Clinical Features of Shock
Hypovolemic Shock
inadequate circulating volume (shock starts and sx are seen with 15% or more fluid volume loss occurs)
acute blood volume loss of 35% or more = life threatening
many causes
compensation = vasoconstriction
assessment: vessels, pressure, labs (fluids, electrolytes, blood, acid/base balance)
tx: give fluids/blood
Hypovolemic Shock and Beta Blockers
if pt is taking beta blockers, they won’t have compensatory tachycardia associated w/ this shock
won’t know if they are in hypovolemic shock until it’s too late b/c we won’t see reflex tachycardia
Hypovolemic Shock and Renal Failure
renal failure will mask the deterioration of the client b/c we won’t see oliguria
pt’s chronic renal failure may be anuric for a considerable amount of time
Hypovolemic Shock and the Cardiac System
Shock and the Vasculature System
low volume shock:
maldistribution shock:
Hypovolemic Shock and the GI System
Hypovolemic Shock and Renal System
Renin: holds on to water and sodium to restore tissue perfusion
Angiotensin II is produced and vasoconstriction occurs b/c of aldosterone being released.
Adrenal cortex is stimulated to produce glucocorticoids > increase in glucose for energy for the body to keep compensatory mechanisms going)
ADH: pt urine output is going to decrease (either oliguric or anuric)
End stages of shock = renal ischemia occurs b/c renal arteries have been constricted for so long, so kidneys aren’t getting any perfusion > AKI > decreased UOP.
Hypovolemic Shock and the Respiratory System
early shock: pt RR can be 2x normal amount
-tachypneic in order to keep up with cardiac O2 demand (tachycardia is occurring) and compensatory mechanisms
as shock progresses: the ventilatory effort will decline, and respirations will be shallow as pt is getting fatigued from tachypnea
Hypovolemic Shock and the Neurological System
body shunts blood to the brain w/in seconds when compensating during shock
MAP > 60 for cerebral blood flow to remain at a normal level
mental function is decreased when acid-base abnormalities and low BP lead to hypoxia
decreased LOC and mental status changes are early signs that something bad is going on w/ pt
Hypovolemic Shock and Metabolic System
O2 deficit increases > cells switching to anaerobic glycolysis > lactic acid production > depression of the myocardium
-tachycardia is occurring and now lactic acid is depressing hearts ability to squeeze at this high rate
lactate levels greater than 4mmol/L means severe acidosis
Types of Shock
Directly related to the 3 major structures of the cardiovascular system:
SIRS
systemic inflammatory response syndrome
widespread systemic inflammatory response (WBC increase)
Associated w/:
most frequently associated w/ sepsis
release of mediators into systemic system > increased permeability of endothelial walls > fluid shifts into intravascular spaces > depletion of intravascular volume > relative hypovolemia
-3rd spacing, edema
Third Spacing Edema
caused by increased capillary permeability
-leaky capillaries are leaking fluid out of cells into tissues
tx: infusion of colloids (aka volume expanders)
- albumin
- hespan
- dextran
Volume Expanders (Colloids)
expand volume of cell itself
colloids go into cells and make cells bigger within vessel walls therefore it makes it harder for that cell to get out of vascular bed and leak into tissues