6 Flashcards
what does oxygen delivery depend on
oxygen delivery DO2DO2 = CO x CaO2CO cardiac output = SV x HRCaO2 arterial oxygen content
body’s compensatory response to tissue hypoxia
tachycardiatachypneaperipheral vasoconstrictionmental depression
common classifications of shock
- Hypovolemic–reduced volume, reduce preload, reduce SV, reduced CO2. Cardiogenic–inability of heart to contract/propel fwd3. Distributive–impaired mx of vascular tone and relative hypovolemia4. Hypoxic–adequate perfusion but inadequate oxygenation
major determinant of arterial oxygen content
amount of HbCaO2= (Hb x SaO2 x 1.34) + PavO2 x 0.003
What does CO depend on
CO = SV x HrSV = preload, after load and contractility
preload
end diastolic volumeincr preload will incr stretch and incr contractility to a point (Frank Starling mx)
afterload
ventricular wall tension or resistance the muscle needs to counter during systoleinfluenced by vascular resistance (low BP is the major determinant of decr after load)
contractility
force and velocity of cardiac muscle contraction
what is blood flow influenced by
assumes blood flow is uniform across tissue bedsbutinfluenced by vasomotor controlcirculating blood volumeactivation of blood components
types of hypovolemic shock
blood lossburnssevere diarrhea, vomitingthird spacing
types of cardiogenic shock
systolic dysfx–CHF, DCM, arrythmias, valvular stenosis/insufficiencydiastolic dysfx–HCM, cardiac tamponade, pericardial fibrosis, tension pneumothorax (sometimes referred to as obstructive shock)
types of distributive shock
sepsisanaphylaxisneurogenicdrugs–anesthetics
types of hypoxic shock
hypoxemiaanemiamethemoglobinemiaCO poisoning cytopathic (cells aren’t able to produce energy from O2 available)
what is Hb affinity for oxygen dependent on
pHtemperature2,3-diphosphoglycerate (DPG)CO2
equation for mean arterial BP
MAP = DAP + 1/3 (SAP-DAP)
decreases in tempincreases in pHdecreases in pCO2decreases in 2,3 DPG
shift oxygen-HB dissociation curve to the LEFTmaking oxygen less available/delivery of less oxygenincreases Hb affinity for oxygen
increases in tempdecreases in pHincreases in pCO2increases in 2,3 DPG
shift oxygen-Hb dissociation curve to the RIGHTmaking oxygen more available/delivers more oxygendecreases Hb affinity for oxygen
tissue hypoxia results from
Decreased PaO2/SaO2Impaired DO2Decreased COreduction in Hb
what is the main determinant of tissue perfusion
CO=SV x HR
three main abnormalities that will result in low CaO2 (arterial oxygen content)
–anemia–altered Hb fx–hypoxemia
oxygen uptake eqn
oxygen uptake VO2; rate at which oxygen leaves HbVO2 = CO x (CaO2-CvO2)FICK equation
if all oxygen available is delivered to tissue and is utilized, how much O2 should remain bound to Hb in venous supply?
If oxygen delivery is adequate, sufficient O2 should remain in venous blood to provide at least 70% saturation of Hb
oxygen extraction ratio
ratio btwn oxygen supply and utilization or oxygen delivery and uptakeO2ER= VO2/DO2 x 100
DO2/VO2 curve and the anaerobic threshold
over a wide range of values, VO2 is INDEPENDENT of DO2if DO2 starts to decrease, eventually it hits critical DO2 point or the anaerobic threshold where now VO2 is DEPENDENT on DO2 and below this threshold anaerobic mechanisms ensue.
defects in oxygen uptake
- diffusional shunting: slow velocity blood, favors oxygen diffusion, less oxygen delivered to target tissues2. diffusional resistance: tissue edema impairs oxygen diffusion to tissues3. AV shunting: low of normal flow and bypass occurs leading to increase oxygen content in venous blood supply4. Perfusion/metabolism mismatch: delivery of oxygen is adequate but it is not taking up by diseased tissue5. cytopathic/metabolic dysfunction: intracellular interference with oxygen/aerobic metabolism