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
major sources of lactate
musclegastrointestinal tract
Why does the body switch to anaerobic mechanism
when DO2 can not meet tissue demandsswitch to anaerobic metabolism to save ATPglucose –>pyruvate —>lactate (via LDH)generates NAD+ but saves ATPwhen oxygen returns ATP can be used to lactate–>pyruvate–>glucose
arterial blood pressure eqn
ABP = CO x SVR
absence of a peripheral pulse vs absence of femoral artery pulse in relation to BP
lack of peripheral pulse SAP 80 mm Hglack of femoral pulse SAP < 60 mm Hg
shock organ in dog vs cat
GI doglung cat
T/F arterial BP is synonymous with perfusion
FALSEABP does not equal perfusionnormal ABP does not rule out hypo perfusion.low BP is not SN and late marker of uncompensated state and failure of SNS
minimum BP o maintain major body systems
MAP 60SAP 90
disadvantages to arterial catheters
technically challenging, time consuminghematoma formationthrombosis hemorrhageinflammationnecrosis distally (cats)
advantages of arterial catheters
GOLD std for BP monitoringcontinuous or intermittent readingsMAP, SAP, DAP
Doppler BP monitoring only reliably monitors what
ONLY SAPbetter than oscillometric methods (which underestimate)in anesthetized cats, doppler may more accurately represent MAP
normal CVP
0-5 cm H20most closely represents end diastolic volume
how many mm Hg in one cm H20
0.74 mm Hg in 1 cm H20
common causes of increased CVP
right heart failurevolume overloadpericardial effusionpleural space diseaseincreased intrathoracic pressure
gold standard for cardiac output measurements
thermodilutionSwan Ganz pulmonary arterial catheter(other methods lithium dilution, transpulmonary thermodilution–minimally invasive)
normal lactate
indicator of hypoperfusion normal < 2 mmol/Lmonitor trendsmay be prognostic indicator
difference between type A and type B lactic acidosis
type A: inadequate DO2 (most common)type B:adequate DO2 w hyperlactatemia from mitochondrial dysfunction
cyanosis of blue MM indicates
> 5 g/dl of deoxygenated Hb in circulation
pulse oximetry is influenced by
pigmenthypothermiavasoconstrictionperipheral hypoperfusionmovementambient light
rough estimate of the relationship if PaO2 and inspired oxygen
PaO2 should be ~5x FIO2ex 21% oxygen in room air x 5 = > 90 mm Hg
what does FAST stand for
focused assessment with sonography for trauma
at what rates does oxygen toxicity occur
FIO2 > 60% for more than 24 hours
unilateral vs bilateral nasal cannulas for oxygen supplementation at flow rate 100 ml/kg/min
unilater 40%bilateral 60%
methods of oxygen suppementation
flow by +/- ecollar/wrapnasal/nasopharyngealtracheal
common sites for IVC
jugular veinsperipheral veins (avoid hind in severe shock patients–GDV)intraosseous (trochanteric fossa, prox humerus, tibial crest)
inotropic support with dopamine (low, med, hi doses)
low 0.5-2.0 mcg/kg/min vasodilationmed 2-10 mcg/kg/min Beta receptors inotropic/contractilityhigh 10-20 mcg/kg/min vasoconstriction, alpha receptors
what is dobutamine avoided in cats
seizures in cats more beta specific inotrope
T/FSIRS may be infectious and/or noninfectious
TRUE
difference btwn SIRS and sepsis
SIRS–noninfxn and infxn causesmost common cause of SIRS is sepsissepsis –SIRS with infxn
septic shock definition
sepsis (SIRS with infxn) and state of acute circulatory failure
MODs
multiple organ dysfunction syndrome
ARDs
acute respiratory distress syndrome
diagnostic criteria for ARDS
- acute onset < 72 hr tachypnea/labored breathing2. presence of risk factors3. pulmonary capillary leak without increased pressure4. inefficient gas exchange5. diffuse pulmonary inflamation
ALI vs ARDS
ALI is less severePaO2/FIO2 ratio< 300 ALI< 200 ARDS
5 causes of hypoxemia
- hypoventilation2. low inspired oxygen FIO23. VQ mismatch4. AV shunting5. diffusion impairment
septic foci in dogs vs cats
GI (most common in dogs)repro (dog >cat)pleural space (cats>dogs)endocarditispancreatitisurinary tract nosocomial (check IVC)
T/F mortality can be as high as 80% with inappropriate use of Ab to treat sepsis
TRUE
describe de-escalation therapy
start Ab approach broad (4 quad–gm + gm - anaerobic, aerobes)then taper/narrow therapy once C&S available
adrenal insufficiency and septic shock
aka critical illness related corticosteroid insufficiencycortisol levels may be high or normal but adrenal response is bluntedleads to refractory hypotensiontx low dose physiology GCC (hydrocortisone)
