Ch. 6 Shock Flashcards
(48 cards)
what determines oxygen delivery
arterial oxygen content (mostly determined by hemoglobin)
cardiac output
what is hypovolemic shock
reduction in circulating intravascular volume –> causes impaired oxygen delivery through a reduction in venous return to the heart and then reduced cardiac output
ex. hemorrhagic, non hemorrhagic like burns/open wounds, severe diarrhea, urinary losses
what is cardiogenic shock
inability of the heart to propel the blood through the circulation
ex. systolic failure (arrhythmia, drugs, CHF, DCM)
diastolic failure (HCM, cardiac tamponade, tension pneumothorax)
what is distributive shock
maldistribution of the vascular volume and massive systemic vasodilation –> amount of blood in the circulation is inadequate to fill the vascular space creating a relative hypovolemia
ex. sepsis (but can lead to hypovolemic, cardiogenic, or hypoxic shock), anaphylaxis, drugs, neurogenic (loss of autonomic nervous stimulation on the vessels)
what is hypoxic shock
adequate tissue perfusion but inadequate arterial oxygen or cellular oxygen utilization
ex. toxins causing methemoglobinemia, anemia, hypoxemia, carbon monoxide poisoning
how does the Frank Starling mechanism relate to pre load?
an increase in end diastolic volume will augment the strength of cardiac contractions
why does increasing the fraction of inspired oxygen do little to increase arterial oxygen content
because oxygen is not well solubilized in plasma, once the hemoglobin is maximally saturated, increasing the fraction of inspired oxygen does very little to increase arterial oxygen content
what are the three main categories of abnormalities that can lead to a reduction in arterial oxygen content
anemia
altered hemoglobin function
hypoxemia
What is Fick’s equation
determination of venous oxygen content
CvO2 = Hb x SvO2 x 1.34 x PvO2 x 0.003
what is the anaerobic threshold
at higher oxygen delivery levels, the consumption of oxygen is independent of its supply
when oxygen delivery is low, however, the consumption becomes more supply dependent
what is the oxygen extraction ratio?
O2ER = VO2/DO2 x 100
this is the ratio between oxygen uptake and oxygen delivery as a percentage
represents an index of the efficacy of tissue extraction of oxygen from the capillary bed
oxygen extraction ratios of different organs are extremely variable
where does the acid in hyperlactatemia come from?
hyperlactatemia from lactate production from glucose does not generate hydrogen ions
hydrogen ions accumulate during anaerobic conditions because the degradation of ATP to ADP releases a H+. Usually, aerobic conditions allow H+ to be consumed but under anaerobic times, the H+ accumulates with lactate creating an acidemic state known as metabolic lactic acidosis
what causes defects in oxygen uptake
diffusional shunting diffusional resistance arteriovenous shunting perfusion/metabolism mismatch cytopathic hypoxia (mitochondrial dysfunction)
What are the four ways the body compensates for shock?
maintaining mean circulatory pressure
maximizing cardiac performance
redistributing perfusion
optimizing oxygen unloading
what are chemoreceptors sensing?
baroreceptors in the carotid and aortic bodies respond to a reduction in O2
chemoreceptors in the brainstem are sensitive to an increase in circulating H+ or CO2
why is a decrease in hematocrit and total protein seen in a shock patient?
there is constriction of the precapillary arterioles that leads to a fall in hydrostatic pressure in capillaries and then a net shift of body fluids from the interstitium into the intravascular space
what is calpain
a proteolytic enzyme involved in reperfusion injury
calpain becomes activated as intracellular calcium increases in shock
calpain will convert xanthine dehydrogenase to xanthine oxidase and then xanthine oxidase will make super oxide when tissues have oxygen again
what is the shock index?
the ratio between heart rate and systolic arterial pressure
ratios greater than 0.9:1 may be suggestive of shock
what would the central venous pressure be in a patient with cardiogenic shock
should be increased! possibly >10 cm H20
what is the gold standard for cardiac output measurements
thermodilution and placement of a pulmonary artery catheter (Swan-Ganz catheter)
also can aid in measuring pulmonary artery occlusion pressure
What is type A lactic acidosis
inadequate oxygen delivery is the most common cause of increased blood lactate
what is type B lactic acidosis
mitochondrial function is impaired but there is normal oxygen delivery
usually associated with diseases like sepsis, diabetes mellitus, neoplasia, drugs, toxins
prolonged states of hypoxia can damage mitochondria and lead to type a and b lactic acidosis
what is sublingual capnometry
a regional perfusion measurement
measures partial pressure of CO2 from the sublingual area
what is near infrared spectroscopy
an optical non-invasive technique used to monitor skeletal muscle tissue oxygen saturation
similar to pulse oximetry but also reflects the arterioles, capillaries, and venules
