Ch. 6 Shock Flashcards
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
what is the percent oxygen for flow by at 2-3 L/min
only about 25-40%
what percent oxygen will you get with nasal cannulas at 100 ml/kg/min
40% for unilateral and 60% for bilateral
how much fluid will remain in the intravascular space 30 min after a crystalloid is given
25%
what is the goal of hypotensive resuscitation
for patients with active hemorrhage, the endpoint of presurgical resuscitation is targeted blood pressure in the lower range around 60 mmHg
what is the goal of limited fluid volume resuscitation
restore intravascular volume using the smallest possible amount of fluid to get to close to physiologic pressure (like MAP 70 mmHg)
based on human literature, what are the recommended SpO2 and hematocrit levels for resuscitation of a shock patient
> 94% SpO2
hct >24%
why should you reperfuse hypothermic patients in shock prior to warming them
it is not really a hypothermia - just a redistribution of perfusion away from non vital regions such as the skin and colon
if you try surface rewarming while they are redistributing, you will cause peripheral vasodilation and a loss of compensation
What receptors does dobutamine act on?
Most effect at beta 1 adrenergic receptors, then beta 2
some activity at alpha adrenergic
Leads to a strong increase in cardiac contractility but reduced effect on systemic vascular resistance
dose is 2-20 mcg/kg/min in dogs, 1-3 mcg/kg/min cats
May cause seizures in cats
What receptors does low dose dopamine affect? what dose is low?
Causes vasodilation through activation of a dopaminergic receptor. has scant activity at the alpha and beta receptors.
dose is 0.5-2 mcg/kg/min
What receptors does intermediate dose dopamine act on?
preferentially acts on beta receptors and stimulates cardiac contractility
dose is 5-10 mcg/kg/min
what receptors does high dose dopamine act on?
in the high range, dopamine will preferentially act at the alpha receptors and then cause a vasoconstriction
dose is 10-20 mcg/kg/min
what receptors does epinephrine act on
potent at alpha and beta receptors
0.05-1 mcg/kg/min
a lot of side effects
what receptors does norepinephrine act on?
mostly alpha agonist
dose is 0.1-2 mcg/kg/min
what receptors does phenylephrine act on
very potent vasoconstrictor acting at the alpha receptors but has potential side effects
dose is 1-3 mcg/kg/min
what receptors does vasopressin act on?
acts on nonadrenergic V1 receptors
dose is 0.5-5 mU/kg/min
what is the definition of SIRS (systemic inflammatory response)?
systemic inflammatory response triggered by infectious or non infectious insults
what is the definition of bactermia
presence of viable bacteria in the blood
what is the definition of sepsis
systemic inflammatory response to infection
what is the definition of severe sepsis
sepsis complicated by organ dysfunction, hypoperfusion, or hypotension
what is the definition of septic shock
state of acute circulatory failure associated with sepsis, with arterial hypotension despite adequate fluid resuscitation, along with the presence of perfusion abnormalities
what is the definition of MODS
multiple organ dysfunction syndrome
presence of altered organ functionality such that homeostasis cannot be maintained without intervention
what is the definition of ARDS
acute respiratory distress syndrome
acute fulminant respiratory failure leading to diffuse lung injury resulting from a variety of causes
what is the criteria for veterinary ARDS
- acute onset (<72 hours) of tachypnea and labored breathing at rest
- presence of known risk factors
- evidence of pulmonary capillary leak without increased pulmonary capillary pressure
- evidence of insufficient gas exchange
- evidence of diffuse pulmonary inflammation
what are some categories for options for diagnostic biomarkers of shock
markers of infection like LPS or bacterial DNA
markers of cellular responsiveness like ICAM or CD11/CD18
products of inflammatory cells and humoral activation like interleukins
acute phase proteins
