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Surgery I > Management of Hypotension > Flashcards

Management of Hypotension Flashcards

1
Q

What is Organ perfusion/oxygenation dependent on?

A
  • Oxygen carrying capacity (CaO2)
  • Cardiac Output (CO; L/min)
  • Vascular resistance (VR)
  • Blood pressure (BP)
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2
Q

How is Oxygen Carrying capacity (CaO2) monitored?

A
  • Packed cell volume/hematocrit
  • Pulse Oximetry (% hemoglobin saturated with oxygen)
  • Healthy dog/cat on 100% O2, not commonly deranged (?)
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3
Q

Why is cardiac output not monitored?

A
  • Would be gold standard in hemodynamic monitoring
    • CO directly related to organ perfusion
    • Takes into consideration: HR, Rhythm, Contractility, Preload (Volume status) afterload, etc
  • BUT:
    • Involved/can cause harm to measure
    • Expensive
    • Takes specific training
    • Global perfusion parameter, does not specifically indicate adequate individual perfusion
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4
Q

What is Vascular resistance

A
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5
Q

What is blood pressure proportional too?

A
  • Proportional to CO (⇡CO = ⇡BP)
  • Proportional to VR (⇡VR = ⇡BP)
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6
Q

What is the problem with regional vascular resistance?

A
  • Complicates organ perfusion/Oxygenation
  • Determines individual organ perfusion
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7
Q

How common in hypotension during anesthesia?

A
  • Most common anesthetic-related complication reported, with incidence of:
    • Mixed health population of dogs - 58%
    • Healthy dogs - 7.5 - 32%
    • Healthy cats - 8 - 30%
  • A healthy dog/cat will generally not become hypotensive when in an adequate plane of anesthesia?
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8
Q

What complications can hypotension cause?

A
  • In people:
    • Acute Kidney injury
    • Acute coronary syndrome
    • Increased all-cause mortality 1 year post anesthetic event
  • Cats - 2.6x increased odds of death
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9
Q

What is Systole?

A

Stroke volume ejection

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10
Q

What is diastole

A

Affected by: Vessel elastance and Smooth muscle tone

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11
Q

What is Hypotension?

A
  • Definition:
    • Systolic <90mmHg
    • MAP <60 mmHg
  • MAP - average blood pressure presented to organs over time
  • Organs-specific minimum perfusion pressure
    • Ex: Brain, Kidneys = 50 mmHg
  • SBP - Map = ~30-40mmHg
    • Where the 90mmHg SBP target originates
    • Can vary depending on morbidities
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12
Q

What are the monitoring methods for Blood Pressure?

A
  • Direct:
    • Artery catheterization
    • Accurate, real-time
    • Ideal for unstable, high-risk patients
    • Not practical in healthy patients - time & Money
  • Indirect:
    • Non-invasive
      • Doppler flow probe
      • Oscillometric
    • Intermittent monitoring
    • Cheaper, easier to have in workflow
    • Modest accuracy/precision when applied correctly
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13
Q

Why is indirect monitoring of blood pressure only modestly accurate?

A
  • Easily influenced by technical error
    • Cuff sizing is important
      • cuff width needs to be 40% of circumference of where it will be placed
      • Why 40? - Ensures cuff balloon makes it all the way around the limb
    • Placement
      • Tight placement, lightly taping around to keep velcro attached
      • Mid-antebrachium ideal (NOT over carpus)
        • Base of tail or hind limb - OK
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14
Q

How does occlusion based technology work to monitor blood pressure?

A
  • Doppler-
    • Inflate cuff with sphygmomanometer
      • Release cuff pressure 3-5 mmHg/second
      • First sound = SBP
    • an estimate
  • Oscillometric-
    • Automated inflation/deflation several times
    • MAP is the only measred value
    • Algorithm estimates SBP and DBP
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15
Q

What are the considerations of to keep in mind for Indirect Blood pressure monitoring?

A
  • Both technologies overestimate hypotensive blood pressure
  • If using 90/60 mmHg threshold for Doppler SBP/Oscillometric MAP respectively ⇢ Will miss some hypotensive patients
  • Doppler - treat for hypotension if <95mmHg
  • Oscillometric - Treat for hypotension if MAP <65mmHg
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16
Q

What causes Hypotension?

A
  • Reduced VR
    • direct vasodilation - Isoflurane, sepsis, ACEIs/Amlodipine
    • Indirect vasodilation - reduced sympathetic tone (opioids, inhalants, alpha-2 agonists, trazadone)
  • Reduced CO
    • Reduced contractility - Isoflurane, DCM, hypovolemia, sepsis
    • Reduced forward stroke volume - DMVD, HCM
    • Reduced HR - opioids, alpha-2 agonists, reduced sympathetic tone
  • Reduced intravascular volume
    • Relative volume deficit - Vasodilation*
    • Absolute - Vomiting, reduced/no intake, hemorrhage
16
Q

What is the approach to treating a Hypotensive patient?

A
  • `Patient’s baseline states (frame perspective)?
    • volume deficit, pediatric, comorbidities?
  • Assess/optimize patient’s depth if too deep and assess for user error in BP measurement
    • (Re-take BP in 5 min to confirm BP not correcting)
  • Treat suspected direct cause
    • Bradycardia = anticholinergic
    • volume deficit = volume
    • Neither of the later = vasopressor
    • Unsure? = vasopressor (rarely wrong)
  • Allow intervention time to work (~5min)
    • Corrected bradycardia &/or still hypotensive = repeat/administer vasopressor
  • Effective Treatment can target any main factor because all are influenced by the drugs used
    • Vascular resistance
    • Cardiac output
    • Intravascular volume
17
Q

Why are IV fluids used during surgery

A
  • Maintenance IVF up to 30 ml/kg/hr:
    • Do not prevent inhalant-induced hypotension
    • Do not alter blood pressure throughout the anesthetic course
    • Do not affect microcirculatory perfusion (vessels < 20um)
  • Main Benefits:
    • maintain a patent IVC/port for medication administration
    • Address volume deficits, over time
18
Q

What maintenance rates are used? Why?

A
  • 5 ml/kg/hr for most dogs/cats
    • higher if concurrent deficit
  • Used due to convention more than anything else
    • we know it isn’t doing anything
19
Q

Why are IV boluses used?

A
  • To address calculated deficits
  • To assess if patient will be fluid responsive, if volume deficit known
  • To bridge time until another treatment is started/works (atropine, Glyco, NE infusion
20
Q

What is the normal heartrate of a small animals under general anesthesia?

A
  • Allometric scaling
    • A normal HR for one dog is not the same for another
    • Larger breed dogs have lower baseline/resting HRs
    • Smaller breed dogs have higher baseline HRs
  • Examples:
    • Great Dane:
      • HR of 40-50 is not bradycardic
      • HR <40 and hypotensive? may need an anticholinergic
      • HR >100-120 = tachycardic
        • And hypotensive? - suspect volume deficit
    • Yorkie:
      • HR 40-50 is bradycardic: anticholinergic unless normotensive
      • HR 100-120 normal
      • HR >160-180 tachycardic
21
Q

What is the suspected complication when a dog presents with tachycardia and hypotension

A

volume deficit

22
Q

What are the vasopressors used in vet med?

A
  • Dopamine
  • Dobutamine
  • Ephedrine
  • Epinephrine
  • Norepinephrine
  • Phenylephrine
23
Q

How are CRIs calculated?

A
  • Desired dose/kg/min X weight = total dose of drug per minute
  • Total dose per minute X 60min (1hr) = Total dose each hour
  • How many hours are needed?
  • Divided by drug concentration and add to any volume of your choice for infusion

Surgery I (37 decks)

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