Intra-operative Blood Pressure Flashcards
What is blood pressure a product of? What does it provide?
cardiac output and systemic vascular resistance
measurable variable of oxygen delivery and hydraulic force that drives blood flow and tissue perfusion
What are immediate, short-term, and long-term controls of blood pressure?
IMMEDIATE = baroreceptor and chemoreceptor reflexes, cerebral ischemic response
SHORT-TERM = capillary shift removes excess volume, renin release from juxtaglomerular cells due to hypotension
LONG-TERM = changes in blood volume and GFR
What are 2 consequences of hypotension?
- decreased cerebral, coronary, and renal perfusion
- GI translocation
What are some consequences of hypertension? What organs are most susceptible?
- edema
- hemorrhage
- myocardial disease
- retinopathy, detachment
- encephalopathy
- herniation
- renal disease
brain and lungs
When is it common to see hypotension during anesthesia?
- immediately after induction
- repetitive induction bolus administration
- high inhalant concentrations
- intraoperative CRIs
When is it common to see hypertension during anesthesia?
- sx: pheochromocytoma, thyroid tumors
- pain
- pre-existing hypertension
- comorbidity
What are the 4 most common sites for arterial pulse palpation, doppler placement, or arterial catheterization?
- dorsal palmar artery
- femoral artery
- palmar arch
- coccygeal artery
What is sphygmometry? How does it compare to manometry?
application of an oclcusive cuff over an artery in a cylindrical appendage
visualization of the positive deflections in the dropping pressure gauge
What are Korotkoff sounds?
direct arterial auscultation for return of arterial sounds
How are smaller patients’ blood pressures estimated by Doppler?
typically underestimates systolic pressure and may better estimate mean pressure
How does oscillometry work?
instrument automatically inflates and deflates a cuff and the machine analyzes the fluctuations of pressure within the cuff
- initial pulse = systolic
- last pulse = diastolic
- maximal oscullations = mean
What is high-definition oscillometry? What 3 things does it accommodate for?
oscillometric measurement that combines both Doppler and oscillometry technology
- faster processing
- extremes of heart rate seen in small animals
- movement variables
What are 4 advantages and disadvantages associated with direct arterial blood pressure monitoring?
ADVANTAGES - continuous, accurate (gold standard!), real-time display, allows for arterial sampling
DISADVANTAGES - complications and risks more common, training required, expensive, time-intensive
What 6 sites are commonly used for direct blood pressure measurements? In what animals is this done with caution?
- dorsal metatarsal artery
- radial/carpal artery
- coccygeal artery
- lingual artery
- femoral artery
- auricular artery
cats and exotics with poor collaterals
What 6 risks are associated with direct arterial blood pressure monitoring?
- hemorrhage
- arterial occlusion/thrombosis*
- infection (stopcocks!)
- digital or extremity ischemia
- embolism
- accidental intra-arterial injection
What 4 site injuries are associated with direct arterial blood pressure monitoring?
- hematoma and bruising
- nerve trauma
- arteriovenous fistula
- aneurysm
What equipment is necessary for direct arterial blood pressure monitoring?
- clippers, gloves, sterile prep
- Lidocaine, 25 g needle
- 22-20 g heparinized catheter
- heparinized saline flushes
- three-way stopcock
- low-volume high-pressure extension cannula
- bandages, adhesives
- flushed transducer
- cable attached to transducer (monitor)
How are animals positioned for dorsal pedal artery catheterization? Where is this artery found?
lateral recumbency, working on the down hindlimb
branch of the cranial tibial artery, located near the hock —> runs craniolateral to medial, proximal to distal over the dorsal surface of the hock
How are animals positioned for femoral artery catheterization? What landmarks are used to locate it?
lateral recumbency, working on the down hindlimb
- CRANIAL: femur
- CAUDAL: pectineus
- within the femoral triangle close to the groin
How are animals positioned for palmar arch catheterization? Where is this artery located?
dorsal recumbency with forelimb extended
branch of the median artery located on the palmar surface of the forefoot abaxial to first digit and distal to carpal pad
What can increase circulation and vessel dilation for arterial catheterization?
warming area up
What is avoided when preparing arterial catheterization site?
- alcohol rinse —> use saline and chlorohexidine/betadine
- aggressive scrubbing
What is a pro and con to using local anesthetics for arterial catheterization? Why isn’t releasing the incision necessary
- PRO - increases comfort
- CON - may obscure vessel palpation and pulsations
may cause arterial spasm
How are catheters prepared for direct BP monitoring? How does placement compare to venous catheterization?
flushed with heparinized saline and separated from stylet then carefully replaced
- angle of entry is increased
- passage through muscular intima needs to be abrupt to observe a flash
How should the catheter be advanced when a flash is observed? When can the stylet be removed?
angle of entry is reduced to 10-15 degrees and seeded 1-2 mm
when prefilled heparinized stopcock is off toward the patient
How does the transducer monitor BP?
- column of saline transmits pressure changes to membrane in transducer
- membrane senses fluctuations and transducer changes the fluctuations to electrical signals
Where should the transducer holder/tray be placed? In what 3 ways does the transducer need to be prepared?
level with the right atrium
- (heparinized) saline priming
- assurance of no air bubbles
- zeroed to atmospheric pressure - 0 at systolic, diastolic, and mean at arterial pressure on anesthesia monitor
How is the transducer zeroed? Where is this done?
exposed to atmospheric pressure to establish a zero pressure reference value against which all intravascular pressures are measured
to the midchest, where the aortic root/right atrium is found at the midaxillary line
What are the 6 major parts of the waveform produced from direct blood pressure monitoring?
- systolic upstroke - aortic valve opens and pressure increases
- systolic peak pressure
- systolic decline - aortic valve begins to close
- dicrotic notch
- diastolic runoff
- end-diastolic pressure - minimum diastolic pressure
What are the main 2 abnormal tracing problems that can occur once the direct BP monitoring gain is set correctly?
- dampening
- resonance
What are 5 causes of resonance on direct BP monitoring? How is the waveform affected?
- long tubing
- overly stiff, non-compliant tubing
- increased vascular resistance
- reverberations in tubing causing harmonics that distort the trace
- non-fully opened stopcock
spiked traces that overstimulate BP
What are 6 causes of dampening on direct BP monitoring? How is the waveform affected?
- air bubbles
- overly compliant, distensible tubing
- catheter kinks
- clots
- injection ports
- low flush pressure or no fluid in flush bag
wide, slurred, flattened tracing that underestimates BP
What should be thought about if a trace is lost during direct BP monitoring?
- Is the arterial catheter clotted?
- Is the artery spasmed? (cool vs. warm leg, pressors?)
- Is the dressing or tape too tight?
- Did the catheter kink going into the patient?
- Did the scale change?
- Did the cable come loose?
What indicated problems with A line?
- prolonged CRT
- pale MM
- cooling
- swelling
What are 4 precautions that need to be heeded with arterial catheterization?
- needles or catheters should not be advanced against resistance
- repetitive attempts can cause spasm and damage vessels
- catheters and stylets should not be reapposed post-separation while under the skin or in vessel to avoid catheter fragmentation
- low compliance, narrow bore, low volume extension sets, and stopcocks should be used
What are arterial lines flushed with? How often? What are 4 risks to excessive flushing?
heparin concentration in saline q 4-6 hrs at slow speeds (1-1.5 mL)
- infection
- embolism
- vessel damage
- rapid volume change can cause hemodynamic instability
How do the different inhalants affect the cardiovascular system?
- Isoflurane and Desflurane can cause sympathetic stimultion and can increase HR, which reduces SV
- Halothane reduces contractility and maintains SVR
- Sevoflurane, Desflurane, and Isoflurane reduce SVR and maintain contractility (truly vasodilatory)
What are 4 causes of intraoperative hypotension?
- decreased preload - dehydration, hemorrhage, fluid loss, Acepromazine, induction agents, decreased venous return, mechanical ventilation
- decreased contractility - arrhythmias, bradycardia
- increased afterload - Dexmedetomidine
- decreased HR - Dexmedetomidine, opioids, induction agents, vagal stimulation
What are some additional causes of intraoperative hypotension?
- vasoconstriction
- hypothermia
- technical issues: cuff size, Doppler securement too tight, limb positioning, retraction and reduced arterial supply, table ties, large dog positioning
- locoregional block sympatholysis
- waiting for surgical stimulation (cats)
- pleural or pulmonary disease restricting preload
What is the general systemic review before treating intra-operative hypotension?
- signalment
- positioning
- preexisting medication: Trazodone, Enalapril
- problem list: low TP, intestinal FB
- surgery
- anesthetics: Acepromazine, label dose of Dexmedetomidine, Propofol
What needs to be ruled out before treating intra-operative hypotension?
technical issues —> attempt other means of pressure measurement
- expect ~10 mmHg difference in cats and small dogs
Why is the plane of anesthesia important to note when deciding to treat intra-operative hypotension?
- if deep - lower the inhalant concentration or CRI (will increase SVR)
- if light - stop repeating induction boluses and administer opioids, sedatives, anti-inflammatories
What fluid therapy is recommended to treat intra-operative hypotension?
- crystalloid bolus
- crystalloid + colloid bolus
- crystalloid + hypertonic saline bolus
How can mechanical ventilation affect intraoperative blood pressure?
- increases depth of anesthesia
- decreases venous return and CO —> if hypotensive, considering stopping or reducing
- V/Q mismatching
- hyperventilation = respiratory alkalosis
- baro/volutrauma
How are pulse rates used when deciding how to treat hypotension?
- HIGH = pursue rule outs for tachycardia and tachyarrhythmias (hemorrhage and third space loss) - administer bolus
- LOW = pursue rule outs for bradycardiac and bradyarrhythmias - warm the patient, remove vagal pressure, use anticholinergic, reduce fluid rate
In what 4 situations does pharmacologic manipulation of hypotension work?
- plane of anesthesia allows for sympathetic response
- volume is adequate or restored
- pre-existing medications allow function
- problem list is addressed
What are some common reasons for intraoperative hypertension?
- technical errors: vasoconstriction, cuff/Doppler wrap issues, patient positioning
- light anesthesia
- hypothermia
- drugs: thyroxine, ketamine, anticholinergics, antibiotic reactions
- hypoxia, hypercarbia
- adrenal diseases: Cushings, pheochromocytoma
- thyroid diseases
- hydrocephalus, syringomyelia
- mast cell release
- pulmonary disease
- renal disease
- large-breed dogs and cats with volume overload
Is the goal of intraoperative hypertension? What should be avoided?
decrease BP by no more than 25% if consistently elevated pathologically - prevention is best!
- withdrawal of anti-hypertensive agents pre-op (rebound hypertension likely)
- systolic spikes
- hypotension
What are the general systematic treatment of itra-operative hypertension?
- review signalment, pre-existing problem list, and medication list
- rule out technical errors
- rule out light plane of anesthesia (non-surgical stimuli and surgical stimuli) —> can increase oxygen flow and vaporizer, administer IV premeds
- reduce fluid volume/rate
- check body temperature
- check oxygen and ventilatory status
What rescue agents are commonly used for pain?
- opioids: hydromorphone, fentanyl, premed
- ketamine
- dexmedetomidine: microdose
- lidocaine
- turn up oxygen flow rate and vaporizer
What rescue agents are commonly used for anxiety?
- midazolam
- acepromazine
- butorphanol
- microdose propofol and alfaxalone (repeated = hypotension)
What resuce agents are commonly used for inflammation?
- local blocks: IV lidocaine
- steoid: dexamethasone sodium phosphate
- NSAIDs: meloxicam, carprofen
Direct arterial blood pressure monitoring requires transducer zeroing post filling with saline in order to pressure reference value against which all intravascular pressures are measured. The transducer is “zeroed” at the level of the
a. The right ear drum
b. The last rib costochondral junction which approximates the jugular vein
c. The coxofemoral joint
d. The vagosympathetic trunk
e. Aortic root which most commonly approximates the manubrium of the sternum in small animals
E
A direct arterial blood pressure waveform on the monitor should show/illustrate/display nicely a single dicrotic notch. If it doesn’t, two problems that may be affecting it are:
a. Dampening and resonance or ringing
b. Fluctuation and straightness
c. Resonation and resonance
d. Resistance and dampening
e. Ringing and dinging
A
All of the following are consequences of direct arterial catheter placement EXCEPT:
a. Fracture
b. Ischemia due to arterial injury
c. Embolism
d. Arterial injury including spasm, thrombosis, hematoma
e. Nerve injury
A
Hypotension is much more common of an intraoperative problem for patients under anesthesia because of all the following EXCEPT:
a. Excessive endotracheal tube length
b. Excessive inhalant (isoflurane/sevoflurane) concentration
c. Excessive CRI (continuous rate infusion) rates
d. Excessive locoregional block (sympatholysis)
e. Technical errors such as hypothermia and vasoconstriction mimicking hypotension
A
Blood pressure can be measured indirectly with an oscillometric device, a sphygmomanometer, or a Doppler device, all of which utilize a “cuff”. To measure appropriately, the the width of this cuff should be:
a. The circumference of the appendage on which its placed
b. 20% of the circumference of the appendage on which its placed
c. 30-40% of the circumference of the appendage on which its placed
d. 80% of the circumference of the appendage on which its placed
e. 10% the circumference of the appendage on which its placed
C
Systemic Vascular Resistance (SVR) is a product of which bed of vascular tissue?
a. Capillaries
b. Vena cava and large veins
c. Venules
d. Veins
e. Arterioles
E
Hypotension is defined as:
a. A SAP >60
b. A consistent MAP <90
c. A consistent MAP (mean arterial pressure) of 80 or below
d. A consistent SAP (systolic arterial pressure) <80 OR a consistent MAP <60
e. A MAP <40
D
Oxygen delivery is a combination of two variables, both of which are assessed intraoperatively via monitoring blood pressure. Which variables are they?
a. Stroke volume and preload
b. Oxygen content and stroke volume
c. Preload, afterload and contractility
d. Cardiac output and stroke volume
e. Cardiac output and oxygen content
E
Dopamine increases blood pressure by acting on which of the following receptor classes?
a. Dopamine, alpha and beta
b. Dopamine and alpha
c. Phosphodiesterase enzymes
d. Just dopamine
e. Acetylcholine
A
Direct arterial blood pressure monitoring relies on a catheter being placed in an artery. In small animals, all of the following are accessible arterial sites in which to place this catheter EXCEPT:
a. The lingual artery
b. The thoracic artery a branch of the mammary artery
c. The dorsal metatarsal artery
d. The coccygeal artery
e. The palmar artery, a branch of the radial artery
B
Intraoperative hypotension can be treated by assessing and addressing all of the following variables that summate or produce MAP (mean arterial pressure) EXCEPT:
a. SV by lowering inhalant concentration
b. HR by warming a patient and administering an anticholinergic if the heart rate is too low
c. SVR by lowering inhalant concentration
d. SV by reducing tidal volume, frequency of mechanical ventilation or simply stopping the mechanical ventilator and allowing the patient to return to spontaneous breathing
e. SV by administering crystalloids and or colloids
A
How can it be confirmed that an arterial catheter was actually put in an artery and not a vein?
- artery = more craniomedial
- higher pressure = blood will spurt out of catheter before the cap is put on
- arterial blood is a brighter red
- may see pulsation of blood within the catheter
