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Anesthesiology > Principles of monitoring > Flashcards

Principles of monitoring Flashcards

1
Q

When should low-tech monitoring be done? What kind of special equipment exists for monitoring patients?

A

ALWAYS

ECG, BP (doppler, ocillometric, direct); pulse oximetry, expiratory, end-tital CO2

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2
Q

What 4 things are done to monitor heart rate/rhythm?

A
  1. Auscultation
    1. Stethoscope/esophageal
    2. Count rate and detect abnormal rhythm
  2. Pulse oximeter (SpO2)
    1. Provides HR (not always accurate if poor signal)
    2. May provide sense of rhythm (plethysmograph)
  3. Doppler BP
    1. Accurate pulse rate and sense of rhythm
  4. ECG
    1. HR number may/may not be accurate
    2. Only way to determine TYPE of rhythm
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3
Q

How is heart rate controlled?

A
  • Parasympathetic (vagal)
    • Sinoatrial (SA), atrioventricular (AV) nodes
    • Muscarinic receptors (M1)
  • Sympathetic
    • SA, AV nodes; ventricular
    • Alpha1 (minimal) and beta1, 2 receptors
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4
Q

What are some causes of bradycardia?

A
  • **Increased parasympathetic tone (Vagal stimulation)
    • Pressure on eyeball
    • Pulling on viscera
    • Drugs (opioids; alpha2 agonists)
    • Possible profound depth of anesthesia (lack of sympathetic tone)
    • High serum K+
    • SA nodal disease
      • Complete heart block
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5
Q

What are some causes of tachycardia?

A
  • Increased sympathetic tone
    • Stimulation; pain
    • Hypovolemia; blood loss
    • Very elevated CO2
    • Hypoxemia
    • Drugs (ketamine, inotropes)
    • Disease (pheochromocytoma; hyperthyroidism)
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6
Q

ECG–general

A
  • Electrical activity of the heart
  • Composite of all the action potentials
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7
Q

What does each wave/interval on the ECG represent?

A
  • P wave = atrial depolarization
  • P-R interval = duration of transmission from atria to ventricle
  • QRS = ventricular depolarization–Q and S normally variable
  • S-T interval = time to repolarization of ventricles
  • T wave = repolarization of ventricles
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8
Q

T/F: The ECG says nothing about the function of the heart

A

TRUE

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9
Q

How do you assess the ECG for rhythm (what all do you check)?

A
  • P wave for every QRS
  • A QRS for every P wave
  • All the QRS’s should look the same
  • All the P waves should look similar
  • R-R intervals should be regular
  • All P-R intervals should be regular (most important interval)
  • T wave–positive or negative–but should not be changing
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10
Q

What are some rhythms that are variations of normal?

A
  • Sinus bradycardia
  • Sinus tachycardia
  • Sinus (respiratory) arrhythmia
  • Wandering pacemaker (P waves vary slightly)
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11
Q

Why is it important to monitor the ECG?

A
  • Arrhythmias are common during the anesthesia period (even in animals w/ no pre-existing cardiac disease)
  • Most are benign requiring no treatment–as long as they do not cause hemodynamic compromise
  • Some may progress to a potential serious outcome–and warrants close observation w/ or w/o treatment
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12
Q

T/F: You can just use the monitor to evaluate heart rate

A

FALSE–count with the doppler, palpation, SpO2, or auscultate!

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13
Q

What abnormalities are detected on the ECG that might sound normal with a stethoscope?

A
  • Abnormalities in conduction (hyperkalemia) will sound regular with a doppler or stethoscope
  • Some arrhythmias when sustained (ventricular dysrhythmia) are regular and can sound like a regular rhythm with a doppler and will produce pulses if rate is not so high as to reduce output
  • AND–we cannot treat dysrhythmia if we don’t know what kind it is
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14
Q

Circulation/perfusion–O2 uptake and delivery

A
  • O2 uptake–functioning lungs
  • Adequate CO for O2 delivery
    • Functioning heart with adequate amount of Hgb to carry O2
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15
Q

Cardiac output–what is it and what does it depend on?

A
  • Volume of blood ejected by the heart (L/min or ml/kg/min)
  • Depends on HR and SV
    • Stroke volume depends on venous return (Frank Starling)
      • Preload; afterload contractility
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16
Q

What specialized equipment does cardiac output require?

A
  • Invasive–catheter into pulmonary artery + computer monitor
  • Lidco
  • Not typically utilized in clinical patients
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17
Q

What are the determinants of blood pressure? Is it easy/good to measure?

A
  • BP = CO X SVR
  • Easy to measure, but not necessarily a good measure of perfusion if SVR is high
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18
Q

What are the expected normal pressures?

A
  • Systole (SAP) = 100-140 mmHg
    • Inotropic phase
  • Diastole (DAP) = 50-70 mmHg
    • Venous return
    • Cardiac filling - coronary perfusion
  • Mean (MAP)–~65-85 mmHg
    • *Pressure that best represents systemic perfusion
    • MAP = (SAP - DAP)/3 + DAP
19
Q

Why do we want good BP?

A
  • For perfusion of tissues
  • In health, most organs are autoregulated over wide range of pressure to maintain flow
    • But when MAP < 80 flow (perfusion) decreases
  • Best to maintain MAP >60
20
Q

How do we measure BP?

A
  • Indirect (non-invasive)
    • Doppler ultrasonic flow
    • Oscillometer
  • Direct (invasive)
    • With arterial catheter and transducer recording system or fluid-filled tubing to a sphygmomameter
21
Q

How does the doppler ultrasonic flow detector work?

A
  • Place the probe over any peripheral artery (dorsal pedal; radial; coccygeal) with generous amount of U/S gel; taped into place
  • Probe has 2 crystals
    • 1 emits ultrasound waves to flowing blood
    • 1 receives waves reflected from moving RBCs
  • Woosh sound–is counted for accurate pulse rate–and irregular rhythm can be appreciated
22
Q

What are the advantages of using doppler?

A
  • Continuous evaluation of pulse rate–there are no false positives
    • Changes in rhythm signal that there is some type of dysrhythmia present (can’t identify the type of dysrhythmia–need ECG)
  • Sudden loss of sound indicates either cardiac arrest or equipment failure
    • Good reason to use esophageal stethoscope for backup
  • Useful for tiny and/or exotic patients
  • Relatively inexpensive
23
Q

What are the steps to setting up/using the doppler?

A
  1. Clip hair
  2. Apply generous amount of ultrasound gel or KY (NOT ECG lube–destroys probe)
  3. Probe placed over peripheral artery (dorsal pedal, radial, coccygeal) and taped in place
  4. Cuff placed proximal (above) to crystal–attached to sphygmonanometer
  5. Inflate cuff until sound disappears–then release SLOWLY until sound returns (systolic)
  6. Difficult to detect diastolic (change in frequency as pressure decreases), therefore only systolic is recorded
24
Q

What are some doppler disadvantages?

A
  • Requires operator for BP
  • First sound that occurs is assumed to be systolic, is it the first weak sound? Or first strong sound?
    • Subject to interpretation
  • No mean
  • Difficult to capture sound if vasoconstriction; hypothermia; poor pressure
25
Q

How does the oscillometer work?

A
  • Automated inflation of cuff then deflation until machine senses flow (oscillations–blood flow under the cuff)
  • The largest oscillations at the highest cuff inflation pressure = mean–most accurate
  • Then algorithm calculates systolic and diastolic
  • Different companies vary in accuracy in animals
    • Cardell and surgivet seem accurate
26
Q

What are the advantages of using an oscillometer?

A
  • Measures mean then calculates systolic and diastolic
  • Automated–can be set at required intervals - q 3-5 min
    • Operator not necessary
  • May store values for review and to display trends; multimodal monitors
27
Q

What are the disadvantages of using an oscillometer?

A
  • Relatively expensive
  • May not secure pressure at extremities of heart rate or during irregular rhythms–requires steady heart rate/rhythm
  • May not read if very hypotensive
  • In between readings–nothing–>listen to doppler or esophageal steth
28
Q

What affects the accuracy of indirect methods when measuring BP?

A
  • Cuffs contain a bladder which is inflated to occlude the arterial flow
  • Bladder width should be 40% (cats) to 40-60% dogs of the circumference of the limb (or tail)
  • Too large width of bladder = lower than actual pressure; too small width of bladder = higher than actual pressure
  • f cuff is too tight = BP erroneously lower; if cuff is too loose = BP erroneously higher
  • Bladder in the cuff should be placed over artery–some cuffs contain bladder throughout the cuff (surgivet)
  • Limb must be straight and not flexed
  • Cuff should be at heart level (below heart = erroneously high BP)
  • Cuff must not slip over a bone/joint
  • Tape around cuff might affect accuracy
29
Q

T/F: For indirect methods (Cardell; surgivet), diastolic typically is underestimated particularly at high pressures but monitors were accurate for mean, systolic at low and moderate hypotensive pressures.

A

FALSE–For indirect methods (Cardell; surgivet), SYSTOLIC typically is underestimated particularly at high pressures but monitors were accurate for mean, DIASTOLIC at low and moderate hypotensive pressures.

30
Q

T/F: Doppler (cats) underestimates true systolic but is a better predictor of mean

A

TRUE

31
Q

How do you directly measure blood pressure (invasive)? Which vessel do you use in each species?

A
  • Arterial catheter (dorsal pedal, coccygeal, radial artery); not always easy, esp. dogs/cats
    • BP usually displayed with transducer + monitor
  • Dog/cat–dorsal pedal, coccygeal, radial
  • Horse–transverse facial, facial, dorsal metatarsal
  • Ruminants–caudal auricular
32
Q

What BP monitoring system is this? Which part is which? How do you initiate the reading?

A
  • Direct pressure set up–using ressure manometer
  • a = arterial catheter
  • b = saline filled tubing (sterile)–saline should not pass by 2nd stopcock
  • c = 3 way stopcock
  • d = saline syringe (could also be saline line attached to bag)
  • e = manometer (avoid fluid entering)
  • Fill saline towards 2nd stopcock; then allow fluid to equilibriate with arterial blood flow–> mean pressure displayed in manometer
33
Q

What are the requirements for direct BP monitoring via a transducer?

A
  • Transducer must be 0’d to atm/calibrated
  • *Transducer must always be at level of the heart
    • ​Too low = inc. pressure
      • Too high = dec. pressure
  • No air bubbles, blood clots in tubing
  • Tubing–ideally non-compliant (stiff); not excessively long (between catheter and transducer)
  • Catheter should be flushed frequently
34
Q

What does the shape of the pressure wave tell us?

A
  • Slope of inotropic phase dec.–dec. inotrophy, SV, CO and will increase w/ catecholamines (inotropes)
  • A narrow wave (dec. volume displacement phase) suggests dec. SVR (vasodilation) and a lower diastolic pressure
  • Positive pressure ventilation - impedes venous return and CO –> BP dec. after each breath
    • If effect is pronounced, suggests hypovolemia
35
Q

What does this pressure wave tell us?

A

Patient is hypovolemic

36
Q

Compare the 2 forms of invasive BP monitoring (3 points about each).

A
  • Electronically
    • More expensive–part of a multiparameter ECG machine
      • Monitor; transducers; tubing–not very portable
    • Provides SAP, DAP, mean with waveform
      • Continuous display
    • Waveform–provides info about quality of inotropy and venous return
  • Sphygmomanometer
    • Relatively inexpensive and very portable (no electronics/monitor involved)
      • Tubing and sphygmo
    • Only provides mean (still useful)
      • Not recommended for continuous display (clots)
    • No waveform
37
Q

How can we “fix” low BP?

A
  1. Evaluate patient depth AND evaluate quality of pulse
    1. Check cuff (transducer) position properly placed
  2. Reduce inhalent if possible
  3. Evaluate HR
  4. Need volume?
  5. Increase inotropy
  6. Or increase SVR (de-vasodilate)
38
Q

What should be checked if a patient is hypertensive?

A
  • Check depth–is he light? Painful?
  • Check cuff transducer/placement
  • Is HR also higher? Or did it get lower?
  • True hypertension not common
    • Neurologic patient
    • Endocrine disease
39
Q

What are some causes of hypertension?

A
  • Light anesthesia
  • Pain
  • Drugs
    • Catecolamines/ketamine
  • Disease processes
    • Inc. intracranial pressure
    • Renal, adrenal diseases
      • Pheochromocytoma
40
Q

What are some causes of hypotension

A
  • Bradycardia
  • Vasodilation
    • Drugs
      • Anesthetics; sedatives
      • Cardiac, renal meds
  • Poor cardiac function–disease or drug-induced or dysrhythmia
  • Hypovolemia/shock/sepsis
41
Q

What are the causes of hypothermia during anesthesia?

A
  • Decreases muscular activity; metabolism and hypothalamic thermostatic activity
  • Evaporated heat loss
    • Open body cavities, surgical scrub solutions
    • Non-insulated surfaces, infused cold solutions
  • Anesthesia-induced vasodilation during induction produces core to peripheral redistribution of body heat
    • May drop 1-1.5C (2-3F) during 1st hour
    • Decreases linearly as heat loss to environment > heat produced metabolically
    • Core temp stabilizes over time (~3hr)
42
Q

What is the significance of hypothermia?

A
  • Down to 96-97F (36C): minimal–some shivering may occur in recovery
    • Shivering increases O2 consumption and can be bad in patients with cardiac and pulmonary diseases
  • Down to 92-94F (33-34C)–decreases anesthetic requirement
    • Prolongs anesthetic recovery–too low to shiver in recovery
  • 89-90F (32-33C)–HR
    • CO decreases–may not respond to treatment (drugs)
    • Significantly reduces anesthetic requirements
    • Blood viscosity increases; may interfere with wound healing mechanisms
43
Q

Temperature monitoring during surgery

A
  • Should be routine
  • Be aware–heavily coated dogs can also become hyperthermic with applied heating
  • Esophageal probes–electric monitoring; continuous
  • Oral thermometer–oral cavity can work well (follow trends)
  • Must be monitored intermittently throughout recovery until normal
44
Q

Heating units: do’s/don’ts

A
  • Forced warm air units–may be the most reliable, effective, and safest method; may be expensive
    • Paper blankets; cloth blankets, washable; burns unlikely
  • Warm water circulating pads/blankets–must be careful to avoid direct contact on the skin–> excessive heat burns can occur (less likely)
    • NEVER use typical heating pads–burns can occur
  • Pads underneath patient during induction and preparation–important to minimize initial heat loss

Anesthesiology (16 decks)

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