Principles of monitoring Flashcards
When should low-tech monitoring be done? What kind of special equipment exists for monitoring patients?
ALWAYS
ECG, BP (doppler, ocillometric, direct); pulse oximetry, expiratory, end-tital CO2
What 4 things are done to monitor heart rate/rhythm?
- Auscultation
- Stethoscope/esophageal
- Count rate and detect abnormal rhythm
- Pulse oximeter (SpO2)
- Provides HR (not always accurate if poor signal)
- May provide sense of rhythm (plethysmograph)
- Doppler BP
- Accurate pulse rate and sense of rhythm
- ECG
- HR number may/may not be accurate
- Only way to determine TYPE of rhythm
How is heart rate controlled?
- Parasympathetic (vagal)
- Sinoatrial (SA), atrioventricular (AV) nodes
- Muscarinic receptors (M1)
- Sympathetic
- SA, AV nodes; ventricular
- Alpha1 (minimal) and beta1, 2 receptors
What are some causes of bradycardia?
- **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
What are some causes of tachycardia?
- Increased sympathetic tone
- Stimulation; pain
- Hypovolemia; blood loss
- Very elevated CO2
- Hypoxemia
- Drugs (ketamine, inotropes)
- Disease (pheochromocytoma; hyperthyroidism)
ECG–general
- Electrical activity of the heart
- Composite of all the action potentials
What does each wave/interval on the ECG represent?
- 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
T/F: The ECG says nothing about the function of the heart
TRUE
How do you assess the ECG for rhythm (what all do you check)?
- 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
What are some rhythms that are variations of normal?
- Sinus bradycardia
- Sinus tachycardia
- Sinus (respiratory) arrhythmia
- Wandering pacemaker (P waves vary slightly)
Why is it important to monitor the ECG?
- 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
T/F: You can just use the monitor to evaluate heart rate
FALSE–count with the doppler, palpation, SpO2, or auscultate!
What abnormalities are detected on the ECG that might sound normal with a stethoscope?
- 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
Circulation/perfusion–O2 uptake and delivery
- O2 uptake–functioning lungs
- Adequate CO for O2 delivery
- Functioning heart with adequate amount of Hgb to carry O2
Cardiac output–what is it and what does it depend on?
- 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
- Stroke volume depends on venous return (Frank Starling)
What specialized equipment does cardiac output require?
- Invasive–catheter into pulmonary artery + computer monitor
- Lidco
- Not typically utilized in clinical patients
What are the determinants of blood pressure? Is it easy/good to measure?
- BP = CO X SVR
- Easy to measure, but not necessarily a good measure of perfusion if SVR is high
What are the expected normal pressures?
- 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
Why do we want good BP?
- 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
How do we measure BP?
- Indirect (non-invasive)
- Doppler ultrasonic flow
- Oscillometer
- Direct (invasive)
- With arterial catheter and transducer recording system or fluid-filled tubing to a sphygmomameter
How does the doppler ultrasonic flow detector work?
- 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
What are the advantages of using doppler?
- 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
What are the steps to setting up/using the doppler?
- Clip hair
- Apply generous amount of ultrasound gel or KY (NOT ECG lube–destroys probe)
- Probe placed over peripheral artery (dorsal pedal, radial, coccygeal) and taped in place
- Cuff placed proximal (above) to crystal–attached to sphygmonanometer
- Inflate cuff until sound disappears–then release SLOWLY until sound returns (systolic)
- Difficult to detect diastolic (change in frequency as pressure decreases), therefore only systolic is recorded
What are some doppler disadvantages?
- 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
How does the oscillometer work?
- 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
What are the advantages of using an oscillometer?
- 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
What are the disadvantages of using an oscillometer?
- 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
What affects the accuracy of indirect methods when measuring BP?
- 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
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.
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.
T/F: Doppler (cats) underestimates true systolic but is a better predictor of mean
TRUE
How do you directly measure blood pressure (invasive)? Which vessel do you use in each species?
- 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
What BP monitoring system is this? Which part is which? How do you initiate the reading?
- 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
What are the requirements for direct BP monitoring via a transducer?
- 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
- Too low = inc. 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
What does the shape of the pressure wave tell us?
- 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
What does this pressure wave tell us?
Patient is hypovolemic
Compare the 2 forms of invasive BP monitoring (3 points about each).
- 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
- More expensive–part of a multiparameter ECG machine
- 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
- Relatively inexpensive and very portable (no electronics/monitor involved)
How can we “fix” low BP?
- Evaluate patient depth AND evaluate quality of pulse
- Check cuff (transducer) position properly placed
- Reduce inhalent if possible
- Evaluate HR
- Need volume?
- Increase inotropy
- Or increase SVR (de-vasodilate)
What should be checked if a patient is hypertensive?
- 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
What are some causes of hypertension?
- Light anesthesia
- Pain
- Drugs
- Catecolamines/ketamine
- Disease processes
- Inc. intracranial pressure
- Renal, adrenal diseases
- Pheochromocytoma
What are some causes of hypotension
- Bradycardia
- Vasodilation
- Drugs
- Anesthetics; sedatives
- Cardiac, renal meds
- Drugs
- Poor cardiac function–disease or drug-induced or dysrhythmia
- Hypovolemia/shock/sepsis
What are the causes of hypothermia during anesthesia?
- 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)
What is the significance of hypothermia?
- 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
Temperature monitoring during surgery
- 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
Heating units: do’s/don’ts
- 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
