Equipment and Monitoring Flashcards
What components are present in the high pressure system of the anesthesia machine?
What is the gas pressure dependent upon?
Begins at cylinder
Ends at cylinder regulators.
Hanger yoke
Yoke block with check valves
cylinder pressure gauge
cylinder pressure regulator
Gas pressure = cylinder pressure
What components are present in the intermediate pressure system of the anesthesia machine?
Begins at pipeline
Ends at the flowmeter valve.
- Pipeline inlets
- Pressure gauges
- Ventilator power inlet
- Oxygen pressure failure system
- Oxygen second stage regulator
- Oxygen flush valve
- Flowmeter valve
Gas pressure = 50psi (if using pipeline) and 45 psi (if using tank)
What components are present in the low pressure system of the anesthesia machine?
Begins at the flowmeter tubes
Ends at common gas inlet
- Flowmeter tubes (Thorpe tubes)
- Vaporizers
- Check valves (if present)
- Common gas outlet (CGO)
Gas pressure = slightly above atmospheric pressure
What are the 5 tasks of oxygen in the anesthesia machine?
see photo in E&M: Anesthesia Machine
- O2 pressure failure alarm
- O2 pressure failure device (failsafe)
- O2 flowmeter
- O2 flush valve
- ventilator drive gas (if pneumatic bellows)
Describe the pin index safety system (PISS)
The PISS prevents inadvertent misconnections of gas cylinders.
Pin configuration on each hanger yoke assembly is different for each gas, making unintended connections of the wrong gas unlikely, but not impossible.
*the presence of more than 1 washer between the hanger yoke assembly and the stem of the tank may allow the PISS to be bypassed.
What is the PISS configuration of Air, Oxygen, and N2O?
Air = 1,5 O2= 2,5 N2O= 3,5
Describe the diameter index safety system (DISS):
DISS prevents inadvertent misconnections of gas hoses. Each gas hose and connector are sized and threaded for each individual gas.
What are the maximum pressures and volumes for cylinders that contain air, O2, and N2O?
Air:
1900 psi
625 L
O2:
1900 psi
660L
N2O: 745 psi 1590 L wt full 20.7 lbs wt empty 14.1 lbs
The bourdon pressure gauge on an O2 cylinder reads 500psi. if the flow rate is 4 L/min, how long will this cylinder provide O2 to the patient?
- Tank capacity (L) / Full tank pressure (psi) = Contents remaining (L) / gauge pressure (psi)
- Contents remaining (L) / flow rate (L/min) = minutes left before take expires
660 L / 1900 psi = X/500 psi = 174 L
174 L/ 4 L per min = 43.4 minutes
Is it ever safe to use on O2 tank in the MRI suite?
Never take a cylinder into the MRI scanner unless it is made of non-magnetic material, such as aluminum.
An MRI safe cylinder will have 2 colors: most of the tank is silver and only the top is the color that signifies the gas it contains.
List 3 safety relief devices that prevent a cylinder from exploding when the ambient temperature increases.
In the event of an environmental fire, there is a safety relief device built into the cylinder that allows the cylinder to empty its contents in a slow and controlled way.
Ex include:
-A fusible plug made of Wood’s metal (melts at elevated temperatures)
-A frangible disk that ruptures under pressure
-A valve that opens at elevated pressures
Gas cylinders should never be exposed to temperatures higher than…
130F (57C) b/c temperature higher than this my lead to fire or explosions
Give 1 example of how the O2 pressure failure device (failsafe) might permit the delivery of a hypoxic mixture. (see photo in E&M Anesthesia machine)
The failsafe device checks pressure (not flow).
If there is a pipeline crossover, then the pressure of the new gas will provide the pressure to defeat the failsafe.
4 examples of how the hypoxia prevention safety device (proportioning device) might permit the delivery of hypoxic mixture:
- Oxygen pipeline crossover
- Leaks distal to the flowmeter valves
- Administration of a third gas (helium)
- Defective mechanic or pneumatic components
What is the difference between the oxygen pressure failure device and the hypoxia prevention safety device?
Oxygen pressure failure device:
A fail-safe device.
Shuts off and/or proportionately reduces N2O flow if O2 pressure drops below 20 psi.
Hypoxia prevention safety device:
Proportioning device.
Prevents you from setting a hypoxic mixture with the flow control valves.
Limits N2O flow to 3 times O2 flow (N2O max ~75%)
Describe the structure and function of the flow tubes:
Internal diameter of the flow tube is narrowest at the base and progressively widens along its ascent.
The annular space is area between the indicator float and side wall of tube. The annular space is also the narrowest at the base and widest at the top. This “variable orifice” architecture provides a constant gas pressure through out a wide range of flow rates.
- Laminar flow is dependent on gas viscosity (Poiseuille)
- Turbulent flow is dependent on gas density (Graham)
What is the safest flowmeter configuration on the anesthesia machine?
(see photo in E&M: Anesthesia machine)
The O2 flowmeter should always be furthest to the right!
Flowmeters are made of glass. They’re the most delicate part of the machine. A leak will allow O2 to escape the low-pressure system, and could result in hypoxic mixture.
The O2 flowmeter should be closest to manifold outlet (on right in USA). If leak develops in any other flowmeter, ti won’t reduce the FiO2 delivered to pt. If leak is in O2 meter, all bets are off.
How do you calculate the FiO2 set at the flowmeter?
FiO2= (air flow rate x21) + (O2 flow rate x100)/ total flow rate
An anesthesia machine uses fresh gas coupling. How do you determine the total tidal volume that will be delivered to the patient?
Vt total= Vt set on ventilator + FGF during inspiration - Volume lost to compliance
When using a ventilator that couple FGF to Vt, what type of ventilator changes will impact Vt delivered to patient?
Making nearly any changes will ultimately impact the Vt delivered.
Vt increases with:
- decreased RR
- increased I:E ratio (ex 1:2 to 1:1)
- increased FGF
- Increased bellow height
Vt decreases with:
- increased respiratory rate
- decreased I:E ratio (ex 1:2 to 1:3)
- decreased FGF
- decreased bellow height
what is the vaporizer splitting ratio? (see photo in E&M: Anesthesia machine
Modern variable bypass vaporizers split FGF into 2 parts:
- Some fresh gas enters the vaporizing chamber and becomes 100% saturated with VA.
- The rest of the gas bypasses the vaporizing chamber and does not pick up any VA.
Before leaving the vaporizer, these 2 fractions mix and this determines the final anesthetic concentration exiting the vaporizer.
By setting the concentration on the dial, you determine the splitting ratio.
Setting a higher concentration directs more FGF towards the liquid anesthetic.
Setting a low concentration directs less FGF towards liquid anesthetic.
What is the pumping effect?
Pumping Effect can increase vaporizer output.
Anything that causes fas that has already left the vaporizer to re-enter the vaporizing chamber can cause the pumping effect. This is generally d/t positive pressure ventilation or use of O2 flush valve.
Variable Bypass Vaporizer:
- Model
- Splitting ratio
- Method of vaporization
- Temperature compensation
- Calibration
- Position
- Elevation compensation
1. Datex-Ohmeda Tec 4, 5, 7ADU Aldain Drager Vapor 19, 2000 2. Variable bypass (slits FGF) 3. Flow over 4. Automatic 5. Agent specific 6. out of circuit 7. Yes
Injector (Desflurane) vaporizer:
- Model
- Splitting ratio
- Method of vaporization
- Temperature compensation
- Calibration
- Position
- Elevation compensation
1. Datex-Ohmeda Tec6 Drager D-Vapor 2. Dual circuit (fresh gas is not split) 3. Gas/vapor blender (heat creates vapor that is injected into FGF) 4. Electronically heated to 39C 5. Agent specific 6. Out of circuit 7. NO
What does the oxygen analyzer measure and where is it located?
Monitors O2 concentration (not pressure) and its the only device downstream of the flowmeters that can detect a hypoxic mixture. Indeed, leaks in anesthesia machine are most likely to occur in the low pressure system.
What 2 things must you do in the event of an oxygen supply line crossover?
- turn ON oxygen cylinder
- disconnect the pipeline oxygen supply. THIS IS KEY STEP!
Simply turning on O2 tank would not save the patient. If an adequate O2 pipeline pressure is present (regardless of the gas inside), it will prevent O2 tank from providing O2.
Pressing the O2 flush valve exposes the breathing circuit to _____ O2 flow and _____ O2 pressure.
flow = 35-75 L/min pressure = 50psi
2 risks of pressing O2 flush valve?
Barotrauma and awareness.
Pressing it during inspiration can cause barotrauma.
B/c gas from O2 flush doesn’t pass through vaporizer, excessive use of O2 flush adds gas to breathing circuit that doesn’t contain VA. It dilutes the PP of VA and may lead to awareness.
Describe the function of the ventilator spill valve in relation to using the O2 flush valve. (see photo in E&M: anesthesia machine)
If the O2 flush is pushed during expiration, the excess flow will first fill the bellows then the rest is vented out the scavenger.
Drive gas compresses the bellows. The flow rate of the drive gas is controlled by the inspiratory flow. This gas is outside the breathing circuit.
Inspiration: Drive gas compresses bellows–> drive gas closes spill valve–> FGF from the ventilator goes to pt.
Expiration: Expired gas refills bellows–> bellows fill completely–> when circuit pressure > 2-4 cmH2O expired gas is directed through the spill valve to the scavenger.
What is volume controlled ventilation?
VC delivers a preset Vt over a predetermined time. Since Vt is fixed, the inspiratory pressure will vary as the patient’s compliance changes. The inspiratory flow is held constant during inspiration.
Fixed: Vt, inspiratory flow rate, inspiratory time
Variable: peak inspiratory pressure
What is pressure controlled ventilation?
PC delivers a preset inspiratory pressure over a predetermined time. Since pressure and time are fixed, the Vt and inspiratory flow will be variable and dependent on the patient’s lung mechanics.
If airway resistance rises or lung compliance decreases, the Vt will suffer and a higher inspiratory flow will be required to achieve the preset airway pressure.
Fixed: Peak inspiratory pressure, inspiratory time
Variable: Vt, inspiratory flow
What decreases Vt during pressure controlled ventilation?
Decreased compliance:
- Pneumoperitoneum
- Trendelenburg position
Increased resistance:
- Bronchospasm
- Kinked ETT
What increases Vt during pressure controlled ventilation?
Increased compliance:
- Release of pneumoperitoneum
- Going from Tburg to supine
Decreased resistance:
- Bronchodilator therapy
- removing airway secretions
Soda lime has become exhausted in the middle of a surgical procedure. what is the best action to take next?
You maybe tempted to increase minute ventilation. While it will remove a greater amount of CO2 from the body, it doesn’t prevent the patient from rebreathing CO2 and may lead to hypercarbia. Instead, if you are unable to replace CO2 absorbent, the appropriate action is to increase the FGF to convert the circle system into a semi-open system.
what is desiccation, and how does it apply to soda lime?
Water is required to facilitate the reaction of CO2 with CO2 absorbent. The granules are hydrated to 13-20% by weight. When the absorbent is devoid of water, it is said to be desiccated. Ethyl violet informs you about exhaustion but it does NOT provide information regarding the water content of the CO2 absorbent.
In the presence of halogenated anesthetics, desiccated SL increases the production of carbon monoxide (des> iso»>sevo) and compound A in the presence of sevo.
- CO can cause carboxyhemoglobinemia
- CA can cause renal dysfunction
7 ways to monitor for disconnection of the breathing circuit:
(Pressure, Volume, ETCO2, and your own vigilance)
- precordial stethoscope
- visual inspection of chest rise
- capnography
- respiratory volume monitors
- low expired volume alarm
- low peak pressure alarm
- failure of bellows to rise with an ascending bellows (not with descending bellows or piston)
*O2 analyzer monitors the concentration of O2 in the breathing circuit. it is NOT a disconnect monitor
What are the OSHA recommendations regarding inhalation anesthetic exposure for health care workers in the operating room?
Halogenated agents alone < or = 2 ppm
N2O alone < or = 25 ppm
Halogenated agents + N2O < or = 0.5 ppm and 25ppm respectively
Open breathing circuit:
No rebreathing
No reservoir
EX: Insufflation
Simple face mask
NC
open drop
Semi-open circuit:
No rebreathing
Has reservoir
EX: Mapleson circuit (FGF dependent on design) circle system (FGF > minute ventilation)
Semi-closed circuit:
Yes (partial) rebreathing
Has reservoir
EX: Circle system (FGF < Minute ventilation)
Closed circuit:
Yes (complete) rebreathing
Has reservoir
EX: circle system with very low FGF and APL closed
What is the purpose of the unidirectional valves in the breathing circuit?
(see photo in E&M: breathing circuits)
To ensure that gas moves in one direction.
- If a valve becomes incompetent, then the patient will rebreathe exhaled gas.
- The definitive fix is to correct the valve
- If this cannot be done, then a closed or semi-closed system should be converted to a semi-open system.
Which mapleson circuit is most efficient for spontaneous ventilation? (see photo in E&M: breathing circuits)
Best: Mapleson A (A > DFE> CB)
Worst: B
Which mapleson circuit is most efficient for controlled ventilation? (see photo in E&M: breathing circuits)
Best: D (DFE > BC > A)
Worst: A
What conditions decrease pulmonary compliance?
How does this affect the peak pressure and plateau pressure?
(see photo in E&M: respiratory)
A decreased pulmonary compliance is usually d/t a reduction in static compliance (PIP and PP increase)
- Endobronchial intubation
- pulmonary edema
- pleural effusion
- tension pneumothorax
- atelectasis
- chest wall trauma
- abdominal insufflation
- ascites
- Tburg postion
- inadequate muscle relaxation
What conditions increase pulmonary resistance?
How does this affect the peak pressure and plateau pressure?
(see photo in E&M: respiratory)
An increased pulmonary resistance is usually d/t a reduction in dynamic compliance (PIP increases and PP is unchanged)
- Kinked ETT
- ETT cuff herniation
- Bronchospasm
- Bronchial secretions
- Compression of the airway
- foreign body aspiration
Describe the 4 phases of normal capnography:
see photo in E&M: respiratory
Phase 1: Exhalation of anatomic dead space (bottom flat line)
Phase 2: Exhalation of anatomic dead space + alveolar gas (slope up)
Phase 3: Exhalation of alveolar gas (plateau)
Phase 4: inspiration of fresh gas that does not contain CO2 (down slope)
Discuss the significance of the alpha and beta angles on the capnograph:
(see photo in E&M: respiratory)
An increased alpha angle (top left corner of capnograph wave form) signifies and expiratory airflow obstruction, such as COPD, bronchospasm, or kinked ETT.
The beta angle (top right corner) is increased in some (but not all) etiologies of rebreathing. It is specific to rebreathing caused by a faulty unidirectional valve, but it will appear normal in other instances of rebreathing (exhausted CO2 absorbent). In the case of CO2 absorbent exhaustion, the baseline increases but the beta angle is normal.
Review 9 abnormal CO2 waveforms in Equipment and monitoring unit under Respiratory section
Airflow obstruction Cardiac oscillations curare cleft low EtCO2 High EtCO2 Inspired CO2 Ban unidirectional valve sample line leak with PPV pt with single lung transplant
Causes of increased EtCO2 as a result of changes in CO2 production and delivery to the lungs:
Increased CO2 production and delivery to the lungs:
- Increased BMR (increased VO2)
- Malignant hyperthermia
- Thyrotoxicosis
- Fever
- Sepsis
- Seizures
- Laparoscopy
- Tourniquet or vascular clamp removal
- Sodium bicarb administration
- Anxiety
- pain
- shivering
- increased muscle tone (after NMB reversal)
- medication SE
Causes of decreased EtCO2 as a result of changes in CO2 production and delivery to the lungs:
Decreased CO2 production and delivery to the lungs:
- Decreased BMR (decreased VO2)
- Increased anesthetic depth
- hypothermia
- decreased pulmonary blood flow
- decreased CO
- hypotension
- Pulmonary embolus
- V/Q mismatch
- medication SE
All the causes of increased EtCO2 that occur as a result of changes in alveolar ventilation:
Decreased alveolar ventilation:
- hypoventilation
- CNS depression
- residual NMB
- COPD
- high spinal
- neuromuscular disease
- metabolic alkalosis (if spontaneous ventilation)
- medication SE
All the causes of increased EtCO2 that occur as a result of equipment malfunction:
- Rebreathing
- CO2 absorbent exhaustion
- unidirectional valve malfunction
- leak in breathing circuit
- increased apparatus dead space
All the causes of decreased EtCO2 that occur as a result of changes in alveolar ventilation:
Increased alveolar ventilation:
- hyperventilation
- inadequate anesthesia
- metabolic acidosis (if spontaneous ventilation)
- Med SE
All the causes of decreased EtCO2 that occur as a result of equipment malfunction:
- ventilator disconnect
- esophageal intubation
- poor seal with ETT or LMA
- sample line leak
- airway obstruction
- apnea
What wavelengths of light are emitted by the pulse Ox? what law is used to make the SpO2 calculation?
(see photo in E&M: respiratory)
Pulse Ox is based the Beer-lambert law, which relates the intensity of light transmitted through a solution and the concentration of the solute within the solution.
The pulse ox emits 2 wavelengths of light:
- red light (660 nm) is preferentially absorbed by deoxyhemoglobin (higher in venous blood).
- Near-infrared light (940 nm) is preferentially absorbed by oxyhemoglobin (higher in arterial blood).
What conditions impair the reliability of the pulse ox?
Decreased perfusion:
- vasoconstriction
- hypothermia
- Reynaud’s syndrome
Dysfunctional Hgb:
- Carboxyhemoglobin (absorbs 660nm to the same degree as oxygenated hemoglobin)
- Methemoglobin (absorbs 660 and 990 equally)
- NOT HgbS or HgbF
Altered optical characteristics:
- Methylene blue
- indocyanine green
- indigo carmine
- NOT fluorescein
Non-pulsatile flow:
- CBP
- LVAD
Motion artifact: Shivering/movement
Other:
- Electrocautery
- Venous pulsation
- NOT jaundice or polycythemia
BP cuff ideal bladder length and width:
Ideal bladder length is long enough to wrap around 80% of the extremity.
Ideal bladder width is 40% the circumference of the patient’s arm.
What factors affect the accuracy of the non-invasive BP cuff measurement?
Falsely increased BP:
- BP cuff too small
- BP cuff too loose
- BP is measured on extremity below the level of the heart
Falsely decreased BP:
- cuff too large
- cuff is deflated too rapidly
- BP measured on extremity above level of the heart.
How does the site of measurement affect the blood pressure reading?
As the pulse moves from the aortic root towards the periphery, systolic pressure increases, diastolic pressure decreases, and the pulse pressure widens. MAP remains constant through the arterial tree.
- At aortic root: SBP is lowest, DBP is highest, and PP is narrowest.
- At dorsalis pedis: SBP is highest, DBP is lowest, PP is widest.
How does arm position affect the NIBP reading?
How about when an arterial line is used?
Blood in the circulation behaves like a column of fluid and follows the rules of hydrostatic pressure.
- If the BP cuff location is above the heart, the reading will be falsely decreased (there is less hydrostatic pressure)
- If the BP cuff location is below the heart, the reading will be falsely increased (there is more hydrostatic pressure).
- For every 10cm change, the BP changes by 7.4 mmHg.
- For every 1 inch change, the BP changes by 2mmHg.
When an a-line is used, the level of transducer is what’s important (the height of the catheter does not matter).
What information can you learn from the arterial BP waveform?
(see photo in E&M: Hemodynamics)
- Systolic BP= peak of waveform
- dyastolic BP= trough of waveform
- pulse pressure= Peak - trough
- contractility = upstroke
- SV= area under the curve
- closure of aortic valve= dicrotic notch
Discuss damping and the interpretation of the high pressure flush test:
Optimal waveform morphology balances the amount of damping with the amount distortion from the transducer system. The high-pressure flush test helps us determine this when we flush the system and observe the oscillations that result (if any).
Optimally damped system: Baseline is re-established after 1 oscillation.
Under-damped system: Baseline is re-established after several oscillations (SBP is overestimated, DBP is underestimated, MAP is accurate)
Over-damped system: Baseline is re-established with no oscillations (SBP is underestimated, DBP is overestimated, and MAP is accurate). Causes include an air bubble or clot in the pressure tubing or low flush bag pressure.
How do you determine the appropriate distance to thread a central line or PA catheter?
- You must know the distance from the site of injury to the vena cava junction.
- You must know the distance from the VC junction to where the tip of the catheter should be placed.
- Add these two numbers to determine the distance from the site of insertion to the tip of the catheter.
Length from various insertion sites to Vena Cava and right atrium junction:
Subclavian= 10cm R IJ = 15cm L IJ = 20cm Femoral= 40cm R medial basilic= 40cm L medial basilic= 50cm
Length from Vena Cava and right atrial junction to Cather tip position:
Right atrium= 0-10cm
Right ventricle= 10-15 cm
Pulmonary artery= 15-30cm
PAOP position 25-35cm
What are the 3 waves and 2 descents on the CVP waveform? what does each one signify?
(see photo in E&M: hemodynamics)
A= RA contraction C= Tricuspid valve elevation into RA X= Downward movement of contracting RV V= RA passive filling Y= RA empties through open tricuspid valve
How do the waves and descents on the CVP waveform correlate with the electrical events in the heart?
A wave= right atrial contraction; just after P-wave (atrial depolarization)
C wave= right ventricular contraction (bulging of tricuspid valve into RA); just after QRS complex (ventricular depolarization)
X descent= RA relaxation; ST segment
V wave= Passive filling of RA; Just after T wave begins (ventricular repolarization)
Y descent= RA empties through open tricuspid valve; after T wave ends
Which factors increase CVP?
Transducer below the phlebostatic axis Hypervolemia RV failure Tricuspid stenosis or regurgitation Pulmonary stenosis Pulmonary hypertension PEEP VSD Constrictive pericarditis Cardiac tamponade
Which factors decrease CVP?
Transducer above the phlebostatic axis
hypovolemia
What conditions cause loss of the A-wave on the CVP waveform?
Loss of the A-wave occurs when synchronized contraction of the right atrium is lost.
- Atrial fibrillation
- V-pacing if the underlying rhythm is a systole
What conditions cause an increased A-wave on the CVP waveform?
A large A-wave is produced when the atria contracts and empties against a high resistance (either at the valve or non-compliant ventricle).
- Tricuspid stenosis
- diastolic dysfunction
- myocardial ischemia
- chronic lung disease leading to RV hypertrophy
- AV dissociation
- junctional rhythm
- V-Pacing asynchronous
- PVCs
What conditions cause a large V-wave on the CVP waveform?
Tricuspid regurgitation allows a portion of the right ventricle volume to pass through the closed but incompetent tricuspid valve during RV systole. This increases the volume and pressure in the RA and manifests as large V-waves.
- tricuspid regurgitation
- acute increase in intravascular volume
- RV papillary muscle ischemia
How does the waveform change as a PA catheter is guided into position? What are the normal pressures at each step?
(see photo in E&M: hemodynamics)
RAP= 1-10 (looks like CVP waveform) RVP= 15-30/0-8 (big zig zag) PAP= 15-30/5-15 (dicrotic notch seen) PAOP= 5-15 (waveform looks similar to CVP)
The tip of the PAC should be positioned in West lung zone___?
(See photo in E&M: hemodynamics)
The tip of the PAC should be in zone III.
In this region, there is a continuous column of blood between the tip of the PAC and the left ventricle. Since LVEDP reflects back through the pulmonary circulation, a tip positioned in zone 3 provides the most accurate estimation of LVEDP.
Zone 3 is defined as Pa>Pv>PA
What is the equation for mixed venous oxygen saturation?
SvO2 = SaO2 - [VO2 / (Q x 1.34 x Hgb x 10)]
Mixed venous oxygen saturation is a function of 4 variables:
Q= cardiac output (L/min)
VO2= Oxygen consumption (mL O2/min)
Hgb= Amount of hemoglobin (g/dL)
SaO2= loading of hemoglobin in arterial blood (%)
What is a normal mixed venous saturation?
65-75%
What conditions are associated with a decreased SvO2?
Increased oxygen consumption:
- stress
- pain
- thyroid storm
- shivering
- fever
Decreased oxygen delivery:
- decreased PaO2
- decreased Hgb
- decreased CO
What conditions are associated with a increased SvO2?
Decreased O2 consumption:
-hypothermia
Increased O2 delivery:
- increase PaO2
- increased Hgb
- increase CO
Relate the phases of the cardiac action potential to the EKG:
Phase0= Depolarization; Na+ --> IN; QRS Phase1= Initial repolarization; Cl- -->IN, K+ -->OUT; QRS Phase2= Plateau; CA++ -->IN; K+ --> OUT; ST segment Phase3= Final repolarization; K+ -->OUT; T wave Phase4= Resting phase; Na+ --> OUT; End of T wave to QRS
What are the 3 types of leads in a 12 lead EKG?
Bipolar leads
limb leads
precordial leads
What region of the myocardial does each EKG lead monitor? What coronary arteries are monitored by each lead? (See photo in E&M: cardiac rhythms)
Leads 1, aVL, V5, V6= Lateral aspect; CxA
Leads 2, 3, aVF= Inferior aspect; RCA
Leads V1, V2= Septum; LAD
Leads V3, V4= Anterior aspect; LAD
List the conditions that cause left axis deviation:
Chronic hypertension left bundle branch block aortic stenosis aortic insufficiency mitral regurgitation
List the conditions that cause right axis deviation:
COPD acute bronchospasm cor pulmonale pulmonary hypertension pulmonary embolus
Recite the heart block poem:
If “R” is far from “P” then you have a first degree.
Longer, longer, longer drop then you have a Wenckebach.
If some “P”s don’t get through then you have a Mobitz 2.
If “P”s and “Q”s don’t agree then you have a 3 degree.
MOA for Class 1 antiarrhythmic drugs:
Give examples of each.
Na+ channel blockers.
1a: Moderate depression of phase 0; prolongs phase 3 repolarization (K+ channel block –> increases QT)
EX: Quinidine, Procainamide, Disopryamide
1b: Weak pression of phase 0; Shortened phase 3 repolarization
EX: Lidocaine, Phenytoin
1c: Stronger depression of phase 0; Little effect on phase 3 repolarization
EX: Flecainide, Propafenone
MOA for Class 2 antiarrhythmic drugs:
Give examples of each.
Beta-Blockers.
Slow phase 4 depolarization in SA node
EX: esmolol, metoprolol, atenolol, propranolol
MOA for Class 3 antiarrhythmic drugs:
Give examples of each.
K+ channel blockers.
Prolongs phase 3 repolarization (increases QT); Increases effective refractory period
EX: Amiodarone, Bretylium
MOA for Class 4 antiarrhythmic drugs:
Give examples of each.
Ca++ channel blockers.
Decreased conduction velocity through AV node
EX: Verapamil, Diltiazem
What EKG findings are consistent with Wolff-Parkinson-White syndrome? (see photo in E&M: cardiac rhythms)
Delta wave caused by ventricular preexcitation
- short PR interval (< 0.12 seconds)
- wide QRS complex
- possible T-wave inversion
What condition increases the risk of torsades de pointes?
Mnemonic: POINTES
Phenothiazines
Other meds (methadone, droperidol, amiodarone with hypokalemia)
Intracranial bleed
No known cause
Type 1 antiarrhythmics
Electrolyte disturbances (low K+, Ca++, or Mg++)
Syndromes (Romano-Ward, Timothy)
What is the treatment for torsades de pointes?
Acute treatment for torsades de pointes includes reversing the underlying causes and/or shorten the QT interval:
- magnesium sulfate
- cardiac pacing to increase the heart rate will reduce action potential duration and the QT interval
List 5 indications for cardiac pacemaker insertion:
- Symptomatic disease of impulse formation (SA node disease)
- Symptomatic disease of impulse conduction (AV node disease)
- Long QT syndrome
- dilated cardiomyopathy
- hypertrophic obstructive cardiomyopathy
*The cardiac output is dependent on the hearts ability to generate a normal rate and rhythm. If the heart can’t, a pacemaker can be placed.
What is the significance of the NBG pacemaker identification code?
Position1 = Chamber paced Position2 = Chamber sensed Position3 = Response to sensed event Position4 = Programmability Position5 = Pacemaker can pace multiple sites
How does atrial pacing affect the QRS complex?
If the atrium is paced, the electrical signal travels through the AV node and the QRS maintains its normal, narrow appearance.
How does ventricular pacing affect the QRS complex?
If the ventricle is paced, the electrical signal is delivered beyond the AV node and the QRS takes a wide appearance.
What conditions increase the risk of failure to capture?
Failure to capture occurs when the myocardium becomes more resistant to depolarization (the pacemaker fires but there may be failure to capture):
- hyper- and hypokalemia
- hypocapnia (Intracellular K+ shift)
- hypothermia
- myocardial infarction
- fibrotic tissue buildup around the pacing leads
- antiarrhythmic medications
How does the cerebral oximeter work? What value is considered a significant change from baseline?
Cerebral oximetry utilizes Near Infrared Spectroscopy (NIRS) to measure cerebral oxygenation.
- Arterial hemoglobin, Venus hemoglobin, and tissue cytochromes absorbed different frequencies of infrared light.
- Cerebral oximetry relies on the fact that cerebral blood volume is 1 part arterial to 3 parts venous; 75% of blood in the brain is on the venous side of circulation.
- Since NIRS does not have the ability to detect pulsatile blood flow, it is primarily a measure of venous oxyhemoglobin saturation and oxygen extraction.
- Decreased cerebral oxygen delivery–> increased cerebral oxygen extraction–> decreased venous hemoglobin saturation.
- A > 25% change from baseline suggests a reduction in cerebral oxygenation.
Types of EEG waveforms: BETA
see photo in E&M: miscellaneous
- 13-30 cycles/sec
- High frequency and low voltage
- Associated with: awake mental stimulation and “light” anesthesia
Types of EEG waveforms: ALPHA
see photo in E&M: miscellaneous
Frequency 8- 12 cycles/sec
-Associated with: Awake but restful state with eyes closed
Types of EEG waveforms: THETA
see photo in E&M: miscellaneous
4-7 cycles/sec
Associated wit: General anesthesia and children during normal sleep
Types of EEG waveforms: DELTA
see photo in E&M: miscellaneous
< 4 cycles/sec
Associated with: General anesthesia, deep sleep, and brain ischemia or injury
Types of EEG waveforms: Burst suppression
see photo in E&M: miscellaneous
Associated with: General anesthesia, hypothermia, cardiopulmonary bypass, and cerebral ischemia (especially if it’s unilateral burst suppression)
Types of EEG waveforms: Isoelectricity
see photo in E&M: miscellaneous
- absence of electrical activity
- associated with deep anesthesia and death
How do brain waves change during general anesthesia?
- induction of general anesthesia is associated with increased beta wave activity.
- light anesthesia is also associated with increased beta wave activity.
- Theta and delta waves predominate during general anesthesia.
- deep anesthesia produces burst suppression.
- At 1.5 to 2.0 MAC, general anesthetics causes complete suppression or isoelectricity.
Name 2 drugs that are most likely to reduce the reliability of the BIS value.
Nitrous oxide increases the amplitude of high frequency activity and reduces the amplitude of low frequency activity. This does not affect the BIS value.
Ketamine increases high frequency activity. This can produce a BIS value that is higher than the level of sedation/anesthesia would otherwise suggest.
What is Macroshock?
Comparatively large amount of current that is applied to the external surface of the body. The impedance of the skin offers a higher resistance, so it takes a larger current to induce the ventricular fibrillation.
What is Microshock?
Comparatively smaller amount of current that is applied directly to the myocardium. The high resistance of the skin is bypassed, so it takes a significantly smaller amount of current to induce ventricular fibrillation.
-A central line, PA catheter, or pacing wires provide a direct conductive pathway to the heart, so they increase the patient’s susceptibility to microshock.
What are the key threshold values for macroshock?
1mA= threshold for touch perception of electrical shock 5mA= maximum current for a harmless electrical shock 10-20mA= "let go" current occurs before sustained contraction 50mA= loss of consciousness 100mA= ventricular fibrillation
What are the key threshold values for microshock?
10uA= maximum allowable current leak in the OR 100uA= ventricular fibrillation
What is the role of the line isolation monitor? What should you do if it alarms?
Assesses the integrity of the ungrounded power system in the OR. It tells you how much current could potentially flow through you or a patient if a second fault occurs.
- primary purpose of LIM is to alert the OR staff of the first fault.
- LIM does NOT (by itself) protect you or the patient from macro- or microshock.
- LIM will alarm when 2-5mA of leak current is detected
- if the alarm sounds, the last piece of equipment that was plugged in should be unplugged.
