Respiratory Monitoring Flashcards
To what aspects can the anesthetist be attentive for “simple observation” monitoring?
Chest rise and fall Circuit bag movement/feel TV and end expiratory TV Color of lips/nails/blood/conjunctiva Work of breathing Respiratory rate and depth Rocking (obstruction), puffing (patent) Airway noise Air felt on palm Precordial stethoscope sounds Tube fog
Disadvantages of precordial/esophageal stethoscopes?
Contraindicated for esophageal varices and cannot detect diffusion abnormalities
Where do you place the precordial chest piece?
4th ICS and LSB
What would the stethoscope finding of a “mill wheel murmur” indicate? What would end-tidal gas analysis show? CVP?
Air embolism; increased nitrogen, decreased CO2; increased CVP
How do you calculate appropriate tidal volumes?
6-8 ml/kg of IDEAL body weight
Positive inspiratory pressures should not exceed __ to __ cm H2O.
35; 40
Insufficient tidal volume will fail to control what 3 factors?
ETCO2, keep alveoli expanded, and deliver volatile anesthetic drugs
What variables on an ABG indicate oxygenation? Ventilation? Acid-base status?
PaO2 and Oxyhgb Sat; PaCO2; pH, bicarb, base excess
5 causes of hypoxia
Hypoxemia, anemic hypoxia, circulatory hypoxia, affinity hypoxia, histiocystic hypoxia
Causes of hypoxemia
Low FiO2, hypoventilation, shunt, diffusion limitations
Most common cause of hypoxia
Cause of anemic hypoxia
Not enough hgb
Cause of circulatory hypoxia
Insufficient cardiac output
Cause of affinity hypoxia
Decreased release of O2 (hypothermia, increased pH, CO poisoning)
Cause of histiocystic hypoxia
Cell won’t accept delivery of O2 (cyanide poisoning)
What effect does high hgb have on cyanosis?
Cyanosis occurs at a higher PaO2 since there are more deoxygenated hgb present even though PaO2 may be adequate; conversely, anemic patients rarely have cyanosis even with low PaO2.
PO2 of 40, 50, 60 = O2 Sat % of __, __, __
70; 80; 90
Average oxygen consumption at rest is _ to _ __ O2/kg/minute
2; 4; mL
VO2 formula
FiO2-FeO2 x Vm/weight in kg
DO2 (lungs) formula
FiO2 x Vm/weight in kg
What effect does increasing FiO2 have if SaO2 is near 100%?
Very little effect
What factors have the greatest effect on VO2 and DO2?
CO and hgb level; CV is the limiting factor for DO2 to tissues.
Alveolar air equation
FiO2 x (Pb-Pwv) - PaCO2/RQ
PAO2 shortcut: FiO2 x6
PaO2 shortcut
FiO2 x5
DO2 (tissues) equation
CaO2 (mls/dL) x CO (mls/min)/kg/100
CaO2 equation
(hgb x oxyhgb x 1.39) + (0.003 x PaO2)
Why doesn’t CPR perfuse the periphery?
CPR cannot achieve sufficient pressure (<50 torr SBP) to perfuse periphery; only central organs and brain get perfused.
What are the dual wavelengths of light used in pulse oxymetry?
660 (red) and 940 (infrared) nm pass through the tissue and vascular beds via LED
Pulse oxymetry requires ________ blood flow.
pulsatile
What can cause errors in pulse oxymetry?
COHgb (false high); MetHgb (If SaO2 >85%, SpO2 low; if SaO2 <85%, SpO2 high); improperly fitting probe (false low); SpO2 <60% (false low); poor perfusion; anemia (false low in Hct <24%); IV methylene blue (false low); blue nail polish (false low); ambient fluorescent light (false high); excessive motion (false low)
What is the disadvantage of using the toe for monitoring pulse oximetry?
Desat/resat detection slow
Under which condition is nose pulse oxymetry unreliable?
Trendelenburg position
What oxymetry probe site can be used for burn patients?
Tongue
Name 6 valid oxymetry probe sites.
Finger, toe, nose, earlobe, tongue, cheek
How is capnography measured? What are the two locations for measurement chamber placement?
Infrared absorption; mainstream and sidestream
What conditions will result in increased CO2 readings? (8)
Increased production - fever, physical activity, seizures, sepsis, hyperthyroidism, trauma and burns, high carb diet
Inefficient evacuation - hypoventilation
What conditions will result in decreased CO2 readings? (7)
Poor transport - hypotension, decreased cardiac output, right to left pulmonary shunt
Decreased production - hypothyroidism, hypothermia, paralysis/motionless patient
Increased evacuation - hyperventilation
What is the relationship between minute ventilation and ETCO2?
Inverse
What is the relationship between VO2 and ETCO2?
Direct
What are some equipment malfunctions that can cause increased ETCO2? Decreased?
Rebreathing, exhausted CO2 absorber, leak in ventilator circuit
Ventilator disconnect, esophageal intubation, complete airway obstruction, poor sampling, leak around ETT cuff
Describe the phases of a normal capnograph.
The appearance of a normal capnograph is fairly rectangular; phase I represents dead space expiration with no rise from baseline; phase II is the sharp rise from baseline that represents mixed dead space and alveolar gas expiration; phase III is the plateau period that signifies alveolar gas expiration and plateau; phase 0 stands for inspiration; phase IV (?) is an upswing that occurs at the end of phase III.
What does a capnography tracing look like with esophageal intubation?
Rapidly extinguishing uncharacteristic waveform (small waves)
What do regular dips in the end-expiratory plateau of capnography signify?
Underventilated lungs or patients recovering from NMB
What does an upward shift in baseline in capnography mean?
Rebreathing of carbon dioxide or miscalibration
What does a capnography waveform look like with restrictive lung disease?
Rounded corners of waveform/sloping downstroke due to air readily exiting the lungs and difficulty getting air into the lungs.
What is the appearance of a capnography waveform with obstructive pulmonary disease?
The plateau phase slopes from low to high due to difficulty with expiration.
How do cardiogenic oscillations change capnography?
The plateau slopes from high to low with rippling waves representing mediastinal vibrations.
What will a nasal cannula capnography waveform look like?
Rounded corners of the wave/no plateau due to lack of seal
What is a factor that can cause inaccurate low ETCO2 readings with nasal cannula sidestream measurement?
Mouth breathing
How are airway resistance and dynamic compliance related?
Inversely
When is dynamic lung compliance measured?
During times of gas flow/active inspiration
______ _________ measured using peak pressures can change from breath to breath while _____ __________ mostly remains unchanged.
Airway resistance; lung compliance
When can static lung compliance be measured?
During times without gas flow such as inspiratory pause or end inhalation
What pressure is used to measure static lung compliance?
Plateau pressure
Plateau pressure __ peak pressure
Less than
Indicates compliance without effects of airway resistance
Plateau pressure/static lung compliance
Which is a more accurate measure of lung compliance? Dynamic compliance or static compliance?
Static compliance
What can cause unusual changes to static lung compliance?
Insufflation, rigidity
What can cause an increase in peak inspiratory pressure and plateau pressure?
Increase in TV or decrease in pulmonary compliance (pulmonary edema, trendelenburg, pleural effusion, ascites, abdominal packing, peritoneal gas insufflation, tension pneumothorax, endobronchial intubation)
What can cause an increase in peak inspiratory pressure without an increase in plateau pressure?
An increase in inspiratory flow rate or airway resistance (kinked ETT, bronchospasm, secretions, foreign body aspiration, airway compression, ETT cuff herniation)
List 3 pulmonary function tests
Forced expiratory volume, forced vital capacity, forced expiratory flow
What is a diffusion capacity test?
Carbon monoxide is inhaled and then measured; tracks gas ability to cross alveolar-capillary membrane; a reduction in diffusible SURFACE AREA can be identified; can ID shunt, VQ mismatch, fibrosis, emphysema.
What is FEV1? Normal results?
Forced expiratory volume over one second; a PFT used to identify airway resistance.
80% of vital capacity
What is FEV 25%-75%? Normal results?
Forced Expiratory Flow between 25% and 75% of exhaled breath; normal is 4-5 liters/second; the 25-75% portion is effort independent and therefore the most objective measurement of airway resistance in MEDIUM airways and the most sensitive indicator of SMALL airway obstructive disease.
What is FEF 25%-75% in restrictive disease?
Normal results (4-5L/sec)
What is FEV1/FVC ratio? Normal results?
Forced Expiratory Volume over Forced Vital Capacity. This ratio declines with age, with normal at least 80%.
What happens to the FEV1/FVC ratio with obstructive lung disease?
It decreases because with obstruction, the patient has difficulty exhaling and therefore will be able to move less air in 1 second.
What happens to the FEV1/FVC ratio with restrictive lung disease?
It increases or remains normal; since lungs have reduced compliance, air will leave the lungs quickly and easily. Since the overall lung capacity is reduced, the amount exhaled in the first second makes up a larger percentage of the total than normal.
How do lung volumes in restrictive lung disease compare to normal lung volumes?
Reduced TLC, FRC, RV, FVC, and FEV1; FEV1/FVC ratio preserved
How do lung volumes in obstructive lung disease compare to normal lung volumes?
Enlarged TLC, RV, FRC; reduced ERV.
Pressure volume loops are an indicator of lung __________.
Compliance/distensibility
Pressure volume loops move counter-clockwise during _____________ ventilation.
positive pressure; they remain completely to the right of the y-axis during positive pressure ventilation except during pressure support when the negative pressure breath trigger occurs briefly to the left of the y-axis
Pressure volume loops move clockwise during _________ _________.
spontaneous respiration; they also move left of the y-axis during inspiration and go left of the y-axis during expiration
Higher pressure moves the loop farther ______ in pressure volume loops.
right
In pressure volume loops, slope represents _____ _________. Flatter slope mean _________ and steeper slope means ________ __________.
Lung compliance; decreased; increased compliance
What is the morphology of a pressure-volume loop on an overdistended lung?
The top develops a flattened tail to the right as pressure continues to rise with no corresponding increase in volume.
What is the approximate shape of a normal flow volume loop?
An upside-down ice cream cone; flow goes clockwise
What is the appearance of a flow volume loop with restrictive lung disease?
Shape is normal; lung volumes are smaller; flows are reduced
What is the appearance of a flow volume loop with obstructive lung disease?
Shape is caved in on the top right (shark fin appearance) indicating expiratory obstruction (rate of flow decreases toward end expiration); lung volumes are larger; flows are reduced
What is the morphology of a flow volume loop with tracheal stenosis/fixed obstruction?
Rounded/flat top and bottom portion; flows cannot reach high rates with fixed obstruction.
What is the appearance of a flow-volume loop with variable EXTRATHORACIC obstruction and why?
Inspiratory curve is flattened and expiratory curve is normal; during inspiration, the pressure around the airway exceeds intratracheal pressure. (“like a straw collapsing”)
