Week 1 - Basic Clinical Monitoring (Respiratory & Metabolic) Flashcards
Cyanosis is a _________ sign of hypoxia
late
PaCO2 is based on _____________ concentration
hydrogen ion
Carbon dioxide reacts with water to produce _________
carbonic acid ——> hydrogen ions
reversible reaction - basis for respiratory involvement in pH balance
How does a colorimetric device work to monitor ventilation following intubation?
Exhaled CO2 reacts with water in the device to form carbonic acid - this raises the pH and changes the color on the indicator
What are the limitations of colorimetric devices used following intubation?
False positives may result from detection of CO2 from air forced into the stomach (or from the presence of carbonated beverages or antacids)
ETCO2 is said to be approximately _______ torr lower than arterial CO2
2-5
this is true for patients without cardiac or pulmonary abnormalities
ETCO2 has been shown to be a ________ sensitive indicator of hypoventilation than clinical observation or pulse oximetry
more
In the following capnogram, what does the segment from B to C represent?
Beginning of expiration
At which point on the capnogram is the ETCO2 measured? What is this called?
point D
* this is termed the Beta angle
How would you interpret the following capnogram?
There is a failure to return to baseline which indicates CO2 rebreathing
What effect would sustained hyperventilation have on ETCO2?
it would decrease
* (there is an initial increase as there is a large amount of CO2, but sustained hyperventilation causes a decrease as the blood content of CO2 is depleted)
What effect would sustained hypoventilation have on ETCO2?
it would increase
* (there is an initial decrease as exhalations are small, but over time the body compensates by removing a greater amount of CO2 with each breath)
In a patient with fever or sepsis, would you expect an increase or decrease in ETCO2?
Increase
* these states cause the body’s metabolic rate to increase - leading to greater production of CO2 at cellular level and a greater degree of CO2 removal with each exhalation
In a patient with pulmonary emolism, what change in ETCO2 might you expect?
Decrease
* this is due to a decreased delivery of CO2 to the alveoli
What might the following capnogram represent?
Asynchrony with ventilator/return of spontaneous ventilation
In states of __________ compliance, minimal force is needed for lung expansion
high
not necessarily a good thing (COPD, Emphysema)
When compliance is low _________ force is needed for lung expansion
more/higher
Lung _______ can be shown by a flow/volume loop
compliance
The following flow volume loop is characteristic of _________ lung disease
obstructive (air can’t get out)
* near normal inhalational volume and flow (bottom half of loop), but severely limited exhalational volume and flow (top half of loop)
* e.g. COPD, emphysema
Because oxyhemoglobin absorbs light differently than deoxyhemoglobin, oxygen saturation can be measured via ___________
pulse oximetry
In the presence of methemoglobin or carboxyhemoglobin, or a patient with sickle cell anemia, a pulse oximeter may falsely _________-estimate the true value of oxygen saturation
over
* methemoglobin and carboxyhemoglobin absorb light in a way similar to oxyhemoglobin - this fools the pulse oximeter into thinking that saturation is normal when the true value is low
The presence of dyes, such as methylene blue, alters the absorbtion of light by a pulse oximeter - this may cause a transient ___________ in measured oxygen saturation
decrease
Hypothermia is defined as a core temperature of less than _______
36 degrees celsius
How do general anesthetics alter thermoregulation?
Reduce shivering
Reduce vasoconstriction (normal vasoconstriction would conserve heat)
What are the 4 types of heat loss?
- radiant
- evaporative
- convective
- conductive
What factors may place a patient at higher risk for hypothermia?
- lengthy surgery
- old age
- lean body mass
- combined epidural and general anesthesia
Hypothermia may increase the risk for what perioperative complications?
- wound infection/delayed healing
- cardiovascular events (MI)
- blood coagulation abnormalities
- length of PACU stay
Consider the oxyhemoglobin dissociation curve - what might cause a shift to the left?
Decreased:
* pCO2
* temperature
Elevated:
* pH (alkalosis)
remember - temporary or localized shifts are part of normal physiology
Consider the oxyhemoglobin dissociation curve - what might cause a shift to the right?
Increased:
* pCO2
* temperature
Decreased:
* pH (acidosis)
remember - temporary or localized shifts are part of normal physiology
A shift to the left of the oxyhemoglobin dissociation curve means that hemoglobin has ______________ affinity for oxygen
higher
at a constant pO2, shift to the left = higher O2 saturation
A shift to the right of the oxyhemoglobin dissociation curve means that hemoglobin has __________ affinity for oxygen
lower
at a constant pO2, shift to the right = lower O2 saturation
The following flow volume loop is characteristic of _________ lung disease
restrictive (minimal air in, minimal air out)
*can be caused by decreased lung compliance (e.g. pulmonary fibrosis) or chest wall movement (e.g. muscular dystrophy, pain)
PE, bronchoconstriction, pneumothorax, asthma
The beta angle of a capnography graph increases with what 3 things?
Rebreathing, malfunctioning inspiratory valves, and prolonged response time compared with respiratory cycle time (especially in children)
The beta angle of a capnography graph decreases with ___________
Decrease in slope of phase III
The alpha angle of a capnography graph decreases with ______
COPD
The alpha angle of a capnography graph increases what 2 things?
Increased peep and airway obstruction
What 2 things can cause an increase in resistance in ventilator flow?
Bronchoconstriction, kinked/obstructed ET tube
What wavelength does oxygenated Hgb absorb light
Red wavelength between 650-750 nm
Infection, hyper metabolic states, and recreational drug use can cause ___________ temperatures
increased
3 phases of thermoregulation?
Afferent thermal setting, Central regulation, and efferent responses.
(We take away efferent responses in anesthesia!)
Examples of efferent responses to hypothermia
Shivering and vasoconstriction
Examples of efferent responses to hyperthermia
sweating
What type of temperature monitoring is most reflective of thermal status?
Core temperature.
-Blood temp via swan, tympanic, distal esophagus, and nasopharynx.
How is variable pitch used in a pulse ox?
Changes in tone as the patient is desaturating. Alerts the provider of a subtle change
How has esophageal intubation been drastically reduced?
Through the monitoring of EtCO2
What are some simple ways to verify, when used with other assessments, gas exchange?
Movement of chest, condensation in the airway device, sense of touch to feel subtle movements of gas exchange
When using disposable EtCO2 devices, a minimum of _____ breaths has been suggested to avoid misinterpretation
6
By what method is continuous ETCO2 accomplished by?
Infrared analysis
What is the difference between diverting and non-diverting sampling of CO2?
Diverting - Extracts gas from the sample tubing and pumps it to the monitor
Non-diverting - Measures gas directly in the breathing system
What do phases D-E represent on the capnogram?
Descent to original baseline (inspiration)
4 Phases of the capnogram
Phase 1 - End of inspiration and beginning of expiration
Phase 2 - Expiratory upstroke
Phase 3 - Plateau phase. Represents alveolar emptying of CO2. (longest phase)
Phase 4 - Rapid decrease in CO2, due to inspiration
What would you interpret this capnogram as?
Cardiac oscillations (generally caused by pulmonary artery pulsatility)
Why is transcutaneous CO2 monitoring not used much in the anesthesia care realm?
Because it does not provide immediate breath to breath verification of ET placement.
Volume flow loops
What can be the cause of decreased compliance?
PE, bronchoconstriction, pneumothorax, insufflation of the abdomen, inadequate muscle relaxation
What is the most helpful test when assessing acid base balance?
ABG
When does the greatest amount of heat loss occur during surgery?
Within the first hour
What core temperature method is considered most ideal for many surgeries?
Tympanic
Due to vasoconstriction that occurs in cold temperatures, what can be a more useful oximetry site?
Sites closer to central circulation
- Forehead, nose, and ear probes.
AANA/ASA guidlines
How much O2 is dissolved in the blood?
.003 mL of O2 per 100 mL of blood
Because we know this, we can determine the remaining amount of Hgb bound to O2
Consider this equation
Hgb + O2 <—-> HgbO2
What does this tell us about the relationship of Hgb to O2?
That this is a reversible reaction. O2 is able to be bound and released from Hbg. This allows for the transfer/oxygenation of O2 to the body.
