Respiratory monitors and equipment 2 Flashcards
Describe an airflow obstruction capnograph.
prolonged upstroke with increased alpha angle
Examples of an airflow obstruction include
COPD, bronchospasm, kinked ETT
Describe cardiac oscillations capnograph
oscillations in the capnograph waveform from C to D
Cardiac oscillations are more common in
children because of close proximity of the heart to the lungs
Cardiac oscillations are caused by the
heart beating against the lungs
What is a curare cleft?
spontaneous breaths during mechanical ventilation
If present during spontaneous ventilation, the presence of a curare cleft suggests
inadequate muscle relaxant reversal (lack of synchronization between intercostal muscles and diaphragm)
Why might we see low EtCO2?
hyperventilation
decreased CO2 production
increased alveolar dead space
Examples of low EtCO2 due to hyperventilation include
light anesthesia, metabolic acidosis
Examples of low EtCO2 due to low Co2 production include
hypothermia
Examples of low EtCO2 due to increased alveolar dead space include
hypotension
pulmonary embolism
Why could we see increased EtCO2 with a normal plateau?
increased CO2 production or decreased alveolar ventilation
Examples of increased EtCO2 due to increased CO2 production include
MH, sepsis, fever, hyperthyroidism
Examples of increased EtCO2 due to decreased alveolar ventilation include
hypoventilation
narcotics
How do we know if the capnography is due to inspired CO2?
look at the baseline. it does not return to zero–> rebreathing
Why could we see rebreathing?
exhausted CO2 absorbent
incompetent expiratory valve
hole in the inner tube of a Bain system
inadequate FGF with Mapleson circuit
rebreathing under the drapes in a patient who is not intubated
An incompetent inspiratory valve will appear on capnography as
a decreased slope during the inspiratory phase (widened beta angle)
waveform may or may not reach zero, depending on the FGF
What would a leak in the sample line during positive pressure ventilation appear as?
the beginning of the plateau is low because alveolar gas is diluted when atmospheric air is aspirated into the sample line
When could a biphasic expiratory plateau occur?
single-lung transplant b/c alveolar gas from the transplanted lung and the diseased lung may have different time constants
Causes of increased EtCO2 include
increased CO2 production and delivery to the lungs
decreased alveolar ventilation
equipment malfunnction
Causes of decreased EtCo2 include
decreased CO2 production and delivery to the lungs
increased alveolar ventilation
equipment malfunction
For EtCO2 to be detected, the following requirements must be met:
- CO2 must be produced during metabolism
- There must be an adequate pulmonary blood flow to deliver CO2 to the lungs for elimination
- There must be an adequate ventilation to transport CO2 to the breathing circuit
- There must be an intact sampling system
What are the two things that you must consider when answering a question about changes in end-tidal CO2?
- What is the cause?
- Does this affect the PaCO2 to EtCO2 gradient
Equipment malfunction that can cause increased EtCO2 includes
rebreathing
CO2 absorbent exhaustion
unidirectional valve malfunction
leak in breathing circuit
increased apparatus dead space
Equipment malfunction that can cause decreased EtCO2 includes
Ventilator disconnect
esophageal intubation
poor seal with ETT or LMA
sample link leak
airway obstruction
apnea
What are examples of increased alveolar ventilation that can result in decreased EtCO2
hyperventilation
inadequate anesthesia
metabolic acidosis (if spontaneous ventilation)
medication side effect
What are examples of decreased alveolar ventilation that can result in increased EtCO2?
hypoventilation
CNS depression
residual NMB
COPD
high spinal
neuromuscular disease
metabolic alkalosis
medication side effect
What are causes of increased CO2 production and delivery to the lungs that can result in increased EtCO2?
increased BMR
malignant hyperthermia
thyrotoxicosis
fever
sepsis
seizures
laryngoscopy
tourniquet or vascular clamp removal
sodium bicarbonate administration
shivering
increased muscle tone (after NMB reversal)
medication side effect
What are causes of decreased CO2 production and delivery to the lungs that can result in decreased EtCO2?
decreased BMR
increased anesthetic depth
hypothermia
decreased pulmonary blood flow
decreased cardiac output
hypotension
pulmonary embolus
V/Q mismatch
medication side effect
pain/anxiety (if breathing spontaneously)
Select the statements that MOST accurately describe pulse oximetry (select 2).
a. oxygenated hemoglobin absorbs light at 940 nm
b. at the peak of the waveform, the ratio of arterial blood to venous blood is reduced
c. it is based on the Beer-Lambert law
d. it is based on the Doppler effect
a. oxygenated hemoglobin absorbs light at 940 nm
c. It is based on the Beer-Lambert law
Select the statements that MOST accurately describe pulse oximetry (select 2).
a. oxygenated hemoglobin absorbs light at 940 nm
b. at the peak of the waveform, the ratio of arterial blood to venous blood is reduced
c. it is based on the Beer-Lambert law
d. it is based on the Doppler effect
a. oxygenated hemoglobin absorbs light at 940 nm
c. It is based on the Beer-Lambert law
The pulse oximeter is based on the _______
Beer-Lambert Law
What does the Beer Lambert law describe?
it relates the intensity of light transmitted through a solution (blood) and the concentration of the solute (hemoglobin) within the solution
Red light is absorbed at
660 nm
Red light is preferentially absorbed by
deoxyhemoglobin (higher in venous blood)
Near-infrared light is absorbed at
940 nm
Near-infrared light is absorbed by
oxyhemoglobin (higher in arterial blood)
As a general rule, monitoring sites ________________ have faster response times
closer to the central circulation
(forehead and ear will be more responsive than the toe)
What is the SpO2 equation?
SpO2= oxygenated hbg/ (oxygenated hbg + deoxygenated Hbg) x 100%
At the trough of the pulse waveform, there is a
greater amount of venous blood in the tissue sample
At the peak of the pulse waveform, there is a
greater amount of arterial blood in the tissue sample
When SpO2 is monitored on the head or esophagus, the Trendelenburg position can cause
venous engorgement resulting in a falsely decreased SpO2 measurement
