Module 8 Flashcards
Which gases are important to the anesthesia provider
O2
CO2
NO
Inhaled Anesthetics
Gas sampling systems can be
Diverting or Non-diverting
Non diverting systems are
Mainstream
Diverting systems are
Side-stream (most used)
What is it called when the analyzer is located in the breathing system
Called non-diverting because the gas isn’t removed from the circuit (continuously analyzed)
The overall response time is
Composer of transit time & rise time
What is transit time?
Time it takes for gas sample to reach analyzer
What is rise time?
Time it takes for analyzer to reach a change in gas composition
The response of diverting or side stream system is dependent upon
The sampling tube inner diameter, the linked & gas sampling rate
In mainstream or non diverting systems, gas flows
Past the analyzer interface; allows for multi gas analysis; requires special adapter; placed near the patients airway ; subject to interference by water vapor, secretions & blood; creates 2 additional places for disconnection
Explain side stream systems
Remote from patient
Any size
More diverse
Continuously drawn from the breathing circuit via the Y piece
Passes through a filter or water trap & then enters the analyzer
What is the disadvantage of side stream analyzer
Clogging/Kinking
Slow/total response time & artifact
Rapid response time & long sampling lines may decrease accuracy of the reading
Multiple breaths will cause dampening, loss of clear peaks & troughs
Gas sampling rate that are screes the fresh gas flow rate has the potential for negative pressure to be created
Leaks can occur inside the monitor & in the tubing
The amount of radiation absorbed is a function of
Partial pressure
Mass spectrometer doesn’t measure partial pressure..
Only proportions
What does Dalton law say?
Partial pressure of all gases in the system add up to the overall pressure of the system
Volumes percent is a
Proportion
The greater number of molecules=
The more radiation is absorbed
Since the absorbable is determined by the number of molecules present,
The amount of radiation absorbed is a function of the partial pressure
Which gas analysis technology is most common?
Infrared, which is dispersive or non dispersive
Gas analysis techniques includes
Mass spectrometry
Infrared analysis
Spectrometry allowed the
Breath by breath identification &quantity indication of up to 8 gases
Spectrometry unit separates the components of a stream of charged particles or ions into a spectrum according to their
Mass & charge ratios
Relative abundance of ions with certain mass & charge ratios is
Deterred & related to the fractional composition of the original gas mixture
Which infrared analysis is used?
Non-dispersive analyzer, which uses a specific wavelength
What is collision broadening
Presence of other gases with overlapping absorption bands
Infrared spectrum ranges from
.4-40 micrometers
Asymmetrical true polyatomic molecules like CO2
Absorb infrared energy when their atoms rotate or vibrate asymmetrically
Symmetric molecules such as nitrogen & oxygen
Doesn’t absorb infrared energy
After the infrared radiation passes though the gas sample in the dispersive analyzer,
The emitted radiation is separated or dispersed into the component wavelength & arranged sequentially; a plot is obtained ( peaks)
In non dispersive analyzer
Only specific wavelengths known to interact with certain gases are passed through the gas sample & an analysis is made
A black box radiator doesn’t reflect any light but
As it’s heated, it radiates the energy as electromagnetic radiation
In the non dispersive analyzer, the gas is drawn through a sample cell/ corvette & the detector
Generates an output signal dependent upon the intensity of the infrared radiation that falls on it; narrow band filter allows radiation of only certain wavelengths
The intensity of the radiation is inversely related to
The concentration of the specific gas being measured
Infrared analyzers must use a
Specific wavelength of radiation according to the absorption peak of each gas to be measured; each analyzer uses a wavelength of 3.3 micrometers to measure inhaled anesthetics
The use of aerosol propellants used in inhalers would
Appear to the analyzer as a transient peak of halogenated agents
Modern analyzers have the capability of
Identifying & quantifying different agents
The IR radiation detectors are
Thermal plied, which is a device that converts thermal energy into electrical energy
Sidestream sampling analyzers continuously withdraw
50-250mL/minute from the breathing circuit
What is the disadvantage of sampling system
Water vapor from the breathing circuit condenses on its way to the sampling corvette & can interfere with optical transmission (water traps/filters are used to protect the optical system from condensation & body fluids)
In photo acoustic spectrometry,
A simple microphone detector is used to detect all the IR absorbing gases
What’s is the disadvantage of photo acoustic spectrometry
It’s sensitive to interference from loud noise & vibration
Ramen spectrometry is based on
The principle that when light strikes gas molecules, most of the energy is re-emitted in the same direction & at the same wavelength as the incoming beam (red shifted spectrum); not limited to gases that are polar
Monoatomic gases like helium & xenon
Do not exhibit Ramen activity
Which gases are measured with ramen spectroscopy
Nitrogen & oxygen
Is ramen spectroscopy still in use?
No due to the laser being broken up by halothane molecules & contaminating
pH sensitive dyes are placed
Between the endotracheal tube & circuit to measure CO2 absorbance (used to confirm tracheal intubation when capnography isn’t available)
Oxygen analyzers can be
Fuel cell (slow change)
Paramagnetic (quick; every breath)
Oxygen is polar & can
Change pressure with a magnet
With the fuel cell, flow of current depends on the uptake of oxygen & the
Voltage developed is proportional to the oxygen partial pressure
Oxygen diffuses into the sensor and a
Reaction takes place at hay creates current similar to a battery
Like a battery, fuel cell has
Limited life span depending on its length or f exposures to oxygen
The paramagnetic oxygen analyzer uses
A magnetic field that I attract oxygen since it has 2 electrons & unpaired orbits
Paramagnetic analyzer compares the pressure difference between
Reference gas & the measured gas as they are exposed to rapidly changing magnetic fields; these pressure differences create sound waves that are sensed by microphone & converted to electrical signal
Does the paramagnetic sensor perform its own periodic calibration?
Yes
The oxygen analyzer in the anesthesia workstation prevents
Hypoxia gas mixtures
Paramagnetic analyzers are utilized for
Inhaled & exhaled oxygen concentrations
The slowly responding galvanic analyzer is incorporated into the machine to
Monitor for hypoxia gas administration
Inspired concentration monitoring is important during
Preoxygenation with 100% oxygen to denitrogenate the lungs as well as monitoring oxygen concentration when this is an ignition source close to airway
In procedures that involve the airway, it is important for oxygen concentration to be less than
30% to decrease the risk of fire
The oxygen analyzer is one of the most important monitors in the breathing system as it is both
Qualitative & Quantitative
What is considered the best method of confirming proper placement of the ET tube following intubation?
Detection of carbon dioxide ( CO2 monitoring)
Multi gas analyzers measure
Inspired & endtidal concentrations of all anesthetic gases including NO; makes it possible to monitor anesthetic uptake & washout & allows high & low concentration alarms
High fresh gas flows & vaporizer setting ensure
That the gas composition & the circuit changes rapidly to speed anesthesia uptake; once a he desired concentration is attained, the vaporizer setting can be decreased
What can be used to prevent anesthetic overdosing?
Anesthetic agent high concentration alarm
The low concentration alarm can prevent
Awareness & shows the vaporizer is either empty or there’s a leak
What is the definition of breathing
Bidirectional movement of gas into the lungs followed by gas moving out of the lungs
By monitoring inhaled & exhaled gas concentration
The breaths that vent the alveoli & breaths that don’t can be distinguished
With capnography, the transition from high concentration to low concentration is
The start of inspiration; from low to high is start of exhalation
Phase 2 is the
Beginning of expiration
Phase 3 is the
Alveolar plateau and correlates with PaCO2
If the beta angle isn’t 90 degrees,
There is rebreathing or mechanical obstruction
If the aloha angle is greater than 90 degrees, the patient
Isn’t exhaling air as fast, resulting in air trapping, bronchospasm/VQ mismatch
Under ideal conditions, the partial pressure of end tidal is
Similar to that of arterial blood, but this is dependent upon how it’s measured & patient physiology including diffusion, ventilation, & cardiac output
For end tidal gas to mirror arterial blood,
The entire gas sample must contain only gas that has been exhaled from well perfumed alveoli; coming from poor perfumed alveoli= contamination
The concentration observed over multiple breaths will
Likely be near to the concentration in the arterial blood
The maximum CO2 value observed in the past
1-2 minutes corresponds more closely with arterial concentration; the lowest end tidal oxygen concentration observed corresponds with arterial concentration
What are some complications of gas monitoring?
Hyperventilation
CO (low perfusion)
Kinked ETT
user error is more common
What is a required standard of the ASA
Monitoring of FiO2 & pulse oximetry
What are the defining characteristics of spontaneous ventilation
Depth & frequency
Frequency most fundamental
Common cause of tachypnea
Periop pain
What are other ways to monitor RR
Thoracic impedance & EKG monitoring (most common)
Acoustic techniques (listening to the face, neck or chest)—-this method suffers from ambient noise interference
The electrical resistance in the thorax changes with
Inflation & deflation of the lungs
Impedance changed with
The change in the shape of the thorax
EKG changed in both
Amplitude & signal & there are changes in the QRS complex occurring during ventilation
Amplitude changes are due to
A change in the overall electrical resistance of the chest due to the increased proportion of air in the chest cavity
Inflation of the lungs also produces a change in
Access to the heart
70% of disconnections occur at the
Y piece
Volume control will deliver a set tidal volume & pressure that will
Increase until the tidal volume is reached
Pressure control delivers a set
Pressure & tidal volume will depend on airway resistance & lung & chest wall compliance
Pressure control can improve both
Ventilation & oxygenation
Subatmospheric pressure alarms alert clinicians to
Negative circuit pressure which could rapidly cause pulmonary edema, atelectasis & hypoxia; this can occur from suction of the scavenging system, patient effort against blocked circuit, or circuit with an inadequate gas flow
Place meant of gastric tube applied to suction can cause negative oressure
When is the continuous pressure alarm triggered
When circuit exceeds 10cm of water for more than 15 seconds, which can be caused by ventilators pressure relief valve, system occlusion or a tight APL valve & spontaneous breathing; forget to turn on ventilator
How to measure minute volume
Tidal volume x RR
The simplest device for the measurement of gas volume is based on a
Rotating vein or propeller calibrated against the specific density of a gas; the rotation of the attached shaft correlates with the volume of gas that is passed by
Force is transmitted to the veins. Y the impact of the gas molecules &
This is converted to a rotational momentum & spins the pinwheel; the count is converted to volume
What are the variables of volume measurement
Gas compositions
Humidity
Altitude
Temperature
Low flows will cause the turbine to
Accelerate more slowly (volume & accuracy due to inertia effects); still safe
Turbulent flow is
Characterized by the formation of eddies or vortices in hay cause increased drag
Resistance is low in laminar or turbulent flow
Laminar
Poiseuille law only applies to
Laminar flow
Rotameters can measure
Gas vapor or liquid flow; floating bobbin rotates to prevent friction
Rotameter must be
Vertical to avoid friction or collision with the wall
You can instantly detect the velocity & direction of tidal flows with the
Pitot tube flow meter; it measures the pressure difference of gas impacting a port & compares that pressure with a static monitor
Pressure difference are proportional to
The flow rate; direction of flow can be determined
Describe Fleish Pneumotachometer
Measures the loss of energy of gas as it passes through a resistive element
The energy lost is measured as a pressure different form the inlet to the outlet of the element
Element assures the follow is laminar
Energy loss is due to viscosity & flow is directly proportional am to the pressure deference
Fleish Pneumotachometer is used
In pulmonary physiology & pulmonary function studies
Turbulent flow fixed orifice flow meters use
The measured pressure differential between 2 ports separated by an orifice
Calculates the pressure difference between the upstream & downstream
Laminar-Upstream
Turbulent-Downstream
A variable orifice flow meter sensors monitors both
Inspiratory & expiratory flows & volumes
Decreased sensitivity at low flows is compensated by the flapper valve between the 2 pressure sensors
Increases in size with larger flows
Gas flow rates can be measured with a heated wire by
Measuring the cooling of the wire from heat transfer to the gas flowing by
Heat transfers a function of the gas velocity
Limited to only laminar flow
Able to measure a wide variety of flow rates
Sensitive flow meter used for monitoring variable flows used
Ultrasound reflection from moving columns of gas or liquid
Signal travel faster when moving with the flow
Difference between the 2 transit times are used to calculate the gas flow rates
Applicable to liquids, gases & multiphase mixtures
Spirometer display include
Time, volume, flow & pressure
Time is always on horizontal axis
FVC ratio used to determine airflow limitation’s & distinguished between obstructive & restrictive lung disease
Inspiration on volume time curves are depicted as
Up slopes
Exhalations
Down slopes
Curves can identify auto PEEP, expiratory limb leaks, forced exhalation & flow transducer miscalibrations
Expiratory curve will not return to base line if there’s a
Limb leak
Square flows represent
Constant inspiratory flows that create shorted inspiratory times & longer exhalation times
Flow volume loops represent
Flow rate versus inspiration & expiratory volumes
Spontaneous loop will show both
Negative & positive pressures, but negative pressure may be absent if PEEP is applied
Respiratory cycle started with
Inhalation, moving clockwise
With ventilation, inspiration requires
An increase in airway pressure & exhalation requires a decrease
Volume control mode & decreased compliance =
Barotrauma
Pressure control & decreased compliance =
Decreased tidal volume
The concentrator only delivers
95% oxygen, not 100%
Compliance is defined as
Changing volume per unit change in pressure & its not fixed
Smaller lung volumes & decreased compliance means a
Rightward & downward shift of the loop
What will be seen before tachycardia, cyanosis & tachypnea
Capnography rise
What’s doesn’t detect breathing system disconnects as rapidly as pressure alarms, but able to detect esophageal intubation, CO change, inadequate pulmonary circulation & embolism
Capnography
A rapid rise in this is an early indicator of limited hyperthermia
Capnography
Continuous monitoring of end tidal CO2 is
A non invasive method for estimating arterial pressure of carbon dioxide
Capnography can identify
Hyperventilation & apnea before the onset of hypoxia
