Flashcards in Anesthesia Gas Monitoring Deck (43)
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1
Patient Safety: Guiding Concern in Development of Monitors
-Oxygen concentration
-disconnect alarms
-end tidal CO2
-pulse ox
-peak pressure monitoring
-anesthesia gas monitoring
--N2O
--desflurane
--sevo
--iso
--oxygen
--CO2
--nitrogen
2
Prevention and Detection
-most adverse outcomes come from misuse by practitioner and/or failure to detect equipment failure when it happens
3
Non diverting gas monitor
-Mainstream, in-line
-sensor is located directly in the gas stream
-only CO2 and oxygen are monitored with this mode (cannot monitor volatile gases)
-oxygen: fuel cell (electrochemical)
-CO2 infrared
4
Diverting gas monitor
-sidestream
-gas is aspirated from sampling site and through a tube to sensor located inside or on top of machine
-ALL gases can be monitored this way
oxygen: paramagnetic
volatiles, nitrous oxide, and CO2 infared
5
Infrared Analysis (Diverting or NonDiverting)
-most often used analysis for CO2, nitrous oxide and volatile agents
-molecules containing dissimiliar atoms will absorb infrared radiation
-this technology does NOT work for oxygen and nitrogen
-tend to underestimate inspired levels and overestimate expired levels at high respiratory rates
6
Infrared Analysis
-most molecules will absorb infrared at specific wavelengths and hence the molecule can be identified and its concentration measured
7
Beer-Lambert Law
-absorption is according to this
-there is a logarithmic dependence between the transmission of light through a substance and concentration of that substance
8
IR Side Stream Sampling Diverting
-continuously aspirates a sample of the gas from patient circuit, usually near where breathing circuit is connected to the airway device
-50-250 ml/min aspirated (may be returned to patient or to scavenging)
-sample direct to place between infrared emitter, optical filter, and infrared detector, which outputs a signal proportional to remaining infrared energy not absorbed by the gases
-to quantify and identify multiple gases simultaneously multiple optical filters are required
-detected signal then amplified and interpreted via microprocessors
9
The Good on side stream sampling
-automatical calibration and zeroing
-quick response time and short warm up
-minimal added dead-space
-low potential for cross-contamination between patients
10
What could be better on side stream sampling
-multiple places that leaks may occur
-more variability in CO2 readings than with in line sampling- accurate with RR 20-40, decreased with increased rate
-slower response to changes than with in line sampling
-water contamination (water traps)
11
Gas Monitoring
-to monitor CO2 the sensor must be positioned between the patient and the circuit, ideally closest to the patient end as possible
why- dead space
12
Dead space: wasted ventilation
-ventilated areas which do not participate in gas exchange
Total deadspace= anatomic + alevolar + mechanical
13
Anatomic deadspace
-airways leading to alveoli
14
Alveolar deadspace
-ventilated areas in lungs without blood flow
15
Mechanical deadspace
-artificial airways including ventilator circuits
16
Inspired Oxygen Analysis
-FiO2 monitor is extremely important in patient safety
-first line of defense against detecting hypoxic mixtures
-but.. ventilation and oxygenation must be considered as two separate entities
-pulse oximetry is a late indicator of hypoxemia
17
Low V/Q
-shunt perfusion: alveoli perfused but not ventilated
(ET tube in mainstream bronchus)
18
V/Q= .8
normal
alveoli perfused and ventilated
19
High V/Q
deadspace ventilation
-alveoli ventilated but not perfused
(cardiac arrest)
20
Two types of oxygen analyzers
1. Paramagnetic (Diverting)
-more expensive, no need to calibrate, fast enough to differentiate oxygen concentrations
2. Electrochemical (Non Diverting)
-galvanic (fuel cell)
-calibration needed
21
Paramagnetic Oxygen Analysis
-unpaired electron in the oxygen molecule is attached to magnetic field
-when oxygen passed through magnetic field it goes to the strongest portion of that field
-expansion, contraction of the gas creates a pressure wave that is a proportional to the oxygen's partial pressure
22
Paramagnetic Oxygen Analyzers
-both inspired and end tidal oxygen levels to be measured even at rapid respiratory rates
-auto calibrates with reference gas (air or known concentration oxygen)
-many monitors combine diverting IR analysis of CO2, volatiles and nitrous oxide with a paramagnetic oxygen analysis using the same side stream sample
23
Electrochemical Oxygen Analysis (Fuel cell or Galvanic)
-oxygen diffuses through sensor membrane and electrolyte to cathode ray tube
-reduced there (gains electrons), allowing a current to flow
-rate at which oxygen enters cell and generates current is proportional to the partial pressure of the gas outside of the membrane
24
Electrochemical Oxygen Analyzer
-usually placed on or near the carbon dioxide canister on the inspiratory side
the good: cheaper
the bad: calibration every 8 hours, need frequent changing
25
End-tidal CO2 monitoring
-validation of proper endotracheal tube placement
-detecting and monitoring of respiratory pathophys
-hyper/hypoventilation
-cardiac function, circuit disconnection or leaks
-adjustment of parameter settings in mechanically ventilated patients
-Estimate PaCO2
26
ETCO2 and cardiac resuscitation
-Non survivors- average ETCO2: 4-10 mmHg
Survivors (to discharge): average ETCO2: >30 mmHg
-if patient is intubated and pulmonary ventilation is consistent with bagging, ETCO2, will directly reflect CO
-flat waveform can establish PEA
-configuration of waveform will change the obstruction
27
Increase in ETCO2
-increased muscular activity (shivering), MH
-increased CO (during resuscitation)
-bicarbonate infusion
-tourniquet release
-effective drug therapy for bronchospasm
-decreased minute ventilation
28
Decrease in ETCO2
-decreased muscular activity (muscle relaxants)
-hypothermia
-decreased CO (cardiac arrest)
-pulmonary embolism
-bronchospasm
-increased minute ventilation
29
normal arterial CO2:
paCO2 values
35-45 mmHg
4.7-6.0 kPA
4.6-5.9%
30
