Measurement Modules
Theory of Operation
A-8 Efficia CM Series Service Guide
patient and sends it to the module. The calculated data is measurement of total
hemoglobin concentration and a percentage value for the SpCO, which reflect blood
levels of carbon monoxide bound to hemoglobin.
The specified PR accuracy is the root-mean-square (RMS) difference between the
measured values and the reference values. The Masimo sensors have been validated
for pulse rate accuracy for the range of 25 – 240 bpm in bench top testing against an
electronic pulse simulator.
Rainbow acoustic monitoring continuously measures a patient's respiration rate based
on airflow sounds generated in the upper airway. Respiratory sounds include sounds
related to respiration such as breath sounds (during inspiration and expiration),
adventitious sounds, cough sounds, snoring sounds, sneezing sounds, and sounds
from the respiratory muscles. The acoustic sensor translates airflow sounds generated
in the upper airway to an electrical signal that can be processed to produce a
respiration rate, RRa, measured as breaths per minute.
IBP
The invasive blood pressure (IBP) measurement produces real-time waveforms and
numeric values for systolic, diastolic, and mean arterial blood pressure. IBP
measurements use an A/D converter. The A/D converter interfaces to the
microprocessor through an SPI connection in the front end interface.
An isolation transformer and opto-coupler provide the required isolation between
isolated and grounded sections of the monitor. Software algorithms filter typical
artifacts like respiratory variation and pressure changes caused by flushing the line or
drawing blood samples.
Temperature
The temperature circuitry processes a signal from a probe containing a thermistor
component whose resistance is temperature-dependent. The thermistors follow the
YSI 400 resistance vs temperature curve. These resistance temperature detectors
(RTDs) measure temperatures because of the physical principle of the positive
temperature coefficient of electrical resistance of metals. The advantage is stable
outputs for long periods of time, ease of recalibration, and accurate readings over
relatively narrow temperature spans. The monitor’s input circuitry conditions and
processes the signal to drive the numeric display.
Respironics CapnoTrak Sidestream CO
2
Module
CapnoTrak is a sidestream sampling system with a 50 ml/minute low sampling rate
that is used to measure the CO
2
of non-intubated and intubated infant, pediatric, and
adult patients using specially designed sampling cannula and airway adapter kits. A
replaceable water filter assembly provides filtration of fluids and contaminants and
protects the system from ingress of these fluids.
Internal to the CapnoTrak Module, infrared light is generated and focused through the
sample cell to a detector on the opposite side. CO
2
from the patient that flows through
the sample cell absorbs some of this infrared energy. The module determines CO
2
concentration in the breathing gases by measuring the amount of light absorbed by
these gases. ETCO
2
is displayed as a numerical value in millimeters of mercury
(mmHg), percent (%), or kilopascals (kPa). In addition, a CO
2
waveform (capnogram)
may be displayed which is a valuable clinical tool that can be used to assess patient
airway integrity and proper endotracheal tube (ETT) placement. Respiration rate is
calculated by measuring the time interval between detected breaths.
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