Theory of Operation
Efficia CM Series Service Guide A-9
Measurement Modules
Respironics LoFlo Sidestream CO
2
Module
LoFlo 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 neonate, infant, pediatric
and adult patients using specially designed sampling cannula and on-airway adapter
kits. These kits incorporate a filter and the sample cell that provides maximum filtration
of fluids and contaminants and protects the system from aspiration of these fluids.
In LoFlo, infrared light is generated by the sensor and beamed through the sample cell
to a detector on the opposite side. CO
2
from the patient that is aspirated into the
sample cell absorbs some of this infrared energy. The monitor 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.
Oridion Sidestream CO
2
Module
Capnography is a non-invasive method for monitoring the level of carbon dioxide in
exhaled breath (etCO2) to assess a patient's ventilatory status. Microstream
®
capnography modules uses Microstream non-dispersive infrared (NDIR) spectroscopy
to continuously measure the amount of CO
2
during every breath, the amount of CO
2
present at the end of exhalation (etCO2), the amount of CO
2
present during inhalation
(FiCO
2
), and the Respiratory Rate.
Infrared spectroscopy is used to measure the concentration of molecules that absorb
infrared light. Because the absorption is proportional to the concentration of the
absorbing molecule, the concentration can be determined by comparing its absorption
to that of a known standard.
The Microstream
®
etCO
2
sampling lines deliver a sample of the inhaled and exhaled
gases from the ventilator circuit or directly from the patient (via an oral/nasal cannula)
into the monitor for CO
2
measurement. Moisture and patient secretions are extracted
from the sample, while maintaining the shape of the CO
2
waveform.
The 50 ml/min. sampling flow rate reduces liquid and secretion accumulation,
decreasing the risk of obstruction in the sample pathway in humid ICU environments.
This low sampling rate is ideally suited to measure a neonate's low tidal volume.
Once inside the Microstream
®
CO
2
sensor, the gas sample goes through a
micro-sample cell (15 microliters). This extremely small volume is quickly flushed,
allowing for fast rise time and accurate CO
2
readings, even at high respiration rates.
The Micro Beam IR source illuminates the micro-sample cell and the reference cell.
This proprietary IR light source generates only the specific wavelengths characteristic
of the CO
2
absorption spectrum. Therefore, no compensations are required when
different concentrations of N
2
O, O
2
, anesthetic agents and water vapor are present in
the inhaled and exhaled breath. The IR that passes through the micro-sample cell and
the IR that passes through the reference cell are measured by the IR detectors.
The microprocessor in the board calculates the CO
2
concentration by comparing the
signals from both detectors.
To Next Page
Loading...
