OM-25AE User Guide & Operating Instructions Rev J

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Manufacturer: Maxtec, Inc

European Representative Airox S.A. Parcd’activities Pau-Pyrenees L’echangeur BP833 64008 PAU Cedex France

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PREFACE This manual describes the function, operation and maintenance of the Maxtec Model OM-25AE hand-held oxygen analyzer. A member of Maxtec's line of oxygen analyzers and monitors, the OM-25AE utilizes the Maxtec MAX-250E oxygen sensor and is engineered for fast response, maximum reliability and stable performance. The OM-25AE is designed primarily for measuring the oxygen concentration supplied from medical oxygen delivery equipment and respiratory care systems. Its external probe and sensor are compatible with industry standard (15 millimeter I.D.) "T" adapters found on most oxygen ventilators and oxygen delivery equipment. The probe is also adaptable to a variety of other sampling configurations.

THANK YOU Thank you for your purchase of a Maxtec MAXO2® oxygen analyzer. We appreciate the time and energy you invest in selecting the equipment best suited to your needs. As repayment, we are supplying you with a reliable, high-quality instrument that, with proper care and operation, will provide you with years of exceptional service. We also encourage your comments or suggestions as to how our equipment, in any way, can better serve your needs. Please feel free to write, FAX or email us at the address on the back of this manual c/o the Maxtec Marketing Department. NOTE: In order to obtain optimum performance from your MAXO2® analyzer, all operation and maintenance must be performed in accordance with this manual. Please read the manual thoroughly before using the analyzer and do not attempt any repair or procedure that is not described herein. Maxtec cannot warrant any damage resulting from misuse, unauthorized repair or improper maintenance of the instrument.

WARNING The sensor of the MAXO2 Oxygen Analyzer (MAXO2) has been tested with various anesthesia gases including Nitrous oxide, Halothane, Isoflurane, Enflurane, Sevoflurane and Desflurane and found to have acceptable low interferance, the device in its entirety (including electronics) is not suitable for use in the presense of a flammable anesthetic mixture. Only the threaded sensor face, flow diverter, and “T” adapter may be allowed to contact such a gas mixture.

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To avoid explosion, do not operate the oxygen analyzer in the presence of flammable anesthetics or in an atmosphere of explosive gases. Operating the oxygen analyzer in flammable or explosive atmospheres may result in fire or explosion. Never allow an excess length of cable near the patient’s head or neck, as such could result in strangulation. Secure excess cable to the bed rail or suitable object. Never use a MAXO2 analyzer with a cable that appears worn, cracked or has damaged insulation. Before use, all individuals who will be using the MAXO2 must become thoroughly familiar with the information contained in this Operation Manual. Strict adherance to the operating instructions is necessary for safe effective product performance. This product will perform only as designed if installed and operated in accordance with the manufacturer’s operating instructions. Use only genuine Maxtec accessories and replacement parts. Failure to do so may seriously impair the analyzer’s performance. Repair or alteration of the MAXO2 beyond the scope of the maintenance instructions or by anyone other than an authorized Maxtec service person could cause the product to fail to perform as designed. Calibrate the MAXO2 weekly when in operation and if enviromental conditions change significantly. (ie, Temperature, Humidity, Barometric Pressure. --- Refer to Calibration section of this manual). Use of the MAXO2 near devices that generate electrical fields may cause erratic readings. If the MAXO2 is ever exposed to liquids (from spills or immersion) or to any other physical abuse, turn the instrument OFF and then ON. This will allow the unit to go through its self test and make sure everything is operating correctly. Never autoclave, immerse or expose the MAXO2 (including sensor) to high temperatures (>70oC). Never expose the device to pressure, irradiation vacuum, steam, or chemicals. To protect the unit from potential leaky battery damage always remove batteries when the unit is going to be stored (not in use for 1 month) and replace dead batteries with recognized name brand AA Alkaline batteries.

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Do not throw away. Dispose of properly in accordance with local regulations. Classification: Protection against electric shock: Internally powered equipment. Protection against water: Ordinary equipment Mode of Operation: Continuous Sterilization: See section 6 Safety of application in the presensence of a flammable anesthetic mixture: See section 8.1 FAILURE TO COMPLY WITH THESE WARNINGS AND CAUTIONS COULD RESULT IN INSTRUMENT DAMAGE AND POSSIBLY JEOPARDIZE THE WELL BEING OF THE PATIENT AND/OR HEALTH CARE PROFESSIONAL.

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TABLE OF CONTENTS 1. SYSTEM OVERVIEW ... 1.1 Base Unit Description ... 1.2 Components Description ... 1.3 MAX-250E Oxygen Sensor 2. SET-UP PROCEDURE ... 2.1 Battery Installation ... 2.2 Calibrating The MAXO2® Analyzer ... 2.2.1 Before You Begin ... 2.2.2 To Calibrate The MAXO2® Analyzer 2.2.3 Automatic Calibration To Room Air. 2.2.4 Factors Influencing Calibration ... 3. OPERATION INSTRUCTIONS ... 4. SENSOR REMOVAL AND REPLACEMENT ... 5. PROBLEM SOLVING ... 6. CLEANING AND MAINTENANCE ... 7. SPECIFICATIONS ... 7.1 Base Unit Specifications ... 7.2 Sensor Specifications ... 8. APPLICATIONS ... 8.1 Exposure to Anesthetic Gases ... 8.2 Calibration Techniques in Pressurized Systems ... 8.3 Calibration Errors ... 8.4 Atmospheres of High Humidity ... 9. SPARE PARTS AND ACCESSORIES ... 10. WARRANTY ...

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1. SYSTEM OVERVIEW 1.1

Base Unit Description

The MAXO2® analyzer (Model OM-25AE) provides unparalleled performance and reliability, due to an advanced design that includes the following features and operational benefits. •

Fast-responding, oxygen-specific, galvanic sensor that achieves 90% of final value in approximately 15 seconds at room temperature.

•

Extra-life oxygen sensor of approximately 900,000 O2 percent hours (minimum 2 years in most normal applications).

•

External probe with 10 ft., extendible cable and diverter fitting for standard 15 mm "T" adapter.

•

Operation using only 2 AA alkaline batteries (2 X 1.5 Volts) or approximately 3000 hours of performance in typical usage. For extra long life, 2 AA lithium batteries may be used.

•

Durable, compact case that permits comfortable, hand-held operation.

•

Large, easy-to-read, 3 1/2-digit LCD display for readings in the 0-100% range.

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Simple operation and calibration using quick-calibrate key functions.

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Self-diagnostic check of analog and microprocessor circuitry.

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Low battery indication.

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Components Description (please refer to page 3) LCD Readout 3 1/2-Digit Display- The 3 1/2-digit liquid crystal display (LCD) provides direct readout of oxygen concentrations in the range of 0-100%. It also displays "CAL" when the calibration mode is entered.

2

"%" Sign- The "%" sign is present during normal operation when the keypad settings are locked. When the keypad settings are unlocked, the "%" sign is not visible. In the calibration mode, the "%" sign flashes every second.

3

Low Battery Indicator- The low battery indicator appears on the LCD display when the power supply voltage drops below acceptable limits. When the "LOW BAT" icon is visible, batteries should be replaced immediately.

B

Keypad

4

ON/OFF Key- (after Calibration) This key is used to turn the instrument on or off. When batteries are installed in the unit and the unit is in the power off mode, the display will be blank. When the ON/OFF key is pressed once, the unit will start to display the oxygen concentration and the keypad is activated. If the ON/OFF key is pressed again, the unit reverts to the power off mode.

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LOCK/UNLOCK Key- The presence of the "%" sign on the LCD readout is an indication that the unit is in its normal "LOCKED" state. The unit must be unlocked in order to be calibrated. Pressing the LOCK key will unlock the keypad and cause the "%" sign to disappear. The unit can then be calibrated if desired. If no other keys are pressed within 10 seconds, the "%" sign will reappear and the unit will revert to the "LOCKED" mode.

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CALIBRATE Key- The Unit will force you to Calibrate the first time power is applied or the sensor is changed. This is indicated on the LCD by the word “CAL”. Pressing the CALIBRATE key will allow the ↑ and ↓ arrow keys to calibrate the unit. Also when the keypad is unlocked, the CALIBRATE key is used in conjunction with the ↑ and ↓ arrow keys to calibrate the unit. When the CALIBRATE key is pressed, "CAL" appears on the LCD readout for 1 second and then the measured calibration concentration is displayed. The calibration value can then be

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1 2

3 LCD Readout

A

7 4 9

6 5 B Keypad

External Probe

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C

OM-25AE 3

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changed using the ↑ and ↓ arrow keys. During calibration, the "%" sign will flash at a once per second rate. When the calibration value is set, pressing the CALIBRATE or LOCK/UNLOCK key will cause the unit to exit the calibration mode and return to normal operation. The unit will also revert to normal operation if 10 seconds elapse and no keys are pressed.

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↑ and ↓ Keys- The ↑ and ↓ arrow keys are used in conjunction with the CALIBRATE key to calibrate the unit. Pressing the ↑ or ↓ key will raise or lower the displayed value in .1% increments. When either of these keys are held down for more than 1 second, the display will scroll at a rate of .4% per second.

C

External Probe

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Sensor with Diverter- The sensor (with diverter) is designed to fit industry standard, 15 mm I.D. "T" adapters.

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Extendible Cable- The extendible cable allows the sensor to be positioned up to 10 feet from the base unit.

1.3

MAX-250E Oxygen Sensor

MAX-250E oxygen sensors offer quick response, stability and extra life on the order of 900,000 percent hours. The MAX-250E is a galvanic, partial pressure sensor that is specific to oxygen. It consists of two electrodes (a cathode and an anode), a teflon membrane and an electrolyte. Oxygen diffuses through the teflon membrane and immediately reacts electrochemically at the gold cathode. Concurrently, oxidation occurs electrochemically at the lead anode, generating an electrical current and providing a voltage output. Electrodes are immersed in a unique gelled weak acid electrolyte which is responsible for the sensors long life and motion insensitive characteristic. Since the sensor is specific to oxygen, the current generated is proportional to the amount of oxygen present in the sample gas. When no oxygen is present, there is no electrochemical reaction and therefore, negligible current is produced. In this sense, the sensor is self-zeroing. CAUTION: The Maxtec MAX-250E oxygen sensor is a sealed device containing a mild acid electrolyte, lead (Pb), and lead acetate. Lead and lead acetate are hazardous waste constituents and should be disposed of properly, or returned to Maxtec for proper disposal or recovery.

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CAUTION: Do not use ethylene oxide sterilization. Do not immerse the sensor in any cleaning solution, autoclave or expose the sensor to high temperatures. CAUTION: Dropping or severely jarring the sensor after calibration may shift the calibration point enough to require recalibration. CAUTION: The flow diverter for the sensor is for use with flowing gases only. Do not use the diverter when performing static sampling, such as in incubators, oxygen tents, oxygen hoods, etc. Do not throw away. Dispose of properly in accordance with local regulations.

2. SET-UP PROCEDURE 2.1

Battery Installation

All MAXO2® analyzer units are powered by two, AA, alkaline batteries (2 x 1.5 Volts) and are shipped without the batteries installed. The battery compartment is accessible from the back side of the unit. To install the batteries: 1) With the thumb, press down on the center of the battery compartment cover and slide the cover off of the instrument case. 2) Install the two, AA, alkaline batteries (2 x 1.5 Volts) in the unit, observing the orientation shown on the label inside the compartment. 3) Slide the battery compartment cover back onto the case. Make sure the tabs on the cover snap into position, securing the cover flush against the case. When batteries are installed in the MAXO2® analyzer, the unit initiates a self-diagnostic test. All segments of the LCD readout are turned on for approximately 2 seconds. When the diagnostic test is completed successfully, the word "CAL" will appear on the display, indicating that the unit is ready for calibration.

2.2

Calibrating the MAXO2® Analyzer

2.2.1 Before You Begin A protective film covering the threaded sensor face must be removed; wait approximately 20 minutes for the sensor to reach equilibrium. Next the MAXO2® Oxygen Analyzer should be calibrated. Thereafter, Maxtec recommends calibration on a weekly basis. However, more frequent calibration will not adversely affect product performance.

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More frequent calibration is required when: •

The temperature of the gas stream changes by more than 3 degrees Celsius.

•

Changes in elevation result in calibration error of approximately 1% of reading per 250 feet. In general calibration of the instrument should be performed when the geographic elevation at which the product is being used changes by more than 500 feet.

The sensor is best calibrated while mounted in the industry standard, 15mm I.D. “T” adapter. As in normal operation, the oxygen sensor responds best when installed in a vertical position with the sensor facing down. In addition, calibration is recommended if the user is unsure when the last calibration procedure was performed or if the measurement value displayed is in question. It is best to calibrate the MAXO2® analyzer to a known documented oxygen concentration at a pressure and flow similar to your clinical application. Calibrating the MAXO2® analyzer at lower concentrations with a known oxygen value is also acceptable and may provide additional accuracy if the calibration gas is closer to the environment in which the MAXO2® analyzer will be used. A “known” value of oxygen is defined as an oxygen source which has a traceable certificate and / or USP certification. Note: Before beginning calibration the MAX-250E sensor must be in thermal equilibrium. You may also need to be aware of other factors which affect device calibration values. For more information, refer to “Factors Influencing Calibration”, section 2.2.4 in this manual.

2.2.2 To Calibrate the MAXO2® Analyzer 1) Place the external probe in a stream of gas of known oxygen concentration. Expose the sensor to the calibration gas at a regulated pressure and flow at a rate of 1-10 liters per minute (2 liters per minute is recommended). 2) Using the ON/OFF key, make sure the unit is in the power on mode. 3) Allow the oxygen reading to stabilize. This will normally take about 30 seconds or more.

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4) Press the LOCK/UNLOCK key to unlock the keypad. The "UL" will appear on the display for about 1 second and then the “%” sign will disappear for the display. 5) Press the CALIBRATE key on the keypad. The word "CAL" will appear on the display for about 1 second and then the "%" sign will start to flash. 6) Use the ↑ and ↓ arrow keys to adjust the displayed oxygen concentration to the level of the known concentration. Pressing the arrow keys changes the value in .1% increments. If the keys are held down for more than 1 second the display will scroll at a rate of .4% per second. Note: If 10 seconds elapse between key actuations, the system will store the latest calibration value and will revert to normal operation. If this occurs inadvertently, simply repeat the calibration procedure. 7) When the calibration value is set, press the CALIBRATE or LOCK/UNLOCK key again to accept the calibration setting and return to normal operation. Note: If the message "CAL", followed by the message "Er" flashes on the display after entering the desired calibration value, the system has determined that the entered value will not allow operation within the specified output range of the sensor. This situation may occur if: a) the operator has inadvertently entered the wrong concentration for the calibration gas. b) the concentration of the calibration gas is not correct. c) the sensor is in need of replacement. d) the operator attempted to adjust the analyzer before allowing sufficient time for the calibration gas to purge out the previous sample. e) the flow and pressure of the calibration gas was not properly regulated. Check these items and repeat calibration. If calibration error continues to occur, contact the service department of the distributor from which the unit was purchased, or you may call Maxtec's Customer Service Department directly.

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2.2.3 Automatic Calibration to Room Air The MAXO2® analyzer can quickly be calibrated to room air (20.9%) using a quick-key shortcut command. This function saves time by setting the calibration value to 20.9% without scrolling the display. To use this function: 1) Place the external probe in room air. 2) Press the LOCK/UNLOCK key to unlock the keypad. 3) Press and hold down the CALIBRATE key. When the "%" sign starts to flash, press the ↓ arrow key to set the calibration value to 20.9%. 4) Release both the CALIBRATE key and the ↓ key. The unit will automatically enter the “LOCKED” condition and return to normal operation.

2.2.4 Factors Influencing Calibration The primary factors influencing the MAXO2® analyzer are temperature, pressure, and humidity.

Effects of Temperature The MAXO2® analyzer will hold calibration and read correctly within +/-3% when in thermal equilibrium within the operating temperature range. The device must be thermally stable when calibrated and allowed to thermally stabilize after experiencing temperature changes before readings are accurate. For these reasons, the following is recommended: 1) Allow adequate time for the sensor to equilibrate to a new ambient temperature. 2) When used in a breathing circuit, place the sensor upstream of the heater. 3) For best results, perform the calibration procedure at a temperature close to the temperature where analysis will occur.

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Pressure Effect Readings from the MAXO2® analyzer are proportional to the partial pressure of oxygen. The partial pressure of Oxygen (PO2) is equal to the percentage of oxygen (%O2) times the absolute pressure (AP) at which the sample enviroment is measured. (PO2=%O2 x AP). Thus the readings are proportional to the concentration if the pressure is held constant. Flow rate of sample gas can affect pressure at the sensor in that back pressure at the sensing point may change. For these reasons, the following is recommended: 1) Calibrate the MAXO2® analyzer at the same pressure as the sample gas. 2) If sample gases flow through tubing, use the same apparatus and flow rates when calibrating as when measuring. 3) The MAXO2® analyzer oxygen sensor has been validated at pressures up to 2 atmospheres absolute. Calibration or operation above this pressure is beyond the intended use.

Humidity Effect Humidity has no effect on the performance of the MAXO2® analyzer other than diluting the gas, as long as there is no condensation. Depending on the humidity, the gas may be diluted by as much as 4%, which proportionally reduces the oxygen concentration from the dry concentration. Environments where condensation may occur are to be avoided since condensate may obstruct passage of gas to the sensing surface, resulting in erroneous readings and slower response time. For this reason, the following is recommended: 1) Avoid usage in environments greater than 95% relative humidity. 2) When used in a breathing circuit, place the sensor upstream of the humidifier.

3. OPERATION INSTRUCTIONS To check the oxygen concentration of a sample gas: (after the unit has been calibrated) 1) Place the external probe in the sample gas stream. When using a standard "T" adapter, make sure the sensor is mounted in the adapter with the flow diverter pointing downward. This will prevent moisture

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from draining to the sensor. Note: It is important that a tight fit exists between the probe and the "T" adapter. 2) Initiate flow of the sample gas to the sensor. 3) Using the ON/OFF key, make sure the unit is in the power on mode. 4) Allow the oxygen reading to stabilize. This will normally take about 30 seconds or more.

4. SENSOR REMOVAL AND REPLACEMENT The OM-25AE is shipped with a new MAX-250E oxygen sensor installed. Although the sensor has a very long expected life, eventually the sensor will require replacement. Removing or installing a sensor, when necessary, is a very simple procedure. To remove and install a new sensor: 1) Grasp the sensor in one hand and, with the other hand, unscrew the cable connector counter-clockwise at the sensor. 2) Pull out the cable connector plug from the expired sensor. 3) Unscrew the flow diverter from the sensor and discard the expired sensor. Note: The sensor contains lead and lead acetate, be sure to dispose of expired sensors in accordance with hospital, local, state and federal regulations. 4) Remove the new sensor from the packaging and remove the protective film from the sensor face. 5) Insert the cable connector plug into the receptacle of the new sensor and tighten the cable connector. 6) Screw the flow diverter onto the new sensor. 7) Calibrate the new sensor. Note: If the analyzer is on when the sensor is detached and replaced, the analyzer will automatically force a re-calibration. The display will read “CAL”.

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5. PROBLEM SOLVING •

If the "LOW BAT" icon is displayed on the LCD readout at any time, the batteries should be replaced as quickly as possible.

•

When the unit is in the power on mode and the LCD displays "000%," the sensor is not connected properly. Check the sensor connection and if the condition persists, contact Maxtec Customer Service.

•

If, at any time, "ErX" (i.e. Er1, Er4, etc.) appears on the LCD readout, contact Maxtec Customer Service.

6. CLEANING AND MAINTENANCE •

When cleaning or disinfecting the MAXO2® analyzer, take appropriate care to prevent any solution from entering the instrument.

•

The MAXO2® analyzer,s surface may be cleaned using a mild detergent and a moist cloth.

•

The MAXO2® analyzer may be disinfected using standard topical disinfectants.

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The MAXO2® analyzer is not intended for steam, ethylene oxide or radiation sterilization.

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Store the MAXO2® analyzer in a temperature similar to its ambient environment of daily use.

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7. SPECIFICATIONS 7.1 Base Unit Specifications Measurement Range: 0.0-100% Resolution: 0.1% Accuracy and Linearity: ±1% of full scale at constant temperature, R.H. and pressure when calibrated at full scale. Total Accuracy: ±3% Actual Oxygen Level over full operating temperature range. Response Time: 90% of final value in approximately 15 seconds at 23oC. Warm-up Time: none required Operating Temperature: 15oC - 40oC (59oF - 104oF) Storage Temperature: -15oC - 50oC (5oF - 122oF) Humidity: 0-95% (non-condensing) Power Requirements: 2, AA Alkaline batteries (2 x 1.5 Volts) Battery Life: approximately 3000 hours in typical use Low Battery Indication: "LOW BAT" icon displayed on LCD Sensor Type: Maxtec MAX-250E galvanic fuel cell Expected Sensor Life >900,000% O2 Hours : Over 2 years in typical applications 3.5"(W) x 5.5"(H) x 1.5"(D) [89mm x 140mm x Dimensions: 38mm] Weight: approximately .92 lbs. (417g) Cable Length: 10 ft. (3m) fully extended Diverter Fitting: fits industry standard, 15 mm "T" adapter

7.2 Sensor Specifications Type: Life:

galvanic fuel sensor (0-100%) 2 years in typical applications

Interferent

Volume % Dry

Interference in O2%

75% 10% 5% 5% 5% 70% 6%

<2% <2% <2% <2% <2% <2% <2%

Nitrous Oxide Carbon Dioxide Halothane Enflurane Isoflurane Helium Sevoflurane

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15%

<2%

8. APPLICATIONS 8.1 Exposure to Anesthetic Gases Because of the unique chemistry of the oxygen sensors provided with the MAXO2® analyzer, there are no ill effects when exposed to commonly used anesthetic gases, however the analyzer is not designed for exposure to flamable gas mixtures. (See WARNING page i)

8.2 Calibration Techniques in Pressurized Systems Similar to other oxygen sensors, the Maxtec MAX series sensors measure the partial pressure of oxygen in a gas stream. This is correlated to read “percent oxygen” on the MAXO2® analyzer. It is important to note that the sensor output is directly proportional to the pressure of oxygen. Thus, one must take into consideration the effect of exposing the sensor to various gas sample pressures. For example, if an analyzer is calibrated to read 20.9% in ambient air (atmospheric pressure) and then exposed to a pressurized gas sample containing a known concentration of oxygen, the analyzer will display a reading greater than the actual oxygen percentage. This is because the analyzer was originally calibrated at atmospheric pressure (0 psig) then exposed to a higher pressure sample (eg, 5 psig). The greater the difference in pressure, the greater the difference in sensor signal (oxygen reading on the analyzer). By the same token, if an analyzer is calibrated on a pressurized gas sample containing a known concentration of oxygen and then exposed to ambient air (atmospheric pressure), the analyzer will display a reading less than the actual oxygen percentage. To avoid confusion, the analyzer can be calibrated at a single point on a gas stream similar to the application. If, for example, the purpose of the analyzer is to measure oxygen in a concentrator or anesthesia application, the optimal results may be attained by calibrating the instrument on a gas of similar concentration and pressure. This would typically be done by connecting to a cylinder of a known high concentration of oxygen calibration gas and adjusting the flow and pressure to match the application before calibrating the instrument.

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8.3 Calibration Errors The MAXO2® analyzer have a self test feature built into the software to detect faulty calibrations. During calibration, if the signal from the oxygen sensor is outside the limits stored within the instrument’s memory, a flashing “CAL Er” is displayed. The error code is displayed to indicate that either the sensor should be replaced or that there is a fault in the calibration process. A few simple hints can prevent calibration errors. If you try to adjust the analyzer display before the reading has stabilized, the “CAL Er” may appear. For example, if the analyzer had just been calibrated on a known high concentration of oxygen source gas and then exposed to ambient air, you should wait until the reading has stabilized. If you try to adjust the display to read 20.9% before the sample line has cleared of high concentration O2, the sensor may actually be exposed to residual high % oxygen. The signal from the sensor would still be high and considered “out of spec” for air, thus resulting in a “CAL Er”. The proper procedure is to wait for the reading to stabilize before adjusting the display. This may take 30 seconds or more. Externally mounted sensors, as found on the OM25-AE and OM25-ME come equipped with diverter tips. The tips help direct the gas in a “T” fitting up to the sensor for analysis. The diverter tips should only be used with a flowing gas. When calibrating in a non-flowing environment, remove the diverter tip.

8.4 Atmospheres of High Humidity The MAXO2® analyzer can be used in applications where the relative humidity of the sample gas ranges from 0 to 95%, non-condensing. However, it should be noted that water vapor exerts its own pressure in the same manner as oxygen does in a sample gas stream. For example, if the analyzer is calibrated in dry gas and then the gas is humidified, the analyzer will correctly display a reading which is slightly lower than previously displayed. This is due to the dilution of oxygen in the sample gas by water vapor. This fact is important to note in systems where there exist both “wet” and “dry” gas streams such as in a ventilator circuit. If the analyzer is measuring oxygen on the “dry side” of the ventilator, it will correctly indicate an oxygen concentration slightly greater than actually found in the “wet side” (delivered to the patient). The water vapor has diluted the gas

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