An E-cylinder reads 900 PSI. A patient requires oxygen at 3 LPM for transport. How long will the cylinder last?

84 minutes. Using the cylinder duration formula: Minutes = (PSI x Cylinder Factor) / Flow = (900 x 0.28) / 3 = 252 / 3 = 84 minutes. The E-cylinder factor is 0.28. This gives approximately 1 hour and 24 minutes of oxygen. Remember to plan for changing the cylinder before it reaches 200 PSI (safe residual).

A Bourdon gauge flowmeter is preferred over a Thorpe tube flowmeter for patient transport because:

It is gravity-independent and works in any position. The Bourdon gauge flowmeter is gravity-independent, meaning it reads accurately regardless of position (upright, tilted, or horizontal). Thorpe tube flowmeters rely on gravity to float the ball indicator and must be upright. This makes Bourdon gauges ideal for ambulance transport. However, Bourdon gauges are NOT accurate with back pressure.

A pressure-compensated Thorpe tube flowmeter differs from a non-compensated Thorpe tube in that it:

Reads accurately even when there is downstream back pressure. A pressure-compensated Thorpe tube flowmeter has the flow control valve upstream of the float tube (flow meter is downstream of the valve). This means the pressure in the flow tube equals the downstream pressure, so the reading remains accurate even with back pressure from nebulizers or other equipment. Non-compensated flowmeters read falsely high with back pressure.

When troubleshooting a ventilator alarm, what should the respiratory therapist do FIRST?

Assess the patient. The patient is ALWAYS assessed first. The alarm may indicate a life-threatening condition (pneumothorax, extubation, respiratory arrest). After assessing the patient — and manually ventilating if needed — then check the circuit, check the machine, and correct the identified problem. Never silence an alarm without investigating the cause.

An oxygen analyzer is calibrated using which two reference points?

21% O2 (room air) and 100% O2. Oxygen analyzers are calibrated using two known concentrations: room air (21% O2) as the low calibration point and 100% O2 as the high calibration point. Calibration should be performed daily or with each new patient. If readings are inaccurate after calibration, the sensor (galvanic fuel cell or polarographic electrode) should be replaced.

4.2 Equipment & Troubleshooting | CRT/RRT Respiratory Therapist Exam | Free Exam Prep

Key Takeaways

Oxygen analyzers should be calibrated daily using room air (21%) and 100% O2; galvanic fuel cell and polarographic (Clark) electrode types
Thorpe tube flowmeters: pressure-compensated (accurate regardless of back pressure) vs. non-compensated (reads inaccurately with back pressure)
Bourdon gauge flowmeters are gravity-independent (any position) and used for transport; NOT accurate with back pressure
Cylinder duration formula: (PSI x cylinder factor) / flow rate (LPM) = minutes remaining
Common cylinder factors: E-cylinder = 0.28, H-cylinder = 3.14
Ventilator alarms require immediate assessment: patient first, then circuit, then machine
Suction equipment: wall suction (continuous or intermittent), portable suction, Yankauer tip (oropharyngeal), suction catheter (ETT)
CPAP/BiPAP troubleshooting: mask leak (most common problem), skin breakdown, aerophagia, claustrophobia, eye irritation

Equipment & Troubleshooting

The Troubleshooting and Equipment Management domain accounts for approximately 14% of the TMC exam. You must understand how respiratory equipment works, how to calibrate and maintain it, and how to systematically troubleshoot problems.

Oxygen Analyzers

Oxygen analyzers measure the FiO2 of delivered gas. Two main types are used:

Type	Mechanism	Response Time	Maintenance
Galvanic fuel cell	Electrochemical reaction generates voltage proportional to O2	10-30 seconds	Replace cell every 6-12 months
Polarographic (Clark electrode)	External voltage applied; current proportional to O2	Faster	Requires batteries and electrode maintenance
Paramagnetic	Measures O2 based on its paramagnetic property	Very fast	Used in ventilators and gas analyzers

Calibration (performed daily or with each patient):

Low point: Room air (21% O2)
High point: 100% O2 source
If readings are inaccurate after calibration, replace the sensor

Flowmeters and Regulators

Thorpe Tube Flowmeters (Most Common):

Glass tube with a floating ball or bobbin that rises proportionally to flow
Read at the center of the ball (or top of the bobbin)
Pressure-compensated: Flowmeter is downstream of the valve; reads accurately even with back pressure
Non-compensated (uncompensated): Flowmeter is upstream of the valve; reads inaccurately with back pressure (reads higher than actual flow)

Bourdon Gauge Flowmeters:

Fixed orifice with a pressure gauge calibrated in LPM
Gravity-independent — works in any position (ideal for transport)
NOT accurate with back pressure (reads higher than actual delivery)
Cannot indicate if there is a downstream obstruction

Gas Cylinder Calculations

Cylinder Duration Formula:

Minutes Remaining = (Gauge Pressure x Cylinder Factor) / Flow Rate

Cylinder Size	Factor	Capacity (Full at 2200 PSI)
D-cylinder	0.16	356 L
E-cylinder	0.28	622 L
G-cylinder	2.41	5,300 L
H/K-cylinder	3.14	6,900 L

Example: An E-cylinder has 1,600 PSI remaining and the patient is on 4 LPM nasal cannula:

Minutes = (1,600 x 0.28) / 4 = 448 / 4 = 112 minutes (about 1 hour 52 minutes)
Safe residual pressure: Change cylinders at 200-500 PSI (do not run dry)

Suction Equipment

Equipment	Use	Key Features
Wall suction (piped)	Hospital rooms, ICU	Continuous or intermittent; most powerful
Portable suction	Transport, field	Battery-operated; less powerful than wall
Yankauer tip	Oropharyngeal suctioning	Rigid, large-bore; for oral secretions
Suction catheter	Tracheal suctioning through ETT	Flexible; size ≤ half ETT ID
Closed suction system	Ventilated patients	In-line; maintains PEEP and FiO2; reduces infection risk

CPAP/BiPAP Troubleshooting

Problem	Cause	Solution
Mask leak	Poor fit, wrong size, mouth breathing	Refit mask, try different size/type, use chin strap or full-face mask
Skin breakdown	Excessive mask pressure, improper fit	Adjust straps, use mask liner/cushion, alternate mask types
Aerophagia	Swallowing air; pressure too high	Reduce pressure, positional changes, evaluate pressure needs
Claustrophobia	Mask discomfort	Try nasal pillows, gradual desensitization, reassurance
Dry mouth/nose	Mouth leak, insufficient humidification	Add heated humidifier, chin strap, full-face mask
Eye irritation	Air leak from top of mask into eyes	Refit mask at nasal bridge, tighten upper straps
Rainout	Condensation in tubing	Adjust humidifier temperature, use heated tubing

Systematic Troubleshooting Approach

For ANY equipment alarm or malfunction, follow this systematic approach:

Assess the patient FIRST — Is the patient in distress? Are they safe?
Manually ventilate if the patient is on mechanical ventilation and in distress
Check the circuit — Look for disconnections, kinks, water accumulation, leaks
Check the machine — Review alarms, settings, displays
Correct the problem — Fix the identified issue
Document — Record the event, findings, and interventions

CRT/RRT Respiratory Therapist Exam

1Introduction: NBRC TMC Exam Overview

2Chapter 1: Patient Data Evaluation

3Chapter 2: Airway Management & Oxygen Therapy

4Chapter 3: Mechanical Ventilation

5Chapter 4: Pharmacology & Equipment

6Chapter 5: Infection Control, Ethics & Professional Practice