4.2 Equipment & Troubleshooting
Key Takeaways
- Oxygen analyzers are calibrated daily at two points: room air (21%) and 100% O2; galvanic fuel cell, polarographic (Clark electrode), and paramagnetic types appear on the exam
- Thorpe tube flowmeters: pressure-compensated reads accurately despite back pressure; non-compensated reads falsely HIGH with back pressure
- Bourdon gauge flowmeters are gravity-independent (work in any position) for transport but read falsely high with back pressure and miss downstream obstructions
- Cylinder duration = (gauge PSI x cylinder factor) / flow (LPM); subtract a 200 PSI safe residual for the strict formula
- Memorize cylinder factors: D = 0.16, E = 0.28, G = 2.41, H/K = 3.14; a full cylinder reads about 2200 PSI
- Ventilator and equipment alarms are worked patient-first: assess the patient, manually ventilate if in distress, then circuit, then machine
- Suction: Yankauer (rigid, oropharyngeal), suction catheter sized at no more than half the ETT internal diameter, and closed in-line systems that preserve PEEP and FiO2
- CPAP/BiPAP troubleshooting centers on mask leak (most common), skin breakdown, aerophagia, claustrophobia, eye irritation, and tubing rainout
Oxygen Analyzers, Flowmeters, and Regulators
Equipment quality control and troubleshooting form a dedicated scored section of the TMC exam, and the items are intensely practical: you calibrate a device, read a flowmeter, calculate how long a tank lasts, or decide what to do when an alarm sounds. Memorizing the device physics turns these into easy points.
Oxygen Analyzers
An oxygen analyzer measures the fraction of inspired oxygen (FiO2) delivered to the patient.
| Type | Mechanism | Response | Maintenance |
|---|---|---|---|
| Galvanic fuel cell | Electrochemical reaction self-generates voltage proportional to O2 | 10-30 s | Replace cell every 6-12 months |
| Polarographic (Clark electrode) | External battery drives current proportional to O2 | Faster | Battery + electrode upkeep |
| Paramagnetic | Exploits oxygen's paramagnetism | Very fast | Built into ventilators/analyzers |
Two-point calibration is performed daily or with each new patient: the low point is room air (21%) and the high point is 100% O2. If the analyzer still reads inaccurately after calibration, replace the sensor — a fuel cell that cannot be calibrated is depleted. Galvanic cells are valued for needing no external power; polarographic electrodes respond faster but need batteries.
Flowmeters and Regulators
Thorpe tube flowmeters use a tapered glass tube with a floating ball or bobbin that rises with flow; read at the center of the ball (or the top of a bobbin). The critical exam distinction is compensation:
- Pressure-compensated: the needle valve sits downstream of the float tube, so the tube always sees 50 psi and reads accurately even with back pressure from a nebulizer or other resistance.
- Non-compensated (uncompensated): the valve sits upstream, so downstream back pressure makes the float read falsely HIGH — the patient actually receives less than the dial shows.
A quick bedside test: with the flowmeter set to zero and plugged into a 50-psi outlet, a pressure-compensated unit shows a momentary surge of the ball before settling at zero; a non-compensated unit does not.
Bourdon gauge flowmeters use a fixed orifice with a pressure gauge calibrated in LPM. They are gravity-independent and work in any position, making them ideal for transport and ambulances. Their weaknesses are tested: they read falsely high with back pressure and cannot detect a downstream obstruction (a kinked line still shows flow on the gauge).
Cylinders, Suction, and Systematic Troubleshooting
Gas Cylinder Calculations
The duration formula is a guaranteed exam item:
Minutes Remaining = (Gauge PSI x Cylinder Factor) / Flow (LPM)
| Size | Factor | Capacity (full at ~2200 PSI) |
|---|---|---|
| D | 0.16 | 356 L |
| E | 0.28 | 622 L |
| G | 2.41 | 5,300 L |
| H/K | 3.14 | 6,900 L |
Worked example: an E-cylinder reads 1,600 PSI and the patient is on 4 LPM nasal cannula. Minutes = (1,600 x 0.28) / 4 = 448 / 4 = 112 minutes (about 1 h 52 min). The strict version subtracts a 200 PSI safe residual first: (1,600 - 200) x 0.28 / 4 = 98 minutes. Always change cylinders before they reach ~200 PSI so the regulator never reads empty and you keep a safety margin during transport.
Suction Equipment
| Equipment | Use | Key Feature |
|---|---|---|
| Wall (piped) suction | ICU, patient rooms | Continuous or intermittent; most powerful |
| Portable suction | Transport, field | Battery-powered; weaker |
| Yankauer tip | Oropharyngeal secretions | Rigid, large-bore |
| Suction catheter | Tracheal suction via ETT | Flexible; size <= half the ETT internal diameter |
| Closed in-line system | Ventilated patients | Maintains PEEP/FiO2; lowers infection risk |
To limit hypoxemia and mucosal trauma, preoxygenate, keep each pass under 10-15 seconds, and apply suction only on withdrawal. Adult wall vacuum is typically -100 to -150 mmHg.
CPAP/BiPAP Troubleshooting
| Problem | Cause | Solution |
|---|---|---|
| Mask leak (most common) | Poor fit, mouth breathing | Refit/resize, chin strap, full-face mask |
| Skin breakdown | Excess pressure, poor fit | Loosen straps, add cushion/liner, rotate interface |
| Aerophagia | Pressure too high; air swallowing | Lower pressure, reposition, reassess settings |
| Claustrophobia | Interface discomfort | Nasal pillows, desensitization, reassurance |
| Eye irritation | Top-of-mask leak into eyes | Reseat at nasal bridge, tighten upper straps |
| Rainout | Tubing condensation | Adjust humidifier temp, use heated tubing |
The Patient-First Troubleshooting Sequence
For any alarm or malfunction, follow this order — the most heavily tested concept in the section:
- Assess the patient FIRST — distress, color, SpO2, chest rise.
- Manually ventilate with a bag-valve device if a ventilated patient is in distress; disconnecting from a suspect machine is acceptable and safe.
- Check the circuit — disconnections, kinks, water, leaks.
- Check the machine — alarms, settings, displays.
- Correct the identified problem.
- Document the event, findings, and interventions.
Never silence an alarm before identifying its cause; a high-pressure alarm may signal a mucus plug or kink, and a low-pressure or apnea alarm may signal a disconnection or accidental extubation.
An E-cylinder reads 900 PSI. A patient requires oxygen at 3 LPM for transport. Using the standard formula (no residual subtraction), how long will the cylinder last?
A Bourdon gauge flowmeter is preferred over a Thorpe tube flowmeter for patient transport because:
A pressure-compensated Thorpe tube flowmeter differs from a non-compensated Thorpe tube in that it:
When troubleshooting a ventilator alarm, what should the respiratory therapist do FIRST?
The cylinder factor for an E-cylinder is _____, and for an H-cylinder it is _____.
Type your answer below
An oxygen analyzer is calibrated using which two reference points?
A CPAP patient complains of air leaking into their eyes during sleep. The BEST solution is to: