CBET Medical Equipment Function 4 — Questions and Answers
Question 1: In a pulse oximeter, which physiological principle is used to differentiate oxygenated from deoxygenated hemoglobin?
- Differential light absorption at two wavelengths (660 nm and 940 nm) (Correct answer)
- Measurement of blood pressure waveform morphology
- Detection of CO2 partial pressure via infrared spectroscopy
- Impedance plethysmography across the finger
Correct answer: Differential light absorption at two wavelengths (660 nm and 940 nm)
Pulse oximeters exploit the fact that oxyhemoglobin and deoxyhemoglobin absorb red (660 nm) and infrared (940 nm) light at different ratios.
Question 2: A patient-controlled analgesia (PCA) pump must include which safety feature to prevent accidental overdose?
- A lockout interval that disables bolus delivery for a set time after each dose (Correct answer)
- A variable drip rate adjusted by nursing staff every hour
- An automatic increase in dose when the patient presses the button repeatedly
- A pressure sensor that detects IV line occlusion only
Correct answer: A lockout interval that disables bolus delivery for a set time after each dose
The lockout interval enforces a mandatory waiting period between boluses, preventing the patient from receiving dangerous cumulative doses.
Question 3: What is the primary function of the inspiratory-to-expiratory (I:E) ratio setting on a mechanical ventilator?
- It controls the proportion of time spent in inhalation versus exhalation during each breath cycle (Correct answer)
- It sets the tidal volume delivered with each breath
- It determines the oxygen concentration in delivered gas
- It adjusts the peak airway pressure alarm threshold
Correct answer: It controls the proportion of time spent in inhalation versus exhalation during each breath cycle
The I:E ratio defines how the breath cycle is divided, affecting gas distribution and hemodynamic impact; normal is approximately 1:2.
Question 4: In electrosurgical units (ESU), the return electrode (dispersive pad) functions by:
- Distributing current over a large surface area to minimize current density at the patient return site (Correct answer)
- Increasing the frequency of current to improve cutting precision
- Grounding the patient to earth to prevent shock
- Concentrating current to coagulate tissue at the return site
Correct answer: Distributing current over a large surface area to minimize current density at the patient return site
The large area of the dispersive pad spreads current so densely is too low to heat tissue, preventing burns at the return site.
Question 5: A phototherapy unit used for neonatal jaundice delivers light primarily in which spectral range?
- Blue-green light (420–500 nm) (Correct answer)
- Red light (620–700 nm)
- Ultraviolet-C (200–280 nm)
- Near-infrared (750–900 nm)
Correct answer: Blue-green light (420–500 nm)
Blue-green light in the 420–500 nm range is absorbed by bilirubin, converting it to water-soluble isomers that can be excreted.
Question 6: Which mechanism allows a double-lumen endobronchial tube to facilitate one-lung ventilation during thoracic surgery?
- Separate lumens allow one lung to be isolated and collapsed while the other is ventilated (Correct answer)
- It delivers 100% oxygen to both lungs simultaneously at high flow
- A balloon in the trachea seals off the airway above the carina
- It uses CPAP on one side and PEEP on the other to equalize pressures
Correct answer: Separate lumens allow one lung to be isolated and collapsed while the other is ventilated
Each lumen opens to one bronchus; clamping one lumen collapses that lung for surgical access while the other continues ventilation.
Question 7: In a hemodialysis machine, the dialysate flow direction relative to blood flow is typically:
- Countercurrent, to maximize the concentration gradient for diffusion across the dialyzer membrane (Correct answer)
- Co-current, to prevent pressure differentials across the membrane
- Perpendicular, to promote ultrafiltration only
- Intermittent, alternating direction every five minutes
Correct answer: Countercurrent, to maximize the concentration gradient for diffusion across the dialyzer membrane
Countercurrent flow maintains a favorable concentration gradient along the entire length of the dialyzer, maximizing solute clearance.
CBET Medical Equipment Function 4
In a pulse oximeter, which physiological principle is used to differentiate oxygenated from deoxygenated hemoglobin?