Equipment & Monitors Flashcards
Ultrasound Propagation
Propagation - sound wave movement
- Air 343 m/sec
- Soft tissue 1,540 m/sec
- Bone 3,000-5,000 m/sec
Wavelength
Distance b/w 2 identical points on adjacent cycles
Measured from peak to peak or trough to trough
Frequency
Cycles per second
Measures pitch
Hertz (Hz)
Inverse correlation w/ wavelength
Human hearing 20-20,000 Hz
Amplitude
Represents sound loudness
Measured in decibels
↑amplitude ↑pressure Δ ↑sound
↓amplitude ↓pressure Δ ↓sound
Attenuation
Absorption
Reflection
Scatter
Refraction
Absorption
Ultrasound wave lost to the body as heat
Wave strength naturally degrades as it travels through tissue
Reflection
Sound wave bounces off tissue boundary
Reduces sound strength as the wave continues on its path deeper into the body
Applying gel helps to reduce reflection
Scatter
Occurs when the ultrasound wave encounters an object smaller than the wave
Causes echo to scatter in all directions, the signal never returns to the transducer
Explains why fluid-filled structures appear anechoic
Refraction
Ultrasound wave bending when it encounters a tissue boundary at an oblique angle
Based on Snell’s law
Open Circuit
No rebreathing
No reservoir
Ex:
- Insufflation
- Simple face mask
- NC
- Open drop
Semi-Open
No rebreathing
Yes reservoir
Ex:
- Mapleson circuit FGF dependent on design
- Circle system FGF > minute ventilation
Semi-Closed
Partial rebreathing
Yes reservoir
Circle system FGF < minute ventilation
Closed
Complete rebreathing
Yes reservoir
Circle system w/ low FGF & APL valve closed
Mapleson A
Best for spontaneous ventilation
Worst for controlled ventilation
FGF inlet away from patient (near the reservoir bag)
APL valve near the patient
Mapleson B
Worst for spontaneous ventilation
FGF inlet & APL valve near the patient
