Probes
Most commonly used Piezoelectric probes:
Phased Array: small footprint, good penetration, 1-5MHz, ideal use: TTE/Lung
Curvilinear: big footprint, excellent penetration, 2-5MHz, ideal use: Lung, FAST, ABD
Linear: mid-sized footprint, good near-field, 2-13MHz, ideal use: vascular/procedural
All have strengths and weaknesses. For the most part, you trade image quality for image depth. Certain exams require a lower frequency for tissue penetration, such as TTE/FATE, Lung, etc. For those, a low-frequency probe may be non-negotiable. Beyond that, we typically use a normal adult-sized linear probe for everything, even blocks in < 3kg newborns! Sometimes you have to make do with what you have.
Loosely...
Lower frequency = lower resolution but deeper tissue penetration
Higher frequency = higher resolution but shallower tissue penetration
Choose your probe accordingly.
Newer probe technology is beginning to come online. Products, such as the ButterflyIQ, that do not rely on piezoelectric technology, but rather proprietary micro-chip technology where with the press of a button one can switch between different types of traditional probes (changing from a liner to a phased array setting), may soon obviate the need for having multiple probes. It is a very exciting time for regional anesthesia and PoCUS enthusiasts.
