Ultrasound In Anaesthesia

ultrasonographyOver the last 10 years, ultrasound has developed into an indispensible tool in anaesthesia and intensive care. Ultrasound is not new to medicine but its use in anaesthesia is. Ultrasound technology is emerging rapidly and the field of anaesthesia is not untouched by its widespread applications.

Uses of ultrasound in anaesthesia:

 Establishing vascular access

 Regional anaesthesia for nerve blocks

 Trans-oesophageal echocardiography tool for cardiac imaging

 Lung imaging

 Viewing blood flows to rule out deep vein thrombosis and peripheral vascular disease

 Assessing depth of epidural space in cases of difficult anatomy

 Role of ultrasound in airway assessment

Basic physics:

Sound is produced when mechanical energy travels

A small current is also produced. The effect was discovered by Pierre Curie in 1883.She received the noble prize for same .This effect is exhibited by certain crystals like quartz, ceramic materials, Rochelle salt. When a voltage is applied across certain surfaces of a solid that exhibits the piezoelectric effect, the solid undergoes some mechanical distortion. Piezoelectric materials used in transducers like e.g. phonograph cartridges, microphones, and strain gauges produces electrical output from a mechanical input, and in earphones and ultrasonic radiators, which produce mechanical output from electrical

All piezoelectric transducers are made of ceramic. Materials generally used on the face of the transducer, it enables the sound waves to be transmitted efficiently into the body (usually a rubbery coating, which is a form of impedance matching). Also, generally a water-based gel is placed between the patient's skin and the probe for better conductance. Partially the sound wave is reflected from the layers between different tissues. There are density changes in the body e.g. blood cells in blood plasma, small structures in organs, etc. sound is reflected from them while ,some of the reflections return to the transducer.

SONOSITE MACHINE WITH LINEAR TRANSDUCER

To generate a 2D-image, the ultrasonic beam is swept. Transducer may be swept mechanically by either rotating or swinging. Or a 1D phased array transducer may be use to sweep the beam electronically. The received data is processed and used to construct the image.

Doppler ultrasonography is used to study blood flow, heart contractility, see inferior vena cava fullness, muscle motion, to do a DVT scan in ICU, regional blocks . The different detected speeds are represented in colour for ease of interpretation, like leaky heart valves: the leak shows up as a flash of unique colour.

Receiver and processor

These detect and amplify the backscattered energy and manipulate the reflected signals for display

Image