25.2 Ultrasound + Echo

Question 1

a) How may ultrasound techniques be used in anaesthetic and critical care practice? (40%)

Answer 1

> > Airway:
• Check for anterior vessels prior to percutaneous tracheostomy.

> > Respiratory:
• Locate pleural effusions to guide
insertion of pleural drains.

• Identify areas of consolidation or oedema.

> > Cardiovascular:
• Identification of vessels for
cannulation, both peripheral and central.

• Transoesophageal/thoracic echo:
to guide fluid management,
assess ejection fraction,
detect air embolism,
assess valvular function,
detect tamponade or even

complete echocardiographic assessment of the
heart.

• Oesophageal Doppler:
optimise filling,
inotrope and vasopressor use.

• Identification of pericardial effusion.

• FAST
(focused assessment with
sonography for trauma) scanning:
assessment of bleeding in thorax or abdomen.

> > Neurological:

• Identification of nerves for peripheral nerve blocks.
• Identification of epidural space.
• Transcranial Doppler ultrasonography.

> > Gastrointestinal:
• To guide insertion of abdominal drain.
• Identification of ascites for drainage.

Question 2

b) What information can echocardiography provide in a haemodynamically unstable patient? (45%)

Answer 2

1. Preload assessment:
   • Reduced left ventricular end-diastolic area
   (LVED) and left ventricular
   end-systolic area (LVES) indicate reduced preload.

• ‘Kissing’ papillary muscles in
systole indicates hypovolaemia.

2. > > Assessment of systemic vascular resistance:

• Normal LVED and reduced
LVES indicate reduced systemic vascular
resistance as seen in anaphylaxis or sepsis.

3. > > Myocardial function:
   • Contractility and thickening of
   myocardium during systole indicate left
   ventricular systolic function.

• Regional wall motion abnormalities
may indicate ischaemia.

• Assessment of right heart function.

4. > > Specific diagnoses:

• Left ventricular outflow tract obstruction.

• Cardiac tamponade.

• Valvular disease, or paravalvular leak
or valve malfunction following replacement.

• Endocarditis.

• Aortic dissection.

• Trauma:
pericardial collection,
myocardial contusion,
mediastinal haematoma,
aortic dissection/transection,
pleural collections.

• Thromboembolic disease:
right ventricular dilatation and dysfunction.

Rarely, thrombus may be seen in the right ventricle or pulmonary arteries.

Question 3

c) What is the Doppler effect? How may this be used in echocardiography? (15%)

Answer 3

The Doppler effect is the change
in perceived frequency of a sound wave
when the source is moving
in relation to the observer.

The frequency, and therefore pitch,
increases as the distance between
observer and source reduces.

V = Delta F x c
_____________
2F0xcos0

V = velocity of object
ΔF = frequency shift (FR − F0)
c = speed of sound in blood
F0 = frequency of emitted sound
θ = angle between sound and object

Ultrasound provides the image
of the structure of the heart itself,

but Doppler provides the information
about all moving aspects of the
echocardiography study:

> > Valve function,
direction of flow,
turbulent flow due to stenosis.

> > Cardiac output.

> > Dynamic obstructions.

> > Coronary artery flow.

Question 4

c) What is the Doppler effect? How may this be used in clinical practice? (20%)

Answer 4

> > Echocardiography:
Flow across valves,
cardiac output,
dynamic obstructions,
coronary artery flow.

> > Fetal wellbeing:
umbilical artery flow,
fetal heart rate.

> > Transcranial Doppler:
cerebral perfusion.

> > Oesophageal Doppler:
blood velocity in descending aorta
to indicate cardiac output and
guide fluid and vasopressor use

> > Peripheral pulses and blood pressure:
assessment of patients with
peripheral vascular disease.