Oesophageal Doppler
30/11/10
OHOA pages 984-986
FANZCA Part II Notes
USES
- non-invasive cardiac output monitor
DESCRIPTION
- measures velocity of blood in descending aorta and calculates SV and Q
- its uses a nomogram based on age, weight and height to estimate aortic diameter (some
models measure aortic root diameter using TOE)
Contra-indications
-
IABP
severe coarctation
known pharyngo-oesophageal pathology
severe bleeding
Indications
- major surgery with large fluid/blood shifts
- high risk patients
- haemodynamic instability
Jeremy Fernando (2010)
METHOD OF INSERTION AND/OR USE
- lubricate probe well
- insert probe into oesophagus via nose or mouth
- turn volume up initially (sharpest sound = best position)
- input age, height and weight
- insert probe to 35-40cm from teeth (T5/6)
- manipulate probe until characteristic Doppler signal found (well defined triangle with black
centre surrounded by red with white in trailing edge) = distribution of RBC velocities @ a
given point in time
- adjust cycle length (5 = good starting point), gain (to decrease ambient noise, start @ 5
also)
- the brighter (whiter) the colour the greater the number of RBCs travelling at the given
velocity
- it is a dynamic monitor so needs refocusing prior to each reading
INFORMATION
- Q = SV x HR
- SV dependent on preload, afterload and contractility
Jeremy Fernando (2010)
-
Q estimated by minute distance
SV measured by stroke distance x aortic root diameter
preload measured by FTc
afterload measured by interpretation of FTc and PV
contractility measured by PV
- Corrected systolic flow Time (FTc) (s) – indexed to preload, normal = 0.33-0.36s,
- Peak velocity (cm/sec) – indexed to contractility, age related, (20yrs 90-120 cm/sec, 90
yrs 30-60 cm/sec)
- Minute distance (cm) - stroke distance (AUC) x HR, linear cardiac output parameter,
distance moved by a column of blood through aorta in 1 minute (<800cm = low flow
state, >1200cm = high flow state)
Actions from readings (need to be interpreted in clinical context)
-
low
low
low
low
SV -> fluid
FTc -> fluid
PV -> inotrope
PV + low FTc -> decrease afterload
COMPLICATIONS/DISADVANTAGES
-
bleeding
perforation
ulceration
stricture formation
learning curve (significant inter and intra-observer variability)
probe displacement requiring repositioning
Jeremy Fernando (2010)