Oesophageal Doppler

OVERVIEW

  • Oesophageal Doppler Cardiac Output Monitor

USES

  • non-invasive cardiac output monitor

Contra-indications

  • IABP
  • severe coarctation
  • known pharyngo-oesophageal pathology or injury
  • oesphagectomy
  • severe bleeding
  • awake patient (relative)

Indications

  • major surgery with large fluid/blood shifts
  • high risk patients
  • haemodynamic instability

DESCRIPTION

  • measures blood flow velocity in the descending aorta using a flexible ultrasound probe
  • measurement is based on the Doppler Principle: a doppler shift in frequency occurs when the ultrasound wave is reflected back from moving RBCs, with the shift in frequency proportional to the velocity of the blood flow
  • measurement is combined with the cross-sectional area of the descending aorta (using a nomogram based on age, weight and height  — some models measure aortic root diameter using TOE)
  • probe contains crystals that produce a continuous ultrasound wave of 4 MHz
  • single use, latex-free, silicone-based
oesophageal-doppler-1

METHOD OF INSERTION AND/OR USE

oesophageal-doppler-2
  • lubricate probe well
  • inserted via the nasal or oral route
  • advanced and rotated in the oesophagus (typically sits at level of the 5th and 6th thoracic vertebrae where the aorta is adjacent and parallel to the oesophagus)
  • some devices display the aortic pressure waveform allowing confirmation of optimal probe position
  • 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 at a given point in time
  • adjust cycle length (5 = good starting point), gain (to decrease ambient noise, start at 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 OBTAINED

Haemodynamic parameters:

  • cardiac output (Q = SV x HR)
    — Q is estimated by minute distance
  • stroke volume (SV is dependent on preload, afterload and contractility)
    — SV is  measured by stroke distance x aortic root diameter
    — stroke distance (AUC) x HR, linear cardiac output parameter, distance moved by a column of blood through aorta in 1 minute (1200cm = high flow state)
  • corrected (systolic) flow time (FTc)
    — indicates preload
    — normal = 0.33-0.36s
    — interpretation of FTc and PV indicates afterload
  • peak velocity (PV)
    — indicates contractility
    — normal range is age related (20yrs 90-120 cm/sec, 90 yrs 30-60 cm/sec)
    — interpretation of FTc and PV indicates afterload
  • heart rate
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Actions from readings (need to be interpreted in clinical context)

  • low SV -> fluid
  • low FTc -> fluid
  • low PV -> inotrope
  • low PV + low FTc -> decrease afterload

PROS AND CONS

Advantages

  • minimally invasive
  • provides real time measurements

Disadvantages

  • learning curve (significant inter and intra-observer variability)
  • probe displacement requiring repositioning
  • difficult to use in an awake patient

Complications

  • esophageal bleeding, ulceration, or perforation
  • stricture formation
  • inaccurate measurements from probe displacement

OTHER INFORMATION

  • Doppler equation: Fd= 2FtVCos θ / C
    • where Ft is the transmitted Doppler frequency, V is the speed of blood flow, Cos θ is the Cosine of the blood flow to beam angle and C is the speed of sound in tissue
  • perioperative use in the UK is supported by NICE guidelines and is embedded in ‘enhanced recovery after surgery’ (ERAS) programmes with financial incentives – this based largely on the surrogate outcome of reduced hospital length of stay

References and Links

  • Morris C. Oesophageal Doppler monitoring, doubt and equipoise: evidence based medicine means change. Anaesthesia. 2013 Jul;68(7):684-8. PMID: 23672246.

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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