Canis ISSN: 2398-2942

Anesthetic monitoring: esophageal stethoscope

Contributor(s): John Dodam

Introduction

Rationale

  • Monitoring of the heart rate, rhythm and character of the heart sounds is one of the basic requirements of anesthetic monitoring.
  • The esophageal stethoscope can be easily used to monitor these parameters.
  • Cardiac output, a product of heart rate and stroke volume, must be maintained to produce adequate tissue perfusion.
  • The normal heart rate in the anesthetized dog is 60-200/min.
  • The esophageal stethoscope consists of a thin, flexible, blind-ended tube, with a number of holes in the side-wall close to the blind end of the tube. There is a thin plastic membrane over the perforated area to prevent fluid entering the lumen of the tube. A variety of diameters are available. It is connected to the Y-piece of a standard pair of stethoscope earphones by means of a small plastic adaptor.

Uses

  • Accurate monitoring of cardiac rate enables appropriate corrective measures to be taken to ensure adequate tissue perfusion if bradycardia or tachycardia develop.
  • Detecting either condition early is beneficial in avoiding cardiac emergencies and arrest.

Pros

  • Simple technique.
  • Equipment required is inexpensive.
  • Allows remote monitoring of the heart without disturbing surgical drapes and when access to the chest area is difficult.

Cons

  • Although, if used carefully, the technique is very safe, it may be possible to cause reflux esophagitis Esophagitis if the esophageal stethoscope is inadvertently advanced through the cardiac sphincter of the esophagus into the stomach.
  • Care should be taken to avoid passing the esophageal stethoscope into the trachea by accident.
    Where endotracheal intubation is going to take place, this should occur prior to placing the esophageal stethoscope
  • The esophageal stethoscope is very soft and flexible, making traumatic damage unlikely, but care should be taken where the esophagus may be unusually fragile and it should not be placed in animals with suspected cranial esophageal foreign bodies or other esophageal pathology.
    Presence of a heart beat does not guarantee an adequate circulation; the information gained must be used in conjunction with the other elements of cardiovascular system monitoring

Alternatives

  • Direct palpation of the chest wall or pulse.
  • Use of a standard stethoscope.

Other methods of monitoring CVS

Preparation

  • Collect all necessary equipment.
  • To avoid advancing the esophageal stethoscope through the cardiac sphincter, premeasure the approximate length for insertion by laying the tube alongside the mouth, neck and chest, and note the length from the level of the canine teeth to the point of the olecranon.

Instrumentation

  • Esophageal stethoscope tube/s.
  • Standard stethoscope earpieces and Y-tubing.
  • Plastic adaptor.
  • Lubricating jelly.

Procedure

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Muir III W W Patient monitoring need not be expensive - breath and heart sound amplifier system. Vet Emerg Crit Care 1, 26-27.

Other sources of information

  • Muir W W et al (1995) Handbook of Veterinary Anesthesia. 2nd edn. Mosby. pp 237-238.


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