Veterinary Anesthesia & Analgesia Support Group
Practical Information for the Compassionate Veterinary Practitioner
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  Pulse Oximeter Monitoring Basics
  Angela Dyer-Corso
  May, 2004

I.  Pulse Oximetry

A.     Measures SpO2 (the saturation of peripheral oxygen – how much hemoglobin in the red blood cells is carrying a full load of oxygen) and pulse rate.  Oxygen delivery to the brain is what keeps the patient alive.

B.     SpO2 should be >95% on 100% O2

C.     Pulse rate should be >70 on a very large dog, > 80 on a medium dog, and >100 on a small dog or cat.

D.     The main reason for a low SpO2 in an anesthetized patient is decreased ventilation

                                                   i.      The animal is not breathing well and you need to assist it

1.      Respiratory rate should be 10 – 12 breaths /min for the average patient.  Small patient may need more breaths.  You can ventilate the patient by closing the pop – off valve in a circulating system/plugging the bag in a non-rebreather, and squeezing the bag to inflate the lungs.  NEVER SQUEEZE THE BAG TO MORE THAN 20 cm H20!!!

2.      Try just occasional breaths at first – the more breaths you give, the less the patient’s brain will stimulate the patient to breathe on it’s own.  Use the patient and the pulse ox. As a guide.

                                                 ii.      The patient has ventilation/perfusion mismatch – the oxygen isn’t getting to the areas in the lungs where the blood is

1.      Check that the machine is hooked up properly

2.      Check that the oxygen is turned on

3.      Check that the endotracheal tube is placed correctly and the cuff is properly inflated.  If the tube is in too far, the gas/O2 will only go to one side of the lungs.  (To position the tube properly, hold the tube up to the side of the patient – the tube should go from the mouth to the thoracic inlet only.  You may need to have a significant length sticking out of the patient’s mouth.)

                                                iii.      The patient’s pulse is weak

1.      Check that the patient isn’t too deep

2.      Check the blood pressure and act accordingly (see section on blood pressure)

                                               iv.      The sensor is slipping off the patient

                                                 v.      The sensor has been at one location for a long time and is too dry or is pinching off blood supply to the area.  The following locations may be used for the pulse ox. probe:  tongue, lips, ear, toe webbing, prepuce, and vulva.

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