DESATURATION

Complete COVER ABCD-A SWIFT CHECK  (1)
Hand ventilate with 100% oxygen
Confirm the FIO2 is appropriate
Confirm the ETCO2 is appropriate, if it is low consider:

Anaphylaxis
Pneumothorax
Air (or other) embolism

Auscultate again, specifically exclude endobronchial intubation (2)

REVIEW AND TREAT OTHER POSSIBLE CAUSES

Underlying cardiopulmonary problems
If bronchial secretions or plugs are suspected (3)
     Posture and suction ETT/bronchi
     Give a "long slow blow" especially in children
     If cardiovascularly stable consider PEEP/CPAP
If acute shunt is suspected (4)
     Ensure the patient is supine and level
If a pneumoperitoneum is present, deflate the abdomen
Consider gas embolism (5)
Pulse oximeter malfunction (6)
     Consider: polycythaemia, methaemoglobinaemia, acute tricuspid incompetence, probe sited distal to an AV fistula.
 

Reassess the situation
If persistent/unstable desaturation consider:
     completing/abandoning surgery
     chest X-ray, blood gases
If stable and well saturated, see Note (5) under Aspiration
     wake the patient up and extubate
If unstable or desaturated, see Note (5) under Aspiration
     admit to ICU/HDU

Top

The figures reported here are based on an analysis of 584 of the first 4000 AIMS anaesthesia incidents. It was judged that correct use of the algorithms would have led to earlier recognition of the problem and/or better management in 16% of the 584 relevant incidents reported to AIMS.
(1) The use of COVER ABCD accounted for 89% of applicable incidents reported to AIMS. Use of the desaturation subalgorithm accounted for a further 9% of applicable incidents.
(2) Endobronchial intubation was the commonest cause of desaturation in an anaesthetised patients reported to AIMS. It should be specifically excluded early. Further details may be found in (6) below.
(3) 2% of incidents were due to bronchial plugs or excessive bronchial secretions, which can produce marked desaturation, especially in young children. A shunt effect is produced, which may be unmasked with abolition of hypoxic pulmonary vasoconstriction with induction of anaesthesia.
(4) "Fat (Obesity) syndrome" refers to the rapid desaturation which may be seen at induction when anaesthetising obese patients, or those with tightly distended abdomens, and accounted for 2% of relevant incidents.
Drug induced abolition of hypoxic pulmonary vasoconstriction and an acute reduction in functional residual capacity resulting in sudden V/Q mismatching is thought to be the cause. The lithotomy and Trendelenberg positions, spontaneous ventilation and hypovolaemia all may exacerbate the problem, resulting in sudden desaturation at the start of a case and progressive desaturation during the maintenance phase.
(5) 0.8% of incidents involved suspected gas embolism.
(6) 1% of incidents involved unusual causes of pulse oximeter malfunction, including acute tricuspid incompetence, polycythaemia and methaemoglobinaemia. Acute tricuspid incompetence may lead to the oximeter sensing the venous pulse. A large plethysmographic wave form and a saturation of 70-75% is commonly seen. Arterial saturation, when directly measured, may be quite adequate. Polycythaemia may lead to artefactually low saturation readouts with high directly measured arterial oxygen saturations or tensions.
Methaemoglobinaemia, depending on its extent, will cause the saturation to approach 85%.
 

Top