Do changes in pulse oximeter oxygen saturation predict equivalent changes in arterial oxygen saturation?

Perkins, Mcauley, Giles Simon, Routledge Helen, Gao, Gao Fang

Description

This study investigates the relation between changes in pulse oximeter oxygen saturation (Sp O 2 ) and changes in arterial oxygen saturation (Sa O 2 ) in the critically ill, and the effects of acidosis and anaemia on precision of using pulse oximetry to predict Sa O 2 . Patients and methods Forty-one consecutive patients were recruited from a nine-bed general intensive care unit into a 2-month study. Patients with significant jaundice (bilirubin >40 μmol/l) or inadequate pulse oximetry tracing were excluded. Results A total of 1085 paired readings demonstrated only moderate correlation ( r = 0.606; P < 0.01) between changes in Sp O 2 and those in Sa O 2 , and the pulse oximeter tended to overestimate actual changes in Sa O 2 . Anaemia increased the degree of positive bias whereas acidosis reduced it. However, the magnitude of these changes was small. Conclusion Changes in Sp O 2 do not reliably predict equivalent changes in Sa O 2 in the critically ill. Neither anaemia nor acidosis alters the relation between Sp O 2 and Sa O 2 to any clinically important extent.

Sujets

• Acidosis
• Anemia
• Critical care
• Pulse oximetry

Informations

• Publié par: biomed
• Publié le: 01 janvier 2003
• Nombre de lectures: 8
• Langue: English

Extrait

Available onlinehttp://ccforum.com/content/7/4/R67

Open Access Research Do changes in pulse oximeter oxygen saturation predict equivalent changes in arterial oxygen saturation? 1 23 45 Gavin D Perkins, Daniel F McAuley, Simon Giles, Helen Routledgeand Fang Gao

1 Specialist Registrar, Intensive Care Unit, Birmingham Heartlands and Solihull NHS Trust (Teaching), Birmingham Heartlands Hospital, Birmingham, UK 2 Specialist Registrar, Intensive Care Unit, Birmingham Heartlands and Solihull NHS Trust (Teaching), Birmingham Heartlands Hospital, Birmingham, UK 3 Nurse Consultant, Intensive Care Unit, Birmingham Heartlands and Solihull NHS Trust (Teaching), Birmingham Heartlands Hospital, Birmingham, UK 4 Specialist Registrar, Intensive Care Unit, Birmingham Heartlands and Solihull NHS Trust (Teaching), Birmingham Heartlands Hospital, Birmingham, UK 5 Consultant in Anaesthesia and Intensive Care Medicine, Intensive Care Unit, Birmingham Heartlands and Solihull NHS Trust (Teaching), Birmingham Heartlands Hospital, Birmingham, UK

Correspondence: F Gao, [e-mail]

Received: 23 September 2002 Revisions requested: 2 December 2002 Revisions received: 10 December 2002 Revisions requested: 25 February 2003 Revisions received: 29 March 2003 Accepted: 12 May 2003 Published: 11 June 2003

Critical Care2003,7:R67R71 (DOI 10.1186/cc2339) This article is online at http://ccforum.com/content/7/4/R67 © 2003 Perkinset al., licensee BioMed Central Ltd (Print ISSN 13648535; Online ISSN 1466609X). This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.

Abstract IntroductionThis study investigates the relation between changes in pulse oximeter oxygen saturation (Sp O ) and changes in arterial oxygen saturation (Sa O ) in the critically ill, and the effects of acidosis 2 2 and anaemia on precision of using pulse oximetry to predict Sa O . 2 Patients and methodsFortyone consecutive patients were recruited from a ninebed general intensive care unit into a 2month study. Patients with significant jaundice (bilirubin >40µmol/l) or inadequate pulse oximetry tracing were excluded. ResultsA total of 1085 paired readings demonstrated only moderate correlation (r= 0.606;P< 0.01) between changes in Sp O and those in Sa O , and the pulse oximeter tended to overestimate actual 2 2 changes in Sa O . Anaemia increased the degree of positive bias whereas acidosis reduced it. 2 However, the magnitude of these changes was small. ConclusionChanges in Sp O do not reliably predict equivalent changes in Sa O in the critically ill. Neither 2 2 anaemia nor acidosis alters the relation between Sp O and Sa O to any clinically important extent. 2 2

Keywordsacidosis, anaemia, arterial oxygen saturation, critical care, pulse oximetry

Introduction Pulse oximetry is used almost universally in the management of critically ill patients in the intensive care unit (ICU) and oper ating theatre [1]. Its uses include the detection of hypoxia [1], avoidance of hyperoxia [2], reduction in the frequency of blood gas analysis [3], titration of fractional inspired oxygen [4] and for weaning from mechanical ventilation [5].

An arterial oxygen saturation (Sa O ) of 90% has been proposed 2 as a target for adequate oxygenation during mechanical ventilation [5]. Previous studies investigating the use of pulse

oximeter oxygen saturation (Sp O ) in intensive care patients 2 have reported that the minimum Sp O levels to maintain Sa O 2 2 at 90% range between 92% and 96% [4,6,7]. However, these studies have not answered the question of whether, after achieving a target Sa O , a subsequent change in Sp O pre 2 2 dicts a corresponding change in Sa O in the critically ill. 2

Some studies have reported that anaemia reduces the preci sion of pulse oximetry [8] by increasing the signal to noise ratio with low haemoglobin concentrations, whereas others failed to demonstrate this phenomenon [9,10]. Acidosis may

ICU = intensive care unit; Sa O = arterial oxygen saturation; SD = standard deviation; Sp O = pulse oximeter oxygen saturation. 2 2

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