Key PointsIn clinical practice, the level of arterial oxygenation can be measured either directly by blood gas sampling to measure partial pressure (PaO2) and percentage saturation (SaO2) or indirectly by pulse oximetry (SpO2).This review addresses the strengths and weaknesses of each of these tests and gives advice on their clinical use.The haemoglobin–oxygen dissociation curve describing the relationship between oxygen partial pressure and saturation can be modelled mathematically and routinely obtained clinical data support the accuracy of a historical equation used to describe this relationship.Educational AimsTo understand how oxygen is delivered to the tissues.To understand the relationships between oxygen saturation, partial pressure, content and tissue delivery.The clinical relevance of the haemoglobin–oxygen dissociation curve will be reviewed and we will show how a mathematical model of the curve, derived in the 1960s from limited laboratory data, accurately describes the relationship between oxygen saturation and partial pressure in a large number of routinely obtained clinical samples.To understand the role of pulse oximetry in clinical practice.To understand the differences between arterial, capillary and venous blood gas samples and the role of their measurement in clinical practice.The delivery of oxygen by arterial blood to the tissues of the body has a number of critical determinants including blood oxygen concentration (content), saturation (SO2) and partial pressure, haemoglobin concentration and cardiac output, including its distribution. The haemoglobin–oxygen dissociation curve, a graphical representation of the relationship between oxygen satur­ation and oxygen partial pressure helps us to understand some of the principles underpinning this process. Historically this curve was derived from very limited data based on blood samples from small numbers of healthy subjects which were manipulated in vitro and ultimately determined by equations such as those described by Severinghaus in 1979. In a study of 3524 clinical specimens, we found that this equation estimated the SO2 in blood from patients with normal pH and SO2 >70% with remarkable accuracy and, to our knowledge, this is the first large-scale validation of this equation using clinical samples. Oxygen saturation by pulse oximetry (SpO2) is nowadays the standard clinical method for assessing arterial oxygen saturation, providing a convenient, pain-free means of continuously assessing oxygenation, provided the interpreting clinician is aware of important limitations. The use of pulse oximetry reduces the need for arterial blood gas analysis (SaO2) as many patients who are not at risk of hypercapnic respiratory failure or metabolic acidosis and have acceptable SpO2 do not necessarily require blood gas analysis. While arterial sampling remains the gold-standard method of assessing ventilation and oxygenation, in those patients in whom blood gas analysis is indicated, arterialised capillary samples also have a valuable role in patient care. Th...

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Based on a systematic review of the scientific literature, the North West Oxygen Group have developed guidelines for oxygen therapy for patients who present with acute breathlessness. The above emergency medicine physicians, chest physicians and intensive care physicians have gained approval from their regional societies to have this document accepted as the agreed regional guidelines for the use of oxygen in the immediate care of breathless patients in the North West of England. Flow charts are also currently being developed, based on these guidelines, for use by ambulance and emergency department staV in the area. It is recognised that the present use of oxygen across these specialties is inconsistent. This protocol will help us to deliver standardised oxygen therapy to breathless patients by paramedics, doctors and nurses. This will also improve the consistency of medical training across these disciplines in the North West.

This study was designed to compare the effects of alfentanil and midazolam pre-medication on patient comfort during and after flexible bronchoscopy. A randomised, double-blind study was performed; 40 patients received alfentanil and 29 midazolam. Subjects completed questionnaires about discomfort and adverse effects immediately post-procedure and 24 h later. The bronchoscopist also completed a questionnaire. No difference in patient discomfort was found immediately post-procedure and no differences were found for amount of topical lignocaine used or minimum oxygen saturation. Operators reported no overall difference between the agents for ease of procedure but about 20% less cough was reported in the alfentanil group (P = 0.02). Patient discomfort scores in the 24h questionnaire were significantly lower in patients given midazolam (P = 0.01 for nasal discomfort, P = 0.003 for throat discomfort) but drowsiness was commoner in this group (P = 0.04). There was no significant difference in patients' reports of cough, nausea or vomiting or their willingness to have a repeat procedure. In conclusion, cough during bronchoscopy was slightly less marked with alfentanil than midazolam pre-medication but this made no difference to the ease of procedure or to overall patient discomfort. Patients given midazolam reported less discomfort when asked about the test 24 h later.