Arterial blood pressure measurement forms part of the minimum standards of patient monitoring set out by the Association of Anaesthetists of Great Britain and Ireland for both general anaesthesia and sedation.1 Regular or continuous blood pressure (BP) monitoring is used in order to provide appropriate care to patients in both the theatre and the intensive care setting. Alone, it allows the assessment of haemodynamic status and stability and, combined with other parameters (i.e. pulse oximetry and capnography), it enables clinicians to detect 93% of adverse events occurring during anaesthesia.2

Pressure is the force exerted per unit of area. The Système International (SI) unit of pressure is the Newton per square metre (N/m2). However, with blood pressure monitoring, the standard unit used clinically is millimetres of mercury (mmHg).Blood pressure = cardiac output × systemic vascular resistanceCardiac output = heart rate × stroke volume

Arterial blood pressure measurement can be invasive blood pressure (IBP) or non-invasive blood pressure (NIBP). Both require specific, respective components and techniques in order to measure BP which will all be described in further detail in this article.