Respiratory Assessment and Oxygen Saturation

Respiratory assessment is the evaluation of breathing and gas exchange, combining observation of respiratory rate, effort, and pattern with measurement of oxygen saturation by pulse oximetry. Because changes in respiration and oxygenation are sensitive early signs of deterioration, this assessment is a central part of surveillance in acute and critical care.

Definition

Respiratory assessment is the systematic evaluation of breathing and oxygenation, integrating clinical observation of respiratory rate, effort, and pattern with measured oxygen saturation, to assess and monitor respiratory function.

Scope

This entry covers the components of respiratory assessment, rate, effort, and pattern of breathing, the principles and limitations of pulse oximetry, and the way oxygenation indices describe the severity of respiratory failure. It explains what these observations mean; it is a reference overview and does not provide oxygen-therapy settings, thresholds, or treatment instructions for individual patients.

Core questions

• What features of breathing (rate, effort, pattern) are observed and what do they indicate about respiratory status?
• How does pulse oximetry estimate oxygen saturation, and what are its principal limitations?
• How is the severity of impaired oxygenation described in a structured way?

Key concepts

• Respiratory rate
• Work of breathing
• Oxygen saturation (SpO2)
• Pulse oximetry
• Oxygenation index
• Hypoxaemia
• Respiratory failure
• Limitations of oximetry (perfusion, motion, dyshaemoglobins)

Mechanisms

Respiratory assessment integrates what can be seen and what can be measured. Observation of the rate, depth, symmetry, and effort of breathing reflects the mechanics of ventilation and the work the patient is doing, while pulse oximetry uses the differential light absorption of oxygenated and deoxygenated haemoglobin to estimate arterial oxygen saturation non-invasively (Jubran, 2015). Oximetry has well-described limitations, including reduced reliability with poor peripheral perfusion, motion, and abnormal haemoglobins, and it reflects oxygenation rather than ventilation. The severity of impaired oxygenation can be graded with structured indices, as in the Berlin definition of acute respiratory distress syndrome, which classifies severity by the ratio of arterial oxygen to inspired oxygen (ARDS Definition Task Force, 2012). Respiratory rate is among the most sensitive early indicators of deterioration and contributes to aggregate early-warning scores (Smith, 2013).

Clinical relevance

Respiratory assessment lets the care team detect impaired breathing and oxygenation, often before other systems show change. This entry describes what the observations and measurements mean and how oxygenation severity is categorised; it characterises concepts and evidence and is not a source of oxygen-delivery settings or treatment directions, which depend on the clinical situation and local protocols.

Evidence & guidelines

Reviews of pulse oximetry describe its physiological basis and its limitations for clinical interpretation (Jubran, 2015). The Berlin definition provides a consensus framework for grading the severity of acute respiratory distress syndrome by oxygenation (ARDS Definition Task Force, 2012). Respiratory rate, a key element of respiratory assessment, is a component of validated deterioration-detection scores (Smith, 2013).

History

Clinical observation of breathing is among the oldest elements of physical examination, but the routine, continuous measurement of oxygen saturation became possible only with the development and spread of pulse oximetry in the late twentieth century, which transformed bedside respiratory monitoring. Parallel work on consensus definitions of respiratory failure produced structured ways to grade oxygenation severity.

Seminal works

• jubran-2015-oximetry
• ardstf-2012-berlin

Frequently asked questions

Does pulse oximetry measure how well a patient is ventilating?

No. Pulse oximetry estimates oxygen saturation, which reflects oxygenation; it does not directly measure ventilation (carbon dioxide clearance), so a normal saturation does not rule out a ventilation problem.

What can make a pulse oximetry reading unreliable?

Poor peripheral perfusion, movement, and certain abnormal forms of haemoglobin can reduce the accuracy of the reading, so oximetry should be interpreted alongside clinical assessment.