Respiratory Rate is the number of breaths taken during a specified period, usually expressed as breaths per minute. It is one of the fundamental vital signs because breathing directly supplies oxygen to the lungs and removes carbon dioxide generated by metabolism. A resting adult commonly has a respiratory rate around 12–20 breaths per minute, although normal values vary with age, activity, sleep, pregnancy and other circumstances. Children normally breathe faster than adults, with infants having substantially higher rates. Respiratory rate includes the frequency of respiratory cycles but does not by itself describe the depth, effectiveness or gas exchange achieved by those breaths.
Breathing is controlled through complex interactions involving the brainstem respiratory centres, peripheral and central chemoreceptors, respiratory muscles and sensory information from the lungs and other tissues. Rising carbon dioxide and associated changes in acidity are particularly important stimuli for ventilation under ordinary circumstances, while oxygen levels become especially important when they fall substantially. The diaphragm is the principal muscle of quiet inspiration, assisted by intercostal and other muscles when ventilatory demand increases. Effective ventilation depends on both respiratory frequency and tidal volume, meaning that two people with the same respiratory rate can have very different minute ventilation and gas-exchange efficiency.
Respiratory rate changes physiologically in response to exercise because increased metabolism generates additional carbon dioxide and requires greater oxygen delivery. Fever, pain, anxiety and metabolic acidosis can also increase respiratory rate. Sleep alters respiratory control and muscle activity, while certain medications, particularly opioids and other central nervous system depressants, can reduce respiratory drive. Lung disease may produce rapid shallow breathing when the respiratory system becomes mechanically inefficient or gas exchange is impaired. Consequently, an elevated rate is a physiological sign rather than a diagnosis and can arise from respiratory, cardiovascular, metabolic, neurological, infectious or psychological causes.
Accurate measurement requires observing actual respiratory movements rather than relying on a person's subjective impression of how quickly they are breathing. Ideally, the person should be at rest, and the observer should assess the pattern without unnecessarily altering the person's breathing. Counting for a full minute can be particularly useful when the rhythm is irregular. Respiratory rate should be considered alongside depth, rhythm, effort and associated signs such as use of accessory muscles, cyanosis, altered consciousness or inability to speak comfortably. Electronic monitoring can provide continuous measurements, but movement, talking and sensor limitations can introduce errors.
Tachypnoea means abnormally rapid breathing, while bradypnoea refers to abnormally slow breathing. Apnoea means cessation of breathing for a clinically significant period, and dyspnoea refers to the subjective sensation of difficult or uncomfortable breathing rather than simply a particular respiratory rate. Hyperventilation refers to ventilation that exceeds the body's metabolic requirement for carbon dioxide elimination and can reduce arterial carbon dioxide, whereas tachypnoea merely describes increased frequency and does not necessarily establish excessive ventilation. These distinctions are important because a patient may breathe rapidly without hyperventilating, or may have substantial respiratory difficulty without an unusually high respiratory rate.
Respiratory rate is particularly valuable in acute clinical assessment because changes can precede more obvious deterioration. A progressively increasing rate can indicate worsening respiratory disease, infection, metabolic disturbance or physiological stress. Conversely, an unusually low rate in someone receiving sedating medication may indicate respiratory depression and requires appropriate clinical assessment. Respiratory rate is incorporated into several early-warning and clinical-observation systems, although thresholds differ according to age and clinical setting. Trends can be more informative than a single value, especially when combined with oxygen saturation, heart rate, blood pressure, temperature and neurological status.
Conditions affecting respiratory rate include asthma, chronic obstructive pulmonary disease, pneumonia, pulmonary embolism, heart failure and severe systemic infection, but increased breathing can also arise from diabetic ketoacidosis, renal failure, pain or anxiety. Neurological injury and medications can suppress respiratory drive. The clinical significance depends on the mechanism and whether ventilation and oxygenation are adequate. A person can have a normal respiratory rate despite serious impaired gas exchange, while another person can have rapid breathing with normal oxygenation because of metabolic or psychological causes. Respiratory assessment therefore requires more than counting breaths.
Respiratory rate is a simple measurement but is subject to considerable observational error. Brief counting intervals can produce inaccurate estimates, and conscious awareness of being observed may alter breathing. It also provides no direct measurement of arterial oxygenation, carbon dioxide concentration or lung mechanics. More detailed investigations such as pulse oximetry, capnography, arterial blood gases, spirometry or imaging may therefore be necessary depending on the clinical question. Its strength is that it is inexpensive, non-invasive and immediately available, making it particularly useful for detecting changes in physiological state when interpreted with other vital signs and clinical findings.
