Tachypnoea

Tachypnoea is an increased respiratory rate (over 20 breaths/minute in adults at rest, over 24 breaths/minute as a sign of acute illness, with age specific limits in children). It is a sign, distinct from dyspnoea (a symptom) and hyperventilation (ventilation exceeding metabolic need, with low PaCO2). Respiratory rate is the vital sign most often mismeasured and most predictive of deterioration: a rate over 24 predicts cardiac arrest and intensive care admission better than heart rate or blood pressure.

Clinical relevance. Tachypnoea in an acutely unwell adult signals sepsis, pneumonia, embolism, heart failure, acidosis, pain or anxiety, and often precedes hypotension or desaturation by hours. Rates over 30 define severe pneumonia (CURB-65), and over 22 contribute to the quick sepsis assessment. Persistent tachypnoea in an apparently well person warrants anaemia, thyroid, cardiac, lung and anxiety evaluation.

Classification.

• Normal adult resting rate 12 to 20 breaths/minute; mild tachypnoea 21 to 24; moderate 25 to 29; severe 30 or more. Children (breaths/minute): infants under 1 year over 50, 1 to 5 years over 40, 6 to 12 years over 30, over 12 years over 20.
• By depth: rapid shallow (restrictive lung disease, pleurisy, pain, fatigue, pneumonia), rapid deep (Kussmaul breathing in metabolic acidosis; hyperventilation in anxiety, salicylate poisoning, pulmonary embolism), and irregular patterns (Cheyne-Stokes breathing, ataxic breathing).
• By driver: hypoxaemia, hypercapnia, acidosis (metabolic), increased dead space, lung stiffness, airway obstruction, pain, anxiety, fever, central stimulation (brain injury, pregnancy, drugs), anaemia, shock, hyperthyroidism.
• Hyperventilation syndrome: functional hyperventilation with respiratory alkalosis and symptoms (paraesthesia, carpopedal spasm, lightheadedness).
• Compensatory tachypnoea: respiratory compensation for metabolic acidosis (diabetic ketoacidosis, renal failure, lactic acidosis, poisoning).

Mechanism. Increased respiratory drive from chemoreceptors (hypoxia, acidaemia, hypercapnia), lung receptors (stretch, irritant, J receptors), higher centres (anxiety, pain, fever) or metabolic demand raises respiratory rate and tidal volume.

History.

• Onset (sudden or gradual), duration, breathlessness, cough, fever, chest pain, palpitations, leg swelling, thirst, polyuria, vomiting, diarrhoea, abdominal pain, drug or poison ingestion (aspirin, antifreeze, methanol), trauma, pain, panic, recent surgery or immobility, pregnancy, fatigue, weight loss, heat intolerance.
• Past history: asthma, chronic obstructive pulmonary disease, heart disease, diabetes, kidney disease, liver disease, thyroid disease, anaemia, sickle cell disease, neuromuscular disease, anxiety, HIV, cancer.
• Drugs: salicylates, theophylline, thyroxine, doxapram, progesterone, caffeine, amphetamines, cocaine, beta agonists, metformin (lactic acidosis), SGLT2 inhibitors (ketoacidosis).
• Home monitoring: previous respiratory rate and saturation.

Examination.

• Count the respiratory rate for a full 60 seconds without telling the patient; note depth, rhythm and effort (accessory muscles, intercostal and subcostal recession, nasal flaring, abdominal paradox).
• Saturation, heart rate, blood pressure, temperature, capillary refill, mental state, glucose; early warning score.
• Kussmaul pattern (deep sighing), fruity breath (ketones), flushed warm skin and sweating (salicylate, sepsis, thyrotoxicosis), pallor (anaemia), dehydration.
• Chest: asymmetry, percussion, auscultation (crackles, wheeze, reduced air entry, pleural rub), tracheal position, subcutaneous emphysema.
• Cardiac: jugular venous pressure, murmurs, gallop, oedema, leg swelling and tenderness.
• Abdomen: peritonism, distension, pregnancy, ascites.
• Neurological: Glasgow Coma Scale, pupils, brainstem signs, neuromuscular power.
• Anxiety: normal saturation, perioral tingling, carpopedal spasm, improvement with distraction.

Red flags.

• Respiratory rate 30 or more, or under 8, or rising on serial counts.
• Saturation under 92% or falling, cyanosis, exhaustion, confusion, drowsiness.
• Heart rate over 130, systolic pressure under 90 mmHg, lactate over 2 mmol/L, oliguria.
• Kussmaul breathing with vomiting and abdominal pain (diabetic ketoacidosis), or with tinnitus and fever (salicylate poisoning).
• Pleuritic pain, haemoptysis, leg swelling (embolism).
• Silent chest, stridor, tracheal deviation.
• Fever with hypotension (sepsis).
• Pregnancy or postpartum with tachypnoea (embolism, peripartum cardiomyopathy).
• Neurological injury with irregular breathing.
• Persistent tachypnoea in a child with feeding difficulty, grunting or recession.

Respiratory. Pneumonia, asthma, chronic obstructive pulmonary disease exacerbation, pulmonary embolism, pneumothorax, pleural effusion, pleurisy, pulmonary oedema, acute respiratory distress syndrome, interstitial lung disease, aspiration, upper airway obstruction, bronchiolitis, atelectasis, rib fracture and chest wall pain.

Cardiac. Acute heart failure, cardiogenic shock, tamponade, arrhythmia, myocardial infarction, aortic dissection, valve disease, congenital heart disease.

Metabolic. Diabetic ketoacidosis, lactic acidosis, uraemic acidosis, salicylate toxicity, toxic alcohol poisoning, renal tubular acidosis, diarrhoea with bicarbonate loss, adrenal crisis, thyroid storm, hepatic encephalopathy.

Infective and systemic. Sepsis, malaria, fever of any cause, severe anaemia, bleeding and hypovolaemia, burns, heat illness.

Neurological and psychological. Brain injury, meningitis and encephalitis, stroke, pontine lesion, anxiety and panic disorder, pain, hyperventilation syndrome.

Physiological and drug related. Pregnancy, exercise, altitude, progesterone, respiratory stimulants (doxapram, theophylline), salbutamol, caffeine, cocaine, amphetamines.

Other. Obesity, ascites, abdominal distension, neuromuscular weakness with rapid shallow breathing (impending failure), sickle cell acute chest syndrome.

1. Count the respiratory rate accurately for 60 seconds, then trend with an early warning score (National Early Warning Score 2: respiratory rate 12 to 20 scores 0, 9 to 11 scores 1, 21 to 24 scores 2, 25 or over or 8 or under scores 3); combine with saturation, heart rate, blood pressure, temperature, consciousness.
2. Bedside: pulse oximetry, 12 lead ECG, capillary glucose and ketones, urine dipstick (ketones, glucose, protein, blood), temperature, peak flow.
3. Arterial or venous blood gas with lactate: pH, PaCO2, bicarbonate, anion gap (sodium minus chloride minus bicarbonate; normal 8 to 12; raised in lactic acidosis, ketoacidosis, uraemia, salicylate, toxic alcohols), osmolar gap, base excess. Use Winter formula for expected PaCO2 in metabolic acidosis (1.5 x bicarbonate + 8, plus or minus 2): tachypnoea beyond this implies a coexisting respiratory alkalosis (salicylate, sepsis, embolism); lower than expected means respiratory failure.
4. Chest radiograph; point of care ultrasound of lung, heart and inferior vena cava; compression ultrasound of legs.
5. Blood tests: full blood count, urea, creatinine, electrolytes, liver function, glucose, C reactive protein, procalcitonin, blood cultures, troponin, natriuretic peptide, D-dimer, thyroid function, salicylate and paracetamol levels, toxic alcohol levels, lactate, ketones, coagulation, group and screen, HIV test, malaria film in endemic travel.
6. CT pulmonary angiography (embolism), CT chest (parenchyma), CT head (central causes), echocardiography, bedside ultrasound for effusion, tamponade or pneumothorax.
7. Neuromuscular: forced vital capacity, negative inspiratory force, neurology review.
8. Hyperventilation syndrome only after organic causes are excluded: Nijmegen questionnaire (over 23), capnography (end tidal CO2 under 4 kPa), provocation by voluntary hyperventilation.
9. Serial reassessment every 15 to 30 minutes in unstable patients; chronic tachypnoea: spirometry, lung volumes, transfer factor, cardiopulmonary exercise test, sleep study.

Limits. Respiratory rate is often estimated or recorded as 16 to 18 without counting, which makes the early warning score unreliable. Rate rises with fever (about 2 to 3 breaths/minute for each degree Celsius) and anxiety. Tachypnoea may be absent in the elderly, opioid affected, exhausted or hypothermic patients with serious disease. A normal rate does not exclude embolism or early sepsis.

Immediate priorities.

• Check airway, breathing, circulation, disability, exposure; sit the patient upright; high flow oxygen if hypoxic (titrate to 94% to 98%, or 88% to 92% if at risk of hypercapnia); intravenous access; monitor; treat the cause concurrently; do not sedate a tachypnoeic patient or give opioids without airway cover because a falling rate can mean exhaustion.
• Sepsis: take cultures and lactate, give broad spectrum antibiotics within 1 hour, 30 mL/kg crystalloid for hypotension or lactate over 4 mmol/L, noradrenaline 0.05 to 0.5 micrograms/kg/minute if mean arterial pressure stays under 65 mmHg after fluids, source control.

Treat by cause.

• Pneumonia: co-amoxiclav 1.2 g intravenously every 8 hours with clarithromycin 500 mg intravenously twice daily (or ceftriaxone 2 g daily with clarithromycin) for severe disease; amoxicillin 500 mg to 1 g three times daily for low severity (5 days); oxygen; fluids.
• Asthma: salbutamol 5 mg nebulised every 15 to 20 minutes, ipratropium 500 micrograms, prednisolone 40 to 50 mg daily, magnesium sulphate 2 g intravenously for severe attacks.
• Chronic obstructive pulmonary disease exacerbation: nebulised salbutamol 2.5 to 5 mg and ipratropium 500 micrograms, prednisolone 30 to 40 mg for 5 days, antibiotics if purulent sputum, controlled oxygen 88% to 92%, non invasive ventilation for pH under 7.35 with PaCO2 over 6.5 kPa.
• Pulmonary embolism: rivaroxaban 15 mg twice daily for 21 days then 20 mg daily, or apixaban 10 mg twice daily for 7 days then 5 mg twice daily, or enoxaparin 1 mg/kg twice daily; alteplase 100 mg over 2 hours for shock.
• Pulmonary oedema: furosemide 40 to 80 mg intravenously, glyceryl trinitrate infusion, continuous positive airway pressure.
• Pneumothorax: needle decompression for tension, then chest drain.
• Diabetic ketoacidosis: 0.9% sodium chloride 1 litre over the first hour, fixed rate insulin 0.1 units/kg/hour, potassium replacement by serum level (add 40 mmol/L when potassium is 3.5 to 5.5 mmol/L), identify the trigger; do not give bicarbonate unless pH under 6.9.
• Salicylate poisoning: activated charcoal 50 g within 1 hour, intravenous sodium bicarbonate 1.5 mg/kg (150 mL of 8.4% over 1 hour) to alkalinise urine (pH 7.5 to 8.5), potassium replacement, early haemodialysis for level over 700 mg/L (5.1 mmol/L), pH under 7.2, renal failure or neurological signs; avoid intubation where possible (worsens acidosis; hyperventilate if needed).
• Toxic alcohols: fomepizole 15 mg/kg intravenously then 10 mg/kg every 12 hours (or ethanol), haemodialysis.
• Lactic acidosis and renal failure: treat the cause, stop metformin, dialysis in severe cases.
• Anaemia and bleeding: transfusion (red cells for haemoglobin under 7 g/dL or symptomatic; 8 g/dL with cardiac disease), stop the bleeding.
• Thyroid storm: propranolol 60 to 80 mg every 4 hours (or 1 mg intravenously), carbimazole 20 mg every 6 hours, hydrocortisone 100 mg every 8 hours, cooling, fluids, Lugol iodine after antithyroid drug.
• Hyperventilation syndrome (after exclusion of organic causes): reassurance, breathing retraining (slow diaphragmatic breathing, nasal breathing), physiotherapy, cognitive behavioural therapy; avoid rebreathing from a paper bag; treat panic disorder with sertraline 50 mg daily if needed.
• Pain: analgesia (paracetamol 1 g every 6 hours, ibuprofen 400 mg every 8 hours, regional block for rib fractures).
• Pregnancy: left lateral tilt, treat embolism, cardiomyopathy and infection.

Disposition.

• Resuscitation or critical care: respiratory rate over 30 or under 8, exhaustion, shock, saturation under 90%, pH under 7.25, need for ventilation or vasopressors.
• Admit: persistent respiratory rate over 24 with an unexplained or serious cause, early warning score 5 or more, new hypoxia, sepsis, embolism, acidosis, poisoning.
• Discharge: normal rate and saturation, explained and treated cause, reliable follow up.

Monitoring. Respiratory rate counted every 15 minutes initially then hourly; continuous saturation; blood gas trend and lactate; early warning score; fluid balance; vital capacity in neuromuscular disease; ECG; glucose and ketones.

Referral and escalation. Critical care outreach and anaesthesia; respiratory, cardiology, endocrinology, toxicology, nephrology (dialysis), neurology, obstetrics; psychology for hyperventilation.

Safety netting. Return urgently for increasing breathlessness, rapid breathing at rest, blue lips, chest pain, drowsiness, confusion, persistent vomiting, or inability to drink. Keep a symptom diary in recurrent episodes; follow breathing retraining exercises.

Special groups. Children: age specific rates; tachypnoea is the most sensitive sign of pneumonia (paediatric thresholds: over 50 in infants, over 40 for ages 1 to 5); bronchiolitis, asthma, sepsis, diabetic ketoacidosis, foreign body, congenital heart disease, dehydration; look for grunting, nasal flaring, recession and head bobbing. Pregnancy: minute ventilation rises 30% to 50%; resting rate stays under 20, so a rate over 20 is abnormal.

Older adults: tachypnoea may be the only sign of pneumonia or sepsis. Obesity, ascites: restrictive rapid shallow breathing. Sedated or head injured: central neurogenic hyperventilation. High altitude: acclimatisation. Endemic regions: malaria (acidotic breathing in children), severe anaemia, tuberculosis, pneumonia, dehydrating diarrhoea (acidosis).