Tachypnea

Etiology

Physiological

Tachypnea is not always an indicator of underlying pathology. A common example of physiological tachypnea is the body's demand for oxygen during exercise, which causes an increase in respiratory rate. Similarly, when ascending to high-altitude areas, a similar increase in the oxygen demand is seen. Medications for pathological conditions can cause the body to increase respiratory rate. Medications and recreational drugs' adrenergic or stimulating effects could explain a higher respiratory rate. For example, a widely used stimulant, caffeine, causes immediate increases in respiratory rate. Tachypnea is also normal in pregnant women, children, infants, and older adults.

Pathological

Below are some of the common pathological causes of tachypnea:

• Stroke
• Sepsis
• Diabetic ketoacidosis
• Pneumonia
• Carbon monoxide poisoning
• Pulmonary embolism
• Pleural effusion
• Chronic obstructive pulmonary disease 
• Allergic reactions
• Anxiety
• Foreign body aspiration
• Post-status motor vehicle accident [2][3]

Epidemiology

Tachypnea in newborns could indicate underlying pathology within the respiratory system that is apparent after delivery. The condition can result from impaired fetal lung fluid clearance, leading to respiratory distress. Transient tachypnea of the newborn has a higher prevalence in preterm infants. Tachypnea occurs in approximately 1 in 100 preterm infants and about 4 to 6 per 1000 infants.[4][5] Tachypnea in adults is defined as breathing more than 20 breaths per minute. Twelve to 20 breaths per minute is a normal range, defined as a normal respiratory rate.

Pathophysiology

Tachypnea is a term used to define rapid and shallow breathing, not to be confused with hyperventilation, when a patient's breathing is rapid but deep. Both are similar in that both may result from a buildup of CO₂ in the lungs, leading to increased CO₂ in the blood.[6] This buildup makes the blood acidic, alerting the brain through chemoreceptors in the medulla. In response, the chemoreceptors signal the pulmonary stretch receptors in the lungs to increase the pace to correct the CO₂ imbalance to oxygen. In doing so, the blood acidity can return to the normal range. When the imbalance is too rapid, too large, or chronic, this is further defined as an acid-base imbalance in respiratory and renal physiology.

Considering the molecular basis describing the equilibrium of each of these factors reinforces why rapid and shallow breathing might occur: CO₂+H₂O ⇔ H₂CO₃ ⇔ HCO³⁻+H⁺

^{CO₂, carbon dioxide; H₂0, water; H, hydrogen; H₂CO₃, carbonic acid; HCO₃, bicarbonate}

• If too much CO₂ is retained, the equilibrium would shift to the right, producing more hydrogen ions and making the blood acidic.
• When breathing is increased, CO₂ is exhaled, shifting the equilibrium back to the left and reducing the blood acidity.
• If breathing alone cannot compensate for the acidity, the kidneys further alkalinize serum by retaining bicarbonate at the tubule level and shifting the equilibrium further to the left.

History and Physical

History

The quality of breathing is assessed via the history of the present illness (if relevant to the chief complaint and when reviewing all systems). Patients may complain of feeling short of breath or unable to get enough air. They may lean forward in a "tripod position" or speak poorly. The feeling can be described as increased breathing, whereas the signs of disequilibrium are defined as cyanosis (peripheral or central), increased work of breathing, or tachypnea. Several terms describe the symptoms of labored breathing, including dyspnea, bradypnea, apnea, acute dyspnea, or chronic dyspnea. However, dyspnea refers specifically to difficulty breathing, and bradypnea refers to slower breathing. On the other hand, patients can present without distress or cease breathing, termed apnea.

Physical Exam

Tachypnea is measured and documented in several ways: by manual counting, monitoring devices, electronic medical records, or a mix of both.[7][8] Tachypnea is also part of the systemic inflammatory response syndrome criteria for sepsis and may differentiate disposition status.[9][10] As such, measurement is important at several points in the visit if a patient is deteriorating, and an initial triage respiratory rate is usually compared to a later measurement when a clinician sees the patient. Patients may have blue-tinged fingers or lips and use accessory or chest muscles to breathe from a lack of oxygen. Infants can present with a blue color in the perioral area, grunting or signs of difficulty breathing, retraction of the chest while breathing, bobbing of the head, and flared nostrils.

Evaluation

Lab Evaluation

Clinicians can evaluate based on oximetry and several lab tests (including but not limited to):

• Arterial blood gases: Estimate oxygen and cCO₂ content, which can help determine the pH and metabolic abnormalities. 
• Glucose: A blood sugar can indicate or rule out diabetic ketoacidosis.
• Basic or comprehensive metabolic panel: Electrolyte values determine any influence on respiratory rate (such as in hyperkalemia).
• Complete blood count: Hemoglobin and white blood count levels determine signs of anemia or infection.
• Toxicology screen: A positive screen for amphetamines or urine metanephrines can narrow the differential.[11]

Procedural Evaluation

• Electrocardiogram: This is usually completed 1 or more times for periodic evaluation; for example, if a clinician suspects a pulmonary embolism or atrial fibrillation, this could explain a higher respiratory rate.
• Pulmonary function tests: To evaluate for obstructive or restrictive lung diseases.
• Intubation: Patients with tachypnea could quickly lose their airway, warranting immediate protection.

Imaging Modalities

A chest x-ray can depict any pulmonary causes of tachypnea, such as pneumothorax, cystic fibrosis, or pneumonia. A chest computed tomography scan showing greater detail can indicate other lung pathologies or potential malignancies. Lung ventilation-perfusion scans are helpful if signs and symptoms indicate a potential pulmonary embolus or pneumonia but could be considered after risk assessments (ie, Wells score or pulmonary embolism rule-out criteria).[12][13] Ultrasound imaging is useful when evaluating newborns, particularly when differentiating respiratory distress syndrome from transient tachypnea.[14][15][16] Ultrasound is also helpful for quick assessments when suspecting pleural effusion, hemothorax, or pericarditis.[17] 

Treatment / Management

Tachypnea is treated depending on the underlying cause. 

Differentiation by Patient Age

If infants present due to transient tachypnea of the newborn, they receive treatment with extra oxygen and, in some cases, may require some time in the neonatal intensive care unit.[15] In children and adults, a broad differential is important so as not to miss the least considered diagnosis, such as a malignancy.[18] Pathology, such as a urinary tract infection, may not cause tachypnea in a young adult but could increase respiratory rate in an older adult. Recently, COVID-19 caused tachypnea in all age groups, and different treatments were utilized.[19](B2)

Respiratory, Cardiac, Endocrine Causes

Respiratory causes such as asthma or chronic obstructive pulmonary disease are treated with short- or long-term bronchodilators, escalating the use of steroids and adjuncts based on clinical discretion, which should correct the tachypnea. Pneumo- or hemothorax typically needs procedural intervention, and acid-base disturbances are treated through ventilation or medication depending on the cause, such as ingestion of excess alcohol, drugs, etc. Similarly, cardiac events such as myocardial infarction, congestive heart disease, or valvular disorders are treated based on severity, as are endocrine causes such as diabetes, hyperthyroidism, Cushing syndrome, or rare causes such as pheochromocytoma. All bacterial infections are treated by varying antibiotic regimens, and viral infections are treated supportively.[20] If patients have multiple underlying pathologies, these are treated in order of priority. For example, diagnosing a rare brain tumor that causes tachypnea may take several visits, though the tachypnea is treated by oxygen.

Differential Diagnosis

A broad differential diagnosis categorized by each system is essential depending on where the patient presents with tachypnea. For emergency clinicians, undifferentiated patients lead to the most life-threatening diagnoses. In contrast, for critical care clinicians, the diagnosis may be known, and they document the progress of respiratory rate and quality. In contrast, a neurologist may prioritize types of strokes that could most likely lead to acute or chronic tachypnea. As such, by age group, some of the common diagnoses are:

Infants and Children

• Respiratory distress syndrome 
• Transient tachypnea of the newborn 
• Pneumonia
• Asthma

Adults

• Pneumonia 
• Pulmonary embolism 
• Congestive heart failure 

Older Adults

• Chronic obstructive pulmonary disease
• Malignancies
• Congestive heart failure

Across age groups, infections are a common diagnosis, as are psychiatric diseases such as generalized anxiety disorder or panic disorder.

Complications

While tachypnea can result from physiological causes such as exercise, pathologic causes are reason for concern. The complications arising from pathologic causes can worsen patient outcomes. Tachypnea can be a symptom of sepsis or acidosis. Patients with lung problems such as pneumonia, pleural effusion, pulmonary embolism, COPD, asthma, or an allergic reaction also present with tachypnea.[21] Congestive heart failure can also be a cause of tachypnea and, if not managed, can progress to worsening heart failure. Since tachypnea is a symptom, changes in respiratory rate indicate if a patient is improving or deteriorating, and as such, changes in medical management are needed. No direct complication can be traced back to tachypnea alone.