Accessory muscle use during respiration is an important clinical sign often indicating increased work of breathing. While mild use can be normal during activities such as exercise, singing, or coughing, marked use often signifies underlying respiratory distress or chronic disease. Understanding the physiology, clinical manifestations, associated conditions, and appropriate interventions is critical for accurate diagnosis and timely management.

Physiology of accessory muscles in respiration

Under normal conditions, the diaphragm and external intercostal muscles are sufficient to maintain ventilation. However, when these muscles become overwhelmed or inadequate, accessory muscles engage to assist breathing. These muscles include:

• Inspiratory Accessory Muscles:

  • Sternocleidomastoid: Elevates the sternum, increasing the anteroposterior and longitudinal dimensions of the thorax.

  • Scalene muscles: Fix and elevate the first two ribs, expanding the upper chest.

  • Pectoralis major and Trapezius: Elevate the chest and thoracic cage.

• Expiratory Accessory Muscles:

  • Internal intercostals: Depress the ribs to reduce thoracic volume.

  • Abdominal muscles: Compress abdominal contents and pull the lower ribs down, aiding forced expiration.

Clinical significance of accessory muscle use

Normal vs. Abnormal Use

Accessory muscle use may be physiologic during increased demand (e.g., exercise) but becomes pathological when observed at rest or in response to minimal activity. Prominent use often suggests:

• Acute respiratory distress

• Diaphragmatic fatigue or paralysis

• Chronic pulmonary disease

• Neuromuscular compromise

The degree of muscle use often correlates with the severity of the underlying pathology.

Emergency assessment and interventions

When a patient presents with increased accessory muscle use, rapid evaluation is essential. Look for signs of acute respiratory compromise, including:

• Altered level of consciousness

• Shortness of breath while speaking

• Tachypnea

• Intercostal and sternal retractions

• Cyanosis

• Nasal flaring

• Wheezing, stridor, or diminished breath sounds

• Diaphoresis and agitation

Immediate interventions include:

• Auscultation for abnormal or absent breath sounds

• Airway management: Clear obstruction, insert airway, intubate if necessary

• Ventilation: Start manual or mechanical ventilation

• Oxygen administration:

  • Low-flow oxygen in mild COPD exacerbation

  • Titrate carefully to avoid suppressing respiratory drive in chronic CO₂ retainers

• Pulse oximetry for oxygen saturation

• Establish I.V. access for fluids and medications

History and physical examination

History taking

If the patient is stable, obtain a comprehensive history, including:

• Onset, duration, and severity of dyspnea, chest pain, cough, fever

• History of respiratory (e.g., COPD, asthma) or cardiac disease (e.g., CHF)

• Neuromuscular conditions (e.g., ALS, myasthenia gravis)

• Collagen vascular diseases (e.g., lupus, rheumatoid arthritis)

• Recent trauma to the chest or spine

• Occupational exposures (asbestos, chemical fumes)

• Smoking status and family history (e.g., cystic fibrosis)

Physical examination

• Assess respiratory rate, rhythm, and depth

• Look for retractions (intercostal, suprasternal, or abdominal)

• Observe skin color, temperature, turgor, and presence of clubbing

• Perform chest auscultation and percussion

• Evaluate for signs of systemic disease or neuromuscular deficits

Medical conditions associated with accessory muscle use

Table 1: The medical causes of accessory muscle use, including severity context and associated findings:

Special populations

Pediatrics

Children fatigue quickly and may decompensate rapidly. Causes of respiratory distress and accessory muscle use include:

• Acute epiglottitis

• Croup

• Asthma

• Pertussis

• Foreign body aspiration

Signs: Supraclavicular/intercostal retractions, nasal flaring, grunting

Geriatrics

In older adults, age-related changes in chest wall compliance can cause baseline accessory muscle use, even without acute pathology. Always correlate findings with other clinical signs.

Diagnostics and investigations

• Chest X-ray

• Pulse oximetry and arterial blood gas (ABG) analysis

• Pulmonary Function Tests (PFTs)

• Complete Blood Count (CBC)

• Sputum culture and Gram stain

• CT scan or V/Q scan (for embolism suspicion)

Management Considerations

• Elevate the head of the bed for comfort and improved ventilation

• Encourage hydration and rest

• Use bronchodilators, corticosteroids, and mucolytics as prescribed

• Educate patients on inhaler technique and medication adherence

• Provide smoking cessation support and infection prevention education

Patient counseling and education

Teach patients:

• Pursed-lip breathing and diaphragmatic breathing (especially in COPD)

• Incentive spirometry to prevent atelectasis

• Coughing and deep breathing exercises

• How to recognize signs of worsening respiratory status

• Importance of avoiding triggers (smoke, allergens)

• Medication use, side effects, and adherence

Conclusion

Accessory muscle use is a visible and crucial clinical marker of respiratory workload and distress. For health professionals, timely recognition, assessment, and appropriate intervention can prevent progression to respiratory failure. Incorporating a comprehensive approach — from emergency management to patient education — enhances clinical outcomes, especially in vulnerable populations.

References

1. Groth, S. S., & Andrade, R. S. (2010). Diaphragm plication for eventration or paralysis: A review of the literature. Annals of Thoracic Surgery, 89(6), S2146–S2150.

2. Weiss, C., Witt, T., Grau, S., & Tonn, J. C. (2011). Hemidiaphragmatic paralysis with recurrent lung infections due to degenerative motor root compression of C3 and C4.

3. Guyton AC, Hall JE. Textbook of Medical Physiology. 13th ed. Philadelphia: Elsevier Saunders; 2016.

4. Marini JJ, Wheeler AP. Acute Respiratory Distress Syndrome. N Engl J Med. 2006;355(8): 768–775. doi:10.1056/NEJMra054341.

5. Kacmarek RM, Stoller JK, Heuer AJ, editors. Egan's Fundamentals of Respiratory Care. 11th ed. St. Louis: Mosby Elsevier; 2016.

6. Brooks BR. El Escorial World Federation of Neurology criteria for the diagnosis of amyotrophic lateral sclerosis. ALS Clinical Practice. 1994;1(1):4–7.

7. Global Initiative for Asthma. Global Strategy for Asthma Management and Prevention, 2023 [Internet]. Available from: https://ginasthma.org/.

8. Global Initiative for Chronic Obstructive Lung Disease (GOLD). Global Strategy for Prevention, Diagnosis and Management of COPD: 2023 Report [Internet]. Available from: https://goldcopd.org/.

9. Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, et al. Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults. Clin Infect Dis. 2007;44(Suppl 2):S27–S72. doi:10.1086/511159.

10. Gheorghiade M, Pang PS. Acute Heart Failure Syndromes. J Am Coll Cardiol. 2009;53(7):557–573. doi:10.1016/j.jacc.2008.10.022.

11. Konstantinides SV, Meyer G, Becattini C, Bueno H, Geersing GJ, Harjola VP, et al. 2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism developed in collaboration with the European Respiratory Society (ERS). Eur Heart J. 2020;41(4):543–603. doi:10.1093/eurheartj/ehz405.

12. Kirshblum SC, Waring W, Biering-Sørensen F, Burns SP, Johansen M, Schmidt-Read M, et al. International Standards for Neurological Classification of Spinal Cord Injury (Revised 2011). J Spinal Cord Med. 2011;34(6):535–546. doi:10.1179/204577211X13207446293695.

13. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 7th ed. Philadelphia: Wolters Kluwer; 2013.

14. Albert RK, Schwab RJ, Rowley JA. Pulmonary Function Testing in the Critically Ill Patient. Chest. 1982;81(6):700–711. doi:10.1378/chest.81.6.700.