Sternocleidomastoid Muscle in Respiratory Assessment

The sternocleidomastoid is a prominent muscle of the neck that also serves an important role in respiration. Although it primarily controls movements of the head and neck, it becomes an accessory muscle of inspiration when ventilatory demands increase.

Visible contraction of this muscle during breathing can provide valuable information about respiratory effort and possible distress.

Understanding the sternocleidomastoid’s anatomy, mechanical function, relationship with the diaphragm, and clinical significance can help respiratory therapists recognize increased work of breathing and identify patients who may be struggling to maintain adequate ventilation.

What Is the Sternocleidomastoid Muscle?

The sternocleidomastoid is a paired muscle located along the lateral portion of the neck. One muscle is present on each side, extending from structures of the upper chest to the skull.

Its name reflects its major anatomical attachments:

• Sterno refers to the sternum.
• Cleido refers to the clavicle.
• Mastoid refers to the mastoid process of the temporal bone.

The muscle originates inferiorly from the sternum and clavicle and travels upward to attach near the mastoid process behind the ear. This orientation allows the sternocleidomastoid to perform several different movements depending on which attachment is stabilized.

During ordinary musculoskeletal activity, the muscle primarily affects the head and neck. During respiratory distress or forceful inspiration, however, its function can change. When the head and neck are stabilized, the sternocleidomastoid can pull upward on the sternum and clavicle, assisting expansion of the upper thorax. This ability is what makes the sternocleidomastoid clinically important as an accessory muscle of inspiration.

Normal Function of the Sternocleidomastoid

Outside the respiratory system, the sternocleidomastoid is mainly responsible for movement and stabilization of the head and neck. When one sternocleidomastoid contracts independently, it can rotate the head toward the opposite side while contributing to lateral movement of the neck.

When both sternocleidomastoid muscles contract together, they can assist with flexion and stabilization of the cervical region. These actions are possible because the muscle normally pulls from its attachments on the sternum and clavicle toward its attachment on the skull. Its action changes when the head is stabilized.

If the head and neck are held relatively stationary, contraction can pull upward on the muscle’s lower attachments. This elevates the sternum and upper chest and allows the muscle to assist inspiration.

This concept illustrates an important feature of respiratory mechanics. Many accessory respiratory muscles become more effective when another part of the body is fixed or supported.

Primary Muscles of Breathing

To understand the respiratory role of the sternocleidomastoid, it is helpful to distinguish accessory muscles from the primary muscles responsible for normal ventilation. The diaphragm is the main muscle of inspiration.

During quiet breathing, the diaphragm contracts and moves downward toward the abdominal cavity. This increases the vertical dimension of the thorax and reduces pressure inside the chest. As thoracic volume increases, alveolar pressure falls below atmospheric pressure. Air then moves through the airways and into the lungs.

The external intercostal muscles can also contribute to inspiration by elevating the ribs upward and outward. This increases the lateral and anteroposterior dimensions of the thorax. The movement of the ribs is sometimes described as a bucket-handle motion, while movement of the sternum resembles the motion of a pump handle.

Together, these actions enlarge the chest cavity and facilitate lung expansion. In a healthy adult at rest, these primary mechanisms normally provide enough muscular force to maintain ventilation without significant assistance from the sternocleidomastoid or other accessory muscles.

What Are Accessory Muscles of Respiration?

Accessory respiratory muscles provide additional mechanical assistance when breathing demands exceed what the primary respiratory muscles can comfortably accomplish. Accessory muscles may participate in either inspiration or expiration.

Major accessory muscles of inspiration include:

• Sternocleidomastoid muscles
• Scalene muscles
• Pectoralis major muscles
• Trapezius muscles
• External intercostal muscles

Accessory muscles of expiration include:

• Rectus abdominis
• External abdominal oblique
• Internal abdominal oblique
• Transversus abdominis
• Internal intercostal muscles

Accessory muscle activity may occur normally during vigorous exercise because metabolic demands and ventilation increase substantially. However, prominent accessory muscle use while a patient is resting is considered abnormal.

When a resting patient visibly recruits muscles of the neck, chest, shoulders, or abdomen to breathe, the finding generally indicates increased work of breathing.

How the Sternocleidomastoid Assists Inspiration

The sternocleidomastoid contributes to inspiration primarily by elevating the sternum and upper chest. For this action to occur effectively, the head and neck must remain relatively stable.

The trapezius and other muscles may help stabilize the upper body so that contraction of the sternocleidomastoid produces movement at its lower attachments rather than simply moving the head.

As the sternum rises, the anteroposterior diameter of the chest increases. This increases thoracic volume and contributes to a reduction in intrathoracic pressure. Because air flows from areas of higher pressure toward areas of lower pressure, the decrease in pressure helps draw air through the airways and into the lungs.

The sternocleidomastoid does not accomplish this alone. The scalene muscles can elevate the first and second ribs. The external intercostal muscles elevate and expand the rib cage. The pectoralis muscles can lift the chest when the arms are fixed. Together, these muscles increase thoracic expansion when additional inspiratory effort is required.

Sternocleidomastoid Use During Quiet Breathing

Prominent sternocleidomastoid activity should generally not occur during normal resting ventilation.

A healthy adult at rest usually breathes with:

• A regular respiratory rhythm
• An appropriate respiratory rate
• Minimal visible effort
• Coordinated chest and abdominal movement
• Passive expiration
• No obvious accessory muscle recruitment

The sternocleidomastoid may become active during strenuous exercise because the body requires increased ventilation. In this setting, accessory muscle recruitment can be an appropriate physiological response.

The clinical concern arises when the sternocleidomastoid becomes visibly active while the patient is sitting or lying quietly at rest. This finding suggests that the patient must recruit additional muscular force to maintain ventilation.

Sternocleidomastoid Use as a Sign of Increased Work of Breathing

The work of breathing refers to the muscular effort required to move air through the airways and expand the respiratory system. Under normal circumstances, this workload is relatively small.

Several abnormalities can significantly increase respiratory workload.

Increased Airway Resistance

Airway resistance increases when airways become narrowed or obstructed.

Examples include:

• Asthma
• COPD
• Bronchitis
• Upper airway obstruction
• Bronchospasm
• Airway secretions
• Foreign-body aspiration

Note: When resistance increases, greater pressure must be generated to produce airflow. The respiratory muscles therefore work harder.

Reduced Lung Compliance

Compliance refers to how easily the lungs and chest wall expand. Conditions that reduce compliance make inspiration more difficult because greater pressure is required to achieve the same amount of lung expansion.

Examples include:

• Acute respiratory distress syndrome
• Pulmonary edema
• Pneumonia
• Pulmonary fibrosis
• Neonatal respiratory distress syndrome

Note: In these situations, accessory inspiratory muscles may be recruited to generate additional thoracic expansion.

Respiratory Muscle Weakness

The respiratory system may also struggle when the muscles themselves become weak. Neuromuscular diseases, spinal cord disorders, diaphragmatic dysfunction, fatigue, and severe systemic illness can impair the ability of respiratory muscles to generate adequate force.

The sternocleidomastoid may become increasingly active as the body attempts to compensate.

Sternocleidomastoid Use in COPD

Chronic obstructive pulmonary disease provides one of the clearest examples of accessory muscle recruitment. Patients with advanced COPD may experience chronic airflow limitation and lung hyperinflation.

Air becomes trapped within the lungs, causing the chest to remain expanded even at the end of expiration. As the lungs become increasingly hyperinflated, the diaphragm becomes flattened. Normally, the diaphragm has a dome-shaped configuration that provides favorable mechanical leverage during inspiration. When flattened, it becomes less effective.

Although the diaphragm may continue contracting, each contraction produces less useful displacement of the abdominal contents and less efficient expansion of the thoracic cavity.

The patient may therefore compensate by increasing use of the sternocleidomastoid, scalene, pectoral, trapezius, and other accessory inspiratory muscles. Prominent neck muscle activity may become visible with each inspiration.

The Tripod Position

Patients with severe COPD or acute respiratory distress may adopt a characteristic posture known as the tripod position.

A patient in the tripod position usually:

• Sits upright
• Leans forward
• Supports the arms on the knees, bed, table, or another fixed surface
• Stabilizes the shoulders and upper extremities

This posture is not random. Fixing the upper body allows accessory muscles to operate more efficiently.

For example, when the arms are stabilized, the pectoralis major muscles can assist with elevation of the chest instead of simply moving the arms. Likewise, stabilization of the upper body improves the mechanical effectiveness of muscles such as the sternocleidomastoid.

The patient is essentially creating a fixed point from which the accessory muscles can generate greater thoracic expansion. Other findings commonly associated with advanced obstructive lung disease may include pursed-lip breathing, prolonged expiration, reduced exercise tolerance, and a chronically expanded chest.

Sternocleidomastoid Use in Upper Airway Obstruction

The sternocleidomastoid may also become active when inspiration is mechanically obstructed. Upper airway obstruction increases the pressure required to draw air through the narrowed airway.

Possible causes include:

• Croup
• Epiglottitis
• Partial foreign-body obstruction
• Postextubation laryngeal edema
• Airway tumors
• Airway trauma

As the patient attempts to overcome the obstruction, increasingly negative intrathoracic pressure may be generated. The sternocleidomastoid and other accessory inspiratory muscles become recruited in an effort to expand the chest and maintain airflow.

Accessory muscle activity in this setting may occur together with stridor, retractions, prolonged inspiration, nasal flaring, and other signs of significant airway narrowing.

Sternocleidomastoid Use and Retractions

Retractions are inward movements of the soft tissues of the chest during inspiration. They occur when a patient generates abnormally negative intrathoracic pressure while attempting to inhale.

Common forms include:

• Intercostal retractions
• Suprasternal retractions
• Supraclavicular retractions
• Subcostal retractions
• Substernal retractions

Retractions are abnormal in a resting adult. They indicate that considerable pressure must be generated to produce inspiration. When prominent sternocleidomastoid contraction occurs together with retractions, the combined findings provide stronger evidence that the patient is experiencing increased work of breathing.

Retractions may occur in asthma, upper airway obstruction, pneumonia, pulmonary edema, ARDS, COPD, and other conditions that substantially increase respiratory workload.

Tracheal Tugging

Tracheal tugging may also accompany severe inspiratory effort. With this finding, the structures of the upper airway appear to move downward during inspiration. The thyroid cartilage may be pulled toward the chest as the patient generates vigorous inspiratory force.

Tracheal tugging together with prominent sternocleidomastoid activity, suprasternal retractions, or other neck muscle recruitment should raise concern for significant respiratory distress.

Nasal Flaring

Nasal flaring is another visible sign that may accompany accessory muscle use. During nasal flaring, the nostrils widen during inspiration. This action attempts to reduce resistance to airflow through the nasal passages.

Nasal flaring is particularly important in infants and young children, although it may occur in adults with severe respiratory distress.

When present together with sternocleidomastoid activity, rapid breathing, or retractions, it provides additional evidence that the patient is using compensatory mechanisms to maintain ventilation.

Sternocleidomastoid Use in Neuromuscular Disease

Accessory muscle activity can also occur when the lungs themselves are relatively normal but the respiratory muscles are weak. Neuromuscular disorders can interfere with the transmission of nerve impulses or reduce the ability of respiratory muscles to contract effectively.

As muscle strength declines, patients may begin to breathe rapidly and shallowly. A rapid, shallow breathing pattern reduces the amount of muscular effort required for each breath, but it may also decrease overall ventilatory efficiency.

As weakness progresses, the patient may increasingly recruit muscles of the neck and upper thorax. Prominent sternocleidomastoid activity may therefore become a sign that the primary inspiratory muscles are no longer generating adequate force independently.

Diaphragmatic Weakness and Paralysis

The diaphragm is particularly important in respiratory muscle weakness. If the diaphragm becomes fatigued, weakened, or paralyzed, accessory inspiratory muscles attempt to compensate.

The sternocleidomastoid can continue elevating the upper chest, but accessory muscles cannot completely replace normal diaphragmatic function. This can lead to abnormal breathing patterns. One important example is paradoxical abdominal movement.

Abdominal Paradox

During normal inspiration, the diaphragm contracts and moves downward. This displacement pushes the abdominal contents outward, causing the abdomen to expand while the chest also enlarges. When the diaphragm is severely weak or paralyzed, this coordinated pattern may be reversed.

Accessory muscles such as the sternocleidomastoid expand the chest and generate negative intrathoracic pressure. Because the diaphragm cannot contract effectively, the negative pressure pulls it upward instead of allowing it to descend.

As a result, the abdomen moves inward during inspiration. During expiration, the opposite pattern may occur, and the abdomen moves outward. This abnormal motion is known as abdominal paradox or paradoxical breathing.

The combination of prominent sternocleidomastoid use and paradoxical abdominal motion can indicate significant diaphragmatic dysfunction or respiratory muscle fatigue.

Rapid Shallow Breathing

Rapid shallow breathing may accompany increasing accessory muscle use. Instead of taking slow, deep breaths, the patient takes small breaths at a faster rate. This pattern can temporarily reduce the muscular effort required for each breath.

However, shallow breathing increases the proportion of each breath that ventilates anatomical dead space rather than the alveoli. As a result, effective alveolar ventilation may decrease.

A patient who develops rapid shallow breathing together with prominent neck muscle activity should be evaluated carefully for respiratory muscle fatigue or impending ventilatory failure.

Speech Changes During Respiratory Distress

A patient’s ability to speak can provide additional information about respiratory function. A patient with adequate ventilatory reserve can usually speak in complete sentences without repeatedly stopping to breathe. As respiratory distress worsens, speech may become fragmented.

Some patients can speak only a few words before requiring another breath. Severe respiratory muscle weakness may produce staccato speech, in which phrases are interrupted by frequent breaths.

Prominent sternocleidomastoid activity accompanied by difficulty speaking should be interpreted as a potentially important sign of increased respiratory compromise.

Other Signs Associated With Accessory Muscle Use

Sternocleidomastoid activity should never be evaluated as an isolated finding. Other signs of increased respiratory workload may include:

• Tachypnea
• Nasal flaring
• Retractions
• Paradoxical breathing
• Pursed-lip breathing
• Tracheal tugging
• Tachycardia
• Sweating
• Restlessness
• Dyspnea
• Reduced tidal volume
• Cyanosis
• Inability to speak in complete sentences

Note: The significance of these findings depends on the patient’s overall condition. A single physical sign does not identify the exact cause of respiratory distress, but multiple abnormal findings can indicate that the patient is struggling to maintain adequate ventilation or oxygenation.

Palpation of the Sternocleidomastoid

Accessory muscle activity can be assessed visually and by palpation. The sternocleidomastoid is particularly useful because it is superficial and relatively easy to observe along the sides of the neck.

During assessment, the clinician can observe the muscle from the front or side of the patient. With increased inspiratory effort, the muscle may become visibly prominent with each breath. Palpation can confirm that the muscle is actively contracting during inspiration.

The trapezius muscles may also be observed from behind or palpated during respiratory assessment.

The presence, absence, or change in accessory muscle activity should be documented together with the patient’s respiratory rate, breathing pattern, oxygenation, chest movement, and other physical findings.

Sternocleidomastoid Use and Breathing Patterns

Accessory muscle recruitment should also be interpreted in relation to the patient’s breathing pattern.

Eupnea

Eupnea describes normal, quiet breathing.

During eupnea:

• Respiratory rate is appropriate
• Tidal volume is adequate
• Inspiration is smooth
• Expiration is passive
• Accessory muscle use is absent or minimal

Note: Prominent sternocleidomastoid activity would therefore be abnormal during true resting eupnea.

Tachypnea

Tachypnea refers to an abnormally increased respiratory rate. Accessory inspiratory muscles may become active if rapid breathing is associated with increased ventilatory demand.

Tachypnea can occur with fever, pain, anxiety, acidosis, hypoxemia, pulmonary disease, and many other conditions. The presence of sternocleidomastoid activity can help determine whether rapid breathing is also associated with increased respiratory effort.

Obstructed Inspiration

When inspiration is obstructed, inspiratory time may become prolonged. The patient may recruit the sternocleidomastoid and other muscles to generate enough pressure to draw air through the narrowed airway.

This pattern should prompt evaluation for upper airway obstruction.

Respiratory Muscle Fatigue

Accessory muscle activity may initially represent successful compensation. However, sustained excessive work of breathing can eventually cause fatigue. Respiratory muscles require oxygen and energy just like other skeletal muscles.

When the workload remains excessively high for a prolonged period, the muscles may no longer be able to maintain the required pressure and ventilation.

Signs that compensation may be failing include:

• Increasing respiratory rate followed by slowing
• Falling tidal volume
• Altered mental status
• Worsening hypercapnia
• Paradoxical breathing
• Increasing accessory muscle use
• Weak cough
• Inability to speak normally
• Declining inspiratory muscle strength

Note: A patient who has been working hard to breathe and then suddenly appears less active should not automatically be assumed to be improving. Reduced muscular activity can sometimes represent fatigue rather than recovery.

Measuring Respiratory Muscle Performance

Clinical observation can be supplemented with objective measurements. Maximum inspiratory pressure is commonly used to assess inspiratory muscle strength. A low value may indicate that the patient lacks sufficient muscular force to sustain adequate ventilation.

Vital capacity can also provide useful information about respiratory muscle performance. A decreasing vital capacity may indicate progressive weakness, particularly in patients with neuromuscular disorders.

Other measurements include respiratory rate, tidal volume, minute ventilation, arterial blood gas values, and oxygen saturation. These objective measurements should be interpreted together with bedside findings such as sternocleidomastoid use.

Sternocleidomastoid Use During Mechanical Ventilation

Accessory muscle activity remains clinically important even when a patient is receiving mechanical ventilation. One purpose of mechanical ventilation is to reduce excessive respiratory workload.

If a mechanically ventilated patient continues to display pronounced accessory muscle activity, the patient may still be working harder than expected.

Possible causes include:

• Inadequate ventilatory support
• Excessive airway resistance
• Bronchospasm
• Secretions
• Auto-PEEP
• Inadequate inspiratory flow
• Trigger asynchrony
• Air leaks
• Pneumothorax
• Pulmonary edema
• Increased respiratory drive

Note: Ventilator settings and patient condition should both be evaluated.

Artificial Airway Resistance

An endotracheal or tracheostomy tube adds resistance to airflow. Because the artificial airway is narrower than the natural airway, the patient may need to generate additional pressure when breathing spontaneously through the tube.

Secretions can further increase resistance. A patient with inadequate ventilatory assistance may therefore recruit the sternocleidomastoid and other accessory muscles to overcome the added load. This is particularly relevant during partial ventilatory support and spontaneous breathing trials.

Trigger Sensitivity and Accessory Muscle Activity

During patient-triggered mechanical ventilation, the patient must generate enough inspiratory effort to trigger the ventilator. If trigger sensitivity is set improperly, excessive effort may be required before a supported breath begins.

The patient may repeatedly contract the diaphragm and accessory muscles in an attempt to initiate inspiration.

Visible sternocleidomastoid activity can therefore sometimes indicate patient-ventilator asynchrony rather than worsening lung disease alone. Ventilator graphics and careful bedside assessment can help identify the cause.

Inadequate Inspiratory Flow

Inspiratory flow must meet the patient’s demand. If the ventilator supplies gas more slowly than the patient desires, the patient may continue generating inspiratory effort throughout the breath.

This can increase respiratory workload and produce obvious accessory muscle activity. Adjustment of inspiratory flow, rise time, mode, pressure support, or other settings may be necessary depending on the type of ventilation being used.

Auto-PEEP and Inspiratory Effort

Auto-PEEP occurs when the lungs do not completely empty before the next breath begins. Residual positive pressure remains within the lungs at end-expiration.

Before the patient can trigger another breath, inspiratory muscles must first generate enough negative pressure to overcome the trapped positive pressure. This can significantly increase inspiratory workload. Auto-PEEP is particularly common in obstructive lung disease and may contribute to pronounced accessory muscle recruitment.

Spontaneous Breathing Trials

Observation of accessory muscles is especially important during ventilator weaning. During a spontaneous breathing trial, ventilatory assistance is reduced so clinicians can determine whether the patient can sustain spontaneous breathing.

A patient tolerating the trial should remain relatively comfortable without a major increase in accessory muscle activity. New or worsening sternocleidomastoid contraction may indicate that the patient’s respiratory workload is becoming excessive.

Other signs of poor tolerance may include:

• Rising respiratory rate
• Reduced tidal volume
• Tachycardia
• Dysrhythmias
• Dyspnea
• Abnormal blood gases
• Reduced vital capacity
• Declining inspiratory strength
• Altered mental status

Note: The decision to continue or stop a spontaneous breathing trial should be based on the overall clinical picture rather than accessory muscle use alone.

Why Sternocleidomastoid Activity Matters

The main clinical value of the sternocleidomastoid is that it provides a visible indication of respiratory effort. Its activity does not diagnose a specific disease. Instead, it tells the clinician that the patient is recruiting additional muscular force to breathe.

This may result from increased airway resistance, decreased compliance, diaphragmatic dysfunction, neuromuscular weakness, excessive ventilatory demand, or problems related to mechanical ventilation.

The finding becomes more concerning when it appears suddenly, worsens over time, or occurs alongside other signs of respiratory distress. Assessment should therefore focus on both the presence of accessory muscle activity and the reason the patient needs additional muscular assistance.

Sternocleidomastoid Practice Questions

1. What is the sternocleidomastoid muscle’s primary respiratory function?
To act as an accessory muscle of inspiration by helping elevate the sternum and upper chest when ventilatory demand increases.

2. Where does the sternocleidomastoid muscle originate?
The sternocleidomastoid originates from the sternum and clavicle.

3. Where does the sternocleidomastoid muscle insert?
It inserts near the mastoid process of the temporal bone and the occipital region of the skull.

4. What are the primary nonrespiratory functions of the sternocleidomastoid?
Its primary nonrespiratory functions include movement and stabilization of the head and neck, including head rotation and cervical flexion.

5. Under what condition can the sternocleidomastoid effectively assist inspiration?
It can effectively assist inspiration when the head and neck are stabilized, allowing the muscle to pull upward on its lower attachments.

6. How does sternocleidomastoid contraction increase thoracic volume?
It elevates the sternum and upper chest, increasing the anteroposterior diameter of the thoracic cavity.

7. Is prominent sternocleidomastoid activity expected during quiet breathing in a healthy adult?
No. Prominent sternocleidomastoid activity is generally absent during normal resting ventilation.

8. What does visible sternocleidomastoid contraction at rest usually indicate?
It usually indicates increased work of breathing and recruitment of accessory inspiratory muscles.

9. During what normal physiological activity may sternocleidomastoid recruitment occur without indicating disease?
It may occur during vigorous exercise when ventilatory demand is substantially increased.

10. Which primary muscle normally performs most of the work of inspiration during quiet breathing?
The diaphragm normally performs most of the work of inspiration during quiet breathing.

11. How does the diaphragm normally contribute to inspiration?
The diaphragm contracts and moves downward, increasing thoracic volume and lowering pressure within the chest so air can enter the lungs.

12. Which muscles may work with the sternocleidomastoid to assist inspiration?
The scalene, external intercostal, pectoralis major, and trapezius muscles may contribute to accessory inspiration.

13. How do the scalene muscles assist inspiration?
The scalene muscles help elevate the first and second ribs, contributing to expansion of the thoracic cavity.

14. Why may the sternocleidomastoid become more active in advanced COPD?
Chronic hyperinflation can flatten the diaphragm and reduce its mechanical effectiveness, causing greater dependence on accessory inspiratory muscles.

15. What happens to the diaphragm when severe lung hyperinflation occurs?
The diaphragm becomes flattened and mechanically disadvantaged, reducing its ability to generate effective inspiration.

16. Why may a patient with COPD assume the tripod position?
The tripod position stabilizes the upper extremities and shoulder girdle, allowing accessory respiratory muscles to work more effectively.

17. What does the tripod position typically look like?
The patient sits upright, leans forward, and supports the arms on the knees, a bed, table, or another fixed surface.

18. How can increased airway resistance lead to sternocleidomastoid recruitment?
Increased airway resistance requires greater pressure and muscular effort to produce airflow, which can cause recruitment of accessory inspiratory muscles.

19. Name three conditions associated with increased airway resistance that may lead to accessory muscle use.
Examples include asthma, COPD, and upper airway obstruction.

20. How can reduced lung compliance increase sternocleidomastoid activity?
Reduced compliance makes the lungs more difficult to expand, requiring greater inspiratory effort and possible recruitment of accessory muscles.

21. Name three conditions in which reduced lung compliance may increase the work of breathing.
Examples include acute respiratory distress syndrome, pulmonary edema, and pneumonia.

22. Why may the sternocleidomastoid become prominent during upper airway obstruction?
The patient must generate greater inspiratory pressure to move air through the narrowed airway, resulting in increased accessory muscle recruitment.

23. What are retractions, and how are they related to increased respiratory effort?
Retractions are inward movements of soft tissues during inspiration caused by excessive negative intrathoracic pressure. They are a sign of increased work of breathing.

24. What types of retractions may accompany sternocleidomastoid use during respiratory distress?
Intercostal, suprasternal, supraclavicular, subcostal, and substernal retractions may occur.

25. Why should sternocleidomastoid activity never be interpreted as an isolated finding?
Sternocleidomastoid activity indicates increased respiratory effort but does not identify a specific cause. It should be interpreted with findings such as respiratory rate, breathing pattern, retractions, chest and abdominal movement, oxygenation, ventilation, and the patient’s overall clinical appearance.

26. What is tracheal tugging, and what does it suggest about respiratory effort?
Tracheal tugging is downward movement of the upper airway structures during inspiration. It can occur with pronounced inspiratory effort and may accompany sternocleidomastoid recruitment.

27. Why is nasal flaring considered a sign of increased work of breathing?
Nasal flaring widens the nostrils during inspiration in an attempt to reduce resistance to airflow, indicating that the patient is increasing respiratory effort.

28. In which patient population is nasal flaring especially significant?
Nasal flaring is especially significant in neonates and young children.

29. How can neuromuscular disease lead to sternocleidomastoid recruitment?
Neuromuscular disease can weaken the primary respiratory muscles, causing the patient to recruit accessory muscles such as the sternocleidomastoid to help maintain ventilation.

30. What breathing pattern commonly develops as respiratory muscle weakness progresses?
Patients often develop rapid, shallow breathing as respiratory muscle weakness progresses.

31. Why can rapid, shallow breathing be less efficient?
Rapid, shallow breathing increases the proportion of each breath that ventilates anatomical dead space, which can reduce effective alveolar ventilation.

32. What is abdominal paradox?
Abdominal paradox is an abnormal breathing pattern in which the abdomen moves inward during inspiration instead of outward.

33. How can diaphragmatic weakness contribute to abdominal paradox?
When the diaphragm is weak, accessory inspiratory muscles expand the chest and create negative intrathoracic pressure that may pull the weakened diaphragm upward, causing the abdomen to move inward.

34. What finding may accompany sternocleidomastoid use in severe diaphragmatic dysfunction?
Paradoxical abdominal movement may accompany sternocleidomastoid use in severe diaphragmatic dysfunction.

35. How can speech provide information about respiratory distress?
A patient with worsening respiratory distress may be unable to speak in complete sentences and may need frequent breaths between words or phrases.

36. What is staccato speech in the context of respiratory weakness?
Staccato speech refers to fragmented speech in which the patient must pause frequently to breathe because ventilatory reserve is limited.

37. Why can sweating accompany severe respiratory distress?
Sweating may occur as part of the physiologic stress response when the patient is exerting substantial effort to maintain ventilation.

38. Why can tachycardia accompany increased work of breathing?
Tachycardia may occur as the body responds to increased respiratory demand, stress, and possible impairment of oxygenation or ventilation.

39. What is the clinical significance of restlessness in a patient with increased accessory muscle use?
Restlessness can be an additional sign of respiratory compromise and should be interpreted with the patient’s overall respiratory status.

40. Why can decreasing accessory muscle activity sometimes be a concerning sign?
If a patient has been working very hard to breathe, a sudden decrease in accessory muscle activity may reflect respiratory muscle fatigue rather than improvement.

41. What bedside measurement can be used to assess inspiratory muscle strength?
Maximum inspiratory pressure can be used to assess inspiratory muscle strength.

42. How can vital capacity help in the assessment of respiratory muscle weakness?
A decreasing vital capacity may indicate worsening respiratory muscle performance, especially in patients with neuromuscular disease.

43. Why is clinical observation still important when objective respiratory measurements are available?
Objective measurements may quantify respiratory function, but observation of breathing pattern, accessory muscle use, chest movement, and distress provides important information that numbers alone may not reveal.

44. Why may a mechanically ventilated patient still use the sternocleidomastoid?
The patient may still be experiencing excessive respiratory workload because of inadequate support, airway resistance, asynchrony, auto-PEEP, or another patient- or ventilator-related problem.

45. How can an artificial airway increase the work of breathing?
An endotracheal or tracheostomy tube can increase airflow resistance, requiring the patient to generate additional pressure during spontaneous breathing.

46. How can secretions affect respiratory workload in a mechanically ventilated patient?
Secretions can increase airway resistance and make it more difficult for the patient to move air, increasing respiratory muscle effort.

47. How can improper trigger sensitivity increase sternocleidomastoid activity?
If the ventilator requires excessive effort to trigger a breath, the patient may repeatedly recruit the diaphragm and accessory muscles to initiate inspiration.

48. How can inadequate inspiratory flow increase work of breathing?
If ventilator flow does not meet the patient’s inspiratory demand, the patient may continue generating muscular effort throughout inspiration.

49. How does auto-PEEP increase the effort required to trigger a ventilator breath?
The patient must first generate enough inspiratory pressure to overcome the positive pressure remaining in the lungs before the ventilator can be triggered.

50. What can new or worsening sternocleidomastoid activity during a spontaneous breathing trial indicate?
It may indicate that the patient’s respiratory workload is becoming excessive and that the patient may not be tolerating the reduction in ventilatory support.

51. Why is the sternocleidomastoid considered an accessory rather than a primary muscle of inspiration?
Because it is not normally required for quiet resting ventilation and is recruited mainly when ventilatory demand or respiratory workload increases.

52. What change in thoracic dimensions occurs when the sternocleidomastoid elevates the sternum?
The anteroposterior diameter of the thorax increases.

53. How does increasing thoracic volume help air enter the lungs?
Increasing thoracic volume lowers intrathoracic and alveolar pressure, allowing air to move into the lungs from the atmosphere.

54. Why is stabilization important for the respiratory action of accessory muscles?
Stabilization provides a fixed point so the muscles can use their contraction to elevate the chest rather than simply move the head, neck, or arms.

55. How do the pectoralis major muscles assist inspiration when the arms are fixed?
With the arms stabilized, the pectoralis major muscles can help elevate the chest and contribute to thoracic expansion.

56. What role do the trapezius muscles play in accessory breathing?
The trapezius muscles help stabilize and elevate structures of the upper thorax so accessory inspiratory effort can be more effective.

57. What normally happens during expiration in a healthy resting adult?
Expiration is primarily passive and occurs as the inspiratory muscles relax and the respiratory system returns toward its resting position.

58. Which muscle groups are commonly recruited during forceful expiration?
The abdominal muscles and internal intercostal muscles are commonly recruited during forceful expiration.

59. How do the abdominal muscles assist forceful expiration?
They compress the abdominal contents and help push the diaphragm upward, decreasing thoracic volume and increasing expiratory pressure.

60. How do the internal intercostal muscles assist expiration?
They pull the ribs downward and inward, reducing thoracic dimensions and helping force air out of the lungs.

61. What is the basic mechanical difference between accessory inspiratory and accessory expiratory muscles?
Accessory inspiratory muscles enlarge the thoracic cavity, while accessory expiratory muscles reduce thoracic volume and increase pressure for expiration.

62. Why can severe airflow obstruction increase accessory muscle recruitment?
The patient must generate greater pressure to move air through narrowed airways, which increases the muscular workload required for breathing.

63. Why can stiff lungs cause visible neck muscle activity?
Stiff lungs require more force to expand, so accessory inspiratory muscles may be recruited to assist chest expansion.

64. Why is sternocleidomastoid activity useful during bedside respiratory assessment?
It is superficial and easy to observe or palpate, making it a practical indicator of increased respiratory effort.

65. From what positions can sternocleidomastoid activity be observed?
It can be observed from the front or side of the patient.

66. What should a clinician assess along with sternocleidomastoid activity?
The clinician should also assess respiratory rate, breathing pattern, chest movement, oxygenation, ventilation, retractions, and the patient’s overall appearance.

67. Why does sternocleidomastoid use not identify one specific disease?
Many different respiratory, neuromuscular, and mechanical problems can increase the work of breathing and cause accessory muscle recruitment.

68. What does a new increase in sternocleidomastoid activity suggest in a previously stable patient?
It suggests that respiratory workload may be increasing and that the patient’s condition should be reassessed.

69. How can chest and abdominal movement help identify abnormal respiratory mechanics?
Normally, the chest and abdomen move in a coordinated pattern, so inward abdominal movement during inspiration may indicate diaphragmatic weakness or paradoxical breathing.

70. What happens to the abdomen during normal diaphragmatic inspiration?
The abdomen typically moves outward as the diaphragm descends and displaces the abdominal contents.

71. What happens to the abdomen during inspiration in abdominal paradox?
The abdomen moves inward during inspiration because the weakened diaphragm is drawn upward rather than descending normally.

72. Why can accessory muscles not completely compensate for severe diaphragmatic dysfunction?
They can expand the upper thorax, but they cannot fully reproduce the normal downward movement and mechanical contribution of the diaphragm.

73. What does a combination of rapid shallow breathing and prominent neck muscle use suggest?
It may suggest that the patient is compensating for increased respiratory load or developing respiratory muscle weakness or fatigue.

74. Why is the patient’s ability to sustain respiratory effort clinically important?
A patient may initially compensate with increased muscle activity, but prolonged excessive effort can lead to fatigue and inadequate ventilation.

75. What overall principle does sternocleidomastoid recruitment illustrate in respiratory care?
It illustrates the balance between respiratory workload and muscle capacity, with accessory muscles being recruited when the normal breathing muscles cannot easily meet ventilatory demand.

76. Why does sternocleidomastoid activity become more concerning when it occurs at rest?
Because resting ventilation should normally require little or no visible accessory muscle activity, so recruitment at rest suggests increased respiratory workload.

77. What can prominent sternocleidomastoid contraction indicate in a patient with emphysema?
It can indicate that hyperinflation has reduced diaphragmatic efficiency and increased dependence on accessory inspiratory muscles.

78. Why does hyperinflation place the diaphragm at a mechanical disadvantage?
Hyperinflation flattens the diaphragm, reducing its normal dome-shaped configuration and limiting the effectiveness of its contraction.

79. What is the normal relationship between chest and abdominal movement during inspiration?
The chest expands while diaphragmatic descent causes the abdomen to move outward in a coordinated pattern.

80. What does seesaw breathing suggest about respiratory mechanics?
Seesaw breathing suggests abnormal chest and abdominal movement associated with severe respiratory effort or impaired respiratory muscle function.

81. How can decreased lung compliance contribute to retractions?
The patient must generate greater negative intrathoracic pressure to expand stiff lungs, which can pull soft tissues inward during inspiration.

82. Why may premature neonates develop marked retractions during respiratory distress?
Their chest walls are relatively compliant while their lungs may be stiff, making inward chest wall movement more likely during strong inspiratory efforts.

83. Why should accessory muscle use during tachypnea be interpreted with other clinical findings?
Tachypnea can result from many causes, so accessory muscle activity must be considered with tidal volume, history, respiratory effort, and the overall clinical condition.

84. What can sternocleidomastoid activity indicate when inspiration is prolonged?
It may indicate that the patient is generating additional muscular effort to overcome inspiratory airflow obstruction.

85. Why might a patient with postextubation laryngeal edema recruit the sternocleidomastoid?
Laryngeal narrowing increases inspiratory resistance, forcing the patient to generate greater effort to move air through the upper airway.

86. What can prominent accessory muscle use during croup suggest?
It can suggest that upper airway narrowing is significantly increasing the work required for inspiration.

87. Why should sternocleidomastoid activity be evaluated in a patient with possible foreign-body aspiration?
A partially obstructed airway can increase inspiratory resistance and cause marked accessory muscle recruitment.

88. How does respiratory muscle fatigue affect the balance between workload and muscle capacity?
Fatigue reduces the muscles’ ability to meet the imposed respiratory workload, increasing the risk of inadequate ventilation.

89. Why can worsening hypercapnia be concerning in a patient with prolonged accessory muscle use?
Worsening hypercapnia may indicate that the patient is no longer maintaining adequate alveolar ventilation despite increased respiratory effort.

90. What can a falling tidal volume indicate in a patient who has been using accessory muscles heavily?
It can indicate that respiratory muscle fatigue is developing and effective ventilation is deteriorating.

91. Why may altered mental status accompany severe respiratory compromise?
Severe abnormalities in oxygenation or ventilation can impair neurologic function and may signal worsening respiratory failure.

92. Why is a weak cough important when evaluating respiratory muscle fatigue?
A weak cough may indicate inadequate respiratory muscle strength and reduced ability to clear secretions effectively.

93. What does declining maximum inspiratory pressure suggest?
It suggests worsening inspiratory muscle strength and reduced ability to generate the pressure needed for effective ventilation.

94. Why is minute ventilation useful when evaluating respiratory performance?
Minute ventilation reflects the total volume of air moved each minute and helps assess whether the patient is maintaining adequate ventilatory output.

95. How can body position contribute to sudden respiratory distress in a mechanically ventilated patient?
Changes in position can alter respiratory mechanics, airway patency, secretion movement, or ventilator interaction, potentially increasing the work of breathing.

96. How can bronchospasm cause sternocleidomastoid recruitment in a ventilated patient?
Bronchospasm increases airway resistance, forcing the patient to generate additional inspiratory effort even when ventilatory support is being provided.

97. Why can pneumothorax cause a sudden increase in accessory muscle activity?
A pneumothorax can impair lung expansion and increase respiratory distress, causing the patient to recruit additional muscles to maintain ventilation.

98. How can pulmonary edema increase the work of breathing?
Pulmonary edema reduces lung compliance and makes the lungs more difficult to expand, increasing the muscular effort required for inspiration.

99. Why can mode asynchrony increase respiratory muscle effort during mechanical ventilation?
If the ventilator mode does not adequately match the patient’s breathing pattern or demand, the patient may have to perform additional work to breathe comfortably.

100. What is the most important clinical interpretation of visible sternocleidomastoid use?
It should be viewed as evidence that the patient is recruiting additional inspiratory muscle effort and should prompt assessment of the cause, severity, and adequacy of ventilation.

Final Thoughts

The sternocleidomastoid is primarily a neck muscle, but it becomes an important accessory muscle of inspiration when respiratory demand increases. By elevating the sternum and upper thorax, it helps enlarge the chest and support airflow into the lungs.

Visible sternocleidomastoid activity at rest is generally abnormal and may indicate increased work of breathing, airway obstruction, COPD, reduced lung compliance, respiratory muscle weakness, ventilator asynchrony, or impending fatigue.

Clinicians should interpret this finding together with respiratory rate, chest movement, retractions, breathing pattern, oxygenation, ventilation, and overall appearance to determine the severity and cause of respiratory distress.