Crackles vs wheezes: what each lung sound means

The deciding feature: popping versus whistling

Crackles, also called rales, are short and discontinuous. They are heard mostly during inspiration and are described as fine or coarse, moist or dry. They occur when small air spaces that have collapsed or filled with fluid pop open as the patient breathes in.

Wheezes are longer and musical. They are produced when air moves through narrowed or compressed small airways, making the airway walls vibrate. They are typically loudest on expiration, and wheezing on both inspiration and expiration suggests more severe narrowing.

Location and timing are part of the finding. Crackles at both bases in a patient with heart failure suggest fluid, while crackles over one lobe with fever suggest consolidation. Auscultate side to side in a consistent order so that a change between assessments is easy to compare.

Conditions each sound suggests, and where they overlap

Crackles are associated with pneumonia, heart failure and pulmonary oedema, where fluid or inflammation fills the alveoli. Wheezes are most often caused by asthma and chronic obstructive pulmonary disease, with other causes including allergic reactions, bronchitis, bronchiolitis in infants and foreign body aspiration.

The overlap matters. Heart failure can produce both crackles and wheezing, and a patient with COPD and pneumonia may have both sounds in different areas. A lung sound points towards a mechanism, not a single diagnosis, so interpret it alongside oxygen saturation, work of breathing, history and other findings.

Absent or very faint breath sounds are a separate finding again. They can mean air or fluid in the pleural space, severe airway narrowing or a collapsed area of lung, and they need the same urgency as a new abnormal sound.

Rhonchi and stridor: the near-misses

Rhonchi are lower-pitched snoring sounds caused by obstruction or turbulent flow in larger airways, often from secretions. Standard teaching notes that rhonchi may change or clear after coughing, which helps separate them from fixed crackles, though this is a teaching point rather than a strict test.

Stridor is a harsh, high-pitched sound, usually on inspiration, caused by narrowing of the trachea or upper airway rather than the small airways. It can be heard without a stethoscope and signals a possible upper airway obstruction, which is treated as an emergency.

For documentation, describe what you hear rather than only naming it: pitch, phase of breathing, location, and whether it changed after coughing or treatment. A clear description lets the next nurse judge whether the sound is improving or worsening.

Nursing priorities for each sound

With new crackles, assess for fluid overload or infection: oxygen saturation, respiratory rate, fluid balance, weight trend and sputum. Position the patient upright, give oxygen under protocol, encourage deep breathing and coughing where appropriate, and report new or spreading crackles with breathlessness.

With wheezes, assess work of breathing, accessory muscle use, ability to speak and oxygen saturation, then give the prescribed short-acting bronchodilator and reassess. Report red flags such as fatigue, reduced consciousness or facial and tongue swelling, which can indicate anaphylaxis.

With stridor, call for immediate help, keep the patient upright and calm, avoid examining the throat in a child with suspected epiglottitis under standard teaching, and prepare airway equipment. Oxygen and other treatment follow local protocol.

Hypothetical exam-style scenario

This is an invented practice item, not a real NCLEX question. A client with an asthma attack had loud expiratory wheezes an hour ago. Now the wheezes are much quieter, the client is drowsy and is using accessory muscles. What does the change most likely mean?

The best answer is worsening airflow obstruction needing urgent escalation. Quieter wheezing with more effort and drowsiness suggests too little air is moving to make sound. Reading it as improvement, offering a rest period, or simply rechecking later are tempting but dangerous because each ignores the rising work of breathing.

Sources and further reading

MedlinePlus: Breath sounds. Definitions of crackles, wheezes, rhonchi and stridor, and associated conditions.

MSD Manual Professional: Wheezing. Wheeze mechanism, causes, inspiratory and expiratory wheeze severity, stridor distinction, red flags, bronchodilator treatment.