Respiratory Assessment and Monitoring: Assessment Types, Breath Sounds, Capnography

 Respiratory Assessment and Monitoring 

If an actual or potential respiratory abnormality is identified during a general ABCDE assessment or while monitoring the patient, a more detailed and focused respiratory assessment can provide further information to guide clinical management. Patients with dyspnoea or acute acute respiratory failure will often also manifest systemic signs and symptoms, including altered consciousness, cardiovascular compromise, and gastrointestinal dysfunction. 

Focused health history 

Subjective information about the respiratory history can be taken from the patient if they are awake, or from other source ( e.g. family, caregivers, etc )

Respiratory symptom enquiry 

Check whether the patient has recently experienced any of the following :

• Cough (productive )
• Haemoptysis 
• Dyspnoea
• Wheeze
• Chest pain
• Fever
• Sleep apnoea 

Focused physical assessment 

• Respiratory rate over 1 min ( normal range is 10- 20 breaths/min).
• Obvious signs of discomfort or distress. 
• Inability to lie flat or cough due to respiratory distress. 
• Inability to complete full sentence. 
• Oxygen therapy.
• Fluid assessment. 
• Respiratory focused assessment 

Respiratory focused assessment 

Inspection 

• Normal
• Pink, moist mucous membranes 
• Mucoid sputum 
• Symmetrical breathing pattern 
• Midline trachea 
• Abnormal
• Pallor or cyanosis dry mucous membranes
• Mucopurulent, purulent, blood in sputum 
• Respiratory asymmetry dyspnoea, tachypnoea. Chest wounds, drains scarring 
• Tracheal deviation 

Palpation 

• Normal
• Bilateral chest expansion non-tender
• Abnormal 
• Unilateral and reduced expansion. 
• Subcutaneous emphysema 
• Localized pain across chest

Percussion 

• Normal 
• Tympanic/resonant in all zones.
• Abnormal 
• Dull/hyper-resonant in all or some zones

Auscultation 

• Normal
• Patient airway 
• Normal breath sounds throughout chest
• Abnormal 
• Stridor
• Abnormal breath sounds, wheeze, crackles, pleural rub, diminished breath sounds

Normal breath sounds 

• Tracheal- heard over the trachea as very loud, harsh, and high-pitched.         
•  Inspiration duration < expiration duration 
• Bronchial- heard over the manubrium as loud, harsh, and high-pitched.           
• Inspiration duration = expiration duration 
• Bronchovesicular- heard below the clavicles, between the scapula as medium pitched.
•  Inspiration = expiration duration 
• Vesicular - heard over areas of lung tissue as soft and low pitched.                        
•  Inspiration duration > expiration duration. 

If the trachea is not in the midline it may be deviated toward the site of injury, as in the case of lung collapse, or away from the site of injury, as in pneumthorax. Note that tracheal deviation is a late sign of respiratory pathology. 

Respiratory landmarking

Any abnormal findings during the health history and physical assessment should be documented and reported according to the specific area of the chest where the abnormality was identified. 

Abnormal percussion sounds

• Dullness - indicates a solid structure, a consolidated or collapsed area of lung or a fluid-filled area, which produce a dull note on percussion. 
• Cause include pleural effusion, infection, and lung collapse. 
• Hyper-resonance - indicates a hollow structure, which produce a hyper-resonant note on percussion. 
• Causes include pneumothorax. 

Abnormal breath sounds

• Wheeze - indicates airway restriction which is typically heard on expiration. An inspiratory wheeze indicates severe airway narrowing. High-pitched when produced in small bronchioles, and low pitched when produced in large bronchi. Monophonic (i.e. single pitch) when heard in an isolated area,  and polyphonic ( i.e. multi-pitched) when heard throughout the lung area.
• Causes include bronchoconstriction, airway inflammation, secretions, and obstruction. 
• Crackles - indicate instability of airway collapsing on expiration. Fine crackles can be heard in small airway, and coarse crackles can be heard in large airway. 
• Causes include pulmonary oedema, secretions, atelectasis, and fibrosis. 
• Pleural rub - indicates inflammation of the parietal and visceral layers of the pleura. Stiff creaking sound heard throughout inspiration and expiration. 
• Causes include pleurisy. 
• Diminished and absent breath sounds- indicate lack of ventilation and respiration. 
• Causes include pneumothorax, pleural effusion, gas trapping, and collapse. 

Causes of key abnormality 

• Consolidation - pneumonia. 
• Collapse - post operative, mucus plugs.
• Pleural effusion - transudate (heart failure ), exudate (neoplasm), empyema.
• Pneumthorax - bullae rupture, trauma (penetrating chest injury )
• Bronchiectasis - tuberculosis, allergic reaction, cystic fibrosis. 

Respiratory Monitoring

Specific respiratory monitoring may be indicated during the care of a critically ill patient. An understanding of the indications and practices associated with these monitoring devices will ensure accuracy of the results. In addition to the respiratory monitoring described in this section, the following systems will provide further support for the respiratory assessment and care of the patient: chest X-ray, mechanical ventilation waveform analysis and blood gas,

Pulse oximetry

This provides continuous, non invasive measurement of oxygen saturation in atrial blood (SpO2). Pulse oximetry is used to asses for hypoxaemia,to detect variations from the patients oxygenation baseline ( e.g. due to procedures or activity level), and to support the use of oxygen therapy.

Method

A probe is placed over a digit, earlobe.cheek, or the bridge of the nose. It emits light at two specific wavelengths-red and infrared. Light passes through the tissue and is sensed by a photodetector at the base of the probe. Most of the emitted light is absorbed by skin (including pigment), bone, connective tissue, and venous vessels (baseline measurement). This amount is constant, so the only relevant fluctuations are caused by increase blood flow during systole. The peak and troughs of the pulsatile and baseline absorption foe each wavelength are detected and the ratios of each are compared. This provide the ratio of oxyhaemoglobin to total haemoglobin (i.e. the saturation). Oxygen content dissolved in plasma is 3% and that bound to haemoglobin is 97%.

Pulse oximetry measures the oxygen content bound to haemoglobin, not the oxygen content dissolved in the blood. Consequently an anaemic patient may still have an oxygen saturation of 100%

It also does not identify whether the patient is making any respiratory effort, oxygen consumption, or carbon dioxide retention.

Limitations

• Accuracy is within 2% only when the SpO2 is less than  70%
• Haemoglobin abnormality-for example, carboxyhaemoglobin (as a result of carbon monoxide poisoning or smoke inhalation) or methaemoglobinaemia ( due to local anesthetics, antibiotics, or radio-opaque dyes).
• Impaired peripheral perfusion-due to hypothermia, hypovolaemia, peripheral vascular disease, or vasoconstriction (distal to blood pressure cuff)
• Heart rate abnormality-weak, arrhythmia, absent.
• Impaired light absorption -due to nail polish, high bilirubin concentration
• Motion artefact -tremor, shivering, ill-fitting probe.

Ongoing care 

• Attach the probe securely.
• Conform that there is a clear pulsatile waveform.
• Set alarm limits-individualized to the patient.
• Observe the probe site 4-hourly for pressure ulceration.
• Confirm abnormal reading with other assessment findings, such as ABG.

Capnography

This provide a measurement of carbon dioxide (CO2) with a continuous waveform at the end of expiration- that is, end tidal CO2 (ETCO2). Capnography is used to assess the adequacy of ventilation, to detect oesophageal intubation (i.e. very little or no CO2 is detected ), to indicate disconnection from the ventilator, and to diagnose circulatory problems,such as pulmonary edema (sudden fall in ETCO2)

Method

Most analysers utilize infrared absorption spectroscopy, whereby the infrared light is absorbed by CO2 at a specific wavelength (4.3 millimicrons). Since the amount of light absorbed is proportional to the concentration of CO2 gas molecules, the concentration of O2 can determined by comparing the measured absorption is expressed as a partial pressure in kPa.

 A large difference between ETCO2  and PaCO2 may represent an increase in the dead space to tidal volume ratio, poor pulmonary perfusion, auto-positive end expiratory pressure (auto-peep), or intra-pulmonary shunting. 

 A progressive rise in ETCO2 may represent hypoventilation, air-way obstruction, or increased CO2 production due to an increase in metabolic rate.

Limitations 

The ETCO2 approximates to PaCO2 only if the patient shows cardiorespiratory stability and is normothermic. It is not so reliable in patients with respiratory failure-for example, ventilation/perfusion mismatch or significant gas trapping (e.g. asthma )

Capnogram

There are four phase

Phase1

Gas is sampled during the start of expiration from the anatomical and sampling device dead space. The concentration of CO2 level is significant this indicates re-breathing of exhaled gas. The commonest causes are failure of the expiratory valve to open during mechanical ventilation, or an inadequate amount of fresh gas in the reservoir of a non- rebreathing face mask.

Phase2 

Gas is sampled from the alveolar gas. The concentration of CO2 rapidly rises.

Phase 3 

This is known as the alveolar plateau, and it represents the CO2 concentration in mixed expired alveolar gas. There is normally a slight increase in CO2 concentration as alveolar gas exchange continues during expiration.  Airway obstruction or a high rate of CO2 production will increase the slope. The gradient can indicate ventilation/perfusion mismatch. 

Phase 4

As inspiration begins there is a rapid fall in the concentration of CO2.

Peak flow meter

This provides a measurement of peak expiratory flow rate (PEFR). Peak flow is used to assess the trends in airway obstruction, but the accuracy of the result is dependent on patient effort. As it is a measure of airflow it cannot detect restrictive ventilatory defects, such as those caused by pulmonary fibrosis, as these reduce lung volume but do not affect airflow. 

Method

The patient is required to take a full breath in and produce a rapid forced maximal expiratory puff in to the single-use mouthpiece attached to the meter. The result is recorded in L/min and is interpreted according to the patient's age, gender, and height. Peak flows can be checked twice daily, preferably at the same time.