- 08 Apr 2022
- Medical Revision
Do you find revising a long process? Spending endless hours Googling? There's no need with Expanded Explanations - the little box with a lot to offer....
We provide you with a detailed overview of a topic alongside related questions in the bank. Now available in our Med Student Finals, MRCP Part 1, MRCP Part 2, MRCP PACES, MSRA, MRCPCH FOP/TAS, MRCPCH AKP, MRCGP (AKT) and MRCS Part A resources.
Here is an example of an Expanded Explanation for Acute Respiratory Distress Syndrome:
- Severe inflammation of the lungs results in an inefficient supply of oxygen to the body that can be life threatening.
- Acute respiratory distress syndrome (ARDS) is severe inflammation of the lungs resulting in a life-threateningly inefficient supply of oxygen to the body.
- ARDS is usually caused by a serious underlying health condition and most people who develop the condition are already hospitalised due to this.
- ARDS comprises the following:
- acute onset (within one week)
- arterial hypoxaemia
- bilateral, fluffy pulmonary infiltrates on chest X-ray, not explained by effusion/nodules or collapse
- non-cardiogenic pulmonary oedema (pulmonary capillary wedge pressure <18cmH20)
- reduced lung compliance
- Diagnosis is based on a combination of examination and imagining findings.
- The severity of ARDS is classified by the degree of hypoxaemia occurring.
- Management is usually based in an Intensive Care setting with ventilation and supportive measurements as well as treating the underlying cause.
- The mortality rate is around 1/3 of all cases; this is often due to the underlying cause.
- Those that do survive often have no lasting lung damage.
- Most cases of ARDS will occur in patients already admitted to hospital.
- It can develop quickly in the community, such as patients with influenza/pneumonia/aspiration.
- Conditions directly affecting the respiratory system include:
- cardiopulmonary bypass
- pulmonary contusion
- smoke inhalation
- oxygen toxicity
- aspiration of gastric contents
- Other conditions include:
- disseminated intravascular coagulation (DIC)
- pancreatitis, uraemia
- drug overdoses (e.g. diamorphine, methadone, barbiturates, paraquat)
- Damage to capillary endothelium and alveolar epithelium and increased capillary permeability result in an accumulation of protein-rich fluid in the alveoli, causing diffuse alveolar damage.
- Activation of neutrophils causes inflammation and further lung damage.
- Patients with ARDS can present with the following:
- severe shortness of breath
- raised respiratory rate
- shallow breathing
- feeling lightheaded
- Some differential diagnosis of ARDS include:
- panic attack
- diabetic ketoacidosis (in early stages, the breathing in shallow and can progress to Kussmaul breathing, indicating severe metabolic acidosis)
- asthma attack
- carbon monoxide poisoning
- Diagnosis and investigations for ARDS are as follows:
- blood including septic screen, cultures
- blood gases
- pulse oximetry
- chest X-ray - pulmonary oedema, bilateral alveolar shadowing, air bronchograms
- Other investigations may include echocardiogram and urine culture. This depends on the clinical scenario and suspected underlying cause.
- No specific treatment is available for ARDS, and management is essentially supportive.
- Management is guided by the severity of hypoxaemia:
- mild (200 mm Hg < PaO2/FiO = 300 mmHg)
- moderate (100 mm Hg < PaO2/FiO = 200 mmHg)
- severe (PaO2/FiO = 100 mmHg)
- Patients usually require management within the Intensive Care Unit.
- Supplemental oxygen is given and patients frequently require mechanical ventilation:
- pressure-controlled, inverse-ratio ventilation is used because this lowers peak airway pressure, reduces barotrauma and creates better distribution of gas in the lungs
- with the addition of positive end-expiratory pressure (PEEP), there is greater alveolar recruitment, increased functional residual capacity, better lung compliance and reduced shunt
- turning the patient into the prone position intermittently allows those dependent parts of the lung that are susceptible to atelectasis to re-expand and improves blood flow to the ventilated parts of the lung
- Guidelines from the American Thoracic Society/European Society of Intensive Care Medicine/Society of Critical Care Medicine Clinical Practice:
- for all patients with ARDS, the recommendation is strong for mechanical ventilation using lower tidal volumes and lower inspiratory pressures
- for patients with severe ARDS, the recommendation is strong for prone positioning for more than 12 h/d
- for patients with moderate or severe ARDS, the recommendation is strong against routine use of high-frequency oscillatory ventilation and conditional for higher positive end-expiratory pressure and recruitment manoeuvres
- Additional evidence is necessary to make a definitive recommendation for or against the use of extracorporeal membrane oxygenation in patients with severe ARDS.
- Other supportive measures include IV hydration and nutritional support, and venous thromboembolism prophylaxis.
- Sepsis should be treated empirically until causative organisms are identified.
- Inhaled nitric oxide (NO) causes selective vasodilatation of the ventilated areas of the lung when inhaled at low concentrations.
- Corticosteroids have been shown to be beneficial in the latter stages of ARDS (ie progressive pulmonary interstitial fibroproliferation is present).
- The prognosis of ARDS is:
- associated with substantial morbidity
- fatal in 1/3 of cases, though usually due to the underlying illness and not directly as a result of ARDS
- The lungs make a full recovery in most cases of those who survive.
- The use of exogenous surfactant in adult patients has no proven value.
- 08 Apr 2022
- Medical Revision