Arterial blood gas (ABG) interpretation is crucial in evaluating a patient’s respiratory gas exchange and acid-base balance. While the normal values on an ABG may slightly vary between analysers, they generally fall within the following ranges: pH of 7.35 – 7.45, pO2 of 10 – 14 kPa, PCO2 of 4.5 – 6 kPa, HCO3- of 22 – 26 mmol/l, and base excess of -2 – 2 mmol/l.

In this particular case, the patient’s medical history raises concerns about a potential diagnosis of pulmonary embolism. The relevant ABG findings are as follows: significant hypoxia (indicating type 1 respiratory failure), elevated pH (alkalaemia), low PCO2, and normal bicarbonate levels. These findings suggest that the patient is experiencing primary respiratory alkalosis.

By analyzing the ABG results, healthcare professionals can gain valuable insights into a patient’s respiratory function and acid-base status, aiding in the diagnosis and management of various conditions.

The recommended daily oral dose for adults is 900 mg, which should be taken in 2-3 divided doses. For severe asthma or COPD, the initial intravenous dose is 5 mg/kg and should be administered over 10-20 minutes. This can be followed by a continuous infusion of 0.5 mg/kg/hour. In the case of a patient weighing 50 kg, the appropriate loading dose would be 250 mg. It is important to note that the therapeutic range for aminophylline is narrow, ranging from 10-20 microgram/ml. Therefore, it is beneficial to estimate the plasma concentration of aminophylline during long-term treatment.

COHb is a measure used to evaluate the presence of carbon monoxide poisoning in individuals who are in good health. hHb refers to deoxygenated haemoglobin.

Further Reading:

Methaemoglobinaemia is a condition where haemoglobin is oxidised from Fe2+ to Fe3+. This process is normally regulated by NADH methaemoglobin reductase, which transfers electrons from NADH to methaemoglobin, converting it back to haemoglobin. In healthy individuals, methaemoglobin levels are typically less than 1% of total haemoglobin. However, an increase in methaemoglobin can lead to tissue hypoxia as Fe3+ cannot bind oxygen effectively.

Methaemoglobinaemia can be congenital or acquired. Congenital causes include haemoglobin chain variants (HbM, HbH) and NADH methaemoglobin reductase deficiency. Acquired causes can be due to exposure to certain drugs or chemicals, such as sulphonamides, local anaesthetics (especially prilocaine), nitrates, chloroquine, dapsone, primaquine, and phenytoin. Aniline dyes are also known to cause methaemoglobinaemia.

Clinical features of methaemoglobinaemia include slate grey cyanosis (blue to grey skin coloration), chocolate blood or chocolate cyanosis (brown color of blood), dyspnoea, low SpO2 on pulse oximetry (which often does not improve with supplemental oxygen), and normal PaO2 on arterial blood gas (ABG) but low SaO2. Patients may tolerate hypoxia better than expected. Severe cases can present with acidosis, arrhythmias, seizures, and coma.

Diagnosis of methaemoglobinaemia is made by directly measuring the level of methaemoglobin using a co-oximeter, which is present in most modern blood gas analysers. Other investigations, such as a full blood count (FBC), electrocardiogram (ECG), chest X-ray (CXR), and beta-human chorionic gonadotropin (bHCG) levels (in pregnancy), may be done to assess the extent of the condition and rule out other contributing factors.

Active treatment is required if the methaemoglobin level is above 30% or if it is below 30% but the patient is symptomatic or shows evidence of tissue hypoxia. Treatment involves maintaining the airway and delivering high-flow oxygen, removing the causative agents, treating toxidromes and consider giving IV dextrose 5%.

The presence of certain clinical features can indicate the possibility of acute severe asthma in children over the age of 5. These features include oxygen saturations below 92%, peak flow measurements below 50% of what is expected, a heart rate exceeding 120 beats per minute, a respiratory rate exceeding 30 breaths per minute, and the use of accessory muscles.

Tension pneumothorax is a condition characterized by certain clinical signs. These signs include pulsus paradoxus, which is an abnormal decrease in blood pressure during inspiration; elevated JVP or distended neck veins; diaphoresis or excessive sweating; and cyanosis, which is a bluish discoloration of the skin. Tracheal deviation to the left is often observed in patients with a right-sided pneumothorax. On the affected side, hyper-resonance and absent breath sounds can be expected. Patients with tension pneumothorax typically appear agitated and distressed, and they experience noticeable difficulty in breathing. Hypotension, a pulse rate exceeding 135 bpm, pulsus paradoxus, and elevated JVP are additional signs associated with tension pneumothorax. These signs occur because the expanding pneumothorax compresses the mediastinum, leading to impaired venous return and cardiac output.

Further Reading:

A pneumothorax is an abnormal collection of air in the pleural cavity of the lung. It can be classified by cause as primary spontaneous, secondary spontaneous, or traumatic. Primary spontaneous pneumothorax occurs without any obvious cause in the absence of underlying lung disease, while secondary spontaneous pneumothorax occurs in patients with significant underlying lung diseases. Traumatic pneumothorax is caused by trauma to the lung, often from blunt or penetrating chest wall injuries.

Tension pneumothorax is a life-threatening condition where the collection of air in the pleural cavity expands and compresses normal lung tissue and mediastinal structures. It can be caused by any of the aforementioned types of pneumothorax. Immediate management of tension pneumothorax involves the ABCDE approach, which includes ensuring a patent airway, controlling the C-spine, providing supplemental oxygen, establishing IV access for fluid resuscitation, and assessing and managing other injuries.

Treatment of tension pneumothorax involves needle thoracocentesis as a temporary measure to provide immediate decompression, followed by tube thoracostomy as definitive management. Needle thoracocentesis involves inserting a 14g cannula into the pleural space, typically via the 4th or 5th intercostal space midaxillary line. If the patient is peri-arrest, immediate thoracostomy is advised.

The pathophysiology of tension pneumothorax involves disruption to the visceral or parietal pleura, allowing air to flow into the pleural space. This can occur through an injury to the lung parenchyma and visceral pleura, or through an entry wound to the external chest wall in the case of a sucking pneumothorax. Injured tissue forms a one-way valve, allowing air to enter the pleural space with inhalation but prohibiting air outflow. This leads to a progressive increase in the volume of non-absorbable intrapleural air with each inspiration, causing pleural volume and pressure to rise within the affected hemithorax.

Pertussis, also known as whooping cough, is a respiratory infection caused by the bacteria Bordetella pertussis. Despite being a bacterial disease, antibiotics do not change the course of the illness once it has taken hold. However, macrolide antibiotics have been proven to shorten the period of contagiousness. Therefore, it is important to administer antibiotics as soon as possible after the onset of symptoms to eliminate the bacteria and reduce further transmission. It is crucial to start antibiotics within three weeks of symptom onset, as they do not affect the progression of the illness or the contagious period.

First-line treatment for pertussis includes macrolide antibiotics. For babies under one month old, clarithromycin is recommended. For children one month and older, as well as non-pregnant adults, azithromycin or clarithromycin are the preferred options. Pregnant women should be treated with erythromycin. In cases where macrolides are not suitable or well-tolerated, co-trimoxazole can be used off-label.

Bronchiolitis is a common respiratory infection that primarily affects infants. It typically occurs between the ages of 3-6 months and is most prevalent during the winter months from November to March. The main culprit behind bronchiolitis is the respiratory syncytial virus, accounting for about 70% of cases. However, other viruses like parainfluenza, influenza, adenovirus, coronavirus, and rhinovirus can also cause this infection.

The clinical presentation of bronchiolitis usually starts with symptoms resembling a common cold, which last for the first 2-3 days. Infants may experience poor feeding, rapid breathing (tachypnoea), nasal flaring, and grunting. Chest wall recessions, bilateral fine crepitations, and wheezing may also be observed. In severe cases, apnoea, a temporary cessation of breathing, can occur.

Bronchiolitis is a self-limiting illness, meaning it resolves on its own over time. Therefore, treatment mainly focuses on supportive care. However, infants with oxygen saturations below 92% may require oxygen administration. If an infant is unable to maintain oral intake or hydration, nasogastric feeding should be considered. Nasal suction is recommended to clear secretions in infants experiencing respiratory distress due to nasal blockage.

It is important to note that there is no evidence supporting the use of antivirals (such as ribavirin), antibiotics, beta 2 agonists, anticholinergics, or corticosteroids in the management of bronchiolitis. These interventions are not recommended for this condition.

This individual, who has been smoking for a long time, is likely to have squamous cell carcinoma of the lung located at the right apex. This particular type of cancer is causing Pancoast’s syndrome. Pancoast’s syndrome typically presents with rib erosion, leading to severe shoulder pain, as well as Horner’s syndrome due to the infiltration of the lower part of the brachial plexus. Additionally, there may be hoarseness of the voice and a ‘bovine cough’ due to a concurrent recurrent laryngeal nerve palsy.

The classic description of Horner’s syndrome includes the following clinical features on the same side as the tumor: miosis (constricted pupil), ptosis (drooping eyelid), anhidrosis (lack of sweating), and enophthalmos (sunken appearance of the eye). A chest X-ray would be able to detect the presence of the apical tumor and confirm the diagnosis.

This individual has presented with an episode of acute asthma. Upon assessment, his initial peak flow is measured at 55% of his personal best, indicating a moderate exacerbation. In such cases, it is recommended to administer steroids, with a suggested dose of prednisolone 40-50 mg taken orally as the initial management step.

Currently, the use of nebulized magnesium sulfate is not recommended for the treatment of acute asthma in adults. However, according to the current ALS guidelines, in severe or life-threatening asthma cases, IV aminophylline can be considered after seeking senior advice. If used, a loading dose of 5 mg/kg should be given over 20 minutes, followed by an infusion of 500-700 mcg/kg/hour. It is important to maintain serum theophylline levels below 20 mcg/ml to prevent toxicity.

In situations where inhaled therapy is not possible, such as when a patient is receiving bag-mask ventilation, IV salbutamol can be considered at a slow dose of 250 mcg. However, it should be noted that there is currently no evidence supporting the use of leukotriene receptor antagonists, like montelukast, in the management of acute asthma.

The BTS guidelines classify acute asthma into four categories: moderate, acute severe, life-threatening, and near-fatal. Moderate asthma is characterized by increasing symptoms and a peak expiratory flow rate (PEFR) between 50-75% of the individual’s best or predicted value, with no features of acute severe asthma. Acute severe asthma is identified by a PEFR of 33-50% of the best or predicted value, along with respiratory rate >25/min, heart rate >110/min, or the inability to complete sentences in one breath.

Life-threatening asthma is indicated by a PEFR <33% of the best or predicted value, SpO2 <92%, PaO2 <8 kPa, normal PaCO2 (4.6-6.0 kPa), and additional symptoms such as silent chest, cyanosis, poor respiratory effort, arrhythmia, exhaustion, altered conscious level, or hypotension. Near-fatal asthma is characterized by raised PaCO2 and/or the need for mechanical ventilation with raised inflation pressures.

The most probable diagnosis in this situation is Goodpasture’s syndrome, a rare autoimmune vasculitic disorder characterized by three main symptoms: pulmonary hemorrhage, glomerulonephritis, and the presence of anti-glomerular basement membrane (Anti-GBM) antibodies. Goodpasture’s syndrome is more prevalent in men, particularly in smokers. It is also associated with HLA-B7 and HLA-DRw2.

The clinical manifestations of Goodpasture’s syndrome include constitutional symptoms like fever, fatigue, nausea, and weight loss. Patients may also experience hemoptysis or pulmonary hemorrhage, chest pain, breathlessness, and inspiratory crackles at the lung bases. Anemia due to bleeding within the lungs, arthralgia, rapidly progressive glomerulonephritis, hematuria, hypertension, and rarely hepatosplenomegaly may also be present.

Blood tests will reveal iron deficiency anemia, an elevated white cell count, and renal impairment. Elisa for Anti-GBM antibodies is highly sensitive and specific, but it is not widely available. Approximately 30% of patients may also have circulating antineutrophilic cytoplasmic antibodies (ANCAs), although these are not specific for Goodpasture’s syndrome and can be found in other conditions such as Wegener’s granulomatosis, which also cause renal impairment and pulmonary hemorrhage.

Diagnosis is typically confirmed through a renal biopsy, which can detect the presence of anti-GBM antibodies. This would be the most appropriate investigation to confirm the diagnosis in this case.

The management of Goodpasture’s syndrome involves a combination of plasmapheresis to remove circulating antibodies and the use of corticosteroids or cyclophosphamide.