Introduction

Asthma is a chronic condition that causes respiratory tract inflammation and airway obstruction. It is a serious disease that affects about 300 million people globally and is characterised by shortness of breath, wheezing, chest tightness, and cough.¹ 

In status asthmaticus, severe asthma attacks that don’t respond to initial treatment and near-fatal asthma progressing to acute respiratory failure, patients require treatment in the ICU. Most of them need to receive ventilatory support either by noninvasive ventilation (NIV) or tracheal intubation.² 

Understanding acute respiratory failure in asthma

Acute respiratory failure is a condition that makes it impossible for the lungs to eliminate carbon dioxide extract oxygen from inhaled gas, or both.³ It has a mortality rate of at least 30% and contributes to 25–40% of ICU admissions.

According to its basic physiological abnormalities, there are two main forms of acute respiratory failure:

Airway disorders

Disorders of the airways, where the need for ventilators and pharmaceutical treatment is determined by increased resistance to airflow.. These conditions are among both chronic obstructive pulmonary disease and asthma.

Alveolar disorders

Disorders of the alveoli, in which the utilisation of higher ventilatory pressures—which might help open up the lungs but also damage the lung—are required due to a decrease in lung flexibility. Some of these conditions include acute respiratory distress syndrome, influenza, pneumonia, and acute cardiogenic pulmonary oedema.² 

Insights into hypoxemic and hypercapnic respiratory failure in asthma: pathophysiology and clinical characteristics

Hypoxemic respiratory failure (type I) in the early stages of asthma is characterised by a blood pressure of oxygen (PaO2) less than 60 mm Hg (a low level of oxygen in the blood)  and an abnormally low or abnormal blood pressure of carbon dioxide (PaCO2), as measured by arterial blood gas examination. 

This is the most prevalent type of respiratory failure that most acute lung disorders cause, and it's usually brought on by fluid filling or alveolar unit collapse (making it harder for the lungs to work). 

As the disease process causes increasing airway blockage, there is less oxygen accessible in the distal airways for absorption through the pulmonary capillaries. These lung units have a drop in blood flow due to hypoxic pulmonary vasoconstriction, but this decline is not as great as the one seen in oxygen availability.

Hypercapnic respiratory failure (type II) is caused by excessive CO₂ production or decreased effective alveolar ventilation and is characterised by a PaCO2 higher than 50 mm Hg, which will result from a prolonged asthmatic crisis. The bicarbonate level (a chemical that helps balance the blood's acidity) is a function of the pH and is dependent on the duration of the hypercapnia.⁴ 

Risk factors linked to a higher chance of dying from asthma

• History of severe, sudden exacerbation
• Previous asthma intubation
• Previous ICU admission for asthma
• At least two asthma-related hospital stays within the previous year
• At least three asthma-related ER visits within the previous year
• Hospitalisation or an asthma emergency room visit in the previous month
• Using two or more SABA canisters (inhalers with fast-acting medication for quick asthma relief) for inhalation each month
• Use of systemic corticosteroids either now or recently discontinued
• Difficulty recognising the presence or extent of an airflow blockage
• Comorbidity (chronic obstructive pulmonary disease or cardiovascular respiratory illness)
• Severe mental illness or psychological issues
• Use of illicit drugs

For individuals who have asthma mortality, risk factors should be managed quickly and aggressively.⁵ 

Management and prevention of acute respiratory failure in asthmatic patients 

The prevention of acute respiratory failure can be achieved by assessing asthma severity, educating asthmatic patients, and managing asthma attacks.

Initially managing patients who don't need mechanical ventilation 

Supplementing with oxygen

When a patient presents with an asthmatic exacerbation, the first step in treating them is to correct substantial hypoxaemia with oxygen. Prehospital healthcare professionals should initiate supplemental oxygen therapy. It is advised to supply oxygen to keep O₂ saturation at SaO2 >90% (>95% in pregnant patients or coexisting cardiac conditions). Oxygen saturation should be observed until there has been a response to bronchodilator medication.⁵

Using inhaled bronchodilators

SABAs

When a patient presents with an acute asthma attack, inhaled SABAs continue to be the cornerstone of treatment.

Many β2-selective SABAs are in use, including pirbuterol, bitolterol, and albuterol (salbutamol). When compared to nonselective medicines, β2 selective drugs have a lower risk of cardiotoxicity at high doses, which makes them favoured.⁵

Anticholinergics

Ipratropium bromide should be regarded as an additional treatment, even if β2 agonists are the preferred (first-line) bronchodilators for treating an acute asthmatic exacerbation.⁵

Corticosteroids

For the majority of individuals experiencing an acute asthmatic exacerbation, systemic corticosteroids are advised. In the outpatient treatment of asthma, systemic corticosteroids have been demonstrated to cause a considerably higher and faster clearance of airway obstruction, lower the rate of hospitalisations, and avoid reoccurrence.

It has also been demonstrated that inhaled corticosteroids lower hospital admission rates.⁵ 

Non-invasive ventilation

Noninvasive ventilation (NIV) is effective in the treatment of hypercapnic respiratory failure resulting from an acute exacerbation of asthma. 

Larger, randomised trials are still required, even if the use of noninvasive ventilation in individuals experiencing an acute asthmatic exacerbation appears promising.

However, there are restrictions on noninvasive ventilation. It ought to just applied to patients who are cooperative and awake. Additionally, it is not suitable for individuals requiring regular suctioning or airway protection, as well as those with facial trauma

Invasive mechanical ventilation

When a patient presents with status asthmaticus, the necessity of mechanical ventilation varies greatly. Intubation and mechanical breathing are typically indicated in cases of progressive hypercapnia, obtundation, and the impending collapse of the heart.

Mechanical ventilation is not necessary when hypercapnia is present alone.⁵

Endotracheal intubation 

It is critical to carry out intubation as soon as it is determined that mechanical ventilation and intubation are required. 

Ideally, this can be done in a controlled environment. To avoid bronchospasm (tightening of the muscles around the airways), the most experienced operator should execute rapid sequence intubation. The easiest way to avoid bronchospasm is to use inhaled albuterol as a pretreatment. It has not been demonstrated that intravenous lidocaine reduces bronchospasm brought on during intubation. 

For patients with status asthmaticus, the oral route is the recommended method of intubation because it permits the use of bigger endotracheal tubes, which reduces airway resistance and improves the suctioning of secretions and mucous plugs. On the other hand, patients who are conscious and require little sedation can undergo nasal intubation.⁵

Long-term monitoring 

Recurrent evaluations are necessary for a patient experiencing respiratory failure. These evaluations can take several forms, from bedside observations to invasive monitoring. These people ought to be brought into a hospital where they can be under constant surveillance. In a critical care setting, continuous monitoring is essential since the majority of patients in need of mechanical ventilation are extremely ill.

It is advised to use capnometry, pulse oximetry, blood pressure, cardiac monitoring, and SaO2. It is recommended to get an arterial blood gas determination 15 to 20 minutes following the initiation of mechanical breathing. Minute ventilation is adjusted based on PaCO2, while efforts to lower FiO2 to a value less than 0.6 are guided by pulse oximetry readings.⁶ 

Summary

Acute respiratory failure is a life-threatening complication of asthma that occurs when the lungs cannot adequately exchange oxygen and carbon dioxide. It is particularly common in severe asthma exacerbations, including status asthmaticus, and often requires intensive care and ventilatory support. There are two types of respiratory failure seen in asthma: hypoxemic (type I), characterised by low oxygen levels, and hypercapnic (type II), marked by elevated carbon dioxide levels.

Effective prevention and management focus on early recognition of risk factors, including a history of severe exacerbations, prior intubations, and frequent hospital admissions. Treatment begins with oxygen supplementation and inhaled bronchodilators, with short-acting beta-agonists (SABAs) as the cornerstone. Corticosteroids help reduce inflammation, and non-invasive ventilation (NIV) may be used for patients with hypercapnic respiratory failure. For more severe cases, invasive mechanical ventilation, including endotracheal intubation, is required.

Long-term management involves regular monitoring of asthma control, patient education, and adjustments to therapy. Preventive strategies are essential to reduce the risk of acute respiratory failure and improve overall patient outcomes.