Respiratory
Question 76 of 180
You are observing a medical student assess a 23 year old man who presents to the Emergency Department with a 2 hour history of shortness of breath. He has a past medical history of asthma and you suspect this is an exacerbation of his condition. The medical student wishes to commence nebulised salbutamol. What is the dose and frequency of nebulised salbutamol in this situation?
Answer:
- In patients with severe asthma that is poorly responsive to an initial bolus dose of β2 agonist, repeat doses of β2 agonists at 15 - 30 minute intervals or consider continuous nebulisation of salbutamol at 5 - 10 mg/hour (requires the appropriate nebuliser).
Acute Asthma
Respiratory
Last Updated: 4th August 2021
Healthcare professionals must be aware that patients with severe asthma and one or more adverse psychosocial factors are at risk of death.
Initial assessment
- Clinical features
- Dyspnoea
- Tachypnoea
- Tachycardia
- Wheezing
- Silent chest
- Cyanosis
- Accessory muscle use
- Altered consciousness
- Collapse
- Peak expiratory flow (PEF) or FEV1
- Peak expiratory flow rate (PEF) or FEV1 are useful and valid measures of airway calibre, and thus of the degree of severity of asthma. PEF is more convenient in the acute situation.
- PEF expressed as a percentage of the patient’s previous best value is most useful clinically, however PEF as a percentage of predicted (dependent on age, height and sex) gives a rough guide in the absence of a known previous best value.
- Pulse oximetry
- Measurement of oxygen saturations (SpO2) determine the need for or adequacy of oxygen therapy and the need for arterial blood gas measurement.
- SpO2 should be maintained between 94 - 98%.
- Blood gases
- Patients with SpO2 ≤ 92% (regardless of whether the patient is on air or oxygen) or other features of life-threatening asthma require arterial blood gas measurement.
- SpO2 < 92% is associated with a risk of hypercapnia which is not detected with pulse oximetry (the risk of hypercapnia with SpO2 > 92% is much less).
- Chest x-ray
- Chest x-ray is not routinely recommended in the absence of:
- Suspected pneumomediastinum or pneumothorax
- Suspected consolidation
- Life-threatening asthma
- Failure to respond to treatment satisfactorily
- Requirement for ventilation
- Chest x-ray is not routinely recommended in the absence of:
Classification
Levels of severity of acute asthma attacks in adults:
| Level of severity | Criteria |
|---|---|
| Moderate |
|
| Severe | Any one of:
|
| Life-threatening | Any one of the following in a patient with severe asthma:
|
| Near-fatal | Raised PaCO2 and/or requiring mechanical ventilation with raised inflation pressures |
Management
- Oxygen therapy
- Give controlled supplementary oxygen to all hypoxaemic patients with acute severe asthma titrated to maintain an SpO2 level of 94 - 98%.
- Do not delay oxygen administration in the absence of pulse oximetry but commence monitoring of SpO2 as soon as it becomes available.
- β2-agonist bronchodilators
- Use high-dose inhaled β2 agonists as first-line agents in patients with acute asthma and administer as early as possible.
- There is no evidence for any difference in efficacy between salbutamol, terbutaline or adrenaline.
- In patients with mild to moderate asthma, β2 agonists can be administered by repeated activations of a pMDI via an appropriate large volume spacer.
- In patients with acute asthma with acute-severe or life-threatening features, the nebulised route is recommended.
- Nebulisers for giving β2 agonists should preferably be driven by oxygen.
- In patients with severe asthma that is poorly responsive to an initial bolus dose of β2 agonist, repeat doses of β2 agonists at 15 - 30 minute intervals or consider continuous nebulisation of salbutamol at 5 - 10 mg/hour (requires the appropriate nebuliser).
- Reserve intravenous β2 agonists for those patients in whom inhaled therapy cannot be used reliably. If intravenous β2 agonists are used, consider monitoring serum lactate to monitor for toxicity.
- Ipratropium bromide
- Add nebulised ipratropium bromide (0.5 mg 4 – 6 hourly) to β2 agonist treatment for patients with acute severe or life threatening asthma or those with a poor initial response to β2 agonist therapy.
- Steroid therapy
- Give steroids in adequate doses to all patients with an acute asthma attack.
- Steroid tablets are as effective as injected steroids provided they can be swallowed and retained.
- Prednisolone 40 – 50 mg or hydrocortisone 400 mg daily (100 mg six hourly) are as effective as higher doses.
- Continue prednisolone 40 – 50 mg daily until recovery (minimum 5 days).
- Do not stop inhaled corticosteroids during prescription of oral corticosteroids.
- Other therapies:
- Magnesium sulphate
- Nebulised magnesium sulphate is not recommended for treatment of adults with acute asthma.
- Consider giving a single dose of IV magnesium sulphate to patients with acute severe asthma (PEF < 50% best or predicted) who have not had a good initial response to inhaled bronchodilator therapy.
- Magnesium sulphate (1.2 - 2 g IV infusion over 20 minutes) should only be used following consultation with senior medical staff.
- Aminophylline
- In an acute asthma attack, IV aminophylline is not likely to result in any additional bronchodilation compared to standard care with inhaled bronchodilators and steroids and may cause side effects such as arrhythmias and vomiting.
- Following consultation with senior medical staff, consider IV aminophylline only in life-threatening or near-fatal asthma.
- Antibiotics
- Routine prescription of antibiotics is NOT indicated for patients with acute asthma.
- Magnesium sulphate
Criteria for hospital admission
- Admit patients with any feature of a life-threatening or near-fatal asthma attack
- Admit patients with any feature of a severe asthma attack persisting after initial treatment
- Patients whose peak flow is greater than 75% best or predicted one hour after initial treatment may be discharged from ED unless they meet any of the following criteria, when admission may be appropriate:
- Still have significant symptoms
- Concerns about adherence
- Living alone/socially isolated
- Psychological problems
- Physical disability or learning difficulties
- Previous near-fatal asthma attack
- Asthma attack despite adequate dose of oral corticosteroid prior to presentation
- Presentation at night
- Pregnancy
Criteria for ITU/HDU referral
Refer any patient:
- Requiring ventilatory support
- With acute severe or life-threatening asthma, who is failing to respond to therapy, as evidenced by:
- Deteriorating PEF
- Persisting or worsening hypoxia
- Hypercapnia
- ABG analysis showing decreased pH or increased H+
- Exhaustion, feeble respiration
- Drowsiness, confusion, altered conscious state
- Respiratory arrest
Follow up
- It is essential that the patient's primary care practice is informed with 24 hours of discharge from the emergency department or hospital following an asthma attack
- Keep patients who have had a near-fatal attack under specialist supervision indefinitely
- A respiratory specialist should follow up patients admitted with a severe asthma attack for at least one year after the admission
Cardiac arrest associated with asthma
Patients most at risk of asthma-related cardiac arrest include those with:
- a history of near-fatal asthma requiring intubation and mechanical ventilation
- hospitalisation or emergency care for asthma in the past year
- low or no use of inhaled corticosteroids
- increasing use and dependence on β2-agonists
- anxiety, depressive disorders and/or poor compliance with therapy
- a history of food allergy in addition to asthma
Causes of cardiac arrest associated with asthma include:
- Severe bronchospasm and mucous plugging leading to asphyxia
- Cardiac arrhythmias caused by hypoxia (or by treatment drugs e.g. β2-agonists or electrolyte abnormalities)
- Dynamic hyperinflation (auto positive end-expiratory pressure (auto-PEEP)) in mechanically ventilated patients; air trapping and 'breath-stacking' causes gradual build up of pressure leading to decreased venous return and blood pressure
- Tension pneumothorax (may be bilateral)
Modifications to resuscitation associated with asthma:
- Follow standard BLS and ALS protocols; ventilation will be difficult because of increased airway resistance; try to avoid gastric inflation
- Intubate the trachea early; there is significant risk of gastric inflation and hypoventilation of the lungs when attempting to ventilate a severe asthmatic without a tracheal tube
- Follow the recommended respiratory rate of 10 breaths/min and tidal volume required for a normal chest rise during CPR (to avoid gas trapping and dynamic hyperinflation)
- If dynamic hyperinflation of the lungs is suspected during CPR, compression of the chest wall and/or a period of apnoea (disconnection of tracheal tube) may relieve gas trapping
- Dynamic hyperinflation increases transthoracic impedance but modern defibrillators are no less effective in patients with higher impedance; as with standard ALS protocol, consider increasing defibrillation energy if the first shock is unsuccessful
- Look for reversible causes using the 4Hs and 4Ts
- Tension pneumothorax can be difficult to recognise during cardiac arrest; it may be indicated by unilateral expansion of the chest wall, shifting of the trachea and subcutaneous emphysema; pleural ultrasound in skilled hands is faster and more sensitive than chest x-ray for detection; early needle decompression followed by chest drain insertion is needed; thoracostomy may be quicker and more effective in the ventilated patient; always consider bilateral pneumothoraces in asthma-related cardiac arrest
- Extracorporeal life support (ECLS) can provide both organ perfusion and gas exchange in cases of otherwise refractory respiratory and circulatory failure
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
