PH = 7.32 ( less than 7.35) so, we have mild acidaemia.
PCO2 = 48 (on arterial blood gas > 40), so we have respiratory acidosis.
Next step is to calculate the metabolic compensation. Since the condition is acute, we expect the HCO3 to increase by 1 for every 10 PCO2 above 40. Accordingly, expected PCO2 should be 24.8. That is very close to 24. So, there is no additional metabolic process.
Mild lactatemia which can be attributed to dehydration or salbutamol therapy. K = 3.4 (can be also related to salbutamol therapy).
Respiratory acidosis in asthma is a critical situation (severe/ life threatening asthma – even if the acidosis is mild).
This patient should be moved to a resuscitation bay, we should inform emergency, ICU and anesthetic consultants about this patient.
Start treatment immediately. (Hit it hard and hit it fast), our aim is to prevent intubating this patient.
- Continuous nebulized salbutamol and add nebulized ipratropium using 15L O2.
- Obtain 2 IV accesses and administer hydrocortisone immediately. The literature does not support the use of high dose corticosteroids in acute asthma. Hydrocortisone 50 mg 4 times a day for 48 hours, followed by oral prednisone, was as effective as 200 mg or 500 mg of hydrocortisone followed by high dose prednisone.3 The effective dose of oral prednisolone is between 30 mg and 50 mg daily.4 High doses of corticosteroids are associated with increased adverse effects, in particular mood disturbance and myopathy.
- Start IV magnesium in one line, (Rowe BH et al, Cochrane review)- MgSO4 for Treating Exacerbation of Acute Asthma in ED- 665 patients (7 trials). The conclusion was: MgSO4 would seem to have limited benefit in non-severe asthma and dramatic effect in the severe subgroup with NNT=3 ( preventing 1 admission in 3 cases). SO, use MgSO4 early in severe asthma.
- Start IV salbutamol in the other line
- Non invasive ventilation (CPAP vs BiPAP). Systemic review of 492 articles identified from the database search, the conclusion was more research is required. However, BiPAP had better effect on improving the work of breathing for patient with severe asthma.
Non invasive ventilation is severe asthma help to:
- Reduce airways resistance
- Broncho dilate
- Counter Atelectasis
- reduce work of breathing
- help to deliver medication to distal tubules
- reduce the cardiovascular impact of changes in intrapleural and intrathoracic pressure.
Ultimately, NIV in asthmatic patient help in the correction of PH and improves ventilation at a lower pressure than that needed for mechanical ventilation and it reduced the need for intubation.
- PEEP = 3-5 (Low)
- iPAP = 7-15
- High I:E ratio (1:5) with prolonged expiratory time
- Target RR < 25
If the above measures fail then we need to proceed to intubate this patient. For intubation, we use Ketamine as the sedating agent and the intubation should be performed by the most experienced doctor available.