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Asthma

ASSESSMENT:

 

All cases of adult dyspnoea should be assessed for acuity: 1

 

Note that wheezing is an unreliable sign of asthma.  There are multiple potential causes of wheezes in humans, and life-threatening asthma may present with no wheezes due to a lack of sufficient ventilatory effect to move air.  Decreased SpO2 is also a late sign of asthma and should be interpreted with caution.2 A return to normocarbia from hypocarbia may also be a sign of deterioration as decreased ventilation will result in decreased EtCO2.3 Asthma is better thought of as a disease of gas trapping and hypercarbia than a disease of insufficient inhalation and hypoxia.  The clinical priority is to get carbon dioxide OUT, not to get oxygen IN.

 

TREATMENTS:

General Principles:

  1. If the patient has an asthma management plan it is appropriate to follow it.

  2. If a peak expiratory flow rate (PEFR) meter is available, record values prior and during/subsequent to treatment

Specific Treatments:

  1. Oxygen

    1. Any patient in asthma should be treated with the goal of achieving normoxia.  Deliver oxygen as required.

  2. Salbutamol  

    1. Salbutamol delivered by metered dose inhaler (MDI) is at least as effective as salbutamol delivered via nebuliser 4, and MDI delivery is associated with less fomite transmission of disease.  For these reasons MDI delivery is the preferred initial route of delivery.

    2. MDI

      1. Use a fresh MDI and spacer for each patient

      2. Shake the MDI several times and prime the spacer unit with salbutamol 6-12 puffs (10 x 100 micrograms)4.

      3. Administer salbutamol 100 micrograms (1 puff) and inhale 4 times; repeat to achieve a dose of 1200 micrograms (12 puffs)

      4. Repeat every 10-20 minutes as needed to achieve resolution of symptoms

    3. Nebuliser

      1. 5 mg by nebuliser, repeated as needed to achieve resolution of symptoms 

    4. Intravenous

      1. The risk to benefit ratio of IV salbutamol is unfavourable and there is no added benefit over inhaled salbutamol. 5 IV salbutamol should be reserved for when inhaled salbutamol delivery is not possible. 

      2. 200 micrograms over 1 minute, then an initial infusion of 5 micrograms/minute adjusted according to response; usual rate 10 to 20 micrograms/minute

    5. Monitor for signs of excessive drug delivery: agitation, tremors, tachycardia, ventricular irritability

  3. Ipratropium Bromide 6

    1. MDI: 21 micrograms – up to eight inhalations (total maximum dose of 168 micrograms)

    2. Nebuliser: 500 micrograms, one time only, subsequent to salbutamol  3 7

  4. IV fluids 7

    1. Hyperventilation associated with asthma can lead to dehydration

    2. 250-500 mL normal saline solution, as required, titrating to effect, continue to monitor BP and breath sounds between dosages

  5. Magnesium Sulphate

    1. Evidence for the use of magnesium in asthma is not definitive.  The safety of repeated doses has not been established, and hypermagnesemia may cause muscle weakness, including respiratory muscle weakness. 5

    2. 2.5 g (10 mmol) given over 15-20 minutes, this may be repeated once after 30 minutes if the patient has not improved. 7 8 9 10

  6. Corticosteroids – choose one of: 5

    1. Prednisolone 37.5 to 50 mg oral 10 9

    2. Hydrocortisone 250 mg IV 7

    3. Dexamethasone 8 mg IV/oral 3

  7. CPAP 3 10 11

    1. Apply CPAP at 10 cmH20 if the patient has severe respiratory distress despite treatment, or an SpO2 less than 92% despite treatment.

    2. Use with caution if the patient has an altered level of consciousness, vomiting or signs of shock.  Immediately discontinue and begin positive pressure ventilation if the patient become apnoeic.

  8. Positive Pressure Ventilation 12

    1. Initiate if the patient becomes apnoeic or has inadequate respiratory effort at 5-8 ventilations per minute with a tidal volume of 6-7 mL/kg of lean body weight. 3

  9. Adrenaline

    1. There is no clear support for the use of adrenaline in asthma in the literature.  However a dose of 300-500 micrograms IM, repeated at 5 minute intervals with no maximum dose, is recommended commonly in paramedic CPGs. 1 2 7

  10. Ketamine 9 10

    1. Although ketamine is reported to have some bronchodilatory effects the purpose of ketamine in severe asthma is to calm patients who are extremely agitated and unable to cooperate with treatment (e.g. with MDI or nebuliser administration).

    2. Administer 1 mg/kg intravenously (up to 100 mg) repeating as required to induce dissociation

  11. Endotracheal Intubation 3

    1. Endotracheal intubation is a last-measure treatment in the asthmatic that is ideally to be avoided.  However, if positive pressure ventilation by bag-valve-mask is insufficiently effective then paramedics may consider intubation.

    2. Tension pneumothorax in asthmatic patients with high airway pressures who are intubated is a significant clinical risk that must be diligently assessed for.

  12. External Chest Compression 1 13

    1. Slow, external, manual external chest compressions (squeezing) have been advocated as one possible treatment to mechanically aid in alleviating gas trapping in the asthmatic patient. There is no clear evidence of benefit, but it would not be inappropriate to trial external chest compression as a last-ditch treatment in refractory asthma, while closely monitoring BP.  If there is an alarming drop in BP chest compressions should be discontinued. 14

 

APPROACH:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References:

 

1.        ACT Ambulance Service. CMG 9 - Respiratory Distress. https://esa.act.gov.au/ (2015). Available at: https://esa.act.gov.au/sites/default/files/wp-content/uploads/CMG-9-RESPIRATORY-DISTRESS-Aug-2015-1.pdf.

2.        Queensland Ambulance Service Clinical Quality and Patient Safety Unit. Clinical Practice Guidelines: Respiratory/Asthma. https://www.ambulance.qld.gov.au (2019). Available at: https://www.ambulance.qld.gov.au/docs/clinical/cpg/CPG_Asthma.pdf.

3.        Ambulance Victoria. Clinical Practice Guidelines for Ambulance and MICA Paramedics. https://www.ambulance.vic.gov.au (2018).

4.        National Asthma Council Australia. Acute asthma. Version 2.0. Australian Asthma Handbook (2019).

5.        Therapeutic Guidelines Ltd. Acute asthma in adults and adolescents. https://tgldcdp.tg.org.au (2015). Available at: https://tgldcdp.tg.org.au/viewTopic?topicfile=asthma-acute-management.

6.        Australian Medicines Handbook Pty Ltd. Ipratropium. https://amhonline.amh.net.au (2019). Available at: https://amhonline.amh.net.au/chapters/respiratory-drugs/drugs-asthma-chronic-obstructive-pulmonary-disease/anticholinergics-inhaled/ipratropium-inhaled.

7.        South Australia Ambulance Service Clinical Performance and Safety Unit. CPG-113-ICP Asthma (Adult) V 1.2 20170803. (2017).

8.        Australian Medicines Handbook Pty Ltd. Magnesium sulfate. https://amhonline.amh.net.au (2019). Available at: https://amhonline.amh.net.au/chapters/obstetric-gynaecological-drugs/drugs-obstetrics/drugs-pre-eclampsia/magnesium-sulfate.

9.        St John Ambulance, N. Z. Clinical Procedures and Guidelines, 2019-2021. (2019).

10.      Wellington Free Ambulance. Clinical Procedures and Guidelines. 146–180 doi:10.1016/B978-141604485-7.50013-5

11.      Warner, G. S. Evaluation of the effect of prehospital application of continuous positive airway pressure therapy in acute respiratory distress. Prehosp. Disaster Med. 25, 87–91 (2010).

12.      WJ, L. et al. Non-invasive positive pressure ventilation for treatment of respiratory failure due to severe acute exacerbations of asthma. Cochrane Libr. (2012).

13.      Allan, J., Williams, B. & Fallows, B. Investigating the Benefits of Out-of-Hospital External Chest Compression. Australas. J. Paramed. 5, (2012).

14.      Harrison, R. Chest compression first aid for respiratory arrest due to acute asphyxic asthma. Emerg. Med. J. 27, 59–61 (2010).