S E V E R E A S T H M A

M A N A G E M E N T A N D V E N T I L AT I O N S T R AT E G I E S

ASTHMA

Characteristics

– Episodic reversible bronchoconstriction

– Airway inflammation

– Increased mucus production

Consequences

– Increased WOB

• Increased airway resistance/Reduced Compliance

– Type 2 Resp failure – Hypercapnia & Hypoxia

• Impaired gas exchange

• V/Q mismatches

CASE MB

• 28/M

• Hx Asthma – Dx 2011 1 Prior hospital admission 1 yr ago – overnight

• Flixotide preventer, takes PRN Ventolin prior to exercise

• Office job, smoker

• BIBA:

• Unwell 1 week – cough/sputum /SOB/wheezy Has been self treating with Ventolin

• Spoke in words, accessory muscle use, diaphoretic, not confused

• RR 30, Sats 88RA, widespread wheeze

ASTHMA SEVERITY

• Severe

– Unable to speak sentances

– Visible breathlessness/Increased WOB

– O2 sats 90-94%

• Life threatening

– Altered mental state/Drowsy/Collapsed

– Poor Resp Effort/Exhausted/Quiet chest

– Cyanotic/O2 sats <90%

RISK FACTORS

• Previous poor control of asthma

– Frequent ED/hospital presentations

– Previous severe exacerbations / ICU & Intubation etc.

• Treatment received prior to presentation

– Frequency of Ventolin use

– Poor compliance with asthma medications /action plans

• Other factors:

– Smoking/Illicit drug use, psychosocial problems

– Comorbidities - cardiovascular or chronic lung disease

INITIAL TREATMENT

• Aims:

– Rapidly reverse bronchoconstriction

– Correct severe hypercapnia/hypoxemia

• Titrated Oxygen

– Sats 92-95%

• Continuous Inhaled Salbutamol

– Nebulizer/MDI

• Ipatropium

• Magnesium

• Steroids – within 1 hour

CASE MB

• Treated with 3 Ventolin nebs/ipratropium/hydrocort/magnesium

• Initial gases pH 7.15, Normal CO2, bicarb 20, Lac 2.4

• CXR clear

• Initial concerns may require ICU admission

• However clinically improved with treatment

• Reviewed by ICU – planned for HDU

CASE MB

Through the night:

– Drowsy/Tiring

– Increased WOB

– Gases relatively unchanged.

• Contacted HDU&ICU – Busy with another code

• Given cont Ventolin nebs with limited effect

• Started on NIV

ADDITIONAL TREATMENTS

Bronchodilators:

• Intravenous infusions

– Beta agonists

• Salbutamol

• Adrenaline

– Ketamine

• Inhalational Anaesthetic agents

– ICU only

• Helium/oxygens

• Methylxanthines – theophylline/aminophylline

– No longer recommended as adjunct in acute asthma

WOB/Resp failure:

– NIV

– Intubation/ventilation

Clinical indications:

– Falling RR

– Drowsiness

– Exhaustion

– Worsening resp failure

MECH VENTILATION• Mech ventilation in asthma is difficult

– Relatively normal alveolar compliance

– High airway resistance high airway pressures

– Prolonged expiration Risk gas trapping

– Gas trapping increases intrinsic PEEP

– Very high peak airway pressures

– Plateau/insp pause pressures

Flow X Resistance

Vol/Complianc

e

+ PEEP

Alveoli

Bronchioles

MECH VENTILATION

Ventilation aims:

• Adequate oxygenation

• Long expiration times

• Avoid breath stacking / volutrauma

• Slower RR, higher I:E ratios

• Avoid large TV

• Manage/Minimize high airway pressures

• PEEP zero

• Monitor plateau pressures

• Consider Permissive Hypercapnia

– Minimize barotrauma to lungs

– Avoid significant acidosis

NIVADV:

• Reduce Fatigue/work of breathing

• Improve oxygenation/ventilation

– V/Q mismatch

– Gas exchange

– Recruitment

– Prevention athelectasis

DIS:

• Increased risk of barotrauma

• May lead to delayed

intubation/associated complications

• General NIV issues

Uses:

• To avoid intubation

• For preoxygenation/ventilatory support

prior to Intubation

– Ketamine DSI

INDUCTION

• Ketamine

– Drug of choice – bronchodilator

• Consider DSI

– Optimizing patient with Ketamine/NIV prior to intubation

• Prone to hypotension post intubation – caution with propofol etc.

– Breath stacking

– Hypovolemia

– Induction drugs

– Tension PTX

CASE MB

• Reviewed by ICU – Trial of Ketamine and Adrenaline infusions in ED as temporising

measure

• Taken up to ICU – Intubated - Ketamine/NIV prior

• Spent 2 nights intubated and further 5 days on the ward

• Discharged home with Preventer (increased dose)

• Seen further 5 weeks later on a night shift for another exacerbation of asthma…

RESOURCES/REFERENCES

• LITFL

– Acute Severe Asthma http://lifeinthefastlane.com/ccc/acute-severe-asthma/

– NIV & Asthma http://lifeinthefastlane.com/ccc/non-invasive-ventilation-niv-and-asthma/

• Australian Asthma Handbook https://www.asthmahandbook.org.au/

• EMRAP – C3 Asthma Summary Aug 2016 – S Swadron, M Herbert

• TheNNT: Quick Summaries of Evidence Based Medicine http://www.thennt.com/

• Ventilator settings in asthma – James Rippey http://scghed.com/2015/11/updated-

suggested-initial-ventilator-settings-112015/