ICU Fellowship Snippet – Asthma Management

As the duty locum intensivist you have been called to urgently review a patient on the medical ward of a small private hospital. The patient, Jane, is a 32 year old female who was admitted to the ward yesterday with shortness of breath.

She presents with shortness of breath often, and has recently been started on a bronchodilator. A local GP registrar was on the ward reviewing another patient and noticed that Jane was working very hard to breathe. The registrar emergently intubated her prior to your arrival.

You arrive on the ward 10 minutes post intubation. The registrar and a ward nurse are hand-ventilating Jane, who is hypoxic – sats 85% and hypotensive BP 75/50mmHg. Outline your management.

Written by Dr Madhuri Anupindi

This is an emergency situation requiring simultaneous urgent evaluation and resuscitation to identify and treat the cause and contributors to her deterioration. My approach would be to activate the emergency response team if available in the hospital for extra personnel, and rapidly assess whether this is an issue with the ETT, a peri-intubation event or a deterioration in the patient’s underlying pathology.

• Call for help, allocate roles, ensure maximum oxygen via BVM, resus and airway trolley present, good IV access and small boluses of metaraminol aiming SBP 90mmHg
• Initial priority is to confirm ETT is in position and not obstructed
  • End tidal co2
  • Fogging/misting
  • Equal air entry
• If concerns that obstructed ETT/oesophageal intubation:
  • Remove ETT, hand bag with guedel, obtain emergency airway equipment
  • LMA if difficulties hand bagging
  • Aim re-intubate with most experienced operator
• If ETT in place not obstructed: patient pathology or peri-intubation event
  • Quick assessment of patient: vital signs, etco2 trace ?obstructed, observe chest wall movement, auscultate, feel compliance of lungs with bagging, look for rash, assess circulation
  • Brief history from staff surrounding medications given (?adequate paralysis), grade of intubation, aspiration and Jane’s history and progress on the ward
  • Investigations: Bedside: ABG, ECG, Imaging: CXR
  • Specific treatment depends on finding
    • Dynamic hyperinflation: stop bagging à disconnect, allow adequate expiration
    • Hypovolemia: fluid bolus of crystalloid
    • Vasodilation secondary to induction drugs: vasopressors
    • Anaphylaxis: rash à adrenaline
    • Pneumothorax à decompress
    • Aspiration during intubation: optimise ventilation settings, may need bronch
    • Endobronchial intubation à withdraw ETT
    • De-recruitment post intubation
    • Worsening community acquired pneumonia: vasopressors for hypotension, ensure appropriate antimicrobial therapy, optimise ventilation settings – may need therapies such as inhaled pulmonary vasodilator
    • Decreased cardiac output due to myocardial depression or arrhythmia: may need inotropes, electrolytes, anti-arrhythmics
    • Dyssynchrony (less likely as just been intubated) à sedation/paralysis
  • Logistics
    • Bring ventilator, monitor from ICU – aim to stabilise/improving trajectory then transfer to ICU
    • Depending on trajectory and resources in this hospital may need early call to a larger unit/retrieval

On further assessment you confirm appropriate ETT position, however Jane has an obstructed etco2 trace with global wheeze and a CXR that shows no pneumothorax or consolidation. Her saturations have increased to 92% and you have been able to transfer her to the hospital’s ICU and place her on the ventilator. What initial settings would you use?

Settings aim to avoid dynamic hyperinflation, optimise oxygenation and ventilation with likely tolerating a degree of hypercapnoea, and minimising barotrauma.

Volume control mode: able to assess plateau pressure – aim < 25 cm h20

• PEEP of 0 initially while paralysed and not triggering breaths
• I:E ratio of 1:4 and assess flow time and volume time waveform to ensure that it returns to baseline during expiration otherwise prolong the expiratory time or reduce respiratory rate à high flow rate 60 – 80L/min to reduce inspiratory time
• RR of 10 but may change depending on I:E ratio and flow/time waveform as just outlined
• Volume of 6ml/kg but may need to decrease if plateau pressures > 25cm h20
• Fio2 of 100% to begin with and then decrease titrating to sats > 92%
• May need to increase peak inspiratory pressure alarm – tolerate high peak pressures as long as plateau pressure < 25 cmh20

Ensure humidified circuit

You’ve mentioned using 0 PEEP for this patient. Briefly outline the rationale for zero PEEP versus low PEEP in asthma?  

The amount of PEEP to use in the intubated asthmatic patient is not clear.

Low PEEP:

• Small amount of external PEEP may decrease end-expiratory alveolar collapse
• When patients are triggering the ventilator, a high intrinsic PEEP can make it difficult for patients to initiate a breath. Adding external PEEP of 60 – 80% of the intrinsic PEEP can help reduce the effort required to trigger the ventilator

Zero PEEP:

• Patients often are generating auto-PEEP so theoretically already are splinting their airways open
• Extrinsic PEEP may then just contribute to dynamic hyperinflation
• In the fully sedated mechanically ventilated patient who is not triggering their own breaths, they do not have work of breathing to overcome so adding extrinsic PEEP risks exacerbating dynamic hyperinflation

What is dynamic hyperinflation and outline two methods to assess for it in the intubated asthmatic patient?

Dynamic hyperinflation is an increase in end-expiratory lung volume due to incomplete expiratory emptying of the lungs in patients with airflow obstruction. It is failure of the lung to return to its functional residual capacity or relaxed volume at the end of expiration.

Expiratory hold manoeuvre:

• End expiratory pause:
  • Occlusion of circuit at end expiration allows alveolar pressure to equilibrate with airway pressure
  • This number minus any extrinsic PEEP applied is the intrinsic PEEP
  • Requires patient to be sedated and paralysed for accuracy
  • This method often underestimates intrinsic PEEP as dynamic airway closure prevents the alveoli with the highest pressure equilibrating with the circuit
• Plateau pressure
  • Measure with an inspiratory hold manoeuvre à pressure falls from the peak (resistance + compliance) to the plateau (static compliance only) which is at no flow and therefore theoretically is equilibrated with alveolar pressure
  • For accurate measurement patient needs to be sedated and paralysed and the circuit should not have significant leak
  • As lung volume increases in dynamic hyperinflation the plateau pressure will also increase

Despite being sedated and paralysed with appropriate ventilator settings, inhaled bronchodilators and IV steroids, she fails to improve. What other treatments are available for severe asthma exacerbations and their mechanism of action?

List the signs of salbutamol toxicity

Examination:

• Tremors
• Tachycardia
• Tachypnoea
• Agitation

Investigations

• Hypokalaemia
• Hyperglycaemia
• Lactic acidosis