Question 2

Last updated 01/10/2015 - 03:43
 Topic: Respiratory Medicine and Mechanical Ventilation
Pass rate
85%
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A 36 year old female is brought into  your Emergency Department with acute shortness of breath. She is unable to provide any history due to her tachypnoea. She is sitting upright in bed grasping the bed sides. She has a respiratory rate of 30 breaths per minute, has a GCS of 15, is afebrile and has a BP of 90/60mmHg. She is using accessory muscles. On auscultation, she has widespread expiratory wheeze spread throughout both lung fields.

a)  In addition to acute severe asthma, what other differential diagnoses of her clinical presentation should be considered?

b)  Assuming     this   patient     has     acute   severe   asthma,      list    your     initial management steps at this stage.

c)  Despite optimal medical  management,  the patient tires. Briefly outline the role of BiPAP in acute severe asthma.

d)  BiPAP fails and the patient is successfully intubated. Following intubation, airway pressures rise and the chest becomes more silent. List other interventions may you consider.

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College Answer

a)  In addition to acute severe asthma, what other differential diagnoses of her clinical presentation should be considered?

Differential diagnoses

•    anaphylaxis ( large % don’t have rash etc – just bronchospasm)
•    Acute exacerbation COPD
•    central foreign body
•    acute pulmonary oedema
•     Pneumothorax
•    Hysterical hyperventilation
•    acute Pulmonary embolus

b)  Assuming     this   patient     has     acute   severe   asthma,      list    your     initial management steps at this stage.

•    Resuscitation/ investigation and definitive management
•    Initial salbutamol nebulisation – continuously. Consider IV infusion
•    IV steroids - ? type and dose .
•    Replace K/Mg
•    Nebulised adrenalin if anaphylaxis still under consideration
•    IV access, bloods including mast cell tryptase cultures/  +/- procalcitonin
•    Portable CXR to exclude pnemothorax / localised consolidation and assess hyperinflation.

c)  Despite optimal medical  management,  the patient tires. Briefly outline the role of BiPAP in acute severe asthma.

Intrinisic PEEP increases the negative intrathoracic pressure the patient must generate to trigger a breath and hence increases WOB. Application of extrinsic PEEP minimises this difference and reduces WOB. IPAP reduces the WOB associated with resistance.

d)  BiPAP fails and the patient is successfully intubated. Following intubation, airway pressures rise and the chest becomes more silent. List other interventions may you consider.

•    Another CXR to check no PTX post PPV
•    Increasing salbutamol
•    Deepen sedation
•    Adding adrenalin/ aminophylline/ ketamine/ Mg ( no evidence) – doses required by candidate
•    Volatile anaesthesia
•    Paralysis- Train of four essential .
•    ? bronchoscopy
•    Measurement of iPEEP

Discussion

a)  In addition to acute severe asthma, what other differential diagnoses of her clinical presentation should be considered?

This is a question about the differential diagnosis of wheeze.

There can be a myriad answers.

UpToDate even has a page about this sort of thing.

  • Extrathoracic causes
    • Anaphylaxis
    • Vocal cord paralysis
    • Laryngeal stenosis
    • Goiter with thoracic inlet obstruction
    • Anxiety with hyperventilation
  • Intrathoracic central airway causes
    • Tracheal stenosis
    • Mediastinal tumours
    • Hyperdynamic airway collapse due to tracehomalacia
    • Mucus plugs
    • Thoracic aortic aneurysm
    • Foreign body inhalation
  • Intrathoracic lower airway causes
    • Bronchitis or bronchiolitis
    • COPD
    • Pulmonary oedema - "cardiac asthma"
    • Airway distortion due to mechanical causes, eg. bronchial mass, bronchiectasis, pneumothorax
    • Exposure to inhaled irritant or corrosive agent, and this includes the aspiration of gastric contents

b)  Assuming     this   patient     has     acute   severe   asthma,      list    your     initial management steps at this stage.

This answer lends itself well to a systematic approach

  • The management would include an immediate attention to the ABCs, with the focus on assessment of the immediate need for intubation and maintenance of normoxia, with simultaneous brief focused history and detailed respiratory examination.
  • Airway:
    • Attention to the airway and assessment of the difficulty of intubation
    • Attention to the patency of the airway and the need for immediate intubation
  • Breathing:
    • High flow humidified oxygen, via face mask or high-flow nasal prongs
    • Continous nebulised salbutamol
    • IV hydrocortisone (100mg)
    • Transition to BiPAP with IPAP and EPAP titrated to effort of breathing
    • Commencement of salbutamol infusion if continous nebs are not helpful in correcting the bronchospasm (as the air entry may be too poor)
    • Consideration of nebulised adrenaline
  • Circulation:
    • correction of hypovolemia, to help prevent the circulatory collapse due to dynamic hyperinflation
  • Electrolyte disturbance:
    • correction of hypokalemia caused by the salbutamol
    • attention to the lactic acidosis, due to salbutamol
    • Titration of magnesium levels to 1.0-1.5mmol/L, to prevent salbutamol-associated arrhythmias
  • Suportive investigations
    • ABG
    • CXR
    • ECG
    • Full set of bloods, including electrolytes and inflammatory markers
    • Viral PCR from nasal swabs to investigate for influenza A / B
    • Procalcitonin
    • Mast cell tryptase

b)  Assuming     this   patient     has     acute   severe   asthma,      list    your     initial management steps at this stage.

The usefulness of positive pressure ventilation in people with intrinsic PEPE is discussed elsewhere.

In summary, positive pressure ventilation decreases effort of breating by applying a positive counter-pressure and thus decreasing the relative amount of intrathoracic pressure which must be generated by the patient's muscles. This decreases the work of breathing. Additionally, it splints the constricted airways, allowing improved CO2 clearance. IPAP increases the pressure gradient during inspiration, improving the flow of gas agains the resistance of the constricted airways. The tight-fitting mask ensures a consistent delivery of the prescribed FiO2.

d)  BiPAP fails and the patient is successfully intubated. Following intubation, airway pressures rise and the chest becomes more silent. List other interventions may you consider.

  • Airway:
    • Check ETT position (rule out intubation of right main bronchus)
    • Check for ETT kinking or blockage
  • Breathing:
    • Rule out pneumothorax with physical examination, bedside ultrasound or CXR
    • Sedate the patient, and paralyse them with cisatracurium
    • Ventilate with mandatory ventilaton using a low respiratory rate, square pressure waveform and low I:E ratio, 1:4 or similar
    • Consider nebulised adrenaline or small IV adrenaline boluses
    • Consider IV ketamine and IV magnesium infusions
    • Consider volatile anaesthetic agents
    • Consider Heliox
    • Consider ECMO if normoxia cannot be maintained in the face of severe bronchospasm
  • Circulation:
    • correct hypovolemia
    • Watch for dynamic hyperinflation and associated loss of preload;
      • may be necessary to disconnect the patient form the ventilator and manually decompress their chest by external pressure

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