Bronchospastic BP Badness

aka Pulmonary Puzzler 013

You arrive at work early and notice a considerable commotion in the resus area of the emergency department. A nurse spots you, and waves at you to come over. The medical team, at the end of their night shift, are stressed, sleep deprived and look worried.

A critically ill young man is now hypotensive following intubation. He was intubated for a severe asthma attack resulting in type 1 and 2 respiratory failure. The team leader asks you for help.


Questions

Q1. What are the most important things to check when there is a problem with a mechanically ventilated patient?

Answer and interpretation

You may remember this question from Pulmonary Puzzle 012 – Man versus Machine — it is repeated for a reason… It’s important!

First determine the severity of the problem — do you need to start immediate resuscitation?

Then assess MASH:

  • Movement of the chest during ventilation —
    is it absent or is movement only on one side? Is the chest hyper-expanded?
  • Arterial saturation (SpO2) and PaO2 —
    obtain an ABG sample
  • Skin colour of the patient (is he turning blue or pinking up?) —
    the SpO2 monitor lags behind the true oxygen saturation of the patient.
  • Hemodynamic stability.

Now you can attempt to diagnose the problem.


Q2. What is the most important first step in managing the patient who is hypotensive soon after intubation?

Answer and interpretation

Disconnect the the endotracheal tube from the ventilator circuit.

In asthmatics, this may be life-saving. If the cause is dynamic hyperinflation (‘gas trapping’) blood pressure will rise over 10-30 seconds as the gas is released.


Q3. What are the likely causes of hypotension following intubation of the asthmatic?

Answer and interpretation

When considering the causes of hypotension or shock, think ‘are they PROVED?’:

  • Cardiogenic
    — P
    ump (e.g. imparied contractility, valve dysfunction)
    — R
    ate (fast or slow or absent) or Rhythm (regular or irregular)
  • Obstructive (e.g. tension pneumothorax, pericardial tamponade, pumonary embolus, dynamic hyperinflation)
  • Volume depletion = hypovolemia (e.g. dehydration, hemorrhage, third spacing)
  • Endocrine (e.g. adrenal insufficiency, hyperthyroidism, hypothyroidism)
  • Distributive shock (e.g. sepsis, anaphylaxis, neurogenic, hepatic failure)
  • ? (e.g. artefact, measurement error, drug adminstration error)

The most important causes to consider following the intubation of a patient with asthma are:

  • ‘Stacking’ or dynamic hyperinflation (gas-trapping) due to excessive ventilation — especially in the patient with bronchospasm.
  • Hypovolemia exacerbated by decreased venous return due to positive intrathoracic pressure.
  • Vasodilation and myocardial depression due to the induction drugs used for rapid sequence intubation (e.g. thiopentone, propofol).
  • Tension pneumothorax due to positive-pressure ventilation.

Q4. What are the other early management priorities?

Answer and interpretation

The patient has already been disconnected from the ventilator circuit.

Important management priorities include:

  • Administer high-flow oxygen (FiO2) via a bag-valve-mask and manually ventilate (usually <10 breaths/min) following adequate disconnection to allow the release of trapped gas.
  • Consider needle thoracostomy for tension pneumothorax — carefully consider whether there is time for confirmation by bedside ultrasound or chest x-ray (there often is), so that an unnecessary invasive procedure is not performed. If the chest is needled, formal intercostal catheter insertion is mandatory.
  • Administer 10-20 mL/kg IV fluid boluses to overcome the cardiovascular effects of induction drugs and/or unmasked hypovolemia. Vasopressors (e.g. metaraminol 0.5-1mg IV boluses) may also need to be administered as a temporizing measure.

Scott Weingart talks about ‘finger thoracostomy‘ as an alternative to needle thoracostomy


Q5. When should you intubate a patient with severe asthma?

Answer and interpretation

Never intubate an asthmatic… unless you absolutely have to!

Intubation and ventilation may be life-saving, but carries significant risks. There are the usual risks such as failed intubation, airway trauma, aspiration, increased risk of stress ulceration and nosocomial pneumonia. But there are additional risks specific to the patient with reactive airways disease.

These include:

  • inadvertent pulmonary hyperinflation.
    — hypotension
    — barotrauma and pneumothoraces
    — PEA arrest due to dynamic hyperinflation.
  • aggravation of bronchospasm.
  • longer term risk of myopathy from the combination of corticosteroids and neuromuscular blockade required to facilitate mechanical ventilation.

Absolute indications for intubation of a patient with severe asthma are:

  • cardiac or respiratory arrest
  • severe hypoxia (e.g. hypoxic seizure)
  • rapidly deteriorating level of consciousness

Relative indications for intubation are:

  • progressive patient fatigue
  • hypercapnea

These relative indications need to be balanced against the risks of intubation. Hyperacute asthma may have hypercapnea due to mechanical limitation of ventilation rather than fatigue, and this may improve with aggressive treatment.


Q6. What are appropriate initial ventilator settings in the intubated asthmatic?

Answer and interpretation

There is no clear evidence for the superiority of one ventilation mode over another (i.e. volume-controlled versus pressure-controlled).

Initial ventilator settings (volume-controlled ventilation):

  • Tidal volume 6-8 mL/kg
  • Slow respiratory rate (e.g 8-10/min)
  • High inspiratory flow rate (e.g 80-100L/min) to allow longer expiratory times
  • PEEP of 0 cmH2O (some experts like a bit of PEEP — more on that another time…)
  • FiO2 titrated to keep SaO2 >93%.

Variations of these settings may be used as long as the main principle of avoiding dynamic hyperinflation (by using small tidal volumes, long expiratory times and a slow respiratory rate) is followed. To my knowledge there is no convincing scientific evidence that this ventilation strategy is more effective than any other.

Expect the following with these initial settings in a patient with asthma:

  • high peak inspiratory pressures (PIP) — don’t worry this does not necessarily correlate with lung barotrauma.
  • respiratory acidosis due to a low target minute ventilation — sedation and neuromuscular blockade may be required to suppress spontaneous ventilation.

Everything settles down, until there is a problem with high airway pressures… Continue on to Pulmonary Puzzle 014: Alarmingly high airway pressures.


References
  • Brenner B, Corbridge T, Kazzi A. Intubation and mechanical ventilation of the asthmatic patient in respiratory failure. J Emerg Med. 2009 Aug;37(2 Suppl):S23-34. Review. PMID: 19683662.
  • Gomersall C. ICU Web — Trouble-shooting mechanical ventilation
  • Holley AD, Boots RJ. Review article: management of acute severe and near-fatal asthma. Emerg Med Australas. 2009 Aug;21(4):259-68. Review. PMID: 19682010.
  • For more Pulmonary cases check out the LITFL Top 150 Chest X-Rays

Pulmonary Puzzler-LITFL 700

CLINICAL CASES

Pulmonary Puzzler

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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