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Chapter 5

The Dying Asthmatic

Rob Orman, MD and Scott Weingart, MD
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Discuss airway and ventilatory management of the asthma patient in extremis who is recalcitrant to standard therapy.

Pearls:

  • Noninvasive positive pressure ventilation is preferred over BVM early on in the management of the patient with severe asthma.

  • A patient with a stone chest that is incredibly difficult to bag should be intubated as quickly as possible with RSI. Prolonged bagging with high pressures can be dangerous due to the risk of gastric insufflation and aspiration.

  • Once intubated, bag with FiO2 of 100% at a slow respiratory rate of 8-10 breaths/minute.

  • When setting the ventilator for the intubated asthmatic, Weingart recommends Increasing the vent’s peak pressure limit from the usual default alarm setting of 40 to whatever it takes to get in a reasonable tidal volume.



  • What distinguishes delayed from rapid sequence intubation (RSI)?

    • RSI refers to the following sequence of events:  preoxygenation, sedation with an induction agent, paralysis, and intubation.

    • Delayed sequence intubation (DSI) differs in that it starts with a dissociative induction agent, ketamine.  Instead of being rapidly followed by a paralytic, it is followed by preoxygenation for 3 minutes, then paralysis, and finally intubation.

    • DSI is used for “a patient requiring emergent airway management but resistant to pre-intubation preparations because of altered mental status”.



Case 1

A patient arrives by private automobile with status asthmaticus.  She is unresponsive with sats of 50-60%. The patient is guppy breathing with small tidal volumes. The provider plans for delayed sequence intubation with ketamine. Albuterol, epi, and Solumedrol are given with no improvement.  With bag-valve-mask assisted ventilation, the provider has difficulty with high airway pressures, resulting in emesis.

 

  • Few patients are more challenging in the ED than the asthmatic in extremis who is recalcitrant to standard therapy.  Asthma is different than other causes of severe respiratory distress.  And there are different forms of asthma as well.

  • Besides cricoid pressure, magnesium, and slowing down ventilations, how else might the provider try to reduce the consequences of breath stacking is this case?

    • Weingart prefers noninvasive positive pressure ventilation to BVM early on in the management.

    • In the rare cases of severe asthma with a ‘stone chest’ that is incredibly difficult to bag, you need to proceed to immediate RSI and get the tube in as quickly as possible.  It’s the only way to safely provide the airway pressures you need.

      • Prolonged bagging with high pressures carries the risk of gastric insufflation and aspiration.

      • Failed attempts at intubation are especially risky in these patients.  As their hypoxia worsens, they may get more acidotic, running a very real risk of cardiac arrest peri-intubation.

  • What drugs are recommended for RSI in this case?

    • Weingart would use ketamine or propofol, followed by a “huge slug” of paralytics so it works as quickly as possible.  He has no preference of succinylcholine versus rocuronium, as long as the dose is high enough.

  • Once this presumably hypercapnic patient is intubated, what is the optimal way to oxygenate and ventilate?  This is the quintessential asthmatic ventilation quandary.

    • While there is an impulse to correct the acidosis and high CO2 by blowing it down quickly and bagging rapidly, this just traps more air.  Asthmatics usually tolerate respiratory acidosis well, at least for the short term

    • Early in the resuscitation, the goal is to deliver enough gas into the alveoli to get the raise the systemic.  Using a bag, squeeze about 500 cc (goal is 250 cc into the alveoli and the remainder fills the dead space) at a rate of one breath every 8-10 seconds.  Start with a low respiratory rate and 100% FiO2.

    • Although it may be difficult, it is usually possible to get air into these patients.  It can be harder to get it out. When still paralyzed, you rely on passive recoil of the chest.  Another option, though it hasn’t been studied, is manual decompression of the chest by pushing on the chest between each breath to expel air.

  • What are the initial recommended vent settings for status asthmaticus?

    • The best vent mode in Weingart’s opinion  is volume assist control.

      • In this vent setting, each breath gets the same volume.  The breath can be initiated by the patient or the vent. If the patient is heavily sedated and/or paralyzed, the vent will deliver the number of breaths set for the respiratory rate. If the patient starts initiating a breath on their own, the vent senses that and delivers an assisted breath at the set volume.

      • Carpio, Andres L. Mora, and Jorge I. Mora. "Ventilation, Assist Control." (2017) PMID: 28722886

    • Start with a low respiratory rate (8-10/min), low tidal volume (8 ml/kg), and zero PEEP.

      • Why zero PEEP?  Asthmatics have self-generated auto-PEEP.  If you add PEEP and are going higher than their auto-PEEP levels, you’re doing them harm because you’re making it harder for them to get gas out.  There are a few arguments for adding PEEP which Weingart argues are not truly benefits:

        • The theoretical benefit of PEEP is that it may make it a little bit easier for patients to exhale.  There is scant evidence supporting this tentative benefit.

        • The real benefit of PEEP is that it makes it easier for the patient to trigger the ventilator, because the patient has to overcome their auto-PEEP for the ventilator to even sense that they want a breath. It’s difficult to breathe with auto-PEEP.  However, Weingart argues that this puported benefit is not an actual benefit, as he doesn’t want the patient to trigger the ventilator. He argues that these severe asthmatics should be heavily sedated to allow their respiratory muscles to recover.

    • Begin with an FiO2 of 100%. Titrate down to whatever level maintains oxygenation

    • Increase the vent’s peak pressure limit from the usual default alarm setting of 40 to whatever it takes to get in a reasonable tidal volume.

      • If this isn’t done, the pressure alarm will continually go off, the patient will not get a sufficient tidal volume, and will remain hypoxemic.

      • Peak pressure is the resistance in the airway circuit when air is flowing.  When bronchioles are constricted and inflamed, they create a lot of resistance.

    • Try to keep the plateau pressure below 30-35 cm of water to minimize barotrauma.

      • This can usually be achieved by keeping the respiratory rate low.

      • The plateau pressure measures what’s happening when air isn’t moving.  It’s the compliance of the lungs. It’s what’s happening in those tiny distal airways and alveoli and is measured at the end of inspiration.

      • If the plateau pressure is too high, despite a low respiratory rate and tidal volume, consider VV ECMO, inhaled anesthetics, or dialysis to remove CO2.  Dialysis can only be done at a center that has ECMO capability as you need an oxygenator which is part of the ECMO circuit.

    • I:E ratios are not set on a ventilator; the I:E ratio is a measured value based on the chosen respiratory rate and inspiratory flow rate.  Weingart looks for an I:E ratio of 1:4 or 1:5, but he’s more concerned about the plateau and flow waveform to see that the patient is fully exhaling between breaths.

  • If ventilation remains difficult, limiting the efficacy of inhaled medications, think about giving intravenous bronchodilators (such as an epi or terbutaline drip).  Inhaled anesthetics and VV ECMO are “fringe” therapies to consider as well.

    • Inhaled anesthetics are bronchodilators with the added benefit of excellent sedation. The literature is replete with case reports and retrospective series on patients with severe asthma recalcitrant to the usual therapy who have had dramatic improvement in pCO2 and acidosis when treated with these volatile anesthetic agents.

    • Vaschetto, R., et al. "Inhalational anesthetics in acute severe asthma." Current drug targets 10.9 (2009): 826-832. PMID: 19799536

    • Turner, David A., et al. "Isoflurane for life-threatening bronchospasm: a 15-year single-center experience." Respiratory care 57.11 (2012): 1857-1864. PMID: 22417969

    • Phipps, P., and C. S. Garrard. "The pulmonary physician in critical care• 12: acute severe asthma in the intensive care unit." Thorax 58.1 (2003): 81-88. PMID: 12511728 PMCID: PMC1746457

  • Is the use of non-invasive positive pressure ventilation in severe asthma helpful or harmful?

    • BIPAP and other types of non-invasive ventilation are exceedingly safe and are unlikely to cause damage to the airways (from the pressure levels that are used).

    • Asthma is typically a problem of exhalation, though at the very severe stages it becomes a problem of inhaling enough gas to get past the dead space.  The cause is twofold:  fatigue of respiratory muscles due to acidosis and encephalopathy due to hypercapnia.  

      • When patients can’t take in an adequate tidal volume, they become hypoxemic and enter a downward cycle of delirium, hypoxemia, and hypercapnia.

      • Often, all these patients need is to blow down their CO2 a little bit and to give them breaths big enough to oxygenate.  Once this happens, they rapidly get better. Sometimes these patients are so delirious that they will not tolerate assisted ventilations.

      • Ketamine can be helpful when this happens -- the patients relax in their dissociative state and tolerate non-invasive ventilation very well.  Oftentimes, these patients don’t even need intubation.

        • The recommended ketamine dose is 0.5-1.0 mg/kg. Since it’s so rapidly acting, you repeat the dose every few seconds until they dissociate.

        • It is imperative that providers and nurses stay at the bedside monitoring the patient, just as they would a procedural sedation. In this case, ketamine is used for procedural sedation, where the procedure is preoxygenation with positive pressure ventilation.

        • That ketamine has a bronchodilatory effect is not well supported in the literature.  

        • Shlamovitz, Gil Z., and Tracy Hawthorne. "Intravenous ketamine in a dissociating dose as a temporizing measure to avoid mechanical ventilation in adult patient with severe asthma exacerbation." Journal of Emergency Medicine 41.5 (2011): 492-494. PMID: 18922662

Jat, Kana R., and Deepak Chawla. "Ketamine for management of acute exacerbations of asthma in children." The Cochrane database of systematic reviews 11 (2011).PMID: 23152273

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