3. Mechanisms of severe asthma flare
• Bronchospasm
• Mucus hypersecretion with airway plugging
• Vascular shunting through bronchial artery to pulmonary artery shunts
• Vocal cord dysfunction
4. Boser SR,et al: Fractal geometry of airway remodeling in human asthma. Am J Respir Crit Care Med172(7):817–823, 2005
Mechanisms of life-threatening
asthma
• Mucus hypersecretion with airway plugging
Airway cast from a healthy person. Airway cast in fatal asthma: irregular tapering,
constrictions, and surface protrusions (ectatic mucous
gland ducts)
5. Galambos C et al, Annals of Amer Thor Soc, 2018
Mechanisms of life-threatening
asthma
• open intrapulmonary anastomosis between bronchial arteries and pulmonary
arteries have been found in children dying suddenly from asthma
6. Daley C et al, AJRCCM Articles in Press. Published on 31-May-2019
Mechanisms of asthma
• Vocal cord dysfunction with inspiratory obstruction seen on CT larynx in 17% of
patients hospitalized with with asthma flare
Example: ratio of vocal cord lateral diameter to tracheal diameter (level 1st tracheal ring)
during normal breathing
Normal and lower limit of normal (LLN) curves were derived from studies in healthy
individuals
7. Darioli and Perret, Am Rev Resp Dis 1984; 129:385-87
Mechanical ventilation of severe
obstructive lung disease
• Permissive hypercapnia is life-saving
• Before ~1983, mechanical ventilation of asthma with a goal of normalizing CO2
resulted in high mortality
8. Darioli and Perret, Am Rev Resp Dis 1984; 129:385-87
Mechanical ventilation of severe
obstructive lung disease
• in 1984, a case series titled “Mechanical controlled hypoventilation in status
asthmaticus” showed benefit of limiting tidal volumes and airway pressures
• Pre-dates “lung protective ventilation in ARDS” by almost 20 years
• During critical phase, arterial CO2 of 90 (and above) results in no obvious long-
term effects
Which change to the ventilator will most effectively reduce risk of auto-PEEP while
maintaining adequate ventilation?
A. Shortening the inspiratory time
B. Reducing the respiratory rate
C. Reducing tidal volume
9. Caramex et al. Crit Care Med. 2005 July ; 33(7): 1519–1528.
Mechanical ventilation of severe
obstructive lung disease
What effects does extrinsic PEEP have on
asthma/COPD?
10. Caramex et al. Crit Care Med. 2005 July ; 33(7): 1519–1528.
Mechanical ventilation of severe
obstructive lung disease
What effects does extrinsic PEEP have on
asthma/COPD?
In a 2005 study, “Paradoxical responses to positive
end-expiratory pressure in patients with airway
obstruction during controlled ventilation”, as external
PEEP was increased to match intrinsic PEEP:
• 1/3rd of patients had improved/reduced FRC
• 1/3rd of patients had no change in FRC
• 1/3rd of patients had increased FRC
• As extrinsic PEEP was increased above intrinsic
PEEP, FRC began rising
Caramez et al.
NIH-PAAuthorManu
aramez et al.
