1	Acute Severe Asthma Murat Sungur, MD Assistant Professor Division of Critical Care Medicine Departments of Anesthesiology and Surgery University of Florida College of Medicine Gainesville, FL 32610-0254
2	Descriptions of Asthma Asthma: ancient Greek for “panting” Definition: a narrowing of the airways in the lungs that causes coughing, wheezing, and gasping for breath. Pathology: airflow obstruction, airway hyper-responsiveness, and airway inflammation.
3	"Coughing" Coughing Wheezing Chest tightness Shortness of breath
4	"About 17 million Americans have..." About 17 million Americans have asthma Rate of asthma increased 75% between 1980 and 1994 Most common chronic childhood disease, affecting about 5 million children 14 people die each day from asthma Nearly 2 million emergency room visits each year
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7	Fatal Asthma
8	Hypoxemia Common Easily corrected with supplemental O₂ Minimal shunt: Collateral ventilation Hypoxic pulmonary vasoconstriction, Obstruction is never complete More severe asthma........Shunt
9	Hypo-, Normo-, then Hyper-capnia Initially and mostly Hypocapnia As airway obstruction progress CO₂ normalize: Normal CO₂ .....indication for ICU admission Finally hypercapnia.....if not correctable… .....intubation
10	Respiratory and Metabolic Acidosis No time for renal compensation Hypercapnia....respiratory acidemia Lactic acidosis Anaerobic metabolism of respiratory muscles Decreased lactate clearance by the liver β-agonists
11	Air Trapping - Dynamic Hyperinflation
12	Dynamic Hyperinflation
13	Dynamic Hyperinflation
14	Dynamic Hyperinflation
15	Pulsus Paradoxus Very negative intra-thoracic pressure during inspiration Mechanism? As respiratory muscle weakness develops, PP disappears More than 12 cm H₂O ....very severe asthma
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17	Admission to ICU Respiratory arrest Coma Poor response to initial treatment Severe airflow obstruction Normal or high PaCO₂ Metabolic acidosis Pulsus paradoxus
18	Management Β₂-agonists Anticholinergics Theophyline Corticosteroid Epinephrine Terbutaline Magnesium infusion Slow bicarbonate infusion
19	Management Β-agonists Continuous inhalation IV: last resort if cardiac arrest is imminent Corticosteroids 60 - 80 mg prednisolone Q6h, taper in two weeks Effect starts in 6 hours
20	Management Ipratropium bromide ?? Theophyline ?? If started level in 6 hours Increased diaphragmatic and myocardial contractility may be helpful Epinephrine: SQ 0.3 – 0.4 ml in extreme cases Terbutaline: same with epi when given SQ
21	Mechanical Ventilation Not too quick but not too late Intubation should be semi-elective not emergent Call an expert for both intubation and MV Sedation
22	Sedation and Neuromuscular Blockade Deep sedation Propofol and ketamine Muscle relaxants Do not use atracurium Histamine release Try to avoid all NMBs
23	Mechanical Ventilation Hypotension after intubation due to: Increased dynamic hyperinflation Dehydration Sedation Use Low I:E ratio.....1:3 Low RR Low Pplat
24	Components of Inflation Pressure
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26	Mechanical Ventilation Initial Settings Mode Pressure controlled RR 8 to 12 breaths / min TV 6 to 7 mL / kg MV 6 to 8 L / min PEEP 0 cm H₂O I:E ratio 1:3 Inspiratory flow Greater than 100 L / min FIO₂1 P_plat< 35 cm H₂O
27	Sample Case 24 y/o woman wit history of asthma Admitted to ER with shortness of breath and wheezing She was in severe respiratory distress and had to be intubated in the ER Continuous β agonist neb and IV corticosteroid Sedated with midazolam and paralyzed with vecuronium
28	Sample Case Very limited air movement in the ICU Volume controlled, CMV, RR 12, TV 500 ml (8 ml / kg), PEEP 5, Peak flow 80 L / min PEEP_i was 20 cm H₂O Ppeak was 94 and Pplatwas 54 cm H₂O pH 7.21, PaCO₂ 54 and PaO₂ 442 with FIO₂ of 1
29	Sample Case CXR....pneumomediastinum, severe hyperinflation and SQ emphysema. Flow rate to 120 L / min, V_t to 400 mL Ppeak 100 and Pplat 34 cm H₂O
30	Sample Case Ppeak 100 and Pplat 34 cm H₂O pH 6.99, PaCO₂ 120 and PaO₂ 93 mmHg (aminophylline and NaHCO₃ infusion started) Transient hypotension RR to 7
31	Sample Case RR to 7 SBP to normal and PEEP_i to 14 cm H₂O Worsening ABGs Isoflurane inhalation with anesthesia machine
32	Sample Case Isoflurane inhalation with anesthesia machine Bilateral pneumothorax (chest tubes placed) pH 6.68, PaCO₂ 202 and P/F 160 with exhaled TV of 100 ml Anesthesia disconnected
33	Sample Case Anesthesia disconnected MV with all other treatments PaCO₂ 180 mmHg, Ppeak 94 and Pplat 32 cm H₂O 36 hours after admission PaCO₂ 80 mmHg
34	Sample Case 36 hours after admission PaCO₂ 80 mmHg 48 hours, near normal PaCO₂ and airway pressures (vecuronium discontinued) Extubated on day 5 Sent to rehab facility secondary to generalized weakness
35	New Therapies Non-invasive mechanical ventilation Continuous magnesium infusion MV with Helium O₂ mixture