A 20-year-old, 80 kg man presents to the ED with acute severe asthma. In ED he has a respiratory arrest and is intubated. He is then transferred to your ICU with the following ventilator settings:
He has a tachycardia 130 bpm and a BP of 80/60. Arterial blood gas analysis shows pH 7.1, PCO2 93 mmHg (12.3 kPa), PO2 69 mmHg (9.0 kPa), HCO3 28 mmol/L SaO2 90%.
Peak pressure, plateau pressure and total PEEP (auto PEEP and intrinsic PEEP acceptable terms)
Leave unchanged. No benefit for PCV, and risks of hyperinflation with rapid changes in resistance. Will need sedation and probably paralysis to tolerate. (If candidates change to PCV must explain risks)
Probably satisfactory; may be able to increase Vt if necessary to help control pCO2
(allowing for adequate expiratory time); “lung protective” strategy not strictly necessary for this situation. High PCO2 most probably relates to gas trapping and is best controlled by changes in flow rate and respiratory rate.
16 b/min is too high. The hypotension suggests significant dynamic hyperinflation. Rate should be immediately reduced to 10 or fewer. This rate with Inspiratory flow rate of 20 L/min and Vt 500 ml gives I:E of 1:1.5. I:E should be 1:3. Optimal respiratory rate to limit hypercapnia is balance between that which limits gas trapping (lower rate) and that which limits hypoventilation (higher rate)
20 L/min is too low, causing prolonged inspiratory time (1.5 sec for Vt 500 ml). Flow should be adjusted up to minimise inspiratory time. Peak pressure will rise, but this should be tolerated so long as plateau pressure is safe.
Extrinsic PEEP in this situation is controversial.
The patient is hypoxic, hypercapneic, and hypotensive.
What additional measurements would you take to assist ventilator management?
Comment on the ventilator settings, and describe what change (if any) you would make in each case.
List the likely causes of this patient’s hypotension
This reference seems almost tailor-made for this topic:
Oddo, Mauro, et al. "Management of mechanical ventilation in acute severe asthma: practical aspects." Intensive care medicine 32.4 (2006): 501-510.