What is the risk of respiratory failure requiring paralysis for mechanical ventilation in asthmatic patients?

Risk of Respiratory Failure Requiring Paralysis in Asthmatic Patients

In severe asthma exacerbations requiring mechanical ventilation, paralytic agents may be necessary in patients who display ventilator dyssynchrony despite adequate sedation, particularly when auto-PEEP persists. 1, 2

Pathophysiology Leading to Need for Paralysis

• Asthmatic patients have prolonged expiratory time requirements due to bronchoconstriction, which leads to incomplete exhalation, air trapping, and auto-PEEP when mechanically ventilated 3
• The combination of auto-PEEP, reduced venous return, and hypotension can lead to cardiovascular collapse during or immediately after intubation 3
• High ventilator pressures associated with mechanical ventilation in asthmatics significantly increase the risk of barotrauma, including pneumothorax, pneumomediastinum, and subcutaneous emphysema 3, 4

Indications for Mechanical Ventilation in Asthma

• Intubation should be considered in patients with persistent or increasing hypercapnia, exhaustion, and depressed mental status 3
• Patients presenting with apnea or coma should be intubated immediately 3
• Intubation should be performed semi-electively before respiratory arrest occurs, as delaying intubation until cardiorespiratory arrest significantly increases mortality 3, 5

Ventilation Strategy to Minimize Risk

• A ventilation strategy with slower respiratory rates (10-14 breaths/min), smaller tidal volumes (6-8 mL/kg), shorter inspiratory times, and longer expiratory times (I:E ratio 1:4 or 1:5) should be used to minimize air trapping and auto-PEEP 2, 3
• Use the largest endotracheal tube available (usually 8 or 9 mm) to decrease airway resistance 2, 3
• Implement permissive hypercapnia (mild hypoventilation) to reduce the risk of barotrauma 2, 6

Sedation Management

• Sufficient sedation should be provided to prevent ventilator dyssynchrony, which can worsen air trapping 3
• Propofol infusion (5-50 mcg/kg/min) can be used as the primary agent, with fentanyl for analgesia and midazolam as a complementary sedative if necessary 3, 7
• Sedation should be avoided in non-intubated asthmatic patients, as it can depress the respiratory center 7

When Paralysis Becomes Necessary

• Paralytic agents should be considered if auto-PEEP persists and the patient displays ventilator dyssynchrony despite adequate sedation 1, 2
• Signs indicating need for paralysis include:
  • Difficulty ventilating despite optimal ventilator settings 1
  • High airway pressure alarms on the ventilator 1
  • Sudden decreases in blood pressure due to auto-PEEP 1
  • Patient fighting the ventilator despite adequate sedation 2, 8

Managing Complications

• If auto-PEEP develops, quickly reduce high-end expiratory pressure by briefly disconnecting the patient from the ventilator circuit to allow PEEP to dissipate during passive exhalation 1, 2
• Compression of the thorax to aid exhalation may relieve hyperinflation and should lead to immediate resolution of hypotension 1
• Monitor for signs of tension pneumothorax, which requires immediate decompression 3

Mortality Risk

• The mortality rate for critically ill asthmatics requiring intubation is between 10% to 25%, primarily from anoxia and cardiopulmonary arrest 5
• Fatal asthma occurs from cardiopulmonary arrest, cerebral anoxia, or complications of treatments such as barotrauma and ventilator-associated pneumonia 5

Rescue Strategies

• In exceedingly rare circumstances when aggressive treatment fails to provide adequate gas exchange, extracorporeal membrane oxygenation (ECMO) may be considered 1, 9
• Asthma is associated with excellent outcomes for patients with refractory respiratory failure requiring ECMO support 9

Common Pitfalls to Avoid

• Never use conventional ventilator settings designed for non-asthmatic patients, as these can worsen air trapping 2, 3
• Avoid high respiratory rates and large tidal volumes which can lead to incomplete exhalation and auto-PEEP 2, 3
• Inadequate sedation can lead to patient-ventilator dyssynchrony and worsen air trapping 3, 8
• Delayed expert consultation should be avoided; obtain expert consultation early for management of mechanical ventilation in severe asthma 3