1. Non-Invasive Ventilation in Status Asthmaticus

Non-invasive ventilation (NIV) can be a valuable tool in managing status asthmaticus by offloading respiratory muscles and stenting airways. In select patients, it may avert the need for invasive mechanical ventilation. However, it’s crucial to recognize that delayed escalation to intubation in NIV failure is associated with increased risks.

A. Physiologic Rationale

• Augmented Alveolar Ventilation: NIV assists in increasing the volume of air reaching the alveoli, improving gas exchange.
• Reduced Work of Breathing: By providing pressure support, NIV lessens the effort required by the patient’s respiratory muscles.
• Airway Stenting: Continuous Positive Airway Pressure (CPAP) helps keep bronchi open, counteracting bronchoconstriction.
• Muscle Offloading: Bi-level Positive Airway Pressure (BiPAP) provides both inspiratory and expiratory support, which can be particularly beneficial for fatigued respiratory muscles.

B. Evidence & Potential Benefits

While robust randomized controlled trial (RCT) data specifically for status asthmaticus is limited, large retrospective cohort studies suggest that NIV use is associated with reduced rates of invasive mechanical ventilation and potentially lower mortality. Common initial NIV pressure settings are often around an Inspiratory Positive Airway Pressure (IPAP) of 8-12 cm H₂O and an Expiratory Positive Airway Pressure (EPAP) of 5-6 cm H₂O, titrated to patient comfort and physiological response.

C. Risks & Predictors of NIV Failure

Potential risks of NIV include barotrauma (though less common than with invasive ventilation) and nosocomial infections, particularly if NIV fails and intubation is delayed. Close monitoring for signs of failure is essential.

Predictors of NIV failure include:

• Severe hypercapnia (PaCO₂ > 60 mm Hg) at initiation or worsening on NIV.
• Significant hypoxemia (PaO₂/FiO₂ ratio < 200).
• Altered mental status or inability to protect the airway.
• Hemodynamic instability.
• Inability to tolerate the mask or cooperate with therapy.

D. Patient Selection Criteria

Indications for NIV Trial:

• Respiratory rate > 25 breaths/minute.
• Heart rate > 110 beats/minute.
• Moderate respiratory acidosis (e.g., pH > 7.25 but < 7.35 with elevated PaCO₂).
• Patient is cooperative and able to protect their airway.
• Accessory muscle use and dyspnea.

Contraindications to NIV:

• Depressed level of consciousness or coma.
• High aspiration risk (e.g., active vomiting, copious secretions).
• Inability to achieve a good mask seal (e.g., facial trauma).
• Severe agitation or inability to cooperate.
• Immediate need for intubation (e.g., respiratory arrest, profound shock).
• Hemodynamic instability unresponsive to initial measures.

E. Monitoring & Escalation Protocols

Patients on NIV require intensive monitoring:

• Continuous monitoring of respiratory rate, tidal volumes (if measurable via ventilator), and oxygen saturation (SpO₂).
• Arterial blood gases (ABGs) typically within 1-2 hours of initiation and then as clinically indicated to assess response (pH, PaCO₂, PaO₂).
• Close observation for clinical signs of improvement (reduced work of breathing, improved air entry) or deterioration.

Predefined triggers for escalation to invasive mechanical ventilation are crucial and should include:

• Worsening hypercapnia or hypoxemia despite optimal NIV settings.
• Decline in mental status.
• Inability to tolerate the NIV mask or interface.
• Development of hemodynamic instability.
• Persistent or worsening signs of respiratory muscle fatigue.

2. Sedative and Paralytic Agents for Rapid Sequence Intubation (RSI)

When intubation is necessary in status asthmaticus, the choice of induction and paralytic agents should prioritize bronchodilation, hemodynamic stability, and rapid onset to ensure safe and effective airway management.

A. Ketamine

• Mechanism: Ketamine is an NMDA receptor antagonist that leads to catecholamine release, resulting in bronchodilation. It also has direct smooth muscle relaxant properties.
• Dosing: Typically an IV bolus of 1–2 mg/kg. An optional infusion of 0.5 mg/kg/h can be considered for ongoing sedation and bronchodilation post-intubation, though evidence for this is less robust.
• Advantages: Preserves airway reflexes to some extent (though not fully relied upon during RSI), generally maintains or increases blood pressure, and provides direct bronchodilation.
• Disadvantages: Can cause hypersalivation (pretreatment with an anticholinergic like glycopyrrolate 0.2 mg IV may be considered), and psychomimetic effects (emergence reactions), which are less of a concern in critically ill, intubated patients.

B. Comparative Induction Agents

C. Paralytic Agents

3. Mechanical Ventilation Strategy: Permissive Hypercapnia

The cornerstone of ventilating a patient with status asthmaticus is to employ a strategy of “permisive hypercapnia.” This involves using low minute ventilation with prolonged expiratory times to minimize dynamic hyperinflation, auto-PEEP (intrinsic PEEP), and the risk of ventilator-induced lung injury (VILI) and barotrauma.

A. Goals & Rationale

• Tolerate Hypercapnia: The primary goal is to allow PaCO₂ to rise (and pH to fall), provided the pH remains above a critical threshold (commonly >7.20), to facilitate lung-protective settings. This avoids the high pressures and volumes that would be needed to normalize PaCO₂ in the face of severe airflow obstruction.
• Prolong Expiratory Time: A long expiratory time (achieved by low respiratory rate and/or high inspiratory flow rate, leading to an I:E ratio of up to 1:3, 1:4, or even 1:5) is crucial to allow for more complete emptying of alveoli and prevent breath stacking (dynamic hyperinflation).

B. Initial Ventilator Settings

C. Monitoring Parameters

• Airway Pressures:
  • Peak Inspiratory Pressure (Ppeak): Reflects total pressure (resistance + elastic). Will be high due to bronchoconstriction.
  • Plateau Pressure (Pplat): Measured via end-inspiratory hold. Reflects alveolar pressure. Goal is < 30 cm H₂O.
  • Auto-PEEP (PEEPi): Measured via end-expiratory hold. Indicates dynamic hyperinflation. Goal is to minimize.
• Blood Gases: Monitor ABGs to assess adequacy of permissive hypercapnia (pH typically > 7.20, PaCO₂ will be elevated) and oxygenation.
• Clinical Assessment: Observe for absence of breath stacking on ventilator waveforms, stable hemodynamics, and adequate oxygenation (SpO₂ 88–92%).

D. Adjustment Algorithms

• If Auto-PEEP is increasing or Pplat > 30 cm H₂O:
  • Decrease respiratory rate further.
  • Decrease tidal volume (if not already at lower limit).
  • Increase inspiratory flow rate (to shorten Ti and lengthen Te).
  • Ensure adequate sedation to prevent patient-ventilator dyssynchrony.
• For Patient-Ventilator Dyssynchrony:
  • Optimize sedation levels. Ensure patient is not “fighting” the ventilator.
  • Brief periods of paralysis may be considered in severe cases if dyssynchrony persists despite deep sedation and is contributing to worsening hyperinflation or gas exchange.

4. Complications of Mechanical Ventilation and Management

Despite careful ventilator management, patients with status asthmaticus are at high risk for complications. Early recognition and prompt intervention are critical to prevent deterioration.

A. Barotrauma (Pneumothorax, Pneumomediastinum)

• Recognition: Sudden onset of desaturation, increased peak airway pressures, decreased breath sounds on one side, subcutaneous emphysema, hypotension, or tracheal deviation (tension pneumothorax). Chest X-ray (CXR) confirms diagnosis.
• Management:
  • Immediately lower airway pressures (reduce Vt, RR, or PEEPe).
  • If tension pneumothorax is suspected, perform needle decompression followed by chest tube insertion.
  • For simple pneumothorax, chest tube insertion is usually required.
  • Adjust ventilator settings to minimize further overdistension (lower Vt, ensure long Te).

B. Cardiovascular Collapse / Hypotension

• Mechanism: High intrathoracic pressures due to dynamic hyperinflation and applied PEEP can impede venous return to the heart, reducing preload and cardiac output, leading to hypotension or even pulseless electrical activity (PEA).
• Recognition: Hypotension, tachycardia, signs of shock (cool extremities, poor capillary refill), or PEA cardiac arrest. Often occurs shortly after intubation or with increases in ventilator support.
• Management:
  • Temporarily disconnect the patient from the ventilator for 15-30 seconds to allow passive exhalation and relieve hyperinflation (especially in arrest/peri-arrest).
  • Reduce ventilator PEEP and/or tidal volume; decrease respiratory rate.
  • Administer intravenous fluids to augment preload (if no signs of fluid overload).
  • Initiate vasopressors if hypotension persists despite fluid resuscitation and ventilator adjustments.
  • Ensure adequate sedation and analgesia, as agitation can worsen intrathoracic pressures.

5. Multidisciplinary Goals-of-Care Conversations

Structured and early discussions about goals of care are essential in severe status asthmaticus, particularly when the clinical course is refractory or prolonged. These conversations help align invasive support decisions, such as ongoing invasive mechanical ventilation (IMV) or consideration of Extracorporeal Membrane Oxygenation (ECMO), with patient preferences and the clinical trajectory.

A. Timing & Participants

• Timing: Initiate these discussions upon ICU admission, or at early signs of refractory disease (e.g., failure to improve after 24-48 hours of IMV, persistently high Pplat despite optimal settings, severe ongoing bronchospasm).
• Participants: A multidisciplinary team approach is best. This typically includes:
  • Critical care physician
  • Pulmonologist (if not primary critical care)
  • Clinical pharmacist (for medication optimization, sedation)
  • Respiratory therapist (for ventilator management insights)
  • Bedside nursing staff
  • Palliative care specialists (can facilitate complex discussions)
  • The patient (if able to participate) and/or their designated family members/surrogate decision-makers.

B. Key Discussion Points

• Current understanding of the patient’s condition and severity of asthma.
• Indications for continued intubation and mechanical ventilation.
• Potential candidacy for advanced therapies like ECMO (if available and appropriate), including risks and benefits.
• Expected recovery timeline and potential short-term and long-term outcomes, including possible functional limitations.
• Exploration of the patient’s values, wishes, and previously expressed preferences regarding life-sustaining treatment.
• Clarification of code status (DNAR/DNI orders) and review of any advanced directives.
• Addressing fears, anxieties, and questions from the patient and family.