# Management of Acute Life-Threatening Asthma Exacerbations in the Intensive Care Unit
## 4 Acute Life-Threatening Asthma Advanced Management in the ICU
### Mechanical Ventilation  
Although life-threatening asthma is rare, a small proportion of patients may require IMV. While IMV is not a specific therapy for asthma, it is offered as a last resort while allowing time for bronchodilator therapy to take effect. Severe airflow limitation is the hallmark of acute asthma exacerbations. Patients with life-threatening asthma may present with severe respiratory distress, hypoxemia, arrhythmias, and pulse paradoxes due to air trapping with cardiovascular instability or, at later stages, hypercapnia and respiratory arrest. High airway pressures and dynamic hyperinflation can lead to air trapping, barotrauma, the development of pneumothorax, and hemodynamic instability [71]. The principle of mechanical ventilation in asthma is to avoid dynamic hyperinflation. The ventilation mode can be volume-assisted or controlled pressure-cycled ventilation with a tidal volume of 6-8 mL/kg IBW as a starting point. Minute ventilation should be adjusted to allow adequate time for the expiratory phase. Higher inspiratory to expiratory ratio (I:E) time is often required at 1:3 or 1:4 with a low respiratory rate (e.g., 12-14/min). In the event of continued breath stacking, disconnecting the ventilator circuit followed by manual decompression is required to improve the dynamic hyperinflation. Figure 2 is a pictorial depiction of the flow-volume loop during airflow obstruction and air trapping during acute asthma [72; 73; 74].  
\begin{table}
\begin{tabular}{c} \hline
**Potential Complications during intubation** \\ \hline Aspiration \\ Barotrauma/volutrauma \\ Cardiovascular collapse \\ Cardiac arrhythmias \\ Cardiac arrest \\ \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 2: Flow volume loops depicting (**A**) normal pattern, (**B**) obstructive pattern, and (**C**) air trapping during severe asthma exacerbation. Yellow: Inspiration; Blue: Expiration and Grey: Air trapping.  
Positive end-expiratory pressure (PEEP) is generally applied to all mechanically ventilated patients to avoid alveolar collapse, and higher levels of PEEP are often utilised for continued lung recruitment during mechanical ventilation in ARDS patients [75; 76]. In patients with asthma, airway obstruction and expiratory flow limitation result in the generation of intrinsic PEEP, which can be measured by performing an expiratory breath hold on the ventilator. Excessive intrinsic PEEP can lead to gas trapping and, consequently, dynamic hyperinflation. Establishing optimal PEEP during mechanical ventilation for patients with asthma is a contentious issue. In practice, most advocate an applied PEEP of zero or reduced levels of PEEP below the intrinsic PEEP to minimise hyperinflation. Permissive hypercapnia is often adopted with deep sedation and neuromuscular paralysis at early stages to prevent patient-ventilator desynchrony. Standard ideal ventilator settings following mechanical ventilation are detailed in Figure 1. Reviews of mechanical ventilation strategies in asthma are described elsewhere by several in-depth reviews [77; 78; 79].