# Management of Acute Life-Threatening Asthma Exacerbations in the Intensive Care Unit
## 4 Acute Life-Threatening Asthma Advanced Management in the ICU
### Non-Invasive Ventilation (NIV)  
Non-invasive ventilation (NIV) has the physiological effects of reducing the work of breathing and alveolar recruitment, improving dynamic lung compliance, offsetting the intrinsic positive end expiratory pressure (PEEP), and improving gas exchange during acute respiratory failure [55; 56]. Intensive care admission and invasive mechanical ventilation (IMV) for acute respiratory failure from asthma are associated with significant morbidity. While NIV is an established practice for hypercapnic respiratory failure for COPD patients, the use of NIV during acute asthma exacerbations remains a contentious issue. Patients with acute severe asthma often present with hypoxemic respiratory failure rather than hypercapnic respiratory failure, and the primary aim is to optimise oxygenation while alleviating airway symptoms with bronchodilator therapy. However, patients with later-stage life-threatening or near-fatal asthma may develop hypercapnic respiratory failure, often necessitating endotracheal intubation and mechanical ventilation. Despite the lack of robust clinical evidence and guidance on using non-invasive ventilation in asthma, more recent retrospective cohort studies documented an increased frequency of NIV use [57; 58; 59; 7]. However, NIV failure can be associated with an increased length of hospital stay and in hospital mortality [60].  
Although multiple randomised controlled trials have been published in this area, the studies consisted of small number of patients and were underpowered to assess robust clinical outcomes such as the need for IMV or mortality. A Cochrane review conducted over a decade ago summarised the findings from five small RCTs of 206 participants and concluded that there was insufficient clinical data to support the use of NIV in status asthmaticus [61]. However, more recently, a systematic review and meta-analysis of 10 pa diatric trials with 558 participants concluded that NIV use is associated with improved gas exchange, lower respiratory rate, and shorter hospital stay [62]. In a large multi-centre retrospective cohort study in ICUs, a quarter of patients received NIV for acute asthma exacerbation, and for those who received invasive mechanical ventilation (27%), 21% received NIV before IMV initiation. Moreover, the use of NIV also increased over the study period, from 18.5% in 2010 to 29.9% in 2017 [57]. However, a third of the studied patients had obesity (32.9%), and a quarter had obstructive sleep apnoea (26.7%), patient groups who are more likely to benefit from NIV [63]. Moreover, these cohort studies do not differentiate between patients with hypoxemic and hypercapnic respiratory failure. Large randomised controlled trials are required to assess the clinical efficacy of NIV in acute asthma exacerbations for preventing IMV and the impact on mortality. While NIV is not an alternative to IMV, the use of NIV should be limited to safe areas where IMV can be utilised rapidly, and at-risk patients can be monitored very closely.