Spontaneous vs Controlled Mechanical Ventilation in Acute Hypoxemic Respiratory Failure

Acute hypoxemic respiratory failure is a condition that can progress to acute respiratory distress syndrome (ARDS), requiring invasive mechanical ventilation to support gas exchange and limit lung injury. ARDS guidelines recommend lung-protective ventilation strategies-specifically low tidal volumes and limited airway pressures-to reduce ventilator-induced lung injury. Observational studies, including the global LUNG SAFE project, have described the epidemiology and management of acute hypoxemic respiratory failure and ARDS. These studies report high mortality rates (global hospital mortality, 38.6%) associated with the severity of lung injury rather than strict fulfilment of ARDS criteria. They also reveal variability in the application of evidence-based ventilation strategies across institutions. This inconsistency highlights a barrier to progress: the lack of conclusive evidence guiding ventilation management in patients with acute hypoxemic respiratory failure.

One unresolved issue is the role of spontaneous breathing during mechanical ventilation. Observational studies suggest that allowing spontaneous effort may reduce need for sedation and increase ventilator-free days. In contrast, preclinical models indicate that spontaneous breathing in severe lung injury may worsen outcomes through mechanisms such as patient-ventilator asynchrony and regional overdistension. This contrast underscores the need to balance potential benefits against physiological risks in the absence of adequate trial data. ARDS guidelines do not provide clear recommendations on this issue due to limited evidence. Only one large RCT has compared controlled ventilation to spontaneous breathing modes, finding no difference in short-term outcomes and not assessing long-term endpoints such as cognitive impairment or quality of life.As a result, clinicians must choose between guideline-based controlled ventilation and approaches that incorporate spontaneous breathing, within the context of evolving sedation practices and recovery goals. Given the variability of acute hypoxemic respiratory failure and the current evidence gap, genuine uncertainty ('clinical equipoise') exists regarding the optimal ventilation strategy. This supports the need for well-designed RCTs to determine whether spontaneous ventilation offers clinical benefit or harm. A recent survey of Nordic clinicians showed support for such a trial in patients with moderately severe acute hypoxemic respiratory failure, underscoring the relevance of this research.

The SVALBARD study is a feasibility and pilot trial comparing spontaneous and controlled mechanical ventilation in patients with acute hypoxemic respiratory failure. The study will evaluate whether it is possible to recruit patients, apply the assigned ventilation strategies, and collect the required data in a reliable way.

In addition, the study will collect descriptive clinical data to better understand patient characteristics and outcomes. The results will be used to improve the design and planning of a future randomized controlled trial.

The trial will accrue 80 patients from eight different intensive care units, four in Norway and four in Denmark.

Inclusion criteria

We will include patients who fulfil all the following criteria:

• Acutely admitted to the ICU
• AND age ≥ 18 years
• AND invasive mechanical ventilation via endotracheal tube or tracheostomy for less than 24 hours
• AND moderate acute hypoxemic respiratory failure, defined as a PaO₂-FiO₂ ratio between 13.3-26.6 kPa (100-200 mmHg) with PEEP ≥ 5 cm H2O, based on arterial blood gas analysis obtained within 2 hours before randomisation.
• AND new pulmonary infiltrate (uni- or bilateral) on chest x-ray or CT-scan obtained no more than 24 hours before randomisation.

Exclusion criteria

• Previously randomised into the SVALBARD trial.
• Informed consent following inclusion expected to be unobtainable
• Patient under coercive measures
• Withdrawal from active therapy or brain death deemed imminent.
• Chronic hypercapnic respiratory failure defined as PaCO2 > 8 kPa (60 mm Hg) in the outpatient setting.
• Listed for lung transplant.
• Acute heart failure / acute myocardial infarction / cardiac arrest during or causing index ICU admission.
• Use of home oxygen.
• Chronic mechanical ventilation for any reason except for non-invasive mechanical ventilation (CPAP/BIPAP) used solely for sleep apnoea disorder.
• Currently receiving ECMO therapy.
• Burns >70 % total body surface.
• Acute brain injury or stroke (any, including subarachnoid haemorrhage, SAH).
• Intracranial hypertension.
• Patients with planned repeat surgical interventions during current stay in ICU.