Immune checkpoint inhibitor (ICI) pneumonitis is an immune-mediated inflammatory lung injury caused by dysregulated T-cell activation following blockade of inhibitory immune checkpoint pathways.1 ICI eligibility has expanded dramatically, from approximately 1.5% of US patients with cancer in 2011 to an estimated 56.5% by 2023.2 Given this expansion in ICI eligibility, the number of patients at risk for pneumonitis has increased accordingly. For the intensivist, this means that a typical ICU now carries a meaningful pretest probability of treating a patient with prior or ongoing ICI exposure.
ICI pneumonitis is a diagnosis of exclusion that requires compatible ICI exposure, characteristic imaging, a negative infectious workup, and corticosteroid responsiveness. Symptoms are nonspecific and include dyspnea, cough, hypoxemia, and fever. The onset is highly variable, with most cohorts reporting a median of two to five months following ICI initiation, although cases may develop as early as days or as late as two years after the first dose.3–5 On high-resolution computed tomography (HRCT) scans, five radiographic phenotypes with distinct prognostic implications have been described, initially by Naidoo and colleagues and independently confirmed by Delaunay and colleagues: organizing pneumonia, ground-glass opacity, nonspecific interstitial pneumonia (NSIP), hypersensitivity pneumonitis, and a diffuse alveolar damage (DAD) or acute interstitial pneumonia (AIP)-like pattern.4–5
The treatment is grade-based, per American Society of Clinical Oncology and National Comprehensive Cancer Network (NCCN) guidelines. Typically, the critical care-relevant subset is Grade 3-4 disease.3,6 These presentations mandate permanent ICI discontinuation, inpatient admission, and intravenous methylprednisolone at 1-2 mg/kg/day with broad empiric antimicrobials. Failure to improve within 48 hours defines steroid-refractory disease, reported in 18.5% of one cohort. All five patients with steroid-refractory disease who received infliximab died, while three out of seven patients who received intravenous immunoglobulin (IVIG) alone died.7 NCCN guidelines recommend IVIG and tocilizumab as preferred second-line agents, with mycophenolate mofetil and infliximab as other options to consider.3
The outcomes are usually poor once a patient with ICI pneumonitis requires mechanical ventilation. In a cohort from Vanderbilt University, all three patients ventilated on presentation died. A recent systematic review of critically ill patients with ICI pneumonitis reported a 26% ICU mortality, with additional deaths over the months that followed.8–9 Patients who progress to ARDS may require mechanical ventilation with standard lung-protective strategies serving as the default approach to management in the absence of disease-specific evidence.9–10
The radiographic phenotypes previously described do not all respond to ventilation in the same way. The American Thoracic Society conditionally recommends higher positive end-expiratory pressure (PEEP) in moderate to severe ARDS, which suits the recruitable DAD or AIP pattern.11 The fibrotic phenotypes behave differently. The interstitial lung disease (ILD) literature consistently shows that higher PEEP produces overdistension rather than recruitment in a stiff lung and is independently associated with mortality.12–13 None of these approaches has been studied specifically in ICI pneumonitis, but physiology argues for caution when the imaging looks fibrotic.
Management otherwise follows standard ARDS principles: lung protective tidal volumes around 6 mL per kg predicted body weight, plateau pressure under 30, driving pressure under 14 where achievable, prone positioning for moderate to severe ARDS with a Pao2 to Fio2 ratio under 150, risk-assessed use of paralytics, and conservative fluid management. The phenotype-specific caveat is PEEP, titrated upward in the recruitable DAD or AIP pattern but held back when the imaging looks fibrotic.
Extracorporeal membrane oxygenation (ECMO) deserves consideration in this population. For reference, a multicenter analysis of 297 cancer patients on venovenous ECMO (VV-ECMO) reported a 60-day survival of only 26.8%, and a Japanese database of 164 patients with ILD on ECMO reported an in-hospital mortality of 74.4%.14–15 ECMO in this population should be considered only if goals of care and realistic functional outcomes are clearly established. Selection should favor patients whose imaging is reversible, whose cancer is controlled or responding, and whose oncologic prognosis justifies the risks of ECMO. ARDS principles are the right starting point, but how aggressively they are applied should depend on the phenotype, the steroid burden, and whether the acute disease can still be reversed.
ICI pneumonitis in the ICU demands more than protocol-driven ventilation. As ICI use continues to expand, prospective data on phenotype-guided management and ECMO selection criteria are urgently needed. Until then, integrating radiographic phenotype, immunosuppression status, and goals of care into each clinical decision remains the most thoughtful approach.
References
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