Common methods of identifying hypercapnic respiratory failure produce meaningfully different cohorts. Brian W Locke, Krishna M Sundar, Jeanette Brown, Ramkiran Gouripeddi.

Evidence Review Table: Hypercapnia: Papers defining groups with hypercapnic respiratory failure, study question, how they identified patients, and key findings

Ouanes-Besbes et al. 2021. Tunisia

• Ouanes-Besbes L, Hammouda Z, Besbes S, Nouira W, Lahmar M, Ben Abdallah S, Ouanes I, Dachraoui F, Abroug F. Diagnosis of Sleep Apnea Syndrome in the Intensive Care Unit: A Case Series of Survivors of Hypercapnic Respiratory Failure. Annals of the American Thoracic Society. 2021 Apr;18(4):727-9. Link to paper
• What is the frequency of undiagnosed sleep apnea among patients admitted to the ICU with hypercapnic respiratory failure?
• Admitted to the ICU 2015-2018, PaCO2 > 6kpa, pH < 7.35. No prior OSA syndrome diagnosis.
• 104 of 124 who undersent HSAT had severe OSA. 34 were low risk by STOP-BANG (<=3 at ICU discharge). 40 declined HSAT or lost to followup. Thus, overall prevalence in survivors was over 50%

Wilson et al., 2021. USA (Michigan)

• Wilson MW, Labaki WW, Choi PJ. Mortality and Healthcare Use of Patients with Compensated Hypercapnia. Annals of the American Thoracic Society. 2021 Dec;18(12):2027-32. Link to paper
• What are the demographic, spirometric, lab value, and outcomes (utilization, mortality) of inpatients with compensated hypercapnic resp failure?
• 18+, hospitalized w/ ABG showing CO2 over 45 and pH 7.35-7.45
• 44.2% mortality over median 592 days with HR 1.09 for each 5 mmHg of co2.

Meservey et al. 2020. USA (Vermont)

• Meservey AJ, Burton MC, Priest J, Teneback CC, Dixon AE. Risk of readmission and mortality following hospitalization with hypercapnic respiratory failure. Lung. 2020 Feb;198(1):121-34. Link to paper
• What features of patients admitted for hypercapnic respiratory failure predict readmission?
• 18 y/o+ admitted (either ICU or floor) with diagnostic code for hypercapnic respiratory failure during 2016. N=202
• Logistic regression on 30d readmission or death: older, dx of peripheral vascular disease, and use of home o2 assoc w increased risk. Very high morb+mortality generally (7% mort during index admission; 23% 30d readmission rate, usually for hypercapnic resp failure.)

Adler et al. 2017. Switzerland

• Adler D, Pepin JL, Dupuis-Lozeron E, Espa-Cervena K, Merlet-Violet R, Muller H, Janssens JP, Brochard L. Comorbidities and subgroups of patients surviving severe acute hypercapnic respiratory failure in the intensive care unit. American journal of respiratory and critical care medicine. 2017 Jul 15;196(2):200-7. Link to paper
• What are the lung, cardiac, and sleep functioning among patients who survive admission for hypercapnic respiratory failure requiring ventilation?
• N=78 patients, consecutive; 1 center Geneva, 2012. Recruited at ICU discharge after surviving: primary admission for Resp failure, PaCO2 over 6.3 kpa and requiring invasive or NIV. Exclude NM dz, iatrogenic, or with persisting confusion
• 21% had been hospitalized in the last yr for resp failure. 67% had COPD. 81 percent of patients without COPD were obese. 29% had OSA known (mostly untreated); 66% of those tested had mod-severe OSA. 51% had COPD&OSA. 44% had HFpEF, ~16%ish had pHTN

Chung et al 2022. Australia

• Chung Y, Garden FL, Marks GB, Vedam H. Population Prevalence of Hypercapnic Respiratory Failure from Any Cause. American Journal of Respiratory and Critical Care Medicine. 2022 Jan 27(ja). Link to paper
• What is the population prevalence of hypercapnia from any cause?
• Identified by initial ABG PaCO2 over 45, excluded iatrogenic causes/sedation. N=891 people, 1135 blood gasses
• 150 per 100k/yr. Acidosis in 55%. Compared to 45-54 yr, each decade prevalence x2.1, 6.2, 15.7, 26.2. Similar to PE