Nicole Mckenzie1, Judith Finn2, Geoffrey Dobb3, Paul Bailey4, Glenn Arendts5, Antonio Celenza6, Daniel Fatovich7, Ian Jenkins8, Stephen Ball4, Janet Bray9, Kwok M Ho10. 1. Prehospital, Resuscitation and Emergency Care Research Unit (PRECRU), Curtin University, Bentley, WA, Australia; Intensive Care Unit, Royal Perth Hospital, Perth, WA, Australia. Electronic address: nicole.mckenzie@curtin.edu.au. 2. Prehospital, Resuscitation and Emergency Care Research Unit (PRECRU), Curtin University, Bentley, WA, Australia; St John Western Australia, Belmont, WA, Australia; Medical School, University of Western Australia, Crawley, WA, Australia; School of Public Health and Preventive Medicine, Monash University, Melbourne, VIC, Australia. 3. Intensive Care Unit, Royal Perth Hospital, Perth, WA, Australia; Medical School, University of Western Australia, Crawley, WA, Australia. 4. Prehospital, Resuscitation and Emergency Care Research Unit (PRECRU), Curtin University, Bentley, WA, Australia; St John Western Australia, Belmont, WA, Australia. 5. Medical School, University of Western Australia, Crawley, WA, Australia; Fiona Stanley Hospital, Murdoch, WA, Australia. 6. Medical School, University of Western Australia, Crawley, WA, Australia; Sir Charles Gairdner Hospital, Nedlands, WA, Australia. 7. Prehospital, Resuscitation and Emergency Care Research Unit (PRECRU), Curtin University, Bentley, WA, Australia; Medical School, University of Western Australia, Crawley, WA, Australia; Emergency Medicine, Royal Perth Hospital, Perth, WA, Australia. 8. Fremantle Hospital, Fremantle, WA, Australia. 9. School of Public Health and Preventive Medicine, Monash University, Melbourne, VIC, Australia. 10. Prehospital, Resuscitation and Emergency Care Research Unit (PRECRU), Curtin University, Bentley, WA, Australia; Intensive Care Unit, Royal Perth Hospital, Perth, WA, Australia; Medical School, University of Western Australia, Crawley, WA, Australia; School of Veterinary and Life Sciences, Murdoch University, Perth, WA, Australia.
Abstract
PURPOSE: International guidelines recommend targeting normocapnia in mechanically ventilated out-of-hospital cardiac arrest (OHCA) survivors, but the optimal arterial carbon dioxide (PaCO2) target remains controversial. We hypothesised that the relationship between PaCO2 and survival is non-linear, and targeting an intermediate level of PaCO2 compared to a low or high PaCO2 in the first 24-h of ICU admission is associated with an improved survival to hospital discharge (STHD) and at 12-months. METHODS: We conducted a retrospective multi-centre cohort study of adults with non-traumatic OHCA requiring admission to one of four tertiary hospital intensive care units for mechanical ventilation. A four-knot restricted cubic spline function was used to allow non-linearity between the mean PaCO2 within the first 24 h of ICU admission after OHCA and survival, and optimal PaCO2 cut-points were identified from the spline curve to generate corresponding odds ratios. RESULTS: We analysed 3769 PaCO2 results within the first 24-h of ICU admission, from 493 patients. PaCO2 and survival had an inverted U-shape association; normocapnia was associated with significantly improved STHD compared to either hypocapnia (<35 mmHg) (adjusted odds ratio [aOR] 0.45, 95% confidence interval [CI] 0.24-0.83) or hypercapnia (>45 mmHg) (aOR 0.45, 95% CI 0.24-0.84). Of the twelve predictors assessed, PaCO2 was the third most important predictor, and explained >11% of the variability in survival. The survival benefits of normocapnia extended to 12-months. CONCLUSIONS: Normocapnia within the first 24-h of intensive care admission after OHCA was associated with an improved survival compared to patients with hypocapnia or hypercapnia.
PURPOSE: International guidelines recommend targeting normocapnia in mechanically ventilated out-of-hospital cardiac arrest (OHCA) survivors, but the optimal arterial carbon dioxide (PaCO2) target remains controversial. We hypothesised that the relationship between PaCO2 and survival is non-linear, and targeting an intermediate level of PaCO2 compared to a low or high PaCO2 in the first 24-h of ICU admission is associated with an improved survival to hospital discharge (STHD) and at 12-months. METHODS: We conducted a retrospective multi-centre cohort study of adults with non-traumatic OHCA requiring admission to one of four tertiary hospital intensive care units for mechanical ventilation. A four-knot restricted cubic spline function was used to allow non-linearity between the mean PaCO2 within the first 24 h of ICU admission after OHCA and survival, and optimal PaCO2 cut-points were identified from the spline curve to generate corresponding odds ratios. RESULTS: We analysed 3769 PaCO2 results within the first 24-h of ICU admission, from 493 patients. PaCO2 and survival had an inverted U-shape association; normocapnia was associated with significantly improved STHD compared to either hypocapnia (<35 mmHg) (adjusted odds ratio [aOR] 0.45, 95% confidence interval [CI] 0.24-0.83) or hypercapnia (>45 mmHg) (aOR 0.45, 95% CI 0.24-0.84). Of the twelve predictors assessed, PaCO2 was the third most important predictor, and explained >11% of the variability in survival. The survival benefits of normocapnia extended to 12-months. CONCLUSIONS: Normocapnia within the first 24-h of intensive care admission after OHCA was associated with an improved survival compared to patients with hypocapnia or hypercapnia.