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Original Investigation
March 19, 2018

Association of Hypercapnia and Hypercapnic Acidosis With Clinical Outcomes in Mechanically Ventilated Patients With Cerebral Injury

Author Affiliations
  • 1Department of Intensive Care Medicine, Frankston Hospital, Frankston, Victoria, Australia
  • 2Faculty of Medicine, Nursing and Health Sciences, Monash University, Victoria, Australia
  • 3Australian and New Zealand Intensive Care Research Center, Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Monash University, The Alfred Centre, Melbourne Victoria, Australia
  • 4The Australian and New Zealand Intensive Care Society Centre for Outcome and Resource Evaluation, Sydney, Australia
  • 5Department of Intensive Care, The Alfred Hospital, Prahran, Victoria, Australia
  • 6Department of Intensive Care Medicine, St Vincent’s Hospital, Sydney, Australia
  • 7University of New South Wales, Australia, Sydney, Australia
  • 8Institute of Neurology, University College London Hospitals NHS Foundation Trust, London, United Kingdom
JAMA Neurol. Published online March 19, 2018. doi:10.1001/jamaneurol.2018.0123
Key Points

Question  What is the association between compensated hypercapnia and hypercapnic acidosis on hospital mortality in mechanically ventilated patients with acute cerebral injury?

Findings  In this cross-sectional study including 30 742 patients with cerebral injury admitted to intensive care units in Australia and New Zealand, hospital mortality was higher in patients with hypercapnic acidosis compared with patients with compensated hypercapnia or normocapnia. In patients with hypercapnic acidosis, the adjusted odds ratio for hospital mortality increased with increasing partial pressure of carbon dioxide, while in patients with compensated hypercapnia, the adjusted odds did not change with increasing partial pressure of carbon dioxide.

Meaning  In mechanically ventilated patients with cerebral injury, hypercapnic acidosis is associated with increased mortality, and compensated hypercapnia appears to have no such association.

Abstract

Importance  Clinical studies investigating the effects of hypercapnia and hypercapnic acidosis in acute cerebral injury are limited. The studies performed so far have mainly focused on the outcomes in relation to the changes in partial pressure of carbon dioxide and pH in isolation and have not evaluated the effects of partial pressure of carbon dioxide and pH in conjunction.

Objective  To review the association of compensated hypercapnia and hypercapnic acidosis during the first 24 hours of intensive care unit admission on hospital mortality in adult mechanically ventilated patients with cerebral injury.

Design, Setting, and Participants  Multicenter, binational retrospective review of patients with cerebral injury (traumatic brain injury, cardiac arrest, and stroke) admitted to 167 intensive care units in Australia and New Zealand between January 2000 and December 2015. Patients were classified into 3 groups based on combination of arterial pH and arterial carbon dioxide (normocapnia and normal pH, compensated hypercapnia, and hypercapnic acidosis) during the first 24 hours of intensive care unit stay.

Main Outcomes and Measures  Hospital mortality.

Results  A total of 30 742 patients (mean age, 55 years; 21 827 men [71%]) were included. Unadjusted hospital mortality rates were highest in patients with hypercapnic acidosis. Multivariable logistic regression analysis and Cox proportional hazards analysis in 3 diagnostic categories showed increased odds of hospital mortality (cardiac arrest odds ratio [OR], 1.51; 95% CI, 1.34-1.71; stroke OR, 1.43; 95% CI, 1.27-1.6; and traumatic brain injury OR, 1.22; 95% CI, 1.06-1.42; P <.001) and hazard ratios (HR) (cardiac arrest HR, 1.23; 95% CI, 1.14-1.34; stroke HR, 1.3; 95% CI, 1.21-1.4; traumatic brain injury HR, 1.13; 95% CI, 1-1.27), in patients with hypercapnic acidosis compared with normocapnia and normal pH. There was no difference in mortality between patients who had compensated hypercapnia compared with patients who had normocapnia and normal pH. In patients with hypercapnic acidosis, the adjusted OR of hospital mortality increased with increasing partial pressure of carbon dioxide, while no such increase was noted in patients with compensated hypercapnia.

Conclusions and Relevance  Hypercapnic acidosis was associated with increased risk of hospital mortality in patients with cerebral injury. Hypercapnia, when compensated to normal pH during the first 24 hours of intensive care unit admission, may not be harmful in mechanically ventilated patients with cerebral injury.

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