Elsevier

Resuscitation

Volume 84, Issue 7, July 2013, Pages 927-934
Resuscitation

Clinical paper
Arterial carbon dioxide tension and outcome in patients admitted to the intensive care unit after cardiac arrest

https://doi.org/10.1016/j.resuscitation.2013.02.014Get rights and content

Abstract

Background

Arterial carbon dioxide tension (PaCO2) affects neuronal function and cerebral blood flow. However, its association with outcome in patients admitted to intensive care unit (ICU) after cardiac arrest (CA) has not been evaluated.

Methods and results

Observational cohort study using data from the Australian New Zealand (ANZ) Intensive Care Society Adult-Patient-Database (ANZICS-APD). Outcomes analyses were adjusted for illness severity, co-morbidities, hypothermia, treatment limitations, age, year of admission, glucose, source of admission, PaO2 and propensity score.

We studied 16,542 consecutive patients admitted to 125 ANZ ICUs after CA between 2000 and 2011. Using the APD-PaCO2 (obtained within 24 h of ICU admission), 3010 (18.2%) were classified into the hypo- (PaCO2 < 35 mmHg), 6705 (40.5%) into the normo- (35–45 mmHg) and 6827 (41.3%) into the hypercapnia (>45 mmHg) group. The hypocapnia group, compared with the normocapnia group, had a trend toward higher in-hospital mortality (OR 1.12 [95% CI 1.00–1.24, p = 0.04]), lower rate of discharge home (OR 0.81 [0.70–0.94, p < 0.01]) and higher likelihood of fulfilling composite adverse outcome of death and no discharge home (OR 1.23 [1.10–1.37, p < 0.001]). In contrast, the hypercapnia group had similar in-hospital mortality (OR 1.06 [0.97–1.15, p = 0.19]) but higher rate of discharge home among survivors (OR 1.16 [1.03–1.32, p = 0.01]) and similar likelihood of fulfilling the composite outcome (OR 0.97 [0.89–1.06, p = 0.52]). Cox-proportional hazards modelling supported these findings.

Conclusions

Hypo- and hypercapnia are common after ICU admission post-CA. Compared with normocapnia, hypocapnia was independently associated with worse clinical outcomes and hypercapnia a greater likelihood of discharge home among survivors.

Introduction

Cardiac arrest (CA) is common1, 2, 3 with an incidence up to 2.0 per 1000 person years.4, 5, 6 CA is associated with a high morbidity and mortality.7, 8 Even among patients admitted to the hospital after return of a spontaneous circulation only 40% are discharged alive.8, 9, 10 Even fewer have sufficient neurological recovery to be able to return home.11 To date, therapeutic hypothermia is the only intervention shown to improve neurological outcome among such patients.12 However, other modifiable components of patient care may also deliver better neurological outcomes. Arterial oxygen and carbon dioxide tension (PaCO2) could be one such factor. Indeed, two studies11, 13 recently explored the relationship between arterial oxygenation and outcomes generating conflicting conclusions. On the other hand, there are very limited data on the relationship between PaCO2 and outcome in cardiac arrest patients.

CO2 may have neuro-protective properties. Mild hypercapnia improves cerebral perfusion,14 which is thought to be decreased in the post resuscitation phase.15 In addition, CO2, has anticonvulsant properties16, 17 as well as anti-inflammatory and anti-oxidants effects.18 On the other hand, hypocapnia has been associated with neuronal injury in animal models19 and after traumatic brain injury.20

Thus, PaCO2 immediately after CA might be important and, because of mechanical ventilation, can be controlled in almost all cases.21, 22 To date, however, the relationship between PaCO2 and outcomes has not been studied. Accordingly, we performed a retrospective observational study using a large bi-national database to determine the relationship between PaCO2 in the first 24 h after intensive care unit (ICU) admission following CA and both survival and discharge home.

Section snippets

Australian and New Zealand Adult Patient Database

We extracted data from the Australian and New Zealand (ANZ) Intensive Care Society Adult Patient Database (ANZICS-APD), a high quality database23, 24, 25, 26 of almost all admissions to ANZ ICUs. Data are collected under the Quality Assurance Legislation of the Commonwealth of Australia (Part VC Health Insurance Act 1973, Commonwealth of Australia) with government support and funding. Each hospital allows the data to be used for appropriate research, governed by the ANZICS Centre for Outcomes

Demographic characteristics

We identified 23,828 patients (Fig. 1); we excluded 5558 (23.3%) who were not mechanically ventilated, 564 (2.3%) who had associated trauma, 475 (2.0%) without hospital mortality data and 689 (2.9%) without ABG data. Hence, 16,542 patients from 125 contributing ICUs were included in the study.

Baseline characteristics are presented in 1. A total of 11,239 (67.9%) were at home prior to hospital admission and 8396 (50.8%) were admitted to ICU directly from the Emergency Department. The mean APACHE

Key findings

In a multi-centre retrospective observational study of more than 16,000 adult patients admitted to ICUs in Australia and New Zealand (ANZ) after non-traumatic cardiac arrest, we examined the independent relationship between PaCO2 and major clinical outcomes. We found that, within 24 h of admission, about one in five patients had at least one episode of hypocapnia, while about 40% had at least one episode of hypercapnia. Nested cohort analyses revealed that such abnormal values most often

Conclusions

Abnormal PaCO2 values are common within 24 h after ICU admission post-CA. After adjustment for potential confounders such abnormalities were associated with changes in outcome. In particular, compared with normocapnia, hypocapnia was associated with an increase in combined mortality and failure to be discharged home and a lower likelihood of being discharged home among survivors. In contrast, hypercapnia was associated with higher likelihood of being discharged home among survivors. Given these

Conflict of interest statement

All authors stated that they had no conflicts of interest to declare.

Acknowledgements

Authorship: Glenn M. Eastwood and Antoine G. Schneider conceived the study interpreted the data and co-drafted the manuscript. Rinaldo Bellomo conceived the study in conjunction with other authors and co-wrote the final manuscript. Michael Bailey performed the statistical analysis and co-wrote the manuscript. Miklos Lipscey, MD, PhD conceived the study in conjunction with other authors, participated in the data collection and critically reviewed the final manuscript. David Pilcher conceived the

References (54)

  • V. Lemiale et al.

    Changes in cerebral blood flow and oxygen extraction during post-resuscitation syndrome

    Resuscitation

    (2008)
  • L. Pynnonen et al.

    Therapeutic hypothermia after cardiac arrest – cerebral perfusion and metabolism during upper and lower threshold normocapnia

    Resuscitation

    (2011)
  • J.P. Nolan et al.

    Post-cardiac arrest syndrome: epidemiology, pathophysiology, treatment, and prognostication. A Scientific Statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke

    Resuscitation

    (2008)
  • S.A. Webb et al.

    Pandemic (H1N1) 2009 influenza (“swine flu”) in Australian and New Zealand intensive care

    Crit Care Resusc

    (2009)
  • T.W. Smith et al.

    Sudden cardiac death: epidemiologic and financial worldwide perspective

    J Interv Card Electrophysiol

    (2006)
  • 2005 American Heart Association Guidelines for cardiopulmonary resuscitation and emergency cardiovascular care

    Circulation

    (2005)
  • C. Warden et al.

    Poisson cluster analysis of cardiac arrest incidence in Columbus, Ohio

    Prehosp Emerg Care

    (2012)
  • I.G. Stiell et al.

    Advanced cardiac life support in out-of-hospital cardiac arrest

    N Engl J Med

    (2004)
  • J.H. Kilgannon et al.

    Association between arterial hyperoxia following resuscitation from cardiac arrest and in-hospital mortality

    JAMA

    (2010)
  • S.A. Bernard et al.

    Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia

    N Engl J Med

    (2002)
  • R. Bellomo et al.

    Arterial hyperoxia and in-hospital mortality after resuscitation from cardiac arrest

    Crit Care

    (2011)
  • R.C. Vannucci et al.

    Carbon dioxide protects the perinatal brain from hypoxic–ischemic damage: an experimental study in the immature rat

    Paediatrics

    (1995)
  • G. Buunk et al.

    Cerebral vasoconstriction in comatose patients resuscitated from a cardiac arrest?

    Intensive Care Med

    (1996)
  • W. Lennox

    The effect on epileptic seizures of varying the composition of the respired air

    J Clin Invest

    (1928)
  • G.H. Pollock et al.

    Central inhibitory effects of carbon dioxide; man

    Proc Soc Exp Biol Med

    (1949)
  • J. Ohyu et al.

    Hypocapnia under hypotension induces apoptotic neuronal cell death in the hippocampus of newborn rabbits

    Pediatr Res

    (2000)
  • J.P. Muizelaar et al.

    Adverse effects of prolonged hyperventilation in patients with severe head injury: a randomized clinical trial

    J Neurosurg

    (1991)
  • Cited by (153)

    View all citing articles on Scopus

    A Spanish translated version of the abstract of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2013.02.014.

    1

    These authors contributed equally to this work.

    View full text