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La pression télé expiratoire en CO₂ n'est pas un paramètre pertinent de surveillance d'un traumatisme crânien grave

Philippe Seguin, MD^*, Jean Paul Bleichner, MD^*, Bernard Branger, MD, Yves Marie Guillou, MD^*, Alain Feuillu, PhD and Yannick Mallédant, MD^*

^* Service d'Anesthésie-Réanimation Chirurgicale,
Département d'Hygiène Hospitalière,
et Laboratoire de Biochimie, Rennes Cedex, France.

Adresser la correspondance à: Dr Philippe Seguin, Service de Réanimation Chirurgicale, CHR-U de Pontchaillou, 2, rue Henri Le Guilloux, 35033 Rennes Cedex, France. Téléphone: 33-(0)-2-99-28-42-46; Télécopieur: 33-(0)-2-99-28-24-21; Courriel: yannick.malledant{at}chu-rennes.fr

Purpose: To evaluate the agreement between end-tidal carbon dioxide (PETCO₂) and arterial CO₂ (PaCO₂) in patients with traumatic brain injury and to document the course of the (PaCO₂ – PETCO2) gradient over time.

Methods: Twenty one traumatic brain injury patients (Coma Glasgow Scale 8) were included in this prospective observational study over a period of six months. Simultaneous determinations of PaCO₂ and PETCO₂ (by infrared capnometry) were recorded. Agreement between PaCO₂ and PETCO₂ was determined by the statistical method described by Bland and Altman. Changes in PETCO₂ over time were compared with changes in PaCO₂. Factors likely to explain a gradient superior to ± 4 mmHg were explored.

Results: One hundred and eleven data pairs were obtained. The bias was 5.5 mmHg with a precision of 5.1 mmHg and limits of agreement ranged from –4.5 mmHg to 15.5 mmHg. The latter exceeded the predefined limits of agreement established to determine interchangeability between methods (± 4 mmHg). PETCO₂ and PaCO₂ changed in opposite directions in 20% of 90 consecutive measurements. Only the duration of ventilation was found to be significantly associated with a gradient superior to ± 4 mmHg.

Conclusions: In this selected population of patients with severe traumatic brain injury, measurements of PETCO₂ and PaCO₂ are not interchangeable. Further, the PaCO₂ - PETCO₂ gradient is not stable over time and cannot predict variations of PaCO₂. The use of PETCO₂ instead of PaCO₂ could be deleterious in patients in whom strict control of PaCO₂ values is required.