The Clinical Utility of End-tidal Carbon Dioxide as a Non-invasive Monitoring of Hyperventilation in Severe Brain Injury

Han, Chul; Lee, Sung Woo; Hong, Yun Sik; Jeong, Dong Min; Lee, Sun Bum; Choi, Sung Hyuk; Moon, Sung Woo

Abstract

PURPOSE: Hyperventilation is no longer recommended as a prophylactic intervention during the first 24 hours after severe head injury. The vasoconstriction caused by reducing carbon dioxide (CO2) levels leads to cerebral ischemia, and multiple arterial punctures may be required in order to monitor hyperventilation in severe brain injury. However, end-tidal CO2 (Petco2) reflects arterial CO2 (Paco2) noninvasively. The aim of this study was to determine whether Petco2 can be successfully used instead of Paco2 to monitor hyperventilation in brain injury patients.
METHODS
From July 1, 2006 to June 30, 2007, 71 patients who visited the emergency department of a hospital after severe brain injury (trauma or acute cerebral disorder) were enrolled. Ten patients with chest trauma, 6 patients who received CPR in the emergency department (ED), and 1 patient who had COPD were excluded. Hemodynamic variables (Glasgow coma scale, mean arterial pressure, heart rate, respiration rate, body temperature, emergency operation, serum lactate concentration) under mechanical ventilation support were measured. The concordance between Petco2 and Paco2 was analyzed by employing a Bland-Altman plot. We defined the normal range for Paco2 and Petco2 [P(a-et)co2] is -5~5 mmHg. We compared the normal and high P(a-et)co2 groups to identify factors affecting the P(a-et)co2.
RESULTS
Excepting 17 patients under exclusion criteria, we analyzed 54 of the total of 71 patients. Thirteen patients (24.1%) were seen to be below 30 mmHg for Paco2. The Pearson correlation coefficient between Paco2 and Petco2 is 0.834 (p < 0.001), and the concordance between Paco2 and Petco2 was similarly high. The patients with high P(aet) co2 showed significantly lower mean arterial pressure and lower arterial pH than patients with normal P(a-et)co2.
CONCLUSION
Petco2 shows high concordance with Paco2 in severe brain injury. However, patients with high P(a-et)co2 showed evidence of poor tissue perfusion. Therefore, the hemodynamic and tissue perfusion state should be considered when attempting to monitor hyperventilation in severe brain injury patients using Petco2.