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Relationship between systemic arterial pressure (SAP) and EtCO2 in patients with hemorrhagic shock

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Capnometry may be useful in monitoring critical ED patients for early signs of shock or pulmonary embolus. However, EtCO2 levels must be interpreted in the context of other parameters giving information about the patient's clinical status. A fall in EtCO2 mav indicate decreased lung perfusion. If ventilation has not changed, the clinician should be alerted to reevaluate the patient for early signs of shock. The aim of this study was to examine the relationship between the changes in systemic arterial pressure (SAP) and in EtCO2 in hemodynamic status usually encountered during hemorrhagic shock.


Data were collected prospectively in EMS-PHU from February 1998 until August 1999. The study population was composed of adult (at least 18 years of age; mean age 47.8± 13.4; rang 18-76 years) 68 patients (25 female, 43 male) with 3rd or 4th stage of hemorrhagic shock (trauma, GI or respiratory hemorrhage). We measured SAP and EtCO2 for 1 min first 5 min, and then each 5 min). For each patient we determined MEES 1, MEES 2, APACHE II, ΔMEES. SAP and EtCO2 were measured with PROPAQ encore, Vital Sings Monitor, Protocol Systems, INC, Beaverton, OR, USA. We measured for each patient ΔEtCO2 and ΔSAP in interval from prehospital setting to hospitalization (674 simultaneous measurements were recorded). All EtCO2 and SAP values are reported in mmHg.


The mean and standard deviation of the ΔEtCO2 was 12.52± 6.36 and of the Δ was 39.95± 18.23. Results are presented in the Figure. Statistics on the 68 individual correlations indicate ΔSAP=0.06 (± 0.18) + 3.97 (± 0.63)× ΔEtCO2 with r=0.91± 0.08.


A linear relationship does exist between the changes in SAP and in EtCO2 in patients with hemorrhagic shock. A 1mmHg change in EtCO2 is associated with ~ 4 mmHg change in SAP. It suggests that small changes in EtCO2 may be useful sign of significant changes in SAP (cardiac output). We conclude that the measurement of EtCO2 during hemorrhagic shock may be useful as a indicator of SAP and successful volume resuscitation.

figure 1

ΔSAP 0 0.18 + 3.63× ΔEtCO2; r=0.89; n=674.

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Grmec, Š., Zabavnik, Z., Batišta, M. et al. Relationship between systemic arterial pressure (SAP) and EtCO2 in patients with hemorrhagic shock. Crit Care 4 (Suppl 1), P147 (2000).

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