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

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Introduction

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.

Methods

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.

Results

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.

Conclusion

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

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