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Use of the Esophageal Doppler and Sublingual Capnometer in the Hemodynamic Assessment of Mechanically Ventilated Surgical Patients

Maine Medical Center, Portland, ME

PURPOSE: Circulatory failure in the critically ill is difficult to assess with the pulmonary artery catheter (PAC). Criticism of this technology has focused on erroneous interpretation of PAC measurement especially in mechanically ventilated patients. The Esophageal Doppler (ED) has emerged as a potential alternative to the PAC. Sublingual Capnometry (SC) allows assessment of end-organ perfusion and therefore provides additional information about circulatory failure.

METHODS: The ED was placed in 28 mechanically ventilated patients with PAC in place. A total of 54 simultaneous ED, PAC and SC measurements were obtained. Arterial blood gases (ABG) were measured concurrently. Hemodynamics, mixed venous oxygen saturation (SvO2), serum lactate and ventilator mode settings were recorded. The Pearson correlation was used to compare measurements. Significance was defined as a p value < 0.05.

RESULTS: PAC cardiac output and ED correlated well (r=0.71, p<0.001) as did cardiac index (r=0.77, p<0.001). ED corrected flow time, a measure of LV filling volume, correlated with PAC cardiac index (r=0.83, p<0.001). While the Pulmonary Artery Wedge Pressure (PAWP) correlated with the End-Diastolic Volume Index (EDVI) (r=0.61, p<0.05), it did not vary with PAC cardiac index (r=0.19, p>0.1) as would be predicted by the Starling mechanism. Similarly, the EDVI did not predict the PAC cardiac index (r=-0.12, p>0.1). As a marker of end-organ perfusion, the difference between the SC PCO2 and arterial PCO2 (PCO2 gap) correlated with the SvO2 (r=-0.49, p<0.05) but not with serum lactate (r=0.20, p>0.05). The serum lactate did not vary with the PAC cardiac index (r=-0.34, p>0.05). The PCO2 gap had the expected inverse correlation with PAC cardiac index (r=-0.68, p<0.01) as did the SvO2 (r=-0.63, p<0.01).

CONCLUSION: The ED provides a fast alternative to the PAC and may obviates the technical limitation imposed by fluctuating intrathoracic pressures. The SC appears to track end-organ perfusion more predictably than serum lactate.

CLINICAL IMPLICATIONS: The ED and SC may be effectively substituted for the PAC and other measures of end-organ perfusion in some critically ill patients.

DISCLOSURE: S. Ahmad, None.