Abstract
Tissue capnometry may be suitable for the indirect evaluation of regional hypoperfusion. We tested the performance of a new sublingual capillary tonometer in experimental hemorrhage. Thirty-six anesthetized, ventilated mini pigs were divided into sham-operated (n = 9) and shock groups (n = 27). Hemorrhagic shock was induced by reducing mean arterial pressure (MAP) to 40 mmHg for 60 min, after which fluid resuscitation started aiming to increase MAP to 75% of the baseline value (60–180 min). Sublingual carbon-dioxide partial pressure was measured by tonometry, using a specially coiled silicone rubber tube. Mucosal red blood cell velocity (RBCV) and capillary perfusion rate (CPR) were assessed by orthogonal polarization spectral (OPS) imaging. In the 60 min shock phase a significant drop in cardiac index was accompanied by reduction in sublingual RBCV and CPR and significant increase in the sublingual mucosal-to-arterial PCO2 gap (PSLCO2 gap), which significantly improved during the 120 min resuscitation phase. There was significant correlation between PSLCO2 gap and sublingual RBCV (r = −0.65, p < 0.0001), CPR (r = −0.64, p < 0.0001), central venous oxygen saturation (r = −0.50, p < 0.0001), and central venous-to-arterial PCO2 difference (r = 0.62, p < 0.0001). This new sublingual tonometer may be an appropriate tool for the indirect evaluation of circulatory changes in shock.
Highlights
Disturbances of the microcirculation are tightly linked to circulatory failure of different origin; evaluation of the microcirculatory status has gained increasing importance in the diagnosis and treatment of critically ill patients
Severe shock state was achieved in the animals of the shock group as indicated by marked and significant changes in macrohemodynamics during the first 60 minutes: mean arterial pressure (MAP) decreased, heart rate (HR) increased, and cardiac index (CI) and global end-diastolic volume index (GEDVI) decreased significantly (Figures 3(a), 3(b), 3(c), and 3(d))
This change in global hemodynamics was accompanied by a significant drop in base excess (BE) in the shock group (T0: 6.4 ± 2.1 and T2: 1.1 ± 2.8 mmol L−1 p < 0.05), while there was no similar change in the sham group (T0: 5.6 ± 1.8 and T2: 5.9 ± 1.9 mmol L−1)
Summary
Disturbances of the microcirculation are tightly linked to circulatory failure of different origin; evaluation of the microcirculatory status has gained increasing importance in the diagnosis and treatment of critically ill patients. The measurement of the partial pressure of carbon dioxide (PCO2) in tissues is a potentially feasible technique for the indirect evaluation of the microcirculation [4, 5]. This parameter reflects the adequacy of regional microvascular blood flow, as intramucosal PCO2 is inversely related to the proportion of well perfused capillaries, and is mainly dependent on tissue perfusion [6, 7]. Acute increases or decreases in the PCO2 of the arterial blood (PaCO2) result in comparable changes in the tissue PCO2 [8]; it should be interpreted in relation to PaCO2. By subtracting PaCO2 from the tissue PCO2, special gap values can be calculated which are more accurate than the mucosal PCO2 alone, as they are independent of concurrent changes in
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