Monitoring the tissue perfusion during hemorrhagic shock and resuscitation: Tissue-to-arterial carbon dioxide partial pressure gradient in a pig model

Abstract

Background: Transcutaneous CO2 (tcPCO2) and arterial CO2 (artPCO2) decoupling occurs during shock states. Our study aimed to test the hypothesis that the gradient between tcPCO2 and artPCO2 (tc-artPCO2) can detect inadequate tissue perfusion during hemorrhagic shock and resuscitation. Methods: This prospective animal study was performed by a qualified and experienced research team using female pigs (LWD, weighing 29–34 kg) at university-based experimental laboratory. Progressive massive hemorrhagic shock was induced in mechanically-ventilated pigs by stepwise blood withdrawal. Next, all the animals were then resuscitated by transfusing the stored blood in stages. A transcutaneous monitor was attached to the animals’ ear to measure the tcPCO2 and transcutaneous oxygen pressure (tcPO2). The pulmonary artery catheter (PAC) and pulse index continuous cardiac output (PiCCO) were used to monitor several hemodynamic parameters. Results: Hemorrhage and blood transfusion precisely impacted hemodynamic and laboratory data, such as cardiac output (CO), stroke volume, mean arterial pressure, heart rate, pulmonary artery wedge pressure, global end-diastolic volume, hemoglobin, and arterial lactate. The tc-artPCO2 level markedly increased as CO decreased. In the analyses of the 42 paired measurements, there were significant correlations of tc-artPCO2 with systemic oxygen delivery (DO2) and CO (DO2: r = -0.83, CO by PAC: r = -0.79; CO by PiCCO: r = -0.74; all P < 0.0001) levels. The critical level of oxygen delivery (DO2crit) was 11.72 mL/kg/min according to tcPO2 (at a threshold of 30 mmHg). The receiver operating characteristic curve analyses revealed that the area under the curves (AUCs) that predicted DO2crit for tc-artPCO2, shock index (SI), and lactate were 0.94 (95% confidence interval, 0.87-1.00); 0.78 (0.63-0.93); and 0.65 (0.47-0.82), respectively. The AUC for tc-artPCO2 was greater in predicting DO2crit than that for SI.Conclusions: tc-artPCO2 was strongly correlated with DO2 during hemorrhagic shock and resuscitation. This less-invasive tc-artPCO2 monitoring can sensitively detect inadequate systemic O2 supply during hemorrhagic shock. Further evaluations are required in different forms of shock in other large animal models and in humans to assess its usefulness, safety, and ability to predict outcomes in critical illnesses.