Validation of the Use of the Arteriovenous Tension Difference in CO2 Under Hyperbaric Conditions

Area under the receiver operating characteristic (ROC) curve constructed from central venous-arterial carbon dioxide tension difference measurements

used to define low cardiac output measured as a cardiac index \< 2.2 L/min/m² by cardiac echocardiography under hyperbaric oxygenation conditions after 15 min at the maximum treatment pressure of 2.5 ATA under FIO2 at 1 (T1) Maximum treatment pressure i.e., 2.5 ATA under FIO2 at 1

Evaluate the concordance at different time points (T0, T1, T2, and T3) between the definition of low cardiac output by cardiac index <2.2 L/min/m² (gold standard) and the Pvc-aCO2 value according to the threshold of 6 mmHg.

The concordance between the two variables will be measured using Cohen's Kappa coefficient for each of the four time points.

Compare cardiac index values measured at T0, T1, T2, and T3 according to three pre-specified groups classified according to Pvc-aCO2 values established by Ospina-Tasco´n et al.: < 6 mmHg; (2) 6.0-9.9 mmHg; (3) ≥ 10 mmHg.

The cardiac index will be measured by cardiac echocardiography under hyperbaric oxygenation conditions. The three groups will be determined according to Pvc-aCO2 values established by Ospina-Tasco´n et al.: (1) \< 6 mmHg; (2) 6.0-9.9 mmHg; (3) ≥ 10 mmHg.

Evaluate the performance of transcutaneous oximetry variations from the subclavian reference electrode after passive leg raising, a non-invasive procedure, as a diagnostic tool for preload dependence.

Area under the receiver operating characteristic (ROC) curve contructed from measurements of transcutaneous oximetry variationsbefore and after passive leg raising (ΔPTcO2). A patient will be considered "preload dependent" if the subaortic ITV measured by echocardiography varies by sup \> 10 % under hyperbaric oxygenation conditions after 15 minutes at the maximumtreatment pressure of 2.5 ATA under FIO2 at 1 (T1). The correlation between ΔPTcO2 and the variation in subaortic ITV measured by echocardiography after passive legraising will so also measured.

Describe clinical parameters related to blood pressures, echocardiographic data and respiratory mechanics changes induced in patients admitted for necrotizing fasciitis complicated by septic shock under hyperbaric oxygen therapy.

at each time point (T0, T1, T2, and T3), will be measured : * Systolic/diastolic/mean arterial pressures * Heart rate * Systolic/diastolic/mean pulmonary arterial pressures estimated by transthoracic echocardiography * End-expiratory central venous pressure by transthoracic echocardiography through analysis of the inferior vena cava. * Cardiac index estimated by echocardiography * TAPSE and S' wave, * Mitral flow analysis * Indexed systemic vascular resistance estimated using Ohm's law. (PAM-PVC)/IC * Indexed pulmonary vascular resistance estimated using the formula : RPT = 10 (Vmax IT/VTI p) + 0.16 * Right ventriculo-arterial coupling measured by the TAPSE/PAPs ratio * Tidal volume relative to theoretical ideal weight * Adjusted external PEEP and total PEEP * Driving pressure measured as plateau pressure minus total PEEP * Respiratory system compliance measured as Vt/(Pplat - total PEEP) * R/I ratio: recruitment-to-inflation ratio * Airway opening pressure