PCO2 Gab Marker of Tissue Adequacy of Cardiac Output in Shock State

1. To assess validity of of central and pulmonary veno - arterial CO2 gradient to predict fluid responsiveness and to guide fluid management and determine the cut off point to continue or stop resuscitation. 2. comparison between PCO2 gab and left ventricular outflow tract velocity time integral to determine whether to continue or stop resuscitation and whether PCO2 gab is a surrogate of cardiac output or not.