The theoretical prediction of safe deep hypothermic circulatory arrest (DHCA) time using estimated tissue oxygen loading

Hyperoxia used with pH-stat gas strategy during cardiopulmonary bypass (CPB) results in the least acid production during Deep Hypothermic Circulatory Arrest (DHCA). Theoretically, pH-stat strategy maximizes capillary perfusion allowing hyperoxia to maximize tissue oxygen loading, which takes advantage of a reduced metabolism (8–16% of normal based on weight) and a 40% increased solubility of oxygen at 18 °C versus 37 °C. Pre-arrest preparation by oxygen loading tissues can delay the conversion from aerobic to anaerobic metabolism thus extending the safe DHCA time [Pearl JM, Thomas DW, Grist GE, Duffy JY, Manning PB. Hyperoxia for Management of Acid–Base Status During Deep Hypothermia with Circulatory Arrest. Ann Thorac Surg 2000;70:751–5].Using the arterial and venous pO2 values on CPB, the hypothetical average tissue pO2 value can be estimated at various temperatures. This combined with known values of oxygen solubility in salt water at various temperatures and the consumption of oxygen at sub-normal temperatures, the safe time of DHCA can be estimated.One table was designed to calculate the average tissue pO2 during hypothermia. A second table was designed to estimate the safe DHCA time based on temperature, patient weight, and the calculated average tissue pO2 from the first table.Traditional methods of DHCA rely primarily on reaching a specified temperature without consideration for tissue oxygen loading. These tables provide indicators that can theoretically guide the clinician in providing a safer DHCA based on the magnitude of tissue oxygen loading.