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

Abstract 

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.

Keywords: Deep Hypothermic Circulatory Arrest, DHCA, Hyperoxia, pH-stat