title: Direct measurement of hepatic tissue hypoxia by using a novel tcpO2/pCO2 monitoring system in comparison with near-infrared spectroscopy.
abstract: OBJECTIVE
  Hepatic hypoxia occurs during liver surgery and transplantation and it may also appear within liver tumours, correlating with prognosis and efficacy of the treatment. The present study measured liver tissue hypoxia by directly using near-infrared spectroscopy (NIRS) and a novel tcpO2/pCO2 monitoring system.
  
  
  METHODS
  Graded hypoxia was achieved in a rabbit model by a stepwise reduction of the fraction of inspired oxygen (FiO2) from 0.3 to 0.0. Animals were allowed to recover from hypoxia at FiO2 of 3.0 indicated by normalised arterial blood gas values. Hepatic tissue oxyhaemoglobin (HbO2), deoxyhaemoglobin (Hb), cytochrome oxidase (Cyt Ox), oxygen partial pressure (pO2) and carbon dioxide partial pressure (pCO2) were measured continuously with the help of NIRS and a Clark-type surface tcpO2/pCO2 monitoring system, throughout the period of hypoxaemia.
  
  
  RESULTS
  There was an immediate reduction in hepatic HbO2 with hypoxia and a simultaneous increase in hepatic Hb. Similarly, hepatic tissue pO2 decreased significantly but tissue pCO2 remained unchanged until the FiO2 was below 0.1. Hepatic HbO2 showed a positive correlation with tissue pO2 (r = 0.53, P < 0.001). Hepatic Hb showed a negative correlation with tissue pO2 (r = 0.47, P < 0.001). Hepatic Cyt Ox decreased significantly with an FiO2 of 0.1 or less and showed a positive correlation with hepatic tissue pO2 (r = 0.64, P < 0.001). A significant correlation was found between hepatic tissue pO2 and arterial blood pO2 (r = 0.44, P < 0.001). Arterial blood pCO2 also correlated with hepatic tissue pCO2 (r = 0.53, P < 0.001) measured by the tcpO2/pCO2 monitoring system.
  
  
  CONCLUSIONS
  The data from the present study suggest that, like NIRS, the tcpO2/pCO2 monitoring system can be reliably used for the direct monitoring of hepatic tissue oxygenation in vivo.
authors.affiliation: Hepatic Heamodynamic Laboratory, University Department of Surgery and Transplantation, Royal Free and University College Medical School, University College London, Royal Free Hospital, London, UK.
authors.forename: Wenxuan
authors.initials: W
authors.lastname: Yang
authors.forename: Tariq
authors.initials: T
authors.lastname: Hafez
authors.forename: Cecil S
authors.initials: CS
authors.lastname: Thompson
authors.forename: Dimitri P
authors.initials: DP
authors.lastname: Mikhailidis
authors.forename: Brain R
authors.initials: BR
authors.lastname: Davidson
authors.forename: Marc C
authors.initials: MC
authors.lastname: Winslet
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Seifalian
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000032:analysis*; D015687:Cell Hypoxia; D003576:Electron Transport Complex IV / Q000032:analysis; D006454:Hemoglobins / Q000032:analysis; D008099:Liver / Q000737:chemistry / Q000503:physiopathology*; D008107:Liver Diseases / Q000503:physiopathology*; D023421:Models, Animal; D008991:Monitoring, Physiologic / Q000295:instrumentation*; D010092:Oximetry; D010100:Oxygen / Q000032:analysis*; D010108:Oxyhemoglobins / Q000032:analysis; D010313:Partial Pressure; D011817:Rabbits; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D006454:Hemoglobins; D010108:Oxyhemoglobins; D002245:Carbon Dioxide; C100003:deoxyhemoglobin; D003576:Electron Transport Complex IV; D010100:Oxygen