The Splanchnic Model of Multiple Organ Failure

Ischemia signifies failure to satisfy the metabolic needs of the cell secondary to either impaired oxygen delivery or the impairment of cellular oxygen extraction and utilization. Incomplete splanchnic cellular resuscitation has been associated with the development of multiple organ system failure and increased mortality in the critically ill patient (1,2). For many years, the merits of augmenting systemic oxygen delivery and consumption and attainment of supranormal levels have been examined and debated as primary treatment goals (3–6). There is convincing evidence that systemic hemodynamic and oxygen transport variables fail to accurately portray the complex interaction between energy requirements and the energy supply at the tissue level (7–9), and that achieving supranormal cardiovascular oxygen transport and utilization indices does not reliably confer improved outcome (i.e., decreased mortality rates and diminished multiple organ system failure) in several clinical conditions (e.g., sepsis, acute respiratory distress syndrome [ARDS]) (10–13). These findings have led to the search for monitoring techniques that directly measure changes in regional tissue bioenergetics. Intestinal tonometry has been proposed as a relatively noninvasive index of the adequacy of aerobic metabolism in organs whose superficial mucosal lining is extremely vulnerable to low flow and hypoxemia, and in which blood flow is sacrificed first in both shock and the cytokine milieu of the systemic inflammatory response (1,14,15). The gastrointestinal tract, therefore, acts like the “canary,” displaying early metabolic changes before other indices of adequate oxygen utilization (16). This chapter reviews the fundamental and clinical underpinnings of splanchnic ischemia and resuscitation, intestinal and subsequently sublingual tonometry, the potential applications and limitations of this technology, its use as a prognostic and treatment end point, and, finally, a consideration of potential future directions.