Intracorporeal Oxygenation

Abstract: The dominant problem in the design of an intracorporeal oxygenator is achieving gas transfer rates sufficient for physiological needs in the space available with acceptably low flow resistance to blood. Design problems still to be solved, when configurations with sufficient gas transfer effectiveness are well identified, are biological tolerance (including adequate blood compatibility), ease of manufacture, and prolonged function.     

Hypercapnia Improves Tissue Oxygenation

Background: Wound infections are common, serious, surgical complications. Oxidative killing by neutrophils is the primary defense against surgical pathogens and increasing intraoperative tissue oxygen tension markedly reduces the risk of such infections. Since hypercapnia improves cardiac output and peripheral tissue perfusion, we tested the hypothesis that peripheral tissue oxygenation increases as a function of arterial carbon dioxide tension (Paco2) in anesthetized humans.

Methods: General anesthesia was induced with propofol and maintained with sevoflurane in 30% oxygen in 10 healthy volunteers. Subcutaneous tissue oxygen tension (Psqo2) was recorded from a subcutaneous tonometer. An oximeter probe on the upper arm measured muscle oxygen saturation. Cardiac output was monitored noninvasively. Paco2 was adjusted to 20, 30, 40, 50, or 60 mmHg in random order with each concentration being maintained for 45 min.

Results: Increasing Paco2 linearly increased cardiac index and Psqo2: Psqo2 = 35.42 + 0.77 (Paco2), P < 0.001.     

Obesity Decreases Perioperative Tissue Oxygenation

Background: Obesity is an important risk factor for surgical site infections. The incidence of surgical wound infections is directly related to tissue perfusion and oxygenation. Fat tissue mass expands without a concomitant increase in blood flow per cell, which might result in a relative hypoperfusion with decreased tissue oxygenation. Consequently, the authors tested the hypotheses that perioperative tissue oxygen tension is reduced in obese surgical patients. Furthermore, they compared the effect of supplemental oxygen administration on tissue oxygenation in obese and nonobese patients.

Methods: Forty-six patients undergoing major abdominal surgery were assigned to one of two groups according to their body mass index: body mass index less than 30 kg/m2 (nonobese) or 30 kg/m2 or greater (obese). Intraoperative oxygen administration was adjusted to arterial oxygen tensions of approximately 150 mmHg and approximately 300 mmHg in random order. Anesthesia technique and perioperative fluid management were standardized. Subcutaneous tissue oxygen tension was measured with a polarographic electrode positioned within a subcutaneous tonometer in the lateral upper arm during surgery, in the recovery room, and on the first postoperative day. Postoperative tissue oxygen was also measured adjacent to the wound. Data were compared with unpaired two-tailed t tests and Wilcoxon rank sum test; P < 0.05 was considered statistically significant.

Results: Intraoperative subcutaneous tissue oxygen tension was significantly less in the obese patients at baseline (36 vs. 57 mmHg; P = 0.002) and with supplemental oxygen administration (47 vs. 76 mmHg; P = 0.014). Immediate postoperative tissue oxygen tension was also significantly less in subcutaneous tissue of the upper arm (43 vs. 54 mmHg; P = 0.011) as well as near the incision (42 vs. 62 mmHg; P = 0.012) in obese patients. In contrast, tissue oxygen tension was comparable in each group on the first postoperative morning.     

Transintestinal Systemic Oxygenation Using Perfluorocarbon

Purpose Perfluorocarbons have an excellent oxygen- and carbon dioxide-carrying capacity. This prompted us to investigate the feasibility of transintestinal systemic oxygenation using perfluorocarbon. Methods A rat hypoventilation model (room air, 20 breaths/min and a tidal volume of 10 ml/kg) was thus established, and FC-77 (Sumitomo-3M, Osaka, Japan) was used as a perfusate. Oxygenated FC-77 was perfused through the small intestine for 4 h. The rats were allocated into three groups as follows. Group 1 (n = 6): hypoventilation only; Group 2 (n = 6): saline was perfused instead of FC-77; Group 3 (n = 6): FC-77 was perfused. Arterial blood samples were drawn from the common iliac artery every 30 min until the end of perfusion. A standard blood gas analysis was performed. Results The PaO₂ level in Group 3 was significantly higher than in Groups 1 or 2 (P = 0.006: at the end of perfusion, Group 1 = 58.6 ± 14.5 mmHg, Group 2 = 65.2 ± 29.4 mmHg, Group 3 = 84.0 ± 35.5 mmHg). The PaCO₂ level in Group 3 was significantly lower than that in Groups 1 or 2 (P = 0.014: at the end of perfusion, Group 1 = 56.8 ± 8.5 mmHg, Group 2 = 52.6 ± 5.7 mmHg, Group 3 = 44.4 ± 11.1 mmHg). Conclusion Our findings indicate that transintestinal systemic oxygenation is indeed possible and could therefore become a useful new modality for respiratory assist.