Intensive Care Med (!991) 17:71-72

IntensiveCare Medicine 9 Springer-Verlag 1991

Assessing tissue perfusion U. Haglund Department of Surgery,UniversityHospital, Uppsala, Sweden In this issue Gys and co-workers [1] compare gastric intramucosal pH (pHi) and subcutaneous oxygen tension (PscO2) on the one hand with traditional perfusion parameters on the other, in patients undergoing elective colorectal surgery. The results of these various measurements were related to the clinical outcome. Previously, Gys et al. demonstrated that reduced gastric pHi correlated to increased mortality in surgical intensive care patients [2] confirming the observations by Fiddian-Green et al. on patients undergoing cardio-vascular surgery [3, 4]. In the present study all patients had a gastric p h i above the lower limit of normality and they all survived without signs of multiple system organ failure which in a way supports the predictive value of gastric pHi for detecting severe systemic complications and critical illness. The interesting question that is highlighted by the results obtained by Gys et al. [1] is whether or not we are measuring the right things when monitoring our postoperative high risk patients. Apparently, variables reflecting systemic or intergrated total body function such as blood pressure, urine output, arterial oxygen tension and cardiac index are sometimes insufficient to detect local organ dysfunction or injury. In the present study measurements of PscO2 intra- and/or postoperatively were able to discriminate the patients that later developed non-lethal postoperative complications while measurements of variables reflecting global total body function were not. However, the absolute value of PscO2 was not a good predictor. Interindividual variation was very great in the present study and the PscO2 data did not indicate a lower line of normality below which the risk for complications become significant. Of 4 patients with an extremely low PscO 2 (< 12 mmHg) 3 developed postoperative complications. More predictive was, on the other hand, failure to respond with a significant increase of PscO2 upon oxygen breathing. Of 10 studied 8 patients failed to respond to this challenge and 6 out of those 8 later developed complications. Admittedly, it could be argued that the very high frequency of complications in the present

rather small group and the extremely low PscO 2 found intraoperatively in some of the patients made the evaluation of the predictive value of PscO2 measurements somewhat difficult. It is of interest to note that the complications encountered in this study were local events: anastomotic dehiscence and intraabdominal abscess, respectively, in 2 patients, wound infection in 2, acalculous cholecystitis and deep venous thrombosis, respectively, in the remaining 2. Inadequate oxygenation of the subcutaneous tissue is not without pathogenetic importance for development of postoperative wound infections [5] and local inadequate oxygenation probably explains anastomotic rupture as well as the abscess. This study emphasizes the importance of studying tissue oxygenation at the individual tissue level. In certain situations, such as respiratory failure or hypovolemia, general and local changes should vary in parallel. However, in others, such as sepsis and local circulatory disturbances, a dissociation are to be expected. For local complications such as wound infection and anastomotic dehiscences the affected tissue (subcutaneous tissue and locally in the colon, respectively) is most likely to demonstrate abnormal oxygenation which not necessarily is reflected systemically. The silastic implanted catheter technique described by Niinikoski and Hunt [6] and later refined by Gottrup et al. [7] seems to be the most optimal technique available today for measurements of subcutaneous tissue oxygenation. Likewise, the tonometric technique originally described by Fiddian-Green and coworkers [3, 8] and recently further validated by Antonsson et al [9], provides an excellent possibility for the study of oxygenation of the gastro-intestinal mucosa. For clinical use the latter technic can be applied for the study of sigmoid colon as well as of gastric mucosa. This technique, as employed by Gys et al [1], could not be expected to detect small areas with locally impaired oxygenation, i.e. a normal gastric pHi does not exclude bad oxygenation at the colonic anastomosis.

U. Haglund: Editorial

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The present study [1] indicates that monitoring the subcutaneous tissue PO2 could be predictive for complications following elective colorectal surgery. In a recent study, Doglio et al. [10] demonstrated that oxygenation of the gastric mucosa was very predictive of outcome in critically ill patients. In sepsis gastric pHi changes correlates well with pHi changes of the small intestine and the colon [11]. The gastrointestinal mucosa is sensitive to hypoxia which rapidly induces increased permeability and within a few hours frank necrosis of the superficial epithelial layer [12]. This layer constitutes a barrier between the lumen and the interior of the body. The breakdown of this barrier facilitates portal invasion of bacteria and bacterial products as well as the release of other toxic factors. From a theoretical standpoint monitoring gastrointestinal mucosal pH should therefore be expected to be more predictive of outcome than subcutaneous pO2 in the critically ill patient. However, these two technologies are measuring different dimensions and are therefore difficult to compare. Low pO 2 should induce tissue acidosis. Normal pO z does not, on the other hand, guarantee normal extraction and utilization, and tells us nothing about the needs of the tissue and, therefore, does not exclude tissue acidosis. We can on the basis of the present study [1] and others [2, 3, 4, 11] conclude that measurements at the tissue level seem to be superior to measurements reflecting systemic body function if the aim is to obtain early warnings. We therefore should reconsider whether we in the post-operative care, as well as in other forms of ICU treatment, are using the right variables in our monitoring. I believe there is convincing evidence for the need of adding technologies (or substituting some of the presently used ones) allowing monitoring of peripheral tissue oxygenation in these circumstances. If so, as has been indicated by Gys et al. [1], subcutaneous tissue pO2 and gastrointestinal intramucosal pH recording techniques are available today. Which to prefer is partly dependent on the reason for monitoring, partly on the costs in a wider concept, including the user friendliness of the technology. It could also be argued that the region monitored should be chosen depending on the most expected or most feared complication.

References 1. Gys T, van Esbroeck G, Hubens A (1991) Assessment of the perfusion in peripheral tissue beds by subcutaneous oximetry and gastric intramucosal pH-metry in elective colorectal surgery. Intensive Care Med 17:78-82 2. Gys T, Hubens A, Neels H, Lauwkers LF, Peeters R (1988) The prognostic value of gastric intramural pH in surgical intensive care patients. Crit Care Med 16:1222 3. Fiddian-Green RG, Baker S (1987) Predictive value of the stomach wall pH for complications after cardiac operations; comparison with other monitoring. Crit Care Med 15:153 4. Fiddian-Green RG (1989) Studies in splanchnic ischemia and multiple organ failure. In: Marston A, Bulkley GB, Fiddian-Green RG, Haglund UH (eds) Splanchnic ischemia and multiple organ failure. Arnold, London, pp 347-363 5. JOnsson K, Jensen J, Goodson W, West J, Hunt T (1987) Assessment of perfusion in postoperative patients using tissue oxygen measurements. Br J Surg 74:263 6. Niinikoski J, Hunt TK (1972) Measurement of wound oxygen with implanted silastic tube. Surgery 71:22-26 7. Gottrup F, Firmin F, Chang N, Goodson W, Hunt T (1983) Continuous direct tissue oxygen tension measurement by a new method using an implantable silastic tonometer and oxygen polarography. Am J Surg 146:399 8. Fiddian-Green RG, McGough E, Pittenger G, Rothman ED (1983) Predictive value of intramural pH and other risk factors for massive bleeding from stress ulceration. Gastroenterology 85:613-620 9. Antonsson JB, Boyle CC, Kruithoff KL, Wang H, Sacristan E, Rothschild HR, Fink MP (1990) Validation of tonometric measurement of gut intramural pH during endotoxemia and mesenteric occlusion in pigs. Am J Physiol 259 [Gastrointest, Liver Physiol 22] :G519 - G523 10. Doglio GR, Pusajo JF, Bonfigli GC, Egurrola MA, Palizas F, Gutierrez G (1990) Predictive value of stomach mucosal pH in ICU patients. Chest 98:545 11. Montgomery A, Almqvist P, Arvidsson D, Lindgren S, Haglund U (1990) Early detection of gastrointestinal mucosal ischemia in porcine E. coil sepsis. Acta Chir Scand 156:613-620 12. Haglund U, Bulkley GB, Granger DN (1987) On the pathophysiology of intestinal ischemic injury. Acta Chir Scand 153:321-324

Dr. U. Haglund Department of Surgery University Hospital S-75185 Uppsala Sweden