Monitoring of tissue PO2 in patients during intensive care

ISOTT from the Beginning: A Tribute to Our Deceased Members (Icons)

ISOTT was founded by Drs. Duane F. Bruley and Haim I. Bicher in the state of South Carolina, USA in 1973. The symposium was jointly held at Clemson University (Clemson, SC, USA) and the Medical College of South Carolina (Charleston, SC, USA), which are geographically located 260 miles apart. This venue resulted from Dr. Bruley's (Clemson University) wish to have a meeting on Oxygen Transport to Tissue and with it to honor the research collaboration between the two universities and Dr. Melvin H. Knisely's accomplishments on studies regarding "blood sludging" in the microcirculation. Because of the unexpected large response to the symposium, Drs. Bruley and Bicher decided to found an international society at this meeting (ISOTT). The purpose of this paper is to summarize the formalization of ISOTT and to honor important contributors to the society who have since passed away. The authors did their best to include a brief overview of our past icons who have excelled in leadership as well as science/engineering, and apologize if someone has been mistakenly left out or if data is inaccurate or incomplete.

Monitoring of tissue-pO2 for invasive diagnostics in angiology and vascular surgery

Hypoxic and ischemic states are the main problem makers in angiology and vascular surgery. It is therefore suggestive to employ the technique of tissue-pO2 measurement for the verification and support of diagnostic and therapeutic measures. Two forms of registration are possible: continuous monitoring of partial oxygen pressures in eight different places and registration in the form of pO2-histograms, which represents a kind of "representative opinion poll" held in the tissue. The effects of a surgical intervention (endarterectomy, bypass operation) and the efficacy of blood flow-promoting drugs were studied in several series. In 9 patients the effect of the blood flow-promoting agent pentoxifylline (3,7-dimethyl-1-(5-oxohexyl)-xanthine) was studied. The pO2-histograms exhibited a shift to the right by an average of 7 mmHg after administration of this drug. Moreover, findings obtained with sodium nitroprusside and nitroglycerin during induced hypotension indicate that the continuous measuring of tissue-pO2 and recording of oxygen pressure distribution curves (pO2-histogram) provide the clinician with essential guidance data for the improvement of diagnostics and therapeutic control.

Theory and methods of local tissue-pO2 monitoring in experimental angiology

The platinum-multiwire-surface electrode after Kessler and Lübbers gives the opportunity of direct measuring of the local tissue-pO2-pressure; this 8-wire electrode with a Pt-wire-diameter of 15 microns operates on the polarographic principle. Each Pt-wire has a hemispheric collecting area of about 30 microns. Pressure ischemia by compression of capillaries is prevented by proportioning the weight (2.1 g) of the electrode. Data output is done by continuous pO2 measuring; pO2 histograms. During the continuous pO2 measurement the electrode stays on the tissue measuring point thus enabling the direct record of quickly proceeding reactions. The pO2-histogram exhibits the statistical distribution of the local partial oxygen pressures in a studied organ, a quasi sample inquiry is performed in the tissue, based on minimum 100 single values that are obtained by repeated manual repositioning of the electrode. By this, values are obtained on the level and distribution of local pO2 in the tissue so that condition and function of the microcirculation can be objectively assessed. Immediate alterations in the local tissue pO2 suggest regulatory adjustment after hemodynamic changes. Technical problems connected with pO2 measurement in clinical use (sterilization, data acquisition and presentation) are described. The presented technique gives the chance to exactly assess the effects of vasoactive drugs on the microcirculation and to quantify the results of operations, for example after bypass-surgery.

Microcirculation and hemorrhagic shock

Blood loss is followed by compensatory cardiovascular readjustments that favor the maintenance of blood flow to central vital organs rather than to peripheral tissues. The microcirculatory changes that occur in skeletal muscle in shock states are of major importance, since skeletal muscle is not only the largest cell mass of the body but also one of the major target organs for neurohumorally mediated compensatory vascular readjustments. Intravital microscopic studies show that the microvascular blood flow in skeletal muscle is intermittent in the early posthemorrhagic period. This probably reflects an interplay between alpha-adrenergic vasoconstrictor and beta-adrenergic vasodilator activities, which serves to enhance a compensatory mobilization of interstitial fluid into the vascular compartment. A period of complete microcirculatory arrest is then seen, followed by reperfusion engaging only 30% to 50% of the capillaries that were seen perfused in resting skeletal muscle. The microvascular blood flow in shock is further characterized by a pronounced heterogeneity in distribution. Many capillaries remain constantly unperfused, while in others a slow, intermittent blood flow is seen. Obstruction of many capillaries by white blood cells and their slow passage through other capillaries seem to be the main reasons for the maldistribution of capillary blood flow in shock. Red blood cell aggregates obstructing capillary blood flow are not seen. The heterogeneous tissue perfusion is accompanied by local variations in cellular hypoxic injury, as is evidenced by multifocal measurements of tissue oxygen tension and by cellular transmembrane potential registrations.(ABSTRACT TRUNCATED AT 250 WORDS)