[The estimation of p50 by the algorithm proposed by Siggard-Andersen. Its experimental assessment in critical patients]. / Calcolo della p50 mediante l'algoritmo proposto da Siggaard-Andersen. Valutazione sperimentale in pazienti critici.

STUDY OBJECTIVE: To determine the ability of O. Siggaard-Andersen algorithm in the estimation of the "in vivo" p50 and standard p50 values from a single blood sample with sO2% less than or equal to 97. DESIGN: comparison between measured and calculated standard p50 values. SETTING: Intensive care unit. PATIENTS: thirteen cardio-pulmonary critical ill patients. Mean age of seventy-four years (range 53-84 years). MEASUREMENT: The experimental measurement of p50 standard (p50st sper) was performed tonometering the venous blood samples (60 specimens) using an IL-237 tonometer at 37 degrees C, with two different gas mixtures to obtain pCO2 at 5.33 kPa (DS = 0.06), and pO2 at levels to achieve sO2% values close to 50%. The gases's complete equilibration was not deemed important. The pO2 values were corrected to a pH of 7.40 using a Bohr factor = -0.48 and the p50 was taken by simple interpolation of points on the sO2%/pO2 diagram. Calculated standard p50 (p50st calc) and calculated "in vivo" p50 on the venous specimens (No. 60) and the correspondent arterial specimens with sO2% less than or equal to 97 (No. 40) were obtained by Siggaard-Andersen's computerized algorithm. Blood specimen analysis was performed by means of an ABL3 Radiometer gas analyzer and an OSM3 Radiometer oximeter. Statistical analysis was made by Anova test for liner regression. RESULTS: There was excellent correlation between the 60 experimental p50st determined by Siggaard-Andersen's oxygen dissociation curve on the same blood samples. The regression equation was: p50st sper = -0.79 + 1.21 x p50st calc, r = 0.90, R2 = 81.1%; with F = 249.5 and less than 10(-5). No good correlation was found between p50st and standards p50 calculated on arterial specimens (p50st calc art): p50 = 1.38 + 0.52 x p50st calc art, r = 0.52, R2 = 26.6%, F = 14 e P less than 10(-3). Regression of in vivo P50 calculated on correspondent venous samples (p50 ven) was: p50 ven = 0.79 = 0.77 x p50 art, r = 0.93, R2 = 87.2%, F = 256 and P less than 10(-5). CONCLUSION: Our results suggest that the curve describes the curve also at high saturation when it is not longer linear. Accurate measurement (including dishemoglobin percentage) and sO2% less than or equal to 97 are necessary. We did not perform experimental measurements of "in vivo" p50 but we postulate that as the p50st was well calculated so too would be the p50 "in vivo" at 37 degrees C.

[Hypoxia and oxygen content during dialysis]. / Ipossia e contenuto di ossigeno durante dialisi.

In a study of 72 patients treated with acetate and bicarbonate dialysis, the Authors verified if hypoxic hypoxia caused by dialysis depends on a deficit in oxygen content with an inherent risk of tissue hypoxia. PO2uv (uncompensated venous oxygen partial pressure) and CQ (cardiac compensation factor) derived from the oxygen absorption curve were studied by a new Ole Siggard-Andersen algorithm. The results do not show a risk of tissue hypoxia in the postdialytic period.

[ARDS in MOFS (multiple organ failure syndrome). How to direct the therapy? A case report of MOFS in AIDS]. / ARDS componente della MOFS (multiple organs failure syndrome) come orientare la terapia? Descrizione di MOFS in AIDS.

A young AIDS patient was admitted to the Intensive Therapy ward of our hospital with ARDS. The case raised the question of how medical and nursing personnel should face the problem of "suitable treatment for a terminally ill patient". Therapy was based on invasive methods such as mechanical ventilation and the insertion of catheters to monitor vital parameters. The evolution of ARDS in MOFS revealed the difficulty of sustaining vital parameters and avoiding pluriorganic damage.

The oxygen status of the arterial blood in the critically ill.

In Critical Care medicine the concepts of Oxygen Delivery, Oxygen Consumption and Tissue Oxygenation have become fundamental in clinical practice but measurements of Oxygen Content and O2 Transport variables require invasive procedures that could be dangerous for critically ill patients and trigger a septic process. Derived indices obtained combining data from a Blood Gas Analyzer with the data from a multi-wavelength spectrophotometer and using the Ole Siggaard-Andersen pH/Blood Gas computerised algorithm might be the non-invasive answer. On 115 arterial blood samples from critically ill patients, we measured pH, pCO2, pO2, oxygen saturation, total hemoglobin concentration and fractions of carboxy- and methemoglobin. The new algorithm was used to calculate: active hemoglobin concentration, total oxygen concentration, actual half-saturation tension, 2,3-diphosphoglycerate concentration, estimated functional shunt, uncompensated mixed venous pO2 (assuming an arterio-venous oxygen difference of 2.3 mmol/L based on a standard oxygen consumption of 11.2 mmol/min and a standard cardiac output of 4.9 L/min) and the cardiac oxygen compensation factor. In Intensive Care all the oxygen parameters may be determined with sufficient accuracy and precision provided the oxygen saturation level is less than 0.97 and provided the definition of oxygen saturation is properly settled and measurements are performed according to the highest state of the art. However, in critically ill patients in evolution our aim is to maintain an 'optimal' paO2 on the plateau of the Oxygen Dissociation Curve (ODC) and the use of mechanical ventilation, high FIO2, fluid challenges and the rapid improvement of the patient's conditions can cause a value for sO2 greater than or less than 0.97 and an improvement or worsening of the paO2. The p50 calculation both in simultaneously drawn arterial and venous blood permits utilisation of derived indices (pO2uv-, CQ) for sO2 greater than 0.97. The Ole Siggaard-Andersen algorithm seems to give correct p50 values, at high saturation values, particularly when discarding unrealistic values for calculated cDPG. The correlation between p50 calculated by the Ole Sigaard-Andersen algorithm with that derived from classical formula shows the superiority of the findings obtained by means of the new algorithm. In critically ill patients the ODC is usually shifted to the right. The new parameters, pO2uv- and CQ, contain useful informations for clinical practise; but rapid changes in Cardiac Index (CI) and VO2/m2 can be ignored by the new algorithm, if these changes are not associated with a rise in ctO2 or pH and pCO2 changes.(ABSTRACT TRUNCATED AT 400 WORDS)