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OBJECTIVE: This paper evaluates a method in which arterial values of pH, carbon dioxide tension (Pco(2)) and oxygen tension (Po(2)) calculated from venous values and pulse oximetry are compared with simultaneously measured arterial values. METHODS: 103 adult patients from three departments (pulmonary medicine, thoracic intensive care and multidisciplinary intensive care) were studied. The patients belonged to three groups: (1) 31 haemodynamically stable patients with a diagnosis of chronic obstructive lung disease (COLD); (2) 49 haemodynamically stable patients without COLD; and (3) 23 haemodynamically unstable patients without COLD. Arterial and venous (peripheral and, where possible, central and mixed) blood samples were taken simultaneously and anaerobically. Peripheral arterial oxygen saturation was measured with a pulse oximeter. The principle of the method is to simulate the transport of venous blood back through the tissues using the respiratory quotient (adding oxygen and removing carbon dioxide) until simulated arterial oxygenation matches that measured by pulse oximetry. RESULTS: Calculated values of arterial pH and Pco(2) had very small bias and standard deviations regardless of the venous sampling site. In all cases these errors were within those considered acceptable for the performance of laboratory equipment, and well within the limits of error acceptable in clinical practice. In addition, the standard deviation (SD) of calculated values of pH and Pco(2) was similar to the variability between consecutive arterial samples. For peripheral oxygen saturation values < or =96%, the method can calculate Po(2) with an SD of 0.93, which may be useful in clinical practice. Calculations made from peripheral venous blood were significantly more accurate than those from central venous blood. CONCLUSION: Arterial pH and Pco(2) can be calculated precisely from peripheral venous blood in a broad patient population. The method has potential for use as a screening tool in emergency medical departments and in medical and surgical wards to assess a patient's acid-base and oxygenation status prior to sampling arterial blood or to help in the decision to refer the patient to the ICU. In departments where arterial blood gas values are used to monitor patients (eg, pulmonary medicine), the method might reduce the number of arterial samples taken by replacing them with peripheral venous blood samples, thus reducing the need for painful arterial punctures.

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The aim of the present study was to evaluate a method for calculating arterial values of pH, carbon dioxide tension (P(CO(2))) and oxygen tension (P(O(2))) from peripheral venous values. In total, 40 patients were studied. Arterial and peripheral venous blood were sampled at a department of respiratory diseases. Arterial values were calculated from venous, and measured and calculated values of arterial pH, P(CO(2)) and P(O(2)) were compared. Measured and calculated values of pH and P(CO(2)) correlated well, with the difference between them having a very small bias and standard deviation (pH -0.001+/-0.013, P(CO(2)) -0.09+/-0.28 kPa) within those considered acceptable for laboratory equipment and clinical practice. All but four patients had peripheral oxygen saturation (S(p,O(2)))

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In non-emergency medical departments such as internal medicine sampling of arterial blood and analysis for acid-base status is not routinely performed. Peripheral venous blood is routinely taken but interpretation of its acid-base status is difficult. This paper presents a method for calculation of arterial acid-base and blood gas status from measurements in peripheral venous blood combined with a pulse oximeter measurement of arterial saturation. The use of the method has been illustrated using the data of three patients with different acid-base, haemodynamic, and metabolic conditions. The sensitivity of the method has been tested for measurement errors including venous blood acid-base and blood gas status and pulse oximetry; errors due to physiological assumptions including the values of RQ and strong acid production at the tissues; and errors due to air bubbles in the blood. Errors due to these effects are relatively insignificant except for errors in calculated arterial PO(2), particularly when SpO(2) is greater than 97%; and errors when the change in base excess across the sampling site due to strong acid production is greater that 1.3 mmol/l.

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A case of severe polyuria elicited by intravenous administration of a normal pharmacological dose of dexamethasone is reported. The polyuria did not respond to treatment with vasopressin. A 15-year-old girl with a brain tumour was referred for surgery. After induction of anaesthesia she received dexamethasone 4 mg i.v., and developed a massive polyuria with hourly diuresis of up to 1250 ml. There was no response to treatment with vasopressin in doses well above those normally used. The patient did not fulfil any known cause of diabetes insipidus, and to our best knowledge, this case is the first with glucocorticoid-induced and vasopressin-resistant polyuria ever reported in man.

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Pneumonia in patients in intensive care units (ICU) is associated with several diagnostic difficulties and high mortality. This study was conducted to describe the diagnostic procedures and clinical characteristics of the pneumonic and critically ill patient in relation to APACHE II score. The material consisted of 193 patients admitted to seven Danish ICUs and is also included in a European epidemiologic survey (EURO.NIS). Twenty-eight (14.5%) developed pneumonia and 18 (9.3%) of these were nosocomial (> 48h after admission). Patients with pneumonia had a significantly higher APACHE II score, duration of stay and mortality. The techniques used to diagnose pneumonia were mainly conventional and did not or only seldom include protected brush, bronchoalveolar lavage or pulmonary biosy. The predominant pathogens isolated in tracheal aspirate were Gram-negative bacilli (50%). The APACHE II scoring system was found to stratify patients with respect to mortality, duration of stay and pneumonia diagnosed in ICU.

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