لخّصلي

Measured and Counted Oxygen Metabolism Parameters o paO2, Hb saturation, haemoglobin fractions, lactate, (pH, paCO2, FiO2, etc.) o Pulmonary shunts, oxygen consumption, a-v difference Anticoagulated (heparinized) arterial blood or arterialized capillary blood from the hyperaemized adult's earlobe or newborn's heel is most suitable to determine oxygen metabolism parameters.Neither is it suitable in the case of disturbances of peripheral circulation: the measured result will correspond to the value in the poorly perfused periphery, and not to arterial blood.Modern calorimeters work on the same principle to determine energy output/ener- gy requirement using indirect calorimetry; 1.0 litre of consumed oxygen is equivalent to energy of 4.8 kcal (20.2 kJ).Pulse oximeters are used to monitor haemoglobin oxygen saturation.

Measured and Counted Oxygen Metabolism Parameters
• paO2, Hb saturation, haemoglobin fractions, lactate, (pH, paCO2, FiO2, etc.)
• Pulmonary shunts, oxygen consumption, a-v difference Anticoagulated (heparinized) arterial blood or arterialized capillary blood from the hyperaemized adult’s earlobe or newborn’s heel is most suitable to determine oxygen metabolism parameters.
Blood paO2 is measured using the Clark-type electrode on the amperometric principle. The electrode is a standard part of acid-base and blood gas parameter analyzers, together with the pH electrode and Severinghaus electrode to determine pCO2. In addition to analyzers intended for clinical and biochemical laboratories, there are also instruments with very simple operation and maintenance for clinical use at the patient’s bedside – Point Of Care Testing (POCT).
Haemoglobin oxygen saturation (SO2) is usually derived in these instruments empirically from paO2, pH and hae- moglobin, from the normal shape and position of the Hb dissociation curve.
A correct result is conditioned by normal oxygen affinity for Hb, a normal 2,3-BPG concentration and the absence of dyshaemoglobins.
The drawbacks and limitations of the approximative method mentioned above are eliminated by direct measu- rement of all haemoglobin type contents in the blood based on their different absorption spectra (oxyhaemoglobin, reduced haemoglobin, carbonyl haemoglobin, methaemoglobin, sulphaemoglobin, foetal haemoglobin, oxygen satu- ration and total oxygen content ctO2). Following ultrasonic red blood cell haemolysis, the haemolyzate is measured by spectrophotometry, and the haemoglobin levels present are computed from their maximum absorptions. The oxyhae- moglobin to total haemoglobin ratio is the usual result of the saturation calculation.
A CO-oximeter is a standard part of the advanced acid-base analyzers used today.
Pulse oximeters are used to monitor haemoglobin oxygen saturation.
The method is based on the principle of different absorption of red (or infrared) light by haemoglobin and oxyhae- moglobin. A sensor emitting radiation with wavelength of 660 nm (red light) and 940 nm (infrared light) is applied to an acral part of the body, usually a finger or earlobe. Light is passed through this part of the body and the transmitted light is measured. The light is absorbed by the tissue and venous, capillary and arterial blood, of which only the arterial com- ponent has a pulsing character. The absorption of light of the two wavelengths by pulsing and non-pulsing components is used to estimate haemoglobin oxygen saturation in arterial blood (SaO2) in percent. Naturally, if the patient’s blood contains other haemoglobin derivatives (COHb, MetHb), the method gives falsely high results of saturation. Neither is it suitable in the case of disturbances of peripheral circulation: the measured result will correspond to the value in the poorly perfused periphery, and not to arterial blood.
Pulse oxymetry is used for its simple and quick application when estimating a patient’s blood oxygenation during anaesthesia in intensive care units and emergency wards, where patients are at risk of rapid development of respira- tory insufficiency.
Pulmonary shunts are usually computed automatically from measured blood gas values in arterial and mixed/cen- tral venous blood, measured oxygen saturation, the FiO2 value, temperature and barometric pressure.
The arteriovenous paO2 difference and the position of the haemoglobin dissociation curve are used to derive the a-v difference in oxygen content, i.e. the content of oxygen available to tissues in that specific situation.
Information on current oxygen consumption can be obtained using instruments continuously analyzing oxygen content in inspired and expired air. Modern calorimeters work on the same principle to determine energy output/ener- gy requirement using indirect calorimetry; 1.0 litre of consumed oxygen is equivalent to energy of 4.8 kcal (20.2 kJ).
In basal condition, the oxygen consumption of an adult is about 3.5 mL.kg-1.min-1. Cardiopulmonary system per- formance is expressed by the maximum oxygen consumption reached under an increasing dynamic load. This corre- sponds to about ten times the basal oxygen consumption in middle-aged men who do not take regular exercise.