Blood gas tensions, and

In patients with status asthmaticus and abnormal blood gas tensions, improvement in vital capacity and blood gas tensions may not accompany apparent relief of bronchospasm following isoproterenol. 

There are several other important factors that can determine whether the gas will be absorbed in blood and then transported from the blood to the perfused tissue. The concentration of the gas in inspired air influences gas tension, and partial pressure can be increased by overventilation. In gas anesthesiology we know that the effects of... 

Qvist, J., R.D. Hill, R.C. Schneider, K.J. Falke, G.C. Liggins, M. Guppy, R.L. Elliott, and P.W. Hochachka (1986). Hemoglobin concentrations and blood gas tensions of free diving Weddell seals. J. Appl. Physiol. 61 1560-1569. 

If sites in the brain that control respiration are damaged, respiration and blood gas tensions will be disrupted. It is also possible that assisted ventilation is required by a stroke patient, and this can alter blood gas tensions temporarily. Renal and respiratory compensations rectify these changes during recovery. 

Lung collapse (atelectasis) reduces FEVi and is likely to affect blood gas tensions, reducing arterial P02. 

Blood gas tensions are usually abnormal arterial PO2 is lower and arterial PC02 higher than normal. Patients may be cyanosed because of an increase in reduced (deoxygenated) haemoglobin in the tissues. 

Q7 If the embolus is quite large and obstructs a significant area of the pulmonary circulation, the affected area of lung will be underperfused or non-perfused. The area may continue to be ventilated for some time, causing a ventilation-perfusion mismatch, which leads to poor gas exchange and abnormal blood gas tensions. The lung volume in the affected area decreases, and this decrease in size can sometimes be seen on a chest X-ray. After some hours, surfactant production declines in the non-perfused area of lung and the alveoli collapse. 

Multiple clinical laboratory determinations have been used to assist in the management of cases of bronchiolitis. Roentgenographic evaluation of the chest in children with bronchiolitis yields variable findings, but may help to distinguish this illness from other entities characterized by wheezing. In children requiring hospitalization, abnormalities in blood gas tensions are frequent and appear to relate to disease severity. Hypoxemia is common and increases the respiratory drive, whereas hypercardia is seen only in the most severe cases. Despite the presence of moderate degrees of hypoxemia, clinical cyanosis is unusual. 

Pickrell, J. A., J. L. Mauderley, B. A. Muggenburg, and U. C. Luft. 1973. Influence of fasting on blood gas tension, pH and related values in dogs. American Journal of Veterinary Research 34 805-808. 

This situation is less common than low-flow priapism and can be classified as congenital due to arterial malformations, traumatic usually associated with penile, perineal or pelvic trauma, iatrogenic following revascularization procedures or idiopathic. The local blood gas tension in these patients is arterial, and therefore the penis is not at risk of ischemia and subsequent fibrosis. 

This is due to overbreathing. It occurs in the hyperventilation syndrome susceptible subjects hyperventilate, perhaps in response to stress, for minutes, days and even weeks. It also occurs in healthy people at high altitude, where ventilation is stimulated by hypoxia. In surgical practice, hyperventilation occurs in patients being overventilated by a mechanical ventilator. In this situation, CO2 is washed out of the body and respiratory alkalosis supervenes. Because of the dangers of this situation, the arterial blood gas tensions should be frequently checked in such patients and the PCO2 should not be allowed to fall below 30mmHg. 

As arterial C02 tension is practically identical to alveolar C02 partial pressure, it can be used as a surrogate measurement. This is desirable as measuring arterial C02 tension involves only a simple blood gas analysis. The term Paco2, therefore, becomes Paco2 and so the equation is often written as... 

Practically speaking, this concept explains the basis for the establishment of partial pressure equilibrium of anesthetic gas between the lung alveoli and the arterial blood. Gas molecules will move across the alveolar membrane until those in the blood, through random molecular motion, exert pressure equal to their counterparts in the lung. Similar gas tension equilibria also will be established between the blood and other tissues. For example, gas molecules in the blood will diffuse down a tension gradient into the brain until equal random molecular motion (equal pressure) occurs in both tissues. 

Tensions of three anesthetic gases in arterial blood as a function of time after beginning inhalation. Nitrous oxide is relatively insoluble (blood gas partition coefficient = 0.47) methoxyflurane is much more soluble (coefficient = 12) and halothane is intermediate (2.3). 

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