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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Autoregulation of the cerebral blood flow is a wellknown fact. In normal man the arterial pressure can vary from 80 mm Hg to 150 mm Hg without a change in the normal cerebral blood flow of 50 ml/100 g/min. The mechanism which is responsible for this autoregulation is not clearly understood. Several theories were proposed to explain this phenomenon. 1. The tissue pressure increases with an increase of the arterial pressure. A mechanical process should neutralize an increase of the cerebral blood flow. 2. The metabolic theory says that a decrease of the blood pressure, without a change of metabolism, involves an increase of the PaCO2, and a decrease of the PaO2. Those two factors provoke a decrease of the vascular tone. 3. The myogenic theory explains autoregulation by the fact that a change of the transmural pressure in the small vessels, involves a change in the activity of the smooth muscles of the vessels. 4. The exact mechanism of the autonomic nervous system in the autoregulation of the cerebral blood flow is still obscure. In some pathological conditions autoregulation is completely lost or is functioning not optimal: hypoxia, hypercapnia and brain contusion. We have measured the cerebral blood flow before and after an intravenous injection of 5 mg thiopental (Pentothal) on occasion of a carotid angiography in man. We noticed a decrease of the cerebral blood flow and at the same moment a decrease of the arterial pressure. We thought that maybe barbiturates could influence autoregulation. Our results could not prove this hypothesis. For ethical reasons we could not make the necessary measurements to prove or to reject this hypothesis (i.e. intracranial pressure, deep controlled hypotension). In the literature there are arguments which support this hypothesis although most workers found an intact autoregulation after a barbiturate anesthesia. Some workers saw that the increase of the cerebral blood flow by increasing the PaCO2 was depressed by barbiturates and exhausted by halothane and cyclopropane. As autoregulation is a more vulnerable mechanism than CO2 reactivity as seen in clinical situations, it could be true that anesthetics do influence autoregulation.
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PMID:Influence of anesthesia on autoregulation of the cerebral blood flow. 102 Jun 37

Local anaesthetic systemic toxicity is a rare but often dramatic complication of regional anaesthesia. Convulsions often follow warning signs, easily recognized when looked for; but they may occur from the first. They are rapidly followed by hypoxia and hypercapnia which greatly enhance the risk of severe cardiac depression, mainly with bupivacaine or etidocaine. Thiopentone is able to stop convulsions quickly, but may further depress the cardiovascular system. Diazepam has been shown to be effective in the treatment of local anaesthetic-induced convulsions. It gives less myocardial depression, but is much slower in effect. Midazolam, a new short-acting benzodiazepine, should be the best choice. Should tracheal intubation become necessary, suxamethonium can be used. Indeed, the principal use of these drugs is to make ventilation easier, so as to restore rapidly correct oxygenation. Severe cardiac depression, often leading to cardiac arrest, may occur from the first or after the appearance of convulsions. It generally follows a regional block carried out with bupivacaine. A few antiarrhythmic drugs have been used to treat ventricular arrhythmias, either in experimental studies (lidocaine, bretylium) or after clinical accidents (lidocaine). Their efficacy and innocuity have to be proved before they can be proposed to treat these accidents. Bradycardia only needs treatment with atropine when it causes severe haemodynamic disturbances. When cardiac arrest occurs, cardiopulmonary resuscitation must be carried out; its mainstays are: oxygen, sodium bicarbonate, adrenaline, calcium and perhaps glucagon. This must be continued for a long time, as late successes have been published.
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PMID:[How should a toxic accident be treated?]. 290 Jun 15