Oxygen and blood in Brain-Brain Protection Part 1

Brain is metabolically very active and its oxygen consumption is about 3.5 - 4.0 ml/100 gm/min.

Electrical activity of neurons (transient depolarization and repolarization with their attendant ionic shifts) consumes about 50% of the total energy production of neurons.

Thus, energy consumption can be reduced significantly by agents that can render the EEG isoelectric (e.g., barbiturates).

The remaining 50% is used to maintain basal cellular homeostasis.Although this portion of the total energy consumption is not amenable to reduction by anesthetic agents, hypothermia can reduce it substantially.

The normal CBF in humans is about 50 ml/100 gm/min.

The response of the brain to ischemia has been well characterized.

When CBF reaches about 20 ml/100 gm/min, EEG isoelectricity occurs.

At a flow of about 15 ml/100 gm/min, evoked responses can no longer be obtained. Although neurons do not immediately die at this flow rate, death will eventually occur if flow is not restored.

Below a flow of 10 ml/100 gm/min, ATP levels decline rapidly (within 5 minutes) and the neuron is

unable to maintain ionic homeostasis. At this point, the neuron undergoes depolarization (anoxic depolarization). By activating several biochemical cascades in a haphazard manner, calcium ultimately leads to neuronal death.

Comments

The pressure volume loop...

In the pressure-volume loop below, cardiac work is best represented by: the area of the curve the slope of the line from points C to D the distance of the line from points C to D the slope of a line from points A to D .. .. ... .... ... .... .... .... In the pressure-volume loop below, cardiac work is best represented by: the area of the curve Cardiac work is the product of pressure and volume and is linearly related to myocardial oxygen consumption. Cardiac work is best represented by the area of the curve of a pressure-volume loop.

Anaphylaxis updates part 2- Empty Ventricle Syndrome

Patients with anaphylaxis should not suddenly sit, stand, or be placed in the upright position. Instead, they should be placed on the back with their lower extremities elevated or, if they are experiencing respiratory distress or vomiting, they should be placed in a position of comfort with their lower extremities elevated. This accomplishes 2 therapeutic goals: 1) preservation of fluid in the circulation (the central vascular compartment), an important step in managing distributive shock; and 2) prevention of the empty vena cava/empty ventricle syndrome, which can occur within seconds when patients with anaphylaxis suddenly assume or are placed in an upright position. Patients with this syndrome are at high risk for sudden death. They are unlikely to respond to epinephrine regardless of route of administration, because it does not reach the heart and therefore cannot be circulated throughout the body

Steroids In Perioperative period...The Multi-purpose Drugs

1-Steroids are not Bronchodilator ,but have well established usefulness in hyper-reactive airway. They are also said to have a permissive role for bronchodilator medication. They can be administered orally, parenterally or in aerosol form 2- Steroids have been commonly used in chemotherapy for prevention of nausea along with other anti-emetic agents . Dexamethasone was found to be highly effective when given immediately before induction rather than at the end of anesthesia . 3- Steroids do exert analgesic effects. Various routes of administration of steroids include parentral, local infiltration at operated site , as an adjuvant in nerve blocks and central-neuraxial blockade. 4 - Steroids cannot be the mainstay of therapy in anaphylaxis because of the delayed onset of action, so they are used as adjunct after initial treatment with epinephrine. 5- Steroids (Dexamethsone) are of value in reduction or prevention of cerebral edema associated with parasitic infections and neopla...

sedationstation

Search This Blog