💊أدويه الجهاز العصبي المركزي 13
#Pharmcology_of_CNS 13
#CNS
#Anesthetics
INHALATION ANESTHETICS
مواضيعنا حا تكون 👇
✔️Potency
✔️Uptake and distribution of inhalation anesthetics
✔️Mechanism of action
✔️ Drugs
💠Inhaled gases are used primarily for maintenance of anesthesia after administration of an IV agent
💠Depth of anesthesia can be rapidly altered by changing the inhaled concentration.
✔️Potency
🔘Potency is defined quantitatively as the minimum alveolar concentration (MAC), the end-tidal concentration of inhaled anesthetic needed to eliminate movement in 50% of patients stimulated by a
standardized incision.
🔘MAC is small for potent anesthetics such as sevoflurane and large for less potent agents such as nitrous oxide.Nitrous oxide alone cannot produce complete anesthesia
🔘The more lipid soluble an anesthetic, the lower the concentration needed to produce anesthesia and, thus, the higher the potency.
✔️Uptake and distribution of inhalation anesthetics
🔘The principal objective of inhalation anesthesia is a constant and optimal brain partial pressure (Pbr) of inhaled anesthetic
ودي مقصود بيها
(partial pressure equilibrium between alveoli [Palv] and brain [Pbr]).
🔘 The alveoli are the “windows to the brain” for inhaled anesthetics.
🔘Because gases move from one body compartment to another according to partial pressure gradients,steady state is achieved when the partial pressure in each of these compartments is equivalent to that in the inspired mixture.
🔘The time course for attaining this steady state is determined by the following factors:
1.Alveolar wash-in
🔸This refers to replacement of normal lung gases with the inspired anesthetic mixture
🔸الزمن البتحتاجو العملية دي بتتناسب عكسيا مع الventilatory rate وطرديا مع
functional residual capacity of the lung
وهو عبارة عن
volume of gas remaining in the lungs at the end of a normal expiration
2.Anesthetic uptake (removal to peripheral tissues other than the brain):
🔸Uptake is the product of gas solubility in the blood,cardiac output (CO), and the gradient between alveolar and blood anesthetic partial pressures.
🔵Solubility in blood
🔹This is determined by a physical propertyof the anesthetic called the blood/gas partition coefficient (the ratio of the concentration of anesthetic in the blood phase to the concentration of anesthetic in the gas phase when the anesthetic is in equilibrium between the two phases)
🔹Agents with low solubility in blood, such as nitrous oxide quickly saturate the blood. In contrast, anesthetic gases with high blood solubility, such as halothane, dissolve more completely in the blood, and greater amounts of anesthetic and longer periods of time are required to raise blood partial pressure
🔹The solubility in blood is ranked as follows: halothane > isoflurane > sevoflurane > nitrous oxide > desflurane.
🔵Cardiac output:
🔹لما يكون عالي معناو الanesthetic بيتم نقلها بسرعة من ال alveoli وبكدا حا يزيد الزمن المحتاجنو عشان يصل للإتزان بين الalveoli وال brain والسبب في دا انو في slow rate of rise in alveolar concentration of gas
🔹وبكدا نستنتج انو
higher CO equals slower induction
Low CO (shock) speeds the rate of rise of the alveolar concentration of gas, since there is less removal to peripheral tissues
🔵Alveolar-to-venous partial pressure gradient of anesthetic:
🔹لما الشرايين تشيل الanesthetic وتوزعها للtissue بتالي الدم الوريدي لما يرجع ال lung بكون في فرق في ال partial pressure ودا بيؤدي ل انو more gas moves into the blood from the lung according to the partial pressure difference
3.Effect of different tissue types on anesthetic uptake:
🔸The time required for a particular tissue to achieve steady state
بتناسب عكسيا معblood flow to that tissue (greater flow results in a more rapidly achieved steady state)
يعني كل ما زاد حا يقل الزمن المحتاجنو عشان يصل لحالة اتزان
وبرضو هو بتناسب طردياً مع capacity of that tissue to store anesthetic (a larger capacity results in a longer time required to achieve steady state)
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