3 - Solutions and Solubility.docx

Inhaled anesthetics in clinical use - Variable-bypass vaporizers are used to deliver most inhaled anesthetics - Depend on relative gas glow and the vapor pressure - **Desflurane requires a special vaporizer** - Due to high vapor pressure and boiling point near room te...

Inhaled anesthetics in clinical use - Variable-bypass vaporizers are used to deliver most inhaled anesthetics - Depend on relative gas glow and the vapor pressure - **Desflurane requires a special vaporizer** - Due to high vapor pressure and boiling point near room temperature - Vaporizer heats and injects agent for predictable output - Isoflurane, sevoflurane, and desflurane are the most commonly used agents - Nitrous is a good adjunct but has side effects - Inhaled anesthetics are potent greenhouse gases environmental impacts **Saturated vapor pressure (SVP)** = pressure exerted by molecules from a volatile substance that escape the liquid phase and become vapor - SVP is directly proportional to the number of molecules of gas within a container at a certain temperature - SVP directly proportional to temperature due to higher kinetic energy and greater conversion to gas phase **Boiling point** = temperature at which vapor pressure equals ambient pressure and the liquid rapidly vaporizes 2 types of vaporizers = **variable-bypass vaporize**r and **heated vaporizer** Nitrous oxide use during long procedures - Risk of diffusion into ETT cuff - Increased cuff pressures tracheal trauma, postoperative discomfort, and cuff rupture - Limiting diffusion in the cuff by - providing equilibrium between the delivered gases and the gases that fill the cuff lumen - use saline to expand cuff **Meyer-Overton Hypothesis** = potency of an anesthetic agent is related to its lipid solubility **[Solubility, Diffusion, and Osmosis ]** - CO2 is more soluble in tissues than in oxygen - Impairments in diffusing capacity is more likely to lead to hypoxemia than hypercarbia - Why do many diffusing impairments present with hypercarbia before hypoxia? - **Henry's Law** = the number of gas molecules dissolved in a liquid is directly proportional to its partial pressure above the liquid - **Solubility coefficients** - Bunsen - Ostwald - **Solubility and temperature** - Solubility of liquids and solids increase with temperature - Solubility of gases decrease with temperature -- think of how soda left in car would explode since gas moves from liquid to area above liquid - Solubility coefficients for respiratory gases - CO2 is 20x more soluble than O2 - Why do we intubate people? Due to CO2 not O2. You can always add more O2 - Nitrous oxide is more soluble than nitrogen -- situations in which nitrous oxide is contraindicated in bowel cases, potential issues with increased airspaces (pneumothorax, pneumocephalus), certain ear surgeries (tympanoplasty), certain eye surgeries - **Partition coefficient = s**olubility of inhalation anesthetics in a variety of different solvents. A partition coefficient is simply the ratio of the concentration of anesthetic in one phase or solvent compared to another - comparison of blood-gas, brain-blood, liver-blood, kidney-blood, muscle-blood, fat-blood - Only care about top 4 in chart in ppt = blood gas and fat-blood - The longer the case, the more anesthetic will go to your fat - Desflurane will go off faster in obsess patients and nitrous doesn't get absorbed - **MAC and Oil solubility** - Isoflurane MAC is 1.17% - chart in ppt is wrong - **Meyer-Overton Hypothesis** = potency of an anesthetic agent is related to its lipid solubility - High potency correlates with slow onset - Oil-gas partition coefficient is proportional to fat-gas partition coefficient - Diffusion and osmosis - **Fick's Law =** rate of diffusion is proportional to the gradient of the concentration (liquid) or partial pressure (gas) - **Graham's Law =** rate of diffusion of gases through a porous membrane is inversely proportional to the square root of the molar mass of the gas - **Bulk flow = ultrafiltration + reabsorption** - **Ultrafiltration:** when the pressure inside the capillary exceeds the osmotic pressure of the blood plasma, fluid is pushed out through the pores in the capillary wall (on arterial side) - **Reabsorption:** When the osmotic pressure of the blood plasma exceeds the outward pressure (on venous side) - Helps regulate the distribution of ECF between plasma and interstitial spaces - **Rate of diffusion** depends on **nature of membrane** and **solubility** of the gas - **Osmosis** = movement of water through a semi-permeable membrane. Water flows to more concentrated side - In events of elevated ICP = use mannitol, hypertonic saline to increase concentration of plasma so water moves from brain to plasma - Hypertonic shrink and crenation - Hypotonic lysis and bursts - **Osmole =** unit of measurement for osmotic activity - 1 Avogadro's number of particles dissolved in a solute that cannot diffuse through a semi-permeable membrane - **Osmotic pressure =** pressure at which osmosis of a solvent into a semi-permeable membrane is prevented - Non-ionizing solutions -- carbon based solutions - Molecular substances with covalent bonds and are polar - Won't dissociate - Ionizing solutions -- salt + non-salt e.g. NaCl - Salts with ionic bonds - Will dissociate into solutions - Osmosis and the gas laws - Osmolarity of body fluids at body temperature - **Tonicity =** osmotic pressure of a solution relative to that of other body fluids - **Molar solution** of any solute contains **1 mol/L** - Effects of mOsm on cells - Hypotonic e.g. ½ NS - Isotonic e.g. NS - Hypertonic e.g. 3% NS