NAP 204 Chemistry, Biochemistry, and Physics of Anesthesia PDF

NAP 204 CHEMISTRY, BIOCHEMISTRY, AND PHYSICS OF ANESTHESIA MICHAEL GRECO, PHD, DNP, CRNA, AGACNP-BC, CHSE, FNAP, FAANA SANDI WOODHEAD SHROYER, DNP, CRNA HOFSTRA-NORTHWELL GRADUATE PROGRAM IN NURSE ANESTHESIA  CLASS OBJECTIVES State the Ideal Gas Law De...

NAP 204 CHEMISTRY, BIOCHEMISTRY, AND PHYSICS OF ANESTHESIA MICHAEL GRECO, PHD, DNP, CRNA, AGACNP-BC, CHSE, FNAP, FAANA SANDI WOODHEAD SHROYER, DNP, CRNA HOFSTRA-NORTHWELL GRADUATE PROGRAM IN NURSE ANESTHESIA  CLASS OBJECTIVES State the Ideal Gas Law Describe the difference between vaporization and humidification Apply Newton's Law of Physics Apply Pressure and Tension to an oxygen cylinder Utilize Avogadro’s number to convert between number of molecules and number of moles Define vaporization and how it relates to volatile anesthetics  PHYSICS a t i o n u l Reg ases T B r e he of G ath Pro ing ces s r gy o f Ene F l ow  PHYSICS Pressure ---------------------------(kPa) Volume ------------------------------(L) Temperature -----------------------(k) Amount ---------------------------(mols)  CELSIUS TO FAHRENHEIT Celsius = (F – 32) / 1.8 Fahrenheit = ( C * 1.8 ) + 32 0 DEGREES KELVIN IS CALLED THE “ABSOLUTE ZERO” = -273 DEGREES C OR -459 DEGREES F  MEASUREMENTS 1 kg = 2.2 lbs 1 inch = 2.54 cm  IDEAL (UNIVERSAL) GAS LAW Pressure, volume, and temperature of an ideal gas are related by the following equation: pV = nRT Where p is absolute pressure V is volume n is the number of moles of gas R is so-called universal gas constant T is the temperature in kelvins (K) A. When air is pumped into a deflated tire, its volume first increases without much increase in pressure B. When the tire is filled to a certain point, the tire walls resist further expansion and the pressure increases with more air. C. Once the tire is inflated, its pressure increases with temperature.  NEWTON’S LAWS 1. Law of Inertia (In-nur-shuh): Object at rest or moving at a constant speed in a straight line tends to stay in motion unless acted upon by another force.  NEWTON’S LAWS 2. Law of Force: Force is equal to mass times acceleration m= Mass in kilograms F= Force a = Acceleration  NEWTON’S LAWS 3. Law of Reciprocal Action: For every action, there is an equal and opposite reaction. DALTONS LAW OF PARTIAL PRESSURES In a mixture of gases, the total pressure exerted by the mixture is equal to the sum of the partial pressures of the individual gases, provided the gases DO NOT mix with each other. P total = P1 + P2 +…PN The total pressure in a mixture of gases is equal to the sum of the pressures of the individual gases (each gas is said to exert partial pressure). The partial pressure of a gas is calculated by multiplying the percent gas (fractional concentration) times the atmospheric pressure. DALTONS LAW OF PARTIAL PRESSURES In the atmosphere at sea level, the partial pressures are: O 2 160mm-Hg (21%) N2 600mm-Hg (79%) Total, 760mm-Hg (100%) DALTON’S LAW OF PARTIAL PRESSURES Volume % = (partial pressure / total pressure) X 100 CLINICAL PROBLEM: 1. What are the partial pressures of N2O and O2 if they are delivered to the patient in a 70%/30% N2O/O2 mixture (assume sea level)? 70% X 760mm-Hg = 532mm-Hg for N2O 30% X 760 mm-Hg= 228-Hg for O2 CLINICAL PROBLEM: 2. What is the partial pressure of O2 in the mountains where the Patm is 550 mmg-Hg? 21% X 550 mm-Hg= 116 mm-Hg CLINICAL PROBLEM: 3. What is the partial pressure of CO2 if its concertation in the end-tidal gases is 5%? 5% X 760 mm-Hg= 38 mmHg  WHAT ARE VAPOR PRESSURES? Vapor pressure of a liquid is where an “equilibrium pressure” is reached inside a closed container à where molecules go from gas to liquid or liquid to gaseous states in continuum The pressure at which the gaseous state is in equilibrium with either the liquid or solid state, or with both. Vapor Pressure is the function of temperature  CRITICAL TEMPERATURE Critical temperature = the highest possible temperature value at which the substance can exist as a liquid  VAPORIZATION Vapor pressure is a measure of the tendency of a material to change into the gaseous or vapor state, and it increases with temperature. The temperature at which the vapor pressure at the surface of a liquid becomes equal to the pressure exerted by the surroundings is called the boiling point of the liquid. Every substance has its unique critical temperature above which it exists only as a gas, irrespective of how much pressure is applied to it. At or below this critical temperature, it can exist in both its liquid and gaseous forms; the latter is called a vapor Question: Is vapor pressure a function of temperature, volume, or pressure?  SATURATED VAPOR PRESSURE Function of temperature VP is the pressure at which the gaseous state is in equilibrium with either the liquid state, solid state, or both. The boiling point of a liquid is the temperature at which the saturated vapor pressure is equal to the atmospheric pressure- essentially the boiling point of a liquid is dependent on the atmospheric pressure. Since atmospheric pressure depends on altitude, the boiling point is depressed as altitude increases. VAPORIZERS FOR VOLATILE AGENTS DALTON’S LAW IN PRACTICE The pressure exerted by an individual gas in a mixture is known as its partial pressure. Assuming we have a mixture of ideal gases, we can use the ideal gas law to solve problems involving gases in a mixture. Dalton's law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases.  VOLATILE AGENTS IN A FLASK (DALTON’S LAW) The vapor pressure is added to a flask of oxygen, what is the percent oxygen and percent of O2 after the Isoflurane is added is (760 – 240 mm Hg)-= 520 mm-Hg. %O2= 𝟓𝟐𝟎𝒎𝒎 𝑯𝒈 𝟕𝟔𝟎 𝒎𝒎 𝑯𝒈 X 100% = 68.4% Vapor Pressures at 20 C Sevoflurane, 170 mm Hg Enflurane, 172 mm Hg Isoflurane, 240 mm Hg Halothane, 244 mm Hg 𝟐𝟒𝟎𝒎𝒎 𝑯𝒈 Desflurance, 669 mm Hg %Isoflurane= 𝟕𝟔𝟎 𝒎𝒎 𝑯𝒈 X 100% = 31.6% 100% O2 PO2= 760 mmHg % O2 = ? % Iso = ? ISO Agent Boiling Vapor MAC Blood: Gas Oil : Gas point pressure coefficent coefficent Desflurane 22.8 C 669 6 0.42 18.7 Isoflurane 48.5 C 240 1.2 1.4 99 Sevoflurane 58.5 C 160 2 0.6 50 N2O - 88.4 C 38,770 107 0.47 1.4 Enlurane 56.5 C 172 1.7 Boiling point at 0 degrees C 760 mmHg Vapor Pressure at 20 degrees C MAC = minimal alveolar concentration PRESSURE AND TENSION Bourdon Gauge Measures High Pressure Measures pressure relative to atmosphere pressure. (not absolute pressure) These are mechanical pressure instruments UNITS OF PRESSURE Unit Conversion: Ø 1 mm Hg = 1.36 cm H2O Ø 1 atm = 760 mm-Hg= 14.7 psi = kPa= 1 bar Ø 1 psi = 54mm-Hg  LAW OF LAPLACE (CYLINDRICALLY-SHAPED STRUCTURES) Law of Laplace states that for a cylindrically shaped structure with an infinitely thin wall, T=PXr T = wall tension P = pressure of liquid within a cylinder r = radius As a structure expands (the radius increases), the tension (force) in the wall of the structure increases.  APPLICATION OF THE LAW OF LAPLACE (CYLINDRICALLY-SHAPED STRUCTURES) BLOOD VESSELS LEFT VENTRICLE LAPLACE : SPHERES Tension = (pressure X radius) / 2 APPLICATION OF THE LAW OF LAPLACE (SPHERICALLY-SHAPED STRUCTURES) HAGEN-POISEUILLE (POY SELL) LAW OF PHYSICS Q=𝝅r4 (P1-P2) /8𝜼𝐥 Q= Flow R=radius of cross section of the tube P= pressure 𝜂= Viscosity of gas or liquid L= length of the tube Changing radius has the most dramatic effect on flow. FLOW OF FLUIDS ! Q=flow 𝜋𝛤 Δ𝑃 Δ𝑃=hydrostatic pressure 𝑄= gradient 8𝑛" n= fluid Viscosity L=length THE SURGEON ALERTS YOU HE ACCIDENTLY RUPTURED AN ARTERY. YOU HANG BLOOD AND NEED TO INFUSE THAT RAPIDLY, WHAT DO YOU DO? Put a large bore angiocath into your patient Increase the height of the IV pole Use a rapid infuser / pressure bag HAGEN-POISEUILLE FORMULA  REYNOLD’S NUMBER Whether flow is laminar or turbulent !"# Re = Laminar flow dependent on gas viscosity 𝜼 (Poiseuille's law) Re= Reynold’s number Turbulent flow dependent on gas density (Grahams law) P= density V= velocity of fluid d= diameter of tube 𝜼= viscosity of fluid  TURBULENT FLOW Flow Becomes Turbulent if: a. Velocity of flow if high b. Tube wall is rough (corrugated) c. There are kinks, bends, narrowing in the tube. RAE Tube- flow is turbulent at the angle (bend). RESISTENCE TO FLOW INCREASES WHEN FLOW BECOMES TURBULENT. Ventilating patients is more difficult when flow is turbulent. VENTURI, BERNOULLI & COANDA EFFECT HENRYS LAW At a constant temperature, the amount of gas dissolved in a solution is directly proportional to the partial pressure of gas over the solution CO2 is 20x more soluble than O2 Oxygen = 0.003 ml/dL/mmHg Carbon dioxide = 0.067 ml/dL/mmHg  HENRYS LAW Permits calculations of dissolved O2 and CO2 in the blood The amount of O2 that dissolves in blood is 0.003mL /100mL blood mm-Hg partial pressure. To calculate the amount of Oxygen dissolved in blood, multiply the partial pressure of O2 by 0.003. How much O2 is dissolved in arterial blood when the PaO2 is 300 mm Hg? 300mm Hg X 0.003 = 0.9mL O2/100mL blood dissolved  HENRY’S LAW KNOW HOW TO DO THIS PROBLEM How much does dissolved O2 increased in the blood when PaO2 increases from 100 mm Hg to 500 mm Hg? Dissolved O2 when PaO2 is 100mm Hg = 100 mm Hg X 0.003= 0.3mL O2/100mL blood; Dissolved O2 when PaO2 is 500 mm Hg = 500 mm Hg X 0.003 =1.5 mL O2/100mL blood; Therefore, dissolved O2 increased 1.2mL O2/100 mL blood (from 0.3 to 1.5mL O2/100mL Blood).  HENRY’S LAW KNOW HOW TO DO THIS PROBLEM If the inspired O2 is given, estimate the PaO2 by multiplying the inspired concentration by 5. How much O2 is dissolved if the FiO2 is 40%? 40 X 5 = 200mm Hg, the estimated PaO2; Amount dissolved = 200 mm Hg X 0.003 = 0.6mL O2/100mL blood The amount of CO2 that dissolves in blood is 0.67mL/100mL blood/mm Hg. To calculate the amount of carbon dioxide that dissolves in blood, multiply the partial pressure of CO2 by 0.067.  HENRY’S LAW KNOW HOW TO DO THIS PROBLEM How much CO2 is dissolved in arterial blood when PaCO2 is 50mm Hg? Dissolved CO2 when PaCO2 = 50mm Hg is 50 mm Hg X 0.067= 3.35 mL CO2/100mL blood We will discuss Henrys Law in Coexisting Diseases Class when we learn Total O2 Carrying Capacity of Blood & oxygen delivery (DO2)  BOYLES LAW At a constant temperature, the volume of a given mass of gas is inversely proportional to the absolute pressure. We know the volume of a full E size cylinder is approximately 5 Liters. The service pressure at which the cylinder is filled is 2000 psig P1V1 = P2V2 2000 X 5 = 15 X V2 V2 = 2000 X 5/15 = 665 Liters So if we use 3 liters of O2, the E type full cylinder will last for about 220 minutes.  BOYLES LAW CLINICAL APPLICATION Squeezing an Ambu bag raises the pressure and decreases the volume During inspiration when breathing spontaneously, intrapulmonary pressure falls and volume increases, During expiration, intrapulmonary pressure increases and volume decreases. Measurement of FRC by body plethysmography uses Boyle’s law.  CHARLES LAW At a constant pressure, volume of gas is directly proportional to the temperature. Clinical Application: 1. The inflatable cuff of a Laryngeal mask airway (LMA) expands when placed into an autoclave for sterilization. 2. One way heat lost from the body is that the air next to the body warms up and rises and from this process, more heat is lost from our patients as they continue to lose heat (important for pediatric patients).  GAY LUSSAC’S LAW At constant volume, the absolute pressure of the given mass of gas is directly proportional to the temperature. CLINICAL APPLICATION: i. Medical gases are stored in cylinders having a constant volume and high pressure (138 Barr in a full O2 / Air cylinder). If these are stored at high temperatures, pressures will rise causing explosions. ii. As a N2O cylinder empties, the pressure in the tank decreases even when N2O liquid is present. i. The Joule-Thompson effect explains the decrease in pressure, as temperature decreases in a constant-volume cylinder = the pressure of the gas in the cylinder decreases. Can These Guys Possible Be Violinists?  AVOGADRO’S NUMBER AND HYPOTHESIS a) Avogadro’s number: the number of molecules in one mole of a substance is 6.022 X 1023 b) Avogadro's hypothesis: one mole of a gas at standard temperature (273 K) and standard pressure (1 atm) occupies a volume of 22.4 liters. Problem: Two moles of gaseous N2O occupy what volume under standard conditions? Under standard conditions, two moles of gaseous N2O occupy 22.4 X 2 = 44.8 liters AVOGADRO’S HYPOTHESIS AND IDEAL GAS EQUATION The law can also be defined as one gram molecule weight (one mole) of a gas contains 6.022X1023 (Avogadro’s number) molecules = occupies 22.4L at STP. PV = n RT is the ideal gas equation R is the universal gas constant = 1.987 J/degree/mole in SI units  CLINICAL APPLICATION: SINCE THE CYLINDER VOLUME IS CONSTANT, TEMPERATURE IS CONSTANT AND R IS ALREADY A CONSTANT P = N PRESSURE SHOWN IN THE BOURDON’S GAUGE IS PROPORTIONAL TO THE NUMBER IF MOLECULES WHICH IS THE AMOUNT OF GAS IN THE CYLINDER. HENCE THE PRESSURE GAUGE ACTS AS A CONTENT GAUGE  CYLINDERS Critical Temperature Gas liquefy if sufficient pressure is applied and the temperature is below a critical value called the critical temperature Adiabatic Processes (Constant Heat) If a cylinder of compressed gas is opened into a closed space (of pipes) the process in the closed space will rise rapidly and the temperature will also rise rapidly, possible to levels that can ignite a flame. This process occurs without gain or loss of energy (heat) Joule- Thompson Effect) JOULE IS COOL When a compressed gas is allowed to escape freely into space, the process is adiabatic and cooling occurs. NITROUS OXIDE CYLINDERS (N2O) OXYGEN CYLINDERS (O2)  Color PSI Liters PIN OXYGEN Green 1900-2200 660 2-5 (white) N2O Blue 745 1590 3-5 Air Yellow 1900 625 1-5 (black/white)  WE CANNOT USE N2O CYLINDERS PRESSURE GAUGES IN THE SAME WAYS WE USE O2 PRESSURE GAUGES N2O CONTAINS BOTH VAPOR AND LIQUID SO THESE GAS LAWS DO NOT APPLY How do anesthesia providers calculate the quantity of N2O? qN2O is stored in cylinders as a liquid qExists partly as liquid and partly as a gas q Through known cylinder weight and measured weight amount of N2O and usage is calculated using Avogadro’s hypothesis. CALCULATION OF N2O: Weight of full N2O Cylinder 5.6 Kg Tare Weight (empty weight) 4.5 Kg Weight of N2O 1.1 Kg Therefore 1.1 Kg of N2O = 22.4 X 1100 560 44 If we administer 2 liters of N2O / min, the cylinder will provide gas for 280 minutes or 4.6 hours.