Chemistry And Physics Of Anesthesiology Quiz! Trivia

Boyle's law states that for a fixed mass of gas at constant temperature, the product of pressure and volume is constant. This concept can be applied to estimate the volume of gas remaining in compressed-gas cylinder by measuring the pressure within the cylinder

The ventilator pressure-relief valve is pressure-controlled via pilot tubing that communicates with the ventilator bellows chamber. As the pressure within the bellows chamber increases during the inspiratory phase of the ventilator cycle, the pressure is transmitted via the pilot tubing to close the pressure-relief valve, thus making the patient breathing circuit "gas-tight." This valve should open during the expiratory phase of the ventilator cycle to allow the release of excess gas from the patient breathing circuit into the waste-gas-scavenging circuit after the bellows has fully expanded. If the ventilator pressure-relief valve were stuck in the closed position, there would be a rapid buildup of pressure within the circle system which would be readily transmitted to the patient. Barotrauma to the patient's lungs would result if this situation were to continue unrecognized.

Some epidemiology studies suggest that chronic exposure to trace concentrations of volatile anesthetic gases constitutes a health hazard to operating room personnel. For this reason, proper and routine use of scavenging systems is recommended in the operating room. It is extremely difficult to keep trace volatile anesthetic gas concentrations within safe limits when they are delivered using a face mask. Although all of the choices in this question can contribute as sources of contamination, leakage around the anesthesia face mask poses the greatest threat.

Factors that influence the rate of flow of a substance through a tube are described by Hagen-Poiseuille law of friction. If diameter of catheter is doubled, flow will increase by a factor 2 raised by the fourth power.

The O2 analyzer is the last line of defense against inadvertent delivery of hypoxic gas mixtures. It should be located in the inspiratory limb of the patient breathing circuit to provide maximum safety. Since the O2 concentration in the fresh-gas supply line may be different from that in the patient breathing circuit, the O2 analyzer should not be located in fresh-gas supply line.

Fail-safe valve is a synonym for pressure-sensor shutoff valve. The purpose of the fail-safe valve is to prevent delivery of hypoxic gas mixtures from the anesthesia machine to the patient in case of failure of the O2 supply. When the O2 pressure within the anesthesia machine decreases below 25 psia, this valve discontinues the flow of N2O or proportionally decreases the flow of all gases. It is important to realize that this valve will not prevent delivery of hypoxic gas mixtures or pure N2O when the O2 rotameter is off but the O2 pressure within the circuits of the anesthesia machine is maintained by an open O2 compressed-gas cylinder or central supply source. Under these circumstances, an O2 analyser would be needed to detect delivery of a hypoxic gas mixture.

Agent-specific vaporizers are designed for each volatile anesthetic. However, volatile anesthetics with identical saturated vapor pressures could be used interchangeably with accurate delivery of volatile anesthetic.

Rectal, esophageal, axillary, nasopharingeal, and tympanic membrane temperature measurements correlate with central temperature in patients undergoing noncardiac surgery. Skin temperature does not reflect central temperature and does not warn adequately of malignant hyperthermia or excessive hypothermia.

Boyle's law states that for fixed mass of gas at constant temperature, the product of pressure and volume is constant. This principle can be used to estimate the volume of gas remaining in compressed-gas cylinders.

After O2 enters the anesthesia machine from a compressed-gas cylinder or from a central supply line, the pressure within the tubing reduced to 45 to 55 psia by the first-stage pressure regulators. This pressure provides for several functions of the anesthesia machine. In addition to the choices in this question, the O2 is also diverted to vaporizing chambers to provide a reliable means to deliver selected concentrations of volatile anesthetic to the patient.

Five types of rotameter indicators are commonly used to indicate the flow of gases delivered from the anesthesia machine. As with all anesthesia equipment, proper understanding of their function is necessary for safe and proper use. All rotameters should be read at the upper rim exept ball floats, which should be read in the middle.

O2 and N2O enter the anesthesia machine from a central supply source or compressed-gas cylinders at pressures greater than 2,000 psia. First-stage pressure regulators reduce this pressure to approximately 50 psia. Prior to entering the rotameters , second-stage O2 pressure regulators further reduce the pressure to approximately 16 psia.

The correct answer is 45 psia because the pressure regulator in the anesthesia machine is designed to reduce the pressure of the gas from the N2O compressed-gas cylinder. The pressure is reduced to 45 psia to ensure that the gas is delivered at a safe and controlled pressure to the patient during anesthesia administration.

E-size O2 cylinder filled with pressure 2,200 psia contains approximately 625 L of gas. According to Boyle's law the volume of gas can be estimated by measuring the pressure within the container. Therefore, when pressure gauge on cylinder shows 1,600 psia, it contains approximately 490 L of O2. At gas flow of 2L/min it will be delivered for 245 min.

Density is the weight in grams of 1 ml of a solution at specific temperature. The ratio of the density of a solution at a specific temperature to the density of cerebrospinal fluid at the same temperature is called baricity. Local anesthetic used for spinal anesthesia can be defined as hypobaric, isobaric, or hyperbaric. Hypobaric local anesthetic solutions are less dense than cerebrospinal fluid, isobaric local anesthetic solutions are equally dense as cerebrospinal fluid, and hyperbaric solutions are more dense than cerebrospinal fluid. The density of normal human cerbrospinal fluid at 37ºC is 1.0001 to 1.0005 (95% confidence limits). Local anesthetic solutions can be made hyperbaric by adding glucose in sufficient quantities to increase the baricity > 1.0008

Failure to oxygenate patients adequately is the leading cause of anesthesia-related morbidity and mortality. All of the choices listed in this question are potential causes of inadequate delivery of O2 to the patient; however, the most frequent cause is inadvertent disconnection of the O2 supply system from the patient ( e.g., disconnection of the patient breathing circuit fron the endotracheal tube).

All of the choices listed in this question can potentially result in inadequate flow of O2 to the patient; however, given the description of the problem, no flow of O2 through the O2 rotameter is the correct choice. In a normal functioning rotameter, gas flows between the rim of the wall of the Thorpe tube, causing the bobbin to rotate. If the bobbin is rotating you can be certain that gas is flowing through the rotameter and that the bobbin is not stuck.

The correct answer is 25 ppm. The National Institute for Occupational Safety and Health (NIOSH) has set the highest trace concentration of N2O allowed in the operating room atmosphere at 25 ppm. This limit is in place to ensure the safety and well-being of healthcare workers who may be exposed to N2O during procedures. Higher concentrations of N2O can have adverse health effects, including dizziness, nausea, and even long-term neurological damage. Therefore, it is crucial to adhere to this limit to maintain a safe working environment.

The pin-index safety system is designed to prevent the attachment of gas-administering equipment to the wrong type of gas line. This system uses a specific arrangement of pins and corresponding holes on both the gas cylinder and the equipment to ensure that they can only be connected in the correct configuration. This helps to avoid dangerous situations where incompatible gases are used, reducing the risk of accidents or damage to the equipment.

The critical velocity for helium is greater than that for nitrogen. For this reason, there is less work of breathing when helium is substituted for nitrogen.

Agent-scecific vaporizers (in contrast to measured-flow vaporizers such as the copper kettle vaporizer) will deliver the same partial pressure of volatile anesthetic regardless to atmospheric pressure. Since the partial pressure of the volatile anesthetic in the brain, not the absolute concentration delivered to the patient. is the most important factor i achieving depth of anesthesia, the clinical effect of a give setting on the vaporizer dial will be affected by atmospheric pressure. In contrast, the concentration of volatile anesthetic (measures as volume percent) delivered from the vaporizer is influenced by atmospheric pressure. This effect may be calculated using following equation:
Cx = C*P/Px
where Cx is the output concentration in volume percent at atmospheric pressure x, C is the dial setting of the vaporizer in volume percent, P is the atmospheric pressure for which the vaporizer is calibrated, and Px is the atmospheric pressure for which Cx is being established.

Compliance is a measure of how easily a substance or system can change its volume in response to a change in pressure. It is defined as the change in volume per unit change in pressure. This means that compliance quantifies the relationship between the change in volume and the change in pressure, indicating how much the volume of a substance or system will change for a given change in pressure.

The saturated vapor pressures of halothane and isoflurane are very similar (≈240 mm Hg at room temperature), so they could be used interchangeably in agent-specific vaporizers.

The ratio of the density of a solution at a specific temperature to the
density of water at that same temperature is called specific gravity. As with density, specific gravity can be used to determine the baricity of local anesthetic solutions. When specific gravity is used, baricity is defined as the ratio of the specific gravity of the local anesthetic solution at a specific temperature to the specific gravity of cerebrospinal fluid at the same temperature. However, this method of determining baricity is less accurate than defining baricity in terms of density

The minimum macroshock current required to elicit ventricular fibrillation is 100 mAmp. Ventricular fibrillation is a life-threatening condition where the heart's electrical signals become chaotic, causing the heart to quiver instead of pumping blood effectively. A macroshock refers to an electrical shock that occurs when current passes through the body externally. A current of 100 mAmp is sufficient to disrupt the heart's normal electrical activity and trigger ventricular fibrillation.

The accurate function of dual-wavelength pulse oxymeters is altered by nail polish. Because blue nail polish has a peak absorbance similar to that of adult deoxygenated hemoglobin (near 660 nm), blue nail polish has the greatest effect on the SaO2 reading. Nail polish causes an artifactual and fixed decrease in SaO2 reading by these devices.

The statement "Extension of the neck can convert an endotracheal intubation to an endobronchial intubation" is false. Extension of the neck does not convert an endotracheal intubation to an endobronchial intubation. Endobronchial intubation occurs when the endotracheal tube is inadvertently inserted into one of the mainstem bronchi instead of the trachea. This can happen due to factors such as improper positioning or incorrect placement of the tube. Extension of the neck does not play a role in this process.

Rotameters consist of a vertically positioned tapered tube, which is smallest in diameter at the bottom (Thorpe tube). Gas enters at the bottom of the Thorpe tube elevating a bobbin or float, which comes to rest when gravity on the float is balanced by the fall in pressure across the float. The rate of gas flow through the tube depends on the pressure drop along the length of the tube, the resistance to gas flow through the tube, and the physical properties (density and viscosity) of the gas. Because few gases have the same density and viscosity, rotameters cannot be used interchangeably.

A scavenging system with closed interface is one in which there is communication with the atmosphere through positive and negative pressure-relief valves. The positive pressure-relief valve will prevent transmission of excessive pressure buildup to the patient breathing circuit, even if there is an obstruction distal to the interface or if the system is not connected to wall suction. However, obstruction of the transfer tubing from the patient breathing circuit to the scavenging circuit is proximal to the interface. This will isolate the patient breathing circuit from the positive pressure-relief valve of the scavenging system interface. Should this occur, barotrauma to the patient's lung can occur.

A size "E" compressed-gas cylinder completely filled with air contains 625 L and should show a pressure gauge reading of 1,800 psia. Therefore, a cylinder with pressure gauge reading of 100 psia would be half full, containing approximately 310 L of air. A half-full size "E" compressed gas cylinder containing air could be used for approximately 30 minutes at flowrate of 10 L/min.

Although controversial, chronic exposure to low concentrations of volatile anesthetics may constitute a health hazard to operating room personnel. Therefore, removal of trace concentrations of volatile anesthetic gases from the operating room atmosphere with scavenger system and steps to reduce and control gas leakage into the environment are required. High-pressure system leakage of volatile anesthetic gases into the operating room atmosphere occurs when gas escapes from compressed-gas cylinders attached to the anesthetic machine (e.g., faulty yokes) or from tubing delivering these gases to the anesthesia machine from a central supply source. The most common cause of ;ow-pressure leakage of anesthetic gases into the operating room atmosphere is the escape of gases from sites located between the flowmeters of the anesthesia machine and the patient, such as a poor mask seal. The use of high gas flows in a circle system will not reduce trace gas contamination of the operating room atmosphere. In fact, this could contribute to the contamination if there is a leak in the circle system.

Automated noninvasive blood pressure (ANIBP) devices provide consistent and reliable blood pressure measurements. Variations in the cuff pressure resulting from arterial pulsations during cuff deflation are sensed by the device and are used to calculate mean arterial pressure. Then, values for systolic and diastolic pressures are derived from formulas, that utilize the rate of change of the arterial pressure pulsations and the mean arterial pressure (oscillometric principle). This methodology povides accurate measurements of arterial blood pressure in neonates, infants, children and adults. The main advantage of ANIBP devices is that they free the anesthesia provider to perform other duties required for optimal anesthesia care. In addition, these devices provide alarm systems to draw attention to extreme blood pressure values and have the capacity to transfer data to automated trending devices or recorders. The improper use of the devices can lead to erroneous measurements and complications. The width of the blood pressure cuff should be approximately 40% of the circumference of the patient's arm. If the width of the blood pressure cuff is too narrow or if the blood pressure cuff is too loosely wrapped around the arm, the blood pressure measurement will be falsely elevated. Frequent blood pressure neasurements can result in edema of the extremity distal to cuff. For this reason, cycling of these devices should not be more frequent than every 1 to 3 minutes. Other complications associated with improper use of ANIBP devices include ulnar nerve paraesthesia, superficial thrombophlebitis, and compartment syndrome. Fortunately, these complications are rare occurrences.

Laminar flow occurs when a substance flows down parallel-sided tube at a rate less than critical velocity. Resistance to laminar gas flow through a tube is directly proportional to the viscosity of the gas and the length of the tube, and inversely proportional to the forth power of the radius of the tube. This is knows as Hagan-Poiseuille law of friction.

The pressure gauge on size "E" compressed-gas cylinder containing N2O shows 750 psia when it is full and will continue to register 750 psia until approximately three quarters of the gas has left the cylinder. A full cylinder of N2O contains 1,600 L. Therefore, when 400 L of gas remain in the cylinder, the pressure within the cylinder will begin to fall.

Anesthetic gases at clinical concentrations are least responsible for killing bacteria in anesthesia machines. While high O2 concentration, metallic ions, shifts in humidity, and shifts in temperature can all contribute to the death of bacteria, anesthetic gases at clinical concentrations do not possess strong bactericidal properties. They primarily function to induce anesthesia and maintain the desired level of sedation in patients.

Baralyme granules are composed primarily of barium hydroxide (20%) and calcium hydroxide (80%). Unlike soda lime, baralyme granules are inherently hard and thus the addition of silica to the granules is not necessary. Furthermore, baralyme granules contain water in form of barium hydroxide octahydrate salt, and therefore can be used more efficiently in dry climates.

Entonox is a commercially available single-cylinder gas mixture of O2 and N2O (1:1 by volume). Bacause the attractive forces between N2O molecules are not as strong when mixed with O2, condensation of N2O does not occur when the ambient temperature is greter than -5,5ºC. Therefore, this gas mixture obeys the principles of Dalton's law, which states that the total pressure exerted by constituents of the gas mixture. The pressure within a size "E" cylinder filled with Entonox is 2,200 psia (partial pressure of N2O 1,100 psia). Thus, partial pressure exerted by N2O in half-full cylinder is 550 psia.

In semiclosed anesthetic-breathing circuits, CO2 is eliminated from the circuit by chemical neutralization. This process is achieved by directing exhaled gases through a container with CO2-absorbent granules, such as soda lime o baralyme. Their efficiency influenced by many factors. Maximum volume of CO2 that can be absorbed by 100 g of granules is 25 L.

The safe storage and handling of compressed-gas cylinders is of vital importance. They should not be stored in extremes of heat or cold and should be unwrapped when stored or when in use. Flames should not be used to detect the presence of gas. Oily hands can lead to difficulty in handling of the cylinder, which can result in dropping the cylinder. This can cause damage or rupture of the cylinder, which can lead to an explosion.

The contribution of the fresh-gas flow from the anesthesia machine to the patient's Vt should be considered when setting the Vt of a mechanical ventilator. Because of the ventilator pressure-relief valve is closed during inspiration, both the gas from the ventilator bellows and the fresh gas flow will be delivered to the patient breathing circuit. In this question 2 L/min, a 1/3 of fresh gas is in inspiration phase. Every breath (6 bpm) ≈330 ml will be augmented to Vt.

The saturated vapor pressure of a volatile anesthetic at room temperature indicates the maximum pressure at which the anesthetic can exist as a vapor. The carrier-gas flow through the vaporizing chamber determines the rate at which the anesthetic is delivered. To ensure that the anesthetic is delivered effectively, the flow rate of the carrier gas should be high enough to maintain the vapor pressure of the anesthetic. In this case, a flow rate of 90 ml/min would be sufficient to deliver the anesthetic effectively from the bubble-through vaporizer.

One mL of enflurane or isoflurane will yield approximately 200 mL of vapor at room temperature. One mL of halothane will yield approximately 230 mL of vapor at room temperature.

According to National Institute for Occupational Safety and Health (NIOSH) regulations, the highest concentration of volatile anesthetic contamination allowed in the operating room atmosphere when administered in conjunction with N2O is 0.5 ppm. This means that the maximum allowable concentration of volatile anesthetic in the operating room atmosphere, when N2O is being used, is 0.5 parts per million. This regulation is in place to ensure the safety of healthcare workers and prevent excessive exposure to volatile anesthetics, which can have harmful effects on health.

The FiO2 delivered to patients from low-flow systems (e.g., nasal cannula) is determined by the size of the O2 reservoir, the O2 flow, and the patient's breathing pattern. As a rule of thumb, assuming a normal breathing pattern, the FiO2 delivered by nasal prongs increases by approximately 0.04 for each L/min increase in O2 flow up to maximum FiO2 of approximately 0.45 (at an O2 flow of 6 L/min). In general, the larger the patient's Vt or faster the inspiratory rate, the lower FiO2 for given O2 flow.

The amount of volatile anesthetic vapor leaving the vaporizing chamber will constitute a fractional volume of the total gas leaving the chamber which is proportional to the ratio of the saturated vapor pressure of the volatile anesthetic and atmospheric pressure. In this quiestion, 40% of the total gas flow leaving the vaporizing chamber will be anesthetic vapor. Since the carrier gas flow is 90 ml/min, 60 ml of anesthetic vapor plus 90 ml of carrier gas will exit the vaporizing chamber (i.e., 150 of 40% anesthetic). A diluent fresh gas flow of approximately 4,000 ml/min wil be required to mix with the 150 ml of 40% anesthetic emerging from the vaporizing chamber to produce a delivered concentration of 1,5%.

Starling's law of fluid exchange across capillaries states that the net direction of fluid flow is determined by the forces tending to move fluid out of the capillaries relative to the forces tending to move fluid into the capillaries. The total outward force is the sum of the pressures generated by the capillary hydrostatic pressure, negative interstitial free-fluid pressure, and interstitial fluid colloid osmotic pressure. The total inward force is the sum of the pressures generated by the interstitial pressure and plasma colloid osmotic pressure.

Any endotracheal tube not constructed of metal has the potential to ignite in an O2-enriched environment. Polyviylchloride (PVC) tubes are ignited most easily. Silicone endotracheal tubes are more difficult to ignite that PVC tubes.

Enflurane have lower than isoflurane and halothane saturated vapor pressure, so enflurane vaporizer filled with halothane or isoflurane will deliver higher-than-expexted concentration of volatile anesthetic.

Vaporization of liquid requires the transfer of heat from the objects on contact with the liquid (e.g., metal cylinder and surrounding atmosphere). For this reason, at high flows atmospheric water will condensate as frost on the outside of compressed-gas cylinders.

The rate of simple diffusion of molecules through a lipid membrane is influenced by factors described in both Graham's law and Fick's law. Graham's law states that the rate of diffusion of a gas through a lipid membrane is directly proportional to the solubility of the gas and is inversely proportional to the square root of the molecular weight of the gas. Fick's law states that the rate of diffusion of a gas through a lipid membrane is directly proportional to the pressure gradient of the gas across the membrane and the area of the membrane, and is inversely proportional to the thickness of the membrane.