Sistemas Flashcards
- What are some components of an anesthesia workstation?
Components of the anesthesia workstation include what was traditionally known as the anesthesia machine (with its pressure‐regulating and gas‐mixing components), vaporizers, the anesthesia breathing circuit, the ventilator, the scavenging system, and various monitoring systems (e.g., ECG, blood pressure, pulse oximetry, and gas analyzers). (220)
- What is the purpose of the fail-safe valve? What triggers the fail-safe valve on the anesthesia machine?
The fail-safe valve protects against the delivery of a hypoxic gas mixture; it is triggered when the oxygen supply pressure drops below 30 psi, causing it to shut off or proportionally decrease the flow of all gases. (221)
- Can a hypoxic mixture be delivered from the anesthesia machine with an intact fail-safe valve? Explain.
Yes – because the fail-safe valve is essentially a pressure sensor; if the oxygen flow is zero but the pressure is still sensed as adequate, a hypoxic mixture might still be delivered. This highlights the critical role of the oxygen analyzer and constant vigilance by the anesthesia provider. (221)
- How are oxygen, nitrous oxide, and air gases that are used in anesthesia typically delivered to the anesthesia machine? At what pressure must these gases be delivered for proper function of the anesthesia machine?
These gases are usually delivered from a central hospital supply via pipelines that use color-coded outlets and noninterchangeable fittings; they must be delivered at approximately 50 psi for the anesthesia machine to function properly. (221)
- How is the delivery of erroneous gases to the anesthesia machine minimized?
Erroneous gas delivery is minimized by the use of color-coded wall outlets and pressure hoses plus noninterchangeable fittings (using systems such as DISS or Quick Connects) that prevent misconnection. (221)
- What is the purpose of the cylinders of oxygen and nitrous oxide that are found on the back of the anesthesia machine?
They serve as backup supplies of oxygen and nitrous oxide in case the central gas supply fails. (222)
- How is an erroneous hookup of a gas cylinder to the anesthesia machine minimized?
Cylinders are color-coded and attached using a hanger yoke assembly that incorporates a pin index safety system (PISS), which ensures that only the correct gas cylinder can be connected to its designated inlet. (222)
- Please complete the following table illustrating the characteristics of compressed gases stored in E-sized cylinders:
Oxygen: Cylinder color – Green; Physical state – Gas; Contents – ~625 L; Full pressure – ~2000 psi. Nitrous Oxide: Blue; Physical state – Liquid and gas; Contents – ~1590 L; Full pressure – ~750 psi. Carbon Dioxide: Gray; Physical state – Liquid and gas; Contents – ~1590 L; Full pressure – ~838 psi. Air: Yellow; Physical state – Gas; Contents – ~625 L; Full pressure – ~1800 psi. (223)
- How is the pressure of oxygen related to the volume of oxygen in an oxygen gas cylinder? What does this mean with regard to calculating the volume of oxygen remaining in a used oxygen cylinder?
Pressure in an oxygen cylinder is directly proportional to the volume of oxygen remaining. For example, if a full oxygen cylinder reads approximately 2000 psi (625 L), a reading of 500 psi (one fourth of full pressure) indicates roughly 1/4 of the oxygen volume remains (~156 L). (223)
- How is the pressure of nitrous oxide related to the volume of nitrous oxide in a nitrous oxide gas cylinder?
Because nitrous oxide is stored as a liquid and gas, its pressure gauge remains constant at about 750 psi as long as liquid is present; only after the liquid is exhausted does the pressure begin to drop, indicating that roughly 75% of the gas has been used. (223)
- Why does atmospheric water vapor accumulate as frost on the outside surface of oxygen tanks and nitrous oxide tanks in use? Does internal icing occur?
The process of vaporization and expansion absorbs heat, cooling the exterior of the cylinders so that atmospheric water vapor condenses as frost; however, internal icing does not occur because the compressed gas inside is virtually free of water vapor. (223)
- What is the purpose of flowmeters on an anesthesia machine?
Flowmeters precisely control and measure the flow of gases to the common gas inlet of the anesthesia machine. (223)
- How do flowmeters on an anesthesia machine work?
Gases flow into a tapered, vertically oriented glass tube where they lift a bobbin or ball; the position of this float, determined by the balance between gas flow pressure and gravity, indicates the flow rate in mL or L per minute. (223)
- Are flowmeters for various gases interchangeable?
No; each flowmeter is calibrated for the specific density and viscosity of its designated gas, so they are not interchangeable. (223)
- Why is the oxygen flowmeter the last flowmeter in a series on the anesthesia machine with respect to the direction in which the gas flows?
Because oxygen is added last to the gas mixture, ensuring that any leaks upstream do not dilute the oxygen concentration, thereby maintaining a safe and predictable oxygen delivery. (223)
- What is the purpose of the oxygen flush valve?
The oxygen flush valve provides a high flow (bypassing the flowmeters and manifold) of oxygen directly to the patient, typically used in emergencies or to quickly fill the breathing circuit. (223-224)
- What is the flow of oxygen delivered to the patient when the oxygen flush valve is depressed?
The oxygen flush valve delivers approximately 35 to 75 L/min of oxygen. (224)
- What is the risk of activating the oxygen flush valve during a mechanically delivered inspiration?
Activation during inspiration can transmit very high airway pressures to the patient’s lungs, potentially causing barotrauma. (224)
- Why do volatile anesthetics require placement in a vaporizer for their inhaled delivery to patients via the anesthesia machine?
Volatile anesthetics are liquids at room temperature; vaporizers are necessary to convert them into a vapor in a controlled and predictable manner so that an accurate concentration can be delivered to the patient. (224)
- What is the heat of vaporization?
The heat of vaporization is the amount of heat (calories) required to convert 1 gram of a liquid into vapor at a specific temperature. (224)
- What is vapor pressure? What influence does temperature have on vapor pressure?
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid; it increases with temperature and decreases as the liquid cools. (224)
- Describe how contemporary vaporizers for volatile anesthetics are classified.
Contemporary vaporizers are classified as agent-specific, variable-bypass, flow-over, temperature-compensated, and out-of-circuit devices. (224)
- Why are contemporary vaporizers unsuitable for use with desflurane?
Desflurane has a very high vapor pressure (near 1 atm at room temperature) which makes it incompatible with conventional vaporizers; specialized heated vaporizers are required. (224)
- What does the term agent-specific refer to?
It means that a vaporizer is designed and calibrated for a single, specific volatile anesthetic agent. (224)