Physics, monitors, machine Flashcards
What is the equation for the time left before the cylinder is depleted
Divide the pressure left (psig) by 3 and then divide by the flow rate
Example: 500 psig left and 10 L/min
166.67/10 = 16 minutes
2200 psig left and 10 L/min
733.3/10 = 1 hour 13 minutes
Fresh gas flow must be equal to at least what to prevent rebreathe get during spontaneous ventilation while using a Mapleson A circuit?
Minute ventilation
What is a Mapleson A circuit?
Semi-open breathing system at relies on fresh gas flow for CO2 rebreathing
How does a Mapleson A circuit work?
Fresh gas flows to the patient, the APL valve is closed and reservoir bag deflated
Patient exhales and it goes out the APL valve, fresh gas accumulates in the reservoir bag and travels proximally to eliminate all exhaled gas
What is the safest flowmeter arrangement
One with oxygen tube down stream from all gases to prevent hypoxic mixtures
Which gas cylinders have to be measured by weight instead of pressure?
Carbon dioxide
Nitrous oxide
Why do carbon dioxide and nitrous oxide have to be measured by weight?
Because according to the ideal gas law, every time a gas is removed, liquid is vaporized to restore equilibrium
How much does a full e-cylinder of nitrous oxide weigh?
8.8 kg
How much does an empty nitrous oxide cylinder weigh
5.9 kg
What does a capnograph of an incompetent expiratory valve look like?
Looks like rebreathing CO2
The inspiratory segment is elevated
What does the capnograph look like with an incompetent inspiratory valve
Prolonged plateau phase
How is left ventricle contractility measured by echo?
dP/dT = rate of rise of ventricular pressure
The greater the force, the faste the rise
Which of the most commonly used gases has the lowest vapor pressure?
Sevoflurane
What is vapor pressure?
The pressure exerted by the vapor phase of a substance in equilibrium with solid and liquid phases at a given temperature in a closed system
What does a higher vapor pressure mean?
It means that substance is more likely to evaporate at a given temperature
What is the vapor pressure of desflurane
669 mm hg
What is the vapor pressure of isoflurane?
238 mm Hg
What is the vapor pressure of sevoflurane?
157 mm Hg
Fresh gas flows must be greater than or equal to what to prevent rebreathing during controlled ventilation using a Mapleson D circuit?
2-3 times minute ventilation
Fresh gas flows must be greater than or equal to what to prevent rebreathing during controlled ventilation using a Mapleson D circuit?
2-3 times minute ventilation
What causes an abrupt drop to zero in the ETCO2?
- Circuit disconnect
- Kinking of the ETT
- Esophageal intubation
What causes a sudden drop in ETCO2?
Partial airway obstruction
Circuit leak
What would cause a rapid decrease in ETCO2?
Pulmonary embolism
Circuit leak
What would cause a gradual decrease in ETCO2?
Hypothermia
Hyperventilating