Week 2- Hazards of ANE Delivery System Flashcards
PaO2 less than 60 mmHg, may be caused by problems with anesthesia delivery system. What problems would this cause with the patient?
Hypoxemia
If the patient is adequately ventilated and the alveolar oxygen concentration is as expected, then the cause of hypoxemia is a:
Problem with the patient
Pulmonary conditions that cause shunting, venous mixture, ventilation-perfusion mismatch, or diffusion defect can cause
Hypoxemia
Examples of pulmonary conditions that can cause hypoxemia:
- pneumonia
- atelectasis
- pulmonary edema
- penumothorax
- hemothorax
- P.E
- Bronchospasm
-proteinosis
*** anemia and shock may also contribute
Causes of inadequate Arterial Oxygenation:
- Failure to deliver adequate oxygen to the alveoli
- Inadequate alveolar ventilation
- Low FIO2
- Intrapulmonary pathology
- Shunt
- Ventilation/ Perfusion mismatch
- Diffusion defects
Causes of Failure to Deliver Oxygen to the Alveoli
(UPSTREAM of the WORKSTATION):
- Liquid oxygen reservoir empty or filled with hypoxic gas (ex. Nitrogen)
- Crossed hospital pipelines
- Crossed hoses or adapter in the OR
- Closed pipeline valves
- Disconnected oxygen hose
- Failure of back-up hospital oxygen reserve
Causes of Failure to Deliver Oxygen to the Alveoli
(WITHIN the machine or circuit)
- Cylinder filled with hypoxic gas
- Empty cylinder
- Incorrect cylinder on oxygen yoke
- Crossed pipes within machine
- Closed oxygen cylinder valve
- Oxygen Flowmeter off
- Failure of proportioning system
- Oxygen leak within the machine or Flowmeter
- Incompetent or absent circuit unidirectional valves
- Breathing circuit leak
- Closed system anesthesia with inadequate fresh oxygen supply.
- Inadequate ventilation
The anesthesia delivery system may cause hypoxemia by delivering insufficient oxygen to the lungs and thereby reducing the :
Alveolar oxygen concentration
Inadequate ventilation, cause by either _______ or ____________, is a well -described cause of alveolar hypoxia
Apnea or low-minute ventilation
This feature allows time for airway management with near-zero pollution of the OR by unscavenged anesthetic. It also prevents the potential liability of forgetting to turn the vaporizer back on (is turned off during intubation).
Pause fresh gas flow (FGF)
Insufficient or low inspired O2 concentrations can be detected via the use of
Oxygen analyzer
The pulse oximeter, while valuable tool, does not replace the:
O2 analyzer
An O2 analyzer by the _________ unidirectional valve may indicate a normal oxygen concentration, but if there is a disconnection between that point and the patient, the patient will not receive the gas.
Inspiratory
In the event of a pipeline crossover, the hypoxic gas would also be delivered from the
Auxiliary O2 Flowmeter
Turning os the oxygen flow control valve may result in no oxygen gas flow due to:
- Shutdown central supply
- O2 hose became disconnected
- Back up cylinder is empty
- O2 piping in machine is obstructed
- O2 flow control valve is obstructed
O2 delivery at the Flowmeter could potentially be compromised if the flow tubes become filled with:
Water
** the source of water is the air pipeline. If the dehumidifying process fail, the air pipeline may deliver air and water, or extreme cases just water.
The “fail-safe” system is sensitive to ________ of oxygen rather than the ______ of O2.
Pressure; flow
*on old machines the N2O flow could be turned on without the O2 Flowmeter also being turned on.
Limitations of all oxygen/nitrous oxide proportioning systems are that they DO NOT _________ the gas that is flowing through the O2 Flowmeter, nor do they prevent administration of a ______________ if the machine has flowmeters for a third or fourth gas that is hypoxic.
Analyze; hypoxic mixture
In the Mapleson circuits, loss of the __________ supply from the machine leads to severe _________ of a hypoxic mixture as the patient uses up the oxygen and replaces it with carbon dioxide.
Fresh gas ; Rebreathing
A leak in the ventilator bellow might allow the drive gas in the ventilator bellow housing to enter the
Patient-circuit
Sources of leaks can include
- valve housings
- circuit hoses
- pressure monitoring
- gas sampling lines
- connection sites
- pressure relief valves
- carbon dioxide absorbents
Proportioning systems ONLY function between ______ and _______ flows.
N2O ; O2
_________ or ________ anesthesia can lead to delivery of a hypoxic mixture
Closed-system or Low-flow
** if O2 content of the circuit gases is not carefully monitored, the uptake of N2O may be low and of oxygen may be high. The resultant mixture could become hypoxic.
Administration of a mixture that contains more oxygen than required results in
Hyperoxia
Flowmeter leaks and inaccurate flowmeters may cause gases to be lost, with resultant high _______________ concentrations.
Oxygen
When carbon dioxide production exceeds elimination, the arterial carbon dioxide increases until equilibrium is achieved.
Hypercarbia
Patients who are breathing spontaneously are prone to hypercarbia because of the depressant effects of __________ on the central respiratory center, weakness from _________, and motor blockade during ________ or _______ anesthesia.
Anesthetics, muscle relaxants, spinal or epidural
Complete or partial airway obstruction can cause:
Hypercarbia
Absorption of carbon dioxide insufflated during laparoscopic surgery often causes:
Hypercarbia
Ventilating with an inadequate tidal volume or respiratory rate reduces ______________ and leads to _____________.
Alveolar ventilation ; Hypercarbia
System relief valves can reduce the volume in the breathing system and cause hypercarbia (T/F)
True
Small tidal volume may cause hypercarbia. Factor that can cause small tidal volumes delivery include:
- High respiratory rate
- short inspiratory time (Low inspiratory/ expiratory ratio)
- low rate of inflow of the ventilator driving gas.
- Decreased pulmonary compliance
Poor pulmonary compliance also causes volume to be lost because some of the tidal volume expands the compliant ________________ tubing.
Breathing-circuit
Causes of hypercarbia: patient factors during spontaneous breathing.
- Central respiratory depression
- muscle relaxants
- motor blockade (Regional anesthesia)
- airway obstruction
- severe pulmonary shunting
- delivery system problems
- Apnea (failure to initiate or continue controlled ventilation)
- Inadequate minute ventilation (low tidal volume or respiratory.rate)
- Increased apparatus dead space
- Missing or incompetent unidirectional valves
- incorrectly assembled circle system
- exhausted carbon dioxide absorbent or channeling
- carbon dioxide absorber bypass open ( older systems)
- unintended administration of CO2
- inadequate FGF in a system without CO2 absorption
T/F: CARBON DIOXIDE ABSORBER MAY CAUSE HYPERCARBIA BY ACTING AS A SOURCE OF LEAKS FROM THE CIRCUIT OR BY FAILING TO ABSORB THE CARBON DIOXIDE PRODUCED BY THE PATIENT.
TRUE
Large volume tubes (ex. “Goosenecks”) placed between the Y-piece of the breathing circle and the airway increase apparatus (mechanical) __________ and may cause hypercarbia if compensatory maneuvers (ex.large tidal volumes) are not employed.
Dead space
Three arrangements of the circle system must be avoided:
- FGF inlet must not be placed between the pt. And expiratory unidirectional valve.
- The APL valve must not be placed between the patient and the inspiratory unidirectional valve
- The reservoir bag must not be between the patient and the inspiratory or expiratory unidirectional valves.
The maple A circuit (Magill attachement) should be used only with __________ patients, and the FGF must be at least _______ times the minute ventilation.
Spontaneously-breathing ; 0.7
The mapleson B and C systems always permit rebreathing of exhaled carbon dioxide because exhaled gas goes directly into a blind pouch. In order to prevent hypercarbia with these systems, FGFs of ______ to _____ times normal minute ventilation must be used and the patient must be hyperventilated.
1.5 - 2.5
In the T-piece systems, Mapleson D, E , F ; FGFs of ______ to ______ times minute ventilation prevent rebreathing at calculated normal minute ventilation.
2.5- 3
** alternatively, reduced FGFs can be employed but hypercarbia is prevented by hyperventilation.
When carbon dioxide elimination exceeds production, PaCO2 decreases.
Hypocarbia
General anesthesia, neuromuscular blocking agents, and hypothermia reduce metabolic rate. If _____________ is not decreased, the patient becomes hypocarbic.
Minute-ventilation
Hyperventilation and the resulting hypercarbia can be caused by simply having either the _________, _________, or both set too high.
Tidal volume, ventilatory rate
By standard breathing circuit tubing connections are _______ mm in diameter. (Anesthetic and respiratory equipment - breathing sets and connector).
Waste gas scavenging system is _____ to ____ mm in diameter.
CGO and tracheal tube connectors are ______ mm in diameter.
22;
19 to 30 mm
15mm
A high subatmospheric pressure in the scavenging system may open the circuit’s ________ valve, transmitting the subatmospheric pressure to the patient’s circuit.
APL
If a ventilator were being used, unrelieved excess ________ pressure in the scavenging system would tend to hold the ventilator pressure-relief valve to its seat, preventing its opening on exhalation and causing _________ to develop in the circuit.
Negative; High pressure
Inadequate circuit volume and negative pressure may occur during spontaneous ventilation in the presence of low ______ rate and inadequate size _________.
FGF ; Reservoir bag (peds size with adult patient).
Most sensitive monitor of ventilation:
Continuous Capnography
A high inspiratory gas-flow rate will be associated with increased________ in the circuit
Peak-pressures
All contemporary ventilators have :
- high pressure alarms
- high pressure limit
Ac continuous-pressure alarm is annunciated usually when the circuit pressure remains in excess of _________ cm H2O for more than 10 seconds.
+15
The Aladdin cartridges must be withdrawn from the slot in the workstation during refilling, to prevent _______ of liquid agent into the workstation
OVERFLOW
Sevoflurane SVP:
Enflurane SVP:
Isoflurane SVP:
Halothane SVP:
160mmhg
175 mmHg
239 mmHg
241 mmHg
Most hazardous filling error would occur if an _________ vaporizer were misfiled with ____________.
Enflurane ; Desflurane
The sequence of vaporizers from upstream to downstream should be such the agent with __________ SVP is upstream (farthest from pt. )
Lowest
**correct sequence would therefore be sevoflurane, enflurane, isoflurane and halothane (closest to the CGO).
If an anesthesia machine is to be used for a patient who is susceptible to MH, it is recommended that the vaporizers are removed and the machine is purge with:
Oxygen
Humidification of inspired gases is desirable because :
- Prevents heat loss caused by evaporation of water from the tracheobronchial tree.
- Maintains moisture in the conducting airways and thereby facilitates ciliary function
- Prevents insensible water loss from the patient by evaporation
May cause bulk water delivery to the patient, thermal trauma to the airway, or obstruction of breathing circuit, or may become an electrical or fire hazard.
Heated humidifier
When using heated humidifiers or nebulizers the anesthesiologist should guard against:
- Fluid overload
- Thermal injury
3, additional sites for disconnection with breathing circuit - Obstruction to gas flow
- Burning of the equipment because of electrical malfunction
- Shock hazards
- Risk of infection transmission via the nebulizer
Cases should not be started if either _____________ or the _____________ is malfunctioning. A discharged _______may require as long as 16 hours to charge.
AC power and the reserve battery.
Usually a back up battery provides power for approx. _______ when its voltage drops to below ~10 V , all power to the machine ceases in order to prevent a deep discharge of the battery.
40 minutes
*** manual ventilation would then be required
Amsorb is a CO2 absorbent that does not contain a ____________ and does not form CO (or compound A) in vitro.
Strong base
Failure of the Fresh Gas Decoupling valve will result in failure to ventilate in the ventilator mode, but ventilation of the lungs will be possible in the _____________ mode.
Manual/bag
Absence or incompetence of the __________ unidirectional valve in the FGD circle breathing system results in inability to ventilate in manual/bag mode but ventilation is possible in __________mode.
Expiratory ; ventilator
Ensures that changes in FGF do not affect the desired (“dialed-in”) tidal volume delivered to patient.
Fresh gas decoupling
