Module 5 Ventilation Circuits Flashcards
Mechanical Ventilation Requirements Depend On:
- Type of Surgery 2. Length of Surgery 3. Patient Position 4. ASA Status
Driving Mechanism of Ventilator
02 or pressurized air
Piston-Driven Ventilators use _____ Motors and have no ______
Electric Motor, No driving gas
Piston-Driven Ventilator positive pressure relief valve opens at
Pressure reaches 75+/- 5 cm H2O the positive relief valve opens
Piston-Driven Ventilator negative relief valve opens at
If the pressure within the piston declines to - 8 cm H2O, the negative relief valve opens & room air is drawn into the piston
The negative relief valve in piston-driven ventilators protects patients from
Protects pt from Negative End Expiratory Pressure (NEEP)
How the anesthetist guards against vent disconnects/ What changes will be noted on disconnect
Pressure Changes
Capnography waveforms
Movement of manual breathing bag
In the event of a oxygen pipeline failure. Will the Piston-ventilator continue to work?
(Clinical Pearl)
Yes, the driving force of piston-ventilators is electric, NOT gas driven
Advantages of Piston Ventilators
Quiet No PEEP Precise TV Electricity Driving force Capable of all ventilation modes Manual bag remain in the breathing circuit during mechanical ventilation
Negatives of Piston Ventilators
Lack of visible standing bellows
Harder to hear is regular cycle
Potential for NEEP
+/- Relief valve
Vent high airways pressure alarm causes
Tube in right main bronchus Bronchospasm Mucus plug Pneumothorax Air trapping Pt. cough, biting tube Pt./Vent Dyssynchrony High peep
Vent low airway pressure alarm causes
ETT cuff deflation Esophageal intubation TV set too low Chest wounds/drains allowing air to escape Disconnect from vent circuit
Safety feature of modern ventilator equipment
Clinical pearl
Apnea (disconnect) alarms are enabled with the first breath sensed
Fixed Alarms
Disconnection
02 sensor
Set Alarms
Volume
Pressure
Rate
Apnea
Apnea/Disconnect alarm is based on:
Chemical monitoring (lack of ETCO2)
Tidal Volume settings are according to ____ ideal body weight
A setting of 4-8 mL/kg of Ideal Body Weight is considered a safe place to start
Fi02 settings are adjusted to produce a minimum of:
SPO2 >90 %
PaO2 > 60 mm Hg
** Airway fires <30%
Normal I:E ratio
1:2
Means expiration time twice that of inspiration
Increasing I:E ratio to 1:3 or 1:4 is used in the presence of what disease process
Increase E to 1:3 or 1:4 in presence of obstructive airway dz. in order to prevent air trapping- cause auto PEEP-I
Describe Inverse Ratio Ventilation (IRV) and how it applied used in ARDS disease process
ARDS Goal is to improve oxygenation Forced inspiratory time to be greater than expiration time Creates auto peep 2:1, 3:1, 4:1
Functions of PEEP
Reduces risk of atelectasis
Increase # of open alveoli
Decrease V/Q mismatch
Why do we need PEEP
Alveoli recruitment
**Placement of ET tube opens the epiglottis and knocks out physiologic PEEP-5 cm H2O recommended
Physiological PEEP
Physiological PEEP (3-5 cm H2O) preserves FRC in normal lungs
PEEP works by
Increasing end expired lung volume & reducing airspace closure at the end of expiration. (Maintains alveoli open/promotes gas exchange)
Trigger window is only seen what ventilator mode
Synchronized Intermittent Mandatory Ventilation (SIMV)
The trigger window controls
the % of time during expiration that the ventilator is sensitive to the patients diaphragm
Sensitivity of trigger window controls
how much negative pressure the patient needs to generate before a breath is triggered
Volume Control Ventilation (VCV) is most common and has what features
Volume limited
Time cycled
Constant flow
Piston Ventilator delivers exact ____ in comparison to VCV
Tidal volumes
Under what vent mode is PIP uncontrolled and vary according to patients compliance and airway resistance
(Clinical Pearl)
Volume Control Ventilation
PIP is the highest level of pressure applied to the lungs during inhalation and is recommended to be
< 35 cm H2O ( decrease barotrauma)
Peak Airway Pressure:
Total pressure needed to deliver the tidal volume. It depends on airway resistance, lung compliance, and chest wall factors
Plateau Pressure:
Pressure required to overcome tissue resistance & inflated alveoli
*Measurement of lung stiffness
Resistive Pressure:
The difference between Peak & plateau pressure is the resistive pressure
Elevated resistive pressure > 10 cm H2O
High PEEP >10 results in what hemodynamic effects
Clinical Pearl
Increase intrathoracic pressure
Decrease venous return & impair CO
Why do mechanical ventilation benefit from the application of PEEP at 5 cm H2O?
(Clinical Pearl)
To replace physiological peep
Pressure Control Ventilation (PCV):
Inspiratory pressure is controlled rather than volume
PCV considerations
Target pressure is adjusted for the desired TV
may result in increased TV at a lower PIP
Pt. with low compliance PCV provides greater TV
PCV standard settings
PCV 20 cm H2O
RR 6-12
I:E ratio 1:2
PEEP-may be O
During PCV in a laparoscopic case if pulmonary compliance improves (release of pneumoperitoneum) TV may increase substantially. What does the anesthetist do?
(Clinical Pearl)
Change mode to pressure control volume guaranteed
If airway resistant increase during PCV delivered VT will decrease substantially. What can cause this?
(clinical Pearl)
Bronchospasm
Kinked endotracheal tube
PCV uses in clinical setting:
Pregnancy Laparoscopic surgery Morbid obesity ARDS One-lung ventilation
Pressure Control Ventilation-Volume Guarantee:
Adjust pressure limits to prevent significant variation in delivered VT
One of 3 modes that supports spontaneous breathing. Utilizes trigger window
SIMV
Intermittent mandatory breaths are delivered in synchrony with and triggered by the patients spontaneous efforts
SIMV-PSV
Pressure support may be added to assist the patient with any spontaneous breaths
Supports spontaneous breathing and protects patient.
PSV-PRO
after 10-30 seconds of apnea adjustable, the mode will revert to PCV or SIMV, In newer machines, if the patient begins breathing again in backup mode the ventilator will switch back to PSV-PRO
Trigger Window:
Controls the amount of time during each expiratory cycle that the ventilator is sensitive to negative pressure generated by diaphragm
SIMV mirrors setting of which other modes
VCV or PCV
Support Spontaneous respirations
Clinical pearl
PSV, SIMV, & (bag) valuable in supporting the patient with spontaneous respirations
Vent mode with RR of 0 and responds to patients effort
PSV is like PCV in that it is a pressure-targeted ventilation mode- but with a RR of zero
PSV is useful to augment the VT of spontaneously ventilating patient during maintenance or emergence
Adults start at 10 cm H2O
Goldilocks Principle and PSV
“Not to low”
“Not to high”
“Just Right”
Normal WOB
If ventilation using PP > 20 torr the stomach may become inflated…Lead to ?
(Clinical Pearl)
Aspiration
When a change in the patient’s condition is noticed what should you do?
(Clinical Pearl)
Think back to the last alteration made to the equipment and determine whether it might have contributed to the change
Frequently encountered in ARDS but can occur in any patient receiving mechanical ventilation
Barotrauma
Barotrauma is associated with?
high peak inspiratory pressure > 40 cm H2O & plateau pressures > 35
02 Flush valve use during inspiration can lead to:
Barotrauma
Ventilator relief valve may stick closed and lead to:
Barotrauma
