Mechanical Ventilation Flashcards
Respiratory Anatomy
what % of each?
Two Zones:
Conducting = trachea branching → bronchi, segmental bronchi → terminal bronchioles, (none of which contain any alveoli) only serves to deliver air to the respiratory zone
– 5% of lung volume
Respiratory = Bronchioles and alveolar ducts; responsible for gas exchange
– 95% of lung volume
Anatomical Dead Space
Conductive airway
-Does not participate in gas exchange
Lung Compliance
– Ability of the lungs to expand
– determined by elasticity or tendancy of form to return to its original state
C =ΔV ÷ ΔP
“Work of breathing”
Energy expended to created pressure gradient that allows airflow easily in and out of the lungs
– Air flows from high-pressure region (mouth/nouse) to low-pressure (lungs)
Tidal Volume
Tidal volume is the volume of air inspired and expired during one breath
– dead space volume and volume of fresh gass entering alveoli for gas exchange
6 to 8 ml/kg for Lung dz; 10-12 ml/kg for healthy lungs
Minute Volume
Minute volume is the volume of air inspired and expired during 1minute
Resistance
2 types
Resistance to breathing is a combination of frictional forces that must be overcome for negative intrathoracic pressure to be created and for air to enter the lungs
– Tissue resistance = need to move or displace the lungs, abdominal organs, ribcage, and diaphragm to create negative pressure
–Air resistance = air moving through the conductive airway dependent on the viscosity and density of the gas, and the length and diameter of the airway
* Ex; bronchospasm, increased secretions, mucosal edema, and physical narrowing or occlusion of endotracheal tubes
Hypoxemia criteria
– PaO2 less than 80 mmHg
– less than 60 mmHg (SpO2 > 90%) being severe hypoxemia
Causes for Hypoxemia
#5
- hypoventilation
- dysfunctional diffusion
- low inspired oxygen
- ventilation/perfusion mismatch caused by dead space ventilation or shunting
- Intrapulmonary shunt
Hypercapnia definition
what can cause it? #4
PaCO2 of more than 45 mmHg, with values over 60 mmHg being considered severe
–can be caused by hypoventilation, high inspired CO2, increased CO2 production, and dead space ventilation
What value is responsible for controlling CO2 levels?
Alveolar ventilation created by breathing
– Amount of fresh gas that moves in and out of the respiratory zone, which participates in gas exchange
–Alveolar ventilation inversely proportional to CO2 levels
(tidal volume - physiological dead space) x RR
Indications for Mechanical Ventilation
#4
- severe hypoxemia despite oxygen supplementation
- severe hypercapnia despite therapy
- excessive respiratory effort and risk of respiratory fatigue or arrest
- severe hemodynamic compromise to reduce oxygen consumption by removal of the work of breathing and change in metabolic rate from drug administration
Causes for hypoventilation that might indicate MV
#7
- Upper airway obstruction
- Respiratory depressant drugs
- Drug overdose
- Neuromuscular toxins
- Neurological disorders
- Pleural space disease
- Excessive dead space
MV needed if therapy not effective
Relation of PaCO2 and TBI
- Hypercapnia leads to vasodilation
- Hypocapnia to vasoconstriction
- affects ICP
MV for Post Arrest Care
Target PaCO2 for cats vs dogs
Effort to reduce tissue oxygen demand by removing the work of breathing, or as a part of respiratory optimization to provide ventilation due to apnea
– Control of PaCO2 to 32–43 mmHg in dogs and 26–36 mmHg in cats to prevent intracranial hypertension
Control Variables for MV
Pressure, Volume, Flow
“Dead Space” Definition
#3
Portion of the tidal volume that does not participate in gas exchange
Characterized as:
1. Apparatus = circuit from the Y-piece to the nose of the patient comprises apparatus dead space
2. Anatomic = conducting airways from the nose to the level of the alveoli
3. Alveolar = alveoli that are ventilated but not perfused in pulmonary capillaries
Physiological Dead Space
Anatomic + Alveolar dead space
–sum of portions that do not participate in gas exchange
–normally should be about the same as anatomic dead space however with V/Q inequality → PDS increases due to increase in alveolar dead space
Ventilator Breath Types: Mandatory
Trigger, Inspiration, Termination
Trigger: ventilator
Inspiratory Flow: ventilator
Termination cyce: ventilator
Ventilator Breath Types: Assisted
Trigger:
Inspiratory Flow:
Termination cycle:
Trigger: Patient
Inspiratory Flow: Ventilator
Termination cycle: Ventilator
Ventilator Breath Types: Spontaneous
Trigger: Patient
Inspiratory flow: Patient
Termination Cycle: Patient
Ventilator Breath Types: Supported
Trigger:
Inspiratory flow:
Termination cycle:
Trigger: Patient
Inspiratory flow: Ventilator
Termination cycle: Patient
Ventilator Mode Classifications
#3
- Continuous mandatory ventilation: All mandatory breaths are delivered
- Intermittent mandatory ventilation: Both mandatory and spontaneous breaths
- Continuous spontaneous ventilation: All spontaneous breaths
Pressure-controlled MV
what becomes the variable?
Pressure-controlled breath = the machine will maintain airway pressure as determined by the operator, and inspiration ends when a preset inspiratory time is reached
– TV and flow rate dependent on the magnitude of the preset airway pressure as well as the resistance and compliance of patient
Volume - controlled MV
Machine will deliver the preset TV over the preset inspiratory time
– Airway pressure reached is dependent on the magnitude of the preset TV and subsequent flow rate
Flow and Volume controll essentially the same
Cycle Variable
Determines the termination of inspiratory flow
Ex: time is the cycle variable for a pressure-controlled breath (I:E Ratio)
Trigger Variable
#4 types
Parameter that initiates breath
–typically set RR
–with synchronization;
– change in airway pressure (pressure trigger)
— or gas flow (flow trigger)
– Volume trigger = drop in airway circuit volume as air moving into the patient from spontaneous effort to initiate a breath
– Time trigger =ventilator initiates inspiration at set time intervals = set ventilation rate
Limit Variable
Parameter that the breath cannot exceed during inspiration, (but does not terminate the breath)
– Ex: in Volume control setting → pressure-limit breath = the ventilator will generate the breath by delivering a preset tidal volume, but will not exceed the limit set for airway pressure
Intermittent mandatory ventilation
Set number of mandatory breaths are delivered but between set breaths patient can breath
– Advanced machines will try to synchronize breaths with patients spontaneous one = SIMV
– operator can only control the minimum RR and MV; there is no control over the Max rate or Max MV since this is determined by the patient
–useful in providing partial respiratory support in patients with unreliable respiratory drive
Intermittent mandatory ventilation complications
Breath stacking can occur in IMV mode when spontaneous breaths and time‐triggered mandatory breaths occur in an overlapping manner, potentially leading to increased incidence of barotrauma and volutrauma to lung tissue
–the use of SIMV helps prevent this
Continuous Spontaneous Ventilation
2 types
what does patient control?
–Breath, RR, I Time, and TV determined by patient
– CPAP and Pressure supported ventilation (PSV)
CPAP
what does patient control?
what are the benefits?
Constant positive airway pressure
–Patients allowed to spontaneously breathe by dictating the timing and depth of every breath through their respiratory drive while still connected to the mechanical ventilator
– increases functional residual capacity and compliance, enhancing gas exchange and oxygenation.
– improve oxygenation in patients by increasing functional residual capacity and compliance
PSV
when is it used?
what type of MV?
Inspiratory flow is raised to a preset level of inspiratory pressure
– form of assisted ventilation where ventilator supplies constant pressure to the airway during the inspiratory phase of the breath
– useful in patients with adequate respiratory drive but compromised ventilatory strength as the positive pressure can help overcome airway resistance
– reduces the effort required to maintain spontaneous breathing in patients with adequate respiratory drive and inadequate ventilatory strength
I:E Ratio
Normal vs dz lungs
I:E ratio of 1:2 typically utilized to ensure the patient has fully exhaled prior to the onset of the next breath
– As RRs are increased, expiratory time will be sacrificed to “squeeze” in the necessary number of breaths → need for reverse or inverse I:E ratio ventilation
– inverse I:E ratio can = breath stacking or intrinsic PEEP as the animal is not able to fully exhale before the start of the next inspiration (has been used to improve oxygenation)
1:1–1:2 for lung dz
PEEP
Amount used for normal and dz lungs
Positive end expiratory pressure
– maintains elevated intrathoracic pressures during exhalation
–Can ↑ O2 efficiency of diseased lungs by recruiting previously collapsed alveoli, preventing further alveolar collapse, and reducing ventilator-induced lung injury
– setting depends on severity of lung dz
5 to 8 cmH2o for lung dz; 0-5 cmH2o for healthy lungs
Negative Effects of PEEP
– ↑ intrathoracic pressure can compromise venous return
– must be calculated with PIP → PEEP of 5 cmH2o will be given WITH PIP of 20 for total pressure = 25 cmH2O (over pressurized)
Control of Breathing
Respiratory center
Area in the medulla oblongata of the brainstem
– Contain individual control centers for functions such as inspiration, expiration, and breath holding
Rise Time
– time it takes to reach peak airway pressure
– Faster rise times indicated in patients with rapid RRs, although caution is advised in animals with small endotracheal tubes due to increased resistance to flow
0.1 to 0.3 seconds
Sine waveforms
characteristic of patient efforts such as are seen with spontaneous breaths CPAP or SIMV.
Square waveforms indicate that the given parameter changes abruptly but is then held at a near constant value for a time
Ramp and exponential waveforms indicate that a parameter is changing gradually over time, with a rate of change that is either constant (ramp) or variable (exponential)
appear in pressure flow or volume settings
Which ventilation mode is this?
what does the highlighten area show?
pressure, flow, and volume scalars typical of volume control modes of ventilation are shown. – inspiratory hold is in place (shaded zones), which gives the pressure scalar (A) the classic appearance of a shark fin with a bite taken out of it
– highlighted area denotes a period of inspiratory hold, = time for intrapulmonary redistribution of gas (“pendelluft”) with a resultant pressure decline from peak inspiratory pressure (PIP) to plateau pressure (Pplat).
– delivery of flow at a constant rate allows for meaningful assessment of airway resistance (Raw).
Which ventilation mode is this?
what do each dashed circle respresent?
pressure, flow, and volume scalars typical of pressure control modes of ventilation are shown
– inspiratory hold = encircled, and this will result in plateau of the volume scalar (C).
– scalars for the second breath are typical of pressure support modes of ventilation.
* PC modes = pressure waveform is now the one with the characteristic shape, whereas the flow waveform typically assumes the shape of an exponential decay.
* inspiratory flow is not expected to reach zero before expiration begins.
* Bc the termination of inspiratory flow occurs when flow is low but not zero the volume waveform shows a minimal plateau (lower dashed circle).
SIMV-PC PSV,
What type of wave forms are these?
Where is PIP and Pplat defined? a,b,c
Pressure waveforms
* Point (a) represents PIP and point (c) indicates Pplat.
* B: shows that when (PEEP) is being applied it is expected that pressure never returns to baseline, but rather remains at this preset level above atmospheric pressure between breaths (dashed line).
* Both PIP (denoted “a” on the figure) and Pplat (denoted “c” on the figure) can be determined. These pressures can be used to calculate dynamic and static compliances,
What type of mode is this?
Define each scalar
Waveform in pressure‐controlled ventilation
– Pressure rises quickly w/ inspiration to set pressure w/ correlating volume increase and positive flow (towards the patient)
– With expiration → pressure instantly lost, volume rapidly decreases and eventually drops to zero as the recoil pushes the air out
–Flow immediately changes to negative (away from patient) and gradually dies down as recoil is satisfied
What type of mode is this?
Define each scalar
Waveform in volume‐controlled ventilation
–Pressure increases linearly during inspiration as target breath volume is achieved through consistent positive flow
–Expiration, the pressure is instantly lost, volume rapidly decreases and eventually drops to zero as the recoil pushes the air out
–Flow immediately changes to negative and gradually dies down as recoil is satisfied.
What type of loops are these?
What is the difference between A and B?
Pressure-Volume loops for machine-triggered (A) and patient-triggered (B) breaths are depicted.
* represent the relationship between changes in pressure and changes in volume in the ventilator circuit
* the loop does not begin at a pressure value of zero. This indicates the patient is on PEEP.
- vertical line and arrow indicate the PEEP value, and one can note that the patient efforts bring airway pressure below this resting value
What does the slope ultimately represent?
what happens if resistance increases?
- dash line connects start and end inspiratory points
- measure of pulmonary compliance
- bowing of the inspiratory limb away from this line reflects the additional pressure required to overcome airway and circuit resistances
what is the difference between the purple and blue loop?
What does loop bowing indicate?
- purple loop is the initial tracing, and the blue loop shows the changes expected to occur with an increase in airway or circuit resistances
loop bows out farther from the dynamic compliance line = greater applied pressure required to overcome resistance and reach a given volume - ↑ bowing of PV loop should prompt to investigate whether the ETT is kinked or obstructed, heat-moisture exchanger occlusion has occurred, or airway suctioning or bronchodilator needed.
What is beaking?
- Excessively large tidal volumes = “beaking” of the terminal portion of the inspiratory limb.
- Beaking reflects further increases in circuit pressure with minimal additional volume increase → alveoli expanded excessively and can only accept additional volume with large pressure increases
What is the difference between LIP and UIP
- lower inflection point (LIP) = point at which pulmonary compliance significantly increases.
- upper inflection point (UIP) = point at which pulmonary compliance significantly decreases because of alveolar overdistention and risk of alveolar injury (volutrauma) is increased
- leak in the ventilator circuit = open, broken, incomplete loop
What is the difference between A, B, C?
Circuit leaks and excessive airway secretions can be detected on flow–volume loops
A. FV loops w/ increased Raw
B. circuit leaks
C: example of a FV loop with saw-tooth appearance to the effort-independent portion of the expiratory limb → reliable indicators of the need for tracheal suction
Comparison of pressure waveform in intermittent mandatory ventilation (IMV) and synchronous intermittent mandatory ventilation (SIMV). Both modes allow for spontaneous breaths in between mandatory breaths.
What type of loop is this and what do the arrows represent?
– typical pressure‐volume loop
– peak represents PIP on the pressure axis and TV on the volume axis.
– inspiratory limb is represented by the upward arrow while the expiratory limb is represented by the downward arrow.
What mode is this?
What does each loop represent?
- PV loop changes depending on lung compliance in pressure‐controlled ventilation
- blue loop represents normal compliance.
- red loop represents decreased compliance with the ventilator achieving lower tidal volume with the same pressure
- green loop represents increased compliance with the ventilator achieving higher tidal volume with the same pressure
What mode does this represent?
What does each loop represent?
PV loop changes depending on lung compliance in volume‐controlled ventilation
* blue loop represents normal compliance
* red loop represents decreased compliance with the ventilator producing higher pressure to achieve the same tidal volume
* green loop represents increased compliance with the ventilator producing lower pressure to achieve the same tidal volume
