Respiratory Assessment Flashcards
PPV-Increased FRC
- FRC is the volume in the lungs at the end of a tidal breath
- When PEEP/CPAP is used
Alveolar Minute Ventilation (VA)
More accurately represents the effective ventilation (the minute volume actually responsible for maintaining the PaCO2)
ṾA = RR x (VT-VDphys)
So it requires accurate measurement of VDphys
Lower Infection Point
lower inflection point on inspiratory limb = place where there is a sudden increase in compliance (set PEEP here to maintain FRC)
Change in the slope at the lower end of the inspiratory curve
Some think that this point can be used to help recruitment of all/most/some of the collapsed and recruitable alveoli -> helps at setting PEEP
The above assumption has been questioned because there are many limitations to this approach: recent ventilation history, variability due to underlying lung disease, presence of decreased compliance of the abdominal and chest wall, the greater importance of the expiratory component of the curve.
pig tail at the bottom indicates patient triggering (bigger the pig tail, higher the WOB to trigger breath)
Diagnostics
Sputum Culture and Sensitivty
Bronchoalveolar Lavage
Diagnstic Imaging-CXR, CT, V/Q Scan
PPV and Nervous System
ICP and Cerebral Perfusion
CPP=MAP-ICP
May decrease CPP secondary to a decreased in mean BP (compromised cardiac function)
CPP can be affect from both sides because MAP may decrease and ICP will increase
ICP increases secondaryto a increased CVP (as venous return from the head may be reduced)
Hyperventilation (PaCO2 < 35) causes cerebral vasoconstriction therefore decreases CP and ICP
This is a temporary effect!
PC CMV Absolute Pressure
Decreased Ti sec
Ti tot Decreased
Te Increase
I:E Decrease
Pmean Decrease
Tracheostomy Tubes Assessment
- Size/type
- Cuff pressure
- Inspection of stoma site
- Inspection and assessment of securing method
- The ties should be just snug enough to get two fingers underneath
Types of Deadspace
- Anatomical Deadspace (VDanat)
- Volume of gas in the conducting airways
- ~ 1 mL/lb = 2.2 mL/kg
- Alveolar deadspace (VDalv)
- Volume of gas ventilating unperfused alveoli
- Physiological deadspace (VDphys)
- The total of anatomical and alveolar deadspace
Arterial Partial Pressure of Oxygen
Abbreviation: PaO2
Description: Oxygen content in arterial blood
Normal: 100-80 mmHg
Measured: ABG
Low Anion Gap
= disruption of anion balance; usually due to a loss of HCO3- balanced by an increased Cl-
- Gastric losses of HCO3-
- Diarrhea
- (Note: not vomiting—this causes hypochloremia and alkalosis)
- Renal loss of HCO3-
- Renal tubular acidosis
PC CMV Absolute Pressures
Decreased in Compliance
Vt Decrease
Ve Decrease
Ti dyn Decrease
PaCO2
The best index of effective ventilation
Is dependant upon the balance of CO2 production and alveolar minute ventilation
It is the inverse of VA (Avleoar minute ventilation; and how fast we are blowing off CO2)
If you have a high CO2 the you are not ventilating
If you have a low CO2 you at least have the ability to do so but we still need to figure out why you are doing it
VCO2 is how fast we are producing CO2
PPV Shunt and Deadspace
There is increased deadspace ventilation as well as an increased shunt in a mechanically ventilated patient resulting in an overall V/Q mismatch
PC CMV Absolute Pressure
Increased in PEEP
PIP Decrease
Pplat Decrease
Pmean Increased
Types of Trach Tubes
Fenestrated-If both the inner and outer cannula are fenestrated suctioning can go through both tubes and poke someone in the back of the neck
Cuffed
PPV and GI System
Increased permeability of gastric mucosa
Increased GI bleeds and gastric ulcers in mechanically ventilated patients
Consider use of antacids or H2-blocking agents to reduce gastric secretions
Potential for gastric distension if PPV done via mask
PC CMV Delta Pressure
Decreased Rate
Ve Decreased
Te Increases
I:E Decrease
Pmean Decrease
PC CMV Delta Pressure
Increased Ti sec
Ti tot Increased
Te Decrease
I:E Increased
Pmean Increased
Ventilator Associated Lung Injury
Ventilator-Induced Injury also be called Ventilator Associated Lung Injury (VALI), which will capture other problems that can be associated with PPV
VAP, air-trapping, ventilator-patient dsy-synchrony (vent is not responsive to patient’s breathing efforts which is uncomfortable and can be dangerous if there are double breaths)
VC VMC Decreased Resistance
PIP Decreases
IPPA
The first thing that should be done is a visual inspection to make sure that the patient is stable
Should repeat the appropriate part of the assessment (at a minimum) after an intervention is completed
Trends are always important
Measuring Compliance Clinically
Truly we are measuring total compliance (Ctotal)
The compliance of the lung (CL) and chest wall (CW) combined
Does CTOTAL = CL + CW ?? NO!
Because the lung and chest wall work in opposite directions, the compliance is effectively half the original components
Ctotal = (CL * CW) / (CL + CW)
The assumption is made that the chest wall compliance is unchanging, thus; changes in Cstat can reflect changes in CL.
PC CMV Absolute Pressure
Increased Rate
Ve Increase
Te Decrease
I:E Increase
Pmean Increase
What determines how long for breath to get out of the body
It is passive so compliance, resistance, (time constant)
VC-CMV
Vt Increased
Everything will increase with the exception of Ve which decrease and I:E Ratio which increased (specifically the E portion of this ratio will decrease)
PPV-Increased Deadspace Ventilation
- Normal VD/Vt is 0.25-0.40 but is increased to 0.40-0.60 in mechanical ventilation
- Distribution of a positive pressure breath goes more to the apices and less to the bases compared to a spontaneous breath
- This happens because in the apices the whole weight of the lung will be pulling down so that the alveoli is already stretched/opened
- Ex. When the patient is standing up the lung will be pulling down
- This happens because in the apices the whole weight of the lung will be pulling down so that the alveoli is already stretched/opened
PPV and the CVS
- Positive pressure ventilation will impede venous return and may result in decreased CO and therefore decrease BP
- Hypotension rarely occurs in normal individuals receiving PPV due to the body’s compensatory mechanisms
- Altered right and left ventilicular function
- Decrease endocradial blood flood
Peak Inspiratory Pressure
The maximum pressure delivered during
Does not necessarily reflect pressures in the lungs
VC VMC Increased Resistance
PIP Increases
Lung Protective Strategies-Ensure the correct placement of ETT
Want 3-5 cm above the carina as the tube will move as the head moves, and if we do not have a buffer zone it can extend too far
Compliance
A measure of the distensibility of the lung
Reciprocal of elastance
Normal is 60-100 mL/cmH2O
< 25 - 30 cmH2O in ARDS
PC CMV
Delta Pressures
Resistance Decreased
Ti dyn Decreased
Disorders and changes in Cstat and CL
Dirsorders in which changes in Cstat may not be reflective of changes in the CL!
VC CMV PEEP Decrease
PIP Decrease
Pplat Decrease
Pmean Decrease
How if Oxygen Carried in the Blood
1) Hemoglobin (Hb)
- Oxyhemoglobin
- Major carrier of O2
- 1.34 of O2 per gram of Hg (when fully saturated)
2) Dissolved in plasma
- Determined by Henry’s Law
- Account for a small percent of O2 transport
- 0.003 mL/dL/mmHg
- PO2*0.003=ml/dl dissolved O2
CvO2 Calculation
CvO2=(Hb x 1.34 ml/g) * SvO2 + (PvO2 x 0.003 ml/100ml/mmHg)
Shunt fraction %
<10%-Compatible with normal lungs
10%-19%-Seldom requires significant ventilatory support
20%-29%-Significant abnormality; requires PEEP or CPAP
30% or more-Severe disease; life-threatening; requires aggressive mechanical ventilation with PEEP
Anion Gap
The anion gap is the difference between the measured cations and the measured anions
Helps determine whether a decrease in HCO3- is due to disruption of normal anion balance or the presence of an abnormal acid anion (i.e. cause of a metabolic acidosis)
Anion Gap = (Na+) - (Cl- + HC03-)
Normal: 9 – 14 mmol/L
PC CMV Pressure Control Delta
Increased PC
PIP Increased
Pplat Increased
Vt Increased
Ve Increased
Pmean Increased
Non-Invasive Interface Assessment
Assess mask fit/leak
Patient comfort
Observation of skin necrosis/irritation
VC CMV Increased Compliance
PIP Decrease
Pplat Decrease
What Forces need to be Overcome for Breathing
When it comes to ventilation the pt. has to overcome reistance (non-elastic resistance-diamater of the airways) and compliance (elastic resistance), and these are not static forces
PPV-Air Trapping
- With increased airway resistance more time is needed for exhalation
- Pt. still in exhalation when the ventilator gives next breath so the air that was not exhaled is now trapped
- If there is not enough time before the next breath it will result in air-trapping
- Air-trapping or auto-PEEP, can also be a result of obstructive lung disease (asthma, COPD)
- Auto-PEEP can be measured through an expiratory pause maneuver
Atelectrauma
- Injury that results due to a repeated opening and closing of the alveoli at low lung volumes
- Can also result in volutrauma because air will only want to enter the open alveoli
- The collapse itself it not always damaging even though it can cause V/Q mismatching but where atelectrauma is damaging is the repeated opening and closing
- Associated with inadequate PEEP as an appropriate PEEP will prevent de-recruitment of alveoli
- Physiologic PEEP is generally 3-5 cmH2O and is caused by the backpressure in the larynx when the vocal cords are closed
- Minimum PEEP is 5 cmH2O
- In neonates can be associated with inadequate CPAP
- A longer Ti and higher PEEP will also allows for more alveoli to open
- Usually occurs in dependent area
Mean Airway Pressure
The average pressure delivered over one minute, as measured by the ventilator
Oxygen Saturation
Abbreviation: SpO2
Description: Oxygen content in arterial blood
Normal: >90%
Measured: Pulse Oximeter
PPV and Renal System
- Response from hemodynamic changes
- Urinary output (UO) when CO causes renal perfusion
- Endocrinological Effects
- Increased ADH release
- Decreased ANP release
- Activation of the renin-angiotensin-aldosterone system
- Abnormal ABGsPaO2 results in decreased renal function and UO
- Function is dramatically decreased when < 40 mmHg
- PaCO2 > 65 mmHg decreases kidney function
When assessing Oxygenation and Ventilation What do we Look at
Ventilator Settings
ABG, SpO2, ETCO2, TC
Ventilator Orders
Endotracheal Tube Assessment
- Size/Type
- Depth
- Should be the same as confirmation on CXR or adjusted to such
- Position in the Mouth
- Should be repositioned Q24 or more frequently
- There are ETT attachment devices that will allow you to easily move the ETT without undoing everything and to help prevent pressure sores
- Cuff pressure
- There are automated cuff pressure monitors
- Inspection and assessment of the securing method
- Look for any skin necrosis/irritation
PPV and Muscle Function
Any muscle not being used is subject to atrophy
In patient’s with prolonged mechanical ventilation both muscle endurance and strength is compromised
VC CMV Decreased Compliance
PIP Increases
Pplat Increase
PC CMV Delta Pressure
Decreased Ti sec
Ti tot Decreased
Te Increase
I:E Decrease
Pmean Decrease
Lung Protective Strategies-Sigh Breaths
Avoid sigh breaths with high tidal volumes and long inspiratory pauses
These sigh breaths are not used very much anymore
Alveolus Partial Pressure of Oxygen
Abbreviation: PAO2
Description: The oxygen content at the alveolus
Calculation: PAO2= [FiO2- (Pbaro-PH2O)] - PaCO2/0.80
PC CMV Delta Pressures
Increased in Compliance
Vt Increase
Minute Ventilation Increase
Ti Dyn Increased
Where is the air in a subcutaneous emphysema
Where is the air in a subcutaneous emphysema is when the air collects underneath the skin
Causes of a High Anion Gap
= presence of an abnormal acid
- Lactic acidosis
- Ketoacidosis
- Diabetes or alcohol abuse
- Toxins
- Methanol
- Ethylene glycol
- Propylene glycol
- Aspirin (acetylsalicylic acid)
- Uremia (kidney failure)
Oxygen Toxicity
Want to try and keep FiO2 lower than 60% as above which this risk for O2 toxicity will greatly increase
So just because a blood gas looks good does not mean there is no work to do
VC CMV Increased Flow
PIP Increased
Tidyn Decreased
Titot Decreased
Te Increase
I:E Decreased
PC CMV Absolute Pressure
Decreased Rate
Ve Decreased
Te Increases
I:E Decrease
Pmean Decrease
Deadspace (VD)
The volume of gas that is inhaled but does not take part in gas exchange
VDphys = VDanat + VDalv
As deadspace increases the work of breathing to maintain alveolar ventilation is increased
For a given PaCO2, as the VD is increased the ṾE must increase as well, in order to maintain PaCO2
At ṾE > 10 LPM there is increased probability of respiratory failure developing 2° to muscle fatigue
Lung Protective Strategies-Minimize De-Recruitment and Atelectrauma
Use the appropriate PEEP
By minimizing the risk of these VILI will minimize the release of inflammatory mediators and the resultant biotrauma
A reliable index of poor oxygenation…
A reliable index of poor oxygenation is if FIO2 > 0.50 and PaO2 < 100 mm Hg and this means that the patient is getting a lot of oxygen but for some reason it is not getting into their blood
PPV-Increase Intrapulmonary Shunt
Perfusion will go to gravity dependent areas and ventilation will go to gravity independent areas
The gravity dependent areas will be located on the posterior side when the patient is lying on their back
Oxygen Index
OI = (FiO2 * MAP *100) / PaO2
A calculation that takes into account the mean airway pressure (MAP)
If you are using FiO2 as a decimal then times by 100 if you are using it was a whole number then you do not need to multiple by 100
Positively correlated with mortality risk
You want a low OI (the lower the better) with <5 being normal
When you are in the 20 you need to begin to look at things such as ECMO because you lungs can no longer properly oxygenate the blood
Assessing Ventilatory Mechanics
- Always looking to see if the follwing are changed
- Compliance
- Resistance
- Auto-PEEP
- Done through an assessment of the:
- Ventilating pressures/volumes
- Waveforms
P(A-a)O2 Critical Number
Critical Numbers > 350 mmHg when a person is on oxygen
Biotrauma
The lung will release inflammatory mediators that will attack lung tissue, as a result of volutrauma and/or atelectrauma
This results in lung injury that resembles ARDS
The inflammatory mediators can also enter the systemic circulation and result in injury in other organs. Meaning that poorly manage ventilation can lead to serious organ dysfunction in other areas of the body. All of the blood in the body will pass through the lungs which is why the inflammatory mediators can travel to the other parts of the body. This also means that severe injury/infection from other parts of the body can result in ARDS from the inflammatory mediators released from other parts of the body
Arterial O2 Content
Abbreviation: CaO2
Description: Total amount of oxygen contained in arterial blood (going to the body)
Calculation: CaO2=(Hb x 1.34 ml/g) * SaO2 + (PaO2 x 0.003 ml/100ml/mmHg)
Normal: 16-22 mL/dL (vol %)
Lung Volume Recruitment Maneuver
Over time the alveolar units will collapse when awake we will sigh or yawn to help prevent this collapse, when a patient is sedated and paralyzed they will be unable to yawn or sigh meaning we will have to do it for them
Use high pressure at 30-40 and hold for 30-40 seconds
VC-CMV-Decreased Rate
Minute Ventilation Decreases
Te Increases
I:E Decrease
Oxygen Dissociation Curve-Left Shift
- Increased Affinity for Oxygen
- Decreased temp
- Decreased 2-3 DPG
- Decreased [H++]
- Increased pH
- CO
- Because once it has bound to CO it will want to bound with more O2 but it is still easier to bond with CO because there is a stronger affinity
The Transmission of Positive Pressure
- Positive pressure ventilation (and use of PEEP) will increases intrapleural pressure, because how much of the pressure we are pushing in it transmitted to pleural membrane, as well as and intrathoracic pressures
- The extent of the transmission is dependent on:
-
Amount of PEEP and PPV
- This become more and more of an issue and PEEP and PPV becomes higher
-
Lung compliance
- Low C (e.g. ARDS): Pressure transmission significantly reduced
- Low compliance means that there is a higher elastic recoil (stiff lungs) and the lungs pulling inwards working against our positive pressure ventilation trying to push outwards
- High C (e.g. COPD): Pressure transmission is highest
- Can be regionally affected due to disease process-eg. pneumonia, atelectasis
- Low C (e.g. ARDS): Pressure transmission significantly reduced
-
Thoracic compliance
- Thoracic compliance is the resistance of the chest to expansion
- Hemodynamic compromise is most likely to occur when thoracic compliance is low (e.g. Abdominal distension, thoracic deformities-Kyphoscoliosis)
-
Amount of PEEP and PPV
VC CMV Decreased Flow
PIP Decrease
Tidyn Increases
Titot Increases
Te Increases
I:E Increases
Plateau Pressure
Reflects the pressure in lung at end inspiration
Requires an inspiratory pause maneuver to measure
PC CMV
Absolute Pressures
Resistance Increased
Ti dyn Increase
Murray Lung Injury Score
- Quantifies the level of lung injury in ALI/ARDSe
- A composite score that takes into account the following four factors:
- CXR findings
- PaO2/FiO2
- PEEP setting
- Lung compliance
- No lung injury would be a score of 0
- Not commonly used clinically but can be used more in research
- The specific scoring will not be testable (but what is above will be)
P/F Normals
Normal P/F ratio is 400 to 500
VC CMV PEEP Increase
PIP Increase
Pplat Increase
Pmean Increases
VC-CMV-Increased Rate
Minute Ventilation Increases
Te Decreases
I:E Increases
Ventilator-Induced Injury
The effect of PPV on the respiratory system
DOPE
When a person deteriorates rapidly well on a mechanical vent we can use the acronym of DOPE, which stands for
- Displacement of ETT
-
Obstruction of ETT
- At this point try to suction the placement, and if the suction gets stuck it means that there is an obstruction
-
Pneumothorax
- Preventing air from entering the lungs.
- When there is a rapid deterioration you will not have enough time to get an x-ray so it is at this time you will want to use your IPPA to determine the likelihood of a pneumothorax
- Equipment Malfunction
PC CMV
Absolute Pressures
Resistance Decreased
Ti dyn Decreased
Shear Stress
Related to atelectrauma
This is the strain exerted on the alveolar wall between the expanded lung unit and de-recruited lung unit
Occurs in interstitial space between the open and the closed alveoli
Capillary injury and release of inflammatory mediators results
This can be a common problem in neonates as the alveoli can collapse easily, and is why we tend to use CPAP with neonates to keep the lung open
Therapeutic Interventions
Chest Tubes
Humidity
Bronchopulmonary Hyigene- VAP Protocol, CPT, bronchoscopy
Ventilator Strategies-Lung proctective, LVRM, prone proning
Readiness for weaning
PC CMV Delta Pressures
Decrease in Compliance
Vt Decrease
Minute Ventilation Decrease
Ti Dyn Decrease
Lung Protective Strategies-Appropraite Volumes
- Use appropriate volumes and make sure not to over ventilate
- 6-8 mL/kg in normal lungs and 4-6 mL/kg in ARDS
- Maintain alveolar pressure <30 cmH2O
- Consider permissive hypercapniaWe don’t always need to ventilate to normal blood gases as sometimes a high CO2 can be used as a protective strategy
- People will not die because there high CO2 is high they will die because their O2 is low, meaning we should sacrifice ventilation before we sacrifice oxygenation
- It is more important to monitor pH than CO2, but we can get orders to just keep pH higher than 7.25
PC CMV Absolute Pressure
Decreased in PEEP
PIP Increased
Pplat Increased
Pmean Decreased
Monitors
Pulse oximeters
Co-Oximeters
Capnographers
Transcutaneous
Pharmacological Intreventions
Inhaled Medications
Systemic Respirtory Medications
Specialty Gases
Ventilator Assessment
Because this is a complexed task it overlap different assessment categories
-
Basic Assessment
- Basic respiratory parameters
- Because ventilator is ventilating the lung, part of chest assessment is checking the ventilator
-
Non-Patient Assessment
- Circuits
- Device check
- Preventative Maintenance
-
Monitoring and Diagnostics
- Continuous display of waveforms/parameters
- Lung mechanics and WOB
-
Therapeutic Intervention
- Supports respiratory system
PPV-Pulmonary Vascular Resistance
- May decrease due to an improved ABGs
- Giving oxygen will dilate vasculature
- May be increased due to compression of alveolar capillaries and over distension of alveoli
- Can also result in a decreased pulmonary perfusion
- This means that both hypoxemia and high pressure from PPV can cause higher PVR, so in order to reverse it we need to known the mechanism that it causing it
- This is difficult to determine at the bedside, but new technology is coming out in order to make this easier
Where is the air in a Pneumothorax
Pneumothorax is when air leaks into the space between the lung and chest wall
PPV and Thoracic Pump
-
Spontaneous Breath
- Diagram contracts to create a negative pressure and the negative pressure will also stretch the vena cava and pulls the venues blood from extremities against gravity, ultimately improving venous return to the heart.
-
Positive Pressure Breath
- The opposite is occurring because we are pushing pressure in and making atrium smaller and restricting venous return.
- We are also assuming the right ventricular output will decrease as well.
- What the picture below is showing will not happen for all pt. as some pt. may be more susceptible than others

Disorders that cause Increase Compliance
Increased Lung Compliance
- Improvement in any of the above, pulmonary emphysema
Increased Thoracic Compliance
- Improvement in any of the above, flail chest, position change—sitting patient up
Non-Patient Assessment-Ventilator Related
- Ventilator Circuit Changed
- Scheduled Change
- Soiled
- Leak Test Failure
- Humidification Delivery Changes
- Ventilator Change
- Routine Change for PM
- Changed- Mechanical Failure
- Not Changed-Patient Unstable
- Device Checks Performed
- Automated
- Pressure Test
PC CMV Absolute Pressures
Increased in Compliance
Vt Increase
Ve Increase
Ti Dyn Increased
Oxygen Dissociation Curve-Right Shift
- Reduced Affinity (tendency to bind) for Oxygen
- Increased temp
- Increased 2-3 DPG
- Increased [H++]
- Decreased pH
- A decrease in the amount of O2 associated with hemoglobin in response to a decreased pH is known as the Bohr Effect
- Decreased pH
Non-Patient Assessment
Airway Safety Equitment
Suction Equitment
Humidification Equitment
Vent/Circuit Maintenance
Oxygen-Dissociation Curve
As each of the four binding sites on a Hgb molecule binds to an O2 molecule its attraction to other O2 molecules will increase. This is why there is the steep curve at the beginning.
Once all the binding sites have been filled up (hemoglobin is saturated) the curve will plateau. This point will be at a saturation of 90% and a PaO2 of ~60 mmHg. Above this point big changes in oxygenation will result in small chnges in PaO2.
At sat of 50% there is a PO2 of 27
Review curve shifts
Right sided shift- increased temp, increased CO2, decreased pH (increased hydrogen ion concentration), increased 2,3 DPG. So increased everything except pH which decreases
PPV and Psychological States
The continued stress of mechanical ventilation can result in:
- Insomnia/Sleep Deprivation
- Anxiety/Frustration
- Withdrawal Syndromes
- Depression
- Feelings of helplessness, loss of control
- Can become psychologically dependent upon the machine
- Fear
VC-CMV Vt Decrease
Everything will decrease with the exception of Ve which increase and I:E Ratio which decreased (specifically the E portion of this ratio will increase)
VC CMV Decreased Insp. Pause
Titotal Decrease
Te Increase
I:E Decrease
Pmean Decrease
TIME CONSTANT
Time Constant=Resistance x Compliance
A single time constant is the time it will take to inflate 63% of alveolar units
Five time constants is when all alveolar units are expanded
RR can be broken down to inspiratory time and by default exhalation time
If exhalation time is too short then we can have air trapping
Strategies to increase Te= Decrease Ti
Causes of a High P(A-a)O2
Oxygen is not being effectively transferred from alveoli to the blood
V/Q Mismatch
Right to Left Shunt
Alveolar hypoventilation
Diffusion Defect
PPV-Mechanical Bronchodilation
Positive pressure dilates the conducting airway
Volutrauma
Related to a high transpulmonary pressure that results in a overdistension of the alveoli, as air will always follow the path of least resistance and will then over distend the non diseased alveoli sac
If the sac becomes rupture and not just over distended then it is considered to be barotrauma not volutrauma
The stretch in the alveoli will cause a “leaky” AC membrane (gaps between the alveoli cells) which cause edema formation in the area which results in the release of inflammation mediators and a presentation that is similar to ARDS (massive inflammation in the lungs) and the edema can leak secondary into the alveoli
P/F Ratio < 300 and <200
< 300 = in acute lung injury (ALI) also known as early ARDS
< 200 = in acute respiratory distress syndrome (ARDS)
Hypoxemia Classifications
Normal PaO2= 100-80 mmHg
Mild PaO2= 60-79 mmHg
Moderate PaO2= 40-59 mmHg
Severe PaO2= Less than 40 mmHg
Barotrauma
The most acute, immediate, and severe form of VILI
Risk increases with the level of alveolar pressure (Pplateau) and the extent of lung injury or previous lung disease
Will occur from trying to push air in too fast
Results in air outside of the alveoli (extra-alveolar air) due to the positive pressure rupturing the A/C membrane
Can result in air-leak disease (diseases when air collects outside of the alveoli)-Subcutaneous emphysema, pneumothorax, pneumomediastinum
PC CMV Absolute Pressure
Increased Ti sec
Ti tot Increased
Te Decrease
I:E Increased
Pmean Increased
PC CMV
Delta Pressures
Resistance Increased
Ti dyn Increase
PC CMV Delta Pressure
Increased in PEEP
PIP Increased
Pplat Increased
Pmean Increased
PaO2/FiO2 Ratio Definition
The ratio of partial pressure arterial oxygen and the fraction of inspired oxygen
Will help to determine the degree of any problems with how the lungs transfer oxygen to the blood
Lung Protective Strategies-PEEP
Use PEEP cautiously in patients predisposed to alveolar rupture
Monitor for auto-PEEP
Pressure vs. Volume Loop-Compliance
Compliance (imaginary line between start of inspiration and expiration)
Increased Compliance
- Left Shift of the curve
- Ex. Advanced Emphysema
Decreased Compliance
- Decreased volume for pressure change
- Will be a right shift of the curve
- Ex. Pulmonary Fibrosis
Where is the air in a Pneumomediastinum
Pneumomediastinum is when air collect into the mediastinum
What is Vol %
Vol% is equal to ml O2/ 100 ml of blood
The amount of O2 in mls that is in 100 ml of blood
VD/VT
The ratio of physiological deadspace to tidal volume
Normal VD/VT = 0.2-0.4
ICU common to be >0.70
>0.60, patient is unlikely to sustain spontaneous ventilation
VD/ VT = (PaCO2 - PECO2) / PaCO2
When CO2 goes up, pH will go down
For end tidal CO2 (PaCO2) which DOES NOT EQUAL PeCO2 which is the total amoutn of CO2 removed in one minute
PeCO2 will be given whenever we have to calculate deadspace
PPV and the Liver
Impaired liver function 2° to decreased CO
PEEP has more impact on hepatic blood flow than PPV (PIP)does
Where is the air in a Interstitial emphysema
Interstitial emphysema is when air collects in the lung supportive tissue known as pulmonary interstitium
PC CMV Pressure Control Delta
Decreased PC
PIP Decrease
Pplat Decrease
Vt Decrease
Ve Decrease
Pmean Decrease
Some results from an IPPA will require an action before a complete assessment can be completed
- Tactile Fremitus and Crackles on Auscultation
- Complete suctioning
- High WOB
- Adjust ventilator settings
When a wedge pressure is higher the 18 what are we concerned about
When a wedge pressure is higher the 18 non cardiogenic pulmonary edema is likely to occur
P(A-a) Normals
In a healthy pt. 21% O2 (room air) will produce a gradient of 5-15 mmHg (10-20 in elderly)
Normal A-a gradient=Age divided by 4 plus 4
Ex. A 40 year year old should have an A-a gradient of less than 14
100% O2 gradient is 100-150 mmHg
The normal range will change depends on how much oxygen the patient is on. This means that the value of using A-a calculation for determining oxygenation will decrease as the patient is on an increased FiO2 (most useful when on room air)
Non-Patient Assessment-Suction Equipment
- Reason for Changing Open Suction Catheter
- Soiled
- Faulty Valve
- Sticky Catheter
- Cutting of Sleeve
- Faulty Instill Pot
- Suction Equipment Changed
- Yankuer
- Yankuer Holder
- Closed Suction Catheter
- Suction Tubing
- Canister Liner
Auto PEEP
Extrinsic PEEP (= PEEPext = PEEPset)
- Directly set on the vent
AutoPEEP or Intrinsic PEEP (= PEEPauto = PEEPint)
- Cannot be determined by simple observation of the ventilatory pressures; can be determined to be present through inspection of the expiratory flow waveform
- Requires an expiratory pause maneuver to measure (i.e. quantify)
Total PEEP (PEEPtot)
- Reflects the total pressure in lung at end expiration
PEEPtot= PEEPext + PEEPauto
Upper Inflection Point
upper inflection point = maximum setting for peak airway pressure
Has been proposed as a way to detect overdistention in the lungs, but this approach appears to be too simplistic as other parts of the lungs will already be over distended by the prior to reaching this point
‘Beak’ or ‘duckbill’=increase in airway pressure without any appreciable increase in volume
Shunt: QS/QT Calculation
Qs/Qt= (CcO2-CaO2)/(CCo2-CvO2)
Where:
Qs = Pulmonary Physiologic Shunt (mL/min)
Qt = Cardiac Output (mL/min)
CCO2 = End-pulmonary-capillary Oxygen Content
CaO2 = Arterial oxygen content
CVO2 = Mixed Venous Oxygen Content
Alveolar Air Oxygen Difference P(A-a)O2
This is a measure of the difference between the alveolar concentration of oxygen and the arterial concentration of oxygen
Will be used to help diagnose the source of hypoxemia and whether it is an intrapulmonary or extrapulmonary problem
Will help to assess the intgreity of the alveolar capillary unit
Ventilator-Induced Injury Categories
Ventilator-Induced Injury can be divided into the following categories
- Barotrauma
- Volutrauma
- Atelectrauma
- Biotrauma
- Oxygen Toxicity
Time Constant
The time required to inflate (or deflate) a lung region
Complete filling requires 5 time constants
1 TC = 63%
2 TC = 86%
3 TC = 95%
In a pressure-controlled breath can be determined by the time it takes for equilibration to occur
Time Constant= Resiatance x Compliance
PPV and CVS- Pt. Most at Risk
Most people will not be affected by this as the body will be able to compensate it is the septic, spinal injury patient that will be very problematic as we exceed the body’s capacity to compensate
Hemodynamically unstable patients (low BP etc.)
Patients with high lung compliance or low thoracic compliance (as transmission of the positive pressure to the thoracic space is greatest in these patients)
Worst case is a COPD pt. (higher lung compliance) with low thoracic compliance
PC CMV Delta Pressure
Increased Rate
Ve Increase
Te Decrease
I:E Increase
Pmean Increase
How Can the Pressure versus Volume Loop Be Measured
Can be measured as a dynamic or static technique
Dynamic: Requires a square inspiratory wave form to interpret – constant flow and no inspiratory pause
Static: Requires paralysis and measures of pressure with small incremental in volume
Shunt: QS/QT
The shunt equation looks at the extent to which venous blood bypasses the capillaries (oxygenation) of the lungs
Increased if pulmonary venous admixture occurs (mixed venous blood exits A/C membrane unchanged)
Alveolar- Air Oxygen Difference
Abbreviation: P(A-a)O2
Description: A measure of the difference between the alveolar concentration of oxygen and the arterial concentration of oxygen
Normal: Age divided by 4 plus 4
Calculation: PAO2 - PaO2
Bronchopulmonary Hygiene
When assessing bronchopulmonary hygiene we need to look for
- Color
- Consistency
- Tolerance by the patient
- Cough
- Spontaneous
- With Stimulation
- Not Present
- Assess for Trends
- Total passes of suctioning needed
Dynamic vs. Static Compliance
Dynamic Compliance: Done during dynamic conditions (i.e. airflow), thus is impacted by Raw! Not too useful clinically.
Cdyn = VTeff/ (PIP - PEEPtot)
Static Compliance: Done during static conditions (i.e. no airflow), thus is a reflection of compliance only!
Cstat = VTeff/ (Pplat - PEEPtot)
At the core of it what is ABGs measuring
Gas Exchange
Oral and Trach Care
Oral and trach care can and often is done at the same time
Non-Patient Assessment-Airway Equipment
- Bedside Respiratory Safety Equipment
- Manual Resuscitator
- Masks
- Airway
- Airway
- PEEP Valve
- Trach Bag
- Oxygen Tank
- Wire Cutters
- Intubation Supplies
- Cricothyrotomy Tray
PC CMV Pressure Control Absolute
Increased PC
PIP Increased
Pplat Increased
Vt Increased
Ve Increased
Pmean Increased
Pressure vs. Volume Loop
A graphical representation of the relationship between pressure and volume during inspiration and expiration
Spontaneous breaths go clockwise and positive pressure go counter clockwise
In pressure control or PS the loop is almost square because of pressure limiting during inspiration
Bottom of loop is either 0 or PEEP level
Top of loop = PIP
Disorders that Increase Resistance
Small ETT, plug in ETT, biting on ETT
Increased bronchospasm, mucosal edema, secretions, and/or airway obstruction
Increased inspiratory gas flow rate
VC CMV Increased Insp. Pause
Titotal Increase
Te Decrease
I:E Increase
Pmean Increases
PC CMV Pressure Control Absolute
Decreased PC
PIP Decrease
Pplat Decrease
Vt Decrease
Ve Decrease
Pmean Decrease
Minute Ventilation
VE
Will typically be monitored by the ventilator
VE=RR x Vt
Pressure Volume Loop-Leaks or Air Trapping
Loop won’t meet the bottom
Resistance
The frictional resistance to gas flow
Varies; is dependant on the driving pressure
Changes throughout inspiration and expiration thus, most commonly, and more simply, calculated during constant flow (ie. VCV)
Normally 1 to 2 cmH2O/L/sec
Intubated, probably 5 to 10 cmH2O/L/sec or more
Raw = (PIP – Pplat) / flow
Transwairway Pressure is (Pm – Palv)
Disorders that Result in Decreased Compliance
Decreased Lung Compliance
- Atelectasis, pneumonia, pulmonary edema, ALI/ARDS, pneumothorax, fibrosis, bronchial intubation
Decreased Thoracic Compliance
- Obesity, ascites, chest wall deformity
Difference between hypoxemia and hypoxia?
Hypoxemia is defined as a condition where arterial oxygen tension (Pao2) is below normal (normal Pao2 = 80–100mmHg).
Hypoxia is defined as the failure of oxygenation at the tissue level.
Generally, the presence of hypoxemia suggests hypoxia.
However, hypoxia may not be present in patients with hypoxemia if the patient compensates for a low Pao2 by increasing oxygen delivery. This is typically achieved by increasing cardiac output or decreasing tissue oxygen consumption.
Conversely, patients who are not hypoxemic may be hypoxic if oxygen delivery to tissues is impaired or if tissues are unable to use oxygen effectively.
Nevertheless, hypoxemia is by far the most common cause of tissue hypoxia.
PC CMV Delta Pressure
Decrease in PEEP
PIP Decrease
Pplat Decrease
Pmean Decrease
Disorders that Decrease Resistance
Bronchodilator administration
Suction and airway care
Use of lower inspiratory gas flow rate
PPV and Metabolism
- PPV takes over all or part of the WOB
- Decreased O2 consumption and CO2 production by respiratory muscles but…
- Hypermetabolism is associated with major illnesses/surgical procedures
- Proper nutritional intake for patient’s size and illness; malnutrition a major concern
- But we now have a tube down their throat blocking their ability to swallow making it more difficult to provide nutrition
- Morphine will also slow down time to move food throughout the body making even more of a problem because the body needs more nutrients
- Proper nutritional intake for patient’s size and illness; malnutrition a major concern
- Hypermetabolism is associated with major illnesses/surgical procedures
Oxygen Saturation of 90%
This is the minimum oxygen concentration that is needed to provide enough oxygen to prevent ischemia in the tissues
Once the O2 sat falls below 90%, the PaO2 drops quickly into the dangerously hypoxic range as fewer and fewer oxygen molecules are bound to Hgb.
We want to try to keep O2 saturation above 90%.
Pressure vs. Volume Loop-WOB
Line drawn down middle of loop
On inspiration (area to right side of line)
On expiration (area to left side of line)
When we are trying to improve oxygenation in ventilation in a pt. what can we do?
1) Increase PEEP
2) Increase FiO2
3) Increase Titotal
- Increase mean airway pressure by increasing the I:E ratio
- 1:1 is a higher I:E ration compared to 1:4 (think of it as 1/1 and ¼ and then then answer for 1:1 is 1 and for 1:4 is 0.25)
PRVC Increased Compliance
PIP Decreases
Pplat Decreases
Tidyn Increases
Pmean Decreases
PRVC Decreased Compliance
PIP Increases
Pplat Increases
Tidyn Decreases
Pmean Increases
PRVC Decreased Compliance
Decreased Tidyn
Aspects of WOB
- Mechanical
- Elastic and non-elastic work
- Metabolic
- Oxygen consumption
- Relationship of work, rate and depth of breathing to muscle fatigue
- Readiness to Wean from ventilator
WOB- Inspiration
Associated with the amount of negtaive pleural pressure that is generated during a ventilatory effort
2/3 Due to Elastic Resistance
1/3 due to Non-Elastic Resistance
WOB- Expiration
Normally passive
High Raw may need more expiratory muscle wokr
Directly Measuring WOB
Uses an esophageal pressure monitor to reflect intrapelural pressure changes
The pressure time product is calculated from the area underneath the generated curve
PTP is a simpler measure than WOB and will parelle the change in effort and VO2 cost of breathing
Pressure Volume Curve
Will be narrow and long in restrictive diseases
Will be wide in obstructive lung diseases
WOB in Normal States
We will try to breath while using a minimal amount of work
A normal healthy young adult will have a Vt of 500-600ml
Work of Breathing in Diseased States
Fast breathing will produce high flow rates which increases Raw
Large tidal volumes will require a strech in the lung and increase elastic work
Both of the above will increase WOB but the body will adapt a RR and Vt in mimize WOB
Oxygen Cost of Breathing
The amount of O2 that is consumed by the ventilatory muscles (VO2R) will give and estimate of respiratory effort
Noral is 2-5% of total VO2
Upon dsypnea this can increase to 30% and even up to 10 times normal amount in COPD. Will also increase with obseity, fibrosis and congestive failure
Measures by (not commonly used)
VO2R=VO2 in active breathing-VO2 apnea
Patient-Ventilator Synchroncy
The compatability between the patient bretahing effort and the ventilator
Important to consider: Mode, Phase Variables
Patient-Ventilator Synchroncy-Triggering
Can be seen on patient assessment as well
on the monitor it will look like random swiggly lines in between breath
Patient-Ventilator Synchroncy- Limit Varible
In volume control if the limit variable is not set properly we may not be meeting inspiratory demands of the patient and instead of a straight steady increase on the pressure waveform there will and a depressed upwards curve
In pressure control the patient will be able to compenstate for the limit varaible through varying flow and volumes
Patient-Ventilator Synchroncy- Time Cycling
Ideally we want to see pressure equilibrium at the end of inspiration in pressure limited mechanical breaths
Patient-Ventilator Synchroncy- Flow Cycling
Many vents will allow for the adjustment of the flow cycle level
Tailor to pt, and situation
Pulse Oximetry
Non-invasive measurement of arterial oxygen saturation
An oximeter is an instrument that measures the amount of light absorded/ transmited through the blood
Based on photoplethysmography and spectrophotometry
Photoplethysmography
Uses light absorption to detect tiny volume changes that occur in the tissues due to blood pulsing in the vascular beds
The amount of light that is absorbed is proportional to the amount of blood flow
Maximum absorption during systols and minimum during diastole
So this detects perfusion/ pulsatile blood flow
Spectrophotometry
Is the science taht uses light wavelengths to measure light absorption through a substance in this case blood
There are two wavelengths that are used in pulse oximetry: Red light (660nm) and infrade light (940 nm)
Lambert Beer Law
Basis of spectrophotometry
The amount of light a substance will absorb depends on the amount of substance and on the concentration of the substances in the sample.
As the concentration of a substance increase so will the light absorded
Pulse Oximeter-The Oximeter
Designed to measure either transmitted or reflected light
Uses LEDs to send the light wavelengths
Has a photodetector to measure the transmitted (or reflected) light
Appropraite Oximtery Sites
Finger, Toe
Ear
Bridge of Nose
Forehead
Infant: Across the foot or hand
Pulse Oximeter-Displayed Values
The displayed value: SpO2
This is called a functional saturation (not to be confused with fractional saturation)
Functional saturation is the ratio of HbO2 to the total Hb available for binding with O2
Functional saturation does not take into account the dysfunctional hemoglobin’s, like HbCO or metHb
Pulse Oximetery Accuracy
+/- 3-5%
You can have false high readings when SpO2 is <80%
The lower the sat the more likely it will read to high which is why it is important to compare against blood gas
Factors the affect pulse oximeter accuracy
Motion
Low perfusion
External lights
False nails/ Nail polish
Wrong type of sensor
Incorrect placement (too tight or loose)
Dysfunctional Hb, anemia
Vascular dyes
How to Trouble Accuracy with Pulse Oximetry
•Motion interference
Low perfusion
Dysfunctional Hb present
Anemia
Venous pulsation
Ambient light interference
Electrical interference
Optical cross talk
Optical shunt
Masimo Radial 7
Uses different wavelengths to calculate and display
SpO2
SpMet- Altered shape of hemoglobin making it difficult to bind to an incorrect number of Fe and can be caused by tropical anaesthetics (Lidocaine)
SpCO
SpHb
SpOC
Venous Oximetry
Combines fibre-optics with an indwelling catheter to allow for continuous monitoring of
SvO2 (via PAC)
SjvO2 (via catheterization of the jugular vein)
Based on reflectance spectrophotometry
Co-Oximetry
=Hemoximetry
Based on the principal that different forms of Hb absords light differently at different wavelengths
Uses four (or more) wavelengths to measure Hb, HbO2, HbCO, and MetHb
Co-Oximetry Measurement
The saturation we see from a co-oximeter is the fraction saturation
Fractional Saturation: Ratio of Hb bound with O2 compared to the total amount of Hb present
Total Hb includes HbO2, Hb, and dsyfunction Hb
Capnography
Capometry: Measurement of CO2 in exhaled gases; provides digital display of EtCO2 value (i.e. a number)
Capnography is a graphic display of CO2 level as they change dueing breathing
Capnography Methods
Infraded absorption spectroscopy is the most common method
Can be main stream (directly in line with flow) which is more accurate. Or side stream which is a line coming off the flow tubing and can easily get damaged or filled with secretions or fluid
Clinical Relevance of Capnography
End tidal CO2 is closely related to PaCO2
A normal PetCO2 averages 3-5 mmHg less than PaCO2
A PaCO2 greater than ETCO2 is indicative of a V/Q mismatch
Can help in confirmation of ETT placement and the effectiveness of CPR
A sudden increase in the P(a-et)CO2 can indicate a pulmonary embolus.
Suptum Culture and Sensitivity
Culture: Determines the presence and identification of bacteria or fungi in the sputum
Sensitivity: Determines which antibotics the culture is sensitive too and will be the most effective
Bronchoalveolar Lavage (BAL)
A bronchoscope is advanced into a lung segment and wedged in the bonchus
Sterile saline is flushed into the segment and then suctioned back up thru the bronchoscope
The sample is collected in a sterile container and is analyzed via a culture and sputum
Can also help determine if an inflammatory process is under way due to the presence of neutrophils, and can somtimes detect food particles is aspiration has occured
CT (Computed Tomography)
Takes on multiple cross sectional images of the chest (or other) about 1 cm apart
Helical CT take these images very quickly and can allow for an angiography to occur when a contrast dye is administered intravascularly
V/Q Scan
The perfusion scan is obtained by injecting radiolabeled albulmin intravanesously
The ventilation scan is obtained by having the patient breathe in a radiolabled gas
A gamma camera collects the images
Lung Mapping
Provide imagining (a “map”) of the distribution of ventilation, allowing localization and quantification of areas of injury
“Quiet” regions are those without ventilation and will not be seen in the scan
Is dynamic monitoring and can provoke continuous monitoring or a spot check
Can help to evaulet optimal PEEP levels and the effect of recruitment maneuver, and other aspects of ventilation
What are the two Methods of Lung Mapping
1) Electrical Impedance Tomography
2) Acoustic Respiratory Monitoring (ARM)
Lung Mapping-Electrical Impedance Tomography
Uses 16-32 electrodes placed around the chest
Impedance between the electrodes is measured
A video reconstruction of ventilation will be created
Lung Mapping-Acoustic Respirtory Monitoring
Uses a series of stethscopes placed around the chest
Ventilation map is created from the sounds
Chest Tubes
Chest tubes are used to help manage pleural diseases
There are a range of sizes
Will typically be connected to either a Heimlich valve or thoracic drainage unit
CXRs are helpful in assessing location and depth for insertion, as well as resolution of the original problem
Percussion and auscultation can be helpful in assessing the effectiveness of this therapy
An assessment of the dressing and/or site can reveal onset of infection and/or air leaks
Passive Humidification
Most common method for our adult patients
Achieved through the use of an HME or HMEF
Active Humidity
Heated humidifier and heated wires in the circuit
Indications
- Bloody secretions
- Thick, tenacious sputum
- Hypothermia (core temp <32 °C)
- Burn patients
- Patients where HME contraindicated
- Neonates; small peds
- High MV or large leaks leakscausing Vte< 70% of inhaled
VAP
Ventilator-associated pneumonias are caused by the micro-aspiration of the micro-organisms in oral and gastric secretions
30-Cuff Pressureto keep secretions out (25-30)
30-HOB at 30 degree angle
30-Suction on EVAC tube
Reducing VAP
Perform gentle suctioning
Minimize circuit changes
Use MDI’s (not SVNs) for med delivery to intubated patients
Daily SATs and SBTs (to reduce duration of intubation)
Use NIV when possible
Perform oral hygiene every 4 hours at minimum
Oral, not nasal, gastric tubes
Measuring gastric residual volumes
Many institutions have a “ventilator bundle” where two or more strategies to reduce nosocomial pneumonia and VAP are combined.
ALI and ARDS Ventilator Strategy
The low compliance necessitates smaller VTto keep plateau pressures < 30 cmH2O
VT in the 4-6 mL/kg range
PEEP is important to maintain recruitment
High levels of PEEP may be indicated
Can use the static (or low-flow) V-P curve to help determine
ABG targets
- The low VT often results in a permissive hypercapniastrategy
- PaCO2 allowed to climb as long as pH > 7.25
- Minimal FiO2 to keep SpO2 > 90% (typically)
TBI Ventilator Strategy
- (Typical) ABG targets:
- Low-normal PaCO2 (35-40 mmHg)
- High-normal pH (7.40-7.45)
- Slightly vasoconstricts vessels to the brain resulting in decreased ICP
- PaO2 80-120 mmHg
- Ventilator settings:
- Typically normal lungs so follow settings for normal lungs
Obstructive Disorders Ventilator Strategies
COPD vs Asthma
- Problems with airway resistance, but by different mechanisms
- Asthma: bronchoconstriction; narrowed airway lumen
- Maximize time
- Push breath in fast and give it time to exhale (increase flow or Ti)
- COPD: the high lung compliance results in “floppy” airways and airway collapse on forced exhalation
- Inhalation is easy and exhalation is difficult
- Both have high time constants resulting in prolonged expiration time required; auto PEEP is common
- Ventilator settings:
- Main goal is to maximize expiratory time in order to decrease the auto PEEP
Criteria for D/C of Ventilatory Support:
Original reason for mechanical ventilation is resolved
Patient has stable vital signs/hemodynamics
Patient should be able to manage WOB on their own
This is where weaning parameters help
Criteria for extubation:
Able to maintain their airway
Good LOC or has TT in place
Cuff leak is present
Is able to protect their a/w
Presence of cough and gag reflexes
Is able to manage their secretions
Look at sxn history, effectiveness of cough
Weaning Parameters
Spontaneous VT4-6 mL/kg
*RR < 35 bpm
*VC > 10 mL/kg
*NIP (MIP) > 20 cmH2O
f/VT< 105 (also known as the RSBI or Tobin score)
MV < 12-15 LPM
So this is what we used to assess know there are also other things we look for as studies have shown that these weaning parameters are not a good indice of how well they will wean
Trends in Weaning
Using weaning parameters alone are not good predictors of succesful weaning and the best parameter in the SBT
Studies have shown that 75% of patients need NO weaning
Weaning should take on the form of screening for readiness for discontinuation from mechanical ventilation rather than an approach that steadily reduces ventilatory support
Still need to balance FVS vs. PVS until SBT is passed
Spontaneous Breathing Trial
Ideall done once daily in combination with a SAT
Patient will be placed on a mode that provides minimal assisstance (PSV, CPAP, T-piece)
Can assess the patient’s spontaneous breathing from 30 min up to 120 min
The longer they have been ventilated, the longer the SBT
Tobin Score and WOB assessed throughout
Ventilator Dependance
Respiratory Factors-Increased ventilatorydemand, muscle atrophy, abnormal lung mechanics (R or C)
Cardiovascular Factors-MI, arrhythmias, hemodynamic instability
Neurological Factors-Decreased drive to breathe, impaired neurotransmission
Psychological Factors-Fear of removal of life support, anxiety, stress, depression, sleep deprivation
MDI
Most common; typically used to deliver bronchodilators and ICS
Requires a special actuator to adapt the MDI to the ventilator circuit (ideally has a chamber to increase aerosol delivery to lung)
Requires timing of the actuation with inspiration
Often the dose is adjusted due to “loss” to the circuit
Nebulizers
Nebulization during inspiration only results in greater delivery of the drug
If the nebulizer is external to the vent it can add to the delivered tidal volume and interfere with triggering
These disadvantages and the increased risk of contamination mean we typically use MDIs
Inhaled antibiotics (e.g. Gentamicin, vancomycin) or mucolytics(i.e. drugs not available in MDI) may be given via nebulized treatment
Nitric Oxide (NO)
A colourless, odorless gas
It is produced endogenously in vascular endothelial cells and is a potent vasodilator
Because it is inhaled it is selective to the pulmonary system and thus is a potent pulmonary vasodilator
Administered via the INOvent
T’s in NO, servo-controls and analyzes levels
Common Uses-ARDS, Pulmonary hypertension, Neonates (PPHN, congenital heart defects)
Effects of Nitric Oxide
The pulmonary vasodilation results in:
Decreased PVR
Decreased pulmonary artery pressures
Decreased intrapulmonary shunting
Better V/Q matching as NO increases blood flow only to ventilatedalveoli by relaxing the smooth muscles of the capillaries supplying these alveoli
Improved oxygenation
Effects are limited to the pulmonary circulation because after diffusing into the capillaries NO immediately binds to hemoglobin