Indications for Ventilation

Question 1

ABG Normals

Answer 1

pH- 7.35-7.45

PaCO2-35-45

HCO3-22-26

SaO2-95-100%

ABG allows for an objective criteria to evaluate, quantitate and classify respiratory failure.

Question 2

PaCO2 in Hypoxemic Respirtory Failure

Answer 2

< 60 mmHg on room air

Question 3

PaCO2 and pH in Hypercapnic Respirtory Failure

Respirtory Acidosis

Answer 3

PaCO2 > 45 mmHg

ph < 7.35

Hypercapnic can cause an acute or acute on chronic

Question 4

Hypoxemia Respirtory Failure

Answer 4

Results in a normal A-agradient when it is due to a decreased PiO2 or hypoventilation. There can be an increased in A-a gradient when the hypoxemia is due to a true shunt, V/Q mismatch, or a diffusion defects

PaCO2 may be low because you might be breathing faster

Question 5

Hypercapnic Respirtory Failure PaO2, PaCO2, P(A-a)O2

Answer 5

PaO2-Low

PaCO2-High

P(A-a)O2-Normal

Question 6

Combined Hypoxemic and Hypercapnic Respirtory Failure PaO2, PaCO2, P(A-a)O2

Answer 6

PaO2-Low

PaCO2-High

P(A-a)O2-High

It is common for hypercapnic respiratory failure to be combined with hypoxemic due to the mechanism of the disease

Question 7

Hypoxemic Respirtory Failure PaO2, PaCO2, P(A-a)O2

Answer 7

PaO2-Low

PaCO2-Normal to Low

P(A-a)O2-High or Normal

Question 8

Name the Classic Indications for Mechanical Ventilation

Answer 8

Apnea

Acute Ventilatory Failure

Impending Ventilatory Failure

Severe Refractory Hypoxemia- Look at oxygenation critical numbers

One sign may be you are giving tons of oxygenation but saturation levels remain low

Question 9

Indication for Mechanicl Ventilation-Apnea

Answer 9

Apnea-The patient needs something to breath for them

Arrest, sedation, OD, drugs, C-spine injury, head trauma

Question 10

Indication for Mechanical Ventilation-Acute Ventilatory Failure

Answer 10

Acute Ventilatory Failure- Determined through look at the ventilation critical numbers

Documented hypercapnia

Question 11

Indication for Mechanical Ventilation-Impending Ventilatory Failure

Answer 11

Impending Ventilatory Failure-Look at patients work of breathing, muscle strength, and lung expansion critical numbers

Air Hunger, tachypnea, diaphoretic, neuromuscular (Guillain-Barre, MS)

Question 12

Indication for Mechanical Ventilation-Impending Ventilatory Failure

Answer 12

Impending Ventilatory Failure-Look at patients work of breathing, muscle strength, and lung expansion critical numbers

Air Hunger, tachypnea, diaphoretic, neuromuscular (Guillain-Barre, MS)

Question 13

Inidcation for Mechanical Ventilation-Severe Refractory Hypoxemia

Answer 13

Severe Refractory Hypoxemia- Look at oxygenation critical numbers

One sign may be you are giving tons of oxygenation but saturation levels remain low

Question 14

Critical Numbers and The Whole Body

Answer 14

THE CLINICAL STATUS OF THE PATIENT IS ALWAYS THE MOST IMPORTANT FACTOR!!!!!!

Remember that the patient’s history will be a good indicator on whether or not they need to be mechanically ventilated

They may commonly have high or low critical numbers

Just because a patient has a normal ABG does not mean we can rule out the need for mechanical ventilation, as there are ALWAYS other parameters that need to be looked at

Question 15

What Critical Numbers Do You Need (Broad Categories)

Answer 15

Inadequate Alveolar Ventilation-Not moving enough air in and out of the lungs

Inadequate Lung Expansion-Collapse of lungs because they are unable to pull them open enough

Inadequate Muscle Strength-Not strong enough to take a breath

Increased Work of Breathing

Hypoxemia

Question 16

Inadequate Alveolar Ventilation

Answer 16

Looks at PaCO2 and pH

Both the critical numbers for a high PaCO2 and a low pH in order to determine that mechanical ventilation is needed

Question 17

PaCO2

Answer 17

Measure of Inadequate Alveolar Ventilation

Normal is 35-45 mmHg

Question 18

PaCO2 Critical Number

Answer 18

>55 mmHg

Question 19

Mechanism for increases in PaCO2

Answer 19

1) Increased Deadspace-Increased deadspace will cause an increased PaCO2 when minute ventilation (VE) cannot be increased enough to compensate
2) Increased CO2 Production-Increased CO2 production will cause an increase in PacO2 when min ventilation cannot be increased enough to compensate

Question 20

Alveolar Ventilation Equation (VA)

Answer 20

VA=RR x (Vt-VDphys)

VA=Alveolar Ventilation

RR= Respirtory Rate

Vt=Tidal Volume

VDphys=Physiological Deadspace

Decreased alveolar ventilation is an indication for mechanical ventilation

Decreased VA can be due to a decreased RR, decreased Vt (with a constant Vd) or an increased Vd (RR and Va remains constant)

Question 21

pH Critical Number

Answer 21

Normal 7.35-7.45

Critical Number is <7.25

Question 22

Inadequate Lung Expansion Critical Numbers

Answer 22

1. Tidal Volume
2. Respirtory Rate
3. Vital Capacity

Question 23

Tidal Volume

Answer 23

Normal is 5-8 ml/kg

Critical Number is <5 mL/kg

Small tidal volumes result in a inadequate lung expansion which will contribute to atelectasis and impaired gas exchange

Usually results in an increased RR to maintain VE

Is a measure of lung expansion

Question 24

Respirtory Rate

Answer 24

Normal is 12-20 bpm

Critical Numbers is >35 bpm

High RR tends to correspond to lower volumes and can lead to respiratory muscle fatigue

Is a measure of lung expansion

Question 25

Vital Capacity

Answer 25

Vital capacity is the voluntary amount of air you can maximally breath in one breathe The volume of air exhaled after a maximal inspiration Normal is 65-75 mL/kg **Critical Number is \< 10 mL/kg** Indicates that both *muscle strength* and *lung expansion* ability and thus the ability to cough and clear the air way A VC of 2 x Vt is needed for an adequate cough (needed to protect your airway)

Question 26

Measuring Vital Capacity

Answer 26

Typically done with a Wright’s (turbine) or a bedside spirometer A Wright’s Spirometer is a cumbersome measurement that we only use on a special type of patient (we don’t need to know the part of a Wright’s Spirometer) Commonly measured in patient’s with progressive muscle weakness (MG, GBS, ALS)

Question 27

Inadequate Muscle Strength

Answer 27

1. Maximum Inspiratory Pressure (MIP) 2. Maximum Expirtory Pressure (MEP) 3. Vital Capacity 4. Maximum Voluntary Ventilation (MVV)

Question 28

Maximum Inspirtory Pressure (MIP)

Answer 28

Normal is -80 and -100 cmH2O **Critical Number: Greater than or equal to -20 cmH2O (i.e. 0 to -20 cmH2O)**- Remember that because it is a negative number less than means less negative A measure of the patient muscle strength Typically a consistent and accurate measurement

Question 29

Maximum Inspiratory Pressure (MIP) and Maximum Expiratory Pressure (MEP) Measurements

Answer 29

Uses nose plugs, a pressure gauge and a one way valve For MIP measurement the one way value will only allow for exhalation and for a MEP measurement the one way value will only allow the release of inspiration MIP measurements are commonly done for progressive neuromuscular disorders (MG, GBS, ALST), and are typically a consistent and accurate measurement. MEP are typically measured in PFT

Question 30

Maximum Expiratory Pressure (MEP)

Answer 30

Normal is \>100 cmH2O **Critical Number: \<40 cm H2O**

Question 31

Maximum Voluntary Ventilation (MVV)

Answer 31

The maximum volume of air that a subject can breathe during a 12-15 second period Units are **liters per minute** Normal is 120-180 lpm **Critical Number \< 2 x VE** Measuring Rarely done (because it is hard on the patient) and only in PFTs

Question 32

Increased WOB

Answer 32

1) Minute Ventilation Deadspace to Tidal Volume Ratio For a given VT, as VD Ÿs the VD/VT Ÿs! And, for a given VD, when VT Ds, the VD/VT Ds! Deadspace-does not take part in gas exchange so if your ratio is greater than 60% you have too much deadspace and not enough working areas Normal is 0.25-0.40 (25-40%) Critical Number \> 0.60 (60%) It takes work to move the air in and out of the deadspace As deadspace increase the work of breathing to maintain alveolar ventilation is increased For any given PaCO2 as deadspace increases then minute ventilation must increase as well, in order to maintain PaCO2 PaCO2 µ ṾCO2/ ṾA where ṾA = RR x (VT-VDphys)

Question 33

Minute Ventilatin (VE)

Answer 33

Normal is 5-6 LPM **Critical Numbers \>10 LPM** At 10 LPM there is increased probability of respiratory failure and developing second degree muscle fatigue The minute ventilation needed to maintained stable PaCO2 may become so high that it cannot be attainted by the patient

Question 34

Deadspace to Tidal Volume Ratio

Answer 34

For a given tidal volume, as deadspace increases so will the tidal volume to deadspace ratio. And for a given deadspace as tidal volume increase so will the tidal volume to deadspace ratio. Deadspace-does not take part in gas exchange so if your ratio is greater than 60% you have too much deadspace and not enough working areas Normal is 0.25-0.40 (25-40%) **Critical Number \> 0.60 (60%)** As deadspace increase the work of breathing to maintain alveolar ventilation is increased. For any given PaCO2 as deadspace increases then minute ventilation must increase as well, in order to maintain PaCO2

Question 35

PaCO2 and ṾCO2/ ṾA

Answer 35

PaCO2 is indirctely porportional to ṾCO2/ ṾA where ṾA = RR x (VT-VDphys)

Question 36

Hypoxemia

Answer 36

1) P(A-a)O2 on 100% Oxygen 2) PaO2/FiO2 3) PaO2/PAO2

Question 37

P(A-a)O2 on 100% Oxygen

Answer 37

= alveolar-arterial gradient Normal on room air: 2 - 30 mmHg Normal on 100% O2: 25 - 65 mmHg **Critical Number: \> 350 mmHg** When the P(A-a)O2 is increased it is due to shunt, diffusion defect, or V/Q mismatch (ie. Hypoventilation and low inspired FiO2 have a normal P(A-a)O2. A-a rule of thumb every 10 years another 4 mmHg difference Anything that increases mean airway pressure will increase oxygenation and PEEP makes the biggest difference

Question 38

PaO2/FiO2

Answer 38

= PF ratio Normal: 350 - 450 Critical Number: \< 200

Question 39

PaO2/PAO2

Answer 39

= arterial to alveolar ratio Shows the percent of oxygen that is in the alveolus that gets thru to the arterial blood Normal: 0.75 - 0.95 **Critical Number: \< 0.15**

Question 40

Physiological Goals of Ventilatory Support

Answer 40

**To Support or Manipulate Gas Exchange-** Ventilation and Oxygenation **To Increase Lung Volume**-End Inspiration, End Expiration, and FRC (increased through recruitment) **To Reduce or Manipulate the WOB** **Minimize Cardiovascular Impairment**-Mechanical ventilation can reduce myocardial demand secondary to hypoxemia and increased WOB

Question 41

Specific Clinical Objectives of Ventilatory Support

Answer 41

To reverse hypoxemia To reverse acute respiratory acidosis To prevent or reverse atelectasis To relieve respiratory distress To reverse ventilatory muscle fatigue To decrease systemic or myocardial oxygen consumption To maintain or improve cardiac output To reduce ICP To stabilize the chest Air will follow the path of least resistance and one lung might be easier to fill than the other and this can cause damage To permit sedation +/- paralysis.

Question 42

Ideal Body Weight Calculation

Answer 42

Males: Wt Kg = 50 + 2.3 (height inches – 60) Females: Wt Kg = 45.5 + 2.3 (height inches – 60)

Question 43

Mild to Moderate Hypoxia-Respirtory Findings

Answer 43

Tachypnea Dyspnea Paleness

Question 44

Severe Hypoxia-Respirtory Findings

Answer 44

Slowed irregular breathing Respirtory Arrest Dyspnea Cyanosis

Question 45

Mild to Moderate Hypoxia-CVS Findings

Answer 45

Tachycardia Mild hypertension Peripheral Vascoconstriction

Question 46

Severe Hypoxia-CVS Findings

Answer 46

Tachycardia Eventual Bradycardia Arrhythmias Hypertension Eventual Hypotension followed by cardiac arrest

Question 47

Mild to Moderate Hypoxia-Neurological Findings

Answer 47

Restlessness Disorientation Headache Lassitude (lack of energy)

Question 48

Severe Hypoxia-Neurological Findings

Answer 48

Somnolence Confusion Blurred Vision Tunnel Vision Loss of cooridnation Impaired judgment Slow reaction time Coma

Question 49

Mild to Moderate Hypercapnia-Respiratory Findings

Answer 49

Tachypnea Dyspnea

Question 50

Severe Hypercapnia-Respiratory Findings

Answer 50

Tachypnea and Eventual bradypnea

Question 51

Mild to Moderate Hypercapnia-CVS Findings

Answer 51

Tachycardia Hypertension Vasodilation

Question 52

Severe Hypercapnia-CVS Findings

Answer 52

Tachypnea Hypertension Eventual Bradycardia and hypotension

Question 53

Mild to Moderate Hypercapnia-Neurological Findings

Answer 53

Headaches Drowsiness

Question 54

Severe Hypercapnia-Neurological Findings

Answer 54

Hallucinations Convulsions Coma

Question 55

Mild to Moderate Hypercapnia-Other Findings

Answer 55

Sweating Redness of Skin