summer study guide - mechanical ventilation II

why do people need mechanical ventilation?

because they are not VENTILATING

• suggest getting an ambu bag or bag valve mask

what should be your highest priority?

ventilation — one of the MOST IMPORTANT life functions

4 reasons to place someone on a ventilator

1. apnea

2. acute ventilatory failure (AVF)/acute respiratory failure (ARF)

3. impending ventilatory failure

4. oxygenation: to reduce WOB (last resort)

what is apnea?

not breathing, not ventilating, or cessation of breathing also known as gasping

how do you know if your patient has apnea?

you OBSERVE it. “hey are you okay?” while you look to see if they’re breathing.

what is acute ventilatory failure (AVF)/acute respiratory failure (ARF)?

PT is unable to maintain SPONTANEOUS ventilation to maintain normal physiologic parameters like PaCO2 and PaO2 (if you don’t first ventilate, you will not oxygenate)

• only need 1 ABG

what will your ABG show for AVF/ARF? what parameter tells about ventilation?

impending ventilatory failure

1. TREND of rising PaCO2 and/or decreasing VT, VC, MIP

2. think of your neuromuscular diseases where parameters like VT, VC, and MIP are important

3. you will be doing several ABGs to notice a TREND of a rising PaCO2

   • other names for a rising PaCO2:

   • hypoventilation: PaCO2>45

   • hypercarbia, hypercapnea: PaCO2>45

what is the last resort to putting someone on the ventilator?

oxygenation: to reduce the WOB

• reason: you can support oxygenation with more oxygen and CPAP

  • CPAP - for off vent

  • PEEP - on vent

the 4 life functions

1. ventilation

2. oxygenation

3. circulation

4. perfusion

what parameters do you look at for ventilation?

• RR

• tidal volume

• chest movement

• breath sounds

• ETCO2

• PaCO2

• ventilation is the #1 life function which is why we look at PaCO2 first on an ABG

what parameters do we look at to access ventilation?

1. WOB

2. capnography monitoring

3. dead space ventilation

assessing ventilation with WOB

• normal: 0.5-0.7 J/L (same in kg-mL)

  • can be measured with a spirometer or manometer

• RR will ↑ and VT will ↓

• hard to measure during spontaneous ventilation

• can be measured during mechanical ventilation

what is capnography monitoring for assessing ventilation?

monitors ECO2, ETCO2, & PETCO2

1. measures exhaled carbon dioxide content using:

   • infrared absorption

   • CORRELATE with an ABG

     • to make sure your capnography is working, get a blood gas and compare the values

capnography monitoring values for assessing ventilation

1. normally the PETCO2 will read LOWER than the PaCO2 on your ABG

   • PaCO2 40 torr (on your ABG)

   • PETCO2 34-36 torr

   • can also be measured as a % → normal is 3-5%

   • an increase in the PETCO2 or PETCO2% would signal a decrease in ventilation (high CO2 or ventilatory failure)

   • a decrease in the PETCO2 or PETCO2% would signal an increase in ventilation (low CO2 or decrease in perfusion)

capnography monitoring for dead space diseases

1. pulmonary disease

   • PaCO2 will be normal but the PETCO2 will be extremely low

   • example: PaCO2 of 40 and PETCO2 of 20

   • remember the equation VD/VT

2. hypovolemia

   • a loss of fluids either by vomiting, diarrhea, or loss of blood

capnography monitoring for intubation

sensor is placed proximal to the PT’s airway connection (at the ET tube)

• low PETCO2 reading following intubation would indicate the tube is in the belly or esophagus

  • during CPR the PETCO2 should stay >10 torr

  • if <10 improve CPR

  • if there’s a sharp increase in CO2 from 10 to 40 torr, check the carotid pulse, you may have one. (called ROSC — Return of SPONTANEOUS, Circulation)

capnography monitoring: false readings

1. secretions can cause FALSE readings and obstruct the sample tube (will read zero)

2. if reading zero or low, check to see if PT got disconnected from the ventilator

3. can occur when PT has been down for an extended period of time without CPR

exhaled CO2 detection devices

• available to detect esophageal intubation (the ones we use in codes or when a PT is initially intubated)

• disposable

• example of color changes:

  • purple (BAD) in the stomach or esophagus

  • yellow = normal = in the lungs where the tube should be = good

when looking at a monitor in the ICU or transporting, what color is the end tidal CO2 reading

YELLOW

dead space ventilation

1. anatomic dead space - the amount of VT that does not enter the alveoli

   • approximately 1 mL per Ib. of ideal body weight (ex. 150 Ib. = 150 mL VD)

   • used to approximate alveolar ventilation

2. alveolar dead space - amount of ventilation that has no blood perfusion

   • occurs with a PE (pulmonary embolism)

3. physiologic dead space is the sum of anatomic and alveolar dead space and is estimated by the dead space to tidal volume (VD/VT) ratio

4. mechanical dead space - amount of circuit tubing between the PT and the wye adapter in the ventilatory circuit

   • approximately 10 mL per inch of flex tubing (6 inches = 60 mL VD)

   • can be used to adjust PaCO2 levels

calculations to measure ventilation

1. minute ventilation (VE)

   • VE = (VT x f)

2. alveolar minute ventilation (VA)

   • VA = (VT - VD) x f

3. dead space to VT ratio (VD/VT)

   • PaCO2 - PETCO2/PaCO2 × 100

   • normal = 20-40% up to 60% for mechanical ventilated PTs

4. dead space ventilation (VD)

   • VD/VT x VT = VD

oxygenation

• parameters: HR, color, sensorium, SaO2, PaO2

• #2 life function

• most common abnormality of the life functions & hardest to treat

indicators of oxygenation (what is important when trying to figure out if PT is having issues with oxygenation)

1. PaO2

   • normal = 80-100 torr

   • partial pressure of O2 dissolved in arterial blood

   • found on your ABG

     • directly measured from the Clark electrode in ABG analyzer/machine

2. SaO2

   • % of hemoglobin in the arterial blood that is bound to oxygen

   • normal = 93-98%

   • SaO2 is directly measured from a sample of blood by CO-oximetry or Hemoximetry

   • estimated by pulse ox

   • calculated by a blood gas analyzer/machine

     • PT needs to have good perfusion and saturation >70% or higher

signs of poor perfusion

remember perfusion is a life function, not an option.

1. shock (not enough oxygen to the tissues)

2. hypotension and conditions that interfere with light

   • erythema - an abnormal redness of skin or mucous membranes caused by dilation and irritation of the superficial capillaries

   • bright lights

SaO2 is recommended for

1. sleep studies

2. resting and exercise desaturation (low oxygen)

3. neonates and children to access oxygenation

ONLY 3 things directly measured on a blood gas report

1. PaCO2 — Servinghaus

   • look at this parameter first

   • accesses ventilation

   • uses Servinghaus electrode

2. pH — Sanz

   • determines if PT is maintaining

   • uses Sanz electrode

3. PaO2 — Clark

   • measures oxygenation (#2 life function)

   • uses Clark electrode

4. everything else on your ABG report is calculated based on the pH, PaCO2, and PaO2. if you have critical values then you may only see these values with everything else being “incalculable.”

calculations that access oxygenation

1. PAO2 - the alveolar air equation

   • calculates the partial pressure of PO2 in the alveoli (PAO2)

   • PAO2 = (PB-pH2O) FiO2 - PaCO2/0.8

   • normal values vary directly with the FiO2 and PB

2. alveolar-arterial oxygen gradient (P(A-a)O2 or A-aDO2 or A-a gradient)

   • estimates the difference between alveolar PAO2 and arterial PaO2

   • best estimated when the PT breathes 100% for 2 mins.

   • A-aDO2 = PAO2 - PaO2

   • normal = 25-65 torr on 100% O2

   • V/Q mismatch = 66-300 torr

   • shunting = >300 torr

   • if PaO2 increases with O2 therapy, PT has V/Q mismatch

     • ex. PT comes into ER, you stick them on room air (RA) and their PaO2 is low. So you decide to put them on O2 and the PaO2 gets better. Then you can say they have V/Q mismatch

   • if PaO2 decreases with O2 therapy, PT has a shunting problem.

     • treatment: PEEP (on vent) or CPAP (off vent)

calculations that access oxygenation cont.

3. arterial oxygen content (CaO2)

   • BEST measurement of O2 delivered to the tissues or best index of oxygen transport

   • important values for eq.: Hb, SaO2, & PaO2

   • CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)

   • oxygen in RBC + oxygen in plasma

   • normal = 17-20%

4. mixed venous oxygen content (CvO2) anything with a v tells us about the ❤ (CO as well)

   • total amount of oxygen carried in the mixed venous blood

   • same calculation as the CaO2, just replace little a’s with v’s because we are using mixed venous instead of arterial blood

   • the blood is drawn from the PULMONARY ARTERY through a balloon tipped, flow-directed catheter

   • CvO2 = (Hb x 1.34 x SvO2) + (PvO2 x .003)

   • normal venous is always lower than arterial

     • 14% (12-16%)

     • if CvO2 and SvO2 decrease then CO will decrease too

5. arterial - venous oxygen content difference (C(a-v)O2

   • the CvO2 is subtracted from the CaO2

   • measures the O2 consumption of the tissues

   • C(a-v)O2 = CaO2 - CvO2

   • normal range: 4-5%

   • used in Fick equation to calculate CO, L/min, or O2 consumption (mL/min)

   • C(a-v)O2 difference will increase when the CvO2 is decreasing and would indicate a decreasing CO

calculations that access oxygenation cont. II

6. shunt equation (QS/QT) — remember, shunting is BAD !!! give PEEP or CPAP

   • the portion of the cardiac output (QT) that is shunted (QT)

   • Qs/QT =(A-aDO2)(.003)/(A-aDO2)(.003) + C(a-v)O2

   • method: arterial (PaO2) and mixed venous blood (pulmonary artery) gases are drawn to analyzed to determine the A-aDO2 and C(a-v)O2

   • normal value: 3-5%

7. arterial oxygen saturation (SaO2)

   • the % of Hb in the arterial blood that is bound to oxygen

   • the SaO2 value routinely reported by a blood gas analyzer is calculated

   • actual saturation can be measured by an oximeter or co-oximeter

   • large differences between the calculated and measured values may be due to elevated carbon monoxide (COHb) levels

   • the PaO2 value can be estimated by subtracting 30 from the SaO2

   • remember the 4, 5, 6 — 7, 8, 9 rule

     • ex. if PT has a saturation (from pulse ox) of 88% then you can estimate your PaO2 on your blood gas to be 58% (88% - 30 = 58%)

calculations that access oxygenation cont. III

8. PaO2/FiO2 ratio or P/F ratio (tells about ALI/ARDS)

   • ALI/ARDS = bad lungs = shunting → CPAP or PEEP

   • ratio partial pressure of arterial oxygen to inspired fractional concentration of oxygen (PaO2/FiO2)

   • used to determine ACUTE LUNG INJURY (ALI) or ACUTE respiratory distress syndrome (ARDS)

   • measures efficiency of oxygen transfer across the lung

   • normal value is 380 torr or greater

   • ATS/ERS criteria (old school)

     • acute lung injury: P/F ratio <300

     • ARDS: P/F <200

   • Berlin criteria (new school)

     • mild ARDS: P/F ratio <200-300

     • moderate ARDS: P/F ratio <100-200, PCWP <18 mmHg, diffuse bilateral infiltrates on x-ray

     • severe ARDS: P/F ratio <100, diffuse bilateral opacities on x-ray

parameters to look for with circulation

• pulse/HR and strength

• CO

parameters to look for with perfusion

1. BP

2. sensorium

3. temperature

4. urine output

5. hemodynamics

assessing patients on the 4 life functions

every PT should be assessed based on the 4 life functions

• if any of them are at risk, the PT must be treated right away

• if any one of them is absent (no breathing, no pulse, and no BP) you have an emergency

• when you have an emergency:

  1. first priority is ventilation (establish an airway and breathe)

  2. second is oxygenation (increase FiO2 or oxygen)

  3. third is circulation (chest compressions, defibrillate, heart drugs, etc.)

  4. fourth is perfusion (maintain BP)

initial settings for mechanical ventilation

1. tidal volume: (VC) 6-10 mL/kg of ideal body weight

2. pressure: (PC) plateau from VC or to achieve target VT or=<35 cmH2O

3. RR: 10-24 breaths/min

4. FiO2: if PT is on room air/no prior info → 40-60%, if PT is currently on oxygen → keep at same level

5. PEEP: if no prior info → 0-6 cmH2O, if PT is currently on PEEP/CPAP → set at the same level

(VC) volume controlled

• pressure is applied to airways until a preset volume is delivered

• maintains VE, because you set a VT and rate on your ventilator. volume will remain constant while your PIP pressure changes to give a preset volume

• used in PTs with normal lungs

• switch to PC if the PIP pressure gets too high on VC

• most vents are volume controlled

  • you’ll see VA-AC or VC-SIMV a lot of the times

(PC) pressure controlled

• positive pressure is applied until a preset volume is reached

• pressure is controlled during the breath

  • PC-AC or PC-SIMV

PC vs VC

• pressure (PC) - use this mode if PT has a lung disorder, high ventilating pressures or high plateau pressures>30 on VC

• volume (VC) - use this mode if PT has normal lungs, if plateau pressure is greater than 30 cmH2O change from VC to PC to protect the lung and prevent barotrauma

assist/control (A/C)

choose this mode if PT needs full support or has no spontaneous breathing, apneic, or gasping

synchronous intermittent mandatory ventilation (SIMV)

• choose this mode if PT is weaning or needs partial support

• great with (PSV, PV) because it helps overcome the resistance of the tube with trying to breathe spontaneously on their own

inverse ratio ventilation (IRV)

• pressure or volume controlled breaths with an inverse I:E ratio

• improves oxygenation

• good when peak inspiratory pressures are greater than 50 cmH2O

airway pressure prelease ventilation (APRV)

• a form of spontaneous breathing at positive pressure level; similar to CPAP

• lowers mean airway pressure (MAP)

• improves oxygenation

pressure regulated volume control (PRVC)

a form of ventilation that keeps pressures at the lowest level, while still providing a preset volume

proportional assist ventilation (PAV, PAV+)

pressure, volume, and flow are proportional to PT’s spontaneous effort

spontaneous breathing options (means they can support their own ventilation while on the vent)

PT breathes spontaneously through ventilator circuit with or without mandatory breaths

1. CPAP

   • PT must be able to spontaneously breathe on their own

     • if PT is hypoventilating (>PaCO2) switch back to full support, PT is unable to breathe on their own

   • used when CO2 level is normal but hypoxemia is present

     • hypoxemia - low oxygen levels in the blood, hypoxia - low oxygen levels in the tissues

   • improves oxygenation

2. pressure support (PS, PSV)

   • used with SIMV during weaning

   • helps overcome the resistance of the ET tube

3. pressure augmentation (paug, VAPS, volume support)

alternatives to mechanical ventilation

• decide when to use bipap (NPPV) instead of mechanical ventilation

• initial settings

  • IPAP 8-12 cmH20

    • manipulates the PaCO2 on your ABG

    • increases the delivered VT

  • EPAP/CPAP 4-6 cmH20

    • manipulates the PaO2 on your ABG

    • increases FRC

disease specific protocols

1. ARDS

   • tidal volume 4-8 mL/kg IBW, start 6 mL/kg

   • maintain plateau pressure <30 mL/kg

   • consider permissive hypercapnea and respiratory acidosis

2. asthma

   • tidal volume 4 mL/kg IBW to decrease air trapping

   • consider permissive hypercapnea and respiratory acidosis

3. people with normal lung function

   • start at 6 mL/kg and may go as high as 10 mL/kg

to normalize a high PaCO2

• remove mechanical dead space

• increase the tidal volume or PIP

• increase the RR

to normalize a low PaCO2

• evaluate the cause (hypoxemia, pain, fever, anxiety)

• decrease RR

• decrease tidal volume or PIP

to increase a low PaO2

• FIRST increase FiO2 by 5-10% (up to 60%)

• THEN increase PEEP levels by 2-5 cmH2O until:

  • acceptable oxygenation is achieved

  • OR unacceptable side effects occur (decreased compliance, decreased cardiac function, barotrauma, increased C(a-v)O2, etc.

to decrease a high PaO2

• FIRST decrease FiO2 to less than .60

• THEN decrease PEEP

what do critical values tell you

if PT requires mechanical ventilation

or if they’re already on the vent, they may need different ventilatory strategies

tidal volume values

• reference range: 5-10 mL/kg PBW

• critical value: <4-5 mL/kg or <300 mL

frequency values

• reference range: 12-20 breaths/min

• critical value: >30-35 breaths/min

rapid shallow breathing index (RSBI) values

• reference range: <105 (good)

• critical: >105 without PS or CPAP

dead space-to-tidal volume ratio (VD/VT) values

• reference range: 0.25-0.40

• critical: >0.60

minute volume (VE) values

• reference range: 5-6 L/min

• critical: >10 L/min

vital capacity (VC) values

• reference range: 65-75 mL/kg

• critical: <10-15 mL/kg

maximum inspiratory pressure (MIP) values

• reference range: -80 to -100 cmH2O

• critical: 0 to -20 cmH2O

VD/VT %dead space values

• normal: 2-40%

• acceptable: <60%

• unacceptable: >60%

Cst (mL/cm) static compliance values

• normal: 60-100 mL/cmH2O

• acceptable: >25 mL/cmH2O

• unacceptable: <25 mL/cmH2O

A-aDO2 (21%) values

• normal: 5-10 mmHg

• acceptable: 10-15 mmHg

A-aDO2 (100%) values

• normal: 25-65 mmHg

• acceptable: 33-300 mmHg

• unacceptable: >300 mmHg

Qs/QT values

• normal: 5%

• acceptable: <20%

• unacceptable: >20%

tidal volume

• the volume measured during inspiration and expiration

• why do you have lungs? the tidal volume you breathe refreshes the gas present in the lungs, removing CO2 and supplying O2 to meet metabolic needs

frequency (F)

• RR

• the breaths you breathe per minute

RSBI

• the only assessment that you’d need to determine if someone needs to be weaned

  • <105 = wean, ready for a spontaneous weaning trail

  • anything >105 = don’t wean, not ready for a spontaneous weaning trail

VD/VT

• even when you breathe at a normal tidal volume (VT) a substantial volume is wasted with each breath; this wasted ventilation is called dead space

• VD/VT is increased with a pulmonary embolism because PT ventilates but they don’t perfuse

MIP

• tells you muscle strength

• anything less than -20 tells you PT should be intubated right away, if PT is already intubated, leave them on mechanical ventilation

• if greater than -20, PT can be extubated

VC (vital capacity)

• should always be 2x the tidal volume

• if less than 1,000 PT should be intubated right away

peak inspiratory pressure

• highest pressure measured at end inspiration

• also known as Peak, PAP, PIP

(VC) volume controlled

• pressure is applied to airways until a preset volume is delivered

• maintains VE, because you set a VT and a Rate on the ventilator. volume will remain constant while your PIP pressure changes to give a preset volume

• used in PTs with normal lungs

• switch to PC if the PIP pressure gets too high on VC

(PC) pressure controlled

• positive pressure is applied until a preset volume is reached

• a pressure is controlled during the breath

auto-PEEP

• if PT is on this, it is really BAD

• other names for auto-PEEP:

  • dynamic hyperinflation

  • air trapping

  • breath stacking

  • INTRINSIC PEEP

  • inadvertent PEEP

  • sneaky PEEP

  • occult PEEP is bad

• you need to prolong the expiratory time on the I:E ratio. auto-PEEP occurs because you don’t allow the PT to fully exhale

  • correct auto-PEEP

    1. decrease IT or increase the ET

    2. INCREASE THE FLOW which decreases the IT

minute ventilation equation

VE = Vt x f

tidal volume equation

VT = Ve/f

monitoring airway pressures to detect changes in lung compliance and airway resistance

• static compliance is measured during end inspiration

• Cst = Vt/Plateau - PEEP

• lung compliance is the relative ease which distends the lung/thorax structure

• plateau pressure is measured at the end of inspiration while PT is forced to hold the volume momentarily (using inflation hold, pause, or plateau)

• a decreased compliance is “BAD LUNGS” think of ARDS

  • PIP increases

  • plateau pressure increase

    • common causes (THINK BAD LUNGS)

    • atelectasis

    • pulmonary edema

    • ARDS

    • pneumonia

  • treatment: INCREASE PEEP, treat the underlying cause

• an increased compliance is emphysema, they have lost lung elasticity, it will take less pressure to inflate the lungs

• normal static compliance is 60-100 mL/cmH2O

example of decreasing compliance

look at the plateau pressure

ex. plateau going from 25 → 29 → 35 = decreasing compliance

RAW

• who likes being RAW? get respiratory STAT, ONLY THE PIP Pressures are increasing !!!

• airway resistance (RAW) is the frictional force that must be overcome during breathing

• normal: 0.6-2.4 cmH2O/L/sec

  • for intubated PTs may be as high as 6 cmH2O/L/sec

• PIP (peak inspiratory pressures) INCREASES and PLATEAU PRESSURES remain the same

• RAW can be estimated by (PIP - Plateau)/flow

• can also use PIP - Plateau to determine how much pressure support to give PT

• common causes for increasing RAW:

  • secretions in the airway so SUCTION

  • BRONCHOSPASM, suction and give bronchodilator (Beta 2 agonist)

example of increasing RAW

plateau pressures remain at 25 while peak pressure goes from 35 → 40 → 46

(PIP (peak pressures) increase and plateau stays the same)