RESP 210 quiz 2 study guide

Inspiratory and expiratory accessory muscles consist of

insp

• scalenes

• sternocleidomastoids

• pectoralis major/minor

• trapezius

exp

• rectus abdominus

• transverse abdominal

• external oblique

• internal oblique

• latissimus dorsi

boyle’s law

• the pressure of a gas will ↑ as volume ↓ with constant mass and temperature

• P1V2= P2V2

PIP definition

• Highest pressure reached during inspiration

• the total pressure during flow

  • Represents the total pressure required to

    • move gas

    • expand the respiratory system

• PIP= baseline + restrictive pressure + elastic pressure

what does PIP overcome?

What does PIP expand?

• The pressure needed to overcome:

  • Airway resistance (Raw)

  The pressure needed to expand:

  • the lungs and chest wall

definition of Pplat

• pressure remaining when flow stops

  • Approximates alveolar pressure

• reflects

  • elastic load

  • respiratory-system compliance

What does Pplat represent

• the pressure needed to

  • hold the delivered volume in the alveoli.

when is Pplat measured?

• Measured during an inspiratory hold

• No gas flow = no resistive pressure

what is the equation for driving pressure

Pplat - PEEP

how does PIP and Pplat effect compliance and Raw?

• ↓ compliance

  • ↑PIP ↑Plat

• good compliance

  • ↓PIP ↓Plat

• ↑ Raw (airway resistance)

  • ↑PIP

  • bigger PIP to plat difference

• smaller PIP to plat difference

  • ↓ Raw (airway resistance)

  • OR normal

for plat, does Raw contribute to measured pressure?

• With no gas flow, airway resistance no longer

  contributes to the measured pressure

what equation measures the pressure used to overcome airway resistance (Raw)?

PIP-Pplat

equations for Pta, Ptt, Ptr, Ptp

• PTA = PIP – Pplat or PTA = Pawo – Palv

  • Transairway pressure

• PTT = Palv – Pbs

  • Transthoracic pressure

• PTR=PTA+PTT or PTR= Pawo−Pbs

  • Transrespiratory pressure

• PTP= Palv - Ppl

  • Transpulmonary pressure

What is the definition for Pta

• Pressure difference between

  • airway opening

  • the alveolus

• The pressure required to

  • overcome airway resistance

  • move air through the airways

What is the definition for Ptt

• This pressure gradient is the difference between

  • the alveolar space

  • the pressure at the body surface.

• It’s the pressure required to expand

  • the lungs AND chest wall together

What is the definition for Ptr

• Pressure across the entire respiratory system

• During positive-pressure ventilation, ____ is the total pressure required to move air through

  • the airways

  • and expand the lungs and chest wall.

What is the definition for Ptp

• the difference between

  • alveolar pressure

  • pleural pressure

what is PTP also called

• alveolar distending pressure

  • keeps the alveoli open

for Palv, what can also be used?

plateau pressure

equation for Vt (volume), flow, time

VT (volume) = flow x Ti

flow = VT/Ti in L/sec

Ti= VT/flow

what is compliance

• COMPLIANCE = Ease of Expansion

• C= ΔV / ΔP

  • Units: mL/cmH₂O

High vs. low compliance

• High compliance: more volume produced by less pressure required

• Low compliance: stiff respiratory system; more pressure required

what is the definition for static compliance

• Reflects the elastic properties of the lungs &chest wall

• Lung compliance measured during a period of no airflow

what is the equation for static compliance

• Cstat= (Vte) / (Pplat−PEEP)

• units of mL/cmH2O

ex:A patient is on AC/VC with Vt = 400 ml, RR = 18, PEEP = 5cmH₂O, FiO₂ = 50%. Measured values are Vte = 415 ml, PIP = 26 cmH₂O and PPlat = 23 cmH₂O. 

• Cstat = Vte / (Plat - PEEP)

  Cstat = 415 ml / (23-5 cmH2O)

  Cstat = 23.05~ about 23.1 mL/cmH₂O

what is the normal value for static compliance

40-50 to 100 mL/cmH2O male

35-45 to 100 mL/cmH2O female

what is the application for static compliance

• Low Values (< 20 mL/cmH₂O): Indicate stiff lungs or decreased elasticity

• seen in

  • ARDS

  • pulmonary fibrosis

  • PNA

  • pulmonary edema

what is the definition for dynamic compliance

• alveolar elasticity and the pressure required to overcome airway resistance during flow

• Affected by

  • compliance (elastic recoil)

  • Raw (airway resistance)

• Accurate measurement requires a passive patient;

• spontaneous effort can distort the result.

what is the equation for dynamic compliance

• Cdyn= (Vte) / (PIP−PEEP)

• units of mL/cmH2O

ex:AC/VC with Vt = 500 ml, RR = 18, PEEP = 5cmH₂O, FiO₂ = 50%.  Measured values are Vte = 510 ml, PIP = 28 cmH₂O and PPlat = 25 cmH₂O.

• Cdyn = Vte / (PIP - PEEP)

  Cdyn = 510 / 23 cmH2O

  Cdyn = 22.2 mL/cmH₂O

what is the normal value for dynamic compliance

50–100 mL/cmH₂O

what is the application for dynamic compliance

• 𝐶𝑑𝑦𝑛 is always less than or equal to Cstat

  • extra pressure is required to overcome airway resistance during gas flow

what is the definition for airway resistance (Raw)

• Opposition to Flow

• Typical inspiratory resistance with an artificial airway

• Bedside clue:

  • PIP rises while Pplat remains unchanged

what is the equation for airway resistance (Raw)

• Raw = PTA / Flow

• Raw = (PIP – Pplat) / Flow

• in units of L/sec

ex: A patient is on AC/VC on square flow pattern with Vt = 500 ml, RR = 18, PEEP = 5cmH₂O, FiO₂ = 50%, Ti = 1.0 sec Measured values are Vte = 510 ml, PIP = 28 cmH₂O and PPlat = 25 cmH₂O.

• Square flow = 0.500 L ÷ 1.0 s = 0.5 L/s. → flow= vt/Ti

• RAW =  (PIP - PLAT) / FLOW (L/S)

• RAW = 3 cmH2O / 0.5 L/sec 

• RAW = 6 cmH2O / L/ sec 

What will ↑ Raw

• Bronchospasm

• Airway or mucosal edema

• Secretions

• ETT

  • Small

  • long

  • bitten

  • kinked

  
  

• Higher inspiratory flow

• positioning

what is the normal value for airway resistance (Raw)

• 6 - 15 cmH₂O/L/s; varies with ETT size and flow

finding LPM

multiple by percentage

ex 1:

Patient is in PS/CPAP mode which is flow cycled. The Esens is set at 75%. The patient's expiratory flow max is 100 LPM. At how many LPM will the breath cycle _____ LPM

• 75% of 1

• 75 × 1 = 75

ex 2:Patient is in PS /CPAP spontaneous breathing trial. Expiratory sensitivity is set at 25%. During this breath the maximum flow is 60 LPM. At how many LPM will the breath cycle

• 25% of 60

• 25 × 0.60 = 15

An Esens setting of 75% gives a longer Ti than 25%. ?

-no → 75 will give shorte Ti than 25%

what is the definiton for time constant

• time it takes for lungs to fill/empty

• DIFFERENT LUNG UNITS = DIFFERENT TIME CONSTANTS

  • uneven distribution of ventilation

• Individual lung units vary in compliance and resistance

short vs long time constant

• Short time constant: fills and empties quickly

  • ARDS

  • pulm fibrosis

  • advanced ILD

• Long time constant: fills and empties slowly

  • COPD

    • increased resistance & compliance

Two lung units have the same resistance. One has normal compliance; the other is stiff. Which fills faster—and which receives less volume

• The stiff unit has the shorter time constant and fills

  faster

  • receives less volume for the same

    pressure

what is the graph for time constant

what is the equation for time constant

TC= Raw x C

ex:

10 × 0.50 ml → 10 × 0.05L = 5s

what is the pecentages for time constant

• 1 TC

  • 63 %

• 2 TC

  • 86%

• 3 TC→ minimum

  • 95%

• 4 TC

  • 98%

• 5 TC

  • 99%

Utilizing time constants in an obstructive disease case study

TC for ARDS example

TC example 1:

A COPD patient in an active viral infection has a compliance of 0.055 ml/cmH₂O and airway resistance (RAW) =  17.1 cmH₂O/L/sec. What is the value of 1 time constant? _____ seconds

17.1  ml/cmH2O/L/sec  x 0.055 ml/cmH2O = 0.9405 seconds - normally round to 0.94 but will accept 0.95 

TC example 2:

 A status asthmaticus with an active viral infection has a compliance of 0.021 ml/cmH₂O and airway resistance (RAW) =  84.1 cmH₂O/L/sec. What is the value of 1 time constant? _____ seconds.

What is the minimum exhalation time required for 3 constants? i:e? TCT? RR? Ti=0.8s

RAW x C = 84.1 x 0.021 = 1.77 seconds -- should be rounded to 1.8 but will accept 1.7

3 time constants = 3 x 84.1 x  0.021 = 5.2983 seconds - round to 5.3

The i:e is Ti/TI: Te/Ti or 1/1: 5.3/1 = 1:5.3

TCT = Ti + Te or 0.8 seconds + 5.3 seconds or 6.1 seconds

RR = 60 / TCT or 60 / 6.1 = 9.84 breaths/minute or about 10

TC example 3:

You are caring for a patient with severe emphysema. The patient has a compliance of 0.099 L/cmH₂O (99 mL/cmH₂O) and an airway resistance (Raw) of 12 cmH₂O/L/s. What is the minimum amount of time needed for exhalation, assuming 3 time constants?

If you select Ti = 1.2 seconds, what would be the highest possible RR possible to allow the patient enough time to exhale 95% of the air in his lungs

3 TC = 3  x 12 x 0.099 = 1.2 seconds x 3 - round to 3.564 seconds - round to 3.6  

TCT = Ti + Te = 3.6 seconds + 1.2 seconds = 4.8 seconds

RR = 60  / TCT --> 60 sec / 4.8 sec = 12.5 breaths - round to 12 or could round to 13 

what condition will need longer exhalation time on vent

Status asthmaticus patient

open loop control systems

• set → deliver

• delivers programmed output

• no feedback-based automatic correction

  • NO feedback

• ex:

  • set VT 500 mL → delivers programmed breath

closed loop control systems

• set → deliver → measure → adjust

• measures delivered output

• compares output w/ set target

• uses feedback to adjust subsequent output

• FEEDBACK IS GIVEN

• ET VT: 450 mL

  ↓

  MEASURED VT: 412 mL

  ↓

  VENTILATOR ADJUSTS OUTPUT

  ↓

  TARGET: 450 mL

positive pressure ventilators

• Positive pressure: Increasing pressure at the airway (like CPAP +10 cmH2O or IPAP +20 cmH2O)

  • ▫ +Pressure means pressure at airway> body surface

negative pressure ventilators

• negative pressure around the thorax (lowers air pressure around the chest/body surface) → drawing air into the lungs and mimicking spontaneous inspiration

• Greater negative pressure→ greater pressure gradient→ greater volume

• ex:

  • Cuirass negative pressure vent

high frequency PPV

• Jet (right) uses RR of 400 – 600/minute

  • fast rate, low Vt

• Delivers very small tidal volumes with extremely short Ti

  • at rates of hundreds of breaths per minute.

• Exhalation remains passive. Used primarily for

  • critically ill neonates

    • pulmonary interstitial emphysema

    • RDS complicated by air leaks.

• Low peak & MAP may help prevent or allow air leaks to heal

electronically powered ventilator

• Electricity provides energy for ventilator operation

• AC power from wall outlet

• Battery (DC) provides backup/transport power

• Powers motors, valves, microprocessors & alarms

pneumatically powered ventilator

• Series of tubes that allow gas to flow inside the vent and between the vent and out to the patient (compressed gas source)

  • Gas flows through pneumatic circuit to get to pt

• High-pressure gas provides energy for ventilation

  • Typically uses

    • medical air

    • and/or O2

• • Source pressure (50 PSI or other) reduced to operating pressure

• Most modern ICU ventilators use pneumatic power for gas

• delivery + electrical power for computerized control.

  • internal pneumatic circuit

  • external pneumatic circuit

  • 
    

• Do not require electricity for basic operation

• Bird Mark 7 = classic example

• Older technology

Internal vs external pneumatic circuit

• Internal pneumatic circuit

  • Valves & tubing inside the vent that control gas flow

  • vent to artificial airway

• External pneumatic circuit

  • Also called the patient circuit

  • Carries flow between vent and patient

  • Can have external or internal expiratory valve

Parts of a ventilator

• Inspiratory limb → carries gas from ventilator to patient

• Wye adapter → connects inspiratory + expiratory limbs to patient

• Expiratory limb → carries exhaled gas back toward ventilator

• Expiratory valve → controls/releases exhaled gas & maintains PEEP

• Flow sensor → measures flow near the patient airway

control panel/ user interface

• Located on the surface of the vent

• Where the operator sets and monitors ventilator function

• Controls may include knobs, buttons, or touchscreen controls

• Used to set ventilator parameters and alarms

ventilator adjuncts

• Humidifier

• Temperature probe

• Nebulizer

• Capnometer

• Bacterial filter

• In-line suction catheter

components of ventilator

• A ventilator has two major components:

  • 1. Drive mechanism – (compressor) which is a mechanical system that produces gas flow to the patient

  • 2. Output control mechanism – one or more valves that determine the flow to the patient

• There are two major types of ventilators:

  • volume displacement

    • old type

  • flow control

How vent delivers a breath, how gas moves through all parts of a vent,

• Two basic functions:

• 1. Generate gas flow

  • A drive mechanism provides the gas/energy needed to deliver the breath

• 2. Control gas delivery

  • Valves and the control system regulate flow, pressure, volume, and timing

• • Modern ventilators use electronically controlled systems to precisely regulate gas delivery

2 types of valves

• flow controlling valve

• expiratory valve

3 types of flow controlling valves

• proportional solenoid valve

  • used in ICU

• stepper motor valve

  • not used much

• digital valves

  • on/off configuration

  • a set of smaller valves

  • To get more airflow, the device opens more of these small valves

flow-controlled valves

• Flow-control valves regulate gas flow to the patient

  • Valves open and close rapidly in small increments to precisely control gas delivery

• Precise regulation of gas flow rate (L/min) into or out of the circuit.

• They allow rapid response to changes in flow & Great flexibility in flow control

• Allows rapid, flexible control of flow, volume, and pressure

expiratory valves

• Control gas leaving the patient circuit during exhalation

  • May be internal to the ventilator or external in the circuit

• Open during exhalation to allow gas to exit the circuit

• Help maintain PEEP by controlling expiratory pressure

• Expiratory valve = controls exhalation + helps maintain PEEP

4 types of ventilators

1. High frequency positive pressure vents

2. infant vents

3. transport vents

4. home vents

infanct ventilators

• Ventilation for infants is more delicate and often uses different strategies/modes:

  • Must monitor parameters closely

  • Provide the appropriate level of support

  • Respond to physiologic changes quickly

• • 2 approaches to infant ventilation

  • Special ventilators designed exclusively for infants and small children

  • Single ventilator for all ages “cradle to grave”

transport ventilators

• Transport requires the same level of ventilation as bedside care

• • Preparation + communication are essential

• • Ventilator vs. BVM? Consider the risks and benefits for the individual patient

• Transport ventilators should be:

• ▫ Compact and lightweight

• ▫ Reliable with adequate battery/gas supply

• ▫ Able to function in challenging transport conditions

home care ventilators

• Home ventilation can provide an alternative to hospital or extended-care settings

• Advances in technology allow long-term ventilatory support at home

• Home ventilators must be simple, user- friendly, and have clear alarms

• Family/caregivers often provide much of the day-to-day care

equation of motion

Pmus + Pvent = Palv + PTA

• Control Mode: AC/VC , 70 kg IBW

  • RR 14 Vt 560 ml FiO2 .60 PEEP 5cmH2O

  • Patient on heavy dose or fentanyl of and versed so VENTILATOR does most, if not all, of the work

• Spontaneous Mode:

  • PS/CPAP 0 cmH2O/5 cmH2O

    • In other words, PEEP 5 cmH2O

  • Patient is breathing with minimal support. PATIENT does MOST of the work

4 control variables

• volume

  • volume and flow remain constant

  • pressure varies

• pressure

  • pressure remains constant

  • volume/flow vary

• flow

  • flow and volume remain constant

  • pressures vary

• time

  • Isn’t used much. You’ll find this in high-frequency jet

    ventilators (neonatal) and a few others

The most common control variables are pressure and volume

volume control

• ______

  • volume and flow remain constant

  • pressure varies

• trigger

  • pt

    • flow pressure

  • time

    • vent

• limit

  • volume

• cycle

  • time

• guaranteed Ve

• barotrauma

  • if not well controlled by alarms

volume control waveforms (flow patterns and shapes)

• Flow pattern

  • constant and square

  • sinusoidal

  
  

• Shape:

  • ascending ramp

  • descending/descelerating

pressure control

• ______

  • pressure remains constant

  • volume/flow vary

  • square/ rectangle

  • higher MAP

    • better oxygenation

  • can lead to volutrauma

    • if not well controlled by tight arm settings

pressure control waveforms (flow patterns and shapes)

• square/contant/rectangular

• increasing/decreasing exponential

- Flow pattern: flow pattern varies, has a descelerating ramp, exponential - Shape: rectangular

3 phase variables

• trigger

• limit

• cycle

TLC for VC,PC, PS

• VC

  • trigger

    • patient

      • flow

      • pressure

    • vent

      • time

  • limit

    • volume

  • cycle

    • time

• PC

  • trigger

    • patient

      • flow

      • pressure

    • vent

      • time

  • limit

    • pressure

  • cycle

    • time

• PS

  • trigger

    • patient

      • flow

      • pressure

  • limit

    • pressure

  • cycle

    • flow

• AC/VC is volume limited, time cycled and can be machine or patient triggered

  AC/PC is pressure limited, time cycled and can be machine or patient triggered

  SIMV VC with PS is volume limited on mandatory breaths but pressure limited in patient triggered breaths

This mode is volume limited, time cycled but can be patient or machine triggered 

AC/VC

trigger: how breath is triggered, sensitivity setting troubleshooting

• How inspiration begins, what starts the inspiratory phase

• how to trigger

  • time

    • set by RR

    • use TCT

  • patient

    • pressure

      • cmH2O

    • flow

      • COPD

  • volume

time trigger

• ex

  • VC

  • use TCT

patient trigger

• spontaneous

  • PS

  • SIMV

• set sensitivity

  • this is patient effort → set in:

    • pressure

    • flow

high vs low pressure sensitivity

• If pressure sensitivity is set high, it requires

  • more patient effort

• If pressure sensitivity is set low, it requires

  • less patient effort

• -1 to -2 cmH2O common for pressure sensitivity setting

how is flow sensitivity triggered

• vent detects a drop of flow in patient circuit during

  • exhalation

• When set properly, flow tends to requires less WOB than pressure sensitivity triggers

high vs low flow sensitivity

• more common than pressure sensitivity

• If flow sensitivity is set high, it requires

  • more patient effort

• If flow sensitivity is set low, it requires

  • less patient effort

too low vs too high flow sensitivity

• If flow sensitivity is set too low, vent will

  • auto-trigger

• If flow sensitivity is set too high, patient will be

  • locked out

volume trigger (Often called ‘manual’ breath)

• Volume triggering is uncommon

• You’ll see this on Drager Babylog and Cardiopulmonary Venturi

• There’s also ‘manual’ triggering

• where you, the RT, push a button and trigger a breath

Patient is on AC/VC Vt 420 ml, RR 12, FiO2 0.35 PEEP 5 cmH2O. Vent cycles quickly from one breath to the next. Actual RR is 28. The pressure indicator doesn’t change at the beginning of each inspiration. Every breath is either assisted or patient-triggered breath.

Problem?

• hiccups

• auscultation from heartbeat

• water in corrugated tubing

• leak

define cycle

How inspiration ends, what ends the inspiratory phase

Cycle variables for modes

• VC

  • time

• PC

  • time

• PS

  • flow

• birdmark 7

4 ways to cycle breath

1. Volume

2. Pressure

3. Flow

4. Time

define time-cycled breaths

• the inspiratory phase ends when a predetermined time has elapsed. At that time

  • the expiratory valve opens and exhaled air is vented out

• Tidal volume = flow x Ti

• AC/VC is volume-controlled, time cycled, because breath ends after Ti ends and VC = Volume Control(led)

time cycle VC

• increases and decreases in compliance do not impact flow pattern or volume. Volume is delivered in a fixed amount of time. Pressure can vary with each breath.

time cycle PC

• volume and flow vary. If compliance goes up or down, flow and volume change. AC/PC limits pressure and cycles with time.

• This mode can be used to protect the lungs from

  • high pressures

• Alarms must be set carefully to make sure patient gets adequate minute ventilation

Pressure cycle

• Inspiration ends in pressure-cycled ventilation when a set pressure is reached at the mouth or upper airway such as a Bird Mark 7

• Advantage: Reduces lung damage caused by high pressures (can be LPS – lung protective strategy)

• Disadvantage: variable Vt and generally lower Vt when compliance decreases or if airway resistance goes up. Could create volutrauma if compliance improves

  • pressure-cycling also happens in volume-controlled breaths when pressure exceeds maximum safety high-pressure limit

flow cycle

• With flow-cycled ventilation, the vent cycles into the expiratory phase once flow reaches predetermined value during inspiration.

• Flow cycling is the most common cycling mechanism

  • reduces resistance

  • easier for pt to trigger next breath

  • continuous gas flow

• When the flow reaches a percentage of peak inspiratory flow, exhalation begins, usually 5 – 80%

what is controlled during exhalation

pressure

baseline variable

expiratory retard

• creates resistance during exhalation

• pursed lip breathing

• rarely used

expiratory hold

• pause at end of expirations

• measures

  • autopeep

• Tells how much air is trapped in the lungs at the end of exhalation

• pt must be

  • passive

  • no active/spont breaths

inspiratory hold

• This inspiratory hold is designed to keep air in the lungs at the end of inhalation, before exhalation valve opens Can also be called inspiratory hold or end-inspiratory pause

• Sometimes, this technique is used to increase peripheral distribution of gas and improve oxygenation

• But if you increase i-time, you also decrease e-time, so keep it all in perspective

expiratory phase

• PERIOD FROM THE END OF INSPIRATION TO THE BEGINNING OF THE NEXT BREATH

• End of Ti to the beginning of the next Ti or simply Te

limit variable: time, pressure, flow

Places a maximum on one (or more) of the 4 control variables

volume limit

• Inspiration is defined at the beginning of inspiratory flow to the beginning of expiratory flow

• Vent can limit variables of volume, time, pressure, or flow

• In AC/VC, the volume limit = set tidal volume. In the picture, the Vt was ‘limited’ at 500 ml