Mechanical Vent 1 Exam 1

spontaneous ventilation

Normal breathing, unassisted in which person creates pressure gradient through muscle and chest wall movement that moves air into and out of the lungs

What happens to intrapleural pressure during spontaneous ventilation?

decreases from -5 to -10 as air enters lungs and then increases back to -5 as the air leaves

What value is alveolar pressure during spontaneous inspiration?

-1 cm H2O inspiration

+1 cm H2O exhalation

What does the equation of motion describe?

The relationships among pressure, volume, and flow during a spontaneous or mechanical breath

finds the positive pressure needed to overcome the compliance and elastane of the lungs during mechanical vent

elastance

tendency of the lungs to return to original form after expansion

compliance

relative ease at which the lungs expand

resistance

frictional forces that must be overcome during breathing

What disease causes increased compliance

emphysema

static compliance formula

Cs = Vt/(Pplat- PEEP)

Airway resistance equation

Raw= (PIP-Pplat)/flow

normal compliance value for spontaneously breathing patient

50-170 mL/cm H2O

normal compliance value for intubated males

40-50 to 100 mL/cm H2O

normal compliance for intubated females

35-45 to 100 ml/cm H2O

Normal resistance value for spontaneous breathing patients

0.6-2.4 cm H2O/ L/s

Normal resistance value for intubated patients

>6 cm H2O/L/s

ideal body weight equation

Males: 106 + 6 (ht - 60)/2.2

Females: 105 + 5 (ht - 60)/2.2

How do PIP and Pplat change as compliance changes?

As compliance decreases, PIP and Pplat both increase

How do PIP and Pplat change as airway resistance changes?

as Raw increases, PIP increases but Pplat stays the same

what happens to Pplat in ARDS patients?

it will increase because compliance is decreasing due to the lungs getting stiff and hard to inflate

How is Pplat measured?

Inspiratory pause (at end inspiration before exhale)

What does Pplat measure?

compliance

What conditions increase airway resistance?

asthma, chronic bronchitis, emphysema, COPD, tumors, thick secretions

1 time constant

63%

2 time constants

86%

3 time constants

95%

4 time constants

98%

5 time constants

100%

definition of time constant

length of time lung units require to fill and empty

intrinsic PEEP

auto-PEEP- incomplete exhalation leading to air trapping

extrinsic PEEP

PEEP applied by the RT on the vent to keep alveoli from complete collapse

Total PEEP

extrinsic PEEP + autoPEEP

Why would we measure total PEEP?

to ensure that there is a safe amount of pressure in the lungs at the end of exhale to prevent hemodynamic instability and barotrauma

expiratory pause

pause at end of exhale before next breath given to measure auto-PEEP

How many variables can the vent control at one time?

1 (pressure, volume, flow, or time)

What will happen with increase Raw in volume control mode?

a large increase in PIP due because more pressure is needed to deliver the set Vt

What will happen with an increase in Raw on pressure control mode?

lower Vt because there will not be enough pressure to overcome the resistance and inflate lungs fully

trigger

variable beginning inspiration

limit

max number a variable can achieve

WILL NOT END INSPIRATION

cycle

variable ending inspiration

What patient trigger requires the least WOB for the patient?

flow triggering

Which 2 triggers are the most commonly used?

flow and pressure

What happens when we increase the peak flow (Vmax)?

Decreased I time, increased E time

What happens when we decrease peak flow (Vmax)?

Increase I time, decrease E time

Variable controlling exhalation

baseline variable

How are home care vents powered?

electrically/ battery powered

Risks of negative pressure ventilation

blood pooling and reduced venous return

can not easily access pt to bathe/turn

which type of mechanical ventilation closely mimics normal mechanics of breathing?

negative pressure

Problems associated with supplemental O2

will not help severe shunting

oxygen toxicity leading to atelectasis

SIMV mode

time or patient triggered

some full mechanical breaths, some spontaneous

will not give full support to spontaneous breaths

used to wean

AC mode

time or patient triggered

set frequency of mechanical breaths but pt can trigger their own

if pt triggers, vent will give full set Vt, FiO2, PEEP

caution for hyperventilation

CMV

time triggered and cycled

vent does ALL of the work-locks pt out

only used if the patient makes no effort at all

HME

artificial nose to provide humidity for mechanical ventilation

can accumulate secretions/moisture increasing Raw

can cause auto-PEEP and increase WOB

Volume control mode

will deliver a set Vt and flow but pressure will vary

Pressure control mode

will maintain a certain pressure but volume and flow will vary

Transairway pressure equation

Pta = Paw - Palv

What is transairway pressure?

the pressure difference between the mouth and the alveoli

pressure needed to get air into the airways

Transpulmonary pressure

pressure difference between the alveoli and pleura

pressure required to maintain alveolar distention

Transrespiratory pressure

pressure difference between the airway opening and body surface

pressure required to inflate lungs during PPV

Normal Cuff pressures

20-25 mmHg

27-34 cm H2O

Causes of low pressure alarms

leak in circuit

patient disconnect

causes of high pressure alarms

coughing/bronchospasm

increased airway resistance

decreased compliance

pt biting tube

What value do we want Pplat to be?

What does an inspiratory pause maneuver measure?

Plateau pressure (Pplat) and static compliance.

What does an expiratory pause maneuver measure?

Intrinsic PEEP (auto-PEEP/air trapping).

What is the ventilator user interface?

The part of the ventilator that allows the RT to set and monitor ventilator settings, alarms, waveforms, and patient data.

How do you resolve a low-pressure alarm?

Check for a patient disconnect or leak in the circuit. Reconnect the patient/circuit and locate and correct any leaks.

How do you resolve a high-pressure alarm?

Assess the patient and airway for coughing, bronchospasm, secretions, biting/kinking of the tube, or decreased compliance. Correct the cause—for example, suction secretions, straighten the tubing, or treat bronchospasm as appropriate.

What is IMV mode?

Intermittent Mandatory Ventilation (IMV) provides a set number of mandatory ventilator breaths while allowing the patient to breathe spontaneously between mandatory breaths.

Minute Ventilation (V̇E)

V̇E = VT × RR

Total Cycle Time (TCT)

TCT = 60 ÷ RR

Inspiratory Time (TI) — square waveform

TI = VT ÷ FlowVT must be in L and flow in L/sec

Expiratory Time (TE)

TE = TCT − TI

Tubing/Circuit Compliance

C = Volume ÷ PressureUnits = mL/cm H₂O

Dynamic Compliance (Cdyn)

Cdyn = VT ÷ (PIP − PEEP)

Tidal Volume from IBW

VT = IBW (kg) × desired mL/kg Your sheet: 6-8 mL/kg

Body Surface Area (BSA)

BSA = √[(Height in cm × Weight in kg) ÷ 3600]