Exam 1 Mechanical Ventilation

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 is-

Cs = Vt/(Pplat- PEEP)

Airway resistance equation is

Raw= (PIP-Pplat)/flow

Normal compliance value for spontaneously breathing patient is

50-170 mL/cm H2O

Normal compliance value for intubated males

40-50 to 100 mL/cm H2O

Normal compliance for intubated females is

35-45 to 100 ml/cm H2O

Normal resistance value for spontaneous breathing patients is

0.6-2.4 cm H2O/ L/s

Normal resistance value for intubated patients is

>6 cm H2O/L/s

Ideal body weight equation for males is

106 + 6 (ht - 60)/2.2

Ideal body weight equation for females is

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 is

63%

2 time constants is

86%

3 time constants is

95%

4 time constants is

98%

5 time constants is

100%

Definition of time constant is

length of time lung units require to fill and empty

Intrinsic PEEP is

auto-PEEP- incomplete exhalation leading to air trapping

Extrinsic PEEP is

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

Total PEEP is

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 is

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 is

variable beginning inspiration

Limit is

max number a variable can achieve WILL NOT END INSPIRATION

Cycle is

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 is

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 is

time or patient triggered some full mechanical breaths, some spontaneous
will not give full support to spontaneous breaths used to wean

AC mode is

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 is

time triggered and cycled
vent does ALL of the work-locks pt out
only used if the patient makes no effort at all

HME is

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 is

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 is

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?

<30