RESC. Mechanical Vent Exam 1

spontaneous ventilation

Breaths that are initiated by the patient (i.e. patient cycled), and volume delivery is determined by the patient (patient cycled). Volume, flow, pressure delivery is based on patient demand/lung characteristics rather than on a value set by the ventilator operator

-The patient controls the timing and the Vt.

**is the body’s mechanism for conducting air in and out of the lungs

What happens to intrapleural pressure during spontaneous ventilation?

decreases from -5cm H20 at end expiration to -10cmH20 at end inspiration

Normal: -5 to -10cmH20

Equation of motion describes relationships between what

describes the relationships between pressure, volume, and flow during a spontaneous or mechanical breath

elastance

the tendency of a structure to return to its original form after being stretched or acted on by an outside force

compliance

the relative ease with which the structure distends

resistance

measurement of the frictional forces that must be overcome during breathing

disease that causes an increase in compliance

emphysema

static compliance formula

Cstat=Vt/(Pplat-PEEP)

airway resistance formula

Raw=PIP-Pplat/flow

*flow needs to be L/sec

Values for compliance

Normal: 50-170mL/cm H20 (0.05-0.17L/cm H20) (spontaneously Breathing)

Intubated:

Men: 40-50mL/cm H20

Women: 35-45mL/cmH20

Values for airway resistance

Normal Value: 0.6-2.4cmH20/L/sec

Intubated: approx. 6 cmH20/L/sec or higher

Ideal Body Weight

Men quick way: 50+2(every inch over 5ft)

Men: 106+6(H in inches-60)/2.2 for kg

Women easy way: 45+2(every inch over 5ft)

Women: 105+5(H in inches-60)/2.2 for kg

How do PIP and Pplat change with changes in compliance?

As PIP and Pplat increase, compliance decreases

How do PIP and Pplat change with airway resistance?

As PIP increases and Pplat stays the same(constant), airway resistance increases

What is occurring when there is an increase in PIP but not an increase in Pplat or there’s an increase in both?

-Increase in PIP, but no increase un Pplat= increase in airway resistance

-Increase in both PIP/Pplat=decreased compliance

What happens to Pplat in ARDS patients?

Pplat will increase because compliance is decreasing causing stiff and hard lungs to inflate

what phase is Pplat measured?

Inspiratory pause (at end inspiration before exhale)

-Measured after a breath has been delivered to the patient and before exhalation begins

What conditions are associated with an increase airway resistance?

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

Time constants

1 time constant equals the amount of time it takes for 63% of the volume to be inhaled or exhaled

2 time constants represent that amount of time for about 86% of the volume to be inhaled or exhaled

3 time constants equal the time for about 95% to be inhaled or exhaled

4 time constants is the time required for 98% of the volume to be inhaled or exhaled

5 time constants=100%

definition of time constant

length of time lung units require to fill and empty

Intrinsic PEEP

Auto-PEEP

side effect of positive pressure ventilation, which leads to air trapping in the lungs

-Patient does not have enough time to exhale completely before the ventilator delivers another breath

Extrinsic PEEP

PEEP applied by the operator on the ventilator

Total PEEP

Intrinsic PEEP + Extrinsic PEEP

Expiratory Pause

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

Inspiratory Pause

Measures plateau pressure or Pplat

Measured after a breath has been delivered to the patient and before exhalation begins

Pplat also known as inflation hold or inspiratory pause

User interface

Control panel on vent

-Located on the surface of the vent and is monitored and set by the vent operator

-Has various knobs or touch pads for setting components, such as tidal volume, rate, inspiratory time, alarms, and FiO2

-The controls regulate 4 ventilatory variables: flow, volume, pressure, and time

How many variables can a vent control at one time?

1 (pressure, volume, flow, or time)

An increase in airway resistance during volume-controlled ventilation will cause what

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

Raw ↑ → PIP ↑, VT same

An increase in airway resistance during pressure-controlled ventilation will cause what

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

Raw ↑ → VT ↓, PIP same (because pressure is fixed)

trigger

variable beginning inspiration

limit

maximum value that a variable (pressure, volume, flow or time) can attain

cycle

variable ending inspiration

What Pt trigger requires the least amount of WOB for patient?

flow triggering

What are the two most used patient-trigger variables?

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 that controls exhalation

baseline variable

How are Homecare Vents powered/classified?

electrically/battery powered

Negative pressure ventilation risks/supplemental O2 problems

blood pooling and reduced venous return
cannot easily access pt to bathe/turn

-will not help severe shunting
-oxygen toxicity leading to atelectasis

IMV Mode (SIMV mode)

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

allows the patient to spontaneously breathe between mandatory, machine, breaths at any desired baseline pressure without receiving mandatory breaths

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 mode

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

what is the use of an 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

Formula: PTA=Paw−Palv

(Pta) =PIP-Pplat ***

Def: Pressure difference between the airway opening and the alveolus

-the pressure difference between the mouth and the alveoli
-pressure needed to get air into the airways

-Pressure needed to overcome airway resistance.

Transpulmonary pressure

Transalveolar

Def: is the pressure difference between the alveolar space and the pleural space

-pressure required to maintain alveolar distention

Transrespiratory pressure

Def: is the pressure difference between the airway opening and the body surface

-Pressure required to inflate the lungs during positive pressure ventilation

Normal cuff pressures

20-25mmHg

27-34cmH20

Causes of low-pressure alarm

-leak in circuit
-patient disconnect

Fix it: reconnect circuit, seal leaks, check cuff, confirm tube placement.

causes of high pressure alarm

-coughing/bronchospasm
-increased airway resistance
-decreased compliance
-pt biting tube

Fix it: suction, unkink tubing, drain water, replace HME, treat bronchospasm, manage compliance issues, use bite block.

Minute ventilation formula

Ve=Vt*f

ARDS is a pathological condition that is associated with a reduction in lung compliance. The formula for static compliance (CS) utilizes the measured plateau pressure (Pplateau) in its denominator (CS = VT /(Pplateau - EEP). Therefore, with a consistent exhaled tidal volume (VT) ,an elevated Pplateau will decrease CS.

Alveolar pressure during spontaneous inspiration?

About −1 cmH₂O.

causes of increased airway resistance

Secretions, bronchospasm, mucosal edema, mucosal inflammation.

Fix it: Tracheobronchial suctioning will remove any secretion buildup and a beta-adrenergic bronchodilator will reverse
bronchospasm.

Does increasing PEEP fix airway resistance problems?

No — compliance is normal; Raw is the issue.

Rising plateau pressure indicates what?

decreased lung compliance

ARDS affects compliance how?

ARDS decreases lung compliance.

dynamic compliance

pulmonary compliance during gas flow,

formula-Vt/(PIP-PEEP)

sensitivity

Setting that controls how easy/hard it is to trigger breath

time

Trigger variable in a controlled mode is

Time is the ventilator trigger variable.

Pulmicort dosage

0.5mg or 0.25mg

Xopenex dosage

0.31mg, 0.63mg, 1.25mg