principles of mechanical ventilation: rt 244

Abby Erickson, RRTReview of RT 110

Performed by:• Hand

• Machine

Available for:• Short term• Long term• Acute care• Extended home

care

S-shaped curve, relationship of plasma PO2 and O2 bound to Hb (SO2)

Flat portion: minor changes in PO2 have little effect on SO2 Strong Affinity!

Steep portion: small drop in PO2 causes a large drop in SO2 Weak Affinity!

Normal: 4-5L/min VA= Vt-VD VA= (Vt-VD)x f ↑ VA = ↓PaCO2, ↑PaO2

• Hyperventilation ↓VA = ↑PaCO2,↓PaO2

• Hypoventilation Alveolar air equation As PaCO2 ↑ by

1mmHg, PaO2 ↓ by 1.25mmHg

..

.

Degree of compensation Acid-base balance Cause: respiratory, metabolic,

mixed Oxygenation – degree of hypoxemia Must interpret in the context of the

clinical picture!! • Requires ventilation status• History, signs, symptoms

Acute changes versus chronic

Pawo: zero* Pbs: zero* Ppl: -5cmH2O -

10cmH2O PA: +1cmH2O -

1cmH2O

*unless pressure applied

Relative ease with which a structure distends• opposite of elastance

Used to describe the elastic forces that oppose lung inflation

V/P = L/cmH2O 50-170ml/cmH2O normal 35/40 -100ml/cmH2O intubated patient Static Compliance Dynamic Compliance

Frictional forces associated with ventilation• Anatomic structures• Tissue viscous resistance

Ability of air to flow depends on• Gas viscosity• Gas density• Length and diameter of the tube• Flow rate of the gas through the tube

Raw = PTA/flow cmH2O/L/sec• PTA ≈ PIP – Pplat• Assumes constant flow

Normal 0.6-2.4 cmH2O/L/sec Intubated patients 5-7cmH2O/L/sec (and higher!)

Attempts to mimic normal physiology

Types:• Iron lung – tank

ventilator• Chest cuirass

Maintained without the need for ETT, tracheostomy, able to talk and eat

Cardiovascular concerns, access to patient

Above normal ventilating rates with below normal ventilating volumes

HFPPV HFJV HFOV

Requires airway interface

Applies pressure to create gradient between mouth and lung

ELECTRICALLY POWERED PNEUMATICALLY POWERED Relies on electricity Wall outlet (AC), battery

(DC) Powers internal motors

which provide gas flow to the patient

High pressure gas source Usually 2 -50psi sources,

air and oxygen Built in reducing valves Pneumatic Fluidic

Pneumatically powered – 50 psi gas sources• Mixture of air and oxygen allow variable

FiO2• Energy to deliver the breath

Electrically powered• Controls the internal function• May be controlled by a microprocessor

(1980’s)

OPEN LOOP CLOSED LOOP “unintelligent” systems Does not respond to

changes in patient condition

Does not measure variables or change them

“intelligent” systems Compares the set

variable to the measured variable

Main inspiratory line Adapter Expiratory line Expiratory valve Adjuncts

• Device to warm/humidify air• Thermometer• Nebulizer• Bacteria filters

Muscle Pressure• Action of the

respiratory muscles

Ventilation Pressure• Produced by the

ventilator

These pressures produce motion (flow) to deliver a volume of gas to the lung; the volume delivered depends on the lung’s characteristics

PRESSURE CONTROLLED BREATHING

VOLUME CONTROLLED BREATHING

Maintains the pressure waveform in a specific pattern

Pressure waveform is unaffected by changes in lung characteristics

Volume and flow waveforms vary with changes in lung characteristics

Maintains the volume waveform in a specific pattern

Volume and flow waveforms remain unchanged

Pressure waveform varies with changes in lung characteristics

Change from exhalation to inspiration Inspiration Change from inspiration to exhalation exhalation

Signal measured by the ventilator Begins, sustains and ends each of the

four phases of the breath• Trigger variable• Limit variable• Cycle variable

MANDATORY SPONTANEOUS Ventilator determines

start time Ventilator determines

tidal volume Ventilator determines

both Machine triggers and/or

cycles the breath

Patient determines start of breath

Patient determines tidal volume delivery

Does not require an endotracheal tube

Use of NPPV has the potential:• to avoid complications of intubation• decrease mortality rates• decrease length of stay

Achieve exhaled tidal volume 5-7ml/kg Patient ventilator synchrony

• Rise time • Inspiratory sensitivity• Expiratory flow cycling• EPAP to offset autoPEEP

Oximetry Alleviating disease/disorder signs and

symptoms

Requires patient cooperation and tolerance

Selection of appropriate interface Starting with low pressure initially Allow the patient to hold the mask Reassurance Requires secure fit, leaks are

acceptable

Mask discomfort Air pressures/Gas flows –gastric

insufflation Aspiration pneumonia Pneumothorax Hypotension Hypoxemia, Mucus plugging Respiratory arrest

Reversal of the cause of respiratory failure

Stabilization of the patient's condition Gradually decreasing the level of

support (both ventilatory and oxygenation)

Gradually increase the amount of time off NPPV

The rest of the book! Stay on top of the reading, this term

moves fast Come and see me for questions,

concerns and further review, I am here to help

Class time is limited so plan on additional time for independent study