Indications for Mechanical Ventilation (2)

7/31/2019 Indications for Mechanical Ventilation (2)

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Indications for mechanical

ventilation

Dr Aidah Abu Elsoud Alkaissi

An-Najah National University

Faculty of Nursing


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Indications for mechanical

ventilation If a patient has a continous decrease in oxygination (PaO2) , an

increase in arterial carbon dipxide level (PaCO2), and a persistent

acidosis (Deceased PH) , mechanical ventilation may be necessary

Conditions such as thoracic or abdominal surgery, drug overdose,

neuromuscular disorders, inhalation injury, COPD, multiple trauma,

shock multisysem failure and coma all may lead to respiratory failure

and the need for mechanical ventilation (chart 25-11) page 616 guide

the decision to plce a patient on a ventilator

A patient with apnea that is not readily reversible also is a candidate formechanical ventilation


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Classification of ventilators

Classified according to the manner in which theysupport ventilation

The rwo general categories are:

Negative pressure and positive pressure ventilators The most common category in use today is the

positive pressure ventilator


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Negative-pressure ventilators

Exert a negative pressure on the external chest

Decreasing the intrathoracic pressure during inspiration allows air toflow into the lung, filling its volume

Physiologically, this type of assissted ventilation is similar tospontaneous ventilation

It is used mainly in chronic respiratory failure associated withneuromascular conditions such as poliomylitis, muscular dystrophy, amyotrophic lateral sclerosis, and mysthenia gravis

It is inappropriate for th unstable or complex patient or the patientwhose condition requires frequent ventilatory changes

Negative pressure ventilators are simple to use and do not requireintubation of the airway consequently they are especially adaptablefor home use


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Pressure-Cycled Ventilators

Ends inspiration when a preset pressure hs been reached

The ventilator cycles on, delivers a flow of air until it reachesa predetermined pressure, then cycles off

Its major limitation is that the volume of air or oxygen canvary as the patients airway resistance or complicationschanges

As a result the tidal volume delivered may be inconsistent,possibly compromising ventilation

Consequently in adults, pressure cycled ventilators areintended ony for short term use

The most common type is the IPPB machine


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Intermittent Positive Pressure Breathing

Is a form of assisted or controlled respiration produced by a ventilatory

apparatus in which compressed gas is delivered under positive

pressureinto a persons airway until a preset pressure is reached

Passive exhalation is allowed through a valve

The specific pressure and volume amounts, a long with the use of any

nebulizing medications, are prescribed individually for patients

The nurse should encourage patients to relax and reassure them that the

machine will automatically shut off airflow at the end of inspiration

The IPP machine may be powered by elecricity or gas and may be

connected with a mouthpiece, mask, or tracheostomy adapter


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Time-Cycled Ventilation

Terminate or control inspiration after a preset time

The volume of air the patient receives is regulated by the length of

inspiration and the flow rate of the air

Most ventilators have a rate control that determines the respiratory rate,But pure time cycling is rarely used for adults

These ventilators are used in newborns and infants


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Volume ctcled ventilators Volume-cycled ventilators are by far the most commonly

used possitive pressre ventilators today

With this type of ventilator, the volume of air to be

delivered with each inspirationis preset

Once this preset volume is deliveredto the patient, theventilator cycles off and exhalation occurs passively

From breath to breath, the volume of air delivered by the

ventilator is relatively constant, ensuring consistent,adequate breaths despite varying airway pressures


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Noninvasive positive pressure ventilation

Patients are considered candidates for noninvasive ventilation if theyhave acute or chronic respiratory failure, acute pulmonary edema,COPD or chronic heart failurewith a sleep related breathing disorder

The device also may be used at home to improve tissue oxygenationand to rest the respiratory muscles while the patient sleeps at night

It is contraindicated for thise who have experienced respiratory arrest,serious dysrhythmias, cognitive impairment, or head or facial trauma

Noninvasive ventilation may also be used for patients at the end of lifeand those who do not want endotracheal intubation but may need short

or long term ventilatory support Bilevel positive airway pressure (biPAP) ventilation offers independenr


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Noninvasive positive pressure ventilation

It delivers two level of positive airway pressure provided viaa nasal or oral mask, nasal pillow or mouthpiece with a tightseal and a portable ventilator

Each inspiration can be intiated either by the patient or by the

machine if it is programmed with a backup rate The back up rate ensure the patient will receive a set number

of breaths per minute

Bi-PAP is most often used for patients who require

ventilatory assisstance at night such as those with severeCOPD or sleep apnea

Tolerance is variable; BiPAP is most successful with highlymotivated patient


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Adjusting the ventilator

The ventilator is adjusted so that the patient is comfortable and

breaths in sync with the machine

If the volume ventilator is adjusted appropriately, the patients

arterial blood gas values will be satisfactory and there will be

little or no cardiovascular compromise

Please read chart 25-12 page 618

Table 25-2 page 619


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Anesthesia machines Oxygen and nitrous oxide are usually supplied from the hospital

pipelines to the anesthesia machine at pressures of 50-55 psi The gas hoses (A narrow channel through which data flows under

pressure) going to the machine are color-coded, and the connecter arespecific for each gas so that nitrous oxide cannot be inadvertently(Done unintentionally, accidentally, often with no one accepting blame)

connected to the oxygen hose or vise versa

If central gas supply is not available or the hospital piping system fails,the machines are equipped with E-size cylinders of both gases, one ortwo cylinders of each gas are connected to yokes (To become joined

securely) on the machine In cylinder, oxygen is stored as a compressed gas

A full E-size cylinder contains about 660 L of oxygen at 2000 psi

As the oxygen is used the pressure falls in direct proportion to theremaining volume, because the E-size cylinder is used to provideoxygen while transporting patient


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Anesthesia machines Knowing how much oxygen is left in a partially used tank is

important Thus 1000 psi would indicate 330 L remaining and 500 psi would

indicate 165 L remaining or sufficient oxygen for 5 L/min flow

for more than 25 min

When the pressure has dropped to about 250 psi, the cylindershould not be used because it no longer has an adequate reserve

Nitrous oxide is stored as a liquid in cylinder and the pressure

above the liquid is 750 psi

A full, E-size cylinder contains about 1600 L of nitrous oxide As the nitrous oxide is used the pressure above the liquid remains

constant


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Anesthesia machines Only when the liquid has been completely vaporized does the

pressure begin to fall

Therefore the nitrous oxide can be almost gone but still show thesame pressure

In contrast to oxygen, the amount remaining in the tank can not bereadily determined

The gases in the cylinders flow through regulators thatreduce thepressure to about 50 psi

The hoses from the hospital gas sources are connected to themachine at the outlet or these regulators

In most machines of recent vintage (A period of origin) a pressureinterlock device shuts off the nitrous oxide flow if oxygen pressureis not present

The gases then flow through individual flowmeters (orrotameters)on the front of the machine so that the gas flow and the

ratio of oxygen to nitrous oxide can be selected by theanesthesiolo ist


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Anesthesia machines From the top of the flowmeters, the gases are mixed and then flow

through a vaporizer in which the inhalational anesthetic of choice is

vaporized and added to the oxygen nitrous oxide mixture

The total gas flow is then delivered from the machine to the patient

With a flow through vaporizer, by definition, all of the fresh gas goingto the patient from the anesthesia machine flows through the vaporizer

The control dials are usually located on top of these vaporizers and are

calibrated in percentages

Most recently manufactured vaporizers are flow and temperaturecompensated, meaning that they are reasonably accurate at all flows

and temperatures used clinically

The filling ports on the vaporizers are usually key indexed so that only

the appropriate vilatile agent can be used


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Anesthesia machines

The copper kettle is one type of bypass vaporizer that may still be

found on many older machines A low flow of oxygen (usually less than 1 L/min) goes through a

separate flowmeter and then through the bypass vaporizer, where thisoxygen is totally saturated with the anesthetic vapor

The saturated oxygen is then combined with the oxygen-nitrous oxide

mixture from the other flowmeter and the total mixture flows fromthe machine to the patient

To calculate the concentration of anesthetic going to the patient, theanesthesiologist must know the barometric pressure, the vapor

pressure of the anethetic agent being used, the oxygen flow throughthe bypass vaporizer, the temperature of the anesthetic liquid in thevaporizer and the combined flow of the oxygen nitrous oxidemixture

The major advantages of bypass vaporizers is that any volatile

anesthetic agent can be used in them


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Anesthesia machines Another important feature of the anesthesia machine is the oxygen flush button

With all new machines, pushing the oxygen flush button allows 100% oxygenfrom the 50 psi line to flow directly to the fresh gas outlet on the machine and thusto the patient

This oxygen flow completely bypasses the flow meters and vaporizers

In most hospitals a semiclosed circle system is used to deliver the fresh gas flow

(including anesthetic gases) to patients The circle system is composed of a container filled with a CO2-absorbing material

(such as soda lime or baralime), two unindirectional valves, an adjustable pressurelimiting valve (APL), a reservoir bag, an inlet connection for fresh gas flow andtwo connections to the patient through corrgated (To shape into folds) breathingor anesthesia hoses

As the patient inspires, gases are drawn through the CO2 absorber and from thefresh gas supply through the inspiratory limb of the corrugated hoses

As the patient exhales, the one-way valve on the inspiratory limb preventsbackflow, and the exhale gases flow through the expiratory limb and through theexpiratory one-way valve


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Anesthesia machines The expiratory limb and valve are easily identified by the condensation

of water vapor along this portion of the circuit The 3L reservoir bag absorbs the peak flow of expired gases and allows

the anesthesiologist to force gas through the CO2 absorber along theinspiratory limb of the circuit and thereby ventilate the patient

The expired gases flow through the CO2 absorber, where the carbon

dioxide is removed from them

Any excess gas is vented through the APL valve, which is yasulltmounted just ahead of the CO2 absorber

The FiO2 sensor is usually mounted in the inspiratory limb just after the

one-way valve It measures the fraction of inspired O2 and can set to alarm if a low

concentration is detected

A low pressure sensor is usually mounted in the expiratory limb near theother one way valveto detect a ventilator malfunction or a disconnectionin the circuit


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Indications for Mechanical Ventilation (2)