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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 for mechanical ventilation

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Classification of ventilators• Classified according to the manner in which they

support 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 to

flow into the lung, filling its volume• Physiologically, this type of assissted ventilation is similar to

spontaneous ventilation• It is used mainly in chronic respiratory failure associated with

neuromascular conditions such as poliomylitis, muscular dystrophy, a myotrophic lateral sclerosis, and mysthenia gravis

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

• Negative pressure ventilators are simple to use and do not require intubation of the airway consequently they are especially adaptable for home use

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Positive-pressure ventilators• Inflate the lungs by exerting positive pressure on the airway, similar

to a bellows mechanism, forcing the alveoli to expand during inspiration

• Expiration occurs passively

• Endotracheal intubation or tracheostomy is necessary in most cases

• These ventilators are widely used in the hospital setting and are increasingly used in the home for patient with primary lung disease

• There are three types of positive pressure ventilators which are classified by the method of ending the inspiratory phase of respiration: pressure-cycled, time-cycled, ande-cycled

• Another type of positive pressure ventilator used for seleted patients in noninvasive positive pressure ventilation

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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

reaches a predetermined pressure, then cycles off• Its major limitation is that the volume of air or oxygen can

vary as the patient´s airway resistance or complications changes

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

• Consequently in adults, pressure cycled ventilators are intended 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 person´s 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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Intermittent Positive Pressure Breathing

Indications

• General indications for IPPB include difficulty in raising respiratory secretions, reduced vital capacity with ineffective deep breathing and coighing, or unsuccessful trials of simpler and less costly methods for loosening secretions, delivering aerosol, or expanding the lungs

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Intermittent Positive Pressure Breathing

Complications• IPPB therapy is used rarely today because of its

inherent hazards which may include: pneumothorax, – mucosal drying, – increased intracranial pressures. – Hemoptysis, gastric distention, – vomiting with possible aspiration, – psychological dependency (especially with long term use as

in COPD patients, – hyperventilation, excessive oxygen administration and

cadiovascular problems

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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, the

ventilator 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• Can be given via facemasks that covers the nose and mouth,

nasal masks or other nasal devices• This eliminates the need for endotracheal intubation or

tracheostomy and decreases the risk of nosocomial infections such as pneumonia

• The most comfortable mode for the patient is pressure controlled ventilation with pressure support

• This eases the work of breathing and enhances gas exchange• The ventilator can be set with a minimum bachup rate for

patients with periods of apnea

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Noninvasive positive pressure ventilation

• Patients are considered candidates for noninvasive ventilation if they have 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 oxygenation and 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 life and 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 via a nasal or oral mask, nasal pillow or mouthpiece with a tight seal 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 severe COPD or sleep apnea

• Tolerance is variable; BiPAP is most successful with highly motivated 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 patient´s 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 are specific 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 or two 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 the

remaining volume, because the E-size cylinder is used to provide oxygen while transporting patient

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ANESTHESIA MACHINES Ohmeda

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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 cylinder should 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 the same

pressure• In contrast to oxygen, the amount remaining in the tank can not be

readily determined • The gases in the cylinders flow through regulators thatreduce the

pressure to about 50 psi• The hoses from the hospital gas sources are connected to the machine

at the outlet or these regulators• In most machines of recent vintage (A period of origin) a pressure

interlock device shuts off the nitrous oxide flow if oxygen pressure is not present

• The gases then flow through individual flowmeters (or rotameters)on the front of the machine so that the gas flow and the ratio of oxygen to nitrous oxide can be selected by the anesthesiologist

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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 going to 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 temperature compensated, 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 this oxygen 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 from the machine to the patient

• To calculate the concentration of anesthetic going to the patient, the anesthesiologist must know the barometric pressure, the vapor pressure of the anethetic agent being used, the oxygen flow through the bypass vaporizer, the temperature of the anesthetic liquid in the vaporizer and the combined flow of the oxygen –nitrous oxide mixture

• 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% oxygen

from the 50 psi line to flow directly to the fresh gas outlet on the machine and thus to 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 pressure limiting valve (APL), a reservoir bag, an inlet connection for fresh gas flow and two connections to the patient through corrgated (To shape into folds) breathing or anesthesia hoses

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

• As the patient exhales, the one-way valve on the inspiratory limb prevents backflow, and the exhale gases flow through the expiratory limb and through the expiratory 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 the inspiratory 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 yasullt mounted 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 the other one way valveto detect a ventilator malfunction or a disconnection in the circuit

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Anesthesia machines• The advantage of the circle system is that much lower flows of

oxygen, nitrous oxide, and anesthetic gases can be used, therby reducing the cost

• The compounds used in the CO2 absorber include an indicator that changes color as the substance becomes exhausted

• For example, the soda lime may turn from white to blue, indicating that the absorbent material must be changed to prevent a buildup of CO2 in the patient

• A semiclosed circuit (or circle system) is typically used where the fresh gas flow into the system may range from 1 to 6 L/min

• During exhalation, some of the expired gases recycle through the CO2 absorber and the excess gas is scavenged (To expel exhaust gases from ) or eliminated (hence (From this source ) semiclosed)

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Anesthesia machines• With a closed circuit system all co2 is absorbed , no gas is

vented from the system and only enough oxygen to meet the basal requirements of the patient (3.5 ml/kg(min) is added to the system

• In an open circuit (as Ayres T-Piece, Magill, or Bain circuits• A relatively high flow of fresh gas is used and most of the

exhaled gas is vented from the circuit• The fresh gas flow rates vary from approximately two thirds

of the patient´s minte volume with the Magill Circuit to at least 100 ml(kg for the Bain or T.piece circuits

• The open circuit system is commonly used for neonates, infants and small children