VENTILATOR THE BASIC- COURSE. HISTORY OF VENTILATOR. Early History of Ancient times . Old testament there is a mention of Prophet Elisha Inducing pressure breathing from his mouth into the mouth of a child who was dying–(Kings 4:34-35). . Hippocrates (460-375 BC) wrote
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THE BASIC- COURSE
Old testament there is a mention of Prophet Elisha
Inducing pressure breathing from his mouth into the mouth of a child
who was dying–(Kings 4:34-35).
Hippocrates (460-375 BC) wrote
the first description of endotracheal intubation his book –‘Treatise on Air’
“One should introduce a cannula into the trachea along
the jaw bone so that air can be drawn into the lungs”.
Two successful designs became popular;
In one - the body of the patient was enclosed in an iron box or cylinder
and the patient’s head protruded out of the end.
The second - design was a box or shell that fitted over the thoracic area only
(Philip Drinkerand Louis Agassiz Shaw)mid-1900s
The first iron lungwas used on October 12, 1928at
-used in a child unconscious from respiratory failure;
-her dramatic recovery, within seconds
popularize the "Drinker Respirator."
Developed a mechanical assister for anesthesiaat Harvard University.
Rancho Los Amigos Hospital, ca. 1953
Mechanical ventilators used increasingly in
Anesthesia and intensive care.
-To treatpoliopatients and
-The increasing use ofmuscle relaxants
HANDS ON VENTILATOR
HANDS ON INTUBATING MANNIQUINE
A DOCTOR SHOULD KNOW
AFTER THIS COURSE ?
MONITORING THE PROGRESS
A ICU STAFF SHOULD KNOW
AFTER THIS COURSE ?
ALARMS AND CARE OF THE PATIENT
Mechanical ventilation is used when a patient is unable to breathe adequately on his or her own.
A mechanism for telling the body that it is time to breath:
This involves CO2 sensors in the brainstem, which signal diaphragmatic movement via the cervical nerves.
The phrenic nerves
The diaphragm contracts –
it increases the volume of the thorax,
by moving down into the abdomen,
making the intra-pleural and intra-alveolar pressure more negative,
creating a pressure gradient between the atmospheric and the alveoli,
and allowing air to pass down through a series of narrowing bronchi into the alveoli.
The alveoli and the pulmonary capillary network,
Derived from the main pulmonary arteries,
oxygen and carbon dioxide diffuse across the concentration gradient
out of and into the alveoli respectively.
The diffusion of CO2 is more effective due to it’s higher solubility.
Characterized by reduced alveolar ventilation
as an increase in the PaCO2 > 50 mmHg
Loss of ventilatory drive due to sedation, narcosis, stroke or brain injury.
Spinal cord injury, cervical – loss of diaphragmatic function,
thoracic – loss of intercostals.
– myasthenia gravis, steroid induced myopathy, protein malnutrition.
Chest Wall– rib fractures or flail chest, obesity, abdominal hypertension, restrictive dressings
Pleura– pleural effusions, pneumothorax, hemothorax.
Airways – airway obstruction (in lumen, in wall, outside wall), laryngeal edema, inhalation of a foreign object, bronchospasm
Thickening of the alveoli (fibrosis)
Increased extracellular fluid – pulmonary edema.
This obstructs gas exchange.
Eg; pulmonary embolus
Shunt (or low V/Q)–where alveoli are perfused but not ventilated
occurs in airway collapse,
pulmonary hemorrhage (contusion), ARDS/ALI.
Inability to extract O2 at cellular level–sepsis, cyanide
or carbon monoxide poisoning
What is it?
Amechanical ventilatoris a machine that generates a controlled flow of gas
into a patient’s airways
Two kinds of ventilators:
Negative pressure and Positive pressure.
Negative Pressure :
-iron lung, the Drinker respirator, and the chest shell
-advantage these ventilators didn’t require insertion of an artificial airway,
-disadvantage they were noisy and made nursing care difficult.
Positive Pressure :
-The Emerson Company in Boston developed the positive pressure ventilator, which was first used at Massachusetts General Hospital.
-deliver a preset tidal volume
-ideal for patients with bronchospasm since the same tidal volume is delivered regardless of the amount of airway resistance
-deliver gases at preset pressure
-decreased risk of lung damage from high inspiratory pressures
-disadvantage is that the patient may not receive the complete tidal volume if he or she has poor lung compliance and increased airway resistance
-deliver a breath until a preset flow rate
These aren’t used
-deliver a breath over a preset time period
expiration is passive
gas flows along a pressure gradient between the upper airway and the alveoli
Flow is either volume targeted and pressure variable, or pressure limited and volume variable.
The pattern of flow may be either sinusoidal (which is normal), decelerating or constant. Flow is controlled by an array of sensors and microprocessors.
Either Volume Controlled(volume limited, volume targeted) and Pressure VariableorPressure Controlled(pressure limited, pressure targeted) and Volume VariableorDual Controlled(volume targeted (guaranteed) pressure limited)
Time cycled- such in in pressure controlled ventilation
Flow cycled- such as in pressure support
Volume cycled- the ventilator cycles to expiration once a set tidal volume
has been delivered: this occurs in volume controlled ventilation
-If an inspiratory pause is added,
then the breath isboth volume and time cycled
what causes the ventilator to cycle from inspiration?
ventilation, pressure support)
1. Theresting point of outward chest spring and inward lung collapse is the
Functional Residual Capacity (FRC):
this is a reservoir for gas exchange .The FRC is the lung’s physiologic reserve, it is a reservoir.
2. Loss of chest wall or lung compliance causes reduced FRC.
3. Exhalation below FRC is active causing dynamic airway collapse,
trapping air in the alveoli (auto PEEP)
4. At residual volume it is not possible to empty alveoli of air further,
due to dynamic airway collapse (airway closure)
5. The closing volume (CV) is the point at which dynamic compression of the airways begins.
6. Such airway closure occurs normally within FRC, and it is known as the closing volume (CV).
With age and disease the CV moves into the tidal breathing range.
7. The CV increases with age, smoking, lung disease, and body position (supine > erect).
8. Airway collapse increases the work of breathing and leads to ventilation-perfusion mismatch
9. In mechanically ventilated patients airway collapse is prevented by applying positive pressure
to the airway throughout the respiratory cycle – CPAP/PEEP
10. PEEP/CPAP works by increasing FRC, maintaining alveolar recruitment facilitating gas
exchange (and removal of CO2 and replenishment of O2), and
reducing the workload of breathing.
11. The patient requires sufficient PEEP to prevent alveolar de-recruitment, but not so much PEEP
that alveolar over-distension, dead space ventilation and hypotension occurs.
12. The ideal level of PEEP is that which prevents de-recruitment of the majority of alveoli,
while causing minimal over-distension.
13. Recruitment maneuvers are used to re-inflate collapsed alveoli, a sustained pressure above
the tidal ventilation range is applied, and PEEP is used to prevent de-recruitment.
14. Auto-PEEP is gas trapped in alveoli at end expiration, due to inadequate time for expiration,
bronchoconstriction or mucus plugging. It increased the work of breathing.
15. The increased work of breathing associated with auto-PEEP can be offloaded by applying CPAP
to the trachea/mouth, and splinting open the connecting airways.
The objective is to set the CPAP level above the auto-PEEP level.
Airway pressure screen
Step 1: - determine the CPAP level
– this is the baseline position from which there is a downward deflection on,
at least, beginning of inspiration, and to which the airway pressure returns
at the end of expiration.
Step 2: is the patient triggering?
-There will be a negative deflection into the CPAP line just before inspiration
-If the curve has a flat top, then the breath is pressure limited,
if it has a triangular or shark’s fin top, then it is not pressure limited
and is a volume breath.
Step 4: what is the flow pattern?
– If it is constant flow (square shaped) this must be volume controlled,
if decelerating, it can be any mode.
-expiratory flow does not return to baseline before inspiration commences
(i.e. gas is trapped in the airways at end-expiration).
Step 4:the patient is triggering –
is this a pressure supported or SIMV or VAC breath?
-This is easy, the pressure supported breath looks completely differently
than the volume control or synchronized breath:
the PS breath has a decelerating flow pattern, and has a flat topped
airway pressure wave. The synchronized breath has a triangular
shaped pressure wave.
Step 5: the patient is triggering – is this pressure support or pressure control?
-The fundamental difference between pressure support and pressure control
is the length of the breath – in PC, the ventilator determined this (the inspired time)
and all breaths have an equal “i” time. In PS, the patient determined the
duration of inspiration, and this varies from breath to breath.
-Each time the ventilator is triggered a breath should be delivered.
If the number of triggering episodes is greater than the number of breaths,
the patient is asynchronous with the ventilator. Further, if the peak flow rate of the ventilator is inadequate, then the inspiratory flow will be "scooped" inwards, and the patient appears to be fighting the ventilator.
Both of these problems are illustrated below
-CV delivers the preset volume or pressure regardless of the patient’s own inspiratory efforts.
-This mode is used for patients who are unable to initiate a breath.
-If it is used with spontaneously breathing patients, they must be sedated and/or pharmacologically paralyzed so they don’t breathe out of synchrony with the ventilator.
-A/C delivers the preset volume or pressure in response to the patient’s own inspiratory effort but will initiate the breath if the patient does not do so within the set amount of time.
-This means that any inspiratory attempt by the patient triggers a ventilator breath.
-The patient may need to be sedated to limit the number of spontaneous breaths since hyperventilation can occur.
-This mode is used for patients who can inititate a breath but who have weakened respiratory muscles.
-SIMV was developed as a result of the problem of high respiratory rates associated with A/C.
-SIMV delivers the preset volume or pressure and rate while allowing the patient to breathe spontaneously in between ventilator breaths.
-Each ventilator breath is delivered in synchrony with the patient’s breaths, yet the patient is allowed to completely control the spontaneous breaths.
-SIMV is used as a primary mode of ventilation, as well as a weaning mode.
-The disadvantage of this mode is that it may increase the work of breathing and respiratory muscle fatigue.
-PSV is preset pressure that augments the patient’s spontaneous inspiratory effort and decreases the work of breathing.
-The patient completely controls the respiratory rate and tidal volume.
-PSV is used for patients with a stable respiratory status and is often used with SIMV to overcome the resistance of breathing through ventilator circuits and tubing.
-PEEP is positive pressure that is applied by the ventilator at the end of expiration.
-Used as an adjunct to CV, A/C, and SIMV to improve oxygenation by collapsed alveoli at the end of expiration.
decreased cardiac output,
increased intracranial pressure.
-CPAP is similar to PEEP except that it works only for patients who are breathing spontaneously.
-The effect of both is comparable to inflating a balloon and not letting it completely deflate before inflating it again. The second inflation is easier to perform because resistance is decreased.
-CPAP can also be administered using a mask.
-This method is used to ventilate each lung separately in patients with unilateral lung disease or with a different disease process in each lung.
-It requires a double-lumen endotracheal tube and two ventilators.
-Sedation and pharmacological paralysis are used to facilitate optimal ventilation and increased comfort for the patient.
8) High Frequency Ventilation (HFV)
-HFV delivers a small amount of gas at a rapid rate (as much as 60-100 breaths per minute.)
-This is used when conventional mechanical ventilation would compromise hemodynamic stability, during short-term procedures, or for patients who are at high risk for pneumothorax.
-Sedation and pharmacological paralysis are required.
-The normal inspiratory:expiratory ratio is 1:2 but this is reversed during IRV to 2:1 or greater (the maximum is 4:1).
-This mode is used for patients who are still hypoxic even with the use of PEEP.
-The longer inspiratory time increases the amount of air in the lungs at the end of expiration (the functional residual capacity) and improves oxygenation by reexpanding collapsed alveoli.
-The shorter expiratory time prevents the alveoli from collapsing again.
-Sedation and pharmacological paralysis are required since it’s very uncomfortable for the patient.
MODE FUNCTION CLINICAL USE
Control Ventilation (CV)Delivers preset volume or pressure Usually used for patients who are apneic regardless of patient’s own inspiratory efforts
Assist-Control Ventilation (A/C)Delivers breath in response to Usually used for spontaneously
patient effort and if patient fails to breathing patients with weakened
do so within preset amount of timerespiratory muscles
Synchronous Intermittent MandatoryVentilator breaths are synchronized Usually used to wean patients from
with patient’s respiratory effort
Pressure Support Ventilation (PSV)Preset pressure that augments the Often used with SIMV during
weaning patient’s inspiratory effort and
decreases the work of breathing
Positive End Expiratory Pressure
(PEEP)Positive pressure applied at the end Used with CV, A/C, and SIMV to
Improve oxygenation by opening collapsed alveoli
Constant Positive Airway PressureSimilar to PEEP but used only with Maintains constant positive pressure
in airways so resistance is decreased
spontaneously breathing patients
Independent Lung Ventilation (ILV) Ventilates each lung separately; Used for patients with unilateral lung
disease or different disease process
In each lung
requires two ventilators and
High Frequency Ventilation (HFV) Delivers small amounts of gas at a Used for hemodynamic instability,
during short-term procedures, or if
patient is at risk for pneumothorax
rapid rate (60-100 breaths/minute);
Inverse Ratio Ventilation (IRV) I:E ratio is reversed to allow longer Improves oxygenation in patients
who are still hypoxic even with PEEP;
keeps alveoli from collapsing
inspiration; requires sedation/
Anesthesiologists use mechanical ventilators in the operating room.
These are “bag in bottle” mechanical bellows which are controlled by three factors:
1) tidal volume, 2) respiratory rate, 3) I:E ratio.
Conventional anesthesia ventilator: the patient is delivered mandatory breaths from a “bag in bottle” ventilator.
He can also draw unsupported spontaneous breaths from an in-line reservoir bag:
-Longer inspiratory times and faster respiratory rates predispose to alveolar gas trapping
Pressure-assist ventilation –
Pressure assist ventilation is pressure control without a set rate.
Patients take pressure controlled breaths at the rate of their choosing,
and the volumes derived are determined by the pressure preset level,
the Ti and the flow demanded.
This is a very comfortable mode,
and is used in weaning from pressure control (the pressure limit is weaned).
“The term “pressure control” refers to an assist control mode”
-A pressure limited breath is delivered at a set rate.
-The tidal volume is determined by the preset pressure limit.
-The flow waveform is always decelerating in pressure control
-Gas flows into the chest along the pressure gradient.
-As the airway pressure rises with increasing alveolar volume the rate of flow
drops off (as the pressure gradient narrows) until a point is reached.
when the delivered pressure equals the airway pressure: flow stops.
-The pressure is maintained for the duration of inspiration .
Obviously, longer inspiratory times lead to higher mean airway pressures
(the “i” time (Ti) is a pressure holding time after flow has stopped).
-The combination of decelerating flow and maintenance of airway pressure
over time means that stiff, noncompliant lung units (long time con
which are difficult to aerate are more likely to be inflated.
-Drawbacks of pressure control? -Pressure control does not guarantee minute ventilation. change in the compliance, then the patient may hypoventilate and become hypoxic.
In volume assist-control -often labelled “volume control”
-patients may receive either controlled or assisted breaths.
-When the patient triggers the ventilator,
he/she receives a breath .
-The patient receives a breath of this type irrespective of
actual minute ventilation requirement, so patients
tend to hyperventilate as they emerge.
Assist control (AC) ventilationinvolves the use of four variables:
- inspiratory flow (as an alternative to I:E ratio)
If the flow rate is too high, the volume is rapidly delivered to only the
most compliant lung tissues (and not to the inelastic diseased tissues),
If the peak flow is too low, the patient will demand more gas than the
ventilator is set up to supply and dysynchrony with the machine occurs
The inspiratory flow rate is measured in liters per minute, and it determines
how quickly the breath is delivered.
The time required to complete inspiration is determined by the tidal volume
delivered and the flow rate:
Ti = VT/Flow Rate.
decelerating flow pattern
tidal volume is identical
The ventilation strategy
-is determined by whether the patient has failure to ventilate or failure to oxygenate.
-The first problem is managed by increasing the patients minute ventilation,
-the second by recruiting collapsed lung units and controlling mean airway pressure.
morphine with lorazepam, midazolam or propofol
For profoundly hypoxemic patients, the addition of a
neuromuscular blocking agent
1. Awake intubation +/- local anesthesia applied topically.
2. Sedation with midazolam +/- local anesthetic.
3. Midazolam + succinylcholine
4. Ketamine + succinylcholine (small babies).
5. Thiopental or propofol + succinylcholine
6. Etomidate + succinylcholine
Respiratory Rate (RR)
-The respiratory rate is the number of breaths the ventilator delivers to the patient each minute.
-The rate chosen depends on the
the type of pulmonary pathology
the patient’s target PaCO2.
-Obstructive lung disease, the rate should be set at 6-8 breaths/minute to avoid the development of auto-PEEP and hyperventilation
-Restrictive lung disease usually tolerate a range of 12-20 breaths/minute.
- Patients with normal pulmonary mechanics can tolerate a rate of 8-12 breaths/minute.
Tidal Volume (VT)
-The tidal volume is the volume of gas the ventilator delivers to the patient with each breath.
-The usual setting is 5-15 cc/kg, based on compliance, resistance, and type of pathology.
-Patients with normal lungs can tolerate a tidal volume of 12-15 cc/kg,
-Patients with restrictive lung disease may need a tidal volume of 5-8 cc/kg.
one must select
-a PEEP (as determined by lung compliance),
-a minute volume (MV 100ml/kg),
-a tidal volume (TV 6ml/kg), and a peak flow.
-The respiratory rate is the MV/TV.
-The peak flow is usually four times the minute ventilation.
-The trigger is either set as “flow-by” or a negative pressure of -2cmH2O
-The fractional inspired oxygen is the amount of oxygen delivered to the patient.
It can range from 21% (room air) to 100%.
-Oxygen toxicity causes structural changes at the alveolar-capillary membrane, pulmonary edema, atelectasis, and decreased PaO2.
Inspiratory:Expiratory (I:E) Ratio
-The I:E ratio is usually set at 1:2 or 1:1.5
-The pressure limit regulates the amount of pressure the volume-cycled ventilator can generate to deliver the preset tidal volume.
-High pressures can cause lung injury, it’s recommended that the plateau pressure not exceed 35 cm H20.
-Caused by airway is obstructed with mucus,the patient coughing, biting on the ETT, breathing against the ventilator, or by a kink in the ventilator tubing.
The following is a summary of the settings that nurses deal with the most.
SETTING FUNCTION USUAL PARAMETERS
Respiratory Rate (RR) Number of breaths delivered usually 4-20 breaths/mt
by the ventilator per minute
Tidal Volume (VT) Volume of gas delivered during usually 5-15cc/kg
each ventilator breath
Fractional Inspired Amount of oxygen delivered by 21%-100% to keep
Oxygen(FIO2) ventilator to patient PaO2>60mmHg or
Inspiratory:Expiratory Ratio Length of inspiration usually 1:2 or 1:1.5
(I:E) compared to length of expiration
Pressure Limit Maximum amount of pressure 10-12cm H2O above
the ventilator can use to PIP; maximum35cmH2O
Noninvasive positive pressure ventilation (NIPPV) include
- patients who don’t have oxygenation problems,
- who are able to manage their secretions, and
- who don’t have an upper airway obstruction.
Continuous Positive Airway Pressure (CPAP)
CPAP can also be delivered through either a nasal mask or a full face mask.
Full face masks- minimize air leaks,
-more claustrophobic- must be removed for the patient to speak or expectorate secretions.
- a smaller air leak leads to greater pressure buildup and gastric distention
Nasal masks - less claustrophic and don’t have to be removed to speak or expectorate,
- they usually have large air leaks BiPAP
Bi-level Positive Airway Pressure (Bi-PAP)- similar to CPAP - BiPAP maintains positive airway pressure during both inspiration and expiration. -The two levels are referred to as inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP). -Benefits of IPAP increased tidal volume and minute ventilation, decreased PaCO2 level, relief of dyspnea, and reduced use of accessory muscles. -Benefits of EPAP increased functional residual capacity, resulting in an increased PaO2 level. -Bi-Pap is usually delivered through a nasal mask, allowing exhalation through the mouth
-Intermittent Positive Pressure Breathing (IPPB) is used after surgery or for a short time after mechanical ventilation has been discontinued.
-The IPPB machine is a pressure-cycled ventilator that delivers compressed
gas under positive pressure into the patient’s airway.
-It’s triggered when the patient inhales,but it allows passive expiration.
-Usually, 10-20 breaths are given every 1-2 hours for 24 hours.
-Benefits of IPPB include
prevention of atelectasis,
promotion of full-lung expansion,
improved oxygenation, and
administration of nebulized medications.
Mechanically Ventilated Patient
Nursing Care of the Endotracheal Tube (ETT)
ETT management consists of
- ensuring a patent airway,
- suctioning pulmonary and oral secretions, and
- providing frequent oral and/or nasal care.
-secure ETT in place
-oral care should be provided every eight hours and as needed.
Bite block -If the patient has a bite block to prevent them from biting on the tube, it must be removed and cleaned or replaced every eight hours.
-If the tube is taped to the patient’s face, the tape must be removed and replaced on the opposite side of the face at least once per day .
-The amount of air in the cuff should be checked every eight hours to ensure that the cuff is not exerting too much pressure on the trachea walls.
-ETT should be confirmed to be the same as prior to the procedure
This includes -a sterile suction kit;
(two separate suction catheters for oral and ETT)
-a bottle of sterile 0.9% sodium chloride;
-a clean bite block, and
-tape torn into appropriately sized pieces.
Nursing Care of the Tracheostomy Tube
-Tracheostomy (trach) care should be done every eight hours
and involves cleaning around the incision,
as well as replacing the inner cannula if the patient has a double-lumen tube.
-prevent breakdown of the skin surrounding the site,
and prevent infection.
-Using sterile technique, the skin and external portion of
the tube is cleaned with hydrogen peroxide.
- inner cannula must be cleaned with hydrogen peroxide, rinsed with 0.9% sodium chloride, and reinserted using sterile technique
- Suctioning should be performed only when the patient needs it; the need should be assessed at least every two hours.
- Pre-oxygenation with 100% O2
- two separate suction catheters for oral and ETT
- size of suction catheter should be 1/3rd of ETT diameter
- Duration of each suction pass should be limited to ten seconds
-The number of passes should be limited to three or less
- saline installation should not be used routinely
Continuous bladder drainage
Catheter should changed once in 72 hours – check patency
-Patients require sedation in order to tolerate mechanical ventilation
- sedatives decrease anxiety and produce amnesia
- analgesics, and
Lorazepam Midazolam Propofol Dexmedetomidine
Onset of action5-15 minutes 1-3 minutes 1 minute Immediately
Half-life 6-15 hours 1 hour < 30 minutes 1.5-3 hours
Loading Dose0.05 mg/kg 0.03 mg/kg 0.5 mg/kg 1 mcg/kg
Infusion rate0.5-5 mg/hr 1-20 mg/hr 0.5-3mg/kg/hr 0.2-0.7 mcg/kg/hr
-Given to patients who are experiencing delirium or “ICU psychosis.”
Symptoms -disorganized thinking,
- audio and visual hallucinations, and
Haloperidol - intravenously in 2-10 mg doses every 2 to 4 hours
Intravenous narcotics – Morphine,fentanyl or hydromorphone
PARALYTICS AGENTS or neuromuscular blocking agents (NMBs)
- must always be administered with other sedatives and narcotics
Two classes of NMBs: - Nondepolarizing (Succinylcholine – for intubation)
- Depolarizing ( Atracurium,Pancuranium,Vecuranium)
- Breath sounds should be assessed at least every four hours
Pleural friction rub
Spontaneous Respiratory Rate and Tidal Volume
-If the spontaneous tidal volume is low
-the patient may not do well with weaning attempts.
-If the respiratory rate is high, particularly with weaning modes indicate -the patient isn’t tolerating the mode,
-or he or she is anxious or trying to communicate.
-The machine detects the percent of hemoglobin that is fully saturated. -pulse oximetry can be a helpful guide when titrating FIO2
-In general, a SpO2 of 92% in white patients, and 95% in black patients indicates adequate oxygenation (PaO2 > 60 mmHg).
-Capnography, also called end tidal CO2, is CO2 measured at the end of exhalation
-a display where a waveform (capnogram) is created, along with a number that closely approximates the PaCO2
-In a hemodynamically stable patient with a normal ventilation/perfusion relationship, the end tidal CO2 (also called PetCO2) is generally 1-5 mmHg less than the PaCO2
-The most useful function of end tidal CO2 measurement is to confirm ETT placement in the lungs.
• Normal pH of body fluids = 7.35-7.45
• pH < 7.35 = acidosis
• pH > 7.45 = alkalosis
• PaCO2 is the partial pressure of dissolved CO2 in blood.
• Normal = 35-45 mmHg
• PaCO2 is directly related to rate and depth of respiration.
It’s a direct indicator of the effectiveness of ventilation.
• As PaCO2 rises, the blood becomes more acidic and pH drops.
• As PaCO2 decreases, the blood becomes more alkaline and pH rises.
• If a change in PaCO2 is the primary alteration, then a respiratory problem exists.
• Bicarbonate (HCO3) is the primary buffer in the body and is able to take up and release H+.
• Normal = 22-26 mmHg
• As HCO3 rises, the blood becomes more alkaline and pH increases.
• As HCO3 drops, the blood becomes more acidic and pH decreases.
• If a change in HCO3 is the primary alteration, then a metabolic problem exists.
• Considered a measure of bicarbonate concentration; includes total of bicarbonate and carbonic acid.
• Normal = 23-27 mEq/L
• Measures excess amount of acid or base present in blood. This is independent of changes in PaCO2; therefore, it’s a measure of metabolic acid-base balance.
• Increased HCO3 = base excess (alkalosis)
• Decreased HCO3 = base deficit (acidosis)
• The amount of oxygen dissolved in plasma (about 3% of total; the other 97% is bound to hemoglobin).
• Normal is 80-100 mmHg in healthy young people breathing room air at sea level; this decreases with age and altitude.
• PaO2 > 60 mmHg is considered acceptable in critically ill, mechanically ventilated adults
The patient is able to ventilate
The patient is able to oxygenate
The patient is able to protect his/her airway
How do I know if the patient is tolerant
intolerant of the trial?
Is the patient suitable for extubation?
Is the patient suitable for extubation?
Weaning & Extubation
Partial Ventilation Support
Normalization of inspiratory times
Driving pressure is targeted to
a tidal volume of 4 - 6ml/kg.
Mean airway pressure, the CPAP level and the FiO2 are reduced to targeted PaO2
As PaCO2 reduces reduce the controlresp.rate
Is the patient able to ventilate?
Is the patient able to oxygenate?
What other factors influence weaning?
FACTORS THAT MAY INTERFERE WITH WEANING
Cardiovascular – pulmonary edema,fluid overload
Gastroinestinal – recurrent aspiration pneumonitis,
ascites or abdominal wounds leading to
Nutrition -protein malnutrition leading to muscular atrophy,
which affects the diaphragm and intercostals
Acid base – metabolic alkalosis reduces respiratory drive.
Conversely, muscles perform poorly in an acidic environment
Electrolytes– hypophosphatemia, hypomagnesemia, hypokalemia, hypocalcemia:
these all affect muscular function and protein metabolism.
Endocrine – muscle weakness due to hypothyroidism or steroid induced myopathy.
Oxygen delivery capacity – the circulating hemoglobin concentration:
anemia increases respiratory drive and cardiac output
Pain control – it is very difficult to wean patients who are in pain
6. For a patient to self ventilate, many body systems must be functioning:
-the cardiopulmonary apparatus,
-the central nervous system,
-the nerves that supply the diaphragm (including the neuromuscular junctions),
-the muscles themselves.
-Moreover the patient must be willing to breath and maintain their own
functional residual capacity (not if there is diaphragmatic splinting due to pain).
-There must be room in the abdomen for the diaphragm and lungs to move into.
-There must be adequate hemoglobin to deliver oxygen to the tissues.
7. Difficult to wean a patient if ongoing inflammatory processes persist in the lungs:
consolidation, fibrosis, auto-PEEP, diffusion defects
8. Muscles must be trained and nourished, and patient-ventilator interaction encouraged
9. most effective method of weaning to discontinuation is spontaneous breathing trials
(SBT). SBTs should not be performed more than once daily.
-T-piece trials consist of alternating intervals of time on the ventilator with intervals of spontaneous breathing.
-T-shaped tube is attached
- endotracheal or tracheostomy tube. - tubing is attached to an oxygen flowmeter
-the other end is open
-watch for signs of hypercapnia
- With CPAP, the patient breathes spontaneously, but has the benefit of the ventilator alarms if he or she has difficulty.
- CPAP maintains constant positive pressure in the airways, which facilitates gas exchange in the alveoli.
-SIMV is a ventilator mode that delivers a preset number of breaths to the patient but coordinates them with the patient’s spontaneous breaths.
-Theventilator may be set to deliver 12 breaths per minute, but the patient’s respiratory rate may be 16 (12 ventilator breaths plus 4 patient-initiated breaths).
-The ventilator rate is usually decreased by one to three breaths at a time and an arterial blood gas (ABG) is obtained 30 minutes after the change
- Placing the patient on the pressure support mode at a level that allows the patient to achieve a spontaneous tidal volume of 10-12 ml/kg.
- During weaning, the level of PS is decreased by 3-5 cm H2O as long as the
patient maintains the desired tidal volume.
Simple bedside pulmonary function tests
Vital capacity (VC)
-The vital capacity is the maximal amount of air that can be exhaled after a maximal inhalation.
-The patient’s vital capacity should be at least 10-15 cc/kg.
Negative inspiratory force (NIF)
-Negative inspiratory force is the ability to take a deep breath and to generate a cough strong enough to clear secretions.
-The patient’s NIF should be at least –20 cm H20.
Tidal volume (VT)
-Tidal volume is the volume of air inspired and expired during a normal respiratory cycle.
-The patient’s tidal volume should be at least 5 ml/kg
-Minute volume is the total volume of air inhaled and exhaled in one minute.
-The patient’s minute volume should be less than 10 liters per minute.
Respiratory rate (RR)
-The respiratory rate is the number of breaths per minute. The patient’s RR should be less than 25 breaths/minute.
Arterial blood gas (ABG)
-An ABG should be done before the patient is extubated. The PaO2 should be at least 50 mmHg on less than 50% oxygen and with no more than 5 cm H20 PEEP.
-Supplemental oxygen requires humidification to prevent drying and irritation of the respiratory tract and to facilitate removal of secretions.
-oxygen delivered through a mask for a few hours after extubation.
-coughing and deep breathing.
-incentive spirometry exercises.
-is used in some institutions to assist patients to take deeper breaths, especially after surgery.
-The IPPB machine is a pressure-cycled ventilator that delivers compressed gas under positive pressure into the patient’s airway.
-It’s triggered when the patient inhales, but it allows passive expiration.
-Benefits of IPPB
-prevention of atelectasis,
-promotion of full-lung expansion,
-improved oxygenation, and
-administration of nebulized medications
Assessment and monitoring
- Breath sounds, pulse oximetry, and vital signs should be assessed and recorded every 15 minutes x 1 hour, every 30 minutes x 1 hour, then every hour until stable
- ABG to be done 30-60 minutes after extubation
-Don’t forget to ask the patient how his or her breathing feels