Basics of Mechanical Ventilation

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• SHAMS ALI SHAH RT PSCCQ

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Introduction

• for essential metabolic processes.
• we extract oxygen from the atmosphere and
  transport it to cells where it is utilized

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• The Primary function is to maintain adequate gas
  exchange in the lungs by delivering safe level of
  oxygen to the lungs and also by eliminating the
  carbon-di-oxide from the lungs.

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VQ Mismatch

• The Normal Pulmonary Vascular bed constricts in
  response of to local alveolar hypoxia, so
  unventilated alveoli receive minimal blood flow.
• Blood flow (Q) is thus matched to Ventilation
  (V)
• Significant regional abnormalities in blood flow
  (i e., PE) or Ventilation (e g., Infiltrate,
  contusion, effusion, Pnemothorax) may overcome
  local auto regulation, causing VQ mismatch and
  result is Hypoxemia

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Pulmonary compliance

• Dynamic Compliance is measured immediately after
  the lung expands. here the pressure is its here
  point.
• Dynamic Compliance (C dyn) VT/PIP-PEEP
• The lung stands in a expanded stat and the
  pressure drops some. the compliance measured here
  is Static Compliance.
• Static Compliance (C Stat) VT/P plateau-PEEP
• RawPIP-plateau Pressure/Flow L/s

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CMV (Assist)

• gt Control Mode with Trigger

CMV
gt Control Mode with No Trigger
SIMV VC PS
gtSynchronized Intermittent Mandatory Volume
Control Ventilation with pressure Support
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SIMV Pressure Control Pressure Support

• gt Synchronized Intermittent Mandatory Ventilation
  with Pressure Control pressure Support

PRVC

• gt Pressure Regulated volume Control Mode

PRVC SIMV PS
gt Pressure regulated Volume Control Mode with
Intermittent mandatory Ventilation and Pressure
Support
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ASB(assisted Spontaneous Breaths)

• gt CPAP with pressure support

PC( pressure Control Mode
gt Airway pressure is set
SIMV PC
gt Synchronized Intermittent mandatory Ventilation
with Pressure Control
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CMV (Assist)

• In this mode the ventilator provides a mechanical
  breath on a preset timing. Patient respiratory
  efforts can be triggered

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Controlled mechanical ventilation (CMV)

• In this mode the ventilator provides a mechanical
  breath on a preset timing. Patient respiratory
  efforts are ignored. This is generally
  uncomfortable.

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PC(pressure Control mode)

• The desired peak air way pressure and arte is
  input
• The effective tidal volume depends on the
  compliance
• The benefit of this mode is preventing from
  barotraumas.
• We should keep on eye on tidal volume

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AUTO FLOW

• Not a specific mode
• Used in all volume mode
• Effective in Inspiratory phase
• Auto flow converts the volume mode to volume
  targeted pressure limit mode.
• The Goal here to deliver the set tidal volume at
  the lowest pressure
• For this it uses the decelerating gas flow
  pattern.

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AUTO FLOW

• Auto flow allows the exhalation valve to behave
  as CPAP valve.
• Allows the patient to alter their flow pattern
• When auto flow is activated a test breath is
  delivered at 5 cm H2O above PEEP. The second
  breath delivered at 75 of set tidal volume. The
  third breath delivers the set tidal volume.

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AUTO FLOW

• The microprocessor algorithm then calculated the
  minimal pressure capable in achieving the target
  volume.
• Auto flow recalculated the each breath and next
  breath reflects with any change of lung
  compliance.
• During expiration period the patient is able to
  cough, exhale, and sigh.

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PRVC
Test breath
Measures vT
Compliance to set vT
less
more
Insp Pressure
Insp Press
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PRVC

• The maximum Inspiratory pressure allowed 5 cm H2O
  below the upper alarm limit.
• The duration of Inspiratory rate determined by RR
  ,I E ratio and Inspiratory time.

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High Frequency Ventilators

• A high frequency ventilator is a ventilator that
  delivers breaths much faster than a conventional
  ventilator. Conventional ventilators may deliver
  about 20 to 60 breaths per minute, but high
  frequency ventilators can deliver close to 1,000
  breaths per minute.

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Types of HFVs

• Oscillating ventilators, or oscillators
• Jet ventilators
• High frequency flow interrupters

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Tidal volume

• For adult patients and older children without
  existing lung disease
• Tidal volume (Vt) is calculated in milliliters
  per kilogram (ml/kg) of a patient's ideal body
  weight (IBW). Traditionally 8-10 ml/kg was
  considered a standard tidal volume, however lower
  volumes are now used due to the increasing
  concern over Barotrauma (injury to the lung by
  overextension). 6 to 8 ml/kg IBW is now common
  practice in ICU.

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Respiratory rate

• respiratory rate is increased in an attempt to
  maintain a normal pCO2 and minimize permissive
  hypercapnia. Increases in respiratory rate are
  generally restricted by the onset of air
  trapping.

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FiO2

• This indicates the amount of oxygen the
  ventilator delivers, expressed as a percentage or
  a number between zero and one.
• FiO2 varies widely depending on the patient's
  condition room air is 21 (0.21). While some
  patients might be adequately oxygenated with an
  FiO2 of less than 40 (0.40).
• Someone with severe hypoxemia, for example, might
  need an initial FiO2 setting of 100 (1.00)
• Arterial blood gases and pulse oximetry values
  will help determine FiO2 settings.

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Trigger

• It controls the sensitivity and methods by which
  the ventilator detects patient Inspiratory
  effort.
• It can be flow-triggered or pressure-triggered.
• If the triggering is too sensitive, there is
  risk of auto-triggering, in which small leaks in
  the circuit might be taken as Inspiratory effort
  of the patient might actually increase

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Flow Trigger

• A breath is initiated when Inspiratory flow
  through the ventilator circuit is recognized by
  the ventilator. This is normally due to the
  patient attempting inspiration, but can also be
  due to other factors, such as a leak in the
  circuit. On some ventilators the flow sensitivity
  (the flow rate threshold for initiating
  inspiration) can be set.

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Pressure Trigger

• A breath is initiated when a negative pressure is
  measured in the Inspiratory circuit, such as when
  the patient attempts inspiration. As with flow
  sensing, some ventilators allow this parameter to
  be set.

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IE ratio

• I
• E

Breathing Cycle
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Inspiratory Time

• Its range is 10 to 80 of total breath cycle
• In SIMV PS the SIMV period is used in calculation
  of Inspiratory time.
• In Pressure support the pt controls the duration
  of inspiration

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Pause Time

• Range is 0 to 30 of breath cycle
• It determines the duration of end Inspiratory
  pause when there is zero gas flow.
• Cause Barotrauma if more

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Inspiratory rise Time

• Range is 0 to 10 of Breath cycle
• It determines the time required for the pressure
  to increase to pre set level

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Pressure Support

• An Specific Airway pressure is set to support
  the patient breath on trigger.

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PEEP

• gt Helps in keeping open the alveoli, moves fluid
  out of alveolus.

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PEEP Disadvantages

• Disadvantages are
• 1. Diminished Cardiac Output
• 2. Regional Hypo perfusion
• 3. NaCl Retention
• 4. Augmentation of ICP
• 5. Paradoxical Hypoxemia

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Peak Pressure

• Peak pressure pPlateau pressure
• (here the pressure means the pressure in ETT
  and airways)

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Auto PEEP(PEEPi)

• 1. Normally at the end of expiration the lung
• volume is equal to FRC
• 2. When the PEEPi occurs the Lung Volume
• is greater than FRC

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Plateau pressure (pPlateau)

• 1. Measuring Lung and Chest wall Recoil in
• Inspiration
• 2. Measures the static compliance or Elastance

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Dead Space calculation/Tidal Volume ratio

• Vd/Vt (PaCO2-PeCO2)/PaCO2
• Where the Vd/Vt is the ratio of dead space over
  tidal volume,PaCo2 is arterial PCO2,PeCo2 is
  exhaled PCO2

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HUMIDIFICATION DURING VENTILATION

• When the upper airway is bypassed, humidification
  during mechanical ventilation is necessary to
  prevent from hypothermia, inspissations of airway
  secretions, destruction of airway epithelium, and
  atelectasis. This may be accomplished using
  either a heated humidifier or a heat and moisture
  exchanger HME.

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Complications from Ventilator
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Complications of Mechanical Ventilator

• Mechanical ventilation is often a life-saving
  intervention, but carries many potential
  complications including pnemothorax, airway
  injury, alveolar damage, and ventilator-associated
  pneumonia.

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Complications of Mechanical Ventilation

• Barotrauma
• Nosocomial Pneumonia
• Positive Water Balance
• Decreased Cardiac Output
• Decreased Renal Perfusion
• Liver congestion

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Barotrauma

• Alveolar rupture from excessive airway pressures
  and/or over distention of alveoli.
• Leads to pnemothorax, pneumomediastinum,
  pneumoperitoneum, or subcutaneous emphysema.

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Complications of Mechanical Ventilation

• Ventilator-associated lung injury
• Diaphragmatic muscle fibers
• Motility of mucocilia in the airways

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Auto PEEP(iPEEP)

• Auto-positive end-expiratory pressure (auto-PEEP,
  also called intrinsic PEEP) exists when there is
  positive airway pressure at the end of expiration
  due to incomplete

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Nosocomial Pneumonia

• The ETT becomes colonized with bacteria therefore
  we have to prevent avoiding cross-contamination.
• Decreasing risk of aspiration Suction only when
  clinically indicated, using sterile technique,
  using water trappers

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Positive Water Balance

• Receptors in right atrium senses a decrease in
  venous return and see it as hypovolemia leading
  to a release of ADH from the posterior pituitary
  gland and retention of sodium and water.
• Decrease of normal insensible water loss due to
  closed ventilator circuit preventing water loss
  from lungs.

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Ventilator Associated lung injury

• Ventilator-associated lung injury (VALI) refers
  to acute lung injury that occurs during
  mechanical ventilation. It is clinically
  indistinguishable from acute lung injury or acute
  respiratory distress syndrome (ALI/ARDS).

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Diaphragmatic muscle fibers

• Controlled mechanical ventilation may lead to a
  rapid type of disuse atrophy involving the
  diaphragmatic muscle fibers, which can develop
  within the first day of mechanical ventilation.

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Motility of mucocilia in the airways

• Positive pressure ventilation appears to impair
  mucociliary motility in the airways, Bronchial
  mucus transport was frequently impaired and
  associated with retention of secretions and
  pneumonia.

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ALARMS
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Check Alarms and trouble shoot

• Low exhaled volume check cuff, Tubes
• High pressure Secretions in airway, Pt biting
  the tube, kinked, hi Paw/decreased lung
  compliance by bronchospasm, right main stem
  bronchus intubation, pnemothorax, pneumonia),
  Patient coughing and/or fighting the ventilator
  anxiety fear pain.gtgtgtSuction patient, Insert
  bite block, Reposition patients head/neck check
  all tubing lengths, Deflate and reinflate cuff,
  Auscultate breath sounds, Evaluate compliance and
  tube position stabilize tube.

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High Airway Pressure
Paw
Decreased
Increased
pPlateau

• Air Leak
• 2. Hyperventilation
• etc

No Change
Increased

• Aspiration,
• 2. bronchospasm,
• 3. secretion,
• 4. tracheal Tube

• Abdominal distension, 2. asynchronous breathing,
• 3. Atelectasis
• 4.auto peep, 5.pnemothorax,
• 6. P.edema

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FAQ
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1.Pt suddenly develops inadequate alveolar
ventilation, the Ventilator setting is okay. What
causes we should rule out .
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• LIFE
• Lung gt Mucous Plugging of bronchus,
• Pnemothorax
• Internal Tubing gt Dislodgment of ETT,
  Right Main
• stem
  intubation, Plugging of
• tube
• Fight gt agitated
• External Tubing gt Dc from Pt, Kinking,
  Biting

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How much PEEP is usually required
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• Most intubated patients should have 5 mmhg PEEP
  in replacement of Physiological PEEP
• PEEP can be increased 10-15 even 20

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What are the problems associated with PEEP
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• These high pressure can cause Barotrauma like
  subcutaneous emphysema, pnemothorax, Tension
  Pnemothorax, venous return to he Heart Impaired
  as Paw increases

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What Level of PEEP will be tolerated by pt
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• With normal heart 10-15
• With sick heart will tolerate above physiologic
  poorly.

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What is AC Mode
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• The tidal volume and rate is input, however the
  machine senses any patient generated effort and
  follows with machine powered breath.

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What are the draw backs of AC Mode
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• The machine may deliver more breaths /minute than
  the set rate can lead to respiratory alkalosis.

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What is CMV mode
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• Control Mechanical ventilation---Delivers pre
  selected ventilator rate ,tidal volume, Machine
  will not allow the patient to initiate any breath.

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What are the indication of CMV
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• Apnea CNS depression,Spinal cord trauma
• Drug overdose
• Neuromuscular paralysis

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What is CPPV
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• Continuous positive airway pressure with
  PEEP----It is CMV with PEEP

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What is CPAP
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• It is PEEP applied in spontaneous inspiration and
  may be administered with or without mechanical
  ventilation. If applied invasively called PEEP

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What is PSV
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• PSV senses initiation of pt spontaneous breath
  and delivers specified pressure support during
  breath.

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Can drug cause VQ Mismatch
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• Any Pulmonary artery Vasodilator such as sodium
  nitroprusside,nitroglycerin,or nifedipine can
  interior the ability of the lung arterioles to
  constricting response to hypoxia
• The episode may exuberate hypoxia by increasing
  perfusion to un oxygenated area of lung which is
  know as shunting.

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What is HPV
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• Hypoxic Pulmonary Vasoconstriction
• It is the response of pulmonary vasculature to
  alveolar hypoxia.
• Oxygenation is maintain by diverting blood flow
  to well ventilated area of the lung

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What five important Components of determine the
Peak Inspiratory pressure
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• Lung thorax compliance
• Airway resistance
• Delivered tidal volume
• Inspiratory flow rate
• End expiratory pressure

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what level the PIP cause Barotrauma
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• At the level of less 50 rarely the Barotrauma
  occurs
• 50 to 70 the probability is 8
• Above 70 the 43

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The PO2 Low what should be done
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• 1.With atelectasis gtSuction, PEEP, Increase
  Tidal volume.
• 2. P.edema gt Increase C O, Di uresis, Dialysis,
  and add PEEP.
• 3. Increasing FIO2 will not be effective if
  shunting is the cause of hypoxia, but should try
  with fio2 if other treatments are being
  instituted.

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Describe Physiologic State If Blood
pH-7.24,PO2-80,PCO2-61,HCO3-25,O2 Sat 92,BE-0
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• Pure respiratory acidosis

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What clinical Conditions may cause this
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• Inadequate respiratory drive(Over sedation, Head
  injury)
• Inability to maintain Work of breathing
• Airway Obstruction(foreign body, blood ,Mucous
  plug, Bronchospasm)

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Describe Physiologic State If Blood
pH-7.56,PO2-100,PCO2-20,HCO3-24,O2 Sat 99,BE- -1
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• Uncompensated respiratory alkalosis

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What clinical Conditions may cause this
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• Hyperventilation from pain, fever, fear, head
  injury or Psychogenic cause

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Describe Physiologic State If Blood
pH-7.35,PO2-120,PCO2-65,HCO3-35,O2 Sat 98,BE- 8
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• compensated Metabolic Acidosis

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What clinical Conditions may cause this
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• Salicylate Toxic city,
• lactic Acidosis from shock Liver disease
• Uremia
• Methanol Intoxication
• Paraldehyde Intoxication
• Ethylene Glycol poisoning(antifreeze)
• Diabetic ketaacidosis,Diarhea

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Describe Physiologic State If Blood
pH-7.58,PO2-130,PCO2-40,HCO3-35,O2 Sat 99,BE- 15
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• Pure Metabolic Acidosis

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What clinical Conditions may cause this
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• Excessive loss of gastric acid,(vomiting,
  Nasogastric suction)
• Severe Dehydration (Contraction alkalosis)
• Ingestion of alkaline substances(milk alkali
  syndrome)

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References

• Colice, Gene L (2006). "Historical Perspective on
  the Development of Mechanical Ventilation". In
  Martin J Tobin. Principles Practice of
  Mechanical Ventilation (2 ed.). New York
  McGraw-Hill. ISBN 978-0071447676.
• Curtis G treble 

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Thanks

• Shams Ali Shah
• RT prince Sultan cardiac Center Qassim Buraidah