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Mechanical ventilation
In the name of GOD Principles of Mechanical ventilation
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Terminology f: rate of breathing Vt: Tidal volume
VA: Alveolar ventilation VD: dead space = 2.2 ml/ kg FiO2: fraction of inspired O2 PEEP: Positive End Expiratory Pressure PASB : Pressure Above Spontaneous Breathing ASB : Assisted Spontaneous Breathing
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Basic pulmonary physiology
Air that moves in and out of a patient's lungs per minute that is L/min  Minute volume (MV) MV =Vt x f Alveolar ventilation (VA)  in contact with the alveolar-capillary gas exchange interface VA = (Vt - VD ) x f Volume-pressure relation: P = V/C
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Plateau pressure (static pressure)
… is the pressure at the end of inspiration with a short breath hold It should not be exceed 30 cmH2O P plateau ~ 1/compliance (P = V/C) volume = P plateau
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Pressure-time diagram for volume controlled constant flow ventilation
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Peak Airway Pressure (dynamic pressure)
…. is pressure during inspiration So related to both airway resistance and compliance compliance and/or resistance  P peak P peak – P plateau < 4 cm H2O (normal gradient) P peak is a vital sign for mechanically ventilated patients. P peak < 35 cmH2O
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Changes in inspiratory airway resistance
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Paw-peak increased but Plateau pressure unchanged:
1. Tracheal tube obstruction and kinking 2. Airway obstruction from secretions 3. Acute bronchospasm Rx: Suctioning and Bronchodilators
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Changes in compliance In this situation P-P gradient is fixid.
increasing compliance → plateau and peak pressures fall decreasing compliance → plateau and peak pressures rise
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Paw-peak and Plateau pressure are both increased:
1. Pneumothorax 2. Lobar atelectasis 3. Acute pulmonary edema 4. Worsening pneumonia 5. ARDS 6. COPD with tachypnea and Auto-PEEP 7. Increased abdominal pressure 8. Asynchronous breathing
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Decreased Paw-peak: 1.Inadequate gas supply, inadvertent change in setting, system air leak, Tubing disconnection, cuff leak, unintended extubation and failure of the ventilator Rx: Manual inflation, listen for leak 2. Hyperventilation: Enough negative intrathoracic pressure to pull air into lungs may drop Paw-Peak
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Measurements
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Measurements
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P –T curve At the start of inflation, the airway pressure immediately rises because of the resistance to gas flow (A), and at the end of inspiratory gas flow the airway pressure immediately falls by the same pressure (A) to an inflexion point.
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P/T F/T V/T curves in VCV
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Increase in Ppeak–Pplat gradient
Increased airway resistance caused by heat and moisture exchanger (HME) Patient biting endotracheal tube Kinked or twisted endotracheal tube Obstruction of endotracheal tube by secretions, mucus, blood Bronchospasm Obstruction of lower airways
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Schematic of two superimposed pressure-time curves showing a small increase in peak inspiratory pressures (Ppeak) with a greater increase in plateau pressures (Pplat). This is characteristic of decreased lung compliance
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Unchanged or decreased Ppeak–Pplat gradient
Pneumonia Atelectasis Mucus plugging of one lung Unilateral intubation Pneumothorax Pulmonary edema (noncardiogenic and cardiogenic) Abdominal distention/pressure
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Spontaneous Breathing
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Positive End Expiratory Pressure
… is the pressure at the end of expiration Serial Elevated PEEP  P plateau and FRC
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1- Extrinsic PEEP (applied PEEP by MV)
cm H2O and be started on 5 cm H2O It improves the oxygenation not CO2 removal It may be increased 3-5 cmH2O Q min It has some side effects: biotraumas and hemodynamic compromise What is the optimal PEEP? 1- increasing PEEP until a complication occurs 2- assessing P plateau
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Optimal PEEP P-V curve monitoring
Cardiac Output monitoring and Venous Oxygen Saturation If SmvO2 decreases after PEEP application  Drop C.O. In this situation  PEEP and/or tidal volume
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P-V curve Adequate PEEP Inadequate PEEP
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PEEP
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PEEP Disadvantages: 1. Decrease BP & CPP 2. Increase PCO2
3. because alveolar injury is often heterogeneous, appropriate PEEP in one region may be suboptimal in another and excessive in another
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2- Intrinsic PEEP …is incomplete alveolar emptying during expiration due to air trapping Ventilator Factors: High inflation volumes, rapid rate, low exhalation time Disease factors: Asthma, COPD (collapsed airway) And has some effects: Decreased C.O. Alveolar rupture increased work of breathing
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Int. PEEP Int. PEEP may be detected in two ways:
(1) evaluating the flow-time trace (exp. Flow not returned to zero before next breath) (2) disconnecting the patient from the ventilator and listening for additional exhaled gas after an exhalation has occurred.
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Pressure cycled Volume cycled
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Indications for mechanical ventilation
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Loss airway protection
No absolute contraindications Loss of airway anatomy Loss airway protection Respiratory and cardiac Failure Apnea / Respiratory Arrest Inadequate ventilation (acute vs. chronic) Inadequate oxygenation Eliminate work of breathing Reduce oxygen consumption Neurologic dysfunction Central hypoventilation/ frequent apnea Comatose patient, GCS < 8 Inability to protect airway
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Control Mechanisms
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Control mechanisms Spontaneous breathing (PSV)
Pressure targeted ventilation Volume targeted ventilation
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1. Spontaneous breathing:
Setting: FiO2 and PEEP Flow and f is dictated by patient
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2. Pressure-Cycled (targeted):
Alters gas flow and volume  fixed preset airway pressure (Paw) for the duration of a preset inspiratory time (Ti ) Advantage: fixed pressure  limit or eliminate alveolar over-distention and barotraumas One problem: changes in compliance or resistance with fixed Paw  variable received volume
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3 . Volume/ Flow-Cycled (targeted)
Deliver a preset volume of gas ( VT)  Paw is variable Advantage: delivery a constant VT changes in compliance or resistance with fixed volume  changes airway pressure
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There are no clinical outcome studies showing benefit of one breath-targeting strategy over the other. Pressure-targeting provide a variable flow tends to synchronize better with patient effort.
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Modes
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1. Controlled Mechanical Ventilation /Assist Control (CMV/AC) 2
1. Controlled Mechanical Ventilation /Assist Control (CMV/AC) 2. Intermittent Mechanical Ventilation (IMV)/Synchronized IMV (SIMV). 3. Continuous Positive Airway Pressure (CPAP) /pressure support ventilation (PSV)
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Controlled Mechanical Ventilation (CMV)
Assist Control (AC)
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Control Mode Ventilation Continuous mandatory ventilation
Continuous mechanical ventilation Controlled mandatory ventilation Intermittent Positive Pressure Ventilation (Dräger) …is a full support mode (machine breaths) All breaths are supported regardless of initiation of breathing and can be set to VCV and PCV Used for: apneic patients, respiratory muscle weakness and LV dysfunction
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(CMV/AC ) Sensitivity pressure  0.5 to 2 cm H2O (1-3 cm H2O Tintinalli) The higher sensitivity  the greater work of breathing After spontaneous breath  the ventilator`s timer resets from this time
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(CMV /AC) CMV  preferred and most commonly used initial mode for acute phase of respiratory failure in ED but CMV : 1. Poor toleration in awake patients 2. Worsening of volume retention in COPD / asthma
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A/C mode
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2. Intermittent Mechanical Ventilation (IMV)
Synchronized IMV (SIMV)
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SIMV (Dräger, Hamilton)
SIMV (VC) + PS (Maquet) VCV-SIMV (Puritan-Bennett, Respironics) Volume SIMV (Viasys) Intermittent demand ventilation IMV  combination of spontaneous vent. and AC IMV  is a partial support mode This ventilator mode provides breaths at a preset rate (machine breath) similar to the AC mode Can be set to PCV and VCV
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(IMV / SIMV ) But in spontaneous breath  only receive a spontaneous VT with no support from the ventilator and has a high work of breathing The synchronized version of IMV  coordination spontaneous and machine breaths SIMV: 1. To prevent excess VT delivered (stacking)  decreased hyperinflation, barotrauma 2. During exhalation from a spontaneous breath exhalation compromised
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3. Continuous Positive Airway Pressure (CPAP)
pressure support ventilation (PSV)
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Is a partial support mode
Assisted Spontaneous Breathing(Dräger) Spontaneous mode(Hamilton, Puritan-Bennett) Pressure support (Maquet) CPAP (Respironic) Pressure Support Ventilation (Viasys) continuous positive-pressure breathing (CPPB ) EPAP Is a partial support mode Breathing control by the patient (spontaneous mode ) , and peak Paw control by machine (pressure targeted)
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PSV
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PSV / ASB / CPAP Help the patient overcome the resistance of the circuit  decreased work of breathing This is not useful in apnea
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CPAP / PSV / ASB CPAP  the least amount of support and used with IPPV or NIPPV Most commonly used in (COPD) , CHF and obstructive sleep apnea with NIPPV ( via a tight-fitting nasal or full face-mask)
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CPAP / PSV / ASB With IPPV  CPAP is typically used as a weaning mode
The CPAP level when transitioning from IMV/PSV or AC mode should be the PEEP level that was being used Reducing the CPAP below the previous PEEP : Loss of alveolar recruitment Atelectasis Hypoxia Increased work of breathing
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CPAP / PSV In partial support:
CPAP range is from 0 up to 35 cm H20 pressure Some ventilators may deliver PSV that achieves a greater range. The average starting point is: 10 cm H20 Use PSV for approximation of spontaneous Vt and the set Vt for mandatory breaths
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(CPAP) benefits Eliminate the work of breathing
To aid in weaning from IMV-base ventilation and is frequently part of a transition strategy from IMV to CPAP
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Breath type & examples
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DRÄGER Evita CMV
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DRÄGER Evita CMV
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DRÄGER Evita SIMV
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DRÄGER Evita SIMV
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DRÄGER Evita 2 CPAP
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DRÄGER Evita CPAP
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DRÄGER Evita PCV
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DRÄGER Evita 4 PCV
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DRÄGER Evita XL SIMV
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Adjunct Ventilator Settings and curves
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1. Oxygen The fraction of inspired O2 (FiO2) is set in a range from 21% (room air; not generally indicated) to 100% In the ED it is common to start at 100% FiO2 to ensure adequate oxygenation and titrate the FiO2 down to nontoxic levels (FiO2< 60%) following the SaO2 via the pulse oximeter (SaO2> 90%) during first 72 h. some practitioners recommend using 95% O2 as the upper limit of FiO2
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2. Inspiration : Expiration (I:E) Ratio
The normal I:E ratio in a spontaneously breathing, non intubated patient is 1:4 Intubated patients commonly achieve I:E ratios of 1:2
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3. Flow rate (Q ) This is the rate of gas delivery (L/min).
The range of flows that can be achieved by current ventilation is from 10 to 160 L/min. Common flow settings are from 40 to 75 L/min. The higher the flow rate, the faster the ventilator will reach its set volume or pressure. Start at Q=60 L/ min A faster flow rate  decreased ins. time A slower flow rate  decreased exp. time
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Flow-time diagram VCV PCV
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Initial ventilator setting
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Pressure triggering The sensitivity of the trigger can be adjusted by changing the pressure drop required for inspiratory cycling to be triggered, and this can be set to a value between −1 cm H2O (very sensitive) and −20 cm H2O (very insensitive) If the setting is too sensitive, minor fluctuations in breathing circuit pressure (e.g. from cardiac pulsations) can trigger the ventilator inappropriately.
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Flow triggering The reduction in return flow that has to be detected for triggering to occur can be adjusted between 1 (very sensitive) and 10 (insensitive) L/min Flow triggering is considered to require less work from the patient to initiate a breath and therefore may enhance patient comfort and reduce the work of breathing.
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Advanced modes BREATH TO BREATH WITHIN A BREATH
Pressure-regulated volume control (PRVC) Auto flow Volume control plus (VC+) Adaptive pressure ventilation (APV) Variable-pressure control (VPC) WITHIN A BREATH Volume-assured pressure support ventilation (VAPSV) Pressure augmentation
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Other modes High Frequency Ventilation Proportional assist ventilation
Airway Pressure Release Ventilation (Bi-level ventilation)  PCV T high : 4 – 6 s T low : 0.2 – 1.5 s P high : up to 40 cmH2O P low : 10 cmH2O
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NON INVASIVE VENTILATION
TUMS
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TUMS
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Noninvasive Ventilation
For prevention of invasive MV in selected patients No need to definitive airway control Candidates : COPD, CHF, Asthma, hypoxia, DNR patients and Immunocompromised patients 1. the airway must be patent, 2. the respiratory drive must be intact, 3. the patient must be cooperative (i.e., awake and alert). TUMS
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Serial assessment and close monitoring Q 30 min ABG Q 1-2 h
Contraindications: Near arrest Severe GIB Anatomic defect of face Up airway obstruction AMS Risk of aspiration and defect in secretion clearance
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Nasal mask TUMS
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Advantages of NIV The potential benefits of NIV over MV are:
a decrease in potential airway injury decrease in VAP probably a shorter length of stay Eating and speech reserved TUMS
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Disadvantages of NIV Pulmonary baro-trauma (volu-trauma)
pressure necrosis of the facial skin, subcutaneous tissue and musculature and patient discomfort aerophgia  gastric dilation  vomiting and aspiration hemodynamic compromise TUMS
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TUMS
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Bi-level ventilation Bi-level ventilation.
A: Baseline pressure cycles between Plow and Phigh with spontaneous, unsupported, patient breaths during high and low phases. Transition from low to high phase is synchronized to the patient’s inspiration, and transition from high to low phase is synchronized to patient’s expiration. B: As in A, but now inspiratory efforts during the Plow phase trigger support (Psupp).
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Bi-level ventilation Bi-level ventilation.
C: As in A, but now inspiratory effort during both Plow and Phigh phase trigger support which is targeted to the same absolute support pressure (Psupp). If Phigh is greater than Psupp, patient effort during Phigh becomes unsupported. D: As in A, but now inspiratory effort during both Plow and Phigh phase trigger support which is set specifically for each phase,relative to the baseline pressure of the phase.
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Approach to NIPPV In hypoxemia: EPAP + 2 cmHâ‚‚O and fix interval IPAP
In hypercapnia: IPAP cmHâ‚‚O and EPAP= 40% IPAP TUMS
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High flow nasal cannula
… can deliver warm and humidified air up to 40 L/min
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5 Special Circumstances and applying ventilatory support
TUMS
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1. Severe Acute Lung Injury and ARDS
Preferred PCV consider permissive hypercapnia. If able to achieve P02> 60 mm Hg on FiO2<60%, the PCO2 may be allowed to be >40 mm Hg if pH> 7.25. if needed, use NaHCO3 Tv  6 – 8 ml / kg F  20 – 25 / min PEEP  8 Monitor P plateau: if > 30 cm H2O  Tv : 4 ml/kg TUMS
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2. Severe Asthma and COPD The defect is decreased gas flow.
In conventional ventilation use higher flow rate and lower respiratory rate to allow more time for exhalation. Tv  ml / kg F  8 – 10 / min Q 80 l/min PEEP  5 ( % intrinsic PEEP) Detection of intrinsic PEEP with wean and chest compression Optimal P plateau < 30 cmH2O TUMS
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Monitoring of treatment in asthma
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3. Pulmonary edema NIPPV is preferred
If the patient is intubated  PEEP is useful But in hypotensive patients  min. PEEP with continuous evaluation TUMS
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5. Traumatic brain injury
Do not lower PC02 < 35 mm Hg, as it may induce severe cerebral vasoconstriction and lead to cerebral ischemia. The goal is PC02: mm Hg. Acceptable to hyperventilate for a patient with an acute herniation syndrome as a bridging maneuver for definitive therapy. TUMS
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Overdose in healthy patient
General Guidelines for Initial Invasive Ventilator Settings in Various Clinical Settings / Rosen`s EM Mode FIO2 (%) VT (mL/kg) F / min I/E PEEP (cm H2O) Overdose in healthy patient CMV, A/C, IMV, SIMV 95 8–10 10–12 1:2 0–5 Status asthmaticus 5–10 8–12 1:4 2.5–10 COPD exacerbation 1:3–1:4 pulmonary edema 8-10 2.5–15 ARDS 6-8 20-25 2.5-10 Hypovolemic shock - 0-5
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complications Pneumothorax Ventilator induced lung injury
Hemodynamic instability Difficult trigger ventilation Auto-cycling (seizure, shivering) Outstripping and double cycling (demand over Vt) Straining over the ventilator (demand over Q) Coughing Failure to MV
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Approach to res. distress
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Weaning
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Indications for extubation
No weaning parameter completely accurate when used alone Numerical Parameters Normal Range Weaning Threshold P/F > 400 > 200 Tidal volume 5 - 7 ml/kg 5 ml/kg Respiratory rate breaths/min < 40 breaths/min Vital capacity ml/kg 10 ml/kg Minute volume 5 - 7 L/min < 10 L/min Greater Predictive Value NIF (Negative Inspiratory Force) > - 90 cm H2O > - 25 cm H2O RSBI (Rapid Shallow Breathing Index) (RR/TV) < 50 < 100 Clinical parameters Resolution/Stabilization of disease process Hemodynamically stable Intact cough/gag reflex Spontaneous respirations Acceptable vent settings FiO2< 40%, PEEP < 8, PaO2 > 75, pH > 7.25 Disorders characterized by systemic effects of M protein, and direct effects of bone marrow infiltration Common examples of methylation-induced silencing: Imprinted genes (Prader-Willi, Angelmann Syndromes) Inactivated 2nd X chromosome in females DNA methylation results in histone deacetylation, compacted chromatin, and repression of gene activity Methylation can have a profound effect in tumorigenesis by silencing tumor suppressors Marino P, The ICU Book (2/e)
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The cause of respiratory failure is improving or has been eliminated,
Criteria : The cause of respiratory failure is improving or has been eliminated, FiO2 < 0.40 PEEP < 8cm H2O No pressors other than dopamine at <5 μg/kg / min or Epinephrine or NorEpi. at < 0.05 µg /kg / min. TUMS
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weaning
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<105 /L Parameter Normal Adult range Threshold for weaning
PaO2/FiO2 >400 200 Tidal Volume 5-7 ml/kg 5 ml/kg RR 14-18 /min <40 /min Minute Vent. 5-7 L/min <10 L/min Vital capacity 65-75 ml/kg 10 ml/kg Peak Inspiratory Pressure >90 cmH2O (F) >120 cmH2O (M) 25 cmH2O RSBI (f/Vt) <50 /L <105 /L TUMS
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The Problem Wean RAPID BREATHING  1 1. Check Vt
Low Vt  Resume vent. support Vt not low  2 2. Check PaCO2 PaCO2 decreased  sedate (anxiety) PaCO2 not decreased  Resume vent. TUMS
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HYPOXEMIA : May be due to low C.O. HYPERCAPNEA:
ABDOMINAL PARADOX : Inward displacement of the diaphragm during inspiration is a sign of diaphragmatic muscle fatigue HYPOXEMIA : May be due to low C.O. HYPERCAPNEA: Increase in PaCO2-PetCO2 = increase dead space ventilation Unchanged gradient: Respiratory muscle fatigue or enhanced CO2 production TUMS
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Weaning
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Tracheal Decannulation
Successful weaning is not synonymous with tracheal decannulation If weaned and not fully awake or unable to clear secretions, leave ETT in place Tracheal decannulation increases the work of breathing due to laryngeal edema and secretions Do not perform tracheal decannulation to reduce work of breathing TUMS
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Inspiratory Stridor Post extubation inspiratory stridor is a sign of severe obstruction and should prompt re-intubation Laryngeal edema (post-ext) may respond to aerosolized epinephrine in children Steroids have no role Most need reintubation followed by tracheostomy TUMS
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TUMS
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Case management TUMS
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Case 1 An l8-year-old otherwise healthy 60-kg female presents with an overdose of benzodiazepines. She requires intubation for airway protection and ventilatory support. There is no evidence of aspiration or an intrinsic lung problem. TUMS
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With VCV setting Target Vm = 7.2 L / min
It is reasonable to assume a normal need for Vm since she has no evidence of hypoperfusion or infection, and she has not ingested an medications known to cause a metabolic acidosis that would require a higher Vm to buffer by induced hypocarbia. TUMS
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Dräger evAita 2 Patient data Ventilator setting Alarm setting TUMS
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Vt and f F= 12 /min Vt = 600 mL (7-10 mL/kg)
This setting will guarantee the desired Vm even if the patient continues to develop respiratory depression from the benzodiazepine ingestion. TUMS
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Pressure Support Ventilation.
Initiate PSV at 10 cm H20 pressure, and then titrate up or down to achieve a spontaneous breath Vt approximately equal to that of the set Vt. TUMS
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Gas Delivery Waveform: Begin with a decelerating waveform.
Maximal Inspiratory Flow : Set the initial Q at 60 L/min. lower Q(Q = 50 L/min) in hypoxemia higher flow (Q = 70 L/min) in exhalation obstruction (e.g. COPD), then evaluate the resultant Paw-peak. TUMS
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If the Q is reduced to 40 L/min and the Paw-peak remains high, :
If the Vt is appropriate, reduce the flow rate by L/min and re-evaluate; repeat if necessary. If the Q is reduced to 40 L/min and the Paw-peak remains high, : 1) the Vt is, in fact, too large for the available lung mass, 2) there is a tube obstruction (partial) 3) the patient has a pleural space occupying disorder (pneumo-, hemo-, hemopneumo-, or hydro-thorax), 4) the patient requires a different mode 5) there is a ventilator dysfunction TUMS
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Order writing 2 1 Then titrate PSV to achieve Vt spont. 600 ml SIMV
ABG 20 min later 1 SIMV f : 12/ min FiO2 : 95% PEEP : 5 cm H2O ASB / CPAP / PSV : 10 cm H2O Flow : 60 L/min Ramp wave TUMS
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The same patient with PCV setting
Vm = 7.2 L/min Mode = ( in E4 , 2 ) PCV+ SIMV, .PCV. PSV. ASB Q = 160 L/min ( devise adjust the Q in response to the patient`s breath.) Wave = ramp F = 12/ min FiO2= 95% PSV =10 cm H2O PEEP=5 cm H2O (Paw Peak ) =PC+ PEEP =25 PC =[(Paw peak) – PEEP] ×2/3 = (35 – 5)× 2/3 =20 cm H2O TUMS
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Order writing 2 1 PC : 20 cm H2O PEEP :5 cm H2O PSV : 10 cm H2O
Q : max (160) L/min Wave : ramp ABG 20 min later 1 SIMV f : 12/ min PC : 20 cm H2O Ti : 1 s FiO2 : 95 %
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Case 2 A 45-year-old, 70-kg male presents with high fevers, cough, and shortness of breath. The ED portable chest film demonstrates bilateral infiltrates as well as lower lobe air bronchograms. While awaiting admission to the hospital for presumed community-acquired pneumonia, the patient develops hypoxia, suffers respiratory failure, and requires urgent intubation. TUMS
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Mode : SIMV-As before, allow the patient to breathe spontaneously when the short acting neuromuscular blockers or heavy sedative (e.g., etomidate, fentanyl, midazolam) used to facilitate intubation wears off. Target Vm :Given the likely acidosis, this patient's Vm needs to exceed the lower limit of normal value. Thus, a target of 9.8 L/minute is a 40% increase above the baseline . TUMS
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initial f= 14 / min Vt = 700 ml One must evaluate the resultant Paw-peak after starting at this setting. One may also need to reduce the tidal volume and increase the rate if the Paw-peak is high and no other mode of ventilation is available. TUMS
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Fi02 : Begin with FiO2 :95% then titrate.
PEEP : ≥5 (to maintain FRC and alveolar recruitment with V/S consideration ) Flow: A longer Ti is ideal for alveolar recruitment and a slow flow rate will complement the decelerating waveform and further prolong the Ti. Then start with a Q of 50 L/min TUMS
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In PCV : the same MODE & Vm … Only set the Ti & PC (longer Ti)
Start with a higher PSV because the pulmonary compliance is less than the normal lungs. Initiate PSV at 15 cm H20 and titrate to achieve similar Vt with the machine and spontaneous breaths. In PCV : the same MODE & Vm … Only set the Ti & PC (longer Ti) Then reevaluate the patient`s condition TUMS
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The end TUMS
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