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67 Cards in this Set
- Front
- Back
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Normal respiratory rate unvented pt
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12-18 bpm
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normal respiratory rate for a vented pt
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8 - 12 bpm
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Minute Ventilation
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VE = VT x f
Normal minute ventilation is 5-10 L/min Estimated by using 100mL/Kg IBW If PaCO2> 45 (increase minute ventilation via f or VT) If PaCO2<35 (decrease ventilation via f or VT) |
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Inspiratory Flow
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Rate of Gas Flow
As a beginning point, flow is normal set to deliver inspiration in about 1 second (range 0.8 to 1.2 sec). producing an I:E ratio of approximately 1:2 or less (usually about 1:4) This can be achieved with an initial peak flow of about 60L/min (range of 40 to 80 L/min Most importantly, flows are set to meet a patient’s inspiratory demand |
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Positive End Expiratory Pressure (PEEP)
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Initially set at 3 - 5 cm H20
Restores FRC and physiological PEEP that existed prior to intubation Subsequent changes are based on ABG results Useful to treat refractory hypoxemia |
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Contraindications for therapeutic PEEP (>5 cm H2))
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Hypotension
Elevated ICP Uncontrolled pneumothorax When coding, DC Peep |
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FIO2
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Initially 100%
Severe hypoxemia Abnormal cardiopulmonary functions post- resuscitation smoke inhalation ARDS After stabilization, attempt to keep FIO2 < 50% Avoids oxygen-induced lung injuries absorption atelectasis oxygen toxicity Patients with mild hypoxemia or normal cardiopulmonary function Drug overdose uncomplicated postoperative recovery FIO2 of 40% Same FIO2 prior to mechanical ventilation |
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Initial Ventilator Settings for PCV
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Rate, TI, and I:E ratio are set in PCV as they are in VV
The pressure gradient (PIP-PEEP) is adjusted to establish volume delivery Initial Pressure setting Set at P plat during VV - adjust to achieve desired VT or Use PIP during VV minus 5 cm H20 (PIP-5) as a starting point adjust to achieve desired VT or If volume readings not available, initiate pressure at 10-15 cm H20 adjust to achieve desired VT In PCV P alv cannot go higher than set pressure, therefore keeping PIP<30 cm H20 can help avoid alveolar overinflation |
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Dual control within a breath
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switches from pressure-controlled to volume-controlled in the middle of the breath.
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Dual control breath-to-breath
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Ventilator operates in either the PS or PC modes
The difference: pressure limit increase or decrease in an attempt to maintain a selected VT (based on the VT of the previous breath) Like having a therapist at the bedside who increases or decreases the pressure limit of each breath based on the VT of the previous breath |
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VAPS
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(Volume assured pressure support)
Esprit Mandatory breaths or PS breaths Meant to combine the high variable flow of a pressure-limited breath with the constant volume delivery of a volume-limited breath During pressure support: VAPS is a safety net that always supplies a minimum VT Breath: initiated by the patient or may be time-triggered Once the breath is triggered, ventilator will attempt to reach the PS setting as quickly as possible This portion of the breath is the pressure control portion and is associated with a rapid variable flow: may decrease WOB |
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VAPS: Settings
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RR
Peak flow PEEP FIO2 Trigger sensitivity Minimum desired Vt Pressure support setting = plateau pressure obtained during a volume controlled breath at the desired Vt Once the delivered VT = Set VT, pressure supported breaths are decreased. Breath is pressure-limited at the pressure-support setting and is flow-cycled at 25% of the initial peak flow If the patient’s inspiratory effort decreases, microprocessor decides minimum set VT will not be delivered-flow decelerates and = set peak flow Breath changes from a pressure-limited to a volume-limited breath |
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PRVC
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Pressure Regulated Volume Control
Volume Targeted, pressure control breath. (APV on Hamilton) |
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Synonyms of PRVC
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Adaptive Pressure Ventilation (APV: Hamilton Galileo; Hamilton Medical, Reno, NV)
Autoflow (Evita 4: Drage Inc; Telford, PA) |
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Settings for PRVC
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Minimum respiratory rate
Target tidal volume Upper pressure limit: 5 cm H2O below pressure alarm limit FIO2 Inspiratory time or I:E ratio Rise time PEEP |
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PRVC: pressure limit
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The pressure limit will fluctuate between 0cm H2O above the PEEP level to 5 cm H2O below the high-pressure alarm setting
The ventilator will signal if the tidal volume and maximum pressure limit settings are incompatible |
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Advantage of PRVC
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Decelerating inspiratory flow pattern
Pressure automatically adjusted for changes in compliance and resistance within a set range Tidal volume guaranteed Limits volutrauma prevents hypoventilation Maintaining the minimum Ppk that provides a constant set Vt Automatic weaning of the pressure as the patient improves Limited staffing - maintain a more consistent VT as compliance increases or decreases |
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Disadvantages of PRVC
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Pressure delivered is dependent on tidal volume achieved on last breath
Intermittent patient effort = variable tidal volumes Asynchrony with variable patient effort Less suitable for patients with asthma or COPD If in assisted breaths the pt’s demand increases, pressure level will decrease at a time when support is most necessary Mean airway pressure will decrease resulting in hypoxemia |
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PRVC Evidence
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No advantage of PRVC over PCV
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Automode
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Automatically shifts between controlled ventilation, supported ventilation & spontaneous ventilation
VC to VS PRVC to VS PC to PS |
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Adaptive Support Ventilation
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(Galileo)
Very versatile mode Based on minimal WOB concept (The Otis Equation) Electronic ventilator management protocol that may improve the safety and efficacy of mechanical ventilation automatic adaptation of the ventilator settings to patient’s passive and active respiratory mechanics |
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Adaptive Support Ventilation: Principle
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For a given level of alveolar ventilation, vent chooses the particular RR that will be least costly in terms of respiratory work.
Adaptive Support Ventilation (ASV) RR: REspiratory rate RC: Respiratory time constant VA: Alveolar ventilation VD: Dead space volume |
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ASV Input
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Ideal body weight: determines dead space
High-pressure alarm: 5 cm H2O above PEEP to 10 cm H2O below set Pmax Mandatory RR PEEP FIO2 Insp time (0.5-2 secs), exp time( 3 x RCe to 12 secs) |
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ASV adjusts
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Inspiratory pressure
I:E ratio Mandatory respiratory rate maintain the target VE (according to IBW) and RR, to avoid both rapid shallow breathing and excessive inflation volumes |
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ASV
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Delivers 100 mL/min/kg of vE for adult and 200mL/min/kg for children: setting knowns as the % minute volume control
Can be set from 20% to 200% Allows the clinician to provide full ventilatory support or to encourage spontaneous breathing and facilitate weaning Variables are measured on a breath-to-breath basis and altered bh the ventilators algorithm to meet the desired targets. If patient breathes spontaneously, ventilator will pressure-support breaths Spontaneous and mandatory breaths can be combined to meet the VE target |
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USES of ASV
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Initially designed to reduce episodes of central apnea in CHF: improvement in sleep quality, decreased daytime sleepiness
Can be used for pts who are at risk for central apnea like those with brain damage. |
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ASV Evidence
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standard management for rapid extubation after cardiac surgery
decreased ventilatory setting manipulations decreased high-inspiratory pressure alarms Outcome: same |
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Proportional Assist Ventilation
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Espirit, PB 840)
Pressure control Patient triggered Pressure limited Flow cycled similar to cruise control Position of accelerator changes to keep speed constant Major impediment is accurate measurement of elastance & resistance breath to breath PAV is always patient triggered: backup reqd ARDS: Further studies are required REsponse to hypocapnia: In ACV ability to reduce VT is impaired, preserved during PAV |
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Airway Pressure Release Ventilation (Bi-Level)
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(Servio I)
Ventilator cycles between two different levels of CPAP - an upper pressure level and a lower level The two levels are required to allow gas to move in and out of the lung Baseline airway pressure is the upper CPAP level, and the pressure is intermittently “released” to a lower level, thus eliminating waste gas Mandatory breaths occur when the pressure changes from high to low Spontaneous breathing: transition of pressure from increase to decrease results in tidal movement of gas Time spend at low pressure (short expiratory time): prevents complete exhalation; maintains alveolar distension |
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APRV SET UP
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Expiratory time variable: decrease enough to prevent derecruitment & increase enough to obtain a suitable VT (0.4 to 0.6s) - Target VT (V-6ml/kg)
If the VT is inadequate - ⇨ expiratory time is lengthened If VT too high (>6ml/kg) ⇨ expiratory time is shortened |
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APRV Settings
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Phigh level set at the MAP level from the previous mode (pressure control, volume control)
Starting off with APRV ⇨ start high (28 cm H2O or less) and work way down. Higher transalveolar pressures recruit the lungs Low PEEP is set at 0-5 cm H2O The inspiratory time is set at 4-6 seconds (the respiratory rate should be 8 to 12 breaths per minute - never more) I:E ratio: at least 8:1 and Time at low pressure level should be brief (0.8 sec) Neuromuscular blockade should be avoided: the patient s/b allowed to breath spontaneously (beneficial) The breaths can be supported with pressure support - but the plateau pressure should not exceed 30cm H2O |
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APRV Weaning
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Two different ways to wean
If lung mechanics rapidly return to normal, patient should be weaned to pressure support. If ARDS is prolonged ⇨ the high CPAP level is gradually weaned down to 10cmH2O ⇨ standard vent wean “Drop and Stretch” - (lower high levels and lengthen expiratory time) |
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APRV Benefits
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Preservation of spontaneous breathing and comfort with most spontaneous breathing occurring at high CPAP
⇩WOB ⇩ Barotrauma ⇩ Circulatory compromise Better V/Q matching |
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APRV Evidence
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APRV vs pressure controlled conventional ventilation patients with ALI after trauma (N=30)
Randomized controlled, prospective trial ⇩ ICU days, ventilator days, better gas exchange, hemodynamic, lung comp, ⇩Need for sedation and vasopressors Oxygenation was significantly better in APRV group before and after proning: sedation use and hemodynamics were similar |
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Mandatory Minute Ventilation (MMV)
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Closed loop ventilation: ventilator changes it’s output based on a measured input variable
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MMV Evidence
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No statistically significant differences for EtCO2, minute volumes, PIP & PEEP
⇩mechanical breaths, MAP generated with MVV |
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Automatic Tube Compensation (ATC)
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Compensates for the resistance of the endotracheal tube
ATC attempts to compensate for ET resistance via closed-loop control of calculated tracheal pressure Inputs type of tube: ET or tracheostomy, and the percentage of compensation desired (10-100%) Improved patient comfort as compared with that for pressure-support ventilation |
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ARDS
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Acute Respiratory Distress Syndrome
a clinical syndrome characterized by a pulmonary disorder resulting from diffuse injury to the alveolar-capillary membrane. Acute Lung Injury (ALI) has been used as a term for hypoxemic respiratory failure, a severe version of which is ARDS |
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Criteria of ARDS:
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Acute onset.
Bilateral diffuse pulmonary infiltrates on chest x-ray. Bedside finding of tachypnea, dyspnea and crackles Pulmonary Capillary Wedge Pressure < 18mm Hg or no evidence of LA hypertension. PaO2/FIO2 < 300 = ALI PaO2/FIO2 < 200 = ARDS One or more underlying disease process known to be associated with ARDS. |
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Management of ARDS
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The cornerstone of treatment is to keep the PaO2 > 60mmHg, without causing injury to the lungs with excessive O2 or volutrauma.
Pressure control ventilation is more versatile than volume control, although breaths should be volume limited, to prevent stretch injury to the alveoli 3 major ARDS strategies involve manipulation of: #1 - MAP #2 - PEEP levels #3 - FIO2 |
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Ventilation Strategies in ARDS
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Keep the PaO2 over 60mmHg or over 50mmHG at the very least
Avoid volutrauma, barotraumas and biotrauma (VIL), by keeping the tidal volumes in the 4-6ml/kg range and airway plateau pressure below 30 cmH2O Peak airway pressure 20-40 cmH2O or <20 cmH2O above PEEP PEEP values of 2-3 cmH2O above lower inflection point (pflex) Lower respiratory rate Inverse ratio ventilation Permissive hypercapnia Low inspiratory flow |
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Advantages of PCV in ALI
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More even gas distribution
Control of MAP |
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Control of mean airway pressure
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It is possible to increase the mean airway pressure, by prolongation of the inspiratory time. Auto-PEEP -
Auto-Peep is harmful in COPD patients due to it’s increase in WOB-but can be used as a tool in treating patients with ARDS. Inverse ratio ventilation, is a key part of the open lung approach to ARDS and is the basis of some pressure controlled modes-BiLEVEL/APRV |
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Open Lung Approach
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Phasic opening and closing of collapsed alveoli causes further injury to lung tissue. (Shear injury). The low tidal volume approach limits the amount of phasic stretch of lung units in inspiration, to prevent (VIL)
Open lung approach, stenting the airways open at end expiration, using PEEP just above “Pflex” (the lower inflection point on the pressure volume curve). |
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PEEP Endpoints:
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Attempt to find the best level of PEEP that delivers the highest PaO2 while avoiding:
Decreased venous return Decreased CO Decreased B/P Increased Shunting Increased VD/VT Barotrauma Volutrauma |
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Alternative Ventilation strategies used in ARDS
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Recruitment maneuvers
Proning PLV HFOV TGI iNO ECMO |
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Recruitment Maneuver
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Sustained increase in airway pressure with the goal to open collapsed lung tissue, after which PEEP is applied sufficient to keep the lungs open
CPAP 30-35 cm H2O for 30 seconds |
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Proning
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Prone position improves ventilation-perfusion matching by taking a ventilated patient from the supine position and turning them on their stomach
Redistributing ventilation to area of better perfusion (dependent or down) More homogenous and expiratory lung volume (EELV) Decreases VIL |
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Proning: Does it work?
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No overall mortality benefit for prone, but analysis does show a temporary improvement in oxygenation (increase in PaO2)
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Partial Liquid Ventilation
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Partial liquid ventilation is a complex and labor intensive procedure.
Requires pt be sedated and paralyzed The FRC is filled with the liquid, and the patient ventilated above it. PLV has the added advantage of lavaging the airways and removing cellular debris In ARDS ther is increased surface tension which can be eliminated by filling the lungs with liquid (PFC) Perflurocarbon: colorless, clear, odorless, inert, high vapor pressure insoluble in water or lipids Liquivent Showed improved compliance and better survival Mechanism of Action Reduces surface tension alveolar recruitment - liquid PEEP Selective distribution to dependent regions increases surfactant phospholipid synthesis and secretion Anti Inflam. properties Improvement in compliance may simply be due to recruitment of alveoli but may be also due to a direct effect on surface tension Other postulated benefits: Barrier against infection washes out inflammatory debris 2 published adult trials of PLV in ARDS have confirmed its s |
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High Frequency Oscillation:
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full tidal volume ventilation, with no cyclic opening and closing of lung units
Rates of 180-900 breaths per minute Lower peak inspiratory pressures for a given mean airway pressure as compared to CMV |
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Lower and upper inflection points:
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At the lower end of the curve, the alveoli are at risk for derecruitment and collapse
At the upper end of the curve the alveoli are at risk of alveolar overdistension |
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Indications for HFOV
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Inadequate oxygenation that cannot safely be treated without potentially toxic ventilator settings and , thus, increased risk of VALI.
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Relative Indications for HFOV
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Alveolar hemorrhage
Sickle cell disease in acute chest syndrome Large air leak with inability to keep lungs open Inadequate alveolar ventilation with respiratory acidosis |
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Clinical Goals of HFOV
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Reasonable oxygenation to limit oxygen toxicity
SAO2: 86 to 92% PAO2: 55 to 90 mm Hg Permissive hypercapnia Allow PaCO2 to rise, but keep arterial pH 7.25 to 7.30 “normal pH, PaCO2, & PaO2 are indicators of OVER ventilation!! |
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The 2 primary variables that control oxygenation are
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FIO2
Mean airway Pressure (mPaw) ** Along with manipulating mPaw & FIO2 - periodic recruitment maneuvers may be helpful ** |
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Mean Airway Pressure (mPaw)
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Use to optimize lung volume and, thus, alveolar surface area for gas exchange
Utilize mPaw to: recruit atelectatic alveoli prevent alveoli from collapsing (derecruitment) Although the lung must be recruited, guard against overdistension. |
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HFOV Oxygenation - Clinical Tips
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Increase mPaw by 1-4 cm H2O to achieve optimal lung volume.
Optimal lung volume is determined by: increase in SAO2 allowing the FIO2 tYou should be able to wean the FIO2 to < 60% within the first 12 hours of HFOV If unable to wean FIO@ consider: A recruitment maneuver (sustained inflation) Increasing the mPaw o be weaned |
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Three variables that control ventilation:
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Tidal Volume
Frequency Amplitude |
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Wiggle Factor
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Start amplitude in the 30’s and adjust until the “wiggle” extends to the lower level of patient's groin.
Adjust in increments of 3 to 5 cm H2O subjectively follow the wiggle objectively follow transcutaneous CO2 and PaCO2 |
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Ideal Body weight calculation
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Males: 106 + [6 x (height in inches - 60)]
Females: 105 + [5 x (height in inches - 60)] |
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Dependence/Failure to Wean
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Cardiovascular Function
ischemia heart failure Metabolic Derangements Hypophosphatemia Hypocalcemia Hypomagnesemia Hypothyroidism (severe) Nutrition Poor-protein catabolism overfeeding-excess CO2 Deconditioning |
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Weaning Strategies
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Start as soon as possible
Success depends generally on Strength of Respiratory muscles Load applied Drive to breathe Has the problem which led to intubation been resolved? Is there a new problem? Identify those factors contributing to dependence that are potentially reversible Sedative-based depression of respiratory drive can lead to inappropriately prolonged dependence on MV |
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Initiate Weaning When there is:
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Adequate Oxygenation
PaO2/FIO2 > 150-200 Vent settings: PEEP <8 and FIO2 < 0.5 pH >7.25 Hemodynamic stability Ability to initiate an inspiratory effort Sedation (esp. with respiratory depressing drugs) has itself been weaned No excessive secretions |
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Methods of Weaning
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Synchronized Intermittent Mandatory Ventilation (SIMV) - no longer the preferred method
Pressure Support Ventilation (PSV) SBT (NBRC preferred method) No support CPAP PS |
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Types of SBTs
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No vent support
Low level of CPAP-closing pressure Low level of PS-airway resistance |
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Weaning Failure
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HR > 140 bpm or a sustained increase of > 20%
RR > 35 breaths/min for >5 min O2 Sats < 90% for > 30s HR with a sustained decrease of > 20% SBP> 180 for 5 min SBT < 90 for 5 min Clinical features: Anxiety, agitation, diaphoresis NB: May not be due to weaning failure and should be treated appropriately |
