RSPT 2372 Ch 3 Full lecture - Principles of MV - PDF

RSPT 2372 Intro to MV Chapter 3 Principles of MV Objectives Summarize the history of events that led to modern mechanical ventilation. Contrast the differences between positive and negative pressure ventilation. Recognize differences in patient interface when considering invasive and nonin...

RSPT 2372 Intro to MV Chapter 3 Principles of MV Objectives Summarize the history of events that led to modern mechanical ventilation. Contrast the differences between positive and negative pressure ventilation. Recognize differences in patient interface when considering invasive and noninvasive mechanical ventilation. Define the timing points that constitute a breath and calculate the respiratory rate from TI and TE. Describe alveolar and dead space ventilation and calculate E and A. Interpret changes in volume, airflow, alveolar and intrapleural pressure over the course of a single breath. Describe the differences between an iron lung and a chest cuirass. Identify the components of a ventilator circuit and the mechanical events during lung inflation and deflation during delivery of a positive pressure breath Objectives Identify the components of a ventilator circuit and the mechanical events during lung inflation and deflation during delivery of a positive pressure breath. Describe the effects of alterations in lung mechanics (CST and Raw) on volume and pressure in volume and pressure control modes. Predict changes in peak inspiratory pressure and plateau pressure when either CST or Raw are altered. Define PEEP and describe its influence on gas exchange and hemodynamics. Describe the variables of interest in an optimal PEEP study. Describe patient scenarios that will lead to increased mean airway and peak inspiratory pressures. Objectives Define pressure support ventilation (PSV) and describe its influence on the work of breathing (WOB). Describe the variables that can be trigger inspiration during mechanical ventilation. Describe the variables that can cycle a breath from inspiration to expiration. Contrast the differences between PC-AC and VC-AC. Contrast the differences between PC-IMV and VC-IMV. Describe the use of automatic tube compensation (ATC). Identify dual modes of ventilation.  Objectives Interpret changes in volume, airflow, alveolar and intrapleural pressure over the course of a single breath. Describe the differences between an iron lung and a chest cuirass. Identify the components of a ventilator circuit and the mechanical events during lung inflation and deflation during delivery of a positive pressure breath. Describe the effects of alterations in lung mechanics (CST and Raw) on volume and pressure in volume and pressure control modes. Predict changes in peak inspiratory pressure and plateau pressure when either CST or Raw are altered. Define PEEP and describe its influence on gas exchange and hemodynamics. Objectives Describe the variables of interest in an optimal PEEP study. Describe patient scenarios that will lead to increased mean airway and peak inspiratory pressures. Define PRVC and VAPS. Describe inspiratory flow waveforms used in mechanical ventilation. Determine the ventilator variables that affect Pao2, pH, and Paco2. Identify the alarms that require clinician adjustment and the levels of priority assigned. Describe the rationale for a sigh breath. Explain the effects of positive pressure ventilation on the lung. Objectives Explain the effects of positive pressure ventilation on the cardiac/cardiovascular system. Describe the central nervous system (CNS), renal, and gastrointestinal effects of positive pressure ventilation. Explain the importance of appropriate sedation protocols during weaning from mechanical ventilation. Describe the influence of Paco2 on intracranial pressure (ICP). Identify the effects of sleep disruption on the ICU patient. List the complications of mechanical ventilation and explain each. Introduction to Mech Vent 1952 Copenhagen polio Negative pressure Negative pressure ventilation ventilation outbreak 50 new admits per day No artificial airway; introduced simple and easy to use Mortality rate 87% 1928 1932 1500 Medical students gave bag mask ventilation (positive 1940s and 1932 1950s pressure) Polio epidemic 165,000 hours “Iron lung” by John Emerson across Europe and US Decreased mortality by 500,000 ppl/year 25% dead or paralyzed Negative pressure Use of positive pressure vents in large halls ventilation due to polio Introduction to Mech Vent Positive pressure ventilation is now the predominate form of mechanical ventilation Bird & Bennett valve Advantages: Less space required, patient access, set precise tidal volume (VT) and backup RR 1960s and early 1970s Volume ventilators available first Time triggered Later patient triggered VILI Ventilator-induced ling injury Understanding cellular inflammatory mediators Large volumes and pressures Applied VT used to be 10-15 mL/kg Now 4-8 mL/kg Introduction to Mech Vent Main goal of Appropriate Additional methods to mechanical ventilatory support reduce VILI: ventilation: depends on: Appropriate PEEP Oxygenation Underlying disease Lung recruitment Ventilation process strategies Length of resolution Permissive of disease process hypercapnia Expected Outcomes Newer pressure limiting modes NIV (Noninvasive Ventilation) Ventilation Gases of interest Nitrogen, oxygen, carbon dioxide Ventilation can be defined as bulk movement of gas into and Refers to amount of oxygen that is out of the lungs. Volume of consumed by the body in a given period of Oxygen time Measured in L/min or mL/kg Uptake (VO2) Normal 250 mL O2/min Volume of Represents the amount of carbon dioxide produced and exhaled by the body in a Carbon given time period dioxide Output Measured in L/min or mL/kg Normal 200 mL CO2/min (VCO2) Inert gas; does not cross AC membrane Nitrogen EXCEPT high altitudes Ventilation Ventilatory cycle One single inspired volume of air + One single volume of expired air = Total cycle time (TCT) (6) Ttot = Ti + Te Ti = when inspiratory flow moves from 0 to peak and back to 0 at end inspiration (2) Te = begins at end inspiration or 0 until next inspiratory cycle (4) Generally Te longer than Ti May include a pause at 0 Ventilation The timing of the ventilatory cycle and its relationship with inspiratory –to-expiratory ratio (I:E ratio) Understanding I time, E time, TCT, and I:E ratio 20 minutes TCT and How to calculate 6 minutes Ventilation Normal adult Normal adult tidal Normal minute respiratory rate volume (VT) = ventilation (MV)= (RR)= 400 - 700 mL or 7 12 bpm 6 L/min or mL/kg of ideal Range 12-20 Range 5-10 L/min body weight breaths/min VE (MV) = VT x f (IBW) Ex. 500 AKA PBW = mL/breath x 12 predicted body breaths/min = weight 6000 mL/min or 6L/min Ventilation Only about 70% of VT reaches alveoli and participates in gas exchange Alveolar ventilation per breath (VA) Remaining 30% fills conducting airways Nares to terminal bronchioles 150 mL/breath About 1ml/lb IBW (VD ant) Anatomic deadspace VD alv alveolar deadspace= alveoli that are ventilated but not perfused VD phys physiologic deadspace = VD ant + VD alv Represents all the inspired gas that DOES NOT participate in gas exchange Ventilation Alveolar ventilation A = (VT – VDphys) × f Ex. (500 mL – 150 mL) x 12 breaths/min = 4200 mL/min or 4.2 L/min Direct relationship between alveolar ventilation, CO2 production and arterial Paco2 A = (0.863 × CO2) ÷ PaCO2 Ex. (0.863 x 200) A increases = CO2 decreases And vice versa As CO2 increases, VA must also increase in order for PaCO2 to remain constant  VE & VA Minute Ventilation & Alveolar Venilation Spontaneou s Breathing Done without conscious awareness Timing and flowrate vary Sleep/wake state and activity Central nervous system (CNS) Phrenic nerves Innervate diaphragm Inspired VT = 500 mL/breath Cough, sneeze, sigh, or exercise=larger volumes Inspiratory cycle of 1 second Average flow rate.5 L/sec or 30L/min  Spontaneous Breathing Diaphragm contracts and descends ↓ intrapleural and intrathoracic pressure Quiet respiration intrapleural pressure -5 cm H2O at passive end expiration -10 cm H2O during inspiration Normal lung-thorax system compliance 100 mL/cm H2O -5 cm H2O press change = 500 mL/breath Normal spontaneous breathing Inspiration =Alveolar press below atmospheric (neg) Expiration Pressure = above atmospheric changes (pos)& exp gas allow for insp This Photo by Unknown Author is licensed under CC BY flow  Negative Pressure Breathing Mechanical ventilation can be invasive or noninvasive Iron Lung Video of the Iron lung United Hayek’s Biphasic Cuirass Ventilator Video of BCV Bronchial hygiene HFCWO This Photo by Unknown Author is licensed under CC BY-NC Cough-assist  Positive pressure breathing Patient “Y” Require a sealed airway The inspiratory limb carries ETT, Trach, Mask gas from the ventilator to the “Y” connector and Cuff endotracheal tube. The Prevents dislodgement expiratory limb is protected Supports resuscitation bag with a one way valve which closes on inspiration to ensure ventilation that only expired gases flow Function of ventilator through the expiratory limb. Heated humidification is required for intubated patients. This Photo by Unknown Author is licensed under CC BY Positive pressure breathing Inspiration Airway pressure ↑ Dependent on machines set parameters and the lung compliance and and resistance Larger Vt = greater peak pressure Lower lung compliance = ↑ Peak and Plateau pressures Expiration Expiratory valve Closes during Inspiratory phase Positive pressure breathing Respiratory Therapists adjust: Flow, volume, time, pressure To provide optimal gas exchange while minimizing the risk of barotrauma Untrained or unexperienced personnel should NOT make changes Ventilator not functioning properly Disconnect and use ambu bag to manually ventilate Troubleshoot  Peak Inspiratory Pressure (PIP) the highest proximal airway pressure attained during the inspiratory phase Pressure control ventilation (PC) PIP is set on the vent; volume varies Volume control (VC) ventilation PIP varies based on set tidal volume (VT) Influenced by: Inspiratory flow, inspiratory flow waveform, resistance of the This Photo by Unknown Author is licensed under CC BY-SA-NC ventilator circuit/endotracheal tube, and lung mechanics (compliance and resistance). Maintaining PIP < 35 cm H2O Decrease risk of barotrauma Box 3-3 pg 103 Plateau pressure (Pplateau) Measured during Inspiratory hold maneuver in Determined by elastic lung tissue recoil in VC absence of airflow = static lung compliance Inspiratory hold for 1 second or less (CST) during VC Under static conditions, Pplateau = alveolar CST = VT / Pplateau – baseline pressure pressure (smallest airways) Used for the calculation of static compliance and airway resistance PIP – Pplateau = airways resistance (RAW) RAW = PIP – Pplateau / Inspiratory flow (L/sec) Baseline Pressure and PEEP Resting airway pressure Baseline pressure same as ambient pressure = 0 Baseline pressure > ambient pressure = PEEP PEEP Maintain alveolar volumes during expiration Prevent alveolar collapse during This Photo by Unknown Author is licensed under CC BY-NC-ND expiration Improve oxygenation Extrinsic PEEP Set intentionally AutoPEEP or Intrinsic PEEP Airtrapping AKA dynamic hyperinflation Incomplete emptying of lungs during expiration Measured with expiratory pause maneuver Can lead to ↑ mean airway pressure (MAP) Patients with obstructive disease prone during MV COPD  Optimal PEEP Appropriate level of PEEP needed to improve and maintain lung volumes and improve oxygenation for patients with acute restrictive pulmonary disease PEEP (3 to 5 cm H2O) Suggested for most MV patients AKA “physiologic PEEP” Achieving optimal PEEP Increase PEEP incrementally until adequate O2 Caution with high PEEP Hypotension Hypovolemia Increased Intracranial pressure (ICP) This Photo by Unknown Author is licensed under CC BY-SA Mean Airway Pressure (Paw) Average pressure in the airways through out respiratory cycle Area under the curve Increase Paw by: Increasing Ti Increase I:E ratio Decrease Te Increase VT Increased intrinsic PEEP AutoPEEP Decreased spontaneous breathing Down ramp decreasing flow pattern Low lung compliance High airway resistance (RAW) Paw = ½ (PIP – PEEP) x (TI / TTOT) + PEEP  Invasive vs. Noninvasive Similarities Differences Positive pressure Cost Must have spontaneous Measuring volumes effort Airway pressure and flow sensing NIV capabilities Apneic patient MV Interface ETT/Trach = MV Mask = NIV Thursday, February 13, 2025 Sample Footer Text 30  Ventilator Principles Pneumatically powered Ventilator powered by high pressure gas source Electrically powered Ventilator powered by electricity Internal compressors, Blowers, Pistons, or bellows Ventilator control systems Pneumatic valves Electrical circuits Micropressor controls Regulate oxygen concentration and gas flow to patient Thursday, February 13, 2025 Sample Footer Text 31  Pneumatically Powered Ventilators Require compressed gas Air, oxygen, or both Modern day Both Micropressor-controlled valves Provide desired oxygen concentration AKA Pneumatically powered micropressor-controlled ventilators Thursday, February 13, 2025 Sample Footer Text 32  Electrically Powered Ventilators First truly sophisticated modern day vent Precise control of: FIO2 VT RR Inspiratory flow Ti Efficient, safe, and reliable Allowed for the development of sophisticated approach to critical care Thursday, February 13, 2025 Sample Footer Text 33  Control Systems Battery back-up Generally uses a combination Some batteries last 2 hours of pressure and electrical/micropressor- Battery issues controlled systems to shape Faulty battery level and deliver the breath. Not keeping a charge Open loop Back up battery does not respond DOES NOT incorporate a Bag mask ventilate feedback signal Closed loop Some vents have onboard gas compressor Adjusts gas flow based on Liquid oxygen systems measured values Thursday, February 13, 2025 Sample Footer Text 34  Control systems Control panel or User interface Mechanical or virtual knobs Buttons Switches To adjust parameters Parameters to adjust Mode FIO2 VT or PC level RR Inspiratory flow/Ti PEEP Pressure support PS Alarms Vent graphic displays Thursday, February 13, 2025 Sample Footer Text 35  36 Trigger variable Mechanism by which a ventilator initiates a patient breath based on change in pressure or flow Ventilator Trigger can be: time (machine-initiated breath) Variables: patient triggered (patient initiated) Breath Patient initiated breaths can be pressure triggered or flow triggered Trigger Neurally adjusted ventilatory assist (NAVA) uses electrical activity of the diaphragm to trigger a breath Thursday, February 13, 2025 Sample Footer Text  Pressure Trigger Patient should be able to Typical pressure trigger.5 to 1.5 cm H2O trigger a breath easily Based on patient effort But not too sensitive Newer vent based on set PEEP Trigger -1.0 = PEEP -1 Auto-triggering Requires effort and contributes to WOB Setting Trigger work = Excess water in Increase in WOB caused by patient circuit triggering Patient movement Auto-triggering can cause Thursday, February 13, 2025 Sample Footer Text hyperinflation and asynchrony37  38 Pressure triggering may not function Pressure Trigger properly in the presence of autoPEEP due to air trapping and trigger work may increase. Thursday, February 13, 2025 Sample Footer Text  Flow Trigger based on a change in airflow from baseline during expiration caused by a patient’s inspiratory effort Bias flow moving through the circuit during expiration Example: 8 L/min bias flow; trigger 2 L/min means when circuit flow is 6 L/min inspiration is initiated Thursday, February 13, 2025 Sample Footer Text 39  Time Trigger Time triggering is based on the set machine respiratory rate Mandatory set RR Mandatory breaths: Time- or patient-triggered breaths initiated and cycled by the ventilator Types of modes Control mode: Time-triggered breaths only Assist mode: Patient-triggered breaths only Assist/control mode: Both patient-triggered or time triggered breaths Examples: VC/CMV, PC/CMV Thursday, February 13, 2025 Sample Footer Text 40  Cycle Variables method by which inspiration is Breath may be: cycled off or stops Pressure limited and FYI Trigger is to start inspiration pressure cycled PCV in assist mode AKA the changeover from Pressure limited and time inspiration to expiration cycled Pressure Control Breath may be cycled by: Ventilation volume Pressure limited and flow pressure cycled time Pressure Support flow Ventilation Thursday, February 13, 2025 Sample Footer Text 41 Patient Cycling Spontaneous breaths: The patient controls both the initiation of the breath and breath termination Patient triggered, patient cycled Used to relieve imposed WOB due to increased airway resistance Pressure support ventilation (PS) Automatic Tube Compensation (ATC) Support inspiration Cycling to exhalation (Patient comfort and synchrony Adjust rise time Flow termination Thursday, February 13, 2025 Sample Footer Text 42 Mandatory Breath Cycling Mandatory breaths: The ventilator delivers the same breath type with every breath Start and/or end of inspiration is determined by ventilator RR or Ti Time or patient triggered Pressure or volume controlled Cycled using time, pressure, or volume Thursday, February 13, 2025 Sample Footer Text 43  44 Switch from inspiration to exhalation when a clinician set inspiratory pressure is attained Used during VC mode Preset press limit (Pmax) Cycle pressure VT variable constant ↓ lung compliance, ↑ Cycle to exhalation earlier, ↓ airway resistance VT ↑ lung compliance, ↓ airway resistance Diuretic effects, bronchodilator Higher than intended VT Pressure Modern day only used as backup safety feature Cycling Thursday, February 13, 2025 Sample Footer Text  Time Cycling Mandatory breath PC-CMV Set RR, Ti, and PIP Inspiration = pressure or time triggered Pressure rises to preset level; RR time cycles to expiration Ti set based on disease state Normal Ti =.6 to 1 seconds I:E ratio 1:2 Adjustment of Ti short Ti = higher inspiratory flows and vice versa Thursday, February 13, 2025 Sample Footer Text 45  46 Time Cycling Obstructive lung disease Ex. COPD ↓ Ti, ↑ Te, ↓ I:E ratio 1:3 or 1:4 Acute Restrictive lung disease Ex. ARDS ↑ Ti, ↑ I:E ratio 1:1 or inverse PC-IRV Inverse ratio ventilation (APRV) Thursday, February 13, 2025 Sample Footer Text  Vent switches from inspiration to expiration by clinician set VT Volume is constant, PIP variable Dependent on patient lung Volume mechanics ↓ Lung compliance or ↑ Cycling airway resistance = ↑ PIP Risk of barotrauma from high pressures led to development of PC  Volume Cycling and ARDS ARDS = inflammatory lung condition Ventilatory strategies for ARDS resulting in leakage of blood and plasma PC ventilation Permissive hypercapnia into alveoli, markedly reduced lung Prone position ventilation compliance, and serious oxygenation Inverse ratio ventilation (IRV) problems. Dual control modes 70’s, 80’s, and 90’s common to use VT 10- HFOV 15 mL/kg IBW ARDS network 1994 Large VT and high PEEPS = increased incidence VILI and mortality Current treatment Antibiotics for PNA or sepsis VT 4-8 mL/kg PIP 30 cm H2O Flow Cycling The ventilator switches from inspiration to expiration when the clinician-set inspiratory flow rate decreases (often set as a percentage of peak inspiratory flow) Dependent on decrease in inspiratory flow Set as a percent of peak inspiratory flow Ex. 25% set flow cycle = cycle to exhalation as flow rate diminishes by 75% Spontaneous breathing modes PSV VT 4-8 mL/kg RR < 25 breaths/min Wean PS based on patient response IMV or SIMV Mandatory breaths at preset rate (PC or VC) ALSO allowing for spontaneous breathing (augmented by PS normally set 5-15 cm H2O) Difficult to use with Obstructive and Restrictive disease  Ventilator Classification / Taxonomy There are five basic modes of ventilation available: Pressure control–continuous Volume control–continuous mandatory mandatory ventilation ventilation (PC-CMV) or “assist/control (VC-CMV) or “assist/control volume pressure control ventilation” Pressure control–intermittent ventilation” mandatory ventilation Volume control–intermittent mandatory (PC-IMV) or “SIMV pressure ventilation control ventilation” (VC-IMV) or “IMV or SIMV volume Pressure control–continuous spontaneous ventilation ventilation” (PC-CSV) or “standalone pressure support (PSV)” Ventilator Classification / Taxonomy Targeting scheme: Distinguishes one ventilatory pattern from another and is the method used by the ventilator to reach specific parameters For primary breath and if applicable, the secondary (spontaneous) breath Ventilator Classification / Taxonomy 7 different targeting schemes Adaptive (a): used in modern MV Signal averaging of previous tidal breaths coupled with auto-adjusting variables make alterations to maintain the desired Set point (s): patient ventilatory parameters. In volume-control mode, volume Bio-variable (b): and flow are set and in pressure- The ventilator may deviate from the set control mode, pressure is set. point of the control variable to mimic the Dual (d): variability seen in normal, spontaneous respiration. Variations within-breaths may Optimal (o): occur in either volume or Auto-adjustments are made to alter pressure control. variables such as respiratory rate, flow, or Servo (r): volume to improve on anticipated Ventilator-sensing technology outcomes (e.g., lowered WOB). adjusts supporting pressures Intelligent (i): based on the patient’s Artificial intelligence programs are used inspiratory effort. to respond to changing patient lung compliance, resistance or effort. Understanding Modes of ventilation  Ventilator Modes May be described by: 5 basic modes VC-CMV control variable All mandatory breaths Pressure or volume VC-IMV breath sequence Mandatory and Spontaneous or mandatory spontaneous targeting scheme employed PC-CMV PC-IMV 7 different (slide 8) PC-CSV Conflicting manufacturers’ All breaths spontaneous terminology to describe these modes Continuous Mandatory Ventilation (CMV or Assist/Control) The control variable can be either volume or pressure, and every breath is mandatory. No entirely spontaneous breaths Every breath is a mandatory breath The patient may trigger inspiration (“assisted” breath), but every breath is machine cycled to expiration No spontaneous breaths occur to initiate inspiration, the ventilator deliver a time-triggered inspiration (control breath), at the set (mandatory) RR Volume control–continuous mandatory ventilation (VC-CMV) Control variable = Volume Breath sequence = Mandatory Patient can trigger inspiration Set VT will be delivered If lung mechanics change (compliance or resistance), airway pressure will vary A worsening lung condition will result in higher peak and mean airway pressures and increased risk of pulmonary barotrauma Pressure control-continuous mandatory ventilation (PC-CMV) Control variable: Pressure Breath sequence: Mandatory Patient can trigger inspiration Set Inspiratory Pressure will be delivered If lung mechanics change (compliance or resistance), tidal volume will vary. A worsening lung condition will result in decreased tidal volume, and may result in hypoventilation and respiratory acidosis with worsening hypoxemia. (A) VC-CMV Time triggered volume ventilation Control ventilation (B) PC-CMV Patient triggered volume ventilation Assist-control ventilation Figure 3-18A-B Intermittent Mandatory Ventilation (IMV) The control variable can be either volume or pressure Early IMV before SIMV Breath stacking due to non- synchronization of mandatory and spontaneous breaths SIMV = improved patient –ventilator asynchrony, delivers mandatory breaths when patient does not trigger Synchronized Intermittent Mandatory Ventilation (VC-SIMV) VC-SIMV Clinician set VT and RR Guaranteed minimum minute ventilation Pt can spontaneously breath between mandatory machine delivered breaths Pt begins to inspire as machine breath is being delivered = assisted breath (preset VT) Spontaneous breaths may be pressure supported Initial ventilator settings are usually set to provide full ventilatory support RR is weaned (reduced) based on patient response Partial ventilatory support Spontaneous breathing trial (SBT) Preferred method for ventilator discontinuance is generally High pressure alarm is important to protect against barotrauma Minute volume and VT alarms to deter hypoventilation  Synchronized Intermittent Mandatory Ventilation (PC-SIMV) PC-SIMV Clinician set Inspiratory pressure and RR VT determined by: Inspiratory pressure, Ti, and patient’s lung mechanics Pt can spontaneously breath between mandatory machine delivered breaths Pt begins to inspire as machine breath is being delivered = assisted breath (preset inspiratory pressure) = PSV (PS + PEEP) Spontaneous breaths may be pressure supported Minute ventilation and VT alarms vary with changes in lung mechanics Hypoventilation due to reduced spontaneous minute volumes (A) VC-SIMV Set VT (B) PC-SIMV Set insp press Figure 3-20A-B  Lung Recruitment Maneuvers Sometimes applied to patients with Plateau pressures should be < 30 ARDS to Improve V/Q mismatch cm H2O Reduce shunting PEEP should be used cautiously PEEP set at 20-25 cm H2O and PC Obstructive lung disease level set about 15 cm H2O Hemodynamic instability 2-3 minutes Increased ICP Followed by decremental decrease FIO2 and PEEP used to achieve in PEEP to identify optimal PEEP There are differences in MV’s when target PaO2 and SaO2 “Safe” FIO2 = 50% to 60% setting PEEP during PC Consult vent manual PEEP directly contributes to MAP  Pressure Support ventilation (PSV) patient-triggered, pressure limited, flow-cycled ventilation which may be used as a stand-alone mode or in conjunction with IMV/SIMV Patients can control RR, inspiratory flows, times, and volumes 5 to 8 cm H2O: With CPAP during spontaneous breathing trials (SBTs) Extubation readiness 5 to 15 cm H2O: Overcome the imposed WOB due to endotracheal or tracheostomy tubes 15 to 25 cm H2O: Further reduce the patient’s WOB PSV is reduced 2 to 4 cm H2O in a stepwise fashion Automatic Tube Compensation (ATC) Variable form of pressure support used as an adjunct to other modes of ventilation which reduces WOB associated with endotracheal tube resistance. Variables are entered into the ventilator such as: ET-tube diameter Percentage of support as determined by the clinical goals and clinician Resting the diaphragm or allowing some patient contribution to WOB Advantage of ATC vs PSV Inspiratory flow control is influenced by intratracheal pressure  Combine the best characteristics of both pressure and volume-control ventilation Dual targeting Allows ventilator to switch between volume control and pressure control during a single inspiration (i.e., within breath adjustment), Dual Modes Adaptive targeting and Adaptive allows ventilator to automatically adjust pressure to achieve Control the desired VT over several breaths (i.e., between breath adjustment). Examples PRVC Volume Support (VS) Automode Adaptive Support Ventilation (ASV) Pressure Augmentation and Volume Assured Support (VAPS) Ventilator Parameters: Flow Waveforms Allow for observation and Pressure-time scalars: monitoring of pressures, flows, Inspiratory time, and volumes Expiratory time in I:E ratio Baseline pressure (e.g., PEEP Examination of pressure–time or CPAP) curves and flow–time curves can Volume–time scalars: provide be very useful to identify: visual confirmation of the Inspiratory trigger patient’s actual inspired and Type of breath expired tidal volumes Inspiratory gas flows and Flow–time scalars: pressures provide a graphic display of Cycle variable inspiratory and expiratory gas Pressures and flows during flow versus time expiration Pressure, Time, and Flow Waveforms Figure 3-29 Inspiratory Pause Maneuver which briefly holds the inspired breath prior to exhalation to obtain an inspiratory plateau pressure Pplateau Used to make determinations of lung mechanics, compliance, and resistance Represents the force required to distend the lung within the thorax at a point of no gas flow Calculating lung mechanics: Total static compliance (CST) = VT ÷ (Pplateau – PEEP) Normal CST = 60 to 100 mL/cm H2O Disease processes that decrease lung compliance: Atelectasis, pneumonia, pulmonary edema, ARDS, pulm fibrosis Processes that decrease thoracic compliance: Thoracic cage deformities, ascites, obesity, and pregnancy  RAW (Airway resistance) = (PIP – P plateau) ÷ inspiratory flow rate. Normal Raw in intubated patients 5 to 10 cm H2O/L/sec Depends on diameter of ETT and insp gas flow rate Factors that may increase RAW: Bronchospasm, increased secretions, mucosal Inspiratory edema, mucus plugging, or ETT obstruction Pause Improve distribution of inspired gases and may improve gas exchange FIO2 FIO2 and barometric pressure (PB) determine the partial pressure of inspired oxygen (P IO2) PIO2 and alveolar ventilation determine the alveolar oxygen tension P AO2 PIO2 (mmHg) = FIO2 (PB – PH2O) Alveolar air equation PAO2 = PIO2 – PACO2 [FIO2 + (1 – FIO2) / R] PACO2 is alveolar carbon dioxide tension R = respiratory quotient (VCO2/VO2) Normal R =.80 Excessive amounts (>50 to 60%) can have adverse reactions Oxygen toxicity Absorption atelectasis The lowest combination of FIO2 and PEEP PaO2 60 – 80 mmHg SaO2 90 – 96%  Alarms National Patient Safety Goals set by Not too sensitive Factory set vs Box 3-10 Alarm the Joint Sentinel events but SAFE Clinician set levels of Priority Commission addresses alarms Any unanticipated event in a Factory : Power healthcare failure, high setting and low source resulting in gas, death or serious injury Clinician: VT, RR, MV, PETCO2 Humidification 37 degrees C Active: heated humidifier Active vs. Passive Passive: HME Passive humidification Added deadspace NOT for NIV or low VT Inadequate Increases secretion viscosity humidification Impair mucociliary transport Avoid thermal injury (>41 degrees C) Airway rewarming Hyperthermia Sigh Breaths Normal spontaneously breathing individuals sigh every 6 to 10 min to keep alveolar units inflated and prevent atelectasis Figure 3-31 A Machine Delivered Sigh Breath Prevent post-op alveolar Abdominal or thoracic surgeries recruitment < 7 mL/kg VT = shallow breathing Use is controversial today after history of “Recommended” VT changes  Effects of Mechanical Ventilation on Organ Systems Pulmonary System Primary function of a mechanical ventilator augment or replace normal ventilation Primary indication for initiation of mechanical ventilation Absent or inadequate spontaneous breathing Goal of mechanical ventilation Support tissue oxygenation and removal of carbon dioxide Important to note a patient’s baseline status when setting specific oxygenation and ventilation goals Ex. COPD, chronic CO2 retention chronic ventilatory failure and prior baseline arterial blood gases may be indicate a compensated respiratory acidosis with mild hypoxemia Ventilating this patient to achieve a normal Paco2 may result in an unwanted alkalosis  Pulmonary System Effects of Consider ventilation and oxygenation separately Oxygenation Mechanica FIO2 and PEEP at lowest necessary combination Complications with FIO2: oxygen l toxicity, ROP, Hypoventilation in COPD Complications with PEEP: Alveolar overdistension, Ventilation Other factors that help with oxygenation Proning, increased PAW (IRV), recruitment maneuvers, airway on Organ clearance, and administration of bronchodilators. Also, fluid management (prevent pulm edema) and pain management Systems (decrease oxygen consumption VO2)  Pulmonary System Effects o Ventilation VT, VE, patients WOB f MV with positive pressure will Increase PAW and intrathoracic pressure = reduce CO and venous return Mechani Goal of MV: Improve alveolar ventilation and maintain appropriate CO2 levels cal Adjust VT 6-8 mL/kg Inspiratory pressure to achieve VT of 6-8 mL/kg Ventilati Ti ; may need longer Te for autoPEEP = decreased Ti on on RR 12-14 Mandatory (with adjustment for goals) pH will decrease acutely about.08 units for each 10 Organ mmHg increase in PaCO2 Ex. pH = 7.2, increase RR see change in PaCO2 on Systems ABG of 20 mmHg = pH 7.36 (7.2 +.16)  Airway Pressures Effects o Higher PIP and Pplateau = increased risk for lung injury VILI (ventilator-induce lung injury) f Volutrauma Excessive VT, overdistension, autoPEEP, Mechani Atelectrauma cal Cyclic opening and closing of alveoli Biotrauma Ventilati Release of inflammatory mediators by injured lung tissue on on Barotrauma Excessive pressures Organ Decreased compliance or increased airway resistance; Look at PIP in VC and VT in PC Systems Effects o Ventilation/Perfusion (V/Q) Mismatch f Normal =.8 V > Q: high V/Q or deadspace; poor perfusion V < Q : V/Q < 1 but > 0: Low V/Q Mechani V/Q 0 = intrapulmonary shunt cal Respiratory Muscles Fatigue from disease process, immobilization, Ventilati use of sedatives/narcotics, paralytics SIMV to build muscle strength post Controlled on on MV Diaphragmatic Dysfunction Organ Develops within hours of MV Measures of function : MIP, RR, VT, and Systems transdiaphragmatic pressures Effects of Mechanical Ventilation on Organ Systems WOB Mucociliary Controlled mode eliminates pt WOB Motility MV impairs airway mucociliary motility Trigger work ( Adequate humidification, suctioning, Mode of ventilation effects on WOB and airway care IMV/SIMV = partial Patient ventilator asynchrony Effects of Mechanical Ventilation on Organ Systems Immune System Cardiac/Cardiovascular Positive pressure ventilation triggers activation Right ventricular output is decreased as of the inflammatory cascade alveolar distention compresses the pulmonary Ventilator-associated pneumonia (VAP); PNA w/i capillaries resulting in increased pulmonary 48 hours or more after MV initiation vascular resistance Compensatory mechanisms, including Increases in heart rate and systemic vascular resistance Maintain blood pressure If compensatory mechanisms are inadequate, hypotension develops NOTE: positive pressure ventilation may be beneficial in patients with left ventricular failure by reducing venous return and decreasing left ventricular afterload  Renal System Effects of Patients receiving mechanical ventilatory support may develop acute renal failure Mechanica Multiple factors Decreased renal blood flow due to decreased cardiac output l Release of inflammatory mediators Humoral pathways Increased sympathetic tone Ventilation on Organ Systems  Gastrointestinal System Effects o Gastrointestinal tract stress ulcers Splanchnic perfusion f Perfusion of abdominal gastrointestinal organs Mechanical ventilation is associated with reduced splanchnic Mechani perfusion Modes of ventilation that accommodate spontaneous cal breathing may improve splanchnic blood flow Paco2 may also influence gut perfusion Ventilati Mucosal breakdown May increase risk of bacterial translocation from the on on gastrointestinal tract to blood and result in nosocomial infection May manifest as an intolerance to enteral feeding Organ Systems Effects of Mechanical Ventilation on Organ Systems CNS/Psychological Cerebral blood flow (CBF) is proportional to cerebral perfusion pressure (CPP) Elevations in ICP may be caused due to increased intrathoracic pressures and reduced venous return Cerebral autoregulation minimizes these effects by maintaining cerebral perfusion Decreased PCO2 is a cerebral vasoconstrictor while increased PCO2 is a cerebral vasodilator Hyperventilation can be used lower ICP May also cause cerebral ischemia and contribute to secondary brain injury Not recommended in the initial treatment of severe traumatic brain injury Many ICU procedures and activities may increase patients’ discomfort, causing anxiety, agitation, pain, or frustration Self-extubation Presence of an endotracheal tube can cause coughing and gagging and increased intrathoracic pressures which may cause transient elevations in ICP ICU delirium Effects of Mechanical Ventilation on Organ Systems Sleep ICU patients suffer from poor sleep quality Maintaining normal circadian rhythms, limiting environmental noise, administration of sedatives and hypnotics helps Sleep disruption Disrupted sleep-wake cycle Sleep fragmentation Repetitive short interruptions in sleep Pain, bright lights, noise, movement, secretions, bronchospasm, patient-vent asynchrony Complications of Mechanical Ventilation Pulmonary and extrapulmonary Pulmonary VILI VAP Head of bed 30-45 degrees Removal of subglottic secretions Most common airway complications Laryngeal edema, Vocal cord injury, and tracheal stenosis ETT cuff maintained a pressures 20-30 cm H2O Barotrauma, Volutrauma, Atelectrauma, Pneumothorax, excessive PEEP Equipment failure Vent malfunction, power failure, Alarms MUST have ambu bag with PEEP valve readily available Oxygen toxicity  Complications of Mechanical Ventilation Extrapulmonary Cardiac/Cardiovascular Renal CNS/Psychological ICU acquired weakness Neuromuscular Nutritional Gastrointestinal Motility often impaired in MV may manifest as feeding intolerance Immune System