Mechanical Ventilation The Basics M.RADHA KRISHNAN BPT,PGDRT,PGDRCM SENIOR RESPIRATORY THERAPIST(ICU) KMCH COIMBATORE. Interesting to compare the viewpoints and biases of medicine/endocrinology articles, and the surgery articles

Mechanical Ventilation Basic concepts Introduction Indications Modes Initial Settings

Basic Physiology Transairway pressure Gradient Gradient between mouth opening pressure (Pao)and Alveolar pressure (PA) During inspiration the gradient becomes more negative as you approach the alveolus. This is an active process; part of the energy used for inspiration is stored in the tissues. This is used in exhalation, which is effectively a passive process. Recall that work = volume x pressure. For infants with their more compliant chest wall, they will have a proportionally greater work of breathing which helps predispose them to respiratory distress. The point at which the recoil between the alveolus and the chest wall is balanced is equivalent to functional residual capacity. I wanted to try to give some background to this slide without getting too weighed down in the physiology of breathing and respiratory failure. Besides, it always confuses me.

Basic Physiology

Negative pressure ventilation Pre = Pao (Zero) - Palv (Negative)

Positive pressure ventilation Prs = Pao (+ve) - Palv (0)

Basic Physiology +ve pressure ventiation PI CmH2o PA CmH20 ∆P FLOW Inspiration 20 +20 In to lungs End inspiration No flow Expiration -20 Out of lungs End exp

Delicate balance between Load and Capacity Depressed Respiratory Drive Drug brain Stem Increased Minute Ventilation Pain, Anxiety, Excessive Feeding Sepsis Increased VD/VT Muscular Disorders Myasthenia Gravis Electrolyte Disorders Prolonged Neuromuscular blockade Increased Elastic Loads Low Lung Compliance Low Thoracic Intrinsic PEEP Loads Capacity Thoracic Wall abnormality Increased Resistive Loads Airway Obstruction Neuromuscular disorder

Type 2 Respiratory Failure Def PaO2 <60 mm Hg PaCO2  45 mm Hg Etiology Gas Exchange failure V/Q Mismatch Shunts Diseases ARDS,Pulmonary Edema, Pneumonia, Pneumothorax, PE PaCO2>45 mm Hg Ventilatory failure Min. Volume COPD, Muscle Weakness, Restrictive Decreased MV is due to 1. Increased load – obstruction 2. Decreased central drive 3.muscle fatigue

WHAT IS A VENTILATOR? Any machine used to PUSH Gas mixture (air & O2) in to the lungs. This can be done by applying positive pressure at the airway either Invasively or Non invasively.

Note that the pressure is applied to the proximal end of the ETT and is not the pressure in the alveoli as some of the pressure will be dissipated across the ETT and the major airways.

Classification of mechanical ventilators Negative pressure ventilators Positive pressure ventilators Tank ventilators Cuirass ventilators

Origins of mechanical ventilation The era of intensive care medicine began with positive-pressure ventilation Negative-pressure ventilators (“iron lungs”) Non-invasive ventilation first used in Boston Children’s Hospital in 1928 Used extensively during polio outbreaks in 1940s – 1950s Positive-pressure ventilators Invasive ventilation first used at Massachusetts General Hospital in 1955 Now the modern standard of mechanical ventilation The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output. 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 Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

Indications – simplified Respiratory Restrictive ARDS ILD Obstructive Bronchial asthma COPD Central airway obstruction Non respiratory Chest wall Cardiac Normal Airway protection Respiratory drive dysfunction

Mechanical Parameters Predicting Impending Failure Criteria Critical Values (Normal) Muscle strength Maximum Inspiratory Pressure Peak Expiratory Pressure Spiro metric data Vital Capacity Tidal Volume Minute Volume Bedside PEFR Respiratory Rate <-20 cm H2O (-50 to –100) <+40 cm H2O (+100 cm H2O) <15mL/Kg (65-75mL/Kg) <5mL/Kg (5-8mL/Kg) >10L/min (5-6L/min) <100L/min (400-600L/min) >35/min Akin to the definition of CCF A MIP of 40 cm H20 is reqd for adeq cough Show the instrument – Bourdon gauge meter Other indications Airway protection Hyperventilation in c. edema

Modes CMV (Controlled Mandatory ventilation) ACMV IMV Synchronized intermittent mandatory ventilation CPAP PS(Pressure support ventilation)

Mechanical Ventilation Basic Concepts Introduction Indications Modes Initial Settings

VOLUME CONTROL Normal emphysema ARDS alveoli

VOLUME CONTROL ADVANDAGE DISADVANTAGE The patients is Guaranted to receive a preset tidal volume High Plateau pressure leads to Baro trauma

Pressure Control ventilation ADVANTAGE DISADVANTAGE Prevent Baro Trauma Low lung compliance and high airway Resistances – Tidal volume drops & drop in minute ventilation & Paco2 Accumulation & respiratory acidosis

Common Modes CMV (Control Mode Ventilation) ACMV (Assist Control Mandatory Ventilation) IMV (Intermittent Mandatory Ventilation) SIMV (Synchronized Intermittent Mandatory Ventilation) PSV (Pressure Support Ventilation ) A/CMV Assist Control mode ventilation: Every breath is mandatory but can be patient triggered

CMV

Control Mode Ventilation CMV Control Mode Ventilation Every breath is mandatory and ventilator triggered with no spontaneous breaths Mandatory breaths at a set frequency and tidal volume delivered to the patient The inspiratory valve is closed to the patient otherwise so that no additional breaths can be taken In anesthesia practice constant flow, volume controlled, pressure limited, time controlled ventilation is administered that is usually limited to 35 cm H2O airway pressure.

ACMV

ACMV ADVANTAGE DISADVANTAGE WOB is very small Pt maintain their Own Pco2 or minute Volume Alvoelar hyperventilation

IMV, volume-limited Ref: Ingento EP and Drazen J: Mechanical ventilators, in Hall JB, Scmidt GA, and Wood LDH(eds.): Principles of Critical Care. New York, McGraw-Hill, Inc., 1992, p.145. “Positive pressure, volume-cycled breaths are delivered at a preset rate similar to control mode ventilation, except that between breaths, the inspiratory valve to the patient is open, allowing for spontaneous breathing.” Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt GA, & Wood LDH(eds.): Principles of Critical Care

IMV TYPE OF BREATH : ASSIST & CONTROL TRIGGERING : ASSIST & CONTROL CYCLING : VOLUME CYCLED COMPLCATION: BREATH STACKING

SIMV, volume-limited Ref: Ingento EP and Drazen J: Mechanical ventilators, in Hall JB, Scmidt GA, and Wood LDH(eds.): Principles of Critical Care. New York, McGraw-Hill, Inc., 1992, p.146. (Would we also want to put slides with pressure mode graphs as well to show the different flow characteristics ??) During SIMV, the ventilator divides time by the set rate to determine cycle-length. During the early part of this cycle, the patient may breath spontaneously without support. During the terminal phase of this cycle (% varies by manufacturer) the ventilator will synchronize a full breath with detected effort by the patient. Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt GA, & Wood LDH(eds.): Principles of Critical Care

CPAP Flow (L/m) Pressure (cm H2O) CPAP level Volume (mL) Time (sec)

CPAP CPAP is PEEP is applied to the airway of a patient who is breathing spontaneously

PSV Patient Triggered, Flow Cycled, Pressure limited Mode Time (sec) (L/m) Flow Cycling Set PS level Pressure (cm H2O) Volume (mL) Time (sec)

PRESSURE SUPPORT VENTILATION Î Spontaneous Tidal Volume Reduces RR Reduces WOB

Initial Settings Mode- ACMV Tidal volume : 7 to 8 ml/kg COPD 6ml/kg & ARDS 5 to 6 ml/kg Fio2 100% or 60% RR NORMAL 16 to 18 b/m PEEP 5 CMH2O I:E RATIO 1:2 , COPD 1:4 PIF 60L/MIN VC Monitor PIP & plateau , PC Monitor Tidal volume & Minute ventilation

Recapitulation Spont. Breath Mandatory Breath Mode Trigger Limit Cycle CMV Time Pres.,Flow Volume/time No A/CMV Pressure or Flow, Time yes PSV Pressure or Flow Flow Only SIMV Pressure or Flow/ Time Yes PCV(PC-CMV) Pressure or flow, Time Pressure/ time Control Volume Pressure

SCALARS Flow/Time Pressure/Time Volume/Time

LOOPS Pressure-Volume Flow-Volume

Spontaneous Breath Inspiration Time (sec) Flow (L/min) Expiration

Mechanical Breath Inspiration Time (sec) Flow (L/min) Expiration

Inspiratory Tidal Volume Volume vs Time Inspiratory Tidal Volume Volume (ml) Inspiration Expiration TI Time (sec)

Transairway Pressure (PTA) Exhalation Valve Opens Begin Expiration Paw (cm H2O) Time (sec) Begin Inspiration PIP Pplateau (Palveolar Transairway Pressure (PTA) } Exhalation Valve Opens Expiration Paw (cm H2O) Time (sec) PIP Inflation Hold (seconds) Airway Resistance Distending (Alveolar) Pressure Expiration Begin Inspiration Begin Expiration

Inspiratory Flow Pattern Beginning of expiration exhalation valve opens Peak inspiratory flow rate PIFR Inspiration Insp. time TI Expiratory Time TE Flow (L/min) Total cycle time TCT Time (sec) Beginning of inspiration exhalation valve closes Expiration

Expiratory Flow Pattern Beginning of expiration exhalation valve opens Inspiration Expiratory time TE Time (sec) Flow (L/min) Duration of expiratory flow Expiration Peak Expiratory Flow Rate PEFR

Components of Pressure-Volume Loop VT Expiration Volume (mL) Inspiration PIP Paw (cm H2O)

Flow-Volume Loop Inspiration PIFR FRC VT PEFR Expiration Flow (L/min) Volume (ml) FRC VT Flow (L/min) PEFR Expiration

Thank you Questions ?