Principles of mechanical ventilation Anton van Kaam, MD, PhD Emma Children s Hospital AMC Amsterdam, The Netherlands
Disclosure Research grant Chiesi Pharmaceuticals Research grant CareFusion
GA: 27 weeks, BW: 900 g ncpap: 7 cmh 2 O, FiO 2 : 0.60 Grunting +, retractions + PH: 7.18, PCO2: 65 mmhg
Basic goals of mechanical ventilation Assist the patient in restoring lung function leading to adequate gas exchange Optimize patient-ventilator interaction Minimize ventilator-induced/associated lung injury
Restoring lung function is only possible if we understand normal physiology and pathophysiology of the lung
Mechanical properties of the lung Elastic recoil Goldsmith & Karotkin: Assisted ventilation of the neonate
Mechanical properties of the lung Static pressure - volume relationship TLC Inflation limb Volume RV Pressure
Mechanical properties of the lung Dynamic pressure - volume relationship TLC Inflation limb Volume FRC Zero flow RV Pressure
Mechanical properties of the lung Surfactant deficiency Goldsmith & Karotkin: Assisted ventilation of the neonate
Chest wall compliance Effect on end-expiratory lung volume Haddad et al.: Pediatric Respiratory Disease
Chest wall compliance Effect of gestational age Gerhardt et al., Acta Paediatr Scand 1980
Mechanical properties of the lung Dynamic compliance TLC Healthy lung Volume V Cdyn= V/ P P RV Pressure
Mechanical properties of the lung Contribution of alveolar surface tension ST Surfactant deficiency Surfactant inhibition ST ST Surfactant layer Alveolar surface tension
Mechanical properties of the lung Dynamic compliance and nrds TLC Healthy lung Volume V C dyn RDS < C dyn healthy RDS lung P V P Pressure
Mechanical properties of the lung End-expiratory lung volume and nrds TLC Healthy lung Volume EELV healthy > ELLV RDS RDS lung EELV Pressure
Low end-expiratory lung volume Effect on dynamic compliance TLC Overexpansion Volume FRC Atelectasis Pressure
Low end-expiratory lung volume Effect on dynamic compliance TLC Overexpansion Volume FRC Atelectasis Pressure
Low end-expiratory lung volume Effect on airway resistance AW Airway resistance AW Lung volume
Low end-expiratory lung volume Effect on work of breathing WOB = force (pressure) x displacement (volume) Goldsmith & Karotkin: Assisted ventilation of the neonate
Low end-expiratory lung volume Effect on work of breathing WOB = force (pressure) x displacement (volume)
Low end-expiratory lung volume Effect on gas exchange Normal Intrapulm Rà L shunt Normaly < 10% Adequate oxygenation with FiO 2 0.21 Air Alveolar collapse Airway obstruction
Lung function changes in preterms Summary Reduction in compliance Reduction in lung volume less compliant part inflation limb increased airway resistance increased work of breathing increased intrapulmonary shunt increased pulmonary vascular resistance (PVR) à respiratory failure
Endotracheal intubation and CMV Additional adverse effects Elimination of glottis function (endogenous PEEP)à loss of additional lung volume Increased airway resistance by ETT and ventilator valves/circuit Increased dead space Increased work of breathing Ventilator induced lung injury
Basic questions How will I deliver the tidal volume? How will I terminate the inspiration phase? How can I determine the optimal expiration time? How can I optimize EELV? How and when will I synchronize patient efforts with the ventilator?
Basic questions How will I deliver the tidal volume? How will I terminate the inspiration phase? How can I determine the optimal expiration time? How can I optimize EELV? How and when will I synchronize patient efforts with the ventilator?
Pressure controlled ventilation vs Volume controlled ventilation
Pressure controlled ventilation Tidal volume depending on compliance P is fixed C RS Vt is variable
Volume controlled ventilation Pressure depending on compliance P is variable C RS Vt is fixed
Volume guarantee ventilation Hybrid mode PCV and VCV Tidal volume stabilization Pressure controlled breaths Tidal volume measured after each breath Adjustment peak inflation pressure
PCV PIP Airway pressure PEEP 5 ml/kg Tidal volume
PCV PIP Airway pressure PEEP 5 ml/kg Tidal volume
PCV+VG Limit PIP PEEP Airway pressure 5 ml/kg Tidal volume
PCV+VG Limit PIP PEEP Airway pressure 5 ml/kg Tidal volume
Volume guarantee ventilation Effect on stability tidal volume RCT N=18 Percentages (%) 40 30 20 10 A/C alone A/C + VG 0 VT > 6 ml/kg PaCO 2 < 35 torr Keszler et al. Ped Pulmonol 2004
Basic questions How will I deliver the tidal volume? How will I terminate the inspiration phase? How can I determine the optimal expiration time? How can I optimize EELV? How and when will I synchronize patient efforts with the ventilator?
Termination of the inspiration Pressure cycled
Termination of the inspiration Pressure cycled Pressure 20 PIP = 20 cmh 2 O PEEP = 5 cmh 2 O 5 Ti Te Time
Termination of the inspiration Pressure cycled Volume cycled
Termination of the inspiration Volume cycled Volume Vt = 6 ml 6 0 Ti Te Time
Volume Controlled Ventilation Volume cycled
Termination of the inspiration Pressure cycled Volume cycled Time cycled
Time cycled pressure limited ventilation Time cycled
Termination of the inspiration Pressure cycled Volume cycled Time cycled Flow cycled
Termination of the inspiration Flow cycling Flow Max = 100% Inspiration Expiration 0 10% max flow Trigger Time
Termination of the inspiration Pressure cycled Volume cycled Time cycled Flow cycled Edi cycled (NAVA)
Termination of the inspiration Diaphragmatic activity (Edi) Pvent Flow Volume Edi
Basic questions How will I deliver the tidal volume? How will I terminate the inspiration phase? How can I determine the optimal expiration time? How can I optimize EELV? How and when will I synchronize patient efforts with the ventilator?
The optimal expiration time? The time constant The time constant of the respiratory system is a measure of how quickly the lungs can inflate or deflate T RS =C L x R AW One time constant is defined as the time it takes to exhale 63% of the inflated tidal volume
The optimal expiration time? The time constant 100 % lung volume remaining 80 60 40 20 0 95% 0 1 2 3 4 5 6 Time constant
The optimal expiration time? The time constant Ventilated newborn infant with: C RS : 0.004 L/cmH 2 O R AW : 30 cmh 2 O/L/sec T RS =0.004 x 30=0.12 sec Time needed to clear 95% Vt= 3x0.12=0.36s Expiration time should be at least 0.4 sec If Te < 0.4 sec increased risk air-trapping!
Basic questions How will I deliver the tidal volume? How will I terminate the inspiration phase? How can I determine the optimal expiration time? How can I optimize EELV? How and when will I synchronize patient efforts with the ventilator?
Oxygenation Compliance Tidal volume Optimizing EELV/PEEP Parameters? (tc)p(a)co 2 Pressure/volume loops Imaging (CXR, EIT)
Basic questions How will I deliver the tidal volume? How will I terminate the inspiration phase? How can I determine the optimal expiration time? How can I optimize EELV? How and when will I synchronize patient efforts with the ventilator?
Patient-ventilator interaction Trigger options Pressure triggering
Patient-ventilator interaction Pressure trigger patient 5 cm H 2 O Insp Exp
Patient-ventilator interaction Pressure trigger patient 4.5 cmh 2 O Insp Exp
Patient-ventilator interaction Trigger options Pressure triggering Flow triggering
Patient-ventilator interaction Flow trigger patient 2.0 L/min Insp Exp
Patient-ventilator interaction Flow trigger patient 1.8 L/min Insp Exp
Patient-ventilator interaction Trigger options Pressure triggering Flow triggering Pneumatic triggering (Graseby capsule)
Patient-ventilator interaction Pneumatic triggering
Patient-ventilator interaction Trigger options Pressure triggering Flow triggering Pneumatic triggering (Graseby capsule) Neural triggering (EMG, NAVA)
Diaphragmatic EMG Optimal triggering? PSV+VG NAVA tube NAVA-NIV Beck et al. Pediatr Res 2009
Patient-ventilator interaction Synchronization modes Synchronized intermittent mandatory ventilation (SIMV) Support triggered breaths limited to SIMV rate Assist/Control ventilation (SIPPV) all triggered breaths supported by the ventilator with a minimum preset A/C rate (back-up rate) Pressure support ventilation (+ CPAP) all triggered breaths supported by the ventilator with a backup rate in case of apnea
Basic principles of CMV Conclusion Basic goal is to restore lung function and adequate gas exchange while minimizing ventilator induced lung injury and patient discomfort Basic knowledge of physiology and pathophysiology of the lung is essential to determine the optimal ventilation mode and settings
Thank you! a.h.vankaam@amc.uva.nl