Raafat Abdel-Azim 1 Bellows assembly Distensible bellows Rigid housing Control Unit

Raafat Abdel-Azim Control Unit Bellows assembly Distensible bellows Rigid housing 2

Raafat Abdel-Azim BS 3 Driving Gas Flow

Raafat Abdel-Azim Spill Exhaust Safety relief Driving Gas Flow BS Insp

Raafat Abdel-Azim BS Spill Exhaust Safety relief Flow 5

Raafat Abdel-Azim BS 6

Raafat Abdel-Azim BS To atmosphere Exp 7

Raafat Abdel-Azim Spill Scavenging Overpressure 8

Raafat Abdel-Azim Spill Valve To scavenging system 9

Spill Valve I & beginning EEnd E (2-4 cmH 2 O) Driving gas Patient’s gas Raafat Abdel-Azim 10

Raafat Abdel-Azim 11

Raafat Abdel-Azim Traditional circle system 12

Raafat Abdel-Azim Traditional circle system 13

Raafat Abdel-Azim Components of the Ventilator Driving Gas Supply Injector (some) Controls (F, V, T, P) Alarms Safety-Relief Valve Bellows Assembly Exhaust Valve Spill Valve Ventilator Hose Connection preset cmH 2 O adjustable 14

Raafat Abdel-Azim Injector Driving gas Air Some ventilators use a device called an injector (Venturi mechanism) to increase the flow of driving gas. As the gas flow meets restriction, its lateral pressure drops (Bernoulli principle). Air will be entrained when the lateral pressure drops below atmospheric. The end result is an increase in the total gas flow leaving the outlet of the injector but no increase in consumption of driving gas 15

Raafat Abdel-Azim Control of Parameters of Ventilation V T V M f (frequency= rate) I:E ratio IFR (Insp. Flow Rate) Maximum Working Pressure 16

Raafat Abdel-Azim 17

Raafat Abdel-Azim 18

Raafat Abdel-Azim Narkomed - Drager 19

Raafat Abdel-Azim Fabius - Drager 20

Raafat Abdel-Azim Cisero - Drager 21

Raafat Abdel-Azim 22 Dameca

IFR (Inspiratory Flow Rate) VT (ml) f (b/min) Cycle time (s) IFRTI (s)TE (s)I:E L/minL/sml/s /20 = : :2 Raafat Abdel-Azim Time (sec) Volume (ml) L/min 30 L/min 23

Inspiratory Waveforms Raafat Abdel-Azim Flow (L/min) ConstantDeceleratingAcceleratingSinusoidal Inspiration Expiration TI 24

Raafat Abdel-Azim The Ventilation Cycle 25

Raafat Abdel-Azim Paw 0 t Pmax Pplat IFE ZEEP IPPV 20 IE Pause 26

Raafat Abdel-Azim Duration of ventilation cycle (sec) f (60/duration) I phase (IF period, IP period) E phase V T, V M T I, T E, I:E FVPTFVPT 27

Raafat Abdel-Azim Inspiratory Phase During the IF period: Paw depends on: The airway resistance (R) The total thoracic compliance (C) (  V/  P) RCRC 28

Raafat Abdel-Azim PP P P P P P P P P P P P P Resistance Flow Rate:  FR  P 29

Raafat Abdel-Azim Paw 0 t 20 N  R  F  R  F Resistance 30

Raafat Abdel-Azim Compliance CC CC P P Volume 31

Raafat Abdel-Azim Compliance P Volume:  V  P P 32

Raafat Abdel-Azim During I pause No gas F into or out of the lungs  Paw depends only on V I & C T Gas redistributes among alveoli This improves gas distribution in the lungs of patients with small AWD (BA, smokers). Pause 33

Raafat Abdel-Azim Paw 0 t 20 CC RR Secretions Bronchospasm Kinked ETT EB intubation CW rigidity Pulmonary edema 34

Compliance =  V/  P Dynamic compliance: = V T /(PIP-PEEP) L/cmH 2 O Static compliance: = V T /(P plat -PEEP) L/cmH 2 O Raafat Abdel-Azim 35

Raafat Abdel-Azim During the expiratory phase VTVT FRC E I  FRC  IA contents Pulmonary edema ARDS PEEP PaO2PaO2 PaO2PaO2 36

Raafat Abdel-Azim Goals of Pulmonary Ventilation 37

Raafat Abdel-Azim To provide adequate minute alveolar ventilation and to  side effects necessary to maintain the desired PaCO 2 PPV   ITP 38

Raafat Abdel-Azim Adequate Ventilation PaCO 2 of 40 mmHg = 5.3% of 760 mmHg 40/760 = Normal resting VCO 2 = 200 ml/min= 0.2 L/min This requires V M of 3.8 L 0.2/ ? = / = Add dead space Goals 3.8 L/min 39

Raafat Abdel-Azim V D phys : ventilated but not perfused N = 1 ml/pound  150 ml in a 70 Kg (154 pound) adult = 0.15 x 10 (f) = Required V M = = A larger V M is required for patients who have  V D or  VCO L/min 5.3 L Goals, Adequate Ventilation For VCO 2 For V D 40

Raafat Abdel-Azim When VCO 2 & V D are stable: V M  1/ PaCO 2 V M x PaCO 2 = constant e.g., PaCO 2 = 50 mmHg with V M = 5 L/min  V M to 7 L/min   PaCO 2 to 36 mmHg Goals, Adequate Ventilation V 1 x P 1 aCO 2 = V 2 x P 2 aCO 2 41

Raafat Abdel-Azim  Side effects Goals  ITP  VR  EDV  CO  PVR  RVA PPV 42

Raafat Abdel-Azim  Goals,  Side Effects PPV  ITP P A > PAP VVDVVD 43

Raafat Abdel-Azim All these effects  mean Paw Therefore, a goal of PPV is to  mean Paw while maintaining adequate ventilation and oxygenation Goals 44

Raafat Abdel-Azim Modes of Pulmonary Ventilation 45

Raafat Abdel-Azim Paw 0 t SB -ve +ve Anesthesia ICU: demand valve   WOB  CPAP 46

Raafat Abdel-Azim Paw 0 t CPAP 47

Raafat Abdel-Azim Paw 0 t IPPV Anesthesia (or sedation) + MR Few days  muscle atrophy ZEEP 48

Raafat Abdel-Azim Paw 0 t PEEP IPPV + PEEP 49

Raafat Abdel-Azim Assisted Ventilation (A) Paw 0 A t S Patient  f and timing Hazard: hypoventilation If  or No S No A 50

Raafat Abdel-Azim Assisted Ventilation (A) Paw 0 CPAP A t Patient  f and timing Hazard: hypoventilation If  or No S No A 51

Raafat Abdel-Azim Paw 0 A+C Provides a minimum f below which  C Assist-Control (AC) 52

Raafat Abdel-Azim Conscious patients are more comfortable on A & AC > C Muscle atrophy is still a problem Most AV don’t provide A or AC AC 53

Raafat Abdel-Azim IMV 0 Paw S t Preset V T and f SB is allowed Muscle atrophy is less likely  IMV   PaCO 2 < apneic threshold  no SB  IMV = IPPV 54

Raafat Abdel-Azim Paw 0 t Triggering window Mandatory S Synch. Mandatory NO Preset V T and f SIMV 55

Raafat Abdel-Azim Paw t Pressure-limited ventilation (PLV) (PCV) Pmax Pplat 0 56

Raafat Abdel-Azim Ventilator Classification Pressure versus Volume Ventilators Single-Circuit versus Double-Circuit Ventilators Bellows Assembly 57

Raafat Abdel-Azim P vs V Ventilators P VentilatorsV Ventilators Changes in R & C change VTVT P Commonly used in Neonates  Barotrauma  Compressible V ICU Most AV Other namesP generators P-limited P-stable Flow generators V-stable 58

Raafat Abdel-Azim ICU Anesthesia 59

Raafat Abdel-Azim Bellows assembly Distensible bellows Rigid housing Driving gas BS to patient E I 60

Raafat Abdel-Azim Drager (End-insp.) Ohmeda (End-exp.) VTVT VTVT 61

Raafat Abdel-Azim NA Drager bellows Ohmeda bellows EExpands partiallyFully expands IEmpties completelyPartially empties Spill valveExternal (visible)Hidden in housing 62

Raafat Abdel-Azim Ascending bellows Descending bellows E Attachment Movement EEP V T adjustment Disconnection or leak 63

Raafat Abdel-Azim Interaction between the Ventilator and Breathing Circuits 64

Raafat Abdel-Azim Preset / delivered V T difference due to: 1.Effect of circuit compliance for all V ventilators: both single circuit and double circuit 2.Effect of FGFR only for double circuit ventilators Interaction 65

Raafat Abdel-Azim Effect of Circuit Compliance Interaction  PIP   Delivered V T  Circuit compliance = Compressible volume (gas compression, tubing distension)  CC= the V of gas that must be injected into a closed circuit to cause a unit  in the circuit P  It is related to the volume of the circuit  P  P V Ventilator tubingVC Anesthesia6 L9 ml/cmH 2 O ICU  (1.5 ml/cmH 2 O) 66

Raafat Abdel-Azim Preset – Del V T difference  CC and PIP Interaction, Circuit Compliance Del V T = Preset V T – [(PIP - PEEP) x CC] (i.e, V T loss = P x CC) Ventilator tubing CC (ml/cmH 2 O) PIP (cmH 2 O) V Loss (ml) Anesthesia ICU Example: 67

Raafat Abdel-Azim Volume loss is specially important in: Patients with  PIP ICU patients Patients with small V T Neonates  PLV Interaction, Circuit Compliance 68

Raafat Abdel-Azim Effect of Fresh Gas Flow Rate (from anesthesia machine) Interaction  FGFR   Delivered V T V FGF from AM 69

Raafat Abdel-Azim Volume added = T I x FGFR T I depends on  I:E  I fraction of the respiratory cycle  ff T I = 60/f x I fraction Example: I:E = 1:2, f = 20, FGFR = 6 L/min T I = 60/20 x 1/3 = 1 s FGFR = 6000 ml/min = 100 ml/s V added = 1 x 100 = 100 ml At a certain I:E,  f   T I   V added Interaction, FGFR I:EI fr 1:1 ½ 1:21/3 1:3 ¼ 70

Raafat Abdel-Azim Interaction, FGFR 71

Raafat Abdel-Azim Volume added is specially important: When making large changes in FGFR O 2 flush 55 L/min (don ’ t use during MV) When delivering small V T For a neonate, changing FGFR from 1 to 5 L/min  double V T Interaction, FGFR 72

Raafat Abdel-Azim Delivered V T = Preset V T - V lost (compression) + V added (An. machine) Interaction 73

Raafat Abdel-Azim Fresh Gas Decoupling (FGD) 74

Circle system with piston ventilator and fresh gas decoupling (FGD) (Dräger Narkomed 6000) Fresh Gas Decoupling (FGD) During the I phase the FG coming from the AWS through the fresh gas inlet is diverted into a separate reservoir by a “decoupling valve” (located between the fresh gas source & the circle BS). In the case of the NM 6000 series, the reservoir bag serves as an accumulator for FG storage until the E phase begins. 75 Raafat Abdel-Azim

During the E phase, the decoupling valve opens, allowing the accumulated FG in the reservoir bag to be drawn into the circle system to refill the piston ventilator chamber. Because the ventilator exhaust valve also opens during the E phase, excess FG & exhaled patient gases are vented into the scavenging system NPR valve = negative pressure relief valve 76

Raafat Abdel-Azim Most FGD systems are designed with either piston-type or descending bellows-type ventilators. Because the ventilator piston unit or bellows in either of these type systems refills under slight negative pressure, it allows the accumulated fresh gas from the reservoir to be drawn into the breathing circuit for delivery to the patient during the next ventilator cycle. As a result of this design requirement, it is not possible for FGD to be used with conventional ascending bellows ventilators, which refill under slight +ve pressure 77

Raafat Abdel-Azim Advantage of FGD  risk of barotrauma & volutrauma With a traditional circle system,  in FGF from the flow meters, or from inappropriate activation of the oxygen flush valve, may contribute directly to V T  excessive FG  pneumothorax, pneumomediastinum, other serious patient injury, or even death. Because systems with FGD isolate the patient from FG coming into the system while the ventilator is in I phase, delivered V T tends to remain stable over a broad range of FGF rates, and the potential risk of barotrauma to the patient is greatly reduced. 78

Raafat Abdel-Azim Disadvantages of FGD 1.The possibility of entraining room air into the patient gas circuit In a FGD system, the ventilator piston unit (or descending bellows) refills under slight -ve pressure. If the total volume of gas contained in the reservoir bag + that returning as exhaled gas from the patient’s lungs is inadequate to refill the ventilator piston unit, -ve patient Paw could develop. To prevent this, a negative pressure relief valve is placed in the FGD BS. If BS P  < a preset threshold value, then the relief valve opens and ambient air is allowed to enter into the patient gas circuit. If this goes undetected, the entrained atmospheric gases could lead to dilution of either or both the inhaled anesthetic agent(s) or an enriched oxygen mixture (lowering an enriched oxygen concentration toward 21%). If allowed to continue, this could lead to intraoperative awareness and/or hypoxia. High-priority alarms with both audible and visual alerts should notify the user that fresh gas flow is inadequate and room air is being entrained. 79

Raafat Abdel-Azim 2.If the reservoir bag is removed during mechanical ventilation, or if it develops a significant leak (from poor fit on the bag mount or a bag perforation), room air may enter the breathing circuit as the ventilator piston unit refills during the expiratory phase. This could also result in dilution of either the inhaled anesthetic agent(s) concentration and/or the enriched oxygen mixture. This type of a disruption could lead to significant pollution of the operating room with anesthetic escaping into the atmosphere. 80

Raafat Abdel-Azim Hazards of Ventilators 81

Raafat Abdel-Azim Apnea –Erroneous setting of ventilator selector switch –Ventilator switched off –Disconnection –Obstruction of inspiratory gas pathway –Ventilator failure Hazards VB 82

Raafat Abdel-Azim Hypoventilation –Circuit leak –Incompetent spill valve –Open APL valve in circuit –Driving gas leak –Improper settings –Ventilator limitation at high airway pressure Hazards PL S 83

Raafat Abdel-Azim 84

Raafat Abdel-Azim  Hyperventilation & dilution of anesthetic gases Bellows leak 85

Raafat Abdel-Azim High airway pressure Exhaust obstruction Obstruction of expiratory gas pathway Ventilator cycling failure Improper settings Oxygen flush during inspiration Bellows leak Hazards 86

Summary of important points Raafat Abdel-Azim Driving gas and patient gas don’t mix The ventilation cycle is controlled by F, V, P and T During the I phase, P aw depends on R and C T Goals of MV are to provide adequate V M (necessary to maintain the desired PaCO 2 ) and to  side effects Modern AV provide a range of ventilatory modes The difference between the delivered V T and the preset V T depends on CC and FGF FGD decreases the risk of barotrauma and volutrauma Hazards of MV can be avoided 87

Examples of questions to assess the ILOs Raafat Abdel-Azim Describe causes and ventilatory management of high airway pressure during inspiratory phase of mechanical ventilation Discuss goals of pulmonary ventilation under anesthesia With IPPV: if f (rate) = 10/min, I: E= 1:1 and FGF= 3 LPM What will be the volume added to the preset tidal volume? 88

Raafat Abdel-Azim Thank you 89