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Mechanical Ventilation

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Chronic airway obstruction - emphysema - chronic asthma - chronic bronchitis ... asthma - chronic bronchitis - bronchiolitis - atelectasis - thromboemboli ... – PowerPoint PPT presentation

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Title: Mechanical Ventilation


1
Mechanical Ventilation
2
Introduction
  • Defined as the support of a patients ventilatory
    needs by artificial means
  • Is an interim life support measure that gives the
    physician an opportunity to medically correct or
    stabilize a patients cardiopulmonary problem
  • Does not cure the patient, even though it may
    prolong life

3
Medical Indication for M. V.
  • Is generally indicated to prevent patient from
    going into respiratory failure or to provide life
    support and stabilize those who are already in
    respiratory failure
  • Resp. failure the inability of the lungs to
    maintain either the normal delivery of O2 to the
    tissues or the normal removal of CO2 from the
    tissues
  • Table 37.2, p. 824 (Egans)

4
Respiratory Failure
  • Two categories - Type I (hypoxemic R.
    F.) - Type II (hypercapnic R. F.)
  • Type I is caused by - V/Q mismatch -
    Intrapulmon. Shunt - alveolar hypoventilation
    - decreased FIO2 - diffusion impair. -
    diffusion/perfusion impairment

5
Resp. Failure (contd)
  • Type II causes - Decreased ventilatory
    drive d/t drugs, brainstem lesions, sleep apnea,
    hypothyroidism - Respiratory muscle
    fatigue, e.g., CNS problems, muscular dystrophy
    - Increased work of breathing d/t
    COPD, pneumothorax, rib fx., pleural
    effusions

6
Respiratory Failure (contd)
  • Clinical manifestations of acute R. F.
  • - restlessness - confusion
  • - tachycardia - diaphoresis
  • - headache - hypotension - central
    cyanosis - tremors - depressed ventilation -
    unconsciousness
  • ID R.F. by a deteriorating clinical picture
    combined with ABG values (PaO2 lt 50 PaCO2 gt 50
    on room air

7
Causes of Impaired Ventilation
  • Chronic airway obstruction - emphysema -
    chronic asthma - chronic bronchitis
  • Restrictive defects - interstitial
    fibrosis - pneumothorax - pleural effusion -
    chest surgery - flail chest - kyphoscoliosis -
    severe obesity - abd. surgery - peritonitis

8
Impaired Vent. (contd)
  • Neuromuscular defects - myasthenia gravis -
    Guillain Barre - multiple sclerosis -
    tetanus - spinal injuries - poliomyelitis -
    drugs an poisons
  • CNS damage or depression d/t - anesthetics -
    narcotics - barbiturates - tranquilizers -
    head trauma

9
Impaired a-c Gas Exchange
  • Due to diseases/conditions such as - fibrosing
    alveolitis - pneumoconiosis - sarcoidosis -
    tumors - pulmonary edema - thromboemboli
  • - pneumonectomy - collagen disease

10
V/Q abnormalities
  • Caused by anatomic and physiologic shunts
  • Anatomic shunt - blood flows from R. side of
    heart to L. side without passing through pulmon.
    vasculature
  • Physiologic shunt d/t - emphysema -
    asthma - chronic bronchitis - bronchiolitis -
    atelectasis - thromboemboli
  • - resp. distress syndrome - pneumonia

11
Goals of Mechanical Vent.
  • Provide adequate ventilation - best indicator
    of alveolar vent. is PaCO2
  • Adequate Oxygenation
  • Reduced work of breathing - Normally WOB
    requires 2-3 of total O2 consumption, but
    decreased compliance and resistance may cause
    200-300 increase in WOB

12
Complications and Hazards of Mechanical
Ventilation
  • Effects on systemic circulation by increased
    intrathoracic pressure
  • Barotrauma - modes such as SIMV and high
    frequency ventilation can help prevent -
    physical findings of pneumothorax
  • Hyperventilation - PaCO2 should not be
    allowed below 35 unless to lower ICP

13
Complications (contd)
  • Effects on other organ systems, i.e., hepatic,
    renal, GI
  • See decreased liver function d/t diaphragm
    pressing down on liver interfering with portal
    blood flow, may see blood clotting problems and
    decr. detoxification of drugs
  • Renal dysfunction and decreased urine output
    caused by incr. prod. of ADH and decr. renal
    blood flow (interstitial edema, decr. PaO2)

14
Complications (contd)
  • GI problems, i.e., bleeding, d/t pressure
    interfering with circulation to spleen and GI
    tract leading to mucosal ischemia and incr.
    effects of acid in tract. Prevention with
    antacids

15
Mech. Vent. Control Circuits
  • Mechanical, i.e., levers, pulleys, and cams
  • Pneumatic, which uses gas pressure to operate
    diaphragms, jet entrainment devices, and pistons
  • Fluidic , which are similar to electronic logic
    circuits and use minute gas flows to operate
    timing systems and pressure switches
  • Electric, which use only simple switches

16
Control Circuits (contd)
  • Electronic, which use devices such as resistors,
    capacitors, diodes, and transistors in an
    integrated circuit. Can range in complexity from
    simple logic gates to microprocessors.

17
Ventilator Drive Mechanisms
  • Lung inflation takes place d/t a pressure
    gradient created between the mouth and alveoli.
    To generate this pressure various drive
    mechanisms are used
  • Seven common types
  • - weighted bellows - blowers
  • - injectors - press. reducing valves -
    pistons (linear nonlinear)
  • - spring-loaded bellows
  • -microprocessor controlled pneumatics

18
Weighted Bellows
  • Pressure generated within the bellows is a
    function of wt. acting on the cross-sectional
    area of the bellows
  • Pressure generated is constant

19
Pressure Reducing Valve
  • Reduces a high input press. to a lower constant
    output press.
  • May be adjustable or preset

20
Blowers
  • Is an electric motor connected to a fan and
    rotates at a high constant speed

21
Injectors
  • Mechanisms powered by press. reducing valves or
    blowers and main function is to increase the
    overall flowrated capability of the ventilator

22
Linear Driven Pistons
  • Pressure is generated with the use of an electric
    motor and a piston
  • Linear motion is transferred to the piston and
    positive pressure is generated during the
    pistons forward stroke

23
Non-linear driven pistons
  • Electric motor rotates a large wheel to which a
    connecting rod and piston are attached and
    positive pressure is generated during the forward
    stroke of the piston

24
Spring-loaded Bellows
  • Tension of a spring applies a continuous downward
    force to top of bellows
  • Pressure in the bellows does not remain constant

25
Microprocessor controlled Pneumatic Drive Systems
  • Use proportional solenoid valves and
    microprocessor controls
  • Uses programmed algorithms to open and close the
    solenoid valves to mimic virtually any flow or
    pressure wave pattern

26
Chatburns Mechanical Ventilator Classification
  • To understand ventilators in general, we need to
    understand basic functions of - Power
    input - Drive mechanisms - Control
    scheme - Output ( pressure, volume, and flow
    waveforms) - Alarm systems

27
Power Input
  • Electric - use 110-115 volts AC (60 Hz),
    can then be converted to DC to power
    electronic control circuits - DC(from lead
    acid batteries), which supplies about 2.5
    amp-hours of energy. Battery will usually power
    a vent. for up to 1 hour (requires 8-12 hours to
    recharge)
  • Pneumatic

28
Drive Mechanisms
  • Compressor - External -
    Internal 1. Piston and cylinder 2.
    Diaphragm 3. Bellows 4. Rotating vane

29
Drive Mechanisms (contd)
  • Motor and linkage - electric motor/rotating
    crank and piston rod - electric
    motor/rack and pinion - electric
    motor/direct (turns compressor - compressed gas
    regulator/direct (gas is used as the motor) i.e.
    PB7200
  • Output control valve - used to regulate the
    flow of gas to the patient

30
Drive Mechanisms (contd)Output Control Valve
  • Electromagnetic Poppet Valve - uses magnetic
    force caused by an electric current to control
    a pneumatic pressure in an on/off fashion
  • Pneumatic Poppet Valve - similar to a
    solenoid valve except it uses a small pneumatic
    press. to control a larger pneumatic press.
    (fluidic)

31
Output Control Valve (contd)
  • Proportional Valve - Is a mass flow control
    valve - similar to a solenoid, but uses a
    stepper motor where it is not just on/off but
    changes the diameter of the outflow port to
    give a variety of waveforms - PB 7200, Hamilton
    Veolar, Servo 900C, Bear 5
  • Pneumatic Diaphragm - mushroom valve,
    exhalation valve

32
Control Scheme
  • A ventilator can directly control only one
    variable at a time pressure, volume, or flow
  • Consists of 1. Control circuits 2.
    Control variables 3. Phase variables 4.
    Modes of ventilation and conditional variables

33
Control Circuits
  • Is the subsystem responsible for controlling the
    drive mechanism and/or the output control valve.
    A vent. may have more than one control circuit,
    which may be of several types.
  • Mechanical, Pneumatic, Fluidic, Electric, and
    electronic

34
Control Variables and Waveforms
  • A vent. may be classified as either a pressure,
    volume, or flow controller, and less often as a
    time controller, and may also be characterized by
    the type of waveforms it can generate.
  • Vents. can also combine control schemes to create
    complex modes, e.g., PB7200 can mix flow-
    controlled breaths with pressure-controlled
    breaths (SIMV PSV)

35
Control Variables and Waveforms (contd)
  • PressureController - the vent. can control
    either the airway pressure or the pressure on the
    body surface, hence the classification of
    positive pressure vs. negative pressure - a
    positive press. controller generates a
    rectangular pressure waveform and an iron lung
    would generate a sinusoidal waveform

36
Control Variables and Waveforms (contd)
  • Volume controller - to be classified as a
    volume controller a vent. must (1) maintain a
    consistent volume waveform in the presence of a
    varying load and (2) measure volume and use the
    signal to control the volume waveform

37
Control Variables and Waveforms (contd)
  • Flow Controller - if the volume change
    remains consistent when compliance and
    resistance are varied, and volume change is
    not measured and used for control -
    Servo 900C is a flow controller because it
    measures flow and adjusts the output control
    valve accordingly

38
Control Variables and Waveforms (contd)
  • Time Controller - if both pressure and
    volume are affected substantially by changes
    in lung mechanics, then the only variables being
    controlled are inspir. and expir. times - see
    this in some high-freq. vents

39
Phase Variables
  • Still use division into 4 phases 1. Change
    from E to I 2. Inspiration 3. Change
    from I to E 4. Expiration
  • In each phase a particular variable is measured
    and used to start, sustain, and end the phase
  • Uses trigger, limit, cycle, and baseline variables

40
Phase Variables (contd)Trigger Variable
  • Trigger variable refers to an initiation of a
    breath when one of the variables of pressure,
    volume, flow, or time reaches a preset value
  • Most common trigger variable is time
  • Other trigger variables include manual and on
    some infant vents. see chest wall movement as the
    trigger variable

41
Phase variables (contd)Limit Variable
  • During inspiration pressure, volume, and flow
    increase above their baseline values
  • A variable is limited if it increases to a
    pre-set value before inspiration ends. In other
    words, inspiration does not end when the variable
    reaches its preset value
  • Limit variable in other words, sustains
    inspiration

42
Phase Variable (contd)Cycle Variable
  • Inspiration ends because some variable (pressure,
    volume, flow, or time) has reached a pre-set
    value
  • This ending variable must be measured by the
    ventilator and used as a feedback signal to end
    inspiratory flow delivery, which then allows
    exhalation to begin

43
Phase Variables (contd)Baseline Variable
  • Baseline variable is the variable that is
    controlled during the expiratory time
  • Pressure is the most practical value to control
    and is used by all commonly used ventilators
  • PEEP, CPAP

44
Conditional Variables
  • Conditional variables can include pressure, tidal
    volume, inspiratory flow, minute ventilation,
    time, etc.
  • If the value of a conditional value reaches some
    pre-set threshold, then some action occurs to
    change the ventilatory pattern, e.g., MA-1 vent.
    when giving a sigh breath (the conditional
    variable is time), or as in SIMV if vent.
    detects pt. effort and window is open then
    spont. breath

45
Output
  • The study of ventilatory operation requires the
    examination of output waveforms
  • The waveforms we look at are pressure, volume,
    and flow
  • Waveforms are grouped into 4 basic
    categories - rectangular - exponential -
    ramp - sinusoidal

46
Rectangular(see with pressure, flow)
47
Sinusoidal(see with volume, flow)
48
Ascending Ramp(see with pressure, volume, and
flow)
49
Descending Ramp(see with flow)
50
Exponential (rise)(see with pressure)
51
Exponential (decay)(see with flow)
52
Characteristic Waveforms
53
Pressure/Volume Curve
54
Flow/Volume Loop
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