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Basics of Mechanical Ventilation
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Normal breath inspiration animation, awake
Diaghram contracts
Chest volume
Pleural pressure
Air moves down pressure gradientto fill lungs
-2cm H20
-7cm H20
Alveolarpressure falls
Normal breath
Lung @ FRC= balance
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Normal breath expiration animation, awake
Diaghram relaxes
Pleural / Chest volume
Pleural pressure rises
Normal breath
Alveolarpressure rises
Air moves down pressure gradientout of lungs
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تغییرات : منحنی
زمان( – 1 فشار
زمان( – 2 حجم
زمان( – 3 جریان
رسم طبیعی تنفسی سیکل یک در را:کنید
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0-1-2-5
Pres
sure
Expiration
Inspiration
+3+2+1
Normal breath
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Time
volu
me
0-1-2-5
Pres
sure
Expiration
Inspiration
+3+2+1
Normal breath
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FLO
W
Expiration
Inspiration
Normal breath
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volu
me
0-1-2-5
Pres
sure
Expiration
Inspiration
+3+2+1
FLO
W
Expiration
Inspiration
Normal breath
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Ventilator breath inspiration animation
Air blown in
lung pressure Air moves down pressure gradientto fill lungs
Pleuralpressure
0 cm H20
+5 to+10 cm H20
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Ventilator breath expiration animationSimilar to spontaneous…ie passive
Ventilator stops blowing air in Pressure gradient
Alveolus-trachea
Air moves outDown gradient Lung volume
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تغییرات منحنیفشار (1 حجم (2
جریان (3رسم مصنوعی تنفس سیکل یک در را
:کنید
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volu
me
0-1-2-5
Pres
sure
+3+2+1
FLO
WNormal breath Mechanical breath
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Origins of mechanical ventilationOrigins of mechanical 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.
Iron lung polio ward at Rancho Los Amigos Hospital in 1953.
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Several ways to ..connect the machine to Pt
• Oro / Naso - tracheal Intubation
• Tracheostomy
• Non-Invasive
Ventilation
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Ventilation = Inspiration + ExpirationInspiration = 1) Start or Triggering 2) inspiratory motive force or control or Mode 3) termination of inspiration or CyclingExpiratory Phase Maneuvers
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Classification (the Basic Questions)
A. Trigger mechanism– What causes the breath
to begin?
B. Limit variable– What regulates gas
flow during the breath?
C. Cycle mechanism– What causes the breath
to end?
A
B C
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1 2 3 4
The four phases of each ventilatory cycle
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Time
volu
me
InspirationExpiration
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Time
volu
me
inspira
tory
motive fo
rce or c
ontrol o
r Mode
Cycling
Start
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Cycling Vs. Limiting
Cycled
Pressure
Time Time
Limited
Pressure
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ببرید نام را مکانیکی تنفس مرحله :چهار1)2)3)4)
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Triggering the Ventilator
flow trigger
pressure trigger
volume Trigger
Time Trigger
Other techniques: Neurally Adjusted Ventilatory Assist (NAVA) Chest impedance Abdominal movement
Flow triggering is considered to be more comfortable,
Increasing the trigger sensitivity: decreases the work of breathing accidental triggering and unwanted breaths
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Trigger
Which Trigger is correct?
flow trigger
pressure trigger
volume Trigger
Time Trigger Mandatory
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all the breaths with mandatory
inspiratory cycling
SpontaneousUnsupported
Mandatory
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Trigger
Which Trigger is correct?
flow trigger
pressure trigger
volume Trigger
Time Trigger
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Trigger
Which Trigger is correct?
flow trigger
pressure trigger
volume Trigger
Time Trigger Mandatory
supported
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Trigger
Which Trigger is correct?
flow trigger
pressure trigger
volume Trigger
Time Trigger MandatorySynchronized
supported
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Triggered
(PSV)
Mandatory(VCV)
spontaneous and mandatory
inspiratory cycling
spontaneous and
mandatory
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No mandatory inspiratory cycling all the breaths are pressure-targeted and trigger inspiratory-cycled
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Which Trigger?
flow trigger
pressure trigger volume Trigger
Time Trigger
Non of the above
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Air INAir OUT
InspirationExpiration
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A certain amount of time is necessary for pressure equilibration (and therefore completion of delivery of gas) to occur between proximal airway and alveoli. TC, a reflection of time required for pressure equilibratlon, is a product of compliance and resistance. In diseases of decreased lung compliance, less time is needed for pressure equilibration to occur, whereas in diseases of increased airway reslstance, more time is required. Expiratory TC is increased much more than inspiratory TC in obstructive airway diseases, because airway narrowing is exaggerated during expiration.
Time Constant = C X R
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3-5 time constant
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C = 100 cc/ Cm H2OR = 1 Cm H2O / L / Sec
Time Constant = ? = R.C =100 cc/ Cm H2O X 1 Cm H2O / L / Sec = 0.1 Sec
Time Constant
C = 50 cc/ Cm H2OR = 1 Cm H2O / L / Sec
TC= ? = R.C =50 CC / Cm H2O X 1 Cm H2O / L / Sec = 0.05 Sec
C = 100 cc/ Cm H2OR = 2 Cm H2O / L / Sec
Time Constant = ? = R.C =100 CC/ Cm H2O X 1 Cm H2O / L / Sec = 0.2 Sec
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C = 40 cc/ Cm H2OR = 4 Cm H2O / L / Sec
Inspiratory Time = ??
TC = C x R = 0.16
IT = 3 x 0.16 = 0.48
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Selection of Appropriate Inspiratory TimeTI too longTI too shortT I = 3-5 time constant Tc = C x R
TI is usually initiated at: 0.5-0.7 sec for neonates, 0.8-1 sec in older children, 1-1.2 sec for adolescents and adultsneed to be adjusted through : individual patient observations and according to the type of lung disease.
T I + T E = Time CycleF ( RR ) = 60/TC I T E T F= 60/ TI +TE
T I = 3-5 time constant Tc = C x R
Many ventilators ask the user to set the I:E ratio and respiratory rate
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V T = 100 cc TI = 0.8 sec Inspiratory Flow = ?Inspiratory Flow = 100 / 0.8 = 125 cc/sec (7.5 L/ Min )
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• RR = 60 I:E = ½ IT = ? ET = ?F= 60/ TI +TE60 = 60 / TI + 2TI = 60/ 3TI
IT = 0.33 ET = 0.66
• IT= 0.8 ET= 1.2Sec• RR=?
F= 60/ TI +TERR = 60 / 0.8+1.2 = 30
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DeceleratingSquareAcceleratingSinusoidal
DeceleratingSquareAcceleratingSinusoidal
Inspiratory Flow/Pressure/Volume Pattern
time
Inspiratory Rise TimeInspiratory Rise Time
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Pressure-controlled inflationPm
ax =
Pin
f + P
EE
Inspiratory Rise TimeInspiratory Rise Time
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Effect of a pressure-limit on a volume-controlled breath
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CyclingTermination of Inspiration (Cycle)
1)Time-cycled 2)Volume-cycled
3) flow-cycled
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VT
Cycling at 25% Flow
Pressure Controlled Ventilation
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Pressure Controlled Ventilation
respiratory resistance and compliance are both lower
both the resistance and compliance of the respiratory system are higher
IT>IT<
Cycling at 25% Flow
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(high resistance), prolonged inspiration a large tidal volume. the next inspiratory phase starts before expiratory gas flow has reached zero
50%
10%ET ET
Over inflation Improve Over inflation
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inspiratory motive force or control or Mode
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Critical Opening Pressure
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The desired tidal volume is set on the ventilator, and the resulting airway pressure excursion is merely observed. Inspiratory volume is thus the primary, or independent, variable (V) and the change in airway pressure (P) resulting from this is the secondary, or dependent, variable.The value of P is determined by the compliance of the respiratory system, which is given by V/P. If the compliance of the respiratory system falls, V remains constant but P increases
Volume Controlled Ventilator
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The desired inflating pressure is set on the ventilator, and the tidal volume that this delivers is merely observed. The change in airway pressure is thus the primary, or independent, variable (P) and the volume change (V) resulting from this is the secondary, or dependent, variable. The value of V is determined by the compliance of the respiratory system, which is givenby (V/P). If the compliance of the respiratory system falls, P remains constant but V falls
Pressure Controlled Ventilator
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A: Volume/time curve for a volume-controlled inspiration witha tidal volume of VT1 litres and an inspiratory time of TIaseconds. The inspiratory flow ( ˙VI ) is the slope of the volume/time : ˙VI = VT 1 / TI a
volume-controlled inspiration
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I time instant
Low VT
High VT
Low Flow
High Flow
volume-controlled inspiration
جاری حجم در تغییر
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Time
PRES
SURE
کنید رسم مختلف های حجم در را فشار تغییرات :منحنی
جاری افزایش (1 حجم
جاری ( 2 حجم کاهش
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VT Constant
I time variable
Low Flow
High Flow
دم زمان در تغییر
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Time
PRES
SURE
کنید رسم دم مختلف زمانهای در را فشار تغییرات :منحنی
دم (1 زمان افزایشدم (2 زمان کاهش
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Inspiration sometimes have two phases, 1)an active ‘flow’ (TI f low) phase during which gas is being delivered to the patient, 2) end-inspiratory pause (TI pause )
TI = TI f low + TI pause
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end-inspiratory pause
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Changes inEnd-inspiratory
Pause
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Pressure profile of a volume-controlled breath with an end-inspiratory pause
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Time
PRES
SURE
در دم مختلف های وقفه در را فشار تغییرات :vcvمنحنی کنید رسم
دم (1 وقفه زمان افزایشدم (2 وقفه زمان کاهش
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FLO
W
تغییرات در جریانمنحنی دم مختلف های وقفه در :vcvرا کنید رسم
دم (1 وقفه زمان افزایشدم (2 وقفه زمان کاهش
FLO
W
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تغییرات در حجممنحنی دم مختلف های وقفه در :vcvرا کنید رسم
دم (1 وقفه زمان افزایشدم (2 وقفه زمان کاهش
volu
me
volu
me
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Volume-controlled inflation
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. A good indicator of adequate tidal volume is:
. . . . . a. good chest rise
. . . . . b. adequate breath sounds
. . . . . c. oxygen saturation = 100%
. . . . . d. a and b
As compliance worsens in a child receiving volume controlled mechanical ventilation, the TV delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change
As resistance increases in a child receiving volume controlled mechanical ventilation, the TV delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change
►
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As resistance decreases in a child receiving volume controlled mechanical ventilation, the TV delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change
As compliance worsens in a child receiving volume controlled mechanical ventilation, the Pressure delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change
As resistance decreases in a child receiving volume controlled mechanical ventilation, the Pressure delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change
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As resistance increases in a child receiving volume controlled mechanical ventilation, the Pressure delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change
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Comparison of ‘volume-controlled’and ‘pressure-controlled’ breaths
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Comparison of ‘volume-controlled’and ‘pressure-controlled’ breaths
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Comparison of ‘volume-controlled’and ‘pressure-controlled’ breaths
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Trigger Inspiratory cycling Inspiratory support Breath type Example
Time Time Yes Mandatory IPPV
Patient Patient Yes Triggered Pressure support
Patient Patient No Spontaneous CPAP
IPPV PSV CPAP
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CONVENTIONAL VENTILATOR SETTINGSFI02Is the patient adequately oxygenated?2 Question
1: ‘how well are this patient’s lungs able to take up the oxygen I am supplying?’2: ‘is enough oxygen being supplied to the patient’s vital organs?’
The clinical assessment of the adequacy of oxygenation is deceptively difficult
Measurement of PaO2 or (SaO2), or both
The PaO2 and SaO2 are not equivalent and provide different information
PaO2/ FiO2A-a Gradient
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CaO2 = ( Hb × 1.34 × SaO2/100 ) + (0.0225 × PaO2 )
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A-a Gradient = PAO2 − PaO2
PAO2 = FIO2 × (Pb − 47) − PaCO2/0.8
PAO2=F IO2 × (Pb + { PEEP/75} − 47) − PaCO2/0.8
oxygenation index OI = 100 × FIO2 × Paw/ PaO2
PAO2/ PaO2 more indicative of V/ Q mismatch and alveolar capillary integrity.VI = )PIP x ventilator rate/min x Paco2) / 1000==================================================================
extra-pulmonary
CaO2 = ( Hb × 1.34 × SaO2/100 ) + (0.0225 × PaO2 )
oxygen delivery D ˙ O2 = ˙Qt × CaO2/ 100
oxygen consumption
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FiO2Pa O2 SaO2 = 95
Pa02 value of 70-75 torr is a reasonable goal
Fi O2 values should be decreased to a level ~0.4 as long as SaO2 remains 95% or above
Rate of diffusion = Area × K × PAO2− PaO2 / d
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RR by ETCPAP
IT / Plateau
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Positive end-expiratory pressure (PEEP)
What is PEEP?Positive pressure measured at the end of expiration.
PHYSIOLOGICAL PEEPPEEP (3 to 5 cm H2O) to overcome the decrease in FRC that results from the bypassing of the glottic apparatus by the ETT
)
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Positive End-expiratory Pressure (PEEP)
PEEP FOR HYPOXAEMIA• ‘to open the lungs and keep them open’• To improve respiratory mechanics,• To reduce intrapulmonary shunt, • To stabilize unstable lung units • To reduce the risks of ventilator-induced lung injury (VILI• Recruit lung in ARDS• Prevent collapse of alveoli• Diminish the work of breathing
What is the goal of PEEP?
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Critical Opening Pressure
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Collapse/ atelectosis/ ARDS
Increases Surface area for gas exchangeOpens the collapsed lung
Collapsed alveoli
After PEEP
PEEP
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PEEP- Indications. • If a PaO2 of 60 mmHg cannot be achieved
with a FiO2 of 60% • If the initial shunt estimation is greater than
25% • Pulmonary edema• ARDS/ALI• Atelectosis
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Complications of positive end-expiratory pressure (PEEP) Pulmonary over-distension Barotrauma Ventilator-induced lung injury (VILI) Increased dead space Impaired carbon dioxide elimination Reduced diaphragmatic force-generating capacity Reduced cardiac output and oxygen delivery Impaired renal perfusion Reduced splanchnic blood flow Hepatic congestion Reduced lymphatic drainageDiminish cardiac outputRegional hypoperfusionAugmentation of I.C.P.?Paradoxal hypoxemiaHypercapnoea and respiratory acidosis
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Prolongation of inspiratory time
INVERSE RATIO VENTILATION
first described in the early 1970s in infants with ARDS
the inspiratory period extends beyond 50% of the total cycle time
IRV can be applied in either volume- (VC) or pressure-controlled (PC) mod.
To maintaining an open lung in ALI/ARDS
requires profound sedation and frequently the use of neuromuscular blockade.
adverse consequences to cardiac output; any perceived benefits to oxygenation maywell be offset by consequent reductions in oxygen delivery.
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AIRWAY PRESSURE RELEASE VENTILATION (APRV)first described in 1987. is a form of bi-level assisted ventilation utilizing continuous positive airway pressure (CPAP) with periodic pressure releases, either to a lower CPAP pressure or to atmospheric pressure The ventilator settings for APRV do not usually include the respiratory frequency but instead :the duration of Phigh, Thigh in seconds;the duration of Plow, Tlow in seconds; absolute value of Phigh and Plow.the patient is able to breathe spontaneously during both of these phases.
Bi-level ventilation
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Bi-level ventilation. the airway pressure cycles between two levels of CPAP. The patient can breath spontaneously during both Phigh and Plow phases, and only receives inspiratory assistance during the low–high transition.
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High-frequency oscillatory ventilation. (HFOV) A system of ventilation which uses respiratory rates between 300 and 900 breaths per minute
Oscillator
ET tube
Carina
Segmental bronchi
Alveoli
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Recruitment maneuvers
PRONE POSITION
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Ventilation
at rest 200 mL.min−1
1) volume of dead space,2) tidal volume, 3) respiratory frequency 4) Positive end-expiratory pressure (PEEP
1) volume of dead space,2) tidal volume, 3) respiratory frequency 4) Positive end-expiratory pressure (PEEP
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Influences on the production of carbon dioxide• Factors associated with increased carbon dioxide production
– Systemic inflammation– Sepsis– Burnt patients– Hyperpyrexia– Thyrotoxic crisis– Muscular activity (seizures, excessive respiratory work)– Predominance of glucose as metabolic substrate– Administration of exogenous bicarbonate
• Factors associated with reduced carbon dioxide production– Hypothermia– Hypothyroidism– Sedation and neuromuscular blockade– Predominance of fatty acids as metabolic substrate
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P CO2 = K X ( V CO2 / MV)
MV = RR X VT
VT = Alveolar Space + Dead Space
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Dead Space Physiological dead space (VD) = Alveolar (VDA) + Anatomical (VDanat)
VD = Alveolar (VDA) + Anatomical (VDanat) +Equipment (VDequip)
Vd/Vt = 0.3
VD / VT = PaCO2 − PE TCO2 / PaCO2
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Tidal Volume and Rate
VT and rate depends on the time constant. In normal lungs :
age-appropriate ventilator rate tidal volume of 7-10 mL/kg
Diseases associated with decreased time constants (decreased static compliance, are best treated with :
small (6 mLlkg) tidal volume and relatively rapid rates
Diseases associated with prolonged time constants (increased airway resistance, e.g., asthma, bronchiolitis)are best treated with:
relatively slow rates and higher (10-12 mLlkg) tidal volume
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Positive end-expiratory pressure (PEEP)effects on CO2
Low levels of PEEP (3 to 5 cmH2O) have little effect Higher levels of PEEP (8 to 15 cmH2O) may increase the Vd/Vt ( mostly with low VT) CO2
in recruitable lung CO2intrinsic PEEP
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General techniques to lower carbondioxide production
Avoidance of pyrexia induced hypothermiaLowering the respiratory quotient (use of fatty acids)Sedation and neuromuscular blockade reduce metabolic rate by around 9%
Conventional mechanical ventilation alveolar ventilation
Adjunctive pulmonary therapiesBronchodilatorsPhysiotherapy
Tracheal gas insufflation
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Permissive hypercapniapotential advantage of permissive hypercapnia: deliberate hypoventilation
reduction in tidal volumes reduction transpulmonary pressures
limit pulmonary injury. In vitro, hypercapnia reduces the activation of: NF-kB, intercellular adhesion molecule-1 (ICAM-1) interleukin-8 (IL-8)in human pulmonary endothelial cells
NF-kB is a key regulatory molecule in the activation of many pro-inflammatory genes, including those that produce ICAM-1 and IL-8, molecules that trigger the movement of leukocytes into the inflamed lung.
In vivo, Hypercapnia may reduce inflammation in experimental lung injury.
Finally, hypercapnia may improve ventilation perfusion matching and intestinal andsubcutaneous tissue oxygenation
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Increase in: pCO2 pO2 MAP
FiO2 no change increase no change
Rate decreaseusually no
changeincrease
PIP/TV decrease increase increase
Inspiratory time
usually no change
increase increase
PEEPusually no
changeincrease increase
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MONITORING RESPIRATORY MECHANICSExhaled Tidal Volumeleak outdecrease in VTE ( PCV) : decrease in compliance or increase in resistance
increase in VTE is indicative of improvement and may require weaning of inflation pressures to adjust the VTE.Peak Inspiratory PressureIn VCV and PRVC, the PIP is determined by compliance and resistance.
increase in PIP decreased compliance (atelectasis, pulmonary edema, pneumothorax) or increased resistance (bronchospasm, obstructed ET).
decreasing the respiratory rate lower PIP in patients with prolonged TC or prolonging the TI
In such patients, a decrease in PIP suggests increased complianceor decreased resistance of the respiratory system.
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CDYN= VTE / ( PIP - PEEP)
VCV and PRVC
PCV
CDYN= VTE / ( PIP - PEEP)
CSTAT= VTE/ (Pplat - PEEP)
Respiratory System Dynamic Complianceand Static Compliance
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Assessment of Auto-PEEP
Auto-PEEP is assessed with the use of an expiratory pause maneuver
-have adverse effects on ventilation and hemodynamic status. Management : decreasing RR or decreasing inspiratory time increasing the set PEEP ("extrinsic" PEEP),
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Ventilator settings1. Ventilator mode2. Respiratory rate3. Tidal volume or pressure settings4. Inspiratory flow5. I:E ratio6. PEEP7. FiO28. Inspiratory trigger
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Assist – Control AC
Trigger windowCan be set
Vent breath Vent breath Synch Vent breath Vent breath
Spont breath sensedSensitivity can be set
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AC
• Patient only gets ventilator breaths• These are just delivered at different times to
coincide with patient spontaneous effort• Can help keep lungs recruited
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SIMV
Trigger window 1 for Vent breath
Vent breath Vent breath Synch Vent Supported Vent breath breath breath
Spont breath sensedTrigger window 2 for supported breath
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Pressure Support
• Because it is difficult to breathe through a ventilator, the vent can help
• It supports spontaneous effort• Pressure support
– No background rate– Patient determines resp rate & I:E– Usually apnoea backup
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Pressure Support
Spontaneous breath sensed by ventilator
Pressure is applied throughout inspiratory effort
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CPAP & PEEP
The constant bit
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CPAP and PEEP
• What do they do for your lungs?
• What about your cardiovascular system?
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BiPAP
• Bi-Level Positive Airway Pressure• 2 PEEPs basically• Patient can breathe at any point
– Easier for patient to tolerate– Less sedation?
• Pressure support can be added if required
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Origins of mechanical ventilationOrigins of mechanical ventilation
•Negative-pressure ventilators (“iron lungs”)
•first used in Boston Children’s Hospital in 1928
•Used extensively during polio outbreaks in 1940s – 1950s
The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output.
Iron lung polio ward at Rancho Los Amigos Hospital in 1953.
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Era of intensive care begun with this
• Positive-pressure ventilators– Invasive ventilation first used at Massachusetts
General Hospital in 1955– Now the modern standard of mechanical
ventilation
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CMV
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CMV
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CMV
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CMV
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CMV
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CMV
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CMV-Volume
Volume
Tidal Volume
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CMV-P
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A/CV
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SIMV
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Pressure Support Ventilation (PSV)Pressure Support Ventilation (PSV)Patient determines RR, VE, inspiratory time – a purely spontaneous mode
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CPAP and BiPAPCPAP and BiPAPCPAP is essentially constant PEEP; BiPAP is CPAP plus PS
•ParametersCPAP – PEEP set at 5-10 cm H2OBiPAP – CPAP with Pressure Support (5-20 cm H2O)
Shown to reduce need for intubation and mortality
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Respiratory Rate• 10-12/Min – Adult
• 20+_ 3 - Child
• 30- 40 - New born
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Respiratory Rate
• Increase – HypoxiaHypercapnoea / Resp.Acidosis
• DecreaseHypocapnoeaResp.AlkalosisAsthma / COPD
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DHIDHI
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Hey not always
the same buddy
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Tidal Volume or Pressure setting
• Optimum volume/pressure to achieve good ventilation and oxygenation without producing alveolar overdistention
• Max = 6-8 cc/kg
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Inspiratory Trigger• Normally set automatically
• 2 modes:
– Airway pressure– Flow triggering
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I:E Ratio
• Normaly 1:2
• Asthma/COPD 1:3, 1:4, …
• Severe hypoxia ARDS/ALI
Pul.Edema 1:1 , 2:1
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FIO2• Goal – to achive PaO2 > 60mmHg or a sat
>90%
• Start at 100% aim 40%
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Vent settings to improve <oxygenation>Vent settings to improve <oxygenation>
•FIO2
•Simplest maneuver to quickly increase PaO2
•Long-term toxicity at >60%• Free radical damage
•Inadequate oxygenation despite 100% FiO2 usually due to pulmonary shunting•Collapse – Atelectasis•Pus-filled alveoli – Pneumonia•Water/Protein – ARDS•Water – CHF•Blood - Hemorrhage
PEEP and FiO2 are adjusted in tandem
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Pulmonary edema
Translocation of fluid to peribroncheal region – helps in oxygenation
PEEP
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DOPE• D- Disposition of ETT• O- Obstruction / kinking• P- Pneumothorax• E- Equipment failure
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Prerequisites to extubation include:
•1) A good cough/gag (to allow the child to protect their airway).
2) NPO about 4 hours prior to extubation (in case the trial of extubation fails and reintubation is required). 3) Minimize sedation. 4) Adequate oxygenation on 40% FiO2 with CPAP (or PEEP) = 4. 5) The availability of someone who can reintubate the patient, if necessary. 6) Equipment available to reintubate the patient, if necessary.