Mechanical Ventilation of the Critically Ill Child:
Where do we stand in 2006?
Ronald C. Sanders Jr., M.D., M.S.Assistant Professor, Dept. of Pediatrics
Division of Critical Care, Shands Children’s Hospital
University of FloridaGainesville, Florida
Outline
Physiological Concepts• Pediatric Considerations• Work of Breathing (WOB)
Indications for Ventilatory Assistance• Initial Settings for Mechanical Ventilation
Mechanical Ventilation and the Pediatric Heart Patient
Basic Respiratory Physiology
West, JB. Respiratory Physiology. 5th Edition. 1995.
Junqueira LC et al.Basic Histology. Fifth Edition.1986.p.390.
Junqueira LC et al. Basic Histology.Fifth Edition.1986.p.395.
Basic Respiratory Physiology
Alveolar Gas Equation
PAO2 = PIO2
-PA
CO2
RPI
O2 = (PB - PH2O) x FIO
2 ; R = 0.8
West, JB. Respiratory Physiology. 5th Edition. 1995
A-a gradient = PAO2- PaO2
( Acceptable gradient < 20 mm Hg onroom air or less than 70 on 100% O2)
Basic Respiratory PhysiologyLi
ters
6
Total Lung Capacity
Vital Capacity
Tidal Volume
Residual Volume
Functional Residual Capacity
Inspiratory Reserve Volume
Expiratory Reserve Volume
8
4
2
0
Distribution of Blood FlowWest Zones
Zone 1
Zone 2
Zone 3
PA
Pa
P
> Pa > Pv
> PA > Pv
a> Pv > PA
PEEP
Definition• Positive end expiratory pressure
Gattinoni L, Caironi P, Pelosi P and Goodman L. What Has CT Taught Us about ARDS? Am J Respir Crit Care Med 2001
Pressure-Volume Relationships
100
75
50
25
0-40 -20 0 20 40
Pressure (cm H20)
Vita
l Cap
acity
(%)
Chest wall
Lung
Chest wall and lung
TLC
FRC
At high lung volumes, complianceof the resp systemis decreased p-vcurve flattens as it becomes fullydistended
At low lung volumesreduced compliancemay be due to stiffeningof chest wall.
Whenever lung volumesfalls below closing volume,lung compliance will alsofall due to derecruitmentof functioning units
Children vs. Adults
Airway• In children, the airway is more anterior and the
epiglottis is floppy.
• The airways are smaller.– Poiseulle’s Law states that resistance is inversely
related to the 4th power of the radius (laminar flow).
Children vs. Adults
Chest Wall• In children, the chest wall is more compliant
which limits the capacity for gas exchange.
• This anatomical feature may necessitate increased respiratory rates to maintain adequate minute ventilation. This leads to increased metabolic activity.
Children vs. Adults
0
10
20
30
40
50
60
70
Premature Term > 2 Years
DiaphragmIntercostal Muscle
Type
I M
uscl
e Fi
bers
(%)
(slo
w-tw
itch,
hig
hly
oxid
ativ
e)
Cote CJ, Ryan JF, Todres ID et al. A practice of anesthesia for infants and children. 2nd ed. Philadelphia: WB Saunders, 1993.
Outline
Physiological Concepts• Pediatric Considerations • Work of Breathing (WOB)
Indications for Ventilatory Assistance• Initial Settings for Mechanical Ventilation
Mechanical Ventilation and the Pediatric Heart Patient
Respiratory System Loads
The combined effect of compliance and resistance constitute the load experienced by the ventilator and ventilatory muscles.
The elastic load is the “pressure” necessary to expand the lungs and chest wall (i.e. volume/compliance).
The resistance load determines the “pressure” necessary to deliver gas at a particular flow rate (i.e. flow x resistance)
FLOWFLOW
VOLUMEVOLUME
RESISTANCERESISTANCE
COMPLIANCECOMPLIANCE
VolumeVolume
ComplianceCompliancePressure =Pressure = + flow x resistance+ flow x resistance
P = Flow x ResistanceP = Flow x Resistance
Compliance = Compliance = ∆∆ VolumeVolume∆∆ Pressure Pressure
Total Work of Breathing
Total Work Total Work of Breathingof Breathing ==
PhysiologicPhysiologicWorkWork
ImposedImposedWorkWork++
Elastic work toElastic work toexpand lungs andexpand lungs andchest wall and flowchest wall and flowresistive work to resistive work to overcome airwayovercome airwayresistanceresistance
Resistive workResistive workimposed by imposed by breathing breathing apparatus (e.g.apparatus (e.g.endotracheal tube,endotracheal tube,breathing circuit, breathing circuit, and ventilatorand ventilator’’ssdemanddemand--flow system)flow system)
WOBT
V
P
P
V
Patient and Ventilator Work
VT
PAW
Pes
Insp
TIME
Exp
WOB P
WOB P + V
WOB V
Evaluating WOB in Ventilated Subjects
• Are there differences in WOB based on mode of ventilation?
Hypothesis: The WOBT will be unchanged between the SV300,VIP and the EV4 despite mode of triggering.
MethodsFor WOB data, airway pressure and flow rate were measured at the proximal end of the ET tube using a differential flow transducer.Intrapleural pressure was measured using an esophageal catheter.The transducers and esophageal catheter were connected to a Bicore CP-100 pulmonary monitor.
MethodsVentilator
BicoreCP-100
0
0
0
VolumeFlowratePES
HME
PNEUMOTACHOGRAPH(MeasurementofVolumeandFlowrate)
EsophagealPressure(P )ES
WOB-Campbell Diagram
II
EE
--4040 --3030 --2020 --1010 00 1010
5050
3535
VVTT
FRCFRC
CCLLCCCWCW
100100
Flow resistive workFlow resistive work
Elastic workElastic work
Imposed workImposed work
Stored energy of theStored energy of thechest wallchest wall
Work imposed byWork imposed bythe breathing app.the breathing app.
PhysiologicPhysiologicWorkWork
% V
ital Capacity
% V
ital Capacity
IntrapleuralIntrapleural pressure (cm Hpressure (cm H220)0)
Total Work of BreathingSV 300 vs VIP Bird
(Both on Pressure Triggering)Pressure Support 5 cm H2O
0
0.2
0.4
0.6
0.8
1
1.2
1.4
SV 300Bird
* p=0.028**p=0.028
*87%**122%
PEEP 0 PEEP 3cm H2O
WOBTJ/L
Sanders RC, Thurman TL, Holt,SJ, Taft K and Heulitt MJ. Work of BreathingAssociated with Pressure Support Ventilation in Two Different Ventilators.
Pediatric Pulmonology. 32:62-70, 2001
Total Work of BreathingSV 300 (Flow Trigger) vs VIP Bird (Pressure Trigger)
Pressure Support 5 cm H2O
0
0.2
0.4
0.6
0.8
1
1.2
1.4
SV 300Bird
* p=0.043**p=0.028
*125%
**144%
PEEP 0 PEEP 3
WOBTJ/L
Sanders RC, Thurman TL, Holt,SJ, Taft K and Heulitt MJ. Work of BreathingAssociated with Pressure Support Ventilation in Two Different Ventilators.
Pediatric Pulmonology. 32:62-70, 2001
POWER BUSY
Digital Analog
12345678
10
910111213141516
BIOPAC Systems, Inc. MP100
Analog C
hannelsZERO SPAN CD 15
ZERO SPAN CD 15
SV300
pneumotach
Transducer
Carrier demodulators
UIM100A
HMETo PigTo Ventilator
All signals collected from the Drager Babylog 8000were routed via the pneumotach.
Transducer
Millennia XKU 300MHZ
a- b Start of deflection of flow to most negative deflection of pressurea - c Start of deflection of flow to maximum flow
SV 300
17.500 18.000 18.500 19.000seconds
0.00000
5.00000
10.0000
15.0000
cmH
20
pres
sure Insp. Flow
Flow
Volume
Insp. PressureExp. Pressure
Pressure
Exp. Flow
Start of deflection of flow
Maximum flow
Most negative deflection of pressure
a b c
Vent signal
Flow, and Pressure are signals received from pneumotach, Flow is integrated for VolumeInsp. Flow, Exp. Flow, Insp. Pressure and Exp. Pressure are signals received from the SV 300 VentilatorVent Signal is a signal received from the ventilator to indicate patient trigger
Patient and Ventilator Work
VT
PAW
Pes
Insp
TIME
Exp
WOB P
WOB P + V
WOB V
a b c
SV 300, Flow Trigger, Pressure Support 5, PEEP 0
17.500 18.000 18.500 19.000seconds
0.00000
5.00000
10.0000
15.0000
cmH
20
pres
sure
a- b Start of deflection of flow to most negative deflection of pressurea - c Start of deflection of flow to maximum flow
a b c
Insp. Flow
Flow
Volume
Exp. Pressure
PressureExp. Flow
Vent signal
Insp. Pressure
84 ms 235 ms
-.38 cmH20
delta p = .53 cmH20
Sanders RC, Thurman TL, Holt,SJ, Taft K and Heulitt MJ. Work of BreathingAssociated with Pressure Support Ventilation in Two Different Ventilators.
Pediatric Pulmonology. 32:62-70, 2001
Evita 4 Flow Trigger, Pressure Support 5, PEEP 0
a- b Start of deflection of flow to most negative deflection of pressurea - c Start of deflection of flow to maximum flow
1.5000 2.0000 2.5000 3.0000seconds
-5.00000
0.00000
5.00000
10.0000
cmH
20
pres
sure
Flow
Volume
Pressure
341 ms
a b c139 ms
-2.48 cmH20
delta p = 3.94 cmH20
Flow, and Pressure are signals received from pneumotach, Flow is integrated for Volume
Sanders RC, Thurman TL, Holt,SJ, Taft K and Heulitt MJ. Work of BreathingAssociated with Pressure Support Ventilation in Two Different Ventilators.
Pediatric Pulmonology. 32:62-70, 2001
Bird (Pressure Trigger)
-5.00000
0.00000
5.00000
10.0000
cm H
20
pres
sure
Flow
Start of deflection of pressure
Volume
Maximum flow
Most negative deflection of pressure
a b c d e
Maximum pressure
Flow
Start of deflection of pressure
~ 440 ms
a- b Start of deflection of pressure to most negative deflection of pressurea - c Start of deflection of pressure to maximum flowa - d Start of deflection of pressure to second increase in pressurea - e Start of deflection of pressure to max pressure
.0000 1.5000 2.0000 2.5000seconds
Flow, and Pressure are signals received from pneumotach, Flow is integrated for Volume
Outline
Physiological Concepts • Pediatric Considerations • Work of Breathing (WOB)
Indications for Ventilatory Assistance• Initial Settings for Mechanical Ventilation
Mechanical Ventilation and the Pediatric Heart Patient
Indications for Mechanical Ventilation
Ventilatory FailureHypoxiaHemodynamic InstabilityICP ManagementAirway protection
Slutsky AS. Consensus Conference on Mechanical Ventilation. Intensive Care Medicine 1994
Ventilatory Failure
A clinical diagnosis!ApneaPaCO2 > 60 (in patient with previous normal lungs)Vital capacity < 15 ml/kgDead space/tidal volume ratio> 0.6
Martin LD, Bratton SL. Principles and Practice of Respiratory Support and Mechanical Ventilation. In: Rogers MC,ed. Textbook of Pediatric Intensive Care, 1996.
Hypoxia
Cyanosis despite FiO2 > 0.6PaO2 < 70 torr with FiO2 > 0.6
AaDO2 > 300 torr with FiO2 = 1.0Qs/QT > 15-20% Qs/QT = Cco2 – Cao2
Cco2 – Cvo2
Martin LD, Bratton SL. Principles and Practice of Respiratory Support and Mechanical Ventilation. In: Rogers MC,ed. Textbook of Pediatric Intensive Care, 1996.
[Normal = 0.03 – 0.07]
Hemodynamic Instability
Imbalance between metabolic supply and demand.
Typically, objective measures of oxygen and ventilation (e.g. PaCO2) are normal.
Agitation, pain, blood draws and performing procedures places the patient in peril.
Hemodynamic Instability
2 y.o male with 3 day history of shortness of breath, lethargy and emesis.
Patient intubated due to respiratory distress.
Determined to have poor pulses & echocardiogram reveals an ejection fraction of ~ 20%.
Dilated Cardiomyopathy Case
0
50
100
150
200
250
300
6.9
7
7.1
7.2
7.3
7.4
7.5
7.6
PaCO2PaO2pH
Extubated
3-18-06
3-13-06 3-16-06
3-21-06
Dilated Cardiomyopathy Case
Dilated Cardiomyopathy Case
0
5
10
15
20
25
30
Base Deficit
Lactate
Fluid Balance+ 450 ml
Lasix, BumexMetalozone
IVF
BNP Level>54,000
Outline
Physiological Concepts • Pediatric Considerations • Work of Breathing (WOB)
Indications for Ventilatory Assistance• Initial Settings for Mechanical Ventilation
Mechanical Ventilation and the Pediatric Heart Patient
Recommended Criteria For Acute Lung Injury (ALI)
Acute onset of respiratory disease with bilateral infiltrates on a frontal chest x-ray.
Pulmonary Artery Wedge Pressure (PAWP) < 18 mm Hg or no clinical evidence of left atrial hypertension[yet may coexist]
Bernard GR et al. The American-European Consensus Conference on ARDS Am J Respir Crit Care Med 1994.
Recommended Criteria For ALI & ARDS
*OxygenationALI PaO2/FiO2 < 300ARDS PaO2/FiO2 < 200
* regardless of PEEP
Bernard GR et al. The American-European Consensus Conference on ARDS Am J Respir Crit Care Med 1994.
Comparison of P/F Ratios
0
50
100
150
200
250
300
350
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43
Time (Days)
Acute Lung Injury [ALI] Case #1
BC was a 5 y.o. with history of renal transplant for ESRD 2º to HUS who presented to an outside hospital for evaluation of fever.
She developed respiratory failure due to CMV pneumonitis that progressed to endotracheal intubation and conventional mechanical ventilation 8 days later.
ALI Case #1Her pulmonary status deteriorated further and she required high frequency oscillatory ventilation (HFOV).
She developed renal failure and pancreatitis.
Her ventilation support was maximized and pulmonary hemorrhage developed.
ALI Case #1After 5 days in the PICU, Tertiary Care Center (TCC) was consulted for Extracorporeal Membrane Oxygenation (ECMO). Patient did not meet criteria.
She was transferred to TCC after a 17 day stay in PICU. Her peak inspiratory pressures were between 40 and 50 cm H2O.
The patient required multiple fluid boluses and she developed refractory hypoxemia and hypercarbia despite maximum support. Care withdrawn after 46 days.
ALI Case #2
JM was a 16 y.o. WM who was involved in a MVA at an intersection in Northwest AR vs. an 18-wheel semi-truck.
He sustained multiple injuries including a clavicle fx, rib fx, pneumothorax, ruptured spleen, T2 spine fx and multiple lung contusions.
ALI Case #2 He required splenectomy and was placed on mechanical ventilation.
During his hospitalization, he developed multiple pneumothoraces and pneumomediastinum requiring several chest tubes. A tracheobronchial tear was suspected, but never confirmed.
He accidently extubated himself on the 2nd day and had a questionable aspiration event.
ALI Case #2 Transferred to TCC 5 days after accident for ventilation management of Acute Respiratory Distress Syndrome (ARDS).
In referring hospital: FIO2 100%, Positive End-Expiratory Pressure (PEEP) 15 cm H2O and Tidal Volume (TV) of 700ml (12.5 ml/kg). Weight = 56 kg
At TCC: FIO2 100%, PEEP 17 cm H2O and TV decreased to 350 ml (6.5 ml/kg)
ALI Case #2
Over the next 45 days, the patient eventually required 18 days of HFOV, developed neuropathy of critical illness, frequent management of pulmonary secretions and eventually tracheostomy.
He was successfully weaned to a tracheostomy collar and transferred to the rehabilitation unit.
His recovery went well, the tracheostomy was reversed and he was discharged home 4 months after the accident.
A-a Gradient Comparison
0
100
200
300
400
500
600
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43
Time (Days)
JM Mean A-a Grad
BC Mean A-a Grad
Alv
eola
r-ar
teria
l oxy
gen
grad
ient
(A
-a g
radi
ent)
Comparison of P/F Ratios
0
50
100
150
200
250
300
350
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43
Time (Days)
PaO 2
/ Fi
O 2
Rat
ios
BM PF Ratios JM PF Ratios
Comparison of P/F Ratios
PaO
2/F
iO2
Rat
ios
Initial Mechanical Ventilation Settings
ObjectivesSupport oxygenation and ventilation while avoiding ventilator-induced injury.
Goals• Peak Inspiratory Pressure (PIP) < 35 cm H2O• Tidal Volume (TV): 6-8 ml/kg• FIO2
< 0.55
Initial Mechanical Ventilation Settings
FIO2at 1.0 (in noncardiac patients)
• Pulse ox > 95% and PaO2> 80 mm Hg
Positive End-Expiratory Pressure (PEEP)• Start at 5 cm H2O and titrate in 2 cm H2O steps
every 5 minutes.
Inspiratory Time (“I Time”)• Newborn 0.6 second• One year to 12 years 0.7 second• Adolescent-Adult 1.0 second
Initial Mechanical Ventilation Settings
Rate: normal for age• < 1 year 30 - 35• 1-6 years 25 - 30• > 6 years 20 – 25(Rates need to be lower in pts with obstructive lung
disease)
Tidal Volume: 6-8 ml/kg in patients with lung injury• TV of 10 ml/kg is reasonable in patients without
lung injury.• Always assess for symmetrical chest sounds and
movement.
I:E ratio: 1:2
Cardiopulmonary Bypass and Respiratory Mechanics
20-30minutes
4hours
7hours
Induction ofanesthesia
OffBypass
Ranieri, VM et al. Time-course of impairment of respiratory mechanics after cardiac surgery and cardiopulmonary bypass. Crit Care Med 1999;
27:1454-1460 .
HLHS Case
5 day old girl with HLHS characterized by poor cardiac function and cyanosis.
Patient taken to the OR for Norwood Stage I correction with modified Sano technique.
HLHS & The Sano Procedure
HypoplasticLeft Heart
Small Aorta Sano Shunt
HLHS Case
Pre-operativeCXR
Post-operativeCXR
HLHS Case
POD #1CXR
POD #3CXR
Cardiopulmonary BypassCongenital Heart Disease
Mechanical Ventilation in the Post-Operative Congenital Heart
What is an appropriate amount of PEEP?
Congenital Heart Disease Pulmonary Vascular Resistance
60
70
80
90
100
110
120
60 100 150 175Lung Volume (ml)
Vasc
ular
Res
ista
nce
(cm
H2O
/L/m
in)
PVR is lowest at FRC!
Summary
Compared to adults, infants and children have developmental features that result in lower respiratory reserves.
After deciding on mechanical ventilation, think of elastic and resistive loads faced by the patient after re-establishing homeostasis.
Always provide PEEP to maintain FRC in order to keep alveoli recruited, PVR decreased and volutrauma/barotrauma minimized.
Go Gators!!