Neonatal Neonatal Assisted Assisted VentilationVentilation

Haresh Modi, M.D.Aspirus Wausau Hospital, Wausau, WI.

History of Assisted VentilationHistory of Assisted Ventilation

Spirophoredeveloped in 1876 with manual device to create negative pressure chamber

Negative pressure :

History of Assisted VentilationHistory of Assisted Ventilation

Dr. Philips Drinker used this idea to develop “Iron lung” in 1929, So many survived “Polio out break” Some to date.

Negative pressure :

Woman in iron lung celebrates 60th birthdayAfter contracting polio, Dianne Odell has spent

most of her life in machine

Updated: 3:37 p.m. CT Feb 21, 2007Associated Press Report

JACKSON, Tenn. - A Jackson woman who contracted polio 57 years ago and continues to rely on an iron lung to breathe recently celebrated her 60th birthday, defying doctors' expectations that she could live so long and so fully. Dianne Odell, who turned 60 last week, is among only 30 to 40 people in the U.S. who depend on the devices.

History of Assisted VentilationHistory of Assisted Ventilation

“Respirator Kit”used to revive apparently dead by blowing air into the lungs or rectum in 1770s in London

Positive Pressure :

History of Assisted VentilationHistory of Assisted Ventilation

The Aerophore pulmonaire :-developed by French Obstetrician for short term ventilation of newborns in 1879

Positive pressure :

History of Assisted VentilationHistory of Assisted Ventilation

The Fell-O’Dwyreapparatus developed in New York for intermittent positive pressure ventilation, 1896

Positive pressure :

Neonatal Assisted VentilationNeonatal Assisted Ventilation

1. Applied Pulmonary Mechanics2. Gas Exchange During Assisted Ventilation3. Ventilator Management4. Practical Hints For Assisted ventilation

Applied Pulmonary MechanicsApplied Pulmonary MechanicsPressure Gradient is Required to Overcome

1.Elastic Properties of Lungs and Chest Wall(Compliance)

2. Resistance to Airflow by Airway and Lung Tissue (Resistance)

Applied Pulmonary MechanicsApplied Pulmonary Mechanics

Δ Volume (L)Δ Pressure (cm H2O)

Compliance =

In neonate chest wall is very distensible so does not contribute substantial elastic load when compared to lungs.

Total compliance ∞ Lung compliance

In RDS most striking abnormality is

DECREASED LUNG COMPLIANCE

Applied Pulmonary MechanicsApplied Pulmonary MechanicsPressure Gradient is Required to Overcome

1.Elastic Properties of Lungs and Chest Wall(Compliance)

2. Resistance to Airflow by Airway and Lung Tissue (Resistance)

Applied Pulmonary MechanicsApplied Pulmonary Mechanics

Δ Pressure(cm H2O)Δ Flow (L/Sec)

Airway resistance ∞ length of airway∞ 1/radius of airway

Viscous resistance ∞ lung tissue

RDS does not contribute to resistance but ET tube does

Resistance =

Resistance is inherent property of lungs to resist airflow

Relationship of Compliance and Resistance :

Time Constant (sec)= Resistance × Compliance

Applied Pulmonary MechanicsApplied Pulmonary Mechanics

Time Constant(sec)

= Resistance(30cm H2O/L/sec)

× Compliance(0.004L/cm H2O)

= 0.12sec × 5

= 0.6 seconds

Gas Exchange During Gas Exchange During Assisted VentilationAssisted Ventilation

1. Carbon Dioxide (CO2) Elimination

2. Oxygen (O2) Uptake

Gas Exchange During Gas Exchange During Assisted Ventilation Assisted Ventilation

CO2 Elimination :

Alveolar Ventilation =(Tidal volume – Dead space)(Frequency)

With a pressure ventilator TV determined by(PIP – PEEP)

Gas Exchange During Gas Exchange During Assisted VentilationAssisted Ventilation

O2 Uptake : Mean Airway Pressure(Paw)linear direct relations

↑Paw = ↑ PaO2

Regardless of change in FiO2

Paw optimizes lung volume and ventilation-perfusion matching

Gas Exchange During Gas Exchange During Assisted VentilationAssisted Ventilation

Paw is augmented by : 1. Inspiratory flow (K)2. Peak Inspiratory Pressure (PIP)3. I:E Ratio(TI, TE)4. Positive End Expiratory Pressure

(PEEP)

1 2 3 4

Paw=K(PIP-PEEP)[TI/(TI+TE)]+PEEP

Ventilator ManagementVentilator Management1. Flow :

Increase in flow will give square wave ventilation, will Increase Paw and therefore oxygenation.

Higher flow is crucial, when TI is shorter

Ventilator ManagementVentilator Management2. Peak Inspiratory Pressure (PIP) :

Δ PIP(Press.Vent.) = Δ TV (Volu.Vent.)Advantages : Disadvantages :1. O2 Uptake 1. Barotrauma Air leaks2. CO2 Elimination 2. BPD

Ventilator ManagementVentilator Management3. I:E Ratio :

Reversed I:E Ratio = ↑Paw = ↑Oxygenation No change in TV= No change in AV=No change in PaCO2

Ventilator ManagementVentilator ManagementFrequency (Rate) :

Rate= AV= CO2 elimination= PaCO2

Short TI= TV= MVShort TE=gas trapping= FRC= compliance with over

distention= inadverant PEEP=Pneumothorax

Ventilator ManagementVentilator Management4. PEEP :

↑ PEEP(at lower range)= Better recruitment of lungs = ↑ PaO2

↑ PEEP(at higher range)=Over distention=↓Cardiac Output=↓PaO2, ↑PaCO2

PEEP just above Critical closing Pressure prevents atelectesis

Gas Exchange During Gas Exchange During Assisted VentilationAssisted Ventilation

Relative effectiveness of Paw on Pao2 :1.↑ PIP &PEEP more than ↑ I:E ratio2.↑ PEEP at higher range is ineffective3.↑Paw=↑Over distention=↑RL Shunt 4.↑ Paw = ↓Cardiac output

Ventilator ManagementVentilator Management

Inspired Oxygen Concentration (FIO2) :

When increasing vent. support first increase FIO2 to .60 to .70 before increasing pressure which may prevent BPD

When weaning vent. support first decrease FIO2 to .40 to.50 before decreasing pressure. Pressure should be weaned before weaning FIO2 further to prevent PTX.

Gas Exchange During Gas Exchange During Assisted VentilationAssisted Ventilation

Summary :-

Ventilator ManagementVentilator ManagementHFOV :

Ventilation above critical closing pressure at ↑PEEP &↑Paw =↑PaO2↓∆P at alveolar level=↑ alveolar ventilation = ↓PaCO2

Practical Hints for Assisted VentilationPractical Hints for Assisted Ventilation

Indications for Assisted Ventilation :

1. Respiratory acidosis with pH < 7.20 to 7.252. Severe hypoxemia, PaO2 < 50 torr. With FIO2 > 0.703. Apnea complicating RDS4. Persistent Fetal Circulation

Practical Hints for Assisted VentilationPractical Hints for Assisted Ventilation

Initial Ventilator Settings :

Normal RDSPIP 12-18 cm H2O 20-25 cmH2OPEEP 2-3 cmH2O 4-5 cmH2ORate 10-20 per minute 20-40 per minuteI:E Ratio 1:2 to 1:10 1:1 to 1:3

Practical Hints for Assisted VentilationPractical Hints for Assisted Ventilation

Acceptable Blood Gas Values :

pH 7.25 – 7.45PaO2 50 – 80 torrPaCO2 35 – 50 torr

With more maturity even higher PaCO2 are tolerated as long as pH is maintained above 7.25

Practical Hints for Assisted VentilationPractical Hints for Assisted Ventilation

Weaning Strategy :

1. First decrease pressure <182. FIO2 <0.403.Rate <154. CPAP of 3 to 4 to overcome ET resistance

Practical Hints for Assisted VentilationPractical Hints for Assisted Ventilation

Summary :

Practical Hints for Assisted VentilationPractical Hints for Assisted Ventilation

Lung DevelopmentLung DevelopmentSignificant Milestones :

1. At 3-4 wks. Lung bud from esophagus.2. At 15-16 wks. Segmentation of bronchi complete.3.At 23-25 wks. Type II pneumatocyte develops.4.At 24 wks. Onwards surfactant production.5.At 34 wks onwards PG production.

Note : Lung maturity lags behind by 2-4 wks in maternal diabetes.

Composition of SurfactantComposition of Surfactant

Role of L/S Ratio and PGRole of L/S Ratio and PG