Ventilator Induced Lung Injury Ventilator Strategies Pathophysiology Matters Donald M. Null, Jr., MD

Donald M. Null, Jr., MD

• I am a consultant for Draeger Medical Company

Factors which predispose immature lung to injury • Surfactant deficiency – Poor saccular compliance – Diffuse atelectasis

• Compliant tracheobronchial tree • Increased surface tension • Marked V/Q mismatch

Factors which predispose immature lung to injury (continued)

• • • •

An increased Vd/Vt An apparent predilection to edema formation Decreased tissue antioxidants Presence of a patent ductus arteriosus

Barotrauma/Volutrauma Biotrauma • Distal airway rather than primitive alveolus is

the most compliant part of the respiratory tract • Distal airway disruption

– – – –

Interstitial emphysema Pneumothorax Pneumomediastinum Pneumopericardium

Barotrauma (continued) • Interstitial space – Larger than an adult – More distensible – PIE worsens compliance

Barotrauma (continued) • Distal airway overdistention – Protein leak – Edema – Hyaline membrane formation

Ventilator Associated Lung Injury • PIP • Volume

Hernandez et. al. Dreyfus et. al. Carlton et. al.

Oxygen Injury • Oxygen is toxic to all tissues • Lack of antioxidant protection • O2 injury perpetuates alveolar noncompliance

Biotrauma

Epigenetics

Goals of Respiratory Support • • • •

Achieve uniform inflation Minimize over and under inflation Minimize inspired oxygen concentration Early appropriate extubation

Lung Recruitment • Increase Mean Airway Pressure • Increase PEEP • Increase Inspiratory Time • Increase Ventilator Rate • Increase Peak Inspiratory Pressure • Increase Tidal Volume

Ventilation • • • • •

Increase Pressure Increase Volume Increase Rate Decrease overexpansion Improve underexpansion

Synchronized Assisted Ventilation in Infants (SAVI,SIMV and AC) Theoretical Advantages • Decreased barotrauma – Airleak – BPD • Decreased ventilator time • Decreased intraventricular hemorrhage • Consistent tidal volume delivery

Volume Ventilation Theoretical Advantages – Stabilization of lung volume – Improved ventilation - perfusion – Stabilization of cerebral blood flow – Decreased air leaks

VGPS and VAPS Theoretical Advantages – – – – –

Stabilization of lung volume Improved ventilation - perfusion Stabilization of cerebral blood flow Decreased air leaks Weaning

MMV

High Frequency Types and Differences – – – –

High frequency positive pressure ventilation High frequency flow interruption ventilation High frequency jet ventilation High frequency oscillatory ventilation

Pressure Transmission

Ventilation Conventional vs High Frequency CV - V = (TV-DV) x F V = AV x F HF - V = TV2 x F

Oxygenation – Mean airway pressure – Delta pressure (tidal volume) – Frequency

Pathophysiology and Ventilator Strategies

Diffuse Alveolar Disease - Need complete recruitment

Mechanisms to Achieve Recruitment 1. Surfactant a. Delivery technique 2. Adequate mean and end expiratory pressure to prevent collapse

Mechanisms to Achieve Recruitment 3. Recruitment maneuvers a. Sigh b. Inspiratory time 4. Adequate target volume

Mistakes 1. Inappropriate pressure changes PIP, PAW, PEEP 2. Use of high FiO2 to treat intrapulmonary shunts

Mistakes 3. Distensability of airways with effect on tidal volumes 4. Inappropriate ventilator rates that predispose to airtrapping

Mistakes 5. Mucus plugging not appropriately addressed

Meconium Aspiration 1. Diffuse Disease 2. Patchy – Overdistention/Atelectasis

Strategies

- Similar to DAD but remembering due to meconium there is a prediliction for air-trapping

- Goal is to minimize overdistention and air-trapping. Recruitment of atelectatic areas as possible.

Basic Strategy • Lower rates for HF or conventional yielding longer expiratory times • Larger tidal volumes for HF or conventional • Surfactant usage

Mistakes - Too small tidal volumes - Too rapid rates - Preconceived appropriate tidal volume

Mistakes Failure to deal with cardiac issues PPHN

Pulmonary Hypoplasia

Bilateral/Diffuse

- Maintain adequate inflation - Avoid overexpansion - Surfactant treatment - Pulmonary hypertension

Unilateral

Management Directed Primarily at Normal Lung - Avoid overexpansion

- Prevent atelectasis - Surfactant treatment - Pulmonary hypertension

Mistakes 1. Using too large tidal volume 2. Failure to address cardiac/ pulmonary hypertension issues 3. Adequate expansion misinterpreted on x-ray

Mistakes 1. Rib counting 2. Tidal volume

Severe Air Leak

Strategies Premature PIE

- Short inspiratory time

- PEEP – Adequate to keep airways open - Rate 40-50 - Tidal volume – 3-4 cc/kg

HFV • Paw 1 cm H20 < CV • Frequency 10-15 Hz • Delta pressure – minimal chest wall movement

Gross Air Leak Adequate Inflation

- Short inspiratory time

- PEEP – 3-4 - Rate – 40-50 - Tidal volume – 3-4 cc/kg

HFV – Gross Air Leak • Paw = or 1 cm H20 > CV • Frequency 10-15 Hz • Delta pressure – chest wall movement

Gross Air Leak Generally Poor Inflation

- Inspiratory time – .35-.4

- PEEP – 5-7 - Rate – 40 - Tidal volume – 5-6 cc/kg

HFV – Gross air leak, generally poor inflation • Paw 1-2 cm H20 > CV • Frequency 10 Hz • Delta pressure-chest wall movement

Summary The enemy of good is better

- Applying ventilatory support in the least traumatic way is best accomplished by applying the support over the mid-portion of the pressure volume curve.

Issues with Ventilation •

A 5 cc/kg tidal volume does not insure prevention of overexpansion or injury

•

A 10 cc/kg tidal volume does not insure over- expansion and injury

Issues with Ventilation (continued) •

Weaning which results in keeping the lung on the lower portion of the PV curve will injure the lung not protect it

- The lung is most vulnerable to injury during recruitment

One must tailor ventilator strategies to match cardiopulmonary pathophysiology

Remember: Cookbooks are good but patients are individuals

Questions