Mechanical Ventilation in ARDS vs COPD

Mechanical Ventilation In ARDS Versus COPD Prof. Dr Alaa Koraa Dr. Hanaa El Gendy

  Normal or      No air trapping Normal  Normal   Little effect  ( < 75% predicted ) Normal or     Air trapping  Normal   -FEV1: normally >80% of FVC. -FVC -FEV1/ FVC ratio -VC -TLC -RV -FRC -MMEFR=FEFR 25-75% of VC -Total compliance - Airway resistance - Work of breathing Restrictive Obstructive PFT

Spirograph In Different Respiratory Diseases

Normal Flow Volume Loop

Flow-Volume Loops In Different Respiratory Diseases

Acute Respiratory Distress Syndrome (ARDS)

It is a clinical syndrome characterized by a pulmonary disorder resulting from diffuse injury to the alveolo-capillay membrane .

Acute Lung Injury (ALI) has been used as a term for hypoxemic respiratory failure, a severe version of which is (ARDS) .

Criteria of ARDS:

Acute onset.

Bilateral diffuse pulmonary infiltrates on chest x-ray.

Bedside finding of tachypnea, dyspnea and crackles.

Pulmonary Capillary Wedge Pressure <18mmHg or no evidence of LA hypertension.

PaO2/FiO2 <300 = ALI. PaO2/FiO2 <200 = ARDS.

One or more underlying disease process known to be associated with ARDS.

What Cause ALI? Direct injury (primary, pulmonary) Indirect Injury (secondary, extrapulmonary)

Pathologic Changes In ARDS

Management Of ARDS

The cornerstone of treatment is to keep the PaO2 >60mmHg, without causing injury to the lungs with excessive O2 or volutrauma.

Pressure control ventilation is more versatile than volume control, although breaths should be volume limited, to prevent stretch injury to the alveoli.

We must have a holistic multisystem approach of the ABCDEFG

Ventilation Strategy in ARDS

* Keep the PaO2 over 60mmHg or over 50mmHg at the very least.

* Avoid volutrauma, barotraumas and biotrauma (VIL) , by keeping the tidal volumes in the 4-6ml/kg range and airway plateau pressure below 30 cmH2O .

* Peak airway pressure 20-40 cmH2O or < 20 cmH2O above PEEP.

* PEEP values of 2-3 cmH2O above lower inflection point (LIP).

* Lower respiratory rate.

* Inverse ratio ventilation.

* Permissive hypercapnia.

* Low inspiratory flow.

The advantages of using PCV in ALI

(1) Gas Distribution:

(2) Control of mean airway pressure

It is possible to increase the mean airway pressure, by prolongation of the inspiratory time auto-PEEP .

Inverse ratio ventilation , is a key part of the open lung approach to ARDS and is the basis of some pressure controlled modes - BiLEVEL /APRV .

Open Lung Approach

Phasic opening and closing of injured lung units causes further injury to lung tissue . The low tidal volume approach amount of phasic stretch of lung units in inspiration, to prevent (VIL).

Open lung approach, stenting the airways open at end expiration, using PEEP just above Pflex” (the lower inflection point on the pressure volume curve).

Static volume pressure curve of an injured lung: the lungs are said to be most compliant between the lower inflection point of the curve and the upper inflection point, beyond which overdistension takes place.

PEEP Endpoints :

Best PaO2

Best O2 delivery

Lowest shunt

Best Qt

Highest compliance

lowest Vd / Vt

Pplat < 30 cm H2O

Best CT areation

Until P/V curve become concave.

What is a recruitment maneuver?

Recruitment maneuvers are used to reinflate collapsed alveoli, a sustained pressure is applied, and PEEP is used to prevent derecruitment.

Measurement of positive end-expiratory pressure (PEEP)-induced alveolar recruitment using the pressure–volume (PV) curve. The PV curves of the respiratory system recorded from zero end-expiratory pressure (ZEEP) and from PEEP are superimposed on a common volume axis. '0' volume corresponds to the end-expiratory lung volume (EELV) on ZEEP. The first point of the PEEP PV curve corresponds to the increase in EELV induced by PEEP (Δ EELV). On this example, the recruitment induced by PEEP is measured at a pressure of 20 cmH2O.

Adjuvant Therapy With Ventilation used in ARDS

1- Prone Position improves ventilation-perfusion matching by:

Redistributing ventilation to area of better perfusion but not the reverse .

More homogeneous end expiratory lung volume (EELV) .

 VIL.

2- Partial liquid ventilation (PLV) with perfluorocarbons, which carry oxygen. The FRC is filled with the liquid, and the patient ventilated above it. PLV has the added advantage of lavaging the airways and removing cellular debris.

Partial liquid ventilation (PLV) with perfluorocarbons

3- High frequency oscillation: full tidal volume ventilation, with no cyclic opening and closing of lung units.

4- Tracheal gas insufflation: 2 or more litres of oxgen are delivered into the major bronchi in expiration to wash out dead space gas.

5- Extracorporeal membrane oxygenation (ECMO)

Chronic Obstructive Pulmonary Disease

Chronic Obstructive Pulmonary Disease ( COPD )

COPD is a preventable and treatable disease with some significant extrapulmonary effects that may contribute to the severity in individual patients. Its pulmonary component is characterized by airflow limitation that is not fully reversible and usually progressive.

Diagnosis

.

Static Lung Volumes

<30 or 30-50 with Chronic Respiratory Failure symptoms <0.7 Very Severe COPD 30-49 <0.7 Severe COPD 50-79 <0.7 Moderate COPD ≥ 80 <0.7 Mild COPD ≥ 80 >0.7 At risk FEV1 % predicted Post-bronchodilator FEV1/FVC Severity

Pathophysiology

What is auto-PEEP?

Auto-PEEP is gas trapped in alveoli at end expiration increased the work of breathing.

Auto PEEP exerts a positive pressure, and normal gas transit cannot be reestablished until there is a pressure gradient from the mouth to the alveoli.

Thus the patient must generate a much higher negative inspiratory pressure to make the pressure within negative with respect to atmospheric pressure.

After the third breath, the airway was occluded at end-expiration using the end-expiratory hold function on the ventilator. During the period of zero flow, pressure in the alveoli and ventilator circuit equilibrate, and the plateau pressure reflects auto or intrinsic positive end-expiratory pressure (PEEPi), indicated by the arrow .

Giving CPAP to a patient who has auto-PEEP

The increased work of breathing associated with auto-PEEP can be offloaded by applying CPAP to the trachea/mouth, and splinting open the connecting airways.

The use of external PEEP in the setting of auto-PEEP may be conceptualized by the "waterfall over a dam" analogy. In this analogy, the presence of dynamic hyperinflation and 10 cmH20 of auto-PEEP is represented in the top panel by the reservoir of water trickling over the dam represented by the solid block. In the middle panel, as long as the external PEEP is less than or equal to the amount of auto-PEEP, the amount of water in the upstream reservoir, representing dynamic hyperinflation, does not increase. However, once the amount of water in the reservoir does increase (bottom panel), dynamic hyperinflation worsens.

THE FOUR COMPONENTS OF COPD MANAGEMENT

1-Assess and monitor disease

2-Reduce risk factors

3-Manage stable COPD

-Education

-Pharmacologic

-Non-pharmacologic

4-Manage exacerbations

Ventilation Strategy in COPD

1-The primary goal is to increase PaO2 to at least 60 mmHg and SaO2 90%.

2-Tidal volumes (8-10 ml/kg).

3-Minute ventilation (115 ml//kg).

4-long expiratory times .

5-High inspiratory flow allow short inspiratory time and therefore longer expiratory time for any given respiratory rate .

6-Lower RR.

7- Volume control ventilation is more versatile than pressure control.

As flow increased from 30 to 60 and 90 L/min (from right to left), frequency increased from (18 to 23 and 26 breaths/min, respectively), Auto-PEEP decreased (from 15.6 to 14.4 and 13.3 cm H2O, respectively) and end-expiratory chest volume also fell. Increases in flow from 30 L/min to 60 and 90 L/min also led to decreases in the swings in Pes from 21.5 to 19.5 and 16.8 cm H2O.

COPD flow and frequency

What about O 2 ?

Long-term oxygen therapy in COPD :

PaO2  55 mm Hg or Sao2  88 %.

PaO2 between 55 and 60 mm Hg Sao2  89 % with evidence of pulmonary hypertension , cor pulmonale , or secondary erythrocytosis (hematocrit >55%).

PaO2  60 mm Hg or Sao2  90 % for patients whose room air PaO2  55 mm Hg or SaO2  88% during exercise or sleep.

Continuous low flow oxygen therapy , not more than 1 - 2L by nasal cannula, (for >15 hs/d) sufficient to correct hypoxemia has been shown to improve survival.

Mechanical Ventilation

A goal of mechanical ventilation is to prevent excessive work of breathing, while maintaining a work of breathing that is sufficient to prevent respiratory muscle atrophy. This can be achieved by using either NIPPV or IIPPV .

Indication and Relative contraindication for NIPPV

Selection Criteria:

Moderate to severe dyspnea with the use of accessory muscles.

Moderate to severe acidosis PH  7.35 and/or PaCO2 > 45 mmHg.

RR > 25 breaths/min.

Exclusion Criteria:

Respiratory arrest.

Cardiovascular instability.

High aspiration risk.

Burn.

Extreme obesity.

Craniofacial trauma.

Advantages Of NIPPV

Decreases need for invasive ventilation and may be associated with improved outcome.

CPAP alone can reduce work of breathing in COPD during weaning and during sleep.

BiPAP weaning may be better than weaning on pressure support via an ETT.

Nocturnal bilevel ventilation:

Is the use of NIPPV at two pressures (for inhalation and exhalation) for at least 4 hours per night.

The two pressures are usually referred to IPAP and EPAP . EPAP is a set pressure that has the same function as PEEP or CPAP and IPAP has the same function as pressure-support ventilation .

Indications of IIPPV: