Overview of mechanical ventilation

Patient ventilator dyssynchrony

NAVA concept,application

NAVA set up, literature

Implications and take home message

Basic

Biphasic

Modes of M.V.Others

Dual

types

subtype

examplesP-CMV

CONTROLLED

V-CMV

A/C BASIC ASSISTED SIMV

PSV Spontaneous CPAP

Ty p e s

Subtypes

PRVC, AUTOFLOW, PRVC, AUTOFLOW, VSINTRABREATH VAPS , PRESSURE AUGM

Example

INTERBREATH

PARTIAL

PAV

DUAL CLOSED LOOP V.

AUTOMODEADAPTIVE SUPPORT V

COMPLETE KBW

NAVA

BIPHASIC

HFOV

APRV

BILEVEL

Patient-Ventilator Dyssynchrony

Overview and definition.

Patient-ventilator interaction can be described as the Patientrelationship between 2 respiratory gears (1) the patients pulmonary system (2) the ventilator

Patient Ventilator Dyssynchrony

Patient-ventilator dyssynchrony occurs when gas delivery from the ventilator does not match the neural output of the respiratory center.

Termination or cycling phase

Inspiratory flow phase trigger phase

expiration phase

Ventilatory cycle simplified.

The 4 Phases Model

Types of P-V dyssynchrony

The 4 Phases Model: Triggering. Adequate flow delivery. Breath termination. Intrinsic positive end-expiratory pressure (autoPEEP).

Types and Causes of Dyssynchrony Trigger Asynchrony. Failure of triggering. Double triggering. Auto triggering.

Flow Asynchrony. Inadequate flow

Termination (cycle) Asynchrony. Delayed termination. Premature termination.

Auto-PEEP.

Dyssynchrony Routinely check for auto-PEEP. Assess synchrony and comfort each visit to mechanically ventilated patient . Regarding the definition and the 2 gears model NAVA = Neurally Adjusted Ventilatory Assist. Is the ideal management of patient-ventilator dyssynchrony.

NAVA is a new mode of mechanical ventilation, where the ventilator is controlled directly by the patients own respiratory center.Sinderby C, Navalesi P Nature 1999

and any variation in the neural respiratory demand is responded to by the appropriate change in Ventilatory assistance. This means the patient is in charge of adjusting his ventilator.

NAVA ConceptPhysiology of spontaneous breathing

NAVA concept

What is best trigger of the ventilator to get the best synchrony? Brain Phernic nerve. The diaphragm. Flow/ pressure /volume. So the patient whole brain is in charge for his respiration rather than part of the clinician brain (Dr., RT , or Nurses.)

NAVA concept The NAVA approach to mechanical ventilation is based on the patients neural respiratory output. Signals from respiratory centre the phrenic nerve diaphragm. Using nasogastric tube to capture the Electrical activity of diaphragm (Edi) and feeds it to the ventilator. The ventilator will respond by providing the requested level of support (NAVA level). As the ventilator and diaphragm work with the same signal, the coupling between the two is virtually instantaneous.

NAVA concept EMGFirst step The issue is to get the raw EMG signals of the diaphragm

Second Reducing the signal tonoise ratio then

Third transform it into simpler measurable format using Fourier analysis

fourth This new wave displayed as sine wave with peak and minimum values of Edi

NAVA set up New terminology Edi (EAdi) stands for Electrical Activity of the di diaphragm is measured in micro Volt (uV) , the corner stone of NAVA. NAVA level the amount of pressure support in cmH2O set for each (uV) of Edi (amplification factor).

NAVA set upInsertion of the specialized nasogastric. To get the Edi which control: trigger on cycle off level of assistance Confirm the position by checking ECG on ventilator screen

NAVA set upNava preview screen gives idea about: 1- synchronization. 2-how much NAVA level needed to start with. 3- additional setting the Edi trigger level, And apnoea backup. 4-cycling to expiration automatic at 70% of Edi.

NAVA set up Outcome will be: peak airway pressure =(Edi X NAVA level) +PEEP tidal volume Vt

Low Vt or Proper Vt Flow

NAVA LEVEL ADJUSTMENT

CNS feed back

Increased measured Edi

Increase impulses to diaphragm

High Vt or Proper Vt Flow

NAVA LEVEL ADJUSTMENT

CNS feed back

Decrease measured Edi

Decrease impulses to diaphragm

Current litrature

Current literature Over all the studies available are of weak power either observational or small number of population. -new ongoing. -paediatric population. Beck and colleagues found that NAVA reduced the number of missed triggers compared to PSV. triggers,Beck J, Brander L,et al , Intensive Care Med 2008.

Moerer et al found that NAVA successfully triggered and cycled the ventilator during the use of a helmet (non-invasive nonventilation interface) in normal subjects.Moerer O, Beck J, Brander, Intensive Care Med 2008.

Current literature Brander and colleagues studied 15 patients with ALI and systematically increased the NAVA level reduced the respiratory drive, unloaded the respiratory muscles ,appropriate VT (5.4 7.2 mL/kg of predicted body weight), and normal hemodynamics.Brander L, Leong-Poi H, Chest 2009;

Colombo D et al, physiologic responce for variable levels of pressure support and NAVA in acute respiratory failure.Intensive care med, 2008

Proposed applications To substitute CPAP or T-piece during SBT. Potential benefit in prolonged mechanical ventilation population. Neonate and small infants. Air leak , autoPEEP problems COPD ? Invasive (NGT) Monitor synchronization in other modes diaphragmatic activity.

Clinical implications

Nasogastric tubes ( types, feeding, change, NEX). Nursing (patient movement and routine ICU care check ECG for position.) Pacemakers and ICDs. Use of ECG (position - monitor). Use of Edi.

Contraindication Brain to diaphragm axis Presence or suspicion of central/brain stem neurologic disorder severe neuromuscular disease Neuromuscular blockers History of heart and/or lung transplantation Sedation and RASS -3/-4. Status epilepticus. Nasogastric tube: Malformation. Bleeding. Varices. Tumor. Infection. stenosis, or rupture

Take Home Message

NAVA new dual closed loop mode Improved synchrony. Lung protection. Unique monitoring capability. Special attention about nasogastric tube and neuro status before implementing NAVA.