Nava

SERVO Education
NAVA STUDY GUIDE

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NAVA STUDY GUIDE
English version
1.6

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| Table of Contents |

TABLE OF CONTENTS

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Introduction
NAVA Workflow
Mode description
Troubleshooting
Alarms
References for NAVA Study Guide

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NAVA STUDY GUIDE
English version
1.6

| Introduction | 1 |1 INTRODUCTION
TABLE OF CONTENTS

1 Introduction
1.1 Neuroventilatory coupling
1.2 Respiratory control
1.3 NAVA accessories
1.4 Edi Catheter
1.5 Edi Module

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English version
1.6

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1 INTRODUCTION
NAVA – Neurally Adjusted Ventilatory Assist is an optional mode of ventilation for the SERVO-i
ventilator.NAVA delivers assist in proportion to and in synchrony with the patient’s Edi signal
(the electrical activity of the diaphragm).
A spontaneous breath starts with an impulse
generated by the respiratory center. The
impulse is transmitted via the phrenic nerves,
which excites the diaphragm. Before the
mechanical effect is achieved, the signal is
modulated and the muscle response is
achieved bychemical coupling.
Contraction of the diaphragm pushes its dome
downwards, creating a negative alveolar
pressure, and gas flows into the lung.

All muscles, including the diaphragm and other respiratory muscles, generate electrical activity
to excite muscle contraction: this electrical excitation is controlled by nerve stimuli.

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NAVA STUDY GUIDE
English version
1.6

|Introduction | 1 |

1.1 NEUROVENTILATORY COUPLING

Health

μV

Disease

μV

μV

ml

ml

Edi
ml

VT

The efficacy of the respiratory muscles and the degree of respiratory demand will determine
the degree of respiratory center output. In a healthy subject, the low amplitude of diaphragm
excitation reflects the fact that neuroventilatory coupling is highly efficient and that only about5% of maximum capacity is used.

NAVA STUDY GUIDE
English version
1.6

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| 1 | Introduction |

In disease, muscle performance may not be up to expectation, leading to an increased output
from the respiratory center with the aim of recruiting additional motor units in the diaphragm.
In this example, the increased signal seen in
COPD and post-polio patients thus reflects
the factthat a larger part of the muscular
reserve is used. Only 5-8% of maximum
capacity is used in healthy subjects, while up
to 40% is used in COPD patients.

If the diaphragm becomes weaker and/or the inspiratory load
increases, the diaphragm´s electrical activation must increase to
maintain a given volume. (Adapted from Sinderby et al JAP 1998)

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The electrical activity of the diaphragm(Edi) is measured in μV (micro volt). 1 μV = 10 V, thus
1,000,000 μV = 1V.

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NAVA STUDY GUIDE
English version
1.6

| Introduction | 1 |

1.2 RESPIRATORY CONTROL
There are three important components in mechanical ventilation:
1.
2.
3.

The timing with which breaths are delivered i.e. the frequency and inspiratory time for
assist delivery.
The magnitude of the deliveredbreaths, i.e. the pressure or volume needed to ventilate
the lungs.
The magnitude of pressure on expiration, which prevents the lungs from derecruiting
between inspirations, i.e. the required PEEP level.

Conventional ventilator technology uses a pressure drop or flow reversal to initiate the assist
delivered to the patient (as shown on the right-hand side of the picture). This is the last step
ofthe signal chain leading to inhalation and is subject to disturbances such as intrinsic PEEP,
hyperinflation and leakage.
The earliest signal that can be registered with
a low degree of invasivity is the excitation of
the diaphragm (as shown on the left-hand side
of the picture).
The signal that excites the diaphragm is
proportional to the integrated output of the
respiratory center and...