3101126 Rev A Vapotherm Oxygen Assist Module Instructions for Use
Page 25
Terminology and Acronyms
Perfusion Index
The Perfusion Index (Pi) is a relative assessment of the pulse strength at the monitoring site, expressed
as a numerical value that ranges from 0.02% to 20%, where the lower values indicate weak pulse
strength, and the higher values indicate strong pulse strength. This index represents the ratio of pulsatile
to non-pulsatile components of the blood at a particular site, with a higher number indicating a higher
proportion of pulsatile blood. The Pi is used to assess the relative effectiveness of different application
sites, and to alert the clinician to changes in the physiological condition of the patient. Clinically, it is
often used to help choose the best body site for pulse oximetry, with clinicians choosing the site in which
the Pi (and thus pulse strength) is highest.
Automatic FiO
2
Control
The automatic FiO
2
control system uses the patient’s measured SpO
2
values to control the delivery
of FiO
2
based on patient need. The system tries to maintain the patient’s SpO
2
level at or near a
preconfigured SpO
2
target by continuously titrating delivered FiO
2
based on the measured SpO
2
. The
system responds to both transient changes in SpO
2
, as well as to long-term changes in the patient’s
FiO
2
requirements.
The control algorithm creates a feedback loop within the gas delivery system. It compares the patient’s
SpO
2
reading to that of the preconfigured SpO
2
target and sets the FiO
2
delivery rate accordingly. The
algorithm makes near immediate adjustments (within 10 seconds) to changes in SpO
2
readings, learns
from past changes, and anticipates short-term changes, thus, acting as what is called a proportional-
integral-derivative controller (PID controller).
For example, the algorithm can make the following automatic FiO
2
delivery adjustments:
•
During periods of normoxia when the SpO
2
reading is stable and remains above the
preconfigured SpO
2
target, the algorithm initiates a gradual weaning/reduction of FiO
2
delivery.
Once SpO
2
readings fall below the preconfigured SpO
2
target, no further weaning takes place.
•
During periods of hypoxemia (SpO
2
reading < SpO
2
target set-point), the algorithm initiates
an increase in FiO
2
delivery, within 10 seconds of detection of hypoxemia. FiO
2
delivery then
continuously rises while hypoxemia persists. The rate of FiO
2
increase is proportionate to the
severity of hypoxemia.
•
During periods of hyperoxemia (SpO
2
reading > SpO
2
target set-point), the algorithm initiates a
reduction of FiO
2
delivery. Depending on the severity of hyperoxemia, reduction starts within 10
seconds, leading to an increased and sustained reduction as long as the patient remains in a
state of hyperoxemia.
Section 21 Terminology
Section 22 Further Reading
Dyspnea
Shortness of breath or air hunger
COPD
Chronic Obstructive Pulmonary Disease
Pi
Perfusion Index
APOD
Adaptive Probe-Off Detection (see Further Reading)
Normoxemia
Normal levels of oxygen in blood
Hypoxemia
Low levels of oxygen in blood
Hyperoxemia
Excessively high levels of oxygen in blood / acidity of blood
PID controller
Proportional-integral-derivative controller
