This document provides an overview of neonatal ventilator graphics and waveforms. It discusses the key waveforms of pressure, volume, and flow and how they depict the respiratory cycle. Specific features of each waveform are described, including how they can reveal conditions like leaks, auto-triggering, gas trapping, and changes in compliance. Pulmonary loops like the pressure-volume and flow-volume loops are introduced and how they can provide information about lung mechanics, resistance, compliance, and other conditions. Interpretation of loop features is covered for various pathological states and responses to treatments.

2. Neonatal Ventilator Graphics
A Clinical Guide
BY:
DR. AHMED HEGAZI
M.SC, MRCPCH
NICU-ADAN HOSPITAL

3. Evolution of ventilator
graphics

4. Principles of Pulmonary
Graphics

5. Principles of Pulmonary
Graphics

6. Waveforms
 Waveforms depict the relationship
between respiratory parameters and time
on a breath-to-breath basis.
 The three most commonly used signals
are pressure (cm H2O), volume (mL),
and flow (mL/s), and these three signals
describe the respiratory cycle.
 When displayed in aggregate, the cyclic
phases of respiration can be
appreciated.

7. Waveforms

8. Volume Waveform
 The volume waveform displays the
changes in delivered volume over time.
 It is determined by integrating the
inspiratory and expiratory flow signals.
 expired volume is usually a bit less
than inspired volume because of air
leak around the uncuffed neonatal
endotracheal tube.

9. Volume Waveform

10. Pressure Waveform
 The pressure waveform represents the
airway pressure throughout the
respiratory cycle.
 Virtually every newborn requiring
conventional mechanical ventilation
receives some degree of PEEP. Thus,
the waveform at end inspiration or the
initiation of inspiration is above the
baseline (zero) value.

11. Pressure Waveform
 Pressure rises during inspiration, reaching
its maximum value, or peak inspiratory
pressure (PIP), then declines during
expiration to the PEEP level.
 The area under a single cycle represents
the mean airway pressure (mean Paw).
 The difference between the PIP and the
PEEP is referred to as the amplitude or
delta P.

12. Techniques to Alter Mean Airway
Pressure

13. Pressure Waveform

14. Changes in PIP and PEEP

15. Change in Inspiratory Time

16. Pressure Overshoot
 Pressure control and pressure
support ventilation utilize an
accelerating-decelerating inspiratory
flow waveform.
 If set too high, it may deliver pressure
too rapidly for the patient’s need. This
creates a condition known as pressure
overshoot.

17. Pressure Overshoot
 The pressure waveform exhibits a
notch and double peak at PIP. Most
ventilators have an adjustable rise
time function to respond to this.

18. Flow Waveform
 The flow waveform is the most complex
because its inspiratory and expiratory phases
each have two components.
 the baseline represents a zero flow state,
meaning that no gas is entering or leaving the
airway.
 anything above the baseline (positive value)
represents inspiratory flow (gas flow into the
patient), and conversely, anything below the
baseline (negative value) represents expiratory
flow (gas flow from the patient).

19. Flow Waveform

20. Flow Waveform
Two major ways in which inspiratory
flow can be delivered to the patient:
 Variable (sinusoidal wave):
pressure control
pressure support ventilation.
 Constant (square wave):
volume targeted ventilation

21. Flow Waveform
 Flow wave form during volume control
ventilation. Inspiratory flow is
continuous, rather than variable, and
produces a characteristic “square”
waveform

22. Flow Waveform
 Increased Expiratory Resistance
1. shallow accelerating expiratory flow
and decreased peak expiratory flow
rate.
2. a longer time to return to baseline
during decelerating expiratory flow

23. Flow Waveform
 Gas Trapping
the decelerating expiratory
component never reaches the
baseline (zero flow state) before the
subsequent breath is initiated.

24. Flow Waveform
Gas Trapping
 It occurs when the expiratory flow is less
than the inspiratory flow, resulting in
more gas entering than leaving the lung.
 This is a potentially dangerous situation
that can lead to alveolar rupture and air
leak.
 Now, careful observation of the flow
waveform can detect this condition,
allowing time to avoid its consequences.

25. Flow Waveform
 Gas Trapping (how to intervene?)
1. decreasing the ventilator rate.
2. decreasing the flow rate.
3. shortening the inspiratory time.
4. increasing the PEEP.
depending upon the clinical condition,
ventilator modality, and underlying
pathophysiology.

26. Cycling Mechanisms
Cycling refers to the mechanism that
transitions inspiration to expiration and
expiration to inspiration.
 Time cycling mechanism:

27. Cycling Mechanisms
 Flow-cycling
As a breath is delivered, the ventilator
notes the peak inspiratory flow rate. The
inspiratory flow rate then decelerates, by
5-25%, the exhalation valve will open,
discharging the remainder of inspiratory
flow

28. Cycling Mechanisms
Flow-cycling
 Flow-cycling takes advantage of the
natural pattern of breathing by
focusing on the baby’s inspiratory flow.
 It prevents gas trapping and the
inversion of the inspiratory:expiratory
ratio during patient-triggered
ventilation.
 It can be used in conjunction with
time-cycling, in that a breath will be
terminated by whichever condition

29. Endotracheal Tube Leaks
 Because cuffed ETTs are not used in
newborns, there will almost always be
some degree of leak around the ETT.
 Most of this occurs during inspiration when
pressure is higher.
 A significant leak may divert gas flow, such
that the decelerating inspiratory flow may
never reach the termination point. The
breath will then be time-cycled, but often
with inadequate pressure or volume

30. Endotracheal Tube Leaks

31. Endotracheal Tube Leaks
 The flow waveform, has virtually no
expiratory component.
 the actual end of the expiratory volume
waveform is shown by (the arrows, and by
the short blue line) which is followed by a
reset artifact (yellow coloured line dropping
to the zero baseline).
 The volume waveform, in the lower panel,
shows almost no expired volume.
 This also results in auto-cycling, with a
rate of 75/m.

32. Auto-cycling (Auto-triggering)
 When it occurs, there may be rapid
delivery of mechanical breaths, inducing
hypocapnia as well as the risk of lung
injury.
 Note the relative uniformity of the
breaths, which helps to distinguish this
from just rapid breathing, where there
will be some variability

33. Auto-cycling (Auto-triggering)
 It may occur during flow-triggered
ventilation if the ventilator interprets an
aberrant flow signal as patient effort.
 This can happen if there is a leak that
exceeds the trigger threshold, and it
may occur anywhere in the path of gas
flow.
 It may also occur from excessive
condensation in the ventilator circuit
(“rainout”).

34. Pulmonary Mechanics and
Loops
 pressure, flow, and volume to time, may be
presented relative to each other “commonly
referred to as loops”.
 The two most frequently used in clinical practice
are the pressure-volume (P-V) loop and the
flow-volume (F-V) loop.
 The interpretation of which can provide valuable
information about the mechanical properties of
the lung, how it is “performing” on a breath-to-
breath basis, and how it responds to changes in
pathophysiology, mechanical ventilation

35. The P-V Loop

36. The P-V Loop

37. The P-V Loop
 It displays the relationship of pressure and
volume during a single breath.
 the origin of the loop does not start at the
origin of the graph because of the application
of positive end-expiratory pressure (PEEP).
 The P-V loop provides
valuable information about
lung mechanics.
The dotted line is the compliance axis , a
measure of the stiffness or elasticity of the
lung.

38. The P-V Loop
“Compliance”
 Compliance is defined as the change in
volume divided by the change in pressure.
Thus, if a 1 cm H2O increase in pressure
results in a 1 mL increase in lung volume,
the axis will be 45°.
 As compliance decreases,
the axis will shift downward
and to the right. Conversely,
as compliance improves,
the axis will shift upward and to the left.

39. The P-V Loop
“work of breathing”
 The work of breathing can be qualitatively
estimated by the P-V loop.
 It is the area bounded by the inflation limb
and a horizontal line connecting the PIP with
the y-axis.
 As the compliance
decreases and the loop
shifts downward and to
the right, this area
increases and more pressure must be
applied to achieve the same lung volume.

40. The P-V Loop
“resistance”
 A line drawn from the midpoint of the
inflation limb to the compliance axis is a
measure of inspiratory resistance.
 a line drawn from the midpoint of the
deflation limb to the compliance axis is
a measure of expiratory resistance.

41. The P-V Loop
“Hysteresis”
 Hysteresis is a term that is used to
describe the difference between the
inflation and the deflation limbs and is
determined by the elastic properties of the
lung.
 Under normal circumstances, the shape of
the P-V loop is oval, resembling a football.
Hysteresis, thus represents the resistive
work of breathing.

42. The F-V Loop

43. The F-V Loop

44. The F-V Loop
 describes the pattern of airflow during
tidal breathing.
 Volume is shown on the x-axis and flow
is shown on the y-axis.
 Like the flow waveform, inspiratory and
expiratory flows are in opposite
directions.

45. The F-V Loop
 Inspiration begins at the origin of the
graph (zero flow) and increases until it
reaches the peak inspiratory flow rate
(PIFR).
 Flow then decelerates, and reaches the
zero flow state at the point where it
crosses the volume axis, representing the
delivered V

46. The F-V Loop
 Expiratory flow begins with the accelerating
phase, reaches the peak expiratory flow rate
(PEFR).
 Then, it decelerates until it returns to the origin
and another zero flow state at end expiration.
 The general shape of the loop should be round
or ovoid and the two halves (inspiratory and
expiratory) should be close to mirror images.

47. Decreased Compliance

48. Lung Compliance

49. Lung Inflation

50. Lung Inflation
“Hyperinflation”
 As the lung approaches maximum filling and tissue
distensibility becomes more limited, the compliance
will decrease, resulting in less volume gain per unit of
incremental pressure, and the slope of the
compliance axis will shift downward.
 This creates an upper inflection point on the P-V
inflation limb and graphically creates a “penguin
beak” or “duck bill” appearance to the loop.

51. Lung Inflation
“Hyperinflation”
 Hyperinflation can be quantified by using a metric
known as the C20/C ratio (Fisher, 1988).
 The C20/C ratio examines the slope of the last 20 %
of the inflation limb and compares it with the linear
portion of the curve.
 If the curve remained linear to the peak pressure, the
ratio would remain at 1.0; if the loop begins to bend to
the right, the slope will decrease and the ratio will
decrease to <1.0.

52. Lung Inflation “Hyperinflation”

53. Lung Inflation “Underinflation”
 Lung inflation below the FRC will also
produce a slope that is less than the linear
portion of the compliance axis.
 Little volume is being delivered at the lower
end of the inflation limb until the opening
pressure has been exceeded and volume
starts to increase, creating a lower inflection
point in the loop.

54. Lung Inflation “Underinflation”
 The loop looks more like a box than a
football.
 Applied pressure does not deliver any
effective volume for much of the inspiratory
phase.
 Similarly, during deflation the lung rapidly de-
recruits when the critical closing pressure is
reached.

55. Pressure Overshoot

56. Pressure Overshoot
 Ventilator modalities that use variable inspiratory
flow, such as PC and PS, may produce flow rates
that exceed the mechanical properties of the lung
and lead to hyperinflation.
 the P-V curve shows a bulge or a notch, and the
pressure waveform shows a double peak at PIP.
 The flow rate may be modulated by a feature
known as rise time, available on most devices,
which allows a qualitative adjustment in the flow
rate.

57. Air Hunger
 If the delivered Vt is inadequate to meet the
patient’s need, air hunger may develop.
 In this situation the baby may be noted to be
“pulling” or displaying increased work of
breathing.
 This creates a distinctive pattern on the P-V
loop, with a “figure of eight” reversal of the
inflation and deflation limbs at the top of the
loop.

58. Increased Inspiratory
Resistance
 Excessive distance between the inflation
limb and the compliance axis represents
increased inspiratory resistance.
 This pattern can often be corrected by
increasing inspiratory flow, inspiratory
time, or PEEP.

59. Elevated Inspiratory
Resistance
 Rather than having an oval or circular
appearance with a discernible peak
inspiratory flow rate, the loop is flat across
most of the inspiratory phase. This suggests
an extrathorcic obstruction

60. Increased Expiratory
Resistance
 It conversely, produces changes in the
deflation limb of the P-V loop, in which
it may be separated or bowed from the
compliance axis.
 Adjustments to correct this might
include increases in expiratory time
and/or PEEP.

61. Elevated Expiratory
Resistance
 Rather than having an ovular or circular
appearance, the loop looks compressed due to
reduction in the PEFR, suggestive of obstructive
airway disease.

62. Surfactant Administration
 Surfactant administration to a newborn
with RDS will lower alveolar surface
tension and improve pulmonary
compliance.
 Because this can happen rapidly, there is
a risk of overdistension of the lung if
pressure is not reduced rapidly enough.

63. Surfactant Administration

64. Surfactant Administration

65. Fixed Airway Obstruction
 both inspiratory and expiratory resistances may
be elevated, resulting in a “compression” of the
F-V loop with lower PIFR and PEFR & Both
inspiratory and expiratory portions of the loop
are flattened.

66. Evaluation of Bronchodilator
Therapy

67. Evaluation of Bronchodilator
Therapy
 . There has been a significant improvement in
both the PIFR and PEFR. The loop has
“opened” and the tidal volume delivery has
also improved

68. Turbulence
 This results from secretions or condensation in
the airway or the ventilator circuit. Turbulence
creates a “noisy” flow signal, which alters both
the flow waveform and the F-V loop.

69. Turbulence
examine the baby and to look carefully for:
 secretions
 condensation
 or other obstructive matter in the airway,
endotracheal tube, sensor, or ventilator circuit
Some centers have used this information to
determine when to suction a mechanically
ventilated baby rather than performing
suctioning on a routine basis.

70. Excessive Dynamic Airway
Collapse
 note the “notching” at end expiration.

71. Excessive Dynamic Airway
Collapse
 EDAC is a condition that may be
congenital or acquired, in which there is
airway luminal narrowing during
expiration creating a severe expiratory
flow restriction.
 The appearance of the F-V loop shows
a rapid decline from the PEFR after a
sharp acceleration to peak