Ventilator Waveforms &

Loops: A Beginners

Approach

DAVID WATERS RN, MA, PGDIP ED, BA(HONS)

MARCIA BIXBY RN, MS, CCRN, APRN-BC

Welcome

Class code: C60M393

Contact hours: 1.00

CERP A credits: 1.00

Faculty Disclosures: None

Learning Outcomes

1. Evaluate the role of waveforms and loops associated with ventilation and respiratory failure of the critically ill patient.

2. Outline the components and their clinical significance of normal and abnormal waveforms and loops.

3. List patient care considerations and safety issues associated with monitoring ventilator waveforms and loops.

David Waters

Oxford,

United Kingdom

Marcia Bixby

Case Study – in the Beginning

Alison

38 yo female with history of asthma since

childhood

Presents to the ED with status asthmaticus

Ralph

• 56 yo with history of hypertension and DM

• Smoked 1PPD – 40 years

• Construction worker

• Traumatic fall - 20 feet off of a scaffolding

Ventilation and Perfusion

To understand failure- you must understand function!!

Ventilation- the air that reaches the alveoli to facilitate gas exchange bringing in oxygen and flushing out carbon dioxide.

Perfusion- the blood that reaches the alveoli via the capillaries.

Ventilation/Perfusion Ratio is the ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli.

Capillary Membrane

Permeability

Increased interstitial volume > increased pressure Lungs – NCPE > ITP

Bowel – bowel edema – > IAP

Brain – cerebral edema - > ICP

Extremities – compartment syndrome

Identify and relieve cause of increased pressure

Restoration of perfusion

Restoration of oxygenation

Allow for restoration of organ function

Compliance and Resistance

Lung Compliance- measure of the lung’s ability

to stretch and expand.

Low Compliance- high elastic recoil-stiff lung

High Compliance- low elastic recoil-pliable lung

Lung Resistance- the resistance of the

respiratory tract to airflow during inspiration and

expiration

Respiratory Failure

Hypoventilation – narcotics, muscular

Airway obstruction/Asthma - RESISTANCE

ARDS/Pneumonia - COMPLIANCE

Pulmonary Embolus

Neuro injury

Burns – Inhalation

Aspiration

Chest/pulmonary trauma

Congestive Heart Failure

Diagnosis – Respiratory Failure

Vitals – tachycardia, tachypnea, dyspnea

Confusion and extreme tiredness

Perfusion deficits

Sats dropping

ABG – hypercarbia , hypoxia despite increase O2 delivery

mixed resp/-metabolic acidosis uncompensated

CXR - CT scan

COMPLIANCE (elasticity) reduced-stiff lung

Case Study - continued

How do you anticipate your assessment of Alison and Ralph to look like?

Vital signs

HR- normal or tachy?

RR – normal or increased?

BP – normal, hypo or hyper?

ABG

PaO2

PaCO2

Mental status

Case Study continued

Because this is a ventilation session – you know Alison and Ralph

will be intubated and mechanically ventilated. HOWEVER:

Alison – unresponsive to nebs and steroids in the ED

What is your threshold for intubation

Why would you intubate her

What mode and pressures do you anticipate to start

Ralph – pneumothorax, fx right ribs, head injury, fx femur

What is your threshold for intubation

Why would you intubate him

What mode and pressures do you anticipate to start

Modes of Ventilation

Basic Concepts

Respiratory rate

Tidal Volume

Oxygen level

PEEP

Minute ventilation – adjust rate and tidal volume

to maintain steady minute ventilation

If lung volume decreases – rate must increase,

PEEP adjusted for compliance/resistance

BiPAP – CPAP - NiPPV

Used as therapy to increase alveolar recruitment

Can be adjusted to patients response

May prevent intubation

Face mask or nasal mask

Uncomfortable

Monitor for aspiration

BiPAP - Bilevel Positive Airway Pressure

CPAP - Continuous Positive Airway Pressure

NiPPV - NonInvasive Positive Airway Pressure

Modes of Ventilation

Non-Invasive :

BiPAP, CPAP, NiPPV

Invasive:

Spontaneous – Assisted – Controlled

Volume - Volume or Pressure

SIMV Assist Control

Pressure Control Pressure Support

APRV HFOV

PEEP and PRESSURE Ventilation

Helps to keep alveoli open

Prevents alveolar collapse on expiration

Higher levels of PEEP increase ITP

Can interfere with cardiac output

Prevents preload

Increases afterload

Monitor hemodynamic response to PEEP

Esophageal pressure monitoring

MONITOR WAVEFORMS

Critical Care Ventilation Detective

Signifies top clues in

ventilation graphic

interpretation

Scalars & Loops – the Basics

Graphical representations of data collated by the

mechanical ventilator

Can be divided into 2 categories

Those measuring 1 parameter over time – scalar, or waveform

Pressure

Flow

Volume

Those measuring 2 parameters over time – loop

Pressure-Volume

Flow-Volume

Pressure-

Time

Scalar

Flow-Time

Scalar

Volume-

Time

Scalar

Pressure-

Volume

Loop

Volume-

Flow

Loop

Scalar:

Pressure-

Time

Typical Pressure-Time Scalar

(Mechanical Breath)

Decreased Compliance

(Elasticity)

Normal

compliance

(C = 100

mls/mbar)

Reduced

compliance

(C = 30

mls/mbar)

Examples of Changes in

Compliance

Increased Airway Resistance

Normal

resistance (R

= 6 mbar/L/s)

Increased

resistance (R

= 40

mbar/L/s)

Examples of Changes in Airway

Resistance

Pressure-Time Scalar: Spontaneous vs

Mechanical Breaths

Scalar:

Flow-

Time

Inspiratory Flow Pattern

Expiratory Flow Pattern

Typical Flow-time Scalar (Spontaneous breaths)

Examples of Flow-time Scalars

Air Trapping

Response to Bronchodilator

Scalar:

Volume-

Time

Typical Volume-Time Scalar

Air Leak/Air Trapping

Loop:

Pressure-

Volume

Components of Pressure-Volume Loop

Typical Pressure-Volume Loops

Air Leak/Air Trapping

Pressure-Volume Loop: Lung

Compliance Changes (Volume

Targeted Ventilation)

Pressure-Volume Loop: Lung

Compliance Changes (Pressure

Targeted Ventilation)

Pressure-Volume Loop:

Overdistension

Birds beak sign

Loop:

Flow-

Volume

Flow-Volume Loop

Air Leak on the Flow-

Volume Loop

Inspiration

Air Trapping on the

Flow-Volume Loop

Increased Airway Resistance

Airway Secretions or

Condensate on the Flow-Volume Loop

Real-time Scenarios:

Interpretation of

Mechanical Ventilation

Graphics

Alison

BP 94/68 mmHg, HR 122 bpm, RR 28 rpm, SpO2

93% on room air & 95% on 4L, afebrile –64

inches, 140 lbs/ 63 kg

Her ABG on 60% venturimask: pH 7.18, PaO2

64, PaCO2 70, HCO3 12 – using accessory

muscles

Intubated and placed on - 100% x 20, TV

6cc/kg – 381 cc , PEEP 5 cm– is this

appropriate at this time?

Should she be sedated ?

How would you sedate her ?

Paralytics?

Ralph – a complicated

patient

Hypoxic – why? Pain from rib fractures, altered MS from concussion/hypoxia

Atelectasis from hypoventilation due to pain, pulmonary contusions?

CXR reveals ground glass appearance bilateral lower lung fields – PTX right resolved, CT good position

ABG: Ph 7.47, PaO2 70 mmHg, PaCO2 33 mmHg, HCO3 18

HCT 9 from 10.3

PF ratio 175

What do you want to do – you can not switch your assignment……

Ralph – a complicated

patient

6 hours later BP 150/78 mmHg, HR 114 bpm, RR 38 rpm, SpO2 85% on 15L

CXR reveals opacities bilateral lower lung fields – PTX right resolved, Chest tube in good position

Intubated due to worsening respiratory status

Breath sounds diminished bilaterally, rales bilat 1/3 up both lung fields

What is happening?

Learning Outcomes

1. Evaluate the role of waveforms and loops associated with ventilation and respiratory failure of the critically ill patient.

2. Outline the components and their clinical significance of normal and abnormal waveforms and loops.

3. List patient care considerations and safety issues associated with monitoring ventilator waveforms and loops.

Contact Details

David: david.waters@bcu.ac.uk

Marcia: teach2rns@aol.com

Resources

Simulated ventilator screen images available from Draeger Medical (2020) https://www.draeger.com/en_uk/Hospital/Downloads

Emrath, E. (2021) The basics of ventilator waveforms. Current Pediatrics Reports. 9, p9-11.

Hess, D. & Kacmarek, R. (2014) Essentials of Mechanical Ventilation. 3rd Ed. McGraw-Hill Education.

Lian, J. (2009) Understanding ventilator waveforms –and how to use them in patient care. Nursing Critical Care. 4(1), p43-55.

Mackenzie, I. (2008) Core topics in mechanical ventilation. Cambridge University Press: Cambridge.