Advanced mechanical vent exam #3

What is a ventilator scalar?

A graphic that plots one variable against time.

What are the three major ventilator scalars?

Pressure-time, flow-time, and volume-time.

What are the axes of a pressure-time scalar?

Y-axis: airway pressure. X-axis: time.

What are the axes of a flow-time scalar?

Y-axis: flow (L/min). X-axis: time.

What are the axes of a volume-time scalar?

Y-axis: volume (mL). X-axis: time.

What is PIP?

Peak inspiratory pressure; the highest airway pressure reached during inspiration.

What is plateau pressure?

Airway pressure measured during an inspiratory hold when airflow is zero.

What is PEEP?

Positive pressure maintained at the end of expiration to help keep alveoli open.

What is inspiratory time (Ti)?

The time spent delivering an inspiratory breath.

What is expiratory time (Te)?

The time available for the patient to exhale.

What is a patient-triggered breath?

A breath initiated by the patient's inspiratory effort.

What is a time-triggered breath?

A breath initiated by the ventilator after a preset time interval.

What does high PIP with a relatively unchanged plateau pressure indicate?

Increased airway resistance.

What are common causes of increased airway resistance?

Bronchospasm, secretions, a kinked tube, or artificial airway obstruction.

What do increased PIP and increased plateau pressure indicate?

Decreased respiratory-system compliance.

What conditions can decrease lung compliance?

ARDS, pulmonary edema, atelectasis, pneumothorax, and reduced chest-wall compliance.

How do you calculate resistive pressure?

PIP − plateau pressure.

What does resistive pressure represent?

The pressure needed to overcome airway and flow resistance during inspiration.

How do you calculate driving pressure?

Plateau pressure − total PEEP.

What does increased driving pressure suggest?

More pressure is required to deliver the breath, potentially indicating decreased respiratory-system compliance.

What does a negative pressure deflection before inspiration suggest?

Patient inspiratory effort or an attempt to trigger a breath.

What is the difference between PIP and plateau pressure?

PIP includes resistive pressure during flow, while plateau pressure reflects respiratory-system distending pressure during a no-flow pause.

What does positive flow usually represent?

Inspiration.

What does negative flow usually represent?

Expiration.

What should expiratory flow do before the next breath?

Return to zero, indicating that exhalation is complete.

What does expiratory flow failing to return to zero indicate?

Possible auto-PEEP or air trapping.

What is auto-PEEP?

Positive pressure remaining in the lungs at the end of expiration because exhalation is incomplete.

What causes auto-PEEP?

High respiratory rate, inadequate expiratory time, airway obstruction, COPD, asthma, or excessive ventilation for the patient's expiratory capacity.

What is dynamic hyperinflation?

Progressive air trapping caused by incomplete exhalation between breaths.

What complications can auto-PEEP cause?

Increased work of breathing, elevated intrathoracic pressure, reduced venous return, and possible hypotension.

What is flow starvation?

When the patient's inspiratory demand exceeds the flow delivered by the ventilator.

What might flow starvation look like on a pressure-time waveform?

A scooped or negative pressure deflection during inspiration.

How can secretions or water in the circuit affect ventilator waveforms?

They can create irregular or distorted flow patterns; secretions may also increase airway resistance.

What are the four common inspiratory flow patterns?

Square/constant, decelerating, ascending, and sinusoidal.

What does square or constant inspiratory flow look like?

Flow remains relatively constant throughout inspiration.

What does decelerating inspiratory flow look like?

Flow begins high and gradually decreases during inspiration.

What does ascending inspiratory flow look like?

Flow gradually increases throughout inspiration.

What does sinusoidal inspiratory flow look like?

Flow rises and falls in a smooth, curved pattern.

What happens to the volume waveform during inspiration?

The waveform rises as gas enters the lungs.

What happens to the volume waveform during expiration?

The waveform falls as gas leaves the lungs.

What should the volume-time waveform do at the end of expiration?

Return to baseline.

What does inspired tidal volume exceeding expired tidal volume suggest?

A possible circuit leak, cuff leak, or other loss of delivered gas.

What can incomplete return toward baseline suggest?

Possible air trapping, incomplete exhalation, or a leak, depending on the waveform and ventilator display.

What is volume-controlled ventilation (VCV)?

A mode in which tidal volume is targeted and airway pressure varies with resistance, compliance, and patient effort.

What is pressure-controlled ventilation (PCV)?

A mode in which inspiratory pressure is targeted and delivered tidal volume can vary.

What happens to tidal volume when compliance decreases during pressure control?

Tidal volume usually decreases if pressure and other conditions remain unchanged.

What is pressure support ventilation (PSV)?

A mode providing pressure assistance during patient-triggered breaths, with tidal volume depending on patient effort and respiratory mechanics.

What is the difference between a scalar and a loop?

A scalar plots a variable against time; a loop plots one variable against another.

What does a pressure-volume loop evaluate?

Compliance, pressure requirements, recruitment, and possible overdistention.

What are the axes of a pressure-volume loop?

Y-axis: volume. X-axis: pressure.

What does a flattened pressure-volume loop suggest?

Decreased compliance; more pressure is needed to deliver volume.

What does improved compliance look like on a pressure-volume loop?

More volume is achieved at a given pressure.

What does beaking at the top of a pressure-volume loop suggest?

Possible overdistention, where additional pressure produces little additional volume.

What is alveolar recruitment?

Opening previously collapsed alveoli to improve ventilation and potentially oxygenation.

How can PEEP help the lungs?

It helps prevent alveolar collapse at end expiration and may improve recruitment.

What can excessive PEEP cause?

Overdistention, increased intrathoracic pressure, and reduced venous return.

What does a flow-volume loop evaluate?

Inspiratory and expiratory flow, tidal volume, and possible airway obstruction or leaks.

What are the axes of a flow-volume loop?

Y-axis: flow. X-axis: volume.

What does a scooped expiratory limb suggest?

Airflow obstruction, such as COPD or bronchospasm.

What does a flow-volume loop that fails to close suggest?

Possible leak or incomplete expiration; confirm using other waveforms and clinical assessment.

What is patient-ventilator asynchrony?

A mismatch between the patient's respiratory effort and the ventilator's delivery of a breath.

What is ineffective triggering?

The patient attempts to inhale, but the ventilator fails to deliver a breath.

What can cause ineffective triggering?

Auto-PEEP, weak respiratory effort, or trigger sensitivity set too low.

What is auto-triggering?

The ventilator delivers a breath without genuine patient inspiratory effort.

What can cause auto-triggering?

Excessive trigger sensitivity, circuit leaks, condensation, or cardiac oscillations.

What is flow asynchrony?

A mismatch between the patient's inspiratory flow demand and the flow supplied by the ventilator.

What is premature cycling?

The ventilator ends inspiration before the patient has finished inhaling.

What is delayed cycling?

The ventilator continues inspiration after the patient is ready to exhale.

What is double triggering?

Two ventilator breaths occur close together with little or no expiration between them.

Why is double triggering concerning?

It can cause breath stacking and unexpectedly high delivered tidal volumes.

What should you assess when patient-ventilator asynchrony occurs?

Patient effort, comfort, respiratory drive, trigger sensitivity, inspiratory flow, cycling, airway patency, and auto-PEEP.

What is capnometry?

Numerical measurement of carbon dioxide.

What is capnography?

Continuous graphical representation of carbon dioxide over time.

What is a typical healthy adult ETCO₂ range?

Approximately 35-45 mmHg.

What does the baseline of a normal capnogram represent?

CO₂-free or nearly CO₂-free inspired gas.

What is Phase I of a capnogram?

The baseline, when gas from the conducting airways is exhaled.

What is Phase II of a capnogram?

The expiratory upstroke, when CO₂ rises as alveolar gas mixes with airway gas.

What is Phase III of a capnogram?

The alveolar plateau, when predominantly alveolar gas is exhaled.

Where is ETCO₂ measured?

At the end of expiration, near the end of the alveolar plateau.

What is Phase 0 of a capnogram?

The inspiratory downstroke, when fresh gas enters and measured CO₂ falls.

What does a normal capnogram look like?

A relatively rectangular waveform with an expiratory upstroke, alveolar plateau, and return to baseline.

What does a shark-fin capnogram indicate?

Airway obstruction, such as bronchospasm, asthma, or COPD.

Why does bronchospasm create a shark-fin waveform?

Narrowed airways cause prolonged, uneven emptying of the lungs.

What does an elevated inspiratory baseline indicate?

Possible rebreathing of CO₂.

What can cause rebreathing?

A faulty valve, exhausted CO₂ absorbent in a circle system, or other breathing-system problems.

What is a curare cleft?

A notch in the alveolar plateau that may indicate spontaneous respiratory effort during mechanical ventilation.

What can cause sudden loss of a capnogram?

Airway displacement or obstruction, circuit disconnection, apnea, cardiac arrest, or severe reduction in perfusion.

What should you do if a capnogram suddenly disappears?

Immediately assess the patient, airway, circuit, and circulation.

What can increasing ETCO₂ indicate?

Decreased alveolar ventilation, increased CO₂ production, or increased CO₂ delivery to the lungs.

What can decreasing ETCO₂ indicate?

Increased alveolar ventilation, decreased pulmonary perfusion, or reduced CO₂ production.

Why might ETCO₂ differ from PaCO₂?

Increased dead space or ventilation-perfusion abnormalities can widen the PaCO₂-ETCO₂ difference.

PIP is 40 and plateau pressure is 24 cmH₂O. What is the resistive pressure?

16 cmH₂O, suggesting increased airway resistance if measurements are valid.

Plateau pressure is 25 and total PEEP is 10 cmH₂O. What is driving pressure?

15 cmH₂O.

A COPD patient has expiratory flow that does not return to zero. What is the likely problem?

Incomplete exhalation with possible auto-PEEP.

A patient has high PIP and high plateau pressure after developing pulmonary edema. What is the likely problem?

Decreased respiratory-system compliance.

A ventilator waveform shows patient effort without a delivered breath. What is this?

Ineffective triggering.

Two breaths occur with almost no exhalation between them. What is this?

Double triggering or breath stacking.

A ventilated patient has a shark-fin capnogram. What should you assess?

Airway patency, breath sounds, bronchospasm, secretions, and expiratory flow.

A capnogram baseline remains above zero during inspiration. What should you investigate?

Rebreathing and the breathing circuit, including valves and CO₂ absorbent where applicable.

What is the first priority when a ventilator graphic suddenly becomes abnormal?

Assess the patient first, then evaluate the airway, circuit, ventilator, and likely cause.