Hamilton G5 (2/2)

Question 1

What does ASV stand for and what is its purpose?

Answer 1

Adaptive Support Ventilation — maintains a minimum minute ventilation (V̇e) independent of the patient’s activity.

Question 2

What happens during a passive ASV breath?

Answer 2

The ventilator does everything; it’s volume-targeted, pressure-controlled, and time-cycled.

Question 3

What happens during an active ASV breath?

Answer 3

The patient participates; the breath is volume-targeted, pressure-supported, and flow-cycled.

Question 4

What type of breath is delivered in ASV when passive?

Answer 4

A VC+-type breath (volume-targeted, pressure-controlled).

Question 5

What is the key parameter set by the clinician in ASV?

Answer 5

The Minute Volume (MV) goal — the ventilator then adjusts RR, Vt, and Ti automatically based on lung mechanics and patient effort.

Question 6

What equation does ASV use to determine the optimal breathing pattern?

Answer 6

The Otis equation — used to find the RR and Vt combination that minimizes the work of breathing (WOB).

Question 7

What should you know about the Otis equation for exams?

Answer 7

You don’t need to memorize the formula — just know it helps the ventilator choose the optimal RR and Ti for the patient based on resistance and compliance.

Question 8

What patient data must be entered for ASV setup?

Answer 8

Gender and height (cm) — the ventilator calculates IBW and anatomical dead space automatically.

Question 9

How does the G5 determine anatomical dead space?

Answer 9

Automatically from IBW (≈ 2.2 mL/kg) assuming no HME and known circuit volume.

Question 10

How is target Minute Ventilation (MV) calculated?

Answer 10

MV = IBW × 100 mL/kg/min. Then a percentage of that target MV is chosen as the goal.

Question 11

What triggers can you choose in ASV?

Answer 11

Flow or pressure trigger (clinician-selected).

Question 12

What is the P-ASV limit and what happens if it’s exceeded?

Answer 12

The maximum pressure the vent can use for control breaths (usually ≤ 30 cmH₂O). If > 30 cmH₂O, target Vt may not be achieved.

Question 13

What is the default high-pressure alarm in ASV?

Answer 13

10 cmH₂O higher than the P-ASV limit.

Question 14

What should be done if using an HME?

Answer 14

Add 10% to IBW to compensate for extra dead space.

Question 15

What is ASV’s time-constant goal?

Answer 15

Aims for 3 time constants (3 TC) — Ti ≈ 3 × the expiratory time constant.

Question 16

What is the maximum inspiratory time (Ti) allowed in ASV?

Answer 16

2 seconds (ASV caps Ti at this value).

Question 17

What does ASV do after the initial test breaths?

Answer 17

Delivers 3 test breaths. Measures resulting RR and Vt. Compares to targets and adjusts to minimize the difference.

Question 18

Describe how ASV uses feedback control.

Answer 18

It continuously evaluates patient effort, resistance, and compliance → recalculates target RR and Vt → adjusts Pinsp and RR to meet targets.

Question 19

What happens when work of breathing (WOB), compliance, or resistance changes?

Answer 19

The ventilator automatically modifies RR, Vt, or Pinsp to maintain the target MV — it’s a continuous feedback loop.

Question 20

What should you do if PaCO₂ > 45 mmHg?

Answer 20

Increase % MinVol to raise minute ventilation and blow off more CO₂.

Question 21

What should you do if PaCO₂ < 35 mmHg and pH > 7.45?

Answer 21

Decrease % MinVol to reduce minute ventilation.

Question 22

When should you not adjust MV in ASV?

Answer 22

When blood gases are normal — no change needed.

Question 23

Why must special attention be given to MAP (Mean Airway Pressure) when changing MV?

Answer 23

Increasing MV raises MAP, which can alter oxygenation and affect hemodynamics.

Question 24

What is the equation for MAP?

Answer 24

MAP = Pmean (average airway pressure over the respiratory cycle).

Question 25

What adjustments can be made if O₂ saturation decreases?

Answer 25

Increase PEEP and/or FiO₂; assess WOB and RR.

Question 26

What happens when a patient begins breathing spontaneously on ASV?

Answer 26

The patient gradually takes over breathing. Passive breaths transition into active ones. The patient can breathe above the set MV target.

Question 27

What changes occur as spontaneous breathing increases?

Answer 27

Controlled frequency (F-control) decreases → may reach zero. Spontaneous breath count rises. Pinsp requirements decrease as the patient’s effort increases.

Question 28

Does zero controlled rate mean full weaning?

Answer 28

Not necessarily — even if F-control = 0, the patient might not be fully weaned yet.

Question 29

What does it mean when Pinsp decreases from 15 → 5 cmH₂O in ASV?

Answer 29

The patient’s effort has increased, indicating progression toward full weaning (5 = almost fully weaned).

Question 30

What is the significance of a Pmean drop during spontaneous ASV?

Answer 30

Indicates improved compliance and reduced pressure requirement to maintain target volume.

Question 31

Which patients should not be placed on ASV?

Answer 31

ARDS, Status asthmaticus, Difficult or complex ventilation patients.

Question 32

Why avoid ASV in ARDS?

Answer 32

ARDS requires tight Vt control (≈ 6 mL/kg). ASV adjusts automatically, risking over-distention. Volume control mode is preferred.

Question 33

Why avoid ASV in status asthmaticus?

Answer 33

These patients have prolonged exhalation and high resistance. ASV’s 3 TC rule can over-estimate Ti, worsening air-trapping.

Question 34

Why avoid ASV in complex or irregular ventilation cases?

Answer 34

Patterns are inconsistent, making automatic targeting unreliable for weaning or pressure adjustment.

Question 35

What are the main benefits of ASV?

Answer 35

Provides the safest ventilatory pattern. Improves patient-ventilator synchrony. Reduces clinician workload/intervention. Lowers airway pressures.

Question 36

In which patient population is ASV most commonly used?

Answer 36

Post-operative patients, particularly cardiac cases.

Question 37

Summarize ASV’s key mechanism in one line.

Answer 37

ASV automatically adjusts RR, Vt, and Ti using feedback from lung mechanics and patient effort to maintain target MV with minimal WOB.