RRT Exam Mnemonics: 12 Memory Tricks for Ventilators and ABGs

Primary acid-base disorder

“ROME: Respiratory Opposite, Metabolic Equal”

1. RRespiratory: pH and PaCO2 move in Opposite directions (PaCO2 up, pH down = respiratory acidosis)
2. OOpposite: PaCO2 down with pH up = respiratory alkalosis
3. MMetabolic: pH and HCO3- move in the same (Equal) direction
4. EEqual: HCO3- down with pH down = metabolic acidosis; HCO3- up with pH up = metabolic alkalosis

Use it when: When the CSE reveals an ABG and you must name the problem before choosing a ventilator change, an oxygen change or a drug.

Careful: ROME names the primary disorder only when one thing is wrong. If PaCO2 and HCO3- both move against the pH (high PaCO2 with low HCO3-), it is a mixed acidosis, and ROME will mislead you. When the pH is normal but both values are abnormal, use the side of 7.40 to pick the primary.

Expected compensation

“1-4, 2-5 (and Winter's for metabolic acidosis)”

1. 1Acute respiratory acidosis: HCO3- rises about 1 mEq/L per 10 mm Hg rise in PaCO2
2. 4Chronic respiratory acidosis: HCO3- rises about 3.5-4 per 10 mm Hg
3. 2Acute respiratory alkalosis: HCO3- falls about 2 per 10 mm Hg fall in PaCO2
4. 5Chronic respiratory alkalosis: HCO3- falls about 4-5 per 10 mm Hg
5. WWinter's formula: expected PaCO2 = 1.5 x HCO3- + 8 (plus or minus 2) in metabolic acidosis

Use it when: When you need to decide whether a CO2 retainer's ABG is chronic and stable or acute-on-chronic, or whether a second disorder is hiding behind the first.

Careful: A measured value outside the expected range means a second primary disorder, not 'extra' compensation; the body never overcompensates. Acute-on-chronic CO2 retention in COPD shows a high HCO3- with a pH that has dropped below the patient's baseline, and that, not the PaCO2 alone, is what pushes you toward NPPV.

Oxyhemoglobin curve shifts

“CADET, face Right!”

1. CCO2 increased
2. AAcidosis (more H+)
3. D2,3-DPG increased
4. EExercise
5. TTemperature increased

Use it when: When a scenario asks why tissue oxygen delivery changes, or why the SpO2 and PaO2 do not match the usual pairing.

Careful: A right shift lowers hemoglobin's affinity (P50 above 27 mm Hg) and helps unloading at the tissues. Carbon monoxide does the opposite: it shifts the curve LEFT and cuts oxygen content, which is why CO is so dangerous. Fetal hemoglobin, alkalosis, hypothermia and stored blood (low 2,3-DPG) also shift left.

Causes of hypoxemia

“Two normal, three wide; shunt won't budge”

Normal P(A-a)O2: low inspired PO2 (altitude) and hypoventilation. Widened P(A-a)O2: V/Q mismatch (the most common cause; responds well to oxygen), diffusion defect (responds to oxygen) and shunt (refractory: the PaO2 barely rises as FiO2 increases, and it needs PEEP or recruitment instead).

Use it when: When you calculate a gradient and must decide what is causing the hypoxemia and whether the answer is oxygen, ventilation or PEEP.

Careful: Compare gradients only at the same FiO2; the normal value rises with FiO2 and with age (roughly age/4 + 4 mm Hg on room air). A shunt over about 30% will not correct with 100% oxygen, which is the cue to add PEEP, not more FiO2.

Sudden deterioration on the ventilator

“DOPE”

1. DDisplacement: tube out of the trachea or in a mainstem bronchus (check ETCO2, breath sounds, tube mark at the teeth)
2. OObstruction: secretions, kink or biting (pass a suction catheter)
3. PPneumothorax: absent breath sounds on one side, tracheal shift, hypotension, rising pressures (decompress)
4. EEquipment failure: disconnection, ventilator fault, oxygen supply

Use it when: When an intubated patient suddenly desaturates or fights the ventilator and the CSE asks what to do first.

Careful: The first action in a crashing ventilated patient is to take the patient off the ventilator and bag with 100% oxygen: if they improve, the problem is the ventilator; if the bag is hard to squeeze, the problem is the tube or the patient. Some versions add S (DOPES) for stacked breaths, meaning auto-PEEP.

High vs low pressure alarms

“High pressure is a Hurdle; low pressure is a Leak”

High-pressure alarm (something is in the way): secretions, biting, kinked tube, coughing, bronchospasm, pneumothorax, mainstem intubation or falling compliance. Low-pressure alarm (gas is escaping): disconnection, a cuff leak or rupture, a circuit leak, or an extubated patient.

Use it when: When the ventilator alarms in a CSE problem and you must choose the cause and the fix without harming the patient.

Careful: In pressure control and pressure-regulated modes the peak pressure is set, so a 'hurdle' shows up as a falling VT and a low minute-volume alarm instead of a high-pressure alarm. In volume control, a patient pulling hard against too low a flow (flow starvation) can also drop the peak pressure.

Peak vs plateau pressure

“Peak climbs alone: it's the Pipe. Peak and plateau climb together: it's the Parenchyma.”

A rising peak pressure with an unchanged plateau widens the peak-plateau gap and means higher airway resistance: bronchospasm, secretions, or a kinked, bitten or narrow tube. Peak and plateau rising together (same gap) means lower compliance: pneumothorax, worsening ARDS or edema, atelectasis, mainstem intubation, abdominal distension or auto-PEEP.

Use it when: When the CSE shows pressure readings or graphics and asks for the cause or the right treatment: bronchodilator or suction vs chest film, decompression or PEEP change.

Careful: Plateau pressure needs an inspiratory hold on a passive patient, so an active patient makes it unreliable. Measure auto-PEEP separately with an expiratory hold. Plateau minus PEEP is the driving pressure, which is worth keeping at about 15 cm H2O or less in ARDS.

Lung-protective ventilation in ARDS

“6, 30, 88, 7.30”

1. 6VT 6 mL/kg predicted body weight (range 4-8)
2. 30Plateau pressure 30 cm H2O or less
3. 88SpO2 88-95% (PaO2 55-80 mm Hg), with PEEP and FiO2 set from the PEEP/FiO2 table
4. 7.30pH goal 7.30-7.45; raise the rate up to 35/min and accept permissive hypercapnia

Use it when: When a CSE patient meets ARDS criteria and you must choose the initial settings or correct a VT or plateau pressure that breaks the rules.

Careful: Use predicted body weight from height and sex, never actual weight; the obese patient whose VT was set on actual weight is a classic trap. For severe ARDS, prone positioning for more than 12 hours a day is recommended. The 2023 global ARDS definition also accepts SpO2/FiO2 of 315 or less and patients on high-flow nasal oxygen at 30 L/min or more.

Ready for a spontaneous breathing trial?

“READY”

1. RReason for intubation is improving or resolved
2. EEffort: the patient triggers spontaneous breaths
3. AAdequate gas exchange: P/F 150-200 or more on PEEP 8 or less and FiO2 0.40-0.50 or less; pH 7.25 or more
4. DDrips and dynamics: hemodynamically stable on no or low-dose vasopressors
5. YYes to a sedation pause: awake enough after a spontaneous awakening trial

Use it when: When the CSE asks whether to start an SBT, continue ventilation, or recommend extubation after a trial.

Careful: READY is a coined screen, and passing it earns an SBT, not extubation. Extubation also needs airway protection (cough strength, secretion load, mental status). For patients at risk of post-extubation stridor, do a cuff-leak test, and for high-risk patients plan extubation to NPPV.

Weaning indices

“105, 20, 10, 10”

1. 105Rapid shallow breathing index (f/VT) under 105 breaths/min/L
2. 20NIF (MIP) more negative than -20 cm H2O (-30 is better)
3. 10Vital capacity over 10 mL/kg (10-15)
4. 10Minute ventilation under 10 L/min

Use it when: When the CSE reveals bedside weaning parameters and asks whether to proceed with a trial or keep the patient on support.

Careful: These are predictors, not the decision: the SBT itself (30-120 minutes on pressure support of 5-8 cm H2O, CPAP or T-piece) decides. Measure RSBI with the patient breathing spontaneously. For NIF, a larger negative number is stronger, so -25 is better than -15.

Information gathering

“Bedside, Blood, Black-and-white”

1. BedsideAppearance, sensorium, vital signs, work of breathing, breath sounds, SpO2
2. BloodABG (with CO-oximetry when CO or methemoglobin is possible); CBC or electrolytes only when they bear on the problem
3. Black-and-whiteChest radiograph

Use it when: In an information-gathering section, when you must pick the data a competent therapist needs right now without over-selecting.

Careful: If the patient is apneic, pulseless or has a tension pneumothorax, act first: a delay to gather data costs points. Specialist tests (PFTs or an exercise test in acute distress, bronchoscopy without an indication) are often scored negatively because they delay care or add risk. Pick what changes the next decision, not everything that could be interesting.

NPPV or intubate?

“Four can'ts: can't breathe, can't protect, can't fit, can't cooperate”

Start with NPPV for a COPD exacerbation with acute respiratory acidosis (pH 7.35 or lower with a raised PaCO2) or for cardiogenic pulmonary edema. Choose intubation instead when the patient can't breathe (apnea, arrest, or worsening despite 1-2 hours of NPPV), can't protect the airway (depressed consciousness, vomiting, copious secretions), can't be fitted with a mask (facial trauma, burns, recent facial or upper-airway surgery), or can't cooperate or stay stable (severe agitation, shock, uncontrolled arrhythmia).

Use it when: In a decision-making section where the patient with hypercapnic failure must be started on NPPV or intubated, or where a patient on NPPV is getting worse.

Careful: Reassess the ABG within 1-2 hours of starting NPPV; if pH and PaCO2 are not improving, intubate, because delayed intubation increases mortality. A low pH alone (for example 7.22) is not an absolute contraindication in COPD if the patient is monitored closely in a unit where intubation is immediately available.