Case one: rationales

Step 1 — Answer: 1, 2, 3, 4, 5, 6

Why 1 is right: 100.9°F on postoperative day 1 is a fever, and in this client it sits alongside diminished bases and shallow breathing rather than standing alone. Why 2 is right: a heart rate of 112 is the compensation for hypoxemia, fever, and a falling blood pressure at once. Why 3 is right: 24 shallow breaths is splinting, and splinting is how the bases collapse. Why 4 is right: 88% on room air is hypoxemia by any standard and is the single most urgent number on the page. Why 5 is right: she was oriented at 2200 and is not oriented now. The change, not the finding, is the cue. Why 6 is right: 620 mL retained after catheter removal is acute retention, not a slow bladder. Why 7 is wrong: a dry, intact dressing on postoperative day 1 is exactly what should be there. Nothing about it requires action. Why 8 is wrong: 3 out of 10 the morning after hip arthroplasty is adequate analgesia. It is a reassuring finding that candidates mark because it appears in a list of abnormal-looking numbers.

Blood pressure is deliberately not offered here. It does its work in Step 2.

The rule: a cue is a finding that is abnormal for this client at this moment, and the strongest cues are the ones that changed.

Step 2a — Answers, in row order: hypoxemia, hypoxemia, retention, opioid effect, opioid effect, retention

Why oxygen saturation 88% with diminished bases points to hypoxemia: low saturation plus reduced air movement at the bases is a gas exchange problem located in the lung. Why respirations 24 and shallow points to hypoxemia: a rate that is fast and shallow is splinting and compensation. Opioid depression slows the rate; it does not raise it. Why 620 mL with no void points to retention: that volume is the definition of the problem. Why overnight patient-controlled analgesia points to opioid effect: it is the exposure that makes the hypothesis worth considering at all. Why pain of 3 out of 10 after hip arthroplasty points to opioid effect: comfortable this early means she has received a substantial amount of opioid. Why a firm, full lower abdomen points to retention: it is the bedside finding that confirms the scan.

Step 2b — Answer: 2

Why 2 is right: a saturation of 88% with diminished breath sounds at both bases locates the problem in gas exchange. Low volume alone lowers blood pressure and raises heart rate, but it does not collapse the bases and it does not usually drop saturation this far on room air. Why 1 is wrong: tachycardia is the one finding that every hypothesis on this page predicts, so it discriminates between none of them. Why 3 is wrong: fever is compatible with low volume, with atelectasis, and with early infection. It argues for nothing in particular. Why 4 is wrong: a full bladder is a real and separate problem, but it neither supports nor excludes low circulating volume.

The rule: the cue that decides an item is the one that is compatible with only some of the explanations, not the one that is compatible with all of them.

Step 3a — Answer: 2 (hypoxemia), 1 (retention), 3 (opioid effect) — that is, hypoxemia first, retention second, opioid effect third.

Why hypoxemia is first: at 88% on room air she is minutes away from harm, and correcting it costs one piece of equipment and no permission. Why retention is second: 620 mL is causing distress and delirium now and risks bladder injury within hours, so it cannot wait a shift, but it will not kill her in the next ten minutes. Why opioid effect is third: it is real and it must be acted on, but her respiratory rate is 24, not 8. A rate that fast is direct evidence against opioid-induced respiratory depression being the active emergency.

Step 3b — Answer: 2

Why 2 is right: prioritization of hypotheses is ordering by speed of harm. The question is what will hurt her soonest if you are wrong about it. Why 1 is wrong: ranking by likelihood is a diagnostic exercise. Here, retention is arguably the most likely explanation for the confusion, and it is still not first. Why 3 is wrong: ease of treatment is a resource consideration, not a safety one. Some of the deadliest problems are also the easiest to treat, which is a coincidence, not a rule. Why 4 is wrong: counting supporting cues rewards whichever hypothesis the case author wrote the most sentences about.

The rule: prioritizing hypotheses is ordering by speed of harm, and that is a different operation from ordering by probability.

Step 4 — Answer: 1, 2, 3, 4

Why 1 is right: hypoxemia is corrected before it is investigated, and the reassessment is part of the intervention. Why 2 is right: sitting her up and opening the bases treats the mechanism that produced the low saturation. Why 3 is right: intermittent catheterization relieves 620 mL of retention, which is both the comfort problem and a contributor to the delirium. Why 4 is right: holding the next dose pending a sedation and respiratory assessment costs nothing, is reversible, and removes a plausible contributor while you work. Why 5 is wrong: restraints treat the nurse's problem, not the client's. Restraining a hypoxemic, delirious older adult increases agitation, increases injury, and leaves the cause untouched. Why 6 is wrong: sedating a client whose confusion is caused by hypoxemia and a full bladder deepens the hypoxemia and hides the deterioration. Why 7 is wrong: this is reasonable, and it is not now. A culture changes nothing in the next hour and requires a specimen she cannot yet produce. Why 8 is wrong: this is also reasonable, and also not now. Ambulating a client at 88% on room air is an intervention aimed at postoperative day 1 in general, not at this client this morning.

The rule: two of the eight wrong options are wrong, and two are correct at the wrong hour. Learn to feel the difference.

Step 5a — Answer, in order: apply oxygen and reassess; raise the head of the bed and coach incentive spirometry; hold the next opioid dose; catheterize per protocol

Why oxygen is first: it is the fastest correction of the most lethal finding, and it requires nothing but reaching for the cannula. Why positioning and spirometry are second: they treat the cause of the desaturation and they take effect over the following minutes while you continue. Why holding the opioid is third: it is a decision, not a procedure, and it takes seconds. Doing it before you leave the bedside prevents another dose from landing while you are gathering catheter supplies. Why catheterization is fourth: it requires a protocol check and equipment, and it is the only one of the four that takes you away from the client's airway.

Step 5b — Answer: 2

Why 2 is right: oxygen is applied before the provider is called. The call is a communication, and communication does not raise a saturation. Why 1 is wrong: catheterization is correct and it is not the action that must precede the call. Why 3 is wrong: holding a dose is correct and takes seconds, but a held dose does not treat 88%. Why 4 is wrong: spirometry requires her cooperation and she is confused. It is second, not first, and it is not the gate on the phone call.

The rule: when an option says notify the provider, ask what you would do while you wait, and do that first.

Step 6a — Answers: improved, improved, unchanged, worsened, improved

Why oxygen saturation is improved: 88% on room air to 94% on 2 liters per minute is a real gain, though it is a supported one and she is not yet independent of the oxygen. Why respiratory rate is improved: 24 to 20 with the head of the bed up and the bases opening. Why orientation is unchanged: she has recovered person and place, and she still does not know the year and is still restless. Partial recovery of orientation over ninety minutes in an older adult is not resolution, and calling it improved is how a nurse stops looking. Why temperature is worsened: 100.9°F to 101.3°F is a rise, and it is now the finding least explained by the interventions performed. Why retained bladder volume is improved: 700 mL out, 40 mL residual. That problem is resolved for now.

Step 6b — Answer: 1

Why 1 is right: mental status is the finding that integrates oxygenation, perfusion, and elimination, and it is the one still abnormal after all three were addressed. If it clears, the plan worked. If it does not, something on this list is still wrong, and the rising temperature says what to look at next. Why 2 is wrong: the dressing was never abnormal and is not sensitive to any of the four interventions. Why 3 is wrong: her pain was already controlled, and the opioid was just held. A pain score will move for reasons that have nothing to do with whether the plan worked. Why 4 is wrong: the bladder was emptied ninety minutes ago. A repeat scan is scheduled surveillance, not the decision point.

The rule: evaluate on the finding that summarizes the most systems, not on the finding that is easiest to measure.

Margin note: "soonest harm beats most likely."

> ☐ I can say the ranking rule without looking. > → BOOK 03 · P3 for the full prioritization framework set.

Takeaway. Prioritizing hypotheses is ordering by speed of harm, and that is a different operation from ordering by probability.