CNN common mistakes
CNN · Understand the traps and how to avoid them.
Memorizing CKD stage numbers as isolated facts and then mixing up the eGFR cutoffs (e.g., calling an eGFR of 35 mL/min/1.73 m2 stage 3a, or treating 'stage 4' as starting dialysis), or substituting a 24-hour creatinine clearance value for an eGFR category.
Candidates cram the stage table the night before and store it as a list of numbers without the anchoring concepts (60, 45, 30, 15), so under time pressure the middle stages blur together; many also never learned that staging is by eGFR, not by creatinine or by symptoms.
What to do instead
Rebuild the table from four anchors only (>=90 with kidney damage, 60-89, 45-59, 30-44, 15-29, <15) and draw it on the scratch sheet before starting. Do 20 practice items where only the eGFR and clinical data are given and you must name the stage plus one nursing implication for that stage.
Reversing the classic prerenal-versus-intrinsic discrimination indices, or applying fractional excretion of sodium to a patient on loop diuretics and treating the result as valid.
The numbers (BUN:creatinine >20:1, FENa <1%, urine osmolality >500, urine Na <20) are learned as a jumble of 'low means prerenal' rules without the underlying logic that prerenal states avidly reabsorb sodium and water, so any item that flips the framing trips them up.
What to do instead
Learn the physiology story once: decreased effective circulating volume -> ADH and aldosterone -> concentrated low-sodium urine. Then memorize the direction of change for each index rather than absolute values, and add a flagged exception card stating that diuretics invalidate FENa and that contrast, aminoglycosides, and myoglobin produce intrinsic patterns with misleading indices.
Choosing an intervention before an assessment when a stem asks for the nurse's first or priority action, such as giving sodium polystyrene sulfonate or calling the provider immediately on seeing a potassium of 6.4 mEq/L.
Clinical instinct and unit habit push toward 'do something,' and priority items are written so the plausible-but-premature action reads as decisive and competent; candidates also forget that in emergency framing the first action is often obtaining the 12-lead ECG or verifying the result by repeat draw.
What to do instead
Adopt a fixed screening order for every priority item: assess/verify -> stabilize ABCs -> notify -> administer. Physically write the sequence at the top of the scratch area and score each option against it before choosing. Practice with hyperkalemia, pulmonary edema, and hypotension-on-dialysis vignettes, where the correct first action is usually ECG, auscultation, or confirming the value.
Labeling an arterial blood gas as a simple single disorder without calculating the expected compensation, so a mixed disorder in a CKD patient (e.g., metabolic acidosis with an inappropriately high PCO2, or a superimposed metabolic alkalosis from vomiting) is misclassified.
Candidates read the pH and the primary PCO2 or bicarbonate and stop there; Winter's formula and the expected-PCO2 range are perceived as math to skip under time pressure, and anion-gap delta calculations are often left undone.
What to do instead
Drill a fixed four-step script on paper: pH -> primary disorder -> calculate expected compensation (Winter's: 1.5 x HCO3 + 8 +/- 2) -> calculate anion gap and delta ratio if acidosis. Run 10 ABG practice sets drawn from renal failure scenarios until the calculation step is automatic rather than optional.
Confusing hemodialysis adequacy metrics, treating Kt/V and urea reduction ratio as interchangeable or as having the same threshold (e.g., accepting a URR of 55% because 'Kt/V was fine'), and mis-answering items about correct pre- and post-dialysis BUN specimen collection.
Both metrics describe urea clearance, so the labels feel fungible; candidates memorize one number and apply it to both, and they rarely study the sampling technique (predialysis draw, postdraw with the slow-flow/rebound method) because it seems like a lab detail rather than a nursing action.
What to do instead
Build a two-column card: Kt/V target >=1.2 (single pool) versus URR target >=65%, with the note that URR is a rough percent reduction while Kt/V is a log-based clearance ratio. Add a sequence card for specimen timing and practice items that deliberately pair one passing metric with one failing metric.
Answering peritoneal dialysis peritonitis items by sending the patient to the unit for intraperitoneal antibiotics first, or missing that a cloudy effluent bag with abdominal pain is the earliest and most reliable sign, while dismissing exit-site redness as the key finding.
Candidates conflate exit-site and tunnel infections with peritonitis, and they default to the medical intervention (antibiotics) rather than the diagnostic nursing action (obtain and send effluent for cell count and culture before the first dose).
What to do instead
Memorize the triad-and-action pattern: cloudy bag + abdominal pain +/- fever -> culture the effluent first, then initiate empiric intraperitoneal therapy per protocol. Make a comparison chart for exit-site infection (erythema, purulent drainage at catheter exit), tunnel infection (tenderness along the tract), and peritonitis, and note that effluent white count >100/mm3 with >50% neutrophils is the diagnostic threshold.
Managing transplant immunosuppression by generic pharmacology intuition (e.g., advising acetaminophen plus an NSAID for post-transplant pain, or accepting any trough level drawn at any time of day), and under-reacting to subtler rejection cues such as a rising creatinine, low-grade fever, or graft tenderness.
Calcineurin inhibitor trough interpretation depends on strict 12-hour timing and consistent assay, which is procedural knowledge candidates rarely rehearse, and the nephrotoxic drug list (NSAIDs, aminoglycosides, contrast, St John's wort, grapefruit) is treated as trivia rather than as a high-yield interaction set.
What to do instead
Create a one-page interaction and monitoring sheet: trough drawn immediately before the next dose, same assay, plus the nephrotoxic and CYP3A4-interacting agents to avoid. Pair it with a rejection-cue drill in which you must spot the earliest abnormal value (creatinine trend) rather than waiting for oliguria.
Selecting patient-education options that describe what the nurse will explain or provide (a handout, a verbal review, instructions to 'limit fluids') instead of options that verify comprehension through teach-back, returned demonstration, or a written plan the patient restates.
Education items look like knowledge items, so candidates pick the option containing the most correct clinical content; they also underestimate how often the tested behavior is confirming learning or accommodating health literacy rather than delivering facts.
What to do instead
When two options contain equally correct clinical content, choose the one where the patient demonstrates or restates the skill. Rehearse teach-back phrasing and add a health-literacy filter: prefer plain language, chunked instruction, and 'show me how you would...' over 'explain to the patient that...'.
Answering vascular-access and infection-control items from personal unit custom rather than published standards, for example accepting a catheter exit site left with intact dried blood, choosing clean gloves alone for catheter connection, or applying transmission-based precautions to a dialysis patient who only needs standard precautions.
Habits learned at the chairside feel authoritative and are often not the same as CDC or KDOQI recommendations, and candidates do not distinguish standard precautions (apply to all patients) from transmission-based precautions (require a specific indication).
What to do instead
Anchor each answer to a named standard: CDC hand hygiene and catheter-care bundle, fistula 'rule of 6s' and the feel-the-thrill/look-for-bruit assessment, and the rule that dialysis units use standard precautions plus dedicated equipment unless a specific transmission indication exists. When two options both seem safe, pick the one that reflects the published bundle rather than unit practice.
Misreading the qualifier in the stem, answering the 'except,' 'least likely,' or 'initial' question as if it were 'best' or 'most likely,' and then defending the choice with correct but off-target reasoning.
Under time pressure candidates pattern-match to the clinical content they recognize and skip the final clause; the recognition of a familiar phrase produces a strong pull toward an answer that is factually true but does not fit the question asked.
What to do instead
Circle or underline the qualifier word before reading the options, and restate the question in your own words in a half-sentence. Before committing, say the chosen option back against the qualifier to confirm the direction matches, and flag any item where you cannot restate the question in one sentence.