# Situation: A nurse works in the pediatric emergency room and the pediatric oncology ward of a government hospital. For a child who swallowed paracetamol once at a known time, the physician orders a serum paracetamol level to plot on the Rumack–Matthew nomogram. When should the nurse arrange for the blood to be drawn?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=629450  
> language: ko  
> subject: Nursing Practice II — Maternal and Child Health Nursing

## 문제

Situation: A nurse works in the pediatric emergency room and the pediatric oncology ward of a government hospital.

For a child who swallowed paracetamol once at a known time, the physician orders a serum paracetamol level to plot on the Rumack–Matthew nomogram. When should the nurse arrange for the blood to be drawn?

## 보기

1. Immediately on arrival, before any treatment
2. Exactly 1 hour after the time of ingestion
3. At least 4 hours after the time of ingestion **✔ 정답**
4. Only after 24 hours, when liver injury appears

**정답: 3**

## 해설

For a single acute ingestion with a known time, the level is drawn 4 hours or later after ingestion and plotted on the nomogram. A level taken before 4 hours cannot be interpreted because absorption is still under way.

## 심화 해설

The timing of serum paracetamol measurement is critical because the Rumack–Matthew nomogram is only valid once drug absorption is essentially complete. A single acute ingestion with a known time requires a blood draw at least 4 hours after ingestion. Drawing earlier produces a value that reflects ongoing absorption rather than the true peak or post-absorption phase, making risk stratification unreliable.

Why the 4-hour threshold matters

After oral ingestion, paracetamol is absorbed primarily in the small intestine. Peak serum concentrations typically occur between 30 minutes and 2 hours in therapeutic dosing, but in overdose, gastric emptying may be delayed, tablet concretions may form, and co-ingested drugs with anticholinergic or opioid effects can slow motility. These factors mean that absorption can remain incomplete well beyond the usual peak time .

The nomogram’s treatment line begins at 4 hours post-ingestion precisely because values obtained before that point cannot be interpreted against the nomogram’s risk zones. A level drawn at 1 or 2 hours may still be rising, and plotting it would underestimate the eventual peak concentration, potentially placing a patient below the treatment threshold when they actually require N-acetylcysteine .

Watch out! A level drawn before 4 hours is not simply “less accurate” — it is uninterpretable on the nomogram. If an early level is obtained for other reasons, it cannot be used to make the decision about antidote therapy.

Absorption phase versus elimination phase

The nomogram assumes the patient is in the elimination phase, when serum concentration is falling in a predictable, first-order manner. During the absorption phase, concentration is rising, and the relationship between time and concentration does not follow the nomogram’s elimination slope. This is why the nomogram’s x-axis begins at 4 hours .

| Timing of blood draw | Interpretation on nomogram | Clinical implication |
| --- | --- | --- |
| Before 4 hours post-ingestion | Cannot be interpreted; absorption may be ongoing | Risk may be underestimated; do not use for treatment decisions |
| At 4 hours or later | Valid for plotting against the treatment line | Reliable for determining need for N-acetylcysteine |
| After 24 hours | Nomogram no longer applies; liver injury markers guide care | Used for prognosis, not initial risk stratification |

Clinical application in the pediatric setting

In a child who swallowed paracetamol once at a known time, the nurse should arrange the blood draw so that the sample is collected at or after the 4-hour mark. If the child arrives at the emergency department 1 hour after ingestion, the nurse should not draw the level immediately for nomogram use. Instead, the sample should be scheduled for the 4-hour point, while the child is monitored and a thorough history is obtained regarding the dose, formulation, and possible co-ingestants .

The decision to treat with N-acetylcysteine hinges on a single, properly timed serum paracetamol concentration plotted on the nomogram. Serial testing may show “line-crossing” between risk zones, but the initial decision still relies on a level drawn at 4 hours or later .

Key point! The 4-hour rule applies to single acute ingestions with a known time. For chronic ingestion, repeated supratherapeutic dosing, or unknown time of ingestion, the nomogram is not used in the same way, and management follows a different pathway .

In pediatric patients, hepatotoxicity from acute paracetamol overdose is less common than in adults, but this does not justify delaying the appropriately timed level. Early recognition and correct timing of the blood draw remain essential because N-acetylcysteine is most effective when started within 8 to 10 hours of ingestion . A level drawn at exactly 1 hour or immediately on arrival would be premature for nomogram interpretation, and waiting 24 hours would miss the window for effective antidote administration.

## 임상 시나리오

Acetaminophen Level TimingRumack-Matthew Nomogram Sampling
For a single acute ingestion with a known time, draw the serum acetaminophen level at least 4 hours after ingestion. The nomogram is only valid once absorption is essentially complete.

A level drawn before 4 hours is uninterpretable, not merely less accurate, because the drug may still be in the absorption phase.

CautionIn overdose, delayed gastric emptying, tablet concretions, or co-ingested anticholinergic/opioid agents can prolong absorption. Do not use an early level to decide on N-acetylcysteine therapy.

## 핵심 개념

- **Rumack-Matthew nomogram** — A graph used to assess acetaminophen overdose risk and guide acetylcysteine therapy based on serum level and time since ingestion.
- **N-acetylcysteine** — The antidote for acetaminophen toxicity that replenishes glutathione and prevents hepatocyte necrosis.
- **Peak serum concentration** — The highest drug level in blood after absorption; in overdose, delayed gastric emptying can shift this later than usual.
- **Acute ingestion** — A single overdose event occurring over a short period, with a known time of ingestion.

## 같은 주제 문제

- [Situation: A nurse works in the neonatal intensive care unit (NICU) of a tertiary hospital…](https://mymerci.kr/pages/nclex_q.php?qn_id=629441)
- [Situation: A nurse works in the neonatal intensive care unit (NICU) of a tertiary hospital…](https://mymerci.kr/pages/nclex_q.php?qn_id=629442)
- [Situation: A nurse works in the neonatal intensive care unit (NICU) of a tertiary hospital…](https://mymerci.kr/pages/nclex_q.php?qn_id=629443)
- [Situation: A nurse works in the neonatal intensive care unit (NICU) of a tertiary hospital…](https://mymerci.kr/pages/nclex_q.php?qn_id=629444)
- [Situation: A nurse on the pediatric cardiology and surgical ward cares for infants with co…](https://mymerci.kr/pages/nclex_q.php?qn_id=629445)
- [Situation: A nurse on the pediatric cardiology and surgical ward cares for infants with co…](https://mymerci.kr/pages/nclex_q.php?qn_id=629446)
- [Situation: A nurse on the pediatric cardiology and surgical ward cares for infants with co…](https://mymerci.kr/pages/nclex_q.php?qn_id=629447)
- [Situation: A nurse on the pediatric cardiology and surgical ward cares for infants with co…](https://mymerci.kr/pages/nclex_q.php?qn_id=629448)

---

More free questions: [기출문제](https://mymerci.kr/)

_학습 참고용입니다. 실제 임상은 최신 지침과 소속 기관 프로토콜을 따르세요._