# Situation: A 58-year-old woman weighing 68 kg is brought to the emergency department with fever, flank pain, and new confusion. A urinary source of infection is suspected. She has no history of heart failure or kidney disease and no known drug allergies. A nursing student asks why serum lactate is followed so closely in this client. Which explanation should the nurse give?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630039  
> language: ko  
> subject: Nursing Practice V — Care of Clients with Maladaptive Patterns of Behavior; Care of Clients with Life-Threatening Conditions, Acute Multi-Organ Problems, High Acuity and Emergency Situations

## 문제

Situation: A 58-year-old woman weighing 68 kg is brought to the emergency department with fever, flank pain, and new confusion. A urinary source of infection is suspected. She has no history of heart failure or kidney disease and no known drug allergies.

A nursing student asks why serum lactate is followed so closely in this client. Which explanation should the nurse give?

## 보기

1. Poorly perfused cells shift to anaerobic metabolism **✔ 정답**
2. Bacteria in the bloodstream release lactic acid directly
3. The kidneys stop excreting lactate once urine output falls
4. Fever speeds the conversion of glucose to lactic acid

**정답: 1**

## 해설

When oxygen delivery does not meet cellular demand, cells switch to anaerobic metabolism and produce lactate, causing metabolic acidosis. A high lactate therefore marks hypoperfusion, and repeated measurements show whether resuscitation is clearing it.

## 심화 해설

Why serum lactate is tracked in suspected sepsis

The client presents with fever, flank pain, and confusion, and a urinary source is suspected. Confusion in this context is a red flag because it may reflect sepsis-associated encephalopathy or, more importantly, cerebral hypoperfusion. When systemic oxygen delivery falls behind tissue demand, cells cannot sustain aerobic respiration and shift to anaerobic metabolism. Pyruvate is then converted to lactate, which accumulates in the blood and produces a high-anion-gap metabolic acidosis [1][2].

A rising serum lactate therefore serves as a biomarker of tissue hypoperfusion, not as a direct bacterial product. Bacteria do not simply “release” lactic acid into the bloodstream; rather, the host’s own poorly perfused cells generate it as a protective attempt to maintain energy production when oxygen is scarce [2]. This distinction is the core of the correct option.

Serial lactate measurements are valuable because they show whether resuscitation is actually restoring perfusion. A falling lactate, or “lactate clearance,” suggests that oxygen delivery is improving and anaerobic metabolism is being reversed. Multiple studies have demonstrated the prognostic accuracy of serial lactate levels, and lactate clearance has been proposed as a therapeutic target during sepsis resuscitation [1]. The Surviving Sepsis Campaign’s Hour-1 Bundle emphasizes rapid measurement of lactate as part of early recognition and management because delays are associated with worsening organ dysfunction and higher mortality [4].

| Option | Why it is incorrect | Key distinction |
| --- | --- | --- |
| 2. Bacteria release lactic acid directly | Lactate is produced by host cells, not secreted by pathogens | Host metabolic response, not bacterial toxin |
| 3. Kidneys stop excreting lactate once urine output falls | Renal clearance contributes to lactate elimination, but hyperlactatemia in early sepsis is driven primarily by increased production from hypoperfusion, not by reduced excretion alone | Production overwhelms clearance |
| 4. Fever speeds conversion of glucose to lactic acid | Fever raises metabolic rate, but the dominant mechanism in sepsis is tissue hypoxia and anaerobic glycolysis from inadequate oxygen delivery | Hypoxia, not hyperthermia |

Watch out! Lactate is an epiphenomenon of the body’s protective response to hypoperfusion or hypoxia. It marks disease severity but is not itself the primary injurious agent [2].

Key point! In a client with suspected sepsis and altered mental status, an elevated lactate should prompt immediate evaluation of perfusion and rapid initiation of the sepsis bundle, including fluid resuscitation and source control [4].References (research sources)

- [1]What Is the Utility of Measuring Lactate Levels in Patients with Sepsis and Septic Shock?Research articleWeinberger J, Klompas M, Rhee C (2021) · DOI: 10.1055/s-0041-1733915

- [2]Update: Clinical Use of Plasma Lactate.Research articleGillespie Í, Rosenstein PG, Hughes D (2017) · DOI: 10.1016/j.cvsm.2016.10.011

- [4]Hour-1 Sepsis Bundle: Updated Evidence.Research articleDe Pascale G, Cutuli SL, Carelli S, Cisterna I, Vecchio PD, Franchini EO, Grilli FL, Lombardi G, Palladini A, Tagliamonte A, Tanzarella ES, Tudimella G, Montini L, Grieco DL, Antonelli M. (2026) · DOI: 10.3390/jcm15156049

## 임상 시나리오

Lactate in Sepsis ResuscitationWhy serial lactate guides perfusion assessment
Serum lactate is a marker of tissue hypoperfusion, not a direct bacterial product. When oxygen delivery falls below cellular demand, cells shift to anaerobic metabolism, converting pyruvate to lactate and causing high-anion-gap metabolic acidosis.

New confusion in suspected urinary sepsis is a red flag for cerebral hypoperfusion or sepsis-associated encephalopathy. Obtain an initial lactate promptly as part of the Hour-1 Bundle.

Serial lactate measurements show whether resuscitation is working. A falling lactate, or lactate clearance, suggests oxygen delivery is improving and anaerobic metabolism is reversing.

CautionDo not attribute rising lactate to bacteria releasing lactic acid or to reduced renal excretion. Treat the hypoperfusion—fluid resuscitation and source control—then reassess lactate to guide ongoing care.

## 핵심 개념

- **Anaerobic metabolism** — Cellular energy production without oxygen, converting pyruvate to lactate when oxygen delivery is inadequate
- **Lactate clearance** — Serial decrease in serum lactate indicating restored tissue perfusion and reversal of anaerobic metabolism
- **Hypoperfusion** — Inadequate oxygen delivery to tissues relative to metabolic demand
- **High-anion-gap metabolic acidosis** — Acid-base disorder caused by accumulation of unmeasured anions such as lactate
- **Sepsis-associated encephalopathy** — Acute brain dysfunction in sepsis, often presenting as confusion or altered mental status

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