集中治療室（ICU）における重症患者の「1時間血清乳酸値」と30日死亡率の関係について

[Relationship between "1-hour serum lactate" level and 30-day mortality in critical care patients in intensive care unit].

• Qilin Yang
• Yinzhou Zhang
• Tianyu Kong
• Zhenhui Zhang
• Xuming Xiong
• Weiyan Chen

抄録

目的:

集中治療室（ICU）の重症患者における「1時間血清乳酸値（1時間Lac）」と30日死亡率との関係を調べる。

OBJECTIVE: To investigate the relationship between 1-hour lactate (1 h Lac) and 30-day mortality in critical care patients in intensive care unit (ICU).

方法:

Medical Information Mart for Intensive Care-IIIデータベース（MIMIC-III）からICU入院後1時間以内の乳酸値の記録がある成人重症患者（年齢≧16歳）を対象に、レトロスペクティブ観察的コホート研究を実施した。1時間後のLac値により、2mmol/L未満、2～4mmol/L、4mmol/L以上の3つのグループに分けた。ベースライン特性を分析した。1時間Lacと30日死亡率との関連を評価するために、多変量ロジスティック回帰分析を行った。30日死亡率に対する1 h Lacの予測値をレシーバー操作特性（ROC）曲線を用いて解析し、最良のカットオフ値に応じてKaplan-Meier生存曲線を行った。また、各分類変数について感度解析を行った。

METHODS: A retrospective, observational cohort study was performed with adult critical patients (age ≥ 16 years old) having lactate records within 1 hour after ICU admission from Medical Information Mart for Intensive Care-III database (MIMIC-III). According to the 1 h Lac level, the patients were divided into three groups: < 2 mmol/L, 2-4 mmol/L, and > 4 mmol/L groups. The baseline characteristics were analyzed. Multivariable Logistic regression analysis was performed to assess the association between 1 h Lac and 30-day mortality. The receiver operating characteristic (ROC) curve was used to analyze the predictive value of 1 h Lac for 30-day mortality, and Kaplan-Meier survival curve was performed according to the best cut-off value. In addition, sensitivity analysis was carried out for each classification variable.

結果:

ICU患者は3,969人で、30日以内に673人が死亡し、総死亡率は16.95%であった。死亡率は、Lac＜2mmol/L群が1,664人、1,588人、4mmol/L超群が717人であった。年齢，ICU期間，ICUの種類，心拍数，白血球数，ヘモグロビン，クレアチニン，逐次臓器不全スコア（SOFA），人工呼吸器の使用，血管作動薬の使用，主な診断に3群間で有意差があった。多変量ロジスティック回帰分析では、Lacの1mmol/L増量は30日死亡リスクの0.24倍と関連していた［オッズ比（OR）＝1.24、95％信頼区間（95％CI）は1.19～1.29、P＜0.000 1］。ROC曲線分析の結果、重症患者の30日死亡率を予測するための1時間LacのROC曲線下面積（AUC）は0.694（95％CIは0.669～0.718）であった。カットオフ値は3.35mmol/Lで，感度は0.499，特異度は0.779，正の尤度比は2.260，負の尤度比は0.643であった。1時間Lacのカットオフ値により，高乳酸群（≧3.35mmol/L）と低乳酸群（＜3.35mmol/L）に分けた．2つのサブグループでは、30日死亡率はそれぞれ31.58%(336/1 064)、11.60%(337/2 905)であった。Kaplan-Meier生存曲線から、高乳酸群の30日累積生存率は低乳酸群に比べて有意に低いことが示された（Log-rank test：χ＝247.72、P＜0.000 1）。多重ロジスティック回帰分析では、年齢、入院時期、ICUの種類、ヘモグロビン、白血球数、血管拡張剤の使用、人工呼吸器の使用、患者の主な診断を調整した後、高乳酸群の30日死亡率は低乳酸群の2.34倍であった（OR = 2.34、95%CIは1.90-2.88、P < 0.000 1）。層別分析の結果、1時間Lacと30日死亡率の関係は安定していた。

RESULTS: A total of 3 969 ICU patients were included, with 673 died in 30 days, and the total mortality was 16.95%. There were 1 664, 1 588, 717 patients in Lac < 2 mmol/L, 2-4 mmol/L and > 4 mmol/L group, respectively. There were significant differences in age, ICU duration, ICU type, heart rate, leukocyte count, hemoglobin, creatinine, sequential organ failure score (SOFA), ventilator application, vasoactive drug use and main diagnosis among the three groups. Multivariable Logistic regression analysis showed that a 1 mmol/L increment in Lac was associated with 0.24 times higher risk of 30-day mortality [odds ratio (OR) = 1.24, 95% confidence interval (95%CI) was 1.19-1.29, P < 0.000 1]. ROC curve analysis showed that the area under ROC curve (AUC) of 1 h Lac for predicting 30-day mortality of severe patients was 0.694 (95%CI was 0.669-0.718). The cut-off value was 3.35 mmol/L with sensitivity of 0.499 and specificity of 0.779, whilst positive likelihood ratio was 2.260, and negative likelihood ratio was 0.643. According to the cut-off value of 1 h Lac, the patients were divided into high lactate group (≥ 3.35 mmol/L) and low lactate group (< 3.35 mmol/L). In the two subgroups, 30-day mortality was 31.58% (336/1 064) and 11.60% (337/2 905), respectively. The Kaplan-Meier survival curve showed that the 30-day cumulative survival rate of high lactate group was significantly lower than that of low lactate group (Log-rank test: χ = 247.72, P < 0.000 1). Multiple Logistic regression analysis showed that the 30-day mortality rate of high lactate group was 2.34 times that the level of low lactate group (OR = 2.34, 95%CI was 1.90-2.88, P < 0.000 1), after the adjustment of age, time of admission, type of ICU, hemoglobin, leukocyte count, use of vasopressor, use of ventilator and main diagnosis of patients. Stratified analysis showed that the relationship between 1 h Lac and 30-day mortality was stable.

結論:

1 h Lacは重症患者の30日死亡率と関連している。1h Lacが3.35mmol/Lより高い重症患者では死亡リスクが有意に上昇した。

CONCLUSIONS: 1 h Lac is associated with 30-day mortality in critical care patients. The risk of death was significantly increased in critically ill patients with 1 h Lac higher than 3.35 mmol/L.