Dynamic ultrasound monitoring of intraperitoneal effusion for predicting complications after laparoscopic gastrectomy

Table 1 General data of patients, n (%)/mean ± SD

Indicators	Results (n = 80)
Gender (male/female)	52 (65.00)/28 (35.00)
Age (years)	59.63 ± 9.21
Height (cm)	165.28 ± 7.82
Body weight (kg)	62.41 ± 9.73
BMI (kg/m2)	22.72 ± 2.07
BMI ≥ kg/m2	18 (22.50)
Hypertension	24 (30.00)
Diabetes	15 (18.75)
Coronary heart disease	8 (10.00)
Chronic liver disease	5 (6.25)
Chronic renal insufficiency	3 (3.75)
WBC (× 109/L)	6.48 ± 1.32
Red blood cell count (× 1012/L)	4.21 ± 0.36
Hemoglobin (g/L)	128.63 ± 11.74
Platelets (× 109/L)	215.74 ± 42.63
ALT (U/L)	32.01 ± 11.04
AST (U/L)	28.74 ± 9.66
ALP (U/L)	82.12 ± 18.53
TBIL (μmol/L)	13.26 ± 4.84
Cr (μmol/L)	87.36 ± 13.12
BUN (mmol/L)	5.21 ± 1.16
Pre-CRP (mg/L)	6.41 ± 2.57
Pre-PCT (ng/mL)	0.08 ± 0.04
Operation time (minutes)	167.53 ± 34.72
Intraoperative bleeding volume (mL)	143.52 ± 47.36
Combined splenectomy	5 (6.25)
Combined pancreatectomy	2 (2.50)
Postoperative hospital stay (day)	11.32 ± 2.58
POD1 body temperature (°C)	37.56 ± 0.39
POD3 WBC (× 109/L)	9.28 ± 2.21
POD5 CRP (mg/L)	34.75 ± 10.16
POD7 CRP (mg/L)	19.83 ± 6.32
POD7 PCT (ng/mL)	0.18 ± 0.06
Postoperative fever	23 (28.75)
Postoperative abdominal distension	17 (21.25)
Postoperative use of anti-infective drugs (%)	93.75

BMI: Body mass index; WBC: White blood cell count; ALT: Alanine aminotransferase; AST: Aspartate aminotransferase; ALP: Alkaline phosphatase; TBIL: Total bilirubin; Cr: Creatinine; BUN: Blood urea nitrogen; CRP: C-reactive protein; PCT: Procalcitonin; POD: Postoperative day.

Table 2 Incidence rate of intraperitoneal effusion, n (%)/mean ± SD

Time point	Number of positive effusion (%)	Maximum effusion depth (mm)	χ2/t	P value
POD1	28 (35.00)	12.56 ± 3.24	-	-
POD3	42 (52.50)	15.48 ± 4.17	5.12	0.024
POD7	37 (46.25)	13.92 ± 3.85	1.21	0.271

P < 0.05 indicated significant difference. The incidence peaked on postoperative day 3 (52.50%). P values are derived from generalized estimating equation models comparing each time point to postoperative day 1. POD: Postoperative day.

Table 3 Assessment of effusion volume, n (%)/mean ± SD

Time point	Effusion volume (mL)	Mild effusion	Moderate effusion	Massive effusion	F/χ2	P value
POD1	38.25 ± 15.62	25 (31.25)	3 (3.75)	0 (0.00)	35.462	< 0.001
POD3	89.74 ± 42.11	22 (27.50)	31 (38.75)	5 (6.25)
POD7	63.38 ± 28.94	33 (41.25)	10 (12.50)	4 (5.00)
Level distribution	-				29.751	< 0.001

P < 0.05 indicated significant difference. Severity was classified as mild (< 50 mL), moderate (50-200 mL), or massive (> 200 mL). P value for volume trend from linear mixed model; distribution comparison from χ² test. POD: Postoperative day.

Table 4 Subgroup analysis of two surgical methods, n (%)

Time point	Total (n = 80)	Distal gastrectomy (n = 56)	Total gastrectomy (n = 24)	P value
POD1	28 (35.0)	18 (32.14)	10 (41.67)	0.412
POD3	42 (52.5)	26 (46.43)	16 (66.67)	0.032
POD7	37 (46.3)	24 (42.86)	13 (54.17)	0.342

P < 0.05 indicated significant difference. Total gastrectomy was associated with a significantly higher incidence of effusion on postoperative day 3 (66.67% vs 46.43%, P = 0.032) and a higher proportion of mixed effusion (41.67% vs 32.14%, P = 0.042). POD: Postoperative day.

Table 5 Determination of the nature of effusion, n (%)

Time point	Total cases of effusion	Simple effusion	Mixed effusion	χ2/t	P value
POD1	28	20 (71.43)	8 (28.57)	-	-
POD3	42	27 (64.29)	15 (35.71)	0.571	0.450
POD7	37	24 (64.86)	13 (35.14)	0.007	0.935
Overall comparison	-	-	-	0.295	0.863

P < 0.05 indicated significant difference. Mixed effusion was defined by the presence of internal echogenic debris, septations, or gas echoes. No significant temporal trend was observed in the proportion of mixed effusion (P > 0.05). POD: Postoperative day.

Table 6 Postoperative inflammation indicators, mean ± SD

Time point/effusion nature	Body temperature (°C)	WBC (× 109/L)	CRP (mg/L)	PCT (ng/mL)	Statistical values	P value
POD1	37.56 ± 0.39	9.28 ± 2.21	34.75 ± 10.16	0.18 ± 0.06
POD3	38.12 ± 0.65	12.36 ± 3.45	58.32 ± 14.28	0.52 ± 0.15	Body temperature F = 29.763	< 0.001
					WBC F = 41.289	< 0.001
					CRP F = 53.471	< 0.001
					PCT F =38.954	< 0.001
POD7	37.45 ± 0.32	8.54 ± 1.78	26.94 ± 8.73	0.22 ± 0.08
Simple effusion group	37.89 ± 0.44	10.75 ± 2.21	43.84 ± 10.62	0.39 ± 0.11
Mixed effusion group	38.56 ± 0.58	14.02 ± 3.12	72.15 ± 12.34	0.67 ± 0.14	Body temperature t = 5.812	< 0.001
					WBC t = 6.524	< 0.001
					CRP t = 7.385	< 0.001
					PCT t = 6.987	< 0.001

P < 0.05 indicated significant difference. Body temperature was the maximum daily value. Comparisons across time points used repeated-measures analysis of variance; between-group comparisons used independent t-tests. WBC: White blood cell count; CRP: C-reactive protein; PCT: Procalcitonin; POD: Postoperative day.

Table 7 Complications, n (%)

Types of complications	Total cases (n = 80)	Simple effusion (n = 43)	Mixed effusion (n = 28)	No effusion (n = 9)	χ2/t	P value
Abdominal infection	9 (11.25)	2 (4.65)	7 (25.00)	0 (0.00)	6.974	0.031
Abscess formation	6 (7.50)	1 (2.33)	5 (17.86)	0 (0.00)	5.782	0.045
Anastomotic fistula	4 (5.00)	1 (2.33)	3 (10.71)	0 (0.00)	2.371	0.305
Secondary surgical intervention	3 (3.75)	0 (0.00)	3 (10.71)	0 (0.00)	4.235	0.057
Total complications	18 (22.50)	4 (9.30)	14 (50.00)	0 (0.00)	19.684	< 0.001

P < 0.05 indicated significant difference. Complications were significantly more common in the mixed effusion group (50.00%) than in the simple (9.30%) or no effusion (0.00%) groups (P < 0.001). P values for specific complications are from χ² or Fisher’s exact tests.

Table 8 Analysis results of generalized estimating equation

Variables	β	SE	Wald χ2	P value	OR (95%CI)
Constant (baseline)	-1.832	0.412	19.799	< 0.001	-
Time = day 3	1.284	0.298	18.518	< 0.001	3.61 (1.99-6.54)
Time = day 7	0.634	0.277	5.243	0.022	1.89 (1.10-3.27)
Surgical approach (total gastrectomy)	0.742	0.315	5.55	0.018	2.10 (1.14-3.87)
High risk factors (yes)	0.615	0.294	4.371	0.037	1.85 (1.04-3.31)
Time × surgical method	-	-	8.362	0.015	-
Time × high risk factors	-	-	7.851	0.02	-

P < 0.05 indicated significant difference. The model analyzed repeated binary measurements (effusion presence/absence) across postoperative day 1, 3, and 7. β: Coefficient estimate; OR: Odds ratio; CI: Confidence interval.

Table 9 Analysis results of linear mixed-effect model

Fixed effect variable	β	SE	t	P value	95%CI
Constant (baseline)	31.52	6.84	4.61	< 0.001	18.11-44.93
Time = day 3	51.36	7.42	6.921	< 0.001	36.72-65.99
Time = day 7	25.13	6.87	3.658	0.001	11.53-38.73
Surgical approach (total gastrectomy)	17.48	6.42	2.723	0.008	4.72-30.25
BMI (kg/m2)	3.24	1.34	2.418	0.019	0.55-5.93
Intraoperative bleeding volume (per 100 mL)	5.76	2.23	2.584	0.011	1.36-10.16

P < 0.05 indicated significant difference. The model included time, surgical approach, and intraoperative blood loss as fixed effects. β: Coefficient estimate; CI: Confidence interval; BMI: Body mass index.

Table 10 Analysis results of logistic regression analysis

Independent variable	β	SE	Wald χ2	P value	OR (95%CI)
Operation time (per 10 minutes)	0.205	0.12	2.902	0.083	1.23 (0.97-1.55)
Bleeding volume (per 100 mL)	0.537	0.213	6.351	0.012	1.71 (1.13-2.59)
Day 3 CRP (per 10 mg/L)	0.35	0.104	11.34	0.001	1.42 (1.15-1.75)
Day 3 PCT (per 0.1 ng/mL)	0.444	0.142	9.813	0.002	1.56 (1.18-2.07)

P < 0.05 indicated significant difference. The outcome was effusion severity (mild < moderate < massive). The Brant test confirmed the proportional odds assumption. β: Coefficient estimate; CI: Confidence interval; CRP: C-reactive protein; PCT: Procalcitonin.

Table 11 Analysis results of Cox regression

Risk factors	β	HR (95%CI)	Wald χ2	P value
Nature of effusion (mixed)	1.352	3.86 (1.62-9.18)	9.714	0.002
Age (years)	0.018	1.02 (0.98-1.06)	1.134	0.287
Surgical approach (total gastrectomy)	0.473	1.60 (0.72-3.56)	1.498	0.221
Day 3 CRP (per 10 mg/L)	0.223	1.25 (1.05-1.49)	6.506	0.011
Day 3 PCT (per 0.1 ng/mL)	0.293	1.34 (1.09-1.65)	7.837	0.005

P < 0.05 indicated significant difference. Mixed effusion, postoperative day 3 C-reactive protein, and postoperative day 3 procalcitonin were independent predictors of complications. β: Coefficient estimate; HR: Hazard ratio; CI: Confidence interval; CRP: C-reactive protein; PCT: Procalcitonin.

Table 12 Results of receiver operating characteristic curve indicators

Indicators	Cut-off value	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	AUC	Youden’s index
CRP (mg/L)	48.5	80	78.3	64	89.3	0.852	0.583
PCT (ng/mL)	0.47	82.9	81.7	67.7	91.2	0.874	0.646
WBC (× 109/L)	10.8	68.6	70	52.9	80.4	0.732	0.386
Combined model	-	88.6	85	0.912	Combined model	-	88.6

The combined model (postoperative day 3 procalcitonin > 0.47 ng/mL + mixed effusion) showed superior predictive performance (area under the curve = 0.912) compared to individual markers. PPV: Positive predictive value; NPV: Negative predictive value; AUC: Area under the curve; CRP: C-reactive protein; PCT: Procalcitonin; WBC: White blood cell count.