Predicting prolonged postoperative ileus in gastric cancer patients based on bowel sounds using intelligent auscultation and machine learning

Table 1 Analysis of data related to gastric cancer patients, n (%)

Characteristics	Total (n = 120)	Characteristics	Total (n = 120)
Age (years)	64 (54.25, 71)	Surgical method
		Open	33 (27.5)
		Laparoscope	87 (72.5)
Gender		Range of excision
Male	80 (66.7)	Distal	53 (44.2)
Female	40 (33.3)	Proximal	21 (17.5)
		Total	46 (38.3)
BMI (kg/m2)	22.79 (20.22, 20.38)	Operation time (min)	280 (225, 339)
Diabetes		Anesthesia duration (min)	325 (271.25, 390)
Yes	11 (9.2)
No	109 (90.8)
Anemia		RTBS (h)	20.4 (15.2, 25.775)
Yes	44 (36.7)
No	76 (63.3)
Hypoproteinemia		NBS (cpm)	1.95 (0.89, 3.06)
Yes	22 (18.3)
No	98 (81.7)
Tumor site		BSVA (dB)	47.179 (44.75, 49.28)
Cardiac	21 (17.5)
Body	63 (52.5)
Antrum	36 (30.0)
Tumor size	4 (3.00, 5.00)	FBS (Hz)	424.32(383.45,485.76)
Stage cTNM
0	17 (14.2)
I	20 (16.7)
II	32 (26.7)
III	41 (34.2)
IV	8 (3.3)

Number of bowel sounds: The number of bowel sounds per minute, measured in counts per minute (CPM). Bowel sound vibration amplitude: The intensity of the bowel sound in the time or frequency domain, measured in decibels (dB). Frequency of bowel sounds: The significant frequency component of the bowel sound, representing the frequency band where the bowel sound energy is concentrated, measured in hertz (Hz). Recovery time of bowel sounds: The first postoperative occurrence of bowel sounds is defined as the first instance when the bowel rate exceeds 1 CPM. NBS: Number of bowel sounds; BSVA: Bowel sound vibration amplitude; FBS: Frequency of bowel sounds; RTBS: Recovery time of bowel sounds; BMI: Body mass index.

Table 2 Characteristics of patients in the training, internal validation and external validation groups, n (%)

Variable	Overall (N = 120)	Training (N = 84)	Validation (N = 36)	P value
Age (years)				0.291
≥ 70	40 (33.3)	25 (29.8)	15 (41.7)
< 70	80 (66.7)	59 (70.2)	21 (58.3)
Gender				0.291
Male	80 (66.7)	59 (70.2)	21 (58.3)
Female	40 (33.3)	25 (29.8)	15 (41.7)
BMI (kg/m2)				0.768
< 18.5	16 (13.3)	10 (16.7)	6 (8.3)
> 18.8 < 25	82 (68.3)	58 (18.1)	24 (18.8)
> 25	22 (18.4)	16 (65.3)	6 (72.9)
Smoking				0.078
Yes	46 (38.3)	37 (40.0)	9 (25)
No	74 (61.7)	47 (60.0)	27 (75)
Drinking				0.345
Yes	21 (17.5)	17 (20.2)	4 (11.1)
No	99 (82.5)	67 (79.8)	32 (88.9)
Hypertension				0.05
Yes	33 (27.5)	28 (33.3)	5 (13.9)
No	87 (72.5)	56 (66.7)	31 (86.1)
Diabetes				0.581
Yes	11 (9.2)	9 (10.7)	2 (5.6)
No	109 (90.8)	75 (89.3)	34 (94.4)
Previous abdominal surgery				0.885
Yes	26 (21.7)	19 (22.6)	7 (19.4)
No	94 (78.3)	65 (77.4)	29 (80.6)
Anemia				1
Yes	44 (36.7)	31 (36.9)	13 (36.1)
No	76 (63.3)	53 (63.1)	23 (63.9)
Hypoproteinemia				0.135
Yes	22 (18.3)	12 (14.3)	10 (16.8)
No	98 (81.7)	72 (85.7)	26 (72.2)
Preoperative potassium				1
Normal	108 (90.0)	76 (90.5)	32 (88.9)
Abnormal	12 (10.0)	8 (9.5)	4 (11.1)
Emergency surgery				0.444
Yes	3 (2.5)	1 (1.2)	2 (5.6)
No	117 (97.5)	83 (98.8)	34 (94.4)
Preoperative bowel preparation				0.784
Yes	114 (95.0)	79 (94.0)	35 (97.2)
No	6 (5.0)	5 (6.0)	1 (2.8)
Tumor size (cm)				0.693
< 5	76 (63.3)	52 (61.9)	24 (66.7)
≥ 5 < 10	36 (30.0)	27 (32.1)	9 (25.0)
≥ 10	8 (6.7)	5 (6.0)	3 (8.3)
Tumor site				0.627
Cardiac	21 (17.5)	13 (15.5)	8 (22.2)
Body	63 (52.5)	46 (54.8)	17 (47.2)
Antrum	36 (30.0)	25 (29.8)	11 (30.6)
Stage cTNM				0.537
0	17 (14.2)	11 (13.1)	6 (16.7)
I	20 (16.7)	13 (15.5)	7 (19.4)
II	32 (26.7)	25 (29.8)	7 (19.4)
III	43 (35.8)	28 (33.3)	15 (41.7)
IV	8 (6.7)	7 (8.3)	1 (2.8)
Surgical method				0.858
Open	33 (27.5)	24 (28.6)	9 (25)
Laparoscope	87 (72.5)	60 (71.4)	27 (75)
Range_of_excision				0.427
Distal	21 (17.5)	17 (20.2)	4 (11.1)
Proximal	53 (44.2)	37 (44.0)	16 (44.4)
Total	46 (38.3)	30 (35.7)	16 (44.4)
Operation time (min)				1
< 275	63 (52.5)	44 (52.4)	19 (52.8)
≥ 275	57 (47.5)	40 (47.6)	17 (47.2)
Anesthesia time (min)				0.803
< 365	43 (35.8)	29 (34.5)	14 (38.9)
≥ 365	77 (64.2)	55 (65.5)	22 (61.1)
RTBS (h)				0.144
< 15	92 (76.7)	68 (81.0)	24 (66.7)
≥ 15	28 (23.3)	16 (19.0)	12 (33.3)
NBS (cpm)				1
≥ 2.436	48 (40.0)	34 (40.5)	14 (38.9)
< 2.436	72 (60.0)	50 (59.5)	22 (61.1)
BSVA (dB)				0.964
< 44.793	88 (73.3)	61 (72.6)	27 (75.0)
≥ 44.793	32 (26.7)	23 (27.4)	9 (25.0)
FBS (Hz)				1
< 461.560	36 (30.0)	25 (29.8)	11 (30.6)
≥ 461.560	84 (70.0)	59 (70.2)	25 (69.4)

NBS: Number of bowel sounds; BSVA: Bowel sound vibration amplitude; FBS: Frequency of bowel sounds; RTBS: Recovery time of bowel sounds; BMI: Body mass index.

Table 3 Association of prolonged postoperative ileus with background and operative variables in bivariate analysis and in multivariable models

Variable	PPOI number (%)	P value	Multivariable OR (95CI)		P value
Age					0.009
≥ 70	11/25 (44)	< 0.001	5.779
< 70	12/59 (56)		(1.620-23.84)
Gender
Male	15/59 (25.4)	0.386
Female	8/25 (32.0)
BMI
< 18.5	4/10 (40.0)	-
≥ 18.8 < 25	16/58 (27.5)	0.181
≥ 25	3/16 (18.8)	0.094
Smoking		0.267
Yes	7/37 (18.9)
No	16/47 (34.0)
Drinking		0.235
Yes	6/17 (35.3)
No	17/67 (25.3)
Hypertension		0.972
Yes	7/28 (25.0)
No	16/56 (28.6)
Diabetes		0.182
Yes	1/9 (11.1)
No	22/75 (29.3)
Previous abdominal surgery		0.36
Yes	8/19 (42.1)
No	15/65 (23.1)
Anemia		0.702
Yes	8/31 (25.8)
No	15/53 (28.3)
Hypoproteinemia		< 0.001	15.0 (3.44-87.19)		< 0.001
Yes	7/28 (25.0)
No	16/56 (28.6)
Preoperative potassium		0.634
Normal	21/76 (27.6)
Abnormal	2/8 (25.0)
Emergency surgery		0.819
Yes	0/1 (0.0)
No	23/83 (27.1)
Tumor size (cm)
< 5	12/52 (23.1)	-
≥ 5 < 10	8/27 (29.6)	0.535
≥ 10	3/5 (60.0)	0.449
Tumor site
Cardiac	3/13 (23.1)	-
Body	14/46 (30.4)	1
Antrum	6/25 (24.0)	0.767
Stage cTNM
0	0/11 (0.0)	-	-
I	5/13 (38.5)	0.091	19.64 (1.57-646.93)		0.042
II	6/25 (24.0)	0.096	5.46 (0.49-149.62)		0.216
III	8/28 (28.6)	0.073	9.71 (0.99-256.35)		0.089
IV	4/7 (57.1)	0.026	98.8 (4.55-4617.35)		0.006
RTBS		0.012	0.15 (0.03-0.59)		0.001
≥ 15	7/16 (43.8)
< 15	16/68 (23.5)
NBS (cpm)		0.001	0.077 (0.01-0.33)		0.001
≥ 2.436	18/64 (28.1)
< 2.436	5/20 (25.0)
BSVA (dB)		0.2
≥ 44.793	5/23 (21.7)
< 44.793	18/61 (29.5)
FBS (Hz)		0.007	8.81 (2.35-10.91)		0.002
≥ 461.560	12/59 (20.3)
< 461.560	11/25 (44.0)

Age, cTNM stage, preoperative hypoproteinemia, and specific bowel sound-related indices (recovery time of bowel sounds, number of bowel sounds, frequency of bowel sounds) were independent risk factors influencing the occurrence of PPOI in patients with gastric cancer. NBS: Number of bowel sounds; BSVA: Bowel sound vibration amplitude; FBS: Frequency of bowel sounds; RTBS: Recovery time of bowel sounds; BMI: Body mass index; PPOI: Prolonged postoperative ileus.