Free air on CT and the risk of peritonitis in peritoneal dialysis patients: a retrospective study

Figures & data

Figure 1. The volume of free air was estimated on the assumption that it was spherical by calculating its cross-sectional area in the plane with a maximum diameter using application software.

Figure 2. Free air was measured on routine computed tomography (CT) examinations from April 2009 to March 2010. Episodes of peritonitis were measured retrospectively from PD introduction to the CT measurement point.

Table 1. Characteristics of the study population.

	Free air+ (n = 29)	Free air– (n = 79)	p Value
Age (≥65 years)	15 (51.7%)	30 (38.0%)	0.2
Gender (male)	16 (55.2%)	50 (62.9%)	0.78
Dialysis history (months)*	30 [14–69]	29 [8–61]	0.49
Diabetes mellitus	12 (41.4%)	24 (30.4%)	0.27
Body mass index (kg/m^2)	21.1 ± 2.9	21.4 ± 3.2	0.7
Automated peritoneal dialysis	8 (27.6%)	23 (29.5%)	0.51
Albumin (g/dL)	3.8 ± 0.3	3.8 ± 0.4	0.46
Low-density lipoprotein  cholesterol (mg/dL)	77.7 ± 26.3	86.9 ± 28.7	0.15
High-density lipoprotein  cholesterol (mg/dL)	45.9 ± 13.2	45.2 ± 12.2	0.92
Triglycerides (mg/dL)	98.3 ± 44.5	103.5 ± 55.3	0.66
Patients with history of peritonitis	17 (58.6%)	21 (26.8%)	0.002

Notes: Continuous variables are expressed as mean ± standard deviation and count data as number (percentage). Continuous data added * are expressed as median [25th–75th percentile].

Free air+ = the appearance of free air in the abdominal cavity on CT and free air– = the absence of free air in the abdominal cavity on CT.

Table 2. Incidence of peritoneal dialysis-related infections.

	Free air+ (n = 29)	Free air– (n = 79)
Exit infection
(Episode/patient-month)	1/55.1	1/43.0
(person-year)	0.22	0.28
Tunnel infection
(Episode/patient-month)	1/83.1	1/82.9
(person-year)	0.14	0.14
Peritonitis
(Episode/patient-months)	1/40.2	1/96.9
(person-year)	0.29	0.12

Note: Free air+ = the appearance of free air in the abdominal cavity on CT and free air– = the absence of free air in the abdominal cavity on CT.

Table 3. Risk ratio of free air for peritonitis.

	Risk ratio of free air for peritonitis	95% confidence interval
Crude model	2.41	2.28–2.55
Adjusted by
Age (≥65 years)	2.29	2.03–2.60
Gender	2.39	2.11–2.71
Age and gender	2.20	1.93–2.51
Stratified by
BMI
<23	2.41	2.02–2.88
≥23	2.01	1.44–2.81
Albumin
<3.8 mg/dL	2.00	1.77–2.26
≥3.8 mg/dL	2.07	1.58–2.72
Diabetes
With diabetes	1.21	0.73–2.00
Without diabetes	2.75	2.37–3.20

Notes: Stratified analysis was done using a model adjusted for age.

BMI, body mass index.

Table 4. Bacterial species causing peritonitis.

	Free air +		Free air–
S. epidermidis	28.1	S. epidermidis	35.5
MSSA	18.8	MSSA	12.9
MRSA	9.4	MRSA	12.9
Acinetobacter sp.	6.3	Enterobacter sp.	6.5
Pseudomonas aeruginosa	6.3	Escherichia coli	3.2
Streptococcus sp.	6.3	Enterococcus sp.	3.2
Enterococcus sp.	3.1	Pseudomonas aeruginosa	3.2
Enterobacter sp.	3.1	α-streptococcus	3.2
Corynebacterium sp.	3.1
Campylobacter	3.1
Micrococcus sp.	3.1
Negative	9.4	Negative	19.4

Notes: Data are expressed as percentages. Causative bacteria were detected from PD fluid cultures at baseline.

Free air+ = the appearance of free air in the abdominal cavity on CT; free air– = the absence of free air in the abdominal cavity on CT; MSSA, methicillin-sensitive Staphylococcus aureus; MRSA, methicillin-resistant Staphylococcus aureus.