## 2 Materials and Methods  
This was an IRB-approved, Health Insurance Portability and Accountability Act compliant, prospective observational study evaluating the intra-abdominal pressure of  
Figure 1: Intra-abdominal abscess drainage as depicted. An increase in intra-abdominal pressure results in an increase in \(P_{\_}{1}\), which we theorize should result in a \(Q_{\_}{Laminar}\) increase. Reproduced with permission from reference [1]. patients with percutaneous drainage catheters for evacuation of intra-abdominal fluid collections while actively performing incentive spirometry. Eligible patients included those with clinical indications for image-guided percutaneous drainage, admitted to the hospital while having daily evaluations of their percutaneous drains, and those who met the minimum inspiratory capacity equal to or greater than 1500 mL (described subsequently). Informed consent to participate in this study was obtained from all patients. Twenty patients (men, 12; women, 8; age range, 23-69 years; average 46 years) with intra-abdominal drainage catheters enrolled in this study. Catheters were inserted in the abdominal cavity for fluid collection and evacuation (\(n=20\)). Fluid collections drained were: tubo-ovarian abscess (\(n=5\)); postoperative pelvic abscesses (\(n=2\)); ascites (\(n=2\)); pancreatic abscesses (\(n=2\)); bilomas (\(n=1\)); pancreatic pseudocysts (\(n=2\)); hepatic hematoma (\(n=1\)); diverticular abscess (\(n=1\)); pelvic cyst (\(n=1\)); liver abscess (\(n=1\)); subphrenic abscess (\(n=1\)). Collections were located in the pelvis (\(n=7\)); RUQ (\(n=4\)); LUQ (\(n=4\)); LLQ (\(n=3\)); RLQ (\(n=1\)). Figure 2 demonstrates the insertion of the drainage catheter for possible abscesses in the abdominal and pelvic regions (Figure 2). There were 2 patients who did not qualify for study inclusion as they were unable to meet the minimum tidal volume inspiratory capacity equal to or greater than 1500 mL; thus, intra-abdominal pressure was measured in 18 patients. Patients were instructed in the use of an incentive spirometer by respiratory therapists and spirometer-drainage catheter experiments were performed under the supervision of an attending board-certified interventional radiologist and a radiology resident. Within a week after drainage, intra-abdominal pressure changes were evaluated by catheter 3 times after a 1500 mL inspiratory pull with incentive spirometry, and also measured 3 times after maximum inspiratory effort. Participants were first told to inspire until the spirometer read 1500 mL, and then told to inspire to their maximum capacity. Criteria selection for patients to enter the study was an inspiratory capacity equal to or greater than 1500 mL. Intra-abdominal pressure was recorded using a pressure monitor connected to the drainage catheter. Changes in intra-abdominal pressure through the catheters with incentive spirometry were measured and compared with baseline tidal volume (0 mmHg2O). The equipment used is shown in Figure 2.  
Figure 2: Equipment Used in Measurement of IAP via Incentive Spirometry. From left to right: saline, incentive spirometer, pressure readout monitor, stopcock connection to drainage catheter (shown in front). Drainage regions were defined as either upper abdominal or lower abdominal based on whether they were above or below the transumbilical plane (an anatomical plane that passes through the umbilicus), or pelvic if they were placed transrectally within the pelvic region. Epigastric drainage was not conducted in this study. A case study below demonstrates the regions as defined in Figure 3.  
The results of the study were grouped by region, comparing pressure increases within the standardized inspiration group and then within the max inspiration group. Statistical analysis was conducted using R Studio version 1.3.1056, and graphs were made using GraphPad Prism version 8.0.0 for Windows, GraphPad Software, San Diego, CA, USA, www.graphpad.com, accessed on 8 October 2022. Non-parametric analyses were used due to the low sample size in each group.