Cataract Surgery in the Medicare Merit-Based Incentive Payment System: Episode-Based Cost Measure Development and Evaluation

Objective

To characterize the development and performance of a cataract surgery episode-based cost measure for the Medicare Quality Payment Program.

Design

Claims-based analysis.

Participants

Medicare clinicians with cataract surgery claims between June 1, 2016, and May 31, 2017.

Methods

We limited the analysis to claims with procedure code 66984 (routine cataract surgery), excluding cases with relevant ocular comorbidities. We divided episodes into subgroups by surgery location (Ambulatory Surgery Center [ASC] or Hospital Outpatient Department [HOPD]) and laterality (bilateral when surgeries were within 30 days apart). For the episode-based cost measure, we calculated costs occurring between 60 days before surgery and 90 days after surgery, limited to services identified by an expert committee as related to cataract surgery and under the influence of the cataract surgeon. We attributed costs to the clinician submitting the cataract surgery claim, categorized costs into clinical themes, and calculated episode cost distribution, reliability in detecting clinician-dependent cost variation, and costs with versus without complications. We compared episode-based cost scores with hypothetical "nonselective" cost scores (total Medicare beneficiary costs between 60 days before surgery and 90 days after surgery).

Main Outcome Measures

Episode costs with and without complications, clinician-dependent variation (proportion of total cost variance), and proportion of costs from cataract surgery-related clinical themes.

Results

We identified 583 356 cataract surgery episodes attributed to 10 790 clinicians and 8189 with ≥ 10 episodes during the measurement period. Most surgeries were performed in an ASC (71%) and unilateral (66%). The mean episode cost was $2876. The HOPD surgeries had higher costs; geography and episodes per clinician did not substantially affect costs. The proportion of cost variation from clinician-dependent factors was higher in episode-based compared with nonselective cost measures (94% vs. 39%), and cataract surgery-related clinical themes represented a higher proportion of total costs for episode-based measures. Episodes with complications had higher costs than episodes without complications ($3738 vs. $2276).

Conclusions

The cataract surgery episode-based cost measure performs better than a comparable nonselective measure based on cost distribution, clinician-dependent variance, association with cataract surgery-related clinical themes, and quality alignment (higher costs in episodes with complications). Cost measure maintenance and refinement will be important to maintain clinical validity and reliability.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Stereotactic Ablative Radiotherapy for Oligo-Progressive Cancers: Results of the Randomized Phase II STOP Trial

PURPOSE/OBJECTIVE(S)

In the metastatic setting, there is uncertain benefit to localized eradication of one or more lesions that are progressing despite systemic therapy. This randomized phase II trial examined if patients with ≤5 sites of oligoprogression benefited from the addition of stereotactic ablative radiotherapy (SABR) to standard of care (SOC) systemic therapy.

MATERIALS/METHODS

Eligibility criteria included age ≥18 years, ECOG performance status 0-2, and oligoprogressive disease, defined as 1-5 lesions actively progressing while on systemic therapy. Patients were required to have at least 3 months of disease stability/response on systemic therapy prior to oligoprogression. After stratifying by type of systemic therapy (cytotoxic vs. non-cytotoxic), patients were randomized 2:1 to SABR to all progressing lesions plus SOC (SABR arm) vs. SOC alone (SOC arm). The trial began exclusive to non-small cell lung cancer but did not meet accrual goals and was expanded in 2019 to include all non-hematologic malignancies. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall survival (OS), lesional control, quality of life (QOL), toxicity, and duration of current systemic agent post-SABR.

RESULTS

Between February 2017 and June 2021, 90 patients with 125 oligoprogressive metastases were enrolled across 8 Canadian institutions, with 59 patients randomized to SABR and 31 to SOC. Median age was 67 years (IQR: 61-73 years) and 39 (43%) were female. The most common primary sites were lung (44% of patients), genitourinary (23%) and breast (13%), with the most common oligo-progressive locations being lung (43%), bone (19%), lymph nodes (14%), and liver (13%). In the SABR arm, the most common fractionations were 35 Gy/5 (38% of lesions) and 50 Gy/5 (18%). Protocol adherence in the SOC arm was suboptimal: 3 patients (10%) withdrew immediately after randomization, and 7 additional patients (23%) received high-dose or ablative therapies. Median follow-up was 31 months. There was no difference in PFS between arms (median PFS 8.4 months in the SABR arm vs. 4.3 months in the SOC arm; however, the curves cross and 2-year PFS was 9% vs. 24% respectively, p = 0.91). Median OS was 31.2 months vs. 27.4 months, respectively (p = 0.22). Lesional control with SABR was 71% vs. 39% with SOC (p = 0.002). Median duration of post-randomization first-line systemic therapy was 10.3 months vs. 7.6 months, respectively (p = 0.71). Treatment was well-tolerated with 2 (3.4%) grade 3 treatment-related toxicities in the SABR arm and no grade 4/5 related events in either arm. QOL did not differ between arms.

CONCLUSION

Despite being a well-tolerated treatment providing superior lesional control, SABR for oligoprogression did not improve PFS or OS. Results may have been impacted by withdrawals and desire for ablative treatments on the SOC arm, and this lack of equipoise may make accrual to phase III trials difficult, although larger studies in select sub-populations are desired. (NCT02756793).

An overview of the together everyone achieves more physical activity (TEAM-PA) trial to increase physical activity among African American women

BACKGROUND

The Together Everyone Achieves More Physical Activity (TEAM-PA) trial is a randomized controlled trial testing the efficacy of a group-based intervention for increasing physical activity (PA) among insufficiently active African American women.

DESIGN

The TEAM-PA trial uses a group cohort design, is implemented at community sites, and will involve 360 African American women. The trial compares a 10-week group-based intervention vs. a standard group-delivered PA comparison program. Measures include minutes of total PA/day using 7-day accelerometer estimates (primary outcome), and body mass index, blood pressure, waist circumference, walking speed, sedentary behavior, light physical activity, and the percentage achieving ≥150 min of moderate to vigorous PA/week (secondary outcomes) at baseline, post-intervention, and 6-months post-intervention.

INTERVENTION

The intervention integrates elements from Social Cognitive Theory, Self-Determination Theory, Group Dynamics Theory, and a focus on collectivism to evaluate different components of social affiliation (relatedness, reciprocal support, group cohesion, and collective efficacy). The intervention integrates shared goal-setting via Fitbits, group-based problem-solving, peer-to-peer positive communication, friendly competition, and cultural topics related to collectivism. Compared to the standard group-delivered PA program, participants in the intervention are expected to show greater improvements from baseline to post- and 6-month follow-up on minutes of total PA/day and secondary outcomes. Social affiliation variables (vs. individual-level factors) will be evaluated as mediators of the treatment effect.

IMPLICATIONS

The results of the TEAM-PA trial will determine the efficacy of the intervention and identify which aspects of social affiliation are most strongly related to increased PA among African American women.

TRIAL REGISTRATION

This study was registered on Clinicaltrials.gov (# NCT05519696) in August 2022 prior to initial participant enrollment.

Family history of FXTAS is associated with age-related cognitive-linguistic decline among mothers with the FMR1 premutation

BACKGROUND

Women who carry a premutation allele of the FMR1 gene are at increased vulnerability to an array of age-related symptoms and disorders, including age-related decline in select cognitive skills. However, the risk factors for age-related decline are poorly understood, including the potential role of family history and genetic factors. In other forms of pathological aging, early decline in syntactic complexity is observed and predicts the later onset of neurodegenerative disease. To shed light on the earliest signs of degeneration, the present study characterized longitudinal changes in the syntactic complexity of women with the FMR1 premutation across midlife, and associations with family history of fragile X-associated tremor/ataxia syndrome (FXTAS) and CGG repeat length.

METHODS

Forty-five women with the FMR1 premutation aged 35-64 years at study entry participated in 1-5 longitudinal assessments spaced approximately a year apart (130 observations total). All participants were mothers of children with confirmed fragile X syndrome. Language samples were analyzed for syntactic complexity and participants provided information on family history of FXTAS. CGG repeat length was determined via molecular genetic testing.

RESULTS

Hierarchical linear models indicated that women who reported a family history of FXTAS exhibited faster age-related decline in syntactic complexity than those without a family history, with that difference emerging as the women reached their mid-50 s. CGG repeat length was not a significant predictor of age-related change.

CONCLUSIONS

Results suggest that women with the FMR1 premutation who have a family history of FXTAS may be at increased risk for neurodegenerative disease, as indicated by age-related loss of syntactic complexity. Thus, family history of FXTAS may represent a personalized risk factor for age-related disease. Follow-up study is needed to determine whether syntactic decline is an early indicator of FXTAS specifically, as opposed to being a more general age-related cognitive decline associated with the FMR1 premutation.

Survey of Healthcare Providers Utilization and Perception of Telehealth On-Treatment Visits During COVID-19 Pandemic

Purpose/Objective(s)

Materials/Methods

Results

Conclusion

Response Inhibition Deficits in Women with the FMR1 Premutation are Associated with Age and Fall Risk

One in 113-178 females worldwide carry a premutation allele on the FMR1 gene. The FMR1 premutation is linked to neurocognitive and neuromotor impairments, although the phenotype is not fully understood, particularly with respect to age effects. This study sought to define oculomotor response inhibition skills in women with the FMR1 premutation and their association with age and fall risk. We employed an antisaccade eye-tracking paradigm to index oculomotor inhibition skills in 35 women with the FMR1 premutation and 28 control women. The FMR1 premutation group exhibited longer antisaccade latency and reduced accuracy relative to controls, indicating deficient response inhibition skills. Longer response latency was associated with older age in the FMR1 premutation and was also predictive of fall risk. Findings highlight the utility of the antisaccade paradigm for detecting early signs of age-related executive decline in the FMR1 premutation, which is related to fall risk. Findings support the need for clinical prevention efforts to decrease and delay the trajectory of age-related executive decline in women with the FMR1 premutation during midlife.

Determination of Total Fumonisins in Corn by Competitive Direct Enzyme-Linked Immunosorbent Assay: Collaborative Study

Fumonisins—mycotoxins produced by some Fusarium species—have been shown to be the causative agent of diseases in horses and other domesticated animals as well as possible carcinogens in humans. A collaborative study was conducted to evaluate the effectiveness of a competitive direct enzyme-linked immunosorbent assay (CD-ELISA) for the determination of total fumonisins (B1, B2, and B3) in corn. The test portion was extracted with methanol–water (7 + 3), filtered, diluted, and tested on the CD-ELISA. Naturally and artificially contaminated corn test portions were sent to 13 collaborators in the United States. Naturally contaminated field test portions were prepared at 3 different levels. Artificially contaminated test portions were spiked at 1.0, 3.0, and 5.0 mg/kg total fumonisins (B1, B2, and B3). Average recoveries of total fumonisins were 120, 100, and 90%, respectively. The relative standard deviations for repeatability ranged from 13.3 to 23.3% and the relative standard deviations for reproducibility ranged from 15.8 to 30.3% across all levels tested. HORRAT values, calculated for each individual sample, ranged from 1.24 to 1.94. This method demonstrated acceptable intra- and interlaboratory precision at the levels tested.

Social Avoidance Emerges in Infancy and Persists into Adulthood in Fragile X Syndrome

Fragile X syndrome (FXS) is characterized by both social approach and social avoidance. However, the age of emergence and developmental trajectory of social avoidance has not been examined. This study investigates the longitudinal developmental trajectory and dynamic nature of social avoidance in males with FXS from infancy through young adulthood (n = 191). Multiple facets of social avoidance were collected using the Social Avoidance Scale (Roberts et al. 2007, 2009). Overall, 81% of males with FXS displayed social avoidance, which emerged during infancy, increased in severity across childhood, and stabilized through adolescence and early adulthood. An exaggerated "warm up" effect was also observed in FXS. This study delineates the complex profile of social avoidance, a common and impairing behavioral feature of FXS.

Rates of cannabis use in patients with cancer

Background

A comprehensive assessment of cannabis use by patients with cancer has not previously been reported. In this study, we aimed to characterize patient perspectives about cannabis and its use.

Methods

An anonymous survey about cannabis use was offered to patients 18 years of age and older attending 2 comprehensive and 2 community cancer centres, comprising an entire provincial health care jurisdiction in Canada (ethics id: hreba-17011).

Results

Of 3138 surveys distributed, 2040 surveys were returned (65%), with 1987 being sufficiently complete for analysis (response rate: 63%). Of the respondents, 812 (41%) were less than 60 years of age; 45% identified as male, and 55% as female; and 44% had completed college or higher education.Of respondents overall, 43% reported any lifetime cannabis use. That finding was independent of age, sex, education level, and cancer histology. Cannabis was acquired through friends (80%), regulated medical dispensaries (10%), and other means (6%). Of patients with any use, 81% had used dried leaves.Of the 356 patients who reported cannabis use within the 6 months preceding the survey (18% of respondents with sufficiently complete surveys), 36% were new users. Their reasons for use included cancer-related pain (46%), nausea (34%), other cancer symptoms (31%), and non-cancer-related reasons (56%).

Conclusions

The survey demonstrated that prior cannabis use was widespread among patients with cancer (43%). One in eight respondents identified at least 1 cancer-related symptom for which they were using cannabis.

Abstract P2-09-09: Risk-reducing surgery and cancer-related distress among female BRCA1 and BRCA2 mutation carriers

Background: Distress levels among female BRCA1 and BRCA2 mutation carriers can be similar to levels reported among breast cancer patients. However, there is a lack of data on long-term psychosocial functioning, and it is not known if uptake of risk-reducing surgery influences long-term cancer related distress in women with a BRCA mutation who are unaffected with cancer. The objective of this study was to evaluate long-term cancer-related distress in women with a BRCA mutation, and to evaluate predictors of distress, including uptake of cancer risk reducing surgery.

Methods: Female BRCA1 or BRCA2 mutation carriers, ages 25-55, and without cancer were eligible to complete the survey online. A validated instrument, Impact of Events Scale (IES)-Revised (Horowitz 1979, Weis & Marmar 1995; 0-80 overall scale), was used to assess current levels of cancer risk-related psychological distress. Respondents were recruited through the Facing Our Risk of Cancer Empowered (FORCE) advocacy organization, which includes women at high risk of breast cancer. This interim analysis is part of a larger multi-center patient preference study of BRCA mutation carriers designed to assess women's willingness to adopt hypothetical treatments to prevent breast cancer. Linear regression was used to evaluate predictors of IES distress levels.

Results: Between January and April 2015, 259 women completed the survey. The mean age of the participants was 41 years, and the mean time since receipt of genetic test results was 3.5 years (range 0-16; median 2 years). One hundred thirty-six (52%) women elected for prophylactic bilateral mastectomy (PBM), 139 (54%) elected for bilateral salpingo oophorectomy (BSO) (93 [36%] women had both surgeries), and 77 (30%) had not undergone risk-reducing surgery. The mean total IES score was 15.1 (range 0-72; median 11). Overall, 54 (21%) women reported moderate or severe cancer-related distress, and those who had undergone risk-reducing surgery reported lower perceived risk of developing breast cancer. Results to date indicate that shorter time since notification of mutation status, not having PBM (with or without BSO) (table), and not completing post-secondary education were independent predictors of higher IES distress scores.

IES severityNo prophylactic surgeryPBM onlyBSO onlyPBM and BSOn (%)77434693Subclinical27 (35)23 (54)16 (35)44 (47)Mild26 (34)13 (30)21 (46)35 (38)Moderate18 (23)5 (12)6 (13)11 (12)Severe6 (8)2 (5)3 (6)3 (3)

Conclusions: This study measured cancer-related distress in a large population of women with BRCA mutations who participate in the FORCE online support community. Higher levels of distress were associated with not having PBM and more recent genetic test disclosure. These findings are specific to a more informed community of women with high levels of understanding of cancer risk than may be seen in the clinical setting.

Citation Format: Liede A, Fairchild A, Friedman S, Amelio J, Hallett DC, Mansfield CA, Metcalfe KA. Risk-reducing surgery and cancer-related distress among female BRCA1 and BRCA2 mutation carriers. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-09-09.

A faith-based community partnership to address HIV/AIDS in the southern United States: implementation, challenges, and lessons learned

Though race and region are not by themselves risk factors for HIV infection, regional and racial disparities exist in the burden of HIV/AIDS in the US. Specifically, African Americans in the southern US appear to bear the brunt of this burden due to a complex set of upstream factors like structural and cultural influences that do not facilitate HIV/AIDS awareness, HIV testing, or sexual risk-reduction techniques while perpetuating HIV/AIDS-related stigma. Strategies proposed to mitigate the burden among this population have included establishing partnerships and collaborations with non-traditional entities like African American churches and other faith-based organizations. Though efforts to partner with the African American church are not necessarily novel, most of these efforts do not present a model that focuses on building the capacity of the African American church to address these upstream factors and sustain these interventions. This article will describe Project Fostering AIDS Initiatives That Heal (F.A.I.T.H), a faith-based model for successfully developing, implementing, and sustaining locally developed HIV/AIDS prevention interventions in African American churches in South Carolina. This was achieved by engaging the faith community and the provision of technical assistance, grant funding and training for project personnel. Elements of success, challenges, and lessons learned during this process will also be discussed.

The association of self-efficacy and parent social support on physical activity in male and female adolescents

OBJECTIVE

Previous research has shown that cognitive factors may account for the relationship between interpersonal factors and health behaviors. Given these findings, the current study sought to further explore the direct and indirect relationship between parental social support and adolescent physical activity (PA).

METHOD

Data were collected from 1,421 sixth graders (73% Black, 54% females, 71% on free or reduced lunch) in South Carolina. Measures for emotional social support, instrumental social support, and adolescent self-efficacy (SE) were assessed and PA was assessed via accelerometry.

RESULTS

Parent instrumental social support was directly related to girls' PA and parent emotional social support was inversely related to girls' PA. Parent instrumental social support was indirectly related to boys' PA through boys' SE. The covaried association of SE with PA was significant for boys and marginal for girls.

CONCLUSIONS

SE for overcoming barriers may be an important construct for understanding the relationship between parent instrumental social support and boys' PA in underserved populations. The mechanisms for engaging in PA may be different for adolescent girls and boys.

Development of clinical trial protocols involving advanced radiation therapy techniques: the European Organisation for Research and Treatment of Cancer Radiation Oncology Group approach

The European Organisation for Research and Treatment of Cancer (EORTC) Master Protocol for phase III radiation therapy (RT) studies was published in 1995 to define in a consistent sequence the parameters which must be addressed when designing a phase III trial 'from the rationale to the references'. This was originally implemented to assist study investigators and writing committees, and to increase homogeneity within Radiation Oncology Group (ROG) study protocols. However, RT planning, delivery, treatment verification and quality assurance (QA) have evolved significantly over the last 15 years and clinical trial protocols must reflect these developments. The goal of this update is to describe the incorporation of these developments into the EORTC-ROG protocol template. Implementation of QA procedures for advanced RT trials is also briefly described as these essential elements must also be clearly articulated. This guide may assist both investigators participating in current ROG trials and others involved in writing an advanced RT trial protocol.

Optimizing pain relief in a specialized outpatient palliative radiotherapy clinic: contributions of a clinical pharmacist

PURPOSE

Bone metastases are the most common cause of cancer pain, with palliative radiotherapy (RT) the mainstay of treatment. However, relief from RT may be delayed, incomplete, or short-lived and therefore optimized pharmacologic therapy is essential. Our objective was to describe the contribution of the clinical pharmacist (CP) to an outpatient palliative RT clinic.

METHODS

The Edmonton Symptom Assessment System, an 11-point scale for measuring nine symptoms, and other validated screening tools were administered, and a medication history performed by the CP. Baseline CP assessment also included opioid toxicity, need for supportive medications, and drug interactions. Anonymized clinical information was collected prospectively and descriptive statistics were compiled including themes of counselling performed by the CP.

RESULTS

The CP reviewed 114 patients over 140 clinic visits (01/2007-12/2008). Median age was 68.3 years, 68.4% were male and 36.8% had prostate cancer. All symptoms improved or stabilized in ≥ 80% by 4 weeks. Median pain score was 6/10 (SD 2.6) at baseline, and 2.1/10 (SD 2.4) by week 4. Average morphine equivalent daily dose was 76.8 mg at baseline and 44.5 mg at week 4. CP assessment included screening for opioid toxicity (87.9%), recommending a change in analgesic (28.9%), and liaison with the community pharmacy (17.1%). Medication counselling took place in 84.3% of visits, on bowel routine (85.6% of the time), opioids (82.2%), and hydration (40.7%).

CONCLUSIONS

The CP plays a key role in holistic patient assessment and optimization of pharmacologic therapy, contributing to improved symptom control of patients receiving palliative RT.

The integration of a family systems approach for understanding youth obesity, physical activity, and dietary programs

Rates of overweight in youth have reached epidemic proportions and are associated with adverse health outcomes. Family-based programs have been widely used to treat overweight in youth. However, few programs incorporate a theoretical framework for studying a family systems approach in relation to youth health behavior change. Therefore, this review provides a family systems theory framework for evaluating family-level variables in weight loss, physical activity, and dietary approaches in youth. Studies were reviewed and effect sizes were calculated for interventions that manipulated the family system, including components that targeted parenting styles, parenting skills, or family functioning, or which had novel approaches for including the family. Twenty-one weight loss interventions were identified, and 25 interventions related to physical activity and/or diet were identified. Overall, family-based treatment programs that incorporated training for authoritative parenting styles, parenting skills, or child management, and family functioning had positive effects on youth weight loss. Programs to improve physical activity and dietary behaviors that targeted the family system also demonstrated improvements in youth health behaviors; however, direct effects of parent-targeted programming is not clear. Both treatment and prevention programs would benefit from evaluating family functioning and parenting styles as possible mediators of intervention outcomes. Recommendations are provided to guide the development of future family-based obesity prevention and treatment programs for youth.

Dexamethasone for the prophylaxis of radiation-induced pain flare after palliative radiotherapy for symptomatic bone metastases: a phase II study

AIMS

Pain flare occurs in over one-third of patients receiving palliative radiotherapy for bone metastases. A single dose of dexamethasone can decrease the incidence of pain flare during the first 2 days immediately after radiotherapy. We conducted a phase II prospective study to investigate the prophylactic role of prolonged dexamethasone.

MATERIALS AND METHODS

Patients with bone metastases treated with a single 8Gy were prescribed 8mg dexamethasone just before palliative radiotherapy and for 3 consecutive days after treatment. Worst pain score and analgesic consumption data were collected at baseline and daily for 10 days after treatment. Analgesic consumption was converted into a total daily oral morphine equivalent dose in the analysis. Pain flare was defined (a priori) as a two-point increase in worst pain on an 11-point numeric rating scale compared with baseline with no decrease in analgesic intake, or a 25% increase in analgesic intake with no decrease in worst pain score. To distinguish pain flare from progressive disease, we required that the worst pain score and analgesic intake returned to baseline levels after the increase/flare.

RESULTS

Forty-one patients were evaluable (32 men, nine women). Their median age was 67 years. The overall incidence of pain flare was 9/41 (22%) within 10 days after the completion of radiotherapy. Most (55%) of these pain flares occurred on day 5. Absence of pain flare was 34/41(83%) and 39/41 (95%) for days 1-5 and 6-10 after the completion of radiotherapy, respectively.

CONCLUSION

Dexamethasone is effective in the prophylaxis of radiotherapy-induced pain flare after palliative radiotherapy for bone metastases. Randomised studies are needed to confirm this finding.

Cationic liposome--plasmid DNA complexes used for gene transfer retain a significant trapped volume

The goal of this study is to determine whether cationic liposomes retain any trapped volume after their complexation to plasmid DNA. This serves two purposes: to further the understanding of the physical nature of liposome/plasmid DNA complexes used in gene therapy and to investigate the potential for codelivery of other encapsulated molecules with the liposome-DNA complexes. Cationic liposomes composed of N,N-dioleoyl-N,N-dimethylammonium chloride and dioleoylphosphatidylethanolamine (DODAC/DOPE, 50/50 mol %) encapsulating an aqueous trap marker were used to prepare liposome-DNA complexes at various charge ratios. The trapped volume before and after DNA binding was measured by two methods: dialysis and filtration. The effect of tissue culture medium on trapped volume was also investigated. A lipid-mixing assay was employed to further characterize the aggregation events that influence trap volume. The trapped volume (Vt) of neutral control liposomes was 1.1 +/- 0.04 microL/mumol, which was not affected by the addition of DNA. For cationic liposomes in the absence of DNA the Vt was 1.45 +/- 0.46 and 1.54 +/- 0.08 microL/mumol, as measured by the filtration and dialysis methods, respectively. After addition of DNA, the residual trapped volume (RVt) decreased to 0.43 +/- 0.1 microL/mumol and 0.47 +/- 0.05 microL/mumol, as determined by each method, respectively. RVt increased as the ratio of cationic lipid to DNA (nmol of lipid/mg of DNA) was increased above 10, a ratio that corresponds to a charge ratio (positively charged lipids to negatively charged phosphate groups) of 1.62. Aggregation and lipid-mixing were greatest at charge ratios coinciding with the lowest trapped volume. In the presence of tissue culture medium, the Vt of cationic liposomes but not neutral liposomes was reduced, suggesting that the salts have a direct effect on cationic liposomes in the absence of DNA. The RVt of both neutral and cationic liposomes in the presence of DNA, however, was not different from that of the liposomes in the absence of DNA. These results suggest that a significant trapped volume is retained by cationic liposomes after binding to plasmid DNA. This is an important finding with regard to the potential use of DNA/liposome complexes in the codelivery of other bioactive molecules at the time of cell transfection.