Yay for math?

On January 19, 2010, in Uncategorized, by Andrea

I admit, I like studies.  Studies make Andrea’s brain happy.  Studies have hard numbers that make sense.  Andrea likes black and white things — these are good things for a g33k (and don’t ever let it escape you — Andrea is a g33k — one who seems to be speaking in the 3rd person today — this is not a good sign).

But sometimes, studies, especially when done by a mathematical computation are not-so-cool.  Like this one that states an average 42 y.o RNY patient with a BMI of 45 would only gain close to 3 years of life by having WLS?  First off, I think that’s off.  Cause if someone is suffering from co-morbidities, those WILL shorten your life expectancy.

The numbers get even more screwbally when looking at younger patients — I apparantly gained more than 5 years.  We don’t know for certain because the numbers were for 35 year olds and I was 25 when I got my guts rearranged.  But we can construe that I got at least the five years.  Yay, me.

I really think patients gain more than a few years.  But then again, I’m not a computer.

Of course, this doesn’t measure the QUALITY of one’s life gained – but of course a computer can’t measure that.

From medpagetoday.com:

Gastric Bypass Extends Life for Most Patients

By John Gever, Senior Editor, MedPage Today
Published: January 18, 2010
Reviewed by Dori F. Zaleznik, MD; Associate Clinical Professor of Medicine, Harvard Medical School, Boston and
Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner

For most patients in most categories, bariatric surgery increases life expectancy, according to a new mathematical model.Only when short-term mortality following bariatric surgery is expected to be high or the likelihood of success is low will the procedure fail to improve life expectancy, researchers reported in the January Archives of Surgery.

Computer modeling predicted that a hypothetical “base case” patient — a 42-year-old woman with a body mass index of 45 — would gain 2.95 years of additional survival following bariatric surgery, according to Daniel P. Schauer, MD, of the University of Cincinnati, and colleagues.

Surgery failed to be beneficial in the model only when 30-day mortality reached 9.5% or the likelihood that surgery would not add life-years was 2% or less, they found.

Baseline 30-day mortality in the model was 0.2%, and the baseline efficacy of surgery in extending life expectancy was 53%.

“While not all patients are guaranteed a good outcome, our model indicates that gastric bypass increases life expectancy for most patient subgroups,” they concluded.

Their analysis was based on a Markov decision model using published data to estimate 30-day mortality following bariatric surgery and the efficacy of surgery in reducing long-term death rates.

The latter had two components: reduction in excess mortality associated with obesity, and research data on long-term mortality following bariatric surgery.

Excess mortality estimates came from National Health Interview Survey data on some 400,000 participants from 1991 to 1996 linked to the National Death Index. Inputs on surgery efficacy were derived from a 2007 study of nearly 8,000 patients who had undergone gastric bypass and the same number of medically treated or untreated obese controls.

That study found that the procedure cut death rates by half during about seven years of follow-up. (See Missing Link Found: Bariatric Surgery Reduces Mortality)

Schauer and colleagues obtained rates of inhospital mortality following bariatric surgery from the 2005 National Inpatient Survey, then multiplied them by three to estimate 30-day mortality.

The researchers explained that according to earlier research, inhospital death rates typically underestimate 30-day mortality by a factor of two to three.

Their threefold correction factor represents “a conservative estimate that biases the model against gastric bypass surgery,” they wrote.

Schauer and colleagues tested this correction factor and other aspects of the model in sensitivity analyses.

The biggest gains in life expectancy occurred in younger women with relatively high BMI values, the model showed.

The age effect was less important than BMI at the time of surgery. A 35-year-old woman with BMI of 45 would gain about 3.2 years of extra life, whereas at 55, a similarly obese woman would gain about 2.5 extra years.

But a 35-year-old woman with BMI of 55 could expect to live five more years with surgery, the model indicated.

Men in general derived less survival benefit from bariatric surgery, particularly with advancing age at the time of the procedure.

At 35, the difference in life expectancy gained was roughly 10%, but by age 75 it had grown to about 50%.

The sensitivity analyses found that relatively large changes in most parameters used in the model did not affect the overall results substantially.

The effect of 30-day mortality on whether or not surgery was beneficial for long-term survival was related to BMI and gender.

For women with a BMI of 40, 30-day mortality of more than 5% would mean surgery was not helpful, but short-term mortality had to exceed 15% for surgery not to be preferable for those with BMI of 55 or more. These thresholds were about 10% higher for men.

The efficacy of surgery in reducing mortality was less important for older men, the analysis also showed. A 75-year-man with a BMI of 35 could expect only a very slight gain in life span — perhaps one or two months.

“Younger patients have lower surgical risk and more time over which to realize the benefits of surgery. For older patients, the gain is smaller, and for some, gastric bypass surgery will decrease life expectancy,” Schauer and colleagues wrote.

However, they identified several potentially serious limitations to the analysis.

The study of long-term mortality following bariatric surgery was conducted at a single center and was not randomized. Additionally, long-term complications, such as need for repeat surgery, were not addressed in the model. Certain other risks that might be heightened after bariatric surgery were excluded as well, and quality of life was not modeled.

“The decision analysis presented here is a step forward in understanding optimal patient selection but also highlights some of the areas for which better data are needed,” the researchers wrote.

The National Institute of Diabetes and Digestive and Kidney Diseases funded the study.

No potential conflicts of interest were reported.

Update: Medscape has included their take:

Gastric Bypass Surgery May Prolong Lives of Morbidly Obese

Nancy Fowler Larson

January 19, 2010 — Morbidly obese Americans could live up to 3 years longer after undergoing gastric bypass surgery, the most popular bariatric surgical procedure, according to a computerized model-based study published in the January issue of the Archives of Surgery.

“While no large-scale randomized controlled trials have compared bariatric surgery with intensive medical management for the morbidly obese, there is evidence from large controlled trials and numerous case series that bariatric surgery is currently the only effective therapy for promoting clinically significant weight loss and improving obesity-associated conditions among adults with a body mass index (BMI) of 40 or higher (calculated as weight in kilograms divided by height in meters squared),” write Daniel P. Schauer, MD, MSc, from the University of Cincinnati Academic Health Center, Ohio, and colleagues. “Several retrospective cohort studies and 1 prospective study suggest that bariatric surgery also improves survival.”

The study sought to weigh the benefits of gastric bypass surgery against its risks in the morbidly obese, who make up 5.1% of the US population.

The researchers created a decision analytic Markov state transition model with multiple logistic regression as inputs to analyze the differences between having gastric bypass, the leading surgery (>65% of all patients who receive bariatric surgery) for the morbidly obese in the United States, vs undergoing no surgery. A 42-year-old woman and 44-year-old man, both with BMIs of 45 kg/m2, were chosen for the researchers’ base case analysis.

To determine in-hospital mortality risk, the authors used 23,281 cases from the 2005 National Inpatient Interview Survey and then adjusted the data for 30-day mortality. During each such cycle, patients’ risk for death was calculated using their BMI, surgical status, age, and sex.

Data from more than 399,000 participants from the 1991 to 1996 National Health Interview Survey were used to calculate excess mortality’s relationship with obesity. Bariatric surgery’s effect on mortality was assumed only in connection with excess deaths associated with obesity. Information about the surgery’s effectiveness was gathered from a recently conducted, substantial observational trial.

Younger, Higher-BMI Participants Had Best Results

The ultimate multivariable logistic regression model used 7 factors — BMI, BMI2, age, age2, sex, sex × BMI, and age × sex — to predict mortality, with a good fit to the data (Hosmer-Lemeshow goodness-of-fit, P > .05; c statistic, 0.83).

The computerized model showed that the 42-year-old female model lived 2.95 years longer (35.03 vs 32.08 years) after undergoing surgery. When 30-day surgical mortality increased to more than 9.5% (baseline 30-day mortality, 0.2%) or when surgical efficacy declined to 2% or less (baseline efficacy, 53%), surgery was not preferred.

The 44-year-old male model would live 2.57 years longer (26.82 vs 24.25 years) after undergoing surgery, according to the model. Surgical treatment was not preferred when 30-day surgical mortality rose above 8.6% (baseline 30-day mortality, 0.55%) or when the effectiveness of the surgery fell to 3% or less (baseline efficacy, 53%).

In both sexes, those who were younger and had a higher BMI had the largest life expectancy increases. In men, the increase was slightly lower for all ages and subgroups.

“The optimal decision for individual patients varies depending on the balance of risks between perioperative mortality, excess annual mortality associated with increasing BMI, and the efficacy of surgery; however, for the average morbidly obese patient, gastric bypass surgery increases life expectancy,” the authors write.

Multiple Study Limitations

The authors noted several limitations to their assessments:

  • Available data do not include BMI and other clinical variables.
  • All data for calculating surgery efficacy are from a single state (Utah).
  • The authors did not model long-term, postsurgical complications, including any necessary revision.
  • Life expectancy was the sole outcome metric, as there are no longitudinal studies exploring quality-of-life improvements.

Acknowledging that not all gastric bypass surgeries produce good results, the study authors concluded that their findings of longer life spans for most subjects will help physicians determine which patients are the best candidates.

“We believe results of this analysis can be used to better inform both patients’ and physicians’ decisions regarding gastric bypass surgery,” the authors write.

The National Institute of Diabetes and Digestive and Kidney Diseases supported the study. The study authors have disclosed no relevant financial relationships.

Arch Surg. 2010;145:57-62.

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