Journal watch: recent studies of note

Recent studies about postoperative VTE risk, preoperative hematocrit, and other topics.


Parameters may help predict risk for postoperative VTE

A defined set of variables can help predict whether a patient is likely to develop venous thromboembolism (VTE) after surgery, according to a new study.

Researchers from Brigham and Women's Hospital in Boston used data from the Patient Safety in Surgery Study, which was funded by the Agency for Healthcare Research and Quality, to create a risk assessment tool for VTE. Among 183,069 patients who had vascular and general procedures, 1,162 experienced VTE, and of these, 11.19% died within 30 days. The study authors examined characteristics of these patients to determine which variables were associated with VTE risk. The results were published in the June issue of the Journal of the American College of Surgeons.

Overall, the following characteristics were associated with higher risk for postoperative VTE:

  • Female sex
  • High American Society of Anesthesiologists class
  • Ventilator dependence
  • Dyspnea before surgery
  • Disseminated cancer
  • Chemotherapy within 30 days
  • Transfusion of more than 4 units of packed red blood cells within 72 hours before surgery
  • Preoperative laboratory values (albumin, <3.5 mg/dL; bilirubin, >1.0 mg/dL; sodium, >145 mmol/L; hematocrit, <38%)
  • Surgical procedure by type
  • Emergency surgery
  • Work relative value units
  • Infected or contaminated wounds.

Using these variables, the authors developed a predictive model for VTE after surgery and a risk score for preoperative assessment, noting that it could allow physicians to more accurately assess the need for perioperative VTE prophylaxis in patients undergoing major surgery.

Preoperative hematocrit may predict outcome

A new retrospective study of a large national database found that abnormal hematocrit levels may predict worse outcomes after noncardiac surgery.

Researchers used data from the Veterans Administration National Surgical Quality Improvement Program database to examine hematocrit level and patient outcome after surgery in 310,311 veterans aged 65 or older. Patients were classified as being anemic (hematocrit <39%), normal (hematocrit 39% to 53.9%) or polycythemic (hematocrit ≥ 54%) before surgery. After surgery, the authors used 30-day mortality rate as the primary outcome measure and a composite end point of 30-day mortality rate and cardiac events as the secondary outcome measure. The study was published in the June 13 Journal of the American Medical Association.

The authors found that the 30-day mortality rate increased by 1.6% for every preoperative percentage-point deviation, positive or negative, from normal hematocrit values. The adjusted risk of cardiac events and death at 30 days also increased in patients with abnormal hematocrits. Further analysis indicated that patients with hematocrits of 39% to 51% had the lowest risk; values lower than 39% and higher than 51% were associated with worse outcomes. These findings were observed in all subgroups except women and patients undergoing emergent surgery.

Because the study was observational, the authors could not determine whether the relationship they observed was causal, and they recommended additional studies to determine whether treating abnormal hematocrits before surgery would improve postoperative outcomes. An accompanying editorial praised the study's overall quality but recommended against applying the results outside the research setting.

Magnesium for acute management of atrial fibrillation

Magnesium's electrophysiologic effects on the heart may make it a safe, effective treatment for acute atrial fibrillation, according to a recent study.

Researchers at the University of Toronto in Ontario examined randomized, controlled trials that compared magnesium with placebo or antiarrhythmic agents in adults presenting with atrial fibrillation that was not postoperative in nature. Trials were obtained from nine databases searched through June 2005 and from abstracts presented at cardiology meetings over the past 10 years. The primary outcomes measured were successful achievement of rate and rhythm control and overall response, while secondary outcomes were time to response and risk for major adverse effects. The results were published in the June 15 Journal of the American College of Cardiology.

The authors found that magnesium helped achieve rate and rhythm control in affected patients (odds ratios, 1.96 [95% CI, 1.24 to 3.08] and 1.60 [CI, 1.07 to 2.39], respectively). Overall response was seen in 86% of patients who received magnesium versus 56% of controls (odds ratio, 4.61 [CI, 2.67 to 7.96]), and patients in the former group responded more quickly to therapy. Risk for major adverse effects was similar in the magnesium and placebo groups (relative risk, 0.85 [CI, 0.44 to 1.61]).

The authors pointed out the advantages of magnesium for atrial fibrillation, noting that it “is inexpensive, easy to use and titrate, and widely available for immediate use in every clinical unit.” However, they also stressed that the studies they analyzed were small and mostly of medium rather than high quality, and that meta-analysis may have overestimated magnesium's clinical efficacy.

Resident work-hour limits don't harm patient care, studies find

Two studies published online by Annals of Internal Medicine in July found that the Accreditation Council of Graduate Medical Education's 2003 regulations limiting residents' work hours have not adversely affected patient care.

In the first study, researchers examined the records of patients at 551 hospitals involved in the Healthcare Cost and Utilization Project's Nationwide Inpatient Survey between January 2001 and December 2004. Patients were classified as receiving medical or surgical care at teaching or nonteaching hospitals.

The researchers compared inpatient mortality rates before and after July 2003, when the work-hour rules took effect. In the 1,268,738 medical patients, the new rules were associated with a decrease of 0.25% in the absolute mortality rate (P= 0.043) and a decrease of 3.75% in the relative risk for death. The rules seemed to have the largest effect on mortality in medical patients older than age 80 (change, –0.71%; P= 0.005) and in medical patients with severe infections (change, –0.66%; P= 0.007). No mortality rate difference was seen in the 243,207 surgical patients studied.

In the second study, which involved a single hospital, researchers examined changes in overall outcome before and after the work-hour rules took effect. They studied 14,260 patients discharged from the hospital's teaching service and 6,664 patients discharged from the nonteaching service between July 2002 and June 2004. After the rules were implemented, patients in the first group had greater improvements in three of seven outcome measures: intensive care unit use, discharge to home or a rehab facility and pharmacist interventions to prevent medication errors. Changes in the other outcome measures—length of hospital stay, readmission rate over 30 days, adverse drug interactions and in-hospital mortality rate—were similar between the two groups.

An editorial that accompanied the studies said that while they add to the body of evidence showing that work-hour limits don't hurt patients' outcomes, the full impact of the rules on patients, families and other health care workers is not yet known. “Most important, the implications of the new rules for the adequacy of education and training remain uncertain,” the editorialists wrote.