Abstract
SummaryBackground & aimsElective surgery induces skeletal muscle wasting driven by an imbalance between muscle protein synthesis and breakdown. From examination of diverse stable isotope tracer techniques, the dynamic processes driving this imbalance are unclear. This meta-analysis aimed to elucidate the mechanistic driver(s) of postoperative protein catabolism through stable isotope assessment of protein turnover before and after abdominal surgery.MethodsMeta-analysis was performed of randomized controlled trials and cohort studies in patients undergoing elective abdominal surgery that contained measurements of whole-body or skeletal muscle protein turnover using stable isotope tracer methodologies pre- and postoperatively. Postoperative changes in protein synthesis and breakdown were assessed through subgroup analysis of tracer methodology and perioperative care.ResultsSurgery elicited no overall change in protein synthesis [standardized mean difference (SMD) −0.47, 95% confidence interval (CI): −1.32, 0.39, p = 0.25]. However, subgroup analysis revealed significant suppressions via direct-incorporation methodology [SMD -1.53, 95%CI: −2.89, −0.17, p = 0.03] within skeletal muscle. Changes of this nature were not present among arterio-venous [SMD 0.61, 95%CI: −1.48, 2.70, p = 0.58] or end-product [SMD -0.09, 95%CI: −0.81, 0.64, p = 0.82] whole-body measures. Surgery resulted in no overall change in protein breakdown [SMD 0.63, 95%CI: −0.06, 1.32, p = 0.07]. Yet, separation by tracer methodology illustrated significant increases in urinary end-products (urea/ammonia) [SMD 0.70, 95%CI: 0.38, 1.02, p < 0.001] that were not present among arterio-venous measures [SMD 0.67, 95%CI: −1.05, 2.38, p = 0.45].ConclusionsElective abdominal surgery elicits suppressions in skeletal muscle protein synthesis that are not reflected on a whole-body level. Lack of uniform changes across whole-body tracer techniques are likely due to contribution from tissues other than skeletal muscle.
Highlights
Skeletal muscle wasting is a key feature of the metabolic response to surgery, known to complicate postoperative recovery and impair clinical outcomes [1]
This date restriction was imposed due to the validation of several clinically suitable stable isotope techniques for protein metabolism occurring throughout the 1980s [21e24]; studies which contributed to increased interest into the effects of surgical trauma on protein turnover during the late 1980s [25,26] and to the development of commercially available gas chromatography-isotope ratio mass spectrometers (GC-IRMS) capable of capturing increased signal sensitivity within complex biological matrices [27]
Where studies did not report the mean and standard deviation of protein turnover measures; median and interquartile ranges were converted to means and standard deviations according to the technique described by Hozo et al [35]
Summary
Skeletal muscle wasting is a key feature of the metabolic response to surgery, known to complicate postoperative recovery and impair clinical outcomes [1]. From examination of diverse stable isotope tracer techniques, the dynamic processes driving this imbalance are unclear This meta-analysis aimed to elucidate the mechanistic driver(s) of postoperative protein catabolism through stable isotope assessment of protein turnover before and after abdominal surgery. Methods: Meta-analysis was performed of randomized controlled trials and cohort studies in patients undergoing elective abdominal surgery that contained measurements of whole-body or skeletal muscle protein turnover using stable isotope tracer methodologies pre- and postoperatively. Subgroup analysis revealed significant suppressions via direct-incorporation methodology [SMD -1.53, 95%CI: À2.89, À0.17, p 1⁄4 0.03] within skeletal muscle Changes of this nature were not present among arterio-venous [SMD 0.61, 95% CI: À1.48, 2.70, p 1⁄4 0.58] or end-product [SMD -0.09, 95%CI: À0.81, 0.64, p 1⁄4 0.82] whole-body measures.
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