linoleic-acid and Critical-Illness

Soybean oil-based lipid injectable emulsion (SO-based ILE) is an 18-carbon, ω-6 macronutrient providing a concentrated source of calories, which can be administered in or with parenteral nutrition to patients unable to tolerate or consume adequate enteral nutrition. Beyond the provision of energy, SO-based ILE provides linoleic and linolenic acid, 2 essential fatty acids necessary for the prevention of essential fatty acid deficiency. However, SO-based ILE with its high levels of ω-6 fatty acids, long-chain triglycerides, phospholipid emulsifiers, and glycerin has been associated with worsening clinical outcomes, including increase of infections, lengthier intensive care and hospital stay, and prolonged mechanical ventilation. Recognizing this, studies have investigated omitting SO-based ILE in the critically ill patient for the first 7 days to observe if clinical outcomes are improved. Unfortunately, there is extremely limited research, and what is available is controversial. National guidelines have analyzed the studies, and they too are challenged to define a clear, high quality of evidence recommendation. It is important for the healthcare clinician to understand the research around this controversy to make best decisions for their patients.

Topics: alpha-Linolenic Acid; Critical Illness; Enteral Nutrition; Fat Emulsions, Intravenous; Fatty Acids, Essential; Fatty Acids, Omega-6; Hospitalization; Humans; Intensive Care Units; Length of Stay; Linoleic Acid; Parenteral Nutrition; Phospholipids; Soybean Oil; Triglycerides

Little is known about endogenous surfactant metabolism in infants, because radioactive isotopes used for this purpose in animals cannot be used in humans. We developed a novel and safe method to measure the endogenous surfactant kinetics in vivo in humans by using stable isotope labeled fatty acids. We infused albumin-bound [U-13C]palmitic acid (PA) and [U-13C]linoleic acid (LLA) for 24 h in eight critically ill infants (mean+/-SD: weight: 3.7+/-1.3 kg: age: 51.3+/-61.6 d) who required mechanical ventilation. The 13C enrichment of PA and LLA in surfactant phosphatidylcholine (PC), obtained from tracheal aspirates, was measured by gas chromatography combustion interface-isotope ratio mass spectrometry. We measured a significant incorporation of both 13C-PA and 13C-LLA into surfactant PC. PC-PA and PC-LLA became enriched after 8.7+/-4.9 h (range: 3.4-17.3) and 10.0+/-7.2 h (range: 3.0-22.4), respectively; the times at maximum enrichment were 49.2+/-8.9 and 45.6+/-19.3 h, respectively. The fractional synthesis rate of surfactant PC-PA ranged from 0.4 to 3.4% per h, whereas the fractional synthesis rate of PC-LLA ranged from 0.5 to 3.8% per h. The surfactant PC-PA and PC-LLA half-lives ranged from 16.8 to 177.7 and 23.8 to 144.4 h, respectively. This method provides new data on surfactant metabolism in infants requiring mechanical ventilation. We found that synthesis of surfactant from plasma PA and LLA is a slow process and that there were marked differences in PC kinetics among infants. This variability could be related to differences in lung disease and could affect the clinical course of the respiratory failure.

Topics: Carbon Isotopes; Critical Illness; Energy Intake; Female; Humans; Infant; Infant, Newborn; Infusions, Intravenous; Kinetics; Linoleic Acid; Male; Palmitic Acid; Phosphatidylcholines; Protein Binding; Pulmonary Surfactants; Serum Albumin; Specimen Handling; Time Factors; Trachea

Lipolysis has been measured in humans by means of stable isotope techniques using labeled palmitic acid (PA) or glycerol as tracers. If other fatty acids (FA) such as linoleic acid (LLA) have the same rate of appearance (Ra) as PA and therefore contribute equally to oxidative and nonoxidative metabolism is unknown. We infused albumin-bound [U-13C]PA and [U-13C]LLA in seven critically ill infants (weight 3.6 +/- 1.3 kg, age 57 +/- 64 d) receiving 20.9 +/- 5.4 kcal. kg-1.d-1 of i.v. glucose only, and measured simultaneously the Ra of PA and LLA from the isotopic enrichment of plasma FFA by mass spectrometry. A needle biopsy of the s.c. adipose tissue was obtained for FA composition. PA in adipose tissue was higher than LLA (40 +/- 6.7 versus 5.4 +/- 3.2 mol %, p < 0.001). The Ra values of PA and LLA were 5.73 +/- 2.79 and 1.34 +/- 0.92 mumol.kg-1.min-1, respectively (p = 0.005). However, the ratio of the FA's Ra to their respective mol% values in adipose tissue was lower for PA than for LLA (0.15 +/- 0.06 versus 0.25 +/- 0.06, p = 0.02). The Ra of LLA acid was higher than could be expected from the FA composition of adipose tissue, thus indicating a preferential release of LLA during lipolysis. In critically ill infants receiving only i.v. glucose, the contribution of LLA to the oxidative and nonoxidative metabolism may be larger than what assumed from the FA composition of plasma and adipose tissue.

Topics: Biological Transport; Critical Illness; Fatty Acids, Nonesterified; Female; Humans; Infant; Infant, Newborn; Linoleic Acid; Linoleic Acids; Lipolysis; Male; Palmitic Acid