Altered Serum Acylcarnitines Profile after a Prolonged Stay in Intensive Care

Nutritional and metabolic modulation of inflammation in critically ill patients: a narrative review of rationale, evidence and grey areas

BACKGROUND

Inflammation is the hallmark of critical illness and triggers the neuro-endocrine stress response and an oxidative stress. Acute inflammation is initially essential for patient's survival. However, ongoing or exaggerated inflammation, due to persistent organ dysfunction, immune dysfunction or poor inflammation resolution, is associated to subsequent hypermetabolism and hypercatabolism that severely impact short and long-term functional status, autonomy, as well as health-related costs. Modulation of inflammation is thus tempting, with the goal to improve the short- and long-term outcomes of critically ill patients.

FINDINGS

Inflammation can be modulated by nutritional strategies (including the timing of enteral nutrition initiation, the provision of some specific macronutrients or micronutrients, the use of probiotics) and metabolic treatments. The most interesting strategies seem to be n-3 polyunsaturated fatty acids, vitamin D, antioxidant micronutrients and propranolol, given their safety, their accessibility for clinical use, and their benefits in clinical studies in the specific context of critical care. However, the optimal doses, timing and route of administration are still unknown for most of them. Furthermore, their use in the recovery phase is not well studied and defined.

CONCLUSION

The rationale to use strategies of inflammation modulation is obvious, based on critical illness pathophysiology and based on the increasingly described effects of some nutritional and pharmacological strategies. Regretfully, there isn't always substantial proof from clinical research regarding the positive impacts directly brought about by inflammation modulation. Some arguments come from studies performed in severe burn patients, but such results should be transposed to non-burn patients with caution. Further studies are needed to explore how the modulation of inflammation can improve the long-term outcomes after a critical illness.

Carnitine Deficiency in Intensive Care Unit Patients Undergoing Continuous Renal Replacement Therapy: A Single-center Retrospective Study

Introduction

Carnitine deficiency is common in patients undergoing intermittent hemodialysis and may also occur during continuous renal replacement therapy (CRRT). We evaluated intensive care unit (ICU) patients undergoing CRRT for carnitine deficiency and its associated risk factors.

Methods

This was a single-center, retrospective, observational study performed between June 2019 and March 2020. The primary outcome was the incidence of carnitine deficiency in ICU patients undergoing CRRT.

Results

Eighty-eight patients underwent 103 blood carnitine concentration measurements. The median age was 68 years (interquartile range: 55-80), Acute Physiology and Chronic Health Evaluation II score was 28 (24-33), Sequential Organ Failure score was 8.5 (5-11), Nutrition Risk in Critically Ill score was 6 (5-7), and blood carnitine concentration was 66.1 μmol/L (51.8-83.3). In total, 34 of 88 patients (38.6%) were found to have carnitine deficiency; however, there was no significant difference in the proportions of patients with carnitine deficiency characterized by disease. CRRT was performed in 44 (50%) patients, and the median blood total carnitine concentration measured after 24 h of CRRT without changing the settings was 65.5 μmol/L (48.6-83.3). The purification volume of CRRT and blood carnitine concentration were negatively correlated (R = -0.63; P = 0.02).

Conclusions

Carnitine deficiency is seen in patients receiving CRRT and may increase in incidence as the purification volume increases, requiring regular monitoring.

Impact of critical illness on cholesterol and fatty acids: insights into pathophysiology and therapeutic targets

Critical illness is characterized by a hypercatabolic response encompassing endocrine and metabolic alterations. Not only the uptake, synthesis and metabolism of glucose and amino acids is majorly affected, but also the homeostasis of lipids and cholesterol is altered during acute and prolonged critical illness. Patients who suffer from critically ill conditions such as sepsis, major trauma, surgery or burn wounds display an immediate and sustained reduction in low plasma LDL-, HDL- and total cholesterol concentrations, together with a, less pronounced, increase in plasma free fatty acids. The severity of these alterations is associated with severity of illness, but the underlying pathophysiological mechanisms are multifactorial and only partly clarified. This narrative review aims to provide an overview of the current knowledge of how lipid and cholesterol uptake, synthesis and metabolism is affected during critical illness. Reduced nutritional uptake, increased scavenging of lipoproteins as well as an increased conversion to cortisol or other cholesterol-derived metabolites might all play a role in the decrease in plasma cholesterol. The acute stress response to critical illness creates a lipolytic cocktail, which might explain the increase in plasma free fatty acids, although reduced uptake and oxidation, but also increased lipogenesis, especially in prolonged critical illness, will also affect the circulating levels. Whether a disturbed lipid homeostasis warrants intervention or should primarily be interpreted as a signal of severity of illness requires further research.

Mid-Term Evolution of the Serum Acylcarnitine Profile in Critically Ill Survivors: A Metabolic Insight into Survivorship

It is unknown if the abnormal acylcarnitine (AC) profile observed early after discharge of a prolonged stay in an intensive care unit (ICU) would persist over time. This prospective observational study aimed to describe the mid-term AC profile evolution in survivors of a prolonged ICU stay (≥7 days). Adults enrolled in our post-ICU follow-up program and who attended the consultation 3 months (M3) after discharge were included. Serum AC concentrations were assessed within 7 days following ICU discharge (T0) and at M3. A total of 64 survivors were analyzed after an ICU stay of 15 (9-24) days. Free carnitine (C0) concentration decreased from 45.89 (35.80-127.5) to 28.73 (20.31-38.93) µmol/L (p < 0.001). C0 deficiency was not observed at T0 but in 7/64 (11%) survivors at M3. The total AC/C0 ratio (normal ≤ 0.4) was 0.33 (0.24-0.39) at T0 and reached 0.39 (0.30-0.56) at M3 (p = 0.001). A ratio >0.4 was observed in 16/64 (25%) at T0 and in 32/64 (50%) at M3 (p = 0.006). The short-chain ACs decreased from 1.310 (0.927-1.829) at T0 to 0.945 (0.709-1.127) µmol/L at M3 (p < 0.001). In parallel, the urea/creatinine ratio and the Sarcopenic Index, respectively, decreased and increased between T0 and M3. This AC profile is suspected to signal a mitochondrial dysfunction and was, especially for short-chain ACs, a marker of protein catabolism.

Serum Acylcarnitines Profile in Critically Ill Survivors According to Illness Severity and ICU Length of Stay: An Observational Study

The acylcarnitine (AC) profile has been shown to be altered in survivors of a prolonged stay in intensive care unit (ICU), with higher short-chain derivates compared to reference ranges. The present study aimed at describing the AC profile of patients surviving a short ICU stay versus patients surviving a >7-day multiple organ dysfunction. Patients discharged from ICU after an elective and non-complicated cardiac surgery (CS) were recruited. For each CS, one to two adults, matched for gender and age, were recruited among patients enrolled in our post-ICU follow-up program after an ICU stay ≥7 days (PS). In both groups, the AC profile was determined during the week following ICU discharge. A total of 50 CS patients (SAPS II 23 (18-27)) survived an ICU stay of 2 (2-3) days and were matched to 85 PS patients (SAPS II 36 (28-51), p < 0.001) who survived an ICU stay of 11 (8-15.5) days. No carnitine deficiency was observed in either group. Their total AC/C0 ratio was similar: 0.355 (0.268-0.415) and 0.358 (0.289-0.417), respectively (p = 0.391). A ratio >0.4 representing a disturbed mitochondrial metabolism was observed in 26/85 (30.6%) PS patients and in 15/50 (30%) CS patients (p > 0.999). The long-chain ACs were elevated in both groups, with a greater increase in the CS group. The short-chain ACs were higher in the PS group: 1.520 (1.178-1.974) vs. 1.185 (0.932-1.895) μmol/L (p < 0.001). The role of the AC profile as potential marker of catabolism and/or mitochondrial dysfunction during the critical illness trajectory should be further investigated.