The Link between Hypermetabolism and Hypernatremia in Severely Burned Patients

Abstract

Hypernatremia is common in critical care, especially in severely burned patients. Its occurrence has been linked to increased mortality. Causes of hypernatremia involve a net gain of sodium or a loss of free water. Renal loss of electrolyte-free water due to urea-induced osmotic diuresis has been described as causative in up to 10% of hypernatremic critical ill patients. In this context, excessive urea production due to protein catabolism acts as major contributor. In severe burn injury, muscle wasting occurs as result of hypermetabolism triggered by ongoing systemic inflammation. In this retrospective study, severely burned patients were analysed for the occurrence of hypernatremia and subsequent signs of hypermetabolism. The urea: creatinine ratio—as a surrogate for hypermetabolism—sufficiently discriminated between two groups. Four of nine hypernatremic burn patients (44%) had a highly elevated urea: creatinine ratio, which was clearly associated with an increased urea production and catabolic index. This hypermetabolism was linked to hypernatremia via an elevated urea- and reduced electrolyte-fraction in renal osmole excretion, which resulted in an increased renal loss of electrolyte-free water. In hypermetabolic severely burned patients, the electrolyte-free water clearance is a major contributor to hypernatremia. A positive correlation to serum sodium concentration was shown.

ICU-Acquired Hypernatremia Is Associated with Persistent Inflammation, Immunosuppression and Catabolism Syndrome

“…In this regard, we must state an even higher incidence of 28.7% in our preselected population with prolonged LOS on a mainly surgical ICU. We assume that at least part of this higher incidence is explained just by profuse catabolism as also shown in a study on severely burned, hypermetabolic patients in our ICU [ 26 ]. In contrast to the existing literature, no impact on mortality was able to be shown for hypernatremic patients in this study.…”

“…A link between PICS and hypernatremia can be established in two ways. On the one hand, hyperosmolar cell stress has been shown to trigger protein metabolism, muscle degradation and immunomodulation [ 32 , 33 , 34 , 35 ], and on the other hand, excessive catabolism has been shown to cause hypernatremia via profuse urine urea excretion, leading to osmotic diuresis and concomitant loss of electrolyte-free water [ 26 , 27 , 28 , 29 , 30 , 31 ]. Despite conceptualizing a potential vicious cycle, of course, the complex physiology behind PICS and hypernatremia cannot be broken down to one simple cause.…”

“…An elevated urea-to-creatinine ratio above 75 (75 mg/dL:mg/dL = 141 mmol/L:mmol/L) has recently been published as a novel biomarker for critical illness-associated catabolism [ 39 ]. Confirmation as a marker for hypermetabolism in severely burned patients has also been done by our group [ 26 ]. In the next step, fluid balance, sodium intake, renal function, urine output, urine sodium output and osmole composition were compared in order to elucidate a possible pathophysiologic link between hypernatremia and PICS ( Figure 2 , Table 3 ).…”

“…The link back to hypernatremia is theoretically done in two ways. On the one hand, persistent catabolism with elevated ureagenesis can lead to profuse urine urea output and subsequently to urea-induced osmotic diuresis with loss of electrolyte-free water and resulting hypernatremia [ 26 , 27 , 28 , 29 , 30 , 31 ]. On the other hand, hypernatremia itself can again promote protein catabolism and also systemic inflammation, primarily via hyperosmolar cell stress [ 32 , 33 , 34 , 35 ].…”

Hipernatremija Intensyviojoje Terapijoje

“…Euvoleminė hipernatremija pasireiškia, kai vandens balansas yra neigiamas, o druskų − normalus. Sumažėjęs vandens vartojimas yra būtinas euvoleminės hipernatremijos veiksnys [8]. Pacientų, kurių vandens vartojimas sumažėjęs (kūdikiai, senyvo amžiaus žmonės), šlapimo koncentracija yra normali arba padidėjusi.…”