The concentration of sodium lactate isotonic solution has long been a technical detail of concern in clinical infusion. It not only relates to whether the osmotic pressure of the solution is close to plasma, but also affects the balance of electrolytes, acid-base status, as well as various metabolic and physiological reactions such as kidney function, heart and lung function in the body. This article takes the representative formula of "sodium lactate isotonic solution" - sodium lactate Ringer's solution (commonly known as lactate Ringer's solution, abbreviated as LR) as an example, systematically sorting out the concentrations, units, and clinical significance of each component, and combining with the precautions in actual use, to help understand why specific concentration settings need to be paid attention to in different contexts.
1、 What is sodium lactate isotonic solution and why should we pay attention to its concentration? Isotonic solution refers to a solution with an osmotic pressure close to that of human plasma, usually between approximately 270 and 300 mOsm/L. Using isotonic solution can smoothly replenish body fluids, reduce drastic changes in the distribution of water inside and outside cells, and avoid adverse reactions such as edema or rapid dehydration. The "isotonic" property of sodium lactate isotonic solution comes from the combined action of multiple small ions in the solution, as well as the presence of lactate ions, which make its osmotic pressure close to plasma. At the same time, it brings an important physiological function: through the metabolic pathway of lactate, lactate can be converted into bicarbonate, which has a certain buffering effect and helps to maintain the relative stability of blood acid-base balance, especially in situations such as surgery or massive bleeding, digestive diseases, etc. It has practical significance.
2、 The composition and concentration of representative formulas (taking the commonly used sodium lactate Ringer solution as an example)
The following values are commonly used formula expressions in clinical practice. Specific manufacturers' products may have slight differences, but the general direction and units are consistent. The common components and concentrations per liter of solution are as follows:
Sodium ion (Na+): about 130 mEq/L
Chloride ion (Cl): about 109 mEq/L
Potassium ion (K+): about 4 mEq/L
Calcium ion (Ca2+): about 15 mEq/L
Lactate (calculated as sodium lactate, often written as lactate, equivalent to lactate concentration): about 28 mEq/L
Total osmotic pressure (osmolarity): about 270-290 mOsm/kg
The above components together form an equilibrium solution close to the osmotic pressure of human serum.
. It should be noted that the unit of lactate is "mEq/L", which can usually be used interchangeably with mmol/L in a one-to-one correspondence, because lactate exists in solution as an equal number of negative ions; Therefore, a lactate concentration of 28 mEq/L is equivalent to a concentration of approximately 28 mmol/L in most scenarios.
3、 Why do these specific concentration combinations occur?
1) The ratio of sodium to chlorine
Sodium lactate Ringer's solution retains a relatively high concentration of sodium ions (about 130 mEq/L), accompanied by a high concentration of chloride ions (about 109 mEq/L), making the overall ion composition close to the main ion levels in adult serum.
. This combination can provide sufficient plasma osmotic pressure while maintaining electrolyte balance, avoiding rapid occurrence of edema or electrolyte imbalance.
2) The presence of potassium and calcium is approximately 4 mEq/L for potassium ions and 15 mEq/L for calcium ions, which enable the solution to maintain the minimum ion levels required for physiological processes such as myocardial and neuromuscular excitability in the short term. The content of calcium is relatively low, mainly used to support muscle and nerve conduction, and to avoid calcium ion related deposition problems caused by high-intensity infusion.
3) The function of lactate is about 28 mEq/L, which is a major characteristic that distinguishes this solution from ordinary physiological saline. Lactic acid, after being metabolized by tissues such as the liver and myocardium in the human body, can form functional bases, namely bicarbonate, which play a buffering role. This makes LR have certain advantages in adjusting acid-base balance compared to pure physiological saline in some cases, especially in situations where regional ischemia, surgery, or trauma lead to increased acid load.
4) The target of overall osmotic pressure for LR is approximately between 270-290 mOsm/kg, which is close to the osmotic pressure of serum and therefore has the property of "isotonic". This proximity helps to achieve a more balanced distribution of medication when it enters the body fluid space, reducing rapid displacement between extracellular and intracellular fluids and lowering the risk of infusion related complications.
4、 Compared with other common infusion solutions, the Cl content of sodium lactate isotonic solution is lower and the ratio of Na+to Cl is closer to serum compared to ordinary physiological saline (09% NaCl). Ordinary physiological saline may pose a risk of high chloride acidosis or a weak acid-base balance when infused in large quantities, while sodium lactate isotonic solution has certain advantages in buffering.
Compared to the "more complex formula" balanced salt solution, LR's lactate composition has the potential to act as an acid-base buffer, but also brings a burden on liver metabolism, as lactate needs to be converted into bicarbonate through liver metabolism. Therefore, in patients with severe liver dysfunction, hypoperfusion, or high lactate metabolism abnormalities, comprehensive evaluation is required when using it.
When renal function is limited, blood potassium levels are high, or there is a risk of acute hyperkalemia, potassium levels also need to be monitored; Although the potassium content is not high, it may still accumulate in high-dose or chronic infusion.
5、 Concentration considerations and practical operation points in clinical use
1) Applicable scenarios
Sodium lactate isotonic solution is often used for fluid resuscitation, pre - and post-operative fluid replacement, abdominal surgery, intensive care, and other scenarios, especially when it is necessary to supplement water and some electrolytes at the same time, and it is hoped that lactic acid can bring a certain buffering effect, which is more advantageous.
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2) The specific dosage depends on the patient's age, weight, disease status, and hemodynamic conditions. The common empirical strategy is to first administer rapid crystalloid fluid resuscitation in low blood volume or shock states, such as intravenous infusion of 0.9% saline or LR or short-term rapid drip (such as 10-
20 mL/kg each time, adjusted according to response), and then adjust based on clinical response and blood test results. For adults, maintenance infusion is often adjusted for individualization in intervals of several liters per day.
3) Special populations and contraindications: For individuals with liver dysfunction, metabolic alkalosis, or those requiring additional bicarbonate supplementation, the buffering effect of LR may be helpful for acid-base status, but attention should also be paid to the metabolic burden of lactate.
Individuals who are at significant risk of hyperkalemia or have renal insufficiency and need to limit potassium intake should use it with caution, and if necessary, choose other crystalloid solutions that do not contain lactate.
Newborns or children may have different dosages and formulations of medication compared to adults, and should follow pediatric medication guidelines and the pediatric dosage provided by the manufacturer.
4) The administration speed and monitoring should be closely monitored during the infusion process, including vital signs, urine output, blood pressure, blood gas analysis, and electrolyte levels. If there are abnormal fluctuations in serum lactate levels, abnormal levels of blood potassium and calcium ions, or changes in alkaline acid status, the plan should be adjusted in a timely manner. Be alert to the adverse effects of excessive fluid on pulmonary edema, cardiac burden, etc. during rapid and large infusion.
6、 Possible Misconceptions and Error Correction
Misconception 1: Lactates directly increase lactate levels, causing lactic acidosis. The fact is that metabolism in the body converts lactate into bicarbonate, which has a buffering effect; Lactic acid accumulation may only occur in cases of extreme liver dysfunction or widespread hypoperfusion, thus requiring a comprehensive clinical assessment.
Misconception 2: isotonic means there is no risk and anyone can use it in large quantities. In fact, local characteristics, ion balance, cardiovascular and renal function status, age, and disease type can all affect whether it is suitable for use and dosage, and individualized evaluation is needed.
Misconception 3: Lactate is just a "buffer" and has nothing to do with electrolytes. In fact, the introduction of lactate is related to the buffering capacity in serum, but its infusion of sodium, potassium, and calcium ions will gradually change the electrolyte state in the body, which needs to be comprehensively considered in the treatment plan.
7、 The main value of sodium lactate isotonic solution in clinical practice lies in providing stable liquid supplementation through a formula close to plasma osmotic pressure, while combining the buffering effect brought by lactate to help maintain acid-base balance and relative stability of electrolyte gradient. In terms of concentration setting, although there are common formulas (Na+about 130 mEq/L, Cl − about 109 mEq/L, K+about 4 mEq/L, Ca2+about 15 mEq/L, lactate about 28 mEq/L, total osmotic pressure about 270-290 mOsm/kg), personalized adjustments must be made based on the patient's liver function, kidney function, acid-base status, serum electrolyte levels, and treatment goals in practical applications. Clinical workers should always place equal importance on osmotic pressure, ion balance, buffering effect, and patient safety when formulating infusion plans. Careful observation and flexible adjustment are necessary to ensure treatment effectiveness while reducing potential risks.
If necessary, more detailed calculation examples, comparisons of drug alternatives, and monitoring points can be provided based on specific usage scenarios to help more accurately grasp and apply concentration in daily clinical practice.
