Clinical use

Glucose 5% is routinely given after surgery to provide free water for hydration of the ICF space and to prevent starvation. Glucose is sometimes infused before surgery as well, in particular when surgery is started late during the day, and, in some hospitals, also as a 2.5% solution during the surgical procedure.

In the perioperative period, infusing a glucose solution with little or no electrolyte content is the most logical way to provide free water to compensate for vaporization from airways and surgical wounds. The glucose component of the fluid is indicated in patients at risk of developing hypoglycemia, such as in diabetes, alcohol dependency, hepatomas, and pancreatic islet cell tumors. Certain drugs, such as propranolol, increase the risk of hypoglycemia.

There seems to be little reason to routinely administer glucose intraoperatively. In the vast majority of patients, hormonal changes associated with surgery raise the blood glucose level sufficiently (by stimulating glycogenolysis and gluconeogenesis) to maintain normoglycemia, or even to reach mild hyperglycemia. The stress response, in turn, makes it difficult for the body to adequately use exogenous glucose to limit gluconeogenesis and protein catabolism (“protein-sparing effect”).

Another argument to refrain from glucose administration intraoperatively is that a very high glucose concentration worsens the cerebral damage that develops in association with cardiac arrest.[8,9] Therefore, glucose solution is contraindicated in acute stroke and not recommended in operations associated with a high risk of perioperative cerebral ischema, such as carotid artery and cardiopulmonary bypass surgery.

Overall, shorter preoperative fasting and fast-track surgery with early postoperative mobilization have limited the use of intravenous glucose treatment in routine surgery.

Modifying the plasma glucose level by glucose infusions and insulin is a tool to reduce complications and improve survival in intensive care and after cardiac surgery.[17–19] Cardiac function may even be improved in patients undergoing cardiac surgery by infusing a solution containing glucose, insulin, and potassium.[20] These special treatments can only be performed if rigorous control of the blood glucose concentration is undertaken. Likewise, glucose infusions in diabetic patients should be monitored with frequent measurements of the blood glucose level.

In Europe, “carbohydrate loading” by mouth is sometimes performed in the evening and morning before abdominal operations. The treatment reduces thirst and hunger sensations and might improve the way the patient copes with hemorrhage. A proposed benefit is that carbohydrate loading reduces the surgery-induced insulin resistance,[21] but this has not been confirmed in more recent work.[14,15]

Electrolytes are often added to the glucose solutions used for maintenance fluid therapy during the postoperative phase. Many preparations already contain half the electrolyte content of a balanced Ringer’s solution. In other cases, sodium and potassium are added based on measurements of the plasma concentrations of these ions.

Patients with postoperative complications impairing gastrointestinal function, who are not able to feed themselves or receive oral nutrition, should be given intravenous 5% glucose solution with electrolytes as maintenance therapy. If no improvement occurs within 7 days the glucose administration should be replaced with full parenteral nutrition containing protein, glucose, and lipids.

Dosing

The basic need for glucose in an adult corresponds to 4 liters of glucose 5% per 24 hours (800 kcal, 2.8 ml/min), which prevents straightforward starvation while not providing adequate nutrition. However, the amount administered to hospital patients is more often guided by the need for “free” body water, which is 2–3 liters per 24 hours. Although the commonly infused amount provides less glucose than the body utilizes, the glucose supplementation reduces muscle wasting.[3] This “nitrogen-sparing effect” of glucose is poorer in association with surgery owing to the accompanying physiological stress response.

The rate of glucose infusion should not increase plasma glucose concentrations above the renal threshold, which is 12–15 mmol/l. Higher levels induce osmotic diuresis in which water and electrolytes losses are poorly controlled. This limit is reached by infusing 1 liter of glucose 5% over 45 min in healthy volunteers.[1]

Because of the ease with which plasma glucose becomes elevated during surgery, most anesthetists prefer to use glucose 2.5% with electrolytes in the perioperative setting. During laparoscopic cholecystectomy 1.4 liters of glucose 2.5% with electrolytes over 60 min raised plasma glucose from normal to the renal threshold for osmotic diuresis (16 mmol/l).[2] The limitations set on the infusion rate owing to the risk of hyperglycemia make both glucose 2.5% and 5% unsuitable for use as plasma volume expanders.

Hypertonic glucose solutions (10% and 20%) must be monitored by measurements of the plasma glucose concentration and frequently need to be supplemented by exogenous insulin. These fluids are used for more ambitious supplementation of calories in postoperative care and also in the intensive care unit.[18]

Glucose metabolism yields CO₂, and the accompanying increased breathing might be a problem in debilitated patients with impaired lung function.

Electrolytes

When used for maintenance therapy, a glucose solution should provide the basic need of electrolytes. The NICE guideline recommends 1 mmol of sodium and 1 mmol of potassium per kilo body weight per 24 hours. The need varies, and it is common to guide the administration by measurements of the serum sodium and potassium concentrations 1–2 times daily.

An infusion containing potassium cannot be given at a high rate because of a risk of cardiac arrhythmias. This means that, in addition to the limitations of the infusion rate given by the risk of hyperglycemia, another risk factor has to be considered. A safe rate of administration is 10 mmol of potassium per hour, which can be increased to 20 mmol per hour if the electrocardiogram is monitored. Therefore, one liter of glucose with 40 mmol/l of sodium and potassium added cannot be infused during a shorter period of time than 4 hours. Owing to the dangers inherent in this therapy, the anesthetist should personally monitor the infusion or else let the fluid be administered via an infusion pump.

Potassium supplementation exceeding the content of a Ringer’s solution is not advisable during the intraoperative period. The reason is that surgery always carries a risk of postoperative kidney failure, which can greatly raise serum potassium. The anesthetist should be aware of the trauma and surgery redistributes potassium to the ICF space owing to stimulation of the adrenergic beta-2-receptors. Hence, the plasma concentration is usually falsely low in the postoperative care unit. The hypokalemia resolves spontaneously within a few hours and should not lead to extreme measures to raise serum potassium, at least not as long as cardiac arrhythmias are absent.

Hyponatremia

Repeated infusion of electrolyte-free glucose solution (usually plain 5%) might induce subacute hyponatremia.[22,23] This complication usually develops 2–3 days after surgery and is characterized by neurological disturbances, nausea, and vomiting.[24] When symptoms appear, serum sodium is usually between 120 and 130 mmol/l (normal level 138–142 mmol/l).

Hyponatremia might cause permanent brain damage if left untreated. Menstruating women are most prone to develop such sequelae.[25] The surgery might be trivial but has often (at some stage) been complicated by sudden hypotension, which boosts the vasopressin concentration. Impaired renal function and liberal postoperative ingestion of soft juice drinks devoid of salt are other risk factors.[22,23]

Treatment in symptomatic patients consists of hypertonic saline, which should be monitored so as to increase serum sodium no faster than 1–2 mmol/l per hour. If hyponatremia has not appeared after surgery the development has probably been more gradual, and serum sodium in such chronic hyponatremia should be raised even more slowly, at 0.5 mmol/l per hour. The reason for the caution is that the brain gradually adapts to the lower osmolality, and damage might occur if the normal concentration is attained rapidly.

The risk of subacute hyponatremia is reduced by limiting the amount of plain glucose 5% to 1 liter only. All other glucose solutions should contain sodium.