Insulin secretion in hypothermic dogs

Dysglycemia, Glycemic Variability, and Outcome After Cardiac Arrest and Temperature Management at 33°C and 36°C

OBJECTIVES

Dysglycemia and glycemic variability are associated with poor outcomes in critically ill patients. Targeted temperature management alters blood glucose homeostasis. We investigated the association between blood glucose concentrations and glycemic variability and the neurologic outcomes of patients randomized to targeted temperature management at 33°C or 36°C after cardiac arrest.

DESIGN

Post hoc analysis of the multicenter TTM-trial. Primary outcome of this analysis was neurologic outcome after 6 months, referred to as "Cerebral Performance Category."

SETTING

Thirty-six sites in Europe and Australia.

PATIENTS

All 939 patients with out-of-hospital cardiac arrest of presumed cardiac cause that had been included in the TTM-trial.

INTERVENTIONS

Targeted temperature management at 33°C or 36°C.

MEASUREMENTS AND MAIN RESULTS

Nonparametric tests as well as multiple logistic regression and mixed effects logistic regression models were used. Median glucose concentrations on hospital admission differed significantly between Cerebral Performance Category outcomes (p < 0.0001). Hyper- and hypoglycemia were associated with poor neurologic outcome (p = 0.001 and p = 0.054). In the multiple logistic regression models, the median glycemic level was an independent predictor of poor Cerebral Performance Category (Cerebral Performance Category, 3-5) with an odds ratio (OR) of 1.13 in the adjusted model (p = 0.008; 95% CI, 1.03-1.24). It was also a predictor in the mixed model, which served as a sensitivity analysis to adjust for the multiple time points. The proportion of hyperglycemia was higher in the 33°C group compared with the 36°C group.

CONCLUSION

Higher blood glucose levels at admission and during the first 36 hours, and higher glycemic variability, were associated with poor neurologic outcome and death. More patients in the 33°C treatment arm had hyperglycemia.

The effect on intermediary metabolism of open-heart surgery with deep hypothermia and circulatory arrest in infants of less than 10 kilograms body weight. A preliminary study

The effects of hypothermic open-heart surgery with circulatory arrest upon intermediary metabolism and endocrine function in small children are still poorly understood. This report presents data obtained in a preliminary study in which seven children of <10 Kg body weight were investigated during and after such procedures. Frequent blood samples were taken from one day preoperatively to seven days postoperatively for estimation of hormone concentrations (insulin, growth hormone, glucagon, cortisol), and intermediary metabolites (glucose, lactate, pyruvate, alanine, glycerol, and 3- hydroxybutyrate).

Marked hyperglycaemia (34·8 ±3·3 mmol/L) was observed during cardiopulmonary bypass probably as a result of the glucose content of the pump prime. Moderate hyperglycaemia persisted for at least seven days postoperatively. A significant increase in lactate concentrations (p < 0·02) was observed during circulatory arrest and peak concentrations of 6·77 +0.87 mmol/L were measured at the end of the operation. Very high blood lactate concentrations were observed at the end of cardiopulmonary bypass in two patients who subsequently died. Peak insulin concentrations (20·7 ± 5·2 mU/L) were lower than those (30-40 mU/L) reported in adults undergoing similar procedures. Glucagon concentrations were significantly elevated during bypass ( p<0·05) to approximately twice the levels reported in adults. Unlike the other hormones, growth hormone concentrations revealed remarkably uniform change, similar to those reported in 'high responding' adults with peak values of 124 ± 26 mU/L, observed during cardiopulmonary bypass. Cortisol concentrations showed no significant changes throughout the study.

Thus, the response of small infants to these procedures differed both qualitatively and quantitatively from that reported in adults. The results suggest that the nature of the prime fluid may be of major importance in the metabolic consequences of such surgery and that glucose and lactate may be better avoided in the pump prime.

Evaluation of glucose management during therapeutic hypothermia at a Tertiary Academic Medical Center

STUDY AIM

Alterations in metabolic function during therapeutic hypothermia (TH) decrease responsiveness to insulin and increase the risk of hyperglycemia. Glycemic control is associated with improved outcomes in selected patients; however, glycemic management strategies during TH are not defined. The objective of this analysis was to evaluate the glycemic metrics and IV insulin administration in critically ill patients during the cooling and rewarming phases of TH.

METHODS

Data from 37 patients who received at least 6h of therapeutic hypothermia for cardiac arrest between January 2007 and January 2010 were retrospectively evaluated, 14 (37.8%) of whom had diabetes.

RESULTS

The mean blood glucose was 9.16±3.22mmol/L and 6.54±2.45mmol/L; p<0.01 during cooling and rewarming, respectively. Twelve (32.4%) patients experienced at least one hypoglycemic event, defined as a blood glucose <4mmol/L. Nineteen (51.4%) patients experienced at least one hyperglycemic event, defined as a blood glucose >11.11mmol/L and 15 (40.5%) patients received IV insulin therapy. Patients on IV insulin had a higher incidence of diabetes (9 vs. 5; p<0.05), higher admission blood glucose (13.89±6.13 vs. 11.03±4.65mmol/L; p=0.11), and a higher incidence of hyperglycemia (14 vs. 2; p<0.01) and hypoglycemia (8 vs. 4; p<0.05). Of the patients on IV insulin, mean insulin requirements during cooling and rewarming were 15.2±16.1 and 7±12.5units/h, respectively.

CONCLUSION

TH is commonly associated with hyperglycemia, hypoglycemia, and the use of IV insulin therapy. Further research is needed to determine optimal glycemic management strategies to prevent hyper- and hypoglycemia in patients during the different phases of TH.

Glucose metabolism and insulin activity during cardiac surgery

Disorders of glucose metabolism were investigated in 177 patients undergoing cardiac surgery. In group I patients, the cardiopulmonary bypass (CPB) priming fluid contained glucose. Patients in group II received neither glucose nor insulin during the operation. Group III received insulin-glucose therapy (IGT) during the operation (insulin, 1 U/kg/h, glucose, 0.5 g/kg/h). At the onset of CPB in group I, hyperglycemia was produced by the glucose load and by a relative reduction in insulin secretion. In group II, the start of the operation was accompanied by a rise in the titer of insulin antibodies. IGT resulted in normalization of the blood glucose level after CPB and stability of the insulin antibody titer during the investigation. The indices of myocardial contractility in group III were better than those of the "glucose-free" group II before and after CPB. In group II, indices of beta-cell function were moderately depressed 16 to 18 hours after the operation. Insulin and c-peptide level measurements demonstrated insulin production in group III on the first postoperative day. The results demonstrate that IGT has some potential benefit for glucose metabolism and myocardial function during cardiac surgery.

Sympathoadrenal system and regulation of thermogenesis

The sympathetic nervous system (SNS) plays a critical role in the regulation of mammalian thermogenic responses to cold exposure and dietary intake. Catecholamine-stimulated thermogenesis is mediated by the beta-adrenergic receptor. In the rat brown adipose tissue is the major site of metabolic heat production in response to both cold (nonshivering thermogenesis) and diet (diet-induced thermogenesis). Measurements of norepinephrine turnover rate in interscapular brown adipose tissue of the rat demonstrate increased sympathetic activity in response to both cold exposure and overfeeding. In adult humans, a physiologically significant role for brown adipose tissue has not been established but cannot be excluded. It appears likely that dietary changes in SNS activity are related, at least in part, to the changes in metabolic rate that occur in association with changes in dietary intake.

Glucose and insulin changes in infants and children undergoing hypothermic open-heart surgery

Marked hyperglycemia was observed in patients undergoing hypothermic open-heart surgery. To evaluate potential mechanisms responsible for hyperglycemia, paired samples were evaluated for glucose and insulin levels in 3 groups of patients. Group 1 consisted of 8 patients less than 2 years of age undergoing cardiac surgery requiring total circulatory arrest; Group 2 consisted of 9 patients less than 2 years of age undergoing open-heart procedures but not requiring total circulatory arrest; Group 3 consisted of 10 patients greater than 2 years of age, none of whom required total circulatory arrest. All 3 groups had striking hyperglycemia during cardiac surgery and in the first few hours after the operation. Despite elevated glucose levels during surgery, insulin levels failed to increase proportionately in response to hyperglycemic stimulus. Subsequently, in a fourth group of 10 patients less than 2 years of age not undergoing total circulatory arrest, the amount of glucose infused was restricted and they did not have hyperglycemia. In children, osmotic diuresis resulting from hyperglycemia after open-heart surgery may be misinterpreted as an index of satisfactory cardiorenal performance. Accordingly, it is recommended that the diluent added to the pump blood prime solution contain no supplemental glucose; also, intraoperative fluid should consist of a balanced electrolyte solution but no glucose.

Insulin secretion in sheep exposed to cold

1. Cold exposure caused a marked decrease in insulin response to intravenous injection of glucose, with a sharply declining response over the first 4 days of cold exposure followed by a constant low response up to 13 days of the experimental cold period. 2. The glucose-induced insulin response was unaffected by concomitant infusion of phentolamine in the warm environment. In contrast, the low response of insulin secretion to glucose during cold exposure was so augmented by concomitant infusion of phentolamine as to exceed the response observed in the warm environment. 3. Intravenous infusion of phentolamine caused an increase in the concentration of plasma insulin in the cold but not in the warm environment. 4. Adrenaline completely abolished the insulin response to glucose in the warm environment. 5. Exposure to cold environment brought about an increase in urinary excretion of adrenaline and noradrenaline and in heart rate, but rectal temperature was unchanged. 6. It is concluded that cold exposure insufficient to cause hypothermia produces a marked decrease in insulin secretion by the pancreas of sheep, mediated through adrenergic alpha-receptors stimulated by augmented sympatho-adrenomedullary activity.

Studies on lipid and carbohydrate metabolism during surface-induced deep hypothermia with circulatory arrest for open-heart surgery

Plasma lipids, blood glucose, plasma insulin (IRI) and serum dopamine-beta-hydroxylase (DBH) were measured in 30 subjects undergoing surface-induced deep hypothermia with circulatory arrest for open-heart surgery. Non-esterified fatty acid (NEFA) in the plasma rapidly increased at the lowest temperature (23 degrees C) reached and other lipids in the plasma decreased during the cooling period. An increase of NEFA and a decrease of triglyceride have been attributed to the action of lipoprotein lipase activity stimulated by heparin. It is also likely that the decrease of other lipids and beta-lipoprotein in the plasma results from the transient hypofunction of the liver due to hypothermia. Blood glucose increased during the cooling period, while plasma insulin showed no significant change. Serum DBH reflecting catecholamine also showed no significant change during the cooling or rewarming periods. Therefore, hyperglycemia in hypothermic open-heart surgery may result from the decrease of peripheral utilization of glucose and from the inhibition of insulin secretion due to the transient pancreatic hypofunction.

The pathogenesis of diabetes mellitus

The precise aetiology of diabetes mellitus remains unknown. There is clearly both a genetic element which is almost certainly multifactorial, due to the multiple and additive effects of genes especially in younger patients, together with environmental factors, especially in older patients.

Evidence is increasing that the genetic element is associated with an underlying defect of the beta cells with a characteristic delayed and subnormal insulin secretion in response to glucose or other insulinogenic stimuli. The same hyposecretory response can often be found in many close relatives and in ‘prediabetes’ where standard carbohydrate tolerance is still normal.

The nature of the defect of the beta cell, its link with the genetic mechanism, and the mechanism leading to total islet failure in some diabetics is not known.

Many factors may be involved simultaneously in a single individual and apart from multiple genes, certain non-genetic factors such as obesity, pregnancy, infection and other stress which result in increased insulin antagonism, lead to additive strains on islet cell function, and may determine the onset of the overt disease in hereditarily predisposed individuals.