Cardiorespiratory, metabolic and endocrine changes after hemorrhage in man

Prehospital Blood Glucose Testing as a Predictor of Impending Hypotension in Adult Trauma Patients

OBJECTIVE

Stress-induced hyperglycemia has been found to increase hemorrhagic shock, morbidity, and mortality in the trauma patient. The purpose of this study is to evaluate whether prehospital point-of-care glucose is an independent predictor of hypotension in the adult trauma patient transported by air ambulance to the receiving trauma center.

METHODS

This retrospective chart review evaluated adult, nondiabetic trauma patients transported by air ambulance at 3 programs in the Midwest for the calendar year 2018. A total of 107 patients met the inclusion criteria. The primary analysis was the determination of an optimal cutoff for the blood glucose diagnostic for predicting a hypotensive outcome followed by chi-square incidence comparison.

RESULTS

The optimal diagnostic cutoff point using Youden's index (J) was determined to be a blood glucose value of 220 mg/dL or greater. Initial glucose values were associated with an increased relative risk of a hypotension outcome (P = .040). Glucose dichotomy was also associated with a mean decrease in systolic blood pressure during transport (P = .016).

CONCLUSION

The findings in this study indicate a point-of-care glucose measurement greater than 220 mg/dL should prompt prehospital clinicians to initiate aggressive balanced resuscitation before arrival at the receiving trauma center in order to prevent worsening hypotension and hemorrhagic shock.

Progress towards in vivo brain 13C-MRS in mice: Metabolic flux analysis in small tissue volumes

The combination of dynamic ¹³C MRS data under infusion of ¹³C-labelled substrates and compartmental models of cerebral metabolism enabled in vivo measurement of metabolic fluxes with a quantitative and distinct determination of cellular-specific activities. The non-invasive nature and the chemical specificity of the ¹³C dynamic data obtained in those tracer experiments makes it an attractive approach offering unique insights into cerebral metabolism. Genetically engineered mice present a wealth of disease models particularly interesting for the neuroscience community. Nevertheless, in vivo¹³C NMR studies of the mouse brain are only recently appearing in the field due to the numerous challenges linked to the small mouse brain volume and the difficulty to follow the mouse physiological parameters within the NMR system during the infusion experiment. This review will present the progresses in the quest for a higher in vivo¹³C signal-to-noise ratio up to the present state of the art techniques, which made it feasible to assess glucose metabolism in different regions of the mouse brain. We describe how experimental results were integrated into suitable compartmental models and how a deep understanding of cerebral metabolism depends on the reliable detection of ¹³C in the different molecules and carbon positions.

Positive end-expiratory pressure may alter breathing cardiovascular variability and baroreflex gain in mechanically ventilated patients

Background

Baroreflex allows to reduce sudden rises or falls of arterial pressure through parallel RR interval fluctuations induced by autonomic nervous system. During spontaneous breathing, the application of positive end-expiratory pressure (PEEP) may affect the autonomic nervous system, as suggested by changes in baroreflex efficiency and RR variability. During mechanical ventilation, some patients have stable cardiorespiratory phase difference and high-frequency amplitude of RR variability (HF-RR amplitude) over time and others do not. Our first hypothesis was that a steady pattern could be associated with reduced baroreflex sensitivity and HF-RR amplitude, reflecting a blunted autonomic nervous function. Our second hypothesis was that PEEP, widely used in critical care patients, could affect their autonomic function, promoting both steady pattern and reduced baroreflex sensitivity.

Methods

We tested the effect of increasing PEEP from 5 to 10 cm H2O on the breathing variability of arterial pressure and RR intervals, and on the baroreflex. Invasive arterial pressure, ECG and ventilatory flow were recorded in 23 mechanically ventilated patients during 15 minutes for both PEEP levels. HF amplitude of RR and systolic blood pressure (SBP) time series and HF phase differences between RR, SBP and ventilatory signals were continuously computed by complex demodulation. Cross-spectral analysis was used to assess the coherence and gain functions between RR and SBP, yielding baroreflex-sensitivity indices.

Results

At PEEP 10, the 12 patients with a stable pattern had lower baroreflex gain and HF-RR amplitude of variability than the 11 other patients. Increasing PEEP was generally associated with a decreased baroreflex gain and a greater stability of HF-RR amplitude and cardiorespiratory phase difference. Four patients who exhibited a variable pattern at PEEP 5 became stable at PEEP 10. At PEEP 10, a stable pattern was associated with higher organ failure score and catecholamine dosage.

Conclusions

During mechanical ventilation, stable HF-RR amplitude and cardiorespiratory phase difference over time reflect a blunted autonomic nervous function which might worsen as PEEP increases.

Characterization of persistent hyperglycemia: what does it mean postinjury?

BACKGROUND

Strict glycemic control has been shown to reduce both morbidity and mortality in critically ill surgical patients; however, overly aggressive management of hyperglycemia may also be associated with deleterious effects. We sought to characterize clinical outcomes associated with different levels of persistent hyperglycemia (PH) in a cohort of severely injured patients with trauma, when a strict glycemic control protocol (target glucose 80-110 mg/dL) was implemented.

METHODS

Data were obtained from a multicenter prospective cohort study evaluating clinical outcomes in blunt injured adults with hemorrhagic shock. Glycemic control was analyzed using the average maximum daily glucose values from postinjury day 2 (>48 hours after injury) to postinjury day 5. PH was defined as a mean glucose value >130 mg/dL, and was categorized into three different severity levels (I-III) based on the distribution of mean 4-day glucose values for the cohort. Separate Cox proportional hazard regression models were then used to determine whether PH was independently associated with mortality and nosocomial infection (NI), and the level of glycemic control that was associated with these poor outcomes.

RESULTS

Overall mortality and NI rates for the study population (n = 862) were 10.8% and 49.6%, respectively. Cox proportional hazard regression revealed that PH was independently associated with almost an 80% higher mortality in patients with mean 4-day glucose values >145 mg/dL (group II) and almost a twofold higher mortality in patients with >165 mg/dL (group III). However, PH was not independently associated with a higher risk of NI at any level. Patients with PH did have a higher incidence of early multiple organ failure (within first 48 hours: 30.2% vs. 41.6% p = 0.001), which preceded the documentation of PH in the majority of patients.

CONCLUSION

Maintenance of daily maximum glucose values <145 mg/dL was independently associated with a survival benefit after injury. Patients with PH, despite aggressive insulin therapy, had a higher incidence of multiple organ failure and an associated higher risk of mortality. However, the strict glycemic control protocol in the current trauma cohort seems to have prevented the association of PH and infectious complications, which has been documented in prior studies. This analysis further validates the importance of strict glycemic control after injury, and highlights the need for further studies on the mechanism responsible for these findings.

Early hyperglycemia predicts multiple organ failure and mortality but not infection

BACKGROUND

Previous studies attempting to characterize the association between early hyperglycemia (EH) and subsequent outcome have been performed without utilization of a strict glycemic control protocol. We sought to characterize the clinical outcomes associated with EH in a cohort of severely injured trauma patients, when a strict glycemic control protocol was used.

METHODS

Data were obtained from a multicenter prospective cohort study evaluating clinical outcomes in blunt injured adults with hemorrhagic shock. Known diabetics and patients with isolated traumatic brain injury were excluded from the analysis. A strict glycemic protocol (target glucose, 80-110 mg/dL) was employed. Cox proportional hazard regression was used to evaluate the effects of EH on multiple organ failure (MOF), nosocomial infection (NI), and mortality, after adjusting for the effects of early death on subsequent infection rates.

RESULTS

Overall mortality, MOF, and NI rates for the entire cohort were 19.6%, 37.5%, and 42.2%, respectively, with a mean Injury Severity Score of 31.6 +/- 14. Cox proportional hazard regression confirmed that EH was independently associated with almost a twofold higher mortality rate and a 30% higher incidence of MOF, but was not an independent risk factor for NI, after controlling for all important confounders. There continued to be no independent association between EH and NI, even when stratified by infection type (pneumonia, catheter-related blood stream infection, or urinary tract infection).

CONCLUSION

These results suggest that EH is a marker of severe physiologic insult after injury, and that strict glycemic control may reduce or prevent the infectious complications previously shown to be associated with hyperglycemia early after injury.

Lower body negative pressure as a model to study progression to acute hemorrhagic shock in humans

Hemorrhage is a leading cause of death in both civilian and battlefield trauma. Survival rates increase when victims requiring immediate intervention are correctly identified in a mass-casualty situation, but methods of prioritizing casualties based on current triage algorithms are severely limited. Development of effective procedures to predict the magnitude of hemorrhage and the likelihood for progression to hemorrhagic shock must necessarily be based on carefully controlled human experimentation, but controlled study of severe hemorrhage in humans is not possible. It may be possible to simulate hemorrhage, as many of the physiological compensations to acute hemorrhage can be mimicked in the laboratory by applying negative pressure to the lower extremities. Lower body negative pressure (LBNP) sequesters blood from the thorax into dependent regions of the pelvis and legs, effectively decreasing central blood volume in a similar fashion as acute hemorrhage. In this review, we compare physiological responses to hemorrhage and LBNP with particular emphasis on cardiovascular compensations that both share in common. Through evaluation of animal and human data, we present evidence that supports the hypothesis that LBNP, and resulting volume sequestration, is an effective technique to study physiological responses and mechanisms associated with acute hemorrhage in humans. Such experiments could lead to clinical algorithms that identify bleeding victims who will likely progress to hemorrhagic shock and require lifesaving intervention(s).

The metabolic effects of moderately severe upper gastrointestinal haemorrhage in man

The metabolic effects of moderately severe gastrointestinal haemorrhage were investigated in man. Before resuscitation, patients had raised circulating concentrations of glucose, lactate, alanine, glycerol and cortisol. After urgent operation for haemorrhage, metabolite concentrations were similar to those of control patients having elective abdominal surgery, but insulin concentrations were higher and cortisol lower in haemorrhage patients. There were no significant differences in nitrogen excretion between haemorrhage patients and their controls, but urinary 3-methyl-histidine excretion by haemorrhage patients was lower indicating decreased muscle protein breakdown. Decreased amino acid release from muscle might account for previously reported imparied wound healing after haemorrhage.

Circulatory and respiratory adaptation in man to acute withdrawal and reinfusion of blood

In eight healthy men 950 g of blood (12.2 17.6% of the blood volume) was withdrawn and reinfused after about half an hour. Respiration and circulation were studied by analyses of expiratory gas, blood gases and data from right heart catheterization. On hemorrhage oxygen uptake and cardiac output decreased by 10 and 28%, repectively; both varied indirectly with the blood loss. The pressures in the right ventricle, pulmonary and systemic arteries fell without relation to the cardiac output. Mean heart rate did not change significantly, but a moderate positive covariation (P less than 0.05) between heart rate and arterial blood pressure was found during bleeding. This result was confirmed by the relative bradycardia noted in the period prior to reinfusion. On refilling of the bood the oxygen uptake and the pulmonary arterial pressures increased above the initial value. The heart rate varied directly with the arterial pressure also during reinfusion. The observations demonstrate a depression of the metabolism and circulation on moderate hemorrhage. Part of these effects is tentatively referred to a lowered set point of the arterial baroreflexes.

Role of the symphato-adrenal system in hemorrhagic hyperglycemia

Arterial and venous plasma glucose concentration was determined at intervals in cats subjected to hemorrhagic hypotension at 50 mm Hg. The rapid rise of arterial plasma glucose after hemorrhage could be attributed to an increase release of glucose from the liver. This hyperglycemia could not be eliminated by bilateral adrenalectomy or by sectioning of the hepatic sympathetic nerves, although the response was somewhat depressed by the latter procedure. On the other hand the hyperglycemia was virtully abolished after adrenalectomy when combined with bilateral sectioning of the major and minor splanchnic nerves. The level of plasma glucagon during hemorrgage increased in cats with an intact sympatho-adrenal system, but was unchanged in animals with combined splanchnic sympathectomy and adrenalectomy. It is concluded that, during hemorrhage, the sumpatho-adrenal system influences the glucose output from the liver by three different reflex mechanisms: (a) release of catecholamines from the adrenal glands; (b) direct sympathetic nerve influence on the liver; and (c) release of glucagon from the pancreas.

Chronic tissue insulin resistance following hemorrhagic shock

Metabolism of fat and muscle tissue was measured for 30 days following shock and reinfusion in rabbits. Tissue insulin resistance in the post-shock period was demonstrated by decreased oxidation of glucose and decreased incorporation of glucose into neutral lipid or glycogen during incubation with insulin. In addition, the insulin stimulated incorporation of amino acids into muscle protein was markedly reduced after shock. Conversely, the capacity of muscle to oxidize leucine was enhanced by shock, even in the presence of insulin. Tissue insulin resistance and increased leucine catabolism are likely to contribute to the general metabolic response to shock and trauma.

Glucose tolerance and insulin response during and after elective skeletal surgery

Six patients undergoing elective femoral osteotomy were subjected to a series of intravenous glucose tolerance tests and plasma insulin determinations in a study of the way in which a standard operation affects carbohydrate metabolism. The glucose tolerance of all patients assumed a diabetic pattern; this was already observable in the test made on admission to the operating theater and was still evident during the last test on the second postoperative day. The changes were most profound during and four hours after the operation. Insulin secretion was suppressed on the day of operation, but exceeded preoperative values in the postoperative period. Urinary excretion of catecholamines was determined in 4 patients; there was no correlation between the degree of insulin suppression and the catecholamine output. The assumption that the hyperglycemic response and insulin suppression are mediated along splanchnic neural pathways was not confirmed in a quadriplegic patient, who responded to an intravenous glucose tolerance test soon after the injury with hyperglycemia, insulin suppression and a low catecholamine output. It is concluded that the hyperglycemia and insulin suppression observed after trauma represent a complex and purposeful metabolic response, in which several causative factors are involved.

Direct measurement of insulin secretory rate: studies in shocked primates and postoperative patients

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