Diagnostic accuracy of calculated serum osmolarity to predict dehydration in older people: adding value to pathology laboratory reports

OBJECTIVES

To assess which osmolarity equation best predicts directly measured serum/plasma osmolality and whether its use could add value to routine blood test results through screening for dehydration in older people.

DESIGN

Diagnostic accuracy study.

PARTICIPANTS

Older people (≥65 years) in 5 cohorts: Dietary Strategies for Healthy Ageing in Europe (NU-AGE, living in the community), Dehydration Recognition In our Elders (DRIE, living in residential care), Fortes (admitted to acute medical care), Sjöstrand (emergency room) or Pfortmueller cohorts (hospitalised with liver cirrhosis).

REFERENCE STANDARD FOR HYDRATION STATUS

Directly measured serum/plasma osmolality: current dehydration (serum osmolality>300 mOsm/kg), impending/current dehydration (≥295 mOsm/kg).

INDEX TESTS

39 osmolarity equations calculated using serum indices from the same blood draw as directly measured osmolality.

RESULTS

Across 5 cohorts 595 older people were included, of whom 19% were dehydrated (directly measured osmolality>300 mOsm/kg). Of 39 osmolarity equations, 5 showed reasonable agreement with directly measured osmolality and 3 had good predictive accuracy in subgroups with diabetes and poor renal function. Two equations were characterised by narrower limits of agreement, low levels of differential bias and good diagnostic accuracy in receiver operating characteristic plots (areas under the curve>0.8). The best equation was osmolarity=1.86×(Na++K+)+1.15×glucose+urea+14 (all measured in mmol/L). It appeared useful in people aged ≥65 years with and without diabetes, poor renal function, dehydration, in men and women, with a range of ages, health, cognitive and functional status.

CONCLUSIONS

Some commonly used osmolarity equations work poorly, and should not be used. Given costs and prevalence of dehydration in older people we suggest use of the best formula by pathology laboratories using a cutpoint of 295 mOsm/L (sensitivity 85%, specificity 59%), to report dehydration risk opportunistically when serum glucose, urea and electrolytes are measured for other reasons in older adults.

TRIAL REGISTRATION NUMBERS

DRIE: Research Register for Social Care, 122273; NU-AGE: ClinicalTrials.gov NCT01754012.

Clinical symptoms, signs and tests for identification of impending and current water-loss dehydration in older people

BACKGROUND

There is evidence that water-loss dehydration is common in older people and associated with many causes of morbidity and mortality. However, it is unclear what clinical symptoms, signs and tests may be used to identify early dehydration in older people, so that support can be mobilised to improve hydration before health and well-being are compromised.

OBJECTIVES

To determine the diagnostic accuracy of state (one time), minimally invasive clinical symptoms, signs and tests to be used as screening tests for detecting water-loss dehydration in older people by systematically reviewing studies that have measured a reference standard and at least one index test in people aged 65 years and over. Water-loss dehydration was defined primarily as including everyone with either impending or current water-loss dehydration (including all those with serum osmolality ≥ 295 mOsm/kg as being dehydrated).

SEARCH METHODS

Structured search strategies were developed for MEDLINE (OvidSP), EMBASE (OvidSP), CINAHL, LILACS, DARE and HTA databases (The Cochrane Library), and the International Clinical Trials Registry Platform (ICTRP). Reference lists of included studies and identified relevant reviews were checked. Authors of included studies were contacted for details of further studies.

SELECTION CRITERIA

Titles and abstracts were scanned and all potentially relevant studies obtained in full text. Inclusion of full text studies was assessed independently in duplicate, and disagreements resolved by a third author. We wrote to authors of all studies that appeared to have collected data on at least one reference standard and at least one index test, and in at least 10 people aged ≥ 65 years, even where no comparative analysis has been published, requesting original dataset so we could create 2 x 2 tables.

DATA COLLECTION AND ANALYSIS

Diagnostic accuracy of each test was assessed against the best available reference standard for water-loss dehydration (serum or plasma osmolality cut-off ≥ 295 mOsm/kg, serum osmolarity or weight change) within each study. For each index test study data were presented in forest plots of sensitivity and specificity. The primary target condition was water-loss dehydration (including either impending or current water-loss dehydration). Secondary target conditions were intended as current (> 300 mOsm/kg) and impending (295 to 300 mOsm/kg) water-loss dehydration, but restricted to current dehydration in the final review.We conducted bivariate random-effects meta-analyses (Stata/IC, StataCorp) for index tests where there were at least four studies and study datasets could be pooled to construct sensitivity and specificity summary estimates. We assigned the same approach for index tests with continuous outcome data for each of three pre-specified cut-off points investigated.Pre-set minimum sensitivity of a useful test was 60%, minimum specificity 75%. As pre-specifying three cut-offs for each continuous test may have led to missing a cut-off with useful sensitivity and specificity, we conducted post-hoc exploratory analyses to create receiver operating characteristic (ROC) curves where there appeared some possibility of a useful cut-off missed by the original three. These analyses enabled assessment of which tests may be worth assessing in further research. A further exploratory analysis assessed the value of combining the best two index tests where each had some individual predictive ability.

MAIN RESULTS

There were few published studies of the diagnostic accuracy of state (one time), minimally invasive clinical symptoms, signs or tests to be used as screening tests for detecting water-loss dehydration in older people. Therefore, to complete this review we sought, analysed and included raw datasets that included a reference standard and an index test in people aged ≥ 65 years.We included three studies with published diagnostic accuracy data and a further 21 studies provided datasets that we analysed. We assessed 67 tests (at three cut-offs for each continuous outcome) for diagnostic accuracy of water-loss dehydration (primary target condition) and of current dehydration (secondary target condition).Only three tests showed any ability to diagnose water-loss dehydration (including both impending and current water-loss dehydration) as stand-alone tests: expressing fatigue (sensitivity 0.71 (95% CI 0.29 to 0.96), specificity 0.75 (95% CI 0.63 to 0.85), in one study with 71 participants, but two additional studies had lower sensitivity); missing drinks between meals (sensitivity 1.00 (95% CI 0.59 to 1.00), specificity 0.77 (95% CI 0.64 to 0.86), in one study with 71 participants) and BIA resistance at 50 kHz (sensitivities 1.00 (95% CI 0.48 to 1.00) and 0.71 (95% CI 0.44 to 0.90) and specificities of 1.00 (95% CI 0.69 to 1.00) and 0.80 (95% CI 0.28 to 0.99) in 15 and 22 people respectively for two studies, but with sensitivities of 0.54 (95% CI 0.25 to 0.81) and 0.69 (95% CI 0.56 to 0.79) and specificities of 0.50 (95% CI 0.16 to 0.84) and 0.19 (95% CI 0.17 to 0.21) in 21 and 1947 people respectively in two other studies). In post-hoc ROC plots drinks intake, urine osmolality and axillial moisture also showed limited diagnostic accuracy. No test was consistently useful in more than one study.Combining two tests so that an individual both missed some drinks between meals and expressed fatigue was sensitive at 0.71 (95% CI 0.29 to 0.96) and specific at 0.92 (95% CI 0.83 to 0.97).There was sufficient evidence to suggest that several stand-alone tests often used to assess dehydration in older people (including fluid intake, urine specific gravity, urine colour, urine volume, heart rate, dry mouth, feeling thirsty and BIA assessment of intracellular water or extracellular water) are not useful, and should not be relied on individually as ways of assessing presence or absence of dehydration in older people.No tests were found consistently useful in diagnosing current water-loss dehydration.

AUTHORS' CONCLUSIONS

There is limited evidence of the diagnostic utility of any individual clinical symptom, sign or test or combination of tests to indicate water-loss dehydration in older people. Individual tests should not be used in this population to indicate dehydration; they miss a high proportion of people with dehydration, and wrongly label those who are adequately hydrated.Promising tests identified by this review need to be further assessed, as do new methods in development. Combining several tests may improve diagnostic accuracy.

Elderly patients' participation in emergency medical services when offered an alternative care pathway

As organizational changes in the healthcare system are in progress, to enhance care quality and reduce costs, it is important to investigate how these changes affect elderly patients' experiences and their rights to participate in the choice of healthcare. The aim of this study is to describe elderly patients' lived experience of participating in the choice of healthcare when being offered an alternative care pathway by the emergency medical services, when the individual patient's medical needs made this choice possible. This study was carried out from the perspective of caring science, and a phenomenological approach was applied, where data were analysed for meaning. Data consist of 11 semi-structured interviews with elderly patients who chose a healthcare pathway to a community-based hospital when they were offered an alternative level of healthcare. The findings show that the essence of the phenomenon is described as "There was a ray of hope about a caring encounter and about being treated like a unique human being". Five meaningful constituents emerged in the descriptions: endurable waiting, speedy transference, a concerned encounter, trust in competence, and a choice based on memories of suffering from care. The conclusion is that patient participation in the choice of a healthcare alternative instead of the emergency department is an opportunity of avoiding suffering from care and being objectified.

Volume Kinetics of Intravenous Fluid Therapy in the Prehospital Setting

Introduction:

To study the volume effect of isotonic and hypertonic crystalloid fluid during ambulance transports after mild trauma, a prospective case-control study was initiated, using the ambulance and helicopter transport system in Stockholm.

Methods:

The hemodilution resulting from intravenous infusion of 1.0 L of Ringer's acetate solution (n = 7) or 250 ml of 7.5% sodium chloride (n = 3) over 30 minutes (min) was measured every 10 min during 1 hour when fluid therapy was instituted at the scene of an accident, or on arrival at the hospital. The dilution was studied by volume kinetic analysis and compared to that of matched, healthy controls who received the same fluid in hospital.

Result:

The hemodilution at the end of the infusions averaged 7.7% in the trauma patients and 9.1% in the controls, but the dilution was better maintained after trauma. The kinetic analysis showed that the size of the body fluid space expanded by Ringer's solution was 4.6 L and 3.8 L for the trauma and the control patients, respectively, while hypertonic saline expanded a slightly larger space. For both fluids, trauma reduced the elimination rate constant by approximately 30%.

Conclusion:

Mild trauma prolonged the intravascular persistence of isotonic and hypertonic crystalloid fluid as compared to a control group.

Modelling of peripheral fluid accumulation after a crystalloid bolus in female volunteers - a mathematical study

OBJECTIVE

To simultaneously model plasma dilution and urinary output in female volunteers.

METHODS

Ten healthy female non-pregnant volunteers, aged 21-39 years (mean 29), with a bodyweight of 58-67 kg (mean 62.5 kg) participated. No oral fluid or food was allowed between midnight and completion of the experiment. The protocol included an infusion of acetated Ringer's solution, 25 ml/kg over 30 min. Blood samples (4 ml) were taken every 5 min during the first 120 min, and thereafter the sampling rate was every 10 min until the end of the experiment at 240 min. A standard bladder catheter connected to a drip counter to monitor urine excretion continuously was used. The data were analysed by empirical calculations as well as by a mathematical model.

RESULTS

Maximum urinary output rate was found to be 19 (13-31) ml/min. The subjects were likely to accumulate three times as much of the infused fluid peripherally as centrally; 1/μ = 2.7 (2.0-5.7). Elimination efficacy, E(eff), was 24 (5-35), and the basal elimination k(b) was 1.11 (0.28-2.90). The total time delay T(tot) of urinary output was estimated as 17 (11-31) min.

CONCLUSION

The experimental results showed a large variability in spite of a homogenous volunteer group. It was possible to compute the infusion amount, plasma dilution and simultaneous urinary output for each consecutive time point and thereby the empirical peripheral fluid accumulation. The variability between individuals may be explained by differences in tissue and hormonal responses to fluid boluses, which needs to be further explored.

The osmotic link between hypoglycaemia and hypovolaemia

OBJECTIVE

Hypoglycaemia is regularly accompanied by hypovolaemia. To suggest a mechanism for this phenomenon, we reviewed data from eight studies conducted by our group and examined the circumstances under which rebound hypoglycaemia develops after intravenous infusion of glucose solutions.

MATERIAL AND METHODS

Forty healthy volunteers and 40 patients received a total of 122 infusions of glucose solutions at different rates, volumes and concentrations. Plasma glucose and the haemodilution were measured repeatedly during and for at least 2 h after the infusions ended. Glucose kinetics was calculated using a one-compartment turnover model and the plasma volume expansion was estimated from changes in Hb.

RESULTS

A strong linear correlation was found between the glucose level and the plasma volume expansion in all series of experiments (p<0.001). After infusion, there was a risk of hypoglycaemia and hypovolaemia developing in healthy volunteers with a high glucose clearance and when infusing glucose solutions of higher concentrations than 2.5 %. Few and mild hypoglycaemic events occurred in patients with insulin resistance, such as in diabetics and in those undergoing surgery. The immediate linear relationship between hypoglycaemia and hypovolaemia suggests an osmotic link between the two parameters. More specifically, infused fluid accompanies glucose during uptake into the cells, while volume expansion by the same fluid has already elicited an effective diuretic response.

CONCLUSION

Hypovolaemia is a consequence of hypoglycaemia after intravenous infusion of glucose solution and is caused by the osmotic translocation of fluid from the extracellular to the intracellular fluid space that occurs despite effective renal elimination.

Intravenous hydration with a 2.5% glucose solution in Type II diabetes

Physicians are often unclear about how fast intravenous glucose solutions should be administered to adequately hydrate patients with Type II diabetes while avoiding hyperglycaemia and excessive plasma volume expansion. The aim of the present study was to analyse the disposition of a 2.5% glucose solution and create a nomogram which could serve as a guide to fluid therapy in these patients. Twelve males (mean body mass index, 29 kg/m2) with Type II diabetes due to insulin resistance, as quantified by an euglycaemic hyperinsulinaemic glucose clamp, received an infusion of iso-osmotic 2.5% glucose solution with electrolytes (70 mmol/l sodium, 45 mmol/l chloride and 25 mmol/l acetate) at individual rates over 30 and 60 min respectively. Blood glucose and haemoglobin levels were measured repeatedly over 3.5 h to estimate the kinetics of glucose and fluid volume. Mean insulin sensitivity was 4.2×10−4 dl·kg−1·min−1·(μ-units/ml)−1. The individualized infusion rates reached the predetermined blood glucose level of 12 mmol/l with a mean difference of 0.2 mmol/l. The disposition of glucose was an important factor governing fluid distribution. The volume of distribution of exogenous glucose averaged 19.8 litres, but for the fluid volume it was only 3.7 litres. The clearance was 0.37 litre/min for glucose and 0.10 litre/min for the fluid volume, and the results of the 30-min and 60-min infusions agreed reasonably well. It is concluded that kinetic analysis can be used to guide the infusion time and infusion rate of 2.5% glucose to reach any predetermined glucose level and volume expansion.

Volume kinetics of glucose 2.5% solution during laparoscopic cholecystectomy

BACKGROUND

Analyses of the distribution and elimination of glucose 2.5% solutions can be used to suggest combinations of infusion rates and infusion times which yield a predetermined plasma glucose level and degree of plasma dilution during surgery.

METHODS

Twelve patients aged between 27 and 51 (mean 40) underwent laparoscopic cholecystectomy. An i.v. infusion of 1.4 litres of glucose 2.5% over 60 min was started when surgery began. A volume kinetic model was fitted to measurements of the plasma glucose concentration and the degree of haemodilution. Nomograms were constructed based on the kinetic results.

RESULTS

The volume of distribution for the glucose and infused fluid and the plasma insulin levels were similar to the ones recorded in previous volunteer studies, but 50-70% lower values were obtained for the clearance of glucose (mean 0.21 litres min(-1)), endogenous glucose production (1.1 mmol min(-1)) and the elimination rate constant for the infused fluid (median 37 ml min(-1)). Urinary excretion was markedly depressed and amounted to 9% of the infused fluid volume 4 h after starting surgery. To prevent hyperglycaemia, nomograms suggested that the infusion should be directed towards a "target" glucose concentration and then slowed down in a controlled way. At steady state, the infused fluid maintains a 3.5% plasma dilution for each mmol that plasma glucose remains above baseline.

CONCLUSION

Metabolic changes warrant careful balancing of infusion rates of glucose 2.5% during laparoscopic cholecystectomy, which is facilitated by a nomogram. Volume expansion from the infused fluid volume should be recognized.

Validation of volume kinetic analysis of glucose 2.5% solution given by intravenous infusion

BACKGROUND

The distribution and elimination of glucose solutions can be analysed by means of a volume kinetic model, but the ability of the model to predict plasma dilution ('model linearity') has not been evaluated.

METHODS

Six male volunteers received four separate infusions of glucose 2.5%: 10 ml kg(-1) and 15 ml kg(-1) over 30 min, and 15 ml kg(-1) and 25 ml kg(-1 )over 60 min. The kinetic model was fitted to measurements of plasma glucose concentration and haemodilution.

RESULTS

The mean volume of distribution for the glucose was 9.2 (SEM 0.4) litres while the infused fluid expanded a central body fluid space (V(1)) of 3.1 (0.3) litres. Increasing the amount of infused fluid, but not the infusion rate, resulted in a proportional increase in the area under the curve for plasma glucose and plasma dilution, the only confounder being glycosuria. The bias of computer simulation was slightly increased by rebound hypoglycaemia, which could occur with the highest infusion rates, but the accuracy was almost identical regardless of whether the kinetic parameters from all 24 experiments or from any of the subgroups were used.

CONCLUSION

The volume kinetic model for glucose 2.5% is linear and can therefore be used for computer simulation as long as marked glycosuria does not occur.

Volume Kinetic Analysis of Fluid Shifts Accompanying Intravenous Infusions of Glucose Solution

Volume kinetics is a mathematical tool for macroscopic (whole-body) evaluation of the distribution and elimination of fluid given by intravenous infusion. Although the kinetic system has mostly been applied to crystalloid fluids, such as Ringer's solution, it has more recently been extended to glucose solution, which is characterized by interdependence between glucose and fluid kinetics. The elimination of glucose, as estimated by a one-compartment open model, serves as the driving force for cellular uptake of glucose and, by virtue of osmosis, of water. Key findings include the observation that the infused fluid, besides being accumulated in the cells, occupies a central body fluid space (V1), which is no larger than 3-4 L, and that the cellular hydration has a much longer time-course than the hydration of V1. This explains the risk of hypovolemia associated with rapid infusion of 5% glucose; the dilution of V1, which is quite substantial owing to the small size of this space at baseline, stimulates a brisk diuresis while the excess water is being "trapped" in the cells along with the glucose. Model linearity has been demonstrated for 2.5% glucose solution and this allows the construction of nomograms for administration of such fluid during surgery and critical illness.

Lower dose of hypertonic saline dextran reduces the risk of lethal rebleeding in uncontrolled hemorrhage

To challenge whether the recommended dose of 4 mL/kg of 7.5% sodium chloride in 6% Dextran (HSD) is optimal for fluid resuscitation in uncontrolled hemorrhage, 30 anesthetized pigs were randomized to receive a 5-min intravenous infusion of either 1, 2, or 4 mL/kg of HSD beginning 10 min after inducing a 5-mm laceration in the infrarenal aorta. In addition to conventional hemodynamic monitoring, the blood loss was calculated as the difference in blood flow rates between flow probes placed proximal and distal to the injury. The results show that the bleeding stopped between 3 and 4 min after the injury and amounted to 338+/-92 mL (mean +/- SEM), which corresponds to 28.5%+/-6.6% of the estimated blood volume. After treatment with HSD was started, six rebleeding events occurred in the 1-mL group, 11 in the 2-mL group, and 16 in the 4-mL group. The amount of blood lost due to rebleeding increased significantly with the dose of HSD and was also associated with a fatal outcome. The total blood loss was 408 mL in the survivors and 630 mL in the nonsurvivors (median, P < 0.007). The mortality in the three groups was 20%, 50%, and 50%, respectively. In conclusion, infusing 4 mL/kg of HSD after uncontrolled aortic hemorrhage promoted rebleeding and increased the mortality, while a dose of 1 mL/kg appeared to be more suitable.

Volume kinetics of glucose solutions given by intravenous infusion

Glucose solutions given by intravenous (i.v.) infusion exert volume effects that are governed by the amount of fluid administered and also by the metabolism of the glucose. To understand better how the body handles glucose solutions, two volume kinetic models were developed in which consideration was given to the osmotic fluid shifts that accompany the metabolism of glucose. These models were fitted to data obtained when 21 volunteers who were given approximately 1 litre of glucose 2.5 or 5% or Ringer's solution (control) over 45 min. The maximum haemodilution was similar for all three fluids, but it decreased more rapidly when glucose had been infused. The volume of distribution for the infused glucose molecules was larger (approximately 12 litres) than for the infused fluid, which amounted to (mean (SEM)) 3.7 (0.3) (glucose 2.5%), 2.8 (0.2) (glucose 5%), and 2.5 (0.2) litres (Ringer). Fluid accumulated in a remote (cellular) body fluid space when glucose had been administered (approximately 0.2 and 0.4 litres, respectively), while expansion of an intermediate fluid space (7.1 (1.3) litres) could be demonstrated in 33% of the Ringer experiments. In conclusion, kinetic models were developed which consider the relationship between the glucose metabolism and the disposition of intravenous fluid. One of them, in which infused fluid expands two instead of three body fluid spaces, was successfully fitted to data on blood glucose and blood haemoglobin obtained during infusions of 2.5 and 5% glucose.

Studies on prolonged acute regional ischemia. III. Early natural history of simulated single and multivessel disease with emphasis on remote myocardium

The early natural history of left anterior descending coronary artery occlusion was studied in 35 open-chest anesthetized dogs observed for 6 hours. Six control dogs underwent isolation of the left anterior descending without occlusion, 13 underwent isolated occlusion of the artery to simulate single-vessel disease, and 14 underwent occlusion of the left anterior descending and 50% stenosis of the circumflex coronary artery to simulate multivessel disease. Regional systolic shortening was measured by ultrasonic crystals. Control dogs had a mild fall in cardiac output (27%) and rise in aortic pressure (15 mm Hg). Ischemia produced immediate dyskinesia (-60% of control systolic shortening), and passive lengthening persisted for 6 hours. All dogs with only occlusion of the left anterior descending artery survived (0% mortality). They were less prone to ventricular fibrillation (46% versus 79%, p less than 0.05), developed compensatory hypercontractility of remote muscle (131% of control systolic shortening, p less than 0.05), mild energy and substrate depletion, and anaerobic metabolism (increased glucose-6-phosphate, p less than 0.05) despite maintenance of "normal" blood flow. In contrast, the early mortality rate was 57% (p less than 0.05) when 50% circumflex stenosis coexisted. Intractable ventricular fibrillation and/or cardiogenic shock caused the deaths. Remote muscle became progressively hypocontractile (61% of control systolic shortening, p less than 0.05), with progressive reduction in stroke work index (less than 0.5 gm-m/kg, p less than 0.05). Remote muscle showed moderate substrate and energy depletion (greater than 60% fall of adenosine triphosphate and creatine phosphate, 37% fall of glutamate) and more pronounced evidence of anaerobic metabolism (glucose-6-phosphate rose greater than 400%, p less than 0.05) despite normal blood flow. Mitochondrial ultrastructure and function remained intact in all hearts. These findings suggest that remote muscle is the principal determinant of mortality after an otherwise nonlethal ischemic event. Functional deterioration despite normal blood flow to remote muscle suggests either autoregulatory failure or substrate depletion as a cause of hypocontractility. The structural and functional integrity of mitochondria in ischemic and remote myocardium implies that salvage is possible despite hemodynamic deterioration and intractable ventricular fibrillation.

Studies on prolonged acute regional ischemia. II. Implications of progression from dyskinesia to akinesia in the ischemic segment

This study analyzed the pattern of regional wall motion in 58 dogs undergoing 4 to 6 hours of left anterior descending coronary artery occlusion. Regional wall motion was measured by ultrasonic crystals and ischemic muscle either remained dyskinetic (-40% of control systolic shortening, n = 26) or progressed toward akinesia (less than 20% of control systolic shortening or greater than 50% reduction in passive lengthening, n = 32). Ten dogs underwent unmodified blood reperfusion. Regional blood flow (radioactive microspheres), histochemical damage (triphenyltetrazolium chloride staining), and mitochondrial function were determined. Hearts showing persistent dyskinesia had more collateral flow (12 versus 2 ml/100 gm/min, p less than 0.05), less histochemical damage (26% versus 63% area at risk/area of nonstaining, p less than 0.05), and better retention of mitochondrial oxidative phosphorylation capacity (adenosine triphosphate, 622 versus 444 nmol/mg protein/min, p less than 0.05), and tended toward mitochondrial calcium accumulation (48 versus 64 nmol/mg protein). Unmodified blood reperfusion after 4 hours of ischemia produced prompt akinesia (-2% +/- 3% systolic shortening) and was associated with increased edema (82% water content), caused the low-reflow phenomenon (19% control subendocardial flow, 13 ml/100 gm/min), and increased histochemical damage (69% triphenyltetrazolium chloride nonstaining, p less than 0.05). These findings suggest that persistent dyskinesia during early ischemia (first 6 hours) may reflect a relatively optimistic sign, as regression to akinesia occurs in muscle with less collateral flow, more impaired mitochondrial function, worsened calcium homeostasis, and more severe histochemical and ultrastructural damage. These observations imply that careful evaluation of ischemic wall motion may provide a valuable insight into potential muscle salvage.

Studies on prolonged acute regional ischemia. I. Evidence for preserved cellular viability after 6 hours of coronary occlusion

Six hours of coronary occlusion has been thought to produce extensive and irreversible transmural damage and no possibility of salvage by reperfusion. This has been based on findings of adenosine triphosphate depletion and histochemical (triphenyltetrazolium chloride nonstaining) and ultrastructural changes (conventional preparatory techniques). This study tests the hypothesis that, in contrast to conventional wisdom, considerable structural and mitochondrial functional integrity remains in cardiac muscle subjected to 6 hours of regional ischemia. Twenty open-chest anesthetized dogs underwent isolation of the left anterior descending coronary artery and were observed for 6 hours. Eight of the 20 did not undergo ischemia and served as controls. Twelve underwent 6 hours of proximal ligation of the left anterior descending coronary artery (30% +/- 2% area at risk). Transmural biopsy specimens were analyzed. Coronary occlusion reduced regional blood flow (radioactive microspheres) to less than 10 ml/100 gm/min (p less than 0.05) and dyskinesia persisted in the area at risk for 6 hours. High-energy phosphates (adenosine triphosphate and creatine phosphate) declined to negligible levels and histochemical damage occurred (49% +/- 12% triphenyltetrazolium chloride non-staining). Mitochondrial ultrastructural changes (low protein denaturation embedding technique) were mild (the integrity of the inner and outer mitochondrial surface membranes and crystal membranes was maintained and myofibrillar degeneration did not occur). Mitochondrial oxidative phosphorylation rate remained at 63% of control levels, respiratory control index remained at 77%, and adenosine diphosphate/oxygen ratio was maintained at 96%. Mitochondrial Ca++ increased with lanthanum (from 26 to 46 nmol/mg protein, p less than 0.05), but irreversible calcium precipitation did not occur; calcium could be mobilized to normal levels (i.e., 13 nmol/mg protein) by ethylenediaminetetraacetic acid chelation. These data support our inference that necrosis does not occur after 6 hours of coronary occlusion and suggest that muscle salvage by reperfusion is possible after at least 6 hours of regional myocardial ischemia.

Cardiogenic shock after acute coronary occlusion. Pathogenesis, early diagnosis, and treatment

The early natural history of left anterior descending coronary artery (LAD) occlusion and the development of cardiogenic shock was studied in 35 open chest anesthetized dogs observed for 6 hours. Six control dogs underwent LAD isolation without occlusion, 13 underwent isolated LAD occlusion to simulate single vessel disease, and 14 underwent LAD occlusion and a 50% left circumflex coronary artery (LCA) stenosis to stimulate multi-vessel disease. Control dogs undergoing anesthesia showed no significant changes in hemodynamics after 6 hours. All dogs with single vessel disease survived and developed immediate and persistent dyskinesis of the anterior wall, a compensatory hypercontractility of remote muscle (131% of control)*, slight energy and substrate depletion and anaerobic metabolism (increased G6P)* despite maintenance of "normal" blood flow through the LCA. In contrast, early mortality was 57% in simulated multi-vessel disease as intractable ventricular fibrillation and/or cardiogenic shock caused the deaths of 7 of 13 dogs (57%)*. Remote muscle became progressively hypocontractile (61% of control)* and caused progressive reduction in stroke work index (less than or equal to 0.5 g x m/kg)*. Remote muscle showed moderate substrate and energy depletion (greater than or equal to 60% fall of ATP and CP, 37% fall of glutamate)* and more pronounced evidence of anaerobic metabolism (G6P rose 373%)* despite "normal" blood flow. These findings suggest that remote muscle is the principle determinant of mortality after an otherwise non-lethal cardiac event.(ABSTRACT TRUNCATED AT 250 WORDS)