Radioimmunoassayable plasma vasopressin associated with surgery

Copeptin's role in traumatic brain injury: The promising quest for a new biomarker

OBJECTIVE

Traumatic brain injury (TBI) necessitates reliable biomarkers to improve patient care. This study explored copeptin as a potential biomarker in TBI and its relation to vasopressin (ADH) in such patients.

METHODS

A cross-sectional study was conducted on 50 TBI patients. Exclusion criteria included specific medical conditions and recent traumatic events. Copeptin and ADH testing were performed within 30 days post-trauma. Patient data, Glasgow Coma Scale (GCS) scores, imaging results, and the need for surgical intervention were obtained from medical charts.

RESULTS

Copeptin levels negatively correlated with GCS scores (ρ = - 0.313, p = 0.027), indicating a potential association with trauma severity. Copeptin levels (mean: 3.22 pmol/L, median 2.027 pmol/L, SD = 3.15) tended to be lower than those found in the normal population, suggesting possible neuroendocrine dysfunction post-TBI. ADH levels (mean: 67.93 pmol/L, median 56.474 pmol/L SD = 47.67) were higher than the normal range and associated with the need for surgery (p = 0.048). Surprisingly, copeptin and ADH levels negatively correlated (r = - 0.491; p < 0.001), potentially due to differences in degradation processes and physiological variations in TBI patients.

CONCLUSION

Copeptin shows potential as a predictive biomarker for assessing TBI severity and predicting patient outcome. However, its complex relationship with ADH in TBI requires further investigation. Careful interpretation is needed due to potential variations in excretion dynamics and metabolism. Larger studies on TBI patient cohorts are essential to validate copeptin as a reliable biomarker and improve patient care in TBI.

Very elevated serum copeptin concentrations occur in a subset of healthy children in the minutes after phlebotomy

OBJECTIVES

Although AVP and its surrogate, copeptin, are mainly regulated by osmotic and volume stimuli, their secretion is also elicited by stress and growth hormone (GH) stimulating agents. The aim of this report is to describe unusual patterns of copeptin response in a subset of children undergoing GH stimulation tests (GH-ST).

METHODS

We conducted a secondary analysis of a cohort of 93 healthy short children with no polydipsia, polyuria or fluid/electrolyte abnormalities, undergoing GH-ST with intravenous arginine, insulin, oral clonidine, or L-Dopa/carbidopa in various combinations. Serum copeptin concentrations were measured 1-3 min after phlebotomy (0 min) and at 60, 90, 120 min during GH-ST.

RESULTS

In 85 subjects (normal response group, NRG) serum copeptin concentrations increased from a 0 min median of 9 pmol/L (IQR 6, 11.5) (all values ≤21) to a median peak between 60 and 120 min of 22 (IQR15, 38) pmol/L, which varied depending on the stimulating agent. Conversely, in the eight outliers, copeptin concentrations decreased gradually from a median of 154 (IQR 61, 439) pmol/L (all ≥40 pmol/L) to values as low as 14 % of the basal value, by 120 min. Test-associated anxiety was described in 17 subjects in the NRG (20 %) and five of the outliers (63 %).

CONCLUSIONS

A distinctive pattern of very elevated serum copeptin concentrations occurred in 9 % of children undergoing GH-ST, similar to reports in previous pediatric studies. Etiology may include pain or stress of phlebotomy. This phenomenon should be recognized for proper interpretation of copeptin values in children.

Postoperative dysnatremia in infants after open-heart surgery occurs frequently and is associated with prolonged intensive care length of stay

BACKGROUND

Dysnatremia after surgery for congenital heart disease (CHD) is well known and has been associated with prolonged pediatric intensive care unit length of stay (PICU-LOS). Fluctuations in plasma sodium levels occur perioperatively. The primary aim of the study was to evaluate the occurrence of dysnatremia during the first 48 h after surgery and whether it was associated with PICU-LOS. The secondary aim was to evaluate if the degree of sodium fluctuations was associated with PICU-LOS.

METHODS

A retrospective observational, single-center study including infants undergoing surgery for CHD. The highest and lowest plasma sodium value was registered for the prespecified time periods. PICU-LOS was analyzed in relation to the occurrence of dysnatremia and the degree of plasma sodium fluctuations. The occurrence of dysnatremia was evaluated in relation to surgical procedure and fluid administration.

RESULTS

Two hundred and thirty infants who underwent 249 surgical procedures were included. Dysnatremia developed in more than 60% within 48 h after surgery. Infants with normonatremia had a 40%-50% shorter PICU-LOS among children in RACHS-1 category 3-6, compared with infants developing either hypo- or hyper-/hyponatremia within 48 h after surgery (p = .006). Infants who had a decline of plasma sodium >11 mmol/L had almost double the PICU-LOS compared to those with a decline of <8 mmol/L.

CONCLUSION

Dysnatremias were common after surgery for CHD and associated with prolonged PICU-LOS. The degree of decline in plasma sodium was significantly associated with PICU-LOS. Fluid administration both in terms of volume and components (blood products and crystalloids) as well as diuresis were related to the occurrence of dysnatremias.

Sodium Abnormalities in Cardiac Surgery With Cardiopulmonary Bypass in Adults: A Narrative Review

Perioperative sodium abnormalities or dysnatremia is not uncommon in patients presenting for cardiac surgery and is associated with increased morbidity and mortality. Both the disease process of heart failure and its treatment may contribute to abnormalities in serum sodium concentration. Serum sodium is the main determinant of serum osmolality, which in turn affects cell volume. Brain cells are particularly vulnerable to changes in serum osmolality because of the nondistensible cranium. The potentially catastrophic neurologic sequelae of rapidly correcting chronic dysnatremia and the time-sensitive nature of cardiac surgery can make the management of these patients challenging. The use of cardiopulmonary bypass to facilitate surgery adds another layer of complexity in the intraoperative management of sodium and water balance. This narrative review examines the definition and classification of dysnatremia. It also covers the etiology and pathophysiology of dysnatremia, implications during cardiac surgery requiring cardiopulmonary bypass, and the perioperative management of dysnatremia.

Hormonal concentrations in bitches with primary uterine inertia

Normal labor is accompanied by sequential changes in blood concentrations of prostaglandin F2alpha (measured as 15-ketodihydro-PGF2 alpha=PGFM), progesterone, estradiol, oxytocin, vasopressin, and of elevated cortisol levels. The aim of this study was to investigate hormone concentrations in dogs diagnosed with primary uterine inertia before and during treatment by cesarean section. The hypothesis was the dogs would have abnormally low plasma concentrations in one or several of the hormones involved in parturition. The study comprised seven bitches with total primary uterine inertia (dystocia group) treated with cesarean section and six healthy bitches (control group) subjected to planned cesarean section. Blood samples were taken before anesthesia, before surgery started, on delivery of the first puppy and on delivery of the last puppy. The progesterone:PGFM ratio in plasma was higher in the dystocia group than in the control group, but the serum estradiol concentration did not differ between groups. The plasma concentrations of oxytocin and vasopressin increased in both groups when the first puppies were delivered, but both hormones were more elevated in the control group than in the dystocia group on delivery of the last puppies. The plasma cortisol concentration increased to the same level in both groups. In conclusion, the ratio between progesterone and PGFM was higher and the oxytocin and vasopressin concentrations lower in the dystocia dogs than in the control dogs. The findings indicate that these hormones are involved in the pathophysiology of total primary uterine inertia in bitches.

How acute is the acute stress response? Baseline corticosterone and corticosteroid-binding globulin levels change 24h after an acute stressor in Japanese quail

Changes in plasma corticosteroid-binding globulin (CBG) capacity can alter free plasma concentration and tissue availability of glucocorticoids (GC) and hence alter the organismal response to stress. However, CBG change in response to stress has not been extensively studied. While it is clear that chronic stress can causes CBG decline and in some species acute stressors can reduce CBG during the 30-60 min of the stressor, more long-term changes in CBG following an acute stressor has received less attention. Here we investigated corticosterone (CORT: the primary GC in birds) and CBG levels 24h after an acute stressor in a unique study system: Japanese quail divergently selected for CORT reactivity to acute stress. Using this model, we examined the interaction of selected CORT reactivity with CBG response to determine if CBG shows a delayed decline in response to an acute stressor and if that decline varies by selected genetic background. We found lowered CBG capacity, elevated total CORT and free CORT 24h after acute stress in all three quail groups. These results demonstrate for the first time in an avian species that exposure to an acute stressor can affect CBG and CORT 24h later.

Postoperative vasopressin and copeptin levels in noncardiac surgery patients: a prospective controlled trial

Further information on the endogenous arginine vasopressin (AVP) response in patients with postoperative systemic inflammatory response syndrome (SIRS) and vasodilatory shock would provide more insight into the pathophysiology of SIRS-associated cardiovascular failure and help indicate AVP therapy. Patients after uncomplicated abdominal surgery without SIRS (n = 10), critically ill patients after noncardiac surgery with SIRS (n = 9), and patients with SIRS plus vasodilatory shock (n = 22) were included in this prospective trial. Plasma AVP (radioimmunoassay) and copeptin (immunoluminometric assay) concentrations together with clinical parameters were documented daily during the first 7 days postoperative. The AVP response significantly differed between the three groups. Patients without SIRS had lower AVP concentrations than SIRS patients with (P = 0.001) or without shock (P = 0.003). Patients with SIRS and shock had higher AVP levels than patients with SIRS alone (P < 0.001). Arginine vasopressin decreased over time (P = 0.007) in all groups. At day 28, nonsurvivors had higher AVP levels than did survivors (P < 0.001). In SIRS patients without shock, serum osmolarity was indirectly associated with AVP levels, whereas mean arterial blood pressure and serum osmolarity were associated with AVP in SIRS patients with shock. Arginine vasopressin and copeptin correlated significantly with each other (P < 0.001; r = 0.76). In patients without hemofiltration, copeptin levels predicted 28-day mortality with high sensitivity and specificity. The postoperative AVP response in noncardiac surgery patients seems well maintained. The possibility that AVP plays a contributory role in the failure to restore vascular tone in patients with vasodilatory shock cannot be excluded but seems less important than in septic or postcardiotomy shock.

Hyponatremia as a complication of cardiac catheterization: a prospective study

BACKGROUND

A decrease in plasma sodium (P(Na)) concentration is common after surgery and attributed to the secretion of antidiuretic hormone in response to such nonosmotic stimuli as pain or nausea. In this setting, acute hyponatremia may lead to seizures, coma, and permanent neurological damage. Sporadic case reports have described severe neurological symptoms caused by hyponatremia occurring within hours after cardiac catheterization. We evaluated the prevalence, contributing clinical circumstances, and course of hyponatremia in patients undergoing cardiac catheterization.

METHODS

We prospectively studied 309 consecutive patients scheduled for an elective cardiac catheterization. Plasma and urine electrolytes and urine osmolarity were measured at baseline and again 1 to 4 hours and 24 hours after the procedure.

RESULTS

P(Na) level was 139.4 +/- 2.3 mEq/L at baseline. At 1 to 4 hours, P(Na) level decreased to 134.2 +/- 3.6 mEq/L (P < 0.0001). Mild (> or =5 to 10 mEq/L), moderate (11 to 14 mEq/L), and severe (> or =15 mEq/L) reductions in P(Na) levels occurred in 50%, 5%, and 0.3% of patients, respectively. At the 24-hour point, P(Na) level increased to 137.3 +/- 2.4 mEq/L, but was significantly lower compared with baseline (P < 0.0001). In hyponatremic patients at the 1- to 4- and 24-hour points, mean urine osmolarity values were 428 +/- 139 and 420 +/- 204 mOsm/kg, respectively; almost every urine sample was inappropriately concentrated. Multivariate logistic regression identified the amount of electrolyte-free water administered to be a predictor for the development of hyponatremia (3.7-fold incremental risk for every 1 L administered to a 70-kg patient).

CONCLUSION

An acute reduction in P(Na) level commonly occurs shortly after cardiac catheterization. The cause of hyponatremia appears to be related to the administration of hypotonic fluids, together with impaired urinary dilutional capacity. Although symptomatic hyponatremia is rare, the diagnosis should be entertained when neurological symptoms develop in this setting.

Effects of acetylpromazine or morphine on urine production in halothane-anesthetized dogs

OBJECTIVE

To assess the influence of preanesthetic administration of acetylpromazine or morphine and fluids on urine production, arginine vasopressin (AVP; previously known as antidiuretic hormone) concentrations, mean arterial blood pressure (MAP), plasma osmolality (Osm), PCV, and concentration of total solids (TS) during anesthesia and surgery in dogs.

ANIMALS

19 adult dogs.

PROCEDURE

Concentration of AVP, indirect MAP, Osm, PCV, and concentration of TS were measured at 5 time points (before administration of acetylpromazine or morphine, after administration of those drugs, after induction of anesthesia, 1 hour after the start of surgery, and 2 hours after the start of surgery). Urine output and end-tidal halothane concentrations were measured 1 and 2 hours after the start of surgery. All dogs were administered lactated Ringer's solution (20 ml/kg of body weight/h, i.v.) during surgery.

RESULTS

Compared with values for acetylpromazine, preoperative administration of morphine resulted in significantly lower urine output during the surgical period. Groups did not differ significantly for AVP concentration, Osm, MAP, and end-tidal halothane concentration; however, PCV and concentration of TS decreased over time in both groups and were lower in dogs given acetylpromazine.

CONCLUSIONS AND CLINICAL RELEVANCE

Preanesthetic administration of morphine resulted in significantly lower urine output, compared with values after administration of acetylpromazine, which cannot be explained by differences in AVP concentration or MAP When urine output is used as a guide for determining rate for i.v. administration of fluids in the perioperative period, the type of preanesthetic agent used must be considered.

Effects of anesthesia, surgery, and intravenous administration of fluids on plasma antidiuretic hormone concentrations in healthy dogs

OBJECTIVE

To evaluate effects of anesthesia, surgery, and intravenous administration of fluids on plasma concentrations of antidiuretic hormone (ADH), concentration of total solids (TS), PCV, arterial blood pressure (BP), plasma osmolality, and urine output in healthy dogs.

ANIMALS

22 healthy Beagles.

PROCEDURE

11 dogs did not receive fluids, and 11 received 20 ml of lactated Ringer's solution/kg of body weight/h. Plasma ADH adn TS concentrations, PCV, osmolality, and arterial BP were measured before anesthesia (T0) and after administration of preanesthetic agents (T1), induction of anesthesia (T2), and 1 and 2 hours of surgery (T3 and T4, respectively). Urine output was measured at T3 and T4.

RESULTS

ADH concentrations increased at T1, T3, and T4, compared with concentrations at T0. Concentration of TS and PCV decreased at all times after administration of preanesthetic drugs. Plasma ADH concentration was less at T3 in dogs that received fluids, compared with those that did not. Blood pressure did not differ between groups, and osmolality did not increase > 1% from To value at any time. At T4, rate of urine production was less in dogs that did not receive fluids, compared with those that did.

CONCLUSIONS AND CLINICAL RELEVANCE

Plasma ADH concentration increased and PCV and TS concentration decreased in response to anesthesia and surgery. Intravenous administration of fluids resulted in increased urine output but had no effect on ADH concentration or arterial BP. The causes and effects of increased plasma ADH concentrations may affect efficacious administration of fluids during the perioperative period in dogs.

The effects of intrinsic vasopressin on urinary aquaporin-2 excretion and urine osmolality during surgery under general anesthesia

A radioimmunoassay has been established to measure urinary aquaporin-2 excretion (u-AQP2). To elucidate how u-AQP2 changes when endogenous vasopressin is increased independently of plasma osmolality, we estimated u-AQP2 during general anesthesia for surgery. We collected urine and blood samples from 50 patients before and 90 and 180 min after anesthetic induction. Plasma (29.1+/-12.6 pg/mL) and urinary (565.1+/-207.0 ng/gCr) vasopressin levels were markedly increased after anesthetic induction. Although no significant alteration of plasma osmolality or serum sodium concentration was observed during 180 min, u-AQP2 was significantly increased (preinduction 224.5+/-24.2 fmol/ mgCr; 90 min 243.3+/-31.8; 180 min 331.4+/-45.9), paralleling an increase of plasma and urinary vasopressin. The plasma vasopressin concentration after anesthetic induction was far in excess of that expected based on plasma osmolality. Individual plasma and urinary vasopressin concentrations correlated significantly with u-AQP2. At 180 min after anesthesia, plasma osmolality did not change, but urine osmolality decreased despite increased u-AQP2, and a preanesthetic positive correlation between urine osmolality and u-AQP2 disappeared. Thus, although u-AQP2 correlates with increased intrinsic vasopressin levels, the increase in u-AQP2 did not directly contribute to urine concentration. Apparently, an escape from the physiologic effects of high vasopressin level occurs during anesthesia via a mechanism independent of aquaporin-2. We conclude that the anesthetic would interfere with the urinary concentrating capacity at the level of AQP2-action.

IMPLICATIONS

The excessive increase of intrinsic vasopressin exactly augmented urinary aquaporin-2 excretion, resulting in urine concentration; however, anesthesia seemed to modify this process possibly by interfering with the aquaporin-2 action.

Projections from the ventrolateral periaqueductal gray to endocrine regulatory subdivisions of the paraventricular nucleus of the hypothalamus in the rat

The ventrolateral periaqueductal gray (vlPAG) mediates quiescence, hyporeactivity, hypotension and bradycardia, a pattern of response evoked by injury or social defeat. These stimuli also evoke increased levels of vasopressin (VP) and adrenocorticotrophic hormone (ACTH). A key central nervous system (CNS) locus mediating endocrine changes is the paraventricular nucleus of the hypothalamus (PVH). We investigated the extent of vlPAG projections to PVH. Anterograde tracer injections into the vlPAG, revealed 'terminal' label in: (1) the medial, dorsal, anterior and lateral parvicellular divisions, and (2) lateral and medial posterior magnocellular divisions of the PVH. Deposits of the retrograde tracer Fast Blue, verified the projection to the PVH arising from the vlPAG.

The plasma ACTH, AVP, CRH and catecholamine responses to conventional and laparoscopic cholecystectomy

OBJECTIVES

We compared the responses of the stress hormones, cortisol, ACTH, vasopressin (AVP), corticotrophin releasing hormone (CRH) and catecholamines to elective conventional and laparoscopic cholecystectomy.

DESIGN

A right upper quadrant transverse incision was used for conventional cholecystectomy, and four 1-2-cm incisions for the laparoscopic procedure (for insertion of surgical instruments, diathermy, fibreoptic telescope and light source, and carbon dioxide insufflation). Blood was sampled immediately prior to premedication (temazepam), after induction of anaesthesia (fentanyl and thiopentone) and at 10-minute intervals until the end of the procedure (N2O maintenance, vecuronium relaxation). A blood sample was taken after reversal, and then at 10-minute intervals for 50 minutes. Plasma sodium and blood pressure were measured at similar intervals. Results are expressed as mean +/- standard error.

PATIENTS

Twelve patients were studied (six in each group).

MEASUREMENTS

Peptide hormones were measured by radioimmunoassay, cortisol by ELISA and catecholamines by HPLC.

RESULTS

The mean premedication hormone values for the conventional and laparoscopic procedures did not increase significantly after induction of anaesthesia. Within 10 minutes of the first incision, however, there was a marked concordant rise in mean plasma ACTH and AVP levels for both procedures (conventional: ACTH, from a premedication value of 10.2 +/- 1.7 to 80.1 +/- 14.3 pmol/l, AVP from 1.2 +/- 0.4 to 117 +/- 24 pmol/l, P < 0.01 for both hormones; laparoscopic: ACTH from 5.8 +/- 2.6 to 55.1 +/- 26.0 pmol/l, AVP from 1.6 +/- 0.11 to 49.2 +/- 27.09 pmol/l). At the end of both types of operation mean levels of ACTH and AVP were still elevated, although the ACTH: AVP ratio had increased. Greater variability in ACTH and AVP responses was seen in the laparoscopic than in the conventional procedure, three patients showing a relatively small response to surgery. Total secretion of ACTH during both types of surgery was not significantly less both during (P < 0.05), and after (P < 0.01) laparoscopic surgery. For both procedures, the timing of AVP and ACTH peaks was significantly related (P < 0.002). A small but significant rise in CRH was observed 30 minutes after the start of surgery for both procedures P < 0.05). The timing of CRH and ACTH peaks was unrelated. The maximum mean plasma cortisol level for the conventional procedure (1268 +/- 147 nmol/l) was reached 20 minutes after reversal of anaesthesia and remained at this level until the end of sampling. The cortisol response was comparable during the laparoscopic procedure but was beginning to fall at 60 minutes post-operatively. Plasma adrenaline responses to the two types of surgery were not significantly different, but the plasma total noradrenaline response to laparoscopic surgery as indicated by the response area during the first 20 minutes was significantly increased (P < 0.02). Plasma sodium, renin activity and initial systolic blood pressure fall were not significantly different during the two procedures.

CONCLUSIONS

For both procedures, the peak of ACTH secretion after incision is likely to be AVP dependent, and the timing of peak levels of these two hormones was significantly related. Subsequent ACTH secretion may be the result of an interaction between AVP and CRH. Laparoscopic cholecystectomy results in a smaller AVP rise than does the conventional procedure, and plasma AVP falls more rapidly post-operatively. During the period of observation, ACTH, CRH, cortisol and adrenaline responses were not significantly lessened by the laparoscopic approach, but there was a significant increase in the noradrenaline response. Stress hormone monitoring may assist further improvements in surgical technique.

Postoperative decline in plasma aspirin-esterase and cholinesterase activity in surgical patients

We studied preoperative and postoperative plasma hydrolysis of aspirin and plasma cholinesterase activity in surgical patients. Postoperative aspirin esterase and cholinesterase activities fell sharply (119 +/- 32 micrograms ml h-1 and 3746 +/- 1068 U l-1 respectively; P < 0.01) in comparison to basal preoperative values (157 +/- 33 micrograms ml h-1 and 4620 +/- 940 U l-1 respectively, P < 0.01). We suggest that alterations in plasma esterase during the postoperative period may be related to the metabolic response to anesthesia- and surgery-induced stress.

Fluid and ion redistribution in skeletal muscle in an animal sepsis model

The redistribution of fluid and electrolytes was investigated in a hyperdynamic sepsis animal model using cecal ligation and puncture (CLP) in Wistar rats. Hyponatremia was not observed. There was a significant shift of sodium, chloride, and water from the extracellular into the intracellular space as early as 12 hours following CLP. These data suggest that the mechanism by which hyponatremia occurs in clinical sepsis is not caused by shift of fluid from the intracellular to the extracellular space as proposed by the sick cell theory. This is more likely to result from fluid retention and dilution of the extracellular space possibly on the basis of antidiuretic hormone secretion.

Does the stress of admission to an intensive care unit influence arginine vasopressin secretion and renal diluting ability?

The pathogenesis of excessive arginine vasopressin (AVP) release and hyponatraemia in euvolaemic intensive care unit (ICU) patients is poorly understood. Stress has frequently been proposed as a possible determinant, but its actual responsibility has not been adequately assessed. Therefore, water-load tests were prospectively performed in 11 patients admitted to the ICU for severe or potentially severe diseases, but who had no other condition which could result in excessive AVP release or impairment of renal diluting ability. Renal diluting ability was normal in 9 patients. Two patients exhibited very slight defects, which might be the consequence of subclinical haemodynamic alterations, since one had a pulmonary embolism and the other manifested a gastrointestinal haemorrhage just after the completion of the water load. Nevertheless, plasma AVP levels decreased in response to the water load in all the patients, resulting in a significant decrease in mean values. Plasma norepinephrine values were found to be elevated both before and after water loading. A highly significant correlation existed between the levels of norepinephrine and those of AVP measured before the load, but was lost after it. In addition, norepinephrine values were markedly elevated in two patients who exhibited strictly normal renal diluting abilities, and no correlation was found between plasma norepinephrine values and any parameter of renal water excretion. Our study shows that the stress of a serious illness and of admission to an ICU does not seem to interfere, by itself, with osmotic regulation of AVP secretion and renal diluting ability, and that sympathetic activation is not, under such circumstances, a predominant stimulus for AVP release.(ABSTRACT TRUNCATED AT 250 WORDS)

Antidiuretic hormone following surgery in children

We studied 13 children subjected to elective tonsillectomy, 6 of whom (study patients) received supplemental intravenous isotonic saline during and after operation, and 7 of whom (controls) did not. Clinical and biochemical evidence of hypovolaemia was present in the control but not in the study patients. Plasma antidiuretic hormone (ADH) and urine osmolality were higher in controls (p less than 0.005 and p less than 0.05 respectively). Plasma sodium concentration and osmolality were similar in the two groups. We conclude that hypovolaemia is the principal stimulus to ADH release following surgery and that, in addition to replacement of observed losses of blood and other fluids by fluids of appropriate composition, hypovolaemia should be prevented by the administration of maintenance quantities of isotonic fluid, rather than exacerbated by fluid restriction, in patients in whom oral fluid intake is interrupted for more than a brief period. Hypotonic and sodium free fluids should be avoided because of the risk of hyponatraemia.

The effect of moderate hypotension on vasopressin levels in normal humans

Isosmotic decreases in central venous pressure do not stimulate arginine vasopressin (AVP) secretion in normal humans, while symptomatic vasovagal hypotension produces large rises in plasma AVP levels. The effects of an asymptomatic fall in arterial pressure on plasma AVP in humans are poorly documented. Heart rate, mean arterial pressure, plasma osmolality, and plasma AVP were measured in seven healthy volunteers during infusion of sodium nitroprusside on two occasions, with and without central venous pressure measurements. On both study days, heart rate increases (5 +/- 3 and 8 +/- 4 beats/min) and mean arterial pressure reductions (12 +/- 3 and 13 +/- 2.0 mm Hg) were comparable. Plasma AVP (3.2 +/- 1.4 and 4.0 +/- 1.7 pg/ml at control) did not change on either study day after nitroprusside titration (30-40 minutes) or after an additional 90 minute observation on the first day. When measured on the second day, central venous pressure declined from 5.6 +/- 1.9 to 2.9 +/- 1.5 mm Hg, p less than .001. Osmolality was constant on both days at all times. Unloading of sinoaortic baroreceptors produced by asymptomatic hypotension, coupled with a moderate reduction in central venous pressure, does not, therefore, stimulate plasma AVP secretion in normal humans. This observation has relevance to understanding the mechanisms involved in the reported increases in plasma AVP during orthostatic stress and in various diseases.

Plasma arginine vasopressin levels and arterial pressure during open heart surgery

A study of plasma arginine vasopressin (AVP) levels and their relation to changes in arterial pressure was undertaken in 13 patients undergoing open heart surgery. Seven of the patients received high doses of intravenous morphine (1 or 2 mg/kg) as part of their anaesthetic, whereas the other six did not. Increases in the AVP levels during cardiopulmonary bypass (CPB) were significant in both groups, but were significantly greater in the patients not receiving morphine (median 86.1 fmol/ml) than in those who did (47.5 fmol/ml). In both groups there was a linear correlation between the natural logarithm of the plasma AVP level and the percentage fall in the mean arterial pressure, although the slope of the relationship was significantly less in the group receiving morphine than in the group not receiving morphine. These results indicate that in patients undergoing cardiac surgery the neuroendocrine reflex control of plasma AVP levels in relation to changes in arterial pressure is intact, but that the sensitivity of the reflex (i.e. the increase in plasma AVP level for a given fall in arterial pressure) is reduced by the administration of high doses of intravenous morphine.

The neuroendocrinology of physical injury

Physical injury of any sort--accidental injury, burns or elective surgery--provokes an immediate neuroendocrine response. Neural input arising from the cerebral cortex, damaged tissues and receptors detecting fluid loss leads to increased secretion of ACTH, growth hormone, prolactin and vasopressin from the pituitary, and to a general activation of the sympathetic nervous system, with rises in adrenaline and noradrenaline concentrations. Secondary changes include stimulation of cortisol and aldosterone and inhibition of insulin and somatomedin secretion. The glucagon concentration and plasma renin activity may also be increased, either immediately or after a delay. The duration of these responses generally depends upon the severity of the injury and differs considerably between hormones, for reasons that are not understood. The only endocrine changes consistently seen at later times after trauma are an increase in insulin secretion, which supersedes the initial suppression, and decreases in the concentrations of T3 and gonadal steroids. Some of the changes in steroid, thyroid and pancreatic hormones differ temporally or even qualitatively from those of their usual stimuli and are unexplained. The initial neuroendocrine response to injury can be construed as playing a defensive role, but the function of the later changes is not understood; it seems likely that they are adaptive in nature, but the scope for therapeutic intervention remains unclear.

Stimulus for vasopressin release during elective intra-abdominal operations

In 12 patients undergoing an upper abdominal operation, blood pressure and peripheral venous blood samples were taken at intervals throughout the procedure. There was no significant increase in plasma vasopressin concentration after induction of anaesthesia or skin incision; within 3 min of opening the peritoneum and commencing intraperitoneal manipulation there was a highly significant rise (P less than 0.01), maintained with fluctuations until closure of the abdomen. There was no correlation between the changes of blood pressure and those in plasma vasopressin level. In 16 patients undergoing elective cholecystectomy similar observations were made to coincide with events believed, on the basis of the first study, to be related to changes in the concentration of vasopressin. There was a significant rise in vasopressin concentration (P less than 0.01) after incision of the peritoneum, 1 min after the start of intraperitoneal manipulation (P less than 0.01) and after deliberate traction on the stomach (P less than 0.01). During operative cholangiography, when there was no intraperitoneal manipulation, there was a significant fall in the vasopressin level. There was no correlation between changes in vasopressin concentration and blood pressure. These findings indicate that during an abdominal operation nervous stimuli, arising from within the peritoneal cavity and probably mediated via the autonomic system, are an important factor responsible for the increased secretion of vasopressin, and, at least in the absence of major changes in blood pressure and osmolality, the determinant factor.

Fluid balance and secretion of antidiuretic hormone following transsphenoidal pituitary surgery. A preliminary series

Hyponatremia developing some days after transsphenoidal pituitary adenectomy is a treacherous complication of uncertain cause. Of 19 patients monitored in a pilot study at the Wessex Neurological Centre, plasma sodium fell below 125 mmol/liter in three patients at times ranging from 6 to 9 days postoperatively. One patient had evidence of inappropriate secretion of arginine vasopressin (AVP), and the other two probably had steroid insufficiency despite apparently adequate steroid cover. In a more detailed study, the fluid and sodium balance of a further 16 patients was monitored for 7 to 11 days following transsphenoidal surgery together with plasma cortisol, renin, and AVP concentrations. No patient became severely hyponatremic. Three developed partial diabetes insipidus. Two patients with Cushing's disease had evidence of postoperative corticosteroid insufficiency despite normal steroid protection. An inappropriately low plasma cortisol concentration was recorded in both. Plasma AVP concentrations did not show a delayed surge postoperatively. Delayed hyponatremia appears to occur most often in patients with hypoadrenalism, as glucocorticoid cover is decreased. It results from water retention combined with natriuresis, and is reversed by glucocorticoid treatment.

Excessive antidiuretic hormone secretion after radical cystectomy

Perioperative plasma antidiuretic hormone (vasopressin) levels were determined in 8 patients undergoing radical cystectomy. Marked elevations of antidiuretic hormone were noted immediately postoperatively in all patients and these levels persisted for 48 hours. Plasma antidiuretic hormone was elevated beyond the physiological levels needed for maintenance of intravascular volume and osmolarity. Excessive antidiuretic hormone secretion is common after radical cystectomy and should be considered in the differential diagnosis of postoperative oliguria in these patients.

The effect of vasopressin on solute and water excretion during and after surgical operations

The relationship between the concentration of plasma arginine vasopressin (AVP), urine volume, and osmolality during and after an abdominal operation was studied in nine patients. In all patients the AVP level rose well above that necessary for maximal antidiuresis (5 fmol ml-1) and then returned to within the normal range (0.5-5.0 fmol ml-1) usually over the next 24 hours. During this period of raised AVP concentration the urine volume, which varied considerably, was closely related to osmolar excretion. With the fall of AVP to normal levels, all but one of the patients eventually exhibited positive free water clearance. However, in most patients the urine remained hypertonic for some hours and its volume continued to be determined mainly by osmolar load which was itself apparently related to glomerular filtration rate. At no time was there a significant relationship between changes in plasma AVP concentration and urinary volume.

Circulating levels of arginine vasopressin before and during the infusion of the hormone in patients presenting with bleeding oesophageal varices

Circulating levels of antidiuretic hormone (ADH) were measured in patients presenting with bleeding oesophageal varices before and during treatment with arginine vasopressin. There was no significant difference in the circulating levels of ADH before and during treatment with arginine vasopressin in patients in which the hormone successfully controlled haemorrhage and those in which it did not. It is concluded that the failure of vasopressin to control variceal haemorrhage in approximately 40% of patients presenting for treatment cannot be attributed to higher circulating levels of the hormone in these subjects.

Arginine vasopressin release following surgical operations

A study of plasma arginine vasopressin (AVP) concentrations in 16 patients undergoing uncomplicated cholecystectomy was carried out to determine the relative importance of the various stimuli to AVP secretion during and after an operation. Eight of the 16 patients were given a high epidural blockade from T4 and T12 and blood samples were taken before, at frequent intervals during and for two days after operation for determination of plasma AVP and osmolarity; systolic blood pressure was measured each time a blood sample was taken. In the 16 patients there was a 1.8-fold rise of plasma AVP after induction of anaesthesia (from 1.7 pmol/l median basal value to 13.1 pmol/l) and an 8.8-fold rise after skin incision, the highest concentration during operation being 102 pmol/l. There was no significant difference in AVP concentrations, urine volumes or plasma osmolality in the control and epidural groups. Systolic blood pressure fell in all patients during operation by between 14 and 54 per cent, the fall being significantly greater in the epidural group. Notwithstanding the evidence that certain nervous impulses do cause an increased secretion of AVP during operation, these results clearly show that in the absence of such stimuli there is still an increased secretion, almost certainly caused by a fall in the blood pressure.

Clonidine after renal ischemia to lessen acute renal failure and microvascular damage

Clonidine, an antihypertensive drug that inhibits renin release and causes a water diuresis in normal animals, was tested for its ability to reduce the severity of post-ischemic acute renal failure produced in rabbits by clamping the left renal pedicle for 1 hour and removing the opposite kidney. Clonidine significantly lessened renal failure when given during, or 1 hours after, the ischemic insult in dehydrated rabbits. It was also effective when given during the ischemic insult in vasopressin-treated water-drinking rabbits but not in control water-drinking rabbits. In vasopressin-treated rabbits, clonidine lessened renal failure observed 2 days after the ischemic insult despite the fact that in the immediate postischemic period it lowered total renal blood flow, produced hypotension, and did not bring about lower plasma renin levels. Clonidine treatment resulted in less outer medullary microvascular damage (demonstrated by colloidal carbon staining), higher outer medullary blood flow 1 to 2 hours after unclamping, fewer casts, and higher creatinine clearance and free water clearance/creatinine clearance 4 to 6 hours after unclamping compared with controls. The effect of clonidine was unrelated to plasma renin activity. Clonidine did not alter plasma vasopressin concentration. Demeclocycline and lithium, two agents that blunt renal responsiveness to vasopressin, had a beneficial effect in dehydrated animals similar to that of clonidine, but the angiotensin II antagonist saralasin and the angiotensin converting enzyme inhibitor SQ20881 did not. Normal rabbits given a large dose of vasopressin in oil plus clonidine had significantly greater urine output and free water clearance and lower urine osmolality than did rabbits given vasopressin in oil alone. These results suggest that clonidine may be beneficial because it prevents ischemic microvascular injury in the renal outer medulla, an effect that may decrease tubular obstruction by lessening desquamation of damaged tubular cells or cell constituents into the tubular lumen. Clonidine may also decrease formation of obstructive hyaline casts in collecting ducts by blunting the kidney's response to vasopressin and increasing tubular fluid flow rate.

Post-surgical hyponatraemia: the role of intravenous fluids and arginine vasopressin

In 14 patients having undergone abdominal surgery, plasma sodium, urine volume and osmolality and the urinary excretion of arginine vasopressin (AVP), the antidiuretic hormone in man, were measured daily for 7 days. Each patient was given 31 of intravenous fluids daily. In 8 patients the fluid was saline and in the other 6 it was dextrose-saline.

The plasma sodium did not change in the saline group whereas it fell in the dextrose-saline group during the day of operation and then remained low. On the day of operation the urinary AVP increased to very high levels in both groups of patients. On that day and during the postoperative period the AVP level and urine osmolality were much higher in the saline group than in the dextrose-saline group, which suggests that a loss or redistribution of extracellular fluid was not the cause of the high AVP. These results taken together suggest that it was the higher AVP level in the saline group that was required to keep the plasma sodium normal. On the other hand, the results suggest that in the dextrosesaline group, although the AVP was lower than in the saline group, it produced a urine osmolality greater than that necessary for balance so that the patients retained water and became hyponatraemic.

The fall in plasma sodium was small compared with that seen in patients with symptoms of water intoxication, but it may nevertheless have clinical effects and is best avoided. The results suggest that in these patients hyponatraemia can be avoided if saline rather than dextrose-saline is given on the day of operation.