Suprasellar and intraventricular blood predict elevated plasma atrial natriuretic factor in subarachnoid hemorrhage

Perioperative Management of Aneurysmal Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage is an acute neurologic emergency. Prompt definitive treatment of the aneurysm by craniotomy and clipping or endovascular intervention with coils and/or stents is needed to prevent rebleeding. Extracranial manifestations of aneurysmal subarachnoid hemorrhage include cardiac dysfunction, neurogenic pulmonary edema, fluid and electrolyte imbalances, and hyperglycemia. Data on the impact of anesthesia on long-term neurologic outcomes of aneurysmal subarachnoid hemorrhage do not exist. Perioperative management should therefore focus on optimizing systemic physiology, facilitating timely definitive treatment, and selecting an anesthetic technique based on patient characteristics, severity of aneurysmal subarachnoid hemorrhage, and the planned intervention and monitoring. Anesthesiologists should be familiar with evoked potential monitoring, electroencephalographic burst suppression, temporary clipping, management of external ventricular drains, adenosine-induced cardiac standstill, and rapid ventricular pacing to effectively care for these patients.

Atrial natriuretic factor: is it responsible for hyponatremia and natriuresis in neurosurgery?

Objective

To evaluate the presence of hyponatremia and natriuresis and their association with atrial natriuretic factor in neurosurgery patients.

Methods

The study included 30 patients who had been submitted to intracranial tumor resection and cerebral aneurism clipping. Both plasma and urinary sodium and plasma atrial natriuretic factor were measured during the preoperative and postoperative time periods.

Results

Hyponatremia was present in 63.33% of the patients, particularly on the first postoperative day. Natriuresis was present in 93.33% of the patients, particularly on the second postoperative day. Plasma atrial natriuretic factor was increased in 92.60% of the patients in at least one of the postoperative days; however, there was no statistically significant association between the atrial natriuretic factor and plasma sodium and between the atrial natriuretic factor and urinary sodium.

Conclusion

Hyponatremia and natriuresis were present in most patients after neurosurgery; however, the atrial natriuretic factor cannot be considered to be directly responsible for these alterations in neurosurgery patients. Other natriuretic factors are likely to be involved.

A copeptin-based classification of the osmoregulatory defects in the syndrome of inappropriate antidiuresis

The syndrome of inappropriate antidiuretic hormone secretion (SIADH), also referred to as syndrome of inappropriate antidiuresis (SIAD), is the most common cause of hyponatremia characterized by extracellular hypotonicity and impaired urine dilution in the absence of any recognizable nonosmotic stimuli for the antidiuretic hormone arginine vasopressin (AVP). Hyponatremia in SIADH is primarily the result of excessive water retention caused by a combination of inappropriate antidiuresis and persistent fluid intake in the presence of impaired osmoregulated inhibition of thirst. It is sometimes aggravated by a sodium deficiency caused by a decreased intake or a secondary natriuresis in response to elevated extracellular volume. Inappropriate antidiuresis usually results from endogenous production of AVP that can be either ectopic (from a malignancy) or eutopic (from the hypothalamus/neurohypophysis). Regardless of its origin, different types of osmotic dysregulation of AVP have been reported with possibly fundamental deviations in treatment need and efficacy. A recent quantitative analysis of 50 patients with SIADH, which underwent serial measurements of copeptin during hypertonic saline infusion, revealed five distinct types of osmoregulatory defect ("type A to E") without affiliation to specific underlying diseases. In addition to apparently impaired osmoregulated inhibition of AVP release in the majority of patients, 12% of patients showed an AVP-independent mechanism of inappropriate antidiuresis, whilst 20% of them presented a reverse relation between hormone release and serum osmolality, presumably related to interrupted nonosmotic inhibitory pathways. The interference of these different types of SIAD with clinical presentation and therapy response will be a relevant subject for future research.

Hyponatremia secondary to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH): therapeutic decision-making in real-life cases

Despite being the most common electrolyte disturbance encountered in clinical practice, the diagnosis and treatment of hyponatremia (defined as a serum sodium concentration <135 mmol/L) remains far from optimal. This is extremely troubling because not only is hyponatremia associated with increased morbidity, length of hospital stay and hospital resource use, but it has also been shown to be associated with increased mortality. The reasons for this poor management may partly lie in the heterogeneous nature of the disorder; hyponatremia presents with a variety of possible etiologies, differing symptomology and fluid volume status, thereby making its diagnosis potentially complex. In addition, a general lack of awareness of the clinical impact of the disorder, a fear of adverse outcomes through overcorrection of sodium levels, and a lack of effective targeted treatments until recent years, may all have contributed to a reticence to actively treat cases of hyponatremia. There is therefore a clear unmet need to further educate physicians on the pathophysiology, diagnosis and management of this important condition. Through the use of a variety of real-world cases of patients with hyponatremia secondary to the syndrome of inappropriate secretion of antidiuretic hormone—a condition that accounts for approximately one-third of all cases of hyponatremia—this supplement aims to provide a comprehensive overview of the challenges faced in diagnosing and managing hyponatremia. These cases will also help to illustrate how some of the limitations of traditional therapies may be overcome with the use of vasopressin receptor antagonists.

Endocrinological disorders affecting neurosurgical patients: An intensivists perspective

Management of critically ill neurosurgical patients is often complicated by the presence or development of endocrinological ailments which complicate the clinical scenario and adversely affect the prognosis of these patients. The anatomical proximity to the vital centers regulating the endocrinological physiology and alteration in the neurotransmitter release causes disturbances in the hormonal homeostasis. This paves the way for development of diverse disorders where single or multiple hormones may be involved which can have deleterious effect on the different organ system. Understanding and awareness of these disorders is important for the treating intensivist to recognize these changes early in their course, so that appropriate and timely therapeutic measures can be initiated along with the treatment of the primary malady.

Principles of neuroanesthesia in aneurysmal subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage is associated with high mortality. Understanding of the underlying pathophysiology is important as early intervention can improve outcome. Increasing age, altered sensorium and poor Hunt and Hess grade are independent predictors of adverse outcome. Early operative interventions imposes an onus on anesthesiologists to provide brain relaxation. Coiling and clipping are the two treatment options with increasing trends toward coiling. Intraoperatively, tight control of blood pressure and adequate brain relaxation is desirable, so that accidental aneurysm rupture can be averted. Patients with poor grades tolerate higher blood pressures, but are prone to ischemia whereas patients with lower grades tolerate lower blood pressure, but are prone to aneurysm rupture if blood pressure increases. Patients with Hunt and Hess Grade I or II with uneventful intraoperative course are extubated in operation theater, whereas, higher grades are kept electively ventilated. Postoperative management includes attention toward fluid status and early management of vasospasm.

Cardiac complications in acute ischemic stroke

Introduction

To characterize cardiac complications in acute ischemic stroke (AIS) patients admitted from an urban emergency department (ED).

Methods

Retrospective cross-sectional study evaluating AIS patients admitted from the ED within 24 hours of symptom onset who also had an echocardiogram performed within 72 hours of admission.

Results

Two hundred AIS patients were identified with an overall in-hospital mortality rate of 8% (n = 16). In our cohort, 57 (28.5%) of 200 had an ejection fraction less than 50%, 35 (20.4%) of 171 had ischemic changes on electrocardiogram (ECG), 18 (10.5%) of 171 presented in active atrial fibrillation, 21 (13.0%) of 161 had serum troponin elevation, and 2 (1.1%) of 184 survivors had potentially lethal arrhythmias on telemetry monitoring. Subgroup analysis revealed higher in-hospital mortality rates among those with systolic dysfunction (15.8% versus 4.9%; P = 0.0180), troponin elevation (38.1% versus 3.4%; P < 0.0001), atrial fibrillation on ECG (33.3% versus 3.8%; P = 0.0003), and ischemic changes on ECG (17.1% versus 6.1%; P = 0.0398) compared with those without.

Conclusion

A proportion of AIS patients may have cardiac complications. Systolic dysfunction, troponin elevation, atrial fibrillation, or ischemic changes on ECG may be associated with higher in-hospital mortality rates. These findings support the adjunctive role of cardiac-monitoring strategies in the acute presentation of AIS.

Serum sodium disorders in patients with traumatic brain injury

Sodium disorders are the most common and most poorly understood electrolyte disorders in neurological patients. The aim of this study was to determine the incidence of sodium disorders and its association with different traumatic brain injuries. This prospective study was conducted in 80 patients diagnosed with moderate and severe traumatic brain injuries. All patients underwent cerebral computed tomography. Incidence of sodium disorders, presence of injuries in the first computed tomography after traumatic brain injury, and level of consciousness were analyzed. Patients that presented other potential causes of sodium disorders and systemic trauma were excluded from the study. The incidence of sodium disturbances was 45%: 20 patients presented hypernatremia and 16 hyponatremia. Refers to all patients with sodium disturbances 53% were detected in the first sample. We recorded at least one measurement <125 mEq/L in 50% of the patients with hyponatremia. A greater incidence of sodium disorders was found in patients with subdural, intracerebral hematoma and with diffuse axonal injury. The incidence of sodium disorders among the patients with diffuse lesions was greater than in the group of patients with brain contusion (P = 0.022). The incidence of sodium disorders is higher in patients with diffuse traumatic brain injuries. No association was found between focal lesions and proportion of sodium disorders.

Sodium Disturbances Commonly Encountered in the Neurologic Intensive Care Unit

Disorders of sodium and water balance are common in patients with central nervous system (CNS) disease. These disorders frequently complicate the treatment course by precipitating or worsening neurological symptoms. These patients are not only at risk for symptoms secondary to dysnatremia but also at risk from the consequences of treatment. If not treated properly, this electrolyte disturbance can vastly increase morbidity and can even lead to death. Appropriate diagnosis and intervention requires an understanding of the physiologic and pathophysiologic mechanisms involved in sodium and water homeostasis.

Aneurysmal subarachnoid haemorrhage and the anaesthetist

The anaesthetist may be involved at various stages in the management of subarachnoid haemorrhage (SAH). Thus, familiarity with epidemiological, pathophysiological, diagnostic, and therapeutic issues is as important as detailed knowledge of the optimal intraoperative anaesthetic management. As the prognosis of SAH remains poor, prompt diagnosis and appropriate treatment are essential, because early treatment may improve outcome. It is, therefore, important to rule out SAH as soon as possible in all patients complaining of sudden onset of severe headache lasting for longer than an hour with no alternative explanation. The three main predictors of mortality and dependence are impaired level of consciousness on admission, advanced age, and a large volume of blood on initial cranial computed tomography. The major complications of SAH include re-bleeding, cerebral vasospasm leading to immediate and delayed cerebral ischaemia, hydrocephalus, cardiopulmonary dysfunction, and electrolyte disturbances. Prophylaxis and therapy of cerebral vasospasm include maintenance of cerebral perfusion pressure (CPP) and normovolaemia, administration of nimodipine, triple-H therapy, balloon angioplasty, and intra-arterial papaverine. Occlusion of the aneurysm after SAH is usually attempted surgically ('clipping') or endovascularly by detachable coils ('coiling'). The need for an adequate CPP (for the prevention of cerebral ischaemia and cerebral vasospasm) must be balanced against the need for a low transmural pressure gradient of the aneurysm (for the prevention of rupture of the aneurysm). Effective measures to prevent or attenuate increases in intracranial pressure, brain swelling, and cerebral vasospasm throughout all phases of anaesthesia are prerequisite for optimal outcome.

Hyponatremia in neurologic patients: consequences and approaches to treatment

BACKGROUND

Hyponatremia is a common fluid-electrolyte disturbance, particularly in patients with neurologic disorders, in part because of the major role the central nervous system (CNS) plays in the regulation of sodium and water homeostasis.

REVIEW SUMMARY

The classification of hyponatremia is based on an assessment of serum sodium concentration ([Na+]), serum and urine osmolality, and body volume status. In most cases, hyponatremia is associated with hypotonicity, which causes water to move into the brain. Adaptive responses limit the impact of cerebral edema in chronic hyponatremia, but CNS symptoms and death may occur in response to rapid or large decreases in serum [Na+]. The prompt correction of serum [Na+] is mandatory in symptomatic patients, but overly rapid correction must be avoided to limit the risk of myelinolysis. In neurologic disorders, euvolemic hyponatremia (usually caused by the syndrome of inappropriate secretion of antidiuretic hormone) must be distinguished from hypovolemic states such as cerebral salt wasting because the treatment of the 2 conditions differs. Vasopressin antagonists represent a new approach to the treatment of euvolemic and hypervolemic hyponatremia secondary to arginine vasopressin dysregulation.

CONCLUSION

The optimal treatment of hyponatremia is controversial, but appropriate treatment must be determined according to the osmolality and volume status of the patient. If left untreated, serious CNS complications and adverse outcomes, including an increased risk of death, can occur.

Pituitary cyst presenting with hyponatremia and increased secretion of brain natriuretic peptide

✓ In most cases of pituitary cyst there are no clinical symptoms and the lesions are found incidentally. The authors report the case of a 60-year-old man with a pituitary cyst causing visual disturbance and hyponatremia. The patient presented with appetite loss and general fatigue. On admission, blood workup showed severe hyponatremia (112 mEq/L), and bitemporal hemianopsia was observed on neurological examination. Magnetic resonance imaging revealed an intra- and suprasellar region cystic mass extending to the frontal base and hypothalamic area. The serum level of brain natriuretic peptide (BNP) was elevated (92 pg/ml) with polyuria and excessive Na excretion. Transsphenoidal surgery was performed to drain the cyst. The cyst wall was partially excised and the cystic fluid was aspirated. The secretion of BNP normalized postoperatively, and the hyponatremia and visual symptoms resolved. Histological examination, including an electron microscopy study, confirmed the diagnosis of a simple cyst. This appears to be the first reported case of a pituitary simple cyst associated with hyponatremia and an elevated BNP level.

Hyponatremia in critically ill neurological patients

BACKGROUND

Hyponatremia is the most common and important electrolyte disorder encountered in the neurologic intensive care unit (NICU). Advances in our knowledge of the pathophysiological mechanisms at play in patients with acute neurologic disease have improved our understanding of this derangement.

REVIEW SUMMARY

Evaluation of hyponatremia requires a structured approach beginning with the measurement of serum and urine osmolalities. Most cases of hyponatremia in the NICU are associated with serum hypotonicity. Iatrogenic causes, most conspicuously inadequate tonicity of intravenous fluids, should be promptly identified and removed when possible. Two main mechanisms are responsible for most non-iatrogenic cases of hyponatremia in patients with neurologic or neurosurgical disease: inappropriate secretion of antidiuretic hormone (SIADH) and cerebral salt wasting syndrome (CSW). Distinction between these two syndromes may be difficult and must be based on an accurate assessment of the patient's volume status. SIADH is associated with normal or slightly expanded volume status and should be treated with fluid restriction. Patients with CSW are hypovolemic and require adequate fluid and sodium replacement. Correction of hyponatremia should not exceed 8 to 10 mmol/L over any 24-hour period to avoid the risk of osmotic demyelination.

CONCLUSIONS

Hyponatremia may complicate the clinical course of many acute neurologic and neurosurgical disorders. It is most often iatrogenic causes, CSW, or SIADH. Physicians working with critically ill neurologic patients should be familiar with management strategies addressing these underlying pathophysiological mechanisms.

Hyponatremia in acute brain disease: the cerebral salt wasting syndrome

Hyponatremia in acute brain disease is a common occurrence, especially after an aneurysmal subarachnoid hemorrhage. Originally, excessive natriuresis, called cerebral salt wasting, and later the syndrome of inappropriate antidiuretic hormone secretion (SIADH), were considered to be the causes of hyponatremia. In recent years, it has become clear that most of these patients are volume-depleted and have a negative sodium balance, consistent with the original description of cerebral salt wasting. Elevated plasma concentrations of atrial or brain natriuretic peptide have been identified as the putative natriuretic factor. Hyponatremia and volume depletion may aggravate neurological symptoms, and timely treatment with adequate replacement of water and NaCl is essential. The use of fludrocortisone to increase sodium reabsorption by the renal tubules may be an alternative approach.

[Hyponatremia in neurologic intensive care: cerebral salt wasting syndrome and inappropriate antidiuretic hormone secretion]

Hyponatraemia is a frequent complication in neurologically injured patients; it is a secondary cerebral injury. Hyponatraemia leads to consciousness problems, convulsions, worsening of the neurological status and thus the neurological evaluation. Hyponatraemia is secondary to free water retention (inappropriate ADH secretion) or to renal salt loss. The cerebral salt wasting syndrome (CSWS) has been described with head injury, subarachnoid haemorrhage and after several sorts of brain insults. It is characterised by an increased natriuresis and diuresis. Diagnosis is based on hyponatraemia, hypernatriuresis, increased diuresis and hypovolaemia. However, inappropriate ADH secretion and CSWS share several diagnostic criteria. The atrial natriuretic factor and the C-type natriuretic factors play a role in the development of the CSWS. The diagnostic approach and monitoring are based on the assessment of sodium and water losses. Therapy is based on correction of the circulating volume and natraemia. Speed of correction is a matter of debate: slow correction presents the risk of further neurological injury whereas rapid correction presents the risk of central pontine myelinosis.

Hyponatremia-induced metabolic encephalopathy caused by Rathke's cleft cyst: a case report

Rathke's cleft cysts are sometimes associated with aseptic meningitis or metabolic encephalopathy due to hyponatremia. We treated such a case manifest by lethargy, fever and electroencephalographic abnormalities. A 68-year-old man was admitted to our ward after experiencing general malaise, nausea and vomiting and then high fever and lethargy. On admission, he was drowsy and had nuchal rigidity and Kernig's sign. Physically, he was pale with dry, thickened skin. He had lost 5.0 kg of body weight in the last month. His serum sodium was 115 mEq/l. He had a low serum osmotic pressure (235 mOsmol/l) and a high urine osmotic pressure (520 mOsmol/l). His urine volume was 1200-1900 ml/24 h with a specific gravity of 1008-1015. The urine sodium was 210 mEq/l. He did not have an elevated level of antidiuretic hormone. Electroencephalograms showed periodic delta waves over a background of theta waves. With sodium replacement, the patient become alert and symptom free, and his electroencephalographic findings normalized. However, the serum sodium level did not stabilize, sometimes falling with a recurrence of symptoms. Magnetic resonance imaging clearly delineated a dumbbell-shaped intrasellar and suprasellar cyst. The suprasellar component subsequently shrunk spontaneously and finally disappeared. An endocrinologic evaluation showed panhypopituitarism. The patient was given glucocorticoid and thyroxine replacement therapy, which stabilized his serum sodium level and permanently relieved his symptoms. A transsphenoidal approach was performed. A greenish cyst was punctured, and a yellow fluid was aspirated. The cyst proved to be simple or cubic stratified epithelium, and a diagnosis of Rathke's cleft cyst was made. The patient was discharged in good condition with a continuation of hormonal therapy. Rathke's cleft cyst can cause aseptic meningitis if the cyst ruptures and its contents spill into the subarachnoid space. Metabolic encephalopathy induced by hyponatremia due to salt wasting also can occur if the lesion injures the hypothalamus and pituitary gland.

Rapid natriuresis and preventive hypervolaemia for symptomatic vasospasm after subarachnoid haemorrhage

To prevent symptomatic cerebral vasospasm, we have used hypervolaemia (HV) or volume expansion in patients with aneurysmal subarachnoid haemorrhage (SAH) in recent years. In these patients we could not perform effective fluid and sodium (Na) replacement because of rapid and overwhelming water and Na loss. Although this phenomenon is characteristic under hypervolaemic states, we regard it important to elucidate the mechanism underlying initiation of vasospasm after aneurysmal SAH. Patients with aneurysmal SAH, operated on within 24 hours of onset, were analysed prospectively. We selected 17 patients in good pre-operative condition. Intravascular volume expansion was accomplished with plasma fractionate or albumin and crystalloid solutions in all patients. We divided the 17 patients into two groups; symptomatic spasm group (S-group) consisting of 4 cases developing transient ischaemic symptoms and non-symptomatic spasm group (NS-group) consisting of 13 cases. In S-group, rapid and marked natriuresis developed characteristically before the onset of ischaemic symptoms. The differences in daily Na balance between the two groups were significant on the 3rd and 5th days (p < 0.05). The mean cumulative Na balance in S-group during the 10 days of the study (-375 +/- 159 mEg) was higher than that of NS-group (-24.4 +/- 225 mEq) (p < 0.05). Rapid natriuresis preceded the development of ischaemic symptoms, and was important as a trigger for symptomatic vasospasm after SAH. We considered that hormonal disorders were implicated in this phenomenon, and atrial natriuretic peptide (ANP), antidiuretic hormone (ADH), renin, and aldosterone were each measured three times during the period, with no significant differences, found between the two groups. It was speculated that another potent natriuretic factor, similar to ANP, induced a rapid selective natriuresis resulting in symptomatic vasospasm.

[Enhancement of cardiac performance for prevention and treatment of delayed cerebral ischemia caused by vasospasm]

Following subarachnoid haemorrhage, delayed cerebral ischaemia from cerebral vasospasm remains the most important cause of mortality and morbidity in patients with surgically secured aneurysms. Therapy with haemodilution, hypertension and volume expansion has been recommended to prevent and treat delayed cerebral ischaemia in these patients on the basis of uncontrolled clinical series (level of evidence III to V, grade C recommendation). Despite the lack of controlled studies, the maintenance of a cardiac index > 3.5 L.min-1.m-2 and a systolic arterial pressure between 120 and 150 mmHg before clipping and 160 to 200 mmHg thereafter is recommended as a prophylactic or therapeutic measure for vasospasm. Close monitoring of neurological and cardiorespiratory status is important to avoid neurologic and systemic complications.

The effects of methylprednisolone and the ganglioside GM1 on acute spinal cord injury in rats

Recent clinical trials have reported that methylprednisolone sodium succinate (MP) or the monosialic ganglioside GM1 improves neurological recovery in human spinal cord injury. Because GM1 may have additive or synergistic effects when used with MP, the authors compared MP, GM1, and MP+GM1 treatments in a graded rat spinal cord contusion model. Spinal cord injury was caused by dropping a rod weighing 10 gm from a height of 1.25, 2.5, or 5.0 cm onto the rat spinal cord at T-10, which had been exposed via laminectomy. The lesion volumes were quantified from spinal cord Na and K shifts at 24 hours after injury and the results were verified histologically in separate experiments. A single dose of MP (30 mg/kg), given 5 minutes after injury, reduced 24-hour spinal cord lesion volumes by 56% (p = 0.0052), 28% (p = 0.0065), and 13% (p > 0.05) in the three injury-severity groups, respectively, compared to similarly injured control groups treated with vehicle only. Methylprednisolone also prevented injury-induced hyponatremia and increased body weight loss in the spine-injured rats. When used alone, GM1 (10 to 30 mg/kg) had little or no effect on any measured variable compared to vehicle controls; when given concomitantly with MP, GM1 blocked the neuroprotective effects of MP. At a dose of 3 mg/kg, GM1 partially prevented MP-induced reductions in lesion volumes, while 10 to 30 mg/kg of GM1 completely blocked these effects of MP. The effects of MP on injury-induced hyponatremia and body weight loss were also blocked by GM1. Thus, GM1 antagonized both central and peripheral effects of MP in spine-injured rats. Until this interaction is clarified, the authors recommend that MP and GM1 not be used concomitantly to treat acute human spinal cord injury. Because GM1 modulates protein kinase activity, protein kinases inhibit lipocortins, and lipocortins mediate anti-inflammatory effects of glucocorticoids, it is proposed that the neuroprotective effects of MP are partially due to anti-inflammatory effects and that GM1 antagonizes the effects of MP by inhibiting lipocortin. Possible beneficial effects of GM1 reported in central nervous system injury may be related to the effects on neural recovery rather than acute injury processes.

Hypervolemic therapy prevents volume contraction but not hyponatremia following subarachnoid hemorrhage

Hyponatremia is common following subarachnoid hemorrhage and has alternatively been attributed to either the inappropriate secretion of antidiuretic hormone or natriuresis causing intravascular volume contraction. We prospectively studied body sodium and intravascular volume regulation in 19 patients, beginning within 3 days after acute aneurysmal subarachnoid hemorrhage occurred, in order to determine the impact of hypervolemic therapy on both hyponatremia and volume contraction and to ascertain whether humoral factors account for hyponatremia. Serial measurements of plasma arginine vasopressin, atrial natriuretic factor, renin activity, aldosterone, and catecholamines were correlated with body sodium and fluid balance, change in blood volume, serum sodium concentration, and osmolality. Six patients (32%) developed hyponatremia, but only 2 had a negative sodium balance. In most patients, levels of atrial natriuretic factor were elevated, while plasma renin activity and aldosterone concentrations were generally suppressed. Plasma arginine vasopressin levels were not suppressed during hypo-osmolality and did not correlate with serum osmolality in hyponatremic patients. Only 1 patient had a decrease in blood volume, which was associated with marked rises in aldosterone and plasma renin activity, but normal serum sodium and plasma atrial natriuretic factor levels. We conclude that following subarachnoid hemorrhage: (1) Hypervolemic therapy prevents volume contraction but not hyponatremia, (2) humoral factors may favor both sodium loss and water retention, and (3) arginine vasopressin regulation is disturbed and may contribute to hyponatremia.