Changes in cerebral blood flow and distribution associated with acute increases in plasma sodium and osmolality of chronic hyponatremic rats

Effect of vasopressin-induced chronic hyponatremia on the regulation of the middle cerebral artery of the rat

Vasopressin (arginine vasopressin, AVP) plays a crucial role in maintaining body fluid homeostasis. Excessive release of vasopressin can lead to hyponatremia. Changes in cerebral circulation during vasopressin-induced chronic hyponatremia are not elucidated. The present study has been designed to investigate the effect of chronic vasopressin-induced hyponatremia on the regulation of the tone of the middle cerebral artery (MCA) of the rat. Chronic hyponatremia was induced in vivo with the help of vasopressin, released continuously from subcutaneously implanted ALZET mini-osmotic pumps, and a liquid diet. After 3.5 days of chronic hyponatremia, the plasma Na⁺ concentration decreased to 119 ± 3 mM. MCAs were isolated and placed in a MOPS-buffered saline solution containing 121 mM Na⁺. Chronic hyponatremia did not affect the response of the MCA to increased intravascular pressure, to the administration of acetylcholine (ACh) and nitric oxide (NO) donor (SNAP, S-nitroso-N-acetyl-DL-penicillamine), and to increased K⁺ concentration, but impaired the response of the MCA to increased extravascular H⁺ concentration. Disturbed response of the MCA to acidosis was associated neither with the impairment of K_ATP channels nor with the activation of vasopressin V₁ receptor. Correction of hyponatremia did not restore the response of the MCA to acidosis. These results indicate that cerebral blood vessels do not fully adapt to prolonged vasopressin-induced hyponatremia.

Hyponatremia and the Brain

Hyponatremia is defined by low serum sodium concentration and is the most common electrolyte disorder encountered in clinical practice. Serum sodium is the main determinant of plasma osmolality, which, in turn, affects cell volume. In the presence of low extracellular osmolality, cells will swell if the adaptation mechanisms involved in the cell volume maintenance are inadequate. The most dramatic effects of hyponatremia on the brain are seen when serum sodium concentration decreases in a short period, allowing little or no adaptation. The brain is constrained inside a nonextensible envelope; thus, brain swelling carries a significant morbidity because of the compression of brain parenchyma over the rigid skull. Serum sodium concentration is an important determinant of several biological pathways in the nervous system, and recent studies have suggested that hyponatremia carries a significant risk of neurological impairment even in the absence of brain edema. The brain can also be affected by the treatment of hyponatremia, which, if not undertaken cautiously, could lead to osmotic demyelination syndrome, a rare demyelinating brain disorder that occurs after rapid correction of severe hyponatremia. This review summarizes the pathophysiology of brain complications of hyponatremia and its treatment.

A Case of Osmotic Demyelination Presenting with Severe Hypernatremia

Osmotic demyelination syndrome is a demyelinating disorder associated with rapid correction of hyponatremia. But, it rarely occurs in acute hypernatremia, and it leads to permanent neurologic symptoms and is associated with high mortality. A 44-year-old woman treated with alternative medicine was admitted with a history of drowsy mental status. Severe hypernatremia (197mEq/L) with hyperosmolality (415mOsm/kgH2O) was evident initially and magnetic resonance imaging revealed a high signal intensity lesion in the pons, consistent with central pontine myelinolysis. She was treated with 0.45% saline and 5% dextrose water and intravenous corticosteroids. Serum sodium normalized and her clinical course gradually improved. Brain lesion of myelinolysis also improved in a follow-up imaging study. This is the first report of a successful treatment of hypernatremia caused by iatrogenic salt intake, and it confirms the importance of adequate fluid supplementation in severe hypernatremia.

Microvascular pathology and morphometrics of sporadic and hereditary small vessel diseases of the brain

Small vessel diseases (SVDs) of the brain are likely to become increasingly common in tandem with the rise in the aging population. In recent years, neuroimaging and pathological studies have informed on the pathogenesis of sporadic SVD and several single gene (monogenic) disorders predisposing to subcortical strokes and diffuse white matter disease. However, one of the limitations toward studying SVD lies in the lack of consistent assessment criteria and lesion burden for both clinical and pathological measures. Arteriolosclerosis and diffuse white matter changes are the hallmark features of both sporadic and hereditary SVDs. The pathogenesis of the arteriopathy is the key to understanding the differential progression of disease in various SVDs. Remarkably, quantification of microvascular abnormalities in sporadic and hereditary SVDs has shown that qualitatively the processes involved in arteriolar degeneration are largely similar in sporadic SVD compared with hereditary disorders such as cerebral autosomal arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Important significant regional differences in lesion location within the brain may enable one to distinguish SVDs, where frontal lobe involvement appears consistently with almost every SVD, but others bear specific pathologies in other lobes, such as the temporal pole in CADASIL and the pons in pontine autosomal dominant microangiopathy and leukoencephalopathy or PADMAL. Additionally, degenerative changes in the vascular smooth muscle cells, the cerebral endothelium and the basal lamina are often rapid and more aggressive in genetic disorders. Further quantification of other microvascular elements and even neuronal cells is needed to fully characterize SVD pathogenesis and to differentiate the usefulness of vascular interventions and treatments on the resulting pathology.

Plasma exchange successfully treats central pontine myelinolysis after acute hypernatremia from intravenous sodium bicarbonate therapy

BACKGROUND

Osmotic demyelination syndrome (ODS) primarily occurs after rapid correction of severe hyponatremia. There are no proven effective therapies for ODS, but we describe the first case showing the successful treatment of central pontine myelinolysis (CPM) by plasma exchange, which occurred after rapid development of hypernatremia from intravenous sodium bicarbonate therapy.

CASE PRESENTATION

A 40-year-old woman presented with general weakness, hypokalemia, and metabolic acidosis. The patient was treated with oral and intravenous potassium chloride, along with intravenous sodium bicarbonate. Although her bicarbonate deficit was 365 mEq, we treated her with an overdose of intravenous sodium bicarbonate, 480 mEq for 24 hours, due to the severity of her acidemia and her altered mental status. The next day, she developed hypernatremia with serum sodium levels rising from 142.8 mEq/L to 172.8 mEq/L. Six days after developing hypernatremia, she exhibited tetraparesis, drooling, difficulty swallowing, and dysarthria, and a brain MRI revealed high signal intensity in the central pons with sparing of the peripheral portion, suggesting CPM. We diagnosed her with CPM associated with the rapid development of hypernatremia after intravenous sodium bicarbonate therapy and treated her with plasma exchange. After two consecutive plasma exchange sessions, her neurologic symptoms were markedly improved except for mild diplopia. After the plasma exchange sessions, we examined the patient to determine the reason for her symptoms upon presentation to the hospital. She had normal anion gap metabolic acidosis, low blood bicarbonate levels, a urine pH of 6.5, and a calyceal stone in her left kidney. We performed a sodium bicarbonate loading test and diagnosed distal renal tubular acidosis (RTA). We also found that she had Sjögren's syndrome after a positive screen for anti-Lo, anti-Ra, and after the results of Schirmer's test and a lower lip biopsy. She was discharged and treated as an outpatient with oral sodium bicarbonate and potassium chloride.

CONCLUSION

This case indicates that serum sodium concentrations should be carefully monitored in patients with distal RTA receiving intravenous sodium bicarbonate therapy. We should keep in mind that acute hypernatremia and CPM can be associated with intravenous sodium bicarbonate therapy, and that CPM due to acute hypernatremia may be effectively treated with plasma exchange.

Clinical semiology and neuroradiologic correlates of acute hypernatremic osmotic challenge in adults: a literature review

The complex interplay between hypernatremic osmotic disturbances and cerebral lesions is yet to be clarified. In this review, we discuss, on the basis of the reported data of hypernatremic CNS challenge in the adult population, the clinical and radiologic features of the condition. Our search captured 20 case studies and 1 case series with 30 patients in total who acquired acute hypernatremia due to different etiologies and developed CNS lesions. We explored the associations between premorbid conditions, clinical presentation, hypernatremic state, correction rate, and radiologic appearance, including the localization of brain lesions and the outcomes. The results revealed that altered mental status was the most commonly reported symptom and osmotic demyelination syndrome in the form of extrapontine myelinolysis was the prevailing radiologic pattern. Finally, we contrasted, when appropriate, clinical and experimental data related to hypernatremic and hyponatremic osmotic insults to aid the understanding of the pathophysiology of CNS osmotic brain injury.

New aspects in the pathogenesis, prevention, and treatment of hyponatremic encephalopathy in children

Hyponatremia is the most common electrolyte abnormality encountered in children. In the past decade, new advances have been made in understanding the pathogenesis of hyponatremic encephalopathy and in its prevention and treatment. Recent data have determined that hyponatremia is a more serious condition than previously believed. It is a major comorbidity factor for a variety of illnesses, and subtle neurological findings are common. It has now become apparent that the majority of hospital-acquired hyponatremia in children is iatrogenic and due in large part to the administration of hypotonic fluids to patients with elevated arginine vasopressin levels. Recent prospective studies have demonstrated that administration of 0.9% sodium chloride in maintenance fluids can prevent the development of hyponatremia. Risk factors, such as hypoxia and central nervous system (CNS) involvement, have been identified for the development of hyponatremic encephalopathy, which can lead to neurologic injury at mildly hyponatremic values. It has also become apparent that both children and adult patients are dying from symptomatic hyponatremia due to inadequate therapy. We have proposed the use of intermittent intravenous bolus therapy with 3% sodium chloride, 2 cc/kg with a maximum of 100 cc, to rapidly reverse CNS symptoms and at the same time avoid the possibility of overcorrection of hyponatremia. In this review, we discuss how to recognize patients at risk for inadvertent overcorrection of hyponatremia and what measures should taken to prevent this, including the judicious use of 1-desamino-8d-arginine vasopressin (dDAVP).

Enhancement of cerebral blood flow using systemic hypertonic saline therapy improves outcome in patients with poor-grade spontaneous subarachnoid hemorrhage

OBJECT

Systemic administration of 23.5% hypertonic saline enhances cerebral blood flow (CBF) in patients with poor-grade spontaneous subarachnoid hemorrhage (SAH). Whether the increment of change in CBF correlates with changes in autoregulation of CBF or outcome at discharge remains unknown.

METHODS

Thirty-five patients with poor-grade spontaneous SAH received 2 ml/kg 23.5% hypertonic saline intravenously, and they underwent bedside transcranial Doppler (TCD) ultrasonography and intracranial pressure (ICP) monitoring. Seventeen of them underwent Xe-enhanced computed tomography (CT) scanning for measuring CBF. Outcome was assessed using the modified Rankin Scale (mRS) at discharge from the hospital. The data were analyzed using repeated-measurement analysis of variance and Dunnett correction. A comparison was made between patients with favorable and unfavorable outcomes using multivariate logistic regression.

RESULTS

The authors observed a maximum increase in blood pressure by 10.3% (p < 0.05) and cerebral perfusion pressure (CPP) by 21.2% (p < 0.01) at 30 minutes, followed by a maximum decrease in ICP by 93.1% (p < 0.01) at 60 minutes. Changes in ICP and CPP persisted for longer than 180 and 90 minutes, respectively. The results of TCD ultrasonography showed that the baseline autoregulation was impaired on the ipsilateral side of ruptured aneurysm, and increments in flow velocities were higher and lasted longer on the contralateral side (48.75% compared with 31.96% [p = 0.045] and 180 minutes compared with 90 minutes [p < 0.05], respectively). The autoregulation was briefly impaired on the contralateral side during the infusion. A dose-dependent effect of CBF increments on favorable outcome was seen on Xe-CT scans (mRS Score 1-3, odds ratio 1.27 per 1 ml/100 g tissue x min, p = 0.045).

CONCLUSIONS

Bolus systemic hypertonic saline therapy may be used for reversal of cerebral ischemia to normal perfusion in patients with poor-grade SAH.

Effect of hypertonic saline on cerebral blood flow in poor-grade patients with subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The goal of this study was to examine the effects of hypertonic saline on cerebral blood flow (CBF) in poor-grade patients with subarachnoid hemorrhage.

METHODS

We administered 23.5% hypertonic saline (2 mL/kg IV) 1 time to 10 patients, 2 times to 7 patients, and 3 times to 1 patient. All patients had transcranial Doppler (TCD), intracranial pressure (ICP) monitoring, and analysis of serum sodium and osmolality; 6 had xenon CT (XeCT). Data were used to characterize the changes in CBF, cerebral vascular resistance (CVR), ICP, cerebral perfusion pressure (CPP), and potential rheological mechanisms of action.

RESULTS

In the first treatment episode, CPP increased 26.8% (P=0.0003, at 28.3 minutes) from a rise in mean arterial blood pressure (ABP) of 10.5% (P=0.02, at 22.2 minutes) and a fall in ICP (-74.7%, P=0.002, at 60.0 minutes). Flow velocity (FV) of the middle cerebral artery increased 70.8% (P=0.00005, at 20.0 minutes), resulting in a corresponding fall in estimated CVR (-26.6%, P=0.01, at 16.3 minutes). The half-lives of effects on ABP, CPP, ICP, FV, and estimated CVR were 20.0, 53.6, 139.1, 42.7, and 27.1 minutes, respectively. In the second treatment episode, all these parameters had the same response except estimated CVR, which did not reach statistical significance. XeCT confirmed the increase in CBF (22.9%, P=0.02) without regional differences. A fall in CBF after hypertonic saline was identified in only a single region of interest in a patient in whom baseline flow was low but not infarcted. Serum sodium rose by 11.4 and 8.8 mmol/L, and osmolality rose by 26.7 and 16.3 mosm/L in the first and second treatment episodes, respectively. Hemoglobin decreased by 0.7 and 0.6 g/L and hematocrit decreased by 1.9% and 2.4% in the first and second treatment episodes, respectively.

CONCLUSIONS

We found that 23.5% hypertonic saline increases CBF in poor-grade patients with subarachnoid hemorrhage. These effects are associated with improved indexes of blood rheology. Potential therapeutic benefits are discussed.