The effects of hyponatraemia and subarachnoid haemorrhage on the cerebral vasomotor responses of the rabbit

Delayed Cerebral Ischemia After Subarachnoid Hemorrhage: Experimental-Clinical Disconnect and the Unmet Need

BACKGROUND

Delayed cerebral ischemia (DCI) is among the most dreaded complications following aneurysmal subarachnoid hemorrhage (SAH). Despite advances in neurocritical care, DCI remains a significant cause of morbidity and mortality, prolonged intensive care unit and hospital stay, and high healthcare costs. Large artery vasospasm has classically been thought to lead to DCI. However, recent failure of clinical trials targeting vasospasm to improve outcomes has underscored the disconnect between large artery vasospasm and DCI. Therefore, interest has shifted onto other potential mechanisms such as microvascular dysfunction and spreading depolarizations. Animal models can be instrumental in dissecting pathophysiology, but clinical relevance can be difficult to establish.

METHODS

Here, we performed a systematic review of the literature on animal models of SAH, focusing specifically on DCI and neurological deficits.

RESULTS

We find that dog, rabbit and rodent models do not consistently lead to DCI, although some degree of delayed vascular dysfunction is common. Primate models reliably recapitulate delayed neurological deficits and ischemic brain injury; however, ethical issues and cost limit their translational utility.

CONCLUSIONS

To facilitate translation, clinically relevant animal models that reproduce the pathophysiology and cardinal features of DCI after SAH are urgently needed.

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.

The single and double blood injection rabbit subarachnoid hemorrhage model

Over the past 30 years, the rabbit subarachnoid hemorrhage model (SAH) has been used for investigating the post-hemorrhage pathology, especially with respect to understanding of the mechanisms of cerebral vasospasm. However, the molecular mechanisms of cerebral vasospasm remain to be elucidated. Furthermore, it is not clear whether the rabbit SAH model is suitable for the investigation of pathological conditions other than cerebral vasospasm, such as early brain injury. Therefore, the properties of the rabbit SAH model need to be validated, and the reasons for using the rabbit should be clarified. This review explores the settings and technical issues of establishing a rabbit cisterna magna single and double blood injection SAH model and discusses the characteristics and feasibilities of the models.

Hyponatremia is predictable in patients with aneurysmal subarachnoid hemorrhage--clinical significance of serum atrial natriuretic peptide

PURPOSE

Serum atrial natriuretic peptide (ANP) that is elevated after aneurysmal subarachnoid hemorrhage (SAH) causes diuresis and natriuresis (cerebral salt wasting) and might exacerbate delayed ischemic neurological deficit (DIND). We investigated relationships among hyponatremia, serum ANP elevation, and the onset of DIND after SAH.

MATERIALS AND METHODS

Thirty-nine consecutive patients (15 women and 24 men) with SAH were assigned to a normonatremia group or a group that developed hyponatremia after SAH. Serum ANP and brain natriuretic peptide were assessed after SAH. All patients remained normovolemic and normotensive. We attributed DIND to vasospasm only in the absence of other causes and when supported by cerebral angiography.

RESULTS

Hyponatremia developed after SAH in 11 patients (28.2%), among whom serum ANP concentrations at 0 and 3 days thereafter were significantly increased. Furthermore, DIND developed in five (45.5%) and two (7.1%) hyponatremic and normonatremic patients, respectively (P < 0.05). The serum ANP levels on day 0 after SAH were higher in Hunt and Kosnik grades 3-4 than in 1-2 and in Fisher groups 3-4 than in 1-2 (P < 0.05).

CONCLUSIONS

Increasing serum ANP concentrations were independently associated with hyponatremia resulting in DIND. Early treatment of hyponatremia might prevent DIND in patients after SAH.

The incidence and pathophysiology of hyponatraemia after subarachnoid haemorrhage

BACKGROUND

Hyponatraemia is common following subarachnoid haemorrhage (SAH) but the pathogenesis is unclear. Objective To establish the incidence, pathophysiology and consequences of hyponatraemia following SAH.

METHODS

A retrospective case-note analysis of all patients with SAH admitted to Beaumont Hospital between January 2002 and September 2003. Three hundred and sixteen cases of SAH were substantiated by computed tomography (CT) scan and angiogram findings. Hyponatraemia was defined as plasma sodium < 135 mmol/l.

RESULTS

One hundred and seventy-nine patients (56.6%) developed hyponatraemia and 62 (19.6%) developed significant hyponatraemia (plasma sodium < 130 mmol/l). The incidence of severe hyponatraemia following hypophysectomy was lower in the period of analysis (5/81, 6.2%, P < 0.01). Hyponatraemia was more common in patients with identified aneurysms (anterior circulation 102/168, 60.7%, posterior circulation 56/95, 60.8%) than in those with no radiological aneurysm (21/54, 38.8%, P < 0.001). Hyponatraemia was more common after aneurysmal clipping (68/103, 66%) or coiling (82/132, 62%) than after conservative treatment (29/81, 36%, P < 0.001). The aetiology of significant hyponatraemia was the syndrome of inappropriate antidiuretic hormone secretion (SIADH) 39/62 (69.2%), cerebral salt-wasting syndrome (CSWS) 4/62 (6.5%), hypovolaemic hyponatraemia 13/62 (21%), hypervolaemic hyponatraemia 3/62 (4.8%) and mixed CSW/SIADH 3/62 (4.8%). Hyponatraemia was associated with longer hospital stay (24.0 +/- 2.6 vs. 11.8 +/- 0.8 days, P < 0.001) but did not affect mortality (P = 0.07). Hyponatraemia developed more than 7 days following SAH in 21.4% and more then 7 days following intervention in 31.8%.

CONCLUSIONS

Hyponatraemia is common following SAH and is associated with longer hospital stay. Clipping and coiling of aneurysms are associated with higher rates of hyponatraemia. SIADH is the commonest cause of hyponatraemia after SAH. Delayed hyponatraemia is common, and has implications for early discharge strategies.

Predicting delayed ischemic deficits after aneurysmal subarachnoid hemorrhage using a transient hyperemic response test of cerebral autoregulation

OBJECTIVE

To assess whether the development of delayed ischemic deficits (DIDs) after aneurysmal subarachnoid hemorrhage can be predicted using transcranial Doppler ultrasonography and the transient hyperemic response test (THRT).

METHODS

An increase in the middle cerebral artery peak flow velocity (FV) of more than 9% of baseline values after 5 to 9 seconds of carotid artery compression was defined as a normal THRT result, indicating good autoregulatory reserve. The transcranial Doppler criteria for vasospasm were a FV of more than 120 cm/s and a Lindegaard ratio of more than 3. Twenty patients with no immediate postoperative neurological deficits were studied. The FVs at all of the major cerebral arteries were measured daily after surgery, and the THRT results were assessed bilaterally.

RESULTS

Five of six patients with abnormal THRT results in the first examination after surgery (primary THRT impairment) developed DIDs; none of the remaining patients developed DIDs (Fisher exact test, P = 0.0004). All five patients with DIDs initially exhibited low FVs but all subsequently developed increases in FVs to values of more than 150 cm/s and four exhibited FVs of more than 200 cm/s. The time of onset of DIDs corresponded to the time of onset of moderate vasospasm (FV > 150 cm/s). None of the patients with initially normal THRT results developed DIDs, although four patients did exhibit late (secondary) THRT impairment, which was associated with FVs of more than 120 cm/s.

CONCLUSION

When the effects of primarily impaired (after surgery) autoregulation are magnified by vasospasm, the risk of DIDs seems to be very high. Vasospasm alone does not seem to cause DIDs. The development of DIDs could therefore be predicted using the THRT for patients after aneurysm clipping.

Cerebral blood flow autoregulation following subarachnoid hemorrhage in rats: chronic vasospasm shifts the upper and lower limits of the autoregulatory range toward higher blood pressures

We sought to determine whether chronic vasospasm following subarachnoid hemorrhage (SAH) would abolish the cerebral blood flow (CBF) autoregulation in anesthetized Sprague-Dawley rats. SAH was induced by intracisternal injection of autologous blood; in control animals saline was injected instead. CBF was measured 48 h after SAH, that is during chronic vasospasm, by laser-Doppler flowmetry over the frontal cortex under condition of hypertension (SAH, n = 6; control, n = 8) or hypotension (SAH, n = 6; control, n = 6). Hyper- and hypotension were induced by increasing mean arterial blood pressure (MABP) stepwise from 90 to 180 mmHg with phenylephrine (0.1-10 micrograms/min i.v.), or by decreasing it from 90 to 40 mmHg by controlled hemorrhage. An autoregulatory index (AI) expressed as delta CBF (%) per 10 mmHg increase or decrease in MABP was employed to analyze CBF response. CBF remained constant (-7 < AI < 7) at MABPs ranging from 60 to 130 mmHg in the control group and from 70 to 140 mmHg in the SAH group, showing CBF autoregulation. In the SAH group, that is, the upper and the lower limits of autoregulatory range were increased by 10 mmHg (p < 0.05). SAH did not increase intracranial pressure significantly (control 9.2 +/- 0.67 vs. SAH 10.0 +/- 1.05 mmHg, n = 5) 48 h after SAH was induced. These results indicate that, during chronic vasospasm, SAH does not abolish the autoregulation process but raises its lower and upper blood pressure limits. The capacity of spastic cerebral arteries to dilate in case of hypotension decreased, while their tolerance to hypertension increased.

Cortical blood flow and cerebral perfusion pressure in a new noncraniotomy model of subarachnoid hemorrhage in the rat

BACKGROUND AND PURPOSE

Acute cerebral ischemia after subarachnoid hemorrhage (SAH) is a major cause of morbidity whose precise etiology is unclear. The purpose of this study was to examine the relationships between cerebral perfusion pressure (CPP) and cortical blood flow during SAH using a new experimental model in the rat.

METHODS

CPP (mean arterial pressure minus intracranial pressure), cortical laser-Doppler flowmetry (LDF), and electroencephalogram were continuously recorded during and after SAH in 16 ventilated rats. SAH was produced by advancing an intraluminal suture from the external carotid artery through the internal carotid artery to perforate the vessel near its intracranial bifurcation.

RESULTS

Eight rats (50%) died within 24 hours of SAH. In all rats, blood was widely distributed throughout the basal, convexity, and interhemispheric subarachnoid spaces and throughout the ventricular system. CPP decreased after SAH at an initial rate of 1.1 +/- 0.2 mm Hg/s, reaching its nadir 59 +/- 9 seconds after the onset of SAH. During the same period, LDF fell at a rate of 1.4 +/- 0.3%/s (P = NS vs CPP). After reaching its nadir, CPP rose at a rate of 0.4 +/- 0.01 mm Hg/s, but LDF continued to fall at 0.2 +/- 0.03%/s (P < .05 vs CPP) reaching a nadir of 21.7 +/- 2.5% significantly later than CPP (189.5 +/- 39 s after SAH, P < .05). No correlation was found between peak changes in CPP and LDF. Electroencephalogram activity followed the changes in LDF, reaching nadir values 289 +/- 55 seconds after SAH.

CONCLUSIONS

These findings demonstrate that although reduced CPP causes the initial decrease in cortical blood flow after SAH, secondary reductions occurring after CPP has reached its nadir are caused by other factors such as acute vasoconstriction. This noncraniotomy model of SAH in the rat has several advantages over existing models.