CO2 reactivity in patients after subarachnoid haemorrhage

Brain Oxygenation Response to Hypercapnia in Patients with Acute Brain Injury

BACKGROUND

Cerebral hypoxia is a frequent cause of secondary brain damage in patients with acute brain injury. Although hypercapnia can increase intracranial pressure, it may have beneficial effects on tissue oxygenation. We aimed to assess the effects of hypercapnia on brain tissue oxygenation (PbtO2).

METHODS

This single-center retrospective study (November 2014 to June 2022) included all patients admitted to the intensive care unit after acute brain injury who required multimodal monitoring, including PbtO2 monitoring, and who underwent induced moderate hypoventilation and hypercapnia according to the decision of the treating physician. Patients with imminent brain death were excluded. Responders to hypercapnia were defined as those with an increase of at least 20% in PbtO2 values when compared to their baseline levels.

RESULTS

On a total of 163 eligible patients, we identified 23 (14%) patients who underwent moderate hypoventilation (arterial partial pressure of carbon dioxide [PaCO2] from 44 [42-45] to 50 [49-53] mm Hg; p < 0.001) during the study period at a median of 6 (4-10) days following intensive care unit admission; six patients had traumatic brain injury, and 17 had subarachnoid hemorrhage. A significant overall increase in median PbtO2 values from baseline (21 [19-26] to 24 [22-26] mm Hg; p = 0.02) was observed. Eight (35%) patients were considered as responders, with a median increase of 7 (from 4 to 11) mm Hg of PbtO2, whereas nonresponders showed no changes (from - 1 to 2 mm Hg of PbtO2). Because of the small sample size, no variable independently associated with PbtO2 response was identified. No correlation between changes in PaCO2 and in PbtO2 was observed.

CONCLUSIONS

In this study, a heterogeneous response of PbtO2 to induced hypercapnia was observed but without any deleterious elevations of intracranial pressure.

Efficacy and safety of remifentanil dose titration to correct the spontaneous hyperventilation in aneurysmal subarachnoid haemorrhage: protocol and statistical analysis for a prospective physiological study

INTRODUCTION

Spontaneous hyperventilation (SHV) is common in aneurysmal subarachnoid haemorrhage (aSAH). The reduction in arterial partial pressure of carbon dioxide (PaCO₂) may change the brain physiology, such as haemodynamics, oxygenation, metabolism and may lead to secondary brain injury. However, how to correct SHV safely and effectively in patients with aSAH has not been well investigated. The aim of this study is to investigate the efficacy and safety of remifentanil dose titration to correct hyperventilation in aSAH, as well as the effect of changes in PaCO₂ on cerebral blood flow (CBF).

METHODS AND ANALYSIS

This study is a prospective, single-centre, physiological study in patients with aSAH. The patients who were mechanically ventilated and who meet with SHV (tachypnoea combined with PaCO₂ <35 mm Hg and pH >7.45) will be enrolled. The remifentanil will be titrated to correct the SHV. The predetermined initial dose of remifentanil is 0.02 μg/kg/min and will be maintained for 30 min, and PaCO₂ and CBF will be measured. After that, the dose of remifentanil will be sequentially increased to 0.04, 0.06, and 0.08 μg/kg/min, and the measurements for PaCO₂ and CBF will be repeated 30 min after each dose adjustment and will be compared with their baseline values.

ETHICS AND DISSEMINATION

This study has been approved by the Institutional Review Board of Beijing Tiantan Hospital, Capital Medical University (KY 2021-006-02) and has been registered at ClinicalTrials.gov. The results of this study will be disseminated through peer-reviewed publications and conference presentations.

TRIAL REGISTRATION NUMBER

NCT04940273.

Therapeutic hypercapnia for prevention of secondary ischemia after severe subarachnoid hemorrhage: physiological responses to continuous hypercapnia

Temporary hypercapnia has been shown to increase cerebral blood flow (CBF) and might be used as a therapeutical tool in patients with severe subarachnoid hemorrhage (SAH). It was the aim of this study was to investigate the optimum duration of hypercapnia. This point is assumed to be the time at which buffer systems become active, cause an adaptation to changes of the arterial partial pressure of carbon dioxide (PaCO₂) and annihilate a possible therapeutic effect. In this prospective interventional study in a neurosurgical ICU the arterial partial pressure of carbon dioxide (PaCO₂) was increased to a target range of 55 mmHg for 120 min by modification of the respiratory minute volume (RMV) one time a day between day 4 and 14 in 12 mechanically ventilated poor-grade SAH-patients. Arterial blood gases were measured every 15 min. CBF and brain tissue oxygen saturation (StiO₂) were the primary and secondary end points. Intracranial pressure (ICP) was controlled by an external ventricular drainage. Under continuous hypercapnia (PaCO₂ of 53.17 ± 5.07), CBF was significantly elevated between 15 and 120 min after the start of hypercapnia. During the course of the trial intervention, cardiac output also increased significantly. To assess the direct effect of hypercapnia on brain perfusion, the increase of CBF was corrected by the parallel increase of cardiac output. The maximum direct CBF enhancing effect of hypercapnia of 32% was noted at 45 min after the start of hypercapnia. Thereafter, the CBF enhancing slowly declined. No relevant adverse effects were observed. CBF and StiO₂ reproducibly increased by controlled hypercapnia in all patients. After 45 min, the curve of CBF enhancement showed an inflection point when corrected by cardiac output. It is concluded that 45 min might be the optimum duration for a therapeutic use and may provide an optimal balance between the benefits of hypercapnia and risks of a negative rebound effect after return to normal ventilation parameters.

Trial registration: The study was approved by the institutional ethics committee (AZ 230/14) and registered at ClinicalTrials.gov (Trial-ID: NCT01799525). Registered 01/01/2015.

High-normal PaCO2 values might be associated with worse outcome in patients with subarachnoid hemorrhage - a retrospective cohort study

BACKGROUND

While both hypercapnia and hypocapnia are harmful in patients with subarachnoid hemorrhage (SAH), it is unknown whether high-normal P_aCO₂ values are better than low-normal values. We hypothesized that high-normal P_aCO₂ values have more detrimental than beneficial effects on outcome.

METHODS

Consecutive patients with aneurysmal subarachnoid hemorrhage (aSAH) requiring mechanical ventilation treated in a tertiary care university hospital were retrospectively analyzed regarding the influence of P_aCO₂ on favorable outcome, defined as modified Rankin scale score < 3 at discharge. Primary endpoint was the difference in the proportion of P_aCO₂ values above 40 mmHg in relation to all measured P_aCO₂ values between patients with favorable and unfavorable outcome.

RESULTS

150 patients were included. Median age was 57 years (p25:50, p75:64), median Hunt-Hess score was 4 (p25:3, p75:5). P_aCO₂ values were mainly within normal range (median 39.0, p25:37.5, p75:41.4). Patients with favorable outcome had a lower proportion of high-normal P_aCO₂ values above 40 mmHg compared to patients with unfavorable outcome (0.21 (p25:0.13, p75:0.50) vs. 0.4 (p25:0.29, p75:0.59)) resulting in a lower chance for favorable outcome (OR 0.04, 95% CI 0.00-0.55, p = 0.017). In multivariable analysis adjusted for Hunt-Hess score, pneumonia and length of stay, elevated P_aCO₂ remained an independent predictor of outcome (OR 0.05, 95% CI 0.00-0.81, p = 0.035).

CONCLUSIONS

A higher proportion of P_aCO₂ values above 40 mmHg was an independent predictor of outcome in patients with aSAH in our study. The results need to be confirmed in a prospective trial.

Time Course of Cerebrovascular Reactivity in Patients Treated for Unruptured Intracranial Aneurysms: A One-Year Transcranial Doppler and Acetazolamide Follow-Up Study

Background

Cerebrovascular reactivity (CVR) is often impaired in the early phase after aneurysmal subarachnoid hemorrhage. There is, however, little knowledge about the time course of CVR in patients treated for unruptured intracranial aneurysms (UIA).

Methods

CVR, assessed by transcranial Doppler and acetazolamide test, was examined within the first postoperative week after treatment for UIA and reexamined one year later.

Results

Of 37 patients initially assessed, 34 were reexamined after one year. Bilaterally, baseline and acetazolamide-induced blood flow velocities were higher in the postoperative week compared with one year later (p < 0.001). CVR on the ipsilateral side of treatment was lower in the initial examination compared with follow-up (58.9% versus 66.1%, p = 0.04). There was no difference in CVR over time on the contralateral side (63.4% versus 65.0%, p = 0.65). When mean values of right and left sides were considered there was no difference in CVR between exams. Larger aneurysm size was associated with increased change in CVR (p = 0.04), and treatment with clipping was associated with 13.8%-point increased change in CVR compared with coiling (p = 0.03).

Conclusion

Patients with UIA may have a temporary reduction in CVR on the ipsilateral side after aneurysm treatment. The change in CVR appears more pronounced for larger-sized aneurysms and in patients treated with clipping. We recommend that ipsilateral and contralateral CVR should be assessed separately, as mean values can conceal side-differences.

Controlled Hypercapnia Enhances Cerebral Blood Flow and Brain Tissue Oxygenation After Aneurysmal Subarachnoid Hemorrhage: Results of a Phase 1 Study

BACKGROUND

This study investigated if cerebral blood flow (CBF) regulation by changes of the arterial partial pressure of carbon dioxide (PaCO2) can be used therapeutically to increase CBF and improve neurological outcome after subarachnoid hemorrhage (SAH).

METHODS

In 12 mechanically ventilated poor-grade SAH-patients, a daily trial intervention was performed between day 4 and 14. During this intervention, PaCO2 was decreased to 30 mmHg and then gradually increased to 40, 50, and 60 mmHg in 15-min intervals by modifications of the respiratory minute volume. CBF and brain tissue oxygen saturation (StiO2) were the primary and secondary endpoints. Intracranial pressure was controlled by an external ventricular drainage.

RESULTS

CBF reproducibly decreased during hyperventilation and increased to a maximum of 141 ± 53 % of baseline during hypercapnia (PaCO2 60 mmHg) on all days between day 4 and 14 after SAH. Similarly, StiO2 increased during hypercapnia. CBF remained elevated within the first hour after resetting ventilation to baseline parameters and no rebound effect was observed within this time-span. PaCO2-reactivities of CBF and StiO2 were highest between 30 and 50 mmHg and slightly decreased at higher levels.

CONCLUSION

CBF and StiO2 reproducibly increased by controlled hypercapnia of up to 60 mmHg even during the period of the maximum expected vasospasm. The absence of a rebound effect within the first hour after hypercapnia indicates that an improvement of the protocol is possible. The intervention may yield a therapeutic potential to prevent ischemic deficits after aneurysmal SAH.

Correlation between angiographic transit times and neurological status on admission in patients with aneurysmal subarachnoid hemorrhage

OBJECT

The use of digital subtraction angiography (DSA) for semiquantitative cerebral blood flow(CBF) assessment is a new technique. The aim of this study was to determine whether patients with aneurysmal subarachnoid hemorrhage (aSAH) with higher Hunt and Hess grades also had higher angiographic contrast transit times (TTs) than patients with lower grades.

METHODS

A cohort of 30 patients with aSAH and 10 patients without aSAH was included. Relevant clinical information was collected. A method to measure DSA TTs by color-coding reconstructions from DSA contrast-intensity images was applied. Regions of interest (ROIs) were chosen over major cerebral vessels. The estimated TTs included time-to-peak from 0% to 100% (TTP0–100), TTP from 25% to 100% (TTP25–100), and TT from 100% to 10% (TT100–10) contrast intensities. Statistical analysis was used to compare TTs between Group A (Hunt and Hess Grade I-II), Group B (Hunt and Hess Grade III-IV), and the control group. The correlation coefficient was calculated between different ROIs in aSAH groups.

RESULTS

There was no difference in demographic factors between Group A (n = 10), Group B (n = 20), and the control group (n = 10). There was a strong correlation in all TTs between ROIs in the middle cerebral artery (M1, M2) and anterior cerebral artery (A1, A2). There was a statistically significant difference between Groups A and B in all TT parameters for ROIs. TT100–10 values in the control group were significantly lower than the values in Group B.

CONCLUSIONS

The DSA TTs showed significant correlation with Hunt and Hess grades. TT delays appear to be independent of increased intracranial pressure and may be an indicator of decreased CBF in patients with a higher Hunt and Hess grade. This method may serve as an indirect technique to assess relative CBF in the angiography suite.

Impaired cerebrovascular reactivity in the early phase of subarachnoid hemorrhage in good clinical grade patients does not predict vasospasm

OBJECTIVE

Subarachnoid hemorrhage (SAH) alters cerebrovascular reactivity (CVR) to carbon dioxide (CO2), which may be related to an increased risk of delayed ischemic neurological deficits (DINDs). We report the results of bedside CVR testing in the acute phase of SAH in good clinical grade patients without established vasospasm or signs of DIND.

MATERIALS AND METHODS

Eighteen patients with SAH and 26 healthy subjects underwent CVR testing using transcranial Doppler with standardized changes in CO₂. None of the patients had clinical or radiological evidence of vasospasm or DIND at time of testing. A CVR index was calculated as the change in the middle cerebral artery blood flow velocity (MCAv) divided by the change in the end-tidal CO₂partial pressure (PCO₂), ∆ MCAv/Δ PCO₂, and values were compared with controls.

RESULTS

SAH patients had lower CVR when compared with normal controls (p = 0.0001 and p = 0.0094, respectively). Impaired CVR was not correlated with future vasospasm (p = 0.2).

CONCLUSIONS

Patients with SAH had significantly lower CVR indexes compared with healthy controls. Although impaired CVR was present in 50 % of the patients early after SAH, no correlation with later occurrence of DINDs was found.

Controlled transient hypercapnia: a novel approach for the treatment of delayed cerebral ischemia after subarachnoid hemorrhage?

Object

The authors undertook this study to investigate whether the physiological mechanism of cerebral blood flow (CBF) regulation by alteration of the arterial partial pressure of carbon dioxide (PaCO2) can be used to increase CBF after aneurysmal subarachnoid hemorrhage (aSAH).

Methods

In 6 mechanically ventilated patients with poor-grade aSAH, the PaCO2 was first decreased to 30 mm Hg by modification of the respiratory rate, then gradually increased to 40, 50 and 60 mm Hg for 15 minutes each setting. Thereafter, the respirator settings were returned to baseline parameters. Intracerebral CBF measurement and brain tissue oxygen saturation (StiO2), measured by near-infrared spectroscopy (NIRS), were the primary and secondary end points. Intracranial pressure (ICP) was controlled by external ventricular drainage.

Results

A total of 60 interventions were performed in 6 patients. CBF decreased to 77% of baseline at a PaCO2 of 30 mm Hg and increased to 98%, 124%, and 143% at PaCO2 values of 40, 50, and 60 mm Hg, respectively. Simultaneously, StiO2 decreased to 94%, then increased to 99%, 105%, and 111% of baseline. A slightly elevated delivery rate of cerebrospinal fluid was noticed under continuous drainage. ICP remained constant. After returning to baseline respirator settings, both CBF and StiO2 remained elevated and only gradually returned to pre-hypercapnia values without a rebound effect. None of the patients developed secondary cerebral infarction.

Conclusions

Gradual hypercapnia was well tolerated by poor-grade SAH patients. Both CBF and StiO2 reacted with a sustained elevation upon hypercapnia; this elevation outlasted the period of hypercapnia and only slowly returned to normal without a rebound effect. Elevations of ICP were well compensated by continuous CSF drainage. Hypercapnia may yield a therapeutic potential in this state of critical brain perfusion. Clinical trial registration no.: NCT01799525 (ClinicalTrials.gov).

CO2 has no therapeutic effect on early microvasospasm after experimental subarachnoid hemorrhage

In addition to delayed vasospasm also early brain injury, which occurs during the first few days after subarachnoid hemorrhage (SAH) when large cerebral arteries are still fully functional, plays an important role for the outcome after SAH. In the current study, we investigated the hypothesis that carbon dioxide (CO2), a strong cerebral vasodilator, has a therapeutic potential against early posthemorrhagic microvasospasm. C57BL/6 mice (n=36) and Sprague-Dawley rats (n=23) were subjected to sham surgery or SAH by filament perforation. The pial microcirculation in the mice was visualized 3 and 24 hours after SAH using intravital fluorescence microscopy. Partial pressure of CO2 (PaCO2) was modulated by hyper- or hypoventilation or by inhalation of 10% CO2. In rats, CO2-mediated changes in cerebral blood flow (CBF) were measured at the same time points using laser Doppler fluxmetry. Increased PaCO2 caused vasodilatation in sham-operated animals. Following SAH, however, cerebral arterioles were nonreactive to CO2. This lack of microvascular CO2 reactivity was accompanied by a complete loss of CO2-induced hyperemia. Our data show that CO2 is not able to dilate spastic microvessels and to increase CBF early after SAH. Future therapeutic approaches will therefore need to address mechanisms beyond CO2.

BOLD MRI and early impairment of cerebrovascular reserve after aneurysmal subarachnoid hemorrhage

Currently no biological or radiological marker is available to identify patients at risk of delayed ischemic deficit (DIND) after aneurysmal subarachnoid hemorrhage (aSAH). We hypothesized whether MR-based quantitative assessment of cerebrovascular reserve (CVR) would detect early radiological markers of vasospasm and DIND. This manuscript describes our initial experience with this population. Five patients with aSAH underwent blood-oxygen level dependent-MRI (BOLD-MRI) with CO2 challenge for assessment of whole brain CVR. Patients were examined as soon as possible after aneurysm treatment. We obtained good quality anatomical and functional images without complications. Initial anatomical cerebrovascular imaging showed no vasospasm in all patients. Two patients had abnormal CVR-MRI tests and both developed DIND. Of the 3 others with normal CVR-MRI, one developed posterior circulation DIND. One patient with a normal CVR-MRI developed angiographic vasospasm but no DIND. Changes in CVR maps as early as 36 h after hemorrhage had good spatial correlation with delayed ischemia during short-term follow-up. Our series shows that MRI with CO2 challenge is feasible in this difficult population. Further developments might allow BOLD-MRI with CO2 challenge to identify patients at risk and provide anatomical correlation with future DIND, opening a new venue for prophylactic treatments. Further study is warranted in a larger patient cohort.

Principles of neuroanesthesia in stroke surgery

Subarachnoid hemorrhage (SAH) is a devastating disease with a high incidence of morbidity and mortality. The main aims of therapy are the prevention of rebleeding and the prevention and treatment of delayed cerebral ischemia. SAH is manifested with a variable combination of symptoms and is accompanied by various systemic disturbances, such as cardiac arrhythmias and insufficiency, neurogenic pulmonary edema, and electrolyte disorders.Successful perioperative treatment - apart from the surgical and endovascular techniques - requires solid knowledge and understanding of the regulation of cerebral hemodynamics, and the effects of subarachnoid hemorrhage and other diseases and various drugs, including the anesthetic agents, on it.In the following, the basic principles of neuroanesthesia for patients with SAH are reviewed.

Time-dependent alterations in functional and pharmacological arteriolar reactivity after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Disturbances in cerebral arteriolar function, in addition to large vessel vasospasm, may be responsible for ischemia after subarachnoid hemorrhage. The purpose of this study was to test the hypothesis that subarachnoid hemorrhage alters cerebral microvascular reactivity.

METHODS

An endovascular filament model was used to induce subarachnoid hemorrhage in halothane-anesthetized male Sprague-Dawley rats. We evaluated pial arteriolar responses to sciatic nerve stimulation, topically applied vasoactive agents (adenosine or sodium nitroprusside), and CO(2) inhalation in rats subjected to subarachnoid hemorrhage at 1 to 5 days after insult.

RESULTS

In sham-operated rats, sciatic nerve stimulation evoked a 23.5+/-1.8% increase in arteriolar diameter, which was significantly attenuated to 13.7+/-0.9%, 12.8+/-2.5%, and 18.8+/-2.9% at 24, 48, and 72 hours after subarachnoid hemorrhage, respectively (P<0.05; n> or =7). At 96 and 120 hours after subarachnoid hemorrhage, sciatic nerve stimulation-induced dilation recovered to sham levels. Somatosensory-evoked potentials were unaltered by subarachnoid hemorrhage. Pial vasodilatation to adenosine (10 micromol/L) and sodium nitroprusside (1 micromol/L) were significantly impaired, by 47% and 41%, respectively, at 48 hours after subarachnoid hemorrhage (P<0.05; n=7). In contrast, CO(2) reactivity was unaffected by subarachnoid hemorrhage.

CONCLUSIONS

Pial arteriolar responses to cortical activation may be decreased in the initial 2 to 3 days after experimental subarachnoid hemorrhage.

Molecular mechanisms of early brain injury after subarachnoid hemorrhage

OBJECTIVES

Increasing body of experimental and clinical data indicates that early brain injury after initial bleeding largely contributes to unfavorable outcome after subarachnoid hemorrhage (SAH). This review presents molecular mechanisms underlying brain injury at its early stages after SAH.

METHODS

PubMed was searched using term 'subarachnoid hemorrhage' and key words referring to molecular and cellular pathomechanisms of SAH-induced early brain injury.

RESULTS

The authors reviewed intracranial phenomena and molecular agents that contribute to the early development of pathological sequelae of SAH in cerebral and vascular tissues, including cerebral ischemia and its interactions with injurious blood components, blood-brain barrier disruption, brain edema and apoptosis.

DISCUSSION

It is believed that detailed knowledge of molecular signaling pathways after SAH will serve to improve therapeutic interventions. The most promising approach is the protection of neurovascular unit including anti-apoptosis therapy.

Transcranial Doppler assessment of cerebral vasospasm

This review summarizes the use of transcranial Doppler (TCD) for assessment of cerebral vasospasm. The basic hemodynamic principles are presented, and used as a basis for discussing findings and interpretation methods. The need for additional information and measurements to correctly interpret TCD velocities is analyzed, and the use of a special extracranial Doppler technique is recommended. The advantages and limitations of the 'Lindegaard Index' (LI) are discussed. The recent advances in the use of TCD for cerebral autoregulation testing are opening up a new and promising avenue in diagnosis, monitoring and treatment of cerebral vasospasm.