Intracranial pressure variation associated with changes in end-tidal CO2

Confined spaces in space: Cerebral implications of chronic elevations of inspired carbon dioxide and implications for long-duration space travel

Cerebrovascular regulation is critically dependent upon the arterial partial pressure of carbon dioxide (P aC O 2 ${P_{{\mathrm{aC}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ), owing to its effect on cerebral blood flow, tissueP C O 2 ${P_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ , tissue proton concentration, cerebral metabolism and cognitive and neuronal function. In normal environments and in the absence of pathology, at least over acute time frames, hypercapnia is usually managed readily via the respiratory chemoreflex arcs and/or acid-base buffering capacity, such that there is minimal impact on cerebrovascular and neurological function. However, in non-normal environments, such as enclosed spaces, or with pathology, extended exposures to elevations inP aC O 2 ${P_{{\mathrm{aC}}{{\mathrm{O}}_{\mathrm{2}}}}}$ can be detrimental to cerebral health. Given the direct effect of protons on cellular function, even if pH is normalized, it is feasible that higher proton concentrations could still produce detrimental effects. Although it seems that humans can work safely in mildly hypercapnic environments for extended periods, chronic respiratory acidosis can cause bone demineralization, renal calcification, perinatal developmental abnormalities, systemic inflammation and impairments in cognitive function and visuomotor skills and can produce cerebral acidosis, potentially inducing sustained alterations in cerebral function. With the advancement of new initiatives in spaceflight, including proposed long-duration missions to Mars, the study of the effects of chronic inspired CO2 on human health is relevant. In this review, we draw on evidence from preclinical, physiological and clinical research in humans to summarize the cerebral ramifications of prolonged and chronic exposures to elevated partial pressures of inspired CO2 and respiratory acidosis.

Acute Effects of Ketamine on Intracranial Pressure in Children With Severe Traumatic Brain Injury

OBJECTIVES

The acute cerebral physiologic effects of ketamine in children have been incompletely described. We assessed the acute effects of ketamine on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in children with severe traumatic brain injury (TBI).

DESIGN

In this retrospective observational study, patients received bolus doses of ketamine for sedation or as a treatment for ICP crisis (ICP > 20 mm Hg for > 5 min). Administration times were synchronized with ICP and CPP recordings at 1-minute intervals logged in an automated database within the electronic health record. ICP and CPP were each averaged in epochs following drug administration and compared with baseline values. Age-based CPP thresholds were subtracted from CPP recordings and compared with baseline values. Trends in ICP and CPP over time were assessed using generalized least squares regression.

SETTING

A 30-bed tertiary care children's hospital PICU.

PATIENTS

Children with severe TBI who underwent ICP monitoring.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We analyzed data from 33 patients, ages 1 month to 16 years, 22 of whom received bolus doses of ketamine, with 127 doses analyzed. Demographics, patient, and injury characteristics were similar between patients who did versus did not receive ketamine boluses. In analysis of the subset of ketamine doses used only for sedation, there was no significant difference in ICP or CPP from baseline. Eighteen ketamine doses were given during ICP crises in 11 patients. ICP decreased following these doses and threshold-subtracted CPP rose.

CONCLUSIONS

In this retrospective, exploratory study, ICP did not increase following ketamine administration. In the setting of a guidelines-based protocol, ketamine was associated with a reduction in ICP during ICP crises. If these findings are reproduced in a larger study, ketamine may warrant consideration as a treatment for intracranial hypertension in children with severe TBI.

Assessment of Dynamic Intracranial Compliance in Children with Severe Traumatic Brain Injury: Proof-of-Concept

Background and Aims

Intracranial compliance refers to the relationship between a change in intracranial volume and the resultant change in intracranial pressure (ICP). Measurement of compliance is useful in managing cardiovascular and respiratory failure; however, there are no contemporary means to assess intracranial compliance. Knowledge of intracranial compliance could complement ICP and cerebral perfusion pressure (CPP) monitoring in patients with severe traumatic brain injury (TBI) and may enable a proactive approach to ICP management. In this proof-of-concept study, we aimed to capitalize on the physiologic principles of intracranial compliance and vascular reactivity to CO₂, and standard-of-care neurocritical care monitoring, to develop a method to assess dynamic intracranial compliance.

Methods

Continuous ICP and end-tidal CO₂ (ETCO₂) data from children with severe TBI were collected after obtaining informed consent in this Institutional Review Board-approved study. An intracranial pressure-PCO₂ Compliance Index (PCI) was derived by calculating the moment-to-moment correlation between change in ICP and change in ETCO₂. As such, “good” compliance may be reflected by a lack of correlation between time-synched changes in ICP in response to changes in ETCO₂, and “poor” compliance may be reflected by a positive correlation between changes in ICP in response to changes in ETCO₂.

Results

A total of 978 h of ICP and ETCO₂ data were collected and analyzed from eight patients with severe TBI. Demographic and clinical characteristics included patient age 7.1 ± 5.8 years (mean ± SD); 6/8 male; initial Glasgow Coma Scale score 3 [3–7] (median [IQR]); 6/8 had decompressive surgery; 7.1 ± 1.4 ICP monitor days; ICU length of stay (LOS) 16.1 ± 6.8 days; hospital LOS 25.9 ± 8.4 days; and survival 100%. The mean PCI for all patients throughout the monitoring period was 0.18 ± 0.04, where mean ICP was 13.7 ± 2.1 mmHg. In this cohort, PCI was observed to be consistently above 0.18 by 12 h after monitor placement. Percent time spent with PCI thresholds > 0.1, 0.2, and 0.3 were 62% [24], 38% [14], and 23% [15], respectively. The percentage of time spent with an ICP threshold > 20 mmHg was 5.1% [14.6].

Conclusions

Indirect assessment of dynamic intracranial compliance in TBI patients using standard-of-care monitoring appears feasible and suggests a prolonged period of derangement out to 5 days post-injury. Further study is ongoing to determine if the PCI—a new physiologic index, complements utility of ICP and/or CPP in guiding management of patients with severe TBI.

Electronic supplementary material

The online version of this article (10.1007/s12028-020-01004-3) contains supplementary material, which is available to authorized users.

Dynamic optic nerve sheath diameter responses to short-term hyperventilation measured with sonography in patients under general anesthesia

BACKGROUND

Rapid evaluation and management of intracranial pressure (ICP) can help to early detection of increased ICP and improve postoperative outcomes in neurocritically-ill patients. Sonographic measurement of optic nerve sheath diameter (ONSD) is a non-invasive method of evaluating increased intracranial pressure at the bedside. In the present study, we hypothesized that sonographic ONSD, as a surrogate of ICP change, can be dynamically changed in response to carbon dioxide change using short-term hyperventilation.

METHODS

Fourteen patients were enrolled. During general anesthesia, end-tidal carbon dioxide concentration (ETCO2) was decreased from 40 mmHg to 30 mmHg within 10 minutes. ONSD, which was monitored continuously in the single sonographic plane, was repeatedly measured at 1 and 5 minutes with ETCO2 40 mmHg (time-point 1 and 2) and measured again at 1 and 5 minutes with ETCO2 30 mmHg (time-point 3 and 4).

RESULTS

The mean ± standard deviation of ONSD sequentially measured at four time-points were 5.0 ± 0.5, 5.0 ± 0.4, 3.8 ± 0.6, and 4.0 ± 0.4 mm, respectively. ONSD was significantly decreased at time-point 3 and 4, compared with 1 and 2 (P < 0.001).

CONCLUSIONS

The ONSD was rapidly changed in response to ETCO2. This finding may support that ONSD may be beneficial to close ICP monitoring in response to CO2 change.

End-tidal carbon dioxide as a measure of stress response to clustered nursing interventions in neurologic patients

BACKGROUND

Guidelines recommend rest periods between nursing interventions for patients with a neurologic diagnosis but do not specify a safe number of interventions.

OBJECTIVES

To examine the physiological stress response to clustered nursing interventions in neurologic patients receiving mechanical ventilation.

METHODS

Prospective, comparative, descriptive design to examine effects of clustered interventions (≥6 interventions in a single nursing interaction) versus nonclustered interventions on patients' stress. Stress response was defined as a 10% change in end-tidal carbon dioxide from before the interaction to (1) 5 and 10 minutes after the start of the interaction, (2) at the end of the interaction, and (3) 15 minutes after the interaction.

RESULTS

The mean percent change in end-tidal carbon dioxide at 5 minutes differed significantly between patients with clustered interventions and patients with nonclustered interventions (6.7% vs -0.2%; P = .001). Patients with clustered interventions were significantly more likely than patients with low clustering to exhibit a stress response at 5 minutes (24.3% vs 0%; P = .01).

CONCLUSIONS

Neurologic patients receiving mechanical ventilation who experienced 6 or more clustered nursing interventions showed a higher mean change in end-tidal carbon dioxide than did patients who received fewer than 6 clustered interventions. These findings suggest that providing fewer interventions during 1 nursing interaction may minimize induced stress in neurologic patients receiving mechanical ventilation.

Transverse sinus stenting for idiopathic intracranial hypertension: a review of 52 patients and of model predictions

BACKGROUND AND PURPOSE

Transverse sinus stenosis is common in patients with IIH. While the role of transverse sinus stenosis in IIH pathogenesis remains controversial, modeling studies suggest that stent placement within a transverse sinus stenosis with a significant pressure gradient should decrease cerebral venous pressure, improve CSF resorption in the venous system, and thereby reduce intracranial (CSF) pressure, improving the symptoms of IIH and reducing papilledema. We aimed to determine if IIH could be reliably treated by stent placement in transverse sinus stenosis.

MATERIALS AND METHODS

We reviewed the clinical, venographic, and intracranial pressure data before and after stent placement in transverse sinus stenosis in 52 of our own patients with IIH unresponsive to maximum acceptable medical treatment, treated since 2001 and followed between 2 months and 9 years.

RESULTS

Before stent placement, the mean superior sagittal sinus pressure was 34 mm Hg (462 mm H(2)0) with a mean transverse sinus stenosis gradient of 20 mm Hg. The mean lumbar CSF pressure before stent placement was 322 mm H(2)O. In all 52 patients, stent placement immediately eliminated the TSS pressure gradient, rapidly improved IIH symptoms, and abolished papilledema. In 6 patients, symptom relapse (headache) was associated with increased venous pressure and recurrent stenosis adjacent to the previous stent. In these cases, placement of another stent again removed the transverse sinus stenosis pressure gradient and improved symptoms. Of the 52 patients, 49 have been cured of all IIH symptoms.

CONCLUSIONS

These findings indicate a role for transverse sinus stent placement in the management of selected patients with IIH.