Early Effects of Passive Leg-Raising Test, Fluid Challenge, and Norepinephrine on Cerebral Autoregulation and Oxygenation in COVID-19 Critically Ill Patients

The effect of passive leg raising test on intracranial pressure and cerebral autoregulation in brain injured patients: a physiological observational study

BACKGROUND

The use of the passive leg raising (PLR) is limited in acute brain injury (ABI) patients with increased intracranial pressure (ICP) since the postural change of the head may impact on ICP and cerebral autoregulation. However, the PLR use may prevent a positive daily fluid balance, which had been recently associated to worse neurological outcomes. We therefore studied early and delayed effects of PLR on the cerebral autoregulation of patients recovering from ABI.

MATERIALS AND METHODS

This is a Prospective, observational, single-center study conducted in critically ill patients admitted with stable ABI and receiving invasive ICP monitoring, multimodal neuromonitoring and continuous hemodynamic monitoring. The fluid challenge consisted of 500 mL of crystalloid over 10 min; fluid responsiveness was defined as cardiac index increase ≥ 10%. Comparisons between different variables at baseline and after PLR were made by paired Wilcoxon signed-rank test. The correlation coefficients between hemodynamic and neuromonitoring variables were assessed using Spearman's rank test.

RESULTS

We studied 23 patients [12 patients (52.2%) were fluid responders]. The PLR significantly increased ICP [from 13.7 (8.3-16.4) to 15.4 (12.0-19.2) mmHg; p < 0.001], cerebral perfusion pressure (CPP) [from 51.1 (47.4-55.6) to 56.4 (49.6-61.5) mmHg; p < 0.001] and the pressure reactivity index (PRx) [from 0.12 (0.01-0.24) to 0.43 (0.34-0.46) mmHg; p < 0.001]. Regarding Near Infrared Spectroscopy (NIRS)-derived parameters, PLR significantly increased the arterial component of regional cerebral oxygen saturation (O2Hbi) [from 1.8 (0.8-3.7) to 4.3 (2.5-5.6) μM cm; p < 0.001], the deoxygenated hemoglobin (HHbi) [from 1.6 (0.2-2.9) to 2.7 (1.4-4.0) μM cm; p = 0.007] and total hemoglobin (cHbi) [from 3.6 (1.9-5.3) to 7.8 (5.2-10.3): p < 0.001]. In all the patients who had altered autoregulation after PLR, these changes persisted ten minutes afterwards. After the PLR, we observed a significant correlation between MAP and CPP and PRx.

CONCLUSIONS

In ABI patient with stable ICP, PLR test increased ICP, but mostly within safety values and thresholds. Despite this, cerebral autoregulation was importantly impaired, and this persisted up to 10 min after the end of the maneuvre. Our results discourage the use of PLR test in ABI even when ICP is stable.

The Use of Noninvasive Multimodal Neuromonitoring in Adult Critically Ill Patients With COVID-19 Infection

INTRODUCTION

Noninvasive neuromonitoring could be a valuable option for bedside assessment of cerebral dysfunction in patients with coronavirus disease-2019 (COVID-19) admitted to intensive care units (ICUs). This systematic review aims to investigate the use of noninvasive multimodal neuromonitoring in critically ill adult patients with COVID-19 infection.

METHODS

MEDLINE/PubMed, Scopus, Cochrane, and EMBASE databases were searched for studies investigating noninvasive neuromonitoring in patients with COVID-19 admitted to ICUs. The monitoring included transcranial Doppler ultrasonography (TCD), the Brain4care Corp. cerebral compliance monitor (B4C), optic nerve sheath diameter (ONSD), near infrared spectroscopy, automated pupillometry, and electroencephalography (EEG).

RESULTS

Thirty-two studies that investigated noninvasive neuromonitoring techniques in patients with COVID-19 in the ICU were identified from a systematic search of 7001 articles: 1 study investigating TCD, ONSD and pupillometry; 2 studies investigating the B4C device and TCD; 3 studies investigating near infrared spectroscopy and TCD; 4 studies investigating TCD; 1 case series investigating pupillometry, and 21 studies investigating EEG. One hundred and nineteen patients underwent TCD monitoring, 47 pupillometry, 49 ONSD assessment, 50 compliance monitoring with the B4C device, and 900 EEG monitoring. Alterations in cerebral hemodynamics, brain compliance, brain oxygenation, pupillary response, and brain electrophysiological activity were common in patients with COVID-19 admitted to the ICU; these abnormalities were not clearly associated with worse outcome or the development of new neurological complications.

CONCLUSIONS

The use of noninvasive multimodal neuromonitoring in critically ill COVID-19 patients could be considered to facilitate the detection of neurological derangements. Determining whether such findings allow earlier detection of neurological complications or guide appropriate therapy requires additional studies.

The importance of monitoring cerebral oxygenation in non brain injured patients

Over the past few years, the use of non-invasive neuromonitoring in non-brain injured patients has increased, as a result of the recognition that many of these patients are at risk of brain injury in a wide number of clinical scenarios and therefore may benefit from its application which allows interventions to prevent injury and improve outcome. Among these, are post cardiac arrest syndrome, sepsis, liver failure, acute respiratory failure, and the perioperative settings where in the absence of a primary brain injury, certain groups of patients have high risk of neurological complications. While there are many neuromonitoring modalities utilized in brain injured patients, the majority of those are either invasive such as intracranial pressure monitoring, require special skill such as transcranial Doppler ultrasonography, or intermittent such as pupillometry and therefore unable to provide continuous monitoring. Cerebral oximetry using Near infrared Spectroscopy, is a simple non invasive continuous measure of cerebral oxygenation that has been shown to be useful in preventing cerebral hypoxemia both within the intensive care unit and the perioperative settings. At present, current recommendations for standard monitoring during anesthesia or in the general intensive care concentrate mainly on hemodynamic and respiratory monitoring without specific indications regarding the brain, and in particular, brain oximetry. The aim of this manuscript is to provide an up-to-date overview of the pathophysiology and applications of cerebral oxygenation in non brain injured patients as part of non-invasive multimodal neuromonitoring in the early identification and treatment of neurological complications in this population.

Systemic and Cerebral Effects of Physiotherapy in Mechanically Ventilated Subjects

BACKGROUND

Physiotherapy may result in better functional outcomes, shorter duration of delirium, and more ventilator-free days. The effects of physiotherapy on different subpopulations of mechanically ventilated patients on respiratory and cerebral function are still unclear. We evaluated the effect of physiotherapy on systemic gas exchange and hemodynamics as well as on cerebral oxygenation and hemodynamics in mechanically ventilated subjects with and without COVID-19 pneumonia.

METHODS

This was an observational study in critically ill subjects with and without COVID-19 who underwent protocolized physiotherapy (including respiratory and rehabilitation physiotherapy) and neuromonitoring of cerebral oxygenation and hemodynamics. PaO2 /FIO2 , PaCO2 , hemodynamics (mean arterial pressure [MAP], mm Hg; heart rate, beats/min), and cerebral physiologic parameters (noninvasive intracranial pressure, cerebral perfusion pressure using transcranial Doppler, and cerebral oxygenation using near-infrared spectroscopy) were assessed before (T0) and immediately after physiotherapy (T1).

RESULTS

Thirty-one subjects were included (16 with COVID-19 and 15 without COVID-19). Physiotherapy improved PaO2 /FIO2 in the overall population (T1 = 185 [108-259] mm Hg vs T0 = 160 [97-231] mm Hg, P = .02) and in the subjects with COVID-19 (T1 = 119 [89-161] mm Hg vs T0 = 110 [81-154] mm Hg, P = .02) and decreased the PaCO2 in the COVID-19 group only (T1 = 40 [38-44] mm Hg vs T0 = 43 [38-47] mm Hg, P = .03). Physiotherapy did not affect cerebral hemodynamics, whereas increased the arterial oxygen part of hemoglobin both in the overall population (T1 = 3.1% [-1.3 to 4.9] vs T0 = 1.1% [-1.8 to 2.6], P = .007) and in the non-COVID-19 group (T1 = 3.7% [0.5-6.3] vs T0 = 0% [-2.2 to 2.8], P = .02). Heart rate was higher after physiotherapy in the overall population (T1 = 87 [75-96] beats/min vs T0 = 78 [72-92] beats/min, P = .044) and in the COVID-19 group (T1 = 87 [81-98] beats/min vs T0 = 77 [72-91] beats/min, P = .01), whereas MAP increased in the COVID-19 group only (T1 = 87 [82-83] vs T0 = 83 [76-89], P = .030).

CONCLUSIONS

Protocolized physiotherapy improved gas exchange in subjects with COVID-19, whereas it improved cerebral oxygenation in non-COVID-19 subjects.

Effects of rapid fluid infusion on hemoglobin concentration: a systematic review and meta-analysis

Background

Rapid fluid administration may decrease hemoglobin concentration (Hb) by a diluting effect, which could limit the increase in oxygen delivery (DO₂) expected with a positive response to fluid challenge in critically ill patients. Our aim was to quantify the decrease in Hb after rapid fluid administration.

Methods

Our protocol was registered in PROSPERO (CRD42020165146). We searched PubMed, the Cochrane Database, and Embase from inception until February 15, 2022. We selected studies that reported Hb before and after rapid fluid administration (bolus fluid given over less than 120 min) with crystalloids and/or colloids in adults. Exclusion criteria were studies that included bleeding patients, or used transfusions or extracorporeal circulation procedures. Studies were divided according to whether they involved non-acutely ill or acutely ill (surgical/trauma, sepsis, circulatory shock or severe hypovolemia, and mixed conditions) subjects. The mean Hb difference and, where reported, the DO₂ difference before and after fluid administration were extracted. Meta-analyses were conducted to assess differences in Hb before and after rapid fluid administration in all subjects and across subgroups. Random-effect models, meta-regressions and subgroup analyses were performed for meta-analyses. Risk of bias was assessed using the Cochrane Risk of Bias Assessment Tool. Inconsistency among trial results was assessed using the I² statistic.

Results

Sixty-five studies met our inclusion criteria (40 in non-acutely ill and 25 in acutely ill subjects), with a total of 2794 participants. Risk of bias was assessed as “low” for randomized controlled trials (RCTs) and ‘low to moderate’ for non-RCTs. Across 63 studies suitable for meta-analysis, the Hb decreased significantly by a mean of 1.33 g/dL [95% CI − 1.45 to − 1.12; p < 0.001; I² = 96.88] after fluid administration: in non-acutely ill subjects, the mean decrease was 1.56 g/dL [95% CI − 1.69 to − 1.42; p < 0.001; I² = 96.71] and in acutely ill patients 0.84 g/dL [95% CI − 1.03 to − 0.64; p = 0.033; I² = 92.91]. The decrease in Hb was less marked in patients with sepsis than in other acutely ill patients. The DO₂ decreased significantly in fluid non-responders with a significant decrease in Hb.

Conclusions

Hb decreased consistently after rapid fluid administration with moderate certainty of evidence. This effect may limit the positive effects of fluid challenges on DO₂ and thus on tissue oxygenation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-04191-x.

Optic nerve sheath diameter is associated with outcome in severe Covid-19

Neurological symptoms are common in Covid-19 and cerebral edema has been shown post-mortem. The mechanism behind this is unclear. Elevated intracranial pressure (ICP) has not been extensively studied in Covid-19. ICP can be estimated noninvasively with measurements of the optic nerve sheath diameter (ONSD). We performed a cohort study with ONSD ultrasound measurements in severe cases of Covid-19 at an intensive care unit (ICU). We measured ONSD with ultrasound in adults with severe Covid-19 in the ICU at Karolinska University Hospital in Sweden. Patients were classified as either having normal or elevated ONSD. We compared ICU length of stay (ICU-LOS) and 90 day mortality between the groups. 54 patients were included. 11 of these (20.4%) had elevated ONSD. Patients with elevated ONSD had 12 days longer ICU-LOS (95% CI 2 to 23 p = 0.03) and a risk ratio of 2.3 for ICU-LOS ≥ 30 days. There were no significant differences in baseline data or 90 day mortality between the groups. Elevated ONSD is common in severe Covid-19 and is associated with adverse outcome. This may be caused by elevated ICP. This is a clinically important finding that needs to be considered when deciding upon various treatment strategies.

The Importance of Neuromonitoring in Non Brain Injured Patients

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2022. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2022. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901.

Effects of positive end-expiratory pressure on lung ultrasound patterns and their correlation with intracranial pressure in mechanically ventilated brain injured patients

Background

The effects of positive end-expiratory pressure (PEEP) on lung ultrasound (LUS) patterns, and their relationship with intracranial pressure (ICP) in brain injured patients have not been completely clarified. The primary aim of this study was to assess the effect of two levels of PEEP (5 and 15 cmH₂O) on global (LUStot) and regional (anterior, lateral, and posterior areas) LUS scores and their correlation with changes of invasive ICP. Secondary aims included: the evaluation of the effect of PEEP on respiratory mechanics, arterial partial pressure of carbon dioxide (PaCO₂) and hemodynamics; the correlation between changes in ICP and LUS as well as respiratory parameters; the identification of factors at baseline as potential predictors of ICP response to higher PEEP.

Methods

Prospective, observational study including adult mechanically ventilated patients with acute brain injury requiring invasive ICP. Total and regional LUS scores, ICP, respiratory mechanics, and arterial blood gases values were analyzed at PEEP 5 and 15 cmH₂O.

Results

Thirty patients were included; 19 of them (63.3%) were male, with median age of 65 years [interquartile range (IQR) = 66.7–76.0]. PEEP from 5 to 15 cmH₂O reduced LUS score in the posterior regions (LUSp, median value from 7 [5–8] to 4.5 [3.7–6], p = 0.002). Changes in ICP were significantly correlated with changes in LUStot (rho = 0.631, p = 0.0002), LUSp (rho = 0.663, p < 0.0001), respiratory system compliance (rho = − 0.599, p < 0.0001), mean arterial pressure (rho = − 0.833, p < 0.0001) and PaCO₂ (rho = 0.819, p < 0.0001). Baseline LUStot score predicted the increase of ICP with PEEP.

Conclusions

LUS-together with the evaluation of respiratory and clinical variables-can assist the clinicians in the bedside assessment and prediction of the effect of PEEP on ICP in patients with acute brain injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03903-7.

The Use of Different Components of Brain Oxygenation for the Assessment of Cerebral Haemodynamics: A Prospective Observational Study on COVID-19 Patients

Introduction: The role of near-infrared spectroscopy (NIRS) for the evaluation of cerebral haemodynamics is gaining increasing popularity because of its noninvasive nature. The aim of this study was to evaluate the role of the integral components of regional cerebral oxygenation (rSO₂) measured by NIRS [i.e., arterial-oxyhemoglobin (O₂Hbi) and venous-deoxyhemoglobin (HHbi)-components], as indirect surrogates of cerebral blood flow (CBF) in a cohort of critically ill patients with coronavirus disease 2019 (COVID-19). We compared these findings to the gold standard technique for noninvasive CBF assessment, Transcranial Doppler (TCD). Methods: Mechanically ventilated patients with COVID-19 admitted to the Intensive Care Unit (ICU) of Policlinico San Martino Hospital, Genova, Italy, who underwent multimodal neuromonitoring (including NIRS and TCD), were included. rSO₂ and its components [relative changes in O₂Hbi, HHbi, and total haemoglobin (cHbi)] were compared with TCD (cerebral blood flow velocity, CBFV). Changes (Δ) in CBFV and rSO₂, ΔO₂Hbi, ΔHHbi, and ΔcHbi after systemic arterial blood pressure (MAP) modifications induced by different manoeuvres (e.g., rescue therapies and haemodynamic manipulation) were assessed using mixed-effect linear regression analysis and repeated measures correlation coefficients. All values were normalised as percentage changes from the baseline (Δ%). Results: One hundred and four measurements from 25 patients were included. Significant effects of Δ%MAP on Δ%CBF were observed after rescue manoeuvres for CBFV, ΔcHbi, and ΔO₂Hbi. The highest correlation was found between ΔCBFV and ΔΔO₂Hbi (R = 0.88, p < 0.0001), and the poorest between ΔCBFV and ΔΔHHbi (R = 0.34, p = 0.002). Conclusions: ΔO₂Hbi had the highest accuracy to assess CBF changes, reflecting its role as the main component for vasomotor response after changes in MAP. The use of indexes derived from the different components of rSO₂ can be useful for the bedside evaluation of cerebral haemodynamics in mechanically ventilated patients with COVID-19.

Intracranial Compliance Assessed by Intracranial Pressure Pulse Waveform

BACKGROUND

Morphological alterations in intracranial pressure (ICP) pulse waveform (ICPW) secondary to intracranial hypertension (ICP >20 mmHg) and a reduction in intracranial compliance (ICC) are well known indicators of neurological severity. The exclusive exploration of modifications in ICPW after either the loss of skull integrity or surgical procedures for intracranial hypertension resolution is not a common approach studied. The present study aimed to assess the morphological alterations in ICPW among neurocritical care patients with skull defects and decompressive craniectomy (DC) by comparing the variations in ICPW features according to elevations in mean ICP values.

METHODS

Patients requiring ICP monitoring because of acute brain injury were included. A continuous record of 10 min-length for the beat-by-beat analysis of ICPW was performed, with ICP elevation produced by means of ultrasound-guided manual internal jugular vein compression at the end of the record. ICPW features (peak amplitude ratio (P2/P1), time interval to pulse peak (TTP) and pulse amplitude) were counterweighed between baseline and compression periods. Results were distributed for three groups: intact skull (exclusive burr hole for ICP monitoring), craniotomy/large fractures (group 2) or DC (group 3).

RESULTS

57 patients were analyzed. A total of 21 (36%) presented no skull defects, 21 (36%) belonged to group 2, whereas 15 (26%) had DC. ICP was not significantly different between groups: ±15.11 for intact, 15.33 for group 2 and ±20.81 mmHg for group 3, with ICP-induced elevation also similar between groups (p = 0.56). Significant elevation was observed for the P2/P1 ratio for groups 1 and 2, whereas a reduction was observed in group 3 (elevation of ±0.09 for groups 1 and 2, but a reduction of 0.03 for group 3, p = 0.01), and no significant results were obtained for TTP and pulse amplitudes.

CONCLUSION

In the present study, intracranial pressure pulse waveform analysis indicated that intracranial compliance was significantly more impaired among decompressive craniectomy patients, although ICPW indicated DC to be protective for further influences of ICP elevations over the brain. The analysis of ICPW seems to be an alternative to real-time ICC assessment.