Physiologic parameters of the Cushing reflex

Association of Dynamic Trajectories of Time-Series Data and Life-Threatening Mass Effect in Large Middle Cerebral Artery Stroke

BACKGROUND

Life-threatening, space-occupying mass effect due to cerebral edema and/or hemorrhagic transformation is an early complication of patients with middle cerebral artery stroke. Little is known about longitudinal trajectories of laboratory and vital signs leading up to radiographic and clinical deterioration related to this mass effect.

METHODS

We curated a retrospective data set of 635 patients with large middle cerebral artery stroke totaling 95,463 data points for 10 longitudinal covariates and 40 time-independent covariates. We assessed trajectories of the 10 longitudinal variables during the 72 h preceding three outcomes representative of life-threatening mass effect: midline shift ≥ 5 mm, pineal gland shift (PGS) > 4 mm, and decompressive hemicraniectomy (DHC). We used a "backward-looking" trajectory approach. Patients were aligned based on outcome occurrence time and the trajectory of each variable was assessed before that outcome by accounting for cases and noncases, adjusting for confounders. We evaluated longitudinal trajectories with Cox proportional time-dependent regression.

RESULTS

Of 635 patients, 49.0% were female, and the mean age was 69 years. Thirty five percent of patients had midline shift ≥ 5 mm, 24.3% of patients had PGS > 4 mm, and 10.7% of patients underwent DHC. Backward-looking trajectories showed mild increases in white blood cell count (10-11 K/UL within 72 h), temperature (up to half a degree within 24 h), and sodium levels (1-3 mEq/L within 24 h) before the three outcomes of interest. We also observed a decrease in heart rate (75-65 beats per minute) 24 h before DHC. We found a significant association between increased white blood cell count with PGS > 4 mm (hazard ratio 1.05, p value 0.007).

CONCLUSIONS

Longitudinal profiling adjusted for confounders demonstrated that white blood cell count, temperature, and sodium levels appear to increase before radiographic and clinical indicators of space-occupying mass effect. These findings will inform the development of multivariable dynamic risk models to aid prediction of life-threatening, space-occupying mass effect.

Dynamic trajectories of life-threatening mass effect in patients with large middle cerebral artery stroke

Background

Life-threatening, space-occupying mass effect due to cerebral edema and/or hemorrhagic transformation is an early complication of patients with middle cerebral artery (MCA) stroke. Little is known about longitudinal trajectories of laboratory and vital signs leading up to radiographic and clinical deterioration related to this mass effect.

Methods

We curated a granular retrospective dataset of 635 patients with large middle cerebral artery (MCA) stroke totaling 108,547 data points for repeated measurements of 10 covariates, and 40 time-independent covariates. We assessed longitudinal trajectories of the 10 longitudinal variables during the 72 hours preceding three outcomes representative of life-threatening mass effect: midline shift (MLS) ≥5mm, pineal gland shift (PGS) >4mm, and decompressive hemicraniectomy (DHC). We used a "backward looking" trajectory approach. Patients were aligned according to the time of outcome occurrence and the trajectory of each variable was assessed prior to that outcome by accounting for both cases and non-cases.

Results

Of 635 patients, 49% were female, and mean age was 69 years. Thirty five percent of patients had MLS ≥ 5mm, 24.1% had PGS >4mm, and DHC occurred in 10.7%. For the three outcomes of interest, backward-looking trajectories showed mild increases in white blood cell count (10 up to 11 K/UL within 72 hours), temperature (up to half a degree within 24 hours), and sodium (1-3 mEq/L within 24 hours) leading up to outcomes. We also observed a decrease in heart rate (75 - 65 beats per minute) 24 hours prior to DHC.

Conclusions

Univariable longitudinal profiling showed that temperature, white blood cell count, and sodium increase prior to radiographic and clinical indicators of space-occupying mass effect. These findings will inform development of multivariable dynamic risk models to aid prediction of life-threatening space-occupying mass effect.

Features derived from blood pressure and intracranial pressure predict elevated intracranial pressure events in critically ill children

Clinicians frequently observe hemodynamic changes preceding elevated intracranial pressure events. We employed a machine learning approach to identify novel and differentially expressed features associated with elevated intracranial pressure events in children with severe brain injuries. Statistical features from physiologic data streams were derived from non-overlapping 30-min analysis windows prior to 21 elevated intracranial pressure events; 200 records without elevated intracranial pressure events were used as controls. Ten Monte Carlo simulations with training/testing splits provided performance benchmarks for 4 machine learning approaches. XGBoost yielded the best performing predictive models. Shapley Additive Explanations analyses demonstrated that a majority of the top 20 contributing features consistently derived from blood pressure data streams up to 240 min prior to elevated intracranial events. The best performing prediction model was using the 30-60 min analysis window; for this model, the area under the receiver operating characteristic window using XGBoost was 0.82 (95% CI 0.81-0.83); the area under the precision-recall curve was 0.24 (95% CI 0.23-0.25), above the expected baseline of 0.1. We conclude that physiomarkers discernable by machine learning are concentrated within blood pressure and intracranial pressure data up to 4 h prior to elevated intracranial pressure events.

Mechanisms of traumatic cardiac arrest in Kuwait: A retrospective study

The objective of this study is to describe the epidemiology and causes of traumatic cardiac arrest (TCA) in Kuwait aiming to provide a preliminary background to update the current guidelines and improve patients' management.This is a retrospective analysis of TCA cases retrieved from emergency medical services archived data between 1 January and 31 December 2017. The TCA cases were sub-grouped based on mechanism of injury then compared in terms of patient demographics, vital signs, patterns of injuries, resuscitation practices, and outcomes.Outcomes; On scene mortality rate and pre-hospital return of spontaneous circulation.Among the 204 TCA patients, 140 patients met the inclusion criteria. This whole group was then divided in to 4 subgroups: road traffic accident (RTA) 76% (n=106), fall from height (FFH) 13% (n = 18), slip/fall 4% (n = 6), and assaults 7% (n = 10). There was significant difference between the four mechanisms in: mean age (P =  < .001), type of injury (P = .005), head injury (P = .005), chest injury (P = .003), GCS score < 9 (P = .004) and initial hypertension (P =  < .001). Initial hypertension and GCS score < 9 were only documented in head injuries of RTA and slip/fall groups. Significant difference was also seen in cardiopulmonary resuscitation (P = .006), airway management (P = .035) and on scene mortality rate (P = .003). All patients who had isolated head injury in FFH were pronounced dead on scene, 60%.Not all TCA incidents are the same, there are different pattern of injuries in each TCA mechanism. Head injuries are predominantly seen in RTA, FFH, slip /falls and chest injuries are seen in assaults. This can influence emergency medical services personals resuscitation plan. Further research is required to address the resuscitation of TCA of different mechanisms.

Metabolic syndrome in relation to risk of meningioma

BACKGROUND

Meningioma is a frequent primary intracranial tumor, the etiology of which is potentially related to adiposity. Metabolic syndrome (MetS) is an increasingly common disease characterized by having at least three of the following conditions: central adiposity, arterial hypertension, dyslipidemia, and insulin resistance. Only one prior study investigated MetS in relation to meningioma risk and found a positive association between the two.

RESULTS

Among 2,027 cases and 20,269 controls, body mass index was positively associated with meningioma (p-value for trend < 0.0001). Arterial hypertension was also associated with an increased risk of meningioma (OR = 1.34; 95% CI = 1.20- 1.49). By comparison, high-density lipoprotein, triglycerides, fasting serum glucose, and use of ACE-inhibitors, AT-II inhibitors, beta-blockers, diuretics, calcium antagonists, nitrates, or statins were not associated with risk of meningioma.

MATERIALS AND METHODS

We conducted a matched case-control analysis using data from the U.K.-based Clinical Practice Research Datalink (CPRD) to analyse medical conditions and treatments related to MetS in cases with meningioma and meningioma-free controls. We identified all cases with an incident diagnosis of meningioma between 1995 and 2015 and matched each to ten controls on age, sex, calendar time, general practice, and number of years of active history in the CPRD prior to the index date. Exposures were assessed using computerised records. We conducted conditional logistic regression analysis to determine relative risks, estimated as odds ratios (ORs) with 95% confidence intervals (CIs), adjusted for confounding factors.

CONCLUSIONS

Obesity and arterial hypertension are positively associated with risk of meningioma. Further studies are needed to better understand potential underlying biologic mechanisms.

Intracranial elastance in isoflurane-anesthetized horses

OBJECTIVE

To determine whether high intracranial pressure (ICP) during spontaneous ventilation (SV) in anesthetized horses coincides with an increase in intracranial elastance (ie, change in ICP per unit change of intracranial volume).

ANIMALS

6 adult horses.

PROCEDURE

Anesthesia was induced and maintained in each horse for 5 hours with isoflurane at a constant dose equal to 1.2 times the minimum alveolar concentration. Direct ICP measurements were obtained by use of a strain gauge transducer inserted in the subarachnoid space, and arterial blood pressure was measured from a carotid artery. Physiologic responses were recorded after 15 minutes of normocapnic controlled ventilation (CV) and then after 10 minutes of SV. Aliquots (3 mL) of CSF were removed from each horse during SV until ICP returned to CV values. Slopes of pressure-volume curves yielded intracranial elastance.

RESULTS

Intracranial elastance ranged from 0.2 to 3.7 mm Hg/mL after removal of the first aliquot of CSF Slopes of pressure-volume curves were largest following removal of the initial CSF aliquot, but shallow portions of curves were detected at relatively high ICPs (25 to 35 mm Hg). A second-order relationship between SV ICP and initial intracranial elastance was found.

CONCLUSIONS AND CLINICAL RELEVANCE

In horses anesthetized with isoflurane, small changes in intracranial volume can cause large changes in ICP Increased intracranial elastance could further exacerbate preexisting intracranial hypertension. However, removal of small volumes of CSF may cause rapid compensatory replacement from other intracranial compartments, which suggests steady-state maintenance of an increase in intracranial volume during isoflurane anesthesia in horses.

Central volume expansion is pivotal for sustained decrease in heart rate during seated to supine posture change

During prolonged, static carotid baroreceptor stimulation by neck suction (NS) in seated humans, heart rate (HR) decreases acutely and thereafter gradually increases. This increase has been explained by carotid baroreceptor adaptation and/or buffering by aortic reflexes. During a posture change from seated to supine (Sup) with similar carotid stimulation, however, the decrease in HR is sustained. To investigate whether this discrepancy is caused by changes in central blood volume, we compared (n = 10 subjects) the effects of 10 min of seated NS (adjusted to simulate carotid stimulation of a posture change), a posture change from seated to Sup, and the same posture change with left atrial (LA) diameter maintained unchanged by lower body negative pressure (Sup + LBNP). During Sup, the prompt decreases in HR and mean arterial pressure (MAP) were sustained. HR decreased similarly within 30 s of NS (65 +/- 2 to 59 +/- 2 beats/min) and Sup + LBNP (65 +/- 2 to 58 +/- 2 beats/min) and thereafter gradually increased to values of seated. MAP decreased similarly within 5 min during Sup + LBNP and NS (by 7 +/- 1 to 9 +/- 1 mmHg) and thereafter tended to increase toward values of seated subjects. Arterial pulse pressure was increased the most by Sup, less so by Sup + LBNP, and was unchanged by NS. LA diameter was only increased by Sup. In conclusion, static carotid baroreceptor stimulation per se causes the acute (<30 s) decrease in HR during a posture change from seated to Sup, whereas the central volume expansion (increased LA diameter and/or arterial pulse pressure) is pivotal to sustain this decrease. Thus the effects of central volume expansion override adaptation of the carotid baroreceptors and/or buffering of aortic reflexes.

Elevated intracranial pressure masks hemorrhagic hypotension in a canine model

Previous clinical studies of blunt trauma patients with severe brain injuries have demonstrated that emergency department vital signs failed to consistently identify life-threatening abdominal injury. One hypothesis to explain this is that bradycardia and systemic hypertension from brainstem injury (the Cushing response) may mask the tachycardia and hypotension ordinarily manifested by hemorrhagic hypovolemia. This would result in inappropriately normal or near-normal emergency department vital signs for otherwise clinically apparent hypovolemia. To test this hypothesis, splenectomized dogs (n = 9) were phlebotomized to a systolic blood pressure (SBP) of 60 mm Hg. Subsequently, intracranial pressure (ICP) was artificially elevated in a controlled, incremental fashion. From a mean SBP of 58.4 +/- 3.9 mm Hg at a baseline ICP of 8.1 +/- 4.2 mm Hg, increases in ICP of only 20 mm Hg significantly raised SBP (in some animals). When ICP reached 70 mm Hg, mean SBP reached 95.1 +/- 8.7 mm Hg (p < 0.001) in spite of profound hemorrhagic hypovolemia. In all subjects, the tachycardia that accompanied hypovolemia tended towards normal with incremental increases in ICP. However, this did not reach statistical significance. In response to elevations in ICP, this hypovolemic canine model displayed normalization of SBP with variable changes in heart rate. These changes could mask hemorrhagic hypotension in humans sustaining multiple system trauma. These experimental data support clinical studies advocating immediate definitive abdominal evaluation in unconscious blunt trauma patients, regardless of vital signs.

Transcranial Doppler and cortical microcirculation at increased intracranial pressure and during the Cushing response: an experimental study on rabbits

The effect of increased intracranial pressure on the flow velocity of the basilar artery was measured with transcranial ultrasonic Doppler in New Zealand White rabbits under alpha-chloralose anesthesia and artificial respiration. Laser Doppler flowmetry served to study changes of the cortical microcirculation. The results confirm a high inverse correlation of the diastolic flow velocity, the pulsatility index, and the resistance index with the cerebral perfusion pressure (CPP). During acute intracranial hypertension, however, these parameters do not show a good correlation with the local cortical blood flow. The absence of a correlation was evident over a wide CPP range down to values of 35 mm Hg. Only at CPP values below this critical threshold is the microcirculation impaired. The threshold is reached at pulsatility index values of more than 2.0 and at resistance index values of more than 0.8. Therefore, transcranial Doppler indices permit the detection of critical reductions of microcirculatory blood flow. The Cushing reaction occurred with a constant time lag of 5.5 +/- 0.7 seconds after the loss of CPP. The Cushing reaction did not establish systolic blood flow, which remained below the functional threshold, as concluded from the temporary loss of somatosensory evoked potentials.