Monitoring of cerebral blood flow autoregulation: physiologic basis, measurement, and clinical implications.

Cerebral blood flow (CBF) autoregulation is the physiologic process whereby blood supply to the brain is kept constant over a range of cerebral perfusion pressures ensuring a constant supply of metabolic substrate. Clinical methods for monitoring CBF autoregulation were first developed for neurocritically ill patients and have been extended to surgical patients. These methods are based on measuring the relationship between cerebral perfusion pressure and surrogates of CBF or cerebral blood volume (CBV) at low frequencies (<0.05 Hz) of autoregulation using time or frequency domain analyses. Initially intracranial pressure monitoring or transcranial Doppler assessment of CBF velocity was utilised relative to changes in cerebral perfusion pressure or mean arterial pressure. A more clinically practical approach utilising filtered signals from near infrared spectroscopy monitors as an estimate of CBF has been validated. In contrast to the traditional teaching that 50 mm Hg is the autoregulation threshold, these investigations have found wide interindividual variability of the lower limit of autoregulation ranging from 40 to 90 mm Hg in adults and 20-55 mm Hg in children. Observational data have linked impaired CBF autoregulation metrics to adverse outcomes in patients with traumatic brain injury, ischaemic stroke, subarachnoid haemorrhage, intracerebral haemorrhage, and in surgical patients. CBF autoregulation monitoring has been described in both cardiac and noncardiac surgery. Data from a single-centre randomised study in adults found that targeting arterial pressure during cardiopulmonary bypass to above the lower limit of autoregulation led to a reduction of postoperative delirium and improved memory 1 month after surgery compared with usual care. Together, the growing body of evidence suggests that monitoring CBF autoregulation provides prognostic information on eventual patient outcomes and offers potential for therapeutic intervention. For surgical patients, personalised blood pressure management based on CBF autoregulation data holds promise as a strategy to improve patient neurocognitive outcomes.

High-resolution perioperative cerebral blood flow autoregulation measurement: a practical and feasible approach for widespread clinical monitoring.

A growing body of evidence demonstrates that excursions of BP below or above the limits of cerebral blood flow autoregulation are associated with complications in patients with neurological injury or for those undergoing cardiac surgery. Moreover, recent evidence suggests that maintaining MAP above the lower limit of cerebral autoregulation during cardiopulmonary bypass reduces the frequency of postoperative delirium and is associated with improved memory 1 month after surgery. Continuous measurement of BP in relation to cerebral autoregulation limits using a virtual patient monitoring platform processing near-infrared spectroscopy digital signals offers the hope of bringing this application to the bedside.

The utilization of caudal hydromorphone for fast-tracking in congenital cardiac surgery in a tertiary-care Children's hospital: An audit.

STUDY OBJECTIVE: Our study sought to audit our institutional practice of routine single-shot caudal epidural hydromorphone injection in children undergoing congenital cardiothoracic surgery to assess perioperative pain control and evaluate for any caudal complications. DESIGN: Retrospective observational study of all patients that received a caudal hydromorphone injection as part of the anesthetic for their cardiac surgical operation between January 2017 and July 2019. SETTING: Pediatric Cardiothoracic Operating Room (OR), Cardiac Intensive Care Unit. PATIENTS: One hundred and twenty-seven patients that received caudal hydromorphone as part of their anesthetic for a cardiac surgical operation. INTERVENTIONS: Caudal epidural injection performed immediately following induction of anesthesia utilizing only hydromorphone. MEASUREMENTS: The primary outcome was well-controlled pain, defined as a score of <4/10 on rFLACC or verbal pain scoring. Secondary outcome measures included in-OR extubation, pain service duration (from first assessment to "sign-off"), complications related to the caudal block, intensive care unit (ICU) length of stay (LOS), and Hospital LOS. MAIN RESULTS: One hundred and nine patients were included in the final analysis. Pain was "well-controlled" on average in 96.3% of patients (105/109). Average pain in the 24-h post-block period was 1.67 (SD = 2.37), with median pain score of 0 [0-3]. Peak pain score remained <4/10 for the entire 24-h post-block period in 22% of patients. 77.1% of caudal hydromorphone patients were extubated in the operating room. The median time to heparinization post-block was 108 min, beyond the ASRA recommendation of 60 min for neuraxial procedures. There were two caudal-related complications: one subcutaneous injection, and one instance of a time to heparinization of less than 60 min (56 min). Neither caudal complication led to patient harm. CONCLUSION: Caudal hydromorphone injection can safely contribute to achieving "well-controlled" pain in the pediatric cardiac surgical population when used as a component of a perioperative pain control plan.

Selected 2019 Highlights in Congenital Cardiac Anesthesia.

This article is a review of the highlights of pertinent literature published in 2019, which is of interest to the pediatric cardiac anesthesiologist. After a search of the United States National Library of Medicine PubMed database, several topics emerged in which significant contributions were made in 2019. The authors of this manuscript considered the following topics noteworthy and were included in this review: advances in pediatric heart transplantation, blood management in pediatric cardiac surgery, the impact of nutrition on outcomes in congenital heart surgery, and the use of vasopressin in patients after Fontan palliation.

Elevated arterial blood pressure after superior cavo-pulmonary anastomosis is associated with elevated pulmonary artery pressure and cerebrovascular dysautoregulation.

BACKGROUND: Elevated arterial blood pressure (ABP) is common after superior bidirectional cavopulmonary anastomosis (BCPA). The effects of elevated ABP after BCPA on cerebrovascular hemodynamics are unknown. We sought to determine the relationship between elevated ABP and cerebrovascular autoregulation after BCPA. METHODS: Prospective, observational study on infants with single-ventricle physiology after BCPA surgery. Continuous recordings of mean ABP, mean cavopulmonary artery pressure (PAP), near-infrared spectroscopy measures of cerebral oximetry (regional cerebral oxygen saturation (rSO2)), and relative cerebral blood volume index were obtained from admission to extubation. Autoregulation was measured as hemoglobin volume index (HVx). Physiologic variables, including the HVx, were tested for variance across ABP. RESULTS: Sixteen subjects were included in the study. Elevated ABP post-BCPA was associated with both, elevated PAP (P<0.0001) and positive HVx (dysautoregulation; P<0.0001). No association was observed between ABP and alterations in rSO2. Using piecewise regression, the relationship of PAP to ABP demonstrated a breakpoint at 68 mm Hg (interquartile range (IQR) 62-70 mm Hg). Curve fit of HVx as a function of ABP identified optimal ABP supporting robust autoregulation at a median ABP of 55 mm Hg (IQR 51-64 mm Hg). CONCLUSIONS: Elevated ABP post-BCPA is associated with cerebrovascular dysautoregulation, and elevated PAP. The effects, of prolonged dysautoregulation within this population, require further study.

Does hypothermia impair cerebrovascular autoregulation in neonates during cardiopulmonary bypass?

BACKGROUND: Autoregulation monitoring has been proposed as a means to identify optimal arterial blood pressure goals during cardiopulmonary bypass, but it has been observed that cerebral blood flow is pressure passive during hypothermic bypass. When neonates cooled during cardiopulmonary bypass are managed with vasodilators and controlled hypotension, it is not clear whether hypothermia or hypotension were the cause of impaired autoregulation. AIM: We sought to measure the effect of both arterial blood pressure and hypothermia on autoregulation in a cohort of infants cooled for bypass, hypothesizing a collinear relationship between hypothermia, hypotension, and dysautoregulation. METHODS: Cardiopulmonary bypass was performed on 72 infants at Texas Children's Hospital during 2015 and 2016 with automated physiologic data capture, including arterial blood pressure, nasopharyngeal temperature, cerebral oximetry, and a cerebral blood volume index derived from near infrared spectroscopy. Cooling to 18°C, 24°C, and 30°C was performed on 33, 12, and 22 subjects, respectively. The hemoglobin volume index was calculated as a moving correlation coefficient between mean arterial blood pressure and the cerebral blood volume index. Positive values of the hemoglobin volume index indicate impaired autoregulation. Relationships between variables were assessed utilizing a generalized estimating equation approach. RESULTS: Hypothermia was associated with hypotension, dysautoregulation, and increased cerebral oximetry. Comparing the baseline temperature of 36°C with 18°C, arterial blood pressure was 44 mm Hg (39-52) vs 25 mm Hg (21-31); the hemoglobin volume index was 0.0 (-0.02 to 0.004) vs 0.5 (0.4-0.7) and cerebral oximetry was 59% (57-61) vs 88% (80-92) (Median, 95% CI of median; P<.0001 for all three associations by linear regression with generalized estimation of equations with data from all temperatures measured). CONCLUSIONS: Arterial blood pressure, temperature, and cerebral autoregulation were collinear in this cohort. The conclusion that hypothermia causes impaired autoregulation is thus confounded. The effect of temperature on autoregulation should be delineated before clinical deployment of autoregulation monitors to prevent erroneous determination of optimal arterial blood pressure. Showing the effect of temperature on autoregulation will require a normotensive hypothermic model.

A Novel Electrocardiogram Algorithm Utilizing ST-Segment Instability for Detection of Cardiopulmonary Arrest in Single Ventricle Physiology: A Retrospective Study.

OBJECTIVE: We evaluated ST-segment monitoring to detect clinical decompensation in infants with single ventricle anatomy. We proposed a signal processing algorithm for ST-segment instability and hypothesized that instability is associated with cardiopulmonary arrests. DESIGN: Retrospective, observational study. SETTING: Tertiary children's hospital 21-bed cardiovascular ICU and 36-bed step-down unit. PATIENTS: Twenty single ventricle infants who received stage 1 palliation surgery between January 2013 and January 2014. Twenty rapid response events resulting in cardiopulmonary arrests (arrest group) were recorded in 13 subjects, and nine subjects had no interstage cardiopulmonary arrest (control group). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Arrest data were collected over the 4-hour time window prior to cardiopulmonary arrest. Control data were collected from subjects with no interstage arrest using the 4-hour time window prior to cardiovascular ICU discharge. A paired subgroup analysis was performed comparing subject 4-hour windows prior to arrest (prearrest group) with 4-hour windows prior to discharge (postarrest group). Raw values of ST segments were compared between groups. A 3D ST-segment vector was created using three quasi-orthogonal leads (II, aVL, and V5). Magnitude and instability of this continuous vector were compared between groups. There was no significant difference in mean unprocessed ST-segment values in the arrest and control groups. Utilizing signal processing, there was an increase in the ST-vector magnitude (p = 0.02) and instability (p = 0.008) in the arrest group. In the paired subgroup analysis, there was an increase in the ST-vector magnitude (p = 0.05) and instability (p = 0.05) in the prearrest state compared with the postarrest state prior to discharge. CONCLUSIONS: In single ventricle patients, increased ST instability and magnitude were associated with rapid response events that required intervention for cardiopulmonary arrest, whereas conventional ST-segment monitoring did not differentiate an arrest from control state.

Prediction of imminent, severe deterioration of children with parallel circulations using real-time processing of physiologic data.

OBJECTIVES: Sudden death is common in patients with hypoplastic left heart syndrome and comparable lesions with parallel systemic and pulmonary circulation from a common ventricular chamber. It is hypothesized that unforeseen acute deterioration is preceded by subtle changes in physiologic dynamics before overt clinical extremis. Our objective was to develop a computer algorithm to automatically recognize precursors to deterioration in real-time, providing an early warning to care staff. METHODS: Continuous high-resolution physiologic recordings were obtained from 25 children with parallel systemic and pulmonary circulation who were admitted to the cardiovascular intensive care unit of Texas Children's Hospital between their early neonatal palliation and stage 2 surgical palliation. Instances of cardiorespiratory deterioration (defined as the need for cardiopulmonary resuscitation or endotracheal intubation) were found via a chart review. A classification algorithm was applied to both primary and derived parameters that were significantly associated with deterioration. The algorithm was optimized to discriminate predeterioration physiology from stable physiology. RESULTS: Twenty cardiorespiratory deterioration events were identified in 13 of the 25 infants. The resulting algorithm was both sensitive and specific for detecting impending events, 1 to 2 hours in advance of overt extremis (receiver operating characteristic area = 0.91, 95% confidence interval = 0.88-0.94). CONCLUSIONS: Automated, intelligent analysis of standard physiologic data in real-time can detect signs of clinical deterioration too subtle for the clinician to observe without the aid of a computer. This metric may serve as an early warning indicator of critical deterioration in patients with parallel systemic and pulmonary circulation.