Influence of Norepinephrine and Phenylephrine on Frontal Lobe Oxygenation During Cardiopulmonary Bypass in Patients with Diabetes

Differential responses of cerebral and renal oxygenation to altered perfusion conditions during experimental cardiopulmonary bypass in sheep

We tested whether the brain and kidney respond differently to cardiopulmonary bypass (CPB) and to changes in perfusion conditions during CPB. Therefore, in ovine CPB, we assessed regional cerebral oxygen saturation (rSO2 ) by near-infrared spectroscopy and renal cortical and medullary tissue oxygen tension (PO2 ), and, in some protocols, brain tissue PO2 , by phosphorescence lifetime oximetry. During CPB, rSO2 correlated with mixed venous SO2 (r = 0.78) and brain tissue PO2 (r = 0.49) when arterial PO2 was varied. During the first 30 min of CPB, brain tissue PO2 , rSO2 and renal cortical tissue PO2 did not fall, but renal medullary tissue PO2 did. Nevertheless, compared with stable anaesthesia, during stable CPB, rSO2 (66.8 decreasing to 61.3%) and both renal cortical (90.8 decreasing to 43.5 mm Hg) and medullary (44.3 decreasing to 19.2 mm Hg) tissue PO2 were lower. Both rSO2 and renal PO2 increased when pump flow was increased from 60 to 100 mL kg-1  min-1 at a target arterial pressure of 70 mm Hg. They also both increased when pump flow and arterial pressure were increased simultaneously. Neither was significantly altered by partially pulsatile flow. The vasopressor, metaraminol, dose-dependently decreased rSO2 , but increased renal cortical and medullary PO2 . Increasing blood haemoglobin concentration increased rSO2 , but not renal PO2 . We conclude that both the brain and kidney are susceptible to hypoxia during CPB, which can be alleviated by increasing pump flow, even without increasing arterial pressure. However, increasing blood haemoglobin concentration increases brain, but not kidney oxygenation, whereas vasopressor support with metaraminol increases kidney, but not brain oxygenation.

Dobutamine-induced alternations in cerebral blood flow of healthy adults: a 3D pseudocontinuous arterial spin labeling study

BACKGROUND

It is unclear whether dobutamine, commonly used clinically in echocardiography and short-term congestive heart failure treatment for promoting increased myocardial contractility, affects brain microcirculatory behavior. Cerebral microcirculation plays an important role in ensuring adequate oxygen transport. Therefore, we investigated the effects of dobutamine on cerebral hemodynamics.

METHODS

Forty-eight healthy volunteers without cardiovascular or cerebrovascular disease underwent MRI to obtain cerebral blood flow (CBF) maps using 3D pseudocontinuous arterial spin labeling before and during the dobutamine stress test. Additionally, cerebrovascular morphology was obtained based on 3D-time-off-light (3D-TOF) magnetic resonance angiography (MRA). Electrocardiogram, heart rate (HR), respiration rate (RR), blood pressure, and blood oxygen were simultaneously recorded before and during dobutamine injection and during recovery (not during MRI). The anatomic features of the circle of Willis and the basilar artery (BA) diameter were assessed on MRA images by two radiologists with extensive neuroimaging experience. Binary logistic regression was used to test for the independent determinants of CBF changes.

RESULTS

HR, RR, systolic (SBP), and diastolic blood pressure (DBP) significantly increased after dobutamine infusion. Blood oxygen levels remained similar. Compared to the CBF in the resting state, the CBF values exhibited significantly lower CBF levels in both grey matter and white matter. Furthermore, compared with the CBF in the resting state, that in the stress state was decreased in the anterior circulation, mainly in the frontal lobe (voxel level P < 0.001, pixel level P < 0.05). Logistic regression showed that body mass index (BMI; odds ratio [OR] 5.80, 95% confidence interval [CI] 1.60-21.01, P = 0.008], resting SBP (OR 0.64, 95% CI 0.45-0.92, P = 0.014), and BA diameter (OR 11.04, 95% CI 1.05-116.53, P = 0.046) were significantly associated with frontal lobe CBF changes.

CONCLUSIONS

Dobutamine-induced stress significantly decreased CBF in the frontal lobe anterior circulation. Individuals with a high BMI and low SBP during the dobutamine stress test are more likely to have a stress-induced CBF decrease. Thus, attention should be paid to blood pressure, BMI, and cerebrovascular morphology of patients undergoing dobutamine stress echocardiography or those receiving intensive care or anesthesia.

A comprehensive review of cerebral oximetry in cardiac surgery

BACKGROUND

Patients who undergo cardiac surgery are at increased risk of stroke, postoperative cognitive decline, and delirium. These neurocognitive complications have led to increased costs, intensive care unit stays, morbidity, and mortality. As a result, there is a significant push to mitigate any neurological complications in cardiac surgery patients. Near-infrared spectroscopy to measure regional cerebral oxygen saturations has gained consideration due to its noninvasive and user-friendly nature. Cerebral oximetry desaturations during cardiac surgery have been linked to an array of adverse clinical outcomes. However, the most effective intraoperative interventions to protect this vulnerable patient population have yet to be ascertained.

AIM OF STUDY

To provide a comprehensive summary of the intraoperative management for cerebral oximetry desaturations during cardiac surgery. The review highlights clinical outcomes from cerebral oximetry use to quantify the importance of identifying cerebral desaturations during cardiac surgery. The review then interrogates possible interventions for cerebral oximetry desaturations in an effort to determine which interventions are most efficacious and to enlighten possible areas for further research.

METHODS

A narrative review of randomized controlled trials, observational studies, and systematic reviews with metanalyses was performed through August 2021.

RESULTS

There is significant heterogeneity among patient populations for which cerebral oximetry monitoring has been studied in cardiac surgery. Further, the definition of a clinically significant cerebral desaturation and the assessment of neurocognitive outcomes varied substantially across studies. As a result, metanalysis is challenging and few conclusions can be drawn. Cerebral oximetry use during cardiac surgery has not been associated with improvements in neurocognitive outcomes, morbidity, or mortality to date. The evidence to support a particular intervention for an acute desaturation is equivocal.

CONCLUSIONS

Future research is needed to quantify a clinically significant cerebral desaturation and to determine which interventions for an acute desaturation effectively improve clinical outcomes.

In-silico analysis of closed-loop vasopressor control of phenylephrine versus norepinephrine

We have previously demonstrated in in-silico, pre-clinical animal models, and finally human clinical studies the ability of a novel closed-loop vasopressor titration system to manage norepinephrine infusion rates to keep mean arterial blood pressure in a very tight range, reduce hypotension time and severity, and reduce overtreatment. We hypothesized that the same controller could, with modification for pharmacologic differences, suitably titrate a lower-potency longer duration of action agent like phenylephrine. Using the same physiologic simulation model as was used previously for in-silico testing of our controller for norepinephrine, we first updated the model to include a new vasopressor agent modeled after phenylephrine. A series of simulation tests patterned after our previous norepinephrine study was then conducted, this time using phenylephrine for management, in order to both test the system with the new agent and allow for comparisons between the two. Hundreds of simulation trials were conducted across a range of patient and environmental variances. The controller performance was characterized based on time in target, time above and below target, coefficient of variation, and using Varvel's criteria. The controller kept the simulated patients' MAP in target for 94% of management time in the simple scenarios and more than 85% of time in the most challenging scenarios. Varvel criteria were all under 1% error for expected pharmacologic responses and were consistent with those established for norepinephrine in our previous studies. The controller was able to acceptably titrate phenylephrine in this simulated patient model consistent with performance previously seen for norepinephrine after adjusting for the anticipated differences between the two agents.

The Regional Cerebral Oxygen Saturation Effect of Inotropes/Vasopressors Administered to Treat Intraoperative Hypotension: A Bayesian Network Meta-analysis

One of the main concerns of intraoperative hypotension is adequacy of cerebral perfusion, as cerebral blood flow decreases passively when mean arterial pressure falls below the lower limit of cerebral autoregulation. Treatment of intraoperative hypotension includes administration of drugs, such as inotropes and vasopressors, which have different pharmacological effects on cerebral hemodynamics; there is no consensus on the preferred drug to use. We performed a network meta-analysis (NMA) to pool and analyze data comparing the effect on cerebral oxygen saturation (ScO 2 ) measured by cerebral oximetry of various inotropes/vasopressors used to treat intraoperative hypotension. We searched randomized control trials in Embase, Ovid Medline, Scopus, Cochrane Central Register of Controlled Trials, and Web of Science. We included studies that enrolled adult patients undergoing surgery under general/spinal anesthesia that compared at least 2 inotropes/vasopressors to treat hypotension. We reviewed 51 full-text manuscripts and included 9 randomized controlled trials in our study. The primary outcome was change in ScO 2 . Our results showed the likelihood that dopamine, ephedrine, and norepinephrine had the lowest probability of decreasing ScO 2 . The suggested rank order to maintain ScO 2 , from higher to lower, was dopamine <ephedrine <norepinephrine <phenylephrine. Drugs in the lower rank order, like phenylephrine, produce higher reductions in ScO 2 . Compared with dopamine, the mean difference (95% credible interval) of ScO 2 reduction was: ephedrine -3.19 (-15.74, 8.82), norepinephrine -4.44 (-18.23, 9.63) and phenylephrine -6.93 (-18.31, 4.47). The results of our NMA suggest that dopamine and ephedrine are more likely to preserve ScO 2 , followed by norepinephrine. Compared with the other inotropes/vasopressors, phenylephrine decreased ScO 2 . Because of the inherent imprecision of direct/indirect comparisons, the rank orders are possibilities, not absolute ranks. Therefore the results of this NMA should be interpreted with caution.

Effect of phenylephrine on cerebral oxygen saturation and cardiac output in adults when used to treat intraoperative hypotension: a systematic review

OBJECTIVE

The objective of this review was to examine the effect of phenylephrine on cerebral oxygen saturation, cardiac output, and middle cerebral artery blood flow velocity when used to treat intraoperative hypotension.

INTRODUCTION

While the etiology of postoperative cognitive dysfunction in adults following surgery is likely multifactorial, intraoperative cerebral hypoperfusion is a commonly proposed mechanism. Research evidence and expert opinion are emerging that suggest phenylephrine adversely affects cerebral oxygen saturation and may also adversely affect cerebral perfusion via a reduction in cardiac output or cerebral vascular vasoconstriction. The administration of phenylephrine to treat intraoperative hypotension is common anesthesia practice, despite a lack of evidence to show it improves cerebral perfusion. Therefore, a systematic review of the effect of phenylephrine on cerebral hemodynamics has significant implications for anesthesia practice and future research.

INCLUSION CRITERIA

Studies of adults 18 years and over undergoing elective, non-neurosurgical procedures involving anesthesia were included. In these studies, participants received phenylephrine to treat intraoperative hypotension. The effect of phenylephrine on cerebral oxygen saturation, cardiac output, or middle cerebral artery blood flow velocity was measured.

METHODS

Key information sources searched included MEDLINE (Ovid), Embase, CINAHL (EBSCO), and Google Scholar. The scope of the search was limited to English-language studies published from 1999 through 2017. The recommended JBI approach to critical appraisal, study selection, data extraction, and data synthesis were used.

RESULTS

This systematic review found that phenylephrine consistently decreased cerebral oxygen saturation values despite simultaneously increasing mean arterial pressure to normal range. Results also found that ephedrine and dopamine were superior to phenylephrine in maintaining or increasing values. Phenylephrine was found to be similar to vasopressin in the extent to which both decreased cerebral oxygen saturation values. Results also showed that phenylephrine resulted in statistically significant declines in cardiac output, or failed to improve abnormally low preintervention values. The effect of phenylephrine on middle cerebral artery blood flow velocity was only measured in one study and showed that phenylephrine increased flow velocity by about 20%. Statistical pooling of the study results was not possible due to the gross variation in how the intervention was administered and how effect was measured.

CONCLUSIONS

This review found that phenylephrine administration resulted in declines in cerebral oxygen saturation and cardiac output. However, the research studies were ineffective in informing phenylephrine's mechanism of action or its impact on postoperative cognitive function.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO (CRD42018100740).

Study of the Effects of Epinephrine on Cerebral Oxygenation and Metabolism During Cardiac Arrest and Resuscitation by Hyperspectral Near-Infrared Spectroscopy

OBJECTIVES

Epinephrine is routinely administered to sudden cardiac arrest patients during resuscitation, but the neurologic effects on patients treated with epinephrine are not well understood. This study aims to assess the cerebral oxygenation and metabolism during ventricular fibrillation cardiac arrest, cardiopulmonary resuscitation, and epinephrine administration.

DESIGN

To investigate the effects of equal dosages of IV epinephrine administrated following sudden cardiac arrest as a continuous infusion or successive boluses during cardiopulmonary resuscitation, we monitored cerebral oxygenation and metabolism using hyperspectral near-infrared spectroscopy.

SETTINGS

A randomized laboratory animal study.

SUBJECTS

Nine healthy pigs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Our study showed that although continuous epinephrine administration had no significant impact on overall cerebral hemodynamics, epinephrine boluses transiently improved cerebral oxygenation (oxygenated hemoglobin) and metabolism (cytochrome c oxidase) by 15% ± 6.7% and 49% ± 18%, respectively (p < 0.05) compared with the baseline (untreated) ventricular fibrillation. Our results suggest that the effects of epinephrine diminish with successive boluses as the impact of the third bolus on brain oxygen metabolism was 24.6% ± 3.8% less than that of the first two boluses.

CONCLUSIONS

Epinephrine administration by bolus resulted in transient improvements in cerebral oxygenation and metabolism, whereas continuous epinephrine infusion did not, compared with placebo. Future studies are needed to evaluate and optimize the use of epinephrine in cardiac arrest resuscitation, particularly the dose, timing, and mode of administration.

Modern technology-derived normative values for cerebral tissue oxygen saturation in adults

Modern near-infrared spectroscopy technology is increasingly adopted to measure cerebral tissue oxygen saturation. However, the normal range of cerebral tissue oxygen saturation in adults with such technology is unknown. We sought to measure cerebral tissue oxygen saturation in healthy volunteers using the novel O3 Regional Oximetry® device (Masimo Corporation, Irvine, CA, USA) and assess its relationship with key physical and haemodynamic characteristics. For ≥5 minutes, we continuously recorded cerebral tissue oxygen saturation, pulse oximetry, cardiac index and mean arterial pressure. We assessed for differences in cerebral tissue oxygen saturation between hemispheres, sex, skin type, comorbidity or smoking status, and for associations between cerebral tissue oxygen saturation and age, height, weight, SpO₂and haemodynamic parameters. We recorded >32,000 observations in 98 volunteers aged 22 to 60 years, including 41 (42%) males. One-fifth had one or more co morbidities ( n=22, 22.5%), one-tenth were either current or former-smokers ( n=13, 13%), and most had a Fitzpatrick skin type of 3 or lower ( n=84, 86%). The mean combined average cerebral tissue oxygen saturation was 67.6% (95% confidence interval 66.8%-68.6%). We found statistically significant differences in cerebral tissue oxygen saturation according to hemisphere and an association between cerebral tissue oxygen saturation and mean arterial pressure and cardiac index. The combined average cerebral tissue oxygen saturation in 98 healthy volunteers was 67.6% with a narrow confidence interval and no combined average cerebral tissue oxygen saturation was below 56%. We also observed statistically significant yet quantitatively small cerebral tissue oxygen saturation differences between hemispheres, and an association between cerebral tissue oxygen saturation and mean arterial pressure and cardiac index.

Conventional or minimized cardiopulmonary bypass support during coronary artery bypass grafting? - An analysis by means of perfusion and body mass index

The use of minimized cardiopulmonary bypass support to reduce the side effects of extracorporeal circulation is still contradictorily discussed. This study compares perfusion operated by conventional (CCPB) and minimized (MCPB) cardiopulmonary bypass support during coronary artery bypass grafting (CABG). This study includes the data of 5164 patients treated at our department between 2004 and 2014. Tissue perfusion during cardiopulmonary bypass support and cardiac arrest was assessed by means of body mass index, hemodilution, blood pressure with corresponding pump flow and venous oxygen saturation, serum lactate, and serum pH. Hemodilution was more pronounced after CCPB: hemoglobin had dropped to 4.47 ± 0.142 g/dL after CCPB and to 2.77 ± 0.148 g/dL after MCPB (P = 0.0022). Despite the higher pump flow in conventional circuits (4.86-4.95 L/min vs. 4.1-4.18 L/min), mean blood pressure was higher during minimized bypass support (53 ± 10 vs. 56 ± 13 mm Hg [aortic clamping], 57 ± 9 vs. 61 ± 12 mm Hg [34°C], 55 ± 9 vs.59 ± 11 mm Hg [aortic clamp removal], P < 0.0001) at all time points. Venous oxygen saturation remained on comparable levels of >70% during both conventional and minimized cardiopulmonary bypass support. The increase in serum lactate was more pronounced after CCPB (8.98 ± 1.28 vs. 3.66 ± 1.25 mg/dL, P = 0.0079), corresponding to a decrease in serum pH to acidotic levels (7.33 ± 0.06 vs. 7.35 ± 0.06, P < 0.0001). These effects were evident in all BMI ranges. Minimized cardiopulmonary bypass support provides efficient perfusion in all BMI ranges and is thus equivalent to conventional circuits.

Preserved frontal lobe oxygenation following calcium chloride for treatment of anesthesia-induced hypotension

Vasopressor agents may affect cerebral oxygenation (rScO₂) as determined by near-infrared spectroscopy on the forehead. This case series evaluated the effect of calcium chloride vs. α and β-adrenergic receptor agonists on rScO₂ in patients (n = 47) undergoing surgery during i.v. anesthesia. Mean arterial pressure (MAP) and cardiac output (CO) were assessed by Model-flow^® and ephedrine (55 ± 3 vs. 74 ± 9 mmHg; 10 mg, n = 9), phenylephrine (51 ± 5 vs. 78 ± 9 mmHg, 0.1 mg, n = 11), adrenaline (53 ± 3 vs. 72 ± 11 mmHg; 1–2 μg, n = 6), noradrenaline (53 ± 5 vs. 72 ± 12 mmHg; 2–4 μg, n = 11), and calcium chloride (49 ± 7 vs. 57 ± 16 mmHg; 5 mmol, n = 10) increased MAP (all P < 0.05). CO increased with ephedrine (4.3 ± 0.9 vs. 5.3 ± 1.2, P < 0.05) and adrenaline (4.7 ± 1.2 vs. 5.9 ± 1.1 l/min; P = 0.07) but was not significantly affected by phenylephrine (3.9 ± 0.7 vs. 3.6 ± 1.0 l/min), noradrenaline (3.8 ± 1.2 vs. 3.7 ± 0.7 l/min), or calcium chloride (4.0 ± 1.4 vs. 4.1 ± 1.5 l/min). Following administration of β-adrenergic agents and calcium chloride rScO₂ was preserved while after administration of α-adrenergic drugs rScO₂ was reduced by app. 2% (P < 0.05). Following α-adrenergic drugs to treat anesthesia-induced hypotension tissue oxygenation is reduced while the use of β-adrenergic agonists and calcium chloride preserve tissue oxygenation.

Anesthetic Management for Cardiopulmonary Bypass

Cardiopulmonary bypass has revolutionized the practice of cardiac surgery and allows safe conduct of increasingly complex cardiac surgery. A brief review of the bypass circuit is undertaken in this review. A more thorough review of the anesthetic management is accomplished including choice of anesthetic medications and their effects. The inflammatory response to cardiopulmonary bypass is reviewed along with interventions that may help ameliorate the inflammation.