Effects of phenylephrine on systemic and cerebral circulations in humans: a systematic review with mechanistic explanations

Phenylephrine and the risk of atrial fibrillation in critically ill patients: a multi-centre study from eICU database

Background

Vasopressors are vital for maintaining blood pressure in critically ill patients, though they carry risks like irregular heartbeats and impaired cardiac oxygen balance. Existing studies have not definitively proven that phenylephrine triggers new atrial fibrillation (AF).

Aims

This study was designed to assess pharmacological associations between phenylephrine utilization and new AF occurrence risk.

Methods

This multicenter retrospective study analyzed eICU database records. Propensity score matching (PSM) balanced baseline confounders. Cox regression models (unadjusted/adjusted) assessed phenylephrine-AF associations.

Results

In this cohort encompassing 51,294 critically ill adults (mean age 62.4 ± 16.6 years; 53.5% male), propensity score matching established comparable cohorts: 2,110 phenylephrine-exposed patients and 6,330 matched controls. The analysis revealed a clinically significant disparity in new AF incidence, with phenylephrine-exposed patients demonstrating a 10.5% event rate (282/2,673) versus 4.9% (2,395/48,621) in non-exposed counterparts (p < 0.001). Multivariable-adjusted Cox proportional hazards models identified a 29% elevated risk of new AF associated with phenylephrine administration (aHR, 1.29; 95%CI, 1.05-1.58). Notably, this association remained robust across multiple sensitivity analyses employing alternative matching methodologies and covariate adjustments.

Conclusion

This evidence positions phenylephrine as a modifiable new AF risk factor in critical care, supporting risk-aware vasopressor selection through benefit-harm analysis.

Care guided by tissue oxygenation and haemodynamic monitoring in off-pump coronary artery bypass grafting (Bottomline-CS): assessor blind, single centre, randomised controlled trial

OBJECTIVE

To assess whether perioperative management guided by near-infrared spectroscopy to determine tissue oxygen saturation and haemodynamic monitoring reduces postoperative complications after off-pump coronary artery bypass grafting.

DESIGN

Assessor blinded, single centre, randomised controlled trial (Bottomline-CS trial).

SETTING

A tertiary teaching hospital in China.

PARTICIPANTS

1960 patients aged 60 years or older who were scheduled for elective off-pump coronary artery bypass grafting.

INTERVENTIONS

All patients had multisite monitoring of tissue oxygen saturation (bilateral forehead and unilateral forearm brachioradialis) and haemodynamic monitoring. Both groups received usual care, including arterial blood pressure, central venous pressure, electrocardiography, and transoesophageal echocardiography when indicated. Guided care aimed to maintain tissue oxygenation within 10% above or below preoperative baseline values, established 24-48 hours before surgery, from the start of anaesthesia until extubation or for up to 24 hours postoperatively. In the usual care group, tissue oximetry and haemodynamic data were concealed, and care was routine.

MAIN OUTCOME MEASURES

The primary outcome was the incidence of a composite of 30 day postoperative complications, which were cerebral, cardiac, respiratory, renal, infectious, and mortality complications. Secondary outcomes included the individual components of the composite outcome, new-onset atrial fibrillation, and hospital length of stay.

RESULTS

Of 1960 patients randomly assigned, data from 967 guided care and 974 usual care patients were analysed. During anaesthesia, the area under the curve for tissue oxygen saturation measurements outside the plus and minus 10% baseline range was significantly smaller with guided care than only usual care: left forehead 32.4 versus 57.6 (%×min, P<0.001), right forehead 37.9 versus 62.6 (P<0.001), and forearm 14.8 versus 44.7 (P<0.001). The primary composite outcome occurred in 457/967 (47.3%) patients in the guided care group and 466/974 (47.8%) patients in the usual care group (unadjusted risk ratio 0.99 (95% confidence interval 0.90 to 1.08), P=0.83). No secondary outcomes differed significantly between groups. The largest observed difference was in incidence of pneumonia, which was less frequent in the guided care group (88/967, 9.1%) than in the usual care group (121/974, 12.4%) and not statistically significant after adjusting for multiple comparisons.

CONCLUSIONS

Guided care by use of multisite near-infrared spectroscopy and haemodynamic monitoring effectively maintained tissue oxygenation near baseline levels compared with usual care. However, no clear evidence was noted that this approach reduced the incidence of major postoperative complications. These findings do not support the routine use of near-infrared spectroscopy and haemodynamic monitoring to maintain tissue oxygenation during off-pump coronary artery bypass grafting.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04896736.

Cerebral oxygenation and hemodynamic changes during ephedrine and phenylephrine administration for transient intraoperative hypotension in patients undergoing major abdominal surgery: a randomized controlled trial

BACKGROUND

Phenylephrine and ephedrine are frequently used vasopressors for treating intraoperative hypotension. However, their impact on cerebral oxygenation and blood flow remains a subject of debate. This study aims to understand their effects on cerebral oxygen saturation and hemodynamics when used for treatment of intraoperative hypotension.

METHODS

The adult patients undergoing major abdominal surgery under general anesthesia were randomly assigned into ephedrine (ED) group or phenylephrine (PE) group. They received an intravenous bolus of either ephedrine or phenylephrine for treating intraoperative transient hypotension. The primary outcome was their effects on regional cerebral oxygen saturation (rScO2). The secondary outcomes included cerebral hemodynamics middle cerebral artery velocity (MCAvm), pulsatility index (PI), and resistance index (RI), as well as systemic hemodynamics arterial blood pressure (ABP), heart rate (HR), cardiac output (CO), cardiac index (CI), stroke volume (SV) and stroke volume index (SVI). Additionally, two indices of cerebral autoregulation, mean flow index (Mxa) and cerebral oximetry index (COX), were calculated in real-time via ICM + software.

RESULTS

Forty patients were included in this study. The initial results showed ephedrine increased rScO2 (p < 0.001), while phenylephrine increased Mxa (p < 0.02) and COX (p < 0.007), respectively. However, upon further linear-mix model analysis, the effects of both drugs on rScO2 (p = 0.944), Mxa (p = 0.093) and COX (p = 0.084) were found to be non-significant. Compared with the hemodynamic parameters during hypotension, the systolic blood pressure (SBP) (p < 0.001), diastolic blood pressure (DBP) (p < 0.001), mean arterial pressure (MAP) (p < 0.001), and MCAvm (p < 0.001) significantly increased after both ephedrine and phenylephrine administration. However, no significant differences were found between the two groups in terms of the changes in MAP (p = 0.549) and MCAvm (p = 0.173). And there were significant increases in CO (p < 0.001), HR (p < 0.001), and CI (p < 0.001) following ephedrine administration, while decreases in HR (p < 0.001), CO (p < 0.001), and CI (p < 0.001) after phenylephrine administration.

CONCLUSION

In the management of intraoperative hypotension, both phenylephrine and ephedrine effectively increase MAP and MCAvm, albeit with their differential effects on CO and HR. It seems that neither vasopressor has a significant impact on cerebral oxygenation and cerebral autoregulation.

Effects of noradrenaline and phenylephrine on cerebral oxygen saturation during cardiopulmonary bypass in cardiac surgery

Cardiopulmonary bypass (CPB) in cardiac surgery is associated with a high risk of postoperative neurological complications. Perioperative use of vasopressors is common to counteract arterial hypotension in this setting. However, use of α-agonist vasopressors has been associated with cerebral desaturations. Given that reductions in cerebral oxygen saturation (S c O 2 ${S_{{\mathrm{c}}{{\mathrm{O}}_2}}}$ ) can increase postoperative neurological dysfunction, we aimed to investigate the impact of noradrenaline (NA) and phenylephrine (PE) onS c O 2 ${S_{{\mathrm{c}}{{\mathrm{O}}_2}}}$ during the CPB period of a cardiac surgery in 36 patients scheduled for an elective cardiac surgery. Patients were randomized to the intra-operative use of either NA or PE. During CPB, mean arterial pressure (MAP) was elevated pharmacologically to predefined thresholds of 60 and 80 mmHg, while CPB flow was kept constant. TheS c O 2 ${S_{{\mathrm{c}}{{\mathrm{O}}_2}}}$ values were recorded for 5 min per MAP threshold. The MAP increased adequately between thresholds of 60 and 80 mmHg (NA, 59 ± 3 vs. 81 ± 3 mmHg and PE, 61 ± 4 vs. 81 ± 3 mmHg; P ˂ 0.01). TheS c O 2 ${S_{{\mathrm{c}}{{\mathrm{O}}_2}}}$ decreased between pressure thresholds of 60 and 80 mmHg (NA, 70 ± 11 vs. 69 ± 11 mmHg and PE, 64 ± 11 vs. 63 ± 11 mmHg; P ˂ 0.01). Reduction inS c O 2 ${S_{{\mathrm{c}}{{\mathrm{O}}_2}}}$ did not differ between vasopressors. The mean relative decrease inS c O 2 ${S_{{\mathrm{c}}{{\mathrm{O}}_2}}}$ across groups was 2.0% (95% confidence interval: 0.6 to 2.1). Elevation in MAP mediated solely by vasopressors induces significant decreases inS c O 2 ${S_{{\mathrm{c}}{{\mathrm{O}}_2}}}$ during cardiac surgery under CPB. However, their impact onS c O 2 ${S_{{\mathrm{c}}{{\mathrm{O}}_2}}}$ remains clinically non-significant according to current guidelines.

Hip Fracture Intervention Study for Prevention of Hypotension Trial: a Pilot Randomized Controlled Trial

BACKGROUND

Hypotension during anesthesia for surgery for hip fracture is common and associated with myocardial injury, stroke, acute kidney injury, and delirium. We hypothesized that maintaining intraoperative blood pressure close to patients' preoperative values would reduce these complications compared to usual care.

METHODS

A pilot feasibility patient- and assessor-blinded parallel group randomized controlled trial. People with unilateral hip fracture aged ≥70 years with capacity to give consent before surgery were eligible. Participants were allocated at random before surgery to either tight blood pressure control (systolic blood pressure ≥80% preoperative baseline and mean arterial blood pressure ≥75 mm Hg) or usual care. Feasibility outcomes were protocol adherence, primary outcome data completeness, and recruitment rate. The composite primary outcome was myocardial injury, stroke, acute kidney injury or delirium within 7 days of surgery.

RESULTS

Seventy-six participants were enrolled, and 12 withdrew before randomization. Sixty-four participants were randomized, 30 were allocated to control, and 34 to intervention. There was no crossover, all 64 participants received their allocated treatment, primary outcome was known for all participants. The composite primary outcome occurred in 14 of 30 participants in the control group compared with 23 of 34 participants in the intervention group (P = .09), relative risk 1.45 (95% confidence interval [CI], 0.93-2.27).

CONCLUSIONS

A randomized controlled trial of tight intraoperative blood pressure control compared to usual care to reduce major postoperative complications after fractured neck of femur surgery is possible. However, the data would suggest a large sample size would be required for a definitive trial.

Role of prophylactic intravenous calcium in prevention of postspinal hypotension among women with preeclampsia undergoing cesarean delivery: a placebo controlled randomized clinical trial

BACKGROUND

Preeclamptic women, in addition to traditional antihypertensive medications, often receive magnesium supplementation and are at increased risk of postspinal hypotension Postspinal hypotension increases the risk of fetomaternal morbidity. Calcium is a physiological antagonist of magnesium in vascular smooth muscle. Therefore, the study hypothesized that calcium is better suited for preserving systemic vascular resistance and preventing postspinal hypotension during cesarean delivery.

OBJECTIVES

The study aimed to evaluate the effect of prophylactic calcium administration on postspinal hypotension in preeclamptic women receiving magnesium supplementation.

METHODS

This prospective, randomized, placebo-controlled, double-blinded, two-arm parallel trial was conducted in preeclamptic women receiving magnesium sulfate supplementation undergoing cesarean delivery. The women were randomized to receive intravenous calcium or a placebo (normal saline) before spinal anesthesia. The study drug (calcium gluconate 500 mg or normal saline) was administered over 15 minutes and ended immediately before spinal anesthesia. The primary outcome measure was the incidence of postspinal hypotension, and secondary outcome measures were postpartum blood loss and maternal and neonatal outcomes.

RESULTS

A total of 100 women (50 each calcium and placebo arm) completed the study. The baseline demographic variables, mean blood pressure and heart rate were comparable. The incidence of postspinal hypotension was significantly lower in the calcium arm compared to the placebo arm (32% vs 60%; Relative risk [95% CI]; 1.87 [1.18-2.97]; P=.007). The mean phenylephrine requirement (5.60±14.59 vs 14.80±22.42 mcg; P=.01) and mephentermine requirement (3.30±5.11 mg vs 5.82±4.97 mg; P=.008) was significantly lower in the calcium group. Furthermore, the calcium group's mean postpartum blood loss was significantly lower (406.90±94.34 vs 472.20±122.49 ml, P=.004). However, the Neonatal Intensive Care Unit admission rate, Apgar score, umbilical artery PH, and maternal serum calcium were comparable.

CONCLUSION

Prophylactic calcium infusion significantly reduces the incidence of postspinal hypotension during cesarean delivery in preeclamptic women receiving magnesium supplementation. Furthermore, the effect of prophylactic calcium in decreasing postpartum blood loss is encouraging. However, large trials are required to validate the findings of this study.

Lassen's Cerebral Autoregulation Plot Revisited and Validated 65 Years Later: Impacts of Vasoactive Drug Treatment on Cerebral Blood Flow

Niels Lassen's seminal 1959 cerebral autoregulation plot, a cornerstone in understanding the relationship between mean arterial pressure (MAP) and cerebral blood flow (CBF), was based on preexisting literature. However, this work has faced criticism for selective data presentation, leading to inaccurate interpretation. This review revisits and validates Lassen's original plot using contemporary data published since 2000. Additionally, we aim to understand the impact of vasoactive drug treatments on CBF, as Lassen's referenced studies used various drugs for blood pressure manipulation. Our findings confirm Lassen's concept of a plateau where CBF remains relatively stable across a specific MAP range in awake humans with normal brains. However, significant variations in cerebral autoregulation among different populations are evident. In critically ill patients and those with traumatic brain injury, the autoregulatory plateau dissipates, necessitating tight blood pressure control to avoid inadequate or excessive cerebral perfusion. A plateau is observed in patients anesthetized with intravenous agents but not with volatile agents. Vasopressor treatments have population-dependent effects, with contemporary data showing increased CBF in critically ill patients but not in awake humans with normal brains. Vasopressor treatment results in a greater increase in CBF during volatile than intravenous anesthesia. Modern antihypertensives do not significantly impact CBF based on contemporary data, exerting a smaller impact on CBF compared to historical data. These insights underscore the importance of individualized blood pressure management guided by modern data in the context of cerebral autoregulation across varied patient populations.

Noradrenaline-induced changes in cerebral blood flow in health, traumatic brain injury and critical illness: a systematic review with meta-analysis

BACKGROUND

Noradrenaline is a standard treatment for hypotension in acute care. The precise effects of noradrenaline on cerebral blood flow in health and disease remain unclear.

METHODS

We systematically reviewed and synthesised data from studies examining changes in cerebral blood flow in healthy participants and patients with traumatic brain injury and critical illness.

RESULTS

Twenty-eight eligible studies were included. In healthy subjects and patients without critical illness or traumatic brain injury, noradrenaline did not significantly change cerebral blood flow velocity (-1.7%, 95%CI -4.7-1.3%) despite a 24.1% (95%CI 19.4-28.7%) increase in mean arterial pressure. In patients with traumatic brain injury, noradrenaline significantly increased cerebral blood flow velocity (21.5%, 95%CI 11.0-32.0%), along with a 33.8% (95%CI 14.7-52.9%) increase in mean arterial pressure. In patients who were critically ill, noradrenaline significantly increased cerebral blood flow velocity (20.0%, 95%CI 9.7-30.3%), along with a 32.4% (95%CI 25.0-39.9%) increase in mean arterial pressure. Our analyses suggest intact cerebral autoregulation in healthy subjects and patients without critical illness or traumatic brain injury., and impaired cerebral autoregulation in patients with traumatic brain injury and who were critically ill. The extent of mean arterial pressure changes and the pre-treatment blood pressure levels may affect the magnitude of cerebral blood flow changes. Studies assessing cerebral blood flow using non-transcranial Doppler methods were inadequate and heterogeneous in enabling meaningful meta-analysis.

CONCLUSIONS

Noradrenaline significantly increases cerebral blood flow in humans with impaired, not intact, cerebral autoregulation, with the extent of changes related to the severity of functional impairment, the extent of mean arterial pressure changes and pre-treatment blood pressure levels.

In vivo optical assessment of cerebral and skeletal muscle microvascular response to phenylephrine

This study aimed to investigate the simultaneous response of the cerebral and skeletal muscle microvasculature to the same phenylephrine (PE) boluses. A hybrid optical system that combines hyperspectral near-infrared spectroscopy (hs-NIRS) and diffuse correlation spectroscopy (DCS) was used to monitor changes in tissue oxygenation and perfusion. Data were collected from the head and hind limb of seven male Sprague-Dawley rats while administering intravenous (IV) injections of PE or saline to all animals. The response to saline was used as a control. Skeletal muscle oxygenation decreased significantly after PE injection, while a statistically underpowered decrease in perfusion was observed, followed by an increase beyond baseline. Vascular conductance also decreased in the muscle reflecting the drug's vasoconstrictive effects. Tissue oxygenation and perfusion increased in the brain in response to PE. Initially, there was a sharp increase in cerebral perfusion but no changes in cerebral vascular conductance. Subsequently, cerebral flow and vascular conductance decreased significantly below baseline, likely reflecting autoregulatory mechanisms to manage the excess flow. Further, fitting an exponential function to the secondary decrease in cerebral perfusion and increase in muscular blood flow revealed a quicker kinetic response in the brain to adjust blood flow. In the skeletal muscle, PE caused a transient decrease in blood volume due to vasoconstriction, which resulted in an overall decrease in hemoglobin content and tissue oxygen saturation. Since PE does not directly affect cerebral vessels, this peripheral vasoconstriction shunted blood into the brain, resulting in an initial increase in oxygenated hemoglobin and oxygen saturation.

Epinephrine vs. phenylephrine infusion for prophylaxis against maternal hypotension after spinal anesthesia for cesarean delivery: a randomized controlled trial

BACKGROUND

The hemodynamic effects of relatively low-dose epinephrine and phenylephrine infusions during cesarean delivery under spinal anesthesia were compared.

METHODS

This randomized controlled trial included full-term pregnant women who underwent elective cesarean delivery. After spinal anesthesia, participants received either epinephrine (0.03 mcg/kg/min) or phenylephrine (0.4 mcg/kg/min) infusion that continued until 5 min after delivery. The primary outcome was a composite outcome of the occurrence of any of hypotension, hypertension, bradycardia, and/or tachycardia. Neonatal outcomes, including umbilical artery blood gas and Apgar scores, were assessed.

RESULTS

In total, 98 patients in each group were analyzed, and the number of patients with the composite outcome was comparable between the epinephrine and phenylephrine groups (30/98 [31%] vs. 31/98 [32%], respectively; P = 0.877). However, the incidence of hypotension was likely lower in the epinephrine group than in the phenylephrine group (P = 0.066), and the number of hypotensive episodes per patient was lower in the epinephrine group than in the phenylephrine group. On the other hand, the incidence of tachycardia was higher in the epinephrine group than that in the phenylephrine group. The incidence of hypertension was comparable between the two groups and none of the participants developed bradycardia. Neonatal outcomes were comparable between the two groups.

CONCLUSIONS

Epinephrine and phenylephrine infusion produced comparable maternal hemodynamics and neonatal outcomes. Epinephrine was associated with a higher incidence of maternal tachycardia and likely lower incidence of maternal hypotension than phenylephrine. IRB number: MD-245-2022.

CLINICAL TRIAL REGISTRATION

This study was registered on May 31, 2023 at clinicaltrials.gov registry, NCT05881915, URL: https://classic.

CLINICALTRIALS

gov/ct2/show/NCT05881915term=NCT05881915&draw=2&rank=1.