Personalizing the Definition of Hypotension to Protect the Brain

A protocolized five strategies in open repair for ruptured abdominal aortic aneurysm

OBJECTIVES

Although the medical field has made significant progress, there has been little improvement in the survival rate of patients with ruptured abdominal aortic aneurysms (rAAAs). We implemented a protocol consisting of five strategies in the management of rAAA patients who underwent open repair surgery.

METHODS

The protocol comprised the following strategies: intentional hypotension <70 mmHg, lung first and kidney last policy (restricted fluid resuscitation and permissive oligoanuria), immediate postoperative extubation, free-water intake with active ambulation, and open abdomen with the routine second-look operation. The study included 13 patients (11 male) with a mean age of 75.5 ± 7.4 (range: 58-87) years who underwent the procedure from 2016 to 2018, with a mean follow-up of 40.1 ± 9.04 months. Five deteriorating to hemodynamic shock and decreased consciousness requiring intubation and ventilation prior to surgery were observed. Two of these patients required preoperative cardiopulmonary resuscitation (CPR).

RESULTS

All patients regained consciousness after surgery, including the two patients who required cardiopulmonary resuscitation. Immediate postoperative extubation was performed in nine patients, but two (22.2%) of them needed re-intubation due to ventilation/perfusion mismatch. Four patients underwent continuous renal replacement therapy, with three of them having anuria for up to 48 h after surgery. Two of these patients made a full recovery. Daily ambulation was carried out for a mean of 4.77 ± 3.5 (range 1-13) days with an open abdomen, during which no significant events were reported. Four cases of colon ischemia/necrosis were identified in the second-look operation, with two patients requiring Hartman's procedure and the other two undergoing left colon partial resection. There were two in-hospital mortalities (15.4%).

CONCLUSIONS

A protocol-based approach, through multidisciplinary team consensus and the development of optimal surgical strategies, could improve clinical outcomes for patients undergoing emergency surgery for rAAA. Further studies with larger sample sizes are needed to refine the protocols.

Cerebral autoregulation derived blood pressure targets in elective neurosurgery

Poor postoperative outcomes may be associated with cerebral ischaemia or hyperaemia, caused by episodes of arterial blood pressure (ABP) being outside the range of cerebral autoregulation (CA). Monitoring CA using COx (correlation between slow changes in mean ABP and regional cerebral O2 saturation-rSO2) could allow to individualise the management of ABP to preserve CA. We aimed to explore a continuous automated assessment of ABPOPT (ABP where CA is best preserved) and ABP at the lower limit of autoregulation (LLA) in elective neurosurgery patients. Retrospective analysis of prospectively collected data of 85 patients [median age 60 (IQR 51-68)] undergoing elective neurosurgery. ABPBASELINE was the mean of 3 pre-operative non-invasive measurements. ABP and rSO2 waveforms were processed to estimate COx-derived ABPOPT and LLA trend-lines. We assessed: availability (number of patients where ABPOPT/LLA were available); time required to achieve first values; differences between ABPOPT/LLA and ABP. ABPOPT and LLA availability was 86 and 89%. Median (IQR) time to achieve the first value was 97 (80-155) and 93 (78-122) min for ABPOPT and LLA respectively. Median ABPOPT [75 (69-84)] was lower than ABPBASELINE [90 (84-95)] (p < 0.001, Mann-U test). Patients spent 72 (56-86) % of recorded time with ABP above or below ABPOPT ± 5 mmHg. ABPOPT and ABP time trends and variability were not related to each other within patients. 37.6% of patients had at least 1 hypotensive insult (ABP < LLA) during the monitoring time. It seems possible to assess individualised automated ABP targets during elective neurosurgery.

Implication of Hypotension in the Pathogenesis of Cognitive Impairment and Brain Injury in Chronic Liver Disease

The incidence of chronic liver disease is on the rise. One of the primary causes of hospital admissions for patients with cirrhosis is hepatic encephalopathy (HE), a debilitating neurological complication. HE is defined as a reversible syndrome, yet there is growing evidence stating that, under certain conditions, HE is associated with permanent neuronal injury and irreversibility. The pathophysiology of HE primarily implicates a strong role for hyperammonemia, but it is believed other pathogenic factors are involved. The fibrotic scarring of the liver during the progression of chronic liver disease (cirrhosis) consequently leads to increased hepatic resistance and circulatory anomalies characterized by portal hypertension, hyperdynamic circulatory state and systemic hypotension. The possible repercussions of these circulatory anomalies on brain perfusion, including impaired cerebral blood flow (CBF) autoregulation, could be implicated in the development of HE and/or permanent brain injury. Furthermore, hypotensive insults incurring during gastrointestinal bleed, infection, or liver transplantation may also trigger or exacerbate brain dysfunction and cell damage. This review will focus on the role of hypotension in the onset of HE as well as in the occurrence of neuronal cell loss in cirrhosis.

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.

Efficacy and safety of ciprofol versus propofol for anesthesia induction in adult patients received elective surgeries: a meta‑analysis

BACKGROUND

Propofol is use widely used in anesthesia, known for its effectiveness, may lead to cardiopulmonary issues in some patients. Ciprofol has emerged as a possible alternative to propofol because it can achieve comparable effects to propofol while causing fewer adverse events at lower doses. However, no definitive conclusion has been reached yet. This meta-analysis aimed to evaluate the efficacy and safety of ciprofol versus propofol in adult patients undergoing elective surgeries under general anesthesia.

METHODS

We searched PubMed, EMBASE, the Cochrane library, Web of Science, and Chinese National Knowledge Infrastructure (CNKI) to identify potentially eligible randomized controlled trials (RCT) comparing ciprofol with propofol in general anesthesia until September 30, 2023. The efficacy outcomes encompassed induction success rate, time to onset of successful induction, time to disappearance of eyelash reflex, and overall estimate means in Bispectral Index (BIS). Safety outcomes were assessed through time to full alertness, incidence of hypotension, incidence of arrhythmia, and incidence of injection-site pain. Continuous variables were expressed as mean difference (MD) with 95% confidence interval (CI), and dichotomous variables were expressed as risk ratio (RR) with 95% CI. Statistical analyses were performed using RevMan 5.4 and STATA 14.0. The quality of the evidence was rated through the grading of recommendations, assessment, development and evaluation (GRADE) system.

RESULTS

A total of 712 patients from 6 RCTs were analyzed. Meta-analysis suggested that ciprofol was equivalent to propofol in terms of successful induction rate, time to onset of successful induction, time to disappearance of eyelash reflex, time to full alertness, and incidence of arrhythmia, while ciprofol was better than propofol in overall estimated mean in BIS (MD: -3.79, 95% CI: -4.57 to -3.01, p < 0.001), incidence of hypotension (RR: 0.63, 95% CI: 0.42 to 0.94, p = 0.02), and incidence of injection-site pain (RR: 0.26, 95% CI: 0.14 to 0.47, p < 0.001). All results were supported by moderate to high evidence.

CONCLUSIONS

Ciprofol may be a promising alternative to propofol because it facilitates achieving a satisfactory anesthesia depth and results in fewer hypotension and injection-site pain. However, we still recommend conducting more studies with large-scale studies to validate our findings because only limited data were accumulated in this study.

TRIAL REGISTRATION

PROSPERO 2023 CRD42023479767.

Intraoperative hypotension in ambulatory surgery centers

STUDY OBJECTIVES

To measure the incidence of intraoperative hypotension (IOH) during surgery in ambulatory surgery centers (ASCs) and describe associated characteristics of patients and procedures.

DESIGN

Retrospective analysis.

SETTING

20 ASCs.

PATIENTS

16,750 patients having non-emergent, non-cardiac surgery; ASA physical status 2 through 4.

INTERVENTIONS

None.

MEASUREMENTS

We assessed incidence of IOH using the definition from the Centers for Medicare & Medicaid Services (CMS) Merit-based Incentive Payment System (MIPS)-mean arterial pressure (MAP) < 65 mmHg for at least 15 cumulative minutes-and three secondary definitions: minutes of MAP <65 mmHg, area under MAP of 65 mmHg, and time-weighted average MAP <65 mmHg.

MAIN RESULTS

30.9% of ASC cases had a MAP <65 mmHg for at least 15 min. The incidence of IOH varied significantly, and was higher among younger adults (age 18-39; 36.2%), females (35.2%), and patients with ASA physical status 2 (32.8%). IOH increased with increasing surgery length, even when time-weighted, and was higher among low complexity (30.6%) than moderate complexity (28.8%) procedures, and highest among high complexity procedures (44.1%).

CONCLUSIONS

There was substantial occurrence of IOH in ASCs, similar to that described in academic hospital settings in previous literature. We hypothesize that this may reflect clinician preference not to intervene in perceived healthy patients or assumptions about ability to tolerate lower blood pressures on behalf of these patients. Future research will determine whether IOH in ACSs is associated with adverse outcomes to the same extent as described in more complex hospital-based surgeries.

Comparison of the hemodynamic effects of opioid-based versus lidocaine-based induction of anesthesia with propofol in older adults: a randomized controlled trial

BACKGROUND

The present study aims to compare the hemodynamic profile of lidocaine and fentanyl during propofol induction of general anesthesia.

METHODS

This randomized controlled trial included patients aged above 60 years undergoing elective non-cardiac surgery. The included patients received either 1 mg/kg lidocaine (n = 50) or 1 mcg/kg fentanyl (n = 50) based on total body weight with propofol induction of anesthesia. Patient's hemodynamics were recorded every minute for the first 5 min then every 2 min until 15 min after induction of anesthesia. Hypotension (mean arterial pressure [MAP] <65 mmHg or >30% reduction from baseline) was treated by intravenous 4 mcg bolus of norepinephrine. Outcomes included norepinephrine requirements (primary), the incidence of postinduction hypotension, MAP, heart rate, intubation condition, and postoperative delirium via the cognitive assessment method.

RESULTS

Forty-seven patients in the lidocaine group and 46 patients in the fentanyl group were analyzed. None in the lidocaine group experienced hypotension, while 28/46 (61%) of patients in the fentanyl group developed at least one episode of hypotension requiring a median (25th and 75th quartiles) norepinephrine dose of 4 (0,5) mcg, p-value <0.001 for both outcomes. The average MAP was lower in the fentanyl group than in the lidocaine group at all time points after anesthesia induction. The average heart rate was comparable between the two groups nearly at all time points after anesthesia induction. The overall intubation condition was comparable between the two groups. None of the included patients developed postoperative delirium.

CONCLUSION

Lidocaine-based regimen for induction of anesthesia reduced the risk of postinduction hypotension in older patients compared to the fentanyl-based regimen.

Incidence of intraoperative hypotension during non-cardiac surgery in community anesthesia practice: a retrospective observational analysis

BACKGROUND

Intraoperative hypotension (IOH) is well-described in the academic setting but not in community practice. IOH is associated with risk of postoperative morbidity and mortality. This is the first report of IOH in the community setting using the IOH measure definition from the Centers for Medicare and Medicaid Services Merit-based Incentive Payment System program.

OBJECTIVES

To describe the incidence of IOH in the community setting; assess variation in IOH by patient-, procedure-, and facility-level characteristics; and describe variation in risk-adjusted IOH across clinicians.

METHODS

Design Cross-sectional descriptive analysis of retrospective data from anesthesia records in 2020 and 2021. Setting Forty-five facilities affiliated with two large anesthesia providers in the USA. Participants Patients aged 18 years or older having non-emergent, non-cardiac surgery under general, neuraxial, or regional anesthesia. Cases were excluded based on criteria for the IOH measure: baseline mean arterial pressure (MAP) below 65 mmHg prior to anesthesia induction; American Society of Anesthesiologists (ASA) physical status classification of I, V, or VI; monitored anesthesia care only; deliberate induced hypotension; obstetric non-operative procedures; liver or lung transplant; cataract surgery; non-invasive gastrointestinal cases. Main outcomes IOH, using four definitions. Primary definition: binary assessment of whether the case had MAP < 65 mmHg for 15 min or more. Secondary definitions: total number of minutes of MAP < 65 mmHg, total area under MAP of 65 mmHg, time-weighted average MAP < 65 mmHg.

RESULTS

Among 127,095 non-emergent, non-cardiac cases in community anesthesia settings, 29% had MAP < 65 mmHg for at least 15 min cumulatively, with an overall mean of 12.4 min < 65 mmHg. IOH was slightly more common in patients who were younger, female, and ASA II (versus III or IV); in procedures that were longer and had higher anesthesia base units; and in ambulatory surgery centers. Incidence of IOH varied widely across individual clinicians in both unadjusted and risk-adjusted analyses.

CONCLUSION

Intraoperative hypotension is common in community anesthesia practice, including among patients and settings typically considered "low risk." Variation in incidence across clinicians remains after risk-adjustment, suggesting that IOH is a modifiable risk worth pursuing in quality improvement initiatives.

Preoperative Identification of Patient-Dependent Blood Pressure Targets Associated With Low Risk of Intraoperative Hypotension During Noncardiac Surgery

BACKGROUND

Intraoperative hypotension (IOH) is strongly linked to organ system injuries and postoperative death. Blood pressure itself is a powerful predictor of IOH; however, it is unclear which pressures carry the lowest risk and may be leveraged to prevent subsequent hypotension. Our objective was to develop a model that predicts, before surgery and according to a patient's unique characteristics, which intraoperative mean arterial pressures (MAPs) between 65 and 100 mm Hg have a low risk of IOH, defined as an MAP <65 mm Hg, and may serve as testable hemodynamic targets to prevent IOH.

METHODS

Adult, noncardiac surgeries under general anesthesia at 2 tertiary care hospitals of the University of Pittsburgh Medical Center were divided into training and validation cohorts, then assigned into smaller subgroups according to preoperative risk factors. Primary outcome was hypotension risk, defined for each intraoperative MAP value from 65 to 100 mm Hg as the proportion of a value's total measurements followed by at least 1 MAP <65 mm Hg within 5 or 10 minutes, and calculated for all values in each subgroup. Five models depicting MAP-associated IOH risk were compared according to best fit across subgroups with proportions whose confidence interval was <0.05. For the best fitting model, (1) performance was validated, (2) low-risk MAP targets were identified according to applied benchmarks, and (3) preoperative risk factors were evaluated as predictors of model parameters.

RESULTS

A total of 166,091 surgeries were included, with 121,032 and 45,059 surgeries containing 5.4 million and 1.9 million MAP measurements included in the training and validation sets, respectively. Thirty-six subgroups with at least 21 eligible proportions (confidence interval <0.05) were identified, representing 92% and 94% of available MAP measurements, respectively. The exponential with theta constant model demonstrated the best fit (weighted sum of squared error 0.0005), and the mean squared error of hypotension risk per MAP did not exceed 0.01% in validation testing. MAP targets ranged between 69 and 90 mm Hg depending on the subgroup and benchmark used. Increased age, higher American Society of Anesthesiologists physical status, and female sexindependently predicted ( P < .05) hypotension risk curves with less rapid decay and higher plateaus.

CONCLUSIONS

We demonstrate that IOH risk specific to a given MAP is patient-dependent, but predictable before surgery. Our model can identify intraoperative MAP targets before surgery predicted to reduce a patient's exposure to IOH, potentially allowing clinicians to develop more personalized approaches for managing hemodynamics.

Intraoperative monitoring of cerebrovascular autoregulation in infants and toddlers receiving major elective surgery to determine the individually optimal blood pressure - a pilot study

INTRODUCTION

Inducing general anesthesia (GA) in children can considerably affect blood pressure, and the rate of severe critical events owing to this remains high. Cerebrovascular autoregulation (CAR) protects the brain against blood-flow-related injury. Impaired CAR may contribute to the risk of cerebral hypoxic-ischemic or hyperemic injury. However, blood pressure limits of autoregulation (LAR) in infants and children are unclear.

MATERIALS AND METHODS

In this pilot study CAR was monitored prospectively in 20 patients aged <4 years receiving elective surgery under GA. Cardiac- or neurosurgical procedures were excluded. The possibility of calculating the CAR index hemoglobin volume index (HVx), by correlating near-infrared-spectroscopy (NIRS)-derived relative cerebral tissue hemoglobin and invasive mean arterial blood pressure (MAP) was determined. Optimal MAP (MAPopt), LAR, and the proportion of time with a MAP outside LAR were determined.

RESULTS

The mean patient age was 14 ± 10 months. MAPopt could be determined in 19 of 20 patients, with an average of 62 ± 12 mmHg. The required time for a first MAPopt depended on the extent of spontaneous MAP fluctuations. The actual MAP was outside the LAR in 30% ± 24% of the measuring time. MAPopt significantly differed among patients with similar demographics. The CAR range averaged 19 ± 6 mmHg. Using weight-adjusted blood pressure recommendations or regional cerebral tissue saturation, only a fraction of the phases with inadequate MAP could be identified.

CONCLUSION

Non-invasive CAR monitoring using NIRS-derived HVx in infants, toddlers, and children receiving elective surgery under GA was reliable and provided robust data in this pilot study. Using a CAR-driven approach, individual MAPopt could be determined intraoperatively. The intensity of blood pressure fluctuations influences the initial measuring time. MAPopt may differ considerably from recommendations in the literature, and the MAP range within LAR in children may be smaller than that in adults. The necessity of manual artifact elimination represents a limitation. Larger prospective and multicenter cohort studies are necessary to confirm the feasibility of CAR-driven MAP management in children receiving major surgery under GA and to enable an interventional trial design using MAPopt as a target.

Beta Blockers can mask not only Hypoglycemia, but also Hypotension

Background:

Beta-adrenergic (β-AR) receptor blockers (BBs) are an essential class of drugs as they have numerous indications. On the other hand, they have numerous unwanted effects which decrease the compliance, adherence, and persistence of this very useful group of drugs.

Objective:

The paper aims to analyze the possibility that an unnoticed side effect may contribute to a less favorable pharmacologic profile of BBs, e.g., a diminished reaction to a sudden fall in BP.

Methods:

We searched two medical databases for abstracts and citations (Medline and SCOPUS). Moreover, we searched the internet for drug prescription leaflets (of the individual BBs).

Results:

Whichever cause of stress is considered, the somatic manifestations of stress will be (partially) masked if a patient takes BB. Stress–induced hypercatecholaminemia acts on β-AR of cardiomyocytes; it increases heart rate and contractility, effects suppressed by BBs. The answers of the organism to hypoglycemia and hypotension share the main mechanisms such as sympathetic nervous system activation and hypercatecholaminemia. Thus, there is a striking analogy: BBs can cover up symptoms of both hypoglycemia (which is widely known) and of hypotension (which is not recognized). It is widely known that BBs can cause hypotension. However, they can also complicate recovery by spoiling the defense mechanisms in hypotension as they interfere with the crucial compensatory reflex to increase blood pressure in hypotension.

Conclusion:

Beta blockers can cause hypotension, mask it, and make recovery more difficult. This is clinically important and deserves to be more investigated and probably to be stated as a warning.

Impact of impaired cerebral blood flow autoregulation on electroencephalogram signals in adults undergoing propofol anaesthesia: a pilot study

Background

Cerebral autoregulation actively maintains cerebral blood flow over a range of MAPs. During general anaesthesia, this mechanism may not compensate for reductions in MAP leading to brain hypoperfusion. Cerebral autoregulation can be assessed using the mean flow index derived from Doppler measurements of average blood velocity in the middle cerebral artery, but this is impractical for routine monitoring within the operating room. Here, we investigate the possibility of using the EEG as a proxy measure for a loss of cerebral autoregulation, determined by the mean flow index.

Methods

Thirty-six patients (57.5 [44.25; 66.5] yr; 38.9% women, non-emergency neuroradiology surgery) anaesthetised using propofol were prospectively studied. Continuous recordings of MAP, average blood velocity in the middle cerebral artery, EEG, and regional cerebral oxygen saturation were made. Poor cerebral autoregulation was defined as a mean flow index greater than 0.3.

Results

Eighteen patients had preserved cerebral autoregulation, and 18 had altered cerebral autoregulation. The two groups had similar ages, MAPs, and average blood velocities in the middle cerebral artery. Patients with altered cerebral autoregulation exhibited a significantly slower alpha peak frequency (9.4 [9.0, 9.9] Hz vs 10.5 [10.1, 10.9] Hz, P<0.001), which persisted after adjusting for age, norepinephrine infusion rate, and ASA class (odds ratio=0.038 [confidence interval, 0.004, 0.409]; P=0.007).

Conclusion

In this pilot study, we found that loss of cerebral autoregulation was associated with a slower alpha peak frequency, independent of age. This work suggests that impaired cerebral autoregulation could be monitored in the operating room using the existing EEG setup.

Clinical trial registration

NCT03769142.

Central Hypovolemia Detection During Environmental Stress-A Role for Artificial Intelligence?

The first step to exercise is preceded by the required assumption of the upright body position, which itself involves physical activity. The gravitational displacement of blood from the chest to the lower parts of the body elicits a fall in central blood volume (CBV), which corresponds to the fraction of thoracic blood volume directly available to the left ventricle. The reduction in CBV and stroke volume (SV) in response to postural stress, post-exercise, or to blood loss results in reduced left ventricular filling, which may manifest as orthostatic intolerance. When termination of exercise removes the leg muscle pump function, CBV is no longer maintained. The resulting imbalance between a reduced cardiac output (CO) and a still enhanced peripheral vascular conductance may provoke post-exercise hypotension (PEH). Instruments that quantify CBV are not readily available and to express which magnitude of the CBV in a healthy subject should remains difficult. In the physiological laboratory, the CBV can be modified by making use of postural stressors, such as lower body "negative" or sub-atmospheric pressure (LBNP) or passive head-up tilt (HUT), while quantifying relevant biomedical parameters of blood flow and oxygenation. Several approaches, such as wearable sensors and advanced machine-learning techniques, have been followed in an attempt to improve methodologies for better prediction of outcomes and to guide treatment in civil patients and on the battlefield. In the recent decade, efforts have been made to develop algorithms and apply artificial intelligence (AI) in the field of hemodynamic monitoring. Advances in quantifying and monitoring CBV during environmental stress from exercise to hemorrhage and understanding the analogy between postural stress and central hypovolemia during anesthesia offer great relevance for healthy subjects and clinical populations.

General anesthetic techniques for enhanced recovery after surgery: Current controversies

General anesthesia technique can influence not only immediate postoperative outcomes, but also long-term outcomes beyond hospital stay (e.g., readmission after discharge from hospital). There is lack of evidence regarding superiority of total intravenous anesthesia over inhalation anesthesia with regards to postoperative outcomes even in high-risk population including cancer patients. Optimal balanced general anesthetic technique for enhance recovery after elective surgery in adults includes avoidance of routine use preoperative midazolam, avoidance of deep anesthesia, use of opioid-sparing approach, and minimization of neuromuscular blocking agents and appropriate reversal of residual paralysis. Given that the residual effects of drugs used during anesthesia can increase postoperative morbidity and delay recovery, it is prudent to use a minimal number of drug combinations, and the drugs used are shorter-acting and administered at the lowest possible dose. It is imperative that the discerning anesthesiologist consider whether each drug used is really necessary for accomplishing perioperative goals.

THE USE OF EPHEDRINE TO TREAT ANESTHESIA-ASSOCIATED HYPOTENSION IN PINNIPEDS

Hypotension is a common adverse effect of general anesthesia that has historically been difficult to measure in pinniped species due to technical challenges. A retrospective case review found seven pinniped cases that demonstrated anesthesia-associated hypotension diagnosed by direct blood pressure measurements during general anesthesia at The Marine Mammal Center (Sausalito, CA) between 2017 and 2019. Cases included five California sea lions (CSL: Zalophus californianus), one Hawaiian monk seal (HMS: Neomonachus schauinslandi), and one northern elephant seal (NES: Mirounga angustirostris). Patients were induced using injectable opioids, benzodiazepines, and anesthetics including propofol and alfaxalone. Excluding the HMS, all patients required supplemental isoflurane with a mask to achieve an anesthetic plane allowing for intubation. Each patient was maintained with inhalant isoflurane in oxygen for the duration of the anesthetic event. Each patient was concurrently administered continuous IV fluids and four patients received fluid boluses prior to administration of ephedrine. All hypotensive anesthetized patients were treated with IV ephedrine (0.05-0.2 mg/kg). The average initial systolic (SAP) and mean (MAP) arterial blood pressures for the CSL prior to ephedrine administration were 71 ± 14 mmHg and 48 ± 12 mmHg respectively. The average SAP and MAP for the CSL increased to 119 ± 32 mmHg and 90 ± 34 mmHg respectively within 5 m of ephedrine administration. The NES initial blood pressure measurement was 59/43 (50) (SAP/diastolic [MAP]) mmHg and increased to 80/51 (62) mmHg within 5 m. The initial HMS blood pressure was 79/68 (73) mmHg and increased to 99/78 (85) mmHg within 5 m following ephedrine administration. All patients recovered from anesthesia. These results support the efficacy of IV ephedrine for the treatment of anesthesia-associated hypotension in pinnipeds.

Heterogeneous impact of hypotension on organ perfusion and outcomes: a narrative review

Arterial blood pressure is the driving force for organ perfusion. Although hypotension is common in acute care, there is a lack of accepted criteria for its definition. Most practitioners regard hypotension as undesirable even in situations that pose no immediate threat to life, but hypotension does not always lead to unfavourable outcomes based on experience and evidence. Thus efforts are needed to better understand the causes, consequences, and treatments of hypotension. This narrative review focuses on the heterogeneous underlying pathophysiological bases of hypotension and their impact on organ perfusion and patient outcomes. We propose the iso-pressure curve with hypotension and hypertension zones as a way to visualize changes in blood pressure. We also propose a haemodynamic pyramid and a pressure-output-resistance triangle to facilitate understanding of why hypotension can have different pathophysiological mechanisms and end-organ effects. We emphasise that hypotension does not always lead to organ hypoperfusion; to the contrary, hypotension may preserve or even increase organ perfusion depending on the relative changes in perfusion pressure and regional vascular resistance and the status of blood pressure autoregulation. Evidence from RCTs does not support the notion that a higher arterial blood pressure target always leads to improved outcomes. Management of blood pressure is not about maintaining a prespecified value, but rather involves ensuring organ perfusion without undue stress on the cardiovascular system.

An Update on the COGiTATE Phase II Study: Feasibility and Safety of Targeting an Optimal Cerebral Perfusion Pressure as a Patient-Tailored Therapy in Severe Traumatic Brain Injury

INTRODUCTION

Monitoring of cerebral autoregulation (CA) in patients with a traumatic brain injury (TBI) can provide an individual 'optimal' cerebral perfusion pressure (CPP) target (CPPopt) at which CA is best preserved. This potentially offers an individualized precision medicine approach. Retrospective data suggest that deviation of CPP from CPPopt is associated with poor outcomes. We are prospectively assessing the feasibility and safety of this approach in the COGiTATE [CPPopt Guided Therapy: Assessment of Target Effectiveness] study. Its primary objective is to demonstrate the feasibility of individualizing CPP at CPPopt in TBI patients. The secondary objectives are to investigate the safety and physiological effects of this strategy.

METHODS

The COGiTATE study has included patients in four European hospitals in Cambridge, Leuven, Nijmegen, and Maastricht (coordinating centre). Patients with severe TBI requiring intracranial pressure (ICP)-directed therapy are allocated into one of two groups. In the intervention group, CPPopt is calculated using a published (modified) algorithm. In the control group, the CPP target recommended in the Brain Trauma Foundation guidelines (CPP 60-70 mmHg) is used.

RESULTS

Patient recruitment started in February 2018 and will continue until 60 patients have been studied. Fifty-one patients (85% of the intended total) have been recruited in October 2019. The first results are expected early 2021.

CONCLUSION

This prospective evaluation of the feasibility, safety and physiological implications of autoregulation-guided CPP management is providing evidence that will be useful in the design of a future phase III study in severe TBI patients.

Cerebral blood flow velocity during simultaneous changes in mean arterial pressure and cardiac output in healthy volunteers

Purpose

Cerebral blood flow (CBF) needs to be precisely controlled to maintain brain functions. While previously believed to be autoregulated and near constant over a wide blood pressure range, CBF is now understood as more pressure passive. However, there are still questions regarding the integrated nature of CBF regulation and more specifically the role of cardiac output. Our aim was, therefore, to explore the effects of MAP and cardiac output on CBF in a combined model of reduced preload and increased afterload.

Method

16 healthy volunteers were exposed to combinations of different levels of simultaneous lower body negative pressure and isometric hand grip. We measured blood velocity in the middle cerebral artery (MCAV) and internal carotid artery (ICAV) by Doppler ultrasound, and cerebral oxygen saturation (ScO₂) by near-infrared spectroscopy, as surrogates for CBF. The effect of changes in MAP and cardiac output on CBF was estimated with mixed multiple regression.

Result

Both MAP and cardiac output had independent effects on MCAV, ICAV and ScO₂. For ICAV and ScO₂ there was also a statistically significant interaction effect between MAP and cardiac output. The estimated effect of a change of 10 mmHg in MAP on MCAV was 3.11 cm/s (95% CI 2.51–3.71, P < 0.001), and the effect of a change of 1 L/min in cardiac output was 3.41 cm/s (95% CI 2.82–4.00, P < 0.001).

Conclusion

The present study indicates that during reductions in cardiac output, both MAP and cardiac output have independent effects on CBF.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04693-6.

Intraoperative hypotension and perioperative acute ischemic stroke in patients having major elective non-cardiovascular non-neurological surgery

PURPOSE

The association between intraoperative hypotension and perioperative acute ischemic stroke is not well described. We hypothesized that intraoperative hypotension would be associated with perioperative acute ischemic stroke.

METHODS

Four-year retrospective cohort study of elective non-cardiovascular, non-neurological surgical patients. Characteristics of patients who had perioperative acute ischemic stroke were compared against those of patients who did not have acute ischemic stroke. Multivariable logistic regression was used to determine whether hypotension was independently associated with increased odds of perioperative acute ischemic stroke.

RESULTS

Thirty-four of 9816 patients (0.3%) who met study inclusion criteria had perioperative acute ischemic stroke. Stroke patients were older and had more comorbidities including hypertension, coronary artery disease, diabetes mellitus, active tobacco use, chronic obstructive pulmonary disease, cerebral vascular disease, atrial fibrillation, and peripheral vascular disease (all P < 0.05). MAP < 65 mmHg was not associated with increased odds of acute ischemic stroke when modeled as a continuous or categorical variable. MAP < 60 mmHg for more than 20 min was independently associated with increased odds of acute ischemic stroke, OR = 2.67 [95% CI = 1.21 to 5.88, P = 0.02].

CONCLUSION

Our analysis suggests that when MAP is less than 60 mmHg for more than 20 min, there is increased odds of acute ischemic stroke. Further studies are needed to determine what MAP should be targeted during surgery to optimize cerebral perfusion and limit ischemic stroke risk.

Development and Evaluation of a Risk-Adjusted Measure of Intraoperative Hypotension in Patients Having Nonemergent, Noncardiac Surgery

Intraoperative hypotension is common and associated with organ injury and death, although randomized data showing a causal relationship remain sparse. A risk-adjusted measure of intraoperative hypotension may therefore contribute to quality improvement efforts.

Regional perfusion monitoring in shock

PURPOSE OF REVIEW

Despite restoration of adequate systemic blood flow in patients with shock, single organs may remain hypoperfused. In this review, we summarize the results of a literature research on methods to monitor single organ perfusion in shock. We focused on methods to measure heart, brain, kidney, and/or visceral organ perfusion. Furthermore, only methods that can be used in real-time and at the bedside were included.

RECENT FINDINGS

We identified studies on physical examination techniques, electrocardiography, echocardiography, contrast-enhanced ultrasound, near-infrared spectroscopy, and Doppler sonography to assess single organ perfusion.

SUMMARY

Physical examination techniques have a reasonable negative predictive value to exclude single organ hypoperfusion but are nonspecific to detect it. Technical methods to indirectly measure myocardial perfusion include ECG and echocardiography. Contrast-enhanced ultrasound can quantify myocardial perfusion but has so far only been used to detect regional myocardial hypoperfusion. Near-infrared spectroscopy and transcranial Doppler sonography can be used to assess cerebral perfusion and determine autoregulation thresholds of the brain. Both Doppler and contrast-enhanced ultrasound techniques are novel methods to evaluate renal and visceral organ perfusion. A key limitation of most techniques is the inability to determine adequacy of organ blood flow to meet the organs' metabolic demands.

Intraoperative hypotension: Pathophysiology, clinical relevance, and therapeutic approaches

Intraoperative hypotension (IOH) i.e., low arterial blood pressure (AP) during surgery is common in patients having non-cardiac surgery under general anaesthesia. It has a multifactorial aetiology, and is associated with major postoperative complications including acute kidney injury, myocardial injury and death. Therefore, IOH may be a modifiable risk factor for postoperative complications. However, there is no uniform definition for IOH. IOH not only occurs during surgery but also after the induction of general anaesthesia before surgical incision. However, the optimal therapeutic approach to IOH remains elusive. There is evidence from one small randomised controlled trial that individualising AP targets may reduce the risk of postoperative organ dysfunction compared with standard care. More research is needed to define individual AP harm thresholds, to develop therapeutic strategies to treat and avoid IOH, and to integrate new technologies for continuous AP monitoring.