Computer-controlled closed-loop norepinephrine infusion system for automated control of mean arterial pressure in dogs under isoflurane-induced hypotension: a feasibility study

Introduction

Intra-operative hypotension is a common complication of surgery under general anesthesia in dogs and humans. Computer-controlled closed-loop infusion systems of norepinephrine (NE) have been developed and clinically applied for automated optimization of arterial pressure (AP) and prevention of intra-operative hypotension in humans. This study aimed to develop a simple computer-controlled closed-loop infusion system of NE for the automated control of the mean arterial pressure (MAP) in dogs with isoflurane-induced hypotension and to validate the control of MAP by the developed system.

Methods

NE was administered via the cephalic vein, whereas MAP was measured invasively by placing a catheter in the dorsal pedal artery. The proportional-integral-derivative (PID) controller in the negative feedback loop of the developed system titrated the infusion rate of NE to maintain the MAP at the target value of 60 mmHg. The titration was updated every 2 s. The performance of the developed system was evaluated in six laboratory Beagle dogs under general anesthesia with isoflurane.

Results

In the six dogs, when the concentration [median (interquartile range)] of inhaled isoflurane was increased from 1.5 (1.5-1.5)% to 4 (4-4)% without activating the system, the MAP was lowered from 95 (91-99) to 41 (37-42) mmHg. In contrast, when the concentration was increased from 1.5 (1.0-1.5)% to 4 (4-4.8)% for a 30-min period and the system was simultaneously activated, the MAP was temporarily lowered from 92 (89-95) to 47 (43-49) mmHg but recovered to 58 (57-58) mmHg owing to the system-controlled infusion of NE. If the acceptable target range for MAP was defined as target MAP ±5 mmHg (55 ≤ MAP ≤65 mmHg), the percentage of time wherein the MAP was maintained within the acceptable range was 96 (89-100)% in the six dogs during the second half of the 30-min period (from 15 to 30 min after system activation). The median performance error, median absolute performance error, wobble, and divergence were - 2.9 (-4.7 to 1.9)%, 2.9 (2.0-4.7)%, 1.3 (0.8-1.8)%, and - 0.24 (-0.34 to -0.11)%·min-1, respectively. No adverse events were observed during the study period, and all dogs were extubated uneventfully.

Conclusion

This system was able to titrate the NE infusion rates in an accurate and stable manner to maintain the MAP within the predetermined target range in dogs with isoflurane-induced hypotension. This system can be a potential tool in daily clinical practice for the care of companion dogs.

Closed-loop anesthesia: foundations and applications in contemporary perioperative medicine

A closed-loop automatically controls a variable using the principle of feedback. Automation within anesthesia typically aims to improve the stability of a controlled variable and reduce workload associated with simple repetitive tasks. This approach attempts to limit errors due to distractions or fatigue while simultaneously increasing compliance to evidence based perioperative protocols. The ultimate goal is to use these advantages over manual care to improve patient outcome. For more than twenty years, clinical studies in anesthesia have demonstrated the superiority of closed-loop systems compared to manual control for stabilizing a single variable, reducing practitioner workload, and safely administering therapies. This research has focused on various closed-loops that coupled inputs and outputs such as the processed electroencephalogram with propofol, blood pressure with vasopressors, and dynamic predictors of fluid responsiveness with fluid therapy. Recently, multiple simultaneous independent closed-loop systems have been tested in practice and one study has demonstrated a clinical benefit on postoperative cognitive dysfunction. Despite their advantages, these tools still require that a well-trained practitioner maintains situation awareness, understands how closed-loop systems react to each variable, and is ready to retake control if the closed-loop systems fail. In the future, multiple input multiple output closed-loop systems will control anesthetic, fluid and vasopressor titration and may perhaps integrate other key systems, such as the anesthesia machine. Human supervision will nonetheless always be indispensable as situation awareness, communication, and prediction of events remain irreplaceable human factors.

Performance of closed-loop systems for intravenous drug administration: a systematic review and meta-analysis of randomised controlled trials

Closed-loop drug delivery systems are autonomous computers able to administer medication in response to changes in physiological parameters (controlled variables). While limited evidence suggested that closed-loop systems can perform better than manual drug administration in certain settings, this technology remains a research tool with an uncertain risk/benefit profile. Our aim was comparing the performance of closed-loop systems with manual intravenous drug administration in adults. We searched MEDLINE, CENTRAL, and Embase from inception until November 2022, without restriction to language. We assessed for inclusion randomised controlled trials comparing closed-loop and manual administration of intravenous drugs in adults, intraoperatively or in the Intensive Care Unit. We identified 32 studies on closed-loop administration of propofol, noradrenaline, phenylephrine, insulin, neuromuscular blockers, and vasodilators. Most studies were at moderate or high risk of bias. The results showed that closed-loop systems reduced the duration of blood pressure outside prespecified targets during noradrenaline (MD 14.9%, 95% CI 9.6-20.2%, I2 = 66.6%) and vasodilators administration (MD 7.4%, 95% CI 5.2-9.7%, I2 = 62.3%). Closed-loop systems also decreased the duration of recovery after propofol (MD 1.3 min, 95% CI 0.4-2.1 min, I2 = 58.6%) and neuromuscular blockers (MD 9.0 min, 95% CI 7.9-10.0 min, I2 = 0%). The certainty of the evidence was low or very low for most outcomes. Automatic technology may be used to improve the hemodynamic profile during noradrenaline and vasodilators administration and reduce the duration of postanaesthetic recovery.Registration: This systematic review was registered with PROSPERO (CRD42022336950) on the 7th of June 2022.

Perioperative Fluid and Vasopressor Therapy in 2050: From Experimental Medicine to Personalization Through Automation

Intravenous (IV) fluids and vasopressor agents are key components of hemodynamic management. Since their introduction, their use in the perioperative setting has continued to evolve, and we are now on the brink of automated administration. IV fluid therapy was first described in Scotland during the 1832 cholera epidemic, when pioneers in medicine saved critically ill patients dying from hypovolemic shock. However, widespread use of IV fluids only began in the 20th century. Epinephrine was discovered and purified in the United States at the end of the 19th century, but its short half-life limited its implementation into patient care. Advances in venous access, including the introduction of the central venous catheter, and the ability to administer continuous infusions of fluids and vasopressors rather than just boluses, facilitated the use of fluids and adrenergic agents. With the advent of advanced hemodynamic monitoring, most notably the pulmonary artery catheter, the role of fluids and vasopressors in the maintenance of tissue oxygenation through adequate cardiac output and perfusion pressure became more clearly established, and hemodynamic goals could be established to better titrate fluid and vasopressor therapy. Less invasive hemodynamic monitoring techniques, using echography, pulse contour analysis, and heart-lung interactions, have facilitated hemodynamic monitoring at the bedside. Most recently, advances have been made in closed-loop fluid and vasopressor therapy, which apply computer assistance to interpret hemodynamic variables and therapy. Development and increased use of artificial intelligence will likely represent a major step toward fully automated hemodynamic management in the perioperative environment in the near future. In this narrative review, we discuss the key events in experimental medicine that have led to the current status of fluid and vasopressor therapies and describe the potential benefits that future automation has to offer.

Closed-Loop Pharmacologic Control of Blood Pressure: A Review of Existing Systems

Blood pressure management is a critical aspect of patient care, particularly in surgical and critical care settings. Closed-loop systems, which utilize real-time data and feedback to adjust treatment interventions, have gained attention for their potential to enhance blood pressure control. This review explores the application of closed-loop systems in blood pressure management. We discuss various closed-loop approaches, including their mechanisms, benefits, and limitations. By harnessing real-time patient data and feedback, closed-loop systems can tailor interventions dynamically, thus enhancing blood pressure regulation. Additionally, we examine the integration of advanced monitoring technologies and artificial intelligence algorithms in closed-loop systems. The review highlights recent studies and their findings, emphasizing the evolving landscape of closed-loop blood pressure management across different clinical scenarios. From the perioperative period to critical care settings, closed-loop systems hold the potential to optimize patient outcomes by precisely adjusting vasopressor administration in response to continuous blood pressure fluctuations. By providing insights into the current state of closed-loop systems for blood pressure control, this review offers a comprehensive overview of their potential contributions to improved patient outcomes and future directions for research and implementation.

Evaluating an advanced double intravenous vasopressor automated system to treat hypotension during spinal anesthesia for cesarean delivery: a randomized controlled trial

BACKGROUND

The optimal treatment of hypotension during spinal anaesthesia is uncertain. A novel double intravenous vasopressor automated (DIVA) system reduces hypotension compared to standard care, and was subsequently modified to an advanced-DIVA (ADIVA) system. The primary objective was to compare ADIVA versus DIVA on incidence of hypotension (systolic BP (SBP) < 80% baseline).

METHODS

We conducted a randomized-controlled trial in women undergoing elective cesarean delivery under spinal anesthesia. SBP and heart rate were measured continuously using a Nexfin monitor. ADIVA delivered 25 μg phenylephrine (heart rate > 60 beats.min^-1) or 2 mg ephedrine (heart rate < 60 beats.min^-1) at SBP 90 to 110% of baseline, 50 μg phenylephrine or 4 mg ephedrine at SBP 80 to 90%, and 75 μg phenylephrine or 6 mg ephedrine at SBP < 80%. ADIVA calculated the trend of SBP; vasopressors were administered rapidly if SBP trended downward, or 30 s if SBP trended upward. In contrast, DIVA delivered 25 μg phenylephrine or 2 mg ephedrine at SBP 90 to 100% of baseline, and 50 μg phenylephrine or 4 mg ephedrine at SBP < 90%. Boluses were followed by a 10-s lockout. Other outcomes included hypertension (SBP > 120% baseline), vasopressor consumption, clinical outcomes, and performance measures from spinal anesthesia to fetal delivery.

RESULTS

We analyzed 94 parturients (ADIVA: n = 46, DIVA: n = 48), with no difference in the incidence of hypotension between ADIVA (78.3%) and DIVA (83.3%, p = 0.677). ADIVA had significantly higher proportion of hypotensive SBP readings, lower phenylephrine consumption and higher umbilical arterial pH. There was no difference in hypertension, bradycardia, ephedrine consumption, intravenous fluid volume, nausea/vomiting, Apgar scores, and umbilical venous pH or lactate. ADIVA maintained SBP higher above baseline with greater fluctuation than DIVA.

CONCLUSION

ADIVA was associated with a greater proportion of hypotensive SBP readings, reduced phenylephrine consumption, and increased umbilical arterial pH than DIVA. Further research is needed to determine the optimal method of vasopressor delivery in parturients undergoing cesarean delivery.

TRIAL REGISTRATION

This study was registered on Clinicaltrials.gov registry (NCT03620942) on 08/08/2018.

Evaluation of indigenously developed closed-loop automated blood pressure control system (claps): a preliminary study

Closed-loop systems have been designed to assist anesthetists in controlling anesthetic drugs and also maintaining the stability of various physiological variables in the normal range. In the present study, we describe and clinically evaluated a novel closed-loop automated blood pressure control system (CLAPS) in patients undergoing cardiac surgery under cardiopulmonary bypass. Forty ASA II-IV adult patients undergoing elective cardiac surgery were randomly allocated to receive adrenaline, noradrenaline, phenylephrine and nitroglycerine (NTG) adjusted either through CLAPS (CLAPS group) or manually (Manual group). The desired target mean arterial blood pressure (MAP) for each patient in both groups was set by the attending anesthesiologist. The hemodynamic performance was assessed based on the percentage duration of time the MAP remained within 20% of the set target. Automated controller performances were compared using performance error criteria of Varvel (MDPE, MDAPE, Wobble) and Global Score. MAP was maintained a significantly longer proportion of time within 20% of the target in the CLAPS group (79.4% vs. 65.5% p < 0.001, 't' test) as compared to the manual group. Median absolute performance error, wobble, and Global score was significantly lower in the CLAPS group. Hemodynamic stability was achieved with a significantly lower dose of Phenyepherine in the CLAPS group (1870 μg vs. 5400 μg, p < 0.05, 't' test). The dose of NTG was significantly higher in the CLAPS group (3070 μg vs. 1600 μg, p-value < 0.05, 't' test). The cardiac index and left ventricular end-diastolic area were comparable between the groups. Automated infusion of vasoactive drugs using CLAPS is feasible and also better than manual control for controlling hemodynamics during cardiac surgery. Trial registration number and date This trial was registered in the Clinical Trial Registry of India under Registration Number CTRI/2018/01/011487 (Retrospective; registration date; January 23, 2018).

Artificial intelligence and anesthesia: A narrative review

Rapid advances in Artificial Intelligence (AI) have led to diagnostic, therapeutic, and intervention-based applications in the field of medicine. Today, there is a deep chasm between AI-based research articles and their translation to clinical anesthesia, which needs to be addressed. Machine learning (ML), the most widely applied arm of AI in medicine, confers the ability to analyze large volumes of data, find associations, and predict outcomes with ongoing learning by the computer. It involves algorithm creation, testing and analyses with the ability to perform cognitive functions including association between variables, pattern recognition, and prediction of outcomes. AI-supported closed loops have been designed for pharmacological maintenance of anesthesia and hemodynamic management. Mechanical robots can perform dexterity and skill-based tasks such as intubation and regional blocks with precision, whereas clinical-decision support systems in crisis situations may augment the role of the clinician. The possibilities are boundless, yet widespread adoption of AI is still far from the ground reality. Patient-related “Big Data” collection, validation, transfer, and testing are under ethical scrutiny. For this narrative review, we conducted a PubMed search in 2020-21 and retrieved articles related to AI and anesthesia. After careful consideration of the content, we prepared the review to highlight the growing importance of AI in anesthesia. Awareness and understanding of the basics of AI are the first steps to be undertaken by clinicians. In this narrative review, we have discussed salient features of ongoing AI research related to anesthesia and perioperative care.

An advanced double intravenous vasopressor automated system to treat hypotension during spinal anaesthesia for caesarean section: A pilot study

BACKGROUND

During spinal anaesthesia for caesarean section, haemodynamic instability may lead to maternal and foetal complications. We developed a novel advanced double intravenous vasopressor automated system (ADIVA) by using a continuous blood pressure and heart rate monitor. Treatment of hypotension was based on three criteria: the drug (phenylephrine or ephedrine) according to the heart rate; the dose of vasopressor determined by the degree of hypotension; a fast or slow bolus of vasopressor administered depending on whether there was a negative or positive gradient of SBP changes, respectively.

OBJECTIVE

The aim of this pilot study was to investigate the feasibility of the ADIVA algorithm.

DESIGN

A prospective pilot study.

SETTING

Single obstetrics and gynaecology centre in Singapore.

PATIENTS

Women undergoing elective caesarean delivery under spinal anaesthesia.

INTERVENTION

Automated administration of ephedrine or phenylephrine based on changes in blood pressure and heart rate (via the ADIVA algorithm) detected on continuous noninvasive haemodynamic monitoring using noninvasive continuous haemodynamic monitor (Nexfin).

MAIN OUTCOME MEASURES

The primary outcome was the incidence of hypotension, defined as SBP less than 80% of baseline. The secondary outcome measures were reactive hypertension, total vasopressor requirement, maternal and neonatal outcomes and system performance.

RESULTS

Forty-five women were recruited. Thirty-one women (69.9%) had at least one reading of hypotension. SBP was within ±20% of the baseline in a mean ± SD of 79.7 ± 17.6% of measurements. Forty-four (97.8%) women required phenylephrine before delivery, while 15 (33.3%) required ephedrine. No rescue medications were required. Three women (6.7%) had nausea and two (4.4%) vomiting. All neonates had APGAR scores of 9 at 5 min.

CONCLUSION

The ADIVA system, with noninvasive continuous haemodynamic monitoring, was able to maintain maternal SBP within ±20% of baseline for the vast majority of the measurements. This system had good maternal and foetal outcomes with minimal intervention from the attending anaesthetist.

TRIAL REGISTRATION

NCT03620942.

Comparison of norepinephrine and phenylephrine infusions for maintenance of haemodynamics following subarachnoid block in lower segment caeserean section

Background and Aims:

Phenylephrine is the vasopressor of choice in spinal anaesthesia–induced maternal hypotension. However, it results in reflex bradycardia and decrease in cardiac output (CO), an effect that is perhaps less evident with the use of norepinephrine. We sought to evaluate the effect of phenylephrine and norepinephrine infusion on maternal systolic blood pressure (SBP), heart rate (HR), intraoperative nausea vomiting (IONV) and fatal Apgar scores.

Methods:

A randomised double-blind study was conducted on 200 American Society of Anesthesiologists (ASA) II–III parturients undergoing caesarean section under subarachnoid block (SAB) who were randomised to two groups A and B to receive variable rate, manually controlled infusions of phenylephrine and norepinephrine targeting maintenance of SBP to 100% of the baseline value. Maternal haemodynamics especially episodes of hypotension, IONV and vasopressor consumption were observed and recorded.

Results:

A statistically significant trend of lower SBP was observed during the first 6 min following intrathecal injection in group A (P value – 0.000). Though a greater number of parturients experienced ≥1 episode of hypotension in Group A vs Group B (13% vs 9%), the difference was, however, statistically insignificant. The incidence of bradycardia was higher in group A than in group B (16% vs 1%) and was found to be statistically significant (P < 0.05). The episodes of hypertension, IONV, maternal vasopressor consumption and neonatal Apgar score were comparable among both the groups.

Conclusion:

A dilute solution of norepinephrine infusion is comparably efficacious to the current gold standard vasopressor phenylephrine in maintaining blood pressure following spinal anaesthesia for caesarean delivery, with a significantly lower incidence of bradycardia.

Blood pressure measurement during cesarean delivery: Evaluation of a beat-to-beat noninvasive device (NexfinTM)

Early detection of arterial hypotension during cesarean delivery under spinal anesthesia is important. This study aims to compare the validity of NexfinTM as beat-to-beat noninvasive blood pressure monitoring with conventional intermittent oscillometric measurement of blood pressure during elective cesarean delivery.This open prospective observational bicentric study was performed between January 2013 and December 2015. We simultaneously recorded arterial blood pressure with both techniques in pregnant women undergoing elective cesarean delivery under spinal anesthesia. The primary outcome was a Bland-Altman analysis of systolic blood pressure measurement comparing NexfinTM and a conventional method. The secondary outcomes were the time to detect the first relevant hypotensive episode and the comparison of both devices using a four-quadrant graph.One hundred and seventy-four parturients completed the study, and 2640 pairs of systolic blood pressure measurements were analyzed. Bias was -10 mmHg with upper and lower limits of agreement of -61 and +41 mmHg. In 73.9% of the cases, the two techniques provided the same information (normotension or hypotension), but the conventional method missed 20.8% of measurements, with NexfinTM detecting 16.2% more hypotensive measurements. The median [25-75 percentiles] duration to detect the first hypotensive measurement was 331 [206-480] seconds for NexfinTM and 440 [300-500] s for intermittent oscillometry (P < .001).The agreement between NexfinTM and an intermittent method for the measurement of systolic blood pressure was not in an acceptable range during cesarean delivery, although NexfinTM may detect hypotension earlier than the standard method.Trial registration: Clinicaltrials.gov identifier: NCT01732133; November 22, 2012.

Development of an automated closed-loop β-blocker delivery system to stably reduce myocardial oxygen consumption without inducing circulatory collapse in a canine heart failure model: a proof of concept study

Beta-blockers are well known to reduce myocardial oxygen consumption (MVO₂) and improve the prognosis of heart failure (HF) patients. However, its negative chronotropic and inotropic effects limit their use in the acute phase of HF due to the risk of circulatory collapse. In this study, as a first step for a safe β-blocker administration strategy, we aimed to develop and evaluate the feasibility of an automated β-blocker administration system. We developed a system to monitor arterial pressure (AP), left atrial pressure (P_LA), right atrial pressure, and cardiac output. Using negative feedback of hemodynamics, the system controls AP and P_LA by administering landiolol (an ultra-short-acting β-blocker), dextran, and furosemide. We applied the system for 60 min to 6 mongrel dogs with rapid pacing-induced HF. In all dogs, the system automatically adjusted the doses of the drugs. Mean AP and mean P_LA were controlled within the acceptable ranges (AP within 5 mmHg below target; P_LA within 2 mmHg above target) more than 95% of the time. Median absolute performance error was small for AP [median (interquartile range), 3.1% (2.2–3.8)] and P_LA [3.6% (2.2–5.7)]. The system decreased MVO₂ and P_LA significantly. We demonstrated the feasibility of an automated β-blocker administration system in a canine model of acute HF. The system controlled AP and P_LA to avoid circulatory collapse, and reduced MVO₂ significantly. As the system can help the management of patients with HF, further validations in larger samples and development for clinical applications are warranted.

Automated closed-loop versus manually controlled norepinephrine infusion in patients undergoing intermediate- to high-risk abdominal surgery: a randomised controlled trial

BACKGROUND

Hypotension occurs frequently during surgery and may be associated with adverse complications. Vasopressor titration is frequently used to correct hypotension, but requires considerable time and attention, potentially reducing the time available for other clinical duties. To overcome this issue, we have developed a closed-loop vasopressor (CLV) controller to help correct hypotension more efficiently. The aim of this randomised controlled study was to evaluate whether the CLV controller was superior to traditional vasopressor management at minimising hypotension in patients undergoing abdominal surgery.

METHODS

Thirty patients scheduled for elective intermediate-to high-risk abdominal surgery were randomised into two groups. In the CLV group, hypotension was corrected automatically via the CLV controller system, which adjusted the rate of a norepinephrine infusion according to MAP values recorded using an advanced haemodynamic device. In the control group, management of hypotension consisted of standard, manual adjustment of the norepinephrine infusion. The primary outcome was the percentage of time that a patient was hypotensive, defined as MAP <90% of their baseline value, during surgery.

RESULTS

The percentage of time patients were hypotensive during surgery was 10 times less in the CVL group than in the control group (1.6 [0.9-2.3]% vs 15.4 [9.9-24.3]%; difference: 13 [95% confidence interval: 9-19]; P<0.0001). The CVL group also spent much less time with MAP <65 mm Hg (0.2 [0.0-0.4]% vs 4.5 [1.1-7.9]%; P<0.0001).

CONCLUSIONS

In patients undergoing intermediate- to high-risk surgery under general anaesthesia, computer-assisted adjustment of norepinephrine infusion significantly decreases the incidence of hypotension compared with manual control.

CLINICAL TRIAL REGISTRATION

NCT04089644.

Techniques for preventing hypotension during spinal anaesthesia for caesarean section

BACKGROUND

Maternal hypotension is the most frequent complication of spinal anaesthesia for caesarean section. It can be associated with nausea or vomiting and may pose serious risks to the mother (unconsciousness, pulmonary aspiration) and baby (hypoxia, acidosis, neurological injury).

OBJECTIVES

To assess the effects of prophylactic interventions for hypotension following spinal anaesthesia for caesarean section.

SEARCH METHODS

We searched Cochrane Pregnancy and Childbirth's Trials Register (9 August 2016) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised controlled trials, including full texts and abstracts, comparing interventions to prevent hypotension with placebo or alternative treatment in women having spinal anaesthesia for caesarean section. We excluded studies if hypotension was not an outcome measure.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study quality and extracted data from eligible studies. We report 'Summary of findings' tables using GRADE.

MAIN RESULTS

We included 125 studies involving 9469 women. Interventions were to prevent maternal hypotension following spinal anaesthesia only, and we excluded any interventions considered active treatment. All the included studies reported the review's primary outcome. Across 49 comparisons, we identified three intervention groups: intravenous fluids, pharmacological interventions, and physical interventions. Authors reported no serious adverse effects with any of the interventions investigated. Most trials reported hypotension requiring intervention and Apgar score of less than 8 at five minutes as the only outcomes. None of the trials included in the comparisons we describe reported admission to neonatal intensive care unit. Crystalloid versus control (no fluids) Fewer women experienced hypotension in the crystalloid group compared with no fluids (average risk ratio (RR) 0.84, 95% confidence interval (CI) 0.72 to 0.98; 370 women; 5 studies; low-quality evidence). There was no clear difference between groups in numbers of women with nausea and vomiting (average RR 0.19, 95% CI 0.01 to 3.91; 1 study; 69 women; very low-quality evidence). No baby had an Apgar score of less than 8 at five minutes in either group (60 babies, low-quality evidence). Colloid versus crystalloid Fewer women experienced hypotension in the colloid group compared with the crystalloid group (average RR 0.69, 95% CI 0.58 to 0.81; 2009 women; 27 studies; very low-quality evidence). There were no clear differences between groups for maternal hypertension requiring intervention (average RR 0.64, 95% CI 0.09 to 4.46, 3 studies, 327 women; very low-quality evidence), maternal bradycardia requiring intervention (average RR 0.98, 95% CI 0.54 to 1.78, 5 studies, 413 women; very low-quality evidence), nausea and/or vomiting (average RR 0.89, 95% CI 0.66 to 1.19, 14 studies, 1058 women, I² = 29%; very low-quality evidence), neonatal acidosis (average RR 0.83, 95% CI 0.15 to 4.52, 6 studies, 678 babies; very low-quality evidence), or Apgar score of less than 8 at five minutes (average RR 0.24, 95% CI 0.03 to 2.05, 10 studies, 730 babies; very low-quality evidence). Ephedrine versus phenylephrine There were no clear differences between ephedrine and phenylephrine groups for preventing maternal hypotension (average RR 0.92, 95% CI 0.71 to 1.18; 401 women; 8 studies; very low-quality evidence) or hypertension (average RR 1.72, 95% CI 0.71 to 4.16, 2 studies, 118 women, low-quality evidence). Rates of bradycardia were lower in the ephedrine group (average RR 0.37, 95% CI 0.21 to 0.64, 5 studies, 304 women, low-quality evidence). There was no clear difference in the number of women with nausea and/or vomiting (average RR 0.76, 95% CI 0.39 to 1.49, 4 studies, 204 women, I² = 37%, very low-quality evidence), or babies with neonatal acidosis (average RR 0.89, 95% CI 0.07 to 12.00, 3 studies, 175 babies, low-quality evidence). No baby had an Apgar score of less than 8 at five minutes in either group (321 babies; low-quality evidence). Ondansetron versus control Ondansetron administration was more effective than control (placebo saline) for preventing hypotension requiring treatment (average RR 0.67, 95% CI 0.54 to 0.83; 740 women, 8 studies, low-quality evidence), bradycardia requiring treatment (average RR 0.49, 95% CI 0.28 to 0.87; 740 women, 8 studies, low-quality evidence), and nausea and/or vomiting (average RR 0.35, 95% CI 0.24 to 0.51; 653 women, 7 studies, low-quality evidence). There was no clear difference between the groups in rates of neonatal acidosis (average RR 0.48, 95% CI 0.05 to 5.09; 134 babies; 2 studies, low-quality evidence) or Apgar scores of less than 8 at five minutes (284 babies, low-quality evidence). Lower limb compression versus control Lower limb compression was more effective than control for preventing hypotension (average RR 0.61, 95% CI 0.47 to 0.78, 11 studies, 705 women, I² = 65%, very low-quality evidence). There was no clear difference between the groups in rates of bradycardia (RR 0.63, 95% CI 0.11 to 3.56, 1 study, 74 women, very low-quality evidence) or nausea and/or vomiting (average RR 0.42, 95% CI 0.14 to 1.27, 4 studies, 276 women, I² = 32%, very-low quality evidence). No baby had an Apgar score of less than 8 at five minutes in either group (130 babies, very low-quality evidence). Walking versus lying There was no clear difference between the groups for women with hypotension requiring treatment (RR 0.71, 95% CI 0.41 to 1.21, 1 study, 37 women, very low-quality evidence). Many included studies reported little to no information that would allow an assessment of their risk of bias, limiting our ability to draw meaningful conclusions. GRADE assessments of the quality of evidence ranged from very low to low. We downgraded evidence for limitations in study design, imprecision, and indirectness; most studies assessed only women scheduled for elective caesarean sections. External validity also needs consideration. Readers should question the use of colloids in this context given the serious potential side effects such as allergy and renal failure associated with their administration.

AUTHORS' CONCLUSIONS

While interventions such as crystalloids, colloids, ephedrine, phenylephrine, ondansetron, or lower leg compression can reduce the incidence of hypotension, none have been shown to eliminate the need to treat maternal hypotension in some women. We cannot draw any conclusions regarding rare adverse effects associated with use of the interventions (for example colloids) due to the relatively small numbers of women studied.

Feasibility of closed-loop titration of norepinephrine infusion in patients undergoing moderate- and high-risk surgery

BACKGROUND

Vasopressor agents are used to prevent intraoperative hypotension and ensure adequate perfusion. Vasopressors are usually administered as intermittent boluses or manually adjusted infusions, but this practice requires considerable time and attention. We have developed a closed-loop vasopressor (CLV) controller to correct hypotension more efficiently. Here, we conducted a proof-of-concept study to assess the feasibility and performance of CLV control in surgical patients.

METHODS

Twenty patients scheduled for elective surgical procedures were included in this study. The goal of the CLV system was to maintain MAP within 5 mm Hg of the target MAP by automatically adjusting the rate of a norepinephrine infusion using MAP values recorded continuously from an arterial catheter. The primary outcome was the percentage of time that patients were hypotensive, as defined by a MAP of 5 mm Hg below the chosen target. Secondary outcomes included the total dose of norepinephrine, percentage of time with hypertension (MAP>5 mm Hg of the chosen target), raw percentage "time in target" and Varvel performance criteria.

RESULTS

The 20 subjects (median age: 64 years [52-71]; male (35%)) underwent elective surgery lasting 154 min [124-233]. CLV control maintained MAP within ±5 mm Hg of the target for 91.6% (85.6-93.3) of the intraoperative period. Subjects were hypotensive for 2.6% of the intraoperative period (range, 0-8.4%). Additional performance criteria for the controller included mean absolute performance error of 2.9 (0.8) and mean predictive error of 0.5 (1.0). No subjects experienced major complications.

CONCLUSIONS

In this proof of concept study, CLV control minimised perioperative hypotension in subjects undergoing moderate- or high-risk surgery. Further studies to demonstrate efficacy are warranted.

TRIAL REGISTRY NUMBER

NCT03515161 (ClinicalTrials.gov).

Prophylactic Norepinephrine Infusion for Preventing Hypotension During Spinal Anesthesia for Cesarean Delivery

BACKGROUND

The use of norepinephrine for maintaining blood pressure (BP) during spinal anesthesia for cesarean delivery has been described recently. However, its administration by titrated manually controlled infusion in this context has not been evaluated.

METHODS

In a double-blinded, randomized controlled trial, 110 healthy women having spinal anesthesia for elective cesarean delivery were randomly allocated to 1 of 2 groups. In group 1, patients received an infusion of 5 µg/mL norepinephrine that was started at 30 mL/h (2.5 µg/min) immediately after intrathecal injection and then manually adjusted within the range 0-60 mL/h (0-5 µg/min), according to values of systolic BP measured noninvasively at 1-minute intervals until delivery, with the objective of maintaining values near baseline. In group 2, no prophylactic vasopressor was given, and a bolus of 1 mL norepinephrine 5 µg/mL (5 µg) was given whenever systolic BP decreased to <80% of the baseline value. The study protocol was continued until delivery. The primary outcomes of the study were the incidence of hypotension and the overall stability of systolic BP control versus baseline compared using performance error calculations. In addition, the incidence and timing of hypotension were further compared using survival analysis.

RESULTS

Three patients were excluded from the analysis. Nine patients (17%) in group 1 had 1 or more episodes of hypotension versus 35 (66%) in group 2 (P < .001). Performance error calculations showed that on average, systolic BP was maintained closer to baseline (P < .001) in group 1. Survival curve analysis showed a significant difference between groups (log-rank test P < .001). Four patients in each group had a recorded heart rate <60 beats/min (P = .98). Despite a much greater rate of administration of norepinephrine in group 1 (median, 61.0 [interquartile range, 47.0-72.5] µg) versus group 2 (5.0 [0-18.1] µg) (P < .001), there was no difference in neonatal outcome as assessed by Apgar scores and umbilical cord blood gas analysis.

CONCLUSIONS

In patients having spinal anesthesia for elective cesarean delivery, a manually titrated infusion of 5 µg/mL of norepinephrine was effective for maintaining BP and decreasing the incidence of hypotension, with no detectable detrimental effect on neonatal outcome. Further investigation of the use of dilute norepinephrine infusions for routine use in obstetric patients is suggested.

Model-based drug administration: current status of target-controlled infusion and closed-loop control

PURPOSE OF REVIEW

Drug administration might be optimized by incorporating pharmacokinetic-dynamic (PK/PD) principles and control engineering theories. This review gives an update of the actual status of target-controlled infusion (TCI) and closed-loop computer-controlled drug administration and the ongoing research in the field.

RECENT FINDINGS

TCI is becoming mature technology clinically used in many countries nowadays with proven safety. Nevertheless, changing populations might require adapting the established PK/PD models. As TCI requires accurate PK/PD models, new models have been developed which should now be incorporated into the pumps to allow more general use of this technology. Closed-loop administration of hypnotic drugs using an electro-encephalographic-derived-controlled variable has been well studied and has been shown to outperform manual administration. Computer administration for other drugs and fluids have been studied recently. Feasibility has been shown for systems controlling multiple components of anaesthesia, but more work is required to show clinical safety and efficiency.

SUMMARY

Evidence in the literature is increasing that TCI and closed-loop technology could assist the anaesthetists to optimize drug administration during anaesthesia.

Fully automated life support: an implementation and feasibility pilot study in healthy pigs

Background

Automated systems are available in various application areas all over the world for the purpose of reducing workload and increasing safety. However, such support systems that would aid caregivers are still lacking in the medical sector. With respect to workload and safety, especially, the intensive care unit appears to be an important and challenging application field. Whereas many closed-loop subsystems for single applications already exist, no comprehensive system covering multiple therapeutic aspects and interactions is available yet. This paper describes a fully closed-loop intensive care therapy and presents a feasibility analysis performed in three healthy pigs over a period of 72 h each to demonstrate the technical and practical implementation of automated intensive care therapy.

Methods

The study was performed in three healthy, female German Landrace pigs under general anesthesia with endotracheal intubation. An arterial and a central venous line were implemented, and a suprapubic urinary catheter was inserted. Electrolytes, glucose levels, acid-base balance, and respiratory management were completely controlled by an automated fuzzy logic system based on individual targets. Fluid management by adaption of the respective infusion rates for the individual parameters was included.

Results

During the study, no manual modification of the device settings was allowed or required. Homoeostasis in all animals was kept stable during the entire observation period. All remote-controlled parameters were maintained within physiological ranges for most of the time (free arterial calcium 73%, glucose 98%, arterial base excess 89%, and etCO₂ 98%). Subsystem interaction was analyzed.

Conclusions

In the presented study, we demonstrate the feasibility of a fully closed-loop system, for which we collected high-resolution data on the interaction and response of the different subsystems. Further studies should use big data approaches to analyze and investigate the interactions between the subsystems in more detail.

Physician-Directed Versus Computerized Closed-Loop Control of Blood Pressure Using Phenylephrine in a Swine Model

BACKGROUND

Vasopressors provide a rapid and effective approach to correct hypotension in the perioperative setting. Our group developed a closed-loop control (CLC) system that titrates phenylephrine (PHP) based on the mean arterial pressure (MAP) during general anesthesia. As a means of evaluating system competence, we compared the performance of the automated CLC with physicians. We hypothesized that our CLC algorithm more effectively maintains blood pressure at a specified target with less blood pressure variability and reduces the dose of PHP required.

METHODS

In a crossover study design, 6 swine under general anesthesia were subjected to a normovolemic hypotensive challenge induced by sodium nitroprusside. The physicians (MD) manually changed the PHP infusion rate, and the CLC system performed this task autonomously, adjusted every 3 seconds to achieve a predetermined MAP.

RESULTS

The CLC maintained MAP within 5 mm Hg of the target for (mean ± standard deviation) 93.5% ± 3.9% of the time versus 72.4% ± 26.8% for the MD treatment (P = .054). The mean (standard deviation) percentage of time that the CLC and MD interventions were above target range was 2.1% ± 3.3% and 25.8% ± 27.4% (P = .06), respectively. Control statistics, performance error, median performance error, and median absolute performance error were not different between CLC and MD interventions. PHP infusion rate adjustments by the physician were performed 12 to 80 times in individual studies over a 60-minute period. The total dose of PHP used was not different between the 2 interventions.

CONCLUSIONS

The CLC system performed as well as an anesthesiologist totally focused on MAP control by infusing PHP. Computerized CLC infusion of PHP provided tight blood pressure control under conditions of experimental vasodilation.

Techniques for preventing hypotension during spinal anaesthesia for caesarean section

BACKGROUND

Maternal hypotension is the most frequent complication of spinal anaesthesia for caesarean section. It can be associated with nausea or vomiting and may pose serious risks to the mother (unconsciousness, pulmonary aspiration) and baby (hypoxia, acidosis, neurological injury).

OBJECTIVES

To assess the effects of prophylactic interventions for hypotension following spinal anaesthesia for caesarean section.

SEARCH METHODS

We searched Cochrane Pregnancy and Childbirth's Trials Register (9 August 2016) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised controlled trials, including full texts and abstracts, comparing interventions to prevent hypotension with placebo or alternative treatment in women having spinal anaesthesia for caesarean section. We excluded studies if hypotension was not an outcome measure.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study quality and extracted data from eligible studies. We report 'Summary of findings' tables using GRADE.

MAIN RESULTS

We included 126 studies involving 9565 participants. Interventions were to prevent maternal hypotension following spinal anaesthesia only, and we excluded any interventions considered active treatment. All the included studies reported the review's primary outcome. Across 49 comparisons, we identified three intervention groups: intravenous fluids, pharmacological interventions, and physical interventions. Authors reported no serious adverse effects with any of the interventions investigated. Most trials reported hypotension requiring intervention and Apgar score of less than 8 at five minutes as the only outcomes. None of the trials included in the comparisons we describe reported admission to neonatal intensive care unit. Crystalloid versus control (no fluids)Fewer women experienced hypotension in the crystalloid group compared with no fluids (average risk ratio (RR) 0.84, 95% confidence interval (CI) 0.72 to 0.98; 370 women; 5 studies; low-quality evidence). There was no clear difference between groups in numbers of women with nausea and vomiting (average RR 0.19, 95% CI 0.01 to 3.91; 1 study; 69 women; very low-quality evidence). No baby had an Apgar score of less than 8 at five minutes in either group (60 babies, low-quality evidence). Colloid versus crystalloidFewer women experienced hypotension in the colloid group compared with the crystalloid group (average RR 0.68, 95% CI 0.58 to 0.80; 2105 women; 28 studies; very low-quality evidence). There were no clear differences between groups for maternal hypertension requiring intervention (average RR 0.64, 95% CI 0.09 to 4.46, 3 studies, 327 women;very low-quality evidence), maternal bradycardia requiring intervention (average RR 0.99, 95% CI 0.55 to 1.79, 6 studies, 509 women; very low-quality evidence), nausea and/or vomiting (average RR 0.83, 95% CI 0.61 to 1.13, 15 studies, 1154 women, I² = 37%; very low-quality evidence), neonatal acidosis (average RR 0.83, 95% CI 0.15 to 4.52, 6 studies, 678 babies; very low-quality evidence), or Apgar score of less than 8 at five minutes (average RR 0.24, 95% CI 0.03 to 2.05, 11 studies, 826 babies; very low-quality evidence). Ephedrine versus phenylephrineThere were no clear differences between ephedrine and phenylephrine groups for preventing maternal hypotension (average RR 0.92, 95% CI 0.71 to 1.18; 401 women; 8 studies; very low-quality evidence) or hypertension (average RR 1.72, 95% CI 0.71 to 4.16, 2 studies, 118 women, low-quality evidence). Rates of bradycardia were lower in the ephedrine group (average RR 0.37, 95% CI 0.21 to 0.64, 5 studies, 304 women, low-quality evidence). There was no clear difference in the number of women with nausea and/or vomiting (average RR 0.76, 95% CI 0.39 to 1.49, 4 studies, 204 women, I² = 37%, very low-quality evidence), or babies with neonatal acidosis (average RR 0.89, 95% CI 0.07 to 12.00, 3 studies, 175 babies, low-quality evidence). No baby had an Apgar score of less than 8 at five minutes in either group (321 babies; low-quality evidence). Ondansetron versus controlOndansetron administration was more effective than control (placebo saline) for preventing hypotension requiring treatment (average RR 0.67, 95% CI 0.54 to 0.83; 740 women, 8 studies, low-quality evidence), bradycardia requiring treatment (average RR 0.49, 95% CI 0.28 to 0.87; 740 women, 8 studies, low-quality evidence), and nausea and/or vomiting (average RR 0.35, 95% CI 0.24 to 0.51; 653 women, 7 studies, low-quality evidence). There was no clear difference between the groups in rates of neonatal acidosis (average RR 0.48, 95% CI 0.05 to 5.09; 134 babies; 2 studies, low-quality evidence) or Apgar scores of less than 8 at five minutes (284 babies, low-quality evidence). Lower limb compression versus controlLower limb compression was more effective than control for preventing hypotension (average RR 0.61, 95% CI 0.47 to 0.78, 11 studies, 705 women, I² = 65%, very low-quality evidence). There was no clear difference between the groups in rates of bradycardia (RR 0.63, 95% CI 0.11 to 3.56, 1 study, 74 women, very low-quality evidence) or nausea and/or vomiting (average RR 0.42 , 95% CI 0.14 to 1.27, 4 studies, 276 women, I² = 32%, very-low quality evidence). No baby had an Apgar score of less than 8 at five minutes in either group (130 babies, very low-quality evidence). Walking versus lyingThere was no clear difference between the groups for women with hypotension requiring treatment (RR 0.71, 95% CI 0.41 to 1.21, 1 study, 37 women, very low-quality evidence).Many included studies reported little to no information that would allow an assessment of their risk of bias, limiting our ability to draw meaningful conclusions. GRADE assessments of the quality of evidence ranged from very low to low. We downgraded evidence for limitations in study design, imprecision, and indirectness; most studies assessed only women scheduled for elective caesarean sections.External validity also needs consideration. Readers should question the use of colloids in this context given the serious potential side effects such as allergy and renal failure associated with their administration.

AUTHORS' CONCLUSIONS

While interventions such as crystalloids, colloids, ephedrine, phenylephrine, ondansetron, or lower leg compression can reduce the incidence of hypotension, none have been shown to eliminate the need to treat maternal hypotension in some women. We cannot draw any conclusions regarding rare adverse effects associated with use of the interventions (for example colloids) due to the relatively small numbers of women studied.

Automated closed-loop resuscitation of multiple hemorrhages: a comparison between fuzzy logic and decision table controllers in a sheep model

Background

Hemorrhagic shock is the leading cause of trauma-related death in the military setting. Definitive surgical treatment of a combat casualty can be delayed and life-saving fluid resuscitation might be necessary in the field. Therefore, improved resuscitation strategies are critically needed for prolonged field and en route care. We developed an automated closed-loop control system capable of titrating fluid infusion to a target endpoint. We used the system to compare the performance of a decision table algorithm (DT) and a fuzzy logic controller (FL) to rescue and maintain the mean arterial pressure (MAP) at a target level during hemorrhages. Fuzzy logic empowered the control algorithm to emulate human expertise. We hypothesized that the FL controller would be more effective and more efficient than the DT algorithm by responding in a more rigid, structured way.

Methods

Ten conscious sheep were submitted to a hemorrhagic protocol of 25 ml/kg over three separate bleeds. Automated resuscitation with lactated Ringer’s was initiated 30 min after the first hemorrhage started. The endpoint target was MAP. Group differences were assessed by two-tailed t test and alpha of 0.05.

Results

Both groups maintained MAP at similar levels throughout the study. However, the DT group required significantly more fluid than the FL group, 1745 ± 552 ml (42 ± 11 ml/kg) versus 978 ± 397 ml (26 ± 11 ml/kg), respectively (p = 0.03).

Conclusion

The FL controller was more efficient than the DT algorithm and may provide a means to reduce fluid loading. Effectiveness was not different between the two strategies. Automated closed-loop resuscitation can restore and maintain blood pressure in a multi-hemorrhage model of shock.

Prophylactic phenylephrine infusion for the prevention of hypotension after spinal anesthesia in the elderly: a randomized controlled clinical trial

STUDY OBJECTIVE

Hypotension frequently occurs during spinal anesthesia (SA), especially in the elderly. Phenylephrine is effective to prevent SA-induced hypotension during cesarean delivery. The objective of this study was to evaluate the efficacy and safety of prophylactic infusion of phenylephrine after SA for orthopedic surgery in the elderly.

DESIGN

This prospective, randomized, double-blind, and placebo-controlled study included 54 patients older than 60 years undergoing elective lower limb surgery under SA (injection of 10 mg of isobaric bupivacaine with 5 μg of sufentanyl).

INTERVENTION

Patients were randomized to group P (100-μg/mL solution of phenylephrine solution at 1 mL/min after placement of SA) or the control group C (0.9% isotonic sodium chloride solution). The flow of the infusion was stopped if the mean arterial blood pressure (MAP) was higher than the baseline MAP and maintained or restarted at 1 mL/min if MAP was equal to or lower than the baseline MAP. Heart rate and MAP were collected throughout the case.

MEASUREMENTS

Hypotension was defined by a 20% decrease and hypertension as a 20% increase from baseline MAP. Bradycardia was defined as a heart rate lower than 50 beats per minute.

MAIN RESULTS

Twenty-eight patients were randomized to group P and 26 patients to group C. MAP was higher in group P than in group C (92 ± 2 vs 82 ± 2 mm Hg, mean ± SD, P< .001). The number of hypotensive episodes per patient was higher in group C compared with group P (9 [0-39] vs 1 [0-10], median [extremes], P< .01), but the number of hypotensive patients was similar between groups (19 [73%] vs 20 [71%], P= 1). The time to onset of the first hypotension was shorter in group C (3 [1-13] vs 15 [1-95] minutes, P= .004). The proportion of patients without hypotension (cumulative survival) was better in group P (P= .04). The number of hypertensive episodes per patient and the number of bradycardic episodes per patient were similar between groups (P= not significant).

CONCLUSION

Prophylactic phenylephrine infusion is an effective method of reducing SA-induced hypotension in the elderly. Compared with a control group, it delays the time to onset of hypotension and decreases the number of hypotensive episodes per patient. More data are needed to evaluate clinical outcomes of such a strategy.

Hemodynamics of Phenylephrine Infusion Versus Lower Extremity Compression During Spinal Anesthesia for Cesarean Delivery: A Randomized, Double-Blind, Placebo-Controlled Study

BACKGROUND

Phenylephrine infusion is the current first-line choice for prevention of spinal hypotension during cesarean delivery. The optimal dosage regimen is still undetermined. A mechanical alternative, lower limb wrapping, has been examined in a few small studies showing moderate success. In this trial, we compared the effect of leg wrapping with low-dose phenylephrine infusion and with placebo treatment on systolic arterial blood pressure during spinal anesthesia for cesarean delivery.

METHODS

In this randomized, double-blinded, placebo-controlled study, healthy women received either phenylephrine (n = 38; initial bolus of 0.25 μg kg and infusion of 0.25 μg kg min), leg wrapping (n = 38), or no treatment (control; n = 36) during spinal anesthesia for elective cesarean delivery. LiDCOplus was used for continuous minimally invasive hemodynamic monitoring. The extent of decrease in systolic arterial blood pressure (for 13 minutes after spinal induction) was the primary outcome. Cardiac output, systemic vascular resistance, stroke volume, heart rate, neonatal acid-base status, and Apgar score were secondary outcome variables. Mixed model analysis of continuous hemodynamic trends during the first 13 minutes after induction of spinal anesthesia was performed.

RESULTS

In the phenylephrine group, the decrease in systolic arterial blood pressure was significantly less (difference in rate of change, 0.09 mm Hg 5 s; 95% confidence interval, 0.02-0.16; P = 0.013); systemic vascular resistance (P < 0.001) was significantly higher; stroke volume (P = 0.41) was similar; and heart rate (P = 0.002) and cardiac output (P < 0.001) were significantly lower compared with the leg wrapping group. Compared with control, the leg wrapping group had a significantly smaller decrease in systolic arterial blood pressure (0.39 mm Hg 5 s; 95% confidence interval, 0.32-0.46; P < 0.001), higher stroke volume (P < 0.001), and higher cardiac output (P = 0.001).

CONCLUSIONS

An initial bolus of phenylephrine followed by a low-dose phenylephrine infusion was superior to leg wrapping and no intervention for the prevention of hypotension during spinal anesthesia for cesarean delivery. Phenylephrine prevented hypotension primarily by restoring systemic vascular resistance and did not cause hypertension or a clinically relevant reduction in cardiac output. Leg wrapping prevented hypotension compared with no intervention by limiting modest early spinal anesthesia-mediated venodilation.

Less Invasive and Inotrope-Reduction Approach to Automated Closed-Loop Control of Hemodynamics in Decompensated Heart Failure

We have been developing an automated cardiovascular drug infusion system for simultaneous control of arterial pressure (AP), cardiac output (CO), and left atrial pressure (PLA) in decompensated heart failure (HF). In our prototype system, CO and PLA were measured invasively through thoracotomy. Furthermore, the control logic inevitably required use of inotropes to improve hemodynamics, which was not in line with clinical HF guidelines. The goal of this study was to solve these problems and develop a clinically feasible system. We integrated to the system minimally invasive monitors of CO and pulmonary capillary wedge pressure (PCWP, surrogates for PLA) that we developed recently. We also redesigned the control logic to reduce the use of inotrope. We applied the newly developed system to nine dogs with decompensated HF. Once activated, our system started to control the infusion of vasodilator and diuretics in all the animals. Inotrope was not infused in three animals, and infused at minimal doses in six animals that were intolerant of vasodilator infusion alone. Within 50 min, our system controlled AP, CO, and PCWP to their respective targets accurately. Pulmonary artery catheterization confirmed optimization of hemodynamics (AP, from 98 ± 4 to 74 ± 11 mmHg; CO, from 2.2 ± 0.5 to 2.9 ± 0.3 L·min(-1)·m(-2); PCWP, from 27.0 ± 6.6 to 13.8 ± 3.0 mmHg). In a minimally invasive setting while reducing the use of inotrope, our system succeeded in automatically optimizing the overall hemodynamics in canine models of HF. The present results pave the way for clinical application of our automated drug infusion system.

Combined use of hyperbaric and hypobaric ropivacaine significantly improves hemodynamic characteristics in spinal anesthesia for caesarean section: a prospective, double-blind, randomized, controlled study

PURPOSE

To observe the hemodynamic changes of parturients in the combined use of hyperbaric (4 mg) and hypobaric (6 mg) ropivacaine during spinal anesthesia for caesarean section in this randomized double-blind study.

METHODS

Parturients (n = 136) undergoing elective cesarean delivery were randomly and equally allocated to receive either combined hyperbaric and hypobaric ropivacaine (Group A) or hyperbaric ropivacaine (Group B). Outcome measures were: hemodynamic characteristics, maximum height of sensory block, time to achieve T8 sensory blockade level, incidence of complications, Apgar scores at 1 and 5 min, and neonatal blood gas analysis.

RESULTS

Group A had a lower level of sensory blockade (T6 [T6-T7]) and longer time to achieve T8 sensory blockade level (8 ± 1.3 min) than did patients in Group B (T3 [T2-T4] and 5 ± 1.0 min, respectively; P < 0.001, both). The incidence rates for hypotension, nausea, and vomiting were significantly lower in Group A (13%, 10%, and 3%, respectively) than Group B (66%, 31%, and 13%; P < 0.001, P = 0.003, P = 0.028).

CONCLUSIONS

Combined use of hyperbaric (4 mg) and hypobaric (6 mg) ropivacaine significantly decreased the incidences of hypotension and complications in spinal anesthesia for caesarean section by extending induction time and decreasing the level of sensory blockade.

TRIAL REGISTRATION

Chinese Clinical Trial Register ChiCTR-TRC-13004622.

Randomized Double-blinded Comparison of Norepinephrine and Phenylephrine for Maintenance of Blood Pressure during Spinal Anesthesia for Cesarean Delivery

Background:

During spinal anesthesia for cesarean delivery, phenylephrine can cause reflexive decreases in maternal heart rate and cardiac output. Norepinephrine has weak β-adrenergic receptor agonist activity in addition to potent α-adrenergic receptor activity and therefore may be suitable for maintaining blood pressure with less negative effects on heart rate and cardiac output compared with phenylephrine.

Methods:

In a randomized, double-blinded study, 104 healthy patients having cesarean delivery under spinal anesthesia were randomized to have systolic blood pressure maintained with a computer-controlled infusion of norepinephrine 5 μg/ml or phenylephrine 100 μg/ml. The primary outcome compared was cardiac output. Blood pressure heart rate and neonatal outcome were also compared.

Results:

Normalized cardiac output 5 min after induction was greater in the norepinephrine group versus the phenylephrine group (median 102.7% [interquartile range, 94.3 to 116.7%] versus 93.8% [85.0 to 103.1%], P = 0.004, median difference 9.8%, 95% CI of difference between medians 2.8 to 16.1%). From induction until uterine incision, for norepinephrine versus phenylephrine, systolic blood pressure and stroke volume were similar, heart rate and cardiac output were greater, systemic vascular resistance was lower, and the incidence of bradycardia was smaller. Neonatal outcome was similar between groups.

Conclusions:

When given by computer-controlled infusion during spinal anesthesia for cesarean delivery, norepinephrine was effective for maintaining blood pressure and was associated with greater heart rate and cardiac output compared with phenylephrine. Further work would be of interest to confirm the safety and efficacy of norepinephrine as a vasopressor in obstetric patients.

Principles of pharmacologic hemodynamic management and closed-loop systems

Every day, physicians in critical-care settings are challenged with the hemodynamic management of patients with severe cardiovascular derangements. There is a potential role for closed-loop (automated) systems to assist clinicians in managing these patients and growing interest in the possible applications. In this review, we discuss the basic principles of critical-care hemodynamic management and the closed-loop systems that have been developed to help in this setting.

A randomized controlled trial of variable rate phenylephrine infusion with rescue phenylephrine boluses versus rescue boluses alone on physician interventions during spinal anesthesia for elective cesarean delivery

BACKGROUND

Phenylephrine infusion is used to reduce hypotension during spinal anesthesia for cesarean delivery. A prophylactic fixed rate infusion regimen may not improve hemodynamic control; a variable rate regimen adjusted in response to changes in arterial blood pressure and heart rate may allow more accurate maintenance of baseline blood pressure. We hypothesized that a combination of crystalloid solution coload with a variable rate phenylephrine infusion and phenylephrine rescue boluses may be associated with fewer physician interventions needed to maintain maternal systolic blood pressure within 20% of baseline and greater hemodynamic stability than crystalloid solution coload with phenylephrine rescue boluses alone.

METHODS

In this prospective, double-blind study, 80 patients received a coload with 15 mL/kg lactated Ringer's solution immediately after the initiation of spinal anesthesia. Patients were randomized to receive a prophylactic variable rate phenylephrine infusion starting at 0.75 μg/kg/min (group P) or infusion of normal saline (group S). Maternal systolic blood pressure was maintained within 20% of baseline with rescue phenylephrine boluses using a preset algorithm. During the predelivery period, the number of physician interventions (primary outcome), hemodynamic performance, nausea/vomiting, and umbilical cord blood gas values were compared between the groups.

RESULTS

One patient from group S was excluded due to protocol violation. Therefore, group P included 40 patients and group S 39 patients. The median (range) number of physician interventions needed to maintain maternal hemodynamics within the target range (0 [0-6] vs 3 [0-9], difference in median: 3, 95% confidence interval of difference: 2-4) and incidence of hypotension (8/40 [20%] vs 35/39 [90%]) were lower in group P compared with group S (P < 0.001). Group P had a higher incidence of hypertension compared with group S (6/40 [15%] vs 0/39 [0%], P = 0.026). The median performance error was closer to baseline (P < 0.001) with a smaller median absolute performance error (P = 0.001) in group P versus group S. In group P, 4/40 (10%) patients had nausea/vomiting compared with 17/39 (44%) in group S (P = 0.001). The number needed to treat was 1.4 women to prevent 1 case of hypotension, and 3 women to prevent 1 case of nausea/vomiting; the rate of hypertension was 1 case per 6.7 women treated. Neonatal outcomes were not different between the 2 groups.

CONCLUSION

Prophylactic variable rate phenylephrine infusion and rescue phenylephrine bolus dosing is more effective than relying on rescue phenylephrine bolus dosing with respect to limiting clinician workload and maternal symptoms during spinal anesthesia for cesarean delivery.

Prophylactic phenylephrine for caesarean section under spinal anaesthesia: systematic review and meta-analysis

We conducted a systematic review to determine the harm and benefit associated with prophylactic phenylephrine for caesarean section under spinal anaesthesia. We included 21 randomised controlled trials with 1504 women. The relative risk (95% CI) of hypotension with phenylephrine infusion – as defined by authors – before delivery was 0.36 (0.18–0.73) vs placebo, p = 0.004; 0.58 (0.39–0.88) vs an ephedrine infusion, p = 0.009; and 0.73 (0.55–0.96) when added to an ephedrine infusion, p = 0.02. After delivery, the relative risks of hypotension and nausea and vomiting with phenylephrine compared with placebo were 0.37 (0.19–0.71), p = 0.003, and 0.39 (0.17–0.91), p = 0.03, respectively. There was no evidence that hypertension, bradycardia or neonatal endpoints were affected. Phenylephrine reduced the risk for hypotension and nausea and vomiting after spinal doses of bupivacaine generally exceeding 8 mg, but there was no evidence that it reduced other maternal or neonatal morbidities.