Global issues in obstetric anaesthesia: perspectives from South Africa, Japan, China, Latin America and North America

South Africa is classified as a low- and middle-income country, with a complex mixture of resource-rich and resource-limited settings. In the major referral hospitals, the necessary skill level exists for the management of complex challenges. However, this contrasts with the frequently-inadequate skill levels of anaesthesia practitioners in resource-limited environments. In Japan, obstetricians administer anaesthesia for 40% of caesarean deliveries and 80% of labour analgesia. Centralisation of delivery facilities is now occurring and it is expected that obstetric anaesthesiologists will be available 24 h a day in centralised facilities in the future. In China, improvements in women's reproductive, maternal, neonatal, child, and adolescent health are critical government policies. Obstetric anaesthesia, especially labour analgesia, has received unprecedented attention. Chinese obstetric anaesthesiologists are passionate about clinical research, focusing on efficacy, safety, and topical issues. The Latin-American region has different landscapes, people, languages, and cultures, and is one of the world's regions with the most inequality. There are large gaps in research, knowledge, and health services, and the World Federation of Societies of Anaesthesiologists is committed to working with governmental and non-governmental organisations to improve patient care and access to safe anaesthesia. Anaesthesia workforce challenges, exacerbated by coronavirus disease 2019, beset North American healthcare. Pre-existing struggles by governments and decision-makers to improve health care access remain, partly due to unfamiliarity with the role of the anaesthesiologist. In addition to weaknesses in work environments and dated standards of work culture, the work-life balance demanded by new generations of anaesthesiologists must be acknowledged.

Establishment of a novel miniature veno-venous extracorporeal membrane oxygenation model in the rat

Recently, veno-venous extracorporeal membrane oxygenation (V-V ECMO) has been commonly used in the world to support patients with severe respiratory failure. However, V-V ECMO is a new technology compared to veno-arterial extracorporeal membrane oxygenation and cardiopulmonary bypass, and there are few reports of basic research. Although continuing research is desired, clinical research that standardizes conditions such as patients' background characteristics is difficult. The purpose of this study was to establish a simple and stably maintainable miniature V-V ECMO model to study the mechanisms of the biological reactions in circulation during V-V ECMO. The V-V ECMO system consisted of an original miniature membrane oxygenator, polyvinyl chloride tubing line, and roller pump. The priming volume of this system was only 8 mL. Polyethylene tubing was used to cannulate the right femoral vein as the venous return cannula for the V-V ECMO system. A 16-G cannula was passed through the right internal jugular vein and advanced into the right atrium as the conduit for venous uptake. The animals were divided into 2 groups: SHAM group and V-V ECMO group. V-V ECMO was initiated and maintained at 50-60 mL/kg/min, and oxygen was added into the oxygenator during V-V ECMO at a concentration of 100% (pump flow:oxygen = 1:10). Blood pressure was measured continuously, and blood cells were measured by blood collection. During V-V ECMO, the blood pressure and hemodilution rate were maintained around 80 mm Hg and 20%, respectively. Hb was kept at >10 g/dL, and V-V ECMO could be maintained without blood transfusion. It was possible to confirm oxygenation of and carbon dioxide removal from the blood. Likewise, the pH was adequately maintained. There were no problems with this miniature V-V ECMO system, and extracorporeal circulation progressed safely. In this study, a novel miniature V-V ECMO model was established in the rat. A miniature V-V ECMO model appears to be very useful for studying the mechanisms of the biological reactions during V-V ECMO and to perform basic studies of circulation assist devices.

The angle of the outflow graft to the aorta can affect recirculation due to aortic insufficiency under left ventricular assist device support

Aortic insufficiency (AI) is a crucial complication during continuous-flow left ventricular assist device (LVAD) support. Our previous clinical study suggested that a larger angle between the outflow graft and the aorta (O-A angle) could cause AI progression. This study examined the effect of the O-A angle on the hemodynamics of AI under LVAD support in an acute animal experimental model. An LVAD was installed in seven calves, with the inflow cannula inserted from the LV apex and with the outflow graft sutured at the ascending aorta. The AI model was made using a temporary inferior vena cava filter inserted from the LV apex and placed at the aortic valve. Cardiac dysfunction was induced by continuous beta-blocker infusion. Hemodynamic values and the myocardial oxygen extraction rate (O₂ER) were evaluated at three O-A angles (45°, 90°, and 135°) over three levels of AI (none, Sellers I-II AI, and Sellers III-IV AI). The recirculation rate, defined as the percentage of regurgitation flow to LVAD output, was calculated. Systemic flow tended to decrease with a larger O-A angle. The recirculation rate was significantly increased with a larger O-A angle (22, 23, and 31% at 45°, 90°, and 135° in Sellers III-IV AI, respectively). Coronary artery flow was decreased at a larger O-A angle (86, 76 and 75 mL/min at 45°, 90°, and 135° in Sellers I-II AI, respectively, and 77, 67, and 56 mL/min at 45°, 90°, and 135° in Sellers III-IV AI, respectively). O₂ER tended to increase with a larger O-A angle (40, 43, and 49% at 45°, 90°, and 135° in Sellers III-IV AI, respectively). A larger O-A angle can increase the recirculation due to AI and can be disadvantageous to LVAD-AI hemodynamics and myocardial oxygen metabolism.

Novel temporary left ventricular assist system with hydrodynamically levitated bearing pump for bridge to decision: initial preclinical assessment in a goat model

The management of heart failure patients presenting in a moribund state remains challenging, despite significant advances in the field of ventricular assist systems. Bridge to decision involves using temporary devices to stabilize the hemodynamic state of such patients while further assessment is performed and a decision can be made regarding patient management. We developed a new temporary left ventricular assist system employing a disposable centrifugal pump with a hydrodynamically levitated bearing. We used three adult goats (body weight, 58-68 kg) to investigate the 30-day performance and hemocompatibility of the newly developed left ventricular assist system, which included the pump, inflow and outflow cannulas, the extracorporeal circuit, and connectors. Hemodynamic, hematologic, and blood chemistry measurements were investigated as well as end-organ effect on necropsy. All goats survived for 30 days in good general condition. The blood pump was operated at a rotational speed of 3000-4500 rpm and a mean pump flow of 3.2 ± 0.6 L min. Excess hemolysis, observed in one goat, was due to the inadequate increase in pump rotational speed in response to drainage insufficiency caused by continuous contact of the inflow cannula tip with the left ventricular septal wall in the early days after surgery. At necropsy, no thrombus was noted in the pump, and no damage caused by mechanical contact was found on the bearing. The newly developed temporary left ventricular assist system using a disposable centrifugal pump with hydrodynamic bearing demonstrated consistent and satisfactory hemodynamic performance and hemocompatibility in the goat model.

Development of a stent-biovalve with round-shaped leaflets: in vitro hydrodynamic evaluation for transcatheter pulmonary valve implantation (TPVI)

This study evaluates a newly designed autologous heart valve-shaped tissue with a stent [stent-biovalve (SBV)] for transcatheter pulmonary valve implantation using the "in-body tissue architecture" technology. In the previously developed SBV with flat-shaped leaflets (FS-SBV), the valve could not close rapidly, because the leaflets were fixed in the open position, which induced regurgitant volume in the closing phase. Therefore, a novel mold to fabricate an SBV with round-shaped leaflets (RS-SBV) was developed, and its hydrodynamic performance with different valve diameters was evaluated in this study. A specially designed, self-expandable, stent-mounted, acrylic mold, which has 3 hemispheres, was placed in dorsal subcutaneous pouches of goats for 2 months. After extraction, the acrylic mold was removed from the implant, and a tubular tissue impregnated with the stent strut was obtained. Half of the tubular tissue with 3 hemispheres was completely folded in half inwards. The acrylic mold was designed, such that the folded half of the tubular tissue became the round-shaped leaflets. The 3 commissure parts were connected to form 3 leaflets, resulting in the preparation of the RS-SBV (internal diameter 25 mm). The RS-SBV closed more rapidly than the FS-SBV in a pulsatile mock circulation circuit under the pulmonary circulation conditions. The regurgitant fraction of the RS-SBV was approximately 6 %, which was lower than that of the FS-SBV. The appropriate pulmonary annulus diameter of the RS-SBV was from 24 to 25 mm based on the pressure difference and effective orifice area.

In vitro hydrodynamic evaluation of a biovalve with stent (tubular leaflet type) for transcatheter pulmonary valve implantation

We have been developing an autologous heart valve-shaped tissue with a stent (stent-biovalve) for transcatheter pulmonary valve implantation (TPVI) using "in-body tissue architecture" technology. In this study, the hydrodynamic performance of a stent-biovalve with tubular leaflets was evaluated by changing its leaflet height in an in vitro test in order to determine the appropriate stent-biovalve form for the pulmonary valve. A specially designed, self-expandable, stent-mounted, cylindrical acrylic mold was placed in a dorsal subcutaneous pouch of goat, and the implant was extracted 2 months later. Only the cylindrical acrylic mold was removed from the implant, and a tubular hollow structure of membranous connective tissue impregnated with the stent strut was obtained. Half of tubular tissue was completely folded in half inwards, and 3 commissure parts were connected to form 3 leaflets, resulting in the preparation of a stent-biovalve with tubular leaflets (25-mm ID). The stent-biovalve with adjusting leaflet height (13, 14, 15, 17, 20, and 25 mm) was fixed to a specially designed pulsatile mock circulation circuit under pulmonary valve conditions using 37 °C saline. The mean pressure difference and effective orifice area were better than those of the biological valve. The lowest and highest leaflet heights had a high regurgitation rate due to lack of coaptation or prevention of leaflet movement, respectively. The lowest regurgitation (ca. 11%) was observed at a height of 15 mm. The leaflet height was found to significantly affect the hydrodynamics of stent-biovalves, and the existence of an appropriate leaflet height became clear.

Sutureless aortic valve replacement using a novel autologous tissue heart valve with stent (stent biovalve): proof of concept

We developed an autologous, trileaflet tissue valve ("biovalve") using in-body tissue architecture technology to overcome the disadvantages of current bioprosthetic valves. We designed a novel biovalve with a balloon-expandable stent: the stent biovalve (SBV). This study evaluated the technical feasibility of sutureless aortic valve replacement using the SBV in an orthotopic position, as well as the functionality of the SBV under systemic circulation, in an acute experimental goat model. Three adult goats (54.5-56.1 kg) underwent sutureless AVR under cardiopulmonary bypass (CPB). The technical feasibility and functionality of the SBVs were assessed using angiography, pressure catheterization, and two-dimensional echocardiography. The sutureless AVR was successful in all goats, and all animals could be weaned off CPB. The mean aortic cross-clamp time was 45 min. Angiogram, after weaning the animals off CPB, showed less than mild paravalvular leakage and central leakage was not detected in any of the goats. The mean peak-to-peak pressure gradient was 6.3 ± 5.0 mmHg. Epicardial two-dimensional echocardiograms showed smooth leaflet movement, including adequate closed positions with good coaptation; the open position demonstrated a large orifice area (average aortic valve area 2.4 ± 0.1 cm2). Sutureless AVR, using SBVs, was feasible in a goat model. The early valvular functionalities of the SBV were sufficient; future long-term experiments are needed to evaluate its durability and histological regeneration potential.

Application of a search algorithm using stochastic behaviors to autonomous control of a ventricular assist device

A ventricular assist device (VAD) is a device with mechanical pumps implanted adjacent to the patient's native heart to support the blood flow. Mechanical circulatory support using VADs has been an essential therapeutic tool for patients with severe heart failure waiting for a heart transplant in clinical site. Adaptive control of VADs that automatically adjust the pump output with changes in a patient state is one of the important approaches for enhanced therapeutic efficacy, prevention of complications and quality of life improvement. However adaptively controlling a VAD in the realistic situation would be difficult because it is necessary to model the whole including the VAD and the cardiovascular dynamics. To solve this problem, we propose an application of attractor selection algorithm using stochastic behavior to a VAD control system. In this study, we sought to investigate whether this proposed method can be used to adaptively control of a VAD in the simple case of a continuous flow VAD. The flow rate control algorithm was constructed on the basis of a stochastically searching algorithm as one example of application. The validity of the constructed control algorithm was examined in a mock circuit. As a result, in response to a low-flow state with the different causes, the flow rate of the pump reached a target value with self adaptive behavior without designing the detailed control rule based on the experience or the model of the control target.

Development of a flow rate monitoring method for the wearable ventricular assist device driver

Our research institute has been working on the development of a compact wearable drive unit for an extracorporeal ventricular assist device (VAD) with a pneumatically driven pump. A method for checking the pump blood flow on the side of the drive unit without modifying the existing blood pump and impairing the portability of it will be useful. In this study, to calculate the pump flow rate indirectly from measuring the flow rate of the driving air of the VAD air chamber, we conducted experiments using a mock circuit to investigate the correlation between the air flow rate and the pump flow rate as well as its accuracy and error factors. The pump flow rate was measured using an ultrasonic flow meter at the inflow and outflow tube, and the air flow was measured using a thermal mass flow meter at the driveline. Similarity in the instantaneous waveform was confirmed between the air flow rate in the driveline and the pump flow rate. Some limitations of this technique were indicated by consideration of the error factors. A significant correlation was found between the average pump flow rate in the ejecting direction and the average air flow rate in the ejecting direction (R2 = 0.704-0.856), and the air flow rate in the filling direction (R2 = 0.947-0.971). It was demonstrated that the average pump flow rate was estimated exactly in a wide range of drive conditions using the air flow of the filling phase.

Evaluation of sympathetic vasoconstrictor response following nociceptive stimulation of latent myofascial trigger points in humans

AIM

Myofascial trigger points (MTrPs) are a major cause of musculoskeletal pain. It has been reported that stimulation of a latent MTrP increases motor activity and facilitates muscle pain via activation of the sympathetic nervous system. However, the magnitude of the sympathetic vasoconstrictor response following stimulation of MTrP has not been studied in healthy volunteers. The aims of this study were to (1) evaluate the magnitude of the vasoconstrictor response following a nociceptive stimulation (intramuscular glutamate) of MTrPs and a breath-hold manoeuvre (activation of sympathetic outflow) and (2) assess whether the vasoconstrictor response can be further modulated by combining a nociceptive stimulation of MTrPs and breath-hold.

METHODS

Fourteen healthy subjects were recruited in this study. This study consisted of four sessions (normal breath group as control, breath-hold group, glutamate MTrP injection group and glutamate MTrP injection + breath-hold group). Skin blood flow and skin temperature in both forearms were measured with laser Doppler flowmetry and infrared thermography, respectively, in each session (before the treatment, during the treatment and after the treatment).

RESULTS

Glutamate injection into MTrPs decreased skin temperature and blood flow in the peripheral area. The magnitudes of the reduction were comparable to those induced by the breath-hold manoeuvre, which has been used to induce sympathetic vasoconstrictor response.

CONCLUSION

The combination of glutamate injection into latent MTrPs together with the breath-hold manoeuvre did not result in further decrease in skin temperature and blood flow, indicating that sympathetic vasoconstrictor activity is fully activated by nociceptive stimulation of MTrPs.

In vivo evaluation of the NEDO biventricular assist device with an RPM dynamic impeller suspension system

Since 1995, the Baylor College of Medicine group has been developing the NEDO Gyro permanent implantable (PI) pump. The Gyro PI pump has achieved outstanding results up to 284 days with no thrombus formation during the left ventricular assist device (LVAD) animal experiments. However, in biventricular assist device (BVAD) animal experiments, thrombus formation did occur. An in vitro experiment showed the reason for thrombus formation was caused by the missed magnetic balance between the impeller and the actuator. On the basis of this result, the revolutions per minute (RPM) impeller suspension system was developed. Six long-term animal studies were performed in bovine models. Survival periods were 90, 80, 60, 51, 48, and 37 days, respectively. No thrombus was observed in the pumps with the exception of one right pump. In that experiment, the thrombus formation may have occurred when the pump had a low flow because of outflow kinking. In this article, the antithrombogenic effect of this RPM impeller suspension system will be discussed.

Antithrombogenicity of the Gyro permanently implantable pump with the RPM dynamic suspension system for the impeller

In 1995, a group at Baylor College of Medicine started to develop the NEDO biventricular assist device (BVAD) using two Gyro permanently implantable (PI) centrifugal pumps. This pump consists of a sealless pump housing and an impeller supported with a double pivot bearing. In May 2001, an RPM dynamic suspension system (RPM-DS) for the impeller was developed to improve durability and antithrombogenicity without a complex magnetic suspension system. From March 2000 to March 2002, eight BVAD bovine experimental studies were performed for more than 1 month. Two pumps were implanted in two cases without the RPM-DS (group A) and in six cases with the RPM-DS (group B). In group A, the survival period was 45 and 50 days. The primary reason for termination was an increase in the requiring power, which was related to deposition of white thrombus on the bottom bearing. In group B, the survival period was 37, 48, 51, 60, 80, and 90 days. The reasons for termination were not related to thrombus formation. No thrombus was observed in the pumps except for one right pump. In that experiment, the thrombus formation may have occurred when that pump had a low flow rate at a level of 1 L/min for 6 hr. These studies demonstrate the apparent antithrombogenic effect of RPM-DS. The NEDO BVAD is ready to move into a 3-month preclinical system evaluation.

Spatial and temporal profiles of flare and hyperalgesia after intradermal capsaicin

Intradermal injection of capsaicin induces a region of visual flare (neurogenic inflammation) and regions with modality specific hyperalgesia. Their temporal and spatial profiles have been studied to elucidate the mechanism behind neurogenic inflammation and hyperalgesia. Until today, the flare response has mainly been quantified by visual inspection. However, recent developments of thermography and laser-Doppler flowmetry have facilitated quantitative measurement of the neurogenic inflammation. The purpose of the present study was (1). to measure the temporal and spatial profiles of neurogenic inflammation and hyperalgesia induced by capsaicin by using thermography/laser-Doppler flowmetry and various sensory tests, and (2). to correlate the parameters related to neurogenic inflammation with the areas of secondary hyperalgesia. Eight healthy volunteers were injected intradermally with 250 microg of capsaicin. Five minutes after the injection, temperature and blood flow were measured by thermography and a laser-Doppler flowmetry, and followed by assessment of visual flare and hyperalgesia. Punctate hyperalgesia, stroking hyperalgesia, and heat hyperalgesia were assessed by von Frey hair, cotton swab, and radiant heat stimulator, respectively. This procedure was repeated 30 and 60 min after the injection. A significant increase in blood flow and temperature was detected by laser-Doppler flowmetry and thermography (F=102.08, P<0.001, and F=8.46, P=0.002, respectively). Throughout the experiment, the areas of visual flare, stroking hyperalgesia, and punctate hyperalgesia were covered by the area of significantly increased blood flow detected 5 min after the injection. The intensity of pain to heat stimuli significantly increased over time at the distal site and the proximal site (P<0.05). However, there was no significant difference between the pain intensity to radiant heat stimuli inside/outside the area of punctate hyperalgesia. These results seem to indicate that a possible contribution of neurogenic inflammation to secondary hyperalgesia (especially to radiant heat stimuli) must be reconsidered.

Physiological adaptation to a nonpulsatile biventricular assist system

Physiological adaptation of the recipient to a nonpulsatile biventricular assist system (NPBVAS) is not well understood. The aim of this study is to evaluate the physiological adaptation of experimental animals after NPBVAS implantation. Since May 2001, four long-term NPBVAS implant experiments in calves were performed. The blood gas and hemodynamic data were analyzed retrospectively. An additional prospective experiment was performed to confirm retrospective findings. All calves (n = 5) lived longer than 5 weeks without complication. In retrospective analysis, there was not a correlation between the O2 content and total blood flow in the pulmonary artery during the 1st postoperative week, but they began to correlate within the 2nd postoperative week. Then, there was a strong correlation after the 3rd postoperative week (r = 0.753). In the prospective experiment, O2 content related to total pulmonary flow after 2 weeks (r = 0.732) was the same as in the retrospective study. Most of the hemodynamic parameters studied became normalized after 14 days. In addition, easier controllability of the blood pumps was demonstrated after the 2nd postoperative week in all five experiments. Experimental results suggested that the native healthy heart accepted NPBVAS by reducing its cardiac output in 2 weeks. In addition, complicated control of the BPVAS was not necessary after 2 weeks of implantation. These results demonstrate the possibility of physiological adaptation to the NPBVAS being established within 2 postoperative weeks.

A comparison of hyperalgesia and neurogenic inflammation induced by melittin and capsaicin in humans

Melittin (a main compound of bee venom) and capsaicin were injected intradermally in healthy human volunteers: (1) to study secondary mechanical hyperalgesia (static hyperalgesia and dynamic hyperalgesia) around the injection site; and (2) to correlate the sensory changes to the neurogenic inflammation assessed by laser-doppler blood flowmetry. Melittin 50 microg and capsaicin 10 microg induced comparable spontaneous pain and increased blood flow (neurogenic inflammation). Intradermal injection of melittin induced regions of secondary mechanical hyperalgesia around the injection site, however, they were not as large as the hyperalgesia induced by capsaicin. This is the first report studying mechanical hyperalgesia induced by melittin in humans, and the results were in agreement with the previous observations in rats. Melittin seems to be a valuable model to study a possible contribution of neurogenic inflammation to hyperalgesia in humans.

Renal function in patients with high serum fluoride concentrations after prolonged sevoflurane anesthesia

BACKGROUND

In studies of methoxyflurane-induced nephrotoxicity, renal-concentrating impairment has been observed only when serum inorganic fluoride concentrations exceed 50 microM. Prolonged sevoflurane anesthesia can result in serum inorganic fluoride concentrations in excess of 50 microM. The authors compared renal function after prolonged sevoflurane anesthesia with that after isoflurane anesthesia. In addition, they measured urinary excretion of N-acetyl-beta-glucosaminidase (NAG), a sensitive index of renal tubular damage, during the 3-day period after anesthesia.

METHODS

Thirty-four healthy patients who underwent either sevoflurane (23 patients) or isoflurane (11 patients) anesthesia at a total gas flow of 61/min for orthopedic surgery scheduled to last at least 5 h were studied. At 16.5 h after cessation of anesthesia, patients were administered 10 units of vasopressin and urine was collected frequently thereafter for evaluation of urinary osmolality. In addition, urinary excretion of NAG was measured before and on days 1-3 after anesthesia. Based on whether peak fluoride concentrations exceeded 50 microM, 23 patients anesthetized with sevoflurane were assigned to a sevofluranehigh group (> 50 microM) or a sevofluranelow (< 50 microM) group.

RESULTS

The eight patients in the sevofluranehigh group had a mean peak fluoride concentration of 57.5 +/- 4.3 microM. A significant, albeit weak, inverse correlation was found between peak fluoride concentration and maximal urinary osmolality after the injection of vasopressin (r = -0.42, P < 0.05). Mean maximum urinary osmolality tended to be lower in the sevofluranehigh group (681 +/- 60 mOsm/kg) than in the other two groups after administration of vasopressin, although the difference among the three groups did not quite reach a statistical significance (P = 0.068). One patient had a transient concentrating defect (maximum urinary osmolality = 390 mOsm/kg) on day 1 after anesthesia. Urinary excretion of NAG in both the sevofluranehigh and sevofluranelow groups was greater on days 2 and 3 after anesthesia than before anesthesia. The increase in urinary NAG excretion was dose related with sevoflurane, but there was no difference in results of routine laboratory renal tests on days 2 and 3 after anesthesia among the three groups.

CONCLUSIONS

The authors concluded that sevoflurane anesthesia results in increased serum fluoride concentration, a tendency toward decreased maximal ability to concentrate urine, and increased excretion of NAG. However, the increase in urinary NAG excretion was not indicative of clinically significant renal damage in these patients with no preexisting renal disease.

Urine concentrating ability after prolonged sevoflurane anaesthesia

Few studies have used the vasopressin test to evaluate urine concentrating ability after sevoflurane anaesthesia. We performed a vasopressin test on the first day after operation to compare the effect of prolonged sevoflurane anaesthesia for orthopaedic procedures (n = 11) with that of isoflurane (n = 10). Mean doses of sevoflurane and isoflurane were 10.6 (SE 0.9) and 8.5 (1.5) MAC-h, respectively. Mean peak serum fluoride concentration in patients anaesthetized with sevoflurane was 41.9 (2.5 mumol litre-1 and exceeded 20 mumol litre-1 for approximately 20 h. Each group showed similar responses to vasopressin. There was no evidence of subclinical nephrotoxicity in patients given prolonged sevoflurane anaesthesia.