Anaesthesia-related morbidity associated with recumbent, low-field magnetic resonance imaging of horses

CASE HISTORY

Medical records from 2009 to 2021 from a private equine referral hospital in Rochester, NH, USA were analysed for cases that underwent general anaesthesia for low-field MRI of the distal limb. These were used to determine peri-anaesthetic morbidity and mortality.

CLINICAL FINDINGS AND OUTCOME

Two hundred and forty-three anaesthetic episodes were recorded in horses undergoing low-field MRI. The peri-anaesthetic complication rate prior to discharge was 6.2% (15/243). No patients experienced a fatal complication. Ninety two of the 243 patients had multiple sites imaged, 90/243 received pre-anaesthetic dantrolene, 134/243 received intra-anaesthetic dobutamine, and 15/243 were positioned in dorsal recumbency. Complications included: abdominal discomfort ("colic"; 9/243), myopathy (4/243), hyphaema (1/243) and carpal fracture (1/243). At the time of discharge, 14/15 complications had resolved. Of 135 horses for which data were available 55 became hypotensive during the procedure (lowest mean arterial pressure < 65 mmHg). Median body weight was 553 (min 363, max 771) kg. Horses were anaesthetised for a median of 150 (min 45, max 210) minutes. There was no evidence of an association between higher body weight (p = 0.051) or longer duration of anaesthesia (p = 0.421) and development of an anaesthetic complication. For categorical variables (dantrolene administration pre-anaesthesia, dobutamine administration during anaesthesia, hypotension (mean < 65 mmHg) during anaesthesia, dorsal vs. lateral recumbency, and imaging of single vs. multiple sites), the 95% CI for the OR included 1, indicating a lack of effect of the variable on the odds of complication.

CLINICAL RELEVANCE

The cases included in this series suggest that low-field MRI under general anaesthesia is a viable option for diagnostic imaging in otherwise healthy horses. Complications occur, but most resolve before discharge.

Function of a mutant ryanodine receptor (T4709M) linked to congenital myopathy

Physiological muscle contraction requires an intact ligand gating mechanism of the ryanodine receptor 1 (RyR1), the Ca2+-release channel of the sarcoplasmic reticulum. Some mutations impair the gating and thus cause muscle disease. The RyR1 mutation T4706M is linked to a myopathy characterized by muscle weakness. Although, low expression of the T4706M RyR1 protein can explain in part the symptoms, little is known about the function RyR1 channels with this mutation. In order to learn whether this mutation alters channel function in a manner that can account for the observed symptoms, we examined RyR1 channels isolated from mice homozygous for the T4709M (TM) mutation at the single channel level. Ligands, including Ca2+, ATP, Mg2+ and the RyR inhibitor dantrolene were tested. The full conductance of the TM channel was the same as that of wild type (wt) channels and a population of partial open (subconductive) states were not observed. However, two unique sub-populations of TM RyRs were identified. One half of the TM channels exhibited high open probability at low (100 nM) and high (50 μM) cytoplasmic [Ca2+], resulting in Ca2+-insensitive, constitutively high Po channels. The rest of the TM channels exhibited significantly lower activity within the physiologically relevant range of cytoplasmic [Ca2+], compared to wt. TM channels retained normal Mg2+ block, modulation by ATP, and inhibition by dantrolene. Together, these results suggest that the TM mutation results in a combination of primary and secondary RyR1 dysfunctions that contribute to disease pathogenesis.

Turn-off fluorescence of S,N-doped carbon dots for determination of two nitro-containing drugs in dosage forms and human plasma

This study describes the development of an environmentally-friend optical nanosensor for the rapid spectrofluorimetric assessment of two nitro-compounds, namely nitrofurantoin and dantrolene in their dosage forms and plasma samples. A one-step synthetic technique successfully created very bright water-soluble carbon quantum dots doped with sulfur and nitrogen (S,N-CQDs). Carbon was derived from citric acid, while nitrogen and sulfur were obtained from thiosemicarbazide. The dimensions of the synthesized dots were measured using a high-resolution transmission electron microscope. FT-IR spectroscopy was used to determine which functional groups were located on their surfaces. The nanosensor's fluorescence emission peaked intensely at 415 nm after excitation at 345 nm with a quantum yield of about 0.52. The inherent fluorescence of the nanosensors gradually decreased upon addition of the studied analytes in increasing concentrations. The fluorescence reduction of nanosensor with the concentrations of the investigated drugs demonstrated linear correlation within the ranges of 0.5-8.0 μg/mL and 1.0-10.0 μg/mL with limits of detection of 0.14 μg/mL (0.59 μM) and 0.23 μg/mL (0.73 μM) for nitrofurantoin and dantrolene, respectively. The recommended method was used to determine the concentrations of the investigated drugs in their commercial capsules, with recoveries ranging from 97.90 % to 101.57 % and low percent RSD values less than 2 %. Moreover, the method was adapted for the in-vitro analysis of the two analytes in spiked human plasma samples with % recoveries from 95.20 % to 102.20 %. The mechanism of interaction between each analyte and the dots was also investigated. The selectivity of the approach for measuring analytes concentration in the presence of excipients, co-formulated medications, or co-administered pharmaceuticals was further evaluated through an interference study. The suggested method's validity was evaluated in accordance with ICH criteria.

Malignant hyperthermia in Poland: A survey study

Malignant hyperthermia (MH) is a life-threatening syndrome caused by sudden, uncontrolled skeletal muscle hypermetabolism in response to inhalation anesthetics and depolarizing relaxants. The estimated incidence of MH is between 1:10,000 and 1:250,000 anesthetic procedures. In Poland, due to lack of reporting, the incidence of MH is unknown. Dantrolene is imported as a life-saving drug (target import) and temporally authorized for sale. The aim of the study was to evaluate the prevalence of malignant hyperthermia in Poland and to assess the accessibility to dantrolene in Poland. A questionnaire was conducted among the chiefs of anesthesia and intensive care units in Poland. During the years 2014 to 2019, 10 episodes of MH have been reported in 238 surveyed polish anesthesia departments. The estimated prevalence is 1:350,000. Eight patients survived the MH crisis. Dantrolene is stocked in 48 (20%) anesthesiology departments. Among the surveyed hospitals, only in 38 (16%) it is possible to administer dantrolene within 5 minutes of suspecting a MH reaction. Less than half units (44%) have an algorithm for the management of MH episode in the operating theaters. The results of the study revealed, that the prevalence of MH in Poland is lower than the prevalence reported in other countries. Access to dantrolene in Poland is limited.

Protein mishandling and impaired lysosomal proteolysis generated through calcium dysregulation in Alzheimer's disease

Impairments in neural lysosomal- and autophagic-mediated degradation of cellular debris contribute to neuritic dystrophy and synaptic loss. While these are well-characterized features of neurodegenerative disorders such as Alzheimer's disease (AD), the upstream cellular processes driving deficits in pathogenic protein mishandling are less understood. Using a series of fluorescent biosensors and optical imaging in model cells, AD mouse models and human neurons derived from AD patients, we reveal a previously undescribed cellular signaling cascade underlying protein mishandling mediated by intracellular calcium dysregulation, an early component of AD pathogenesis. Increased Ca2+ release via the endoplasmic reticulum (ER)-resident ryanodine receptor (RyR) is associated with reduced expression of the lysosome proton pump vacuolar-ATPase (vATPase) subunits (V1B2 and V0a1), resulting in lysosome deacidification and disrupted proteolytic activity in AD mouse models and human-induced neurons (HiN). As a result of impaired lysosome digestive capacity, mature autophagosomes with hyperphosphorylated tau accumulated in AD murine neurons and AD HiN, exacerbating proteinopathy. Normalizing AD-associated aberrant RyR-Ca2+ signaling with the negative allosteric modulator, dantrolene (Ryanodex), restored vATPase levels, lysosomal acidification and proteolytic activity, and autophagic clearance of intracellular protein aggregates in AD neurons. These results highlight that prior to overt AD histopathology or cognitive deficits, aberrant upstream Ca2+ signaling disrupts lysosomal acidification and contributes to pathological accumulation of intracellular protein aggregates. Importantly, this is demonstrated in animal models of AD, and in human iPSC-derived neurons from AD patients. Furthermore, pharmacological suppression of RyR-Ca2+ release rescued proteolytic function, revealing a target for therapeutic intervention that has demonstrated effects in clinically-relevant assays.

[A case of neuroleptic malignant syndrome caused by discontinuation of psychotropic drugs]

A 71-year-old woman with schizophrenia and diabetes discontinued psychotropic drugs due to right purulent knee bursitis. Five days after discontinuation, she presented with a fever of >40°C, severe disturbance of consciousness, lead-pipe muscle rigidity, tachypnea, and hypertension. She was diagnosed with neuroleptic malignant syndrome (NMS) induced by the discontinuation of psychotropic drugs. The patient's symptoms improved after dantrolene administration and systemic management. We investigated the clinical characteristics of cases with NMS induced by the discontinuation of psychotropic drugs reported in Japan, including the present case. When psychotropic drugs are discontinued, patients should be monitored for signs of NMS. Strict management of early onset NMS is needed to prevent the condition from worsening.

Diagnosis and Treatment of Neuroleptic Malignant Syndrome in the Intensive Care Unit: A Case Report

Neuroleptic malignant syndrome is a neurological emergency caused by dysregulation of dopaminergic neurotransmission. While it is typically characterized by muscle rigidity, fever and altered mental status, it may have a heterogeneous and non-specific presentation, leading to delays in diagnosis and treatment. Treatment involves cessation of dopamine-receptor antagonists and supportive measures, but in more severe cases, bromocriptine, dantrolene, benzodiazepines and/or electroconvulsive therapy should be considered. We present the case of a 66-year-old man with severe neuroleptic malignant syndrome, diagnosed due to need for continuous invasive ventilation in an Intensive Care Unit, after successful treatment for respiratory sepsis. The patient recovered after electroconvulsive therapy and administration of bromocriptine. This unusually severe case illustrates the need for a high level of suspicion for neuroleptic malignant syndrome in critically ill patients with malignant catatonic syndromes, allowing for an early diagnosis and potentially lifesavingtreatment.

[Case of fulminant-malignant hyperthermia occurring on sixth sevoflurane anesthesia]

We report a case of fulminant-malignant hyperthermia that occurred after five uneventful sevoflurane anesthetic procedures. A 7-year-old girl with bronchial asthma was scheduled for closure of palatal fistula under general anesthesia, after five previous uneventful operations under sevoflurane anesthesia. Anesthesia was induced with propofol and vecuronium, and maintained with nitrous oxide, oxygen, and sevoflurane. Body temperature at the beginning of operation was 37.0 degrees C. After 5 hr 10 min, sudden tachycardia and elevations in body temperature and PET(CO2) were noticed. Sevoflurane was discontinued and body surface cooling, hyperventilation with 100% oxygen, and administration of dantrolene sodium 2 mg x kg(-1), furosemide 4 mg, and 7% NaHCO3 solution 10 ml were started on a suspicion of malignant hyperthermia. Body temperature, heart rate, and PET(CO2) reached to 40.1 degrees C, 190 beats x min(-1), and 60 mmHg, respectively, with metabolic acidosis. Twenty minutes after starting dantrolene infusion, these values decreased to 38 degrees C, 150 beats x min(-1), and 39 mmHg, respectively. Laboratory examination showed that serum potassium, CK, AST, ALT, and LDH concentrations and urine myoglobin level were within normal ranges. Clinical symptoms of this patient fulfilled the diagnostic criteria of fulminant-malignant hyperthermia. The trigger drug was considered to be sevoflurane despite the five previous uneventful sevoflurane anesthetic procedures.

Ischemia/reperfusion induce renal tubule apoptosis by inositol 1,4,5-trisphosphate receptor and L-type Ca2+ channel opening

Recent studies suggest that besides the L-type calcium channel, two calcium channels on the endoplasmic reticulum (ER), the inositol 1,4,5-trisphosphate receptor (InsP3R) and ryanodine receptor (RyR), may play a role in the apoptotic process of renal tubular cells induced by ischemia/reperfusion (I/R) injury. We used antimycin A to induce cell I/R injury in vitro and found an elevation of the cytosolic calcium concentration and consequently apoptosis. Blocking either the L-type calcium channel with nicardipine or the InsP3R with TMB-8 can inhibit cytochrome c release, activate caspase 3 and decrease the apoptotic cell number. However, blocking the RyR with dantrolene had no effect. We further found that Ca(2+) influx through the L-type channel is needed for the opening of the InsP3R which activates a cascade of Ca(2+) release from the ER store. To test these blockers in vivo, in a rat renal I/R model, pretreatment with nicardipine and TMB-8, but not dantrolene, can protect renal function. Taken together, our results suggest that after I/R injury, Ca(2+) influx through the L-type calcium channel triggers the Ca(2+) release from the InsP3R and finally induces apoptosis. The InsP3R could be a new target for the treatment of renal I/R injury.

The ryanodine receptor mediates early zymogen activation in pancreatitis

Acute pancreatitis is characterized by the pathologic activation of zymogens within pancreatic acinar cells. The process requires a rise in cytosolic Ca(2+) from undefined intracellular stores. We hypothesized that zymogen activation is mediated by ryanodine receptor (RYR)-regulated Ca(2+) release, because early zymogen activation takes place in a supranuclear compartment that overlaps in distribution with the RYR. Ca(2+) signals in the basolateral, but not apical, region of acinar cells observed during supraphysiologic agonist stimulation were dependent on RYR Ca(2+) release. Inhibition of RYR or depletion of RYR-sensitive Ca(2+) pools each reduced pathologic zymogen activation in isolated acinar cells, but neither treatment affected amylase secretion. Inhibition of RYR also inhibited zymogen activation in vivo. We propose that Ca(2+) release from the RYR mediates zymogen activation but not enzyme secretion. The findings imply a role for the RYR in acute pancreatitis.

Anaesthesia for caesarean delivery of a malignant hyperthermia susceptible parturient

The anaesthetic management for Caesarean delivery of a parturient with a strong family history of malignant hyperthermia (MH) is presented. Before surgery an anaesthetic machine that was in regular use was prepared by replacing all rubber or disposable components and flushing with O2 at 10 L.min-1 for one hour. Dantrolene prophylaxis was not used, and the patient received a bupivacaine and fentanyl spinal anaesthetic. Hypotension was treated with ephedrine. Current management of the MH patient no longer mandates a dedicated vapour-free machine, dantrolene is not indicated as pre-treatment, and amide local anaesthetics are considered safe. The role of vasopressors and ergot preparations is less clear.

Multiple-pulse stimulation and dantrolene in malignant hyperthermia

A potentially fatal condition, yet preventable, malignant hyperthermia (MH) lacks a satisfactory noninvasive diagnostic test. Studying the effects of intravenous dantrolene (3 mg/kg) on electrically stimulated skeletal muscle, we found that this approach does not conclusively distinguish between normal humans and those susceptible to malignant hyperthermia but nonetheless yielded important information about the action of dantrolene in man and in MH. Supramaximal single- and multiple-pulse stimulation of the common peroneal nerve produced stable torque responses of the dorsiflexor muscles (monitored in vivo), which dantrolene suppressed. With the multiple-pulse stimulation (5-6 pulses) this torque suppression was significantly less in MH-susceptible subjects than in control subjects. This distinction, also observed in MH swine, confirms this animal as a good model for human MH. That dantrolene's effect in MH can be more completely reversed with high frequency stimulation is intriguing; presumably, excitation-contraction coupling differs in MH and normal muscle.

[Vecuronium in dystrophia myotonica (Curschmann-Steinert)]

An emergency laparotomy was performed in a 31-year-old female (body wt 48 kg) with known myotonic dystrophy. Premedication with dantrolene (1 mg/kg i.v.) was used to prevent a myotonic response. Muscle relaxation was monitored electromyographically. Following induction with fentanyl (0.3 mg) and thiopental (200 mg), muscle relaxation was achieved with 2 mg vecuronium titrated for about 3 min until the T1-response was reduced to 10%. The recovery time was normal. A repetitive dose of 0.5 mg vecuronium was necessary after 20 min, when the T1 reached 60%. Extubation and the early postoperative period were uneventful. Because of the unknown predisposition of our patient for the development of malignant hyperthermia, anesthesia was performed with trigger-free anesthetics.

The anaesthetic management of the malignant hyperthermia susceptible parturient

An overall management plan for malignant hyperthermia susceptible (MHS) parturients is presented based on the experience of managing 14 of these patients. A summary of the pertinent features of their deliveries and care plus a case report of one of these parturients is described. Discussion centres around the problems of diagnosis of malignant hyperthermia susceptibility in pregnancy, the differential diagnosis and management of fever and tachycardia in a MHS parturient during labour and the use of dantrolene prophylaxis. Management of the MHS parturient in labour includes temperature and heart-rate monitoring, provision for cooling, and ready availability of a vapour-free anaesthetic machine. A large-bore intravenous infusion for hydration and for potential therapy of a MH crisis is essential. Epidural analgesia, using 2-chloroprocaine, is recommended. Emergency and elective Caesarean section anaesthesia are discussed. The importance of being prepared for a potential crisis is stressed with particular emphasis on early diagnosis by monitoring of temperature at two sites, of heart rate and rhythm with a continuous ECG and of end-tidal carbon dioxide, should a general anaesthetic be required. Recommendations are made for appropriate anaesthetic agents for both regional and general anaesthesia. Treatment of a MH crisis is outlined, with emphasis on availability of appropriate resuscitative drugs.

Effect of thyroid status on K+-stimulated metabolism and 45Ca exchange in rat skeletal muscle

In the perfused hindlimbs of hypo-, eu-, and hyperthyroid rats, high K+o (20 mM) markedly stimulated glucose uptake, lactate production, and O2-consumption to levels increasing with the thyroid status. At Ca2o+ less than 50 microM, all the responses became transient. In the hypothyroid preparations, caffeine (5 mM) produced no stimulation, but in those obtained from eu- and hyperthyroid rats, it increased all the metabolic parameters as well as K+ release in proportion to thyroid status. In isolated soleus and extensor digitorum longus muscles, both high K+o and caffeine stimulated 45Ca-efflux, with the response increasing in proportion to thyroid status. This stimulation was reduced by 70-100% with dantrolene (10(-5) M), which in earlier studies was shown to suppress the metabolic effects of high K+o and caffeine. High K+o also increased 45Ca-influx but produced no change in muscle calcium contents. The results support the idea that thyroid hormones control substrates availability and energy consumption in skeletal muscle by increasing the amount of sarcoplasmic reticulum and thereby the rate of Ca2+ mobilization into the cytosol.

Respiratory response to partial paralysis in anesthetized dogs

The ability to maintain alveolar ventilation is compromised by respiratory muscle weakness. To examine the independent role of reflexly mediated neural mechanisms to decreases in the strength of contraction of respiratory muscles, we studied the effects of partial paralysis on the level and pattern of phrenic motor activity in 22 anesthetized spontaneously breathing dogs. Graded weakness induced with succinylcholine decreased tidal volume and prolonged both inspiratory and expiratory time causing hypoventilation and hypercapnia. Phrenic peak activity as well as the rate of rise of the integrated phrenic neurogram increased. However, when studied under isocapnic conditions, increases in the severity of paralysis, as assessed from the ratio of peak diaphragm electromyogram to peak phrenic activity, produced progressive increases in inspiratory time and phrenic peak activity but did not affect its rate of rise. After vagotomy, partial paralysis induced in 11 dogs with succinylcholine also prolonged the inspiratory burst of phrenic activity, indicating that vagal reflexes were not solely responsible for the alterations in respiratory timing. Muscle paresis was also induced with gallamine or dantrolene, causing similar responses of phrenic activity and respiratory timing. Thus, at constant levels of arterial CO2 in anesthetized dogs, respiratory muscle partial paralysis results in a decrease in breathing rate without changing the rate of rise of respiratory motor activity. This is not dependent solely on vagally mediated reflexes and occurs regardless of the pharmacological agent used. These observations in the anesthetized state are qualitatively different from the response to respiratory muscle paralysis or weakness observed in awake subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Developing drug literatures. 1. Bibliometrics of baclofen and dantrolene sodium

The literatures of two antispastic drugs, baclofen and dantrolene sodium, were studied bibliometrically for their first decade and were found to be generally similar. Baclofen had 93 papers and dantrolene sodium had 70. About a quarter of the baclofen papers were in a foreign language, whereas almost all dantrolene sodium papers were in English. Baclofen literature had a lower nonscholarly content, but the scholarly increase, 5%, was the same for both. Both drugs had an average of 12 references per paper. The literatures of both drugs had a similar degree of internal cohesiveness; almost half of their papers referred to other papers in the same drug collection. The first human paper for baclofen was the second published; for dantrolene sodium, it was the eleventh. The distribution of journals carrying papers on each of these drugs followed Bradford's law. Two authors per paper was the average for each drug. The productivity of authors approximated Lotka's law for both drugs. About two-thirds of the papers of both drugs had a drug-word in their titles. The literature of both drugs contained about 15% legendary papers, typical of clinical pharmacology. The most intense papers, 15 for baclofen and 11 for dantrolene sodium, were identified, using citation, bibliographic coupling, and co-citation frequencies. A generalization predicts what might be expected from the literature of future antispastic drugs.