Pulse oximetry and oxygenation assessment in small animal practice

Oxygen is essential for the cellular respiration of all aerobic organisms so it is important that the amount of oxygen present within the circulation can be measured. In clinical veterinary practice, a non-invasive method of measuring oxygen saturation of arterial blood is necessary for the rapid, reliable assessment of a patient's oxygen status, whether anaesthetised or in the intensive care unit. Pulse oximetry is considered to be essential for the safe conduct of anaesthesia by the Association of Anaesthetists of Great Britain and Ireland, and the American Society of Anesthesiologists, because a failure to recognise hypoxaemia is a major cause of preventable death. This article describes how oxygen is carried within the blood and the basic technology behind the pulse oximeter, together with some of its pitfalls and limitations

Review of hypoxaemia in the anaesthetized horse: predisposing factors, consequences and management

Objectives: To discuss how hypoxaemia might be harmful and why the horse is particularly predisposed to developing it. To review the strategies that are used to manage hypoxaemia in anaesthetised horses, to describe how successful these strategies are and the adverse events associated with them. Databases used: Google Scholar and PubMed using the search terms – horse; pony; exercise; anaesthesia; hypoxaemia; oxygen; mortality; morbidity; ventilation perfusion mismatch. Conclusions: Although there is no evidence that hypoxaemia is associated with increased morbidity and mortality in anaesthetised horses, most anaesthetists would agree that it is important to recognise and prevent or treat it. The favourable anatomical and physiological adaptations of the horse for exercise, adversely affect gas exchange once the animal is recumbent. Hypoxaemia is recognised more frequently than in other domestic species during general anaesthesia, although its incidence in healthy horses remains unreported. The management of hypoxaemia in anaesthetised horses is challenging and often unsuccessful. Positive pressure ventilation strategies to address alveolar atelectasis in humans have been modified for implementation in the recumbent anaesthetised horse, but are often accompanied by unpredictable and unacceptable cardiopulmonary adverse effects, and some strategies are difficult or impossible to achieve in adult horses. Furthermore, the anticipated beneficial effects of these techniques are inconsistent. Increasing the inspired fraction of oxygen during anaesthesia is often unsuccessful since much of the impairment in gas exchange is a direct result of shunt. Alternative approaches to the problem involve the manipulation of pulmonary blood away from atelectatic regions of lung to better ventilated areas. However, further work is essential, with particular focus upon survival associated with general anaesthesia in the horse, before any technique can be accepted into widespread clinical use

Cardiac output affects the response to pulsed inhaled nitric oxide in mechanically ventilated anesthetized ponies determined by CT angiography of the lung

OBJECTIVE To measure changes in regional lung perfusion using CT angiography in mechanically ventilated, anesthetized ponies administered pulsed inhaled nitric oxide (PiNO) during hypotension and normotension.ANIMALS 6 ponies for anesthetic 1 and 5 ponies for anesthetic 2.PROCEDURES Ponies were anesthetized on 2 separate occasions, mechanically ventilated, and placed in dorsal recumbency within the CT gantry. Pulmonary arterial, right atrial, and facial arterial catheters were placed. During both anesthet-ics, PiNO was delivered for 60 minutes and then discontinued. Anesthetic 1: hypotension (mean arterial pressure < 70 mmHg) was treated using dobutamine after 30 minutes of PiNO delivery. Following the discontinuation of PiNO, dobutamine administration was discontinued in 3 ponies and was continued in 3 ponies. The lung was imaged at 30, 60, and 105 minutes. Anesthetic 2: hypotension persisted throughout anesthesia. The lung was imaged at 30, 60, and 90 minutes. At all time points, arterial and mixed venous blood samples were analyzed and cardiac output (Qt) was measured. Pulmonary perfusion was calculated from CT image analysis.RESULTS During PiNO delivery, perfusion to well-ventilated lungs increased if ponies were normotensive, leading to increased arterial oxygenation, reduced alveolar dead space, and reduced alveolar to arterial oxygen tension gradient. When PiNO was stopped and dobutamine administration continued, alveolar dead space and venous admixture increased, in contrast to when dobutamine and PiNO were both discontinued.CLINICAL RELEVANCE If PiNO is administered to mechanically ventilated, anesthetized ponies with concurrent hypotension and low Qt, this must be supported to achieve favorable redistribution of pulmonary perfusion to improve pulmonary gas exchange

Behavioral and cardiopulmonary effects of dexmedetomidine alone and in combination with butorphanol, methadone, morphine or tramadol in conscious sheep

Objective: To compare cardiopulmonary and sedative effects following administration of dexmedetomidine alone or with butorphanol, methadone, morphine or tramadol in healthy sheep. Study design: Randomized crossover study. Animals: Six Santa Inês sheep, five females, one male, aged 12–28 months and weighing 40.1 ± 6.2 kg. Methods: Sheep were assigned treatments of dexmedetomidine (0.005 mg kg−1; D); D and butorphanol (0.15 mg kg−1; DB); D and methadone (0.5 mg kg−1; DM); D and morphine (0.5 mg kg−1; DMO); or D and tramadol (5.0 mg kg−1; DT). All drugs were administered intravenously with at least 7 days between each treatment. Rectal temperature, heart rate (HR), respiratory rate (fR), invasive arterial pressure, blood gases and electrolytes were measured prior to administration of drugs (baseline, T0) and every 15 minutes following drug administration for 120 minutes (T15–T120). Sedation was scored by three observers blinded to treatment. Results: HR decreased in all treatments and fR decreased in DM at T30 and DMO at T30 and T45. PaCO2 was increased in D, DB and DM compared with baseline, and PaO2 decreased in D at T15 and T45; in DB at T15 to T75; in DM at T15 to T60; in DMO at T15; and in DT at T15, T30 and T75. There was a decrease in temperature in D, DB and DM. An increased pH was measured in D at all time points and in DT at T30–T120. inline image and base excess were increased in all treatments compared with baseline. There were no statistical differences in sedation scores. Conclusions and clinical relevance: The combination of dexmedetomidine with butorphanol, methadone, morphine or tramadol resulted in similar changes in cardiopulmonary function and did not improve sedation when compared with dexmedetomidine alone

Capteur électrochimique à fer pour la maîtrise de L. pneumophila : application à l'analyse de l'eau dans les tours aéro-réfrigérantes

L. pneumophila (Lp) est une bactérie pathogène opportuniste colonisant fréquemment les réseaux d'eau artificiels. Les bactéries présentes dans les microgouttelettes d'eau contaminée sont inhalées par l'être humain et, sous certaines conditions, peuvent conduire à une pneumopathie (maladie du légionnaire) létale dans 10 à 15 % des cas. Les tours aéroréfrigérantes (TAR) sont les systèmes les plus fréquemment incriminés dans la contamination en raison de conditions de croissance microbiologique favorables conduisant à la présence de Lp à des taux élevés, y compris au sein de biofilms. Si des opérations de nettoyage et de désinfection à base de biocides sont réalisées dans le cadre de l'entretien ou lors d'une contamination excessive, elles doivent être proportionnées et justifiées afin de limiter les rejets polluants dans l'environnement. Par ailleurs, il a été montré que la présence de Lp est accrue à partir de concentrations en fer de l'ordre du micromolaire dans l'eau. Si les besoins en fer de la bactérie sont reconnus, l'impact des formes Fe(II) et Fe(III) et des concentrations observées dans les eaux de TAR sur la population bactérienne reste inconnu, surtout lors de la formation du biofilm à Lp. L'objectif principal de ce travail est donc de définir la relation entre les deux formes du fer et la persistance/croissance de Lp afin de proposer le développement d'un procédé original basé sur l'électrochimie pour la maîtrise de Lp dans les TAR. Les travaux présentés dans ce manuscrit se sont focalisés dans un premier temps sur la mise au point d'un capteur électrochimique fonctionnalisé par la résine cationique Nafion®, permettant la détermination des concentrations micromolaires du Fe(II) et Fe(III) par voltammétrie cyclique. Les performances analytiques (répétabilité, reproductibilité, sensibilité, exactitude et sélectivité) du capteur ont ensuite été évaluées dans des solutions synthétiques. Dans un deuxième temps, l'influence du Fe(II) et Fe(III) sur la formation de biofilms mono-espèces à Lp a été étudiée en se basant sur un modèle existant. L'analyse des biofilms formés en présence de Fe(II) et/ou Fe(III) a été effectuée par numération des Unités Formant Colonie (UFC) et par quantification des Unités Génomes (UG ; qPCR). Les modifications majeures observées, notamment en termes de pertes de viabilité/cultivabilité, ont été confirmées par observation en microscopie confocale à balayage laser (MCBL). Cette étude a montré que la présence du Fe(III) avait un impact négatif sur la viabilité et la cultivabilité des bactéries adhérées contribuant à leur mort ou à leur transition vers la phase viable-non cultivable (VBNC). Le capteur électrochimique a ensuite été testé en milieu réel en effectuant des détections dans une eau provenant d'une TAR prototype. La justesse du capteur a été démontrée lors de la détermination des concentrations en Fe(II) et Fe(III). Enfin, un premier lien a pu être établi entre la présence du fer et le statut de Lp dans les eaux de TAR.L. pneumophila (Lp) is an opportunistic pathogenic bacterium which frequently colonizes artificial water systems. Bacteria present in contaminated microdroplets of water are inhaled by human beings and, under certain conditions, can lead to a lethal pneumopathy (Legionnaires' disease) in 10 to 15% of cases. Cooling towers are systems which are the most frequently involved in contamination due to favorable microbiological growth conditions leading to the presence of Lp at high levels, within biofilms included. If cleaning and disinfection operations based on biocides are carried out as part of maintenance or during excessive contamination, they must be proportionate and justified in order to limit pollutant release into the environment. Besides, it has been shown that the presence of Lp is increased when iron concentrations are in the micromolar range in water. While the iron requirements of the bacterium are recognized, the impact of Fe(II) and Fe(III) on the bacterial population remains unknown, especially during the formation of the Lp biofilm. The main objective of this work is therefore to define the relationship between the two forms of iron and the persistence/growth of Lp in order to come up with the development of an original method based on electrochemistry for the control of Lp in cooling towers. The present work initially focuses on the development of an electrochemical sensor functionalized by the cationic resin Nafion®, allowing the determination of micromolar concentrations of Fe(II) and Fe(III) by cyclic voltammetry. The analytical performances (repeatability, reproducibility, sensitivity, accuracy and selectivity) of the sensor were then evaluated in synthetic solutions. The influence of Fe(II) and Fe(III) on the formation of mono-species biofilms in Lp was then studied based on an existing model. Analysis of biofilms formed in the presence of Fe(II) and/ or Fe(III) was performed by colony forming unit (CFU) counts and quantification of Genome Units (UG; qPCR). The major differences observed, particularly in terms of viability/cultivability losses, were confirmed by observation by confocal laser scanning microscopy (CLSM). This study showed that the presence of Fe(III) had a negative impact on the viability and cultivability of the adhered bacteria contributing to their death or their transition to the viable-non-cultivable (VBNC) state. The electrochemical sensor was then tested in a real environmental sample by carrying out measurements in water taken from a cooling tower prototype. The accuracy of the sensor was demonstrated during the determination of Fe(II) and Fe(III) concentrations. Finally, a first relationship has been established between the presence of iron and the status of Lp in cooling tower waters

Families’ Experiences of Continuous Glucose Monitoring in the Management of Congenital Hyperinsulinism: A Thematic Analysis

Background and AimsIn patients with congenital hyperinsulinism (CHI), recurrent hypoglycaemia can lead to longstanding neurological impairments. At present, glycaemic monitoring is with intermittent fingerprick blood glucose testing but this lacks utility to identify patterns and misses hypoglycaemic episodes between tests. Although continuous glucose monitoring (CGM) is well established in type 1 diabetes, its use has only been described in small studies in patients with CHI. In such studies, medical perspectives have been provided without fully considering the views of families using CGM. In this qualitative study, we aimed to explore families’ experiences of using CGM in order to inform future clinical strategies for the management of CHI.MethodsTen patients with CHI in a specialist centre used CGM for twelve weeks. All were invited to participate. Semi-structured interviews were conducted with nine families in whom patient ages ranged between two and seventeen years. Transcripts of the audio-recorded interviews were analysed using an inductive thematic analysis method.ResultsAnalysis revealed five core themes: CGM’s function as an educational tool; behavioural changes; positive experiences; negative experiences; and design improvements. Close monitoring and retrospective analysis of glucose trends allowed for enhanced understanding of factors that influenced glucose levels at various times of the day. Parents noted more hypoglycaemic episodes than previously encountered through fingerprick tests; this new knowledge prompted modification of daily routines to prevent and improve the management of hypoglycaemia. CGM use was viewed favourably as offering parental reassurance, reduced fingerprick tests and predictive warnings. However, families also reported unfavourable aspects of alarms and questionable accuracy at low glucose levels. Adolescents were frustrated by the short proximity range for data transmission resulting in the need to always carry a separate receiver. Overall, families were positive about the use of CGM but expected application to be tailored to their child’s medical condition.ConclusionsPatients and families with CHI using CGM noticed trends in glucose levels which motivated behavioural changes to reduce hypoglycaemia with advantages outweighing disadvantages. They expected CHI-specific modifications to enhance utility. Future design of CGM should incorporate end users’ opinions and experiences for optimal glycaemic monitoring of CHI

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability