Comparison of droplet spread in standard and laminar flow operating theatres: SPRAY study group.

BACKGROUND: Reducing COVID-19 transmission relies on controlling droplet and aerosol spread. Fluorescein staining reveals microscopic droplets. AIM: To compare the droplet spread in non-laminar and laminar air flow operating theatres. METHODS: A 'cough-generator' was fixed to a theatre trolley at 45°. Fluorescein-stained 'secretions' were projected on to a series of calibrated targets. These were photographed under UV light and 'source detection' software measured droplet splatter size and distance. FINDINGS: The smallest droplet detected was ∼120 µm and the largest ∼24,000 µm. An average of 25,862 spots was detected in the non-laminar theatre, compared with 11,430 in the laminar theatre (56% reduction). The laminar air flow mainly affected the smaller droplets (<1000 µm). The surface area covered with droplets was: 6% at 50 cm, 1% at 2 m, and 0.5% at 3 m in the non-laminar air flow; and 3%, 0.5%, and 0.2% in the laminar air flow, respectively. CONCLUSION: Accurate mapping of droplet spread in clinical environments is possible using fluorescein staining and image analysis. The laminar air flow affected the smaller droplets but had limited effect on larger droplets in our 'aerosol-generating procedure' cough model. Our results indicate that the laminar air flow theatre requires similar post-surgery cleaning to the non-laminar, and staff should consider full personal protective equipment for medium- and high-risk patients.

Thymectomy: its role in the management of myasthenia gravis.

The management and clinical course of patients with myasthenia gravis admitted to a neurological intensive therapy unit (ITU) for thymectomy over a 66 month period were reviewed. There were 53 patients, 20 male and 33 female, mean age 35.2 years (18-74) and median ITU stay of 5 days (2-30). Indications for thymectomy were thymic enlargement on computed tomography (34%), persistence of generalized symptoms (38%), a combination of both (20%), steroid side effects or dependency (4%) and progressive bulbar symptoms (4%). Following thymectomy, thymic histology revealed thymic follicular hyperplasia (26/53; 49%), atrophy (11/53; 21%), thymoma (12/53; 23%) and normal thymus (4/53; 8%). Post-operatively 23% required prolonged intubation (> 48 hrs); two patients required a tracheostomy 10 and 13 days post-operatively. Plasma exchange was required for two patients (3.8%) due to persistent severe myasthenic weakness. Three patients (6%) developed a post-operative chest infection and one pseudomembranous colitis. There were no post-operative mortalities during the study period. After 2 years, 35% of patients were in remission and 46% had ocular or mild generalized symptoms only. Thymectomy for myasthenia gravis is followed by sustained clinical improvement in the majority of patients. The appropriate post-operative management of these patients is best undertaken in a specialized neuro-intensive care setting. Copyright Rapid Science Ltd

Proposed link between Helicobacter pylori and sudden infant death syndrome.

Helicobacter pylori may be linked to sudden infant death syndrome (SIDS) through synthesis of inflammatory cytokines, particularly interleukin-1, which can produce fever, activation of the immune system, and increased deep sleep. A relatively minor respiratory or enteric infection, together with overwrapping and prone sleep position could then induce terminal hypoxemia. Alternatively, H. pylori produces large amounts of urease which, if aspirated in gastric juice, could reach the alveolae, react with plasma urea, and produce ammonia toxicity leading to respiratory arrest. Epidemiological similarities between H. pylori and SIDS are presented along with possible transmission mechanisms for H. pylori which support this hypothesis.

Skeletal muscle extra-aortic counterpulsation in dogs with dilated cardiomyopathy.

Skeletal muscle extra-aortic counterpulsation was performed in seven dogs with dilated cardiomyopathy. A left latissimus dorsi dynamic descending thoracic aortomyoplasty was used as the autologous counterpulsator. Pulse train stimulation in diastole was used to initiate contraction and fibre type transformation. Two of the dogs died within 48 hours of surgery. The device was successfully activated in the five remaining dogs, but in one individual it failed within 48 hours of activation. Serial echocardiographic examinations of dogs in which the device functioned successfully (n = 4) showed trends towards the decrease in the left ventricular systolic internal dimension, left ventricular diastolic internal dimension, E-point to septal separation and left atrial diameter in systole seven to 14 days following the procedure, although these changes failed to persist in the long-term. The results suggest that skeletal muscle for cardiac assistances such as extra-aortic muscle counterpulsation, might be a therapeutic option for dogs with cardiac failure due to dilated cardiomyopathy.

The incidence of significant pericardial effusion and tamponade following major aortic root surgery.

OBJECTIVE: To examine the hypothesis that the incidence of significant pericardial effusion following aortic root surgery is higher than anticipated after cardiac surgery. DESIGN: A retrospective data analysis. SETTING: A tertiary referral centre for cardiothoracic surgery. SUBJECTS: All patients undergoing aortic root surgery either with or without aortic valve replacement between January 1991 and July 1993. RESULTS: Three patients developed late cardiac tamponade (7-10 days post-operatively) and a further three developed clinically significant pericardial effusions as a result of post-pericardiotomy syndrome. The 31.6% (95% confidence limit: 12.5-56%) incidence of significant pericardial effusions following aortic root surgery is therefore significantly higher than anticipated after cardiac surgery (0.8-6). CONCLUSION: These data support the hypothesis that the incidence of significant pericardial effusion following aortic root surgery is higher than anticipated after cardiac surgery. We recommend that echocardiography is routinely performed during the post-operative period in these patients to exclude significant pericardial effusions.

Aortic root replacement and extraanatomic bypass for interrupted aortic arch in an adult.

We describe an unusual case of interrupted aortic arch, aneurysmal ascending aorta, and aortic regurgitation in a 24-year-old man. He presented with general malaise, weakness of his legs, and hypertension. A single-stage operation was performed in which the aortic root was replaced with concomitant extraanatomic bypass of the interrupted segment of the aortic arch. He made a full recovery and has returned to work.

Preconditioning in isolated superfused human muscle.

Studies in isolated superfused rabbit papillary muscles indicate that preconditioning (PC) is not confined to arterially perfused myocardium. In the present study PC of isolated human right atrial trabeculae was investigated avoiding the problems of invasive experimentation in patients. Atrial trabeculae were suspended in an organ bath, superfused with Tyrode's solution and field stimulated at 1 Hz. After stabilization, muscles were randomly allocated to five groups (n = 8 per group). Control (C) muscles had no additional treatment. PC was induced by 3 min rapid pacing at 3 Hz with hypoxic substrate-free buffer, followed by reoxygenation with substrate for 12 min. In two additional groups 8-p-sulfophenyltheophylline (SPT) was added to the superfusate either during stabilization in controls (C+SPT) or during preconditioning (PC+SPT). In the final group, R-phenyl-isopropyl adenosine (R-PIA) was added to the superfusate for 5 min to see whether or not this could substitute for preconditioning. All muscles were then exposed to 90 min hypoxia with no substrate and pacing at 3 Hz, followed by 120 min reoxygenation at 1 Hz. Recovery of developed tension was significantly improved by PC 46.5 +/- 2.4% v 24.6 +/- 2.3% in controls) and this protective effect was blocked by the addition of SPT without adversely affecting controls (recovery in PC+SPT, 25.8 +/- 4.1% and C+SPT, 22.7 +/- 2.9%). R-PIA protected the muscles to a similar extent as PC (43.8 +/- 1.9%). These data provide evidence for the involvement of adenosine in preconditioning in human myocardium.

Myoplasty--a surgical option for end-stage heart failure.

Congestive heart failure is a growing problem in the Western world, which modern therapeutic options are doing little to ameliorate. Dynamic cardiomyoplasty may be one option which has great potential. This article reviews the use of skeletal muscle for circulatory assist and suggests that, with further work, it should take a significant place in the treatment armamentarium.

Clearance of gentamicin during cardiac surgery.

Treatment with an aminoglycoside plus flucloxacillin is commonly used to prevent wound infection and endocarditis after cardiac surgery. Cardiopulmonary bypass, blood transfusion and the lack of a steady state greatly affect handling of gentamicin. Urinary gentamicin excretion is not predictable in terms of preoperative risk factors possibly because there is no clear relationship between serum levels and gentamicin clearance. A study was performed to determine whether the existing prophylactic regimen gave adequate serum levels during surgery and to compare renal excretion of gentamicin and the trough serum levels. Ten patients received gentamicin (1.5 mg/kg at the start of surgery followed by 80 mg tds for 2 days) and flucloxacillin 500 mg qds for 2 days. Serum and urinary concentrations of gentamicin were assayed during surgery and in the early postoperative period. The median apparent serum half-life during the first 8 h was 2.5 h (95%CI 1.7-3.2 h). The median gentamicin clearance was 37 mL/min(95%CI 23-64 mL/min) and the creatinine clearance 85 mL/min (95%CI 72-210 mL/min). Serum levels remained above 1 mg/L during surgery but urinary concentrations varied between 0.4 and 364 mg/L (median 70 mg/L). At 24 h (but not 8 or 16 h), trough serum levels appeared to be related to the amount of gentamicin excreted but the relationship was not quite statistically significant (P = 0.057). Despite the effects of cardiopulmonary bypass, therapeutic serum gentamicin levels were maintained during surgery and reduced renal excretion in the postoperative period was associated with raised levels.

Antibiotic prophylaxis in cardiac surgery: factors associated with potentially toxic serum concentrations of gentamicin.

Aminoglycosides are commonly used with flucloxacillin in the prevention of wound infection and endocarditis after cardiac surgery. Earlier studies suggested that the use of aminoglycosides is associated with a small but significant rise in serum creatinine. A regression analysis was performed to identify the preoperative and postoperative factors of importance in determining serum gentamicin concentrations. Serum assays might then be confined to those at particular risk of elevated serum levels. Patients received gentamicin 1.5 mg/kg at the start of surgery followed by 80 mg tds for two days in addition to flucloxacillin. Trough and peak serum gentamicin concentrations were assayed on the first and second days after surgery and urine concentrations were measured with each full catheter bag. Patient characteristics, drug therapy, operation, fluid balance and routine investigations were recorded. A total of 95 of 104 patients were evaluable. Linear discriminant analysis of factors selected by forward stepwise regression identified ten of the 15 patients with subsequent elevated gentamicin concentrations, by using age, and preoperative serum creatinine, systolic blood pressure and serum aspartate transaminase. After operation, factors such as serum creatinine, the quantity of frusemide administered in 24 h, and the integral of the systolic blood pressure over 24 h identified 12 of the 15 patients. However, no satisfactory model could predict urinary concentrations. The discriminant function using preoperative factors prospectively identified 11 of 12 patients with elevated trough levels from a total of 101 further patients. Postoperative gentamicin concentrations cannot reliably be predicted from patient characteristics. Trough assays should be performed or prophylactic courses limited to 24 h.

Physiology and clinical applications of cardiopulmonary exercise testing.

Advances in the technology of gas exchange analysers have made cardiopulmonary exercise testing a relatively simple, cheap and reliable diagnostic tool. Its practice and uses include grading the severity of heart failure, evaluation of the cause of exertional dyspnoea and monitoring a patient's response to therapy. Areas of debate and future development are highlighted.

Management of massive haemoptysis.

Massive haemoptysis is rare but associated with a high mortality. Even in a major regional cardiothoracic centre only one or two cases will be seen annually. As a consequence, no consensus about its investigation and management has emerged, with the result that much time may be lost on inappropriate investigation and treatment may be misdirected.

Metabolic analysis of latissimus dorsi coupled to a mock circulation.

A mock circulation system has been used to examine the metabolic and hemodynamic responses of untrained and trained latissimus dorsi muscle in a normal animal model. The metabolic response of untrained latissimus dorsi to differing stimulation regimes runs parallel to its mechanical performance. The ratio of power generated to oxidative capacity (a measure of metabolic efficiency) was maintained to a greater extent in muscle trained for 5 months subjected to specific fatigue tests, falling by only 20% (as opposed to 80% observed in untrained control muscle). This approach to studying metabolic and hemodynamic performance may have relevance when skeletal muscle is used for cardiac assistance.

Transesophageal atrial pacing for intraoperative sinus bradycardia or AV junctional rhythm: feasibility as prophylaxis in 200 anesthetized adults and hemodynamic effects of treatment.

Sinus bradycardia (SB) or atrioventricular junctional rhythm (AVJR) may produce circulatory insufficiency in anesthetized surgical patients, especially those with cardiovascular disease. Chronotropic drugs have been the preferred initial treatment, except when epicardial pacing is available. Alternative methods include transvenous or transcutaneous pacing. Drugs may be ineffective or have undesirable effects. Transvenous pacing is time consuming and risky, and transcutaneous pacing is not universally applicable or effective. Transesophageal atrial pacing (TAP) lacks these disadvantages, but unavailability of equipment and unfamiliarity with the method has discouraged widespread use. Feasibility of TAP as prophylaxis for intraoperative SB or AVJR was tested with approved or investigational devices in 200 anesthetized surgical patients, not necessarily with cardiovascular disease or having cardiac surgery. Of these, 84 later had incidental SB < or = 60 beats/min, and 23 of these 84 had SB < or = 50 beats/min. Thirteen patients had AVJR (72 +/- 4 beats/min; mean +/- SEM). TAP at 80 beats/min for SB, or at a rate sufficient to overdrive AVJR, was effective initial treatment in all patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of transesophageal atrial pacing stethoscope in adult surgical patients under general anesthesia.

Sinus bradycardia (SB) and atrioventricular junctional rhythm (AVJR) commonly cause circulatory insufficiency in anesthetized surgical patients. Treatment is usually with drugs, which can be ineffective or have adverse effects. Cardiac pacing might be preferred, but the transvenous or epicardial routes are too invasive for routine use, and transcutaneous pacing fails to preserve atrial transport function. Transesophageal atrial pacing (TAP) lacks these disadvantages, yet unavailability of inexpensive products has prevented more widespread use. Therefore, a pacing esophageal stethoscope (PES) fabricated by addition of bipolar electrodes to disposable esophageal stethoscopes routinely used for intraoperative monitoring, was evaluated in 100 anesthetized adults. TAP thresholds (10-msec pulses) and hemodynamic effects of TAP as treatment for incidental SB (< or = 60 beats/min) or AVJR were determined. Minimum TAP thresholds (mean +/- standard error) in 48 males were 7.3 +/- 0.3 mA and in 51 females were 8.5 +/- 0.4 mA. Corresponding inferior alveolar ridge-to-electrode distances were 32.5 +/- 0.2 and 30.4 +/- 0.2 cm. For 48 patients with SB < or = 60 beats/min (54 +/- 1 beats/min), TAP (81 +/- 1 ppm) produced average 15, 11, and 14 mmHg increases in systolic, diastolic, and mean arterial pressure, respectively (P < 0.001). For 11 patients with AVJR (71 +/- 5 beats/min), TAP (92 +/- 3 ppm) produced average 23 and 15 mmHg increases in systolic and mean arterial pressure, respectively (P < 0.05). There were no apparent complications of TAP. TAP with a PES appears practical, safe, and effective for prophylaxis and treatment of SB or AVJR in anesthetized surgical patients.

Aortic counterpulsation for up to 28 days with autologous latissimus dorsi in sheep.

This article reports the development and assessment of an entirely autologous extraaortic counterpulsation system using skeletal muscle (latissimus dorsi). The technique has been performed and assessed in 16 sheep to quantify the effectiveness of counterpulsation over periods up to 28 days and to optimize the stimulation regimens for muscle contraction and fiber-type transformation. Hemodynamic changes have been quantified by calculation of the endocardial viability ratio. This has shown an increase of between 12% and 89% for 28 days. The wide variety of increase observed has been related to the development of an optimum flap configuration. The technique of surface impedance monitoring of flap blood flow has allowed the start of electrical stimulation after 48 hours with the introduction of hemodynamic benefit (1:4 mode) during the process of fiber-type transformation (in situ training). Extraaortic counterpulsation with autologous latissimus dorsi has been shown to be effective and safe for as long as 28 days. It has not been associated with any thromboembolic or infective complications, which we attribute to the exclusion of any foreign material in the design.