COVID-19 safety: aerosol-generating procedures and cardiothoracic surgery and anaesthesia - Australian and New Zealand consensus statement.

INTRODUCTION: Coronavirus disease 2019 (COVID-19) is a contagious disease that is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Health care workers are at risk of infection from aerosolisation of respiratory secretions, droplet and contact spread. There are a number of procedures that represent a high risk of aerosol generation during cardiothoracic surgery. It is important that adequate training, equipment and procedures are in place to reduce that risk. RECOMMENDATIONS: We provide a number of key recommendations, which reduce the risk of aerosol generation during cardiothoracic surgery and help protect patients and staff. These include general measures such as patient risk stratification, appropriate use of personal protective equipment, consideration to delay surgery in positive patients, and careful attention to theatre planning and preparation. There are also recommended procedural interventions during airway management, transoesophageal echocardiography, cardiopulmonary bypass, chest drain management and specific cardiothoracic surgical procedures. Controversies exist regarding the management of low risk patients undergoing procedures at high risk of aerosol generation, and recommendations for these patients will change depending on the regional prevalence, risk of community transmission and the potential for asymptomatic patients attending for these procedures. CHANGES IN MANAGEMENT AS A RESULT OF THIS STATEMENT: This statement reflects changes in management based on expert opinion, national guidelines and available evidence. Our knowledge with regard to COVID-19 continues to evolve and with this, guidance may change and develop. Our colleagues are urged to follow national guidelines and institutional recommendations regarding best practices to protect their patients and themselves. ENDORSED BY: Australian and New Zealand Society of Cardiac and Thoracic Surgeons and the Anaesthetic Continuing Education Cardiac Thoracic Vascular and Perfusion Special Interest Group.

The Use of a Preoperative Mitral Valve Model to Guide Mitral Valve Repair.

BACKGROUND: Mitral valve repair is commonly used to address degenerative or functional changes to the mitral valve apparatus and surrounding ventricular anatomy. Preoperative transoesophageal echocardiogram (TOE) is routinely used to evaluate and identify the precise anatomic location of mitral valve pathology in order to guide repair. However, surgeons currently lack specific guidance regarding the approximate dimensions of the mitral valve they should aim for in order to achieve optimal valve function and avoid adverse outcomes. Therefore, through an observational study, we aimed to develop and test the accuracy of a preliminary mathematical model which represents the geometric relationship between various clinically relevant components of the mitral valve and its surrounding structures. METHODS: Using established trigonometric principles, the geometric relationship shared between several mitral valve components was represented in a two-dimensional (2D) model and described in a mathematical equation. The output variable of the model is the anteroposterior diameter of the mitral valve. To assess the accuracy of the mathematical model, we compared the model-predicted anteroposterior (AP) diameter against AP diameter measured by postoperative TOE in 42 cases. RESULTS: The root mean squared error (RMSE) of model predicted AP diameter compared to measured AP diameter was 0.43 cm. The mean absolute percentage error (MAPE) of the model was 17.7%. In 34 out of 42 cases, model-predicted AP diameters were within 25% of AP diameters measured by postoperative TOE. CONCLUSIONS: Preliminary testing of a simple mathematical model has shown its relative accuracy in representing the geometric relationship between several mitral valve variables. Further research and refinement of the model is required in order to improve its accuracy. We are encouraged that, with further improvement, the model has the potential for clinical application.

A Phase 1 Study of a Novel Bidirectional Perfusion Cannula in Patients Undergoing Femoral Cannulation for Cardiac Surgery.

OBJECTIVE: Leg ischemia is a serious complication of femoral artery cannulation. The primary aim of this study was to assess the safety and efficacy of a novel bidirectional femoral arterial cannula (Sorin Group USA, a wholly owned subsidiary of LivaNova PLC, Arvada, CO USA) that provides both antegrade and retrograde flow, in patients undergoing peripheral cannulation for cardiopulmonary bypass during cardiac surgery. METHODS: Patients undergoing routine cardiac surgery requiring femoral artery cannulation for cardiopulmonary bypass were identified preoperatively. Informed written consent was obtained in all cases. Bidirectional cannula insertion used either a surgical cut-down and wire through needle approach or a percutaneous technique. Flow in the superficial femoral artery was assessed using Doppler ultrasound after commencement of cardiopulmonary bypass. Lower limb perfusion was assessed using reflectance near-infrared spectroscopy to measure regional oxygen saturations in the cannulated limb during cardiopulmonary bypass. RESULTS: Fifteen patients (median age = 61.3 years, range = 26-79 years, 10 males, 5 females) underwent femoral arterial cannulation using the novel bidirectional femoral cannula between August 2016 and May 2017. Fourteen cannulae were inserted directly into the femoral artery via a surgical cut-down and wire through needle technique. One bidirectional cannula was inserted using a percutaneous insertion technique. Indications included minimally invasive mitral and aortic valve surgery, thoracic aortic aneurysm repair, and redo cardiac surgery. The median duration of cardiopulmonary bypass was 129 minutes (range = 53-228 minutes). The cannula was inserted and positioned without difficulty in 14 of 15 patients. Incorrect sizing and arterial spasm prevented correct cannula positioning in one patient. Antegrade flow in the superficial femoral artery was observed on Doppler ultrasound in 12 of 12 patients in which this was performed. Continuous stable distal perfusion was demonstrated in the cannulated limb in 14 of 15 patients. No procedural complications occurred in the immediate or convalescent postoperative period. CONCLUSIONS: This study demonstrates that in patients undergoing femoral arterial cannulation for cardiopulmonary bypass during cardiac surgery, the use of a novel bidirectional cannula is safe and easy to insert and provides stable distal perfusion of the cannulated limb. Use of the device should largely obviate the need to insert a separate downstream perfusion cannula or use other techniques to protect against lower limb ischemia. Further research on a larger scale and in different patient populations is now warranted.

Pressure and Flow Characteristics of a Novel Bidirectional Cannula for Cardiopulmonary Bypass.

OBJECTIVE: Femoral arterial cannulation is associated with a significant risk of lower limb ischemia. The aim of the study was to assess the pressure and flow in the femoral artery using a novel bidirectional femoral cannula in a sheep model of peripheral cardiopulmonary bypass. METHODS: Peripheral cardiopulmonary bypass was established using a multistage venous cannula inserted into the internal jugular vein and the bidirectional or a conventional arterial cannula into the femoral artery in seven adult ewes. Systemic and distal perfusion pressures and flow rates were measured during cardiopulmonary bypass with flow rates of 1, 2, 3, and 4 L/min. Lower limb venous oxygen saturation and lactate levels were also measured. RESULTS: A significantly higher blood flow in the lower limb using the bidirectional cannula was observed and compared with a conventional cannula at all flow rates (mean flow 115 mL/min vs 10 mL/min, P < 0.05). The mean distal perfusion pressure was also significantly higher in the bidirectional cannula group (86 mm Hg vs 45 mm Hg at 4 L/min of flow, P < 0.05). The bidirectional cannula was associated with higher venous oxygen saturations in the lower limb than in the conventional cannula group; however, lower limb lactate production was similar in the two groups. CONCLUSIONS: This in vivo data demonstrates superior distal flow and pressure characteristics of a novel bidirectional cannula compared with a conventional femoral cannula during peripheral cardiopulmonary bypass.

Echocardiographic measurement of mitral intertrigonal distance is an adjunct to annuloplasty ring sizing.

BACKGROUND AND AIM OF THE STUDY: Annuloplasty sizing with standard valve sizers may be imprecise and difficult in minimally invasive procedures. It is hypothesized that a constant clinical conversion factor relates the echocardiographic aortic annulus diameter (AAD) and the intertrigonal distance (ITD) in patients with degenerative mitral regurgitation (MR). This may provide another method to size the annuloplasty ring required for mitral valve repair. METHODS: An observational study of 50 patients with degenerative MR undergoing robotic-assisted surgery was conducted. All patients underwent surgery between September 2005 and November 2007. The AAD at the base of the aortic leaflets was measured using intraoperative two-dimensional transesophageal echocardiography. The ITD was measured independently under direct vision during surgery. The echocardiographic ITD was then determined by dividing the AAD by 0.8, and the value for each patient compared to the corresponding surgical measurement. Agreement was assessed statistically using the Bland-Altman method. RESULTS: The limits of agreement were -3 mm (t = 2.010; 49 df; p = 0.05; 95% CI: -4 to -2 mm) to 3 mm (t = 2.010; 49 df; p = 0.05; 95% CI: 2 to 4 mm). In 86% of cases (43/50), the differences between the two methods was < or = 2 mm. CONCLUSION: In most cases of degenerative mitral valve disease the echocardiographic ITD measurement is clinically acceptable, and may serve as an adjunct to existing methods when sizing the annuloplasty ring required for repair.

Parasternal intercostal block with ropivacaine for pain management after cardiac surgery: a double-blind, randomized, controlled trial.

OBJECTIVE: The purpose of this study was to test the hypothesis that administration of a parasternal intercostal block using ropivacaine 0.75% improved analgesia in postoperative cardiac surgical patients. DESIGN: Randomized, controlled, double-blinded trial. SETTING: Teaching hospital. PARTICIPANTS: Eighty-eight cardiac surgery patients. INTERVENTIONS: Ropivacaine 0.75% with 5 doses each side, total dosage 40 mL (300 mg), via parasternal intercostal injection or saline before insertion of the sternal wires and closure of the sternal wound. MEASUREMENTS AND MAIN RESULTS: At extubation, patients who had a parasternal intercostal block with ropivacaine had visual analog and numerical rating pain scores approximately 50% less than those in the saline group (29.5 [standard deviation (SD) = 24.3] v 53.2 [SD = 24.1], ropivacaine v saline, respectively, p < 0.001). Patients who received ropivacaine used approximately 50% less PCA morphine (12.0 [SD = 5.4] v 23.2 [SD = 8.3] total morphine equivalents in milligrams, ropivacaine v saline, respectively; p < 0.001) in the first 12 hours postoperatively, with a continued reduction in dosages for the ensuing 12 to 24 hours (18.8 [SD = 9.6] v 23.7 [SD = 10.0] total morphine equivalents in milligrams, ropivacaine v saline; p = 0.028). CONCLUSIONS: A ropivacaine parasternal intercostal block is a safe, simple, and effective adjunct for optimizing of pain control and reducing opioid analgesics after adult cardiac surgery. This study provides clinicians with an effective treatment for sternal wound pain.

Feedback effects of circulating norepinephrine on sympathetic outflow in healthy subjects.

The amplitude of low-frequency (LF) oscillations of heart rate (HR) usually reflects the magnitude of sympathetic activity, but during some conditions, e.g., physical exercise, high sympathetic activity results in a paradoxical decrease of LF oscillations of HR. We tested the hypothesis that this phenomenon may result from a feedback inhibition of sympathetic outflow caused by circulating norepinephrine (NE). A physiological dose of NE (100 ng.kg(-1).min(-1)) was infused into eight healthy subjects, and infusion was continued after alpha-adrenergic blockade [with phentolamine (Phe)]. Muscle sympathetic nervous activity (MSNA) from the peroneal nerve, LF (0.04-0.15 Hz) and high frequency (HF; 0.15-0.40 Hz) spectral components of HR variability, and systolic blood pressure variability were analyzed at baseline, during NE infusion, and during NE infusion after Phe administration. The NE infusion increased the mean blood pressure and decreased the average HR (P < 0.01 for both). MSNA (10 +/- 2 vs. 2 +/- 1 bursts/min, P < 0.01), LF oscillations of HR (43 +/- 13 vs. 35 +/- 13 normalized units, P < 0.05), and systolic blood pressure (3.1 +/- 2.3 vs. 2.0 +/- 1.1 mmHg2, P < 0.05) decreased significantly during the NE infusion. During the NE infusion after PHE, average HR and mean blood pressure returned to baseline levels. However, MSNA (4 +/- 2 bursts/min), LF power of HR (33 +/- 9 normalized units), and systolic blood pressure variability (1.7 +/- 1.1 mmHg2) remained significantly (P < 0.05 for all) below baseline values. Baroreflex gain did not change significantly during the interventions. Elevated levels of circulating NE cause a feedback inhibition on sympathetic outflow in healthy subjects. These inhibitory effects do not seem to be mediated by pressor effects on the baroreflex loop but perhaps by a presynaptic autoregulatory feedback mechanism or some other mechanism that is not prevented by a nonselective alpha-adrenergic blockade.