High-flow nasal oxygen vs. standard oxygen therapy for patients undergoing transcatheter aortic valve replacement with conscious sedation: a randomised controlled trial

BACKGROUND

Minimally invasive surgery is becoming more common and transfemoral transcatheter aortic valve replacement is offered to older patients with multiple comorbidities. Sternotomy is not required but patients must lie flat and still for up to 2-3 h. This procedure is increasingly being performed under conscious sedation with supplementary oxygen, but hypoxia and agitation are commonly observed.

METHODS

In this randomised controlled trial, we hypothesised that high-flow nasal oxygen would provide superior oxygenation as compared with our standard practice, 2 l min^-1 oxygen by dry nasal specs. This was administered using the Optiflow THRIVE Nasal High Flow delivery system (Fisher and Paykel, Auckland, New Zealand) at a flow rate of 50 l min^-1 and FiO₂ 0.3. The primary endpoint was the change in arterial partial pressure of oxygen (pO₂) during the procedure. Secondary outcomes included the incidence of oxygen desaturation, airway interventions, the number of times the patient reached for the oxygen delivery device, incidence of cerebral desaturation, peri-operative oxygen therapy duration, hospital length of stay and patient satisfaction scores.

RESULTS

A total of 72 patients were recruited. There was no difference in change in pO₂ from baseline using high-flow compared with standard oxygen therapy: median [IQR] increase from 12.10 (10.05-15.22 [7.2-29.8]) to 13.69 (10.85-18.38 [8.5-32.3]) kPa vs. decrease from 15.45 (12.17-19.33 [9.2-22.8]) to 14.20 (11.80-19.40 [9.7-35.1]) kPa, respectively. The percentage change in pO2 after 30 min was also not significantly different between the two groups (p = 0.171). There was a lower incidence of oxygen desaturation in the high-flow group (p = 0.027). Patients in the high-flow group assigned a significantly higher comfort score to their treatment (p ≤ 0.001).

CONCLUSION

This study has demonstrated that high flow, compared with standard oxygen therapy, does not improve arterial oxygenation over the course of the procedure. There are suggestions that it may improve the secondary outcomes studied.

TRIAL REGISTRATION

International Standard Randomised Controlled Trial Number (ISRCTN) 13,804,861. Registered on 15 April 2019. https://doi.org/10.1186/ISRCTN13804861.

Ex vivo perfusion of the swine heart as a method for pre-transplant assessment

We describe a cost-effective, reproducible circuit in a porcine, ex vivo, continuous warm-blood, bi-ventricular, working heart model that has future possibilities for pre-transplant assessment of marginal hearts donated from brain stem dead donors and hearts donated after circulatory determination of death (DCDD). In five consecutive experiments over five days, pressure volume loops were performed. During working mode, the left ventricular end systolic pressure volume relationship (LV ESPVR) was 23.1±11.1 mmHg/ml and the LV preload recruitable stroke work (PRSW) was 67.8±7.2. (Standard PVAN analysis software) (Millar Instruments, Houston, TX, USA) All five hearts were perfused for 219±64 minutes and regained normal cardiac function on the perfusion system.They displayed a significant upward and leftward shift of the end systolic pressure volume relationship, a significant increase in preload recruitable stroke work and minimal stiffness. These hearts could potentially be considered for transplantation. The circuit was effective during reperfusion and working modes whilst proving to be successful in maintaining cardiac function in excess of four hours. Using an autologous prime of approximately 20% haematocrit (Hct), electrolytes and blood gases were easy to control within this period using standard perfusion techniques.

Impact of xenon anaesthesia in isolated cardiopulmonary bypass on very early leucocyte and platelet activation and clearance: a randomized, controlled study

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with leucocyte and platelet activation and also organ dysfunction. Xenon has been found to have organ-protective effects. We therefore investigated the effect of isolated CPB on leucocyte and platelet activation and the efficacy of xenon in inhibiting these changes.

METHODS

Isolated CPB was conducted according to strict standardized clinical criteria using blood from healthy volunteers. They were randomized to an air-oxygen mixture (control group) vs xenon-oxygen mixture (xenon group). Blood samples were drawn at 5, 15, 30, 60, and 90 min from commencement of circuits and analysed for haemoglobin concentrations, white cell, neutrophil, monocyte, lymphocyte, and platelet counts. Leucocyte and platelet activation and also complex formation were determined by measuring levels of CD14++ monocytes, CD16+ monocytes, platelet-monocyte complexes, and platelet-neutrophil complexes (PNC). Differences between and within the groups were analysed with Student's t-test.

RESULTS

Biomarker levels were not different between the groups. The data were pooled to identify the effects of isolated bypass. The neutrophils, monocytes, platelets, CD14++ monocytes, and CD16+ monocytes decreased within 5 min of the bypass experiments, whereas the percentage of platelet-CD++ monocyte complexes and PNC increased.

CONCLUSIONS

Isolated CPB elicited rapid, substantial leucocyte and platelet activation, and xenon had no impact on inhibiting these changes.

The Papworth BiVent tube: a new device for lung isolation

Provision of one lung ventilation can be technically challenging, particularly for anaesthetists who are only occasionally required to isolate one lung from the other. A new double lumen endotracheal tube, the Papworth BiVent Tube, has been designed to enable rapid and reliable lung isolation using any bronchus blocker without the need for fibreoptic endoscopic guidance. In this study, an airway-training manikin was used to assess ease of tracheal intubation and lung isolation using the Papworth BiVent tube. Ease of intubation was compared to a single lumen endotracheal tube and a conventional double lumen endobronchial tube. Ease of lung isolation when using a bronchus blocker was compared to a single lumen tube combined with a bronchial blocker. Tracheal intubation using the Papworth BiVent tube was found to be easier than when using a conventional double lumen endobronchial tube. Lung isolation using the Papworth BiVent tube used in combination with a bronchus blocker was achieved more reliably and rapidly than when using a single lumen tube and bronchus blocker.

Xenon anaesthesia may preserve cardiovascular function in patients with heart failure

BACKGROUND

The hypothesis that xenon anaesthesia provided haemodynamic stability was tested in patients with heart failure in a prospective, randomized, single-blind design.

METHODS

Twenty-six patients scheduled for implantation of a cardioverter-defibrillator (ICD) received xenon 60-65% in oxygen (xenon group, n = 12) or propofol 3 mg/kg/h (propofol group, n = 14), both combined with remifentanil 0.2 microg/kg/min. After induction of anaesthesia with etomidate and remifentanil, heart rate (HR), mean arterial pressure (MAP) and left ventricular ejection fraction (LVEF) were recorded. After 60 min of propofol or xenon anaesthesia, the same parameters were recorded.

RESULTS

While HR decreased in both groups, MAP was unchanged with xenon (73 vs. 76 mmHg) and decreased with propofol (from 78 to 64 mmHg, P < 0.02). LVEF was stable in both groups [32% vs. 37%, xenon (NS), and 30% vs. 34%, propofol (NS)]. Preload, as measured by end-diastolic volume (EDV), did not change (66 vs. 63 ml with xenon; 79 vs. 81 ml with propofol, both NS). Afterload, as determined by end-systolic pressure-volume product (ESPV), decreased with propofol (6760 vs. 4920 ml mmHg) but not with xenon (4060 vs. 3780 ml mmHg, P < 0.01 between groups).

CONCLUSION

With propofol, MAP is reduced and LVEF is not increased in spite of reduced afterload. In contrast, MAP and LVEF are maintained with xenon.

Effect of PEEP and inhaled nitric oxide on pulmonary gas exchange during gaseous and partial liquid ventilation with small volumes of perfluorocarbon

BACKGROUND

Partial liquid ventilation, positive end-expiratory pressure (PEEP) and inhaled nitric oxide (NO) can improve ventilation/perfusion mismatch in acute lung injury (ALI). The aim of the present study was to compare gas exchange and hemodynamics in experimental ALI during gaseous and partial liquid ventilation at two different levels of PEEP, with and without the inhalation of nitric oxide.

METHODS

Seven pigs (24+/-2 kg BW) were surfactant-depleted by repeated lung lavage with saline. Gas exchange and hemodynamic parameters were assessed in all animals during gaseous and subsequent partial liquid ventilation at two levels of PEEP (5 and 15 cmH2O) and intermittent inhalation of 10 ppm NO.

RESULTS

Arterial oxygenation increased significantly with a simultaneous decrease in cardiac output when PEEP 15 cmH2O was applied during gaseous and partial liquid ventilation. All other hemodynamic parameters revealed no relevant changes. Inhalation of NO and instillation of perfluorocarbon had no additive effects on pulmonary gas exchange when compared to PEEP 15 cmH2O alone.

CONCLUSION

In experimental lung injury, improvements in gas exchange are most distinct during mechanical ventilation with PEEP 15 cmH2O without significantly impairing hemodynamics. Partial liquid ventilation and inhaled NO did not cause an additive increase of PaO2.

Dobutamine stress echocardiography after coronary artery bypass grafting. Transthoracic vs biplane transoesophageal imaging

Graft failure or progressive native vessel disease can be a serious problem after coronary artery bypass grafting. However, because of poor image quality it may be difficult to evaluate these patients by transthoracic stress echocardiography. The purpose of this study, therefore, was to evaluate the effectiveness of dobutamine stress echocardiography in the detection of myocardial territories with compromised vascular supply (due to either an obstructed native vessel without graft, and obstructed graft, or a native vessel obstructed distal to bypass graft insertion with < or = 50% luminal diameter reduction on angiography) after coronary artery bypass grafting and to determine additional information obtained by biplane transoesophageal stress echocardiography. Sixty patients (54 men, mean age 59 +/- 8.5 years) who had undergone coronary bypass grafting (total number of graft vessels 198) were evaluated from 6 months to 14 years (mean 6.2 years) after surgery. Transthoracic dobutamine stress echocardiography, biplane transoesophageal dobutamine stress echo, and coronary angiography were performed and evaluated by independent examiners. An infusion of dobutamine up to a maximum of 40 micrograms.kg-1.min-1 was administered, and additional atropine (0.25-1.0 mg) was given if 85% of age-predicted maximal heart rate was not reached. Biplane transoesophageal echocardiography was performed in the transgastric short-axis view as well as transoesophageal 4- and 2-chamber views, allowing division of the left ventricle into a 14-segment scheme. Wall motion abnormalities induced with dobutamine stress were used to predict regional vascular insufficiency. A 4-point scale, ranging from 'excellent' (1) to 'impossible' (4) was used to assess each system's ability to evaluate all left ventricular segments. Forty-five patients, of whom 35 were identified by transthoracic echocardiography (sensitivity 78%), had at least one territory with a compromised vascular supply. In 15 patients, the vascular supply was uncompromised, with 13 showing no wall motion abnormalities inducible by transthoracic echocardiography (specificity 86%). However, biplane transoesophageal echocardiography had a higher sensitivity and specificity than transthoracic echocardiography in detecting compromised vascular supply, 93% and 93%, respectively. The former system correctly classified the vascular supplies in 113 of 120 vascular territories (94%), according to whether they were compromised or uncompromised. This was significantly more (P < 0.05) than by classification with transthoracic dobutamine echocardiography, by which system only 102 of the 120 vascular territories were correctly assessed (85%). Compared with the conventional transgastric monoplane short-axis view, examination using three different views via a biplane probe results in a higher sensitivity (93% vs 84%). Assessed on a 4-point scale, the ability to evaluate all left ventricular segments was 2.3 +/- 0.7 (mean +/- SD) for transthoracic echocardiography and 1.7 +/- 0.7 (P < 0.01) for biplane transoesophageal echocardiography. After coronary artery bypass grafting transthoracic dobutamine stress echocardiography has acceptable accuracy in the detection of regional vascular insufficiency. However, this accuracy can be improved using the higher image quality of transoesophageal echocardiography, combined with the advantages of several different views obtained by biplane transoesophageal echocardiography.