Numerical Simulation of a Biventricular Assist Device with Fixed Right Outflow Cannula Banding During Pulmonary Hypertension.

As a left ventricular assist device is designed to pump against the systemic vascular resistance (SVR), pulmonary congestion may occur when using such device for right ventricular support. The present study evaluates the efficacy of using a fixed right outflow banding in patients receiving biventricular assist device support under various circulatory conditions, including variations in the SVR, pulmonary vascular resistance (PVR), total blood volume (BV), as well as ventricular contractility. Effect of speed variation on the hemodynamics was also evaluated at varying degrees of PVR. Pulmonary congestion was observed at high SVR and BV. A reduction in right ventricular assist device (RVAD) speed was required to restore pulmonary pressures. Meanwhile, at a high PVR, the risk of ventricular suction was prevalent during systemic hypotension due to low SVR and BV. This could be compensated by increasing RVAD speed. Isolated right heart recovery may aggravate pulmonary congestion, as the failing left ventricle cannot accommodate the resultant increase in the right-sided flow. Compared to partial assistance, the sensitivity of the hemodynamics to changes in VAD speed increased during full assistance. In conclusion, our results demonstrated that the introduction of a banding graft with a 5 mm diameter guaranteed sufficient reserve of the pump speed spectrum for the regulation of acceptable hemodynamics over different clinical scenarios, except under critical conditions where drug administration or volume management is required.

Low-flow hypothermic crystalloid perfusion is superior to cold storage during prolonged heart preservation.

BACKGROUND: Preservation of donor hearts for transplantation has traditionally been performed with the use of static cold storage. We have developed and tested a novel gravity-powered system of cold crystalloid perfusion for prolonged donor heart preservation. METHODS: Greyhounds were anesthetized; their hearts were arrested with cold cardioplegic solution and excised. Hearts were allocated to 12 hours of perfusion preservation (n = 6) or cold storage in ice (n = 5). Non-preserved hearts (n = 5) served as a normal reference group. Perfusion hearts were perfused (20 mL/min, 8-12°C) with a novel oxygenated nutrient-containing preservation solution. After preservation, the recovery of the hearts was assessed in a blood-perfused working heart rig over 2 hours in terms of function, blood lactate level, myocardial adenosine triphosphate, and histology. RESULTS: After 2 hours of reperfusion, in comparison with cold storage hearts, perfused heart function curves showed superior recovery of cardiac output (P = .001), power (P = .001), and efficiency (0.046 ± 0.01 vs 0.004 ± 0.003 joules/mL O2, P = .034). Myocardial adenosine triphosphate content (mmol/mg protein) was reduced significantly from the normal level of 26.5 (15.9, 55.8) to 5.08 (0.50, 10.4) (P = .049) in cold storage hearts but not in perfused hearts. Over a period of 2 hours, lactate levels in the blood perfusate were significantly lower in the perfusion group than in the cold storage group (P < .05). CONCLUSIONS: Continuous hypothermic crystalloid perfusion provides myocardial preservation superior to cold storage for long-term heart preservation, with potential applicability to marginal and donation after circulatory death hearts.

Non-invasive estimation and control of inlet pressure in an implantable rotary blood pump for heart failure patients.

We propose a dynamical model for mean inlet pressure estimation in an implantable rotary blood pump during the diastolic period. Non-invasive measurements of pump impeller rotational speed (ω), motor power (P), and pulse width modulation signal acquired from the pump controller were used as inputs to the model. The model was validated over a wide range of speed ramp studies, including (i) healthy (C1), variations in (ii) heart contractility (C2); (iii) afterload (C2, C3, C4), and (iv) preload (C5, C6, C7). Linear regression analysis between estimated and extracted mean inlet pressure obtained from in vivo animal data (greyhound dogs, N = 3) resulted in a highly significant correlation coefficients (R(2) = 0.957, 0.961, 0.958, 0.963, 0.940, 0.946, and 0.959) and mean absolute errors of (e = 1.604, 2.688, 3.667, 3.990, 2.791, 3.215, and 3.225 mmHg) during C1, C2, C3, C4, C5, C6, and C7, respectively. The proposed model was also used to design a controller to regulate mean diastolic pump inlet pressure using non-invasively measured ω and P. In the presence of model uncertainty, the controller was able to track and settle to the desired input within a finite number of sampling periods and minimal error (0.92 mmHg). The model developed herein will play a crucial role in developing a robust control system of the pump that detects and thus avoids undesired pumping states by regulating the inlet pressure within a predefined physiologically realistic limit.

In vivo validation of pulsatile flow and differential pressure estimation models in a left ventricular assist device.

Implantation of sensors to measure hemodynamic parameters such as pulsatile pump flow and differential pressure (head) in an implantable rotary pump (IRBP) requires regular in situ calibration due to measurement drift. In addition, risks associated with sensor failure and thrombus formation makes the long-term implantation in patients problematic. In our laboratory, two stable and novel dynamical models for non-invasive pulsatile flow and head estimation were proposed and tested in vitro using mock circulatory loop experiments with varying hematocrit (HCT). Noninvasive measurements of power and pump speed were used as inputs to the flow model while the estimated flow was used together with the pump rotational speed as inputs to the head estimation model. In this paper, we evaluated the performance of the proposed models using in vivo experimental data obtained from greyhound dogs (N=5). Linear regression analysis between estimated and measured pulsatile flows resulted in a highly significant correlation (R(2) = 0.946) and mean absolute error (e) of 0.810 L/min, while for head, R(2) = 0.951 and e = 10.13 mmHg were obtained.

Successful use of ECMO in adults with life-threatening infections.

Two cases of critically ill patients who received extracorporeal membrane oxygenation (ECMO) using different forms of circuitry and for different indications are presented. Both patients had life-threatening infections with septic shock and were not able to be supported by conventional means. The first patient had staphylococcal septicaemia and received venoarterial ECMO for circulatory failure. The second patient had psittacosis and received venovenous ECMO for respiratory failure. We discuss the expanding indications for this technology and the role it has to play in adult intensive care.

Outcomes of coronary artery bypass grafting: a 3 year analysis using the Society of Thoracic Surgeons Database.

BACKGROUND: Accurate risk factor analysis is a critical element in contemporary cardiac surgical practice. In the USA, the Society of Thoracic Surgeons Database allows institutions and individual surgeons to carry out detailed patient risk assessment and to review their cardiac surgical outcomes in a comparative fashion. METHODS: To evaluate outcomes of isolated coronary artery bypass grafting, data from all patients operated upon at the Alfred Hospital, Melbourne, Australia, over a 3 year period were entered into the Society of Thoracic Surgeons Database. RESULTS: Our results (mortality and morbidity) compared favourably with those contained within this large international database. CONCLUSION: It is hoped that a similar Australasian database can be established to facilitate a meaningful local risk assessment and a comparative analysis of outcomes of cardiac surgical procedures.

Reverse telescope anastomotic technique reduces the incidence of bronchial stricture.

BACKGROUND: Bronchial stricture remains a major problem after lung transplantation. We hypothesized that a "reverse" telescope anastomosis, where the donor bronchus is sleeved external to the recipient bronchus, would be associated with a lower incidence of anastomotic stricture. METHODS: Over a 12-month period our Unit performed 35 consecutive single and bilateral sequential lung transplantations. The 56 bronchial anastomoses were constructed as a conventional (n = 27) or as a reverse (n = 29) telescope. RESULTS: Bronchial strictures developed in 48% of the conventional anastomoses but in only 7% of the reverse anastomoses (p < or = 0.05). Furthermore, the reverse telescope anastomosis eliminated the need for stenting. CONCLUSIONS: This technique greatly reduced the need for dilatation, debridement, and stent placement and may reduce the morbidity and mortality associated with anastomotic complications.

Preliminary experience with inhaled nitric oxide for acute pulmonary hypertension after heart transplantation.

BACKGROUND: Substantial interest has developed in the physiologic and therapeutic role of nitric oxide in the last few years. In patients with pulmonary hypertension it appears to be a useful selective pulmonary vasodilator; however, many issues of both staff and patient safety remained unanswered. METHODS: This study examines further safety issues and also presents preliminary clinical experience in patients after orthotopic heart transplantation with pulmonary hypertension and right-sided ventricular failure. RESULTS: Atmospheric levels of nitric oxide and nitrogen dioxide are 100 times less than occupational health standards. When nitric oxide is used at 70 parts per million in the presence of a fraction of inspired oxygen greater than 0.60, nitrogen dioxide levels in the circuit exceed the published short-term exposure limit of the American Conference of Government Industrial Hygienist of 5 parts per million. CONCLUSION: Staff safety appears confirmed, but despite encouraging clinical results, further longer term safety and efficacy studies are indicated.

Inhaled nitric oxide used as a bridge to heart-lung transplantation in a patient with end-stage pulmonary hypertension.

We describe a 40-yr-old woman who received inhaled nitric oxide (NO) as a therapeutic bridge to heart-lung transplantation for end-stage primary pulmonary hypertension. After 10 yr of increasing disability, the patient presented in October 1993 with severe dyspnea, right ventricular angina, and syncope. As predicted by a prior vasodilator trial, prostacyclin produced as initial favorable clinical and hemodynamic response. With the recurrence of severe symptoms and hemodynamic compromise, inhaled NO was successfully tried at 40 ppm, initially via a face mask and later via a transtracheal Scoop catheter. The patient was "bridged" to heart-lung transplant after 68 d of therapy (mean dose of NO, 50.4 +/- 23 ppm). The explanted lungs revealed no evidence of significant NO toxicity, and the explanted heart was successfully transplanted into another patient. Inhalation of NO via a transtracheal catheter is a useful and practical treatment of refractory pulmonary hypertension. The limits of NO therapy in terms of duration and dosage have not been determined.

Comparison of patient-controlled analgesia and nurse-controlled infusion analgesia after cardiac surgery.

A randomized, controlled clinical trial was conducted on 72 patients undergoing elective cardiac surgery to compare patient-controlled analgesia (PCA) to nurse-titrated infusion of morphine. Pain and nausea scores were assessed at 5, 20, 32 and 44 hours after cardiopulmonary bypass. Serum cortisol estimations were performed at 24 and 48 hours, and morphine consumption was measured at 0-24 and 24-48 hours. There was no difference between pain scores (P = 0.72), nausea scores (P = 0.52), serum cortisol at 24 and 48 hours (P = 0.32 and P = 0.34), and morphine consumption at 0-24 and 24-48 hours (P = 0.16 and P = 0.12). There was also no difference in the time to tracheal extubation (P = 0.79) and discharge from ICU (P = 0.64). There was a significant association between pain and serum cortisol at 48 hours (P = 0.023). This study also found a tenfold difference in the amount of morphine used (range = 11 to 108 mg), with no significant association with patient age or sex. We could find no significant benefit from the routine use of PCA in cardiac surgical patients.

A comparison of amiodarone and digoxin for treatment of supraventricular arrhythmias after cardiac surgery.

Despite the widespread use of amiodarone in non-surgical patients, its role in the management of supraventricular tachyarrhythmias after cardiac surgery is not clear. We set out to compare the relative efficacy of amiodarone and digoxin in the management of atrial fibrillation and flutter in the early postoperative period. This prospective randomised trial comprised 30 patients, previously in sinus rhythm, who developed sustained atrial fibrillation or flutter following myocardial revascularisation, valve surgery or combined procedures. Amiodarone was administered as an intravenous loading dose followed by a continuous infusion. Digoxin was given as an intravenous loading dose followed by oral maintenance therapy. Electrocardiographic and haemodynamic monitoring was continued for 24 h after the commencement of treatment. There was a marked reduction in heart rate in both groups, mainly in the first 6 h, from 146 to 89 beats per minute in the amiodarone group and from 144 to 95 in the digoxin group. At the end of the 24 h, one of the 15 patients in the amiodarone group and 3 of the 15 patients in the digoxin group remained in atrial fibrillation. No patient in either group developed adverse reactions. We conclude that intravenous amiodarone therapy is safe and at least as effective as digoxin in the initial management of arrhythmias after cardiac surgery.

Effectiveness of nursing involvement in bedside monitoring and control of coagulation status after cardiac surgery.

OBJECTIVE: This study explores: (1) the feasibility of involvement of nursing staff in routine bedside testing of activated clotting time and (2) joint implementation with resident medical staff of a preformulated plan for management of mediastinal bleeding after cardiac surgery. DESIGN: Patients were divided randomly into two groups, an experimental group (n = 108) subjected to ACT testing and management by protocol, and a control group (n = 146) treated by independent medical decisions. RESULTS: Bleeding, volume of blood replaced, abnormal coagulation profiles and reoperations to control bleeding and its consequences were all reduced in the study group. CONCLUSION: We concluded that bedside measurement of activated clotting time by nursing staff, associated with therapy based on a flow diagram, enhanced the overall management of early mediastinal bleeding after cardiac surgery as compared with independent management decisions by resident medical staff. In addition, the method provided a sensitive and reliable means of detecting and correcting rebound heparinization in the early postoperative period.

Initial clinical experience with the Haemopump left ventricular assist device.

The Haemopump is an intra-arterial, axial flow, temporary left ventricular assist device. The intra-cardiac pump assembly is connected by a flexible drive shaft to a high speed motor and a drive console. The pump is placed in the left ventricle via the femoral artery, iliac artery or abdominal aorta. Blood is withdrawn from the left ventricle and pumped in a continuous, non-pulsatile fashion into the descending thoracic aorta. We report the use of the Haemopump to provide circulatory assistance in 2 patients with severe graft dysfunction following cardiac transplantation. Both patients were successfully weaned from the Haemopump after 6 and 3 days of support. The first patient subsequently died of overwhelming fungal sepsis and the other remains well 3 months after transplantation with normal left ventricular function. The Haemopump is an effective temporary cardiac assist device for application in severe left ventricular failure.

Adaptation of the quadrupole mass spectrometer to multipatient anaesthesia gas monitoring.

A series of modifications designed to increase the suitability of the quadrupole mass spectrometer for multipatient gas monitoring in the operating suite are presented and evaluated. The adaptations include a pressure-stabilised long capillary inlet system and computer control of the quadrupole filter together with tuning, calibration and subsequent multitheatre analysis and display of clinical information. A pilot study of three months clinical monitoring provided documentation of contributions towards the safety and effectiveness of anaesthesia. These included indication of equipment malfunction, and fluctuations in gas exchange associated with inappropriate ventilation, haemodynamic instability and variations in body temperature. Limited accuracy for carbon dioxide and a low signal-to-noise ratio together with rapid ageing of electron multipliers were identified as problems still only partially solved.

Inhalation of carbon dioxide mixtures for sensorineural deafness. Evaluation of a rebreathing method.

A laboratory study in 11 healthy subjects was conducted to evaluate the performance of a rebreathing device as a means of raising the effective carbon dioxide level in the inspiratory mixture. In all subjects, there was a sustained rise in end-tidal carbon dioxide levels and a transient rise in end-tidal nitrogen tensions associated with an equivalent fall in end-tidal oxygen levels. Although the rise in end-tidal carbon dioxide tensions was variable, the mean elevation for the 11 subjects (from 36 to 43 mm Hg) was not equivalent to elevations reported to follow inhalation of 5% carbon dioxide mixtures. Nevertheless, the volume of the device was sufficient to cause a marked depression of the end-tidal oxygen level (to 67 mm Hg) in one subject. Despite the simplicity and cost-effectiveness of the rebreathing method, it cannot be recommended in the treatment of sudden or fluctuant sensorineural deafness.

Remote monitoring by mass spectrometry during anaesthesia. Evaluation of a suitable inlet system.

We describe a three-stage mass spectrometer inlet system suitable for use in operating theatres and evidence of its performance in delay and response times to step changes in oxygen and halothane concentrations. At 55 m and a sampled gas flow of 100mlmin-1, the inlet imposed a delay of 21s and prolonged the 10-90% response to 310ms for oxygen and 510ms for halothane. A linear relationship between inlet length and 10-90% response time at constant sampled gas flow was demonstrated for halothane but not for oxygen. Our results compared with those of other workers support the chosen compromise between practical flexibility and convenience versus maximum speed of response that was adopted in this system design.

An anaesthetic circuit to improve patient monitoring by gas analysis.

This circuit is designed to maximise the range of respiratory variables that can be monitored by a mass spectrometer either alone, or preferably in association with blood gas analysis. In particular, it permits monitoring of respiratory dead space, lung shunt, ventilation, and gas exchange, as well as inspired and end-expired gas concentrations. Laboratory and clinical data indicate satisfactory performance of the circuit both clinically and analytically. The circuit is most suitable for controlled ventilation where, by operating as a "minute volume divider", it confers stability of minute volume on the manual ventilation technique.