Left ventricular diastolic function during short-term positive end-expiratory pressure ventilation in dogs

Simultaneous recordings of left ventricular (LV) pressure and volume (sonomicrometry) were made in acutely instrumented dogs anaesthetized with pentobarbital during intermittent positive pressure ventilation with zero and positive end-expiratory pressure at 10 and 20 cmH2O (PEEP10 and PEEP20). Pericardial pressure was measured continuously in order to obtain transmural LV pressure. PEEP reduced LV end-diastolic volume and transmural pressure significantly. This was accompanied by significantly reduced stroke volume. LV peak diastolic filling rate, calculated as dV/dtmax, was significantly reduced when PEEP was applied, independent of LV volume alterations. LV diastolic compliance, assessed by the slope of LV pressure-volume relationship during LV filling, decreased significantly with increasing PEEP levels. A positive correlation was observed between reductions in peak diastolic filling rate and reductions in end-diastolic volume. The reduced peak diastolic filling rate, on the other hand, was closely correlated to reduced LV diastolic compliance. Isovolumetric relaxation rate (T) increased slightly at the highest PEEP level. This could, however, not be related to a reduced LV diastolic filling rate. The close association between reduced LV diastolic compliance and reduced diastolic filling rate may indicate that a tamponade-like effect is involved in the reduction of LV preload observed during PEEP ventilation.     

Hemodynamic changes during laparoscopy with positive end–expiratory pressure ventilation

Hemodynamic measurements were performed in 10 healthy women undergoing elective laparoscopy for the investigation of infertility. A standardized anesthetic technique which included the application of positive end-expiratory pressure (PEEP), 0.49 kPa (3.7 mmHg) was utilized. The following variables were studied: cardiac output, stroke volume and left ventricular ejection time (determined non-invasively with impedance cardiography), heart rate, blood pressure, total peripheral vascular resistance and end-tidal carbon dioxide (ET-CO2). The combination of 25 degrees head-down tilt and PEEP ventilation during laparoscopy was associated with a pressure response that restored arterial pressures to essentially pre-anesthetic levels. Net cardiac effects were small. With this regime low pressure 0.7-1.1 kPa (5-8 mmHg) intra-abdominal insufflation with CO2 was associated with only minor cardiovascular changes. There were no indications that 0.49 kPa PEEP during laparoscopy produced adverse cardiovascular effects. The application of PEEP reduced (P less than 0.001) ET-CO2. There was no net increase in ET-CO2 after CO2-insufflation compared to the measurement after induction of anesthesia. This is in contrast to earlier studies without PEEP where a significant net increase in ET-CO2 was reported after CO2-insufflation.     

Xenon alters right ventricular function

Background: In contrast to other volatile anesthetics, xenon produces less cardiovascular depression with fewer fluctuations of various hemodynamic parameters, but reduces cardiac output (CO) in vivo . Besides an increase in left ventricular afterload and reduction of heart rate, an impairment of the right ventricular function might be an additional pathophysiological mechanism for the reduction of CO. Therefore, we used an animal model to study the effects of xenon as a supplemental anesthetic on right ventricular function, especially right ventricular afterload.
Methods: Right ventricular function was monitored with a volumetric pulmonary artery catheter in 11 pigs during general anesthesia with thiopental. Six animals received additional 70% (volume) xenon (equivalent to 0.55 MAC minimum alveolar concentration). Parameters for systolic function, afterload, and preload were calculated at baseline and during 50 min of xenon application, and in a corresponding control group. Significant differences were detected by multivariate analyses of variance for repeated measures.
Results: Xenon reduced CO on average by 30% and increased pulmonary arterial elastance by 60%, which led to a reduction of the right ventricular ejection fraction by 25%. Whereas right ventricular preload remained stable, maximal slope of pulmonary artery pressure and the right ventricular elastance increased. No effect on the ratio of stroke work and end-diastolic volume was found.
Conclusion: The reduction in CO during xenon anesthesia was partly due to an impairment of the right ventricular function, mainly caused by an increased afterload, without an impairment of systolic ventricular function.     

The open lung concept: effects on right ventricular afterload after cardiac surgery

Background. The open lung concept (OLC) is a method of ventilationintended to maintain end-expiratory lung volume by increasedairway pressure. Since this could increase right ventricularafterload, we studied the effect of this method on right ventricularafterload in patients after cardiac surgery. Methods. We studied 24 stable patients after coronary arterysurgery and/or valve surgery with cardiopulmonary bypass. Patientswere randomly assigned to OLC or conventional mechanical ventilation(CMV). In the OLC group, recruitment manoeuvres were applieduntil was greater than 50 kPa (reflecting an open lung). This value was maintained by sufficient positiveairway pressure. In the CMV group, volume-controlled ventilationwas used with a PEEP of 5 cm H₂O. Cardiac index, right ventricularpreload, contractility and afterload were measured with a pulmonaryartery thermodilution catheter during the 3-h observation period.Blood gases were monitored continuously. Results. To achieve > 50 kPa, 5.3 (3) (mean, SD) recruitment attempts were performed with a peak pressureof 45.5 (2) cm H₂O. To keep the lung open, PEEP of 17.0 (3)cm H₂O was required. Compared with baseline, pulmonary vascularresistance and right ventricular ejection fraction did not changesignificantly during the observation period in either group. Conclusion. No evidence was found that ventilation accordingto the OLC affects right ventricular afterload.     

Maintained cardiac output during positive end-expiratory pressure ventilation in open-chest pigs

Background: Does ventilation with positive end-expiratory pressure (PEEP) act to reduce cardiac output (CO) not only by impeding venous return but also by inducing myocardial depression? The present study was aimed to demonstrate the possible existence of this latter mechanism. Methods: Eight pigs of Swedish native breed weighing 20–25 kg and 10–12 weeks old were anaesthetized, tracheotomized and connected to a volume-controlled ventilator. To prevent intra-thoracic pressure from interfering with venous return, the heart and juxtacardiac vessels were exposed to atmospheric pressure by opening and retracting the chest and pericardium. Heart rate (HR), CO, stroke volume (SV), mean arterial (MAP), mean right (MRAP) and left (MLAP) atrial pressures were recorded before and after retransfusion of 500 ml of autologous blood. This procedure was carried out twice in each animal - during ventilation with zero and with 15 cm H₂O of PEEP. Results: Comparison of the two ventilation modes before volume load revealed negligible differences in HR, CO, SV, MAP, MRAP and MLAP. Moreover, the changes evoked by volume load were practically identical. Conclusions: Addition of PEEP to regular positive pressure ventilation does not induce any haemodynamically detectable myocardial depression in the piglet.     

Myocardial cooling and right ventricular function in patients with right coronary artery disease: antegrade vs. retrograde cardioplegia

Background: Protection of the right ventricular (RV) myocardium during ischaemia in cardiac surgery is difficult, especially in patients with severe right coronary artery (RCA) disease. Retrograde coronary sinus cardioplegia is thought to distribute uniformly, but doubts still remain as to its adequacy in RV preservation. This study evaluated distribution of antegrade vs. exclusively retrograde coronary sinus cold blood cardioplegia by assessing myocardial cooling and compared the effects on RV function. Methods: Fifty-eight patients scheduled for elective coronary artery surgery - 29 patients with significant RCA disease and another 29 with no significant RCA stenosis (controls) - were randomised to receive either antegrade or retrograde cold blood cardioplegia through either aortic root or conventional self-inflating coronary sinus catheter (RCA-ante, RCA-retro, C-ante and C-retro groups). RV function was assessed by fast-response thermodilution. Myocardial temperatures were measured in the anterior and posterior wall of the right and left ventricle. Results: Cooling of the posterior wall of the RV was effective only in the control patients given antegrade cardioplegia (14.7°C), whereas in the other groups the lowest myocardial temperatures there remained above 20°C (RO.001). In patients with obstructed RCA both antegrade and retrograde cold cardioplegia led to uneven cooling of the myocardium. After cardiopulmonary bypass the RV ejection fraction (RVEF), RV stroke work index (RVSWI) and cardiac index (CI) were significantly reduced in the RCA-retro group, and RVSWI and CI in the C-retro group, too. Regression analysis showed an inverse relationship between the temperatures of the posterior walls of the ventricles and changes in the RVEF and CI. Conclusions: Retrograde and antegrade cardioplegia alone were not effective in reducing the temperature of the posterior wall of the RV in the patients with obstructed RCA, in whom with retrograde cardioplegia RV haemodynamics were impaired for 1 hour following bypass. Neither retrograde nor antegrade cardioplegia alone can be relied on to protect the posterior wall of the RV in the patients with obstructed RCA.     

Plasma concentrations of atrial natriuretic factor during positive end-expiratory pressure ventilation in dogs with normal or impaired left ventricular function

The influence of positive end-expiratory pressure (PEEP) ventilation on plasma concentrations of atrial natriuretic factor (ANF) was studied in dogs anesthetized with sodium pentobarbital during normal cardiac function and during acutely impaired left ventricular function. Left ventricular impairment was induced by injecting repeated doses of polystyrene microspheres with a diameter of 50 microns into the main left coronary artery, causing a severe depression of left ventricular performance. This was accompanied by doubling of ANF concentrations measured in blood sampled from aorta. Application of PEEP (10 cmH2O (0.98 kPa] reduced plasma ANF in dogs both with normal and impaired left ventricular function. The decrease was significantly greater during left ventricular impairment compared to control, 31 and 19%, respectively. A positive correlation was observed between plasma ANF and transmural left ventricular end-diastolic pressure when all data were pooled, but not between ANF and transmural right atrial pressure. This implies that transmural left ventricular end-diastolic and hence transmural left atrial pressure probably is the principal determinant of acute ANF release in this model. Reduced plasma ANF in response to PEEP even during acute left ventricular impairment when ANF release was augmented, was probably due to diminished atrial distension during PEEP ventilation.     

Assessment of ventricular function by thermodilution in controlled ventilation with positive end expiratory pressure

Controlled mechanical ventilation with PEEP can induce important haemodynamic modifications. The aim of this study was to focus on right ventricular function, often altered with that kind of respiratory support. Bed-side assessment of right ventricular function was made possible through thermodilution technique. Eleven patients receiving PEEP from 0 to 15 cmH2O were studied. Right ventricular end-diastolic volume (RVEDV), cardiac output (CO) and right ventricular ejection fraction (RVEF) were obtained for each patient. Increasing PEEP produced the same disturbances in nine patients, i.e. decreased RVEF. Blood volume expansion brought back to normal the haemodynamic values. Two patients had a decrease in CO and RVEF associated with an increase in RVEDV. In one of these two patients, dobutamine corrected the RV dysfunction. Using thermodilution technique, abnormalities of RV preload can be accurately assessed. From these data, the most appropriate treatment can then be chosen.     

间歇正压通气和呼气末正压通气对犬眼内压的影响

目的 探讨间歇正压通气(IPPV)和呼气末正压通气(PEEP)对犬眼内压(10P)的影响.方法 实验犬8只,麻醉后分别监测基础条件下和各种机械通气条件下的IOP、CVP、MAP.结果 实施20 ml/kg和30 ml/kg两种不同潮气量的IPPV时IOP差异无统计学意义.实施10、15、20cm H20三种不同压力值的PEEP时IOP均显著升高(P<0.01).结论 IPPV对IOP影响不大,PEEP可使IOP显著升高.     

Stem cells improve right ventricular functional recovery after acute pressure overload and ischemia reperfusion injury

BACKGROUND: In many clinical scenarios, a relatively untrained right ventricle may be subjected to acute elevations in pulmonary artery and right ventricular pressures. The right and left heart are distinctly different in this regard and there is currently no in vivo model to study right ventricular ischemia in the setting of acute pressure overload. In acute injury, cardiomyocytes produce tumor necrosis factor, which mediates a proinflammatory pathway, eventually leading to myocardial dysfunction. Stem cells have been shown to reduce the production of proinflammatory mediators by the ischemic myocardium and protect the myocardium. Pretreatment with stem cells has been shown to protect the left ventricle. The effect of acute pressure overload to the untrained right ventricle is still not well understood. Furthermore, it is unclear whether pretreatment with stem cells would protect the right ventricle when it is subjected to acute pressure overload and concomitant ischemia reperfusion injury. The purpose of this study was (1) to create a simple model of acute pressure overload for the study of concomitant right ventricular ischemia and reperfusion, and (2) to evaluate the effect of pretreatment with stem cells prior to ischemia reperfusion injury. MATERIALS AND METHODS: Isolated rat hearts were perfused with the modified Langendorff technique with the latex balloon in the right ventricle instead of the left, with a pressure-transduced balloon being used to create an acute elevation in right ventricular pressure before ischemia. In the first of a two-series experiment, there were two experimental groups (N = 8 per group): one with right ventricular balloon end-diastolic pressure (EDP) of 5 mmHg (physiological), and the other with an EDP of 40 mmHg (pathologic). In the second series, the hearts with the higher balloon pressure (EDP 40 mmHg) were divided into two experimental groups (N = 5 per group). The control group was not pretreated. One group was pretreated with human mesenchymal stem cells 5 min immediately prior to ischemia reperfusion injury. Right ventricular developed pressure (RVDP), contractility (+dP/dt), and compliance (-dP/dt) were continuously assessed. Additionally, mesenchymal stem cells (MSCs) in culture were stressed by hypoxia and activation was determined by measuring vascular endothelial growth factor-A (VEGF) and hepatocyte growth factor (HGF) production by enzyme-linked immunosorbent assay. RESULTS: Recovery of RVDP, +dP/dt, and -dP/dt was significantly higher (P < 0.001) in the group with lower EDP compared to the group with the higher EDP [RVDP: 79.53 +/- 6.34 versus 54.28 +/- 10.76%; +dP/dt: 76.54 +/- 8.79 versus 38.75 +/- 19.74%; -dP/dt: 72.29 +/- 7.02 versus 30.54 +/- 12.44%]. In the higher EDP groups, pretreatment with human mesenchymal stem cells significantly improved myocardial function recovery (P < 0.01) when compared to controls [RVDP: 75.76 +/- 7.97 versus 59.10 +/- 11.18%; +dP/dt: 71.78 +/- 10.36 versus 54.93 +/- 12.64%; -dP/dt: 77.38 +/- 11.09 versus 59.30 +/- 15.20%]. Further, hypoxic MSCs demonstrated significantly greater VEGF and HGF release than controls. CONCLUSION: This compounded injury model allowed the study of right ventricular dysfunction in the setting of acute pressure overload and ischemia. Additionally, we have also demonstrated that pretreatment with stem cells of an acutely pressure overloaded right ventricle prior to ischemia reperfusion injury improves functional recovery. This is the first report of a modified Langendorff technique to study right ventricular function in the setting of acute pressure overload and ischemia and the effect of pretreatment with stem cells.     

Effect of controlled mechanical ventilation without positive end-expiratory pressure on right ventricular function after coronary artery bypass graft surgery

To evaluate the changes in right ventricular function during controlled mechanical ventilation (CMV) without positive end-expiratory pressure (PEEP) and during spontaneous breathing, we compared right ventricular ejection fraction (RVEF), right ventricular end-diastolic volume index (RVEDVI), and right ventricular end-systolic volume index (RVEDVI) using a thermodilution technique after coronary artery bypass graft surgery. Patients were divided into two groups on the basis of changes in RVEDVI from CMV to spontaneous breathing: group U (n = 6) consisted of patients whose RVEDVI increased during spontaneous breathing compared with mechanical ventilation, group D (n = 3) consisted of patients whose RVEDVI decreased during spontaneous breathing compared with mechanical ventilation. PVRI values during CMV in group D were significantly larger than those in group U. Patients in group U showed no increase in RVEDVI, or decrease in RVEF during CMV without PEEP. However, the remaining 3 patients in group D showed an increase in RVEDVI and a decrease in RVEF during CMV. Mean PAP, RAP, RV systolic pressure, RV end-diastolic pressure, PWP, HR, and mean arterial pressure in both groups were comparable, and showed no significant difference at each of the measured points by 24hrs postoperatively. Then, RVEF, RVEDVI and RVESVI measured by thermodilution technique is useful in evaluating ventricular function at bedside in ICU.(Mitsuhata H, Enzan K, Matsumoto S, et al.: Effect of controlled mechanical ventilation without positive end-expiratory pressure on right ventricular function after coronary artery bypass graft surgery. J Anesth 5: 363–369, 1991)     

Clinical application of differential ventilation with selective positive end-expiratory pressure in adult respiratory distress syndrome

Differential ventilation in the lateral position with positive end-expiratory pressure (PEEP) selectively applied to the dependent lung (DVSP) has been shown to reduce venous admixture and improve oxygenation without compromizing cardiac output in short term studies of patients with acute respiratory failure. We have applied this ventilation technique as a long-term treatment in severe adult respiratory distress syndrome (ARDS) in an open clinical trial. Eleven patients with ARDS of varying aetiology were treated with DVSP for a total of 34 days.
Median duration of conventional ventilatory therapy before start of DVSP was 5 days (1 to 18 days), inspiratory oxygen fraction (F₁***₂) was 0.61 ±0.16 (mean±s.d.), resulting in a mean arterial oxygen tension (Pao₂) of 7.1±2.1 kPa (Pao₂/F₁o₂= 11 ± 4 kPa). A gradual improvement in gas exchange was seen during the first 24 h of DVSP such that Pao₂ increased to 8.4±1.4 with a decreased F₁o₂ (0.52±0.14) resulting in an increased Pao₂/F₁o₂ (16±5 kPa). Five out of the eleven patients survived. No major complication was noted using DVSP as a method. We found a steady improvement in gas exchange over the first 24 hours in most patients. However, mortality rate was no lower than expected. Drawbacks with DVSP were increased demand on staff and difficulties with adequate endo-bronchial suctioning.     

The use of intraoperative bedside lung ultrasound in optimizing positive end expiratory pressure in obese patients undergoing laparoscopic bariatric surgeries

BackgroundAnesthetic management of patients with obesity undergoing laparoscopic abdominal surgeries requires careful plan for intraoperative mechanical ventilation aiming to avoid lung atelectasis and/or overdistention. There are conflicting data on the optimum positive end expiratory pressure (PEEP) during these surgeries. We hypothesized that lung ultrasound could be used for PEEP titration during laparoscopic surgery.ObjectiveThe purpose of this study is to evaluate the effectiveness of intraoperative individualized lung ultrasound-guided PEEP in obese patients undergoing laparoscopic bariatric surgery on intraoperative partial arterial oxygen tension (PaO₂) and early postoperative pulmonary complications.MethodsA randomized controlled trial included 40 adult patients with body mass index (BMI) > 35 kg/m² undergoing laparoscopic bariatric surgery. Patients were randomized into: control group (n = 20) who received PEEP 4 cm.H₂ O and ultrasound-guided group (n = 20) who received individualized lung ultrasound stepwise PEEP. All patients received volume-controlled ventilation with a tidal volume of 6 mL/kg of ideal weight and a fraction of inspired oxygen of .5.The primary outcome was the difference in partial arterial oxygen tension (PaO₂) between the control group and the ultrasound-guided group. The secondary outcomes included the incidence of early postoperative pulmonary atelectasis, respiratory failure, bronchospasm, hypoxia or pneumothorax.SettingsGeneral surgery operating theatre at Cairo University hospitals.ResultsUltrasound-guided group showed higher PO₂ after PEEP optimization and postoperatively compared with control group (P = .005, and P = .01 respectively). Also, ultrasound-guided group showed no postoperative complications compared with control group that had 5 cases who developed postoperative pulmonary complications in the form of hypoxia and basal collapse in the first 24 hour postoperatively chest x ray (0% versus 25%, P = .047).ConclusionIn patients with obesity undergoing laparoscopic bariatric surgery, the use of lung ultrasound individualized stepwise PEEP approach improved oxygenation, compliance and reduced the incidence of postoperative pulmonary atelectasis and hypoxia without causing hemodynamic instability.