Doppler evaluation of right ventricular outflow impedance during positive-pressure ventilation

The effect of positive-end-expiratory pressure on stroke volume variation: An experimental study in dogs

Stroke volume variation (SVV) may be affected by ventilation settings. However, it is unclear whether positive-end-expiratory pressure (PEEP) affects SVV independently of the effect of driving pressure. We aimed to investigate the effect of driving pressure and PEEP on SVV under various preload conditions using beagle dogs as the animal model. We prepared three preload model, baseline, mild and moderate haemorrhage model. Mild and moderate haemorrhage models were created in nine anaesthetized, mechanically ventilated dogs by sequentially removing 10 mL/kg, and then an additional 10 mL/kg of blood, respectively. We measured cardiac output, stroke volume (SV), SVV, heart rate, central venous pressure, pulmonary capillary wedge pressure and the mean arterial pressure under varying ventilation settings. Peak inspiratory pressure (PIP) was incrementally increased by 4 cmH₂ O, from 9 cmH₂ O to 21 cmH₂ O, under PEEP values of 4, 8, and 12 cmH₂ O. The driving pressure did not significantly decrease SV under each preload condition and PEEP; however, significantly increased SVV. In contrast, the increased PEEP decreased SV and increased SVV under each preload condition and driving pressure, but these associations were not statistically significant. According to multiple regression analysis, an increase in PEEP and decrease in preload significantly decreased SV (P < .05). In addition, an increase in the driving pressure and decrease in preload significantly increased SVV (P < .05). Driving pressure had more influence than PEEP on SVV.

Hemodynamic Effects of Noninvasive Positive-Pressure Ventilation Assessed Using Transthoracic Echocardiography

Aims:

The aim of this study is to measure the effect of positive-pressure ventilation on heart chamber dimensions, left ventricular (LV) systolic function, LV diastolic function, right ventricular (RV) systolic function, and RV pressure using transthoracic echocardiography.

Settings and Design:

This is a prospective study in a single secondary health-care center.

Materials and Methods:

A total of 107 patients with obstructive sleep apnea on continuous positive airway pressure (CPAP) therapy were recruited as participants between April and September 2016. Transthoracic echocardiography was performed twice on each participant, before and 15 min after, they used their own CPAP machines, and the echocardiography parameters of both scans were compared.

Statistical Analysis Used:

The parametric paired t-test was used to compare heart chamber dimensions, left heart diastolic function, left heart systolic function, right heart systolic function, and right heart pressure effect, without and with CPAP. These data were further examined among several subgroups defined by CPAP when the cutoff point was set at 8 cmH₂O and 10 cmH₂O. The level of significance was set at 0.05. Statistical analyses were performed using IBM SPSS version 22 (IBM, Armonk, NY, USA).

Results:

There were statistically significant reductions, after the application of CPAP, in the heart dimensions, and LV and RV systolic function. There were no significant changes in diastolic function. Concerning right heart pressure, with CPAP, there was a significant increase in the inferior vena cava (IVC) diameter and there was also a significant decrease in IVC variability from 44.56% ± 14.86% to 36.12% ± 11.42%. The maximum velocity of tricuspid regurgitation (TR) decreased significantly from 180.66 ± 6.95 cm/s to 142.30 ± 52.73 cm/s. Such changes were observed in both low and high CPAP subgroups.

Conclusions:

When placed on positive pressure, the clinically significant change in IVC diameter and variability and change in trans-TR velocity mean that it would be inaccurate to predict right heart chamber pressure through echocardiogram. Alternative methods for predicting right heart pressure are recommended.

Multiparameter Predictor of Fluid Responsiveness in Cardiac Surgical Patients Receiving Tidal Volumes Less Than 10 mL/kg

Introduction We hypothesize that respiratory variation in the pulmonary artery tracing predicts fluid responsiveness (primary hypothesis) and that inclusion of multiple physiologic waveforms as well as ventilator settings in a predictive model of fluid responsiveness would lead to improvements in the clinical utility of this class of metrics (secondary hypothesis). Methods Blood pressure tracings were prospectively recorded in 35 patients immediately following cardiac surgery. Fluid bolus administration data, ventilator settings, and cardiac output were recorded prospectively before and after fluid boluses given at the discretion of the treating physician. Results We observed statistically significant but limited relationships between pulmonic (r(2) = .26, P = .0052) and systemic (r(2) = .13, P = .011) pulse pressure variation and changes in cardiac index. A multiparameter estimate of fluid responsiveness, which included respiratory variation in central venous pressure and pulmonary artery pressure, indexed tidal volumes, positive end-expiratory pressure, and mean airway pressure, was also correlated with change in cardiac index (r(2) = .42, P = .0056). Using the area under the curve (AUC) technique to compare specificity and sensitivity, dynamic indicators (AUC = 0.74, 0.67, and 0.81 for systemic arterial respiratory [pulse pressure] variation, pulmonic arterial respiratory [pulse pressure] variation, and the multiparameter estimate, respectively) outperformed static estimates (0.49 and 0.48 for central venous pressure and pulmonary artery diastolic pressure, respectively). Conclusion While integration of multiple physiologic waveforms as well as ventilator parameters improves the predictability of fluid responsive metrics in the setting of lung-protective ventilation, the composite index may still be of limited predictive value.

The impact of inspiratory pressure on stroke volume variation and the evaluation of indexing stroke volume variation to inspiratory pressure under various preload conditions in experimental animals

PURPOSE

Stroke volume variation (SVV) measures fluid responsiveness, enabling optimal fluid management under positive pressure ventilation. We aimed to investigate the effect of peak inspiratory pressure (PIP) on SVV under various preload conditions in experimental animals and to ascertain whether SVV indexed to PIP decreases the effect.

METHODS

Mild and moderate hemorrhage models were created in nine anesthetized, mechanically ventilated beagle dogs by sequentially removing 10 and then an additional 10 ml/kg of blood, respectively. In all the animals, PIP was incrementally increased by 4 cmH2O, from 5 to 21 cmH2O. SVV was measured by arterial pulse contour analysis. Stroke volume was derived using a thermodilution method, and central venous pressure and mean arterial pressure were also measured.

RESULTS

SVV increased according to PIP with significant correlation at baseline, with mild hemorrhage and moderate hemorrhage. PIP regression coefficients at baseline and in the mild and moderate hemorrhage models were 0.59, 0.86, and 1.4, respectively. Two-way repeated-measures analysis of variance showed that PIP and the degree of hemorrhage had a significant interaction effect on SVV (p = 0.0016). SVV indexed to PIP reflected the hemorrhage status regardless of PIP changes ≥9 cmH2O.

CONCLUSIONS

PIP is significantly correlated with SVV, even under hypovolemia, and the effect is enhanced with decreasing preload volumes. Compared with SVV, the indexed SVV was less susceptible to higher inspiratory pressures.

The Effects of Open Lung Ventilation on Respiratory Mechanics and Haemodynamics in Atelectatic Infants after Cardiopulmonary Bypass

Acute lung injury (ALI) frequently occurs in infants after cardiopulmonary bypass (CPB) surgery and it sometimes develops into acute respiratory distress syndrome in critically ill infants, which can be life threatening. This study investigated the effects of open lung ventilation on the haemodynamics and respiratory mechanics of 64 infants (34 males; 30 females) with a mean ± SD age of 8.3 ± 0.3 months who developed ALI following CPB surgery. Open lung ventilation significantly improved the respiratory mechanics and oxygenation parameters of the infants, including the partial pressure of oxygen in arterial blood (PaO2), the ratio of PaO2/FiO2 (fraction of inspired oxygen), peak inspiratory pressure, static compliance and airway resistance. It is concluded that open lung ventilation can greatly improve oxygenation and respiratory mechanics in infants with ALI following CPB surgery.

Lung protective ventilatory strategies in acute lung injury and acute respiratory distress syndrome: from experimental findings to clinical application

This review addresses the physiological background and the current status of evidence regarding ventilator-induced lung injury and lung protective strategies. Lung protective ventilatory strategies have been shown to reduce mortality from adult respiratory distress syndrome (ARDS). We review the latest knowledge on the progression of lung injury by mechanical ventilation and correlate the findings of experimental work with results from clinical studies. We describe the experimental and clinical evidence of the effect of lung protective ventilatory strategies and open lung strategies on the progression of lung injury and current controversies surrounding these subjects. We describe a rational strategy, the open lung strategy, to accomplish an open lung, which may further prevent injury caused by mechanical ventilation. Finally, the clinician is offered directions on lung protective ventilation in the early phase of ARDS which can be applied on the intensive care unit.

Is tissue Doppler echocardiography the Holy Grail for the intensivist?

Assessment of left ventricular diastolic function in the critically ill patient remains a difficult issue in clinical practice. Combined use of routine transmitral and pulmonary venous Doppler patterns in conjunction with tissue Doppler imaging have been claimed to allow bedside diagnosis of diastolic dysfunction. Although in the previous issue of Critical Care it was clearly demonstrated there might be a difference in load dependency of the early myocardial tissue Doppler velocity between lateral and septal placed sample volume, there remain still several unanswered questions, particularly with respect to the preload dependency of these indices.

Open lung ventilation does not increase right ventricular outflow impedance: An echo-Doppler study

OBJECTIVE

Ventilation according to the open lung concept (OLC) consists of recruitment maneuvers, followed by low tidal volume and elevated positive end-expiratory pressure (PEEP). Elevated PEEP is associated with an increased right ventricular afterload. We investigated the effect of OLC ventilation on right ventricular outflow impedance during inspiration and expiration in patients after cardiac surgery using transesophageal echo-Doppler.

DESIGN

A prospective, single-center, crossover, randomized, controlled clinical study.

SETTING

Cardiothoracic intensive care unit of a university hospital.

PATIENTS

Twenty-eight patients scheduled for elective cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

In the intensive care unit, each patient was ventilated for approximately 30 mins according to both OLC and conventional ventilation. During OLC ventilation, recruitment maneuvers were applied until PaO2/FiO2 was >375 torr (50 kPa); during conventional ventilation no recruitment maneuvers were performed.

MEASUREMENTS AND MAIN RESULTS

Transesophageal echo-Doppler measurements were performed at end-inspiration and end-expiration in a steady-state condition, 20 mins after initiation of a ventilation strategy. Mean acceleration of flow was determined in the long axis of the pulmonary artery in a transverse axis view. During OLC ventilation, a total PEEP of 14 +/- 4 cm H2O was applied vs. 5 cm H2O during conventional ventilation. Mean acceleration during expiration was comparable between groups. During inspiration, OLC ventilation did not cause a decrease of mean acceleration compared with expiration, whereas this did occur during conventional ventilation.

CONCLUSIONS

Despite the use of elevated PEEP levels, ventilation according to OLC does not change right ventricular outflow impedance during expiration and decreases right ventricular outflow impedance during inspiration.

The effect of open lung ventilation on right ventricular and left ventricular function in lung-lavaged pigs

INTRODUCTION

Ventilation according to the open lung concept (OLC) consists of recruitment maneuvers, followed by low tidal volume and high positive end-expiratory pressure, aiming at minimizing atelectasis. The minimization of atelectasis reduces the right ventricular (RV) afterload, but the increased intrathoracic pressures used by OLC ventilation could increase the RV afterload. We hypothesize that when atelectasis is minimized by OLC ventilation, cardiac function is not affected despite the higher mean airway pressure.

METHODS

After repeated lung lavage, each pig (n = 10) was conventionally ventilated and was ventilated according to OLC in a randomized cross-over setting. Conventional mechanical ventilation (CMV) consisted of volume-controlled ventilation with 5 cmH2O positive end-expiratory pressure and a tidal volume of 8-10 ml/kg. No recruitment maneuvers were performed. During OLC ventilation, recruitment maneuvers were applied until PaO2/FiO2 > 60 kPa. The peak inspiratory pressure was set to obtain a tidal volume of 6-8 ml/kg. The cardiac output (CO), the RV preload, the contractility and the afterload were measured with a volumetric pulmonary artery catheter. A high-resolution computed tomography scan measured the whole lung density and left ventricular (LV) volumes.

RESULTS

The RV end-systolic pressure-volume relationship, representing RV afterload, during steady-state OLC ventilation (2.7 +/- 1.2 mmHg/ml) was not significantly different compared with CMV (3.6 +/- 2.5 mmHg/ml). Pulmonary vascular resistance (OLC, 137 +/- 49 dynes/s/cm5 versus CMV, 130 +/- 34 dynes/s/cm5) was comparable between groups. OLC led to a significantly lower amount of atelectasis (13 +/- 2% of the lung area) compared with CMV (52 +/- 3% of the lung area). Atelectasis was not correlated with pulmonary vascular resistance or end-systolic pressure-volume relationship. The LV contractility and afterload during OLC was not significantly different compared with CMV. Compared with baseline, the LV end-diastolic volume (66 +/- 4 ml) decreased significantly during OLC (56 +/- 5 ml) ventilation and not during CMV (61 +/- 3 ml). Also, CO was significantly lower during OLC ventilation (OLC, 4.1 +/- 0.3 l/minute versus CMV, 4.9 +/- 0.3 l/minute).

CONCLUSION

In this experimental study, OLC resulted in significantly improved lung aeration. Despite the use of elevated airway pressures, no evidence was found for a negative effect of OLC on RV afterload or LV afterload, which might be associated with a loss of hypoxic pulmonary vasoconstriction due to alveolar recruitment. The reductions in the CO and in the mean pulmonary artery pressure were consequences of a reduced preload.

Why protect the right ventricle in patients with acute respiratory distress syndrome?

Even a slight increase in pulmonary vascular resistance can overload a normal right ventricle, which ejects blood through a low-pressure circuit. In a clinical setting, a persistent increase in pulmonary vascular resistance produces acute cor pulmonale. From an echocardiographic point of view, may be defined as the combination of a paradoxical septal motion, reflecting systolic overload, with right ventricular enlargement, reflecting diastolic overload. In patients with acute respiratory distress syndrome, this complication reflects the severity of the pulmonary disease involving the microvasculature but may also be caused or exacerbated by an aggressive ventilatory strategy. In the past, conventional respiratory support used in acute respiratory distress syndrome to obtain normocapnia was associated with a poor prognosis and a high frequency of acute cor pulmonale, suggesting some relation between the two findings. This prognosis has greatly improved with protective ventilation. At the same time, the incidence of acute cor pulmonale has diminished in acute respiratory distress syndrome, and the prognosis of this specific complication has also improved, suggesting that the right ventricle may develop some adaptation against persistent overload. Past lessons, however, have taught us that this potential may be limited and lead us to recommend right ventricular protection during mechanical ventilation.

Increasing respiratory rate to improve CO2 clearance during mechanical ventilation is not a panacea in acute respiratory failure

BACKGROUND

Increasing respiratory rate has recently been proposed to improve CO2 clearance in patients with acute respiratory failure who are receiving mechanical ventilation. However, the efficacy of this strategy may be limited by deadspace ventilation, and it might induce adverse hemodynamic effects related to dynamic hyperinflation.

SETTING

An intensive care unit of a university hospital.

PATIENTS

We studied 14 patients with acute respiratory failure during the adjustment of ventilator settings on the first day of mechanical ventilation in volume-controlled mode.

MEASUREMENTS

After determining the positive end-expiratory pressure that suppresses any intrinsic positive end-expiratory pressure at a respiratory rate of 15 breaths/min, we compared blood gas analysis, respiratory measurements, and Doppler evaluation of right ventricular systolic function by using two different respiratory strategies with the same airway pressure limitation (plateau pressure, < or =25 cm H2O), a low-rate conventional respiratory strategy with a respiratory rate of 15 breaths/min, and a high-rate strategy with a respiratory rate of 30 breaths/min.

RESULTS

Compared with the low-rate strategy, the high-rate strategy neither significantly reduced PaCO2 (47 +/- 8 vs. 51 +/- 7 mm Hg with the low-rate strategy) nor significantly improved PaO2 (99 +/- 40 vs. 95 +/- 35 mm Hg with the low-rate strategy). It significantly increased alveolar deadspace to tidal volume ratio (21% +/- 8%, vs. 14% +/- 6% with the low-rate strategy) and produced dynamic hyperinflation, resulting in a substantial intrinsic positive end-expiratory pressure (6.4 +/- 2.7 cm H2O). Right ventricular outflow impedance was increased, resulting in a significant drop in the cardiac index (2.9 +/- 0.6 vs. 3.3 +/- 0.7 L/min/m with the low-rate strategy).

CONCLUSION

We conclude that a high respiratory rate strategy during mechanical ventilation in patients with acute respiratory failure did not improve CO2 clearance, produced dynamic hyperinflation, and impaired right ventricular ejection.