Multicenter Randomized Comparison of Xenon and Isoflurane on Left Ventricular Function in Patients Undergoing Elective Surgery

Background: Volatile anesthetics are commonly used for general anesthesia. However, these can induce profound cardiovascular alterations. Xenon is a noble gas with potent anesthetic and analgesic properties. However, it is uncertain whether xenon alters myocardial function. The aim of this study was therefore to investigate left ventricular function during anesthesia with xenon compared with isoflurane.

Methods: The authors performed a randomized multicenter trial to compare xenon with isoflurane with respect to cardiovascular stability and adverse effects in patients without cardiac diseases scheduled for elective surgery. Two hundred fifty-nine patients were enrolled in this trial, of which 252 completed the study according to the protocol. Patients were anesthetized with xenon or isoflurane, respectively. Before administration of the study drugs and at four time points, the effects of both anesthetics on left ventricular function were investigated using transesophageal echocardiography.

Results: Global hemodynamic parameters were significantly altered using isoflurane (P < 0.05 vs. baseline), whereas xenon only decreased heart rate (P < 0.05 vs. baseline). In contrast to xenon, left ventricular end-systolic wall stress decreased significantly in the isoflurane group (P < 0.05 vs. baseline). Velocity of circumferential fiber shortening was decreased significantly in the xenon group but showed a more pronounced reduction during isoflurane administration (P < 0.05 vs. baseline). The contractile index (difference between expected and actually measured velocity of circumferential fiber shortening) as an independent parameter for left ventricular function was significantly decreased after isoflurane (P < 0.0001) but unchanged using xenon.     

ASO Author Reflections: Impact of Preoperative MRI on Patients With Screen-Detected Invasive Breast Cancer Undergoing Breast-Conserving Surgery

Annals of Surgical Oncology -     

Antidiuretic hormone release during laparoscopic donor nephrectomy

BACKGROUND: During laparoscopic procedures, increased intra-abdominal pressure may cause transient renal dysfunction due to impaired renal blood flow and induction of neurohormones. However, the relationship between antidiuretic hormone (ADH) secretion and increased intra-abdominal pressure is poorly understood. HYPOTHESIS: Laparoscopic donor nephrectomy (LDN) is associated with an increase in plasma ADH concentration, which influences renal function in both the donor and transplanted graft. OBJECTIVES: To evaluate plasma ADH levels during LDN and to correlate ADH levels with graft function. DESIGN AND INTERVENTIONS: In 30 patients who underwent LDN, plasma ADH levels were collected before insufflation, during surgery, after desufflation, and 24 hours after the procedure. In 6 patients who had open donor nephrectomy, blood samples were obtained as controls. Furthermore, graft function, operative characteristics, and clinical outcome were compared. SETTING: University hospital. RESULTS: In the LDN group, mean ADH levels during pneumoperitoneum and 30 minutes postinsufflation were significantly higher compared with preinsufflation values (P<.001). Twenty-four hours after LDN, mean ADH levels had returned to normal values. There were no significant differences in ADH levels in the open donor nephrectomy group. No significant differences in either intraoperative diuresis, blood pressure readings, or postoperative graft function were documented among the 2 groups. CONCLUSIONS: In this study, LDN was associated with an increase in plasma ADH that appeared to be related to increased intra-abdominal pressure. We conclude that the increased ADH concentrations during LDN are not associated with clinically significant changes in either the kidney donor or the transplanted graft.     

Exogenous Surfactant Preserves Lung Function and Reduces Alveolar Evans Blue Dye Influx in a Rat Model of Ventilation-induced Lung Injury

Background: Changes in pulmonary edema infiltration and surfactant after intermittent positive pressure ventilation with high peak inspiratory lung volumes have been well described. To further elucidate the role of surfactant changes, the authors tested the effect of different doses of exogenous surfactant preceding high peak inspiratory lung volumes on lung function and lung permeability.

Methods: Five groups of Sprague-Dawley rats (n = 6 per group) were subjected to 20 min of high peak inspiratory lung volumes. Before high peak inspiratory lung volumes, four of these groups received intratracheal administration of saline or 50, 100, or 200 mg/kg body weight surfactant; one group received no intratracheal administration. Gas exchange was measured during mechanical ventilation. A sixth group served as nontreated, nonventilated controls. After death, all lungs were excised, and static pressure-volume curves and total lung volume at a transpulmonary pressure of 5 cm H2 O were recorded. The Gruenwald index and the steepest part of the compliance curve (Cmax) were calculated. A bronchoalveolar lavage was performed; surfactant small and large aggregate total phosphorus and minimal surface tension were measured. In a second experiment in five groups of rats (n = 6 per group), lung permeability for Evans blue dye was measured. Before 20 min of high peak inspiratory lung volumes, three groups received intratracheal administration of 100, 200, or 400 mg/kg body weight surfactant; one group received no intratracheal administration. A fifth group served as nontreated, nonventilated controls.

Results: Exogenous surfactant at a dose of 200 mg/kg preserved total lung volume at a pressure of 5 cm H2 O, maximum compliance, the Gruenwald Index, and oxygenation after 20 min of mechanical ventilation. The most active surfactant was recovered in the group that received 200 mg/kg surfactant, and this dose reduced minimal surface tension of bronchoalveolar lavage to control values. Alveolar influx of Evans blue dye was reduced in the groups that received 200 and 400 mg/kg exogenous surfactant.     

At surfactant deficiency, application of "the open lung concept" prevents protein leakage and attenuates changes in lung mechanics

OBJECTIVE: To evaluate whether mechanical ventilation using "the open lung concept" during surfactant depletion can attenuate the deterioration in pulmonary function. DESIGN: Experimental, comparative study. SETTING: Research laboratory of a large university. SUBJECTS: Eighteen adult male Sprague-Dawley rats, weighing 280-340 g. INTERVENTIONS: Twelve rats were anesthetized, mechanically ventilated with 100% oxygen, and randomly divided into two groups (n = 6 each). The open lung group underwent six saline lavages at different ventilator settings that prevented alveolar collapse. The settings (expressed as frequency/peak inspiratory pressure/positive end-expiratory pressure/inspiratory:expiratory ratio) were 30/26/6/1:2 during the first lavage, 100/27/10/1:1 during the next two lavages, and 100/33/15/1:1 during the last three lavages and during the remaining ventilation period. The ventilated control group underwent six saline lavages with settings at 30/26/6/1:2. After the lavages, peak inspiratory pressure and positive end-expiratory pressure were increased in this group by 2 cm H2O each for the remaining study period. An additional group of six animals were killed immediately after induction of anesthesia and served as healthy controls. Blood gases were measured before lavage, immediately after the last lavage, and thereafter hourly. At the end of the 4-hr study period, we constructed pressure-volume curves from which we determined total lung capacity at a distending pressure of 35 cm H2O (TLC35). Subsequently, total lung volume at a distending pressure of 5 cm H2O (V5) was determined, followed by bronchoalveolar lavage. RESULTS: In the ventilated control group, PaO2, V5, and TLC35 were significantly decreased and protein concentration of bronchoalveolar lavage was significantly increased compared with the healthy control group. In the open lung group, PaO2 did not decrease after the lavage procedure, and V5, TLC35, and the protein concentration of bronchoalveolar lavage were comparable with the healthy controls. CONCLUSION: We conclude that application of the open lung concept during surfactant depletion attenuates deterioration in pulmonary function.     

Medications for analgesia and sedation in the intensive care unit: an overview

Critically ill patients are often treated with continuous intravenous infusions of sedative drugs. However, this is associated with high risk for over-sedation, which can result in prolonged stay in the intensive care unit. Recently introduced protocols (daily interruption and analgosedation) have proven to reduce the length of intensive care unit stay. To introduce these protocols, new agents or new regimens with the well established agents may be required. In this article we briefly discuss these new regimens and new agents, focusing on the short-acting substances.     

End-expiratory lung volume during mechanical ventilation: a comparison with reference values and the effect of positive end-expiratory pressure in intensive care unit patients with different lung conditions

Introduction

Functional residual capacity (FRC) reference values are obtained from spontaneous breathing patients, and are measured in the sitting or standing position. During mechanical ventilation FRC is determined by the level of positive end-expiratory pressure (PEEP), and it is therefore better to speak of end-expiratory lung volume. Application of higher levels of PEEP leads to increased end-expiratory lung volume as a result of recruitment or further distention of already ventilated alveoli. The aim of this study was to measure end-expiratory lung volume in mechanically ventilated intensive care unit (ICU) patients with different types of lung pathology at different PEEP levels, and to compare them with predicted sitting FRC values, arterial oxygenation, and compliance values.

Methods

End-expiratory lung volume measurements were performed at PEEP levels reduced sequentially (15, 10 and then 5 cmH₂O) in 45 mechanically ventilated patients divided into three groups according to pulmonary condition: normal lungs (group N), primary lung disorder (group P), and secondary lung disorder (group S).

Results

In all three groups, end-expiratory lung volume decreased significantly (P < 0.001) while PEEP decreased from 15 to 5 cmH₂O, whereas the ratio of arterial oxygen tension to inspired oxygen fraction did not change. At 5 cmH₂O PEEP, end-expiratory lung volume was 31, 20, and 17 ml/kg predicted body weight in groups N, P, and S, respectively. These measured values were only 66%, 42%, and 34% of the predicted sitting FRC. A correlation between change in end-expiratory lung volume and change in dynamic compliance was found in group S (P < 0.001; R ² = 0.52), but not in the other groups.

Conclusions

End-expiratory lung volume measured at 5 cmH₂O PEEP was markedly lower than predicted sitting FRC values in all groups. Only in patients with secondary lung disorders were PEEP-induced changes in end-expiratory lung volume the result of derecruitment. In combination with compliance, end-expiratory lung volume can provide additional information to optimize the ventilator settings.