Comparison of extravascular lung water volume with radiographic findings in dogs with experimentally increased permeability pulmonary edema

Stroke volume variation (SVV) and pulse pressure variation (PPV) as indicators of fluid responsiveness in sevoflurane anesthetized mechanically ventilated euvolemic dogs

Changes in stroke volume variation (SVV) and pulse pressure variation (PPV) in response to fluid infusion were experimentally evaluated during vecuronium infusion and sevoflurane anesthesia in 5 adult, mechanically ventilated, euvolemic, beagle dogs. Sequential increases in central venous pressure (CVP; 3-7[baseline], 8-12, 13-17, 18-22 and 23-27 mmHg) were produced by infusing lactated Ringer's solution and 6% hydroxyethyl starch solution. Heart rate (beats/min), right atrial pressure (RAP, mmHg), pulmonary arterial pressure (PAP, mmHg), pulmonary capillary wedge pressure (PCWP, mmHg), transpulmonary thermodilution cardiac output (TPTDCO, l/min), stroke volume (SV, ml/beat), arterial blood pressure (ABP, mmHg), extravascular lung water (EVLW, ml), pulmonary vascular permeability index (PVPI, calculated), SVV (%), PPV (%) and systemic vascular resistance (SVR, dynes/sec/cm⁵) were determined at each predetermined CVP range. Heart rate (P=0.019), RAP (P<0.001), PAP (P<0.001), PCWP (P<0.001), TPTDCO (P=0.009) and SV (P=0.04) increased and SVR (P<0.001), SVV (P<0.001) and PPV (P<0.001) decreased associated with each stepwise increase in CVP. Arterial blood pressure, EVLW, PVPI and the arterial partial pressures of oxygen and carbon dioxide did not change. The changes in SVV and PPV directly reflected the fluid load and the minimum threshold values for detecting fluid responsiveness were SVV ≥11% and PPV ≥7% in dogs.

[Minimally invasive cardiopulmonary monitoring with the PiCCO Plus system]

Insertion of a central venous catheter and an arterial catheter would be indicated in hemodynamically unstable or severely hypoxic patients in critical care units. In this setting, cardiorespiratory monitoring by transpulmonary thermodilution (TPTD) can be considered minimally invasive given that only a single arterial thermodilution catheter and a single central venous catheter are required to be connected to a specific monitor (the PiCCO Plus, Pulsion Medical Systems, Munich, Germany). TDTP simultaneously measures cardiac output, preloading, and cardiac function in hemodynamically unstable patients and predicts the response to volume. The technique can be managed by any health care professional. In hypoxic patients, TDTP identifies cases of pulmonary edema that might benefit from a negative fluid balance, evaluates pulmonary vascular permeability, facilitates our understanding of pathophysiologic mechanisms of hypoxemia, and predicts the likelihood of deleterious hemodynamic effects of positive end-expiratory pressures.

Evidence of pulmonary oedema triggered by exercise in healthy humans and detected with various imaging techniques

This review summarizes current literature on pulmonary oedema triggered by above-ground exercise in healthy humans from studies that use various imaging techniques to detect oedema. Eleven studies were identified, comprising of 137 subjects (mean age = 28 years). Eighty per cent (n = 110) were males, and 20% (n = 27) were female. The studies were grouped into three different categories according to the severity of the exercise protocol, which were either prolonged, submaximal exercise of 15-min to 2 h in duration at approx. 50-75%VO(2max) and not to exhaustion (PROLONGED, n = 44), a VO(2max) test lasting 16-20 min in which the intensity of exercise was only maximum for about 2 min at the end of the test (GXT, n = 15), and maximum or near maximum effort exercise protocols at or near volitional exhaustion where the goal was to finish in the fastest possible time or maintain the highest possible workload (MAX EFFORT, n = 78). Only 16% of the subjects showed signs of oedema from PROLONGED exercise and no subjects (0%) showed signs of oedema from GXT exercise. Surprisingly, approx. 65% of the subjects showed signs of oedema triggered by MAX EFFORT exercise (chi(2) test of association; P < or = 0.01), which was independent of both sex, the level of hypoxia (inspired PO(2) = 106-118 mmHg vs. 149 mmHg), the timing of the post-exercise imaging (<10, >30 but <60 min, or >60 min) and VO(2max) (approx. 3.0 vs. approx. 4.8 L min(-1)). The data suggests that the chances of triggering pulmonary oedema from exhaustive MAX EFFORT exercise is 4x more compared with PROLONGED exercise. As well, the likelihood of triggering pulmonary oedema may be independent of lung size, sex, moderate levels of hypoxia, and aerobic fitness.

Hypertonic-hyperoncotic solutions improve cardiac function in children after open-heart surgery

OBJECTIVES

Hypertonic-hyperoncotic solutions are used for the improvement of micro- and macrocirculation in various types of shock. In pediatric intensive care medicine, controlled, randomized studies with hypertonic-hyperoncotic solutions are lacking. Hypertonic-hyperoncotic solutions may improve cardiac function in children. The primary objective of this controlled, randomized, blinded study was to evaluate the hemodynamic effects and safety of hypertonic-hyperoncotic solution infusions in children shortly after open-heart surgery for congenital cardiac disease. The secondary objective was to determine whether the administration of hypertonic-hyperoncotic solutions could be a potential and effective therapeutic option for preventing a probable capillary leakage syndrome that frequently occurs in children after open-heart surgery.

METHODS

The children were randomly assigned to 2 groups of 25. The hypertonic-hyperoncotic solution group received Poly-(O-2)-hydroxyethyl-starch 60.0 g, with molecular weight of 200 kDa, Na+ 1232 mmol/L and osmolality of 2464 mOsmol/L (7.2% sodium chloride with 6% hydroxyethyl-starch 200 kDa). The isotonic saline solution group received isotonic saline solution (0.9% sodium chloride). Atrial and ventricular septal defects were corrected using a homograft patch. Monitoring consisted of an arterial, a central venous, and a thermodilution catheter (PULSIOCATH). Cardiac index, extravascular lung water index, stroke volume index, mean arterial blood pressure, and systemic vascular resistance index were measured (Pulse Contour Cardiac Output technique). Immediately after surgery, patients were loaded either with hypertonic-hyperoncotic solution or with isotonic saline solution (4 mL/kg). Blood samples (sodium concentration, osmolality, thrombocyte count, fibrinogen, and arterial blood gases) were drawn directly before; immediately after; 15 minutes after; and, 1, 4, 12, and 24 hours after the end of volume loading. Hemodynamic parameters were registered at the same time. The total amount of dobutamine required was documented, as well as the 24- and 48-hour fluid balances.

RESULTS

In the hypertonic-hyperoncotic solution group, cardiac index was 3.6 +/- 0.26 L/min per m2 before volume administration and increased to 5.96 +/- 0.27 after the administration of the study solution (64%). Fifteen and 60 minutes after administration, the cardiac index remained significantly elevated (5.55 +/- 0.29 L/min per m2 and 4.65 +/- 0.18 L/min per m2, respectively) and returned to preadministration values after 4 hours. In the isotonic saline solution group, the cardiac index did not change during the entire observation period (3.39 +/- 0.21 before and 3.65 +/- 0.23 L/min per m2 after isotonic saline solution). The systemic vascular resistance index decreased in the hypertonic-hyperoncotic solution group after administration from 1396 +/- 112 to 868 +/- 63 dyn/sec per cm(-5)/m2. The decrease of systemic vascular resistance index in the hypertonic-hyperoncotic solution group was transiently significant within 60 minutes after administration but stayed lower than before volume load (999 +/- 70 dyn/sec per cm-(5)/m2). In the isotonic saline solution group, we found no statistically relevant change in systemic vascular resistance index. Stroke volume index significantly increased after hypertonic-hyperoncotic solution infusion (53.9 +/- 3.0 mL/m2 directly after, 48.8 +/- 2.46 mL/m2 15 minutes after, and 41.4 +/- 2.2 mL/m2 60 minutes after) when compared with stroke volume index before administration (32.4 +/- 2.6 mL/m2). In the hypertonic-hyperoncotic solution group, an increase in mean arterial blood pressure remained transiently significant within 60 minutes after administration when compared with the isotonic saline solution group, in which the mean arterial blood pressure remained unchanged. Both central venous pressure and heart rate were unchanged during the whole time of observation in both groups. In the hypertonic-hyperoncotic solution group, extravascular lung water index decreased from 10.6 +/- 1.2 to 5.6 +/- 1.2 mL/kg and remained significantly decreased 15 minutes after (6.5 +/- 1.2 mL/kg) when compared with before volume administration. In the isotonic saline solution group, extravascular lung water index increased from 12.3 +/- 1.1 mL/kg to 18.1 +/- 1.7 mL/kg directly after administration and remained elevated for 60 minutes after volume loading (15.6 +/- 1.5 mL/kg). In all patients, no hypoxia (Pa(O2)<60 mm Hg) or hypercapnia (Pa(CO2) >60 mm Hg) was observed. Arterial blood gas analysis showed pH and base excess within physiologic range, and this did not change throughout the whole period of observation. After infusion of hypertonic-hyperoncotic solution, sodium concentration increased from 139.2 +/- 0.7 to 147.5 +/- 0.7 mmol/L. The maximum sodium concentration was 153 mmol/L, measured immediately after hypertonic-hyperoncotic solution in 1 patient. The total amount of fluid infused was similar in both groups. The postoperative need for infused dobutamine in the patients in the hypertonic-hyperoncotic solution group was decreased compared with the isotonic saline solution group (46.9 +/- 8.8 microg/kg vs 308.2 +/- 46.6 microg/kg). No patient presented with severe bleeding. Short- and long-term cardiac and neurologic outcome was not reduced and all patients left the hospital in a clinically sufficient state.

DISCUSSION

This study demonstrates a profound increase of cardiac index after the administration of hypertonic-hyperoncotic solution in children after uncomplicated open-heart surgery, suggesting a positive inotropic effect. The total amount of catecholamine was lower, assuming that hypertonic-hyperoncotic solution reduces the need for positive inotropic support. The observed positive cardiac effect of hypertonic-hyperoncotic solution may even be intensified by the decreased afterload (decreased systemic vascular resistance index). According to the Frank-Starling relation, an effective tool in the treatment of low cardiac output are an elevated preload while afterload is diminished. Therefore, we postulate that hypertonic-hyperoncotic solution may be helpful in preventing or attenuating low cardiac output failure in childhood. Capillary leakage syndrome also is a frequent problem after cardiopulmonary bypass. For quantification of edema formation, extravascular lung water index measurement is a useful tool. Using this approach, we provided evidence that the infusion of hypertonic-hyperoncotic solution is transiently able to reduce extravascular lung water index. This reduction was transient but might prevent the triggering of a clinically relevant capillary leakage syndrome. This is in line with in vitro studies demonstrating that hypertonic-hyperoncotic solution improves microcirculation by reducing vascular permeability. The single administration of hypertonic-hyperoncotic solution infusion was safe, and no adverse effects, such as hemostatic disturbances, were observed.

CONCLUSIONS

A single infusion of hypertonic-hyperoncotic saline solution after cardiac surgery is safe despite the hypertonicity and the colloid component of the hypertonic-hyperoncotic saline solution. In children after cardiopulmonary bypass surgery, the administration of hypertonic-hyperoncotic saline solution increased cardiac index by elevating stroke volume index in combination with a lowered systemic vascular resistance index. Extravascular lung water index transiently decreased, suggesting that hypertonic-hyperoncotic saline solution effectively counteracts the capillary leakage that often occurs after cardiac surgery in children. Additional investigations might elucidate whether the temporary effects of hypertonic-hyperoncotic saline solution are beneficial in the treatment of severe capillary leakage after complicated cardiac surgery. It has to be shown that hypertonic-hyperoncotic saline solution is a long-lasting, effective treatment strategy for low cardiac output failure in children that is caused by sepsis, multiorgan failure, and endothelial edema. We have provided evidence to pediatric intensive care clinicians that the single administration of hypertonic-hyperoncotic saline solution might be a useful and safe treatment in the amelioration of contractility, inotropy, and the possible treatment of early-onset capillary leakage.

Acute respiratory distress syndrome

Several combination therapies have been described throughout this article: in all likelihood, it is combination therapy that will allow improved survival of ARDS patients. As medicine moves into the future, clinical trials evaluating the efficacy of therapies for ARDS will be performed. In human critical care medicine, a large forward step was taken when ALI and ARDS were clearly defined. Unfortunately. as good as the definition is, ALI and ARDS occur secondary to many different underlying pathologic processes,perhaps obscuring the benefits of certain therapies for ARDS based on the underlying condition, for example, trauma versus sepsis. Selection of patients entering any ARDS trial is crucial: not only must those patients meet the strict definition of ARDS but the underlying disease process should be clearly identified. Identification of patients suffering from different disease processes before the onset of ARDS will allow for stratification of outcomes according to the intervention and the underlying pathology--comparing apples to apples and not to oranges. We are in a unique position in veterinary medicine. Although frequently financially limited by our clients, we have the opportunity to achieve several goals. First, we need to clearly define what constitutes ALI and ARDS in veterinary medicine. Do we want to rely on the human definitions? Probably not; however, as a group, we need to determine what we will accept as definitions. For example, we may not be able perform right heart catheterizations on all our patients to meet the wedge pressure requirement of human beings of less than 18 mm Hg. Do we agree that a PAOP of less than 18 mmHg is appropriate for animals, and is it appropriate for all animals? Will we accept another measure, for example, pulmonary artery diameter increases with echocardiographic evidence of acceptable left heart function? What is acceptable left heart function? As veterinarians, what do we consider to be hypoxemia? Is it the same in all species that we work with? What do we define as acute onset? Most human ARDS cases occur while patients are in hospital being treated for other problems, whereas many of our patients present already in respiratory distress. If we are unable to ventilate patients for economic or practical reasons, what do we use as the equivalent of the Pao2/Flo, ratio'? Reliance on the pathologist is not reasonable, because many disease processes can look similar to ARDS under the microscope. If anything, ALI and ARDS are clinical diagnoses. It is time for veterinarians to reach a consensus on the definition for ALI and ARDS in our patients. Only when we have a consensus of definition can rational prospective clinical trials of therapies be designed.