Frédéric Michard

Goal-directed fluid management based on pulse pressure variation monitoring during high-risk surgery: a pilot randomized controlled trial

IntroductionSeveral studies have shown that maximizing stroke volume (or increasing it until a plateau is reached) by volume loading during high-risk surgery may improve post-operative outcome. This goal could be achieved simply by minimizing the variation in arterial pulse pressure (ΔPP) induced by mechanical ventilation. We tested this hypothesis in a prospective, randomized, single-centre study. The primary endpoint was the length of postoperative stay in hospital.MethodsThirty-three patients undergoing high-risk surgery were randomized either to a control group (group C, n = 16) or to an intervention group (group I, n = 17). In group I, ΔPP was continuously monitored during surgery by a multiparameter bedside monitor and minimized to 10% or less by volume loading.ResultsBoth groups were comparable in terms of demographic data, American Society of Anesthesiology score, type, and duration of surgery. During surgery, group I received more fluid than group C (4,618 ± 1,557 versus 1,694 ± 705 ml (mean ± SD), P < 0.0001), and ΔPP decreased from 22 ± 75 to 9 ± 1% (P < 0.05) in group I. The median duration of postoperative stay in hospital (7 versus 17 days, P < 0.01) was lower in group I than in group C. The number of postoperative complications per patient (1.4 ± 2.1 versus 3.9 ± 2.8, P < 0.05), as well as the median duration of mechanical ventilation (1 versus 5 days, P < 0.05) and stay in the intensive care unit (3 versus 9 days, P < 0.01) was also lower in group I.ConclusionMonitoring and minimizing ΔPP by volume loading during high-risk surgery improves postoperative outcome and decreases the length of stay in hospital.Trial registrationNCT00479011

Bedside assessment of extravascular lung water by dilution methods: temptations and pitfalls.

Objectives:To review the advantages and limitations of dilution methods to assess extravascular lung water (EVLW) at the bedside and to discuss the clinical value of EVLW measurements. Data Source:Experimental and clinical studies were searched in PUBMED by using “extravascular lung water” and “dilution method” as keywords and further selected as studies investigating either the reliability or the clinical usefulness of dilution methods to assess EVLW. Related articles and the reference lists of selected studies were scanned for additional relevant references. Conclusions:Both the double-indicator (thermo-dye) dilution and the single-indicator (cold saline) dilution methods showed close agreement with gravimetric measurement of EVLW (the reference ex vivo method) and have the advantage of being available at the bedside. Most limitations of dilution methods have been described in experimental conditions and lead to an underestimation of EVLW. These limitations include large pulmonary vascular obstruction, focal lung injury, and lung resection. Dilution methods provide an easy and clinically acceptable estimation of EVLW in most critically ill patients, including those with acute respiratory distress syndrome (ARDS). Assessing EVLW may be useful to predict outcome, to diagnose pulmonary edema, to better characterize patients with ARDS, to guide fluid therapy, and to assess the value of new treatments or ventilatory strategies in patients with pulmonary edema.

Online monitoring of pulse pressure variation to guide fluid therapy after cardiac surgery.

BACKGROUND: The arterial pulse pressure variation induced by mechanical ventilation (&Dgr;PP) has been shown to be a predictor of fluid responsiveness. Until now, &Dgr;PP has had to be calculated offline (from a computer recording or a paper printing of the arterial pressure curve), or to be derived from specific cardiac output monitors, limiting the widespread use of this parameter. Recently, a method has been developed for the automatic calculation and real-time monitoring of &Dgr;PP using standard bedside monitors. Whether this method is to predict reliable predictor of fluid responsiveness remains to be determined. METHODS: We conducted a prospective clinical study in 59 mechanically ventilated patients in the postoperative period of cardiac surgery. Patients studied were considered at low risk for complications related to fluid administration (pulmonary artery occlusion pressure <20 mm Hg, left ventricular ejection fraction ≥40%). All patients were instrumented with an arterial line and a pulmonary artery catheter. Cardiac filling pressures and cardiac output were measured before and after intravascular fluid administration (20 mL/kg of lactated Ringer’s solution over 20 min), whereas &Dgr;PP was automatically calculated and continuously monitored. RESULTS: Fluid administration increased cardiac output by at least 15% in 39 patients (66% = responders). Before fluid administration, responders and nonresponders were comparable with regard to right atrial and pulmonary artery occlusion pressures. In contrast, &Dgr;PP was significantly greater in responders than in nonresponders (17% ± 3% vs 9% ± 2%, P < 0.001). The &Dgr;PP cut-off value of 12% allowed identification of responders with a sensitivity of 97% and a specificity of 95%. CONCLUSION: Automatic real-time monitoring of &Dgr;PP is possible using a standard bedside monitor and was found to be a reliable method to predict fluid responsiveness after cardiac surgery. Additional studies are needed to determine if this technique can be used to avoid the complications of fluid administration in high-risk patients.

Factors influencing the estimation of extravascular lung water by transpulmonary thermodilution in critically ill patients

Objective:To investigate factors that may influence the estimation of extravascular lung water (EVLW) with a single (cold) indicator compared with assessment using two indicators (thermo-dye dilution). Design:Post hoc analysis of an electronic hemodynamic database. Setting:Surgical intensive care unit of a university hospital. Patients:Forty-eight critically ill patients monitored by the thermo-dye dilution technique in the postoperative period. Interventions:None. Measurements and Main Results:The EVLW was simultaneously assessed by the thermo-dye dilution technique (EVLWref) and estimated by transpulmonary thermodilution (EVLWest). EVLWref index ranged between 1 and 40 mL/kg (mean 10 ± 7 mL/kg) and EVLWest between 2 and 39 mL/kg (mean 9 ± 6 mL/kg). EVLWref was closely correlated (r = .96) with EVLWest. The mean difference (bias) between EVLWref and EVLWest was −0.5 ± 1.9 mL/kg. The bias was not influenced by the weight, height, body surface area, body mass index, Pao2, intrathoracic blood volume, cardiac output, or dosage of vasoactive agents. In contrast, the bias was slightly but significantly influenced by EVLWref, Pao2/Fio2 ratio, tidal volume, and level of positive end-expiratory pressure. Conclusions:In our surgical intensive care unit population, the estimation of EVLW by transpulmonary thermodilution was influenced by the amount of EVLW, the Pao2/Fio2 ratio, the tidal volume, and the level of positive end-expiratory pressure. However, compared with the double indicator method, transpulmonary thermodilution estimation remained clinically acceptable even in patients with severe lung disease.

Pulse pressure variation: beyond the fluid management of patients with shock

In anesthetized patients without cardiac arrhythmia the arterial pulse pressure variation (PPV) induced by mechanical ventilation has been shown the most accurate predictor of fluid responsiveness. In this respect, PPV has so far been used mainly in the decision-making process regarding volume expansion in patients with shock. As an indicator of the position on the Frank–Starling curve, PPV may actually be useful in many other clinical situations. In patients with acute lung injury or with acute respiratory distress syndrome, PPV can predict hemodynamic instability induced by positive end-expiratory pressure and recruitment maneuvers. PPV may also be useful to prevent excessive fluid restriction/depletion in patients with pulmonary edema, and to prevent excessive ultrafiltration in critically ill patients undergoing hemodialysis or hemofiltration. In the operating room, a goal-directed fluid therapy based on PPV monitoring has the potential to improve the outcome of patients undergoing high-risk surgery.

Assessing cardiac preload or fluid responsiveness? It depends on the question we want to answer.

between these extreme values [4]. Therefore, for physiological reasons, we cannot accurately predict fluid responsiveness simply by assessing cardiac preload. Does it mean that assessing cardiac preload is useless? No, because assessing preload is useful in answering another clinical question: “Does our fluid challenge effectively increase cardiac preload?” The increase in ventricular end-diastolic volumes (i.e. in preload) as a result of fluid therapy depends on the partitioning of the fluid into different cardiovascular compartments organized in series. In this regard, when venous capacitance is increased or ventricular compliance is decreased, fluid infusion will increase intravascular blood volume, but not necessarily cardiac preload [5]. Thus, a patient can be a non-responder to a fluid challenge because preload does not increase or because his heart is operating on the flat portion of the Frank-Starling curve. In the first case, giving more fluid may be useful to increase cardiac preload and hence output significantly, while in the second case only an inotrope may improve cardiac output. Thus, assessment of cardiac preload as well as fluid responsiveness are useful for the clinician, but definitely not to answer the same question. References

Extending inspiratory time in acute respiratory distress syndrome

ObjectiveTo assess the short-term effects of extending inspiratory time by lengthening end-inspiratory pause (EIP) without inducing a clinically significant increase in intrinsic positive end-expiratory pressure (PEEPi) in patients with acute respiratory distress syndrome (ARDS). DesignControlled, randomized, crossover study. SettingTwo medical intensive care units of university hospitals. PatientsSixteen patients with early (≤48 hrs) ARDS. InterventionWe applied two durations of EIP (0.2 secs and extended) each for 1 hr while keeping all the following ventilatory parameters constant: Fio2, total PEEP (PEEPtot = applied PEEP + PEEPi), tidal volume, inspiratory flow, and respiratory rate. The duration of extended EIP was titrated to avoid an increase of PEEPi of ≥1 cm H2O. Measurements and Main ResultsDespite an increase in mean airway pressure (20.6 ± 2.3 vs. 17.6 ± 2.1 cm H2O, p < .01), extended EIP did not significantly improve Pao2 (93 ± 21 vs. 86 ± 16 torr [12.40 ± 2.80 vs. 11.46 ± 2.13 kPa] with 0.2 secs EIP, NS). However, although the difference in Pao2 between the two EIP durations was <20 torr (<2.66 kPa) in 14 patients, two patients exhibited a >40 torr (>5.33 kPa) increase in Pao2 with extended EIP. Extended EIP decreased Paco2 (62 ± 13 vs. 67 ± 13 torr [8.26 ± 1.73 vs. 8.93 ± 1.73 kPa] with 0.2 secs EIP, p < .01), which resulted in a higher pH (7.22 ± 0.10 vs. 7.19 ± 0.09 with 0.2 secs EIP, p < .01) and contributed to a slight increase in arterial hemoglobin saturation (94 ± 3 vs. 93 ± 3% with 0.2 EIP, p < .01). No significant difference in hemodynamics was observed. ConclusionIn patients with ARDS, extending EIP without inducing a clinically significant increase in PEEPi does not consistently improve arterial oxygenation but enhances CO2 elimination.

Monitoring Right-to-left Intracardiac Shunt in Acute Respiratory Distress Syndrome

To the Editor: We read with interest the article by Jacobe and colleagues (1) published in the May 2003 issue of Critical Care Medicine concerning the outcome of critically ill children after bone marrow transplantation. One of the authors’ major conclusions is that patients with pneumonia or pneumonitis who do not significantly improve within 48–72 hrs of intensive care unit (ICU) admission should probably not be offered prolonged lifesupporting therapy. However, this conclusion is based on the observation of patients with respiratory failure who had, for their majority, a viral or fungal infection. We doubt whether this advice can be extrapolated to critically ill bone marrow transplant patients with bacterial infections. In a retrospective study, we found that a bacteremia precipitating ICU admission was associated with a better outcome in a general population of critically ill adult patients with hematologic malignancies (2). This could be attributed to the fact that bacteremia was a treatable and potentially rapidly reversible complication compared with all other complications that can precipitate ICU admission in this population, such as invasive pulmonary aspergillosis, viral pneumonia, or chemotherapy-induced organ failure. We analyzed in our database whether this finding was also present in allogenic bone marrow transplant recipients. Between 1997 and 2002, we admitted 38 adult bone marrow transplant recipients to our ICU. In-hospital and 6-month mortality rates in nonventilated vs. ventilated patients were 25% (2 of 8) vs. 83.3% (25 of 30; p .004) and 37.5% (3 of 8) vs. 83.3% (25 of 30), respectively. After adjustment for the severity of illness (Acute Physiology and Chronic Health Evaluation II or Simplified Acute Physiology Score II, ventilation and vasopressor need), bacteremia was again independently associated with a better outcome (odds ratio, 0.11; 95% confidence interval, 0.015–0.84, p .03). In-hospital mortality rate in ventilated bone marrow recipients was 57.4% (4 of 7) in those with bacteremia compared with 91.3% (21 of 23) in those without bacteremia (p .07). Patients with bacteremia were ventilated for a median duration of 3 days (range, 1–6 days). It can be questioned whether this finding can be extrapolated to all bacterial infections, including bacterial pneumonia. However, Gruson et al. (3) reported an ICU mortality of 91% in critically ill bone marrow recipients without proven infectious pneumonia compared with 56% in those with proven infectious pneumonia (p .03). In another study from the same group comparing the outcome of 54 critically ill immunocompromised patients with pulmonary infiltrates randomized to receive noninvasive or invasive ventilation (4), mortality rates in patients with a documented infection, which was for the majority caused by bacteria, was 48.3% compared with 90.4% in those without a documented infection. However, as there were more documented infections in the group receiving noninvasive ventilation, the beneficial effect of the documentation of an infection was only statistically significant in this group (29% vs. 89%, p .006) and not in the group receiving invasive ventilation (71% vs. 92%, p .21). Whether the better outcome in these patients is directly related to the identification of a pathogen or to the presence of a (documented or presumed) bacterial infection as a treatable complication should be evaluated in future studies. Nevertheless, these results clearly indicate that the decision not to prolong ventilation in critically ill bone marrow transplant patients who do not improve after 48 hrs of ICU admission may not be suitable for patients with a pulmonary bacterial infection.

Influence of tidal volume on stroke volume variation. Does it really matter

Vt group. In accordance with the findings of Reuter et al. [1], the pre-infusion pulse pressure variation was greater (20±11 vs 8±5%, p<0.05) in the “high” Vt group (Fig. 1) and correlated with Vt (r=0.46, p<0.01). Interestingly, the fluid loading-induced increase in cardiac output was also greater (18±13 vs 7±7%, p<0.05) in the “high” Vt group (Fig. 1) and weakly, but significantly (r=0.35, p<0.05), correlated with Vt. These findings support the notion that the Vt influences not only the SVV but also the hemodynamic response to volume loading. This may explain why the SVV has been found to be a reliable predictor of fluid responsiveness in patients with a Vt ranging between 8 and 15 ml/kg [2, 3, 4]. Therefore, we believe that the influence of Vt on SVV cannot be considered as a major limitation to its use as a predictor of fluid responsiveness in most mechanically ventilated patients.

Predicting fluid responsiveness with stroke volume variation despite multiple extrasystoles

Objective:To investigate the ability of a new stroke volume variation algorithm to predict fluid responsiveness during general anesthesia and mechanical ventilation in animals with multiple extrasystoles. Design:Prospective laboratory animal experiment. Setting:Investigational laboratory. Subjects:Eight instrumented pigs. Interventions:Eight anesthetized and mechanically ventilated pigs were monitored with an arterial line and a pulmonary artery catheter. Multiple extrasystoles were induced by right ventricular pacing (25% of heart beats). Arterial pressure waveforms were recorded and stroke volume variation was computed from the new and from the standard algorithm. The new stroke volume variation algorithm is designed to restore the respiratory component of the arterial pressure waveform despite multiple ectopic heart beats. Cardiac output was measured before and after 56 fluid boluses (7 mL/kg of 6% hydroxy ethyl starch) performed at different volemic states. Measurements and Main Results:A positive response to fluid boluses (>15% increase in cardiac output) was observed in 21 of 56 boluses. The new stroke volume variation was higher in responders than in nonresponders (19% ± 5% vs. 12% ± 3%, p < .05), whereas the standard stroke volume variation was similar in the two groups (29% ± 8% vs. 26% ± 11%, p = .4). Receiver operating characteristic curve analysis showed that the new stroke volume variation was an accurate predictor of fluid responsiveness (sensitivity = 86%, specificity = 85%, best cutoff value = 14%, area under the curve = 0.892 ±, whereas the standard stroke volume variation was not (area under the curve = 0.596 ± 0.077). Conclusions:In contrast to the standard stroke volume variation, the new stroke volume variation algorithm was able to predict fluid responsiveness in animals with multiple ventricular extrasystoles.