Utilidad de las maniobras de reclutamiento (contra)

Effects of fluid load on cardiovascular function during stepwise lung recruitment manoeuvre in healthy dogs

The aim of this study was to evaluate the effects of a stepwise lung recruitment manoeuvre (RM) on cardiac output (CO) in mechanically ventilated dogs, with or without a previous fluid load. Eight healthy adult Beagle dogs were enrolled in a prospective crossover study. Following sedation with dexmedetomidine and methadone, anaesthesia was induced with propofol and maintained with isoflurane. CO (thermodilution method) and direct arterial blood pressure were monitored. The dogs were mechanically ventilated in a volume-controlled mode (tidal volume, VT = 10 mL/kg; positive end-expiratory pressure [PEEP] = 0 cm H2O) until normocapnia was achieved (end tidal CO2 35-45 mmHg). The RM was then performed in a pressure-controlled mode, with progressive increases of the PEEP and end-inspiratory pressure of 5 cm H2O, until 15 cm H2O and 30 cm H2O were reached, respectively. After the RM, the ventilatory mode was returned to volume-control, and the PEEP was sequentially decreased to 10, 5 and 0 cm H2O. Baseline ventilation was maintained for 30 min. Next, 10 mL/kg of lactated Ringer's solution was administered within 10 min, prior to a second RM. The CO was determined before each RM (baseline) and at each pressure step. A repeated measures ANOVA test was used to compare data. Compared to baseline, CO decreased during the RM in both groups. However, there was a significantly higher CO during the second RM at the highest pressure step (P<0.05) and during all decreasing pressure steps (P<0.05). In conclusion, a previous crystalloid fluid load could reduce the impact of a RM on CO in healthy dogs.

[Recommendations of the Infectious Diseases Work Group (GTEI) of the Spanish Society of Intensive and Critical Care Medicine and Coronary Units (SEMICYUC) and the Infections in Critically Ill Patients Study Group (GEIPC) of the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC) for the diagnosis and treatment of influenza A/H1N1 in seriously ill adults admitted to the Intensive Care Unit]

The diagnosis of influenza A/H1N1 is mainly clinical, particularly during peak or seasonal flu outbreaks. A diagnostic test should be performed in all patients with fever and flu symptoms that require hospitalization. The respiratory sample (nasal or pharyngeal exudate or deeper sample in intubated patients) should be obtained as soon as possible, with the immediate start of empirical antiviral treatment. Molecular methods based on nucleic acid amplification techniques (RT-PCR) are the gold standard for the diagnosis of influenza A/H1N1. Immunochromatographic methods have low sensitivity; a negative result therefore does not rule out active infection. Classical culture is slow and has low sensitivity. Direct immunofluorescence offers a sensitivity of 90%, but requires a sample of high quality. Indirect methods for detecting antibodies are only of epidemiological interest. Patients with A/H1N1 flu may have relative leukopenia and elevated serum levels of LDH, CPK and CRP, but none of these variables are independently associated to the prognosis. However, plasma LDH> 1500 IU/L, and the presence of thrombocytopenia <150 x 10(9)/L, could define a patient population at risk of suffering serious complications. Antiviral administration (oseltamivir) should start early (<48 h from the onset of symptoms), with a dose of 75 mg every 12h, and with a duration of at least 7 days or until clinical improvement is observed. Early antiviral administration is associated to improved survival in critically ill patients. New antiviral drugs, especially those formulated for intravenous administration, may be the best choice in future epidemics. Patients with a high suspicion of influenza A/H1N1 infection must continue with antiviral treatment, regardless of the negative results of initial tests, unless an alternative diagnosis can be established or clinical criteria suggest a low probability of influenza. In patients with influenza A/H1N1 pneumonia, empirical antibiotic therapy should be provided due to the possibility of bacterial coinfection. A beta-lactam plus a macrolide should be administered as soon as possible. The microbiological findings and clinical or laboratory test variables may decide withdrawal or not of antibiotic treatment. Pneumococcal vaccination is recommended as a preventive measure in the population at risk of suffering severe complications. Although the use of moderate- or low-dose corticosteroids has been proposed for the treatment of influenza A/H1N1 pneumonia, the existing scientific evidence is not sufficient to recommend the use of corticosteroids in these patients. The treatment of acute respiratory distress syndrome in patients with influenza A/H1N1 must be based on the use of a protective ventilatory strategy (tidal volume <10 ml / kg and plateau pressure <35 mmHg) and positive end-expiratory pressure set to high patient lung mechanics, combined with the use of prone ventilation, muscle relaxation and recruitment maneuvers. Noninvasive mechanical ventilation cannot be considered a technique of choice in patients with acute respiratory distress syndrome, though it may be useful in experienced centers and in cases of respiratory failure associated with chronic obstructive pulmonary disease exacerbation or heart failure. Extracorporeal membrane oxygenation is a rescue technique in refractory acute respiratory distress syndrome due to influenza A/H1N1 infection. The scientific evidence is weak, however, and extracorporeal membrane oxygenation is not the technique of choice. Extracorporeal membrane oxygenation will be advisable if all other options have failed to improve oxygenation. The centralization of extracorporeal membrane oxygenation in referral hospitals is recommended. Clinical findings show 50-60% survival rates in patients treated with this technique. Cardiovascular complications of influenza A/H1N1 are common. Such problems may appear due to the deterioration of pre-existing cardiomyopathy, myocarditis, ischemic heart disease and right ventricular dysfunction. Early diagnosis and adequate monitoring allow the start of effective treatment, and in severe cases help decide the use of circulatory support systems. Influenza vaccination is recommended for all patients at risk. This indication in turn could be extended to all subjects over 6 months of age, unless contraindicated. Children should receive two doses (one per month). Immunocompromised patients and the population at risk should receive one dose and another dose annually. The frequency of adverse effects of the vaccine against A/H1N1 flu is similar to that of seasonal flu. Chemoprophylaxis must always be considered a supplement to vaccination, and is indicated in people at high risk of complications, as well in healthcare personnel who have been exposed.

[Respiratory and hemodynamic changes during lung recruitment maneuvering through progressive increases and decreases in PEEP level]

OBJECTIVE

To evaluate the respiratory and hemodynamic changes during lung recruitment maneuvering (LRM) through stepwise increases and decreases in PEEP level.

DESIGN AND SETTING

A retrospective study in a 17-bed ICU was carried out.

PATIENTS

Twenty-one patients with acute respiratory failure and bilateral pulmonary infiltration.

INTERVENTION

LRM was carried out, consisting of stepwise increases in PEEP (4 cmH(2)O every 3 minutes), with fixed ventilation pressure, until reaching a maximal value of 36 cmH(2)O PEEP (ascending branch), followed by progressive decreases in PEEP (2 cmH(2)O every 3 minutes) until establishing the open-lung PEEP at the value associated to maximum respiratory compliance (Crs) (descending branch). Continuous hemodynamic monitoring was performed using an esophageal echodoppler probe.

RESULTS

Crs gradually decreased in the ascending branch of the LRM, and progressively increased surpassing the initial value after establish the open-lung PEEP in the descending branch, reducing the ventilation pressure and increasing the SpO(2)/FiO(2) ratio. Hemodynamic changes primarily consisted of a fall in cardiac output and left ventricular preload, together with an increased heart rate and cardiac contractility. At comparable levels of PEEP and mean airway pressure, these changes were more pronounced during the descending branch of the LRM.

CONCLUSIONS

1) LRM increased Crs, improving oxygenation and decreasing ventilation pressure; 2) the main hemodynamic consequence was the drop in cardiac output and left ventricular preload; and 3) the unequal hemodynamic derangement in both branches, at the same level of PEEP and mean airway pressure, showed that, along with intrathoracic pressure, other factor such as Crs and hypercapnia may have influenced the hemodynamic consequences of this type of LRM.

[Acute lung injury and acute respiratory distress syndrome: a genomic perspective]

Genomics have allowed important advances in the knowledge of the etiology and pathogenesis of complex disease entities such as acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Genomic medicine aims to personalize and optimize diagnosis, prognosis and treatment by determining the influence of genetic polymorphisms in specific diseases. The scientific community must cope with the important challenge of securing rapid transfer of knowledge to clinical practice, in order to prevent patients from becoming exposed to unnecessary risks. In the present article we describe the main concepts of genomic medicine pertaining to ALI/ARDS, and its currently recognized clinical applications.

[The basics on mechanical ventilation support in acute respiratory distress syndrome]

Acute Respiratory Distress Syndrome (ARDS) is understood as an inflammation-induced disruption of the alveolar endothelial-epithelial barrier that results in increased permeability and surfactant dysfunction followed by alveolar flooding and collapse. ARDS management relies on mechanical ventilation. The current challenge is to determine the optimal ventilatory strategies that minimize ventilator-induced lung injury (VILI) while providing a reasonable gas exchange. The data support that a tidal volume between 6-8 ml/kg of predicted body weight providing a plateau pressure < 30 cmH₂O should be used. High positive end expiratory pressure (PEEP) has not reduced mortality, nevertheless secondary endpoints are improved. The rationale used for high PEEP argues that it prevents cyclic opening and closing of airspaces, probably the major culprit of development of VILI. Chest computed tomography has contributed to our understanding of anatomic-functional distribution patterns in ARDS. Electric impedance tomography is a technique that is radiation-free, but still under development, that allows dynamic monitoring of ventilation distribution at bedside.

[Peri-operative atelectasis and alveolar recruitment manoeuvres]

Respiratory complications are a significant cause of post-operative morbidity and mortality. Peri-operative atelectasis, in particular, affects 90% of surgical patients and its effects can be prolonged, due to changes in respiratory mechanics, pulmonary circulation and hypoxaemia. Alveolar collapse is caused by certain predisposing factors, mainly by compression and absorption mechanisms. To prevent or treat these atelectasis several therapeutic strategies have been proposed, such as alveolar recruitment manoeuvres, which has become popular in the last few years. Its application in patients with alveolar collapse, but without a previous significant acute lung lesion, has some special features, therefore its use is not free of uncertainties and complications. This review describes the frequency, pathophysiology, importance and treatment of peri-operative atelectasis. Special attention is paid to treatment with recruitment manoeuvres, with the purpose of providing a basis for the their rational and appropriate use.