Therapeutic optimization including inhaled nitric oxide in adult respiratory distress syndrome in a polyvalent intensive care unit

Role of nitric oxide in management of acute respiratory distress syndrome

The current mortality rate of patients suffering from acute respiratory distress syndrome (ARDS) is between 45% and 92%, with most dying within the first two weeks of the illness. In an effort to combat such an alarmingly high mortality rate, various treatment therapies such as low tidal volume ventilation strategies, corticosteroid therapy, and use of nitric oxide (NO) have been attempted in the management of patients with ARDS. Three cases which were admitted to the ICU and confirmed to have ARDS were unable to be weaned from ventilatory support, and nitric oxide therapy was initiated. It improved patients' oxygenation for short periods of time but did not affect the mortality. The patients could not be weaned from the ventilator and expired.

Inhaled nitric oxide in ARDS

The role of nitric oxide (NO) in numerous physiologic systems only recently has been discovered. When used as a gas, inhaled NO (iNO) has many unique properties that cause immediate improvements in pulmonary hemodynamics and oxygenation. Acute benefits in physiologic parameters have been demonstrated in numerous studies of iNO in acute respiratory distress syndrome (ARDS), but recent randomized controlled trials have failed to show improvement in outcome. The addition of other treatments that prolong or enhance the affect of iNO or its use with other ventilator modalities such as prone positioning or high-frequency ventilation offer hope that iNO may be beneficial in select groups of patients.

Comparison of prone positioning and continuous rotation of patients with adult respiratory distress syndrome: results of a pilot study

OBJECTIVE

To compare prone positioning and continuous rotational therapy with respect to oxygenation and hemodynamics in patients suffering from adult respiratory distress syndrome (ARDS).

DESIGN

Randomized, prospective pilot study.

SETTING

Intensive care unit at a university hospital.

PATIENTS

Twenty-six mechanically ventilated patients with ARDS from nontraumatic causes.

INTERVENTIONS

Twelve patients were turned prone (group 1), 14 patients underwent continuous axial rotation from one lateral position to the other with a maximum angle of 124 degrees in specially designed beds (group 2). All patients had received inhaled nitric oxide (NO) therapy before positioning.

MEASUREMENTS AND MAIN RESULTS

Gas exchange and hemodynamics were assessed using a pulmonary artery catheter. In both groups, an improvement in PaO2/RFIO2-ratio and intrapulmonary shunt fraction occurred after initiation of NO as well as during the first 72 hrs of positioning therapy. During the study period, seven patients died in group 1 and nine patients in group 2 (p = NS). Comparing the areas under the curve during the first 72 hrs, no significant differences with respect to PaO2/FIO2-ratio, PaCO2, positive end-expiratory and peak inspiratory pressure levels, intrapulmonary shunt fraction, the alveolar-arterial oxygen difference, and oxygen delivery and consumption, as well as cardiac index, pulmonary and arterial blood pressures, and pulmonary arterial occlusion pressure could be detected between the groups. Prone positioning was tolerated well, continuous rotational therapy had to be modified according to hemodynamic instability in three patients.

CONCLUSIONS

In severe lung injury, continuous rotational therapy seems to exert effects comparable to prone positioning and could serve as alternative when prone positioning seems inadvisable.

[Acute renal failure profile and prognostic value in severe acute pancreatitis]

BACKGROUND

Acute renal failure (ARF) complicating severe acute pancreatitis (SAP) carries a high mortality. Clinically useful scores to define patients who will develop this complication are lacking. We try to determine the incidence of ARF and variables predicting the appearance and severity of the episodes.

MATERIAL AND METHOD

Retrospective study of all SAP patients admitted in an intensive care unit between 1991 and 1998 (n = 154).

RESULTS

ARF incidence was 42%. Haemodynamic instability, APACHE II and Ranson score were related to ARF development. 62.2% of severe ARF patients had multiple organ failure (MOF). Mortality was 71.2% compared to 6.8% in patients without ARF (39.9% in mild ARF and 94.6% in severe ARF). Etiology relates to mortality (prerenal [46.4%], after severe hypotensive episode [71.4%], in MOF [93.3%]; p < 0.005). 63.6% patients required replacement therapy (hemofiltration [HF] 95.5%), with a mortality of 89.3% (100% for intermittent dialysis compared to 88% with HF). In 32% patients treated with HF, ARF improved (when initiated early mortality was 76.9% compared to a 100% when initiated in more advanced stages) (p < 0.001). Logistic regression analysis showed that ARF severity and haemodynamic failure were related with mortality.

CONCLUSION

ARF is a frequent and early complication of SAP, worsening its prognosis. FRA severity is related to the outcome. Need of replacement therapy supposes a high mortality. In this setting, HF seems to have advantages over conventional dialysis.

Inhaled nitric oxide fraction is influenced by both the site and the mode of administration

OBJECTIVE

Inhaled nitric oxide (NO) can be delivered continuously or sequentially (= during inspiration) at different locations of the ventilation circuit. We have tested the influence of locations, modes of NO administration and the ratio of the inspiratory time over the respiratory cycle time (I/I + E ratio) on the accuracy of NO fractions, delivered by 2 devices: Opti-NO and Flowmeter.

METHODS

We used a simplified lung model consisting of a ventilation circuit with a Y piece, a tracheal tube, a 150 ml dead-space volume and a 5 liter balloon. Three fractions (3, 6, 9 ppm) were administered continuously or sequentially, in controlled volume, in 4 different sites on the inspiratory branch above the Y piece: i) just after the water trap, ii) just before the Y piece; below the Y piece: iii) just after the Y piece, iv) into the endotracheal tube. In addition, different I/I + E ratios (25, 33, 50, 80%) were studied. The delivered NO fractions were measured in the balloon by chemiluminescence (CLD 700, Ecophysics). A linear regression analysis was used to test the relationship between administered and measured NO fractions for the 3 fractions (3, 6 and 9 ppm) in sequential and continuous modes. Intercept values were compared to zero and slopes to the identity line.

RESULTS

When NO was administered in the continuous mode upstream the Y piece, NO fractions measured in the balloon corresponded to the administered fractions. In contrast, below the Y piece, the measured NO fractions were significantly lower than the administered NO fractions. In the sequential mode, above and below the Y piece, the delivered NO fractions were within the manufacturer's range.

CONCLUSIONS

For the continuous NO delivery, locations above the Y piece are mandatory. However, locations below the Y piece imposes a sequential system, which can also be used for the sites located above the Y piece.

Nitric oxide for ARDS--what is the evidence?

We critically reviewed English-language articles indexed on MEDLINE from 1966-1998 and those cited in indexed articles describing or investigating administration of nitric oxide (NO) in adult respiratory distress syndrome (ARDS). Studies evaluating NO exclusively in the pediatric population and in conditions other than ARDS (chronic obstructive pulmonary disease, asthma, cardiac surgery, pulmonary hypertension) were excluded, as were those published exclusively as abstracts. Of the 22 papers selected, 5 studies were dose-response trials, eight were comparative, and the rest were noncomparative. Dose-dependent decreases in pulmonary artery pressures and increases in arterial oxygenation were observed; however, the minimal effective dose varied. Several short-term noncomparative and small noncomparative prospective trials concluded that NO improves oxygenation and decreases pulmonary vasoconstriction without effects on systemic hemodynamics. However, evidence that NO improves outcomes in patients with ARDS is insufficient because mortality remained high, and the number of subjects in each study was low. Since improvements in oxygenation are not seen in all patients and outcomes or mortality might not be altered, NO should be reserved for selected patients in whom conventional therapy is not sufficient to maintain acceptable oxygenation levels.

The metabolic fate of long-term inhaled nitric oxide

PURPOSE

The fate of inhaled nitric oxide (NO) has not been precisely defined in critically ill patients. This study aimed at defining the effects of long-term NO inhalation on circulating NO byproduct levels.

MATERIAL AND METHODS

During NO therapy, plasma and urine from 13 critically ill patients were sampled daily for determination of the stable byproducts of NO (nitrite [NO2-] and nitrate [NO3-]. Routine monitoring data included inhaled NO concentration, hemodynamic parameters, arterial blood gases, creatinine clearance, and C-reactive protein.

RESULTS

For the first 24 hours of NO inhalation (6.3+/-1.1 ppm), NO3- plasma concentration increased (from 13.3+/-5.4 to 52.3+/-17.6 micromol/L), but NO2- plasma concentration was not affected. The NO3- plasma concentration was correlated with the C-reactive protein level, the inhaled NO concentration. Renal excretion of NO metabolites was unaltered by NO inhalation. The NO3 concentrations returned to baseline when NO therapy was discontinued.

CONCLUSION

Long-term NO inhalation was associated with a consistent increase in the NO3- plasma concentration. NO byproducts may be implicated in the systemic effects associated with this treatment.

The efficacy of inhaled nitric oxide in the treatment of acute respiratory distress syndrome. An evidence-based medicine approach

Nitric oxide is an endothelial relaxing factor. When given as an inhalational agent in the acute respiratory distress syndrome (ARDS), it vasodilates well ventilated areas of lung and improves oxygenation. Nitric oxide is a highly reactive molecule with myriad biologic effects, both potentially beneficial and toxic; its use as an inhalational agent in ARDS is experimental. This article reviews the available studies of inhaled nitric oxide.

The use of inhaled nitric oxide in a wide variety of clinical problems

Inhaled nitric oxide (NO) clearly decreased pulmonary vascular resistance in pediatric patients with pulmonary hypertension, regardless of the underlying origin of the pulmonary hypertension. In persistent pulmonary hypertension of the neonate (PPHN) and CHD, the use of inhaled NO appears to improve the outcome of these patients. In acute respiratory distress syndrome (ARDS) and surfactant deficiency the role of inhaled NO therapy remains unclear. The use of inhaled NO is safe in a carefully monitored setting with a delivery system designed to minimize the generation of NO2.

Inhaled nitric oxide in acute respiratory distress syndrome: a pilot randomized controlled study

This pilot randomized controlled clinical trial of patients with ARDS was implemented to study the impact of inhaled nitric oxide (inhNO) on lung function, morbidity, and mortality. Thirty patients with ARDS were randomly allocated to usual care or usual care plus inhNO. The optimal dose of inhNO was determined to be between 0.5 and 40 parts-per-million daily. All therapeutic interventions were standardized. ARDS resulted mainly from sepsis (25 of the 30). During the first 24 h, the hypoxia score increased greatly in patients treated with inhNO +70.4 mm Hg (+59%) versus +14.2 mm Hg (+9.3%) for the control group (p = 0.02), venous admixture decreased from 25.7 to 15.2% in the inhNO group, and from only 19.4 to 14.9% in the control group (p = 0.05). After the first day of therapy no further beneficial effect of inhNO was detected. Forty percent of the patients treated with inhNO were alive and weaned from mechanical ventilation within 30 d after randomization compared with 33.3% in the control group (p = 0.83). The 30-d mortality rate was similar in the two groups; most deaths (11 of 17) were due to multiple organ dysfunction syndrome. This study shows that inhNO, in this population, may improve gas exchange but does not affect mortality.

Inhaled nitric oxide versus conventional therapy: effect on oxygenation in ARDS

A randomized, controlled clinical trial was performed with patients with acute respiratory distress syndrome (ARDS) to compare the effect of conventional therapy or inhaled nitric oxide (iNO) on oxygenation. Patients were randomized to either conventional therapy or conventional therapy plus iNO for 72 h. We tested the following hypotheses: (1) that iNO would improve oxygenation during the 72 h after randomization, as compared with conventional therapy; and (2) that iNO would increase the likelihood that patients would improve to the extent that the FI(O2) could be decreased by > or = 0.15 within 72 h after randomization. There were two major findings. First, That iNO as compared with conventional therapy increased Pa(O2)/FI(O2) at 1 h, 12 h, and possibly 24 h. Beyond 24 h, the two groups had an equivalent improvement in Pa(O2)/FI(O2). Second, that patients treated with iNO therapy were no more likely to improve so that they could be managed with a persistent decrease in FI(O2) > or = 0.15 during the 72 h following randomization (11 of 20 patients with iNO versus 9 of 20 patients with conventional therapy, p = 0.55). In patients with severe ARDS, our results indicate that iNO does not lead to a sustained improvement in oxygenation as compared with conventional therapy.

The Utility of Nitric Oxide in the Postoperative Period

Inhaled nitric oxide (iNO) is a pulmonary-selective vaso dilator with minimal bronchodilator activity in humans. NO also inhibits platelet and neutrophil activation and adhesion and inhibits ischemia-reperfusion injury. The pulmonary vasodilatory property of iNO causes a reduc tion in pulmonary vascular resistance and improvement in arterial oxygenation in a wide spectrum of diseases characterized by pulmonary hypertension and hypox emia. Promising examples of diseases for which NO may provide beneficial physiologic effects are primary and secondary pulmonary hypertension, right ventricu lar failure, cardiac transplantation, pulmonary embo lism, protamine reactions, acute respiratory distress syndrome, lung transplantation and, perhaps, chronic obstructive airways disease. The usefulness of iNO may be improved by concomitant therapy with pulmonary- selective intravenous vasoconstrictors (eg, Almitrine; Vectarian, Neuilly, France) and cGMP phosphodiester ase V inhibitors (eg, Zaprinast; Research Biochemicals International, Natick, MA). Almitrine improves oxygen ation, synergistically with iNO, and may be useful in disease states characterized primarily by hypoxemia. Zaprinast may be useful for weaning iNO and avoidance of rebound pulmonary hypertension.

Inhaled nitric oxide for severe acute respiratory distress syndrome: a blessing or a curse?

The effects of inhaled nitric oxide (NO) in two young adults who developed severe acute respiratory distress syndrome are presented. Modest improvements in gas exchange and reductions in pulmonary artery pressures occurred after the initiation of treatment with inhaled NO. However, both patients became "dependent" on the inhaled NO for stabilization of their cardiopulmonary function. Repeated attempts to discontinue the inhaled NO resulted in life-threatening deterioration in gas exchange and hemodynamic instability. Prolonged family discussions were held regarding the withdrawal of inhaled NO and other life-sustaining therapies, when the irreversible nature of the patients' lung disease became apparent. However, both families were strong in their desire to continue all therapies--due in large part to the single organ nature of the disease process. Both patients died while receiving inhaled NO and escalating doses of sedative and analgesics. Based on this experience, it is recommended that clearly defined goals or endpoints for the discontinuation of inhaled NO should be established before its initial administration. If these goals are not achieved, then the therapy should be considered a failure and withdrawn. A similar strategy should be applied to all life-sustaining therapies in the intensive care unit setting (e.g., mechanical ventilation, vasopressors, dialysis). This requires that critical care clinicians effectively communicate the difference between aggressive supportive care and definitive treatment of the underlying disease process to patients or their families, or both. Furthermore, until the results of ongoing clinical trials of inhaled NO become available, it is recommended that its administration be restricted to medical centers examining its use in clinical trials.

Inhaled nitric oxide: clinical applications, indications, and toxicology

PURPOSE

Although the analogy of nitric oxide (NO) to Endothelium-derived Relaxing Factor remains controversial, medical use of exogenous NO gas by inhalation has grown exponentially. This review presents the mechanisms of action of inhaled NO in pulmonary hypertension, hypoxaemia, inflammation and oedema, as well as its therapeutic and diagnostic indications with emphasis on acute respiratory distress syndrome (ARDS) and toxicology.

SOURCE

Two medical databases (Current Contents, Medline) were searched for citations containing the above-mentioned key words to December 1996. Moreover, many presentations in congresses such as 4th International Meeting of Biology of Nitric Oxide, 52nd and 53rd Annual Meeting of Canadian Anaesthetists' Society or 10th Annual Meeting of European Association of Cardiothoracic Anaesthesiologists were used.

PRINCIPAL FINDINGS

Inhaled NO is now recognized as an invaluable tool in neonatal and paediatric critical care, and for heart/lung surgery. Other clinical applications in adults, such as chronic obstructive pulmonary disease and ARDS, require a cautious approach. The inhaled NO therapy is fairly inexpensive, but it would seem that it is not indicated for everybody with regards to the paradigm of its efficiency and potential toxicity. The recent discovery of its anti-inflammatory and extrapulmonary effects open new horizons for future applications.

CONCLUSION

Clinical use of inhaled NO was mostly reported in case series, properly designed clinical trials must now be performed to establish its real therapeutic role. These trials would permit adequate selection of the cardiopulmonary disorders, and subsequently the patients that would maximally benefit from inhaled NO therapy.

Inhaled nitric oxide in burn patients with respiratory failure

BACKGROUND

Inhaled nitric oxide (NO) has the potential to improve ventilation/perfusion matching and decrease pulmonary artery pressure in patients with profound respiratory failure.

METHODS

Eight patients, average age of 35 years (range, 2.5-77 years) and burn size 49% (range, 19-80%), with inhalation injury and respiratory failure failing conventional management (average Pao2/FiO2 ratio (PFR) 85) were given inhaled NO at 20 ppm.

RESULTS

An immediate mean increase in PFR of 10% and a decrease in pulmonary artery mean pressure of 7.8% was noted. At 24 hours, the average improvement in PFR was 28% and that in pulmonary artery mean pressure was 7.7%. Although not reaching statistical significance, these changes were more pronounced in those patients who went on to survive. There was no hypotension attributed to NO administration, and maximum methemoglobin levels averaged 0.9%.

CONCLUSIONS

Inhaled NO can be safely administered to selected burn patients with severe respiratory failure who are perceived to be failing conventional support. Although current data are not adequate to support its general use, an immediate and sustained improvement in PFR and pulmonary artery mean pressure may correlate with eventual recovery of pulmonary function. Continued evaluation in controlled settings seems warranted and is in progress.

Interest of a therapeutic optimization strategy in severe ARDS

STUDY OBJECTIVE

Evaluate the interest of the response to a therapeutic optimization as a predictor of prognosis in ARDS.

DESIGN

Prospective study.

SETTING

ICU of a University Hospital.

PATIENTS

Thirty-six consecutive patients with severe ARDS addressed for extracorporeal carbon dioxide removal (ECCO2R).

INTERVENTIONS

We studied the response during the first 2 days after arrival to the therapeutic optimization strategy consisting in a combination of the following: (1) decrease in extravascular lung water (diuretics or hemofiltration); (2) selection of the best ventilatory mode; (3) permissive hypercarbia; and (4) correction of hypoxemia by alveolar recruitment, additional continuous oxygen insufflation, body position changes (prone position), inhaled nitric oxide, enhancement of hypoxic pulmonary vasoconstriction with almitrine, and drainage of pleural or mediastinal effusions. In patients remaining severely hypoxemic despite these modalities, ECCO2R was then proposed.

MEASUREMENTS AND RESULTS

Thirty-six patients were addressed after 8.3+/-5.5 days of mechanical ventilation. On arrival, mean simplified acute physiologic score was 46.8+/-14.2, multiple system organ failure score was 1.8+/-1.6, Murray score was 3.4+/-0.4, PaO2 was 75.3+/-31.3 (fraction of inspired oxygen [FIO2]=1) for a positive end-expiratory pressure level of 12.3+/-3.4 cm H2O. Nineteen of 36 patients improved their gas exchange within 2 days and their mortality was 21%. The seventeen remaining patients did not improve PaO2/FIO2; PaCO2 and airway pressures remained high and their mortality was 88%. This different response to therapeutic optimization appeared using stepwise logistic regression as the most predictive factor for mortality (p<0.05).

CONCLUSIONS

In patients with severe ARDS, the response to an early performed therapeutic optimization used to improve hypoxemia appeared to be a highly discriminant factor distinguishing deceased from surviving patients.

Experimental therapies to support the failing lung

Many conventional therapies are designed to treat acute lung injury. Although evidence exists that improved outcomes are a result of these therapies, mortality remains high in this population. Perhaps one of the key reasons why mortality remains high in the failing lung population is that current therapies do not "cure" the problem; current therapies are designed to support the lung, rather than fix the pulmonary problem. In this paper, a review of new and experimental therapies to support the failing lung are presented. Therapies such as prone positioning, nitric oxide, and mediator therapies are addressed. It is likely that newer therapies offer the most hope for improving the high mortality associated with acute lung injury.