How the Human Factor may effect NIV success?

The success of NIMV largely depends on the acceptance and compliance of the patient, and these are likely to be associated with the way that this method of ventilation is applied by the operator. The learning and training process that a hospital team gains throughout the years may be important in this respect. Literature data indirectly raise this suspicion.

For example, in 1992 Foglio et al. concluded, after a retrospective study, that the use of NIMV was not more effective than standard medical treatment alone in acute respiratory failure (ARF) due to decompensated COPD, but the same group showed opposite results some time later, so that in an accompanying editorial Brochard stated that „it was possible that some learning effects explained part of the improvement in the success rate“. t is, therefore, possible that the increased experience of medical and paramedical personnel, deriving from the systematic use of NIMV over the years, may modify clinical practice (i.e. the severity of patients treated) and patients' outcome.

Another issue recently raised by Girault et al is that an important difference could exist between results reported in „protocol-driven” prospective clinical trials and those deriving from „everyday” routinary clinical practice. The inclusion into a structured protocol could in some way influence the level of patient' care and the staff's behaviour thus giving a further better contribution to the outcome. To this respect the Authors retrospectively analysed all the patients treated with NIMV over the past two years in a medical ICU for different causes of respiratory failure (hypercapnic, hypoxemic and weaning/post-extubation). He reported a success rate, respectively, of 62%, 51% and 86% for the three groups thus confirming results comparable with those of the current literature. Although this study does not add any new piece of information with respect to predictors of NIMV failure, it confirms the feasibility and effectiveness of NIMV in the „real life” scenario, even out of any protocol-driven trial.

Several studies have demonstrated that NIMV is not more demanding for the personnel than standard medical therapy or invasive ventilation, but interestingly enough. Chevrolet et al. stated that NIMV was a time-consuming and difficult-to-apply procedure for nurses, while 10 years later they concluded that this technique, in experienced hands, „ appears not to influence the nurses' workload in the ICU significantly&rdquor;. Very recently Carlucci et al. have shown that the clinical practice of applying NIMV for an acute exacerbation of COPD may change over time, so that with increased staff training, more severely ill patients may be treated with a reduced risk of failure. In the current study the severity of the episodes of acute respiratory failure, defined by pH and APACHE II score at admission, worsened significantly during the study period and it was possible to identify, 5 years after the beginning of NIMV practice (year 1997), a significant decrease in pH at admission, thus allowing the Authors to identify two different periods: 1992–1996 (first period) in which the mean pH at admission was 7.25±0.07 and 1997–1999 (second period) during which the mean pH at admission was significantly lower (7.20±0.08, p<0.0001). In the first period (92–96) the severity of acidosis (pH and PaCO₂) and of illness (APACHE II), were significantly worst in the patients in which NIMV failed. In the second period (97–99) NIMV failures differed only for an higher APACHE II score (p<0.006).

Interestingly, failures of the first period had the same pH value at admission as

the successes in the second period (7.21±0.06 vs. 7.21±0.08, respectively).

The relative risk of failure of patients treated by NIMV according to the severity of the respiratory failure at admission, was calculated for pH of 7.30 and 7.25. Compared with a patient with a pH of 7.30 treated in the second period, a patient with a pH of 7.25 has a 1.5-fold (95% CI 1–3.8) higher risk of failure if treated in the years 97–99 vs. a 3.3-fold (95% CI 2.2–5.1) higher when treated in the years 92–96 (p=0.03). Increased confidence with the technique may allow the same team to treat more severely ill patients outside the respiratory intensive care unit (RICU), with an overall and significant reduction of the total NIMV cost per year.

Equipment and in particular ventilators and monitoring systems may be also important in determining NIMV success, since the technology used in NIMV has changed in the last decade and may have influenced the typology of the patients treated, since the success of NIMV may depend on its acceptance. In particular, home care ventilators are now equipped with software developed to compensate for air-leaks, with new non-rebreathing devices and systems of triggering, so that the patient-ventilator interaction and carbon-dioxide clearance may be better. The materials and the shapes of facial masks used for NIMV have also dramatically improved over time so that the newer and more sophisticated interfaces may influence the tolerance to NIMV and therefore the possibility to treat more severely ill patients with the same good outcomes.