Fig. 44.1
BIAP bilevel positive airway pressure, CO cardiac output, CPAP continuous positive airway pressure, LV left ventricle, NIMV non invasive mechanical ventilation, OHCM obstructive hypertrophic cardiomyopathy, PRV pulmonary vascular resistance, RV right ventricle. Colors: haemodynamic effects (in red); respiratory effects (in blue) (Modified from Wiesen et al. [5] with permission)
44.3 NIMV Versus Standard Medical Treatment in ACPE
In 2013, a meta-analysis was published that included 32 studies (2,916 participants) to determine the effectiveness and safety of NIMV in the treatment of ACPE. NIMV added to standard medical treatment (SMT) has several benefits compared with SMT alone [4]:
Reduction in the need for ETI, with risk difference (RD) of −12 % (95 % CI −0.19 to −0.04) and a number needed to treat (NNT) of 8 [4]. Lower ETI favored BIPAP-treated patients (RR 0.45, 95 % CI 0.26–0.80) [4]. This effect is important because of the related complications of IMV. Patients with hypoxic respiratory failure due to ACPE treated with NIMV have the lowest intubation rate (10 %) compared with other etiologies [6].
The impact on mortality remains controversial [3]. The largest randomized trial [1], with a total of 1,069 patients, did not show an effect on short-term mortality. This trial was included in the Cochrane meta-analysis [4], which showed significantly reduced hospital mortality (RR 0.66, 95 % CI 0.48–0.89). However, the evidence for this potential benefit is derived from small trials. No difference was found in hospital mortality comparing CPAP and BIPAP directly [4].
Reduction in intensive care unit length of stay by 1 day [4].
There were no significant increases in the incidence of acute myocardial infarction with NIMV during its application [4], an adverse outcome that was found in some previous studies.
Less progressive respiratory distress and neurological failure (coma) [4].
In summary, the use of NIMV is an important part of the treatment of ACPE, and the sooner it is started, the better. We need to “ventilate the patient” instead of “oxygenate the patient.”
44.4 NIMV in APCE and Cardiogenic Shock
There are two groups depending on the haemodynamic effect of the NIMV [5]:
The afterload-dependent group: Patients with a dysfunctional left ventricle (even with myocardial infarction) with high pulmonary capillary wedge pressure (PCWP) are extremely sensitive to changes in afterload. Patients with a PCWP ≥19 mmHg experience improvement in their cardiac output (CO) with the addition of 3–8 cmH2O of positive end-expiratory pressure (PEEP) [5].
The preload-dependent group: Patients with normal heart, hypovolemia, right ventricular infarction, or obstructive hypertrophic myocardiopathy. In all these patients, NIMV can decrease CO, so adequate intravascular repletion must be ensured.
Thus, patients with ACPE with left ventricule dysfunction and cardiogenic shock can have positive hemodynamic effects by using NIMV with moderate levels of PEEP and CPAP. These patients have tenuous hemodynamic status, therefore inappropriate ventilation settings could have severe deleterious effects [5]. Careful programming and close monitoring to avoid asynchrony and leaks are important.
44.5 CPAP or BIPAP?
According to blood gas analyses, one should choose CPAP in hypoxemic patients and BIPAP in patients who are hypercapnic or in global respiratory failure. But one should also be mindful of clinical factors, and it is not always possible to wait for blood gas analyses to decide, initially, the modality of NIMV. The initial choice and programming should be guided by physical signs (e.g., breathing pattern, respiratory fatigue signs), comorbidity, patient´s physical features and pressure, flow curve analysis, and blood gas analysis. Cardiac wasting syndrome, pleural effusion, and ascites (three common conditions in advanced heart failure patients) and chronic obstructive pulmonary disease (COPD), a common comorbidity in heart failure patients, should be kept in mind.
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