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CHAPTER 44: Noninvasive Ventilation 381

Helium-Oxygen Mixture: The use of a helium-oxygen mixture for of intubation might have been observed in the oxygen group. This study
NIPPV has received much enthusiasm due to the physical properties has other limitations. Severely ill patients, who required “lifesaving or
of helium gas in reducing resistance by promoting a more laminar emergency intervention” were excluded and could have benefited from
flow profile, with early promising results when a helium-oxygen NIPPV, patients had mild hypoxemia and a very low intubation rate (3%)
mixture was used for COPD exacerbations. 87,88 Relatively large recent was observed in this study.
clinical trials have evaluated patients with known or suspected COPD A more recent multicenter clinical trial evaluated the potential
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and acute dyspnea, hypercapnia, and several signs of decompensation. clinical benefit of CPAP use, with 7.5 to 10 cm H 2O, when initiated
Unfortunately, these studies were unable to demonstrate a significant out-of-hospital setting and continued in-hospital ICU to treat acute
clinical benefit when a helium-oxygen mixture compared to conven- CPE compared to oxygen therapy at 15 L/min in the control group. Two
tional gas mixture for NIPPV was applied. 89,90 One possible reason hundred and seven patients were included over 3 years. The CPAP inter-
for these nonpositive results is that the rate of ETI has progressively vention group demonstrated significantly better and faster resolution of
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declined in the groups treated with air-oxygen mixtures, making more clinical symptoms as well as a lower presence of intubation criteria and
difficult to evidence a difference in favor of helium. a tendency for a lower death rate at day 7 although this last parameter
■ CARDIOGENIC PULMONARY EDEMA was not statistically different.
CPAP or PSV and PEEP CPAP is often considered cheaper and easier to apply
Pathophysiology: Continuous positive airway pressure (CPAP) and in clinical practice compared with PSV and PEEP. One trial suggested
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NIPPV elevates intrathoracic pressure, decreases shunting, and that acute myocardial infarction was more common with PSV and PEEP
improves arterial oxygenation and dyspnea in patients with cardio- than CPAP but this has not been subsequently confirmed. This differ-
genic pulmonary edema (CPE). Interestingly, NIPPV can both sub- ence was probably ascribable to randomization bias but it invites caution in
stantially lessen the work of breathing and improve cardiovascular patients with coronary heart disease. 99,105,106 One study compared intra-
function by decreasing the left ventricular afterload in nonpreload- venous bolus therapy of high-doses of nitrates to a more conventional
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dependent patients and also reducing the right and left ventricular medical therapy plus NIPPV. High-dose nitrate bolus therapy was far
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preload. Most patients with CPE improve rapidly under medical more effective clinically than NIPPV and resulted in better outcomes.
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therapy. A few, however, develop severe respiratory distress and/or These studies draw attention to the vulnerability of patients with CPE,
refractory hypoxemia/hypercapnia and require ventilatory support particularly those with coronary heart disease and to the fact that
until the medical treatment starts to work. This is particularly com- NIPPV cannot replace adequate medical therapy. 98,105
mon in elderly patients, who may also have a mild degree of associ- In some small studies, NIPPV was more effective regarding improve-
ated chronic bronchitis. 93,94 Several NIPPV modalities have been used ment in physiologic parameters or faster to improve respiratory fail-
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successfully, with the mainly goal being to avoid ETI and or hasten the ure compared to CPAP in patients with acute CPE, but no difference
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improvement provided by medical therapy. regarding mortality rate or tracheal intubation was demonstrated.
The 3CPO trial also compared both modes of NIPPV and clinical
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Clinical Evidence: Positive pressure applied at the mouth was already
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shown in the 1930s to improve patients’ dyspnea in case of CPE. outcomes were similar in both groups, including mortality and intuba-
tion rates, myocardial infarction, mean length of hospital stay, and clini-
Evidence of therapeutic efficacy of positive pressure use during acute
CPE was also shown in 1985, by Räsänen et al randomized 40 patients cal changes at 1 hour after start of treatment. Similar results comparing
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both modes of NIPPV were observed in another clinical study.
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with acute CPE and respiratory failure to conventional therapy or
It is important to draw attention to the fact that most of the studies
CPAP of 10 cm H 2O administered by face mask. The interventional indicating benefits of CPAP or PSV and PEEP included patients who,
group showed a better improvement of gas exchange, a decrease of
respiratory work, and a tendency for less intubation rate. Subsequently, on average, had marked hypercapnia and acidosis indicating acute frank
ventilatory failure.
A relatively large multicenter study conducted
94,98,99,105
other randomized trials comparing either CPAP or pressure support
plus PEEP (PSV and PEEP) to standard therapy found similar benefits by Nava and colleagues in patients with pulmonary edema found major
benefits of NIPPV only in the subgroup of hypercapnic patients, with no
with the two techniques in terms of arterial blood gases and breathing
rate improvement. Both NIPPV modes used in the emergency depart- significant benefits in terms of ETI rate or outcome in the overall popu-
lation that included both hypercapnic and nonhypercapnic patients.
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ment or in the ICU significantly reduced the rate of ETI. 94,97-99
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Recently published guidelines recommended NIPPV use in patients In sum, NIPPV use during CPE seems an important treatment that
with acute CPE, dyspnea, and respiratory rate >20 breaths/min to could reduce mortality, especially in the subgroup presented with hyper-
improve clinical symptoms. Nevertheless, attention should be paid in capnia. The conventional medical therapy remains the cornerstone, and
NIPPV, whether it is performed with CPAP or PSV and PEEP, should be
patients with low blood pressure (systolic blood pressure <85 mm Hg),
vomiting, altered level of consciousness, and suspected pneumothorax. In associated as soon as possible to medical therapy when treating patients
with CPE.
more recent European guidelines, the level of evidence (level B-class IIa)
for NIPPV use to treat acute CPE was lower than that formerly ■
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recommended. 101 HYPOXEMIC RESPIRATORY FAILURE
This decrease in the level of recommendations was mainly due to the Pathophysiology: Applying PEEP at the airway opening has been
publication of the 3CPO trial, the larger clinical multicenter, controlled shown to increase functional residual capacity and to improve respi-
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study performed in the emergency department, which evaluated the ratory mechanics and gas exchange in patients with acute hypoxemic
possible benefits of NIPPV use in acute CPE. Patients admitted with a respiratory failure. These findings led physicians to use CPAP as a
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clinical diagnosis of acute CPE, chest radiography of pulmonary edema, means of preventing clinical deterioration and reducing the need for
respiratory rate >20 breaths/min, and pH <7.35 were randomized to ETI. 98,112 Nevertheless, some physiological and clinical results do not
conventional pharmacological therapy plus NIPPV (CPAP or PSV and support the use of CPAP even in mild forms of ARDS, and better
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PEEP) or standard oxygen therapy. The study included 1069 patients clinical outcomes have been reported with the combined use of PSV
and it showed that NIPPV was associated with higher reduction in and PEEP. 8,114,115 In patients with severe hypoxemia, ventilatory sup-
dyspnea, heart rate, and earlier resolution of metabolic abnormalities port should be able to relieve the dyspnea, improve oxygenation, and
than standard oxygen therapy. Intubation rates, 7 and 30 days mortality decrease the patient’s effort to breathe. Combined PEEP and PSV are
rates (9.8% vs 9.5%, and 16.4% vs 15.2%) were similar in the control and needed to achieve these goals.
NIPPV groups, respectively. It should be noticed that a high incidence of The compromise between setting PEEP and pressure support level
crossover (15%) was observed in the oxygen group, as a rescue therapy, during NIPPV use may be challenging, since the total pressure deliv-
and consequently without this cross over possibility, a much higher rate ered by the ventilator is often limited to avoid inducing excessive
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