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488 PART 4: Pulmonary Disorders

Current guidelines recommend NIV as definitive and first-line TABLE 54-2 Selection Criteria for NIV for ACRF
therapy for COPD-related ACRF, 10,89,90 particularly in patients with
persistent hypercapnic ventilatory failure despite optimal medical Selection Criteria
therapy. Most centers administer NIV via a full face or nasal mask and Inclusion Criteria Exclusion Criteria (any may be present)
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pressure-support ventilation, although helmet interfaces, poncho wraps,
and other ventilator modes can support NIV. For the dyspneic ACRF A. Appropriate diagnosis with potential A. Cardiorespiratory exclusions
patients who preferentially mouth breathe, a full-face mask is prefer- reversibility (eg, AECOPD, acute left a. Respiratory arrest
able to minimize oral air leakage. The full-face mask also requires less ventricular failure) b. Life-threatening hypoxemia
patient cooperation than the other interfaces. A tight-fitting mask allows B. Established need for ventilatory assistance c. Hemodynamically unstable requiring
substantial ventilatory assistance yet provides for brief periods off of the a. Moderate to severe respiratory distress inotropes/pressors (unless in a critical
ventilator during which patients can speak, inhale nebulized medica- b. Accessory muscle use or abdominal care unit)
tions, expectorate, and swallow liquids. paradox d. Undrained pneumothorax
NIV has been systematically evaluated in several large studies. The out- c. Tachypnea >25 breaths/min B. Airway exclusions
comes from these studies have been synthesized by several groups. 92,93 d. Blood gas derangement persistent a. Unable to protect airway
A Cochrane meta-analysis of 14 randomized controlled studies of despite immediate maximum b. Vomiting, high aspiration risk
NIV versus usual medical care (UMC) included a total of 758 patients standard medical treatment on c. Viscous or copious secretions
with ACRF. Age ranged from 63 to 76 years, admission pH 7.26 to controlled oxygen therapy for no d. Craniofacial trauma or fixed nasopha-
92
39 to 73 mm Hg more than 1 hour ryngeal abnormality
7.34, admission Pa CO 2 57 to 87 mm Hg, admission Pa O 2 >45 mm Hg or e. Recent facial, upper airway, or
and FEV 0.68 to 1.03 L. The eight largest studies enrolled 40 or more pH <7.35, Pa CO 2
1
patients. Five studies were conducted in an ICU setting and the remain- Pa O 2 /Fi O 2 <200 gastroesophageal surgery
der in medical wards or progressive care units. Mean duration of NIV C. Conscious and cooperative f. Facial burns
was 4.3 days (range, 3-10 days). The combined analysis demonstrated a. Able to protect airway g. Unable to fit mask
that: Treatment failure was less likely with NIV than UMC (RR 0.48; C. Neurocognitive exclusions
95% CI 0.37, 0.63) with an NNT of 5 (95% CI 4, 6) and mortality was a. Delirium/agitation/severe cognitive
reduced by 48% (RR for death 0.52; 95% CI 0.35, 0.76; NNT 10 (95% impairment
CI 7, 20). Notably, the mortality reduction was evident regardless of D. Other exclusions
whether ACRF was treated in an ICU or in a general ward. Additionally, a. Extreme obesity
there was a 60% reduction in requirement for intubation with NIV, b. Patient moribund, comfort care goals
, and pH. Hospital in place
and rapid improvements in respiratory rate, Pa CO 2
length of stay was reduced by 3.24 days although the trend to reduced Data from Zhu GF, Zhang W, Zong H, et al. Effectiveness and safety of noninvasive positive-pressure ven-
ICU LOS (4.71 fewer days) did not reach significance. Interestingly, tilation for severe hypercapnic encephalopathy due to acute exacerbation of chronic obstructive pulmo-
was heterogeneous between studies and was nary disease: a prospective case-control study. Chin Med J (Engl). December 20, 2007;120(24):2204-2209.
the improvement in Pa O 2
not significantly different at 1 hour after initiation of treatment. The
finding of another meta-analysis revealed essentially similar findings to achieve an EPAP of 2 to 5 cm H O (to counterbalance PEEPi) and
2
for survival and clinical improvement, but subgroup analysis suggested an IPAP can be increased by 2 to 5 cm H O every 10 minutes, to a target
2
that the benefit was limited to patients with severe but not mild ACRF. of 15 to 18 cm H O (equivalently, 2-5 cm H O PEEP with 13-16 cm H O
2
2
2
This hypothesis has not been tested in a prospective, stratified fashion. 94 pressure support) to assist alveolar ventilation or patient tolerability has
NIV has been used for prolonged periods (more than 1 week) and has been reached. 89,101 Higher pressures can sometimes be used, but they
been shown to relieve symptoms, reduce respiratory rate, increase tidal tend to be limited by air leak or mask discomfort. The PEEP component
volume, improve gas exchange, and lessen the amplitude of both the of NIV is important and does not usually cause incremental hyper-
102
95
diaphragmatic electromyogram and the transdiaphragmatic pressure. inflation. Indeed, continuous positive airway pressure (CPAP) alone
103
96
Complications of the mask have been minor and few; local skin break- (without ventilatory assistance) reduces the work of breathing, improves
down has been attributed to the tight-fitting mask but can be avoided gas exchange, leads to subjective benefit, and sometimes can avert intuba-
by applying a patch of wound care dressing. Only a few patients can- tion 104-106 when applied to patients with ACRF. When PEEP was added to
not tolerate face or nasal masks, and some of these patients respond pressure-support ventilation in ventilated patients with COPD, inspira-
to judicious and carefully monitored use of anxiolytics. Aspiration of tory effort fell another 17%, and patient-ventilator synchrony improved. 79
gastric contents has only rarely been noted in these patients, even when The use of helium-oxygen mixtures as a driving gas for NIV has
a nasogastric tube is not routinely placed; however, impaired mentation been considered attractive because of theoretically beneficial alterations
probably increases this risk. However, in selected patients with severe in gas density and reduction in resistive pressure gradients across the
hypercapnic encephalopathy but stable hemodynamics, NIV may be as inflamed and mucus impacted respiratory tree. However, in 204 patients
effective as in less cognitively impaired patients, although predictably, with AECOPD requiring NIV for severe dyspnea and hypercarbia (Pa CO 2
those patients require higher levels of inspiratory pressure support and >45 mm Hg), use of heliox (35% Fi O 2 ) as a driving gas was no less likely
prolonged ICU stays. 97 to be associated with requirement for intubation than air:oxygen mix-
Careful patient selection is essential for successful NIV in ACRF and ture with the same Fi O 2 . 107
is summarized in Table 54-2. Although a nasal mask is objectively NIV is not uniformly successful in patients with ACRF. Essential
98
108
as effective and well tolerated as a full-face mask, we typically begin to successful patient-NIV synchrony are trigger settings for inspira-
99
therapy with a full-face mask. Gel-insert masks are preferable in an tion, pressurization rates (rapid pressurization reduces diaphragm work
effort to prevent skin breakdown of the nasal bridge. Claustrophobia but results in increased leak) and inspiratory-to-expiratory cycling
is quite frequent on initial application and may be effectively circum- (mask leaks can result in delayed cycling). These aspects are reviewed
vented by enlisting the patient (if capable) to hold the mask lightly in in detail in Chap. 44. A salutary response is typically evident within
position without securing the head-straps. Additionally, we attempt to 10 minutes of beginning NIV, as indicated by a falling respiratory
use 3 to 5 cm H O expiratory positive pressure (EPAP) only for the first rate and heart rate as well as by the patient’s subjective assessment.
2
several minutes. Thereafter, inspiratory positive pressure (IPAP) of 5 to Occasional patients feel claustrophobic and may show objective worsen-
8 cm H O is delivered using a pressure limited mode on a noninvasive ing with NIV. Although we occasionally use pharmacologic anxiolytic
2
ventilator until the patient is able to tolerate the mask comfortably and therapy with success, this course has obvious attendant risks and should
synchronize with the ventilator. After applying head-straps, we aim only be undertaken with appropriate safeguards.
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