Page 697 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

516 PART 4: Pulmonary Disorders

ventilated patients with KS (∼20 cm H O/L/s) and refractory to bron- 3 hours in acutely ill patients, suggesting that IPPV lowers surface
2
chodilators. This may stem from torsion or narrowing of the central tension by altering the surfactant lining layer. Mechanical insufflator-
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airways, which may be determined by bronchoscopic examination. 41 exsufflator devices used with pressures of negative 20 to 30 cm H O
2
■ OXYGEN THERAPY and positive 20 to 30 cm H O may also be beneficial to clear secretions.
2
Alternatively, a volume-preset, time-cycled device may be used.
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In patients with acute hypercapnic respiratory failure, NIV by full
A primary goal is to correct hypoxemia by increasing the fraction of face mask or nasal mask should be considered first-line therapy (see
) until an oxyhemoglobin saturation of 90% to
inspired oxygen (Fi O 2 Chap. 44). Advantages of NIV over invasive ventilation in general
92% is achieved. Adequate saturation by pulse oximetry should be include decreased need for sedation and paralysis, decreased incidence
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confirmed by arterial blood gas analysis, which also helps establish the of nosocomial pneumonia, decreased incidence of otitis and sinusitis,
acid-base status. If adequate oxygenation cannot be achieved with face- and improved patient comfort. Disadvantages include increased risk of
mask oxygen, NIV should be initiated unless there are indications for aspiration and skin necrosis, and less control of the patient’s ventilatory
intubation (see below). 42,43 status compared with invasive ventilation. 36,51
Hypoxemia causes pulmonary vasoconstriction and may precipitate
Although nocturnal NIV is firmly established in the management of
right ventricular failure in patients with preexisting right heart disease. KS patients with chronic respiratory failure, 52,53 limited data are avail-
Its causes include alveolar hypoventilation, V ˙ /Q ˙ inequality, and intra- able regarding its efficacy in acutely ill patients. 54-57 In one report of
pulmonary shunt. Right-to-left intracardiac shunts have also been
44 the use of noninvasive ventilation in 164 patients with heterogeneous
reported in the setting of thoracic deformity. Low mixed venous Pa O 2 forms of ARF, only five patients had restrictive lung disease. All five
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–
(Pv ), a frequent finding in patients with pulmonary hypertension and patients improved on noninvasive ventilation, although one subse-
O 2
low cardiac output, further lowers arterial oxygenation in the setting of quently required intubation. Noninvasive ventilation was also helpful in
V ˙ /Q ˙ inequality. four patients with KS and ARF failing conventional medical therapy. 57
■ HEMODYNAMIC MANAGEMENT using a loose-fitting full face mask. We start with 0 cm H O continuous
Following the guidelines of Meduri and colleagues, we initiate NIV
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2
Evaluation of shock in patients with KS is similar to that described positive airway pressure (CPAP) and 8 to 10 cm H O pressure support,
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elsewhere in this text (see Chaps. 31 and 33). Hypotensive patients not and increase CPAP to 3 to 5 cm H O and pressure support to the level
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responding to an initial volume challenge should be considered for required to achieve an exhaled tidal volume ≥7 mL/kg and a respiratory
central venous catheter placement (and rarely right heart catheteriza- rate ≤25/min, adequate gas exchange, and improved patient comfort.
tion), measurement of the central (or mixed) venous oxyhemoglobin Noninvasive negative pressure ventilators are not feasible in most
saturation, lactate, and/or bedside echocardiography to further direct acute situations because they generally require patients to lie flat and
therapy. Mechanical ventilation is indicated for nearly all patients with coordinate their breaths with the ventilator. Difficulties with fit
persistent shock, in part to redirect blood flow from the muscles of res- and applying the device adequately to the distorted chest wall further
piration, which can account for as much as 25% of the cardiac output. 45,46 complicate their use. Still, negative pressure ventilators have averted
Mechanical ventilation and sedation decrease oxygen consumption (and intubation in rare cases and have been used successfully in the long-
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thus supplemental oxygen requirement) and lactate generation. term management of patients with KS. 58
When sepsis causes shock, patients with chest wall deformity and pul-
monary hypertension may not mount a hyperdynamic response. When ■ INTUBATION AND MECHANICAL VENTILATION
right ventricular failure causes shock, a vicious cycle ensues. As the right Intubation is indicated for cardiopulmonary arrest, impending arrest,
ventricle fails, cardiac output and systemic blood pressure fall, limiting refractory hypoxemia or hypercapnia, mental status changes, and shock.
perfusion to the right ventricle from the aortic root. Right ventricular Intubation can be difficult because of spinal curvature and tracheal
end-diastolic volume increases and shifts the interventricular septum distortion, and because patients with small lung volumes desaturate
to the left, decreasing left ventricular compliance and further reduc- quickly. Airway visualization with fiberoptic bronchoscopy may be use-
ing cardiac output and systemic blood pressure. Ensuring an adequate of 1.0 is
circulating volume and correcting hypoxemia to reduce pulmonary ful in some cases. During the peri-intubation period, an Fi O 2
desirable, although it should be decreased to nontoxic levels as tolerated
vasoconstriction are the first goals of therapy. Increasing systemic blood once the patient has been stabilized on the ventilator. Decreasing oxygen
pressure with norepinephrine may increase perfusion pressure to the consumption with sedatives, use of positive end-expiratory pressure
right ventricle. 47 – in
We consider lower extremity Doppler exams to evaluate for venous (PEEP), and increasing Pv are strategies that allow for nontoxic Fi O 2
O 2
most patients. Positional maneuvers, such as placing the patient in the
thromboembolism; however, a single lower extremity Doppler exam is lateral decubitus position, may improve oxygenation in patients with
insufficiently sensitive to rule out venous thromboembolism as a cause asymmetric chest walls, but care must be taken to secure the airway.
of clinical decompensation. Serially negative Doppler exams provide Hypercapnic respiratory failure results from an imbalance between
an added sense of security as does a negative D-dimer. Computed respiratory muscle strength and respiratory system load; identifying
tomographic (CT) pulmonary angiography is preferable to ventilation- and correcting reversible elements of this imbalance is fundamental to
perfusion imaging in chest wall deformity, and may provide additional should be
clues regarding the etiology of ARF. In the absence of venous thrombo- recovery. During artificial support, baseline values of Pa CO 2
targeted to avoid alkalemia and bicarbonate wasting.
embolism, preventive therapy with prophylactic doses of unfractionated Respiratory muscle fatigue is treated with 48 to 72 hours of complete
heparin is indicated. The use of low molecular weight heparin as a pro- rest on the ventilator, with early nutritional supplementation and cor-
phylactic intervention does not appear to be superior to unfractionated rection of metabolic irregularities. To rest, patients must be comfortable,
heparin. 48 quiet, and synchronized with the ventilator, triggering breaths to avoid
■ NONINVASIVE VENTILATION disuse atrophy, but not working excessively to avoid fatigue. Transient
cessation of sedatives is useful, however, so that daily neurological
Decreased pulmonary compliance lowers lung volume, which in turn assessments can be performed.
limits cough efficiency and mucus clearance. To improve compliance In patients with bronchospasm and an increase in the peak-to-plateau
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and treat atelectasis, short periods (15-20 minutes) of intermittent gradient, it is prudent to consider bronchodilators and systemic steroids.
positive-pressure ventilation (IPPV) delivered by mouthpiece 4 to 6 times With attention to delivery technique, bronchodilator responsiveness is
daily using inflation pressures between 20 and 30 cm H O have been assessed by measuring airway resistance 15 to 30 minutes after inhalation.
2
recommended. IPPV increases lung compliance by 70% for up to Bronchoscopy may be indicated in nonresponders to evaluate for airway
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