SISTEMA DE INFORMACIÓN PARA LA INFANCIA (SIPI)

Many intensivists decide to institute mechanical ventilation based on a patient’s facial appearance. 9 _{Gilston has provided}

an insightful description of many signs that go unstated in reviews on mechanical ventilation. 9 _{Consider, for example,}

the mouth. At an early stage of respiratory distress, the mouth opens slightly and to a variable extent during inhala- tion ( Fig. 4-3 ). At a later stage, the mouth opens throughout the respiratory cycle. Patients may switch to mouth breath- ing perhaps to decrease respiratory work 9 , 10 _{and physiologic}

dead space ventilation. 9 _{An open mouth is sometimes seen}

in patients with a tracheostomy ( Fig. 4-4 ) and in patients

receiving ventilator support. 9 _{The tongue may be seen to jerk}

in unison with inspiratory efforts. 9

Some distressed patients also exhibit pursed-lip breath- ing during exhalation (see Fig. 4-3 ). 9 _{In stable, ambulatory}

patients with COPD, pursed-lip breathing is associated with an increase in tidal volume, 11 _{a decrease in respira-}

tory rate, 11 _{and, in patients with severe obstruction, with a}

decrease end-expiratory lung volume. 12 _{Pursed-lip breath-}

ing can improve the arterial tensions of both carbon diox- ide (PaCO2) and oxygen (PaO2), whereas oxygen uptake ( ˙VO2 ) remains unchanged. 11 _{The latter finding suggests that pursed-}

lip breathing may allow a decrease in cardiac output without changing tissue oxygenation. 11 _{Alternatively, if cardiac output}

does not decrease, pursed-lip breathing may increase mixed venous oxygen saturation, resulting in better tissue oxy- genation. 11 _{Pursed-lip breathing is thought to improve gas}

exchange by preventing airway collapse. As a result, gas trap- ping is decreased, resulting in an increase in tidal volume. 11

FIGURE 4-2 Respiratory effort during unassisted respiration. Recordings of flow ( inspiration upward ), esophageal ( Pes ), gastric ( Pga ), and transdia- phragmatic ( Pdi ) pressures and electrical activity of the diaphragm ( Edi ) in a stable patient with COPD ( left ) and in a patient with respiratory failure ( right ). The green vertical lines indicate the onset of inspiratory flow and the red vertical lines indicate the onset of expiratory flow. The excursions in Pes and Edi in the patient in respiratory failure are three times greater than in the stable patient, signifying heightened respiratory motor output. The increase in Pga during exhalation in the patient with respiratory failure signifies expiratory muscle recruitment.

Pes cm H 2 O Pga cm H 2 O Pdi cm H 2 O Edi % max Flow L/ s –1.5 30 0 30 0 30 0 50 0 0 1.5 0 5 10 15 0 5 10 15 Time, seconds

A few patients in respiratory distress moan during exhala- tion. Such moans have been compared with the grunting that is typical of neonates with the respiratory distress syndrome. 9

Grunting results from glottic closure and expiratory muscle recruitment during early exhalation. 13 _{It is associated with a}

rise in transpulmonary pressure and oxygenation. 13 _{If grunting}

is prevented by tracheal intubation, oxygenation deteriorates. 13

Use of continuous positive airway pressure (CPAP) improves oxygenation and eliminates grunting. 14 _{The improvement in}

oxygenation may result from grunting acting as a natural form of PEEP that recruits collapsed alveoli and partially overcomes inequalities in gas distribution caused by differing time con- stants. Of course, grunting also can arise with disease outside the thorax, such as with an acute abdomen. 15

Nasal flaring, another facial sign of respiratory distress, is caused by contraction of the alae nasi, the dilator muscle of the external nares. 10 _{In adults, nasal flaring reduces nasal}

resistance by approximately 40% to 50% and total airway resistance by approximately 10% to 30%. 10 _{Factors regulating}

alae nasi activity include chemical stimuli that cause hyper- pnea (hypoxia and hypercapnia), 10 , 16 , 17 _{inspiratory resistive}

loading, 17 _{and local stimuli (negative intraluminal nasal}

pressure). 16 _{The proportion of patients in respiratory distress}

who present with nasal flaring is unknown, as is the level of interobserver agreement in detecting flaring. Ventilator sup- port reduces or eliminates alae nasi activity. 18 , 19

Diaphoresis, often best detected on the forehead, 9 _accom-

panies respiratory distress in some patients. Among forty- nine patients admitted to the emergency ward for acute bronchial asthma, Brenner et al 20 _{found that nine patients}

had profuse sweating. This subgroup displayed greater abnormalities in peak expiratory flow rate and PaCO2. In patients with respiratory distress, diaphoresis may result from increased work of breathing, 21 _{sympathetic stimula-}

tion, 21 , 22 _{and hypercapnia-associated cutaneous vasodila-}

tion. 21 , 23 _{In contrast, diaphoresis in patients with heart failure}

often is associated with hypoperfusion of the skin, vasocon- striction, and cold extremities. 21

FIGURE 4-3 Change in facial appearance during the development and resolution of acute respiratory failure resulting from conges- tive heart failure and exacerbation of chronic obstructive pulmonary disease. Left upper panel: The patient is dyspneic and her mouth is open on inhalation. Right upper panel: The patient exhibits pursed- lip breathing on exhalation. Over the ensuing 24 hours, the patient developed hypercapnic respiratory failure and failed a trial of nonin- vasive ventilation (not shown). Left lower panel: The patient is intu- bated and receiving mechanical ventilation. Right lower panel: The patient is successfully extubated 4 days after institution of mechanical ventilation.

FIGURE 4-4 Change in the configuration of the mouth in a patient with a tracheostomy who becomes dyspneic. Left: The patient is resting during full ventilator support and his mouth is closed. Middle: Twelve minutes after disconnection from the ventilator, the patient has developed dyspnea and anxiety and his mouth is open. Right: Thirty minutes after reconnection to the ventilator, the patient’s respiratory distress has resolved and his mouth is closed.

Mentation can be evaluated by inspection of the face and by simple questioning. With early respiratory distress, nearly all patients are anxious, and their eyelids are retracted. As distress increases, the level of consciousness often decreases, and the lids tend to fall ( Fig. 4-5 ). Instead of remaining alert to their surroundings, patients gaze vacantly ahead. 9 _{If respi-}

ratory failure is left untreated, apathy leads to drowsiness and then coma. These changes in mentation arise because of the underlying cause of respiratory failure (decreased car- diac output in cases of shock, impaired neurologic function in sepsis), acute hypercapnia, 24 _{or to a lesser extent, hypox-}

emia. 24 , 25 _{In a classic description, Campbell noted that most}

(nonhypotensive) patients with an exacerbation of COPD have preserved consciousness on arrival to the emergency room despite Pa_O2 being as low as 20 to 40 mm Hg. 25 _Although

extremely useful in overall patient assessment, facial signs of respiratory distress do not necessarily translate into an auto- matic decision to intubate a patient ( Fig. 4-5 ).

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