tidal volumes or severe bronchospasm. (d)You may hear normal breath
sounds if only the midline of the thorax is auscultated. (e)In cardiac arrest
situations, low exhaled carbon dioxide levels are seen in both very-low-
flow states and in esophageal intubation. In addition, colorimetric changes
may be difficult to discern in reduced lighting situations, and secretions
can interfere with color change.
203.The answer is e.(Tintinalli, pp 193-194.)This ECG shows third-
degree, or complete AV block.Note that there is no relationship between
the P waves and QRS complexes.The P waves occur regularly, but since
there is no AV conduction, the ventricles do not respond to the P waves. An
escape pacemaker at a rate slower than the atrial rate drives the ventricles,
producing regular QRS complexes independent of the P waves.
In contrast, normal sinus rhythm (a)has a rate between 60 and
100 beats per minute with every P wave followed immediately by a QRS com-
plex(1:1 conduction). First-degree AV block (b)has a PR interval greater
than 0.20 seconds. Every P wave is still followed by a QRS complex (1:1
conduction). Second-degree Mobitz I (Wenckebach) AV block (c)occurs
when there is a progressive delay in AV conduction, manifested by a grad-
ually increasing PR interval, followed by a dropped QRS complex. The pat-
tern then spontaneously repeats. Second-degree Mobitz II AV block (d)
occurs when there is a constant delay in AV conduction (prolonged PR
interval), followed by a dropped QRS complex. It is important to recognize
these distinct dysrhythmias as their etiologies are different and subtle treat-
ment differences exist.
204.The answer is b. (Tintinalli, pp 252-255.) This patient is in
neurogenic shock.He suffered an acute cervical spine injury after his fall
onto rocks and has hypotensionandbradycardia.The pathophysiology
behind neurogenic shock is still under investigation but it’s thought to be
partially caused by disrupted sympathetic outflow tractsandunopposed
vagal tone.Note that all other forms of shock attempt to compensate for
hypotension with tachycardia. Neurogenic shock lacks sympathetic innerva-
tion; therefore, bradycardia results. Given that this is a trauma patient, all
other sources for hypotension must be ruled out. He should be treated with
cervical spine immobilization and IV fluids. Pressors may be needed if
hypotension does not respond to fluids or fluid overload becomes a concern.
Hypovolemic shock (a)occurs when there is inadequate volume in
the circulatory system, resulting in poor oxygen delivery to the tissues.
228 Emergency Medicine