Page 1625 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1144 PART 10: The Surgical Patient

improvement in FEV1 and VC. Abdominal binders can improve lung decreased lower limb muscle tone, supine as well as orthostatic hypoten-
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function in patients with tetraplegia by a similar mechanism. The loss sion, and absolute (HR <60) or relative bradycardia, the most common
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of FVC appears to lessen over time after incomplete tetraplegia. 29,30 arrhythmia after acute SCI. Cardiac contractility is also reduced by
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Despite the known effects of SCI on respiratory function, the degree decreased sympathetic output. Arrhythmias are most common during
of pulmonary function recovery after SCI is variable and also depends the first 2 weeks after SCI and also include atrioventricular blocks,
on the degree of reversible cord edema and inflammation above the level supraventricular tachycardia, ventricular tachycardia, and primary car-
of injury, and is weakly predicted by initial PFTs. 31 diac arrest. The severity of the cardiovascular dysfunction correlates
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■ VENTILATOR WEANING AND TRACHEOSTOMY with the level of SCI and degree of axonal degeneration within the
dorsal lateral funiculi that carry the sympathoexcitatory fibers. Less
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The majority of patients with SCI at or below C4 level are eventually severe SCI injuries between T1 and T6 levels result in milder degrees of
weaned from mechanical ventilation but the average time on mechani- cardiovascular dysfunction. The effects of reduced sympathetic output
cal ventilation has been reported to be 65 days for patients with high are usually most pronounced during the first 2 to 6 weeks postinjury and
cervical level (ie, ≥C4) injury, 22 days in patients with C5-C8 levels, and usually improve over time.
12 days for patients with thoracic-level injuries. A patient in whom Loss of sympathetically mediated vascular tone with thoracic or cervi-
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several weeks or more of ventilator dependence is anticipated, early cal level injuries and decreased venous compression by paralyzed lower
tracheotomy is advisable. Patients with complete lesions at or above C3 limb muscles lead to a propensity toward orthostatic hypotension.
will be permanently ventilator dependent. In contrast, vasodilation from trauma-induced systemic inflamma-
Patients who require mechanical ventilation after 10 to 14 days and tory response or sepsis is usually associated with tachycardia and a
are not expected to successfully tolerate extubation within the next hyperdynamic circulation but may be associated with a relatively
several days should be evaluated for tracheostomy. Tracheostomy carries hypodynamic circulation in the presence of hypovolemia, myocar-
surgical risks such as bleeding, infection, and tracheal injury; however, dial stunning, or preexisting cardiac disease. Pneumothorax, cardiac
the benefits outweigh the risks of prolonged endotracheal intubation. tamponade, and bleeding from traumatic injuries should be ruled out
Tracheostomy may be performed via open or percutaneous dilatational before attributing hypotension to neurogenic shock.
methods based on local expertise and anatomical considerations. Adrenal insufficiency (AI) may complicate neurogenic shock. One
Tracheostomy helps improve oral care, patient comfort, decreases the retrospective study reported a 22% incidence of acute AI, defined
need for sedation, improves suctioning and clearance of secretions, as a random cortisol <15 g/dL, in the presence of neurogenic shock
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allows more aggressive spontaneous breathing trials, and provides after acute cervical SCI. In hypotensive patients, stress dose steroids
less dead space ventilation, possibly leading to earlier weaning from may lower vasopressor requirements; however, there is no conclusive
mechanical ventilation. Early tracheostomy after spinal stabilization is data demonstrating improvement of outcome in critically ill patients
associated with a low risk of infection even after the anterior approach receiving empiric steroid treatment. 38
incision for cervical stabilization and there does not appear to be any ■
benefit derived by separating these procedures by 2 weeks. 33 HEMODYNAMIC MONITORING
Liberation of the patient from mechanical ventilation can begin after The method of hemodynamic monitoring is determined by the degree
the acute illness has resolved and surgical procedures are completed of instability, the response to resuscitation, technical considerations, and
to allow for early patient mobilization. In addition, the patient should the expertise of the intensivist.
be hemodynamically stable on low (eg, ≤50%) inspired oxygen con- Central venous pressure (CVP) has been traditionally used to assess
centration with an intact mental status and the ability to follow simple adequacy of intravascular volume particularly in neurocritical care.
commands. Once these criteria are met, a spontaneous breathing However, recent studies have failed to demonstrate a clinically useful
trial can be attempted, and if well tolerated, the patient may be correlation between absolute CVP or change in CVP with intravascular
extubated. In a patient with a tracheostomy, a trach-collar trial will volume or right ventricular preload. 39,40 By the same token, the pul-
eliminate the ventilator circuit from the equation and may allow for monary artery occlusion pressure measured by Swan-Ganz catheters
earlier weaning. is not a reliable indicator of intravascular volume or left ventricular
Failure to wean after spinal trauma has been associated with longer preload. 39,41,42 If pulmonary artery catheter monitoring is utilized, the most
hospital and ICU stays, and a higher incidence of ventilator-associated accurate data include the pulmonary artery pressures, cardiac output,
pneumonia (VAP). Extubation failures are mainly due to pulmonary and true mixed venous blood gas values.
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mechanical insufficiency, inadequate pulmonary toilet, and sedation or Bedside cardiac ultrasound provides a less invasive, dynamic (real-
neurological issues. Difficult to wean patients may be discharged to a time visualization), and more direct determination of ventricular pre-
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rehabilitation center on mechanical ventilation and weaned post-ICU. load and global or regional wall motion or contractility and can rule out
In suitable patients without bulbar dysfunction, weaning to noninvasive cardiac tamponade.
ventilation may be an appropriate option, but requires skilled and dedi- Other dynamic indices of preload responsiveness such as pulse
cated personnel. 35 pressure variability with respiration may be superior predictors of
fluid responsiveness versus static parameters ; however, they require
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HEMODYNAMIC ISSUES: CARDIOVASCULAR sinus rhythm, mechanical ventilation with adequate and constant tidal
COMPLICATIONS AND NEUROGENIC SHOCK volumes, and no significant respiratory effort during triggering. The
response of CO to passive leg raising (PLR) may be predictive of fluid
Hemodynamic instability is common after acute SCI and may be multi- responsiveness regardless of cardiac rhythm or breathing, but heavy
factorial. Hypotension may be due to hypovolemia secondary to blood sedation is needed to eliminate catecholamine-induced changes in CO
loss, dehydration, systemic inflammation from trauma or infection unrelated to preload responsiveness. More studies are needed in this
(vasodilation, decreased intravascular volume), neurogenic (vasodilation, area and in any event, PLR is contraindicated with vertebral, pelvic, or
inappropriate bradycardia), arrhythmias, myocardial stunning, pneu- lower-extremity trauma, or intracranial hypertension.
mothorax, or cardiac tamponade from associated trauma. No single method of hemodynamic monitoring will yield useful
Neurogenic hypotension or “shock” is caused by injury to the auto- data in all situations and the intensivist must utilize the most accurate
nomic component of the spinal cord arising from the high thoracic information available coupled with the clinical context—physical exam,
and cervical regions, T1-T6 level and above, resulting in decreased metabolic parameters including lactate, blood gases, CXR, ECG, and
sympathetic outflow with preserved vagal mediated parasympathetic organ function assessment, and the response to a given treatment to
tone (Fig. 119-10) resulting in vasodilation, reduced venous return from achieve optimal hemodynamics.

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