Page 1529 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1048 PART 10: The Surgical Patient

potentially necessitating mechanical ventilatory assistance. Judicious lung water and predispose the surgical patient to perioperative respira-
parenteral analgesia as well as regional, intercostal, and epidural anes- tory failure. Although a young, healthy patient with significant car-
thesia may also be useful in these situations. diopulmonary reserve might tolerate these insults, an elderly surgical
Neurosurgical patients and those who have suffered head trauma patient with a brittle cardiorespiratory status is more likely to develop
should be monitored closely for signs of increased intracranial pressure. respiratory failure unless extreme caution is taken with fluid resuscita-
If clinical signs cannot be easily elicited, an intracranial pressure moni- tion, involving close, constant monitoring of central hemodynamics.
toring device should be placed. Apart from the identification of mass Pulmonary edema occurring in the head-injured and subarachnoid
lesions that may require evacuation, the mainstay of treatment for these hemorrhage patients, or neurogenic edema, may be associated with a
patients is reduction of cerebral edema through the maintenance of transient increase in hydrostatic pressure because of intense sympathetic
cerebral blood flow and oxygenation and the avoidance of hypercapnia discharge, although it has been suggested that there may be a component
(see Chap. 86). The vascular surgery patient requires close monitor- of increased capillary permeability as well in those patients. Therefore,
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ing of perfusion, particularly in the arterial territorial distribution of monitoring of pulmonary capillary hydrostatic pressure can be helpful
the repaired vessel. Skin temperature, Doppler ultrasound, and digital in determining therapeutic approaches to the head-injured patient with
pressure measurements are required in the ICU setting to identify prob- pulmonary edema.
lems with vascular anastomoses as early as possible and permit early High-pressure pulmonary edema does not resolve immediately after
corrective measures. In the immediate postoperative period carotid vascular pressures are normalized. The implication of this finding is
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artery surgery patients are at higher risk for developing neurologic com- that the timing of the measurement of pulmonary artery wedge pressure
plications from reocclusion at surgical sites of vascular repair, and careful (PAWP), which is used as a reflection of pulmonary capillary hydro-
monitoring of the neurologic status as well as maintenance of adequate static pressure, is crucial in determining whether pulmonary edema
oxygenation and perfusion are essential to avoid such complications. is considered to be due to high vascular pressures or to an increase in
Following GI surgical procedures, the gut should be used early for capillary permeability. Ordinarily, the presence of normal or low PAWP
enteral nutrition whenever appropriate. When that is not possible and in the presence of pulmonary edema would be regarded as evidence of
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a prolonged period of decreased motility is anticipated, decompression capillary-leak pulmonary edema. However, this is not the case when the
of the GI tract is necessary to prevent distention and to monitor the PAWP is measured during the lag phase of resolution of high-pressure
volume and character of losses. This intervention, together with replace- pulmonary edema after PAWP has been decreased.
ment of measured losses as well as determination of serum electrolytes, Diuretics such as furosemide clear edema by decreasing the central
allows early identification and correction of abnormalities and the blood volume and pulmonary capillary hydrostatic pressure. However,
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prevention of complications. Patients who develop sepsis following GI these agents may produce effects on gas exchange before pulmonary
surgical procedures should be considered to have a source of that sepsis edema has cleared. Accordingly, diuretic therapy and fluid manage-
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within the abdomen until proven otherwise. Early aggressive investiga- ment of the oliguric, hypoxemic perioperative patient may confuse the
tion for identifying such a source of sepsis is essential in order to avoid student of critical care at several levels. First, oliguria in the immediate
further deterioration in the ICU. postoperative period is not necessarily due to reduced blood flow to the
The gut has also been considered to play a major role in the patho- renal cortex (prerenal oliguria), so fluid challenges aimed at increasing
genesis of multiple organ dysfunction syndrome and decontamination renal blood flow may not be appropriate in this setting. The consequent
of the GI tract has been suggested as a prophylactic measure in this increase in pulmonary blood volume and pressure predictably increases
syndrome, but there is a major concern about promoting the growth of pulmonary edema. On the other hand, diuretic therapy in such a patient
resistant microorganisms by such intervention. 26 will increase urine output, even when the oliguria is due to reduced renal
Stress ulcers resulting in GI hemorrhage are a sequela not only of blood flow, thereby aggravating the prerenal failure. The best approach to
GI surgery, but of other forms of critical illness. Prophylactic measures this common perioperative conundrum is to recognize that urine output
against stress ulceration directed at decreasing acid injury to the gastro- may be an unreliable index of adequate perfusion in the immediate post-
duodenal mucosa are an essential part of the management of critically operative period, and to seek other indices of perfusion through careful
ill patients. 27 history-taking, physical examination, and first-hand knowledge of the
patient’s perioperative course. For example, a prior history of congestive
heart failure predicts susceptibility to fluid overload, and thus should
PERIOPERATIVE RESPIRATORY FAILURE slow the physician’s hand in administering fluid. Similarly, familiarity
In the period before, during, and after surgical treatment, patients are with the patient’s preoperative blood pressure, heart rate, heart sounds,
unusually vulnerable to respiratory failure owing to special manifesta- pulse volume, and digital perfusion allow the discerning physician to
tions of pulmonary edema, atelectasis, hypoventilation, aspiration, detect early signs of hypoperfusion requiring volume replacement. Often,
sepsis, and hypotension. Awareness of the factors promoting each of these the critical distinction between fluid overload and hypovolemia is not
interrelated processes makes possible an effective prevention program or clear even to the astute clinician, and in such cases central hemodynamic
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early diagnosis and treatment of perioperative respiratory failure. measurements can be helpful. Alternatively, numerous noninvasive
methods for assessment of volume responsiveness can provide valuable
■ PULMONARY EDEMA information. For example, trends over time in the respiratory variations
in arterial pressure and stroke volume can provide important qualitative
Of the forces in the Starling equation governing transcapillary fluid flux, information on fluid responsiveness in patients receiving mechanical
the ones of particular relevance to surgical patients are microvascular ventilation with no spontaneous breathing effort. In spontaneously
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hydrostatic pressure and pulmonary capillary permeability. breathing patients, examining the stroke volume (or its surrogates)
Microvascular Pressure: As indicated, secretion of ADH and aldosterone response to a simple test like passive leg-raising has been shown to be a
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is a major component of the metabolic response to surgery and trauma. valuable approach. However, it needs to be emphasized that an increase
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Both hormones tend to conserve water and decrease urine output in in stroke volume in response to fluids does not mean that the patient
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the postsurgical patient. However, a focus on increasing urine output needs this increase in his/her stroke volume.
in the surgical patient by administering large volumes of fluid without Pulmonary Capillary Permeability: A frequent cause of increased capillary
regard to this metabolic response could easily result in fluid overload and permeability and respiratory failure in the surgical patient is unrecog-
pulmonary edema, leading to hypoxemia. Guidelines for fluid resuscita- nized sepsis, which is commonly seen in the abdomen; this source often
tion in the perioperative period that focus primarily on urine output and requires a surgical or percutaneous radiologic approach. Therefore, a
fluid replacements based on empirical values can increase extravascular major component of the prevention and treatment of respiratory failure
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