Late Resuscitation

Table 63-13 summarizes end points for late resuscitation, and Figure 63-10 presents an algorithm for management. Fluid administration is an integral, mandatory component of late resuscitation. The adequacy of resuscitation should not be judged by the presence of normal vital signs but by normalization of organ and tissue perfusion. The role of the anesthesiologist-intensivist is to recognize the presence of ongoing shock after traumatic hemorrhage and resuscitate the patient with the appropriate fluid, in the appropriate amount, at the appropriate time.

Late resuscitation begins once bleeding is definitively controlled by surgery, angiography, or the passage of time. The practitioner's goal at that time is to rapidly restore normal perfusion to all organ systems while continuing to support vital functions. Hypoperfusion caused by hemorrhagic shock triggers a predictable cascade of biochemical events that will cause physiologic derangements persisting

TABLE 63-13 -- Goals for late resuscitation *

Maintain systolic blood pressure >100 mm Hg

Maintain hematocrit above individual transfusion threshold

Normalize coagulation status

Normalize electrolyte balance

Normalize body temperature

Restore normal urine output

Maximize cardiac output by invasive or noninvasive measurement

Reverse systemic acidosis

Document decrease in lactate to normal range

*Fluid administration should be continued until adequate systemic perfusion can be verified.

The search for the optimal end point of resuscitation has led to several different hemodynamic, acid-base, and regional perfusion targets. Table 63-14 summarizes modalities that are available to gauge the adequacy of resuscitation, along with the shortcomings of each technique. Although the flow of blood to tissue beds is a determinant of tissue perfusion, pressure should also be an important consideration. The left ventricular stroke work index is a variable that accounts for both flow and pressure. Furthermore, left ventricular power output has been used to quantify left ventricular performance. These indices were compared with purely flow-derived hemodynamic and oxygen transport variables as markers of perfusion and outcome in critically injured patients during resuscitation.^[98] A consecutive series of 111 patients were monitored with a volumetric pulmonary artery catheter during the first 48 hours of resuscitation. The ability to clear lactate in less than 24 hours and survival were studied. Survivors had significantly higher stroke work and left ventricular performance than nonsurvivors did. These variables, in addition to heart rate, were the only ones that were significantly related to lactate clearance and survival. The higher stroke work and left ventricular performance

TABLE 63-14 -- Methodologies for assessment of systemic perfusion

Technique	Shortcomings
Vital signs	Will not indicate occult hypoperfusion
Urine output	May be confounded by intoxication, diuretic therapy, circadian variation, or renal injury
Systemic acid-base status	Confounded by respiratory status
Lactate clearance	Requires time to obtain laboratory result
Cardiac output	Requires placement of a pulmonary artery catheter or use of noninvasive technology
Mixed-venous oxygenation	Difficult to obtain, but a very accurate marker
Gastric tonometry	Requires time to equilibrate, subject to artifact
Tissue-specific oxygenation	Investigational techniques; may not indicate satisfactory systemic perfusion

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Figure 63-10 Algorithm for the management of late hemorrhagic shock. HCT, hematocrit; HR, heart rate; PA, pulmonary artery; PT, prothrombin time; SBP, systolic blood pressure.

Monitoring resuscitation with clinical variables and monitoring the adequacy of systemic oxygen delivery with invasive monitors may be supplemented in the future with an approach that assesses the return of adequate metabolism, respiration, and oxygen transport in peripheral tissue beds. One minimally invasive technique that has been proposed is tissue oxygen monitoring (skin, subcutaneous tissue, or skeletal muscle). Skeletal muscle blood flow decreases early in the course of shock and is restored late during resuscitation, thus making the skeletal partial pressure of oxygen a sensitive indicator of low flow.^[99]

Tissue hypercapnia has been suggested as a universal indicator of critically reduced perfusion (also see Chapter 74 ). Management of gastric mucosa PCO₂ through gastric tonometry has been used in trauma patients as an indicator of restoration of splanchnic blood flow, and distal gut pH has shown promise as a reliable indicator. ^[100] The esophageal wall has also been demonstrated to be an appropriate site for tissue PCO₂ measurements during hemorrhagic shock,^[101] and recently, the most proximal area of the gastrointestinal tract, the sublingual mucosa, has been shown to be a useful site for measurement of PCO₂ . When sublingual PCO₂ exceeded a threshold of 70 mm Hg (normal = 45.2 ± 0.7 mm Hg), its positive predictive value for the presence of physical signs of circulatory shock was 100%. ^[102] Inadequate tissue perfusion, as indicated by these specific monitors or by the traditional systemic markers of serum lactate, base deficit, and decreased pH, must be promptly treated once hemorrhage has been controlled. The rate at which a shock patient's lactate returns to the normal range is strongly correlated with outcome: failure to reach the normal range

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