Page 1667 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1186 PART 10: The Surgical Patient

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in burn tissue can be restored only with expansion of the extracellular LABORATORY STUDIES
space. Most edema occurs locally at the burn site and is maximal at Although the initial lactate is a strong predictor of mortality, 18,22,61 it is
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around 24 hours postinjury. 16,22,25,27,28,42,53 The rate and extent of edema not clear how serum lactate can be used as a resuscitation end point. 26,61,62
formation in major burn injury far exceed the intended beneficial effect Although lactate and base deficit (BD) are resuscitation markers that act
of inflammatory system activation. 16,45 The edema itself results in tissue as independent variables, 61-63 there is a low correlation between urinary
hypoxia and increased tissue pressure with circumferential injuries. output, mean arterial pressure, serum lactate, and base deficit. Serum
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Aggressive fluid therapy can correct the hypovolemia but will accentuate lactate trends provide greater information regarding the homeostatic
the edema process. 16,17,45,54 status. 64,65 Determinations of BD do not demonstrate the same predictive
power; the effect of specific correction of the BD during fluid resuscita-
FIRST-LINE MONITORING tion is unknown. 41,61,63 There are insufficient data to make recommenda-
tions on the use of BD or lactate as resuscitation guidelines during burn
Although urine output and heart rate are the primary modalities for resuscitation or as independent predictors of outcome in patients with
monitoring, the current standards for monitoring fluid therapy in large burns. 22,26,62,66 Hematocrits of 55% to 60% are not uncommon in the
patients with large burns are not necessarily supported by data. 12,13,24,55 early postburn period. Trying to normalize a hemoglobin or hematocrit
Reliance on hourly urine output as the sole index of optimum resuscita- during the resuscitation period invariably leads to fluid overload and
tion sharply contrasts with the lack of clinical studies demonstrating the cannot be used to monitor fluid resuscitation.
ideal hourly urine output during resuscitation. The American Burn
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Association Practice Guidelines for Burn Shock Resuscitation recom- ■ RESUSCITATION END POINTS
mend 0.5 mL/kg/h urine output in adults and 0.5 to 1.0 mL/kg/h in chil-
dren weighing <30 kg. 22,26,27,47 Lesser hourly urinary outputs in the first End points of resuscitation have been the subject of numerous strategies
27
48 hours postburn almost always represent inadequate resuscitation. 54 with conflicting results. 12,19,22,32,41,43,44,46 Many authors feel that urine output
No factor other than airway protection is as critical in the early post- and traditional vital signs (heart rate and mean arterial pressure)
burn period as vascular access. Ideally, it is wise to obtain peripheral are too insensitive to ensure appropriate fluid replacement in burn
intravenous access away from burned tissues. Most patients with small- injuries. 26,40,59,62 In children, trends in heart rate, blood pressure, and capil-
17
44
to medium-sized burns do not require central catheters. Reliable periph- lary refill toward normal are reasonable therapeutic end points. In adults,
eral veins should be used to establish an IV line. Use vessels underlying arterial blood pressure is relatively insensitive to the adequacy of fluid
burned skin only if necessary. If it is impossible to establish peripheral replacement; pulse rate is more helpful. In older patients or those taking
venous access, intraosseous lines may be necessary, and may safely be β-blockers, pulse rate becomes less reliable. Urine output can be taken
placed in patients of any age. These tools obviate the need for cut downs to reflect organ perfusion; however, urine must be nonglycosuric to be
17
in burn patients. If unable to insert an intraosseous line, central venous accurate. Hypertonic saline can increase urine output due to an osmotic
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access may be necessary using a short, large bore rapid infusion line diuresis that does not accurately reflect volume status. Although urine
made specifically for large volume resuscitation. A patient undergoing output does not precisely mirror renal blood flow, it remains the most
resuscitation should have a urinary catheter placed so that hourly urine readily accessible and easily monitored index of resuscitation. 54,67
outputs may be monitored. In children, diapers can be weighed for accu- ■
rate outputs. Nasogastric tubes should be considered in patients with FLUID CREEP
>20% TBSA burns, as they will experience gastroparesis and probable The use of excessive volumes for resuscitation is being documented with
emesis. The attached burn diagrams for adults and children will help increasing frequency in many burn centers. 30,68 Burn care providers have
1
guide the clinician in providing the optimal fluid resuscitation. become more aggressive with the administration of benzodiazepines
Hemodynamic monitoring and treatment of deviation from nor- and narcotics, which may result in additional fluid demands. 18,28,67,69-71
movolemia are the fundamental tasks in intensive care. A pulse rate Outreach education in burn care has contributed to a new problem:
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<110 beats/min in adults usually indicates adequate volume, with rates excessive resuscitation given by first responders and nonburn physicians.
>120 beats/min usually indicative of hypovolemia. Narrowed pulse Thus, many patients arrive at a burn center having received much of
pressure correlates with reduced stroke volume and provides an earlier their first 24 hour fluid requirements in just an hour or two. 30
indication of shock than systolic blood pressure alone. Noninvasive
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blood pressure measurements by cuff are rendered inaccurate because ■ VITAMIN C RESUSCITATION
of the interference of tissue edema and read lower than the actual blood
pressure. Resuscitation based on a blood pressure cuff will provide a del- The landmark study by Tanaka et al showed that high-dose ascorbic
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eterious amount of overresuscitation to a burn patient. An arterial catheter acid during the initial 24 hours postburn reduced fluid requirements
placed in the radial artery is the first choice, followed by the femoral artery. by 40%, reduced burn tissue water content 50%, and reduced ventilator
The clinical benefits led to a clear reduction in edema and body
72,73
days.
■ PULMONARY ARTERY/CENTRAL VENOUS CATHETERS weight gain and were associated with reduced respiratory impairment
17,72,73
The decision to perform invasive hemodynamic monitoring requires and reduced requirement for mechanical ventilation. Although not
in mainstream use in the United States, the findings are meaningful to
careful consideration. The lack of benefit associated with goal-directed experienced burn care practitioners, and may gain traction in the future.
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supranormal therapy has resulted in waning enthusiasm for the use of
pulmonary artery catheters. 57,58 The most applicable cardiac output-
related variable to manipulate in burn patients is preload. Pulmonary PREVENTABLE COMPLICATIONS
indicators of preload. As long as other signs of adequate tissue perfu- ■ HYPOTHERMIA
artery occlusion pressure and central venous pressure are not good
22
sion are normal, the temptation to normalize filling pressures should be The profoundly adverse effects of hypothermia cannot be overstated.
avoided. The use of end points demonstrating the adequacy of oxygen Strategies to vigorously prevent hypothermia include a warmed room,
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delivery has not yet found a place in the management of burn shock 40,46,59 warmed inspired air, warming blankets, and countercurrent heat
and use of pulmonary artery catheters in burn resuscitation has fallen exchangers for infused fluids. Metabolic responses can be minimized
out of favor. Lithium dilution cardiac output monitoring (LiDCO) and by treating the patient in a thermoneutral environment (32°C). During
3
other less invasive monitoring tools such as transpulmonary thermodi- hydrotherapy, in the operating room, and in the burn unit during a
lution, the PiCCO, and the esophageal Doppler hold great promise for resuscitation, maintain the room temperature at 85°F and 35% to 40%
monitoring the burn patient through the acute resuscitation phase. 60 humidity to minimize heat loss and decrease metabolic rate.

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