Question 16

Created on Thu, 05/21/2015 - 16:10
Last updated on Mon, 05/01/2017 - 17:44
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Outline the methods available to estimate fluid balance in the critically ill patient  and briefly discuss their advantages and limitations. (You may tabulate your answer).

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College Answer

Method

Advantages

Limitations

Clinical – oedema, JVP,
skin turgor, hydration of tongue

Simple, easily done by the
bedside, not time consuming

Lack specificity

Intake–output chart

Simple method, reasonably
accurate in most patients

Labour intensive,
Insensible water losses not factored in, Losses through leaks in bed, drain disconnections and in the case of burns patients, severe evaporative water losses not taken inot account

Body-weight

May be useful in
uncomplicated critically ill patients

Not routinely used in all
ICUs, time consuming, labour intensive, difficult in the ventilated patient, (zeroing has to be done properly with sheets and pillows), addition of moisture from perspiration and spills can change baseline weight
Correlation with I-O charts not high.

CVP/ PCWP/Echo

Used to predict
intravascular status

Significant limitations

EVLW

Shown to be of value in a trial comparing it with PAC

Invasive technique

Research methods include
Bioelectrical impedance, determination of total body water and plasma volume using radionuclide techniques

Research tools, do not lend
themselves to serial measurements

Discussion

This tabulated reponse is difficult to improve upon. It is reasonably comprehensive, and it remains within the realms of the achievable for a crazed exam candidate.

The college answer seems to ask about the estimation of total body water, rather than any other sort of fluid-related assessment. The candidate who carried on about estimation of fluid responsiveness would have been penalised.

The table mentioned above could be treated in a slightly more granular fashion, and I will attempt to do this with some references, expanding on some omitted details (for instance, it is perhaps insufficiently enlightening to simply say that the pulmonary artery catheter and CVP have "significant limitations").

Estimation of Fluid Balance in the Critically Ill Patient

Method

Advantages

Disadvantages

Clinical estimates
  • Cheap
  • Easily performed at the bedside
Fluid balance chart
  • Cheap
  • Easily performed at the bedside
  • Accuracy depends on accuracy or recording
  • Usually, cumulative balance records are inaccurate and tend to disagree with body weight measurements
  • This technique fails to estimate losses into incontinence pads, spilled secretions, sweat, evaporative losses from wounds, and losses via the lungs; in short "insensate" losses are forgotten.
Daily weights
  • Easily performed in the presence of specialised bed equipment
  • Accuracy depends on accuracy of recording
  • Requires expensive bed equipment
  • Requires attention to detail - one must ensure the same amount of bedding and on-bed equipment is with the patient each time, otherwise fluctuations in weight may occur. Usually, there is about 3.5kg of nonremovable hardware in the bed together with the patient.
  • Correlates poorly with bedside charts
  • Lack of evidence for cost-effectiveness
CVP
  • Easily performed at the bedside
  • Constant monitoring is possible
PAWP
TTE
  • Interpreter-dependent
  • Serial assessments across a series of clinicians may yield variation purely due to technique
  • Yields information regarding chamber filling volumes rather than total body fluid volume - and then you infer the fluid balance from this.
  • Not universally accepted as a method to assess intravascular volume
  • Only accurate when compared to the (known to be useless) clinical examination by an expert.
PAC or PiCCO EVLW
  • Invasive
  • Labour-intensive (thermodilution measurement)
  • Association with cardiac function makes it difficult to use lung water to estimate whole-body fluid balance
Bioimpedance
  • Experimental technique, yet to be validated
  • Does not agree with thermodilution measurements
  • Most of the available methods measure transthoracic bioimpedance, which relies on the absence of pleural effusion, and is usually useless in cardiac surgery or thoracic trauma
Tritium indicator dilution
 

References

Schneider, Antoine G., et al. "Estimation of fluid status changes in critically ill patients: Fluid balance chart or electronic bed weight?." Journal of critical care27.6 (2012): 745-e7.

Schoeller DA, van Santen E, Peterson DW, Dietz W, Jaspan J, Klein PD: Total body water measurement in humans with 18O and 2H labeled water. Am J Clin Nutr 1980, 33(12):2686-2693

Charra, Bernard. "Fluid balance, dry weight, and blood pressure in dialysis."Hemodialysis International 11.1 (2007): 21-31.

Stephan, F., et al. "Clinical evaluation of circulating blood volume in critically ill patients—contribution of a clinical scoring system†." British journal of anaesthesia 86.6 (2001): 754-762.

Chung, Hsaio-Min, et al. "Clinical assessment of extracellular fluid volume in hyponatremia." The American journal of medicine 83.5 (1987): 905-908.

Schneider, Antoine Guillaume, et al. "Electronic bed weighing vs daily fluid balance changes after cardiac surgery." Journal of critical care 28.6 (2013): 1113-e1.

Perren, A., et al. "Fluid balance in critically ill patients. Should we really rely on it?." Minerva anestesiologica (2011).

Wilson, John N., et al. "Central venous pressure in optimal blood volume maintenance." Archives of Surgery 85.4 (1962): 563-578.

Piccoli, Antonio, et al. "Relationship between central venous pressure and bioimpedance vector analysis in critically ill patients." Critical care medicine28.1 (2000): 132-137.

Marik, Paul E., Michael Baram, and Bobbak Vahid. "Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares." CHEST Journal 134.1 (2008): 172-178.

Mitchell, John P., et al. "Improved outcome based on fluid management in critically III patients requiring pulmonary artery catheterization." American Review of Respiratory Disease 145.5 (1992): 990-998.

Bethlehem, Carina, et al. "The impact of a pulmonary-artery-catheter-based protocol on fluid and catecholamine administration in early sepsis." Critical care research and practice 2012 (2012).

Schwann, Nanette M., et al. "Lack of effectiveness of the pulmonary artery catheter in cardiac surgery." Anesthesia & Analgesia 113.5 (2011): 994-1002.

Wheeler, A. P., et al. "Pulmonary-artery versus central venous catheter to guide treatment of acute lung injury." N Engl J Med 354.21 (2006): 2213-2224.

Nguyen, Viviane TQ, et al. "Handheld echocardiography offers rapid assessment of clinical volume status." American heart journal 156.3 (2008): 537-542.

Schuller, D., et al. "Fluid balance during pulmonary edema. Is fluid gain a marker or a cause of poor outcome?." CHEST Journal 100.4 (1991): 1068-1075.

Marik, Paul E. "Hemodynamic parameters to guide fluid therapy." Transfusion Alternatives in Transfusion Medicine 11.3 (2010): 102-112.

Monnet, Xavier, et al. "Assessing pulmonary permeability by transpulmonary thermodilution allows differentiation of hydrostatic pulmonary edema from ALI/ARDS." Intensive care medicine 33.3 (2007): 448-453.

Mattar, J. A. "Application of total body bioimpedance to the critically ill patient. Brazilian Group for Bioimpedance Study." New horizons (Baltimore, Md.) 4.4 (1996): 493-503.

Foley, Kieran, et al. "Use of single-frequency bioimpedance at 50 kHz to estimate total body water in patients with multiple organ failure and fluid overload." Critical care medicine 27.8 (1999): 1472-1477.

Barry, Ben N., et al. "Lack of agreement between bioimpedance and continuous thermodilution measurement of cardiac output in intensive care unit patients."Critical Care 1.2 (1997): 71.

House, Andrew A., et al. "Volume assessment in mechanically ventilated critical care patients using bioimpedance vectorial analysis, brain natriuretic peptide, and central venous pressure." International journal of nephrology 2011 (2010).

Vincent, Jean-Louis, et al. "Clinical review: Update on hemodynamic monitoring-a consensus of 16." Crit Care 15.4 (2011): 229.