Fluid management

The objectives of postoperative fluid management are:

1) to maintain an adequate intravascular volume

2) to reduce the excessive interstitial fluid overload

3) to prevent congestive heart failure and subsequent pulmonary edema.

We are able to evaluate the postoperative fluid balance of an individual patient by:

1) obtaining accurate central venous pressure, pulmonary capillary wedge pressure, pulmonary diastolic pressure

2) assessing the adequacy of cardiac output

3) evaluating the patient input output record

4) obtaining daily weight records and comparing them to preoperative weight

5) determining the postoperative hematocrit

6) determining the postoperative hourly urine output and specific gravity

7) clinical examination of the patient.

Management is governed by the following principles:

1) Patients who have a low central venous pressure and pulmonary artery di-astolic pressure in conjunction with a low cardiac output and a low hematocrit should have packed red blood cells infused to increase the intravascular volume.

2) Patients with a low CVP, a low pulmonary artery diastolic pressure and a low cardiac output who have a normal or high hematocrit should have one of two modes of therapy.

In the early postoperative period where significant interstitial fluid volume exists, 12.5-25 grams of mannitol is given IV to shift fluid from the interstitial to the intravascular space and subsequently to the urine. The utilization of 50 cc of 25% albumin accomplishes the same shift of fluid from the interstitial to the in-travascular space; however, it does not provide an adequate diuresis. IV Lasix 10-40 mg IV push may be given both in conjunction with mannitol and in conjunction with albumin to ensure the loss of the excessive interstitial fluid volume.

In patients who are further postop and who have demonstrated by examination of the I & O record and the daily weights that their interstitial fluid volume is normal, yet who still have a low filling pressure and evidence for intravascular fluid depletion, should be treated with intravascular volume replacement. It is our choice to use fluids that have their own oncotic pressure so that they remain in the intravascular space for prolonged periods of time. Our preference is to give 250 cc volumes of 5% albumin or equivalent volumes of Hespan.

In individuals in whom the CVP and pulmonary artery diastolic pressures are elevated, the cardiac output is down, and clinical evidence suggests congestive heart failure or pulmonary edema efforts should be turned to reducing intravas-cular volume. Under these circumstances, furosemide or ethacrynic acid diuresis is the treatment of choice. In addition, utilization of digoxin for patients with significant histories of congestive heart failure may be utilized. Oxygen via mask or nasal prongs may be used to improve arterial oxygen saturation while morphine may be given to rapidly decrease preload and help bring the patient out of his congestive heart failure state.

In addition to the above one must be careful to evaluate the serum and urine glucose levels on patients known to be diabetic. Excessive glucose loss in the urine can provide for rapid intravascular depletion due to the osmotic diuresis. The

situation should be quickly recognized and treated with the appropriate use of insulin.

Electrolyte Management

Postoperative electrolyte status should be evaluated by: 1) serum and urine electrolytes; 2) serum and urine osmolality determinations; 3) serum and urine creatinine and BUN; 4) by performing a good daily clinical examination. Therapy regulating disturbances in fluid electrolyte status should be as follows:

1) In conditions where there is evidence of excessive total body water with a drop in serum sodium, serum osmolality and increase in body weight, fluid restriction is indicated. These individuals should be put on fluid limits between 1,000 and 1,500 cc per day.

2) In cases where there is evidence of intravascular volume depletion with elevated serum sodium, serum osmolality, and elevated urine specific gravity and osmolality with a diminution in urine sodium, intravascu-lar volume replacement as described previously is indicated.

3) Due to the obligatory diuresis that all of our patients undergo, significant urinary potassium loss may be anticipated. It is therefore mandatory that all postoperative cardiac surgical patients have frequent serum potassium determinations and IV bolus infusions of potassium chloride to maintain stable normal levels. It is our policy to give potassium as 10 mEq IV boluses in 50 cc D5W over an hour. Several of these boluses are usually given the first and second postoperative days.

Postoperative Bleeding

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