Studies on water and electrolyte metabolism in postoperative patients
It has been well known for many years that the patients who have undergone major surgery tend to restrict the urinary excretion of sodium and increase the potassium. There are many reports warning of the hazards of infusing a large amount of sodium chloride following surgery. This was emphasized by Matas(1924) and demonstrated in balance studies by Coller et al.(1945).
Retention of sodium and increased excretion of potassium are due to the increased production of aldosterone, a metabolic response to surgery. This causes a decreased urinary Na**+ /K**+ ratio. However, plasma sodium tends to be lovered following surgical trauma, a phenomena which Moore(1952) called "sodium paradox". A secondary factor affecting water metabolism is the anti-diuretic hormone. Thus, metabolic changes in the postoperative state are extremely complex. The problems of water and electrolyte replacement after surgery are difficult for surgeons.
Hong et al.(1961). Kim(1963) and Lee(1965), in their studies on water and electrolyte metabolism, reported that the sodium excretion rate is greater in the Korean than in the occidentals, because although the Korean protein intake is less, the sodium chloride intake is greater. Because the Korean sodium excretion ratio is greater than the occidentals it was postulated that a different pattern of metabolic changes following surgery might be found in the Korean.
Hence, this investigation was undertaken to clarify the pattern of water and electrolyte metabolism in postoperative Korean patients and to establish the proper mean for fluid replacement after surgery.
Twenty patients who had major surgery were used for study and divided into groups. Those who had liver cirrhosis, congestive heart failure, nephrosis or pregnancy which were known to increase aldosterone ascretion were exclude. Group Ⅰ received only 5% dextrose in water and no sodium during this experiment. In Group Ⅱ, 500ml of the daily fluid requirement was replaced with 5% dextrose in saline(adminstering 77 milliequivalents of sodium and chloride) daily except on the day of operation. Group Ⅲ recetived only 5% dextrose in water as in Group Ⅰ, but treated with 0.04mg/kg of Florinef acetate(9-alpha-fluorohydrocortisone) before operation, so that aldosterone activity was maximum on the day of operation.
In all cases, 24 hour urines were collected from 8 A.M. to next 8 A.M. and samples of venous blood were collected 12 hours after the beginning of each collection period for 5 days, beginning a day before operation and continuing for 4 days after operation. The following measurements were made pre- and postoperatively: volume, osmolality, urinary and plasma sodium, potassium and
chloride, the daily balance of water and electrolytes, and urnary Na**+/K**+ ratio to evaluate the aldosterone activity of each group.
The results may be summarized as follows:
1. Plasma osmolality showed a marked decrease on the 2nd day in Group Ⅰ, but it remained relatively stable in Groups Ⅱ and Ⅲ.
2. Plasma sodium also showed a marked decrease on the 4th day in Group Ⅰ, but it was relatively unchanged in Groups Ⅱ and Ⅲ.
3. Plasama potassium was elevated in all 3 group after operation.
4. The plasma chloride pattern was similar to that of the plasma sodium in all groups.
5. Each group showed water retention in the first 24 hours postoperatively. Diuresis began from the 2nd day. On the 3rd and 4th days, Group Ⅰ(no-sodium) excreted more urine than Groups Ⅱ and Ⅲ, even more than preoperative day excretion. This might be due to a water diuresis secondary to the infusion of sodium-free water. Despite the fact that each group had the same volume of fluid, Group Ⅰ fell into a severe negative water balace on the 3rd and 4th days. Groups Ⅱ and Ⅲ showed only a mild degree of negative balance.
6. The urinary osmolality of each group increased in the first 24 hours after surgery, but the amount of osmolal material excreted was decreased because of reduction in the urine volume.
7. The excretion of sodium in the urine was not decreased in the first 24 hours postoperatively in Groups Ⅰ and Ⅱ but did decrease gradually by the 3rd and 4th days. However in Group Ⅲ, there was a marked decrease beginning on the first day. Group Ⅰ fell into a severe negative sodium balance in the early postoperative days because of the continuing excretion of sodium. Groups Ⅱ and Ⅲ showed a mild negative balance.
8. The excretion of potassium in the urine was increased slightly in the first 24 hours postoperatively in all 3 groups.
9. In all groups, the excretion rate of chloride was parallel to that of sodium throughout entire study.
10. The urinary Na**+/K**+ ratio dropped to 3.0/1 and 2.3/1 on the first day of the postoperative period in Groups Ⅰ and Ⅱ, respectively, and in both groups the lowest value (2.0/1 and 1.6/1, respectively) on the 3rd day. Two cases of Group Ⅲ
who had similar major operation to those in Groups Ⅰ and Ⅱ showed the lowest ratio(1.2/1) on the first day.
As Moore(1952) stated, lowered plasma osmolality and plasma sodium in the postoperative period of Group Ⅰ might be a result of "sodium paradox", but there should not be any hazard in giving saline as long as the urinary excretion of sodium continues. The hyponatremia should be corrected by infusing saline as proved
in Group Ⅱ. Since aldosterone activity following surgical procedure is less pronounced in the Korean, there should not be an unnecessary restriction saline infusion in postoperative Korean patients.