Читать книгу Disorders of Fluid and Electrolyte Metabolism - Группа авторов - Страница 49

The permissive use of hypotonic or even near-isotonic solutions in concert with the non-osmotic release of AVP in response to postoperative stress including pain and nausea frequently leads to a positive water balance and, thus, hyponatremia. In a prospective study conducted in surgical wards, 4.4% of 1,088 patients developed hyponatremia ([Na⁺] <130 mEq/L) in the first week post-surgery. Of those, 94% had received hypotonic fluids, and AVP was detectable in all in whom it was measured [43]. Most patients (42%) were euvolemic and only 8% showed signs of volume depletion. Hyponatremia was observed most commonly with organ transplantation, cardiovascular and trauma surgery. In studies focusing on cardiac surgery, hyponatremia prevalence reports ranging from 12% [44] ([Na⁺] <133 mEq/L) to 59% ([Na⁺] <135 mEq/L) have been published [45]. Similarly, Okada et al. [46] found hyponatremia in 53% of patients ensuing within 2 days after esophageal or head-and-neck surgery if they had received hypotonic maintenance fluids; with the use of isotonic fluids the hyponatremia rate was 16%. Children seem to be at increased risk of developing postoperative hyponatremia. In a prospective study on 81 pediatric patients (mean age 10 years), 31% developed hyponatremia ([Na⁺] <135 mEq/L) at 24 h after surgery [47]. Au et al. [48] compared the prevalence of postoperative hyponatremia in 145 children receiving either hypotonic or isotonic fluids. Moderate hyponatremia ([Na⁺] 125–130 mEq/L) occurred in 10.3 and 3.5% and severe hyponatremia ([Na⁺] <125 mEq/L) in 2.6 and 0%, respectively.

The use of high volume non-conductant (and therefore electrolyte-free) irrigation solutions used in transurethral prostatectomy can lead to marked absorption of water resulting in often severe and symptomatic dilutional hyponatremia [49]. The prevalence of this so-called transurethral resection syndrome is not well studied but smaller examinations reported a rate of 0.8–2% [50, 51].

Hyponatremia is a frequently encountered complication after trans-sphenoidal surgery, with a typical delayed drop of serum [Na⁺] approximately at the end of post-operative week 1 [52]. This time pattern may well pose a risk for patients that are discharged early after surgery. A triphasic sequence of diabetes insipidus, hyponatremia, and diabetes insipidus again is also sometimes observed [53, 54]. Although the underlying mechanism is not entirely understood, the release of AVP stores from axons that have been disrupted by the surgical procedure is the most likely cause [55, 56]. However, cerebral salt wasting and in some cases glucocorticoid deficiency may also contribute. In a recent paper, collating data from 10 published studies on the subject and comprising 2,947 patients, delayed hyponatremia occurred in 3.6–19.8% patients [57].