— Some 38 hospitals are arrayed against the Department of Revenue in this case. The hospitals claim exemption from sales or use taxes on certain substances and machines because of the statutory exemptions for prescription drugs and prostheses. RCW 82.08.0281, 82.12-.0275, 82.08.0283, 82.12.0277. The Department's initial deficiency assessments for these taxes were affirmed by its Interpretation and Appeals Division and, on the hospitals' appeal, by the Board of Tax Appeals. The Superior Court reversed, and the case is here on the Department's appeal.
Many details have been shed along the way. Remaining at issue here are only lab reagents and nutrition products1 in the prescription category, and heart-lung machines in the prosthesis category. We affirm the Superior Court on the prescription issue and reverse it on the prosthesis issue.
The Board ruled that reagents and nutrition products were within the statutory class of prescription items, but were not exempt because the hospitals did not show separate charges to the patients for these items. It held that the heart-lung machines were not prostheses because they only temporarily fulfilled a body function. Reversing the Board, the Superior Court held that the prescription exemption did not turn on proof of sale to a patient, and that permanent replacement of a body function was not necessary to qualify an item as a prosthesis.
The Department directly contests the Superior Court's prosthesis ruling, but it does not directly challenge the prescription issue ruling. Instead, it contends here for the first *785time that reagents and nutrition products are not prescription items- We hold that the Department's appeal on the prescription issue is foreclosed by the doctrine of invited error. We hold that heart-lung machines simply do not qualify for exemption under the statute.
The Department's position at every stage of this litigation has been that reagents and nutrition products were prescription items.2 Its only argument was that the exemption was unavailable for want of proof that the items were resold to patients. The Department's Interpretation and Appeals Division stated in its final determination:
We do not dispute that laboratory reagents may be drugs or other substances which are generically classified as "prescription" items. Also, they are used by hospitals in the diagnosis, treatment, and prevention of disease and ailments in humans. However, at the time of their purchase by hospitals from suppliers they are not prescribed for any person or any purpose. Moreover, they are admittedly not purchased for resale to any person. For these reasons the criteria of the statutes for tax exemption are not met.
(Italics ours.) Regarding nutrition products, the final determination stated:
If any portion of [nutrition products] are sold outright to patients or administered to patients, by prescription, hospitals need not collect sales tax upon the identifiable charges to patients for such things and may receive a refund of any sales or use tax paid by the hospitals on such items.
(Italics ours.)
The Department never contended that the exemption should be denied because the items were not administered to patients by prescription. Its position is reflected in the following portion of the final determination:
The conclusions contained in this Final Determination may result in some entitlement to either corrections of tax assessments or tax refunds in some specific hospitals' cases, regarding . . . nutrition products. The burden rests exclusively with each individual hospital to show that it has made identifiable charges to patients for these things.
*786(Italics ours.) Before the Board, the Department framed the issue as follows:
Whether the hospitals have qualified for the sales and use tax exemption granted to prescription drugs when they have not shown that both [sic] a drug is prescribed and sold to a patient?
While the issue as framed by the Department refers both to "prescription" and "sale" requirements, the record shows mention of the prescription requirement only in passing. The main focus always concerned the existence of a documented sale.
In its memorandum before the Board, the Department characterized the final determination as follows:
In its determination, the Department agreed that specific nutrition products such as Osmolite and Ensure constituted "other substances other [sic] than food for . . . cure, mitigation, treatment ... of disease ..." which are prescribed by a pharmacist or practitioner.
(Italics ours.) Also from the Department's Board memorandum:
The Department in its determination agreed that reagents, in the form of either drugs or other substances, would be considered prescription items. However, the reagents do not satisfy the requirement for the prescription drug exemption because the reagents are not resold to the patient.
(Italics ours.) The Department further stated its position to the Board as follows:
We do not particularly contest the fact that the drugs might, in a medical sense, all be termed prescription drugs in the sense that one simply cannot obtain these over the counter, that is not the issue. . . . Where, if the hospitals have separate line items, a sale of a prescription drug, and of course, provides proof that it was made pursuant to a prescription, the department has allowed the sale.
(Italics ours.) Finally, the Department proposed and the Board adopted the very finding of fact that it now challenges:
[Ljaboratory reagents, and nutrition products may be administered to a patient only upon the written prescription of a physician, or upon an oral prescription that is subsequently reduced to writing.
*787It also proposed the following conclusion of law, which was substantially adopted by the Board:
[L]aboratory reagents, and nutrition products which would otherwise qualify as prescription items are not entitled to the prescription drugs exemption because there is no separate line item proving resale to patients.
(Italics ours.) A more perfect example of invited error cannot be imagined. We will not consider the Department's new position on prescription items. Davis v. Globe Mach. Mfg. Co., 102 Wn.2d 68, 77, 684 P.2d 692 (1984); Western Nat'l Assur. Co. v. Hecker, 43 Wn. App. 816, 821, 719 P.2d 954 (1986).
In proceedings before the Board and the Superior Court, the prosthesis issue has involved a war of conflicting dictionary definitions, in which the main skirmish has revolved around whether a heart-lung machine "replaced" an organ of the body, and whether the replacement, if any, is permanent or temporary. The Department argued that only permanent replacements qualify as prostheses; the trial court held that permanence is not required. We need not venture into this conflict, for application of the statute exempting prosthetic devices does not turn on whether an item is a prosthesis, for not every prosthesis is exempt and the machines in question, even if prostheses, do not qualify for exemption.
RCW 82.08.0283 provides, in relevant part:
Exemptions — Sales of . . . prosthetic and orthotic devices, . . . The tax levied by RCW 82.08.020 shall not apply to sales of . . . prosthetic . . . devices prescribed for an individual by a person licensed under chapters 18.25, 18.57, or 18.71 RCW or dispensed or fitted by a person licensed under chapter 18.35 RCW . . .
There is no need to construe or interpret a statute when its language is plain. Northwest Steel Rolling Mills, Inc. v. Department of Rev., 40 Wn. App. 237, 240, 698 P.2d 100, review denied, 104 Wn.2d 1006 (1985); Bernstein v. State, 53 Wn. App. 456, 460, 767 P.2d 958, review denied, 112 Wn.2d 1024 (1989). Statutory words are to be given their ordinary meaning. Pacific Northwest Alloys, Inc. v. State, *78849 Wn.2d 702, 306 P.2d 197 (1957). A statute must be construed to avoid strained results or absurd consequences. Briggs v. Thielen, 49 Wn. App. 650, 654, 745 P.2d 523 (1987), review denied, 110 Wn.2d 1020 (1988). Tax exemptions must be construed narrowly, and the burden of establishing the exemption falls on the taxpayer. Department of Rev. v. Schaake Packing Co., 100 Wn.2d 79, 83, 666 P.2d 367 (1983). Reading RCW 82.08.0283 in light of these construction principles, we conclude that the heart-lung machines simply do not come within the exemption.
The record shows that heart-lung machines are sold only to hospitals, not to patients. They become part of the hospitals' surgical equipment, used routinely in all surgical procedures involving the heart and lungs. The machines are not sold to a hospital because they have been prescribed for an individual, and they are not sold to patients at all. Indeed, their use is not "prescribed" in the common medical meaning of the word, let alone prescribed for or dispensed to an individual by any of the practitioners identified. Webster's Third New International Dictionary 1792 (1966).3 The hospitals have failed to show that these machines qualify for the exemption because they are prescribed for the particular use of specific individuals.
The Superior Court's order concerning prescription items is affirmed; its order concerning prostheses is reversed.
Alexander, C.J., concurs.
Reagents are used to analyze body fluids for diagnostic purposes. Nutrition products are liquid diets formulated to provide balanced nutrition as a sole source of nourishment.
The hospitals did not specifically adduce evidence before the Board to show that these were prescription items, obviously because the Department had already conceded the point.
RCW 82.08.0283 refers to chiropractors (RCW 18.25), osteopaths (RCW 18.57), physicians (RCW 18.71), and hearing aid dispensers (RCW 18.35).