<PAGE>

                                                                   Exhibit 10.21

                         RECEIVABLES PURCHASE AGREEMENT

     This Receivables Purchase Agreement (this "Agreement") is made as of the
14th day of May, 2002 (the "Effective Date") by and between Hudson Respiratory
Care Inc., a California corporation ("Seller"), and HRC Holding Inc., a Delaware
corporation ("Purchaser").

                                 R E C I T A L S

     A.   Seller has an interest in certain intercompany receivables identified
on Schedule A hereto in the aggregate face amount of $8,000,000 (the
"Receivables").

     B.   Seller desires to sell the Receivables to Purchaser, and Purchaser
desires to purchase such Receivables, on the terms and subject to the conditions
of this Agreement.

                                A G R E E M E N T

     In consideration of the foregoing recitals and the respective covenants and
agreements contained herein, the parties agree as follows:

                                    ARTICLE 1
                                PURCHASE AND SALE

     1.1  Sale and Purchase of the Receivables. Seller hereby sells, conveys,
transfers, assigns and delivers to Purchaser without recourse, representation or
warranty by Seller, and Purchaser hereby purchases from Seller, all of Seller's
right, title and interest in and to the Receivables, free and clear of any lien,
pledge, charge, easement, security interest, deed of trust, mortgage,
right-of-way, encroachment or encumbrance.

     1.2  Consideration. The consideration for the sale and transfer of the
Receivables (the "Purchase Price"), shall be $8,000,000, which consideration is
being paid to Seller by Purchaser concurrently herewith.

                                    ARTICLE 2
                            COVENANTS AND AGREEMENTS

     2.1  Further Assurances. Seller agrees and covenants to execute,
acknowledge and deliver any further deeds, assignments, conveyances and other
assurances, documents and instruments of transfer, reasonably requested by
Purchaser, and will take any other action consistent with the terms of this
Agreement that may reasonably be requested by Purchaser, for the purpose of
assigning, transferring, granting, conveying and confirming to Purchaser, or
reducing to possession, the Receivables pursuant to this Agreement. Seller
further agrees that it shall transfer to Purchaser any funds received by Seller
in connection with such Receivables.

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                                                                   Exhibit 10.21

     2.2  Expenses; Transfer Taxes. Each of the parties shall pay all costs and
expenses incurred by it or on its behalf in connection with this Agreement and
the transactions contemplated hereby. Seller shall pay any transfer or stamp
taxes, charges, fees, levies or other assessments imposed by reason of the
transactions contemplated hereby.

                                    ARTICLE 3
                            MISCELLANEOUS PROVISIONS

     3.1  Entire Agreement. This Agreement constitutes the full and entire
agreement and understanding between the parties with regard to the subject
matter of this Agreement. All prior and contemporaneous agreements, covenants,
representations and warranties, express or implied, oral and written, of the
parties with regard to the subject matter of this Agreement are superseded by
this Agreement.

     3.2  Governing Law. The validity, construction, and performance of this
Agreement, and any action, claim, suit, litigation, proceeding, arbitration or
mediation arising out of or relating to this Agreement shall be governed by the
Laws of the State of California, without regard to the Laws of the State of
California as to choice or conflict of Laws.

     3.3  Successors and Assigns. Each of the terms, provisions, and obligations
of this Agreement shall be binding upon, shall inure to the benefit of, and
shall be enforceable by the parties and their respective legal representatives,
successors and permitted assigns.

     3.4  Notices. All notices and other communications given or made pursuant
hereto shall be in writing and shall be deemed to have been given or made if in
writing and delivered personally or sent by registered or express mail (postage
prepaid) or by telecopier to the parties at the following addresses and
facsimile numbers:

          if to Purchaser to:

                HRC Holding Inc.
                27111 Diaz Road
                P.O. Box 9020
                Temecula, California 92589-9020
                Facsimile: (909) 676-1578

          if to Seller to:

                Hudson Respiratory Care Inc.
                27111 Diaz Road
                P.O. Box 9020
                Temecula, CA 92589-9020
                Facsimile: (909) 676-1578

<PAGE>

                                                                   Exhibit 10.21

<PAGE>

     IN WITNESS WHEREOF, each of the parties has executed this Agreement as of
the date first set forth above.

SELLER:                                   PURCHASER:

HUDSON RESPIRATORY CARE INC.,             HRC HOLDING INC.,
a California corporation                  a Delaware corporation


By:_____________________________          By:__________________________________
   Name:                                     Name:
   Title:                                    Title:

<PAGE>

                          ACKNOWLEDGEMENT OF ASSIGNMENT

     Pursuant to that certain Receivables Purchase Agreement, dated as of May
14, 2002 (the "Purchase Agreement"), by and between Hudson Respiratory Care
Inc., a California corporation ("Hudson") and HRC Holding Inc., a Delaware
corporation ("HRC"), the undersigned each acknowledge and agree to the
assignment of the Receivables (as defined in the Purchase Agreement) to HRC as
provided in the Purchase Agreement. Each of the undersigned hereby agree to make
only to HRC or a party designated by HRC all future payments on such
Receivables.

ACKNOWLEDGED AND AGREED:

Hudson RCI AB


By: _____________________________
    Name:
    Its:

Hudson RCI GmbH


By: _____________________________
    Name:
    Its:

Kiewclass (M) Sdn. Bhd


By: _____________________________
    Name:
    Its:

Hudson RCI (UK) Holdings Limited


By: _____________________________
    Name:
    Its:

Gibeck, Inc.


By: _____________________________
    Name:
    Its:

<PAGE>

                                   Schedule A


List of intercompany receivables purchased:


Accounts Receivable from:

Hudson AB account # 2634                             $4,148,613.24
Hudson AB account # 2896                             $  266,904.14
Hudson Germany account #813                          $1,682,954.26
Hudson UK account # 100257                           $  603,004.27
Hudson AB Kiewclass account # 4550                   $   93,499.09

Other receivables:

Hudson Germany GL 121050                             $  225,000.00
Hudson Germany GL 141050                             $  461,523.00
Gibeck, Inc.                                         $  518,502.00

Total                                                $8,000,000.00