<PAGE>

                                                                   Exhibit 10.16

                         SUPPLEMENT NO. 1 dated as of May ___, 2002, to the
                    PLEDGE AGREEMENT dated as of April 7,1998, among HUDSON
                    RESPIRATORY CARE INC., a California corporation (the
                    "Borrower"), RIVER HOLDINGS CORP., a Delaware corporation
                    ("Holding") and each subsidiary of the Borrower listed on
                    Schedule I hereto (each such subsidiary individually a
                    "Subsidiary Pledgor" and collectively, the "Subsidiary
                    Pledgors"; the Borrower, Holding and Subsidiary Pledgors are
                    referred to collectively herein as the "Pledgors") and
                    BANKERS TRUST COMPANY, a New York banking corporation
                    ("BTCo.% as collateral agent (in such capacity, the
                    "Collateral Agent") for the Secured Parties (as defined in
                    the Credit Agreement referred to below)

     A. Reference is made to (a) the Credit Agreement dated as of April 7, 1998
(as amended, supplemented or otherwise modified from time to time, the "Credit
Agreement"), among the Borrower, Holding, the lenders from time to time party
thereto (the "Lenders"), BTCo., as administrative agent for the Lenders,
Collateral Agent, swingline lender and as issuing bank (in such capacity, the
"Issuing Bank") and (b) the Holding Guarantee Agreement dated as of April 7,
1998 (as amended, supplemented or otherwise modified from time to time, the
"Holding Guarantee Agreement"), between Holding and the Collateral Agent.

     B. Capitalized terms used herein and not otherwise defined herein shall
have the meanings assigned to such terms in the Credit Agreement.

     C. The Pledgors have entered into the Pledge Agreement in order to induce
the Lenders to make Loans and the Issuing Bank to issue Letters of Credit.
Pursuant to Section 5.11 of the Credit Agreement, each Domestic Subsidiary of
the Borrower that was not in existence or not a Subsidiary on the date of the
Credit Agreement is required to enter into the Pledge Agreement as a Subsidiary
Pledgor upon becoming a Subsidiary if such Subsidiary owns or possesses property
of a type that would be considered Collateral under the Pledge Agreement.
Section 24 of the Pledge Agreement provides that such Subsidiaries may become
Subsidiary Pledgors under the Pledge Agreement by execution and delivery of an
instrument in the form of this Supplement. The undersigned Subsidiary (the "New
Pledgor") is executing this Supplement in accordance with the requirements of
the Credit Agreement to become a Subsidiary Pledgor under the Pledge Agreement
in order to induce the Lenders to make additional Loans and the Issuing Bank to
issue additional Letters of Credit and as consideration for Loans previously
made and Letters of Credit previously issued.

     Accordingly, the Collateral Agent and the New Pledgor agree as follows:

     SECTION 1. In accordance with Section 24 of the Pledge Agreement, the New
Pledgor by its signature below becomes a Pledgor under the Pledge Agreement with
the same force and effect as if originally named therein as a Pledgor and the
New Pledgor hereby agrees (a) to all the terms and provisions of the Pledge
Agreement applicable to it as a Pledgor thereunder and (b) represents and
warrants that the representations and warranties made by it as a Pledgor
thereunder are true and correct on and as of the date hereof. In furtherance of
the foregoing, the New Pledgor, as security for the payment and performance in
full of the Obligations (as defined

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                                                                   Exhibit 10.16
                                                                               2

in the Pledge Agreement), does hereby create and grant to the Collateral Agent,
its successors and assigns, for the benefit of the Secured Parties, their
successors and assigns, a security interest in and lien on all of the New
Pledgor's right, title and interest in and to the Collateral (as defined in the
Pledge Agreement, except the Collateral as it relates to the New Pledgor shall
not include the New Pledgor's interest in the one share of Industrias Hudson
held by the New Pledgor) of the New Pledgor. Each reference to a "Subsidiary
Pledgor" or a "Pledgor" in the Pledge Agreement shall be deemed to include the
New Pledgor. The Pledge Agreement is hereby incorporated herein by reference.

     SECTION 2. This Supplement may be executed in counterparts, each of which
shall constitute an original, but all of which when taken together shall
constitute a single contract. This Supplement shall become effective when the
Collateral Agent shall have received counterparts of this Supplement that, when
taken together, bear the signatures of the New Pledgor and the Collateral Agent.
Delivery of an executed signature page to this Supplement by facsimile
transmission shall be as effective as delivery of a manually signed counterpart
of this Supplement.

     SECTION 3. The New Pledgor hereby represents and warrants that set forth on
Schedule I attached hereto is a true and correct schedule of all its Pledged
Securities.

     SECTION 4. Except as expressly supplemented hereby, the Pledge Agreement
shall remain in full force and effect.

     Section 5. THIS SUPPLEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN
ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD FOR PRINCIPLES
OF CONFLICTS OF LAWS.

     SECTION 6. In case any one or more of the provisions contained in this
Supplement should be held invalid, illegal or unenforceable in any respect,
neither party hereto shall be required to comply with such provision for so long
as such provision is held to be invalid, illegal or unenforceable, but the
validity, legality and enforceability of the remaining provisions contained
herein and in the Pledge Agreement shall not in any way be affected or impaired.
The parties hereto shall endeavor in good-faith negotiations to replace the
invalid, illegal or unenforceable provisions with valid provisions the economic
effect of which comes as close as possible to that of the invalid, illegal or
unenforceable provisions.

     SECTION 7. All communication and notices hereunder shall be in writing and
given as provided in Section 15 of the Pledge Agreement. All communications and
notices hereunder to the New Pledgor shall be given to it in care of the
Borrower.

     SECTION 8. The New Pledgor agrees to reimburse the Collateral Agent for its
reasonable out-of-pocket expenses in connection with this Supplement, including
the reasonable fees, other charges and disbursements of counsel for the
Collateral Agent.

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                                                                   Exhibit 10.16
                                                                               3

     IN WITNESS WHEREOF, the New Pledgor and the Collateral Agent have duly
executed this Supplement to the Pledge Agreement as of the day and year first
above written.

                                    IH HOLDING LLC,

                                    By:  HUDSON RESPIRATORY CARE INC., its
                                         Managing Member

                                    By:  _______________________________________
                                         Name:
                                         Title:
                                         Address:

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                                                                   Exhibit 10.16

                                    DEUTSCHE BANK TRUST COMPANY
                                    AMERICAS (f/k/a Bankers Trust
                                    Company), as Collateral Agent,


                                      by

                                          ________________________________
                                          Name:
                                          Title:

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                                                                   Exhibit 10.16
                                                                   Schedule I to
                                                                  Supplement No.
                                                         to the Pledge Agreement

                      Pledged Securities of the New Pledgor
                      -------------------------------------

                                  CAPITAL STOCK


               Number of      Registered       Number and         Percentage of
    Issuer     Certificate      Owner        Class of Shares          Shares
    ------     -----------      -----        ---------------          ------




                                 DEBT SECURITIES

     Issuer           Principal Amount          Date of Note      Maturity Date
     ------           ----------------          ------------      -------------