EXHIBIT 4.1(a)


                     Amendment No. 1 to the Credit Agreement



<PAGE>
                             AMENDMENT NO. 1 TO THE
                                CREDIT AGREEMENT


                                                    Dated as of January 24, 1997

         AMENDMENT NO. 1 TO THE CREDIT AGREEMENT, among MEDIQ/PRN LIFE SUPPORT
SERVICES, INC., a Delaware corporation (the "Borrower"), MEDIQ INCORPORATED, a
Delaware corporation ("MEDIQ"), PRN HOLDINGS, INC., a Delaware corporation
(together with MEDIQ, the "Parent Guarantors"), the banks, financial
institutions and other institutional lenders parties to the Credit Agreement
referred to below (collectively, the "Lenders") and Banque Nationale de Paris as
administrative agent (the "Administrative Agent") for the Lenders and
NationsBank N.A., as documentation agent (the "Documentation Agent").

         PRELIMINARY STATEMENTS:

         (1) The Borrower, the Parent Guarantors, the Lenders, the
Administrative Agent and the Documentation Agent have entered into a Credit
Agreement dated as of October 1, 1996 (the "Credit Agreement"). Capitalized
terms not otherwise defined in this Amendment have the same meanings as
specified in the Credit Agreement.

         (2) The Borrower seeks to acquire Universal Hospital Services, Inc., a
Minnesota corporation ("UHS"), (the "UHS Acquisition") and, in order to finance,
together with advances under the existing Facilities, such acquisition, has
requested that certain Lenders (the "Affected Lenders" or the "Incremental Term
B Lenders") increase their Commitments under the Term B Facility (the
"Incremental Term B Commitments") and the Working Capital Facility, and amend
certain provisions of the Credit Agreement in order to provide such financing
and for certain other purposes.

         (3) The Required Lenders and the Affected Lenders are, on the terms and
conditions stated below, willing to grant the request of the Borrower and the
Borrower and such Lenders have agreed to amend the Credit Agreement as
hereinafter set forth.



<PAGE>

         SECTION 1. Amendments to the Credit Agreement. The Credit Agreement is,
effective as of the date hereof and subject to the satisfaction of the
conditions precedent set forth in Section 2(a) hereof, hereby amended as
follows:

         (a) Section 1.01 is amended by inserting therein the following
definitions in appropriate alphabetical order:

            "`BERS' means Biomedical Equipment Rental and Sales, Inc., a
Subsidiary of UHS.

            "'UHS' means Universal Hospital Services, Inc., a Minnesota
corporation.

            "`UHS Acquisition' means the acquisition of the common stock of UHS
by the Borrower or any of the Borrower's Ongoing Subsidiaries, as permitted
under this Agreement."

            "'UHS Acquisition Closing Date' means any Business Day on which the
UHS Acquisition occurs."

         (b) The definition of "Acquisition Facility Sublimit" in Section 1.01
is amended by deleting clause (iii) thereof and substituting therefor the
following:

            "(iii) the excess of the aggregate amount of Subordinated Notes
outstanding at such time over the principal amount of the NutraMax Note to the
extent secured by the NutraMax Letter of Credit multiplied by 66%."

         (c) The definition of "Borrower's Account" is amended by deleting
therefrom the account number "200877-001-91" and substituting therefor the
account number "202330-001-77".

         (d) The definition of "EBITDA" is amended by inserting immediately
before the proviso thereto the following:

            "and (g) all one-time expenses of the Borrower and its Affiliates
incurred in connection with the UHS Acquisition for severance expenses, lease
related expenses and facility closure expenses".

         (e) The definition of "Leverage Ratio" is amended (i) by inserting in
the seventh line thereof, immediately preceding the words ", so long as", the
phrase "multiplied by 66%", and (ii) by adding at the end thereof the following:
",except with respect to the UHS Acquisition, in which case the 12-month
trailing EBITDA of UHS shall be adjusted for the EBITDA of BERS included in such
calculation for the period of time that said EBITDA of BERS is not actually
reflected in the aforesaid EBITDA of UHS, in which case such EBITDA of UHS shall
be the pro forma EBITDA of UHS and BERS for such period."

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<PAGE>

         (f) The definition of "Senior Leverage Ratio" is amended by adding at
the end thereof the following: ",except with respect to the UHS Acquisition, in
which case the 12-month trailing EBITDA of UHS shall be adjusted for the EBITDA
of BERS included in such calculation for the period of time that said EBITDA of
BERS is not actually reflected in the aforesaid EBITDA of UHS, in which case
such EBITDA of UHS shall be the pro forma EBITDA of UHS and BERS for such
period."

         (g) The definition of "Term B Borrowing" is amended by adding at the
end thereof the following:

            "and Incremental Term B Advances made on the UHS Acquisition Closing
Date."

         (h) Section 2.01(b) is amended by (i) inserting "(i)" immediately after
the heading "The Term B Advances" and (ii) adding a new clause (ii) at the end
thereof to read as follows:

            "(ii) Each Incremental Term B Lender severally agrees, on the terms
and conditions hereinafter set forth, to make a single advance to the Borrower
on the UHS Acquisition Closing Date in an amount not to exceed such Incremental
Term B Lender's Incremental Term B Commitment as set forth in Schedule I hereto
(each such advance being an "Incremental Term B Advance"). Such Term B Borrowing
shall consist of Incremental Term B Advances made simultaneously by the
Incremental Term B Lenders ratably according to their Incremental Term B
Commitments. Amounts borrowed under this Section 2.01(b)(ii) and repaid or
prepaid may not be reborrowed."

         (i) The table contained in Section 2.04(a) is amended by (i) deleting
each figure "8,500,000" therein and substituting for each such figure the figure
"13,000,000" and (ii) deleting each figure "15,000,000" therein and substituting
for each such figure the figure "21,750,000".

         (j) Section 2.14(a) is amended by adding at the end thereof the
following:

            "and, on the UHS Acquisition Closing Date, an aggregate amount of up
to $45,000,000 of Incremental Term B Advances to finance a portion of the UHS
Acquisition".

         (k) Section 2.14(c) is amended by inserting therein, immediately after
"Section 5.01(p)", the following:

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<PAGE>


            ", to provide up to $5,000,000 of the financing for the UHS
Acquisition".

         (l) Section 4.01(i) is amended by inserting therein, immediately after
"provided that", the following:

            ", other than with respect to the UHS Acquisition as permitted under
Section 5.02(f)(i),".

         (m) Section 5.01(n) is amended by substituting for the date "November
15, 1996" the phrase the date that is 45 days following the UHS Acquisition
Closing Date" and by adding after the phrase "the Term B Facilities " the
parenthetical "(including the Incremental Term B Advances)".

         (n) Section 5.02(b)(ii)(B) is amended by deleting therein the figure
"$100,000,000" and substituting therefor the figure "$140,000,000".

         (o) Section 5.02(b)(ii) is amended by adding at the end thereof a new
subsection (H) to read as follows:

            "intercompany Debt owed to the Borrower in connection with the UHS
Acquisition, so long as such Debt is evidenced by an intercompany note in form
and substance satisfactory to the Administrative Agent, and".

         (p) Section 5.02(f)(i) is amended (i) by inserting in the second line
thereof, immediately following "Acquisition Advances", the following ", Working
Capital Advances, Incremental Term B Advances" and (ii) by inserting therein,
immediately before "provided that", the following:

            "or constituting the purchase of at least 90% of the common stock of
UHS in a transaction approved by the Board of Directors of UHS so long as UHS
becomes a wholly owned Subsidiary of the Borrower on the UHS Acquisition Closing
Date in a transaction approved by the Board of Directors of UHS or constituting
the payment of consideration for the merger of UHS and the Borrower or a wholly
owned Subsidiary of the Borrower,"

         (q) Section 5.02(f)(i)(2) is amended by adding at the end thereof the
following:

            "except with respect to the UHS Acquisition, in which case such
Leverage Ratio shall not be more than 3.75 to 1.0".

                                       4
<PAGE>


         (r) Section 5.02(f)(i)(3) is amended by adding at the end thereof the
following:

            "except with respect to the UHS Acquisition, in which case such
amount shall not exceed 6.5 multiplied by the 12-month trailing EBITDA of UHS
(adjusted for the EBITDA of BERS included in such calculation for the period of
time that said EBITDA of BERS is not actually reflected in the aforesaid EBITDA
of UHS, in which case such EBITDA of UHS shall be the pro forma EBITDA of UHS
and BERS for such period)".

         (s) Section 5.02(f)(i)(4) is amended by (i) deleting therefrom the
following:

            "shall not exceed $100,000,000"

and (ii) adding at the end thereof the following:

            "plus the aggregate amount of Advances made by the Lenders and used
for all such Investments outstanding at any time on and after the UHS
Acquisition Closing Date shall not exceed $140,000,000."

         (t) Section 5.04(f) is amended by inserting in the eighth line thereof
immediately after the word "Investments" the following: ", except with respect
to the UHS Acquisition, in which case the 12-month trailing EBITDA of UHS shall
be adjusted for the EBITDA of BERS included in such calculation for the period
of time that said EBITDA of BERS is not actually reflected in the aforesaid
EBITDA of UHS, in which case such EBITDA of UHS shall be the pro forma EBITDA of
UHS and BERS for such period."

         (u) Schedule 1 is supplemented by adding with respect to the Working
Capital Commitment of each of BNP and NationsBank, $2,500,000, and adding
Incremental Term B Commitments for each of BNP and NationsBank, in the amount of
$22,500,000.

         SECTION 2. Conditions of Effectiveness. (a) This Amendment shall become
effective as of the date first above written when, and only when, the
Administrative Agent shall have received (x) counterparts of this Amendment
executed by the Borrower, the Required Lenders and each Affected Lender, or, as
to any of the Lenders, advice satisfactory to the Administrative Agent that such
Lender has executed this Amendment and (y) for the ratable account of the
Lenders, 1/10% of the sum of the Term A Advances, the Term B Advances, the
Acquisition Commitments and the Working Capital Commitments as such Advances and
Commitments shall be outstanding immediately prior to the effectiveness of this
Amendment (i.e. $260,000). The effectiveness of this Amendment is conditioned

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<PAGE>


upon the accuracy of the factual matters described herein. This Amendment is
subject to the provisions of Section 9.01 of the Credit Agreement.

         (b) This Amendment shall be null and void and of no effect if, on or
before April 23, 1997 (or such later date before July 15, 1997 as the Affected
Lenders may consent to in writing), the following conditions shall not have been
satisfied:

            (1) The Administrative Agent shall not have additionally received
all of the following documents, each such document (unless otherwise specified)
dated the date of receipt thereof by the Administrative Agent (unless otherwise
specified) and in sufficient copies for each Lender, in form and substance
satisfactory to the Administrative Agent (unless otherwise specified):

               (i) Certified copies of (x) the resolutions of the Board of
Directors of (A) the Borrower approving this Amendment, the Collateral
Documents, amendments or supplements thereto contemplated hereby and the matters
contemplated hereby and thereby and (B) each other Loan Party evidencing
approval of the Consent, the Collateral Documents, amendments or supplements
thereto contemplated hereby and the matters contemplated hereby and thereby and
(y) all documents evidencing other necessary corporate action and governmental
approvals, if any, with respect to this Amendment, the Consent, the Collateral
Documents, amendments or supplements thereto contemplated hereby and the matters
contemplated hereby and thereby;

               (ii) A certificate of the Secretary or an Assistant Secretary of
the Borrower and each other Loan Party certifying the names and true signatures
of the officers of the Borrower and such other Loan Party authorized to sign
this Amendment, the Consent, the Collateral Documents, amendments or supplements
thereto contemplated hereby to any of which they are or are to be a party and
the other documents to be delivered hereunder and thereunder;

               (iii) Counterparts of a consent with respect to this Amendment
No. 1, in form satisfactory to the Administrative Agent, executed by each of the
Loan Parties (other than the Borrower);

               (iv) A favorable opinion of Drinker, Biddle & Reath, counsel for
the Loan Parties, as to such matters as the Administrative Agent may reasonably
request;

               (v) A certificate signed by a duly authorized officer of the
Borrower stating that:

                                       6
<PAGE>


               (x) The representations and warranties contained in the Loan
Documents as amended hereby, Section 3 hereof, and in each of the Collateral
Documents and amendments and supplements thereto delivered pursuant to this
Section 2 are correct on and as of the date of such certificate as though made
on and as of such date other than any such representations or warranties that,
by their terms, refer to a date other than the date of such certificate; and

               (y) No event has occurred and is continuing that constitutes a
Default; and

               (vi) Notes payable to the order of the Affected Lenders; and

            (2) Each of the following conditions shall have been satisfied:

               (i) The Borrower and any additional Loan Party, as appropriate,
shall have delivered all such documents, agreements, certificates or instruments
as shall be required or as the Administrative Agent shall have requested
pursuant to Section 5.01(o);

               (ii) All governmental and third party consents and approvals
necessary in connection with the UHS Acquisition shall have been obtained and
remain in effect, and all applicable waiting periods shall have expired without
any action being taken by any competent authority, and no law or regulation
shall be applicable which, in the case of any of the foregoing, restrains,
prevents or imposes materially adverse conditions upon the rights of any Loan
Party to transfer or otherwise dispose of shares of UHS acquired in the tender
offer, if applicable, the exercise by any transferee of any Loan Party of all
ownership rights with respect to the shares of UHS stock acquired in connection
with any such tender offer or otherwise owned by any Loan Party, or the
consummation of a merger if not completed prior to the UHS Acquisition Closing
Date;

               (iii) All Advances made by the Lender Parties shall be in
compliance with Regulations G, T, U and X of the Board of Governors of the
Federal Reserve System; and

               (iv) The Borrower shall have retained Murray, Devine & Co. to
prepare and deliver a letter attesting to the Solvency of the Borrower after
giving effect to the acquisition of UHS.

                                       7
<PAGE>


         SECTION 3. Representations and Warranties of the Borrower. The Borrower
represents and warrants as follows:

         (a) The Borrower is a corporation duly organized, validly existing and
in good standing under the laws of the jurisdiction indicated in the recital of
the parties to this Amendment.

         (b) The execution, delivery and performance by each Loan Party of this
Amendment and the Loan Documents, as amended hereby, to which it is or is to be
a party, and the consummation of the transactions contemplated hereby, are
within such Loan Party's corporate powers, have been duly authorized by all
necessary corporate action and do not (i) contravene each such Loan Party's
charter or by-laws, (ii) violate any law (including, without limitation, the
Securities Exchange Act of 1934, as amended, and the Racketeer Influenced and
Corrupt Organizations Chapter of the Organized Crime Control Act of 1970), rule
or regulation (including, without limitation, Regulation X of the Board of
Governors of the Federal Reserve System), or any order, writ, judgment,
injunction, decree, determination or award, binding on or affecting any Loan
Party or any of its Subsidiaries or any of their properties, (iii) conflict with
or result in the breach of, or constitute a default under, any contract, loan
agreement, indenture, mortgage, deed of trust, lease or other instrument binding
on or affecting any Loan Party, any of their Subsidiaries or any of their
properties or (iv) except for the Liens created under the Collateral Documents,
as amended hereby, or any amendments or supplements thereto contemplated hereby,
result in or require the creation or imposition of any Lien upon or with respect
to any of the properties of any Loan Party or any of its Subsidiaries.

         (c) No authorization or approval or other action by, and no notice to
or filing with, any governmental authority or regulatory body or any other third
party is required for the due execution, delivery, recordation, filing or
performance by any Loan Party of this Amendment, any of the Collateral Documents
or any amendments or supplements thereto contemplated hereby to which each such
Loan Party is or is to be a party, or any of the Loan Documents, as amended
hereby, to which it is or is to be a party except for such approvals as shall
have been obtained by the UHS Acquisition Closing Date.

         (d) This Amendment and each of the Collateral Documents and amendments
and supplements thereto contemplated hereby to which each Loan Party is a party
have been duly executed and delivered by each such Loan Party. This Amendment
and each of the other Loan Documents, as amended hereby, to which each Loan
Party is a party are, and each of the other Collateral Documents and amendments
and supplements thereto contemplated hereby to which each such Loan Party is or
is to be a party, when delivered hereunder, will be, legal, valid and binding
obligations of each such Loan Party, enforceable against each such Loan Party in

                                       8
<PAGE>

accordance with their respective terms, including as to each entity that shall
become a Loan Party on the UHS Acquisition Closing Date, as to each such Loan
Party on the UHS Acquisition Closing Date.

         (e) There is no action, suit, investigation, litigation or proceeding
affecting any Loan Party or any of their Subsidiaries (including, without
limitation, any Environmental Action) pending or threatened before any court,
governmental agency or arbitrator that (i) would be reasonably likely to have a
Material Adverse Effect or (ii) purports to affect the legality, validity or
enforceability of this Amendment, the Collateral Documents, any amendments or
supplements thereto contemplated hereby or any of the other Loan Documents, as
amended hereby, or the consummation of any of the transactions contemplated
hereby.

         (f) As of the UHS Acquisition Closing Date, the Collateral Documents
and amendments or supplements thereto consisting of security agreements or
mortgages to which any Loan Party is or is to be a party, when delivered
hereunder, will create valid and perfected first priority liens and security
interests in and to the Collateral covered thereby, securing the payment of the
Secured Obligations (in each case, as defined in such Collateral Documents or
amendment or supplement thereto); and the execution, delivery and performance of
this Amendment, each of the Collateral Documents and any amendments or
supplements thereto contemplated hereby do not adversely affect the Liens
created under any of the Collateral Documents.

         SECTION 4. Reference to and Effect on the Loan Documents. (a) On and
after the effectiveness of this Amendment, each reference in the Credit
Agreement to "this Agreement", "hereunder", "hereof" or words of like import
referring to the Credit Agreement, and each reference in the Notes and each of
the other Loan Documents to "the Credit Agreement", "thereunder", "thereof" or
words of like import referring to the Credit Agreement, shall mean and be a
reference to the Credit Agreement, as amended by this Amendment.

         (b) The Credit Agreement, the Notes and each of the other Loan
Documents, as specifically amended by this Amendment, are and shall continue to
be in full force and effect and are hereby in all respects ratified and
confirmed. Without limiting the generality of the foregoing, the Collateral
Documents and all of the Collateral described therein do and shall continue to
secure the payment of all Obligations of the Loan Parties under the Loan
Documents, in each case as amended by this Amendment.

         (c) The execution, delivery and effectiveness of this
Amendment shall not, except as expressly provided herein, operate as a waiver of
any right, power or remedy of any Lender or the Agent under any of the Loan
Documents, nor constitute a waiver of any provision of any of the Loan
Documents.

                                       9
<PAGE>


         (d) Except as otherwise provided in this Amendment, from and after the
UHS Acquisition Closing Date, all references to (i) Term B Lenders shall include
the Incremental Term B Lenders, (ii) Term B Advances shall include all Term B
Advances made by the Incremental Term B Lenders and (iii) Term B Commitments
shall mean the Incremental Term B Commitments of the Incremental Term B Lenders
hereunder.

         SECTION 5. Costs, Expenses. The Borrower agrees to pay on demand all
costs and expenses of the Agent in connection with the preparation, execution,
delivery and administration, modification and amendment of this Amendment, and
the other instruments and documents to be delivered hereunder (including,
without limitation, the reasonable fees and expenses of counsel for the Agent)
in accordance with the terms of Section 9.04 of the Credit Agreement.

         SECTION 6. Execution in Counterparts. This Amendment may be executed in
any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed shall be deemed to be an original
and all of which taken together shall constitute but one and the same agreement.
Delivery of an executed counterpart of a signature page to this Amendment by
telecopier shall be effective as delivery of a manually executed counterpart of
this Amendment.

         SECTION 7. Governing Law. This Amendment shall be governed by, and
construed in accordance with, the laws of the State of New York.

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers thereunto duly authorized, as of the date
first above written.

                                       MEDIQ/PRN LIFE SUPPORT SERVICES, INC.

                                       By: /s/ Jay M. Kaplan
                                          --------------------------------------
                                          Title: Senior Vice President - CFO


                                       BANQUE NATIONALE DE
                                          PARIS, as Administrative Agent and as
                                          Lender

                                       By /s/ Alan Mustacchi
                                          --------------------------------------
                                          Title: Vice President

                                       By /s/ Steve Kovacs
                                          --------------------------------------
                                          Title: Assistant Vice President



                                       10
<PAGE>



                                       NATIONSBANK, N.A., as
                                         Documentation Agent and as Lender

                                       By /s/ Ashley M. Crabtree
                                          --------------------------------------
                                          Title: Senior Vice President


                                       THE FIRST NATIONAL BANK OF BOSTON

                                       By /s/ Kimberly F. Harris
                                          --------------------------------------
                                          Title: Vice President


                                       CAISSE NATIONALE DE CREDIT AGRICOLE

                                       By /s/ Craig Welsh
                                          --------------------------------------
                                          Title: First Vice President


                                       CREDITANSTALT CORPORATE FINANCE, INC.

                                       By /s/ Gregory F. Mathis
                                          --------------------------------------
                                          Title: Vice President

                                       By /s/ Clifford L. Wells
                                          --------------------------------------
                                          Title: Vice President


                                       FIRST SOURCE FINANCIAL, LLP
                                       By: First Source Financial, Inc.
                                       as Agent/Manager

                                       By /s/
                                          --------------------------------------
                                          Title:



                                       11
<PAGE>


                                       METROPOLITAN LIFE INSURANCE COMPANY

                                       By /s/ James R. Dingler
                                          --------------------------------------
                                          Title: Assistant Vice President


                                       LASALLE NATIONAL BANK

                                       By /s/ Olga Georgiev
                                          --------------------------------------
                                          Title: First Vice President


                                       MASSACHUSETTS MUTUAL LIFE INSURANCE
                                         COMPANY

                                       By /s/
                                          --------------------------------------
                                           Title: Managing Director


                                       MELLON BANK, N.A.

                                       By
                                          --------------------------------------
                                          Title:


                                       MERRILL LYNCH SENIOR FLOATING RATE
                                         FUND, INC.

                                       By /s/ Anthony R. Clemente
                                          --------------------------------------
                                          Title:


                                       PILGRIM AMERICA PRIME RATE TRUST

                                       By /s/ Michael J. Bacevich
                                          --------------------------------------
                                          Title: Vice President

 

                                       12
<PAGE>



                                       SUMMIT BANK

                                       By /s/ Gail L. Powers
                                          --------------------------------------
                                          Title: Vice President


                                       USTRUST

                                       By /s/ Thomas Macina
                                          --------------------------------------
                                          Title: Vice President


                                       VAN KAMPEN AMERICAN CAPITAL PRIME RATE 
                                          INCOME TRUST

                                       By /s/ Jeffrey W. Maillet
                                          --------------------------------------
                                         Title: Senior Vice President & Director


                                       RESTRUCTURED OBLIGATIONS BACKED BY SENIOR
                                         ASSETS B.V.

                                       By its Managing Director, ABN
                                         TRUSTCOMPANY (NEDERLAND) B.V.


                                       By /s/ Christopher E. Jensen
                                          --------------------------------------
                                          Title: Managing Director

                                      By /s/ Chancellor LGT Senior Secured
                                             Management, Inc.
                                         ---------------------------------------
                                         Title:


                                       MERRILL LYNCH PRIME RATE PORTFOLIO

                                       By /s/ Anthony R. Clemente
                                          --------------------------------------
                                          Title:



                                       13
<PAGE>


                                       SENIOR DEBT PORTFOLIO

                                       By Boston Management and Research, 
                                          as Investment Advisor

                                       By /s/ Payson F. Swaffield
                                          --------------------------------------
                                          Title: Vice President

                                       CERES FINANCE LTD.

                                       By /s/
                                          --------------------------------------
                                          Title: Director


                                       CAPTIVA FINANCE LTD.

                                       By /s/
                                          --------------------------------------
                                          Title: Director


                                       14
<PAGE>



                                       AMARA-1 FINANCE LTD.

                                       By /s/
                                          --------------------------------------
                                          Title: Director


                                       AMARA-2 FINANCE LTD.

                                       By /s/
                                          --------------------------------------
                                          Title: Director




                                      15