<PAGE>
                                                                   EXHIBIT 10.18


                          SECOND AMENDMENT AND CONSENT

         SECOND AMENDMENT AND CONSENT, dated as of October 12, 2001 (this
"Amendment"), to the Credit Agreement, dated as of October 25, 1999 (as amended,
supplemented or otherwise modified prior to the date hereof, the "Credit
Agreement"), among UNIVERSAL HOSPITAL SERVICES, INC., a Minnesota corporation
(the "Borrower"), the several lenders from time to time parties thereto (the
"Lenders"), KEY CORPORATE CAPITAL INC., as collateral agent, HELLER FINANCIAL
INC., as syndication agent, CANADIAN IMPERIAL BANK OF COMMERCE, as
administrative agent for the Lenders (in such capacity, the "Administrative
Agent"), and CIBC WORLD MARKETS CORP., as lead arranger and book manager
thereunder. Capitalized terms not otherwise defined herein shall have the same
meanings as specified therefor in the Credit Agreement.

                                    RECITALS

         The Borrower has requested that the Administrative Agent and the
Lenders consent to the acquisition by the Borrower of all of the Capital Stock
of Narco Medical Systems, Inc. ("Narco"), and, subject to certain conditions, to
agree to amend the Credit Agreement as set forth in this Amendment, and the
Administrative Agent and the Lenders are willing to give such consent and to
agree to such amendments, but only on the terms and subject to the conditions
set forth in this Amendment.

         NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, the Borrower, the Administrative Agent and the Lenders hereby
agree as follows:

         1. Consent. On and as of the Consent Effective Date (as hereinafter
defined), notwithstanding the provisions of Section 9.9 of the Credit Agreement
to the contrary, the Administrative Agent and each of the Lenders hereby consent
to the acquisition by the Borrower or a wholly-owned Domestic Subsidiary of the
Borrower of all of the Capital Stock of Narco (the "Narco Acquisition");
provided that:

              (a) The purchase price for the Narco Acquisition shall be payable
         solely in cash and shall not exceed $8,500,000 in the aggregate
         (subject to adjustment for changes in net assets provided for in the
         Narco Acquisition Documents);

              (b) The Administrative Agent shall have received, with a copy for
         each Lender, not later than October 15, 2001, substantially final
         drafts of the stock purchase agreement and related material acquisition
         documents pertaining to the Narco Acquisition and such drafts shall be
         acceptable to the Administrative Agent in all respects, and the
         definitive versions of such stock purchase and related material
         acquisition documents shall be executed and delivered in the form of
         such drafts with no material amendments or material modifications
         thereto, except to the extent approved by the Administrative Agent
         (such definitive stock purchase agreement and related acquisition
         documents, the "Narco Acquisition Documents");
<PAGE>

              (c) The Administrative Agent shall be reasonably satisfied with
         all material certificates, opinions and other material documents
         delivered in connection with to the Narco Acquisition Documents and all
         legal matters related to the Narco Acquisition;

              (d) The Narco Acquisition shall be consummated on the terms and
         conditions set forth in the Narco Acquisition Documents without any
         amendment, waiver or modification thereto, except to the extent
         approved by the Administrative Agent;

              (e) The Narco Acquisition shall be consummated on or prior to
         November 15, 2001;

              (f) Concurrently with the consummation of the Narco Acquisition,
         each of the requirements set forth in Section 8.11 of the Credit
         Agreement shall be satisfied;

              (g) The Narco Acquisition shall satisfy the requirements set forth
         in clauses (i), (ii), (iii), (v) and (vi) of the definition of
         "Permitted Acquisition" set forth in the Credit Agreement as if the
         Narco Acquisition were an acquisition referred to in such definition
         (it being agreed that it shall not be a requirement of the consent
         provided in this Section 1 of this Amendment that the Narco Acquisition
         satisfy the requirements set forth in clause (iv) of the definition of
         "Permitted Acquisition", and that the consummation of the Narco
         Acquisition shall not affect the calculations of consideration under
         such clause (iv) of the definition of "Permitted Acquisition" in
         respect of any Permitted Acquisitions); and

              (h) Either (i) the Initial Public Offering shall have been
         consummated prior to October 31, 2001, or (ii) the Increase Effective
         Date shall have occurred.

         2. Amendments to Credit Agreement. On the Increase Effective Date (and
only if the Increase Effective Date occurs), the Credit Agreement shall be
hereby amended as follows:

              (a) Section 5.5(c) of the Credit Agreement shall be amended by
         deleting subsection (i) thereof in its entirety and substituting in
         lieu thereof the following:

              "(i) 100% of the Net Proceeds of any sale or issuance of debt
              securities, and 75% of the Net Proceeds of any sale or issuance of
              any equity securities, in either case by the Borrower or any
              Subsidiary, whether in a public offering, a private placement or
              otherwise, but excluding any equity investment made by J.W. Childs
              or its Affiliates, its limited partners or the limited partners of
              its Affiliates, any equity investment made by any officer or
              employee of the Borrower pursuant to the Shareholder Agreement or
              any stock option plan, and any equity investment made by the
              selling parties in connection with a Permitted Acquisition,
              provided


                                       2
<PAGE>

              that in connection with the Initial Public Offering, the Borrower
              shall prepay the Revolving Credit Loans in an amount equal to the
              lesser of (i) the amount of Revolving Credit Loans outstanding and
              (ii) 75% of the Net Proceeds of the Initial Public Offering, and
              shall reduce the Revolving Credit Commitments in an amount equal
              to 60% of the Net Proceeds of the Initial Public Offering,".

              (b) The Credit Agreement is hereby amended by deleting Schedule 1
         in its entirety and inserting in lieu thereof the new Schedule 1
         attached hereto.

         3.   Effectiveness.

              (a) Consent Effectiveness. The effectiveness of this Amendment and
         the consent provided for in Section 1 of this Amendment is subject to
         the satisfaction of the following conditions precedent (the date of
         such satisfaction, the "Consent Effective Date"):

                    (i)   the receipt by the Administrative Agent of this
              Amendment duly executed and delivered by duly authorized officers
              of the Borrower, the Administrative Agent and the Required
              Lenders;

                    (ii)  the receipt by the Administrative Agent of any other
              documents relating hereto or to the Narco Acquisition that the
              Administrative Agent shall reasonably request prior to such date;

                    (iii) after giving effect to the consent provided for in
              Section 1 hereof, the representations and warranties contained in
              the Credit Agreement and in the other Loan Documents will be true
              and correct in all material respects as if made on and as of the
              Consent Effective Date and no Default or Event of Default will
              have occurred and be continuing.

              (b) Increase Effectiveness. The effectiveness of the amendments to
         the Credit Agreement provided for in Section 2 of this Amendment shall
         occur on October 31, 2001, subject to the satisfaction of the following
         conditions precedent (such date, upon satisfaction of such conditions,
         the "Increase Effective Date"):

                    (i)   the Consent Effective Date shall have occurred;

                    (ii)  the receipt by the Administrative Agent of this
              Amendment duly executed and delivered by duly authorized officers
              of Lenders having Credit Exposure Percentages aggregating at least
              66 2/3% and of the New Lender (as defined below);

                    (iii) the receipt by the Administrative Agent of any other
              documents relating hereto that the Administrative Agent shall
              reasonably request prior to such date;

                                       3
<PAGE>

                    (iv)  the receipt by the Administrative Agent for the
              account of the New Lender of a Revolving Note conforming to the
              requirements of the Credit Agreement payable to New Lender in the
              principal amount of $10,000,000 and executed and delivered by a
              duly authorized officer of the Borrower;

                    (v)   the receipt by the Administrative Agent, with a
              counterpart for each Lender and the New Lender, a certificate of
              each Loan Party existing as of the Increase Effective Date, dated
              the Increase Effective Date, substantially in the form of Exhibit
              G to the Credit Agreement or other form satisfactory to the
              Administrative Agent, with appropriate insertions and attachments,
              satisfactory in form and substance to the Administrative Agent,
              executed by the President or any Vice President and the Secretary
              or any Assistant Secretary of such Loan Party; including without
              limitation (A) attachment of true and complete copies of the
              articles of incorporation and by-laws of each Loan Party existing
              as of the Increase Effective Date, certified as of the Increase
              Effective Date as complete and correct copies thereof by the
              Secretary or an Assistant Secretary of such Loan Party, (B) a copy
              of the resolutions, in form and substance satisfactory to the
              Administrative Agent, of the Board of Directors of each Loan Party
              existing as of the Increase Effective Date authorizing (i) the
              execution, delivery and performance of this Amendment and the
              other Loan Documents to which it is a party, (ii) the borrowings
              contemplated hereunder and (iii) the granting or continuation by
              it of the Liens created pursuant to the Security Documents,
              certified by the Secretary or an Assistant Secretary of such Loan
              Party as of the Increase Effective Date, which certificate shall
              be in form and substance satisfactory to the Administrative Agent
              and shall state that the resolutions thereby certified have not
              been amended, modified, revoked or rescinded; (C) a certificate of
              each Loan Party existing as of the Increase Effective Date as to
              the incumbency and signature of the officers of such Loan Party
              executing this Amendment and any Loan Document satisfactory in
              form and substance to the Administrative Agent; and (D)
              certificates dated as of a recent date from the Secretary of State
              or other appropriate authority, evidencing the good standing of
              each Loan Party existing as of the Increase Effective Date (i) in
              the jurisdiction of its organization and (ii) in each other
              jurisdiction where its ownership, lease or operation of property
              or the conduct of its business requires it to qualify as a foreign
              Person except, as to this subclause (ii), where the failure to so
              qualify could not have a Material Adverse Effect;

                    (vi)  receipt by the Administrative Agent, with a
              counterpart for each Lender and the New Lender, of an executed
              legal opinion of Dorsey & Whitney LLP, counsel to the Loan Parties
              existing as of the Increase Effective Date, with respect to this
              Amendment and the transactions contemplated hereby in form and
              substance reasonably satisfactory to the Administrative Agent; and

                                       4
<PAGE>

                    (vii) after giving effect to the amendments provided for
              herein, the representations and warranties contained in the Credit
              Agreement and in the other Loan Documents will be true and correct
              in all material respects as if made on and as of the Effective
              Date and no Default or Event of Default will have occurred and be
              continuing.

         4.   Assignment and Acceptance. By its signature hereto, the financial
institution listed on the signature pages hereto as the "New Lender" (the "New
Lender") hereby, effective as of the Increase Effective Date:

              (a) irrevocably assumes without recourse to the Administrative
         Agent or any Lender New Lender's Revolving Credit Commitment and
         related rights and obligations under the Credit Agreement in the
         principal amount as set forth on Schedule 1 to the Credit Agreement (as
         amended by this Amendment).

              (b) (i) represents and warrants that it is legally authorized to
         enter into the Credit Agreement; (ii) confirms that it has received a
         copy of the Credit Agreement, together with copies of the financial
         statements delivered pursuant to Section 8.1 thereof and such other
         documents and information as it has deemed appropriate to make its own
         credit analysis and decision to enter into the Credit Agreement; (iii)
         agrees that it will, independently and without reliance upon the
         Administrative Agent or any other Lender and based on such documents
         and information as it shall deem appropriate at the time, continue to
         make its own credit decisions in taking or not taking action under the
         Credit Agreement, the other Loan Documents or any other instrument or
         document furnished pursuant hereto or thereto; (iv) appoints and
         authorizes the Administrative Agent to take such action as agent on its
         behalf and to exercise such powers and discretion under the Credit
         Agreement, the other Loan Documents or any other instrument or document
         furnished pursuant hereto or thereto as are delegated to the
         Administrative Agent by the terms thereof, together with such powers as
         are incidental thereto; and (v) agrees that it will be bound by the
         provisions of the Credit Agreement and will perform in accordance with
         its terms all the obligations which by the terms of the Credit
         Agreement are required to be performed by it as a Lender including, if
         it is organized under the laws of a jurisdiction outside the United
         States, its obligation pursuant to subsection 5.11(b) of the Credit
         Agreement.

              (c) Agrees that it shall, from and after the Increase Effective
         Date, be a party to the Credit Agreement and have the rights and
         obligations of a Lender thereunder and under the other Loan Documents
         and shall be bound by the provisions thereof.

         5.   Representations and Warranties. To induce the Administrative Agent
and the Lenders to enter into this Amendment, the Borrower hereby represents and
warrants that after giving effect to the consents and amendments provided for
herein, the representations and warranties contained in the Credit Agreement and
the other Loan Documents will be true and



                                       5
<PAGE>

correct in all material respects as if made on and as of the date hereof and no
Default or Event of Default will have occurred and be continuing.

         6.   No Other Amendments or Consents. Except as expressly amended
hereby, the Credit Agreement and the other Loan Documents shall remain in full
force and effect in accordance with their respective terms, without any waiver,
amendment or modification of any provision thereof.

         7.   Counterparts. This Amendment may be executed by one or more of the
parties hereto on any number of separate counterparts and all of such
counterparts taken together shall be deemed to constitute one and the same
instrument.

         8.   Expenses. The Borrower agrees to pay and reimburse the
Administrative Agent for all of the reasonable out-of-pocket costs and expenses
incurred by the Administrative Agent in connection with the preparation,
execution and delivery of this Amendment, including, without limitation, the
reasonable fees and disbursements of Cadwalader, Wickersham & Taft, counsel to
the Administrative Agent.

         9.   No Defenses, Release. None of the Borrower nor any other Loan
Party has any claims, counterclaims, offsets or defenses to the Loan Documents
or the Obligations, or if any such Person does have any claims, counterclaims,
offsets or defenses to the Loan Documents or the Obligations, the same are
hereby waived, relinquished and released in consideration of the execution and
delivery of this Amendment by the Lenders parties hereto. By its execution
hereof and in consideration of the mutual covenants contained herein and the
accommodations granted to the Borrower hereunder, the Borrower on behalf of
itself and the other Loan Parties expressly waives and releases any and all
claims and causes of actions any of them may have, or allege to have (and all
defenses which may arise out of any of the foregoing), whether known or unknown,
against the Administrative Agent or any Lender or any of their Affiliates,
employees, directors, officers, attorneys or agents, arising out of the credit
relationship between the Borrower and the Lenders up to and including the date
of this Amendment.

         10.  Integration. This Amendment, the Credit Agreement and the other
Loan Documents represent the agreement of the Borrower, the Administrative Agent
and the Lenders with respect to the subject matter hereof, and there are no
promises, undertakings, representations or warranties by the Administrative
Agent or any Lender relative to the subject matter hereof not expressly set
forth or referred to herein or in Credit Agreement or the other Loan Documents.

         11.  APPLICABLE LAW. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED
AND INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

                            [SIGNATURE PAGES FOLLOW]

                                       6

<PAGE>



                  IN WITNESS WHEREOF, the parties hereto have caused this
Amendment to be executed and delivered by their proper and duly authorized
officers as of the day and year first above written.


                                    UNIVERSAL HOSPITAL SERVICES, INC.



                                    By:  __________________________________
                                        Name:
                                        Title:


                                    CANADIAN IMPERIAL BANK OF
                                       COMMERCE, AS ADMINISTRATIVE AGENT



                                    By:  __________________________________
                                        Name:
                                        Title:


                                    KEY CORPORATE CAPITAL INC., AS COLLATERAL
                                       AGENT AND AS A LENDER



                                    By:  __________________________________
                                        Name:
                                        Title:


                                    CIBC INC.



                                    By:  __________________________________
                                        Name:
                                        Title:


                                 Signature Page
                        Universal Hospital Services, Inc.
                Second Amendment and Consent to Credit Agreement


<PAGE>

                                    FLEET NATIONAL BANK



                                    By:  __________________________________
                                        Name:
                                        Title:


                                    HELLER FINANCIAL, INC., AS SYNDICATION
                                       AGENT



                                    By:  __________________________________
                                        Name:
                                        Title:


                                    NATIONAL BANK OF CANADA



                                    By:  __________________________________
                                        Name:
                                        Title:



                                    By:  __________________________________
                                        Name:
                                        Title:


                                    TRANSAMERICA BUSINESS CAPITAL CORPORATION,
                                      as successor in interest to TransAmerica
                                      Business Credit Corporation


                                    By:  __________________________________
                                        Name:
                                        Title:


                                    USB AG, STAMFORD BRANCH, AS NEW LENDER



                                    By:  __________________________________
                                        Name:
                                        Title:


                                 Signature Page
                        Universal Hospital Services, Inc.
                Second Amendment and Consent to Credit Agreement


<PAGE>



                                                                      SCHEDULE 1

               LENDERS, COMMITMENTS AND APPLICABLE LENDING OFFICES

<TABLE>
<CAPTION>

Lender and Lending Offices                     Revolving Credit Commitment
--------------------------                     ---------------------------
<S>                                                   <C>
CIBC Inc.                                             $17,500,000

Applicable Lending Offices:

Base Rate Loans and Eurodollar Loans:
425 Lexington Avenue
New York, New York  10017
Attention: Agency Services
Telephone: 212-856-3704
Telecopy: 212-856-3763

Fleet National Bank                                   $10,000,000

Applicable Lending Offices:

Base Rate Loans and Eurodollar Loans:
100 Federal Street
MS 01-11-02
Boston, Massachusetts 02211
Attention: Pauline So
Telephone: 617-434-3219
Telecopy:  617-434-4929


Heller Financial, Inc.                                $17,500,000

Applicable Lending Offices:

Base Rate Loans and Eurodollar Loans:
500 West Monroe Street
Chicago, Illinois 60661
Attention: Mike Sznajder
Telephone: 312-441-7470
Telecopy: 312-441-7598
</TABLE>

<PAGE>

<TABLE>
<CAPTION>

Lender and Lending Offices                     Revolving Credit Commitment
--------------------------                     ---------------------------

<S>                                                   <C>
Key Corporate Capital Inc.                            $12,500,000

Applicable Lending Offices:

Base Rate Loans and Eurodollar Loans:
127 Public Square
MS OH-01-27-0600
Cleveland, OH  44114
Attention:  Cindy Aukerman
Telephone: 216-689-3656
Telecopy: 216-689-3298


National Bank of Canada                               $10,000,000

Applicable Lending Offices:

Base Rate Loans and Eurodollar Loans:
225 West Washington, Suite 1100
Chicago, Illinois 60606
Attention: James J. Kelly
Telephone: 312-558-8879
Telecopy: 312-558-6461


Transamerica Business Capital Corporation,
as successor in interest to Transamerica
Business Credit Corporation                           $10,000,000

Applicable Lending Offices:

Base Rate Loans and Eurodollar Loans:
555 Theodore Fremd Avenue,
Suite C 301
Rye, New York 10580
Attention:  Paul Durosko
Telephone: 914-925-7217
Telecopy: 914-921-5883
</TABLE>


<PAGE>

<TABLE>
<CAPTION>

Lender and Lending Offices                     Revolving Credit Commitment
--------------------------                     ---------------------------
<S>                                                   <C>

UBS AG Stamford Branch                                $10,000,000

Applicable Lending Offices:

Base Rate Loans and Eurodollar Loans:
677 Washington Boulevard
Stamford, Connecticut 06901

Attention: Lynne Alfarone
Telephone: 203-719-4308
Telecopy:  203-719-3888

                                                      -----------
Total:                                                $87,500,000
                                                      ===========
</TABLE>