<PAGE>

                                                                     EXHIBIT 4.5

                                 AMENDMENT NO. 1
                    TO AMENDED AND RESTATED VOTING AGREEMENT


         THIS AMENDMENT NO. 1 TO AMENDED AND RESTATED VOTING AGREEMENT
("Amendment") is made and entered into as of August 11, 1999, by and among
SYMBION, INC., a Tennessee corporation formerly named "UniPhy Healthcare, Inc."
(the "Company"), and those Persons identified on Exhibit A attached hereto
(collectively, the "Investors" and each individually an "Investor").

                                R E C I T A L S:

         WHEREAS, the Company and the Investors are parties to that certain
Amended and Restated Voting Agreement, dated as of June 25, 1999 (the "Voting
Agreement");

         WHEREAS, the Company and certain of the Investors are parties to that
certain Securities Purchase Agreement, dated as of July 6, 1999 (the "Purchase
Agreement");

         WHEREAS, Section 1(B) of the Purchase Agreement grants an option (the
"Option") of limited duration to Richland Ventures III, L.P. ("RVIII") to
purchase up to 3,191,489 shares (the "Option Shares") of the common stock, no
par value (the "Common Stock"), of the Company, at a purchase price of $1.88 per
share;

         WHEREAS, in the event that RVIII purchases the Option Shares, the
Company and the Investors desire that RVIII obtain the rights and obligations of
an "Investor" and an "ARC Key Shareholder" under the Voting Agreement;

         WHEREAS, the Company may, pursuant to Section 1(C) of the Purchase
Agreement, issue and sell up to 5,319,149 shares (the "Reserve Shares") of
Common Stock (including the Option Shares) to any person or entity (each, a
"Reserve Share Purchaser");

         WHEREAS, in the event that a Reserve Share Purchaser purchases Reserve
Shares, the Company and the Investors may desire that such Reserve Share
Purchaser have the rights and obligations of an "Investor," a "UniPhy Preferred
Shareholder," a "UniPhy Founder" or an "ARC Key Shareholder" under the Voting
Agreement;

         WHEREAS, the Company and the Investors desire to amend the Voting
Agreement as set forth in this Amendment, pursuant to Section 2.3 of the Voting
Agreement; and

         WHEREAS, capitalized terms used herein without definition shall have
the same meanings ascribed to such terms in the Voting Agreement.

         NOW, THEREFORE, in consideration of the foregoing and the respective
covenants and agreements contained herein, the sufficiency of which is hereby
acknowledged, the parties hereby agree and consent to the following:

                               A G R E E M E N T:

1.  RVIII Amendment. The Voting Agreement is hereby amended by adding and
appending the following as Section 3 of the Voting Agreement:

<PAGE>

          3. Addition of RVIII as a Party. Notwithstanding the provisions of
          Section 2.3 or any other Section hereof, upon the occurrence of: (i)
          the exercise by Richland Ventures III, L.P. ("RVIII") of the option
          (the "Option") to purchase up to 3,191,489 shares (the "Option
          Shares") of Common Stock at a purchase price of $1.88 per share which
          was granted to RVIII in Section 1(B) of that certain Securities
          Purchase Agreement, dated as of July 6, 1999 (the "Purchase
          Agreement"), among the Company and certain purchasers identified in
          such agreement, and the purchase of Option Shares by RVIII, and (ii)
          the execution and delivery to the Company by RVIII of a counterpart of
          this Amended and Restated Voting Agreement (as then amended), adopting
          and accepting the terms hereof, and (iii) acceptance and
          countersignature of such counterpart by the Company:

                  (a) RVIII shall be a party to this Amended and Restated Voting
          Agreement; and

                  (b) Exhibit A attached to this Amended and Restated Voting
          Agreement shall be amended to add RVIII as a person identified
          thereon, and RVIII shall be, and shall be included within the
          definition of, an "Investor" for purposes of this Amended and Restated
          Voting Agreement; and

                  (c) RVIII shall be, and shall be included within the
          definition of, an "ARC Key Shareholder," for purposes of this Amended
          and Restated Voting Agreement; and

                  (d) RVIII shall have, and be entitled and subject to, all of
          the rights, benefits, duties and obligations of an "Investor" and an
          "ARC Key Shareholder" under this Amended and Restated Voting
          Agreement, subject to the terms hereof.

2. Director Nominee Amendment. The Voting Agreement is hereby further amended by
deleting the current text of Section 1.2(vii) of the Voting Agreement in its
entirety, and replacing such text with the following:

          "(vii) one (1) person nominated jointly by Richland Ventures II, L.P.
          and  Richland Ventures III, L.P., and".

3. Reserve Share Purchasers Amendment. The Investors' Rights Agreement is hereby
further amended by adding and appending the following as Section 4, and
Sections 4.1 and 4.2  thereunder, of the Investors' Rights Agreement:

         4. Addition of Reserve Share Purchasers as Parties.

                  4.1 Reserve Share Purchasers. The parties hereto acknowledge
         and agree that, pursuant to Section 1(C) of the Purchase Agreement, the
         Company may issue, offer and sell up to 5,319,149 shares (the "Reserve
         Shares") of Common Stock (including the 3,191,489 Option Shares) to any
         person or entity (each, a "Reserve Share Purchaser"). Notwithstanding
         the provisions of Section 6(c) or any other Section hereof, upon the
         occurrence of: (i) the purchase from the Company by a

                                       2
<PAGE>

         Reserve Share Purchaser of Reserve Shares (but not including the
         purchase of Option Shares by RVIII, which is addressed in and governed
         by Section 3 above), and (ii) the execution and delivery to the Company
         by such Reserve Share Purchaser of a counterpart of this Amended and
         Restated Voting Agreement (as then amended), adopting and accepting the
         terms hereof, and (iii) acceptance and countersignature of such
         counterpart by the Company:

                           (a) such Reserve Share Purchaser shall be a party to
         this Amended and Restated Voting Agreement; and

                           (b) Exhibit A attached to this Amended and Restated
         Voting Agreement shall be amended to add such Reserve Share Purchaser
         as a person identified thereon, and such Reserve Share Purchaser shall
         be, and shall be included within the definition of, an "Investor" for
         purposes of this Amended and Restated Voting Agreement; and

                           (c) subject to Section 4.2 below, such Reserve Share
         Purchaser shall be, and shall be included within the definition of,
         either of a "UniPhy Preferred Shareholder," a "UniPhy Founder" or an
         "ARC Key Shareholder" (as designated by the Company pursuant to Section
         4.2 below), for purposes of this Amended and Restated Voting Agreement;
         and

                           (d) subject to Section 4.2 below, such Reserve Share
         Purchaser shall have, and shall be entitled and subject to, all of the
         rights, benefits, duties and obligations of an "Investor" and a "UniPhy
         Preferred Shareholder," a "UniPhy Founder" or an "ARC Key Shareholder"
         (as designated by the Company pursuant to Section 4.2 below) under this
         Amended and Restated Voting Agreement, subject to the terms hereof.

                  4.2 Designation as UniPhy Preferred Shareholder, UniPhy
         Founder or ARC Key Shareholder. The Company shall have the right, power
         and authority, to determine, in its discretion, in negotiation or
         agreement with one or more Reserve Share Purchasers or otherwise,
         whether or not a particular Reserve Share Purchaser shall (in addition
         to becoming a party hereto and an "Investor" hereunder) be identified
         and/or designated as a "UniPhy Preferred Shareholder," a "UniPhy
         Founder" or an "ARC Key Shareholder" for purposes of this Amended and
         Restated Voting Agreement, and thereby have, and be entitled and
         subject to, all of the rights, benefits, duties and obligations of such
         designation or identification under this Amended and Restated Voting
         Agreement, pursuant to Sub-sections 4.1(c) and (d) above.

4. Requisite Approval. Upon execution and delivery of this Amendment by the
Company and Investors representing the requisite percentage of Investor Shares
set forth in Section 2.3 of the Voting Agreement, this Amendment shall
constitute and be deemed to be an amendment to and part of the Voting Agreement.

5. No Other Changes. Except as expressly set forth or contemplated in this
Amendment, the terms and conditions of the Voting Agreement shall remain in
place and shall not be

                                       3
<PAGE>

altered, amended or changed in any manner whatsoever, except by any further
amendment to the Voting Agreement made in accordance with the terms of the
Voting Agreement, as hereby amended.

6. Counterparts. This Amendment may be executed in any number of counterparts
and by the different parties hereto on separate counterparts, each of which when
executed and delivered shall be deemed an original effective for binding the
parties hereto, but all of which shall together constitute one and the same
instrument.

                                       4
<PAGE>


         IN WITNESS WHEREOF, the parties hereto have executed this Amendment to
Amended and Restated Voting Agreement, and hereby consent to the amendment and
modification of the Voting Agreement provided herein, as of the date first above
written.


THE COMPANY:

SYMBION, INC.


By: /s/ Richard E. Francis, Jr.
    -----------------------------------------

Name:  Richard E. Francis, Jr.

Title: President and Chief Executive Officer



INVESTORS:


UNIPHY PREFERRED SHAREHOLDERS:

ABS CAPITAL PARTNERS, L.P.


       /s/ ABS Partners, L.P.
       --------------------------------------------

By:    /s/ Frederick L. Bryant
       --------------------------------------------

Name:  Frederick L. Bryant
       --------------------------------------------

Title: General Partner
       --------------------------------------------


/s/ Clifford G. Adlerz
---------------------------------------------------
Clifford G. Adlerz


/s/ Randy W. Cook
---------------------------------------------------
Randy W. Cook


---------------------------------------------------
Paul Davis


/s/ Richard E. Francis, Jr.
---------------------------------------------------
Richard E. Francis, Jr.


/s/ R. Dale Kennedy
---------------------------------------------------
R. Dale Kennedy



                                       5
<PAGE>

---------------------------------------------------
Tod Lambert


MARTIN INVESTMENT PARTNERSHIP II


       /s/ Charles N. Martin, Jr.
       --------------------------------------------

Name:  Charles N. Martin, Jr.
       --------------------------------------------

Title:
       --------------------------------------------



---------------------------------------------------
Kenneth C. Mitchell


PACIFIC VENTURE GROUP, L.P.

By:      PVG Equity Partner, L.L.C.,
         its General Partner

/s/ Eve M. Kurtin
--------------------------------------------
By: Eve M. Kurtin
Title: Member


PVG ASSOCIATES, L.P.

By: PVG Equity Partner, L.L.C.,
    its General Partner


/s/ Eve M. Kurtin
--------------------------------------------
By: Eve M. Kurtin
Title: Member


/s/ Patrick R. Rooney
--------------------------------------------
Patrick R. Rooney


/s/ Teresa F. Sparks
--------------------------------------------
Teresa F. Sparks


/s/ Gregg Stanley
--------------------------------------------
Gregg Stanley


/s/ Anthony Taparo
--------------------------------------------
Anthony Taparo


                                       6
<PAGE>


ARC KEY SHAREHOLDERS:


ARTHUR S. DEMOSS FOUNDATION

----------------------------------------------

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


/s/ Jerry M. Eyler
----------------------------------------------
Jerry M. Eyler


FIRST AVENUE PARTNERS, L.P.

/s/ Front Street, LLC
---------------------------------------------

By:    /s/ Donald M. Wilds
       --------------------------------------

Name:  Donald M. Wilds
       --------------------------------------

Title: Managing Member of the General Partner
       --------------------------------------


---------------------------------------------
William H. Freeman


---------------------------------------------
J. Michael Gould


HEALTH TECH AFFILIATES, INC.

---------------------------------------------

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


HLM/CB FUND, L.P.

---------------------------------------------

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

                                       7
<PAGE>


HLM PARTNERS VII, L.P.

---------------------------------------------

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


---------------------------------------------
W. Lawrence Hough


PIPER JAFFRAY, INC.

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


---------------------------------------------
B. Max Lauderdale


/s/ Charles N. Martin, Jr.
---------------------------------------------
Charles N. Martin, Jr.


/s/ Charles T. Neal
---------------------------------------------
Charles T. Neal


---------------------------------------------
Richard Panek


---------------------------------------------
Thomas Patten


---------------------------------------------
Keith B. Pitts


---------------------------------------------
Gary J. Prosterman


                                       8
<PAGE>

RICHLAND VENTURES II, L.P.


       /s/ Jack Tyrrell
       ---------------------------------------

Name:  Jack Tyrrell
       ---------------------------------------

Title: Partner
       ---------------------------------------


----------------------------------------------
Ann R. Schaaf


SOUTH ATLANTIC PRIVATE EQUITY FUND IV (QP), LIMITED PARTNERSHIP

         By:   South Atlantic Private Equity Partners IV, Limited Partnership,
               its General Partner


                      /s/ Donald W. Burton
                      ---------------------------------------

               Name:  Donald W. Burton
                      ---------------------------------------

               Title: Chairman
                      ---------------------------------------


SOUTH ATLANTIC PRIVATE EQUITY FUND IV, L.P.

         By:   South Atlantic Private Equity Partners IV, Limited Partnership,
               its General Partner


                     /s/ Donald W. Burton
                     ----------------------------------------

               Name: Donald W. Burton
                     ----------------------------------------

               Title: Chairman
                      ---------------------------------------


-------------------------------------------------------------
Cal Turner, Jr.


/s/ William V.B. Webb
-------------------------------------------------------------
William V.B. Webb


WW TWO, L.P.

-----------------------------------------------------

By:
       ----------------------------------------------

Name:
       ----------------------------------------------

Title:
       ----------------------------------------------


-----------------------------------------------------
James A. Webb, III


                                       9
<PAGE>



UNIPHY FOUNDERS:



--------------------------------------------
Peter Davidson


/s/ Shannon W. Fiser
--------------------------------------------
Shannon W. Fiser


THE FRANCIS IRREVOCABLE TRUST, ANN FRANCIS, TRUSTEE


       /s/ Richard E. Francis, Jr.
       ---------------------------------------

Name:  Richard E. Francis, Jr.
       ---------------------------------------

Title:
       ---------------------------------------



/s/ Victor Giovanetti
----------------------------------------------
Victor Giovanetti


/s/ George M. Goodwin
----------------------------------------------
George M. Goodwin


----------------------------------------------
Marlene D. Kelley


/s/ H. Edward Kleine III
----------------------------------------------
H. Edward Kleine III


----------------------------------------------
Darrell Naish


----------------------------------------------
Richard Panek


/s/ Vickie R. Warren
----------------------------------------------
Vickie R. Warren


                                       10
<PAGE>

                                  EXHIBIT A

                              SCHEDULE OF INVESTORS

UNIPHY PREFERRED SHAREHOLDERS

ABS Capital Partners, L.P.*
Clifford G. Adlerz*
Randy W. Cook*
Paul Davis*
Richard E. Francis, Jr.*
R. Dale Kennedy*
Tod Lambert
Martin Investment Partnership II*
Kenneth C. Mitchell*
Pacific Venture Group, L.P.*
PVG Associates, L.P.*
Patrick R. Rooney*
Teresa F. Sparks*
Gregg Stanley*
Anthony Taparo*

ARC KEY SHAREHOLDERS

Arthur S. Demoss Foundation*
Jerry M. Eyler*
First Avenue Partners, L.P.*
William H. Freeman
J. Michael Gould
Health Tech Affiliates, Inc.
HLM/CB Fund, L.P.*
HLM Partners VII, L.P.*
W. Lawrence Hough
Piper Jaffray, Inc.*
B. Max Lauderdale
Charles N. Martin, Jr.*
Charles T. Neal*
Thomas Patten
Keith B. Pitts
Gary J. Prosterman
Richland Ventures II, L.P.*
Ann R. Schaaf
South Atlantic Private Equity Fund IV (QP)*
South Atlantic Private Equity Fund IV, L.P.*
Cal Turner, Jr.*
William V.B. Webb*
WW Two, L.P.*
James A. Webb, III

* ANTI-DILUTION INVESTOR

<PAGE>


UNIPHY FOUNDERS

Peter Davidson
Shannon W. Fiser
The Francis Irrevocable Trust, Ann Francis, Trustee*
Victor Giovanetti
George M. Goodwin
Marlene D. Kelley
H. Edward Kleine III
Darrell Naish
Richard Panek
Vickie R. Warren




* ANTI-DILUTION INVESTOR



                                       2