Quite awhile back, I designed something similar. It wasn't a single string, but rather a series of IF statements that build the sql string, something like the following. I didn't try to guess which fields of yours are required and which are not.
Code:
Dim sFields As String, sValues As String
' first include all required fields in the sFields string
sFields = "CR_Number, Procedure_Name" ' add others as needed
' then the Values for the required fields
sValues = "'" & frmMain.txtCRNumber & "', '" & frmMain.txtProcedure.Text & "'"

' now handle optional fields and values
sFields = sFields & ", Unit_Admit_Datetime"
If dtUnitAdmitDate<>0# Then
    sValues = sValues & ", #" & dtUnitAdmitDate & "#"
Else 
    sValues = sValues & ", " &  Null
End If
' P.S. Don't remember, if inserting a new record must all fields be included in the field list?
' If not, just don't add it and it should be populated with its default new record values which may be Null

' handle other optional fields/values
When the above is all done, you should be able to modify your main sql statement something like:
Code:
 "Insert Into Master_Review(" & sFields & ") VALUES (" & sValues & ")"
The above sample was "air code" therefore, typos may exist