Looks like that exists as a command on the client which does some checking and then sends use_action_slot_item_server as a command.
Code:
__text:0055D5E3 ; use_action_slot_item(CCommand const&)
__text:0055D5E3 __ZL20use_action_slot_itemRK8CCommand proc near ; DATA XREF: sub_728F5+92o
__text:0055D5E3 push ebp
__text:0055D5E4 mov ebp, esp
__text:0055D5E6 push edi
__text:0055D5E7 push esi
__text:0055D5E8 push ebx
__text:0055D5E9 sub esp, 1Ch
__text:0055D5EC call ___i686_get_pc_thunk_bx
__text:0055D5F1 mov edi, ds:(_engine_ptr - 55D5F1h)[ebx]
__text:0055D5F7 mov eax, [edi]
__text:0055D5F9 mov edx, [eax]
__text:0055D5FB mov [esp], eax
__text:0055D5FE call dword ptr [edx+68h]
__text:0055D601 test al, al
__text:0055D603 jnz short loc_55D60D
__text:0055D605
__text:0055D605 loc_55D605: ; CODE XREF: use_action_slot_item(CCommand const&)+31j
__text:0055D605 ; use_action_slot_item(CCommand const&)+99j
__text:0055D605 add esp, 1Ch
__text:0055D608 pop ebx
__text:0055D609 pop esi
__text:0055D60A pop edi
__text:0055D60B pop ebp
__text:0055D60C retn
__text:0055D60D ; ---------------------------------------------------------------------------
__text:0055D60D
__text:0055D60D loc_55D60D: ; CODE XREF: use_action_slot_item(CCommand const&)+20j
__text:0055D60D call __ZN10C_TFPlayer16GetLocalTFPlayerEv ; C_TFPlayer::GetLocalTFPlayer(void)
__text:0055D612 test eax, eax
__text:0055D614 jz short loc_55D605
__text:0055D616 mov dword ptr [esp+4], 9
__text:0055D61E mov [esp], eax
__text:0055D621 call __ZN20CTFPlayerSharedUtils28GetEconItemViewByLoadoutSlotEP10C_TFPlayeri ; CTFPlayerSharedUtils::GetEconItemViewByLoadoutSlot(C_TFPlayer *,int)
__text:0055D626 mov esi, eax
__text:0055D628 test eax, eax
__text:0055D62A jz short loc_55D641
__text:0055D62C mov [esp], eax
__text:0055D62F call __ZN14C_EconItemView13GetStaticDataEv ; C_EconItemView::GetStaticData(void)
__text:0055D634 test eax, eax
__text:0055D636 jz short loc_55D641
__text:0055D638 test byte ptr [eax+0A4h], 40h
__text:0055D63F jnz short loc_55D660
__text:0055D641
__text:0055D641 loc_55D641: ; CODE XREF: use_action_slot_item(CCommand const&)+47j
__text:0055D641 ; use_action_slot_item(CCommand const&)+53j ...
__text:0055D641 mov eax, [edi]
__text:0055D643 mov ecx, [eax]
__text:0055D645 lea edx, (aUse_action_s_0 - 55D5F1h)[ebx] ; "use_action_slot_item_server\n"
__text:0055D64B mov [esp+4], edx
__text:0055D64F mov [esp], eax
__text:0055D652 call dword ptr [ecx+1A8h]
__text:0055D658 add esp, 1Ch
__text:0055D65B pop ebx
__text:0055D65C pop esi
__text:0055D65D pop edi
__text:0055D65E pop ebp
__text:0055D65F retn
__text:0055D660 ; ---------------------------------------------------------------------------
__text:0055D660
__text:0055D660 loc_55D660: ; CODE XREF: use_action_slot_item(CCommand const&)+5Cj
__text:0055D660 mov [esp], esi
__text:0055D663 call __ZN14C_EconItemView15GetItemQuantityEv ; C_EconItemView::GetItemQuantity(void)
__text:0055D668 test eax, eax
__text:0055D66A jle short loc_55D641
__text:0055D66C mov dword ptr [esp+4], 0
__text:0055D674 mov [esp], esi
__text:0055D677 call __Z17UseConsumableItemP14C_EconItemViewPN4vgui5PanelE ; UseConsumableItem(C_EconItemView *,vgui::Panel *)
__text:0055D67C jmp short loc_55D605
__text:0055D67C __ZL20use_action_slot_itemRK8CCommand endp