I am an anaesthetist,is pcr enough or do we have to look at the thorax tomography before surgeries
This is an emerging area of advice. It really depends on the pre-test probability of COVID-19 in your region, and the urgency of surgery.
The Royal College of Surgeons, Edinburgh make the following recommendation
9th April 2020
Patients who present as abdominal emergencies who have an abdominal CT in their diagnostic investigations should also have a Chest CT scan (ref ––Updated General Surgery Guidance on Covid-19 – Intercollegiate / ASGBI 5th April 2020).
Due to its low sensitivity and the low pre-test probability of disease (Scotland), computed tomography should only be deployed in very specific circumstances
Your pre-test probability may be much higher which might justify CT chest if you don't have time to do rtPCR, and antibody studies.
I can't comment on rt-PCR.
Recent findings (which can be listened to in this MedCram Youtube clip, by Roger Seheult, MD on Covid-19 diagnosis), in summary says
Lung ultrasound rivals CT imaging for fast and accurate bedside diagnosis and monitoring of coronavirus infection