Final answer:
The most appropriate action would be to identify possible reasons for denial of pain.
Step-by-step explanation:
The most appropriate action if the patient does not report any pain after a thoracotomy for tumor resection would be to identify possible reasons for denial of pain. This could involve checking for cultural factors that may influence pain expression and perception in Native Americans. Additionally, it would be important to assess the patient's psychological well-being and past experiences with pain to determine if they have any fears or concerns that may affect their reporting of pain.