Final answer:
The client with a thoracotomy and chest tube showing 150 mL of bright-red blood in the collection chamber should be assessed first as it indicates active bleeding, a life-threatening condition requiring immediate attention.
Step-by-step explanation:
The nurse should assess the client with the thoracotomy and chest tube first. The presence of 150 mL of bright-red blood in the collection chamber from the past hour indicates active bleeding and can quickly lead to hemodynamic instability or hypovolemic shock. This is a life-threatening condition and requires immediate attention.
In comparison, the absence of bowel sounds after a bowel resection and colostomy, coffee-ground emesis after tonsillectomy, and pain after knee arthroplasty, while important, are not as immediate life-threatening as significant bleeding post-thoracotomy. Although each client needs to be assessed and monitored carefully, prioritizing care is crucial in a situation where the patient's life could be at immediate risk.