Final answer:
The dose of morphine for John when he presses the PCA button depends on his prescribed dose and should be determined by his healthcare provider based on his pain level and medical condition.
Step-by-step explanation:
Intravenous patient-controlled analgesia (PCA) allows patients to self-administer pain medication within prescribed parameters. In the case of John, the dose of morphine that he is meant to receive each time he presses the PCA button would depend on his prescribed dose, which should be determined by his healthcare provider based on his pain level and medical condition. It's important for John to communicate any changes in his pain level to his healthcare provider, so they can adjust his medication accordingly.
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