According to the PMBOK Guide, 6th edition, Section 11.4.3.1, Risk Thresholds, risk thresholds are the level of risk exposure above which risks are addressed and below which risks may be accepted. Risk thresholds are determined by the organization’s risk appetite, which is the degree of uncertainty that an organization is willing to accept in pursuit of its goals. Therefore, when the project manager is informed by the risk owner that the exposure from two high-impact risks are hitting the risk thresholds, the project manager should complete an assessment and confirm the response with the sponsors, who are the key stakeholders for the project and have a low risk appetite. The project manager should not update the project management plan, perform an assumptions and constraints analysis, or implement mitigation measures without first consulting with the sponsors and obtaining their approval. References: PMBOK Guide, 6th edition, Section 11.4.3.1, Risk Thresholds