Emergency care nurses (ECNs) face several challenges when they assess patients with different symptoms, signs, and conditions to determine patients’ care needs. Patients’ care needs do not always originate from physical or biomedical dysfunctions. To provide effective patient-centred care, ECNs must be sensitive to patients’ unique medical, physical, psychological, social, and existential needs. Clinical practice guidelines (CPGs) provide guidance for ECNs in such assessments. The aim of this study was to evaluate the quality of CPGs for comprehensive patient assessments in emergency care. A quality evaluation study was conducted in Sweden in 2017. Managers from 97 organizations (25 emergency medical services and 72 emergency departments) were contacted, covering all 20 Swedish county councils. Fifteen guidelines were appraised using the validated Appraisal of Guidelines for Research & Evaluation II (AGREE II) tool. The results revealed that various CPGs are used in emergency care, but none of the CPGs support ECNs in performing a comprehensive patient assessment; rather, the CPGs address parts of the assessment primarily related to biomedical needs. The results also demonstrate that the foundation for evidence-based CPGs is weak and cannot confirm that an ECN has the prerequisites to assess patients and refer them to treatment, such as home-based self-care. This may indicate that Swedish emergency care services utilize non-evidence-based guidelines. This implies that ECN managers and educators should actively seek more effective ways of highlighting and safeguarding patients’ various care needs using more comprehensive guidelines.