Theories and Conceptual Models in Nursing and Advanced Nursing Practice
Introduction
Theories in nursing provide an organized body of knowledge that defines the nursing practices, what the nurses are supposed to do in every situation, and why they need to do it.  The theories act as the framework of fundamental concepts and provide a purpose to guide the nursing practice at more concrete or specific stages. Butts (2013) and Fawcett et al. (2018) stated that the major categories of theories that guide the nursing and advanced nursing practices include grand theory, middle-range theory and practice level theory, need-based theories, interaction theories, outcome theories, descriptive theories, factor-isolating theory, explanatory theory, and prescriptive theories.  The nursing theorist explained that the theories describe the connection between the patient, environment, health and nursing goals, role, and functions.  Additionally, the conceptual model defines the nursing ideas, statement, and concepts; organize a framework for nursing practices, direct clinical practice, clinical and professional leadership, consultation, ethical decision making and collaboration, quality improvements especially DNP and APN programs and research.
Evaluation of theories and Conceptual Models
Nursing Theories
Grand nursing theory addresses and focuses on the nursing met paradigm components such as the patient (person), nursing, health, and environment (Smith & Parker, 2015). However, the theory does not guide specific nursing care interventions rather it focuses on providing a general framework and ideals in nursing. Butts (2013) mentioned that grand theories provide an abstract, wider scope and complex demand for more intense research for clarification in the nursing environment and advance nursing practices. Additionally, middle-range theories address a specific phenomenon in nursing (Brand£o et al., 2017).  However, the middle range nursing theories have a limited scope compared to the grand theories while they present nursing and advance nursing concepts and propositions at lower levels.
Finally, the practice level nursing theories provide a narrow scope and focus on a specific patient population within a framed set time. Butts (2013) explained that the practice level nursing theories are effective in providing a framework of nursing interventions and practices as well as provide a suggestion of the outcomes or the effects of the nursing practices. Based on this perspective, the practice-level nursing theories have more direct effects on the nursing practices as well as in advanced nursing practices, shaping the nursing interventions, their impact, and potential outcomes.
Conceptual Nursing Models
The conceptual models in nursing identify various components, their interactions, and patterns in nursing and in advance nursing practices. The conceptual nursing models include Consensus Model for advanced Practices Registered nurse regulations, Hamrics Integrative model, Calkins model, Browns Framework, and Shulers models of nurse practitioner practice among other models (Spross & Lawson, 2009; Fawcett, 2016; Fawcett et al., 2018). Each model focuses on a specific section and complements the focus of other models to contribute to nursing practices as well as advanced nursing practice. However, no model offers a comprehensive approach to nursing practices or advanced nursing practices. Nevertheless, an integrated approach and multi-application of various models contribute to an expected outcome.
 Regardless of the classification of the nursing theory and the conceptual models, each theory and model, compliment the other since no single theory or model can fit all the nursing care, intervention, and suggest outcomes. However, the combination of different theories from the abstraction (grand, middle-range, practice-led theories) to goal orientation (descriptive, factor-isolating, explanatory, prescriptive) to need-based, interaction theories complement each other to shape, define and direct the nursing practices as well as advanced nursing practices to achieve the patients outcome.
Conclusion
The nursing theories and conceptual models provide the foundation of nursing and advanced nursing today.  The nursing theories and models provide a guiding framework for the development of knowledge, direct education, research processes, and practices. Further, the conceptual models are an abstraction of reality, provide a visualization of the reality to simplify the thinking processes, give direction for search regarding various phenomena of central interest in nursing as well as suggest potential solutions. Thus, the nursing theories and models help in the recognition of what sets the foundation of the current nursing practices, providing a definition of purpose and role in the healthcare environment. Besides, the nursing and conceptual models provide a rationale for interventions and enhance the development of knowledge.  
References
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