Inpatient care represents a challenge for health professionals because the requirements for each patient are diverse. Timing is a key element in patient care at hospitals because almost all follow a schedule of interventions such as medication management, food management, laboratory sampling, testing, and visits. This alters the patient's own routine, which is already disturbed by the changes brought about by the disease, sleep disturbances and family dependency. Displacing the patient’s lifestyle and family or work environment with the hospital environment that disengages their vital functions and daily activities from environmental factors can generate great stress. The environmental cues given by the social environment are changed by the regular hospital characteristics of noise peaks and constant light. Changes in routines and rhythms can alter the patient’s recovery process and ability to adapt.

Understanding the presence of biological rhythms in healthy subjects and patients in relationship with their external environment, can contribute and strengthen the scientific rationale for nursing practice. Although there is abundant literature related to the topic of biological rhythms and their role in the homeostasis of the individual and disease, so far there is no middle-range theory that integrates existing knowledge of biological rhythms and patient care. The purpose of this paper is to propose a middle-range theory for inpatient circadian care.

Time is a phenomenon that affects the biological activities of organisms. Time-bound activities are present at all levels of biological organization from the cellular to the systemic level and are known as biological rhythms. Biological rhythms are known to all physiological phenomena that occur in a cyclical manner in living organisms. The importance of biological rhythms in living organisms stimulated the development of chronobiology, a line of physiology that was born with the congress on biological rhythms in Cold Spring Harbor (1960) directed by Prof. Dr. Franz Halberg [1]. Chronobiology studies the temporal organization of biological processes at the molecular, cellular, tissue, systemic and the individual levels, and the interactions between this organization and their environment, in order to establish a correlation between environmental events and the organization of biological functions.

Biological rhythms are mechanisms that prepare the body for predictable changes in the environment. One predictable event that occurs repeatedly over time at a constant interval is the day-night cycle [2, 3]. Biological rhythms are classified into three groups according to the 24-hour day: Ultradian rhythms are rhythms shorter than 24 hours; Infradian rhythms are rhythms lasting longer than 24 hour (weeks, months, or seasons); and Circadian rhythms have a period of about one day (the term circadian rhythm was coined by Franz Halderg from the Latin circa, “around” and dian “day”, which literally means “about a day”) [4]. Circadian rhythms are the most often studied rhythms due to their clinical implications and physiology [5-7].

Most physiological and behavioral functions in humans change over day and night. These changes allow organisms to anticipate and adapt to changes in the environment of light and dark which are linked to the rotation of the earth in a precise and controlled way [8-10]. This rhythmicity is generated by specific structures called endogenous biological clocks that are genetically encoded to generate internal organic fluctuations that respond to presence or absence of external signals. These fluctuations allow the development of adaptive processes by the individual towards environmental changes [11]. These changes provide the individual internal temporal order essential for the survival of the species. The main function of this internal order is to optimize metabolism and ensure the proper use of energy to sustain vital body processes, which requires a command from the central nervous system [6].

In mammals, the temporal control is performed from the suprachiasmatic nucleus (SCN), located in the hypothalamus. The SCN acts as a pacemaker through the expression of at least a dozen genes called clock genes. However, new evidence suggests that peripheral clocks exist in tissues of some organs to modulate many aspects of physiology and behavior, allowing for temporal homeostasis [12, 13].

Addition to the internal factors, there are external factors that synchronize the internal clock to changes in the environment (the external synchronizers are called Zeitgebers or “time-givers”). The strongest synchronizer is the cycle of light/dark, which adjusts the timing of the circadian clock to a 24-hour interval. In addition to the light/dark cycle, various other factors such as food habits, social and working hours, and the administration of drugs for medical purposes may also affect biological rhythms in humans [5, 6, 14]. The light/dark cycle determines the sleep/wake cycle, one of the vital biological rhythms that is fundamental for life, body homeostasis, and recovery of body daily wear. This cycle is determined by endogenous factors, but also by external cues such as light and noise levels and working hours. Sleep/wake patterns can be unique to each individual and their alteration can cause health problems.

Illness and hospitalization processes constitute an important risk factor for disruption of the rest/activity and sleep/wake rhythms, which are also modified by other factors including age, anxiety, depression, pain, medication management, and hospital environment. Factors such as light and noise, typical of the hospital environment, can alter the beginning of the sleep phase [15, 16].

The TICC proposed theory has one key concept: adaptation. This concept is fundamental in the model of Roy, one of the theoretical models that support current nursing practice worldwide [17]. Several middle-range theories derived from the Roy adaptation model apply to all nursing practice and propose that the objective of patient care is to restore balance and conserve energy homeostasis [17]. Hospitalization processes cause a disturbance in life, requiring a period of compensation followed by adaptation, which can be positive or negative, and complete or incomplete [18]. These changes require the organism to implement strategies to effectively ensure its survival against challenges in everyday situations and critical periods of changes in the environment. Adaptation, homeostasis and survival are the goal of nursing care [19, 20].

Currently there is enough scientific evidence showing that rhythmicity and adaptability are key elements in the phenomenon of biological rhythms. Evidence also shows how these elements can determine health or disease. However, there is widespread lack of understanding among health professionals about this evidence and the implications of clinical interventions, care, and environmental factors, such as lighting, noise and sleep disturbances in hospitalized patients [21].

The method employed in order to develop the middle-range theory about the “Inpatient Circadian Care (TICC)” was the same one employed for the development of the middle-range theory in aviation nursing: “Flight Nursing Expertise: towards a middle-range theory” [22].

Initially, key concepts were stated by the authors based on their previous knowledge and professional experience. The following key concepts were established: chronobiology, biological rhythms, circadian rhythms, hospital, and adaptation. These concepts guided an exhaustive literature review using databases such as PubMed, SciELO Public Health, and internet Google Scholar. The data search was done using the key terms: biological rhythms, chronobiology, circadian rhythms, nurse care, middle-range theories, and adaptation. The search was performed taking into account a period of 6 decades from 1950 to 2013. Finally, an analysis of the information and a discussion were done, supported by all the information that was found and the decades of experience in basic and clinic research for each author in the disciplines of nursing, medicine, chronobiology, neuroscience and genetics. In order to strengthen the conceptual frame of this theory, we integrated theoretical elements with clinical practice. Connections between concepts of chronobiology and the characteristics of the care for the hospitalized patient, focusing on the nursing care were examined. In order to build this new theory, inductive and deductive reasoning processes, supported in empiric evidence and experience, were used.

The middle-range “Inpatient Circadian Care” (TICC) has three basic building blocks:

1) The patient or circadian subject (time subject)

2) The synchronization process of a patient’s biological rhythms

3) Hospital staff, synchronizers of a patient’s biological rhythms and time-giver (Zeitgebers).

The following concepts arise from this theory: the circadian subject “I clock”; the “synchronization” process of biological rhythms of an individual, and the temporal environment or time giving environment represented in this model by the hospital staff “clockmaker” (Fig. 1).

Concept definitions:

“Synchronization” Process

Under disease conditions the circadian human being loses synchronization between the oscillations of the biological clock and the rest of the body, resulting in internal clock desynchronization with periods different from the 24-hour cycle (early or late phase). This can develop in patients with chronic diseases such as diabetes, hypertension, or cancer [52, 53]. It may also be present in depressive states and other psychiatric disorders [54]. Given the high incidence and susceptibility of people to suffer from internal desynchronization, research and clinical observations suggest that individual genetic factors play a determinant role in both acute and chronic medical conditions [55, 56]. Desynchronization of circadian rhythms (eg, sleep/wake cycle) is promptly manifested as sleep disturbance, persistent fatigue, hypnotic drug dependence, and impaired mood, including depression [57].

Fig. (1). Inpatient Circadian Care (TICC). Biological rhythms are regulated by the environment due to the presence of timers or Zeitgebers (1). Disease is characterized by structural and functional changes that can be caused by alterations in biologic rhythms and/or interfere with the internal rhythms of the individual (2). Hospitalization represents a new environment for the patient, with new ambient timers that can complicate the recovery of the patient (3). The role of nursing is to intervene with the factors, both external and individual, that contributes to the desynchronization of the internal rhythms to favor patient´s recovery.

Temporal Environment as a Synchronizer

The spatial and temporal environments intervene in each of the concepts of ill person, nursing, and health in a complex person-environment interaction [58]. The circadian human being is subjugated to continuous adaptation through external time signals (Zeitgebers), with light being the most powerful, followed by feeding time, daily activity and resting, social interaction, and exercising. All these factors allow the individual to keep adapted and guided to the temporal environment in his daily activities [59-61]. Nevertheless, an asynchrony can present between the internal and external clocks, and the illumination/darkness cycle, caused by multiple factors: rapid travels through hour time zones, nocturnal working time, and exposition to excessive bright light at night. All of these factors generate desynchronization with the external time-givers [60, 62].

This state is called chronodisruption that is defined as a significant disturbance of the temporal internal order of the physiological, biochemical and behavioral circadian rhythms. Chronodisruption is associated with a higher incidence of metabolic syndrome, cardiovascular diseases, cognitive and affective disorders, sleep disorders, some types of cancer, premature aging, and accidents [63, 64]. Chronodisruption can be potentiated by the hospital as a new environment for the patient, a place where ambient clues appear different from clues generally found in daily activities: illumination, noise, infrastructure, temperature, workers, ventilation, security, visiting time, number of patients in each room, clinical assessment, invasive procedures, laboratory tests, and medications intake. All these elements together can alter the circadian synchroni-zation of a patient physiologically, psychologically, and socially.

There is strong scientific evidence that demonstrates a reciprocal relationship between a robust endogenous circadian system and the presence of regularly programed Zeitgebers. During disease, the correct function of the circadian synchronization system can be more dependent on exposure to intentionally programmed stimuli. Light levels, physical activity, temperature, and feeding are key elements for the internal synchronization of the central circadian clock and peripheral circadian oscillators. In such conditions, a regularly programed exposure to Zeitgebers, based on rational and scientific criteria, would be very important to recovery and well being [107]. Avoiding desynchronization and promoting circadian homeostasis contributes to optimal physiological function, general good health, and reduced susceptibility to comorbidities in persons with an acute or chronic illness [108]. For the health system, paying attention to circadian principles could reduce costs by preventive interventions that diminish patient complications and reduce hospital stay (Fig. 2).

Fig. (2). The circadian nursing care of the hospitalized patient and costs in health system. A scientific nursing practice that makes the accurate intervention to correct the disruption of the patient´s biological rhythms can reduce costs by avoiding prolonged hospitalary stays and severe complications in the patient (1). An inappropriate attention of the patient without considering biological rhythm´s synchronizing and desynchronizing factors implies the probability of raising costs in the attention of health services and inappropriate quality of attention (2).

Chronobiology applied to patient care has broad implications for clinical practice, basic clinical research, and the training of new health care professionals. Knowledge of human circadian variations (physiological, psychological, behavioral, and social), as well as knowledge of how a disease behaves during a 24-hour period, considering its signs and symptoms, as well as the desired and undesired side effects of medications, will generate an appropriate care plan for the timing needs of the patient. A care plan should includes ensuring a stable external environment for the individual, with suitable light-dark cycles, low noise, constant temperature, and proper drug and food administration. In addition minimizing isolation and encouraging social interaction should be introduced into the plan of care for any long-term patient. This holistic approach presents an integration of existing scientific knowledge on chronobiology and the art and skill of nursing practice.

The patient is in continuous interaction with the environment (family, group, community, society, and hospital room) and, accordingly, experiences particular life styles and responses to health and disease. The need to have an updated knowledge base on biological rhythms requires that the nurse interact with other disciplines, both basic biomedical sciences and clinicians. Given that certain circadian traits are inherited, understanding the genetic architecture of molecular mechanisms of the circadian clock regulation can provide the necessary knowledge for individualizing patient care, and thus facilitating a rational therapeutic approach to their hospital care.

Finally, the performance of nursing care based on current scientific knowledge of chronobiology can positively impact the costs of health systems to detect and prevent elements of the individual or the environment that may disrupt or interfere with the patient's recovery. This can help reduce hospitalization time, medical and surgical complications, and reduce morbidity and mortality. However, more research is required in the area of circadian nursing care to determine the practical utility of this theory and to generate new knowledge that can strengthen the training of new professionals and the quality of current professional nursing practice.

The authors confirm that this article content has no conflict of interest.