Sustained and Continuous Operations

Bradley N. Younggren

Benjamin Harrison

OBJECTIVES

After reading this section, the reader will be able to:

1. Define continuous and sustained operations.

2. Explain what effects sustained operations can have on cognition, decision making, and fine motor skills.

3. Describe some of the pharmaceuticals that are available that can help with both sleep and alertness as is mission required.

4. List the other practical aspects of sustained operations that must be considered prior to execution of such a mission.

HISTORICAL PERSPECTIVE AND DEFINITION

If the human body requires approximately 8 hours of sleep per day for the average person, then one could assume that operations could be extended up to 16 continuous hours. This crude definition does not take into account other integral factors, such as level of activity and complexity of functioning required. Nevertheless, it does serve as a foundation from which we can define such operations, thereby classifying the existing research and identifying areas for further studies.

Researchers have started to recognize that there may be differences between short-term sustained operations (SUSOPS) and long-term sustained and continuous operations. It might be most effective to define short-term SUSOPS as any time of continuous operations for a period of time <1 week. Long-term SUSOPS can, therefore, be defined as any time >1 week in duration. It is important to point out that these are fairly arbitrary definitions that will continue to evolve as a larger body of literature develops to support these concepts. Currently, this helps explain some of the different physiologic effects we see in both instances.

THE EFFECT OF SUSOPS ON THE HUMAN BODY

There are numerous scenarios where tactical operators are required to perform for longer periods of time than would be considered the norm. The human body is known to respond to a number of stressors to include fatigue, sleep deprivation, and a negative energy balance (1). Studies have looked at these factors in a number of different research scenarios in both short-term and long-term SUSOPS. Interestingly, there appears to be some differences between the two types of operations. Most civilian tactical operations will be more short term in nature. As such, that information will most likely be more pertinent to the medical director of a special weapons and tactics (SWAT) or special response team (SRT).

There are some commonalities that apply to both scenarios that are worth reviewing. It is apparent that both acute and chronic exercise will cause core temperatures to be lower when exposed to cold because of a larger peripheral heat loss (2,3). The shivering response is also blunted in SUSOPS, which could potentially contribute to lower core body temperatures. Additionally, the increased heat gradient generated could lead to larger losses in core body temperatures (1).

Short-Term SUSOPS

Most of the research on SUSOPS has centered on the effect cold exposure has on the physiologic response mechanisms in the human body. Although providing excellent research, this preference has also highlighted the need for researchers to begin looking at the effects of long-term operations in hot, air environments.

Researchers have shown that repeated, intermittent exposures to cold water over a 10-hour period can blunt the shivering response (4). This is important because shivering is one of the body’s mechanisms to generate heat and increase core body temperature. Additionally, Castellani et al. showed that in an 84-hour SUSOP with cold air exposure, there was a greater fall in core body temperature than compared to controls (5). This fall in core body temperature was hypothesized to be due to either a blunted shivering response or to a larger thermal gradient which resulted in greater losses in core body temperature. It is difficult to isolate one stressor as the cause of the blunted shivering response, but it is thought that fatigue plays a role in the recalibration of the response to cold (6, 7 and 8).

Interestingly, in Castellani’s study the vasoconstrictor response was not impaired as was anticipated. In fact, it appears to be enhanced, thereby exhibiting a pattern referred to as insulative acclimatization. This process transfer’s heat to the subcutaneous muscles to support exercise, while decreasing the amount of heat lost to the environment (1).

Research has also shown that underfeeding can contribute to impaired thermoregulatory response to cold (9, 10 and 11) even in the presence of normal plasma glucose. This change appears to be most prevalent in the presence of exercise. In SUSOPS, we need to anticipate whether individuals are going to be moving or sedentary during the mission, and plan accordingly. It is very important to point out that these effects were evident even in the presence of eating; individuals just weren’t meeting their metabolic demand in the presence of exercise.

Long-term Sustained and Continuous Operations

Although these are more likely relevant in the military arena, it is still useful to review some of the changes that occur over longer periods of time. In general, there is an increased risk of hypothermia over time. This is from the combined effects of three factors: (i) decreased shivering which results in less heat production, (ii) blunting of the peripheral heat retention mechanism, and (iii) a decrease in core body temperature. In longer operations, the decreased overall weight and percentage of fat results in physiological changes that affect heat retention. Most of this research comes from studies on Army rangers who are perhaps the prime example of people exposed to long-term SUSOPS.

In general, the physiologic changes that occur in the body must be taken into account when planning for SUSOPS. The impact of weather, exercise, and nutritional intake must be taken into account when assessing for operational requirements.

PHARMACOLOGICAL COUNTERMEASURES FOR SLEEP DEPRIVATION AND FATIGUE IN SUSTAINED TACTICAL OPERATIONS

Tactical SUSOPS may lead to sleep deprivation and fatigue due to alterations in sleep patterns and long periods of sleeplessness. Sleep deprivation has been shown to cause fatigue, impair cognitive function, slow decision making, and alter mood; all of which can potentially compromise a tactical mission. Although there is a lack of solid clinical trials directly assessing the effectiveness of drugs that counteract fatigue and sleeplessness on law enforcement tactical operators, conclusions may be drawn from studies looking at therapeutics for SUSOPS in the military and aviation literature. Medical personnel in support of SUSOPS have therapeutic options available to assist operators maintain their reaction time and decision making, which is critical for successful mission completion. This section will briefly review the medical options that may be utilized to battle fatigue-related problems.

In general, cognitive function and reaction times decrease 30% to 40% during the first night and 60% to 70% after two nights of sleep deprivation (SD), leading to operation ineffectiveness (7). Naps of 2 hours can recuperate performance levels, but may result in sleep inertia and cognitive slowing for up to 2 hours after napping. Full-length sleep periods are optimal but often not feasible due to operational requirements and lack of comfortable, quiet sleep environments

Stimulants/Alertness-Enhancing Drugs

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