General Supportive Care
KEY POINTS
1 Failure to systematically review the available database relevant to prior history, events immediately preceding presentation, vital organ performance, and therapy prescribed before and during hospitalization often leads to misinterpretation, inappropriate care plans, or ineffective communications among caregivers that translate into adverse outcomes or protracted hospital stays.
2 Although the ICU practitioner must intercede quickly and decisively when action is needed to avert disaster, in most circumstances, the clinician’s prime objective should not be to reestablish “normal physiology” as quickly as possible but rather to encourage smooth resolution or adaptation to the pathophysiologic insult.
3 In the presence of uncertainty, conducting a closely observed “therapeutic minitrial” is a key element in the successful management of fragile or unstable patients. After the initial evaluation has been completed and a course of action has been decided, the patient and physician are often well served by implementing the proposed change under close observation for a brief interval, before formalizing the ongoing orders.
4 Uncertainty regarding the needed dose of medication (e.g., diuretics) often can be addressed, valuable time can be saved, and prescription errors can be avoided by verbalizing therapeutic intent and boundaries to the nurse and writing goal-oriented orders when possible to do so.
5 Concerned family members may seek or be offered information from multiple caregivers with differing perspectives, knowledge, and attitudes. One or two physicians must be identified as the primary contact(s) and one responsible family member identified as the conduit for important medical interchanges. To maintain confidence, the family must understand the logic of the management plan. Each ICU needs to establish and enforce a policy for family-caregiver communications that encourages trust, inspires confidence, meets the emotional needs of the family, and facilitates rather than impedes optimal care delivery.
6 Although certain consequences of protracted bed rest are well known to most practitioners, many subtle repercussions are either unknown or ignored. Physiologic adaptations to gravity affect nearly all organ systems, and release from gravitational stress may set in motion changes that delay recovery. Unrelieved recumbency has particularly adverse implications for the respiratory, cardiovascular, and neuromuscular systems.
7 Bedridden patients must be repositioned every 2 h unless there is an important contraindication to do so. Motion about the gravitational plane (Fowler’s, reverse Trendelenburg, sitting positions) helps preserve vascular reflexes and reduces the tendency for peridiaphragmatic (basilar) atelectasis. The lateral decubitus and prone positions effectively stretch and drain the nondependent lung. Modern low air-cushioned beds can be programmed to effectively rotate the patient around the craniocaudal axis in an attempt to ensure such benefits and preserve skin integrity.
8 Anxiety and pain occur almost universally in the ICU setting. The skillful team blends the use of anxiolytics with psychotropics, analgesics, physical measures, environmental modifications, and concerted attempts to establish two-way communication. Attempts to encourage “normal” sleep-wake, lighting, and activity cycles may include “batching” of the routine monitoring observations and patient manipulations as well as the systematic use of hypnotics, analgesics, and anxiolytics where appropriate. Early intervention and the synergistic use of psychotropics help alleviate pain and disorientation.
9 Aggressive respiratory therapy is essential to the care of patients with impaired lung expansion, retained secretions, and bronchospasm. These techniques, which include repositioning, deep breathing, coughing, inhalation of a bronchodilator, and chest physiotherapy, must be targeted to the specific problem at hand and used only as long as clearly indicated—either as a prophylactic measure or as a treatment of demonstrated benefit.
10 Oxygen supplementation can be accomplished by nasal prongs and catheters, closed or open face masks, or a sealed airway (endotracheal tube). The selection is influenced by the range and precision of the FiO2 required, patient tolerance, and the empirical response. The need for external humidification and the efficiency of humidifier required are determined by the flow of oxygen delivered relative to the total minute ventilation and the need to bypass the upper airway. Because disposable hygroscopic (heat-moisture exchanging) units may clog, impose dead space, and exhibit declining efficiency at high levels of ventilation, they may be unsuitable for severely ill patients and for those who have a high secretion burden or a marginal ventilatory reserve.
Certain aspects of management are common to critical care, independently of the precipitating cause for admission. These background details of day-to-day nursing and respiratory care help determine the eventual success or failure of specific management approaches leveled at the primary problems. This chapter reviews the basic elements of evaluation and therapy that apply to most patients in an intensive care unit (ICU) environment.
▪ BEDSIDE EVALUATION OF THE CRITICALLY ILL PATIENT
Therapeutic Perspective
The term intensive care implies the potential for rapid changes in clinical status. Therefore, the patient must be monitored carefully, and the lines of communication among caregivers must be kept open. To care for the most critically ill, a knowledgeable and responsive physician must be continuously accessible and committed to reevaluating the patient as often and as long as required. The complexity of many critical illnesses demands that the physician evaluate each case with a strong background in physiology, intervene thoughtfully but promptly when indicated, and reassess frequently. There must be a short “feedback loop” linking intervention, result, and midcourse correction. In a field in which many key disorders are poorly defined (acute respiratory distress syndrome [ARDS], sepsis, etc.), it is often impossible to apply with confidence the results of population-based clinical trials to the individual patient. Decision support tools such as computer-aided displays of patient data, handheld digital databases for drugs and diseases (e.g., PDAs loaded with medical text information), and immediate access to the entire electronically encoded medical record make impressive contributions to the goal of correct and timely intensive care. Remote access, however, cannot take the place of frequent bedside visits and effective verbal communications regarding goals, problems, and progress.
Except under exceptional circumstances, vital communications concerning a complex database are too severely strained by long-distance discussions for complicated decision making. In recent years, however, advances in telecommunications have facilitated economical and timely transfer of massive data files (e.g., as required for radiographic imaging and streamed video), thereby improving the capacity for decision making at a distance.
Although not yet equivalent for bedside evaluation, such techniques are rapidly improving and clearly offer the future possibility for care delivery of a uniform standard “24/7” or for a single specialtytrained physician to be involved simultaneously in the care of multiple patients at different sites. Although isolated measurements are unquestionably important, trends in the data stream are often of equal or greater value. For many variables, the trending interval ideally should include the prehospital period. Answers to such questions as “What is the patient’s chronic blood pressure, weight, cardiac rhythm, blood chemistries, medication listing, or PaCO2?” may determine the appropriate management goals.
The ICU practitioner must intercede quickly and decisively when action is clearly necessary. In most circumstances, however, the clinician’s prime
objective should not be to reestablish “normal physiology” as quickly as possible, but rather to encourage smooth resolution or adaptation to the pathophysiologic insult. A working diagnosis and updated plan of action must be clearly formulated and communicated. Because the clinician cannot always foresee the consequences, it is important to question the data quality and to consider alternative explanations before intervening—what really is known for certain and what must be better established?
objective should not be to reestablish “normal physiology” as quickly as possible, but rather to encourage smooth resolution or adaptation to the pathophysiologic insult. A working diagnosis and updated plan of action must be clearly formulated and communicated. Because the clinician cannot always foresee the consequences, it is important to question the data quality and to consider alternative explanations before intervening—what really is known for certain and what must be better established?
Elements of the Bedside Evaluation
To be maximally effective, the intensivist must quickly probe, organize, prioritize, and integrate an extensive body of information flowing from verbal and written communications, monitored data, laboratory output, and imaging studies (Table 18-1). Using the available database and his/her own observations at the time of evaluation, the physician formulates a listing of current problems, ranks their urgency and relative priority, and thoughtfully devises a plan of action. When things become hectic and/or risk is high for errors of omission or commission, 5 or 10 min spent away from the bedside in a quiet setting to analyze the database, identify the major problems and possibilities, and decide on the management approach nearly always is time well invested.
TABLE 18-1 ELEMENTS OF THE BEDSIDE EVALUATION | ||||||||||||||||||||||||||||||||||||||||||||
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Caution is indicated whenever making management decisions without diagnostic certainty. Conducting a closely observed “therapeutic minitrial” is a key element in the successful management of fragile or unstable patients, especially when the physician is uncertain regarding the outcome of a planned intervention. After the evaluation has been completed and a course of action has been decided, the patient and physician are often well served by implementing the proposed change under direct observation for a brief interval, before formalizing the order. This approach is particularly helpful when making ventilator adjustments, position changes, or alterations in the infusion rates of fluids or rapidly acting drugs, the effects of which can be monitored directly (see “Volume Challenge” in Chapter 2).
Accessing the Decisional Database
Skillful ICU practitioners not only integrate a vast array of data pertaining to the individual under treatment but also bring to bear the most appropriate therapy. Many decisions need to be made very quickly, and securing the needed information has the potential to consume enormous time. Faced with uncertainty and many competing priorities, the temptation is strong to forgo making a decision, to rely on memory, or to trust the verbal counsel of readily available colleagues. Potential for error and, consequently, the opportunity to improve care are high. The dramatic development of computer and communications technology has enabled partial closure of the information gap. Over a few short years, most physicians have been made aware of or now make active use of computerized medical records, remote digital access to laboratory data, and imaging studies from unit-based workstations or personal computers. Impressive displays of trended information as well as raw and processed data can be configured to the user’s specific needs. A somewhat smaller but growing proportion of physicians now use the powerful search engines of public or private electronic libraries to rapidly identify and retrieve relevant articles from the medical literature. The first steps toward this goal of timely information access have already been taken—not only by bedside computers, but also by hand-carried computers and PDAs of ever-increasing power. These
units not only package vital references, drug information, and periodically updated digests of evidence-based practice (e.g., Up-to-Date) but also allow wireless access to the Internet and to the hospital’s own local network (intranet) for timely retrieval of patient-specific data. Without question, the potential benefits and consequences of this extraordinary leap into the information age have only begun to develop.
units not only package vital references, drug information, and periodically updated digests of evidence-based practice (e.g., Up-to-Date) but also allow wireless access to the Internet and to the hospital’s own local network (intranet) for timely retrieval of patient-specific data. Without question, the potential benefits and consequences of this extraordinary leap into the information age have only begun to develop.
Verbal Communications
As most experienced practitioners realize, the ICU tends to function best with a team approach in which caregivers of varied descriptions (physicians, nurses, therapists, etc.) are professionally acquainted, mutually respected, and equally committed. All must be apprised of the current therapeutic objectives. The day-to-day routines and the expectations for the unit must be well understood, ideally with an awareness of the work schedules and priorities of all involved. Despite the unquestioned value of “hard data,” overreliance on “the numbers” to guide decision making fosters an immature and dangerous style of practice. Drawing from momentby-moment observations made over extended periods, a well-trained nurse or therapist is often the caregiver with the best insight regarding the relation of events and medications to evolving problems, tolerance of current therapy, and the probable effects of intended interventions (weaning from mechanical ventilation, mobilization, transport, reaction to medication, mental status, airway secretions, etc.). The clinician must seek their active involvement and advice in the planning process. For the team to operate with maximum effectiveness, the nurse, respiratory therapist, and unit pharmacologist (if available) should make formal rounds with the physician to share observations and advice as well as to be kept abreast of the doctor’s current thinking and care plan. The specific objectives of therapy and conditions or developments for which the doctor desires to be contacted should be communicated explicitly. Enormous benefit accrues from well-thought-out protocols and goal-directed orders that account for patient response. Uncertainty regarding the appropriateness and dosage of certain medications often can be addressed, valuable time can be saved, and prescription errors can be avoided by communicating the intent of treatment. The latter strategy lends flexibility and allows timely dosage adjustment (e.g., for fluids and/or diuretics). A very common error is to write an order, to assume that it was carried out, and then to fail to follow up on the result of its execution. Setting clear goals for the nurse or the therapist, allowing for “online” modification of dosing in accordance with those goals, and automatic notification when the goals cannot be met tighten the linkage between patient and caregivers. (“Adjust the furosemide drip to maintain output > input by at least 1 L per shift” is more likely to succeed than “Give 40 mg furosemide IV TID.”) Goal-directed order writing extends many of the same advantages offered by formalized care protocols (e.g., for heparin adjustment or insulin delivery) to a much broader and less-constrained therapeutic context.
Family Communications
It is difficult to overestimate the importance of direct, unambiguous communication with the family. The ICU environment holds undeniable potential for miscommunication as the concerned family member may seek or receive information and advice from many caregivers with differing perspectives, knowledge, and attitudes. Generally speaking, trust in the fast-paced, high-tech unit and in the care team that makes potentially life-saving or life-threatening decisions has eroded somewhat over the years. Respect and engagement are the two watchwords. Families usually wish to know the “real story” and to understand the perceptions and approach— primary and contingency plans—of the attending physician. If care is obviously futile or should be withdrawn, a frank discussion is in order, especially if the family has initiated the conversation. But if the outcome is uncertain and there are logical steps to be taken to reverse the crisis, the family needs to know this as well. They also must perceive the physician’s positive attitude toward resolution of the illness, whenever this is possible to realistically convey. Telling the family that there is little hope when the situation is ambiguous is likely to alienate the family, as often they perceive that the team is not genuinely trying or has already given up.
The tone and content of communication should not always be serious—humor does wonders to bridge the gap between caregiver and the vulnerable recipients of care. One or two physicians must be identified as the primary contact(s). Clearly, the family must be allowed to visit the patient as soon as appropriate after admission or in an unanticipated emergency. Continual presence of at least one family member at the bedside may be culturally mandated. In fact, there is a strong trend to design or modify ICUs so that the family can
remain close to the patient at all times, encouraged to directly observe many aspects of care that were previously “out of bounds”—even cardiopulmonary resuscitation. Some recently published data support this newer practice. Even though some caregivers with the best intentions maintain unrestricted access to the patient, many believe it wisest to restrict routine visiting hours to two or three predictably “quiet periods” in the work day (e.g., late morning, late afternoon, early evening), especially in high-acuity ICUs. The approach should be individualized. Continual contact often threatens to confuse and emotionally exhaust the worried family, seldom benefits the comatose or sedated patient, encourages interchange of microbial pathogens, and interferes with caregiving. Whatever the local policy, it is wise to set aside a time in the day when the physician reliably communicates progress and plans and receives vital feedback from family members. Some well-functioning units reserve a specific hour each day (e.g., 1:00 to 2:00 PM) during which the intensivist can be scheduled (by the unit clerk) to discuss progress and plans with the patient’s relatives. To reduce the emotional strain on both family and staff in an inherently unstable environment, it is important to emphasize that monotonic improvement (albeit desirable) seldom occurs, that minor setbacks and complications are to be anticipated, and that it is often most appropriate to view the general trend over days to weeks—not minutes to hours. Clearly defining the likely diagnoses and plausible alternatives, the team’s approach, the strategy for action, and contingency plans helps instill confidence and trust.
remain close to the patient at all times, encouraged to directly observe many aspects of care that were previously “out of bounds”—even cardiopulmonary resuscitation. Some recently published data support this newer practice. Even though some caregivers with the best intentions maintain unrestricted access to the patient, many believe it wisest to restrict routine visiting hours to two or three predictably “quiet periods” in the work day (e.g., late morning, late afternoon, early evening), especially in high-acuity ICUs. The approach should be individualized. Continual contact often threatens to confuse and emotionally exhaust the worried family, seldom benefits the comatose or sedated patient, encourages interchange of microbial pathogens, and interferes with caregiving. Whatever the local policy, it is wise to set aside a time in the day when the physician reliably communicates progress and plans and receives vital feedback from family members. Some well-functioning units reserve a specific hour each day (e.g., 1:00 to 2:00 PM) during which the intensivist can be scheduled (by the unit clerk) to discuss progress and plans with the patient’s relatives. To reduce the emotional strain on both family and staff in an inherently unstable environment, it is important to emphasize that monotonic improvement (albeit desirable) seldom occurs, that minor setbacks and complications are to be anticipated, and that it is often most appropriate to view the general trend over days to weeks—not minutes to hours. Clearly defining the likely diagnoses and plausible alternatives, the team’s approach, the strategy for action, and contingency plans helps instill confidence and trust.
Communications and Records
In addition to discussions with other caregivers, the physician must review the chart record, nursing notes, orders, medication and therapy lists, bedside data board, ventilator sheet, and laboratory record. Increasingly, all such information is incorporated into an electronic medical record (EMR) and the caregivers are given direct responsibility for detailed documentation and for entering orders that are not transcribed but are immediately entered. This new emphasis on electronic documentation—in many cases designed as much as a billing instrument than a communication tool—has given rise to templated notes laden with “cut and paste” entries and unnecessary replication of laboratory data. The need to communicate and document through the computer has taken its toll on effective communication among caregivers and discourages the physician from returning to the bedside. Just how the benefits and detriments of the electronic medical record (EMR) play out in the ICU has yet to be fully experienced.
The need to carefully review the current listing of medications with the patient’s ongoing and resolved problems clearly in mind cannot be overemphasized. To prevent delays and errors, it is a good idea to enter intended orders at the time of the bedside visit. The nursing record often provides an overlooked and valuable source of information. Puzzling entries with the potential to influence decision making should be clarified by direct verbal communication. Calculations required to synthesize the clinical picture and formulate revisions to the care plan (e.g., anion gap, systemic vascular resistance, respiratory compliance, airway resistance) should be automated or made quickly available at the bedside. Specific attention should be directed to the patient’s weight, net fluid balance, intake, urinary and fecal output (Ins and Outs), diet, and drugs (those scheduled and those given as needed). Sedatives, antibiotics, vasoactive agents, and diuretics tend to be of special interest. The volume and description of expectorated or suctioned airway secretions and gastric aspirates should be noted.
Laboratory Data
The most recently obtained values for arterial blood gases, hemoglobin concentration, leukocyte and platelet counts, serum glucose, blood urea nitrogen (BUN), creatinine, electrolytes, and urinalysis must be reviewed in every patient for whom they are available. Serial tests for liver or cardiac enzymes, leukocyte differential, coagulation profile, drug levels, renal function tests, and so on may be of unusual interest in specific patients. As already noted, trends in such data often are more meaningful than individual test results.
Physical Examination and Monitoring
The contribution of the physical examination has become devalued as our technical abilities to image noninvasively, to monitor cardiorespiratory function, and to use laboratory data have improved. However, certain key bits of information that are impossible to gather quickly by other means should be assessed by physical examination one or more times daily in virtually every patient with cardiorespiratory instability or compromise.
Although the directed physical examination is the practical standard, outstanding clinicians are sufficiently disciplined to quickly but systematically assess certain aspects of the physical examination each day, not only to detect areas of concern but also to develop the background against which to gauge any future changes.
Although the directed physical examination is the practical standard, outstanding clinicians are sufficiently disciplined to quickly but systematically assess certain aspects of the physical examination each day, not only to detect areas of concern but also to develop the background against which to gauge any future changes.
Vital Signs
Review of the vital signs record is a frequent starting point in the bedside evaluation. What are often overlooked, however, are the degree of variability and telling relationships among individual parameters. For example, heart rate may not parallel the height of fever or may be inappropriately slow for the clinical setting of congestive failure, as suggested by a disjunction between elevations ofheart rate and respiratory rate. Extreme respiratory variation evident on an arterial or pulse oximetry tracing suggests relative hypovolemia and/or the paradox associated with severe airflow obstruction, severe left heart failure, or pericardial disease. Vital signs may change markedly with sleep or level of alertness. In the ventilated patient who makes spontaneous efforts, minute ventilation should be considered a vital sign. Wide variations of minute ventilation, especially when they occur abruptly, suggest that agitation may be responsible for the higher values. (This variability becomes an important consideration when prescribing sedatives and analgesics and when evaluating the ventilation requirements of a weaning candidate.)
Mental Status and Neuromuscular System
The categories of the Glasgow Coma Scale serve as a reminder of the gross characteristics to be screened and followed: best verbal, motor, and eye opening (and pupillary) responses. Muscle tone and strength, facial appearance, eye movements, pupillary size and reactivity, peripheral reflexes, and asymmetry should be noted. Signs of fear, anxiety, depression, and delirium should be elicited actively by attempting to engage the patient in meaningful conversation as well as light banter. (A well-timed sense of humor tests high-level integrative mental capacity, builds trust, reduces anxiety, and serves to narrow the communication gulf that separates patient and physician.) It is important to question the nursing staff regarding how well the patient has been sleeping, especially if delirium is suspected, dyspnea is questioned, or weaning is contemplated.
Cardiovascular System
Sequential cardiovascular examinations can reveal a new gallop, murmur, rhythm disturbance, paradoxical pulse, neck vein distention, basilar rales, dryness of the mucous membranes, diaphoresis, edema, impaired capillary refill, and other signs that provide clues to underlying pathophysiology. This knowledge should be interpreted in conjunction with an examination of electrocardiographic and arterial pressure tracings, echocardiographic and radiographic information, and data from a pulmonary artery catheter, when available. Serial examinations are especially important in the setting of myocardial infarction, acute endocarditis, or other potentially life-threatening, rapidly changeable conditions.
Respiratory System
Consecutive physical examinations of the respiratory system should focus on the quality, intensity, and symmetry of breath sounds; the presence or absence of regional percussion dullness; the breathing pattern; the audibility and distribution of wheezes, rales, rubs, rhonchi, and bronchial breath sounds; and the vigor and effectiveness of breathing efforts. Pulse oximetry can be extremely helpful when adjusting inspired oxygen fraction (FiO2), positive end-expiratory pressure (PEEP), position, or ventilator settings. Mechanically ventilated patients require a careful review of the record documenting minute ventilation, oxygen, pressure requirements (peak, plateau, mean, and end-expiratory), gas exchange efficiency, patient-ventilator synchrony, integrity of the breathing circuit, and machine mode and settings (as detailed in Chapter 5).
Renal and Electrolyte Status
Although urine output and composition often should be followed closely, not every patient in the ICU requires an indwelling bladder catheter. However, because the urinary output of the healthy kidney tends to parallel intravascular fluid volume and serves as a useful indicator of vital organ perfusion, patients with questionable cardiovascular status often benefit from continuous urometry. The clinician should allow a trend to evolve over 1 to 3 h before making radical interventions based primarily on urinary output because oliguria may be transient or may respond only slowly to corrective action. Moreover, it is prudent to keep in mind the recent changes in therapy, cardiovascular status, sleep-wake cycles, and serum electrolytes in making the interpretation. The color, pH, specific
gravity, glucose and electrolyte concentrations, results of tests for leukocyte esterase, erythrocytes, hemoglobin, and a review of sediment characteristics and pending urine cultures aid in assessing fluid status as well as in determining the etiology and severity of many common disorders. BUN and creatinine should be compared with previous values. This data should be considered in conjunction with the daily and cumulative I&O record, the daily weight trend, and the listing of medications in assessing the fluid balance. Weight should be compared with those of previous hospital days and the admission value as well as with weights recorded previously in clinical or prior admissions. Arterial blood gases and serum electrolytes should be reviewed, and anion gap and serum osmolality should be estimated.
gravity, glucose and electrolyte concentrations, results of tests for leukocyte esterase, erythrocytes, hemoglobin, and a review of sediment characteristics and pending urine cultures aid in assessing fluid status as well as in determining the etiology and severity of many common disorders. BUN and creatinine should be compared with previous values. This data should be considered in conjunction with the daily and cumulative I&O record, the daily weight trend, and the listing of medications in assessing the fluid balance. Weight should be compared with those of previous hospital days and the admission value as well as with weights recorded previously in clinical or prior admissions. Arterial blood gases and serum electrolytes should be reviewed, and anion gap and serum osmolality should be estimated.
Gastrointestinal/Nutritional Status
Daily assessments should include a review of nutritional intake. The volume and character of gastric aspirates and stool output also must be tracked. To evaluate gut motility, the physical examination of the abdomen always should include auscultation. The persistent absence of stool or gas output despite enteral intake may suggest obstipation or bowel obstruction, especially when the abdomen becomes noticeably distended. When confronting a quiet abdomen, it is important to palpate deeply and to attempt to elicit signs of peritoneal inflammation. Ascites, excessive bowel gas, gastric distention, and gut edema may explain a visibly distending abdomen. A “tight belly” may explain high ventilator cycling pressures or, if extreme, a dwindling urinary output. In such cases, bladder pressure should be transduced and measured (see Chapter 5).
Apparatus
Extensive use of equipment and devices characterizes the care delivered to critically ill patients. Intravascular lines and pumps should be inspected quickly, and their sites of entry should be examined for evidence of phlebitis, local cellulitis, or purulence. The dressings that cover suspicious points of catheter insertion must be taken down, and the wound beneath must be examined carefully, preferably at the time of routine dressing changes. When specialized life-support equipment is used (e.g., balloon pump), the key variables relevant to its operation and the level of support must be noted. Enteral catheters and endotracheal tube anchoring devices should be inspected and the ventilator circuit examined for collected water. The essential data provided by the bedside cardiac monitor and the ventilator display are reviewed with each visit to the bedside.
Imaging Data Radiographs, computed tomograms (CT), and ultrasonic images have become integral to the evaluation of the critically ill patient. Rounds should incorporate a review of such data, which often redirect thinking or confirm diagnoses made by other means.
▪ THERAPEUTIC SUPPORTIVE CARE
Intensive life support has no evolutionary precedent. Before modern civilization, our primate ancestors were at constant risk of predatory attack and disease. Survival required foraging and continuous vigilance; our predecessors seldom re mained off their feet or motionless for longer than a few hours at a time. Most conditions that now prompt admission to the ICU would previously have resulted in a quick demise. Deprived of food and water and unable to take shelter from the elements and natural enemies, the sick individual became vulnerable to many of the traumatic, infectious, and environmental problems that now are easily manageable. A philosopher or anthropologist could argue effectively that evolutionary pressures encourage elimination (rather than survival) of those weak enough to fall prey to catastrophic disease or severe trauma. Because the recumbent position is central to the extended life support but is inherently unnatural, a working knowledge of the physiology of sustained bed rest and immobility is fundamental to understanding the rationale and consequences of ICU confinement.
Physiology of Bed Rest
Noncardiorespiratory Effects of Recumbency
Certain consequences of protracted bed rest are well known to most practitioners, whereas other, subtler repercussions are either unknown or ignored. Physiologic adaptations to gravity affect nearly all organ systems, and release from gravitational stress may set in motion changes that impede recovery.
Neuromuscular
While under the influence of gravity, contracting skeletal muscles compress the veins and lymphatics, counteracting the gravitational forces that would
otherwise cause the body fluids to pool in the legs and lower abdomen. Contraction of muscles used in maintaining the upright posture and locomotion preserves muscle bulk and strength. Symmetry of upper as well as lower extremities should be noted and tracked. Lack of movement, hypoalbuminemia, and the persistently upright torso encourage edema to form in the hands and the lower arms. Asymmetry of the edema that forms suggests an upper extremity thrombosis—which occur quite commonly in patients with ipsilateral PICC and subclavian or internal jugular catheters. Moreover, muscular traction and gravitational stresses help the bones retain calcium. It is not known what level of fiber tension or duration of contraction is necessary to sustain these benefits. It is clear, however, that release of the skeletal muscles from their diurnal activity for longer than 24 to 48 h initiates metabolic processes that eventually culminate in tissue atrophy and impressive physiologic changes.
otherwise cause the body fluids to pool in the legs and lower abdomen. Contraction of muscles used in maintaining the upright posture and locomotion preserves muscle bulk and strength. Symmetry of upper as well as lower extremities should be noted and tracked. Lack of movement, hypoalbuminemia, and the persistently upright torso encourage edema to form in the hands and the lower arms. Asymmetry of the edema that forms suggests an upper extremity thrombosis—which occur quite commonly in patients with ipsilateral PICC and subclavian or internal jugular catheters. Moreover, muscular traction and gravitational stresses help the bones retain calcium. It is not known what level of fiber tension or duration of contraction is necessary to sustain these benefits. It is clear, however, that release of the skeletal muscles from their diurnal activity for longer than 24 to 48 h initiates metabolic processes that eventually culminate in tissue atrophy and impressive physiologic changes.
Aerospace science and experiments in healthy volunteers have yielded impressive data on the effects of bed rest in healthy individuals (Table 18-2). Skeletal muscles quickly lose tone when not supporting the body’s weight. After only 72 h, the loss of myofibrillar protein is under way—even in a well-nourished, physiologically unstressed subject. The greatest protein losses occur in the muscle groups that normally bear the greatest postural burden—legs and dorsal trunk. The rates at which bulk and strength diminish are believed to be functions of the length at which the muscle fiber is immobilized as well as the completeness of relaxation. As indicated by the devastating weakness that results from extended pharmacologic paralysis, neural excitation may be a crucial factor in preserving muscle function. Intense stimulation may not be required to dramatically slow the pace of sarcomere depletion, and although active movement is clearly better than passive manipulation of resting muscle, physical therapy of the immobilized patient aids significantly in preventing contractures.