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the space occupied by a substance or a three-dimensional region; the capacity of such a region or of a container.
blood volume the plasma volume added to the red cell volume; see also blood volume.
closing volume (CV) the volume of gas in the lungs in excess of the residual volume at the time small airways in the dependent portions close during maximal exhalation; see also closing volume.
deficient fluid volume a nursing diagnosis accepted by the North American Nursing Diagnosis Association, defined as decreased intravascular, interstitial, and/or intracellular fluid. This refers to dehydration, water loss alone without change in sodium. See also fluid volume. Formerly called fluid volume deficit.

When a person engages in normal physical activity and the environmental temperature is 20°C (68°F), the body loses about 2400 ml of water in 24 hours. About 1400 ml are lost in urine, 200 ml in feces, and 100 ml in sweat. The remaining 700 ml are lost through what is called insensible water loss, which takes place by diffusion through the skin and by evaporation from the lungs. About 300 ml of water diffuse through the epithelial cells daily. The lungs excrete about 400 ml per day.

A deficit of fluid volume occurs when there is either an excessive loss of body water or an inadequate compensatory intake. Etiologic factors include active loss through vomiting, diarrhea, gastric suctioning, drainage through operative wounds and tubes, burns, fistulas, hypermetabolic states, and drug-induced diuresis. Insufficient intake of water can be caused by nausea, immobility with inaccessibility of water, and lack of knowledge about the necessity of adequate fluid intake.
Patient Care. Assessment of the patient's hydration status includes monitoring lab data for such signs as increased packed red blood cell volume, increased plasma protein level, elevated specific gravity of urine, and increased blood urea nitrogen (BUN) out of proportion to a change in serum creatinine. In the absence of other problems, the serum sodium should remain within normal limits.

Recording daily weight gives information about the amount of water gained or lost each day. If there is a fluid volume deficit, intake and output measurements can give evidence of fluid imbalance. The urine appears concentrated and is usually well below the criterion of 50 ml of output per hour. Other objective assessment data include hypotension and a decrease in venous filling and in pulse volume and pressure. The mucous membranes are dry, as is the skin, which loses its turgor. The patient may complain of thirst and the body temperature may be elevated.

Patients at risk for profound and potentially fatal fluid volume deficit, as in severe burns, should be assessed frequently for mental acuity status and orientation to person, place, and time. Measures to improve hydration status should take into account the patient's ability to drink and retain fluids by mouth, preferences for certain fluids, and whether hot or cold drinks are preferred. The goal of oral fluid intake should be about 2000 ml per day. Explanations about the importance of an adequate fluid intake and assuring the availability of fresh water and fluids attractive to the patient can help reach the desired goal. Intravenous administration of fluids, especially isotonic saline, may be necessary if oral replacement is not possible. In severe and intractable fluid volume deficit a central venous catheter may be used to evaluate the extent of fluid loss and to guide replacement therapy.
excess fluid volume a nursing diagnosis accepted by the North American Nursing Diagnosis Association, defined as increased isotonic fluid retention; see also fluid volume. Factors contributing to this include (1) arterial dilatation, as occurs in the inflammatory process; (2) reduced oncotic pressure, as in hypoproteinuria (particularly a deficit of albumin, which is responsible for 80 per cent of oncotic pressure), lymphatic obstruction, and increased capillary permeability, which allows water to escape into the tissues and produce swelling; (3) renal retention of sodium and consequently of water, as seen in renal failure; (4) inadequate circulation of blood through the general circulation, as in congestive heart failure, or through the portal circulation, as in liver failure; and (5) overproduction or administration of adrenocortical hormones.

Hypervolemia can occur when a patient receives excessive fluid replacement or repeated tap water enemas or, much less frequently, drinks more fluids than are eliminated. Characteristics of fluid volume excess include obvious swelling, localized or generalized; weight gain; pulmonary congestion with accompanying shortness of breath, orthopnea, and abnormal breath sounds; a fluid intake greater than output; distended neck veins; and changes in central venous and pulmonary artery pressures.
expiratory reserve volume the maximal amount of gas that can be exhaled from the resting end-expiratory level.
fluid volume the volume of the body fluids, including both intracellular fluid and extracellular fluid.
forced expiratory volume (FEV) the volume that can be exhaled from a full inhalation by exhaling as forcefully and rapidly as possible for a timed period. Times are denoted by subscripts, such as FEV0.5, FEV1.0, FEV2.0, and FEV3.0 for FEV values for 0.5, 1, 2, and 3 seconds.
inspiratory reserve volume the maximal amount of gas that can be inhaled from the end-inspiratory position.
mean corpuscular volume (MCV) the average volume of erythrocytes, conventionally expressed in cubic micrometers or femtoliters (μm3 = fL) per red cell, obtained by multiplying the hematocrit (in l/L) by 1000 and dividing by the red cell count (in millions per μL): MCV = Hct/RBC. Automated electronic blood cell counters generally obtain the MCV directly from the average pulse height of the voltage pulses produced during the red cell count. These instruments obtain the hematocrit indirectly from the equation Hct = MCV × RBC.
minute volume (MV) the quantity of gas exhaled from the lungs per minute; tidal volume multiplied by respiration rate.
packed-cell volume (PCV) hematocrit.
plasma volume the total volume of blood plasma, i.e., the extracellular fluid volume of the vascular space; see also blood volume.
red cell volume the total volume of red cells in the body; see also blood volume.
residual volume (RV) the amount of gas remaining in the lung at the end of a maximal exhalation.
risk for deficient fluid volume a nursing diagnosis accepted by the North American Nursing Diagnosis Association, defined as being at risk for vascular, cellular, or intracellular dehydration. See also deficient fluid volume.
stroke volume the quantity of blood ejected from a ventricle at each beat of the heart; called also stroke output.
tidal volume the amount of gas passing into and out of the lungs in each respiratory cycle.


Abbreviation for inspiratory reserve volume.


inspiratory reserve volume.


abbreviation for inspiratory reserve volume. See pulmonary function test.


Abbreviation for inverse ratio ventilation;
inspiratory reserve volume.


(vent?i-la'shon) [ ventilatio, an airing]
1. The movement of air into and out of the lungs.
2. Circulation of fresh air in a room and withdrawal of foul air.
3. In physiology, the amount of air inhaled per day. This can be estimated by spirometry, multiplying the tidal air by the number of respirations per day. An average figure is 10,000 L. This must not be confused with the total amount of oxygen consumed, which is on the average only 360 L/day. These volumes are more than doubled during hard physical labor.

abdominal displacement ventilation

A noninvasive type of artificial ventilation that relies on displacement of the abdominal contents to move the patient's diaphragm.

adaptive support ventilation

Abbreviation: ASV
A mode of mechanical ventilation in which the minute ventilation is not allowed to fall below a set threshold (e.g., in adults, below 100 ml/kg/min), but the inspiratory pressure, inspiratory time, and tidal volume are all adjusted by the ventilator to the patient's needs.

airway pressure release ventilation

A type of mechanical ventilation in which patients breathe spontaneously at any phase of the ventilator's duty cycle at high continuous positive airway pressures (CPAP). Periodically, the level of CPAP is lowered to eliminate waste gases from the circuit.

alveolar ventilation

The movement of air into and out of the alveoli. It is a function of the size of the tidal volume, the rate of ventilation, and the amount of dead space present in the respiratory system. It is determined by subtracting the dead space volume from the tidal volume and multiplying the result by the respiratory rate.

assist-control ventilation

A type of mechanical ventilation with a minimum frequency of respirations determined by ventilator settings. It also permits the patient to initiate ventilation at the same tidal volume or pressure as set on the ventilator.

asynchronous ventilation

In emergency cardiac or critical care, the administration of artificial breaths to a patient that are timed independently of chest compressions.

continuous positive-pressure ventilation

A method of mechanically assisted pulmonary ventilation. A device administers air or oxygen to the lungs under a continuous pressure that never returns to zero.

differential lung ventilation

The use of different ventilatory strategies in each lung in a patient with focal lung disease, e.g., a patient undergoing surgery to remove a tumor in one lobe of a lung but not another, or a patient with more severe COPD on one side of the chest than another. This technique requires a double-lumen endotracheal tube.

dual control ventilation

Mechanical ventilation initiated by either a change in airway pressures or by a change in gas flowing through the ventilator circuit. Dual control is asserted when pressure limited breaths are delivered and the pressure changes from breath to breath to meet a desired delivered tidal volume. It improves the coordination between the patient's respiratory efforts and machine-generated breaths.

high-frequency jet ventilation

A type of ventilation that continuously ventilates at 100 to 150 cycles/min. It is used in respiratory failure to provide continuous ventilation without the side effects of positive-pressure ventilation.

high-frequency oscillatory ventilation

Abbreviation: HFOV
Pulmonary ventilation with multiple rapid breaths given at small tidal volumes. It limits the stretching and collapse of the alveoli that occur in conventional mechanical ventilation.

high-frequency percussive ventilation

Mechanical ventilation that decreases peak and end-expiratory pressure by delivering hundreds of shallow (low tidal volume) breaths per minute. It is a time-cycled, pressure-limited mode of ventilation.

intermittent mandatory ventilation

Abbreviation: IMV
Machine ventilation that delivers pressurized breaths at intervals while allowing for spontaneous breathing.

intermittent positive-pressure ventilation

A mechanical method of assisting pulmonary ventilation, using a device that inflates the lungs under positive pressure. Exhalation is usually passive.
Synonym: breathing, intermittent positive-pressure

inverse ratio ventilation

Abbreviation: IRV
Mechanical ventilation in which the normal temporal relationship between inspiration and expiration is reversed (the inspiration time is longer than the expiratory time). It is sometimes used in severely hypoxemic patients who have not responded to other ventilatory maneuvers. Because it is uncomfortable for patients, paralysis and sedation are needed.

liquid ventilation

A ventilatory technique used to treat both premature infants with surfactant-deficient lungs and adults with acute respiratory distress syndrome.

mandatory minute ventilation

Ventilatory support that provides mechanical breaths when the patient's spontaneous breathing does not achieve the preset mechanical ventilatory rate.

maximum sustainable ventilation

The normal maximum breathing pattern that can be maintained for 15 min (usually approx. 60% of maximum voluntary ventilation).

maximum voluntary ventilation

The maximum amount of gas that can be ventilated into and out of the lungs in a voluntary effort in a given time, measured in liters per minute.

mechanical ventilation

Any form of artificially supplied ventilation.

minute ventilation

Abbreviation: MV
The volume of air inhaled and exhaled in 60 sec. See: minute volume
Enlarge picture

noninvasive ventilation

The use of airway support administered through a face (nasal) mask instead of an endotracheal tube. Inhaled gases are given with positive end-expiratory pressure often with pressure support or with assist control ventilation at a set tidal volume and rate. Numerous studies have shown this technique to be as effective as, and better tolerated than, intubation and mechanical ventilation in patients with exacerbations of COPD.
See: illustration

positive-pressure mechanical ventilation

Mechanical ventilatory support that applies positive pressure to the airway. The objectives include improving pulmonary gas exchange, relieving acute respiratory acidosis, relieving respiratory distress, preventing and reversing atelectasis, improving pulmonary compliance, preventing further lung injury, and avoiding complications. Positive-pressure ventilation can be life saving, but complications such as toxic effects of oxygen, laryngeal injury, tracheal stenosis, alveolar injury, barotrauma, pneumonia, and psychological problems may occur.
See: pressure, positive end-expiratory

pressure support ventilation

A type of assisted ventilation that supplements a spontaneous breath. The patient controls the frequency and the duration and flow of inspiration from the ventilator.

protective ventilation

A type of mechanical ventilation in which tidal volumes are set to avoid overstretching the alveoli, and pressures at the end of an inhaled breath are set to avoid alveolar collapse.

pulmonary ventilation

The inspiration and expiration of air from the lungs.

reduced ventilation

Respiratory depression.

synchronized intermittent mandatory ventilation

Abbreviation: SIMV
Periodic assisted ventilation with positive pressure initiated by the patient and coordinated with spontaneous patient breaths.
See: intermittent mandatory ventilation

transtracheal catheter ventilation

An emergency procedure in which a catheter is placed percutaneously through the cricothyroid membrane and attached to a high-pressure, high-flow jet ventilator. This form of ventilation is used for patients with an upper airway obstruction who cannot be intubated.

volume-controlled ventilation

A form of mechanical ventilation in which the peak inspiratory flow rate, fraction of inspired oxygen, positive end-expiratory pressure, respiratory rate, and tidal volume are preset and delivered to the patient.
Synonym: volume-cycled ventilation; volume-limited ventilation

volume-cycled ventilation

Volume-controlled ventilation.

volume-limited ventilation

Volume-controlled ventilation.

inverse ratio ventilation

Abbreviation: IRV
Mechanical ventilation in which the normal temporal relationship between inspiration and expiration is reversed (the inspiration time is longer than the expiratory time). It is sometimes used in severely hypoxemic patients who have not responded to other ventilatory maneuvers. Because it is uncomfortable for patients, paralysis and sedation are needed.
See also: ventilation


inspiratory reserve volume


Abbreviation for inspiratory reserve volume.


inspiratory reserve volume.
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