tidal volume

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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.

ti·dal vol·ume (VT),

the volume of air that is inspired or expired in a single breath during regular breathing.
Synonym(s): tidal air

tidal volume

The volume of air inhaled or exhaled in a single breath.

tidal volume (TV, Vt)

Etymology: AS, tid, time; L, volumen, paper roll
the amount of air inhaled and exhaled during normal ventilation. Inspiratory reserve volume, expiratory reserve volume, and tidal volume make up vital capacity. See also pulmonary function test.

tidal volume

Lung physiology The volume of air drawn into the lungs during inspiration from the end-expiratory position, which leaves the lungs passively during expiration in the course of quiet breathing. See Lung volumes. Cf Residual volume.

ti·dal vol·ume

(tī'dăl vol'yūm)
The volume of air inspired or expired in a single breath during regular breathing.
Synonym(s): tidal air.

tidal volume

The volume of air entering and leaving the lungs during a single respiratory effort, whether the rate is normal, high or low.

tidal volume

the amount of air taken in to the lungs by an animal breathing normally at rest, during each respiratory cycle (each breath). In humans this is about 0.5 dm3 (500 cm3).


in physiology and medicine, refers to pulmonary ventilation, the movement of air in and out of the lungs, whether during normal breathing, or by artificial means. total ventilation or minute volumeE (or I) is the volume breathed out (or in) in litres per minute: the tidal volume multiplied by the number of breaths per minute. May be measured, e.g. by collecting the expired gas over a known time (Douglas bag method), or by integrating inspired or expired airflow with respect to time (by pneumotachograph). The effective component, alveolar ventilationA, refers to that which reaches the regions of the lungs where gas exchange occurs, and is equal to the total ventilation minus dead space ventilationD. Normally, at rest, A : D = 2:1 or typically, E - D = A, 6 - 2 = 4 L.min-1. When ventilation increases in exercise, the dead space is unchanged, so D rises only in proportion to the rise in frequency of breaths, but E rises relatively more as tidal volume also increases. See also artificial ventilation, dead space, lung volumes and capacities.
Lung volumes.

lung volumes

measurements made as part of pulmonary function tests; the volumes that move in and out during the normal breathing cycle, and with deliberate additional effort, can be measured directly by spirometry with the subject breathing through a closed circuit in and out of a cylinder inverted over water, or into a vitalograph, or by pneumotachograph; the residual volume can be measured only indirectly by dilution methods (usually with helium) or by whole body plethysmography. See also ventilation. See figure and table overleaf .
Table 1: Lung volumes
VT (TV)Tidal volumeVolume of inspired/expired air moving in and out with each breath
Inspiratory and expiratory reserve volumesUsed when tidal volume increases above that at rest
VCVital capacityVolume that can be inspired/expired after full expiration/inspiration
FEV1Forced expiratory volume in 1sVolume exhaled in the first second, with maximal effort after full inspiration
FRCFunctional residual capacityVolume remaining in the lungs at end-expiration; decreases as tidal volume increases
RVResidual volumeRemains after a maximal expiratory effort; cannot be exhaled
TLCTotal lung capacityVital capacity + residual volume

ti·dal vol·ume

(tī'dăl vol'yūm)
Volume of air inspired or expired in a single breath during regular breathing.
Synonym(s): tidal air.

tidal volume,

n the amount of air inhaled and exhaled during normal ventilation.

tidal volume

the amount of gas passing into and out of the lungs in each respiratory cycle.
References in periodicals archive ?
Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome.
2] = fractional inspired concentration of oxygen; PEEP = positive end-expiratory pressure in centimeters of water pressure; Vt = tidal volume (in milliliters); b/min = breaths per minute.
Tidal hyperinflation during low tidal volume ventilation in acute respiratory distress syndrome.
Determinants of tidal volumes with adaptive support ventilation: a multicenter observational study.
Consequently, when currents were delivered through these electrodes, only unwanted latissimus and serratus muscle contractions occurred and no tidal volume resulted.
When the studies were divided into these two groups, breathing control significantly increased tidal volume following training programs (SMD 1.
4) In patients with primary lung pathology, aiming for these goals can lead to high airway pressures (barotrauma), large tidal volumes (volutrauma) and high inspired oxygen concentrations (oxygen toxicity).
Several studies in adults have described ventilator concepts that may reduce or prevent further lung injury, including low tidal volume ([V.
2] of 21 percent, heart rate (HR) < 120 beats a minute, spontaneous respiratory rate < 30 breaths a minute, exhaled tidal volume [greater than or equal to] 400 mL on synchronous intermittent mandatory ventilation one to two breaths and pressure support ventilation 5 cm [H.
The baseline percentage leak around the endotracheal tube was calculated for each patient using the first five minutes' averaged values of inspired and expired mechanical tidal volume according to the equation:
The tidal volume was adjusted to achieve a peak tracheal pressure of 7-10 mmHg (~20 mL).
It offers the ability to set a tidal volume as small as 2 mL for neonates weighing as little as 300 grams without having to change to another ventilator.