In medicine, saline is a general phrase referring to a sterile solution of sodium chloride in
water, but is only sterile when it is to be placed parenterally; otherwise, a saline solution
is a salt water solution. The sterile solution is typically used for intravenous infusion,
rinsing contact lenses, nasal irrigation, and often used to clean a new piercing. It
is also a good medium to store an avulsed tooth until it can be re-implanted by a dentist.
Saline solutions are available in various formulations for different purposes. Salines
are also used in cell biology, molecular biology, and biochemistry experiments.
Concentrations Concentrations vary from low to normal to
high. High concentrations are used rarely in medicine but frequently in molecular biology.
Normal Normal saline is the commonly used phrase
for a solution of 0.90% w/v of NaCl, about 300 mOsm/L or 9.0 g per liter.a Less commonly,
this solution is referred to as physiological saline or isotonic saline, neither of which
is technically accurate. NS is used frequently in intravenous drips for patients who cannot
take fluids orally and have developed or are in danger of developing dehydration or hypovolemia.
NS is also used for aseptic purpose. NS is typically the first fluid used when hypovolemia
is severe enough to threaten the adequacy of blood circulation, and has long been believed
to be the safest fluid to give quickly in large volumes. However, it is now known that
rapid infusion of NS can cause metabolic acidosis. Normal saline was invented by Holland's Hartog
Hamburger in 1896. Hamburger's solution was only intended for in vitro study of RBC lysis
and was never intended for clinical use. The solution is 9 grams of sodium chloride
dissolved on water, to a total volume of 1000 ml. As 1 grams NaCl occupies 0.18 level teaspoons,
9 grams NaCl is 1.62 level teaspoons. The mass of 1 millilitre of normal saline is 1.0046 gram
at 22 °C. The molecular weight of sodium chloride is approximately 58.5 grams per
mole, so 58.5 grams of sodium chloride equals 1 mole. Since normal saline contains 9 grams
of NaCl, the concentration is 9 grams per liter divided by 58.5 grams per mole, or
0.154 mole per liter. Since NaCl dissociates into two ions – sodium and chloride –
1 molar NaCl is 2 osmolar. Thus, NS contains 154 mEq/L of Na+ and Cl−. It has a slightly
higher degree of osmolarity than blood Nonetheless, the osmolarity of normal saline is a close
approximation to the osmolarity of NaCl in blood.
One litre of 0.9% Saline contains: 154 mEq of sodium ion = 154 mmol/L
154 mEq of chloride ion = 154 mmol/L Usage
For medical purposes, saline is often used to flush wounds and skin abrasions. Normal
saline will not burn or sting when applied. Saline is also used in I.V. therapy, intravenously
supplying extra water to rehydrate patients or supplying the daily water and salt needs
of a patient who is unable to take them by mouth. Because infusing a solution of low
osmolality can cause problems, intravenous solutions with reduced saline concentrations
typically have dextrose added to maintain a safe osmolality while providing less sodium
chloride. As the molecular weight of dextrose is greater, this has the same osmolality as
normal saline despite having less sodium. The amount of normal saline infused depends
largely on the needs of the patient. Saline is also often used for nasal washes
to relieve some of the symptoms of the common cold. The solution exerts a softening and
loosening influence on the mucus to make it easier to wash out and clear the nasal passages
for both babies and adults. In this case "home-made" saline may be used: this is made by dissolving
approximately half a teaspoon of table salt into 240ml of clean tap water. In very rare
instances, amoeba Naegleria fowleri infection can occur if amoeba enters the body through
the nose, therefore water used for nasal irrigation should be sterile.
Ophthalmic drug administration
Eye drops are saline-containing drops used as an ocular route to administer. Depending
on the condition being treated, they may contain steroids, antihistamines, sympathomimetics,
beta receptor blockers, parasympathomimetics, parasympatholytics, prostaglandins, non-steroidal
anti-inflammatory drugs or topical anesthetics. Eye drops sometimes do not have medications
in them and are only lubricating and tear-replacing solutions.
Injection/ophthalmic drug administration Syringe designed saline drops are distributed
in modern needle-exchange programmes as drugs efficiently can be administrated either by
injection, or ophthalmic, which is compared to intravenous use; By demonstration, the
elimination of latanoprost acid from plasma is rapid after either ophthalmic or intravenous
administration. However, ophthalmic use is done with sterile filtered drugs that is potent
in quite small doses, and with adjusted acidity of pH 7.0-7.5 after the drug has been added,
to avoid eye damage. The human eye has a pH of approximately 7.5, water has 7.0.
Hypertonic saline Hypertonic saline — 7% NaCl solutions are
considered mucoactive agents and thus are used to hydrate thick secretions in order
to make it easier to cough up and out. 3% hypertonic saline solutions are also used
in critical care settings, acutely increased intracranial pressure, or severe hyponatremia.
Inhalation of hypertonic saline has also been shown to help in other respiratory problems,
specifically bronchiolitis. Hypertonic saline is currently recommended by the Cystic Fibrosis
Foundation as a primary part of a cystic fibrosis treatment regimen.
An 11% solution of xylitol with 0.65% saline stimulates the washing of the nasopharynx
and has an effect on the nasal pathogenic bacteria. This has been used in complementary
and alternative medicine, and anecdotal evidence shows possible benefit for preventing infectious
problems Mechanism of action
Aerosol — Nebulized hypertonic saline treatments disrupt the interaction between glycosaminoglycans
and IL-8, rendering IL-8 susceptible to proteolytic degradation with subsequent decrease in neutrophil
chemotaxis; all of this ultimately reducing inflammation.
Other Other concentrations commonly used include:
Half-normal saline, often with "D5", contains 77 mEq/L of Na and Cl and 50 g/L dextrose.
Quarter-normal saline has 39 mEq/L of Na and Cl and almost always contains 5% dextrose
for osmolality reasons. It can be used alone in Neonatal Intensive Care Units.
Hypertonic saline may be used in perioperative fluid management protocols to reduce excessive
intravenous fluid infusions and lessen pulmonary complications. Hypertonic saline is used in
treating hyponatremia and cerebral edema Rapid correction of hyponatremia via hypertonic
saline, or via any saline infusion > 40 mmol/L greatly increases risk of central pontine
myelinolysis, and so requires constant monitoring of patient response. Water privation combined
with diuretic block does not produce as much risk of CPM as saline administration does;
however, it does not correct hyponatremia as rapidly as administration of hypertonic
saline does. Due to hypertonicity, administration may result in phlebitis and tissue necrosis.
As such, concentrations greater than 3% NaCl should normally be administered via a central
venous catheter, also known as a 'central line'. Such hypertonic saline is normally
available in two strengths, the former of which is more commonly administered:
3% NaCl has 513 mEq/L of Na and Cl. 5% NaCl has 856 mEq/L of Na and Cl.
NaCl solutions that are less commonly used are 7% and 23.4%, both of which are used,
often in conjunction with supplementary diuretics, in the treatment of traumatic brain injury.
Dextrose 4% in 0.18% saline is used sometimes for maintenance replacement.
Solutions of saline with added ingredients In medicine, common types of salines include:
Lactated Ringer's solution Acetated Ringer's solution
And in cell biology, in addition to the above the following are used:
Phosphate buffered saline TRIS-buffered saline
Hank's balanced salt solution Earle's balanced salt solution
Standard saline citrate HEPES-buffered saline
Gey's balanced salt solution History
Saline was believed to have originated during the Indian Blue Cholera pandemic that swept
across Europe in 1831. William Brooke O'Shaughnessy, a recent graduate of Edinburgh Medical School,
proposed in an article to medical journal The Lancet to inject cholera patients with
highly oxygenated salts to treat the "universal stagnation of the venous system and rapid
cessation of arterialisation of the blood" seen in severely dehydrated cholera patients.
He found his treatment harmless in dogs, and his proposal was soon adopted by the physician
Thomas Latta in treating cholera patients to beneficial effect. In the following decades,
variations and alternatives to Latta's solution were tested and used in treating cholera patients.
These solutions contained a range of concentrations of sodium, chloride, potassium, carbonate,
phosphate, and hydroxide. The breakthrough in achieving physiological concentrations
was accomplished by Ringer in 1831, when he determined the optimal salt concentrations
to maintain the contractility of frog heart muscle tissue. Normal saline is considered
a descendant of the pre-Ringer solutions, as Ringer's findings were not adopted and
widely used until decades later. The term "normal saline" itself appears to have little
historical basis, except for Hartog Jakob Hamburger's 1882–83 in vitro studies of
red cell lysis that incorrectly suggested that 0.9% was the concentration of salt in
human blood. See also
Intravenous therapy Saline water
Salinometer Notes
a^ In chemistry, a one normal of NaCl is 0.5 molar NaCl assuming complete dissociation.
Physiological dissociation is approximately 1.7 ions per mole, so one normal of NaCl is
1/1.7 = 0.588 molar. This is roughly 4 times more concentrated than medical "normal saline"
of 0.154 molar. Advancements in packaging IV infusions:
References