Hypotension, also known aslow blood pressure, is acardiovascular condition characterized by abnormally reduced blood pressure.[1]Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood[2] and is indicated by two numbers, thesystolic blood pressure (the top number) and thediastolic blood pressure (the bottom number), which are the maximum and minimum blood pressures within thecardiac cycle, respectively.[3] Asystolic blood pressure of less than 90millimeters of mercury (mmHg) ordiastolic of less than 60 mmHg is generally considered to be hypotension.[4][5] Different numbers apply to children.[6] However, in practice, blood pressure is considered too low only if noticeable symptoms are present.[7]
For many people, excessively low blood pressure can cause dizziness and fainting or indicate serious heart, endocrine orneurological disorders.[17]
For some people who exercise and are in top physical condition, low blood pressure could be normal.[21][22]A single session of exercise can induce hypotension, and water-based exercise can induce a hypotensive response.[23]
Treatment depends on the cause of the low blood pressure.[4] Treatment of hypotension may include the use ofintravenous fluids orvasopressors.[24] When using vasopressors, trying to achieve amean arterial pressure (MAP) of greater than 70 mmHg does not appear to result in better outcomes than trying to achieve an MAP of greater than 65 mmHg in adults.[25]
For many people, low blood pressure goes unnoticed.[4] For some people, low blood pressure may be a sign of an underlying health condition, especially when it drops suddenly or occurs with symptoms.[5] Older adults also have a higher risk of symptoms of low blood pressure, such as falls, fainting, or dizziness when standing or after a meal.[4] If the blood pressure is sufficiently low, fainting (syncope) may occur.[17]
Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension:[5]
Reduced blood volume,hypovolemia, is the most common cause of hypotension.[27] This can result fromhemorrhage; insufficient fluid intake, as in starvation; or excessive fluid losses from diarrhea or vomiting. Hypovolemia can be induced by excessive use ofdiuretics.[16] Low blood pressure may also be attributed to heat stroke which can be indicated by absence of perspiration, light headedness and dark colored urine.[28]
Other medications can produce hypotension by different mechanisms. Chronic use ofalpha blockers orbeta blockers can lead to hypotension.[16] Beta blockers can cause hypotension both by slowing the heart rate and by decreasing the pumping ability of the heart muscle.[16]
Orthostatic hypotension, also calledpostural hypotension, is a common form of low blood pressure.[17] It occurs after a change in body position, typically when a person stands up from either a seated or lying position.[40] It is usually transient and represents a delay in the normal compensatory ability of the autonomic nervous system.[41] It is commonly seen inhypovolemia and as a result of various medications.[17] In addition to blood pressure-lowering medications, many psychiatric medications, in particularantidepressants, can have this side effect.[42] Simple blood pressure and heart rate measurements while lying, seated, and standing (with a two-minute delay in between each position change) can confirm the presence of orthostatic hypotension.[43] Taking these measurements is known asorthostatic vitals.[17] Orthostatic hypotension is indicated if there is a drop of 20 mmHg in systolic pressure (and a 10 mmHg drop in diastolic pressure in some facilities) and a 20 beats per minute increase in heart rate.[43]
Vasovagal syncope is a form ofdysautonomia characterized by an inappropriate drop in blood pressure while in the upright position.[18] Vasovagal syncope occurs as a result of increased activity of thevagus nerve, the mainstay of theparasympathetic nervous system.[18] Patients will feel sudden, unprovoked lightheadedness, sweating, changes in vision, and finally a loss of consciousness.[18] Consciousness will often return rapidly once the patient is lying down and the blood pressure returns to normal.[44]
Another, but rarer form, ispostprandial hypotension, a drastic decline in blood pressure that occurs 30 to 75 minutes after eating substantial meals.[19] When a great deal of blood is diverted to theintestines (a kind of "splanchnic blood pooling") to facilitatedigestion andabsorption, the body must increasecardiac output and peripheralvasoconstriction to maintain enough blood pressure to perfuse vital organs, such as the brain.[45] Postprandial hypotension is believed to be caused by the autonomic nervous system not compensating appropriately, because of aging or a specific disorder.[45]
Hypotension is a feature ofFlammer syndrome, which is characterized by cold hands and feet and predisposes to normal tensionglaucoma.[20]
Blood pressure is continuously regulated by theautonomic nervous system, using an elaborate network ofreceptors,nerves, andhormones to balance the effects of thesympathetic nervous system, which tends to raise blood pressure, and theparasympathetic nervous system, which lowers it.[2] The vast and rapid compensation abilities of the autonomic nervous system allow normal individuals to maintain an acceptable blood pressure over a wide range of activities and in many disease states.[2] Even small alterations in these networks can lead to hypotension.[9]
For most adults, the optimalblood pressure is at or below 120/80 mmHg.[48] If the systolic blood pressure is <90 mmHg or the diastolic blood pressure is <60 mmHg, it would be classified as hypotension.[5] However, occasional blood pressure readings below 90/60 mmHg are not infrequent in the general population,[49] and, in the absence of some pathological cause, hypotension appears to be a relatively benign condition in most people.[49] The diagnosis of hypotension is usually made by measuring blood pressure, either non-invasively with asphygmomanometer or invasively with anarterial catheter (mostly in an intensive care setting). Another way to diagnose low blood pressure is by using themean arterial pressure (MAP) measured using an arterial catheter[50] or by continuous, non-invasive hemodynamic monitoring which measures intra-operative blood pressure beat-by-beat throughout surgery. A MAP <65 mmHg is considered hypotension.[50] Intra-operative hypotension <65 mmHg can lead to an increased risk of acute kidney injury,[51] myocardial injury[51] or post-operative stroke.[52] While an incidental finding of hypotension during a routine blood pressure measurement may not be particularly worrying, a substantial drop in blood pressure following standing, exercise, or eating can be associated with symptoms and may have implications for future health.[48] A drop in blood pressure after standing, termed postural or orthostatic hypotension, is defined as a decrease in supine-to-standing BP >20 mm Hg systolic or >10 mm Hg diastolic within 3 minutes of standing.[53][48] Orthostatic hypotension is associated with increased risk of future cardiovascular events and mortality.Orthostatic vitals are frequently measured to assist with the diagnosis of orthostatic hypotension,[43] and may involve the use of atilt table test to evaluate vasovagal syncope.[44]
Treatment depends on the cause of the low blood pressure.[4] Treatment may not be needed for asymptomatic low blood pressure.[54] Depending on symptoms, treatment may include drinking more fluids to prevent dehydration, taking medicines to raise blood pressure, or adjusting medicines that cause low blood pressure.[4] Addingelectrolytes to a diet can relieve symptoms of mild hypotension, and a morning dose ofcaffeine can also be effective.[55] Chronic hypotension rarely exists as more than a symptom. In mild cases, where the patient is still responsive, lying the person on their back and lifting the legs increases venous return, thus making more blood available to critical organs in the chest and head.[55] TheTrendelenburg position, though used historically, is no longer recommended.[56]
Hypotensive shock treatment always follows the following four steps. Outcomes, in terms of mortality, are directly linked to the speed at which hypotension is corrected.[9] Still-debated methods are in parentheses, as are benchmarks for evaluating progress in correcting hypotension. A study on septic shock provided the delineation of these general principles.[57] However, since it focuses on hypotension due to infection, it does not apply to all forms of severe hypotension.
Blood pressure support with avasopressor (all seem equivalent concerning risk of death, withnorepinephrine possibly better thandopamine).[58] Trying to achieve amean arterial pressure (MAP) of greater than 70 mmHg does not appear to result in better outcomes than trying to achieve a MAP of greater than 65 mmHg in adults.[25]
Ensure adequate tissue perfusion (maintain SvO2 >70 with use of blood ordobutamine)[9]
Fludrocortisone is the first-line therapy (in the absence of heart failure) for patients with chronic hypotension or resistant orthostatic hypotension.[17] It works by increasing the intravascular volume.[17]
The clinical history provided by the caretaker is the most important part in determining the cause of hypotension in pediatric patients.[62] Symptoms for children with hypotension include increased sleepiness, not using the restroom as much (or at all), having difficulty breathing or breathing rapidly, orsyncope.[62] The treatment for hypotension in pediatric patients is similar to the treatment in adults by following the four first steps listed above (see Treatment).[9] Children are more likely to undergointubation during the treatment of hypotension because their oxygen levels drop more rapidly than adults.[62] The closing of fetal shunts following birth can create instability in the "transitional circulation" of the fetus, and often creates a state of hypotension following birth; while many infants can overcome this hypotension through the closing of shunts, a mean blood pressure (MBP) of lower than 30 mmHg is correlated with severe cerebral injury and can be experienced by premature infants who have poor shunt closure.[63]
Hypotension, from Ancient Greekhypo-, meaning "under" or "less" + Englishtension, meaning "'strain" or "tightness".[64] This refers to the under-constriction of the blood vessels and arteries which leads to low blood pressure.[65]
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^Ripollés Melchor, J.; Espinosa, Á; Martínez Hurtado, E.; Casans Francés, R.; Navarro Pérez, R.; Abad Gurumeta, A.; Calvo Vecino, J. M. (September 2015). "Colloids versus crystalloids in the prevention of hypotension induced by spinal anesthesia in elective cesarean section. A systematic review and meta-analysis".Minerva Anestesiologica.81 (9):1019–1030.ISSN1827-1596.PMID25501602.
^Mitchell ES, Slettenaar M, vd Meer N, Transler C, Jans L, Quadt F, Berry M (2011). "Differential contributions of theobromine and caffeine on mood, psychomotor performance and blood pressure".Physiol. Behav.104 (5):816–822.doi:10.1016/j.physbeh.2011.07.027.PMID21839757.S2CID7003053.Theobromine ... lowered blood pressure relative to placebo
^William Marias Malisoff (1943).Dictionary of Bio-Chemistry and Related Subjects. Philosophical Library. pp. 311, 530, 573.
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^abWalsh, M., Devereaux, P. et al. Relationship between Intraoperative Mean Arterial Pressure and Clinical Outcomes a er Noncardiac Surgery. Anaesthesiology. 2013;119:507-515.
^Bijker J., Persoon S., Peelen L., et al. Intraoperative Hypotension and Perioperative Ischemic Stroke a er General Surgery. Anesthesiology. 2012;116(3):658-664.
^Sharma, Sandeep; Hashmi, Muhammad F.; Bhattacharya, Priyanka T. (2019),"Hypotension",StatPearls, StatPearls Publishing,PMID29763136, retrieved2020-01-23
^abChisholm, Peter; Anpalahan, Mahesan (April 2017). "Orthostatic hypotension: pathophysiology, assessment, treatment and the paradox of supine hypertension".Internal Medicine Journal.47 (4):370–379.doi:10.1111/imj.13171.ISSN1445-5994.PMID27389479.S2CID205208140.
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