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Why was this consensus statement developed? Advances in clinical practice are sometimes inhibited by a multitude of different options that need to be selected. There has been significant variation in the treatment of spinal anaesthesia-induced hypotension. These guidelines are designed to provide clinicians with specific best-practice plans that will cover a wide range of drug and equipment availability. Detailed recommendations are provided for the management of hypotension in resource-rich and resource-poor environments. How does this consensus statement differ from other available guidelines? The American Society of Anesthesiologists/Society for Obstetric Anesthesia and Perinatology Task Force, and the UK National Institute for Health and Care Excellence, have made generic recommendations on this topic 1, 2. We are unaware of detailed guidelines from any organisations. We aim to offer independent, pragmatic advice that will be of benefit to clinicians and the women we treat. Hypotension is a very common consequence of the sympathetic vasomotor block caused by spinal anaesthesia for caesarean section. Maternal symptoms such as nausea, vomiting and dyspnoea frequently accompany severe hypotension, and adverse effects on the fetus, including depressed Apgar scores and umbilical acidosis, have been correlated with severity and duration of hypotension. Ephedrine, a mixed α- and β-adrenergic agonist, became the drug of choice in obstetric anaesthesia following work that found that it was the best vasopressor for preservation of uterine blood flow in a sheep model of drug-induced hypertension. However, higher doses of ephedrine, used clinically in attempts to reduce hypotension, were found not to improve neonatal acidosis, but rather the reverse 3; this is now acknowledged to be because ephedrine has a direct effect on fetal metabolism that negates any improvement in uterine blood flow produced by normalising blood pressure 4, 5. Clinical work dating from the 2000s indicated that α-adrenergic agonists are effective at reducing hypotension, and associated with less neonatal acidosis than ephedrine 6. National practice guidelines suggest the use of both ephedrine and phenylephrine for the management of hypotension; UK guidelines from 2011 state that: ‘Women who are having a caesarean section under regional anaesthesia should be offered intravenous ephedrine or phenylephrine, and volume pre-loading with crystalloid or colloid to reduce the risk of hypotension occurring during caesarean section’ 2. American guidelines from 2016 provide more detail: ‘Intravenous fluid preloading or co-loading: intravenous fluid preloading or co-loading may be used to reduce the frequency of maternal hypotension after spinal anesthesia for cesarean delivery; do not delay the initiation of spinal anesthesia in order to administer a fixed volume of intravenous fluid. Ephedrine or phenylephrine: either intravenous ephedrine or phenylephrine may be used for treating hypotension during neuraxial anesthesia; in the absence of maternal bradycardia, consider selecting phenylephrine because of improved fetal acid–base status in uncomplicated pregnancies’ 1. Surveys of clinical practice indicate that there has been a shift away from what was the almost universal use of ephedrine as the vasopressor of choice. In the UK, a 1999 survey found that 95% of respondents used ephedrine alone during caesarean section 7; in 2011, 89% of respondents used phenylephrine, and the remainder used metaraminol or ephedrine 8. A survey carried out in the USA in 2007 noted that 32% of respondents used ephedrine for vasopressor prophylaxis and treatment of hypotension, 26% and 23%, respectively, used phenylephrine, and the remainder used either agent according to maternal heart rate 9. Klöhr et al. found 15 different definitions of hypotension in 63 studies of hypotension following spinal or combined spinal-epidural anaesthesia for caesarean section, performed between 1999 and 2009 10. Definitions varied between those using an absolute blood pressure value, ranging from 80 mmHg to 100 mmHg, a decrease of 0–30% from a baseline or a combination of an absolute value and a percentage decrease. Some studies distinguished between severe hypotension and lesser (mild-moderate) degrees. All studies used the systolic arterial pressure (SAP) measured in the arm, in a variety of body positions; all but one 11 used the non-invasive oscillometric method. Baseline blood pressure readings were usually taken just before performing spinal anaesthesia, although occasionally at an earlier stage, such as on admission to the labour ward. The baseline was estimated from one, two or three replicate readings. Applying these different definitions to a cohort of women having elective caesarean section gave incidences for hypotension varying between 7.4% and 74.1% 10. The most common definitions of hypotension used in research studies were either ‘< 80% baseline’, or ‘< 100 mmHg OR < 80% baseline’ 10. A 1999 survey in the UK found that most consultant obstetric anaesthetists use a threshold of either 100 or 90 mmHg 7. The SAP is a less important variable than mean arterial pressure (MAP) as a determinant of organ perfusion; however, because methods used to measure blood pressure in routine clinical practice did not include the mean until recent decades, it is unlikely to be adopted for the definition of obstetric hypotension without considerably more supportive data. Most of the studies identified by Klohr et al. were at elective caesarean section; few included women in labour 12. Arterial pressure increases during labour; using baseline values taken in the antenatal period or at the start of labour was shown to reduce the incidence of recorded hypotension, defined as a decrease < 80% baseline value, after epidural analgesia 13. Many studies of hypotension at caesarean section did not include hypertensive women. The SAP threshold for pregnancy-induced hypertension or pre-eclampsia is > 140 mmHg 14. Nausea and vomiting are significantly more frequent during spinal anaesthesia for caesarean section than during non-obstetric surgery. The aetiology of this is multifactorial 15. Acute hypotension reduces cerebral perfusion, induces transient brainstem ischaemia and activates the vomiting centre. Transient cerebral hypoxia may occur, as studies using near-infrared spectroscopy (NIRS) show that hypotension is accompanied by a significant decrease in maternal regional cerebral blood volume, cerebral oxygen saturation and oxygenation 16. This is consistent with the observation that supplemental oxygen may relieve this nausea 17, 18. Spinal anaesthesia decreases splanchnic blood flow by approximately 20% 19, which may be accentuated by accompanying systemic hypotension. The resulting splanchnic hypoperfusion releases emetogenic factors such as serotonin from the gastro-intestinal tract. Finally, acute sympathetic blockade may cause unopposed vagal action and subsequent hyperactivity in the gastro-intestinal tract 20. Regardless of the aetiology, the use of prophylactic vasopressors significantly reduces the incidence of intra-operative nausea and vomiting during caesarean section 21. Dizziness and decreased levels of consciousness may follow severe and prolonged maternal hypotension, but are blood pressure is The effect of hypotension on fetal during caesarean section in although research that a decrease of > in uterine blood flow in and in a Clinical have from studies that with and without hypotension, or duration of hypotension. of women with hypotension significant acidosis and hypotension of more than duration was associated with a significant in umbilical and of of hypotension may be more important than A transient decrease in blood pressure did not neonatal Apgar incidence of fluid or the need for oxygen in the Hypotension for less than did not neonatal more than of maternal hypotension was associated with at of important in acid–base during spinal anaesthesia for caesarean is the choice of vasopressor used to hypotension. from studies were recent clinical suggest that phenylephrine, as an is associated with neonatal acid–base than ephedrine Ephedrine has higher than phenylephrine, with umbilical arterial of and in doses this is associated with neonatal higher and and levels 5. These of fetal sympathetic metabolism by ephedrine the use of phenylephrine for during caesarean section in umbilical clinical in neonatal have not been these of phenylephrine ephedrine improved clinical in the is as The available studies show in the incidence of fetal acidosis either ephedrine or phenylephrine was used to blood pressure during spinal anaesthesia for caesarean both in or those with acute fetal effects on and the of resulting in In such as bradycardia, may from The clinical to α- and β-adrenergic and and fetal effects Ephedrine not has but direct which the and duration of Ephedrine increases heart rate and by has a direct with at clinical at higher than it may with a in maternal et using found the of a phenylephrine to spinal hypotension to be et al. estimated the to spinal hypotension or nausea to be However, doses of this may be associated with increases in systemic and bradycardia, and a of 100 is more common this et al. found benefit using doses of or phenylephrine to hypotension, in with doses of 100 The of phenylephrine to ephedrine for using is is a mixed α- and at doses used has both direct and it sympathetic it for to as a A recent used a of for is the by is a agonist, with with direct in higher heart than with doses of phenylephrine The for of hypotension is et al. found a of for In has for and at are more significant at higher is a mixed α- and β-adrenergic that has both direct and effects to the of and is available and fetal effects although it is a agent in a of and of this drug is that it does not The of clinical management is the of maternal blood on of the adverse effects of hypotension. 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A vasopressor with is the choice to reverse the effects of spinal phenylephrine has the most use However, and decreased associated with phenylephrine have research on and which have to β-adrenergic effects in to studies to phenylephrine in the of obstetric spinal anaesthesia have found that may be a to phenylephrine however, there are the use of such a agent in a such as the labour studies of and metaraminol A survey found that there are of phenylephrine available in the UK 8. 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