Acute tocolysis

Pathophysiological interpretation of fetal heart rate tracings in clinical practice

The onset of regular, strong, and progressive uterine contractions may result in both mechanical (compression of the fetal head and/or umbilical cord) and hypoxic (repetitive and sustained compression of the umbilical cord or reduction in uteroplacental oxygenation) stresses to a human fetus. Most fetuses are able to mount effective compensatory responses to avoid hypoxic-ischemic encephalopathy and perinatal death secondary to the onset of anaerobic metabolism within the myocardium, culminating in myocardial lactic acidosis. In addition, the presence of fetal hemoglobin, which has a higher affinity for oxygen even at low partial pressures of oxygen than the adult hemoglobin, especially increased amounts of fetal hemoglobin (ie, 180-220 g/L in fetuses vs 110-140 g/L in adults), helps the fetus to withstand hypoxic stresses during labor. Different national and international guidelines are currently being used for intrapartum fetal heart rate interpretation. These traditional classification systems for fetal heart rate interpretation during labor are based on grouping certain features of fetal heart rate (ie, baseline fetal heart rate, baseline variability, accelerations, and decelerations) into different categories (eg, category I, II, and III tracings, "normal, suspicious, and pathologic" or "normal, intermediary, and abnormal"). These guidelines differ from each other because of the features included within different categories and because of their arbitrary time limits stipulated for each feature to warrant an obstetrical intervention. This approach fails to individualize care because the "ranges of normality" for stipulated parameters apply to the population of human fetuses and not to the individual fetus in question. Moreover, different fetuses have different reserves and compensatory responses and different intrauterine environments (presence of meconium staining of amniotic fluid, intrauterine inflammation, and the nature of uterine activity). Pathophysiological interpretation of fetal heart rate tracing is based on the application of the knowledge of fetal responses to intrapartum mechanical and/or hypoxic stress in clinical practice. Both experimental animal studies and observational human studies suggest that, just like adults undertaking a treadmill exercise, human fetuses show predictable compensatory responses to a progressively evolving intrapartum hypoxic stress. These responses include the onset of decelerations to reduce myocardial workload and preserve aerobic metabolism, loss of accelerations to abolish nonessential somatic body movements, and catecholamine-mediated increases in the baseline fetal heart rate and effective redistribution and centralization to protect the fetal central organs (ie, the heart, brain, and adrenal glands), which are essential for intrauterine survival. Moreover, it is essential to incorporate the clinical context (progress of labor, fetal size and reserves, presence of meconium staining of amniotic fluid and intrauterine inflammation, and fetal anemia) and understand the features suggestive of fetal compromise in nonhypoxic pathways (eg, chorioamnionitis and fetomaternal hemorrhage). It is important to appreciate that the timely recognition of the speed of onset of intrapartum hypoxia (ie, acute, subacute, and gradually evolving) and preexisting uteroplacental insufficiency (ie, chronic hypoxia) on fetal heart rate tracing is crucial to improve perinatal outcomes.

Optimizing the management of acute, prolonged decelerations and fetal bradycardia based on the understanding of fetal pathophysiology

Any acute and profound reduction in fetal oxygenation increases the risk of anaerobic metabolism in the fetal myocardium and, hence, the risk of lactic acidosis. On the contrary, in a gradually evolving hypoxic stress, there is sufficient time to mount a catecholamine-mediated increase in the fetal heart rate to increase the cardiac output and redistribute oxygenated blood to maintain an aerobic metabolism in the fetal central organs. When the hypoxic stress is sudden, profound, and sustained, it is not possible to continue to maintain central organ perfusion by peripheral vasoconstriction and centralization. In case of acute deprivation of oxygen, the immediate chemoreflex response via the vagus nerve helps reduce fetal myocardial workload by a sudden drop of the baseline fetal heart rate. If this drop in the fetal heart rate continues for >2 minutes (American College of Obstetricians and Gynecologists' guideline) or 3 minutes (National Institute for Health and Care Excellence or physiological guideline), it is termed a prolonged deceleration, which occurs because of myocardial hypoxia, after the initial chemoreflex. The revised International Federation of Gynecology and Obstetrics guideline (2015) considers the prolonged deceleration to be a "pathologic" feature after 5 minutes. Acute intrapartum accidents (placental abruption, umbilical cord prolapse, and uterine rupture) should be excluded immediately, and if they are present, an urgent birth should be accomplished. If a reversible cause is found (maternal hypotension, uterine hypertonus or hyperstimulation, and sustained umbilical cord compression), immediate conservative measures (also called intrauterine fetal resuscitation) should be undertaken to reverse the underlying cause. In reversible causes of acute hypoxia, if the fetal heart rate variability is normal before the onset of deceleration, and normal within the first 3 minutes of the prolonged deceleration, then there is an increased likelihood of recovery of the fetal heart rate to its antecedent baseline within 9 minutes with the reversal of the underlying cause of acute and profound reduction in fetal oxygenation. The continuation of the prolonged deceleration for >10 minutes is termed "terminal bradycardia," and this increases the risk of hypoxic-ischemic injury to the deep gray matter of the brain (the thalami and the basal ganglia), predisposing to dyskinetic cerebral palsy. Therefore, any acute fetal hypoxia, which manifests as a prolonged deceleration on the fetal heart rate tracing, should be considered an intrapartum emergency requiring an immediate intervention to optimize perinatal outcome. In uterine hypertonus or hyperstimulation, if the prolonged deceleration persists despite stopping the uterotonic agent, then acute tocolysis is recommended to rapidly restore fetal oxygenation. Regular clinical audit of the management of acute hypoxia, including the "the onset of bradycardia to delivery interval," may help identify organizational and system issues, which may contribute to poor perinatal outcomes.

Progestogens for maintenance tocolysis in symptomatic women. A systematic review and meta-analysis

OBJECTIVE

Prevention of preterm birth (PTB) with progestogens after an episode of threatened preterm labour is still controversial. As different progestogens have distinct molecular structures and biological effects, we conducted a systematic review and pairwise meta-analysis to investigate the individual role played by 17-alpha-hydroxyprogesterone caproate (17-HP), vaginal progesterone (Vaginal P) and oral progesterone (Oral P).

METHODS

The search was performed in MEDLINE, ClinicalTrials.gov and the Cochrane Central Register of Controlled Trials (CENTRAL) up to 31 October 2021. Published RCTs comparing progestogens to placebo or no treatment for maintenance tocolysis were considered. We included women with singleton gestations, excluding quasi-randomized trials, studies on women with preterm premature rupture of membrane, or receiving maintenance tocolysis with other drugs. Primary outcomes were preterm birth (PTB) < 37 weeks' and < 34 weeks'. We assessed risk of bias and evaluated certainty of evidence with the GRADE approach.

RESULTS

Seventeen RCTs including 2152 women with singleton gestations were included. Twelve studies tested vaginal P, five 17-HP, and only 1 oral P. PTB < 34 weeks' did not differ among women receiving vaginal P (RR 1.21, 95%CI 0.91 to 1.61, 1077 participants, moderate certainty of evidence), or oral P (RR 0.89, 95%CI 0.38 to 2.10, 90 participants, low certainty of evidence) as opposed to placebo. Instead, 17-HP significantly reduced the outcome (RR 0.72, 95% CI 0.54 to 0.95, 450 participants, moderate certainty of evidence). PTB < 37 weeks' did not differ among women receiving vaginal P (RR 0.95, 95%CI 0.72 to 1.26, 8 studies, 1231 participants, moderate certainty of evidence) or 17-HP (RR 0.86, 95%CI 0.60 to 1.21, 450 participants, low certainty of evidence) when compared to placebo/no treatment. Instead, oral P significantly reduced the outcome (RR 0.58, 95% CI 0.36 to 0.93, 90 participants, low certainty of evidence).

CONCLUSIONS

With a moderate certainty of evidence, 17-HP prevents PTB < 34 weeks' gestation among women that remained undelivered after an episode of threatened preterm labour. However, data are insufficient to generate recommendations in clinical practice. In the same women, both 17-HP and vaginal P are ineffective in the prevention of PTB < 37 weeks'.

Beneficial Extracardiac Effects of Cardiovascular Medications

Cardiovascular diseases are the most common cause of death worldwide, with cardiovascular medications being amongst the most common medications prescribed. These medications have diverse effects on the heart, vascular system, as well as other tissues and organ systems. The extra cardiovascular effects have been found to be of use in the treatment of non-cardiovascular diseases and pathologies. Minoxidil is used to manage systemic hypertension with its well-known side effect of hirsutism used to treat alopecia and baldness. Sildenafil was originally investigated as a treatment option for systemic hypertension; however, its side effect of penile erection led to it being widely used for erectile dysfunction. Alpha-1 blockers such as terazosin are indicated to treat systemic hypertension but are more commonly used for benign prostatic hyperplasia and post-traumatic stress disorder. Beta blockers are the mainstay treatment for congestive heart failure and systemic hypertension but have been found useful to help in patients with intention tremors as well as prophylaxis of migraines. Similarly, calcium channel blockers are indicated in medical expulsion therapy for ureteric calculi in addition to their cardiovascular indications. Thiazides are commonly used for treating systemic hypertension and as diuretics. Thiazides can cause hypocalciuria and hypercalcemia. This side effect has led to thiazides being used to treat idiopathic hypercalciuria and associated nephrolithiasis. Spironolactone is commonly utilized in treating heart failure and as a diuretic for edema. It's well described anti-androgen side effects have been used for acne vulgaris and hirsutism in polycystic ovarian syndrome. This review article discusses how the various extracardiovascular effects of commonly used cardiovascular medications are put to use in managing non-cardiovascular conditions.

The Effects of Nitroglycerin on the Oxytocin Dose-Response Profile in Oxytocin-Desensitized and Naïve Human Myometrium: An In Vitro Study

BACKGROUND

Nitroglycerin is used for acute reduction in uterine tone. Prolonged oxytocin exposure causes desensitization of oxytocin receptors. It is unknown if nitroglycerin exposure impacts the subsequent action of oxytocin in the setting of oxytocin receptor desensitization. This study investigated the effects of nitroglycerin on oxytocin-desensitized and oxytocin-naïve human myometrium and the subsequent response to oxytocin dose-response testing in vitro.

METHODS

Myometrial samples from 17 elective cesarean deliveries were divided into strips and allocated to 1 of 4 groups: (1) oxytocin desensitized and no nitroglycerin; (2) oxytocin desensitized and nitroglycerin; (3) oxytocin naïve and nitroglycerin; and (4) oxytocin naïve and no nitroglycerin. Final analysis included 28 strips per group. Nitroglycerin groups were exposed to incremental concentrations of nitroglycerin, while no nitroglycerin groups were kept in control (physiological salt) solution. All groups then underwent oxytocin dose-response testing. Primary outcome was motility index (amplitude × frequency; grams × contractions per 10 minutes [g·c/10 min]). Secondary outcomes were amplitude (g), frequency (contractions/10 minutes), and area under the curve (g·s). All outcomes (nitroglycerin and oxytocin dose-response periods) were expressed as a percentage change from baseline. Values were log transformed, compared using regression modeling and reported as the ratio of 2 geometric means (relative difference).

RESULTS

No significant difference was observed in motility index following nitroglycerin administration in oxytocin-desensitized versus oxytocin-naïve groups (relative difference = 19.0%; 95% confidence interval [CI], -32.6 to 109.9; P = .55). On oxytocin dose-response testing, motility index was highest in oxytocin-naïve and no nitroglycerin samples (group 4) (1.356 g·c/10 minutes) followed by oxytocin-naïve and nitroglycerin (group 3) (0.882 g·c/10 minutes), oxytocin-desensitized and no nitroglycerin (group 1) (0.769 g·c/10 minutes), and oxytocin-desensitized and nitroglycerin (group 2) (0.651 g·c/10 minutes) samples. Motility index was significantly reduced in group 1 vs 4 (relative difference = -43.3%; 95% CI, -66.5 to -4.1; P = .034) and group 2 vs 4 (relative difference = -52.0%; 95% CI, -70.9 to -20.8; P = .004). While in groups 3 vs 4, both amplitude (relative difference = -17.8%; 95% CI, -30.9 to -2.2; P = .27) and area under the curve (AUC; relative difference = -17.5%; 95% CI, -30.7 to -1.8; P = .030) were reduced.

CONCLUSIONS

Nitroglycerin-induced relaxation was not different between oxytocin-desensitized and oxytocin-naïve human myometrial strips in vitro. However, oxytocin-induced contractility was attenuated after nitroglycerin exposure in both oxytocin-desensitized and oxytocin-naïve samples, with maximum attenuation observed in desensitized tissues. This finding warrants further clinical studies to explore uterine responsiveness to oxytocin in women with oxytocin-augmented labors after nitroglycerin administration.

Fetal heart rate monitoring in labor: from pattern recognition to fetal physiology

The journey of human labor involves hypoxic and mechanical stresses as a result of progressively increasing frequency, duration and strength of uterine contractions and resultant compression of the umbilical cord. In addition, occlusion of the spiral arteries during myometrial contractions also leads to repetitive interruptions in the utero-placental circulation, predisposing a fetus to progressively worsening hypoxic stress as labor progresses. The vast majority of fetuses are equipped with compensatory mechanisms to withstand these hypoxic and mechanical stresses. They emerge unharmed at birth. However, some fetuses may sustain an antenatal injury or experience a chronic utero-placental insufficiency prior to the onset of labor. These may impair the fetus to compensate for the ongoing hypoxic stress secondary to ongoing uterine contractions. Non-hypoxic pathways of neurological damage such as chorioamnionitis, fetal anemia or an acute fetal hypovolemia may potentiate fetal neurological injury, especially in the presence of a super-imposed, additional hypoxic stress. The use of utero-tonic agents to induce or augment labor may increase the risk of hypoxic-ischemic injury. Clinicians need to move away from "pattern recognition" guidelines ("normal," "suspicious," "pathological"), and apply the knowledge of fetal physiology to differentiate fetal compensation from decompensation. Individualization of care is essential to optimize outcomes.

Peri-operative management of percutaneous fetoscopic spina-bifida repair: a descriptive review of five cases from the United Kingdom, with focus on anaesthetic implications

We present a case-based review of the first five percutaneous fetoscopic in-utero spina bifida repair procedures undertaken in the UK. Our focus is on implications of anaesthesia and analgesia for the mother and fetus, provision of uterine relaxation and fetal immobilisation while providing conditions conducive to surgical access. Minimising risks for fetal acidosis, placental and fetal hypoperfusion, maternal and fetal sepsis and maternal fluid overload were the foremost priorities. We discuss optimisation strategies undertaken to ensure fetal and maternal well-being under anaesthesia, shortcomings in the current approach, and possible directions for improvement.

Intrapartum cardiotocography patterns observed in suspected clinical and subclinical chorioamnionitis in term fetuses

AIM

To evaluate the cardiotocography (CTG) features observed in suspected intrapartum chorioamnionitis in term fetuses according to the recently suggested criteria for the pathophysiological interpretation of the fetal heart rate and their correlation with perinatal outcomes.

METHODS

Retrospective analysis of nonconsecutive CTG traces. 'CTG chorioamnionitis' was diagnosed either based on a persistent rise in the baseline for the given gestation or on a persistent increase in the baseline fetal heart rate during labor >10% without preceding CTG signs of hypoxia and in the absence of maternal pyrexia. Perinatal outcomes were compared among cases with no sign of chorioamnionitis, in those with only CTG features suspicious for chorioamnionitis and in those who developed clinical chorioamnionitis.

RESULTS

Two thousand one hundred and five CTG traces were analyzed. Of these, 356 fulfilled the criteria for "CTG chorioamnionitis". Higher rates of Apgar <7 at 1 and 5 min (21.6% vs 9.0% and 9.8% vs 2.0%, respectively, P < 0.01 for both) and lower umbilical artery pH (7.14 ± 0.11 vs 7.19 ± 0.11, P < 0.01) and an over fivefold higher rate of neonatal intensive care unit admission (16.6% vs 2.9%, P < 0.01) were noted in the 'CTG chorioamnionitis' group. Differences in the incidence of abnormal CTG patterns were noted between cases who eventually had clinical evidence of chorioamnionitis (89/356) and those showing CTG features suspicious for chorioamnionitis in the absence of clinical evidence of chorioamnionitis (267/356).

CONCLUSION

Intrapartum CTG features of suspected chorioamnionitis are associated with adverse perinatal outcomes.

Continuous cardiotocography during labour: Analysis, classification and management

The use of continuous intrapartum electronic fetal heart rate monitoring (EFM) using a cardiotocograph (CTG) was developed to enable obstetricians and midwives to analyse the changes of fetal heart rate during labour so as to institute timely intervention to avoid intrapartum hypoxic-ischaemic injury. Although CTG was initially developed as a screening tool to predict fetal hypoxia, its positive predictive value for intrapartum fetal hypoxia is approximately only 30%. Even though different international classifications have been developed with the aim of defining combinations of features that help predict intrapartum fetal hypoxia, the false-positive rate of the CTG is high (60%). Moreover, there has not been a demonstrable improvement in the rate of cerebral palsy or perinatal deaths since the introduction of CTG into clinical practice approximately 45 years ago. However, there has been a significant increase in intrapartum caesarean section and operative vaginal delivery rates. Unfortunately, existing guidelines employ the visual interpretation of CTG based on 'pattern recognition', which is fraught with inter- and intra-observer variability. Therefore, clinicians need to understand the physiology behind fetal heart rate changes and to respond to them accordingly, instead of purely relying on guidelines for management. It is very likely that such a 'physiology-based' approach would reduce unnecessary operative interventions and improve perinatal outcomes whilst reducing the need for 'additional tests' of fetal well-being.

Obstetric use of nitroglycerin: Anesthetic implications

Nitroglycerin has been used in anesthetic practice for induced hypotension and managing perioperative hypertension and myocardial ischemia. Contrary to the continuous low dose infusions (5-20 mcg/min) used for the same, intravenous bolus dosages are sometimes administered at the behest of obstetricians for removal of retained placenta. Use of nitroglycerine in managing retained placenta is undertaken as a last resort when other measures fail to relax the uterine smooth muscles. Intravenous nitroglycerine relaxes smooth muscle cells by releasing nitric oxide thus causing prompt cervico-uterine relaxation. However, administration of nitroglycerine in this manner is not without risks which should be kept in mind while using it for obstetric purposes. We hereby report a case of 22-year-old female scheduled for manual removal of placenta where unpredictable and unexpected hypoxemia was observed following nitroglycerine administration.

Inhaled and intravenous treatment in acute severe and life-threatening asthma

Management of life-threatening acute severe asthma in children and adults may require anaesthetic and intensive care. The inhaled route for drug delivery is not appropriate when only small respiratory gas volumes are shifted; the i.v. route may be associated with greater side-effects. Magnesium sulphate i.v. has a place in acute asthma management because it is a mild bronchodilator, and has a stabilizing effect on the atria which may attenuate tachycardia occurring after inhaled and i.v. salbutamol. If intubation and ventilation are required, a reduction in bronchoconstriction by any means before and during these procedures should reduce morbidity. This narrative review aims to show strengths and weakness of the evidence, present controversies, and forward opinions of the author. The review contains a practical guide to the setting up, use and efficiency of nebulizers, metered dose inhalers, and spacers (chambers). It also presents a commonsense approach to the management of severe asthmatics in whom delay in bronchodilatation would cause clinical deterioration. When self-inhaled agents have had no effect, i.v. drugs may help avoid intubation and ventilation. The review includes suggestions for the use of inhaled anaesthetics, anaesthetic induction, and brief notes on subsequent ventilation of the lungs.

Nitroglycerin for management of retained placenta: a multicenter study

The primary aim was to determine if sequential administration of oxytocin and nitroglycerin is effective for management of retained placenta when performed by obstetricians with no experience of the method. Secondary aims were to examine possible adverse effects of nitroglycerin. One hundred and five women with retained placenta were randomly selected to receive either 1 mg nitroglycerin or placebo tablets sublingually if intravenous oxytocin had failed to expel the placenta. At two of the hospitals some of the midwives were familiar with the use of nitroglycerin. The other midwives and all the participating obstetricians had no clinical experience of the method. In the treatment group, detachment of placenta following nitroglycerin occurred in 37.3% of the women compared to 20.4% in the placebo group (P = 0.056). In the two hospitals with some experience of the method, placenta was removed in 9 of 19 (47.4%) women in the nitroglycerin group compared to 3 of 17 (15.0%) women in the placebo group. No adverse effects of clinical importance were registered. Although the difference between the two groups did not reach statistical significance, the higher success rate in the two hospitals with some experience could indicate that clinical experience is of importance in order to achieve placental detachment.

Anaesthesiological considerations on tocolytic and uterotonic therapy in obstetrics

AIM

Significant side effects of tocolytic and uterotonic substances may be of concern to the anaesthesiologist. Recently, new drugs have been introduced having less side effects for both the mother and the neonate.

METHODS

A literature search was undertaken mainly focusing on meta-analyses, to review the possible side effects that might affect the course of anaesthesia and to suggest which precautions should be considered to prevent the occurrence of significant interactions with anaesthetic manipulations and drugs.

RESULTS

Magnesium sulphate has a proven benefit in lowering systolic blood pressure and preventing the occurrence of eclampsia, but not as a tocolytic. beta-adrenergic agonists are being abandoned due to the availability of tocolytic agents causing less side effects. Calcium channel blockers (CCB) are frequently used but can cause major maternal cardiovascular complications. Nitroglycerin seems to be appreciated as an acute tocolytic rather than a routine substance during pre-term labour. Cyclo-oxygenase-2 inhibitors are still under investigation but their tocolytic benefit is questionable mainly due to foetal side effects. Atosiban is considered the first-choice tocolytic. With respect to oxytocic drugs, oxytocine, prostaglandines and methylergometrine may all cause serious side effects especially when combined. The cardiovascular side effects of prostaglandins and methylergometrine can be life-threatening. Both oxytocin and carbetocin have a rather low risk for maternal complications.

CONCLUSION

Atosiban and CCB are at least as effective tocolytic agents as beta-mimetics but have significantly less side effects. Magnesium sulphate can cause neuromuscular blockade, especially when combined with CCB. Concerning oxytocic agents, short-acting oxyctocin and long-acting carbetocin have the least side effects as compared with prostaglandins and methylergometrine.

Acute myocardial infarction associated with pregnancy

Acute myocardial infarction (AMI) during pregnancy or the early post-partum period is rare but has been shown to be associated with poor maternal as well as fetal outcome. Major changes in both diagnosis and treatment of AMI in the nonpregnant patient have lead to improved outcome which may also affect pregnant patients. The purpose of this paper is to review available information related to the pathophysiology and clinical profile and provide recommendations for the diagnosis and management of AMI occuring during pregnancy and the early post-partum period.

The effects and selectivity of beta-adrenoceptor agonists in rat myometrium and urinary bladder

Recent evidence supports a role for beta(3)-adrenoceptors in human non-pregnant and pregnant myometrium. The present study was designed to characterize the pharmacology of beta-adrenoceptors involved in the function of non-pregnant rat myometrium by comparison of the activity of several beta-adrenoceptor agonists and antagonists in isolated rat uterus and urinary bladder. Contractions of myometrial and detrusor strips were induced by adding 1 nM oxytocin and 15 mM KCl respectively. Cumulative concentration-response curves to the selective beta(3)-adrenoceptor agonists, CL 316243 and BRL 37344 and the selective beta(2)-adrenoceptor agonist ritodrine were obtained in the presence and absence of the selective beta(2)-adrenoceptor antagonist ICI 118551 and the non-selective beta-adrenoceptor antagonist bupranolol. Both BRL 37344 (pD(2)=6.79+/-0.09) and ritodrine (pD(2)=6.89+/-0.19) produced potent inhibition of oxytocin-induced contractions in myometrial strips; CL 316243 was inactive at concentrations up to 10 microM. Concentration effect curves to both BRL 37344 and ritodrine were shifted (10 to 30-fold) to the right in the presence of ICI 118551 (10 nM). BRL 37344 (pD(2)=8.51+/-0.21) and CL 316243 (pD(2)=8.61+/-0.24) produced potent inhibition of detrusor strips, while ritodrine was almost 100-fold less potent (pD(2)=5.83+/-0.17). The response to all agonists was significantly attenuated by pretreatment with bupranolol (10 microM), but only ritodrine was affected by ICI 118551 (1 microM). These results demonstrate that relaxation of rat myometrium is mediated by beta(2)-adrenoceptors while, consistent with previous reports, the beta(3)-subtype is primarily responsible for relaxation of rat detrusor.

Prevention of birth asphyxia: responding appropriately to cardiotocograph (CTG) traces

Birth asphyxia is a broad term that refers to intrapartum asphyxia sufficient to cause neurological damage in some newborns and, rarely, intrapartum or neonatal death. Cerebral palsy and long-term neurological complications such as learning difficulties and motor impairments may be due to causes other than birth asphyxia. Several intrapartum events may cause asphyxia (i.e. hypoxia and metabolic acidosis) leading to the likelihood of neurological injury. The cardiotocograph (CTG) is a screening tool that is used to assess fetal well-being during labour and to identify the possibility of asphyxia. Abnormality of the CTG, sometimes severe enough to be described as a pathological trace, is commonly termed 'fetal distress', although many fetuses with such traces may not have hypoxia and metabolic acidosis. In current practice, the events are appropriately termed 'pathological CTG trace' or 'acidotic pH' rather than 'fetal distress'. Accurate interpretation of CTG is essential, and it is important to recognize a fetus that shows a pathological CTG in labour that may imply possible hypoxia and birth asphyxia. Considering the wider clinical picture in interpreting the CTG, and taking timely and appropriate action based on the findings, may help prevent birth asphyxia.

Myometrial expression of small conductance Ca2+-activated K+ channels depresses phasic uterine contraction

Mechanisms regulating uterine contractility are poorly understood. We hypothesized that a specific isoform of small conductance Ca2+-activated K+ (SK) channel, SK3, promotes feedback regulation of myometrial Ca2+ and hence relaxation of the uterus. To determine the specific functional impact of SK3 channels, we assessed isometric contractions of uterine strips from genetically altered mice (SK3T/T), in which SK3 is overexpressed and can be suppressed by oral administration of doxycycline (SK3T/T+Dox). We found SK3 protein in mouse myometrium, and this expression was substantially higher in SK3T/T mice and lower in SK3T/T+Dox mice compared with wild-type (WT) controls. Sustained contractions elicited by 60 mM KCl were not different among SK3T/T, SK3T/T+Dox, and WT mice. However, the rate of onset and magnitude of spontaneously occurring phasic contractions was muted significantly in isolated uterine strips from SK3T/T mice compared with those from WT mice. These spontaneous contractions were augmented greatly by blockade of SK channels with apamin or by suppression of SK3 expression. Phasic but not tonic contraction in response to oxytocin was depressed in uterine strips from SK3T/T mice, whereas suppression of SK3 channel expression or treatment with apamin promoted the predominance of large coordinated phasic events over tone. Spontaneous contractions and the phasic component of oxytocin contractions were blocked by nifedipine but not by cyclopiazonic acid. Our findings suggest that SK3 channels play an important role in regulating uterine function by limiting influx through L-type Ca2+ channels and disrupting the development of concerted phasic contractile events.