Obstetric anaesthesia is a steadily progressing speciality. It has evolved from the traditional practices such as ‘chloroform’ for labour analgesia, to protocolised safe procedures. The modern obstetric anaesthesiologist plays the role of a ‘peripartum physician’ who ensures quality in care. Obstetric anaesthesiologists of today with compelling evidence, a sound knowledge of maternal anatomy and physiology, and a strong backup of advanced technology including monitoring devices, airway equipment, and ultrasound (US) bear only a small resemblance to their traditional counterparts. Obstetric critical care with its fast-evolving modalities of care is also developing to match the advances and novel concepts in obstetric perioperative care. Keeping this in mind, we did a thorough literature search related to obstetric anaesthesia and critical care in various databases and the information thus obtained is presented in this article.
Multiple options are currently available for labour analgesia, although lumbar epidural still remains the best option in terms of analgesia. Randomised controlled trials show that low doses of local anaesthetics (LAs) such as bupivacaine, levobupivacaine, and ropivacaine in combination with newer adjuvants such as dexmedetomidine and dexamethasone are effective for epidural analgesia and can avoid opioid-induced side-effects.[1,2] However, dexmedetomidine is not yet approved for use in pregnancy by the United States Food and Drug Administration.
Programmed intermittent epidural bolus (PIEB) is a novel technique in which a programmed pump automatically delivers boluses at predetermined time intervals and the drug solution disperses more widely and uniformly in the epidural space. PIEB technique can be combined with patient-controlled epidural boluses. A recent study has shown that the technique improves patient comfort and satisfaction, decreases total LA consumption, gives longer duration of analgesia, reduces breakthrough pain, and results in reduced motor blockade.
Dural puncture epidural technique is a novel technique in which the spinal needle is passed through the epidural needle but no drug is injected intrathecally. It was thought that this technique will become popular owing to the more rapid onset of analgesia and better confirmation of midline placement, especially in the obese parturients. However, studies comparing this technique with other techniques such as traditional epidural, both single and in combination with PIEB technique, have yielded mixed results with trivial differences between them.[4,5]
US-guided neuraxial techniques have improved access to the epidural and intrathecal space, by identifying the midline, depth of space, and optimum angle of needle insertion especially in parturients with obesity, scoliosis, and pre-eclampsia.[6,7] A recently introduced novel US software called the automatic spine level identification system automatically identifies vertebral landmarks in real time when the operator slides the US transducer over the lumbar spine.
Among non-neuraxial techniques, remifentanil intravenous patient-controlled analgesia (IV-PCA) provides effective labour analgesia but with potential side effects such as maternal hypoxia, respiratory or cardiac arrest, pruritus, nausea, and vomiting. Datasets of the RemiPCA SAFE network database from 6 consecutive years show that maternal hypoxia was 24.7% with remifentanil along with a low neonatal oxygen supplementation rate at 5%.
Immersive virtual reality is an emerging non-pharmacological technology that involves distraction of the patient and creation of a virtual environment that has the cognitive capacity to distract the parturient from pain. The parturient receives visual and auditory feedback and is able to interact with the virtual environment. Studies have shown that this technique is effective in relieving pain and anxiety especially in the first stage of labour and patients prefer to use it during daytime and when pain scores are less than 8.
REGIONAL ANAESTHESIA FOR CAESAREAN SECTION
Neuraxial block is the anaesthetic technique of choice for lower segment caesarean section (CS). US-guided spinal anaesthesia (SA) increases success at first pass and reduces the number of postoperative complications (postpartum backache and headache) and can be used for difficult spinal and as a routine practice in elective procedures.[13,14]
The incidence of post-spinal hypotension (PSH) varies from 7.4%-74.1% and to prevent associated complications, a systolic blood pressure (SBP) target of ≥90% of the baseline level, or 100 mm Hg is recommended during CS.[15,16] Besides the measures of left uterine displacement and IV crystalloid co-loading, use of prophylactic variable rate phenylephrine started at 25–50 μg/min immediately after the intrathecal LA injection, and titrated to baseline SBP and pulse rate are recommended for preventing hypotension. Norepinephrine 6 μg bolus intravenously or by computer-controlled infusion (5 μg/ml) has been found to be effective with lower incidence of bradycardia, although further studies are needed to establish its safety. Drugs such as ondansetron can prevent PSH and post-anaesthesia shivering during CS. Perfusion index and pleth variability index are simple noninvasive tools that can be used for the prediction of PSH. Low-dose (≤ 8 mg) hyperbaric bupivacaine for SA during caesarean delivery results in reduced efficacy but is associated with decreased frequency of PSH.
Novel nerve blocks such as quadratus lumborum block, transversus abdominis plane block, and wound infiltration (single injection/continuous infusion) can be a part of multimodal analgesia regimens after CS. Intrathecal morphine 50-100 μg or diamorphine 300 μg and paracetamol, non-steroidal anti-inflammatory drugs (NSAIDs) or IV dexamethasone administered after delivery are other recommended pharmacological options for post-caesarean analgesia.
The incidence of post-dural puncture headache (PDPH) or meningeal puncture headache after SA is 0.8%-5% and nearly 50%-80% after accidental dural puncture (0.51%-1.5%) in obstetric patients.[22,23] Conservative treatment modalities include caffeine 300 mg orally in repeated doses, gabapentin, aminophylline, and adrenocorticotropic hormone.[24,25] Epidural blood patch still remains the gold standard of treatment for severe PDPH (pain scores >8) performed after 24-48 hours of meningeal puncture at or below the puncture site, with a blood volume of around 20 mL being effective in 50%-80% of women. Mild to moderate headache can be managed with analgesics and nerve blocks (greater occipital nerve block or sphenopalatine ganglion block).[26,27]
Studies have shown that acute postoperative pain is more in patients with postpartum depression. Parturients who experience unintentional dural puncture are more likely to experience chronic disability headaches at 2 and 6 months postpartum.
GENERAL ANAESTHESIA FOR CAESAREAN SECTION
The 2021 National Institute for Health and Care Excellence (NICE) caesarean birth guideline recommends a decision-to-delivery interval of within 30 minutes for category-1 CS. General anaesthesia (GA) has limited indications such as category 1 CS, confirmed coagulopathy, unknown coagulation status, hypovolaemia, and haemodynamic or respiratory failure. Pregnant women have a higher risk of difficult or failed intubation, the development of hypoxaemia during induction, intubation and extubation, and pulmonary aspiration. The incidence of failed tracheal intubation during GA for CS is 9%. Algorithms for airway management in obstetrics including failed tracheal intubation, and ‘cannot intubate, cannot oxygenate’ situations should be followed along with preoperative fasting guidelines.[31,32]
The head elevated laryngoscopy position (a 25-degree head elevation) combined with the ramped position is the optimum position during induction of GA. The ramped position can be achieved using pillows or specific devices (e.g., Oxford Head Elevating Laryngoscopy Pillow (HELP) ®).
Difficult Airway Society (DAS)/All India Difficult Airway Association guidelines recommend the use of cricoid pressure (10-30N) by backward, upward, rightward, and posterior manoeuvre during rapid sequence induction. There is limited evidence for its effectiveness in decreasing aspiration risk and it also has the potential for making airway management more difficult if incorrectly applied. These guidelines recommend a low threshold to release/reduce cricoid pressure if it impedes laryngoscopic view or passing of the endotracheal tube/mask or supraglottic airway device.
Recent advances in obstetric airway management include the use of videolaryngoscopy, transnasal humidified rapid-insufflation ventilatory exchange for oxygenation which extends safe apnoea time, second generation supraglottic airway devices such as the Proseal laryngeal mask airway (LMA), i-gel and the LMA-Supreme and airway exchange catheters.
Although videolaryngoscope (VL) is recommended as a back-up device after a failed attempt with direct laryngoscopy, it may soon be recommended as a first-line device for an optimised first attempt of laryngoscopy and endotracheal intubation. Glidescope, C-MAC VL, MacGrath VL, and Airway scope (Pentax) have all been used as first-line rescue devices in obstetric patients. The recent DAS guidelines recommend that VLs and second generation supraglottic devices should be immediately available on the labour floors.
Pre-emptive neck US and the marking of cricothyroid membrane are useful in the obese parturients. Gastric US before induction can determine the presence of stomach contents above a particular threshold and decrease the risk of aspiration.
The ObsQoR-11 is a scoring tool in the English language, developed and validated in parturients in the United Kingdom. It is used to assess the quality of recovery after CS and has been translated into many languages, including Hindi.
Enhanced recovery after caeserean delivery (ERAC) is currently a topic of both academic and clinical interest. It involves the multidisciplinary team efforts of the anaesthesiologist, obstetrician, nursing staff, hospital, and patient through the perioperative period [Table 1]. Implementation of ERAC results in significant reduction in the length of hospital stay with better postoperative pain relief and reduced opioid requirement for caesarean delivery. However, poor level of literacy of target population, big rural and urban divide with the inability to recognise early warning signs, and lack of trained staff for ERAC protocols are the prime barriers for implementation of ERAC in our country.
MANAGEMENT OF OBSTETRIC COMORBIDITIES
Causes of maternal morbidity and mortality
Major obstetric haemorrhage (MOH), hypertensive disorders of pregnancy (HDP), cardiovascular causes, sepsis, and thrombotic events are the leading causes of serious maternal morbidity (SMM) globally.[36,37] Increasing age at parity, obesity, chronic hypertension, diabetes, artificial fertility treatment, and multiple pregnancies are important risk factors, which can be assessed by useful tools such as California Maternal Quality Care Collaborative (CMQCC) risk-assessment tool and the obstetric co morbidity index (OB-CMI). Pre-existing chronic illness, infections like human immunodeficiency virus and tuberculosis, access to healthcare, mental health and ethnicity influence maternal outcomes.
High neuraxial block, failed neuraxial block, difficult/failed airway, cannot intubate cannot ventilate situation, LA systemic toxicity, and anaphylaxis are documented as anaesthetic causes for SMM. Every anaesthetic team must be prepared to manage such scenarios. Simulation-based training in technical and non-technical skills are found extremely useful. Transthoracic echocardiogram and point of care US (POCUS) can help in identifying the cause for collapse.
Major obstetric haemorrhage
The International Federation of Gynecology and Obstetrics recommendations for MOH management suggest ‘care bundles’ to be implemented. Uterotonics are advised for all women in the third stage of labour to prevent postpartum haemorrhage (PPH). Obstetric early warning scores and shock index (SI), the ratio of pulse rate to SBP have been used to recognise and predict severe haemorrhage, the need for blood transfusion and intensive care unit (ICU) admission. Carbetocin, a synthetic oxytocin analogue, is suggested as the first-line alternative to oxytocin, due to heat stability and less haemodynamic side effects. The recommendation is to administer a single dose of 100 μg slowly intravenously immediately on delivery of the baby. However, further research is needed to establish its effects in high-risk pregnancy.
Quantification of blood loss using combination of gravimetric techniques, volumetric drapes, and colorimetry is more accurate than visual assessment which might underestimate the loss. The World Health Organization (WHO) has added IV tranexamic acid 1 gm in ‘first response care’ for haemorrhage following the World Maternal Antifibrinolytic (WOMAN) trial.[41,42] However, reports from Tranexamic Acid for Preventing Postpartum Hemorrhage (TRAAP) 1 and 2 trials do not entirely support this. Point-of-care test (POCT) of coagulation based on viscoelastometry including rotational thromboelastometry (ROTEM) and thromboelastography have been found very useful and been endorsed by the NICE and Royal College of Obstetricians and Gynaecologists. Limitations include the cost and feasibility. These bedside rapid tests enable rapid response, but high costs and feasibility of use in an emergency are important limitations. Massive transfusion protocol appropriate to the healthcare facility must be established. Current thoughts suggest moving away from fixed ratio transfusion to goal directed transfusion based on coagulation tests and blood cell counts aiming for haemoglobin level >7 g/dl, platelets >75,000/μl, fibrinogen >2 g/dl, and international normalised ratio <1.5. The goal is to replace red blood cells without volume overload and unnecessary transfusion of sparsely available products as elicited by OBS Cymru project.[43,44] Fibrinogen concentrates have been used as alternative to transfusion of blood products but their cost-effectiveness is yet to be assessed. Fresh frozen plasma or cryoprecipitate as replacement for factors and platelets must be administered only if indicated.
Hypertensive disorders of pregnancy
HDP may present with life-threatening complications; hence, early recognition and management becomes crucial. Diagnostic criteria for severe pre-eclampsia include high BP>/= 160/110 mmHg with or without one significant end-organ dysfunction like cardiac failure, cerebrovascular events, eclampsia, HELLP (haemolysis, elevated liver enzymes, and low platelets) syndrome, reduced foetal blood flow, or any sign of foetal distress. Atypical presentation may not necessarily include proteinuria or raised BP but the systemic effects of the disease process may last up to six weeks. Plane-wave US scanning for evaluation of ocular blood flow in women at risk for pre-eclampsia can help in early diagnosis.
The treatment goal in pregnant women with chronic hypertension is BP <140/90 mm Hg [Chronic Hypertension and Pregnancy (CHAP) trial]. Tighter control provides better outcomes [Control of Hypertension in Pregnancy Study (CHIPS trial). The target should be a SBP of not more than 130-135 mm Hg and diastolic BP 80-85 mm Hg. Hydralazine, labetalol, and calcium channel blockers remain the mainstay of antihypertensive therapy. The role of magnesium has been well established in the prevention and reduction of seizures in pre-eclampsia. Further investigations evaluating cardiac status may be indicated based on signs and symptoms as elicited by the 2019 American College of Obstetricians and Gynecologists (ACOG) guidelines. Restrictive fluid strategy, fluid and electrolyte balance, continuous invasive BP monitoring (in those with uncontrolled high BP, organ failure, and morbid obesity), optimal BP control, regular foetal monitoring, and identifying and managing early signs of organ dysfunction are the keys to successful outcomes.
Low-dose aspirin in a preventive role has been studied extensively and is not a contraindication for regional anaesthesia (RA). RA is the preferred mode except in the presence of absolute contraindications: coagulopathy, acute pulmonary oedema, uncontrolled seizures, and haemodynamic instability like hepatic rupture or HELLP syndrome. Neuraxial technique may be safely performed in experienced hands with platelet count >70,000/μL, while avoided if counts are <50,000/μL. In patients with platelet count 50,000-70,000/μL, the decision has to be taken weighing the risks and benefits. Precautions to prevent haemodynamic variability during the administration of GA and RA along with NSAIDs for pain relief have been recommended in the ACOG guidelines 2020 unless there is the risk of renal dysfunction.
Concept of Pregnancy Heart Team and Cardiac Obstetrics
Pregnancy heart team/cardiac obstetrics is a novel concept of great interest. The Maternal Levels of Care Consensus Statement suggests stratifying patients and allocating appropriate levels of care. Cardiac Disease in Pregnancy (CARPREG) score and modified WHO (mWHO) classification help in risk stratification. Patients with pulmonary artery hypertension and cardiomyopathies are at a higher risk compared to women with simple congenital heart disease. Peripartum cardiomyopathy (PPCM) is the most common diagnosis for pregnant women with heart failure and the differential diagnosis includes Takotsubo or stress cardiomyopathy, exacerbation of a pre-existing cardiomyopathy, such as familial cardiomyopathy, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, or left ventricular non-compaction cardiomyopathy. Role of bromocriptine in the treatment of PPCM is being studied. Artificial intelligence-based activity trackers and screening tests such as routine 12-lead electrocardiograms may identify early signs of heart failure. The Tamil Nadu Pregnancy and Heart Disease Registry was initiated to generate data which have identified significant number of women with cardiac diseases.
Venous thromboembolism (VTE) is an important cause of SMM especially during the postpartum period. Obesity, thrombophilia, APLA (Antiphospholipid antibodies) syndrome, assisted fertility, multiple pregnancy, surgical delivery, and sedentary life are major risk factors, which can be assessed by the VTE risk assessment tool as suggested by the NICE and RCOG guidelines.
No strong evidence exists related to anticoagulant drug dose and timing from the latest Cochrane review.
CRITICAL CARE IN OBSTETRICS
An approximately 3% to 8% of pregnant women require obstetric care unit admissions in our nation. Focused obstetric critical care services which comprise level 3-4 care contribute tremendously toward reduction in SMM. These specialised obstetric critical care units are scarce and resource intensive. Hence, validated tools like modified early obstetric warning score (MEOWS) based on physiologic criteria have been developed to recognise, triage, and treat high risk patients in a timely and judicious manner to appropriate clinical settings. The OB-CMI is useful for prospectively quantifying the risk of severe maternal morbidity and need for ICU admission in antenatal parturients.[38,55]
As the burden of critical illness continues to rise, obstetric critical care specialists need to also incorporate tools like POCUS to detect, manage, monitor, and prognosticate critical illnesses, including complex pre-existing cardiac diseases. POCUS, especially lung US, has been reliably shown to surpass the chest radiogram `in the diagnosis of pulmonary oedema and pleural effusions. Incorporating lung US using the bedside lung ultrasound in emergency (BLUE) protocol with rapid obstetric bedside echocardiography can help differentiate causes of unexplained dyspnoea or cardiopulmonary dysfunction, especially in cases of pre-eclampsia. The number of B-lines (> 3) in at least 2 bilateral lung zones is a definitive finding of interstitial syndrome and a real-time lung US benefit in the assessment of extravascular lung water, disease progression, or resolution. It has also emerged as a useful aid for pregnant patients with coronavirus disease-19 to diagnose and treat respiratory failure.
POCUS is useful in guiding resuscitation during PPH along with being a quick and reliable tool to rule out intraperitoneal haemorrhage postsurgically or following trauma.
ROTEM has an established role in the prolonged management of PPH in the ICU, wherein it has displayed the potential to reduce blood product requirement thereby aiding in goal directed patient blood management and overall recovery.[40,55,57]
Maternal sepsis is one of the leading causes of death across the globe especially in the developing world and a major cause of ICU admission. Physiological changes delay detection of maternal sepsis and hence enhanced vigilance is warranted as the organ dysfunction secondary to sepsis usually results in cardiac dysfunction. Use of obstetrically modified quick sequential organ failure assessment has been recommended to overcome the physiological changes which mask the detection of sepsis.[55,58]
The cardio-depressant effects of inflammatory interleukins, oxidative stress, and mitochondrial dysfunction leading to cardiomyocyte apoptosis has been implicated in sepsis-induced cardiomyopathy. Hence, learning the skills of transthoracic echocardiography assists in rapid assessment of haemodynamic function, need for vasopressors, and guides treatment modalities. Revised definitions of septic shock lay emphasis on monitoring of serum lactate levels >2 mmol/L. The hour-one bundle approach concept needs to be adapted aggressively within the first hour of recognition of sepsis. It consists of sending blood cultures with early appropriate use of broad spectrum antibiotics, respiratory and haemodynamic stabilisation using balanced salt solutions (avoidance of sodium containing solutions) and vasopressors (norepinephrine as first line), early source control within 12 hours, monitoring lactate levels, urine output, and prevention of complications and sequelae.[55,59]
Successful outcomes with the use of extracorporeal membrane oxygenation have been reported in pregnancy both antepartum and postpartum. Perimortem caesarean delivery, that is, resuscitative hysterotomy or resuscitative uterine interventions is currently done if return of spontaneous circulation is not possible within 5 minutes of maternal cardiac arrest. It facilitates resuscitation by relieving aorto-caval compression in the mother. It should be performed as quickly as possible without wasting time on abdominal preparation, asepsis, or sophisticated surgical equipments (only a scalpel is required).
Obstetric anaesthesia is steadily progressing with the incorporation of newer technology and a better understanding of the maternal anatomy and physiology. Newer concepts and modalities in labour analgesia and anaesthesia for CS including RA techniques and airway management are coming up. Techniques such as POCUS including lung US and gastric US and POCTs of coagulation based on viscoelastometry are on the anvil to revolutionise perioperative obstetric care. The use of scoring systems is now a new norm, especially in obstetric critical care. All these have led to an improvement in the quality of perioperative obstetric care and improved perioperative maternal outcomes.
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Conflicts of interest
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