Anaesthetic challenges and management during pregnancy: Strategies revisited.

During pregnancy, an obstetrician can encounter various complications and sometimes require surgery or operative intervention for delivery. However, the role of anaesthesiologists during such clinical scenario is grossly under-estimated. Without any close coordination and team work among obstetricians, neonatologists and an anaesthesiologist, morbidity and mortality can increase during these surgical interventions. The clinical scenario can become more challenging if the parturient suffers from any comorbid diseases. The present article reviews some of the common challenging scenarios during pregnancy that an anaesthesiologist frequently encounters during routine practice. Anaesthetic management has been discussed briefly and separately for each trimester and post-partum period. The article also aims at gaining in-depth knowledge of these obstetrical and surgical emergencies so as to ensure close-knit team work among obstetricians, anaesthesiologists, intensivists and a neonatologist.

INTRODUCTION

Administration of anaesthesia for obstetric and non-obstetric surgery during pregnancy has always been a challenge to the attending anaesthesiologists. Data from developing nations is lacking, but statistics from the developed world reveals that 1-2% of all obstetric patients present for emergency non-obstetric surgery once in their lifetime.[1] Numerous diseases and their complications during pregnancy can cause hospitalization of a pregnant female, which may require surgical intervention. Surgical emergencies such as torsion of ovarian cysts, appendicitis, strangulated hernias, traumatic injuries, etc., during pregnancy warrant immediate treatment.[2] The risk of surgery is not much different from the general population, but anaesthetic management is extremely challenging during this period.[3] Safety of both the mother and the foetus in utero is the prime objective while delivering anaesthesia services during these emergency surgical procedures.[2] In spite of new advancements in clinical arena and technology, anaesthesiologists have to face numerous challenging tasks in delivering safe anaesthesia services. Besides socio-cultural barriers, clinical challenges, which include but are not limited to changing population characteristics, such as advanced maternal age, obesity, comorbidities, including diabetes, severe anaemia, cardiac diseases, etc., all produce a huge uphill task for anaesthesiologists.

Complete knowledge of various physiological aspects [Table 1] related to pregnancy and the pharmacological profile of various drugs is mandatory to conduct safe anaesthesia. Both regional and general anaesthesia (GA) are associated with potential complications, some of which may be rare but can be fatal or permanently disabling.[4] The precautions during surgical procedures revolve around prevention of four ‘H,’ that is, hypotension, hypoxemia, hypovolaemia and hypothermia. Keeping in mind the altered physiology of the mother and giving due consideration to the functional integrity of uterine blood flow, an anaesthesiologist has to be aware of certain common important goals[56] during all three trimesters, which include but are not limited to:

Table 1

Physiological changes during normal pregnancy

Minimal alteration in maternal physiologic parameters.

Optimization of utero-placental perfusion during any surgical procedure

Optimal oxygenation of maternal blood

Avoidance of use of any drug contra-indicated in pregnancy

Prevention of any premature uterine contraction/activity

Prevention of incidence of four ‘H,’ that is, hypotension, hypoxemia, hypovolaemia and hypothermia.

As such, for administration of anaesthesia during pregnancy, the period of gestation for conduct of anaesthesia can be divided into the following major categories:

First trimester

Second trimester

Third trimester

Labour analgesia

Anaesthesia for operative delivery

Post-partum period.

PRE-ANAESTHETIC CHECK-UP, COUNSELING AND PREMEDICATION

Whatever the period of gestation, the most important step in all of them is thorough pre-operative evaluation. This whole exercise involves close coordination between the anaesthesiologist, the obstetrician and the paediatrician as safety of both mother and foetus is the prime objective. Ideally, such operative interventions require early referral to tertiary care institutes to save both the mother and the foetus. Many of the clinical signs and symptoms such as heart murmur, tachypnoea, dyspnoea, benign ECG changes, premature beats, etc., present commonly during normal pregnancy and may confuse the attending anaesthesiologist with a suspicion of underlying comorbidity.[78] Particular attention is to be paid to airway examination as this subset of the population invariably has oedema of the airway as a result of hormonal impact. Difficulties can be encountered during bag-mask ventilation and laryngoscopy as a result of oedema and breast engorgement. Difficult airway cart should always be ready as multiple attempts at intubation in lieu of vocal cord oedema and increased risk of bleeding. In such cases, preference should be given to a smaller sized endotracheal tube and avoidance of nasal intubation. Pre-oxygenation with 100% oxygen for 3-5 min gives ample time for airway securing under GA, which should preferably be administered with rapid sequence induction and intubation.[1278]

Whether it is an obstetrical or non-obstetrical emergency, efforts should be directed at minimal radiological exposure of the foetus for any diagnostic intervention.[9] Thorough counseling of the parturient and her relatives eases the pressure to a large extent. Pre-operatively, besides routine investigations, adequate arrangement of blood should be ensured whenever a major surgical intervention is anticipated. Premedication should include H2 blockers or sodium citrate to minimize the risk of aspiration as lower oesophageal sphincter tone is reduced due to circulating progesterone especially after 16 weeks of gestation.[12] Analgesics and sedatives should be used judiciously keeping in mind the duration of gestation and type of surgery. Positioning issues are of great concern as after 20 weeks of gestation, incidence of aorto-caval compression increases. Keeping a wedge under the right lower back or the left lateral tilt of the table by 10-15 degrees can be immensely useful to prevent decreased venous return and cardiac output, thereby preventing reduced perfusion to the uterus also.[123] During emergency management of acute pain, caution should be exercised while using heavy doses of non-steroidal anti-inflammatory drugs so as to prevent the possible risk of premature closure of ductus arteriosus. The gravid uterus while compressing upon the inferior vena cava also causes dilatation of the epidural venous plexus. These physiological changes causes extensive spread of local anaesthetics and enhanced risk of inadvertent intravascular injection.[123] At least, 3-4 anaesthetic plans should be chalked out at this stage considering the possibility of difficult airway, difficult regional anaesthesia and non-fasting status.

ANAESTHETIC CONSIDERATIONS

The anaesthetic aspects assume significant proportions related to the type of surgery. If possible, any elective general surgical procedure should be avoided during the gestation period. The emergency surgery can also have various implications as it can be cardiac or non-cardiac, obstetric or non-obstetric. The anaesthetic impact and clinical implications are a little different during the three trimesters.

The first trimester

The physiological parameters during pregnancy are affected profoundly, which alters the normal responses to the effects of anaesthesia. The physiological changes during pregnancy in various organs are an adaptation response to the changed metabolic profile and various demands and stresses arising out of pregnancy. The basic aims during the first trimester revolve around avoidance of any drug or technique, which can interfere with proper embryological development. As the physiological functions are grossly altered after the 6-8-week period and as such oxygenation, normovolaemia and stable haemodynamic parameters are the prime objective during administration of anaesthesia during this period.[4]

These physiologic changes affect nearly all major organ systems, including the cardio-vascular, pulmonary, renal, hepatic, nervous systems, and lead to numerous metabolic changes as an adaptation response.[4] The increasing requirements of both the maternal and the foetal tissues put extra demand for increased oxygen consumption, but progressively decreasing functional residual capacity makes a parturient more vulnerable to hypoxemia. Normal hyperventilation of pregnancy causes washout of CO2, resulting in relative hypocarbia. The notable and significant anaesthetic implications during this period include decrease minimum alveolar concentration, faster inhalational induction resulting from decreased functional residual capacity, rapid induction with soluble agents and greater risk of hypoxemia due to decreased functional residual capacity, and increased oxygen consumption.[10] Excessive mechanical ventilation during GA can cause decreased CO2 resulting in intense vasoconstriction, leading to decreased maternal cardiac output and compromising uterine blood flow.

Titration of anaesthetic drugs is highly mandatory as the requirements are reduced during this period, both for inhalational and intravenous drugs. The significant cardiovascular changes include increased blood, plasma and RBC volume; increased cardiac output; increased heart rate; and benign arrhythmias such as ST, T and Q-wave changes, with left axis deviation in some of the parturients.[78] The goals of anaesthetic management involve careful differentiation of these changes from patients with overt cardiac pathologies such as presence of systolic murmur (>grade-III), diastolic murmur and severe symptomatic arrhythmias.

Along with the above changes, hormonal changes during pregnancy can cause increased weight gain and vascularity. As a result, breast enlargement, laryngeal oedema and increased antero-posterior diameter of the chest affects the soft tissues of the neck, making airway management difficult. Instrumentation of the oro-nasal airway has to be meticulous as there is high risk of bleeding due to increased vascularity of the mucous membranes. There are chances that patients given GA and succinylcholine have to be ventilated for prolonged periods as plasma cholinesterase levels are decreased in more than 30% of the parturients. Neuromuscular monitoring is of immense help in patients with marked reduction of plasma cholinesterase levels.[101112131415]

Foetal monitoring should be ideally carried out using a Doppler ultrasound during this period. Pre-, intra- and post-operative foetal monitoring are very essential for any kind of emergency surgical procedure. The risks to the foetus are high and regional anaesthesia should be the first choice wherever possible because of complications normally associated with GA in this subset of the population, especially difficult airway and a high risk of aspiration.[6] The risk of teratogenicity in the foetus is highest during the first trimester and all necessary drugs should be administered after a closed discussion of the anaesthesiologist with the obstetrician.

Second trimester

General practice has been to delay surgery until the second trimester in order to reduce the risk of spontaneous abortion and preterm labour. By this period, most of the physiological changes have achieved a plateau level and management of anaesthesia becomes relatively safer than in the first or the third trimester. Though the second trimester is considered a relatively safer period for any emergency surgery as compared with the first and third trimesters, but it is also associated with some major physiologic alterations, which can jeopardizes the life of both the mother and the foetus. Difficulty in airway management increases further. The gravid uterus starts compressing the greater vessels and aorto-caval compression can be very hazardous during the administration of general or regional anaesthesia.

The most common non-obstetrical surgical emergencies complicating pregnancy are acute appendicitis, cholecystitis and intestinal obstruction. The less common surgical conditions include torsion of ovarian cysts or masses, cholelithiasis, adrenal tumour, hernias, complications of inflammatory bowel disease or abdominal pain of unknown aetiology[316] [Table 2]. The aorto-caval compression can be avoided to some extent by a left lateral position or by keeping a wedge under the right side during supine position. Venocaval compression also increases the distension of the epidural venous plexus, which results in increased risk of inadvertent intravascular injection of local anaesthetics (LAs) as well as rapid spread of the LA drug due to decreased capacity of the epidural space. There is a marked increase in the levels of pro-coagulant factors, resulting in a hyper-coagulable state during pregnancy, which starts during late first trimester and attains a plateau level during second trimester onwards. These changes warrant thrombo-prophylaxis in the high-risk patients who are prone to develop this complication from 2nd trimester onwards.[17]

Table 2

Various surgical emergency pathologies during pregnancy in order of decreasing frequencies

Third trimester

Decision-making in the third trimester becomes a little easier as one can proceed for caesarean section before the major surgery. All other difficulties encountered during the first two trimesters regarding airway management get accentuated due to increased airway oedema as a result of hormonal interactions. An emergency surgery beyond 28 weeks can be undertaken with simultaneous administration of steroids, which provide an essential cover for foetal lung maturation and prevent any possible incidence of acute respiratory distress syndrome in the neonate.[11] The precautions exercised in the second trimester hold equally good for the third trimester as well, with increased incidence of aorto-caval compression now by a much larger gravid uterus as compared with that in the 2nd trimester. Regional anaesthesia remains the preferred choice even during this period keeping in mind the inherent risk of GA in parturients. GA should be used with caution as inhalational anaesthetics have the capability of providing profound uterine relaxation and possible chances of post-partum haemorrhage.[1819]

Analgesics, sedatives and anaesthetics must be used with caution for caesarean delivery as they can have a profound effect on neonatal health and Apgar scores. A few of the drugs, surgical and anaesthetic stress have the propensity to suppress lactation, which may or may not be of transient duration and as such necessitates extreme vigil during conduct of anaesthesia. One big concern during this period is the possible secretion of various drugs through breast milk, which can have effects on the newborn during lactation especially opioids and sedatives.

Labour analgesia

Labour analgesia has always been associated with myths and controversies since its inception both in developed and developing nations. Right from introduction of labour analgesia into clinical practice since the early 1950's, the obstetrical anaesthesia science has undergone a sea of change with the advent of modern techniques; monitoring gadgets and availability of newer, safe and effective drugs.[20] As a consequence, the quality of labour analgesia methodology has improved tremendously over the last two decades. The birth of obstetrical anaesthesiology as a sub-speciality has further enhanced the growth and progress of labour analgesia science.[21] Though non-pharmacological methods such as water bath, intra-dermal sterile water injections, TENS, hypnosis and acupuncture are still being practiced today in various parts of the globe, yet the mainstay in provision and progression of labour analgesia has been the pharmacological methods.[22]

Parenteral opioids such as pethidine, fentanyl, tramadol, butorphanol and remifentanil have been used successfully for labour analgesia but not a single drug is free from side effects when administered in a little higher doses.[23242526] Somewhat less effective are inhalational agents such as Entonox and the short-acting fluoride anaesthetic sevoflurane, but even they are also not devoid of side effects especially at higher doses.[2728] It is the technical advancements in regional anaesthesia, which has propelled labour analgesia to newer horizons. Epidural and combined spinal epidural analgesia using lower dose regimens of LAs and opioids have been revolutionary in achieving the desired goals of labour analgesia.[29] Continuous epidural infusions through infusion pumps, patient-controlled analgesia and computer-integrated, patient-controlled epidural analgesia are the modern methods of the drug delivery system, which have largely been instrumental in popularizing the science of painless labour.[303132]

The advent of newer LA like levo-bupivacaine and ropivacaine has further enhanced the safety levels of labour analgesia.[33] The addition of adjuvants such as opioids [Table 3], α-2 agonists such as clonidine and dexmedetomidine, neostigmine, etc., enable achievement of not only the desired analgesia with a lower doses of LA, but also results in prolongation of the analgesic effect.[34353637] On a whole, lower consumption of doses of LAs has virtually made painless labour free of various side effects, which are associated with higher doses of the anaesthetic agents. Though a few researches believe that pain-alleviating intervention during labour is associated with a higher incidence of operative delivery, there is no substantial literary evidence to support these claims.[38]

Table 3

Doses of the commonly used opioids for labour analgesia

Anaesthesia for operative delivery

A recent trend has demonstrated an increase in the number of caesarean sections both in the developed and developing nations for one indication or the other.[394041] The more plausible reasons for these surgical interventions include advanced and timely foetal monitoring, which diagnose the early foetal compromise as well as increasing patient preference for the operative deliveries.[18] Now it has been successfully well established that regional anaesthesia is much safer than GA for caesarean section and the majority of the operative procedures for delivery are being carried out under regional anaesthesia throughout the world.[42] Maternal preference, comorbid diseases and urgency of surgery also determine to a large extent the type of anaesthesia to be employed.[434445] Whatever the type of anaesthesia is to be administered, the most significant aspect is the decreased number of maternal deaths especially in the developed nations as result of advanced anaesthetic care.[46]

GA is indicated in a number of conditions such as[47]

Patient's refusal for regional anaesthesia

Coagulation abnormalities

Various contra-indications of regional anaesthesia such as severe active infection at the back, neurological diseases, deformities of the spine, etc

Foetal compromise necessitating urgent operative intervention.

The most challenging aspect of an obstetric patient receiving GA involves management of a difficult airway.[48] The anatomic and physiologic changes during pregnancy make the scenario of airway management very challenging such as soft tissue oedema of the upper airway, weight gain, breast enlargement, increased mucosal vascularity with an increased propensity to bleed, as well as a high risk of aspiration pneumonitis.[12] The hormonal imbalance decreases the tone of the upper oesophageal sphincter and therefore there is always a risk of aspiration in these patients in spite of adequate fasting. The increased gastric emptying time and increased intra-abdominal pressure due to a gravid uterus further enhance the risk of pulmonary aspiration.[49] A rapid sequence induction and intubation is the method of choice for securing the airway in such patients and numerous anaesthetic techniques are available to suppress the stress response associated with airway manipulation and intubation.[50] The availability of newer supraglottic devices such as, proseal laryngeal mask airway and intubating laryngeal mask airway have further eased the administration of GA and management of a difficult airway.[4851]

Regional anaesthesia is not only associated with avoidance of airway manipulation, but also has the advantage of avoiding the poly-pharmacy practiced in GA. Regional anaesthesia also enables the parturient to remain awake during the surgical intervention and feel the first cry of the baby, which is a good psychological boost for overly anxious patients.[1852] Though spinal and epidural techniques have been equally useful, spinal is more common and significant when quick delivery is required and also the cost effectiveness of spinal anaesthesia is more comforting to the patient's relatives as compared with epidural especially in developing countries.[4253] Epidural is more versatile technique as it can be used for labour analgesia and if the need arises operative intervention can be performed with the same catheter. The provision of a prolonged post-operative pain-free period makes this technique a first choice of many parturients. This method also has the advantage of extending the block height if the sensory level shows early regression during the surgical procedure. The increased costs as well as a longer time taken for achieving an adequate block are a few of its main disadvantages.[5354] However, with the addition of adjuvants such as opioids and α-2 agonists, sensory anaesthesia is achieved in a much quicker time and that too with a lower dose of LAs.[37] The combined spinal epidural anaesthesia has the dual advantage of spinal as well as of epidural anaesthesia. It not only produces a rapid and dense block, but equally produces a post-operative pain-free period through top-up doses. The utility of this methodology is very significant especially in high-risk patients such as patients having cardiac disease, diabetes and pre-eclampsia.[55] Though many anaesthesiologists prefer GA for eclampsia patients, graded epidural technique with titration of local anaesthetic dose is equally good in compromising situations. The stable haemodynamics achieved are very essential considering the deranged pathophysiology in pre-eclampsia patients.[56]

Post-partum period

This stage begins after the delivery of placenta and last up to 6 weeks. As far as possible, surgeries should be avoided during the 6 weeks after delivery. The normal physiological parameters are being restored back to the non-pregnant level during these 6 weeks and as such, the responses to anaesthetic interventions can be unpredictable or exaggerated. The most common emergency during immediate post-partum is the high risk of post-partum haemorrhage for which an anaesthesiologist is often called for during surgical intervention.[57] Moreover, many tubal ligation procedures are being performed during this period in developing nations such as India as it ensures maximum patient compliance for the purpose of family planning goals.

The physiological changes resemble almost the early part of the first trimester and have almost similar anaesthetic implications in the background of these changes. Largely, the risk of any surgery is generally reduced as only the maternal body has to bear the brunt. Still there exists a chance for excretion of drugs into the breast milk, which are administered as a part of the treatment regimen.

Post-partum, anatomical changes are distinct, which helps vastly in accomplishment of tubal ligation. The most significant aspect in patients with cardiac disease during this period is the sudden increase in blood volume due to auto-transfusion after delivery, which can precipitate congestive cardiac failure. The rate of oxytocin infusion has to be adjusted and should be given at 60-80 mIU/min as rapid infusion can cause profound lowering of systemic vascular resistance and elevation of pulmonary vascular resistance, which results in decreased cardiac output. Methylergometrine and PGF2-α can cause severe hypertension, tachycardia and increased pulmonary vascular resistance, which can be very hazardous in cardiac patients.

Drugs usage during pregnancy

The Food and Drug Administration (FDA) created the following rating system in 1979 to categorise the potential risk to the fetus for a given drug. Many modifications have been done in the rating system since then, with addition and omission of various drugs depending upon the results of various randomised trials and studies.

Category A: Controlled human studies have demonstrated no foetal risk [Tables 4 and 5].

Table 4

List of common anaesthetic drugs and their classification as per FDA category

Table 5

List of some common drugs, which can be used safely in pregnancy and relevant to anaesthesiologists and intensivists

Category B: Animal studies indicate no foetal risk, but no human studies, or adverse effects in animals, but not in well-controlled human studies.

Category C: No adequate human or animal studies, or adverse foetal effects in animal studies, but no available human data.

Category D: Evidence of foetal risk, but benefits outweigh risks.

Category X: Evidence of foetal risk. Risks outweigh any benefits.

The human embryo is most vulnerable during the first trimester to the teratogenic effects of various drugs.[2] Apart from the teratogenic effects, many of these drugs are responsible for premature labour, abortion and growth retardation. Fortunately most of the anaesthetic and sedative agents are free from teratogenic effects, but that also imply these drugs to be used in a minimal dosage format using the titration effect.[58]

CONCLUSION

Anaesthetic management during pregnancy is altogether a different challenge than administering anaesthesia to non-pregnant females as there are numerous endocrinal, systemic and physiological alterations. Thorough knowledge and understanding of these facts can help in delivering safe anaesthesia services. Whatever procedure is carried out during this period, besides considering the patho-physiological aspects of pregnancy, universal precautions remains the same. It requires a good team effort from all quarters, especially the anaesthesiologist and the obstetrician, to provide a safe atmosphere for both the mother and the foetus.