update in anaesthesia

52 Pages·1998·0.38 MB·English

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A journal for anaesthetists in developing countries
WORLD ANAESTHESIA
EDITORIAL No 9 1998 ISSN 1353-4882
The WHO and UNICEF recently reported that in Contents: No 9
developing countries maternal mortality ratios range l Editorial
from 190 per 100,000 live births in Latin America and l Physiological Changes Associated with
the Caribbean to 870 per 100,000 in Africa. Extremely Pregnancy
high ratios of over 1000 per 100,000 live births are l Anaesthesia for Caesarean Section
found in Eastern and Western Africa, where the UN
l The Role of the Anaesthetist in the
have estimated that up to one of seven women die from
Management of Pre-eclampsia
pregnancy-related causes. The most common causes of
l Interscalene Brachial Plexus Block
death during pregnancy include haemorrhage, abortion,
l Physiology of the Kidney
sepsis and obstructed labour.
l Neuropharmacology - Intracranial
Caesarean section is one of the commonest emergency
Pressure and Cerebral Blood Flow
operations and anaesthetists have a major role in the l Prediction and Management of Difficult
care of the obstetric patient in both theatre and the labour
Tracheal Intubation
suite. This edition of Update reviews aspects of obstetric
l Self Assessment Questions
anaesthesia by authors from Nepal, South Africa and
l Extracts from Journals
USA.
l Practical Techniques in Developing Countries
We also include two basic science articles, including a l Answers to MCQ Questions
self assessment section and a review of some recent
l Letters
publications from international anaesthesia journals.
We are aware that our readership is very varied and we our sister publication (cid:210)World Anaesthesia(cid:211) can both
always appreciate feedback on Update. Constructive be found at our website http://www.nda.ox.ac.uk/
criticism is essential to improve the journal. Update and wfsa
PHYSIOLOGICAL CHANGES ASSOCIATED WITH PREGNANCY
Christopher F. Ciliberto and Gertie F. Marx pressure from the expanding uterus. These
Department of Anaesthesiology, Albert Einstein alterations create unique requirements for the
College of Medicine, Jacobi 1226, 1300 Morris anaesthetic management of the pregnant woman.
Park Avenue, Bronx, New York 10461, USA.
CARDIOVASCULAR SYSTEM
Physiological and anatomical alterations develop The pregnancy-induced changes in the
in many organ systems during the course of cardiovascular system develop primarily to meet
pregnancy and delivery. Early changes are due, in the increased metabolic demands of the mother and
part, to the metabolic demands brought on by the fetus.
fetus, placenta and uterus and, in part, to the
Blood Volume increases progressively from 6-8
increasing levels of pregnancy hormones,
weeks gestation (pregnancy) and reaches a
particularly those of progesterone and oestrogen.
maximum at approximately 32-34 weeks with little
Later changes, starting in mid-pregnancy, are
change thereafter. Most of the added volume of
anatomical in nature and are caused by mechanical
Editors: Drs Iain Wilson, Roger Eltringham Sub Editors: Drs Henry Bulwirwa (Uganda), David Conn,
Mike Dobson, Frank Walters and Mr Mike Yeats Distribution: Dr Ray Sinclair, Department of Anaesthesia, Royal
Cornwall Hospital (Treliske), Truro, Cornwall Designed and Typeset by : Angela Frost
1
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1
2 Update in Anaesthesia
blood is accounted for by an increased capacity of increase in intravascular volume by 300-500 ml of
the uterine, breast, renal, striated muscle and blood from the contracting uterus to the venous
cutaneous vascular systems, with no evidence of system. Following delivery this autotransfusion
circulatory overload in the healthy pregnant woman. compensates for the blood losses and tends to
The increase in plasma volume (40-50%) is further increase cardiac output by 50% of pre-
relatively greater than that of red cell mass (20- delivery values. At this point, stroke volume is
30%) resulting in hemodilution and a decrease in increased while heart rate is slowed.
haemoglobin concentration. Intake of supplemental
Cardiac Size/Position/ECG. There are both size
iron and folic acid is necessary to restore hemoglobin
and position changes which can lead to changes in
levels to normal (12 g/dl). The increased blood
ECG appearance. The heart is enlarged by both
volume serves two purposes. First, it facilitates
chamber dilation and hypertrophy. Dilation across
maternal and fetal exchanges of respiratory gases,
the tricuspid valve can initiate mild regurgitant
nutrients and metabolites. Second, it reduces the
flow causing a normal grade I or II systolic murmur.
impact of maternal blood loss at delivery. Typical
Upward displacement of the diaphragm by the
losses of 300-500 ml for vaginal births and 750-
enlarging uterus causes the heart to shift to the left
1000 ml for Caesarean sections are thus
and anteriorly, so that the apex beat is moved
compensated with the so-called (cid:210)autotransfusion(cid:211)
outward and upward. These changes lead to common
of blood from the contracting uterus.
ECG findings of left axis deviation, sagging ST
Blood Constituents. As mentioned above, red cell segments and frequently inversion or flattening of
mass is increased 20-30%. Leukocyte counts are the T-wave in lead III.
variable during gestation, but usually remain within
Blood Pressure. Systemic arterial pressure is never
the upper limits of normal. Marked elevations,
increased during normal gestation. In fact, by
however, develop during and after parturition
midpregnancy, a slight decrease in diastolic pressure
(delivery). Fibrinogen, as well as total body and
can be recognized. Pulmonary arterial pressure
plasma levels of factors VII, X and XII increase
also maintains a constant level. However, vascular
markedly. The number of platelets also rises, yet
tone is more dependent upon sympathetic control
not above the upper limits of normal. Combined
than in the nonpregnant state, so that hypotension
with a decrease in fibrinolytic activity, these changes
develops more readily and more markedly
tend to prevent excessive bleeding at delivery.
consequent to sympathetic blockade following
Thus, pregnancy is a relatively hypercoagulable
spinal or extradural anaesthesia. Central venous
state, but during pregnancy neither clotting or
and brachial venous pressures remain unchanged
bleeding times are abnormal.
during pregnancy, but femoral venous pressure is
Cardiac Output increases to a similar degree as progressively increased due to mechanical factors.
the blood volume. During the first trimester cardiac
Aortocaval Compression. From mid-pregnancy,
output is 30-40% higher than in the non-pregnant
the enlarged uterus compresses both the inferior
state. Steady rises are shown on Doppler
vena cava and the lower aorta when the patient lies
echocardiography, from an average of 6.7litres/
supine. Obstruction of the inferior vena cava reduces
minute at 8-11weeks to about 8.7litres/minute flow
venous return to the heart leading to a fall in cardiac
at 36-39 weeks; they are due, primarily, to an
output by as much as 24% towards term. In the
increase in stroke volume (35%) and, to a lesser
unanaesthetised state, most women are capable of
extent, to a more rapid heart rate (15%). There is a
compensating for the resultant decrease in stroke
steady reduction in systemic vascular resistance
volume by increasing systemic vascular resistance
(SVR) which contributes towards the hyperdynamic
and heart rate. There are also alternative venous
circulation observed in pregnancy.
pathways, the paravertebral and azygos systems.
During labor, further increases are seen with pain in During anesthesia, however, these compensatory
response to increased catecholamine secretion; this mechanisms are reduced or abolished so that
increase can be blunted with the institution of significant hypotension may rapidly develop.
labour analgesia. Also during labour, there is an
Update in Anaesthesia 3
Obstruction of the lower aorta and its branches RESPIRATORY SYSTEM
causes diminished blood flow to kidneys, Changes within the respiratory system are of great
uteroplacental unit and lower extremities. During significance to the anaesthetist.
the last trimester, maternal kidney function is
Respiratory Tract. Hormonal changes to the
markedly lower in the supine than in the lateral
mucosal vasculature of the respiratory tract lead to
position. Furthermore, the fetus is compromised by
capillary engorgement and swelling of the lining in
insufficient transplacental gas exchange.
the nose, oropharynx, larynx, and trachea.
Venous Distension increases approximately to Symptoms of nasal congestion, voice change and
150% during the course of gestation and the venous upper respiratory tract infection may prevail
ends of capillaries become dilated, causing reduced throughout gestation. These symptoms can be
blood flow. These vascular changes contribute to exacerbated by fluid overload or oedema associated
delayed absorption of subcutaneously or with pregnancy-induced hypertension (PIH) or pre-
intramuscularly injected substances. Distension of eclampsia. In such cases, manipulation of the airway
the extradural veins heightens the risk of vascular can result in profuse bleeding from the nose or
damage during institution of a regional block. The oropharynx; endotracheal intubation can be
increased venous volume within the rigid spinal difficult; and only a smaller than usual endotracheal
canal reduces the volume or capacity of the tube may fit through the larynx. Airway resistance
extradural and intrathecal spaces for local is reduced, probably due to the progesterone-
anaesthetic solutions. This will therefore increase mediated relaxation of the bronchial musculature.
the spread of injected drugs.
Lung Volumes. Upward displacement by the gravid
Clinical Implications. Despite the increased uterus causes a 4 cm elevation of the diaphragm,
workload of the heart during gestation and labour, but total lung capacity decreases only slightly
the healthy woman has no impairment of cardiac because of compensatory increases in the transverse
reserve. In contrast, for the gravida with heart and antero-posterior diameters of the chest, as well
disease and low cardiac reserve, the increase in the as flaring of the ribs. These changes are brought
work of the heart may cause ventricular failure and about by hormonal effects that loosen ligaments.
pulmonary oedema. In these women, further Despite the upward displacement, the diaphragm
increases in cardiac workload during labour must moves with greater excursions during breathing in
be prevented by effective pain relief, optimally the pregnant than in the non-pregnant state. In fact,
provided by extradural or spinal analgesia. Since breathing is more diaphragmatic than thoracic
cardiac output is highest in the immediate during gestation, an advantage during supine
postpartum period, sympathetic blockade should positioning and high regional blockade.
be maintained for several hours after delivery and
From the middle of the second trimester, expiratory
then weaned off slowly.
reserve volume, residual volume and functional
residual volume are progressively decreased, by
TEACHING POINT
approximately 20% at term. Lung compliance is
There is a 30% reduction in volume of local
relatively unaffected, but chest wall compliance is
anaesthetic solution required at term when compared
to the non-pregnant woman, to achieve the same reduced, especially in the lithotomy position.
block.
Ventilation and Respiratory Gases . A progressive
Aortocaval compression and its sequelae must be increase in minute ventilation starts soon after
avoided. No woman in late pregnancy should lie conception and peaks at 50% above normal levels
supine without shifting the uterus off the great around the second trimester. This increase is effected
abdomino-pelvic vessels. During labour, the
by a 40% rise in tidal volume and a 15% rise in
parturient should rest on her side, left or right.
respiratory rate (2-3 breaths/minute). Since dead
During Caesarean section and for other indications
space remains unchanged, alveolar ventilation is
demanding the supine position, the uterus should be
about 70% higher at the end of gestation. Arterial
displaced, usually to the left, by placing a rigid
and alveolar carbon dioxide tensions are decreased
wedge under the right hip and/or tilting the table left
by the increased ventilation. An average PaCO of
side down.
2
4 Update in Anaesthesia
32mmHg (4.3 kPa) and arterial oxygen tension of in pregnancy is justified.
105mmHg (13.7 kPa) persist during most of
Mechanical Changes. The enlarging uterus causes
gestation. The development of alkalosis is
a gradual cephalad displacement of stomach and
forestalled by compensatory decreases in serum
intestines. At term the stomach has attained a
bicarbonate. Only carbon dioxide tensions below
vertical position rather than its normal horizontal
28mmHg (3.73 kPa) will lead to a respiratory
one. These mechanical forces lead to increased
alkalosis.
intragastric pressures as well as a change in the
During labour, ventilation may be further angle of the gastroesophageal junction, which in
accentuated, either voluntarily (Lamaze method of turn tends toward greater oesophageal reflux.
pain control and relaxation) or involuntarily in
Physiological Changes. The hormonal effects on
response to pain and anxiety. Such excessive
the gastrointestinal tract are an issue of debate
hyperventilation results in marked hypocarbia and
among anaesthetists. Relaxation of the lower
severe alkalosis, which can lead to cerebral and
oesophageal sphincter has been described, but there
uteroplacental vasoconstricton and a left shift of
have been differing views about the effect on motility
the oxygen dissociation curve. The latter reduces
of the gastrointestinal tract and the times at which
the release of oxygen from haemoglobin with
it is most prominent. Many believe that there is also
consequent decreased maternal tissue oxygenation
retardation of gastrointestinal motility and gastric
as well as reduced oxygen transfer to the fetus.
emptying, producing increased gastric volume with
Furthermore, episodes of hyperventilation may be
decreased pH, beginning as early as 8-10 weeks of
followed by periods of hypoventilation as the blood
gestation. Recent studies, however, have shed a
carbon dioxide tension (PaCO ) returns to normal.
2 different light on the subject. Measuring peak plasma
This may lead to both maternal and fetal hypoxia.
concentrations of drugs absorbed exclusively in the
Oxygen consumption increases gradually in duodenum in both non-pregnant and pregnant
response to the needs of the growing fetus, volunteers, at different times of gestation, it was
culminating in a rise of at least 20% at term. During shown that peak absorption occurred at the same
labour, oxygen consumption is further increased interval in all women with the exception those in
(up to and over 60%) as a result of the exaggerated labour. This suggests that gastric emptying is
cardiac and respiratory work load. delayed only at the time of delivery.
Clinical Implications. The changes in respiratory
Thus, the raised risk of aspiration is due to an
function have clinical relevance for the
increase of oesophageal reflux and decreased pH of
anesthesiologist. Most importantly, increased
gastric contents. The heightened incidence of
oxygen consumption and the decreased reserve due
difficult endotracheal intubations worsens the
to the reduced functional residual capacity, may
situation.
result in rapid falls in arterial oxygen tension despite
careful maternal positioning and preoxygenation.
Even with short periods of apnea, whether from TEACHING POINT
obstruction of the airway or inhalation of a hypoxic The gravida should be considered a to be a (cid:210)full
mixture of gas, the gravida has little defense against stomach(cid:211) patient with increased risk of
the development of hypoxia. The increased minute aspiration during most of gestation.
ventilation combined with decreased functional
residual capacity hastens inhalation induction or
Pulmonary Aspiration of gastric contents can
changes in depth of anaesthesia when breathing
occur either following vomiting (active) or
spontaneously.
regurgitation (passive). Aspiration of solid material
GASTROINTESTINAL SYSTEM causes atelectasis, obstructive pneumonitis or lung
Since aspiration of gastric contents is an important abscess, while aspiration of acidic gastric contents
cause of maternal morbidity and mortality in results in chemical pneumonitis (Mendelson(cid:213)s
association with anesthesia, an examination of the syndrome). The most serious consequences follow
controversy surrounding gastrointestinal changes aspiration of acidic materials containing particulate
Update in Anaesthesia 5
matter as may follow swallowing certain antacids the lower oesophageal sphincter tone. This is
such as magnesium trisilicate. Clear antacids such especially beneficial in women in labour who have
as sodium citrate (0.3 Mol) or bicarbonate should not been starved and and require emergency surgery.
be used. While the incidence of pulmonary Lastly, histamine H - receptor antagonist the night
2
aspiration of solid food has decreased due to patient before and the morning of delivery may reduce
education, that of gastric acid has remained constant. secretion of hydrochloric acid (ranitidine 150mg
orally).
Clinical Implications. The danger of aspiration is
almost eliminated when regional anaesthesia or METABOLISM
inhalational analgesia is used. During general All metabolic functions are increased during
anaesthesia airway protection by means of a cuffed pregnancy to provide for the demands of fetus,
endotracheal tube is mandatory. Although awake placenta and uterus as well as for the gravida(cid:213)s
intubation is safest, discomfort and the lack of increased basal metabolic rate and oxygen
patient cooperation and discomfort prevent it being consumption. Protein metabolism is enhanced to
the routine method for securing the airway. The supply substrate for maternal and fetal growth. Fat
endotracheal tube is placed immediately following metabolism increases as evidenced by elevation in
loss of consciousness after induction of general all lipid fractions in the blood. Carbohydrate
anesthesia. metabolism, however, demonstrates the most
dramatic changes. Metabolically speaking, pregnant
TEACHING POINT women live in a state of (cid:210)accelerated starvation.(cid:211)
Special precautions should be heeded, even First, nutritional demands of the growing fetus are
when induction to intubation time is expected to met by the intake of glucose and, second, secretion
be brief, to prevent the regurgitation: of insulin in response to glucose is augmented. As
a) supine position with lateral tilt to early as 15 weeks of gestation, maternal blood
minimise any increase in intragastric glucose levels after an overnight fast are
pressure considerably lower than in the nongravid state.
b) preoxygenation prior to induction then Hypoglycaemia. Optimal blood glucose levels in
no positive pressure ventilation prior to pregnant women range between 4.4 to 5.5mmol/1
insertion of the endotracheal tube to (80 to 100mg/dl). In healthy non-pregnant
prevent distention of the stomach with gas individuals, signs of hypoglycaemia usually begin
(rapid sequence induction) when the blood glucose level declines to
approximately 2.2mmol/1 (40mg/dl); in pregnant
c) cricoid pressure (Sellick’s maneouvre)
women, however, hypoglycaemia is defined as a
during induction which is maintained until
concentration below 3.3mmol/1 (60mg/dl).
endotracheal tube placement in the
Hypoglycaemia initiates the release of glucagon,
trachea has been confimed. Cricoid
cortisol and, importantly, catecholamines. In the
pressure should be applied to the cricoid
anaesthetised state, however, these compensatory
cartilage whilst supporting the
mechanisms, particularly the release of epinephrine
back of the neck. This occludes the
(adrenaline), are blocked. Autonomic derangements
oesophagus, thus obstructing the path of
in the form of hypotension and tachycardia tend to
regurgitation.
ensue during high regional blockade or deep general
anaesthesia, which may mask the symptoms and
The acidity and volume of gastric content can be
signs of hypoglycaemia.
reduced by pharmacologic interventions which may
prove invaluable. Most importantly, a nonparticulate RENAL PHYSIOLOGY
oral antacid, 30ml of sodium citrate 0.3 Mol or Renal plasma flow and glomerular filtration rate
bicarbonate, should be given immediately prior to begin to increase progressively during the first
induction of general anesthesia to all women. In trimester. At term, both are 50-60% higher than in
addition, if available, metoclopramide, 10 mg IV, the non-pregnant state. This parallels the increases
should be administered 15 - 30 minutes before in blood volume and cardiac output. The elevations
induction to promote gastric emptying and increase in plasma flow and glomerular filtration result in an
6 Update in Anaesthesia
elevation in creatinine clearance. Blood urea and General Anaesthesia. Induction and changes in
serum creatinine are reduced by 40%. The increase depth of inhalation anaesthesia occur with greater
in glomerular filtration may overwhelm the ability rapidity in pregnant women than in non-pregnant
of the renal tubules to reabsorb leading to glucose subjects. Pregnancy enhances anaesthetic uptake
and protein losses in the urine. Thus, mild glycosuria in two ways. The increase in resting ventilation
(1-10gm/day) and/or proteinuria (to 300mg/day) delivers more agent into the alveoli per unit time,
can occur in normal pregnancy. There is also an while the reduction in functional residual capacity
increase in filtered sodium, but tubular absorption favors rapid replacement of lung gas with the
is increased by an increase in aldosterone secretion, inspired agent. In addition, there is a reduction in
via the renin-angiotensin mechanism (see anaesthetic requirements, with a fall in the minimum
Physiology of the Kidney page24). There is also a alveolar concentrations (MAC) of halogenated
decrease in plasma osmolality. This is a measure of vapors. When measured in ewes MAC was 25-
the osmotic activity of a substance in solution and 40% lower in gravid as compared with nonpregnant
is defined as the number of osmoles in a kilogram animals.
of solvent. In practice it indicates that the plasma
The decreased functional residual capacity has a
concentrations of electrolytes, glucose and urea,
further effect on the management of general
fall if more water than sodium, for example, is
anaesthesia. As referred to earlier, the resultant
retained. Over the whole period of gestation there
reduction in oxygen storage capacity, together with
is retention of 7.5L of water and 900mmol of
the elevated oxygen consumption, leads to an
sodium.
unusually rapid decline in arterial oxygen tension
After the 12th week of gestation, progesterone can in the apnoeic anaesthetised gravida.
induce dilation and atony of the renal calyses and
There are also alterations in the response to
ureters. With advancing gestation, the enlarging
intravenous agents, in particular prolongation of
uterus can compress the ureters as they cross the
their elimination half-lives consequent to the greater
pelvic brim and cause further dilatation by
distribution volume (resulting from the pregnancy-
obstructing flow. These changes may contribute to
induced increase in plasma volume). Thus, the
the frequency of urinary tract infections during
mean elimination half-life for thiopentone in gravid
pregnancy. The effect of postural compression of
women is more than doubled in comparison with
the aortic branches perfusing the kidneys has been
that in nongravid young patients.
discussed.
Serum Cholinesterase. Serum cholinesterase
DRUG RESPONSES
levels fall by 24-28% during the first trimester
The response to anaesthetic and adjuvant drugs is
without a marked change for the remainder of
modified during pregnancy and the early
gestation. However, even lower levels (about 33%
puerperium. The most pertinent alteration is a
reduction) develop during the first 7 postpartum
reduced drug requirement, manifest in both regional
days. The decreased levels of the enzyme are still
and general anaesthesia.
sufficient for normal hydrolysis of clinical doses of
Regional Anaesthesia. From the late first trimester suxamethonium or chloroprocaine during gestation.
to the early puerperium, a smaller dose of local Postpartum, however, approximately 10% of
anaesthetic is required to obtain the desired level of women will be at risk of a prolonged reaction to
spinal or extradural blockade. During the last months suxamethonium.
of gestation, approximately two-thirds of the normal
Clinical Implication. These altered drug responses
dose is adequate. This altered response, which is
must be taken into consideration whenever a patient
due to CSF and hormonal changes and an increase
is pregnant or in the early puerperium.
in volume of the epidural veins, subsides
progressively in the early postpartum period.
Update in Anaesthesia 7
ANAESTHESIA FOR CAESAREAN SECTION
Dr Charles Collins, Consultant Trainer in
Anaesthesia, Health Services Partnership either due to obstetric complications causing
Project International Nepal Fellowship, Nepal significant antepartum haemorrhage or, very
commonly, prolonged labour leading to exhaustion
Dr Anek Gurung, Specialist Anaesthetist, Western
and dehydration. This is particularly noticeable in
Regional Hospital, Pokhara, Nepal
the hot season.
Caesarean section (LSCS) is one of the commonest
The pregnant mother is at greater risk of pulmonary
operations performed in the developing world and
acid aspiration, as regurgitation of acidic stomach
is often carried out in difficult circumstances. As
contents is more likely than in non-pregnant patients.
with any operation, the anaesthetist should first
This can lead to catastrophic aspiration pneumonitis.
think about all the problems that may occur as it is
always better to be prepared for trouble than to be The patient with hypertensive disease of pregnancy
taken by surprise. may have abnormal clotting function and multiple
other complications of this disease.
The problems concern 5 areas:
Risks to the fetus include hypoxia and acidosis if
1. The patients
placental blood flow is reduced. Since maternal
2. The surgery (and the surgeon!)
blood pressure is maintained at the expense (if
3. The drugs (both anaesthetic drugs and any necessary) of placental perfusion, by the time a
takenby the patient) significant drop in maternal blood pressure has
been measured the fetus has already suffered from
4. Equipment
reduced placental perfusion. The general condition
5. The anaesthetist of the fetus should be considered.
1. Problems with the patients What is the state of the fetus preoperatively? How
Caesarean section is often said to be the unique significant is any “fetal distress”? Is there an
situation where the anaesthetist has to deal with 2 obstetric complication, such as cord prolapse, that
patients under the same anaesthetic. The health of puts the fetus at imminent risk and requires the
the baby has to be considered as well as that of the quickest possible intervention? Are there more
mother. than one fetus?
Risks to the mother. Changes in maternal Risks to mother and fetus. Both need to be protected
physiology are described elsewhere in this journal, from the “supine hypotensive syndrome” (aorto-
as are problems associated with hypertensive disease caval compression). This occurs when the maternal
of pregnancy. Any other significant concurrent inferior vena cava and, to a lesser extent, the aorta
disease, such as maternal diabetes or sickle cell are compressed by the gravid uterus if the mother is
disease, will have to be handled in the usual way. allowed to lie on her back.
The important changes affecting anaesthesia are:
2. Problems with the surgery
Pregnant women are at risk of hypoxia. They are Ask yourself the following questions:
more difficult to oxygenate than non-pregnant Who is the surgeon, how experienced, how long
patients due to changes in their respiratory does he expect to take and what incision is planned?
mechanics and they use the oxygen more quickly Are blood and other intravenous fluids available?
because of a higher metabolic rate. This situation Is there a surgical complication such as placenta
can be made worse by other factors. Obesity makes praevia that could cause serious intra-operative
control of the airway more difficult and interstitial haemorrhage ?
fluid retention may make the larynx harder to
Does your surgeon lift the uterus right out of the
visualise for successful intubation.
abdominal cavity after delivery in order to suture
Although fluid retention is a feature of pregnancy, it? (Under regional anaesthesia this is very
a more common problem is the risk of hypovolaemia uncomfortable and is rarely necessary.)
8 Update in Anaesthesia
3. Problems with drugs Is there a range of equipment for difficult intubation:
As with any patient, the pregnant woman may be introducers, a range of laryngoscope blades and
taking drugs for concurrent diseases which have to handles and endotracheal tubes ?
be considered, e.g. steroids, anti diabetic medication.
Is there resuscitation equipment ready for the patient
They may also be taking drugs that can react with
having a regional anaesthetic? What resuscitation
anaesthetic drugs, e.g. antidepressant medication.
equipment is ready for the baby?
With all drugs, beware of the weight of the patient
What sterile needles are available for spinal
and try and weigh her if possible. Do not believe
anaesthesia?
average doses quoted in textbooks but give drugs as
Is there any monitoring equipment available ?
mg/kg. This is particularly important in Asia where,
in the authors’ experience, fully grown women at 5. Problems with the anaesthetist
term may only weigh 35 to 40kg. Finally, you should consider how experienced you
are with any particular technique and how long you
There is a moderate reduction in psuedo-
expect to take. Can you obtain the help of another
cholinesterase in pregnant women compared with
anaesthetist? This is a good policy if you are
the non-pregnant population (at least in Caucasians).
expecting a difficult intubation or other problems.
This is more notable immediately post-partum.
Lastly, and probably as important as anything else,
Although the initial dose of suxamethonium is the
do you have a trained assistant? Do they know how
same, its effect may be prolonged. If suxamethonium
to do cricoid pressure correctly? Are they strong
has not been correctly stored it may not be fully
enough to turn the patient on to her side if you get
effective.
into trouble?
Ketamine causes a rise in blood pressure. It should
Having considered all the potential difficulties,
not be given to mothers with hypertension but is
make a plan for your anaesthetic.
well worth considering if a mother is being
resuscitated from hypovolaemia. Ergometrine,
given to encourage uterine contraction immediately
Plan for Anaesthesia
after delivery, frequently causes nausea and
vomiting. It is better to use oxytocin in the awake Preoperative preparation
patient having a regional or local anaesthetic. Peroperative induction
maintenance
Are all general anaesthesia including emergency
recovery
drugs available?
Postoperative care
Drugs used for the anaesthetic may affect the fetus.
Anaesthetic drugs cross the placenta and therefore
a “deep” anaesthetic will sedate the baby and risk
PREOPERATIVE PREPARATION
birth apnoea. Narcotics and sedatives should not be
Visit the patient , take a history and examine them.
given to the mother prior to delivery. Gallamine
Consider the state of the maternal cardiovascular
crosses the placenta and will affect the fetus. Other
system, whether or not you expect a difficult
neuromuscular blocking agents are safe.
intubation and also the state of the fetus. Give
4. Problems with equipment antacid as described in the table 1. If ranitidine is
What anaesthetic equipment is available? Is there not available, give antacid pre-operatively.
adequate oxygen , either in cylinders or as a
Explain the type of anaesthetic that you plan to use
functioning oxygen concentrator? Is the power
and what the patient can expect to happen before,
supply reliable?
during and after surgery. Try to gain the patient’s,
Does the sucker work and is there a back up and her family’s agreement for what you plan to do.
manually operated sucker? If the patient is at high risk then this should be
explained to the family concerned.
Does the table tilt and is there a suitable wedge
available?
Update in Anaesthesia 9
Table 1 Before starting anaesthesia check the following:
Elective case Ranitidine 150 mg orally l Antacids, sucker, availability of blood,
the night before and oxygen and an assistant who can do cricoid pressure.
90 minutes pre op
l Establish good IV access with a reliable large
bore cannula and start an IV infusion of Normal
Sodium Citrate 30 mls orally
Saline or Ringer’s Lactate (Hartmann’s solution).
immediately pre op
l Place a wedge on the operating table, under
the right side of the patient so that she is tilted to the
Emergency Ranitidine 50 mg IV
left by 15 to 20 degrees.
immediately decision made to
operate l Always have at hand the drugs and equipment
necessary to perform an urgent general anaesthetic
Sodium Citrate 30 mls orally or resuscitation of mother or child. Whatever
immediately pre op technique you start with, you may end up giving a
general anaesthesic.
High risk Ranitidine 150 mg orally 6 hrly
1. Local Anaesthetic (LA)
labour (e.g. Diabetic)
The local anaesthetic infiltration is normally carried
Sodium Citrate 30 mls orally if out by the surgeon. Work out the maximum safe
proceeds to Caesarean section dose of the drug being used and add adrenaline at
the rate of 5 micrograms per ml of LA. This is a 1
Premedication should not be given because it will in 200,000 solution of adrenaline (easily made by
depress the baby’s respiration and conscious level adding 0.1ml of adrenaline 1:1000 to each 20mls of
at birth. If naloxone is available for the baby (or LA).
nalbuphine as a second-best alternative), then
If available give oxygen to the mother until delivery.
pethidine may be given to the mother during labour.
Using a 100mm needle two long bands of skin are
A good alternative to pethidine in labour is to use
infiltrated either side of the proposed incision.
inhalational analgesia, either with a 50/50 mixture
Keep the needle parallel to the skin and beware that
of nitrous oxide and oxygen (Entonox), or with
the abdominal wall is very thin at term. Do not stick
trichloroethylene (Trilene) in air. Trilene is easy to
the needle into the uterus. After incising the skin,
use, cheap and effective. It can be used for analgesia
the rectus sheath is infiltrated. In order to
in labour and other situations, e.g. change of burns
anaesthetise the parietal peritoneum, a further 10mls
dressings, setting of simple fractures. The simplest
of solution is injected under the linea alba, once it
system for delivery is a draw over vapouriser (e.g.
is reached and, lastly, 5mls is injected into the loose
OMV) with some tubing, a face-mask and a one-
visceral peritoneum of the uterus at the point of the
way valve at the patient end. Note that it must never
incision in the lower segment.
be used in the presence of soda lime. Provided
about 1% Trilene is used (half way between max Reassure the patient and explain that after the local
and min on a Cyprane inhaler scale) and the mother anaesthetic has been given, she will still feel certain
holds the mask herself, it is safe. If she begins to sensations of touch. She may experience discomfort
move from analgesia to anaesthesia then she will if the head is well engaged in the pelvis. However,
drop the mask and become fully conscious again. the anaesthetic will prevent her feeling significant
pain.
ANAESTHESIA
Three anaesthetic techniques are possible: Supplementation is a problem because of the
effects on the fetus and the first choice is to give
1. Local infiltration anaesthesia with or without
nothing until the cord is clamped, after which small
supplementation.
doses of narcotic or sedative may be used. Probably
2. Regional anaesthetic
the safest supplementation is nitrous oxide in oxygen
3. General anaesthetic or Trilene in air (+/- oxygen), as described above.
10 Update in Anaesthesia
Ketamine should be used cautiously, in as low a mother may experience considerable
dose as possible, and only intravenously. In discomfort.
analgesic doses of 0.25mg/kg, it has little effect on l It takes time to establish and gives less surgical
the baby and, although it crosses the placenta exposure.
easily, doses up to a total of 1mg/kg can be used.
l It requires experience on the part of the
Full anaesthetic doses of 2mg/kg will sedate the
surgeon.
baby and may cause chest wall rigidity which
It is probably most suitable when a reasonably
complicates resuscitation. If ketamine is used then
diazepam or promethazine should be given to reduce experienced surgeon has limited anaesthetic backup.
the problems of hallucinations on emergence. These 2. Regional anaesthetic blockade
should only be given after the cord has been cut. Either epidural (extradural) or spinal (subarachnoid)
Ketamine also causes contraction of the uterus and blocks may be used. A combined spinal + epidural
should probably be avoided in cases of significant technique is commonly practised in UK which has
fetal distress. Atropine may be needed in some the advantages of a dense subarachnoid block, with
adults with ketamine because of excess salivary the potential for topping up the anaesthetic via the
secretions. epidural if necessary. In addition the epidural may
be used for postoperative analgesia. This combined
Other points with local and regional anaesthesia:
Atropine is also useful in combating the discomfort technique is rarely done in the developing world
and will not be further discussed.
and nausea that some patients feel on surgical
traction on the peritoneum. Epidural anaesthesia is commonly used in developed
countries for analgesia during labour and can
If ergometrine is used to contract the uterus after
therefore easily be used to produce anaesthesia for
delivery it will cause vomiting which may be
Caesarean sections with larger doses of local
awkward to manage in the supine position during
surgery. If it is the only drug available give it very anaesthetic. However, epidurals are technically
more difficult to perform than spinal anaesthesia
slowly intravenously, preferably with the infusion
and require more specialised equipment, which is
running. Oxytocin is better, either in a drip at 10-
20 units in 1000mls running at 2 to 3mls/minute or often not available in the developing world. There
are significant and potentially fatal complications
a 5 to 10 units IV bolus slowly intravenously.
and they require experienced anaesthetists and
NB. if these drugs are mistakenly given prior to
midwives for their safe use.
delivery, constriction of the uterus can be a
The main advantage of epidurals is that they are
catastrophe for the baby. There is no need to
suitable for prolonged use e.g., in labour and for
draw up the oxytocin until it is needed after
delivery of the baby and on checking with the post Caesarean section pain relief. Another
indication for the experienced anaesthetist is as a
surgeon.
choice in patients in poor condition since surgical
The main advantages of local anaesthesia
analgesia can be established slowly with small
infiltration are:
repeated doses of local anaesthetic, thereby
l It is safe, especially for mothers in poor minimising cardiovascular instability. However,
condition and those who are hypotensive. since equipment to perform epidurals is often not
l There is a reduction in bleeding because of available, they are not always a practical technique
the adrenaline. for routine anaesthesia for Caesarean section.
Anaesthesia takes longer to develop compared with
l It is a suitable technique for the single operator
subarachnoid block and is induced by using
/ anaesthetist although any supplementation
increments of either 2% lignocaine with 1:200,000
is best avoided.
adrenaline or 0.5% bupivacaine. Note that 0.75%
l It is inexpensive, requiring minimal resources.
bupivacaine is not recommended for anaesthesia
The disadvantages are: for LSCS. Since epidural anesthesia is not routinely
used in many places it will not be further dealt with
l It is not always a perfect technique and the
here.