CHALLENGES IN

CONJOINT TWINS : ANAESTHETIC PERSPECTIVE

DrVarun Singla

PGIMER, Chandigarh

HISTORY

The most popular conjoint twins were

Chang and Eng Bunker born in Siam in

1811. (Siamese twins)

1st successful seperation of conjoint twins

was performed in 1689 by Konig.

EMBRYOLOGY

Conjoint twins monochorionic

monoamniotic twins

Incomplete embryonic division occurs

late at around day 13-14 of conception.

Chorion, amnion and embryonic disc

have already formed by that time.

Kuafman MH. The emryology of conjoint twins. Childs Nerv Syst. 2004

Theories for Conjoint twinning

The FISSION theory

◦ Well established

◦ Numerous studies

The FUSION theory

◦ Animal model+ study of >1800 reported

cases of conjoint twins

◦ Fusion – ventral or dorsal : at sites of absence

of ectoderm

Spencer : Theoretical and analytical embryology of conjoint twins. Clin Anat 2000

EPIDEMIOLOGY

Very rare

1 in 50,000 to 100,000 births

Indian incidence (1 in 50,000)

Twinning is more common in Indian and

African populations

Female: Male = 3:1

Possible etiologic factors - Chronic

malnutrition and intra-uterine hypoxia

TYPES

Spencer’s embryological classification*◦ Ventral union (87%) Rostral (48%)

Cephalopagus( 11%, top of head to umbilicus)

Thoracopagus (19%, conjoined heart)

Omphalopagus (18%, including lower thorax)

Caudal (11%)

Ischiopagus (lower abdomen and genitourinary system)

Lateral (28%)

Parapagus (pelvis and variable trunk)

◦ Dorsal union (13%) Craniopagus (5%, cranial vault)

Rachipagus (2%, vertebral column)

Pyopagus (6%, sacrum)

*Adapted from Spencer

Can conjoint twins be separated?

Only in the last 30 years, has separation

techniques become increasingly

sophisticated.

The success of surgery depends on

◦ Where the twins are joined.

◦ How many organs are shared

◦ Experience and skill of the surgical team

Most cases of separation are extremely

risky and life-threatening.

The Seo classification of conjoined

heart and surgical seperability

Type Degree of fusion Seperability

I No significant fusion Easy

II Fusion of the great

vessels

Easy

III Atrial fusion Possible

IIIa Mirror image right atrial

fusion

Possible

IIIb Other type of atrial

fusion

Possible

IV Atrioventricular fusion Not possible

V Single heart in one of

the twins

Not possible

Investigations

Choice of investigation will depend on the area of union.

Thoraco-omphalopagus twins:◦ Essential investigations – ECHO, ECG & MRI.

◦ Cardiac catheterization

◦ CT, USG & HIDA scan for liver involvement.

◦ Where the livers are fused, it is important to document presence of separate gall bladders and hepatic veins.

◦ Not possible to define biliary anatomy before seperation , should be addressed during the procedure.

◦ Gastrointestinal contrast studies and angiography – have not been helpful.

Craniopagus

◦ MRI and cerebral angiography- cerebral

vascular architecture.

Hormonal assay – adrenal and thyroid

function( independent and optimal)

Angiographic or radioisotopic imaging of

the cross-circulation (definitive) – to be

assessed before separation procedure.

ANAESTHETIC MANAGEMENT

Anaesthiosologists, team and equipment.

Planning

Rehearsel

Positioning

Induction

Airway management

Monitoring

Fluid management

Pharmacology

Mechanical ventilation

Surgical counterparts

Post- operative care

Planning & Rehearsel

Multidisciplinary team approach

Two sets of anaesthesiologists, team, equipment and drugs.

Discussion about the transport, positioning, airway management, crossing of drugs and possible hemodynamic changes.

Minimal personnel & equipments, their placement and movement inside the OR to avoid overcrowding.

Rehearsel of the parts to be played by each member of the anaesthesia team to avoid confusion & mistakes on the day of surgery.

Involvement of parents in all steps of planning.

Positioning

Primary concern - requires not only preoperative planning but also innovation.

Synchronized lifting

Proper padding and covering (prevent injury and hypothermia)

“Y” shaped position – thoraces moved as far away from each other as possible (during airway management).

Slight lateral decubitus position- avoids compromise of pulmonary mechanics from the weight of the overlying twin with supine positioning.

Hypertension in one twin due to circulatory crossover (shunting of blood from the other twin) – pharmacological treatment of hypertension in one twin could be disastrous for the other twin with low normal arterial pressure. Hence, physiological methods of lowering arterial pressure by using gravity to influence the shunting of blood has been advised.

Induction

Concurrent anaesthetic depression of the other twin on i.vinduction of one twin, when significant cross-circulation, necessitates facemask ventilation of other twin while intubating the first.

Sequential induction,

when insignificant cross-circulation, avoids the need to ventilate one twin while intubating the other & drug dosage is based on each individual twin weight.

Concurrent vs sequential induction

(depending on cross-circulation)

Airway Management

Conventional direct laryngoscopy –technically unfavourable due to poor visualization (ETT blocking the limited direct line of site) and face-to-face neonate positioning.

Fibreoptic intubation – time consuming & technically difficult as the tongue and hypopharynx are not retracted (however, permits excellent diagnostic and therapeutic airway evaluation in intubated conjoint twins).

Mair & mair reported the use of SAVI (rigid Seldinger-assisted videotelescopicintubation) technique with the advantage of unobstructed airway view as the telescope precedes the ETT.

Specially constructed plastic seats have been used with twins in the upright position allowing slight rotation and hyperextension of the infant heads.

For thoracopagus twins, lateral position with slight twisting of the head can lead to reasonably normal intubating position.

Monitoring

Essential monitoring – ECG, pulse oximetry, capnography, urine output, arterial and central venous catheters.

Regular blood gas analyses to be undertaken throughout the procedure.

All the monitoring cables and i.v lines should be colour-coded to avoid confusion.

BIS monitoring for quick identification of cross-circulation (intra-operative).◦ Hard to obtain & accuracy questionable in

neonates

Pharmacology

All drugs and intravenous fluids to be calculated on a combined weight basis. (if insignificant cross-circulation, drug dosages based on each twin weight)

Cross-circulation drugs given intravenously have an altered and unpredictable effect.

Cross-circulation found to be more in thoracopagusand craniopagus twins

Estimation of circulatory mixing (cardiac output percentage exchanged) useful to help calculate drug dosage and fluid replacement.

Reduced incremental doses should be titrated against response, minimize the dangers of compounding drug effects in one twin.

Degree of cross-circulation is dynamic dependent on both twins’ relative SVR.

Mechanical ventialtion

Sequential ventilation vs concurrent ventilation

Sequential ventilation – precise timing of ventilatory phases so that the inspiratoryphase of one twin coincides with the expiratory phase of the other (shared diaphragm).

Concurrent ventilation – inspiratory and expiratory phases of both the twins coincide with each other (separate diaphragm)

Disparity between ETCO2 of two twins

can be due to difference in compliance

and resistance of lungs, cross-circulation

(different blood levels of muscle relaxant)

and associated congenital heart diseases.

Surgery

Critical steps – hepatobiliary seperation

Clamping & separation of vascular shunts

and cross-circulation early during

separation surgery prevent hypovolemic

shock from ‘stealing’ of blood through the

shared vessels.

Intra-op problems

Unusual position of twins

Prolonged operation

Over-crowding

Difficult access

Intra-op complications

Massive blood loss

Hypotension

Hypokalemia, hypocalcemia

ETT & intravenous line dislodgement

Hypoxia and hypercarbia

Acidosis

Hypothermia

Post-op care

Following prolonged operative procedures, it is necessary to electively paralyze and mechanically ventilate for 48 to 72 hours.

Shift to ICU, meticulous monitoring with particular attention to cardiac underperformance (poor cardiac output).

The critical period for conjoined twins is 3-4 days after surgery.

Fluid and electrolyte replacement should be accurately administered as there will be huge losses when large prosthetic closure has been used.

Strict infectious precautions must be exercised to avoid sepsis, particularly when there are large skin defects.

Risk of accidental decannulation (face-to-face position) – ties can be placed around neck as well as around axilla for added security.

Survival & Outcome

Survival rare when there is cardiac or cerebral fusion

Hoyle et al analyzed all attempts at surgical seperation until 1987 & found:

◦ Surgical seperation attempted on 167 occasions

◦ Overall survival – 64%

◦ Mortality among various subgroups: Thorac(51%), cranio(48%) and omphalo(32%). Mortality with ischio(19%) and pyo(23%) was lower.

◦ Moratlity 70% for emergent and 20% for elective procedures

Hoyle RM. Surgical seperation of conjoint twins. Surg Gynecol Obstet. 1990

The critical factors, which have resulted in

improvements in surgical outcomes, have

been review of experience, improvements

in the accuracy of radiology imaging

technology, and advancements in surgical

techniques and anaesthesia.

Intensive rehabilitation is needed in most

twins because of the malformation and

position of their spines.

Routine procedures

Diagnostic studies like CT, MRI, TEE(due to poor window for TTE), MRA, cardiac catheterization with angiography are commonly performed before separation procedure.

GA vs Sedation??

GA prefered over sedation because of the long duration of studies and need for prolonged breath-holding during image acquisition.

Sedation has been associated with hypoxia in high-risk children during MRI & CT scan.

ETHICAL ISSUES

Whether to sacrifice one for the other??

Consent authority

Accepted operative risks

Post-operative quality of life

Societal values, legal issues, institution

Wishes of the parent

Loose ends

Is conjoint status more physiological than seperation??◦ Able to both cooperate and individualate as they

grow older

◦ Immediate seperation advised when one twin’s health status threatens the other’s survival, or abnormalities threaten the progress of one or both twins.

Timing of surgery◦ Early – better as less scarring (skulls will not have

hardened in craniopagus), best chance for psychological well-being.

◦ Late(>12 months) – seperation anxiety

THANK YOU