Asst.professor in Anaesthesiology,

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HYPOTHYROIDISM AND OBSTETRIC ANAESTHESIA
DR A. Vasukinathan MD DA

• Asst.professor in
  Anaesthesiology,
• Kanyakumari govt.
  medical college,
• 
  Nagercoil.

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• Hypothyroidism is a clinical condition resulting
  from inadequate circulating levels of thyroid
  hormones.
• The prevalance in pregnancy is 0.3.

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OBSTETRIC COMPLICATIONS

• Anaemia
• Pre-eclampsia
• IUGR
• Placental abruption
• PPH
• Fetal Distress during labour

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Causes

• Primary
• Auto immune hypothyroidism (Hashimotos
  Thyroiditis)
• Iatrogenic
• - 131I treatment
• - Thyroidectomy
• - Irradiation therapy of neck for lymphomas
• Iodine deficiency

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• Transient
• Withdrawal of thyroxine treatment in patients
  with intact thyroid
• Sub acute thyroiditis
• Secondary
• Hypopituitarism
• Isolated TSH deficiency
• Hypothalamic disease

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DIAGNOSIS

• Normal T4 in Pregnancy-8-16mg/dl(lt2.8)
• Normal TSH in Pregnancylt10mIU/dl(gt88)
• Primary Hypothyroidism has a low T3 , T4 and a
  raised TSH level.
• Secondary Hypothyroidism has a low T3 , T4 and
  TSH levels

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TREATMENT

• Levothyroxine - 1.5µg/kg (100-150 µg/day) orally
  similar to non pregnant woman no adverse effects
  on fetus.
• TSH measurements are done 2 months after
  initiation of treatment.

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IMPORTANCE TO THE ANAESTHETIST

• General Weight gain ,obesity and its
  complications

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• Cardiovascular
• Earliest clinical manifestations
• Hypodynamic cardiovascular system
• Reduced Heart Rate
• Stroke Volume
• Cardiac Output
• Myocardial contractility
• Increased PVR , BP
• Angina, Cardiac failure, Pericardial effusion,
  Conduction abnormalities.
• Unresponsive Baroreceptor reflexes.

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• Pulmonary reduced surfactant production.
• Ventilatory drive in response to hypoxia and
  hypercarbia is reduced.
• MBC and diffusion capacity are reduced.
• Pleural effusion.

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• Blood Secondary Anemia
• Plasma volume is reduced and circulation rate is
  slow.
• Coagulation abnormalities-Platelet
  dysfunction-reduced clotting factors
• Adrenal Cortex Atrophy with reduced Cortisol
  production.
• Inappropriate ADH secretion- water retention and
  hyponatremia.
• CNS Lethargy, delayed tendon reflexes.
• GIT Delayed gastric emptying, constipation,
  Ileus and ascites.
• Temperature regulation increased susceptibility
  to cold.
• Metabolism Decrease in BMR.
• Musculoskeletal System- abnormal response to
  peripheral nerve stimulator.

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COMPLICATIONS

• Increased sensitivity to anaesthetic drugs
• Secondary to reduced cardiac output,
• Decreased blood volume,
• Abnormal baroreceptor function
• Decreased hepatic metabolism
• Decreased renal excretion.

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Complication related to the airway

• Airway compromise
• Secondary to myxedematous swelling of the upper
  airway
• Macroglossia
• Edematous vocal cords
• Goiter
• The risk of regurgitation and aspiration
• Delayed gastric emptying time

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SYMPTOMS

• Tiredness Weakness
• Dry Skin Feeling
  cold
• Hair loss Poor
  memory
• Constipation Dyspnea
• Hoarseness of voice Menorrhagia
• Paresthesia
• Weight gain with poor appetite
• Difficulty in concentration

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SIGNS

• Dry coarse skin
• Cold peripheral extremities
• Puffy face and feet
• Macroglossia
• Bradycardia
• Hypertension
• Delayed Tendon Reflexes.

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MANAGEMENT OF ANAESTHESIA

• Sensitivity to depressant drugs.
• Hypodynamic cardiovascular system characterized
  by decreased cardiac output due to reduction in
  Heart rate and Stroke Volume.
• Slowed metabolism of drugs particularly opioids.
• Unresponsive baroreceptor reflexes.
• Decreased intravascular fluid volume

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• Impaired Ventilatory response to arterial
  hypoxemia and / or hypoxia.
• Delayed gastric emptying.
• Impaired clearance of free water resulting in
  hyponatremia.
• Hypothermia.
• Anemia.
• Hypoglycemia.
• Primary adrenal insufficiency.

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PRE-OPERATIVE ASSESSMENT

• Clinical assessment of the patient
• Airway assessment
• Hematological as they are usually anemic
• Coagulation Profile
• Cardiovascular and pulmonary Cardiomegaly and
  pleural effusion
• ECG low voltage complexes, ST , T wave
  abnormalities
• Echo for LV function and pericardial effusion
• Lipid Profile
• Thyroid Profile

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Premedication

• Judicious use of opioids - Ventilatory depression
• Thyroxine, the morning dose can be given on the
  day of surgery.
• Cortisol supplement is optional.
• Perioperative Thyroid hormones in IHD or Valvular
  Heart Disease- Controversy.

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ANAESTHESIA - REGIONAL OR GENERAL

• Regional anaesthesia is preferred if the location
  of the surgery permits

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Regional anaesthesia

• Doses of local anaesthetic drugs may be reduced.
• Metabolism of amide local anaesthetics is slow
  leads to development of systemic toxicity.
• Land marks difficult to identify.
• Hemodynamic side effects are exaggerated

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General anaesthesia

• Induction of anaesthesia-
• Ketamine is the ideal induction agent
  theoretically
• Recovery is inconsistent.
• Barbiturates or benzodiazepines may produce
  sudden fall in BP.
• Rapid sequence induction is preferred because of
  delayed gastric emptying.
• Succinyl Choline is the preferred drug for
  intubation.

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Maintenance of anaesthesia

• Nitrous oxide with small doses of a short acting
  opioids and a non depolarizing muscle relaxant
  may be used.
• Pancuronium is the relaxant of choice because of
  its mild sympathomimetic effects.
• Volatile anaesthetics are not recommended because
  of
• 1.Extreme sensitivity.
• 2.Vasodilatation may cause a sudden fall in BP.

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Monitoring

• Early recognition of hypotension, bradycardia,
  and hypothermia.
• 1. Pulse oximetry
• 2. ECG
• 3. NIBP
• 4. CVP
• 5. Temperature

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• Hypotension can be treated with vasopressor
  (ephedrine 2.5-5mg).
• Acute primary adrenal insufficiency
• Hypotension persists despite treatment with
  intravenous fluids and sympathomimetic drugs.
• Maintenance of body temperature
• Increasing the temperature of operating room
• Warming inhaled gases
• Passing intravenous fluids through a blood
  warmer.

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Recovery

• Reversal of muscle relaxants
• Acetyl cholinesterase inhibitor and an anti
  cholinergic agent.
• Removal of ET tube- should be considered only
• When the patient is awake
• Maintaining airway
• Normothermic
• Adequate lung volumes

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DELAYED RECOVERY

• Prolonged effects of anaesthetic drugs
• Extreme sensitivity to the Ventilatory depressant
  effects of opioids.

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Postoperative period

• Prolonged post-operative observation is necessary
• Continuous monitoring of temperature pulse, BP,
  CVP, and oxygen saturation is mandatory.
• Maintaining the airway is also important.

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Myxedematous Coma

• Decompensated hypothyroidism-rare
• Coma
• Hypoventilation
• Hypothermia
• Bradycardia
• Hypotension
• Severe dilutional hyponatremia.

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• Predisposing Factors
• Infection, trauma, cold, CNS depressant drugs,
  and Surgery.
• Treatment
• Medical emergency with a mortality rate of 15- 20
  
• Immediate aggressive treatment.
• Specific Measures
• L-Thyroxine (T4) 300-500µg bolus IV followed by a
  maintenance dose of 50µg / day.
• T3 40µg bolus (slow infusion) followed by a
  maintenance dose of 10-20µg / day.

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• Supportive measures
• Intravenous hydration with a glucose containing
  saline solution.
• Maintenance of Temperature
• Electrolyte imbalance correction.
• Stabilization of the cardiac and pulmonary
  system.
• Aggressive external warming is not recommended
  peripheral vasodilatation, hypotension and cardio
  vascular collapse
• Hemodynamic status and hypothermia usually
  improve within 24 hrs.
• I.V. hydrocortisone 100-300 mg / day is
  prescribed to treat possible adrenal
  insufficiency.

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EMERGENCY SURGERY IN SEVERE HYPOTHYROIDISM

• Possibility of developing severe CVS instability
  intraoperatively and myxedematous coma in the
  post-operative period is high.
• I.V. tri-iodothyronine 25-50µg bolus plus a
  continuous infusion is effective within 6 hours
  with a peak rise of BMR in 36-72 hrs.
• Amrinone, an Inovasodilator may improve
  myocardial contractility since its mechanism of
  action does not depend on beta receptors.
• Corticosteroid coverage.

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Conclusion

• Well-controlled hypothyroidism do not present
  much difficulty
• Sub clinical or untreated hypothyroidism
  presenting as an emergency, are at considerable
  risk.
• Do proper preoperative assessment of the patients
  
• Appropriate treatment to avoid complications in
  the perioperative phase.

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