مخاطبین : رزیدنتهای محترم داخلی و فلوهای محترم غدد
مفید و خلاصه از :
Thyroid function in seriously ill or hospitalized patients —
majority of hospitalized patients have a low serum T3 concentration;
from 15 to 20% of hospitalized patients and up to 50 % of patients in ICU have low serum T4 concentrations (low T4 syndrome).
The serum TSH concentration may also be low
Abnormalities in the T3 concentration have been noted in patients undergoing elective or emergency surgery, independent of the type of anesthesia.
Previously, these patients were thought to be euthyroid and the term “euthyroid sick syndrome” was used to describe the laboratory abnormalities. The term “nonthyroidal illness” is now preferred since experimental data suggest that these patients develop acquired transient central hypothyroidism.
In general, thyroid function should not be assessed in seriously ill patients unless there is a strong suspicion of thyroid dysfunction.
When thyroid dysfunction is suspected in critically ill patients, measurement of serum TSH alone is not appropriate for the evaluation of thyroid function. Instead, measurement of TSH, total T4, free T4, T3, and sometimes reverse T3 is necessary.
Is preoperative measurement of TSH necessary? —
Despite the relatively high prevalence of thyroid disease in the general population, we believe there is no need to screen for thyroid disease during the preoperative medical consultation.
However, if the history and physical examination are suggestive of thyroid disease, it is reasonable to try to make the diagnosis since it can have effects upon perioperative management.
For patients with known thyroid disease taking thyroid medication, monitoring of thyroid function on at least an annual basis is part of routine care.
HYPOTHYROIDISM — Hypothyroidism affects many bodily systems that might influence perioperative outcome :
• The systemic hypometabolism that is associated with hypothyroidism results in a decrease in cardiac output that is mediated by reductions in heart rate and contractility.
• Hypoventilation occurs because of respiratory muscle weakness and reduced pulmonary responses to hypoxia and hypercapnia.
• Decreased gut motility results in constipation.
• A variety of metabolic abnormalities can occur in hypothyroidism, including hyponatremia due to a reduction in free water clearance, reversible increases in serum creatinine, and reduced clearance of some drugs (eg, antiepileptics, anticoagulants, hypnotics, and opioids).
• Reduced clearance of vitamin K-dependent clotting factors, however, results in higher warfarin requirements during hypothyroidism, and falling requirements during treatment with thyroid hormone.
• Patients with hypothyroidism have a decrease in red blood cell mass and a normochromic, normocytic anemia.
Surgical outcomes —
undiagnosed patients with hypothyroidism : intraoperative hypotension, cardiovascular collapse, and extreme sensitivity to opioids, sedatives, myxedema coma
The hallmarks of myxedema coma are decreased mental status and hypothermia, but hypotension, bradycardia, hyponatremia, hypoglycemia, and hypoventilation are often present as well.
There are few data on surgical outcomes in subclinical hypothyroid patients.
In a prospective study comparing postoperative outcomes (after coronary artery bypass grafting) in patients with known preoperative subclinical hypothyroidism and euthyroid patients, there were no significant differences in major adverse cardiovascular events or other outcomes (wound problems, mediastinitis, leg infection, respiratory complications)]. Similar results were reported in a study of outcomes after percutaneous transluminal coronary angioplasty .
management of patients with recently diagnosed hypothyroidism who require surgery :
A useful definition of severe hypothyroidism includes patients with myxedema coma, with severe clinical symptoms of chronic hypothyroidism such as altered mentation, pericardial effusion, or heart failure, or those with very low levels of total thyroxine (eg, less than 1.0 mcg/dL) or free thyroxine (eg, less than 0.5 ng/dL)
All other patients with overt hypothyroidism (elevated serum TSH, low free thyroxine) can be treated as having moderate disease.
Subclinical hypothyroidism is , by definition, mild disease.
Subclinical hypothyroidism —
Based upon the studies in patients undergoing CABG and PTCA described above , we suggest not postponing surgery in patients with subclinical hypothyroidism (elevated serum TSH, normal free T4).
Moderate (overt) hypothyroidism —
we suggest that patients with moderate overt hypothyroidism undergo urgent or emergent surgery without delay, with the knowledge that minor perioperative complications might develop.
On the other hand, it is prudent to postpone surgery until the euthyroid state is restored when hypothyroidism is discovered in a patient being evaluated for elective surgery.
When a diagnosis of moderate hypothyroidism is made preoperatively and surgery cannot be postponed , we suggest initiating thyroid hormone replacement therapy as soon as the diagnosis is made.
Generally, young patients are started on close to full replacement doses of thyroxine (T4, 1.6 mcg/kg), while elderly patients or patients with cardiopulmonary disease are started on 25 to 50 mcg daily with an increase in dose every two to six weeks.
Severe hypothyroidism —
these patients should be considered high risk and surgery should be delayed until hypothyroidism has been treated.
If emergency surgery must be performed in a patient with severe hypothyroidism and there is concern about existing or precipitating myxedema coma , patients should be treated with both T3 and T4 to rapidly normalize thyroid function.
As an example, T4 is given in a loading dose of 200 to 300 mcg IV followed by 50 mcg daily. T3 is given simultaneously in a dose of 5 to 20 mcg IV followed by 2.5 to 10 mcg every 8 hours depending upon the patient’s age and coexistent cardiac risk factors.
Rarely, Addison’s disease will be present in a patient with primary hypothyroidism due to Hashimoto’s thyroiditis.
In addition, patients with central (secondary) hypothyroidism may have inadequate pituitary adrenal reserve as euthyroidism is restored.
If the status of the pituitary adrenal axis is uncertain and deficiency is considered likely, patients should be given stress doses of steroid until the integrity of the axis is ascertained.
Use of an arterial line and Swan-Ganz catheter should be considered cardiopulmonary disease exists.
In the postoperative period, the patient’s fluid and electrolyte status, especially the serum sodium, will need to be followed closely.
In addition, a high index of suspicion for the development of an ileus, neuropsychiatric symptoms, and an infectious process without the presence of a fever is required.
Suspected hypothyroidism —
When thyroid dysfunction is suspected in critically ill patients, measurement of TSH, total T4, free T4, T3, and sometimes reverse T3 is necessary.
Patients with severe nonthyroidal illness may have transient central hypothyroidism, and in these patients, it may be difficult to distinguish nonthyroidal illness from true central hypothyroidism, particularly in patients with a history of hypothalamic or pituitary disease.
In this setting, nonurgent surgeries should be postponed and clinical status and thyroid function tests (TSH, free T4) should be monitored every 4-6 weeks.
In patients with transient central hypothyroidism due to nonthyroidal illness, thyroid tests should return to normal, whereas the thyroid test abnormalities will persist in patients with true central hypothyroidism
If the diagnosis of hypothyroidism is in doubt in a critically ill patient (because of the difficulty assessing thyroid function in this population) and surgery cannot be postponed, we treat with thyroid hormone replacement in the preoperative and perioperative period if there is clinical evidence to suggest a diagnosis of hypothyroidism (eg, bradycardia and hypothermia along with slow mentation, puffy face, a possible personal or strong family history of thyroid disease, or personal history of hypothalamic or pituitary disease or cranial irradiation).
In the absence of suspected myxedema coma, repletion should be cautious, beginning with approximately half the expected full replacement dose of thyroxine (0.8 mcg/kg for young patients and 25 to 50 mcg daily for the elderly or patients with cardiopulmonary disease).
Cardiovascular surgery —
Patients with hypothyroidism who are scheduled to undergo cardiovascular interventions or surgery require special consideration.
The risk of precipitating or worsening unstable coronary syndromes with thyroid hormones conflicts with the concern that untreated hypothyroidism might worsen heart failure or hypotension in the cardiac surgical patient.
no adverse outcomes in cardiac patients with mild to moderate hypothyroidism who had cardiac surgery or catheterization without thyroid replacement
Angina is not an absolute contraindication to thyroid hormone replacement if the patient has symptomatic hypothyroidism.
Some patients will experience improvement in their angina symptoms with therapy
Thus, angina may improve and it does not often first appear during T4 replacement therapy.
Presently, most patients with angina have coronary artery revascularization first and T4 is prescribed afterwards
In patients with angina treated medically, the dose of T4 should begin with 25 micrograms/day and is increased 25 micrograms every 2-6 weeks, depending upon response.
Patients receiving chronic T4 therapy who undergo surgery and are unable to eat for several days do not need to be given T4 parenterally. If oral intake cannot be resumed in five to seven days, then T4 should be given intravenously or intramuscularly.
The dose should be approximately 70 to 80 percent of the patient’s usual oral dose because that is about the fraction of oral T4 that is absorbed. We typically give 80 percent
Atrial fibrillation occurs in about 8 percent of patients with hyperthyroidism and is more common in elderly patients .
• Even subclinical hyperthyroidism is associated with increased rates of atrial ectopy and a threefold increased risk of atrial fibrillation.
• Weight loss
In patients with untreated or poorly controlled hyperthyroidism, an acute event such as surgery can precipitate thyroid storm, a potentially life-threatening condition
Thus, all elective surgeries should be postponed in patients with newly discovered overt hyperthyroidism until the patient has achieved adequate control of their thyroid condition (usually 3-8 weeks
In our experience, patients with subclinical hyperthyroidism (low TSH, normal free T4 and T3) can typically proceed with elective surgeries.
Unless contraindicated, we typically administer a beta blocker preoperatively to older patients (>50 years) or younger patients with cardiovascular disease, and taper after recovery.
Preoperative preparation for urgent or emergent surgery IN overt hyperthyroidism —
require preoperative preparation, typically with beta blockers and thionamides.
If hyperthyroidism is severe and the need for surgery is urgent, we also add potassium iodide solution (SSKI, one to five drops three times daily) one hour after thionamides.
Extreme caution is necessary before administering SSKI to a patient with known or suspected toxic nodular goiter since iodine, in the absence of a thionamide to block organification, may exacerbate the hyperthyroidism.
Patients with toxic nodular goiter who are intolerant or unable to take thionamides should be pretreated with beta blockers alone,
whereas patients with Graves’ hyperthyroidism who are allergic to or are intolerant of thionamides can be treated with the combination of beta blockers and iodine.
In the preoperative period, the hyperthyroid patient requiring urgent surgery should be evaluated for possible cardiopulmonary disease and all efforts should be focused upon optimizing the patient’s condition.
Use of an arterial line and Swan-Ganz catheter should be considered if cardiopulmonary disease exists.
Beta blockers —
beta blockers are as effective as a thionamide for preoperative preparation of the hyperthyroid patient
in the absence of contraindications, we administer a beta blocker preoperatively to patients with overt hyperthyroidism undergoing nonthyroid surgery.
The longer acting beta blockers (eg, atenolol) are preferred in patients who are candidates for therapy because an oral dose taken one hour before surgery will usually maintain adequate beta blockade until the patient is able to take oral medications postoperatively
We typically start with atenolol 25 to 50 mg daily and increase the dose as needed to maintain the pulse rate below 80 beats/minute; up to 200 mg daily may be needed for the symptomatic treatment of hyperthyroidism and control of tachycardia.
Beta blockers should be continued until the patient’s thyroid disease is under control. Intravenous propranolol (0.5 to 1 mg over 10 minutes followed by 1 to 2 mg over 10 minutes every few hours) can be used to control fever, hypertension, and tachycardia intraoperatively .
Patients with relative contraindications to beta blockade may better tolerate beta 1-selective agents, such as atenolol or metoprolol, although even these drugs cannot be considered completely safe in patients with asthma or chronic obstructive pulmonary disease.
Calcium channel blockers can also be used for rate control in patients in whom beta blockers are contraindicated.
Thionamides and iodine —
thionamides should be initiated with the aim of controlling hyperthyroidism in the postoperative period.
Methimazole (10 mg two to three times daily or 20 to 30 mg once daily) is usually preferred to propylthiouracil (PTU), except during pregnancy, because of its longer duration of action (allowing for single daily dosing) and a lesser degree of toxicity.
PTU (100 to 150 mg every 6-8 hours) is also preferred by some clinicians for the initial treatment of thyroid storm since it reduces T4-to-T3 conversion.
we suggest adding iodine (potassium iodide solution, SSKI, one to five drops three times daily) at least one hour after thionamides are administered, if hyperthyroidism is severe and the need for surgery is urgent.
Iodine blocks release of T4 and T3 from the gland and thereby shortens the time to achieving a euthyroid state
it can be started 10 days preoperatively for urgent procedures that are scheduled more than 10 days in the future, but which cannot be delayed until the patient is chemically euthyroid following a thionamide.
Iopanoic acid (which is also rich in iodine) blocks both release of T4 and T3 from the gland and T4-to-T3 conversion,
Iodine and iopanoic acid should not be used as primary therapy (without thionamides) in patients with toxic nodular goiter because the iodine load can exacerbate the hyperthyroidism.
Patients who cannot take oral medications postoperatively will need rectal administration of thionamides, which should be ordered well in advance from the pharmacy
Patients with toxic nodular goiter who are intolerant or unable to take thionamides should be pretreated with beta blockers alone.
In contrast, in patients with Graves’ disease, exogenous iodine is unlikely to exacerbate hyperthyroidism by acting as substrate.
Thus, for patients with Graves’ hyperthyroidism who are allergic to or are intolerant of thionamides, the combination of beta blockers and iodine can be used for preoperative preparation.
Intraoperative and postoperative concerns —
In the operative and postoperative period, particular attention should be focused upon the patient’s cardiac status and the patient should be monitored for the possible development of arrhythmias, cardiac ischemia, and congestive heart failure
Thyroid storm —
usually occurs during surgery or in the first 18 hours after the procedure. The mortality rate for patients with thyroid storm can be as high as 40 percent.
Clinical features of thyroid storm include :
• Cardiovascular symptoms such as tachycardia to rates that can exceed 140 beats/minute, along with CHF in many patients
• Hyperpyrexia to 104 to 106ºF
• Agitation, delirium, psychosis, stupor, or coma
• Severe nausea, vomiting, and/or diarrhea, and hepatic failure with jaundice