MANAGEMENT OF CYANOTIC SPELLS
Dr.Shashikant Dewangan
Definition-
Cyanotic spell is also known as ‘tet’ spell or hypercyanotic spell. This is a sudden onset, occasionally progressive event seen in infants with Tetralogy of Fallots. It is associated with progressive cyanosis, hyperpnea (increased rate and depth of breathing) and disappearance of heart murmur. If not treated in time it may ultimately lead to altered sensorium, neurological complications and death.
Other cardiac causes of cyanotic spells-(A) Tricuspid atresia with pulmonary stenosis
(B) Transposition of Great arteries with pulmonary stenosis
(C) Single ventricle physiology with PS or pulmonary atresia.
Mechanism of Cyanotic spells-
?Spasm of RVOT,Anxiety,Crying
Pathophysiology-
In a typical case of Tetralogy of Fallot the pressures in the right ventricle and left ventricle are equal. Hence the level of cyanosis and onset of cyanotic spell is determined the systemic vascular resistance and the level of pulmonary stenosis component. In case of mild pulmonary stenosis the right ventricular pressures are usually less than the left ventricle and hence the shunt is usually left to right. However, if the pulmonary stenosis is severe (due to any of the causes described later) then the right ventricular after load becomes high and hence the right ventricular pressures become high. If the systemic vascular resistance is low (which is usually the case in TOF with cyanotic spells) then the shunt flow becomes right to left. This results in progressive cyanosis. Low arterial pO2s lead to stimulation of the carotid receptors and the brain stem nuclei respectively which then leads to increased rate and depth of breathing which further increases the venous return to the right side of the heart and further right to left shunt of deoxygenated blood, thus leading to a vicious cycle. If not broken then it would ultimately lead to death.
Certain theories have also been postulated as possible explanation for the cause of cyanotic spells. These theories have basically compared the onset of cyanotic spells to exercise in normal individuals where there is fall in systemic arterial oxygen saturation during exercise and which reverses once exercise stops. In cyanotic spells this process of low systemic oxygen saturation continues and ultimately leads to progressive metabolic acidosis. These theories are:
a) Woods et al (1) - Postulated that hypoxemic spells are caused by spasm of the infundibulum of the right ventricle which precipitates a cycle of progressively increasing right to left shunting and metabolic acidosis.
b) Surge in Catecholamine release leads to increased myocardial contractility and infundibular stenosis. (Both these theories don’t explain the cause of cyanotic spells in patients with TOF with Pulmonary atresia)c) Guntheroth et al (1) – episodes of paroxysmal hyperpnea are the cause rather than the effect of cyanotic spells. Hyperpnea increases the systemic venous return leading to right to left shunt as well as oxygen consumption through increase work of breathing.
d) Kothari et al (1) – argued against the commonly held views mentioned above and suggested the role of stimulation of mechanoreceptors in the right ventricle to be the cause of spells.
Increased contractility (due to catecholamine) and decreased right ventricular size (due to various factors) can trigger a reflex resulting in hyperventilation, some peripheral vasodilation without bradycardia, and this may initiate a spell. This mechanism he argued, explains most of the precipitating events and many other issues about cyanotic spells more satisfactorily.PEAK AGE GROUP- 2-4 months
CLINICAL MANIFESTATIONS-
The spells occur most frequently in the morning or initially awakening or after episode of vigorous crying.The infant becomes hyperpneic and restless ,cyanosis increases and gasping respiration ensues,and syncope may follow.The spells may last from a few minutes to a few hours but are rarely fatal.The onset is usually spontaneous and unpredictable.Infants who are mildly cyanotic at rest are often more prone to the development of hypoxic spells because they have not acquired the homeostatic mechanism to tolerate rapid lowering of arterial oxygen saturation.
MANAGEMENT OF HYPOXEMIC SPELLS -
A) Knee chest position-.Placment of the infant on the abdomen in knee-chest position while making certain that infant’s clothing is not to constrictive(4). Three mechanisms may be involved(3).
· First, reduction of systemic venous return by trapping venous blood in the lower extremities reduces right to left shunt at the ventricular level (evidenced by reduced arterial lactate levels)
· Second,reduced arterial blood flow to the legs reduces venous wash out from the leg muscles.
· Third ,squatting may also increase SVR a known mechanism to reduce right to left ventricular shunt.
Calming and holding the infant in a knee-chest position may abort progression of an early spells.If the child is very agitated it is difficult to achieve to knee-chest position.In this situation it is favourable to hold the child in parents shoulder with knees bent and oxgen is administered by another person from behind.
B) Oxygen- Oxygen to improve oxygenation. It is better given in nebulized form .
C) Morphine- Depresses respiratory center→abolishes hyperpnea→ decreases Systemic Venous Return. While giving this, facilities for ventilation should be available.
D) Inj Metoprolol- 0.1mg/kg over 5 min, repeat every 5 min to max 3 doses , then start infusion 1-5 mcg/kg/min. The mode of action of metoprolol is similar to Propranolol. Another short acting B-blocker that can be used is Inj Esmolol(0.5mg/kg over 1 min then 50mcg/kg/min over 4 min.
E) Propanolol- 0.1-0.2 mg/kg intravenously over 5 min. Reduces dynamic RV outflow obstruction and slow the heart rate thereby decreasing R→L shunting.More important propanolol may increase Systemic Vascular Resistance by antagonizing the vasodilating effects of β2 adrenergic stimulation.
Propanolol reduces platlet aggregation and propanolol also shift the oxyhemoglobin dissociation curve to the right thereby helping in cyanotic spells.(6)
F) Ketamine- 0.25- 1.0 mg/kg. IV or IM→ has dual benefit causes sedation and ↑ SVR(3).
G) Phenylephrine Hydrochloride- 0.01 mg/kg IV (slowly) or 0.1 mg/kg SC or IM (↑ SVR – dose to be titrated to BP response).
H) Methoxamine- 0.10mg/kg IV over 5-10 min. Leads to ↑ Systemic Vascular Resistance.
I) IV fluids- preferably initially as bolus of 10-20cc/kg which may be increased to 60cc/kg. Bolus fluid should be isotonic saline or colloid. Extra volume can be given in cyanotic spell as the physiology is not inductive to CCF and also because of a restrictive RV physiology.
J) Inj NaHCO3-(1-2 meq/kg intravenously slowly). To correct metabolic acidosis(MUST BE GIVEN)thereby eliminates the respiratory center –stimulating effects of acidosis.
K) Transfuse PRBC’s- 5-10 ml / kg IV over 5 hrs.
L) Correct Tachyarrhythmia- Improve diastolic filling and cardiac output.
M)Premature attempts to obtain blood samples may cause further agitation and counterproductive and should be avoided.
Long Term Management –
Medical-
1.It is important to educate parents to recognize the spell and know what to do.
2.Oral propanolol therapy ,0.5-1.5 mg/kg every 6 hours,is used to prevent hypoxic spells(4).Propanolol effectively abolishes spells for at least 3 months in 80% patients(4).
3.Maintenance of good dental hygiene and practice of antibiotic prophylaxis against SBE are important.
4.Ballon dilatation of the right ventricular outflow tract and pulmonary valve has been attempted to delay repair for several months.
5.A relative iron deficiency state should be detected and treated.Iron deficient children are more susceptible to cerebrovascular complications.Hemoglobin and hematocrit values are usually normal so RBC indices and peripheral smear examination should be done.
Surgical-
Palliative Shunt Procedures-
Shunt procedures are performed to increase pulmonary blood flow-
Indications-
1. Neonates with TOF and pulmonary atresia
2. Infants with hypoplastic pulmonary annulus
3. Infants younger than 3-4 months with medically unmanageable hypoxic spells
4. Infants weighing less than 2.5 kg
A. Classic Blalock-Taussing shunt-(SA-PA)-Usually performed for infants older than 3 months because the shunt is often thrombosed in younger infants.
B. Modified Blalock-Taussing shunt-A Gore-Tax interposition is placed between the subclavian artery and the ipsilateral PA.The surgical mortality rate is less than 1%.
C. Potts operation-anastomosed between the descending aorta and left pulmonary artery.No longer recommended because it may result in heart failure and pulmonary hypertension.
D. Waterson Shunt-anastomosed between ascending aorta and right PA.
Complications include CHF,Pulmonary hypertension and kinking of PA at the site of anastomosis.
Complete Repair Surgery-
Indications-
1. Oxygen saturation less than 75 to 80%.
2. Occurrence of hypoxic spell
3. Mildly cyanotic infants who have had previous shunt surgery
4. Asymptomatic children with coronary artery anomalies.
Timing-
Symptomatic infants may have primary repair at any time after 3-4 months.Most centers prefer primary elective repair by 1 to 2years of age .
Procedure- Total repair of defect is carried out under cardiopulmonary bypass,circulatory arrest and hypothermia.The procedure include –
· Patch closure of VSD
· Widening of the RVOT
· And Pulmonry valvotomy
Surgical mortality rate is 2-3%
Complications-
1. Bleeding problem during the post-operaitve period
2. Pulmonary valve regurgitation
3. CHF,usually transient
4. RBBB over 90% pts and well tolerated
5. Complete heart block <1%
References:
1) Neches W., Park S., and Ettedgui J., Tetralogy Of Fallot and Tetralogy of Fallot with Pulmonary Atresia In : Garson A., Bricker J., Fisher D., and Neish S.(Eds), The Science and Practice of Pediatric Cardiology, 2nd edition Vol.1, 1999, Williams and Wilkins.
2) Nelson Textbook of PEDIATRICS 18th EDITION.
3) Park Pediatric Cadiology for Practitioners 5th Edition.
4) Garson A,Gillette P.C. and McNamara,D.G. Propranolol the preferred palliation for tetralogy of Fallot. Am. J. cardiology,47:1098,1981
5) Ponce,F.E.et al Propanolol palliation of tetralogy of fallot,experience with long term drug treatment in pediatric pts. Pediatrics 52: 100,1973
6) Drug therapy in Infants and Children with Cardiovascular disorder by Lea & Febiger
7) Pediatric cardiac intensive care by Williams & wilkins. 2nd edition.
8) Internet references.
No comments:
Post a Comment