The Effect of Dexmedetomidine on Oxygen During One Lung Ventilation in Pediatric Surgery.

The children who will undergo OLV (one lung ventilation) through general anesthesia will be divided into two groups:

The first will be intravenous infusion of dexmedetomidine at 0.4 mcg / kg / hour, and the second will be intravenous infusion of normal saline.

We will take three samples of arterial blood gas (ABG) during the surgery at certain times. We record the hemodynamic values, PaO2, and calculate the value of the shunt Qs / Qt.

Lung isolation or one lung ventilation OLV means the mechanical separation of the lungs with independent ventilation of one lung from the other, in order to provide a suitable space for the work of the surgeon, and to protect a healthy lung from bleeding or edema caused by lung damage. OLV can lead to a mismatch in the ventilation / perfusion (V / Q) ratio resulting in increased intrapulmonary shunt as well as hypoxia.

Hypoxic pulmonary vasoconstriction HPV is the most important preventive mechanism against hypoxemia, as blood flow moves from the unventilated lung to the ventilated lung to maintain an adequate arterial oxygen transport rate, HPV is a defense mechanism against hypoxia as it reduces pulmonary shunt. So that there is less oxygen drop than expected. HPV reaches its maximum effect in 15 minutes, resulting in decreased pulmonary shunt, homogenization of ventilation / perfusion ratio, and improved oxygen delivery. HPV is affected by various factors: changes in pulmonary pressure, alkalosis, vasodilators, anesthetic agents etc. Among these factors, anesthetic inhaled gases have the greatest effect on HPV.

Pulmonary shunt: It is the sum of the physiological shunt (poorly ventilated air sacs) and the anatomical shunt and the pulmonary shunt fraction (Qs/Qt) is calculated from the equation Qs/Qt = (CcO2 - CaO2)/(CcO2 - CvO2) Qs: blood flow through the shunt, Qt : total blood flow, Cc'O2 : pulmonary capillary content of O2, CaO2 : arterial content of O2, CvO2 : venous mixed content of O2 100% O2 test: often performed in a cardiac catheterization lab, operating room, or ICU, the patient breathes 100% O2 until nitrogen is washed out from their lungs (20 minutes). The oxygen concentration even in poorly ventilated units will approach 100%. This means that the partial pressure and blood saturation are equal in the poorly ventilated and well-ventilated alveolar units, thus the physiological pulmonary shunt is canceled and the anatomical pulmonary shunt remains After lung isolation and OLV application, we perform anesthesia maneuvers on the ventilator and adjust the applied ventilators in order to maintain adequate oxygenation of the patient: increased PEEP, increased FLOW, increased tidal volume Vt, increased Pmax, increased FiO2, thus eliminating the physiological pulmonary shunt and the anatomical pulmonary shunt remains, in total we apply 100% O2 testing.

Dexmedetomidine is a selective agonist for α2 receptors whose affinity for α2 receptors is eight times more than clonidine. At a dose of 0.3 mg / kg it activates protein G and inhibits norepinephrine secretion. When given in larger doses or infusion it stimulates the peripheral α2 receptors; It reduces the levels of norepinephrine in the plasma by more than 90%, thus reducing the cells' metabolism and their need for oxygen.Sympathetic blocker: Reduces heart rate, blood pressure and oxygen consumption of the heart muscle. Studies have shown that alpha-adrenergic blockade abolished pulmonary vasoconstriction that responds to norepinephrine but not to hypoxia. That is, it does not affect the blood supply and HPV of the unventilated lung, widens the blood vessels of the ventilated lung, and reduces the anesthetic requirements (affecting HPV); Reduces 30% of the need for propofol; It reduces desflurane concentration and its subsequent inhibitory effect on HPV. It may also lead to transient increases in pulmonary artery pressure related to its direct effects on vascular smooth muscle through alpha-adrenergic receptors.

Eligibility Criteria:
Inclusion Criteria:

1. As per the American Society of Anesthesiologists (ASA) classification I-I physical condition children undergoing thoracic surgery with OLV.
2. From one day old to 12 years old.
3. There is no prejudice in terms of gender.
4. This study practically does not exclude any child who will undergo OLV even in the presence of cardiac, renal or hepatic diseases.

Or even in the presence of cardiac stimulants and supports (dopamine or dopamine), provided that the general condition is stable, which allows surgery and OLV.

Exclusion Criteria:

1. Premature infants: due to immaturity of the lung and insufficient formation of the surfactant.
2. Cystic Fibrosis: The depressor for surfactant and lung immaturity is not permitted to perform the OLV technique
3. There is no contraindication for the administration of dexmedetomidine in children except those who show signs of allergy to the dexmedetomidine.
4. This study does not exclude practically any child who will undergo OLV.
5. During operating surgery: The child is excluded from the study if hypoxia occurs (SpO2 \<90%) and did not respond to maneuvers and anesthetic techniques (Increase PEEP Increase the FLOW, Tidal volume, increase Vt, Pmax increased pressure, FiO2 increased) Then the lungs are periodically ventilated with positive pressure, and the OLV technique is switched off and the child is excluded from the pilot study.
6. During operating surgery: If there is a drop-in heart rate less than 60 beats / minute and it does not respond to atropine or an increased dose of Cardiac tonics (dopamine).

At this time the infusion of dexmedetomidine is stopped, it is assumed that there is no very slow pulse, and if it does, it is likely that the primary cardiac lesion is the cause.