The Effect of Dexmedetomidine on Oxygen During One Lung Ventilation in Pediatric Surgery.
Condition: One Lung Ventilation OLV; Esophageal Atresia; Hydrocystoma; Pneumonectomy; Pleura; Abscess
MeSH terms: Esophageal Atresia
Study type: Interventional

Summary: 
      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.
    

Detailed description: 
      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.
    

Intervention name(s): Dexmedetomidine; Placebo
Intervention type(s): Drug; Drug
Intervention description(s): Infusion syringes are supplied with a concentration of 0.25 mcg / mL (dexmedetomidine or placebo) either 80 mcg / 20 mL, 200 mcg / 50 mL, or 400 mcg / 100 mL.
It begins with infusion of 4 ml within 10 minutes and then continues infusion, depending on the child's weight, at 1.6 ml / kg / h.
All injections will be prepared randomly by a doctor who did not participate in the study, and then placed in unmarked infusion pumps, given to an anesthesiologist (more than 10 years experience in pediatric anesthesia) without knowledge of the infusion content. The randomization process is carried out via sealed envelope technique.
The injections in both groups will be stopped before the skin is closed. Both patients and anesthesiologists blinded the study drug (dexmedetomidine or placebo) by infusion of solution (dexmedetomidine or placebo). Depending on the size in ml, to ensure that there is no bias and blindness to the medical team about what the drug is.; The same anesthesia, the same amount of Saline solution will be administered, instead of dexmedetomidine, with the same protocol
Other intervention name(s): Precedex; Saline
Intervention MeSH terms: Dexmedetomidine
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Treatment
Keywords: Dexmedetomidine; One lung ventilation OLV; Hypoxic pulmonary vasoconstriction HPV; Pulmonary shunt fraction Qs / Qt