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Oral case 19

Created: 6/9/2004

A 7-year old 20 kg girl is to undergo bilateral ureteral re-implantation for vesicoureteral reflux. Her history is positive for long standing asthma, with three admissions for severe bronchospasm in the past four years. Each has required steroid therapy. An episode of post-intubation croup occurred after tonsillectomy at age 4. Medications include theophylline and cromolyn. Blood pressure is 110/70 mmHg, heart rate is 100 bpm, oral temperature is 37.5 degrees centigrade, and the hematocrit is 35.

 Preoperative evaluation

I. Respiratory evaluation and preparation of asthmatic for surgery

1. What additional aspects of the child's asthmatic history do you want to know?

2. What laboratory tests would help evaluate the child's respiratory status?

3. What medications should be continued?

4. Would you add additional medications?

5. Describe the pharmacology of cromolyn.

6. Discuss the mechanism of action of theophylline versus sympathomimetic amines, and their effects when used together.

Phosphodiesterase inhibitors like theophylline decrease the breakdown of cyclic adenosine monophosphate, or cAMP, and beta adrenergic agents stimulates sarcolemmal adenyl cyclase, increasing cAMP from adenosine triphosphate. These agents have synergistic effects when used together.

7. How does increased intracellular cAMP affect myocardial function?

Protein kinases are activated, increasing calcium influx and its effect on contraction. Diastolic relaxation, or lusitropy, is improved as well, by stimulating reuptake of calcium, and the dissociation of contractile apparatus. Both systolic and diastolic function is improved.

 Renal function

1. Preoperative creatinine is 1.8 mg %. What is the significance of this, regarding anesthetic management?

 Selection of preoperative medication

1. Should narcotics be included in the preoperative medication?

2. Are any narcotics contraindicated?

3. Are any drying agents contraindicated?

4. Which drying agents are contraindicated, and why?

 Intraoperative course

I. Choice of anesthesia

1. Would an inhalation induction be advantageous in this patient? Why or why not?

2. What inhalation agent would you use, and why?

3. Describe interactions of theophylline with inhalational agents.

4. Which anesthetic system would you select, and why?

5. Would you consider a low-flow system? Why or why not?

 Airway management-paediatrics

1. How do you choose the correctly sized endotracheal tube?

2. Would you use a cuffed or a noncuffed tube? Why?

3. What are the differences between a pediatric and an adult airway?

4. List factors contributing to postintubation croup.

5. How would you manage humidification?

6. How would you manage control of temperature?

 Management of difficult ventilation

1. When the endotracheal tube is inserted, it becomes very difficult to ventilate the lungs. What is your differential diagnosis?

2. What would you do?

3. Which drugs would you give?

4. Describe the cardiovascular effects of various bronchodilators.

5. Would end-tidal CO2 be an important monitor? Why or why not?

 Fluid management

1. How would you calculate the overnight deficit and determine maintenance fluid?

Since she is close to her basal metabolic rate, basal requirements would follow the "4-2-1" rule, and at 20 kg weight, her maintenance fluid requirement would be 60 ml/hr. If she has been NPO for six hours, perioperative replacement would be 10-ml/kg bolus.

2. How long should pediatric patients be NPO prior to surgery?

For patients with no aspiration risk, newborns may have milk up to four hours and clear liquids up to two hours prior to surgery. Children from six months age to three years may have milk up to six hours prior, and children over three years may have milk up to eight hours prior.

3. What is third space loss?

This describes a volume, which has a similar composition to interstitial volume, and a volume, which correlates with the degree of injury. It becomes important in certain cases like major intra-abdominal operations, hemorrhagic shock, burns, and sepsis. It represents a functionless volume, which does not participate in changing fluid shifts, and it requires additional fluid replacement in order to maintain tissue perfusion.

3. What is your method of fluid replacement?

Estimated blood loss from observation or lap sponges would be replaced by three parts of crystalloid for each ml of blood. For moderate surgical trauma, about 3 ml/kg would be added to replace third space loss, and hypotension upon induction would be a sign of masked hypovolemia, for which additional fluid replacement would be required.

4. What indications do you use for intraoperative blood replacement?

5. During infusion of the only available blood unit, the patient develops hypotension. What is your differential diagnosis?

6. What is your treatment?

7. Would you give type-specific blood now?

 Postoperative care

I. Management of ventilation postoperatively

1. When should the child be extubated?

2. What are the advantages of deep versus awake extubation?

3. What variables of ventilation do you use to determine if the child is ready for extubation?

 Management of low urine output

1. One hour after arrival in the recovery room, the recovery room nurse calls to tell you that the child has no urine output. What is your differential diagnosis?

2. What is your management?

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