Urologic Investigation and Surgery




GENERAL PRINCIPLES


The anesthesia risk depends on the state of the child’s renal function and any other disease process that may be present.



  • 1.

    Most children who come for investigation or surgery of the lower urinary tract have good renal function.


  • 2.

    Many of those who require renal biopsy have mild renal dysfunction (usually insufficient to influence anesthesia risk).


  • 3.

    All children in renal failure are seriously ill and present multiple problems for the anesthesiologist.


  • 4.

    Renal disease may be part of a syndrome and therefore requires consideration of all aspects of the condition (see Appendix 1 ).


  • 5.

    Surgery of the genitalia may have significant psychological effects on small children; effective postoperative pain relief may minimize these effects.


  • 6.

    Many urologic procedures are now performed endoscopically and the provisions for laparoscopy should be applied (see Chapter 13, page 339 ).





CHILDREN WITH GOOD RENAL FUNCTION


Anesthesia Management—Minor Procedures


Children almost always require general anesthesia for minor procedures, such as cystoscopy, retrograde pyelography, circumcision, or hypospadias repair. Healthy children undergoing brief investigative procedures or operations are almost all treated as outpatients.


Preoperative




  • 1.

    Oral sedative premedication (midazolam) is useful for some children, especially those who require repeated surgery.



Perioperative




  • 1.

    Induce anesthesia with inhalational or intravenous anesthetics.


  • 2.

    Maintain anesthesia with N 2 O, O 2 , and sevoflurane or isoflurane by mask, laryngeal mask airway (LMA), or tracheal tube.


  • 3.

    Provide regional analgesia for postoperative pain control whenever possible (see Chapter 5 ). If the block is performed before the surgery commences, less anesthetic drugs will be required during surgery and awakening will be rapid and pain-free.



    • a.

      For circumcision: perform a penile block (see Chapter 5, page 161 ) using bupivacaine without epinephrine. Ropivacaine should not be used for this block because of its vasoconstrictor properties. EMLA cream may be applied to the incision to augment the block.


    • b.

      For hypospadias repair, perform a caudal block (see Chapter 5, page 153 ).




Postoperative




  • 1.

    Give supplementary analgesia as required; those children with a successful regional block will require few additional medications. Outpatients are usually discharged from the hospital 1 hour after recovery. Anticipate the need for additional analgesia at home as the block wears off. For optimal pain relief, instruct parents to administer a suitable analgesic (e.g., acetaminophen with codeine) before the pain occurs.



Anesthesia Management—Major Genitourinary


Surgical Procedures


Apply anesthesia management as for minor procedures (see previous discussion), plus the following:



  • 1.

    Use general endotracheal anesthesia with muscle relaxants and controlled ventilation.


  • 2.

    Be prepared for major hemorrhage: Insert a reliable large-bore intravenous line, measure blood losses carefully, and replace fluids as indicated.


  • 3.

    Use regional analgesia when possible to provide postoperative pain relief. For example, for reimplantation of ureters, a single-shot caudal provides analgesia for the first few hours or an indwelling epidural catheter, provides analgesia for up to 3 days. Intercostal nerve blocks or, preferably, a lumbar epidural block provides good analgesia after renal surgery. Establish the block before surgery.


  • 4.

    Children who have dilated ureters may develop hypertension postoperatively. This may require treatment.


  • 5.

    For special considerations for Wilm tumor, see Chapter 13 .





CHILDREN WITH POOR RENAL FUNCTION OR RENAL FAILURE


These children may have many physiologic and psychological disturbances.


Special Anesthesia Problems




  • 1.

    Anemia (usually normochromic, normocytic) may be present but with standard care under the supervision of a renal unit, this should not be severe, the objective of pretransplant care is to avoid significant anemia.


    Anemia in renal failure is caused by:



    • a.

      Decreased erythropoietin production. If erythropoietin is reduced, the hemoglobin concentration (Hb) will not exceed 7 to 9 g/dl. Recombinant human erythropoietin therapy may not be effective if severe uremia is present


    • b.

      Decreased erythrocyte survival and increased hemolysis


    • c.

      Increased bruising and bleeding from increased capillary fragility


    • d.

      Iron and/or folic acid deficiency


    • e.

      Bone marrow depression due to increased blood urea nitrogen (BUN)



    The presence of anemia leads to compensatory changes; that is, increased cardiac output and increased red blood cell (RBC) 2,3-diphosphoglycerate (2,3-DPG), although the latter is minimal. The P 50 values are similar to those of children with normal renal function.


    Treatment with erythropoietin and supplemental iron will increase the hemoglobin concentration to near 10 gm/dl, which is the target level. After successful renal transplantation, the Hb increases further.


    Blood transfusions, once contraindicated pre-transplant, are now recognized to improve post-transplantation graft survival.


  • 2.

    Coagulopathy may be present, caused by:



    • a.

      Increased capillary fragility


    • b.

      Functional platelet defect (decreased adhesiveness), possibly due to increased guanidinosuccinic acid


    • c.

      Thrombocytopenia due to bone marrow depression


    • d.

      Drugs (e.g., heparin, acetylsalicylic acid)



    Coagulopathy if present is usually of minor significance and does not usually represent a contraindication to epidural catheter placement.


  • 3.

    Acid-base imbalance:



    • a.

      Children produce even more acid than adults; when urinary ammonia production decreases, a metabolic acidosis predominates and plasma bicarbonate falls to 12 to 15 mEq/L. This is compensated to a variable degree by respiratory alkalosis.


    • b.

      In long-standing stable renal failure, H + displaces Ca ++ from bone and K + from intracellular fluid.



  • 4.

    Fluid and electrolyte changes. Children undergoing dialysis (particularly hemodialysis) are likely to be slightly hypovolemic. The timing of the last dialysis is critical as hypovolemia may result in precipitous hypotension in response to inhalation agents or intravenous drugs. More information regarding the volume status may be obtained from the nephrology team (e.g., the number of liters of fluid that were removed during the most recent dialysis).



    • a.

      “Sodium losers” are those children with polycystic kidneys or severe pyelonephritis (tubular damage is disproportionately greater than glomerular injury):



      • i.

        Normotension or slight hypotension is present.


      • ii.

        Edema is present uncommonly.


      • iii.

        Hypokalemia is present in some.


      • iv.

        Renal function is improved by increasing intake of sodium and water; sodium restriction may rapidly lead to severe hyponatremia.



    • b.

      “Sodium retainers” are often children with glomerulonephritis; salt retention, hypertension, and edema predispose them to cardiac failure.


    • c.

      Potassium shifts due to displacement of K + from the cells by H + :



      • i.

        High serum K + levels


      • ii.

        Depressed excitability of muscles and nerves. This is particularly significant if the cardiac muscle is affected—further sudden rises in K + (e.g., with succinylcholine or increased acidosis) may precipitate cardiac arrest.



    • d.

      Calcium shifts:



      • i.

        If displacement of Ca ++ by H + is prolonged, osteoporosis may develop.



    • e.

      Anion changes:



      • i.

        Plasma bicarbonate (HCO 3 ) is decreased.


      • ii.

        Plasma (SO 4 ), (HPO 4 ) and (Cl ) are increased.




  • 5.

    Cardiovascular problems:



    • a.

      Hypertension may result from abnormalities of extracellular fluid regulation, fluid overload, and derangement of the renin-angiotensin-aldosterone system:



      • i.

        In many children (those with hypertension secondary to sodium and water retention), this can be controlled conservatively (i.e., by careful moderate salt restriction).


      • ii.

        In some children, the BP can be titrated against sodium and water content during dialysis.


      • iii.

        In others, drug therapy with diuretics and vasodilators is necessary.


      • iv.

        In a few, even large doses of antihypertensive agents fail to control the hypertension (which is probably caused by overproduction of renin). Retinopathy and/or encephalopathy may develop, and bilateral nephrectomy may become necessary.


      • v.

        Hypertensive crisis may occur, occasionally in the perioperative period. Diazoxide (5 mg/kg) has commonly been used for this indication, but a labetalol infusion is now the therapy of choice.



    • b.

      Congestive heart failure may occur with advanced renal failure, as a result of hypertension, volume overload, anemia, electrolyte imbalance, and the effects of an arteriovenous (AV) fistula:



      • i.

        Digitalis therapy is difficult to control.


      • ii.

        Pericardial effusion and tamponade may occur.



    • c.

      Fatty degeneration of the myocardium may occur secondary to chronic renal failure.



  • 6.

    Pulmonary congestion:



    • a.

      The alveolar-arterial partial oxygen pressure difference (A-aDO 2 ) may be large.


    • b.

      Sodium and water retention, left ventricular failure, and hypoproteinemia contribute to the development of “uremic lung.”


    • c.

      Pleural effusions may develop.



  • 7.

    Gastrointestinal disturbances:



    • a.

      Anorexia, nausea, and vomiting (due to bacterial breakdown of urea to ammonia in the gastrointestinal tract) may aggravate the water, electrolyte, and acid-base imbalance. Gastric emptying may be delayed.



  • 8.

    Multiple medications:



    • a.

      Many of these children are receiving long-term steroid therapy with resultant osteodystrophy, Cushingoid state, and glycosuria.




      • Continue steroid therapy perioperatively.



    • b.

      Antihypertensive polypharmacy: potential cardiovascular instability under anesthesia must be anticipated. (Do not discontinue these drugs before surgery.)


    • c.

      Digitalis and diuretic therapy may lead to K + depletion and thus to increased susceptibility to cardiac arrhythmias.


    • d.

      Antibiotics (e.g., gentamicin) may prolong the effect of nondepolarizing muscle relaxants.


    • e.

      Antimetabolites (e.g., azathioprine) that are highly protein-bound may increase the bioavailability of other protein-bound drugs by displacing them from the protein molecule.



  • 9.

    Reduced immunity (risk of infection): it is vital to practice very careful asepsis.


  • 10.

    Poor quality of life and potentially major psychological disturbances:



    • a.

      Resulting from chronic debilitating disease


    • b.

      Heightened by the uremic state and knowledge of a life-threatening condition




In summary, these children may have:



  • 1.

    Reduced O 2 carrying capacity, which is dependent on a stressed cardiovascular system


  • 2.

    Incipient or apparent cardiac failure:



    • a.

      Left ventricular failure if hypertensive, hypervolemic, and anemic


    • b.

      Right ventricular failure (late)



  • 3.

    Greater risk of cardiac arrest (e.g., due to increased K + and acidosis)


  • 4.

    Intolerance of inaccurate administration of blood, other fluids, and electrolytes


  • 5.

    Cardiovascular instability due to long-term administration of antihypertensive drugs


  • 6.

    Coagulopathy


  • 7.

    Low resistance to infection


  • 8.

    Very low tolerance to further discomfort, however minor (e.g., finger prick, movement from one bed to another)



Many of the problems of chronic renal failure may be significantly reduced when the child is on a renal dialysis program and under close medical supervision. However, some children are underweight, some are hypertensive, and other disease processes may be present. Every child should be very carefully assessed preoperatively.


N.B. Many children with impaired renal function are undergoing hemodialysis regularly and therefore have an AV shunt or fistula usually in the arm. Special care must be taken to ensure that this shunt is well protected and kept functioning throughout the perioperative period. The child must not be allowed to lie on that limb at any time, and it should not be used for blood pressure determinations. The function of the AV fistula should be monitored perioperatively (Doppler flowmeter).


Preoperative Assessment and Preparation


Pay careful attention to the following physical and psychological aspects:



  • 1.

    Children in a dialysis program are usually dialyzed 12 to 18 hours before surgery. Check the postdialysis fluid and electrolyte status and body weight.


  • 2.

    Plan ahead so that the child’s discomfort is not increased and any necessary disturbances are minimized.


  • 3.

    Psychological preparation and support are of special benefit to these children and are safer than depressant medication. Some sedation may help.


  • 4.

    Check results of laboratory tests:



    • a.

      Blood transfusions may be given if deemed desirable and may help pretransplant. Packed RBCs are preferable. However, transfusion is of temporary benefit only.


    • b.

      Serum potassium: values less than 5 mEq/L are acceptable, even in an emergency; levels greater than 6 mEq/L are unacceptable.



      • i.

        If the serum K + level is increased, surgery is usually delayed until hemodialysis has been performed.


      • ii.

        In an emergency, K + can be lowered rapidly by giving 0.5 g/kg glucose as a 10% solution with 1 unit of regular insulin added for each 5 g of glucose.



    • c.

      Acid-base balance:



      • i.

        A pH greater than 7.32 is acceptable. If necessary, administer sodium bicarbonate (NaHCO 3 ) for correction of acidosis, even if sodium (Na + ) levels are elevated.


      • ii.

        Correction must be cautious and gradual. If the serum calcium (Ca ++ ) level is low, sudden correction may precipitate tetany or convulsions.





Anesthesia Management




  • 1.

    Pay meticulous attention to details of asepsis.


  • 2.

    For brief procedures (e.g., insertion of a peritoneal catheter) in a poor-risk child who is cooperative and emotionally stable, use local anesthesia (1% to 2% lidocaine without epinephrine; maximum, 3 mg/kg).


  • 3.

    For all other cases and if in doubt, use general anesthesia.


  • 4.

    Anesthesia drugs and renal failure:



    • a.

      Children with renal failure vary in their response to opioids. Use these with caution. Morphine and meperidine may exert prolonged effects owing to a failure to excrete/dialyze active metabolites (M6G and normeperidine, respectively). In contrast, fentanyl, alfentanil, and sufentanil are relatively safe because their metabolites are inactive. Remifentanil may be the ideal intraoperative opioid for these children.


    • b.

      Propofol and thiopental should be used cautiously in reduced doses; less protein binding results in an increased free active fraction. Ketamine and etomidate may result in less hypotension.


    • c.

      Inhalational anesthetics are eliminated via the lungs and hence are most useful. Fluoride nephrotoxicity does not occur with the current ether anesthetics.


    • d.

      Succinylcholine may be used as a single dose provided that the serum potassium (K + ) concentration is 5.5 mEq/L or less (serum K + increases 0.5 to 1 mEq/L after succinylcholine in children with renal failure; this produces no ECG changes because the hyperkalemia is chronic. If a peripheral neuropathy is present, however, succinylcholine may cause greater increases in serum K + and arrhythmias). Succinylcholine should only be used if a rapid sequence induction is deemed necessary and should be preceded by a small dose of a nondepolarizing relaxant.


    • e.

      Muscle relaxants, nondepolarizing: cis -atracurium and vecuronium are drugs of choice. Rocuronium has a slower onset of action but a similar duration of action in children with and without renal failure. Pancuronium and gallamine are partially or completely excreted by the kidneys and should be avoided.


    • f.

      Local anesthesia drugs have not been extensively studied in children with renal failure; they may be used in normal doses for “single-shot” techniques. Repeat doses or infusions might be dangerous if clearance of the drug is delayed.




Preoperative




  • 1.

    Dose requirements for drugs in children with renal failure are more variable than in those with normal renal function; titrate doses carefully.


  • 2.

    Do not discontinue antihypertensive drugs.


  • 3.

    Premedicate when required (e.g., PO or IV midazolam).


  • 4.

    Check all medications that have been given and note their last dose before surgery.


  • 5.

    Check the location of a shunt or fistula. Avoid any pressure to this area, and monitor function (Doppler flowmeter).


  • 6.

    Ensure that all supportive drugs are available in the operating room.


  • 7.

    Ensure that adequate supplies of blood and other fluids are available (including washed cells if and when indicated).



Perioperative




  • 1.

    Give 100% O 2 by mask.


  • 2.

    Apply monitors:



    • a.

      Precordial stethoscope


    • b.

      ECG and pulse oximeter


    • c.

      Automated blood pressure— do not use a limb with a shunt or fistula



  • 3.

    Ensure that the limb with the shunt or fistula is easily accessible. Monitor function throughout the procedure.


  • 4.

    Induce anesthesia with propofol (2 to 4 mg/kg), thiopental 2 to 3 mg/kg (more may be required) or if dehydrated, consider ketamine (1 to 2 mg/kg) or etomidate (0.3 mg/kg), followed by N 2 O/O 2 and sevoflurane.


  • 5.

    For intubation:



    • a.

      Do not give succinylcholine unless the serum K + concentration is less than 5.5 mEq/L (see previous discussion)—and always pretreat with a nondepolarizing agent. Always limit succinylcholine to a single dose.


    • b.

      Otherwise give cis-atracurium, rocuronium, or vecuronium for intubation.



  • 6.

    Maintain anesthesia with N 2 O/O 2 and isoflurane with a nondepolarizing muscle relaxant.


  • 7.

    Control the ventilation in all procedures that last longer than 15 minutes. Use moderate hyperventilation to compensate for metabolic acidosis and to encourage K + movement back into the cells. In general, it is advised to control ventilation to maintain the arterial carbon dioxide pressure (PaCO 2 ) at the usual level for that particular child.


  • 8.

    Administer fluids to ensure adequate blood volume for satisfactory BP, good peripheral perfusion, and function of an AV fistula or shunt.



    • a.

      Give balanced salt solutions (but avoid all potassium-containing solutions [i.e., lactated Ringer’s solution]) to replace the preoperative deficit and for perioperative maintenance.


    • b.

      For small blood losses, replace with maintenance solution.


    • c.

      For significant blood losses, replace with washed RBCs and salt-poor albumin.



      • i.

        Check Hb and hematocrit (Hct); keep Hct below 30%.


      • ii.

        Avoid overtransfusion.




  • 9.

    Antagonize muscle relaxants at the end of surgery.



Postoperative




  • 1.

    Ensure good ventilation and oxygenation.


  • 2.

    Carefully titrate opioid doses (repeated doses of morphine and its metabolites accumulate in renal failure; M6G cannot be removed by dialysis); monitor the effect and give supplements if necessary.


  • 3.

    Ensure that the shunt or fistula is functioning; record this fact.


  • 4.

    Check Hb, Hct, electrolytes, and blood gases.


  • 5.

    Consult a nephrologist for continuing care.


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Mar 27, 2019 | Posted by in ANESTHESIA | Comments Off on Urologic Investigation and Surgery
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