Pediatric Otorhinolaryngology: Diagnosis and Treatment, 1st Ed.

10

Anesthesia for Pediatric Otolaryngology

Rosalie F. Tassone and Timothy B. McDonald

Children who present to the hospital for otolaryngology procedures and operations frequently require anesthesia to tolerate procedures and operations that would otherwise be extremely uncomfortable and painful. Consultation with a pediatric anesthesiologist is important for the comprehensive care of the pediatric patient. This chapter is divided into three sections: preoperative evaluation, intraoperative management, and postoperative care. Each section will highlight the concerns of the anesthesiologist for the care of the pediatric patient.

Preoperative Evaluation

The preoperative evaluation allows the anesthesiologist to integrate the patient's medical history, physical status, and planned procedure into an anesthetic management plan tailored to the patient's perioperative course. Identification of areas of concern in the patient with a complex medical history facilitates discussion and planning of postoperative disposition, such as the need for postoperative intensive care. Additionally, anesthetic consultation and evaluation before the day of surgery may also increase operating room efficiency and decreased cancellations on the day of surgery, although not all children need a preoperative evaluation.1

The American Society of Anesthesiologists (ASA) has created a physical status classification system, based on the severity of the patient's systemic disease (Table 10.1). For example, the assessment of the otherwise healthy child (ASA 1) for a routine operation such as placement of bilateral myringotomy tubes may not warrant a separate trip to the anesthesiologist. However, if this child has a complex medical history such as concomitant congenital heart disease or a bleeding disorder (ASA 3 or 4), preoperative evaluation would be helpful in the planning of the intraoperative management, which may be far from routine.

The preoperative assessment includes taking a thorough medical history to assess any associated medical problems that might affect the anesthetic or surgical outcome. Of keen interest to the pediatric anesthesiologist is a history of problems associated with anesthesia in the child or the child's family, such as malignant hyperthermia (MH), latex allergy or allergies to anesthetic medications.

Identification and medical optimization of chronic conditions, such as a history of premature birth, reactive airway disease, systemic disease, bleeding disorders, developmental delay, or acute conditions such as in the child with an active upper respiratory tract infection may occur at the preoperative evaluation. Also, workup of additional associated concerns can be scheduled and performed before the day of surgery, such as the assessment of a potentially unstable cervical spine in the child with Trisomy 21 or the preoperative assessment of a bleeding disorder.2

Premature Neonates

Neonates who are born prematurely (<37 weeks of gestation) are at risk for increased apnea and bradycardia after general anesthesia.2,3 Neonates born prematurely, who are under 60 weeks postgestational age should be admitted to the hospital for postoperative apnea and bradycardia monitoring overnight after administering sedatives or general anesthesia. Likewise, full-term newborns are at increased risk of apnea and bradycardia for the first 4 weeks of life and should be admitted to the hospital for overnight observation as well.2,4

Table 10.1 ASA Physical Status Classification System

ASA Physical Status

Description

ASA Physical Status 1 (ASA 1)

A normal healthy patient

ASA Physical Status 2 (ASA 2)

A patient with mild systemic disease

ASA Physical Status 3 (ASA 3)

A patient with severe systemic disease

ASA Physical Status 4 (ASA 4)

A patient with severe systemic disease that is a constant threat to life

ASA Physical Status 5 (ASA 5)

A moribund patient who is not expected to survive without the operation

ASA Physical Status 6 (ASA 6)

A declared brain-dead patient whose organs are being removed for donor purposes

Additionally, if the surgery is an emergency, the physical status classification is followed by “E” (for emergency).

Upper Respiratory Tract Infection

In general, pediatric patients have a higher incidence of respiratory events than adults, and the child with an active respiratory tract infection is at an even higher increased risk for respiratory-related anesthetic complications such as laryngospasm, bronchospasm, and hypoxemia.2 Classically it has been shown that the risk of respiratory complications decreases 4 to 6 weeks after an upper respiratory tract infection has resolved;2 however, it sometimes can be difficult to schedule a child's procedure at a time when the child is not actively ill. Preoperative assessment can be helpful in creating a plan where the child may be at the least risk for complications from an upper respiratory tract infection and maximum benefit from the surgery. Some sources suggest that a shorter time after an upper respiratory tract infection has resolved might be acceptable, with careful assessment and caution.2,5

Obstructive Sleep Apnea

Children with long-standing obstructive sleep apnea may develop significant cor pulmonale or pulmonary hypertension. Postoperatively they are at risk for perioperative hypoxemia and acute right heart failure.2 These children are also exquisitely more sensitive to sedatives and narcotics.6,7 It is postulated that this may likely be a result of upregulation of mu-receptors in the brainstem, where an increased respiratory sensitivity to fentanyl has been shown after recurrent hypoxia in a rat model.8

Mediastinal Masses

Masses in the neck may sometimes be associated with extension of the mass into the mediastinum. If a mediastinal mass is suspected, a preoperative work-up including imaging studies is prudent to help plan for the anesthetic induction and intraoperative care. Patients with an anterior mediastinal mass are at increased risk of cardiopulmonary compromise and, possibly, arrest on induction of anesthesia. The planning of appropriate personnel and equipment, such as flexible fiberoptic scopes, invasive lines, and possible cardiopulmonary bypass, may be necessary for the care of these patients.9

Physical Examination

A physical examination of the patient is an important step in preoperative assessment. Observation of the general well-being and demeanor of the patient can yield a sense as to how the child might separate from the parents. It has been shown that children who are anxious before surgery require more pain medication postoperatively and may exhibit maladaptive behavioral changes postoperatively as well.10,11Parental anxiety has also been shown to influence the pediatric patient's anxiety.11 Counseling the patient and family at a time before the surgery may be helpful in alleviating perioperative anxiety.

Vital signs, including temperature, may also indicate presence of systemic disease. Examination of the airway includes use of the Mallampati classification (Fig. 10.1), which has been shown to predict the ease of intubation, and is based on the visibility of the base of uvula, faucial pillars, and the soft palate. Scoring may be done with or without phonation. A high Mallampati score (class 4) is associated with more difficult intubation, and an increased severity of obstructive sleep apnea.12,13

In addition to the Mallampati classification of the airway, the anesthesiologist will also assess airway abnormalities that may be present such as masses, tracheal deviation, absent structures, range of motion of the head and neck, and thyromental distance.

Intraoperative Management

General Considerations

Preprocedure Debriefing

The patient presenting for pediatric otolaryngology surgery has much to gain from all members of the operating room team, by taking advantage of a preprocedure debriefing.14 Even the relatively routine pediatric otolaryngology case will involve some degree of airway sharing, some mindfulness related to room configuration, need for special airway equipment considerations, and decisions about medication management for maintaining anesthesia, pain control, and prophylaxis against postoperative nausea and vomiting (PONV).

The debriefing also provides for special consideration about the availability of special airway equipment, implant devices (such as cochlear implants), appropriate room configuration, plans for use of a facial nerve monitor (and, therefore, avoidance of long-acting paralytic agents), potential risk of fire, and other special needs of the patient and surgeon.14 During this time, the otolaryngologist and anesthesia provider should agree on whether a preformed or atypical size endotracheal tube may also be needed for the case.

image

Figure 10.1 Mallampati classification. Class I: Full visibility of the tonsils, uvula, and soft palate in the airway. Class II: Visibility of hard and soft palate, and upper portion of the tonsils and uvula. Class III: Soft and hard palate, and base of the uvula are visible. Class IV: Only the hard palate is visible.

Nitrous Oxide

With the propensity of nitrous oxide to accumulate and cause increased pressure in closed mucosa-lined spaces, the otolaryngologist and anesthesia provider should also discuss the use of nitrous oxide on a case-by-case basis.15 This is especially true for pediatric otolaryngology cases involving middle ear surgery. In addition, operating personnel should remain mindful of the fact that nitrous oxide supports combustion and should assure to some degree that oxygen is minimized when there is a measurable risk of fire in any otolaryngology case.16

Difficult Airway

Failure to appropriately manage a difficult airway of a child in respiratory distress or one who is deeply anesthetized and cannot be mask ventilated or intubated remains a significant source of potentially preventable patient harm. Preoperative preparation includes a detailed assessment and search for signs, symptoms, anatomical predictors, and syndrome associations that might suggest the potential of less than straightforward airway management.

While assembling and preparing the appropriate equipment for cases that may involve difficult airway management, consideration of the ASA difficult airway algorithm may prove useful. The algorithm contemplates a list of potential equipment for the team to consider that includes, but is not limited to, appropriate masks, a variety of laryngoscope blades with and without optics, endotracheal tubes, fiberoptic scopes and screens, laryngeal mask airways, jet ventilation methodologies, boogie use, and surgical tracheostomy/cricothyrotomy sets.17

Unlike cooperative adults and older adolescent patients, securing the difficult airway in the fully awake child can prove extremely challenging.18 Therefore, most pediatric difficult airway cases proceed with a decision to provide some sedation or anesthetic. Here, effective communication between the otolaryngologist and anesthesia provider becomes paramount. In general, attempts are made to provide adequate sedation/anesthesia while maintaining spontaneous ventilation. This approach allows for “waking up the child” in the event airway management difficulties ensue.

Foreign Body Aspiration

Basically, two anesthetic approaches exist for retrieving an aspirated foreign body in a child: (1) deeply anesthetized, spontaneously breathing method and (2) controlled ventilation and brief paralysis. Of course, the goal is to provide the surgeon with optimal conditions to safely retrieve the entire foreign body with minimal complications. Each approach has its own advantages and disadvantages.

The spontaneously breathing approach decreases the likelihood that the anesthesia provider will force the foreign body more deeply in the trachea or bronchus with the administration of positive pressure ventilation. The downside to this approach may include a significantly increased time for induction of a deep plane of anesthesia and the increased likelihood of patient movement during laryngoscopy and bronchoscopy if the depth of anesthesia is inadequate.

The paralyzed, controlled ventilation approach decreases the likelihood of any movement and, for at least a brief time, provides the surgeon with the optimal circumstance of an anesthetized patient with full muscle relaxation. The downside to this approach rests with the possibility that the foreign body will not be retrievable as intact during the period of apnea once laryngoscopy ensues. In this case, the anesthesia provider may need to provide positive pressure ventilation to maintain adequate oxygenation while potentially forcing the foreign body deeper into the airway.

Ultimately, either approach may be reasonable, based upon the individual facts and presentation of the case. Effective communication between the otolaryngologist and anesthesia provider is essential before and during the procedure.

Airway Laser Surgery

In addition to usual challenges of sharing the child's airway between the surgeon and the anesthesiologist, two specific issues related to the use of laser include reducing the risk of airway fire and the preparation for the possible need for jet ventilation or insufflation techniques.

The fire triangle in the airway consists of (1) an ignition source, in this case, the laser; (2) fuel (endotracheal tube); and (3) oxidizing agent (oxygen or nitrous oxide). Reducing the risk of airway fire involves the use of fire-resistant endotracheal tubes and the minimization of an oxidizing-rich environment with avoidance of nitrous oxide and the blending of oxygen and air to the lowest possible fraction of inspired oxygen while still maintaining adequate blood oxygen levels.19

During use of a laser during airway surgery, all personnel in the operating room must be prepared to immediately extinguish an airway fire, reduce the flow of oxidizing gases, and determine the need for removal and possible replacement of the endotracheal tube. In the microscope-assisted laser procedures, ventilation during moments without an endotracheal tube in place can take place with Venturi jet ventilation or with a spontaneous breathing child. If Venturi jet ventilation is employed, the team must recognize the possibility for the known complications of pneumomediastinum, pneumothorax, and pneumopericardium. Minimizing the amount of force generated by the jet ventilator can minimize the likelihood of these complications. In addition, the surgeon must take special care to ensure that the tip of the jet ventilation apparatus is appropriately “aimed” at the lumen of the trachea.

Malignant Hyperthermia

Malignant hyperthermia (MH) is a hypermetabolic state triggered by exposure to any of the potent inhalation agents and/or succinylcholine.20 The key diagnostic features of MH are muscle rigidity, unexplained increase in exhaled carbon dioxide, acidosis, hyperthermia, hyperkalemia, and rhabdomyolysis.20 The incidence ranges from 1:10,000 to 1:100,000 anesthetic exposures while the genetic prevalence appears to be approximately1:3000 persons. Often, the earliest manifestations of MH during a surgical procedure include an unexplained increase in exhaled carbon dioxide and tachycardia.20These signs may be accompanied by muscular rigidity. In the event the diagnosis of MH is made, this becomes an operating room emergency that will require large numbers of personnel to assist. The steps for the management of MH are shown in Table 10.2.21

With prompt identification and appropriate treatment, the mortality has dropped from 80% in the 1970s to less than 5% at present. Genetic counseling is appropriate following a documented case of MH in a family member.20

Postoperative Care

After the conclusion of surgery and anesthesia, the pediatric patient has time to recover in the postanesthesia care unit (PACU). This is a time and place where monitoring patients is still important as it is a time of transition to recovery. This section will review some of the common issues in the PACU.

Pain Control

Adequate control of pain is one of the most fundamental concerns for care of the postoperative patient. Effective pain control is beneficial at multiple levels as it reduces morbidity and mortality, encourages earlier mobilization and faster recovery.4 Assessment of pain should be done at regular intervals so that a patient has adequate pain relief without being oversedated. Medications given intraoperatively for pain relief should be incorporated into the postoperative pain relief regimen. It is important to understand the pharmacokinetics of pharmacodynamics of medications given intraoperatively and postoperatively such that the patient does not develop inadequate pain relief or oversedation once discharged.

Table 10.2 Management of Malignant Hyperthermia

1. Discontinue triggering agents

2. Discontinue surgery whenever possible

3. Hyperventilate

4. Administer the first intravenous dose of dantrolene (2.5 mg/kg)

5. Begin cooling methods

6. Treat hyperkalemia—consider insulin and glucose

7. Obtain laboratory tests to ascertain degree of metabolic derangement

8. Maintain adequate urine output

9. Assess and treat for rhabdomyolysis

Several classes of drugs can be used for treatment of postoperative pain (Table 10.3). Frequently, nonopioid analgesics, such as acetaminophen, may be administered preoperatively by mouth or intraoperatively per rectum. Other nonopioid analgesics such that the nonsteroidal anti-inflammatory drugs (NSAIDs) may be given orally (aspirin, ibuprofen, naproxen, diclofenac) or intravenously (ketorolac). Although a retrospective review of pediatric patients who underwent tonsillectomy with or without adenoidectomy revealed no significant frequency of postoperative hemorrhage in patients who received ketorolac,22 a quantitative systematic review of NSAIDs and the risk of operative site bleeding after tonsillectomy noted that of four bleeding end points (intraoperative blood loss, postoperative bleeding, hospital admission, and reoperation because of bleeding), only reoperation happened significantly more often with NSAIDs.23 Thus, use of this class of drugs should be discussed with the surgeon before administration as many otolaryngologists prefer avoiding this class of drugs for certain procedures.

Narcotics are another class of drugs that may be useful in obtaining pain relief for children. Based on the age of the child and nature of the surgery, narcotics may be a good choice for pain control. Fentanyl, morphine, and hydromorphone have all been used to control pain intraoperatively and postoperatively. It is important to note that with these agents, respiratory depression may occur, especially in the patient with a history of obstructive sleep apnea. These patients have been shown to be more sensitive to this class of drugs6,7 and smaller doses can sometimes yield adequate effect. Support of the airway and use of opioid antagonists may be necessary in cases where respiratory depression occurs. It is important to note that opioid antagonists, such as naloxone, are not devoid of complications themselves. Complications including flash pulmonary edema have been reported.24 Overnight monitoring of the patient with a history of obstructive sleep apnea who also receives narcotics postoperatively may sometimes be necessary.

Codeine is an oral narcotic often prescribed for postoperative pain relief. Codeine is converted to its active metabolite, morphine, by the highly polymorphic CYP2D6 pathway of the cytochrome P4502D6 system. It should be noted that fatalities and life-threatening respiratory depression have been reported in patients identified as ultra-rapid metabolizers.25 Judicious use of codeine and other opioids that use the CYP2D6 pathway should be exercised in children with sleep apnea syndrome. These adverse outcomes may be avoided by CYP2D6 genetic testing before prescribing.26 Genetic testing at this time is not commercially available.

Table 10.3 Commonly Used Pharmacologic Agents for Pain Relief

Drug

Route

Usual Dose (mg/kg)

Acetaminophen

PO

10–20

Acetaminophen

PR

20

Ibuprofen

PO

10–20

Codeine

PO

0.5–1

Ketorolac

IV/IM

0.5

Fentanyl

IV

0.5–1

Morphine

IV

0.02–0.05

PO, per os (by mouth); PR, per rectum; IV, intravenous; IM, intramuscular.

Complications

Airway Obstruction

Airway obstruction is one of the most common concerns in the postoperative patient after airway surgery. Many perioperative factors made contribution to the development of postoperative airway obstruction. These include a history of sleep apnea or central apnea, anatomic narrowing of the airway, laryngospasm, bronchospasm, administration of narcotics, mechanical causes, and severe bleeding. Severe airway obstruction may lead to sudden pulmonary edema, secondary to strong negative-pressure inspiratory force against a closed glottis. Pink frothy secretions may be seen if the case is severe enough. Treatment consists of relief of the obstruction, with consideration of endotracheal intubation, supplemental oxygen administration, continuous positive airway pressure, and potential administration of diuretics.

Emergence Agitation

Emergence agitation is common in the pediatric population, and occurs in approximately18 to 80% of children undergoing anesthesia.27 It is most common in children who present for short procedures under general anesthesia with inhalation agents, and its mechanism remains unclear. It can increase the distress of health care providers and families, expose the child to potential injury, and delay recovery after anesthesia.27 Treatments for emergence agitation range from allowing the child to settle in time without medication to pharmacologic intervention with benzodiazepines, narcotics, propofol or dexmedetomidine. Alternative techniques such as acupuncture have also been shown to be helpful.28

Postoperative Nausea and Vomiting

Preoperative nausea and vomiting (PONV) is common in children undergoing otolaryngology procedures, and has been reported to be as high as 50 to 89% posttonsillectomy.29 It is troublesome to patients and families, and is known to delay discharge. Some of the risk factors include age older than 3 years, surgery lasting longer than 30 minutes, or a patient or family history of PONV.29,30 Prophylaxis administration of one or more agents including dexamethasone, 5-hydroxy-tryptamine-3 antagonists, droperidol, or promethazine is recommended.31 Dexamethasone has also been shown to be effective in reducing PONV as well as decreasing swelling, improving oral intake, and decreasing postoperative pain.32

Conclusion

The anesthetic management of the child undergoing otolaryngology procedures ranges from the straight forward and mask induction and myringotomy tube placement to the very complex neck exploration and reconstruction in a child with comorbidities and potentially difficult airway. Consultation and collaborative planning between the surgeon and anesthesiologist to create a comprehensive and thoughtful perioperative plan is important in the care of the pediatric patient, all with the goal, as Keats described, of “a sleep full of sweet dreams, and health, and quiet breathing.”

References

1. Wittkugel EP, Varughese AM. Pediatric preoperative evaluation–a new paradigm. Int Anesthesiol Clin 2006;44(1):141–158

2. Maxwell LG, Yaster M. Perioperative management issues in pediatric patients. Anesthesiol Clin North America 2000;18(3): 601–632

3. Welborn LG, Greenspun JC. Anesthesia and apnea. Perioperative considerations in the former preterm infant. Pediatr Clin North Am 1994;41(1):181–198

4. Coté CJ, Zaslavsky A, Downes JJ, et al. Postoperative apnea in former preterm infants after inguinal herniorrhaphy. A combined analysis. Anesthesiology 1995;82(4):809–822

5. Tait AR, Malviya S. Anesthesia for the child with an upper respiratory tract infection: still a dilemma? Anesth Analg 2005;100(1):59–65

6. Brown KA, Laferrière A, Lakheeram I, Moss IR. Recurrent hypoxemia in children is associated with increased analgesic sensitivity to opiates. Anesthesiology 2006;105(4):665–669

7. Brown KA, Laferrière A, Moss IR. Recurrent hypoxemia in young children with obstructive sleep apnea is associated with reduced opioid requirement for analgesia. Anesthesiology. 2004;100(4):806–810; discussion 5A

8. Moss IR, Brown KA, Laferrière A. Recurrent hypoxia in rats during development increases subsequent respiratory sensitivity to fentanyl. Anesthesiology 2006;105(4):715–718

9. Frey TK, Chopra A, Lin RJ, et al. A child with anterior mediastinal mass supported with veno-arterial extracorporeal membrane oxygenation. Pediatr Crit Care Med 2006;7(5):479–481

10. Kotiniemi LH, Ryhänen PT, Valanne J, Jokela R, Mustonen A, Poukkula E. Postoperative symptoms at home following day-case surgery in children: a multicentre survey of 551 children. Anaesthesia 1997;52(10):963–969

11. Kain ZN, Caldwell-Andrews AA, Mayes LC, et al. Family-centered preparation for surgery improves perioperative outcomes in children: a randomized controlled trial. Anesthesiology 2007;106(1):65–74

12. Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J 1985;32(4):429–434

13. Nuckton TJ, Glidden DV, Browner WS, Claman DM. Physical examination: Mallampati score as an independent predictor of obstructive sleep apnea. Sleep 2006;29(7):903–908

14. Haynes AB, Weiser TG, Berry WR, et al; Safe Surgery Saves Lives Study Group. A surgical safety checklist to reduce morbidity and mortality in a global population. N Engl J Med 2009;360(5):491–499

15. Hohlrieder M, Keller C, Brimacombe J, et al. Middle ear pressure changes during anesthesia with or without nitrous oxide are similar among airway devices. Anesth Analg 2006;102(1):319–321

16. Neuman GG, Sidebotham G, Negoianu E, et al. Laparoscopy explosion hazards with nitrous oxide. Anesthesiology 1993;78(5):875–879

17. Amathieu R, Combes X, Abdi W, et al. An algorithm for difficult airway management, modified for modern optical devices (Airtraq laryngoscope; LMACTrach™): a 2-year prospective validation in patients for elective abdominal, gynecologic, and thyroid surgery. Anesthesiology 2011;114(1):25–33

18. Fiadjoe J, Stricker P. Pediatric difficult airway management: current devices and techniques. Anesthesiol Clin 2009;27(2):185–195

19. Corvetto MA, Hobbs GW, Taekman JM. Fire in the operating room. Simul Healthc 2011; 6(6):356-359

20. Hopkins PM. Malignant hyperthermia: advances in clinical management and diagnosis. Br J Anaesth 2000;85(1):118–128

21. Larach MG, Localio AR, Allen GC, et al. A clinical grading scale to predict malignant hyperthermia susceptibility. Anesthesiology 1994;80(4):771–779

22. Agrawal A, Gerson CR, Seligman I, Dsida RM. Postoperative hemorrhage after tonsillectomy: use of ketorolac tromethamine. Otolaryngol Head Neck Surg 1999;120(3):335–339

23. Møiniche S, Rømsing J, Dahl JB, Tramèr MR. Nonsteroidal antiinflammatory drugs and the risk of operative site bleeding after tonsillectomy: a quantitative systematic review. Anesth Analg 2003;96(1):68–77

24. Horng HC, Ho MT, Huang CH, Yeh CC, Cherng CH. Negative pressure pulmonary edema following naloxone administration in a patient with fentanyl-induced respiratory depression. Acta Anaesthesiol Taiwan 2010;48(3):155–157

25. Kelly LE, Rieder M, van den Anker J, et al. More codeine fatalities after tonsillectomy in North American children. Pediatrics 2012;129(5):e1343-e1347

26. Sadhasivam S, Myer Lii CM. Preventing opioid-related deaths in children undergoing surgery. Pain Med 2012;13(7):982-983, doi 10.1111/j.1526-4637.2012.01419.x

27. Vlajkovic GP, Sindjelic RP. Emergence delirium in children: many questions, few answers. Anesth Analg 2007;104(1):84–91

28. Lin YC, Tassone RF, Jahng S, et al. Acupuncture management of pain and emergence agitation in children after bilateral myringotomy and tympanostomy tube insertion. Paediatr Anaesth 2009;19(11):1096–1101

29. Collins CE, Everett LL. Challenges in pediatric ambulatory anesthesia: kids are different. Anesthesiol Clin 2010;28(2):315–328

30. Eberhart LH, Geldner G, Kranke P, et al. The development and validation of a risk score to predict the probability of postoperative vomiting in pediatric patients. Anesth Analg 2004;99(6):1630–1637

31. Gan T.J., Meyer T., Apfel C.C., et al. Consensus guidelines for managing postoperative nausea and vomiting. Anesth Analg 2003;97(1):62–71

32. Cardwell M, Siviter G, Smith A. Non-steroidal anti-inflammatory drugs and perioperative bleeding in paediatric tonsillectomy. Cochrane Database Syst Rev 2005;(2):CD003591