Respiratory complications in the postanesthesia care unit: A review of pathophysiological mechanisms

Canadian Journal of Respiratory Therapy

Volumn 49, Issue 4, 2013, Pages 21-29

  Karcz, Marcin ^a   Papadakos, Peter J ^a  

^a UNIVERSITY OF ROCHESTER   (United States)

Author keywords

Alveolar hypoventilation; Atelectasis; Postanesthesia care unit; Pulmonary shunt; Respiratory complications; Ventilation perfusion mismatch

Indexed keywords

ANESTHETIC AGENT; CARDIOVASCULAR AGENT; NEUROMUSCULAR BLOCKING AGENT; OPIATE; SEDATIVE AGENT;

ARTERIAL HYPOXEMIA; ARTIFICIAL VENTILATION; ATELECTASIS; DIFFERENTIAL DIAGNOSIS; DIFFUSION IMPAIRMENT; GENERAL ANESTHESIA; HUMAN; HYPOXEMIA; LUNG ALVEOLUS HYPOVENTILATION; NEUROMUSCULAR BLOCKING; OXYGEN EXTRACTION FRACTION; PATHOPHYSIOLOGY; POSITIVE END EXPIRATORY PRESSURE; PRACTICE GUIDELINE; PULMONARY SHUNT; RECOVERY ROOM; RESPIRATION DEPRESSION; RESPIRATORY TRACT DISEASE; REVIEW; RISK FACTOR; VQ MISMATCH;

EID: 84934784459     PISSN: 12059838     EISSN: 23686820     Source Type: Journal    
DOI: None     Document Type: Review

References (130)

1. Rose DK, Cohen MM, Wigglesworth DF, DeBoer DP, Math M. Critical respiratory events in the postanesthesia care unit: Patient, surgical, and anesthetic factors. Anesthesiology 1994;81:410-8.
2. Pedersen T, Viby-Mogensen J, Ringsted C. Anaesthetic practice and postoperative pulmonary complications. Acta Anaesthesiol Scand 1992;36:812-8.
3. Hines R, Barash PG, Watrous G, O'Connor T. Complications occurring in the postanesthesia care unit: A survey. Anesth Analg 1992;74:503-9.
4. Mathew JP, Rosenbaum SH, O'Connor T, Barash PG. Emergency tracheal intubation in the postanesthesia care unit: Physician error or patient disease? Anesth Analg 1990;71:691-7.
5. Beard K, Jick H, Walker AM. Adverse respiratory events occurring in the recovery room after general anesthesia. Anesthesiology 1986;64:269-72.
6. Fleischmann KE, Goldman L, Young B, et al. Association between cardiac and noncardiac complications in patients undergoing noncardiac surgery: Outcomes and effects on length of stay. Am J Med 2003;115:515-20.
7. Qaseem A, Snow V, Fitterman N, et al. Risk assessment for and strategies to reduce perioperative pulmonary complications for patients undergoing noncardiothoracic surgery: A guideline from the American College of Physicians. Ann Intern Med 2006;144:575-80.
8. Smetana GW, Lawrence VA, Cornell JE. Preoperative pulmonary risk stratification for noncardiothoracic surgery: Systematic review for the American College of Physicians. Ann Intern Med 2006;144:581-95.
9. Lawrence VA, Cornell JE, Smetana GW; American College of Physicians. Strategies to reduce postoperative pulmonary complications after noncardiothoracic surgery: Systematic review for the American College of Physicians. Ann Intern Med 2006;144:596-608.
10. Daley MD, Norman PH, Colmenares ME, Sandler AN. Hypoxaemia in adults in the post-anaesthesia care unit. Can J Anaesth 1992;38:740-6.
11. Lundquist H, Hedenstierna G, Strandberg A, et al. CT assessment of dependent lung densities in man during general anaesthesia. Acta Radiol 1995;36:626-32.
12. Gunnarsson L, Tokics L, Gustavsson H, et al. Influence of age on atelectasis formation and gas exchange impairment during general anaesthesia. Br J Anaesth 1991;66:423-32.
13. Hachenberg T, Mollhoff T, Holst D, et al. The ventilation perfusion relation and gas exchange in mitral valve disease and coronary artery disease: Implications for anesthesia, extracorporeal circulation, and cardiac surgery. Anesthesiology 1997;86:809-17.
14. Gunnarsson L, Tokics L, Lundquist H, et al. Chronic obstructive pulmonary disease and anaesthesia: Formation of atelectasis and gas exchange impairment. Eur Respir J 1991;4:1106-16.
15. Warner DO, Warner MA, Ritman EL. Atelectasis and chest wall shape during halothane anesthesia. Anesthesiology 1996;85:49-59.
16. Tokics L, Strandberg A, Brismar B, et al. Computerized tomography of the chest and gas exchange measurements during ketamine anaesthesia. Acta Anaesthesiol Scand 1987;31:684-92.
17. Hedenstierna G, Rothen HU. Atelectasis formation during anesthesia: Causes and measures to prevent it. J Clin Monit Comput 2000;16:329-35.
18. Magnusson L, Spahn DR. New concepts of atelectasis during general anaesthesia. Br J Anaesth 2003;91:61-72.
19. Rahn H, Farhi LE. Gaseous environment and atelectasis. Fed Proc 1963;22:1035-41.
20. Joyce CJ, Williams AB. Kinetics of absorption atelectasis during anesthesia: A mathematical model. J Appl Physiol 1999;86:1116-25.
21. Dantzker DR, Wagner PD, West JB. Instability of lung units with low VA/Q ratios during O2 breathing. J Appl Physiol 1975;38:886-95.
22. Nunn JF, Coleman AJ, Sachithanandan T, et al. Hypoxaemia and atelectasis produced by forced expiration. Br J Anaesth 1965;37:3-12.
23. Rothen HU, Sporre B, Engberg G, et al. Prevention of atelectasis during general anaesthesia. Lancet 1995;345:1387-91.
24. Rothen HU, Sporre B, Engberg G, et al. Influence of gas composition on recurrence of atelectasis after a reexpansion maneuver during general anesthesia. Anesthesiology 1995;82:832-42.
25. Froese AB, McCulloch PR, Sugiura M, et al. Optimizing alveolar expansion prolongs the effectiveness of exogenous surfactant therapy in the adult rabbit. Am Rev Respir Dis 1993;148:569-77.
26. Wollmer P, Schairer W, Bos JA, et al. Pulmonary clearance of 99mTc-DTPA during halothane anaesthesia. Acta Anaesthesiol Scand 1990;34:572-5.
27. Otis DR Jr, Johnson M, Pedley TJ, et al. Role of pulmonary surfactant in airway closure: A computational study. J Appl Physiol 1993;75:1323-33.
28. Agostoni E. Mechanics of the pleural space. Physiol Rev 1972;52:57-128.
29. Reber A, Nylund U, Hedenstierna G. Position and shape of the diaphragm: Implications for atelectasis formation. Anaesthesia 1998;53:1054-61.
30. Rothen HU, Sporre B, Engberg G, et al. Re-expansion of atelectasis during general anaesthesia: A computed tomography study. Br J Anaesth 1993;71:788-95.
31. Marshall BE, Hanson CW, Frasch F, et al. Role of hypoxic pulmonary vasoconstriction in pulmonary gas exchange and blood flow distribution. 2. Pathophysiology. Intensive Care Med 1994;20:379-89.
32. Moudgil R, Michelakis ED, Archer SL. Hypoxic pulmonary vasoconstriction. J Appl Physiol 2005;98:390-403.
33. Sykes MK, Loh L, Seed RF, et al. The effect of inhalational anaesthetics on hypoxic pulmonary vasoconstriction and pulmonary vascular resistance in the perfused lungs of the dog and cat. Br J Anaesth 1972;44:776-88.
34. West JB. Pulmonary Pathophysiology: The Essentials, 8th edn. Philadelphia: Lippincott Williams & Wilkins, 2012.
35. Stemp LS, Ramsay MA. Oxygen may mask hypoventilation: Patient breathing must be ensured. APSF Newslett 2004;20:80.
36. Aldrich TK, Prezant DJ. Indications for mechanical ventilation. In: Tobin MJ, ed. Principles and Practice of Mechanical Ventilation. New York: McGraw-Hill, 1994:155-89.
37. West JB. Assessing pulmonary gas exchange. N Engl J Med 1987;316:1336-8.
38. Hoyt JW. Debunking myths of chronic obstructive pulmonary disease. Crit Care Med 1997;25:1450-1.
39. Fu ES, Downs JB, Schweiger JW. Supplemental oxygen impairs detection of hypoventilation by pulse oximetry. Chest 2004;126:1552-8.
40. Hedenstierna G, Santesson J. Breathing mechanics, dead space and gas exchange in the extremely obese, breathing spontaneously and during anaesthesia with intermittent positive pressure ventilation. Acta Anaesthesiol Scand 1976;20:248-54.
41. Wahba RW. Perioperative functional residual capacity. Can J Anaesth 1991;38:384-400.
42. Morton CP, Drummond GB. Change in chest wall dimensions on induction of anaesthesia: A reappraisal. Br J Anaesth 1994;73:135-9.
43. Froese AB, Bryan AC. Effects of anesthesia and paralysis on diaphragmatic mechanics in man. Anesthesiology 1974;41:242-55.
44. Warner DO, Warner MA, Ritman EL. Human chest wall function while awake and during halothane anesthesia. I. Quiet breathing. Anesthesiology 1995;82:6-19.
45. Jones JG, Faithfull D, Jordan C, et al. Rib cage movement during halothane anaesthesia in man. Br J Anaesth 1979;51:399-407.
46. Lumb AB, Petros AJ, Nunn JF. Rib cage contribution to resting and carbon dioxide stimulated ventilation during 1 MAC isoflurane anaesthesia. Br J Anaesth 1991;67:712-21.
47. Mankikian B, Cantineau JP, Sartene R, et al. Ventilatory pattern and chest wall mechanics during ketamine anesthesia in humans. Anesthesiology 1986;65:492-9.
48. Morel DR, Forster A, Gemperle M. Noninvasive evaluation of breathing pattern and thoraco-abdominal motion following the infusion of ketamine or droperidol in humans. Anesthesiology 1986;65:392-8.
49. Hedenstierna G, Strandberg A, Brismar B, et al. Functional residual capacity, thoracoabdominal dimensions, and central blood volume during general anesthesia with muscle paralysis and mechanical ventilation. Anesthesiology 1985;62:247-54.
50. Darquenne C, Paiva M, Prisk GK. Effect of gravity on aerosol dispersion and deposition in the human lung after periods of breath holding. J Appl Physiol 2000;89:1787-92.
51. Altemeier WA, McKinney S, Glenny RW. Fractal nature of regional ventilation distribution. J Appl Physiol 2000;88:1551-7.
52. Verbanck S, Linnarsson D, Prisk GK, et al. Specific ventilation distribution in microgravity. J Appl Physiol 1996;80:1458-65.
53. Tokics L, Hedenstierna G, Svensson L, et al. V/Q distribution and correlation to atelectasis in anesthetized paralyzed humans. J Appl Physiol 1996;81:1822-33.
54. Landmark SJ, Knopp TJ, Rehder K, et al. Regional pulmonary perfusion and V/Q in awake and anesthetized-paralyzed man. J Appl Physiol 1977;43:993-1000.
55. Glenny RW, Robertson HT. Fractal modeling of pulmonary blood flow heterogeneity. J Appl Physiol 1991;70:1024-30.
56. Hedenstierna G. Contribution of multiple inert gas elimination technique to pulmonary medicine. 6. Ventilation-perfusion relationships during anaesthesia. Thorax 1995;50:85-91.
57. Reber A, Bein T, Högman M, et al. Lung aeration and pulmonary gas exchange during lumbar epidural anaesthesia and in the lithotomy position in elderly patients. Anaesthesia 1998;53:854-61.
58. Eastwood PR, Szollosi I, Platt PR, Hillman DR. Comparison of upper airway collapse during general anaesthesia and sleep. Lancet 2002;359:1207-9.
59. Knill RL, Moote CA, Skinner MI, et al. Anesthesia with abdominal surgery leads to intense REM sleep during the first postoperative week. Anesthesiology 1990;73:52-61.
60. Rahman MQ, Kingshott RN, Wraith P, et al. Association of airway obstruction, sleep, and phasic abdominal muscle activity after upper abdominal surgery. Br J Anaesth 2001;87:198-203.
61. Wu A, Drummond GB. Sleep arousal after lower abdominal surgery and relation to recovery from respiratory obstruction. Anesthesiology 2003;99:1295-302.
62. Sarton E, Teppema L, Nieuwenhuijs D, et al. Opioid effect on breathing frequency and thermogenesis in mice lacking exon 2 of the mu-opioid receptor gene. Adv Exp Med Biol 2001;499:399-404.
63. Shafer SL, Varvel JR. Pharmacokinetics, pharmacodynamics, and rational opioid selection. Anesthesiology 1991;74:53-63.
64. Bouillon T, Schmidt C, Garstka G, et al. Pharmacokinetic pharmacodynamic modeling of the respiratory depressant effect of alfentanil. Anesthesiology 1999;91:144-55.
65. Bailey PL, Lu JK, Pace NL, et al. Effects of intrathecal morphine on the ventilatory response to hypoxia. N Engl J Med 2000;343:1228-34.
66. Catley DM, Thorton M, Jordan C, et al. Pronounced, episodic oxygen desaturation in the postoperative period: Its association with ventilatory pattern and analgesic regimen. Anesthesiology 1985;63:20-8.
67. Alexander CM, Gross JB. Sedative doses of midazolam depress hypoxic ventilatory responses in humans. Anesth Analg 1988;67:377-82.
68. Flogel CM, Ward DS, Wada DR, Ritter JW. The effects of largedose flumazenil on midazolam-induced ventilator depression. Anesth Analg 1993;77:1207-14.
69. Fink BR. Influence of cerebral activity in wakefulness on regulation of breathing. J Appl Physiol 1961;16:15-20.
70. Cammu G, De Witte J, De Veylder J, et al. Postoperative residual paralysis in outpatients versus inpatients. Anesth Analg 2006;102:426-9.
71. Hayes AH, Mirakhur RK, Breslin DS, Reid JE, McCourt KC. Postoperative residual block after intermediate-acting neuromuscular blocking drugs. Anaesthesia 2001;56:312-8.
72. Eriksson LI, Sundman E, Olsson R, et al. Functional assessment of the pharynx at rest and during swallowing in partially paralyzed humans: Simultaneous videomanometry and mechanomyography of awake human volunteers. Anesthesiology 1997;87:1035-43.
73. Eikermann M, Groeben H, Husing J, Peters J. Accelerometry of adductor pollicis muscle predicts recovery of respiratory function from neuromuscular blockade. Anesthesiology 2003;98:1333-7.
74. Sundman E, Witt H, Olsson R, Ekberg O, Kuylenstierna R, Eriksson LI. The incidence and mechanisms of pharyngeal and upper esophageal dysfunction in partially paralyzed humans. Pharyngeal videoradiography and simultaneous manometry after atracurium. Anesthesiology 2000;92:977-84.
75. Igarashi A, Amagasa S, Horikawa H, Shirahata M: Vecuronium directly inhibits hypoxic neurotransmission of the rat carotid body. Anesth Analg 2002;94:117-22.
76. Eriksson LI, Sato M, Severinghaus JW. Effect of a vecuroniuminduced partial neuromuscular block on hypoxic ventilatory response. Anesthesiology 1993;78:693-9.
77. Dahan A, Ward DS, van den Elsen M, et al. Influence of reduced carotid body drive during sustained hypoxia on hypoxic depression of ventilation in humans. J Appl Physiol 1996;81:565-72.
78. van de Borne P, Oren R, Somers VK. Dopamine depresses minute ventilation in patients with heart failure. Circulation 1998;98:126-31.
79. Tusman G, Böhm SH, Suarez-Sipmann F, et al. Alveolar recruitment improves ventilatory efficiency of the lungs during anesthesia. Can J Anaesth 2004;51:723-7.
80. Nicholas TE, Power JH, Barr HA. The pulmonary consequences of a deep breath. Respir Physiol 1982;49:315-24.
81. van Kaam AH, Lachmann RA, Herting E, et al. Reducing atelectasis attenuates bacterial growth and translocation in experimental pneumonia. Am J Respir Crit Care Med 2004;169:1046-53.
82. Oczenski W, Schwarz S, Fitzgerald RD. Vital capacity manoeuvre in general anaesthesia: Useful or useless? Eur J Anaesthesiol 2004;21:253-9.
83. Tokics L, Hedenstierna G, Strandberg A, et al. Lung collapse and gas exchange during general anesthesia: Effects of spontaneous breathing, muscle paralysis, and positive endexpiratory pressure. Anesthesiology 1987;66:157-67.
84. Hedenstierna G, Tokics L, Lundquist H, et al. Phrenic nerve stimulation during halothane anesthesia: Effects of atelectasis. Anesthesiology 1994;80:751-60.
85. Rothen HU, Sporre B, Engberg G, et al. Reexpansion of atelectasis during general anaesthesia may have a prolonged effect. Acta Anaesthesiol Scand 1995;39:118-25.
86. Dyhr T, Laursen N, Larsson A. Effects of lung recruitment maneuver and positive end-expiratory pressure on lung volume, respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery. Acta Anaesthesiol Scand 2002;46:717-25.
87. Dyhr T, Nygards E, Laursen N, et al. Both lung recruitment maneuver and PEEP are needed to increase oxygenation and lung volume after cardiac surgery. Acta Anaesthesiol Scand 2004;48:187-97.
88. Neumann P, Rothen HU, Berglund JE, et al. Positive endexpiratory pressure prevents atelectasis during general anaesthesia even in the presence of a high inspired oxygen concentration. Acta Anaesthiol Scand 1999;43:295-301.
89. Herriger A, Frascarolo P, Spahn DR, et al. The effect of positive airway pressure during pre-oxygenation and induction of anaesthesia upon duration of non-hypoxic apnoea. Anaesthesia 2004;59:243-7.
90. Rusca M, Proietti S, Schnyder P, et al. Prevention of atelectasis formation during induction of general anesthesia. Anesth Analg 2003;97:1835-9.
91. Fulmer JD, Snider GL. ACCP-NHLBI national conference of oxygen therapy. Chest 1984;86:234-47.
92. Hanson CW 3rd, Marshall BE, Frasch HF, Marshall C. Causes of hypercarbia with oxygen therapy in patients with chronic obstructive pulmonary disease. Crit Care Med 1996;24:23-8.
93. Leach RM, Bateman NT. Acute oxygen therapy. Br J Hosp Med 1993;49:637-44.
94. Squadrone V, Coha M, Cerutti E, et al. Continuous positive airway pressure for treatment of postoperative hypoxemia: A randomized controlled trial. JAMA 2005;293:589-95.
95. Squadrone, E, Frigerio, P, Fogliati, C, et al. Noninvasive vs invasive ventilation in COPD patients with severe acute respiratory failure deemed to require ventilatory assistance. Intensive Care Med 2004;30:1303.
96. Paus-Jenssen, ES, Reid, JK, Cockroft, DW, et al. The use of noninvasive ventilation in acute respiratory failure at a tertiary care center. Chest 2004;126:165.
97. Kramer N, Meyer TJ, Meharg J, Cece RD, Hill NS. Randomized, prospective trial of noninvasive positive pressure ventilation in acute respiratory failure. Am J Respir Crit Care Med 1995;151:1799.
98. Huerta S, DeShields S, Shpiner R, et al. Safety and efficacy of postoperative continuous positive airway pressure to prevent pulmonary complications after Roux-en-Y gastric bypass. J Gastrointest Surg 2002;6:354-58.
99. Tobias JD. Noninvasive ventilation using bilevel positive airway pressure to treat impending respiratory failure in the postanesthesia care unit. J Clin Anesth 2000;12:409-12.
100. Albala MZ, Ferrigno M. Short-term noninvasive ventilation in the postanesthesia care unit: A case series. J Clin Anesth 2005;17:636-9.
101. Hillberg RE, Johnson DC. Noninvasive ventilation. N Engl J Med 1997;337:1746-52.
102. McMahon AJ, Fischbacher CM, Frame SH, et al. Impact of laparoscopic cholecystectomy: A population-based study. Lancet 2000;356:1632-7.
103. Weller WE, Rosati C. Comparing outcomes of laparoscopic versus open bariatric surgery. Ann Surg 2008;248:10-5.
104. Guller U, Jain N, Hervey S, Purves H, Pietrobon R. Laparoscopic vs open colectomy. Outcomes comparison based on large nationwide databases. Arch Surg 2003;138:1179-86.
105. Zacks SL, Sandler RS, Rutledge R, Brown RS Jr. A populationbased cohort study comparing laparoscopic cholecystectomy and open cholecystectomy. Am J Gastroenterol 2002;97:334-40.
106. Sharma KC, Brandstetter RD, Brensilver JM, et al. Cardiopulmonary physiology and pathophysiology as a consequence of laparoscopic surgery. Chest 1996;110:810-5.
107. Wahba RW, Béïque F, Kleiman SJ. Cardiopulmonary function and laparoscopic cholecystectomy. Can J Anaesth 1995;42:51-63.
108. Wittgen CM, Andrus CH, Fitzgerald SD, et al. Analysis of the hemodynamic and ventilatory effects of laparoscopic cholecystectomy. Arch Surg 1991;126:997-1000.
109. Kendall AP, Bhatt S, Oh TE. Pulmonary consequences of carbon dioxide insufflation for laparoscopic cholecystectomies. Anaesthesia 1995;50:286-9.
110. Sprung J, Whalley DG, Falcone T, et al. The impact of morbid obesity, pneumoperitoneum, and posture on respiratory system mechanics and oxygenation during laparoscopy. Anesth Analg 2002;94:1345-50.
111. Mäkinen MT, Yli-Hankala A. Respiratory compliance during laparoscopic hiatal and inguinal hernia repair. Can J Anaesth 1998;45:865-70.
112. Hirvonen EA, Nuutinen LS, Kauko M. Ventilatory effects, blood gas changes, and oxygen consumption during laparoscopic hysterectomy. Anesth Analg 1995;80:961-6.
113. Mullett CE, Viale JP, Sagnard PE, et al. Pulmonary CO2 elimination during surgical procedures using intra-or extraperitoneal CO2 insufflation. Anesth Analg 1993;76:622-6.
114. Leighton TA, Liu SY, Bongard FS. Comparative cardiopulmonary effects of carbon dioxide versus helium pneumoperitoneum. Surgery 1993;113:527-31.
115. Andersson L, Lagerstrand L, Thorne A, et al. Effect of CO2 pneumoperitoneum on ventilation-perfusion relationships during laparoscopic cholecystectomy. Acta Anaesthesiol Scand 2002;46:552-60.
116. Bures E, Fusciardi J, Lanquetot H, et al. Ventilatory effects of laparoscopic cholecystectomy. Acta Anaesthesiol Scand 1996;40:566-73.
117. Bolden N, Smith CE, Auckley D, et al. Perioperative complications during use of an obstructive sleep apnea protocol following surgery and anesthesia. Anesth Analg 2007;105:1869.
118. Hwang D, Shakir N, Limann B, et al. Association of sleepdisordered breathing with postoperative complications. Chest 2008;133:1128-34.
119. Gupta RM, Parvizi J, Hanssen AD, Gay PC. Postoperative complications in patients with obstructive sleep apnea syndrome undergoing hip or knee replacement: A case-control study. Mayo Clin Proc 2001;76:897.
120. Loadsman JA, Hillman DR. Anaesthesia and sleep apnoea. Br J Anaesth 2001;86:254-66.
121. Cullen DJ. Obstructive sleep apnea and postoperative analgesia-a potentially dangerous combination. J Clin Anesth 2001;13:83-5.
122. Dhonneur G, Combes X, Leroux B, Duvaldestin P. Postoperative obstructive apnea. Anesth Analg 1999;89:762-7.
123. Gross JB, Bachenberg KL, Benumof JL, et al. Practice guidelines for the perioperative management of patients with obstructive sleep apnea: A report by the American Society of Anesthesiologists Task Force on Perioperative Management of patients with obstructive sleep apnea. Anesthesiology 2006;104:1081.
124. Lamarche Y, Martin R, Reiher J, Blaise G. The sleep apnoea syndrome and epidural morphine. Can Anaesth Soc J 1986;33:231.
125. Kehlet H. Multimodal approach to control postoperative pathophysiology and rehabilitation. Br J Anaesth 1997;78:606-17.
126. Berg H, Roed J, Viby-Mogensen J, et al. Residual neuromuscular block is a risk factor for postoperative pulmonary complications: A prospective, randomised, and blinded study of postoperative pulmonary complications after atracurium, vecuronium and pancuronium. Acta Anaesthesiol Scand 1997;4:1095-103.
127. Ballantyne JC, Carr DB, deFerranti S, et al. The comparative effects of postoperative analgesic therapies on pulmonary outcome: Cumulative meta-analyses of randomized, controlled trials. Anesth Analg 1998;86:598-12.
128. Rodgers A, Walker N, Schug S, et al. Reduction of postoperative mortality and morbidity with epidural or spinal anaesthesia: Results from overview of randomised trials. BMJ 2000;321:1493.
129. Walder B, Schafer M, Henzi I, et al. Efficacy and safety of patientcontrolled opioid analgesia for acute postoperative pain: A quantitative systematic review. Acta Anaesthesiol Scand 2001;45:795-804.
130. O'Connor BS, Vender JS. Oxygen therapy. Crit Care Clin 1995;11:67-78.