Influencing Intraoperative Gastric Regurgitation Factors A
Prospective
Bhagwan
Random
Study
of
Nasogastric
Drainage
Satiani, MB; John T. Bonner, MD; H. Harlan Stone, MD
prospective study was conducted to determine the incigastric regurgitation and aspiration during general anesthesia in 146 patients randomized with respect to presence of a nasogastric tube. A bland dye was instilled in the \s=b\
Tube
A
dence of "silent"
stomach to serve as the determinant marker. The overall incidence of regurgitation was 8.9% and of aspiration, 2.1% in spite of the uniform use of an endotracheal tube. The incidence of regurgitation was twice as high when anesthesia was given by an inexperienced anesthetist (11% vs 5.6%) and in patients without nasogastric tubes (12% vs 6%), although such differences were not statistically significant. The primary agent used, difficulty of endotracheal intubation, location of surgical incision, and duration of anesthesia did not alter the incidence of regurgitation or aspiration. No correlation was found between the detection of subclinical aspiration and the development of postoperative
pulmonary complications. (Arch Surg 113:721-723, 1978) been realized that death can occur from the of food or vomitus during anesthesia. In small even amounts of clear gastric juice aspirated fact, intraoperatively can be lethal.1 In a survey by the Associa¬ tion of Anesthetists in the United Kingdom as to the cause of 1,000 consecutive anesthetic deaths, aspiration was found to be responsible for 110 of the deaths.2 Massive aspiration of gastric contents, nevertheless, must be differentiated from the relatively small amounts occasion-
ally aspirated during operation. To our knowledge, studies
done to determine the exact incidence of "silent" régurgi¬ tation and aspiration have varied considerably as have the anesthetic agents used and the methods of intubation.1·12 To obtain more factual information on the incidence of gastric reguritation and aspiration during general endo¬ tracheal anesthesia and to assess the value of a nasogastric tube in the prevention of this one complication, a prospec¬ tive random study was conducted on the Trauma Service at the Grady Memorial Hospital, Atlanta. Between Sept 1, 1976, and May 31, 1977, 146 patients were included in the study. The following patients, however, were routinely excluded: patients brought to the operating room without a nasogastric tube in place; patients still in shock; patients in whom the operative procedure was less than 30 minutes; and patients suspected of having perforated a gastric or duodenal ulcer.
has
long It aspiration
Accepted for publication Dec 8, 1977. From the Departments of Surgery (Drs Satiani and Stone) and Anesthesiology (Dr Bonner), Emory University School of Medicine, Atlanta. Reprint requests to Department of Surgery, Emory University School of Medicine, 69 Butler St, Atlanta, GA 30302 (Dr Stone).
MATERIALS AND METHODS After apparently all stomach contents had been suctioned out by of a No. 14 French sump nasogastric tube, 2 ml of indigotindisulfonate sodium (indigo carmine) was instilled down the tube and then flushed with 30 ml of normal saline solution. Randomization was based on the patient's hospital number: an odd last digit dictating nasogastric tube removal and an even number, tube retention. Anesthetic induction followed: with preoxygenation by mask ventilation first, rapidly given intravenous thiopental sodium next, then succinylcholine chloride-induced apnea, and finally endotracheal intubation. Most patients also received 3 mg of tubocurarine chloride prior to anesthetic induction. Presence of the instilled dye in the oropharynx or endotracheal tube was specifically looked for during intubation as well as prior means
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and after removal of the endoctracheal tube. The diagnosis of dye régurgitation and/or aspiration was made, however, only if such a finding was confirmed by the staff or senior resident anesthesiologist attending that individual case. The exact time of such a positive finding was then noted on the anesthesia record. Essentially all patients were maintained in the supine position during operation. The primary anesthetic agent, type of incision, duration of the operative procedure, and other critical events of anesthesia were routinely noted. Anesthetists of varying experience performed the trachéal intubations. Staff physicians, senior residents, and senior nurse anesthetists were arbitrarily categorized as "experienced"; in the "inexperienced" group were rotating interns, dental resi¬ dents, physician assistants, and medical students. Intubation was rated as being difficult if more than one attempt was required. Soft-cuffed endotracheal tubes made of polyvinyl chloride plastic were always used, with the tube sizes varying from 7.5 to 9 mm (average, 8.5 mm). After the lungs had been inflated to an airway to
pressure of 20 cm of water, the cuff on the endotracheal tube was blown up with whatever volume was necessary to produce an effective seal against gas leak. All patients were followed postoperatively for both clinical and
radiological evidence of atelectasis and/or pneumonia. Where applicable, the 2 method was used for statistical analysis. RESULTS
The average age of the 146 patients was 36.3 years, with range of 15 to 83 years. On comparison of the two study groups, ie, those with nasogastric tubes inserted during anesthetic induction and maintenance and those without, there was no statistically significant difference with respect to age, race, sex, type of anesthetic agent used, anesthetist's experience, duration of anesthesia and opera¬ tion, difficulty of intubation, endotracheal tube size, or
Table 1—Incidence of
Anesthesia
There
was no
substantial difference in the incidence of
régurgitation for experienced vs inexperienced anesthe¬ tists, type of anesthetic agent used, ease of endotracheal intubation, or size of endotracheal tube (Table 2).
The average duration of anesthesia was 2.7 hours, with a range of 45 minutes to eight hours, whereas the average duration of the actual operation was two hours (ranging from 30 minutes to seven hours). In either case, elapsed time was not influential in determining the likelihood of
and
Aspiration"
Nasogastric Tube
Regurgitated Aspirated as well "None ot the differences
Used
Not Used
Total
( = 81) 5(6.2%) 1(1.2%)
( = 65) 8(12.3%) 2 (3.1%)
( = 146) 13(8.9%) 3(2.1%)
was
statistically significant (P
.05).
>
Table 2.—Influence of Anesthesia and Incision* No. of
Patients
Surgical Incision Upper abdominal
Experienced Inexperienced Primary anesthetic agent
53 91
Ethrane Halothane Nitrous oxide Other Difficulty of intubation
5
3 (5.7)
10(11.0)
64
_
"None of the differences
(6.3) 7(12.1) 1 (11 1)
6
(9.4) 2(6.1) 3(9.1) 2(12.6)
33 33 16
Easy
Difficult
Régurgitations (%)
79 58 9
Lower abdominal Elsewhere Anesthetist training
a
primary surgical diagnosis. Régurgitation and Aspiration The diagnosis of régurgitation was based on the presence of dye in the pharynx, larynx, trachea, endotra¬ cheal tube, or trachéal aspirant. This occurred 13 times, giving an overall incidence of 8.9% (Table 1). Dye discov¬ ered below the vocal cords, in the endotracheal tube, or in trachéal secretions was taken to represent aspiration and was noted in three (2.1%) patients. Régurgitation was more commonly seen in the older patient (average age of 47.7 years vs 35.2 years for those not regurgitating) although the difference was not statis¬ tically significant. The incidence of silent régurgitation was also not substantially different with respect to the different types of abdominal incision (Table 2).
Régurgitation
was
133 13
statistically significant (P
11
(8.3) 2(15.4)
>
.05).
gastric régurgitation. Of the 13 patients who were considered to have regurgi¬ tated, six had dye visible in the pharynx on intubation and two of these had a positive trachea! aspirant at this time as well. Four other patients had dye detected in their oropharynx during the operative procedure or on extubation. The exact time of régurgitation in the remaining three patients was not recorded. Nasogastric
Tube
Régurgitation of instilled dye was noted in five (6.2%) of the 81 patients in whom the nasogastric tube had been retained as compared with eight (12.3%) of the 65 patients in whom the tube had been removed prior to induction of anesthesia (Table 1). Aspiration occurred in one and two patients of these groups, respectively. Although the inci¬ dence of régurgitation was twice as high in those without nasogastric tubes as when the tube had been left in place, it statistically significant (P > .05). pulmonary complication, ie, atelectasis and/or pneu¬ monia, developed in 25 of the patients. However, no was
not
A
substantial differences were noted with respect to these complications and the use of a nasogastric tube, incidence of régurgitation or silent aspiration, or difficulty of endo¬ tracheal intubation. COMMENT
The incidence of silent régurgitation and aspiration during general anesthesia has been reported to vary
between 8% and 25%.35 Before the acceptance of almost
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routine endotracheal intubation, pharyngeal packs were often advocated in an effort to reduce the incidence of such aspiration even though it was recognized that aspiration was relatively common and usually well tolerated." The lack of substantial complications in such patients was noted in spite of the fact that intrapulmonic barium was seen on chest roentgenograms the morning after barium had been deposited in the mouths of sleeping patients.6 A similar study confirmed barium aspiration in 10% of the patients postoperatively, yet volume and character of the aspirant seemed to be the important factors determining any consequence of such aspiration.7 The relatively low incidence of silent régurgitation and aspiration in the present series is not surprising. Gastric emptying time is approximately doubled whenever preoperative narcotics and a mixture of hyposcyamine sulfate, atropine sulfate, and scopolamine HBR (belladon¬ na alkaloids) are given to elective operative cases.8 However, all patients in this report not only had their gastric contents removed preoperatively by means of suctioning, but they also were not premedicated in the same manner as an elective patient would be. Although emptying the stomach before induction of anesthesia is a routine practice in surgical emergencies, particulate matter, such as large pieces of swallowed meat, are impos¬ sible to evacuate through the lumen of an ordinary naso¬ gastric tube. In addition, the tube can act as a wick, allowing silent régurgitation by making the lower esophageal sphincter incompetent." In spite of these drawbacks, the potentially protective aspect of a nasogastric tube, especially in regard to diminishing the liquid volume of retained gastric contents, may be exceedingly important. A pH of less than 2.5 and a volume greater than 25 ml
to represent the critical levels leading to major complications of gastric acid aspiration.10·" In the classic study by Mendelson,1 aspiration occurred in 68% of the women in the delivery room; 50% of these were not recognized until a later date. The pH of the aspirated material was a major determinant in eventual outcome, since a 60% mortality was reported in those patients who aspirated gastric juice with a pH of less than 2.5. In a recent study, even after more than four hours of starva¬ tion, total gastric volumes in excess of 40 ml were found in 29% of the patients and a pH of less than 2.5 was found in more than 40% of patients operated on as emergencies.12 Consideration has therefore been given to buffering the acid contents of the stomach prior to induction of anes¬ thesia and to the administration of antibiotics for systemic effect to patients suspected of having had a silent régurgi¬ tation or aspiration."' Antacid has been shown to substantially raise the pH level and to reduce by tenfold the number of patients who are at risk of having aspiration pneumonia develop while undergoing a cesarean section." Nevertheless, aspiration pneumonia has been found to occur after neutralization of gastric contents to a pH as high as 3.5.11 In a prospective study of elective operations, the percentage of patients having a mean gastric pH of less than 2.5 was reduced from 52% to only 1% by the preoperative oral administration of antacid.14 As noted in previous studies,4 subclinical aspiration in the present series could not be correlated with the development of pulmonary complications after operation. This is in contrast to patients who have obvious and massive aspira¬ tion because the complication rate is high and the mortality seem
may
even
reach 70%.15
References 1. Mendelson CL: The aspiration of stomach contents into the lungs during obstetric anesthesia. Am J Obstet Gynecol 52:191-205, 1946. 2. Edwards G, Morton HJV, Wylie WD: Deaths associated with anesthesia: Report of 1,000 cases. Anesthesiology 11:194-222, 1956. 3. Culver GA, Makel HP, Beecher HK: Frequency of aspiration of gastric contents by the lungs during anesthesia and surgery. Ann Surg 133:289-292, 1951. 4. Blitt
CD, Gutman HL, Cohen DD, et al: "Silent" regurgitation and aspiration during general anesthesia. Anesth Analg 49:707-713, 1970. 5. Berson J, Adriani J: "Silent" regurgitation and aspiration during anesthesia. Anesthesiology 15:644-649, 1954. 6. Amberson JB: Aspiration bronchopneumonia. Int Clinics 3:126-138,
1937. 7. Gardner AMN: Aspiration of food and vomit. Q J Med 106:227-245, 1958. 8. Chase HF: Role of delayed gastric emptying time in the etiology of
aspiration pneumonia. Am J Obstet Gynecol 56:673-679, 1948. 9. Cameron JL, Reynolds J, Zuidema GD: Aspiration in patients with tracheostomies. Surg Gynecol Obstet 136:68-70, 1973. 10. Teabeaut JR: Aspiration of gastric contents: Experimental study. Am
J Pathol 28:51-62, 1952. 11. Roberts RB, Shirley MA: Reducing the risk of acid aspiration during caeserean section. Anesth Analg 53:859-868. 1976. 12. Hester JB, Heath ML: Pulmonary acid aspiration syndrome: Should prophylaxis be routine? Br J Anaesth 47:630-631, 1975. 13. Taylor G: Acid pulmonary aspiration syndrome after antacids: A case report. Br J Anaesth 47:615-617, 1975. 14. Hutchinson BR, Newson AJ: Preoperative neutralization of gastric acidity. Anaesth Intensive Care 3:198-203, 1975. 15. Cameron JL, Mitchell WH, Zuidema GD: Aspiration pneumonia: Clinical outcome following documented aspiration. Arch Surg 106:49-52, 1973.
Downloaded From: http://archsurg.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/24/2015
Prospective
Bhagwan
Random
Study
of
Nasogastric
Drainage
Satiani, MB; John T. Bonner, MD; H. Harlan Stone, MD
prospective study was conducted to determine the incigastric regurgitation and aspiration during general anesthesia in 146 patients randomized with respect to presence of a nasogastric tube. A bland dye was instilled in the \s=b\
Tube
A
dence of "silent"
stomach to serve as the determinant marker. The overall incidence of regurgitation was 8.9% and of aspiration, 2.1% in spite of the uniform use of an endotracheal tube. The incidence of regurgitation was twice as high when anesthesia was given by an inexperienced anesthetist (11% vs 5.6%) and in patients without nasogastric tubes (12% vs 6%), although such differences were not statistically significant. The primary agent used, difficulty of endotracheal intubation, location of surgical incision, and duration of anesthesia did not alter the incidence of regurgitation or aspiration. No correlation was found between the detection of subclinical aspiration and the development of postoperative
pulmonary complications. (Arch Surg 113:721-723, 1978) been realized that death can occur from the of food or vomitus during anesthesia. In small even amounts of clear gastric juice aspirated fact, intraoperatively can be lethal.1 In a survey by the Associa¬ tion of Anesthetists in the United Kingdom as to the cause of 1,000 consecutive anesthetic deaths, aspiration was found to be responsible for 110 of the deaths.2 Massive aspiration of gastric contents, nevertheless, must be differentiated from the relatively small amounts occasion-
ally aspirated during operation. To our knowledge, studies
done to determine the exact incidence of "silent" régurgi¬ tation and aspiration have varied considerably as have the anesthetic agents used and the methods of intubation.1·12 To obtain more factual information on the incidence of gastric reguritation and aspiration during general endo¬ tracheal anesthesia and to assess the value of a nasogastric tube in the prevention of this one complication, a prospec¬ tive random study was conducted on the Trauma Service at the Grady Memorial Hospital, Atlanta. Between Sept 1, 1976, and May 31, 1977, 146 patients were included in the study. The following patients, however, were routinely excluded: patients brought to the operating room without a nasogastric tube in place; patients still in shock; patients in whom the operative procedure was less than 30 minutes; and patients suspected of having perforated a gastric or duodenal ulcer.
has
long It aspiration
Accepted for publication Dec 8, 1977. From the Departments of Surgery (Drs Satiani and Stone) and Anesthesiology (Dr Bonner), Emory University School of Medicine, Atlanta. Reprint requests to Department of Surgery, Emory University School of Medicine, 69 Butler St, Atlanta, GA 30302 (Dr Stone).
MATERIALS AND METHODS After apparently all stomach contents had been suctioned out by of a No. 14 French sump nasogastric tube, 2 ml of indigotindisulfonate sodium (indigo carmine) was instilled down the tube and then flushed with 30 ml of normal saline solution. Randomization was based on the patient's hospital number: an odd last digit dictating nasogastric tube removal and an even number, tube retention. Anesthetic induction followed: with preoxygenation by mask ventilation first, rapidly given intravenous thiopental sodium next, then succinylcholine chloride-induced apnea, and finally endotracheal intubation. Most patients also received 3 mg of tubocurarine chloride prior to anesthetic induction. Presence of the instilled dye in the oropharynx or endotracheal tube was specifically looked for during intubation as well as prior means
Downloaded From: http://archsurg.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/24/2015
and after removal of the endoctracheal tube. The diagnosis of dye régurgitation and/or aspiration was made, however, only if such a finding was confirmed by the staff or senior resident anesthesiologist attending that individual case. The exact time of such a positive finding was then noted on the anesthesia record. Essentially all patients were maintained in the supine position during operation. The primary anesthetic agent, type of incision, duration of the operative procedure, and other critical events of anesthesia were routinely noted. Anesthetists of varying experience performed the trachéal intubations. Staff physicians, senior residents, and senior nurse anesthetists were arbitrarily categorized as "experienced"; in the "inexperienced" group were rotating interns, dental resi¬ dents, physician assistants, and medical students. Intubation was rated as being difficult if more than one attempt was required. Soft-cuffed endotracheal tubes made of polyvinyl chloride plastic were always used, with the tube sizes varying from 7.5 to 9 mm (average, 8.5 mm). After the lungs had been inflated to an airway to
pressure of 20 cm of water, the cuff on the endotracheal tube was blown up with whatever volume was necessary to produce an effective seal against gas leak. All patients were followed postoperatively for both clinical and
radiological evidence of atelectasis and/or pneumonia. Where applicable, the 2 method was used for statistical analysis. RESULTS
The average age of the 146 patients was 36.3 years, with range of 15 to 83 years. On comparison of the two study groups, ie, those with nasogastric tubes inserted during anesthetic induction and maintenance and those without, there was no statistically significant difference with respect to age, race, sex, type of anesthetic agent used, anesthetist's experience, duration of anesthesia and opera¬ tion, difficulty of intubation, endotracheal tube size, or
Table 1—Incidence of
Anesthesia
There
was no
substantial difference in the incidence of
régurgitation for experienced vs inexperienced anesthe¬ tists, type of anesthetic agent used, ease of endotracheal intubation, or size of endotracheal tube (Table 2).
The average duration of anesthesia was 2.7 hours, with a range of 45 minutes to eight hours, whereas the average duration of the actual operation was two hours (ranging from 30 minutes to seven hours). In either case, elapsed time was not influential in determining the likelihood of
and
Aspiration"
Nasogastric Tube
Regurgitated Aspirated as well "None ot the differences
Used
Not Used
Total
( = 81) 5(6.2%) 1(1.2%)
( = 65) 8(12.3%) 2 (3.1%)
( = 146) 13(8.9%) 3(2.1%)
was
statistically significant (P
.05).
>
Table 2.—Influence of Anesthesia and Incision* No. of
Patients
Surgical Incision Upper abdominal
Experienced Inexperienced Primary anesthetic agent
53 91
Ethrane Halothane Nitrous oxide Other Difficulty of intubation
5
3 (5.7)
10(11.0)
64
_
"None of the differences
(6.3) 7(12.1) 1 (11 1)
6
(9.4) 2(6.1) 3(9.1) 2(12.6)
33 33 16
Easy
Difficult
Régurgitations (%)
79 58 9
Lower abdominal Elsewhere Anesthetist training
a
primary surgical diagnosis. Régurgitation and Aspiration The diagnosis of régurgitation was based on the presence of dye in the pharynx, larynx, trachea, endotra¬ cheal tube, or trachéal aspirant. This occurred 13 times, giving an overall incidence of 8.9% (Table 1). Dye discov¬ ered below the vocal cords, in the endotracheal tube, or in trachéal secretions was taken to represent aspiration and was noted in three (2.1%) patients. Régurgitation was more commonly seen in the older patient (average age of 47.7 years vs 35.2 years for those not regurgitating) although the difference was not statis¬ tically significant. The incidence of silent régurgitation was also not substantially different with respect to the different types of abdominal incision (Table 2).
Régurgitation
was
133 13
statistically significant (P
11
(8.3) 2(15.4)
>
.05).
gastric régurgitation. Of the 13 patients who were considered to have regurgi¬ tated, six had dye visible in the pharynx on intubation and two of these had a positive trachea! aspirant at this time as well. Four other patients had dye detected in their oropharynx during the operative procedure or on extubation. The exact time of régurgitation in the remaining three patients was not recorded. Nasogastric
Tube
Régurgitation of instilled dye was noted in five (6.2%) of the 81 patients in whom the nasogastric tube had been retained as compared with eight (12.3%) of the 65 patients in whom the tube had been removed prior to induction of anesthesia (Table 1). Aspiration occurred in one and two patients of these groups, respectively. Although the inci¬ dence of régurgitation was twice as high in those without nasogastric tubes as when the tube had been left in place, it statistically significant (P > .05). pulmonary complication, ie, atelectasis and/or pneu¬ monia, developed in 25 of the patients. However, no was
not
A
substantial differences were noted with respect to these complications and the use of a nasogastric tube, incidence of régurgitation or silent aspiration, or difficulty of endo¬ tracheal intubation. COMMENT
The incidence of silent régurgitation and aspiration during general anesthesia has been reported to vary
between 8% and 25%.35 Before the acceptance of almost
Downloaded From: http://archsurg.jamanetwork.com/ by a Karolinska Institutet University Library User on 05/24/2015
routine endotracheal intubation, pharyngeal packs were often advocated in an effort to reduce the incidence of such aspiration even though it was recognized that aspiration was relatively common and usually well tolerated." The lack of substantial complications in such patients was noted in spite of the fact that intrapulmonic barium was seen on chest roentgenograms the morning after barium had been deposited in the mouths of sleeping patients.6 A similar study confirmed barium aspiration in 10% of the patients postoperatively, yet volume and character of the aspirant seemed to be the important factors determining any consequence of such aspiration.7 The relatively low incidence of silent régurgitation and aspiration in the present series is not surprising. Gastric emptying time is approximately doubled whenever preoperative narcotics and a mixture of hyposcyamine sulfate, atropine sulfate, and scopolamine HBR (belladon¬ na alkaloids) are given to elective operative cases.8 However, all patients in this report not only had their gastric contents removed preoperatively by means of suctioning, but they also were not premedicated in the same manner as an elective patient would be. Although emptying the stomach before induction of anesthesia is a routine practice in surgical emergencies, particulate matter, such as large pieces of swallowed meat, are impos¬ sible to evacuate through the lumen of an ordinary naso¬ gastric tube. In addition, the tube can act as a wick, allowing silent régurgitation by making the lower esophageal sphincter incompetent." In spite of these drawbacks, the potentially protective aspect of a nasogastric tube, especially in regard to diminishing the liquid volume of retained gastric contents, may be exceedingly important. A pH of less than 2.5 and a volume greater than 25 ml
to represent the critical levels leading to major complications of gastric acid aspiration.10·" In the classic study by Mendelson,1 aspiration occurred in 68% of the women in the delivery room; 50% of these were not recognized until a later date. The pH of the aspirated material was a major determinant in eventual outcome, since a 60% mortality was reported in those patients who aspirated gastric juice with a pH of less than 2.5. In a recent study, even after more than four hours of starva¬ tion, total gastric volumes in excess of 40 ml were found in 29% of the patients and a pH of less than 2.5 was found in more than 40% of patients operated on as emergencies.12 Consideration has therefore been given to buffering the acid contents of the stomach prior to induction of anes¬ thesia and to the administration of antibiotics for systemic effect to patients suspected of having had a silent régurgi¬ tation or aspiration."' Antacid has been shown to substantially raise the pH level and to reduce by tenfold the number of patients who are at risk of having aspiration pneumonia develop while undergoing a cesarean section." Nevertheless, aspiration pneumonia has been found to occur after neutralization of gastric contents to a pH as high as 3.5.11 In a prospective study of elective operations, the percentage of patients having a mean gastric pH of less than 2.5 was reduced from 52% to only 1% by the preoperative oral administration of antacid.14 As noted in previous studies,4 subclinical aspiration in the present series could not be correlated with the development of pulmonary complications after operation. This is in contrast to patients who have obvious and massive aspira¬ tion because the complication rate is high and the mortality seem
may
even
reach 70%.15
References 1. Mendelson CL: The aspiration of stomach contents into the lungs during obstetric anesthesia. Am J Obstet Gynecol 52:191-205, 1946. 2. Edwards G, Morton HJV, Wylie WD: Deaths associated with anesthesia: Report of 1,000 cases. Anesthesiology 11:194-222, 1956. 3. Culver GA, Makel HP, Beecher HK: Frequency of aspiration of gastric contents by the lungs during anesthesia and surgery. Ann Surg 133:289-292, 1951. 4. Blitt
CD, Gutman HL, Cohen DD, et al: "Silent" regurgitation and aspiration during general anesthesia. Anesth Analg 49:707-713, 1970. 5. Berson J, Adriani J: "Silent" regurgitation and aspiration during anesthesia. Anesthesiology 15:644-649, 1954. 6. Amberson JB: Aspiration bronchopneumonia. Int Clinics 3:126-138,
1937. 7. Gardner AMN: Aspiration of food and vomit. Q J Med 106:227-245, 1958. 8. Chase HF: Role of delayed gastric emptying time in the etiology of
aspiration pneumonia. Am J Obstet Gynecol 56:673-679, 1948. 9. Cameron JL, Reynolds J, Zuidema GD: Aspiration in patients with tracheostomies. Surg Gynecol Obstet 136:68-70, 1973. 10. Teabeaut JR: Aspiration of gastric contents: Experimental study. Am
J Pathol 28:51-62, 1952. 11. Roberts RB, Shirley MA: Reducing the risk of acid aspiration during caeserean section. Anesth Analg 53:859-868. 1976. 12. Hester JB, Heath ML: Pulmonary acid aspiration syndrome: Should prophylaxis be routine? Br J Anaesth 47:630-631, 1975. 13. Taylor G: Acid pulmonary aspiration syndrome after antacids: A case report. Br J Anaesth 47:615-617, 1975. 14. Hutchinson BR, Newson AJ: Preoperative neutralization of gastric acidity. Anaesth Intensive Care 3:198-203, 1975. 15. Cameron JL, Mitchell WH, Zuidema GD: Aspiration pneumonia: Clinical outcome following documented aspiration. Arch Surg 106:49-52, 1973.
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