Prevention of pulmonary gastric contents aspiration

Abstracts

JUSTIFICATIVA E OBJETIVOS: Apesar da baixa incidência, a aspiração pulmonar do conteúdo gástrico pode ter conseqüências devastadoras para o indivíduo. A diminuição na função do esfíncter esofágico e dos reflexos protetores das vias aéreas causadas pela depressão da consciência, predispõe os pacientes a esta grave complicação. Neste artigo, foi realizada uma revisão dos aspectos fisiológicos associados ao refluxo gastroesofágico, bem como os métodos utilizados para preveni-lo. CONTEÚDO: São feitos comentários sobre os mecanismos envolvidos na aspiração do conteúdo gástrico, suas conseqüências e métodos de prevenção, incluindo recentes guias de jejum pré-operatório elaborados após revisão da literatura, o uso racional de drogas que atuam no pH e volume gástrico e, finalmente, o efeito de diferentes métodos de manutenção da via aérea na prevenção da aspiração pulmonar. CONCLUSÕES: A aspiração pulmonar do conteúdo gástrico, apesar de pouco freqüente, exige cuidados especiais para sua prevenção. Guias de jejum pré-operatório elaborados recentemente sugerem períodos menores de jejum, principalmente para líquidos, permitindo mais conforto aos pacientes e menor risco de hipoglicemia e desidratação, sem aumentar a incidência de aspiração pulmonar perioperatória. O uso rotineiro de drogas que diminuem a acidez e volume gástrico parece estar indicado apenas para pacientes de risco. O melhor método de proteção da via aérea contra a aspiração continua sendo a intubação traqueal. Outros métodos de manutenção da via aérea vêm sendo adotados, mas a eficácia na prevenção da aspiração ainda é inferior, embora representem importante alternativa em casos de falha de intubação traqueal.

COMPLICAÇÕES

REVIEW ARTICLE

Prevention of pulmonary gastric contents aspiration^*

Prevención de la aspiración pulmonar del contenido gástrico

Eduardo Toshiyuki Moro, TSA, M.D.

Anestesiologista dos Hospitais Santa Lucinda e UNIMED; Instrutor do CET do Conjunto Hospitalar de Sorocaba/PUC - SP

^{Correspondence}

SUMMARY

BACKGROUND AND OBJECTIVES: Despite its low incidence, aspiration of pulmonary gastric contents may have devastating consequences. Esophageal sphincter function and protective airway reflexes decrease caused by conscience depression, predisposes patients to this severe complication. This article is a review of physiological aspects associated to gastroesophageal reflux, as well as of the methods to prevent it.

CONTENTS: Comments are made about the mechanisms involved in gastric contents aspiration, its consequences and preventive methods, including recent preoperative fasting guidelines developed after review of the literature, the reasonable use of drugs acting on gastric pH and volume, and finally the effects of different airway control methods on pulmonary aspiration prevention.

CONCLUSIONS: Aspiration of pulmonary gastric contents, despite its low frequency, demands special preventive care. Recently developed preoperative fasting guidelines suggest shorter fasting periods especially for liquids, allowing more comfort to patients and less risk of hypoglycemia and dehydration, without increasing the incidence of perioperative pulmonary aspiration. The routine use of drugs decreasing gastric acidity and volume seems to be indicated only for poor risk patients. The best method to protect airways against aspiration is still tracheal intubation. Other airway control methods have been adopted, but their efficacy in preventing aspiration is lower, although representing major alternatives in cases of intubation failure.

Key Words: COMPLICATIONS: pulmonary aspiration

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: No obstante de la baja incidencia, la aspiración pulmonar del contenido gástrico puede tener consecuencias devastadoras para el individuo. La disminución en la función del esfínter esofágico y de los reflejos protectores de las vías aéreas causada por la depresión de la conciencia, predispone los pacientes a esta grave complicación. En este articulo, se realizo una revisión de los aspectos fisiológicos asociados al reflujo gastroesofágico, bien como los métodos utilizados para prevenirlo.

CONTENIDO: Fueron hechos comentarios sobre los mecanismos envueltos en la aspiración del contenido gástrico, sus consecuencias y métodos de prevención, incluyendo recientes guías de ayuno pre-operatorio elaborados después de revisión de la literatura, el uso racional de drogas que actúan y el pH y volumen gástrico, y, finalmente, el efecto de diferentes métodos de manutención de la vía aérea en la prevención de la aspiración pulmonar.

CONCLUSIONES: La aspiración pulmonar del contenido gástrico, no obstante sea poco frecuente, exige cuidados especiales para su prevención. Guías de ayuno pre-operatorio elaborados recientemente sugieren períodos menores de ayuno, principalmente para líquidos, permitiendo más comodidad a los pacientes y menor riesgo de hipoglicemia y deshidratación, sin aumentar la incidencia de aspiración pulmonar perioperatoria. El uso rutinario de drogas que diminuyen la acidez y volumen gástrico parece estar indicado apenas para pacientes de riesgo. El mejor método de protección de la vía aérea contra la aspiración continua siendo la intubación traqueal. Otros métodos de manutención de la vía aérea están siendo adoptados, más la eficacia en la prevención de la aspiración aun es inferior, aun cuando representen importante alternativa en casos de falla de intubación traqueal.

INTRODUCTION

Recent studies have suggested that perioperative pulmonary aspiration is an uncommon event however with devastating impact ¹. In 1946, Mendelson has already established a relationship between feeding and aspiration of pulmonary gastric contents during labor under general anesthesia. He has described two syndromes: the first would be the inhalation of solid food leading to airways obstruction and death or massive atelectasis. The second, named after him, would be liquid contents aspiration when laryngeal reflexes are depressed by general anesthesia ². These patients would develop cyanosis, tachycardia and tachypnea. Mendelson has shown in rabbits that the development of the syndrome would depend on the acid pH of aspired material ³.

In this article, mechanisms involved in regurgitation and aspiration of pulmonary gastric contents are evaluated together with some preventive methods.

INCIDENCE

A review of the literature suggests that the incidence of perioperative pulmonary aspiration is relatively low and has suffered minor changes in recent years. In 1986, a study of the Scandinavian Teaching Hospital has observed that the incidence of aspiration varied from 0.7 to 4.7 per 10 thousand anesthesias ⁴. A publication 10 years later has observed an incidence of 2.5 per 10 thousand in the Norwegian Hospital ⁵.

Mayo Clinic studies have observed similar incidence in adults (3.1 per 10 thousand) ⁶ and children (3.8 per 10 thousand) ⁷. Another North-American study has observed a higher incidence in children (10.2 per 10 thousand) ⁸.

Frequency varies widely among patients. So, elderly, higher ASA physical status patients, pregnant women, patients suffering from gatroesophageal reflux, obese and patients submitted to urgency surgeries are at higher risk for aspiration ^1,9. In addition, pain, anxiety, diabetes mellitus, renal failure, conscience depression, alcohol and drugs (opioids, benzodiazepines, anticholinergic) which delay gastric emptying ^3,9.

Based on recently available data, pulmonary gastric contents aspiration seems to be only slightly more frequent in children as compared to adults. Children also seem to be less severely affected by aspiration ¹⁰.

MORBIDITY AND MORTALITY

Morbidity attributed to aspiration is characterized by the presence of pulmonary infiltrates at chest X-rays, by the need for antibiotics or bronchodilators and by ventilatory support duration ⁹ (Table I).

Brazilian Journal of Anesthesiology, 2004; 54: 2: 261 - 275

Prevention of pulmonary gastric contents aspiration

Eduardo Toshiyuki Moro

In a Mayo Clinic study ⁶, 27% of pulmonary aspiration patients needed ventilatory support for more than 24 hours.

Major retrospective studies performed in different centers have shown mortality rates varying from zero to 4.5% ^4-8.

In the UK, the "Confidential Enquirer into Maternal Deaths" has presented accurate data on post-gastric content aspiration mortality in obstetrics, from 1957 to 1998 ¹¹. For anesthesia-related deaths, the proportion attributed to pulmonary aspiration has progressively decreased from 50% to 65% fifty years ago, to up to 12% in recent 10 years. This decrease is clearly the result of replacing general anesthesia by spinal blocks in obstetric anesthesia ¹¹.

PHYSIOLOGY

Physiological mechanisms preventing gastric contents regurgitation and aspiration include lower esophageal sphincter, upper esophageal sphincter and laryngeal reflexes.

Gastric Contents

Critical values for aspiration pneumonitis risk derived from animal models are gastric contents volume above 0.4 ml.kg^-1 and pH lower than 2.5 ¹². However, a study performed with cats has shown that gastric volume necessary for spontaneous regurgitation was 20.8 mL.kg^{-1 13}. Other investigators consider residual gastric volume between 0.8 and 8 mL.kg^-1 as a risk factor for aspiration ^13-16.

A critical review of the literature has revealed that lower pH and higher gastric volume are major risk factors for pulmonary aspiration in animal models. However, differences among species make human extrapolation difficult and inaccurate ¹⁷. In addition, healthy patients with prolonged preoperative fasting often have gastric volume above 0.4 mL.kg^-1 and pH below 2.5 ^18-21.

So, in spite of evidences of direct relationship between aspired volume and pneumonitis severity ¹⁴, the ratio between gastric and aspired volume has been questioned and its validity needs further studies ²².

In 1833, Beaumont has already recorded that after fluid ingestion, stomach would empty in less than 1 hour, while emptying time for solids was much longer ²³. The dependence on gastric motility for solid material emptying explains this difference, since in case of fluids there is no such dependence ²⁴. Water and fluids cross the stomach very fast. Half of 500 ml isotonic saline solution bolus is emptied and/or absorbed by the stomach in 12 minutes ^25,26. Half of 750 ml bolus disappears in 20 minutes ^21,27,28 and 80% to 95% of ingested fluids disappear in one hour ^29,30.

However, gastric emptying time for solids varies considerably.

Among types of ingested food, lipids emptying is slower, proteins emptying is faster and carbohydrates emptying is intermediate ³¹. There is no absolute definition of solid food. In practical terms, solid is every food in this state in the stomach ²³. So, gelatin is solid before ingestion, but is not in solid state in the stomach. On the other hand, milk forms solid components in the stomach and takes hours to be emptied.

Lower Esophageal Sphincter

Seemingly there is no true anatomic sphincter, but muscle fibers of the junction of esophagus and stomach, which are disposed in circle acting as a true sphincter.

The trend to regurgitation is not directly dependent on lower esophageal sphincter pressure, but on the difference between this pressure and intra-gastric pressure. Antiemetics, cholinergic drugs, succinylcholine and antacids increase lower esophageal sphincter pressure, while anticholinergics, thiopental, opioids and inhalational anesthetics decrease it. Atracurium, vecuronium, ranitidine and cimetidine have no effect on lower esophageal sphincter ³².

Upper Esophageal Sphincter

Helps preventing aspiration by acting on the transition exerted by the cricopharyngeal muscle between esophagus and hypopharynx. During anesthesia, and even during normal sleep, there is a change in its function and tone ³³.

With the exception of ketamine, anesthetic drugs decrease upper esophageal sphincter tone. In addition, patients receiving neuromuscular blockers may be at risk of aspiration, even with TOF (train of four) of 0.7, because upper esophageal sphincter tone and swallowing are still decreased ^34-36.

Laryngeal Reflexes

Airway reflexes protect lungs against aspiration. There are four well-defined reflexes ¹⁰: apnea with laryngospasm, cough, expiration (forced expiration without preceding inspiration) and Spasmodic Panting (superficial breathing with frequency of 60 movements per minute for less than 10 seconds).

Two hours after outpatient general anesthesia recovery, upper airway reflexes sensitivity has not returned to normal ³⁷. This decrease in reflexes seems to be present not only in the intraoperative period, but also in premedicated patients and in the postoperative period, probably for a long than expected period. In addition, elderly people have less active airway reflexes and should be considered at increased risk for aspiration ^37-40.

PREVENTION

Methods to prevent pulmonary aspiration include gastric contents control, gastroesophageal reflux decrease and airway protection. This is achieved with preoperative fasting, gastric acidity decrease, gastric emptying stimulation and esophageal sphincter competence maintenance ⁴¹. Airway protection requires cricoid cartilage pressure (Sellick's maneuver) ⁴², adequate patient positioning, tracheal intubation under rapid sequence induction or with awaken patient and nasogastric tube aspiration before anesthetic induction ⁴³.

GASTRIC CONTENTS CONTROL

Preoperative Fasting

The objective of preoperative fasting is to decrease gastric contents regurgitation risk and degree, thus preventing pulmonary aspiration and its consequences.

The old orientation "nothing by mouth after midnight" has been replaced by shorter preoperative fasting periods. There are several benefits when patients, especially children, ingest fluids before anesthesia, including higher satisfaction and less irritability, gastric pH increase, decreased risk for lipolysis hypoglycemia and dehydration ^15,21,44-46.

Studies in different centers involving children ingesting different types of clear fluids (water, tea, coffee, fruit juice without pulp, all without alcohol and with little sugar) in variable volumes have concluded that fluid ingestion, without volume limitation, may be safely allowed 2 hours or more after surgery ^23,47.

In general, stomach acid secretion production rate is 0.6 mL.kg^-1.h^{-1 21}, but it may reach 500 ml.h^-1 with fasting and hunger ^19,30,48. It has been observed in many cases a decrease in gastric pH with increased preoperative fasting duration ⁴⁹. Anxiety is an emotional stimulation able to increase HCI production, similarly to the cephalic phase of gastric secretion ^17,48,50,51, which explains increased volume and decreased gastric pH after prolonged fasting ^{17,27,49,52,53}. Increased gastric pH in patients receiving fluids 2 to 3 hours before surgery could be result of the dilution of acid secretions and/or decrease in their production by the decrease in anxiety and hunger levels. Gastric volume decrease in patients receiving fluids few hours before surgery could be due to gastric motility stimulation by cold fluid entrance and/or physical stomach distension ^15,17,27,54.

In spite of all knowledge obtained to date, it is not possible to surely predict gastric contents. Healthy patients under prolonged fasting may, during surgery, present vomiting with contents of previous day meal. Others may present hypoglycemia, dehydration and irritability. However it seems reasonable to conclude that unrestricted ingestion of clear fluids for healthy patients 2 hours or more before surgery has a more than acceptable risk/benefit ratio ^{7,8,11,21,55,56}.

The American Society of Anesthesiologists, through the ASA Task Force on Preoperative Fasting ⁵⁷, has developed practical guidelines for preoperative fasting and for the use of drugs involved in decreasing gastric volume and acidity. Based on an extensive literature review, guidelines are aimed at healthy patients of all ages submitted to elective procedures, and do not include patients at increased aspiration risk. Such recommendations may be adopted, modified or rejected according to individual clinical needs and are subject to periodic reviews according to the evolution of knowledge on the subject.

Recommendations are summarized as follows (Table II):

Brazilian Journal of Anesthesiology, 2004; 54: 2: 261 - 275

Prevention of pulmonary gastric contents aspiration

Eduardo Toshiyuki Moro

• Clear fluids (water, tea, coffee, fruit juice without pulp, all without alcohol and with little sugar): 2 hours fasting for all ages;

• Breast milk: 4 hours fasting for neonates and infants;

• Light diet (tea and toasts) and non breast milk: up to 6 hours fasting is accepted for children and adults;

• Pediatric formula: 6 hours fasting for neonates and infants;

• Solids: 8 hours fasting for children and adults.

Many investigators have studied the implementation of new preoperative fasting guidelines to replace the old recommendation "nothing by mouth after midnight". Ferrari ⁵⁸ has evaluated 51 institutions in the USA and Canada and has concluded that the approach preconized by the American Society of Anesthesiologists represents most pediatric institutions in North America. Investigations in the UK, Scotland, Germany and Norway have also shown that more flexible preoperative fasting measures have been adopted by most institutions in those countries without increasing complication rates ^59-62.

Some points should also be mentioned:

Studies in adults have shown no difference in gastric contents of patients chewing sugarless gums immediately before surgery ^16,63. Even so, Splinter ²³ suggests 2 hours fasting for chewing gum and sweets.

A recent study with healthy non obese pregnant women who were not in labor, has not found difference in gastric contents after the ingestion of 300 ml of water as compared to prolonged fasting ⁶⁴.

The American Society of Anesthesiologists Task Force on Obstetrical Anesthesia ⁶⁵ recommends that moderate clear fluid ingestion may be allowed for pregnant women in uncomplicated labor. When there is other associated risk factor (diabetes, morbid obesity, difficult airway), or patients are at high risk to evolve to C-section, fluid restriction should be determined in a case-by-case basis. As to solids, the committee agrees that 8 hours or more for elective C-sections is the most adequate period.

Labor patients should not ingest solids.

Mechanisms involved in increased pulmonary aspiration risk in obese patients do not include increase in gastric contents because it is not higher as compared to the volume of non-obese patients. Other factors, such as intra-gastric, abdominal and lower esophageal sphincter pressures probably play a more important role in aspiration pathophysiology of obese patients ⁶⁶.

According to the Norwegian National Consensus, preanesthetic medication may be ingested by adults with 150 ml of water up to one hour before anesthesia. The same is true for children but with the limitation of 75 ml of water ²³.

Gastric Acidity Decrease

Many clinical studies have been performed in Anesthesia about the use of H₂ receptor antagonists and proton pump blockers in healthy patients to evaluate their effects on gastric volume and pH ⁶⁷.

A single 150 mg ranitidine dose few hours before anesthetic induction significantly increases gastric pH, in addition to decreasing its volume ^67-69.

Protons pump blockers prescription, however, requires the understanding of its pharmacology. Studies have shown that such drugs are more effective if administered in two successive doses: one the night before and the other in the morning of anesthesia ^67-69.

Although being possible to show that these drugs increase gastric pH and decrease its volume, the ASA Task Force considers that there are no evidences supporting their routine use in healthy patients, but only in risk patients, since there is no proven decrease in aspiration, morbidity or mortality rate with the use of such drugs in healthy patients ⁵⁷.

The efficacy of preoperative antacids to decrease gastric acidity is proven but there are no evidences that these solutions act on gastric volume. Particulate antacids may increase the risk for pulmonary injury in case of aspiration and should be avoided. So, preoperative antacids (non-particulate such as sodium citrate) should only be prescribed to risk patients ⁵⁷.

Anti-emetics (e.g.: droperidol and ondansetron) are also solely indicated for patients at higher risk for aspiration ⁵⁷.

Nasogastric Tube

Nasogastric tubes are commonly inserted in risk patients before anesthesia, aiming at stomach emptying. However, it seems that upper and lower esophageal sphincters function is impaired as compared to the function in patients without nasogastric tubes ^42,70. Sellick recommends in his original study ⁴² that the tube should be removed before anesthetic induction. However, two studies with cadavers have shown that the efficacy of the Sellilck's maneuver is not decreased with its presence ^71,72. So, the tube would act as a safe passage for gastric contents when effective cricoid cartilage compression is applied. Based on these data, Smith ⁹ suggests that the tube should be left in situ during rapid sequence induction associated to Sellick's maneuver.

There are no significant differences in pulmonary aspiration rate when different tube sizes are used ⁷³.

A cuff associated to the tube has been successfully used aiming at occluding the cardia, thus gastroesophageal reflux ⁷⁴. This tube with gastric cuff has been studied together with laryngeal mask. It has been observed that the tube does not interfere with laryngeal mask insertion and that this would not prevent tube insertion. So, this association represents a good option for difficult airways manipulation in patients at risk for aspiration ⁷⁵.

Cricoid Cartilage Pressure

Cricoid cartilage pressure (Sellick's maneuver) has become universal practice during anesthetic induction in patients with potentially full stomach ⁷⁶. Such maneuver, when correctly performed, prevents gastric inflation in children ⁷⁷ and adults ^78,79, in addition to increasing upper esophageal sphincter tone ⁸⁰. Lower esophageal sphincter tone decreases with such compression ⁸¹, suggesting the presence of pharyngeal mechanoreceptors promoting reflex relaxation of this sphincter. This effect, however, does not seem to cause gastroesophageal reflux ⁸².

The incorrect application of the maneuver may deform cricoid cartilage, close vocal cords and impair ventilation, especially in women ⁸³. Strength applied should be sufficient to prevent aspiration, but not so strong to cause airway obstruction or allow for esophageal rupture in case of vomiting. Cephalad and backward direction of the strength applied seems to improve laryngoscopic visualization ⁸⁴.

A major scenario to be considered is tracheal intubation failure in patients with full stomach under cricoid cartilage compression. In this situation, a laryngeal mask may help ventilation and oxygenation, but studies have shown that Sellick's maneuver prevents its correct positioning ^85,86. So, if laryngeal mask is used during tracheal intubation failure, it may be necessary to temporarily interrupt the maneuver to help ventilation, oxygenation and intubation through the laryngeal mask. Interruption seems to be a reasonable option since cricoid cartilage compression may become ineffective after few minutes of application ⁸⁷.

EFFECTS OF DIFFERENT AIRWAY CONTROL METHODS ON ASPIRATION RISK

Tracheal Intubation

Tracheal intubation is the most effective method to protect airways in anesthetized patients. However, some studies performed with intubated patients in intensive care units, have shown that high volume and low pressure cuffs have allowed the leakage of stain to the trachea ^88,89. Mechanism involved might be microaspiration through the glottis by small channels between the cuff and tracheal mucosa ⁹⁰. The lubrication of cuffs with gel has significantly decreased leakage ^90,91.

Laryngeal Mask

Laryngeal mask is associated to decrease in pressure barrier represented by lower esophageal sphincter ⁹². A study of patients under general anesthesia with positive pressure ventilation has shown that in the group using laryngeal mask there has been a significant increase in gastroesophageal reflux as compared to the group using tracheal tube with cuff ⁹³. There is also reflux in patients under spontaneous ventilation and laryngeal mask ⁹⁴. In fact, there are no significant differences in regurgitation rate between groups spontaneously ventilating or under positive pressure ventilation ^95,96. Time for laryngeal mask removal at the end of general anesthesia seems to influence reflux rate since those who had the mask removed when able to spontaneously open their mouths had a lower incidence of reflux as compared to those who had their masks removed before consciousness recovery ⁹⁷.

The development of a new laryngeal mask model, ProSeal (Laryngeal Mask Company, Henley on Thames, UK), allows the introduction of orogastric tube through an esophageal opening for better gastric contents drainage, in addition to a better gastric inflation blockade during positive pressure ventilation. A recent study has shown that ProSeal is more effective than traditional laryngeal masks to prevent reflux, what makes it a good option for patients at aspiration risk and failed tracheal intubation ^98,99.

COPA and Combitube

"COPA" (Cuffed Oropharyngeal Airway) is even less effective than the laryngeal mask to prevent regurgitation ¹⁰⁰, thus not being indicated for patients at aspiration risk.

Combitube, although protecting against regurgitation and allowing gastric contents drainage, requires a trained professional, since its use is associated to complications such as sore throat, dysphagia and hematomas. So, in emergency situations when airway protection is needed, combitube benefits should be counterbalanced with possible associated complications ⁹.

OTHER PREVENTIVE GASTRIC ASPIRATION MEASURES

Forecasting of Difficult Tracheal Intubation

The first step of difficult airway algorithm, developed by the American Society of Anesthesiologists is the identification of patients with potential difficult tracheal intubation ¹⁰¹. In some cases, such as facial trauma, some congenital syndromes or morbid obesity, difficulty may be easily identified. However, in less evident cases, intubation difficulty may only appear after anesthetic induction, when protective reflexes are abolished, and may expose patients to aspiration risks. So, the forecasting of difficult intubation may be done through some parameters, such as Mallampati's test ¹⁰², thyroginean distance or other tests available in the literature ¹⁰³.

Patients Positioning ³

Patients at risk for aspiration should be placed in the horizontal position with elevated dorsum approximately 30º with relation to the rest of the body. This position will prevent regurgitation, but if it happens, table position should be immediately changed so that the head is positioned below the trunk, thus preventing aspiration.

TRACHEAL INTUBATION WITH AWAKEN PATIENT OR UNDER RAPID SEQUENCE INDUCTION

Awaken Patient

Once a potential difficult airway is identified, the safest intubation method is with the patient awaken and under spontaneous ventilation ¹⁰³.

Tracheal intubation may be performed after mild sedation, maintaining airways protective reflexes. Antisialogogues, such as atropine or scopolamine, should be administered and oropharynx should be topically anesthetized with spray lidocaine (10%). Glossopharyngeal and upper laryngeal nerves blockade might be useful for those mastering the technique ¹⁰¹.

Rapid Sequence

Rapid sequence induction traditionally involves preparing the equipment, which should include, in addition to tracheal intubation material, one aspirator, one backup laryngoscope and equipment for intubation failure (laryngeal mask, fastrack, fibroscope); 100% oxygen administration under facial mask for 1 minute; short onset and duration intravenous opioid and anesthetics (e.g.: propofol and alfentanil) and finally an also short onset and duration neuromuscular blocker ^3,104.

Succinylcholine has been used for 50 years by most anesthesiologists as the neuromuscular blocker of choice to intubate full stomach patients, since it is the drug which best meets the above-mentioned criteria. However, complications such as malignant hyperthermia, fatal hyperkalemia, bradyarhythmias, intragastric and intraocular pressure increase have encouraged the search for adepolarizing neuromuscular blockers with shorter onset and duration, without succinylcholine side-effects, hence, the introduction of rocuronium as an alternative for patients under pulmonary aspiration risk. To assure onset and intubation conditions similar to succinylcholine, preconized dose is 1 mg.kg^-1 or more, which implies longer duration, impairing its use for short procedures or those with possibilities of difficult intubation ^105-108.

Succinylcholine or rocuronium, intubation with awaken patient, fibroscopy etc., all have advantages and disadvantages. The anesthesiologist should decide the best alternative on a case-by-case basis ¹⁰⁹.

ASPIRATION PNEUMONITIS

Pulmonary aspiration is defined as inhalation of oropharynx or stomach contents through the larynx to low respiratory tract ^110,111. Several pulmonary syndromes may be present after aspiration, depending on quantity and nature of the material. Aspiration pneumonitis (Mendelson's syndrome) is a chemical injury caused by sterile gastric contents aspiration, while aspiration pneumonia is an infection caused by inhalation of colonized material especially coming from oropharynx. Other syndromes include mechanical airway obstruction, pulmonary abscess and chronic interstitial fibrosis ^110,111.

Gastric material aspiration causes intensive pulmonary inflammation. Patient may present with cough, wheezing, tachypnea, cyanosis, pulmonary edema, hypoxemia and arterial hypotension, with rapid progression to respiratory distress syndrome and death. Many patients may present only with cough or wheezing and decreased oxygen saturation associated to radiological evidences of aspiration ¹¹².

Treatment includes oxygen administration and/or ventilatory support, when necessary. Preventive antibiotics are not indicated because they may turn patient susceptible to secondary infection by more resistant organisms. Antibiotics are indicated for patients with aspiration pneumonitis not resolved 48 hours after aspiration ¹¹³. Steroids are not recommended because multicentric randomized and controlled studies have failed in proving their benefits ^114,115.

Bronchoscopy should be performed in patients under suspicion of solid material aspiration causing airway obstruction. Pulmonary washing under direct view is also indicated for solid material aspiration ³.

CONCLUSIONS

Pulmonary gastric contents aspiration, although uncommon, requires special preventive care. Recently developed preoperative fasting guidelines suggest shorter fasting periods, especially for fluids, allowing more comfort to patients and less risk for hypoglycemia and dehydration, without increasing the incidence of perioperative pulmonary aspiration. The routine use of drugs decreasing gastric acidity and volume seems to be indicated only for risk patients. The best way to protect airways against aspiration is still tracheal intubation. Other airways maintenance methods have been used but their efficacy in preventing aspiration is still lower, although representing major alternatives for tracheal intubation failure. Cricoid cartilage compression, rapid sequence induction or induction with awaken patient, in addition to patient's positioning, play an important role in preventing pulmonary aspiration.

REFERENCES

Apresentado (Submitted) em 01 de abril de 2003

Aceito (Accepted) para publicação em 24 de junho de 2003

• 01. Warner MA - Is pulmonary aspiration still an import problem in anesthesia? Review article, Current Op Anaesthesiology, 2000;13:215-218.
• 02. Mendelson CL - The aspiration of stomach contents into the lungs during obstetric anesthesia, Am J Obst Gynecol, 1946;52:191-205.
• 03. Ortenzi AV, D`Ottaviano CR - Jejum Pré-Operatório e o Paciente de Estômago Cheio em: Atualização em Anestesiologia, SAESP, 1996;94-106.
• 04. Olsson GL, Hallen B, Hambraeus-Jonzon K - Aspiration during anaesthesia: a computer-aided study of 185,358 anaesthetics. Acta Anaesthesiol Scand, 1986;30:84-92.
• 05. Mellin Olsen J, Fasting S, Gisvold SE - Routine preoperative gastric emptying is seldom indicated. A study of 85,594 anaesthetics with special focus on aspiration pneumonia. Acta Anaesthesiol Scand, 1996;40:1184-1188.
• 06. Warner MA, Warner ME, Weber JG - Clinical significance of pulmonary aspiration during the perioperative period. Anesthesio- logy, 1993;78:56-62.
• 07. Warner MA, Warner ME, Warner DO et al - Perioperative pulmonary aspiration in infants and children. Anesthesiology, 1999;90:66-71.
• 08. Borland LM, Sereika SM, Woelfel SK et al - Pulmonary aspiration in pediatric patients during general anesthesia: incidence and outcome. J Clin Anesth,1998;10:95-102.
• 09. Alexander NG, Graham S - Gastroesophageal reflux and aspiration of gastric contents in anesthetic practice. Anesth Analg, 2001;93:494-513.
• 10. Flick RP, Schears GJ, Warner MA - Aspiration in pediatric anesthesia: is there a higher incidence compared with adults? Current Op Anesth, 2002;15:323-327.
• 11. Department of Health and Social Security. Deaths due to complications of anaesthesia. In: Report on confidential enquirer into maternal deaths in England and Wales. London: Her Majesty's Stationary Office, 1957-1998.
• 12. Roberts RB, Shirley MA - Reducing the risk of acid aspiration during cesarean section. Anesth Analg, 1974;53:859-868.
• 13. Plourde G, Hardy JF - Aspiration pneumonia: assessing the risk of regurgitation in the cat. Can Anesth Soc J, 1986;33:345-348.
• 14. Raidoo DM, Rocke DA, Brock-Utne JG et al - Critical volume for pulmonary acid aspiration: reappraisal in a primate model. Br J Anaesth, 1990;65:248-250.
• 15. Splinter WM, Schaefer JD - Unlimited clear fluid ingestion two hours before surgery in children does not affect volume or pH of stomach contents. Anaesth Intensive Care, 1990;18:522-526.
• 16. Soreide E, Holst-Larsen H, Veel T et al - The effects of chewing gum on gastric contents prior to induction of general anesthesia. Anesth Analg, 1995;80:985-989.
• 17. Macuco MV - Jejum pré-operatório: validade de critérios. Rev Bras Anestesiol, 1998;48:295-308.
• 18. Kallar SK, Everett LL - Potential risks and preventive measures for pulmonary aspiration: new concepts in preoperative fasting guidelines. Anesth Analg, 1993;77:171-182.
• 19. Hutchinson A, Maltby JR, Reid CR - Gastric fluid volume and pH in elective inpatients. Part I: coffee or orange juice versus overnight fast. Can J Anaesth, 1988;35:12-15.
• 20. Maltby JR, Reid CR, Hutchinson A - Gastric fluid volume and pH in elective inpatients. Part II: coffee or orange juice with ranitidine. Can J Anaesth, 1988;35:16-19.
• 21. Schreiner MS, Triebwasser A, Keon TP - Ingestion of liquids compared with preoperative fasting in pediatric outpatients . Anesthesiology, 1990;72:593-597.
• 22. Schreiner MS - Gastric fluid volume: is it really a risk factor for pulmonary aspiration? Anesth Analg, 1998;87:754-756.
• 23. Splinter WM, Schreiner MS - Preoperative fasting in children. Anesth Analg, 1999;89:80-89.
• 24. Andres JM, Mathias JR, Clench MH et al - Gastric emptying in infants with gastroesophageal reflux. Measurement with a technetium-99m-labeled semisolid meal. Dig Dis Sci, 1988;33: 393-399.
• 25. Côté CJ - Changing concepts in preoperative medication and NPO status of pediatric patient, em: Barash PG - ASA Refresher Courses in Anesthesiology, 1995;22:101-116.
• 26. Minami H, McCallum RW - The physiology and pathophysiology of gastric emptying in humans. Gastroenterology, 1984;86: 1592-1610.
• 27. Agarwal A, Chari P, Singh H - Fluid deprivation before operation. The effect of a small drink. Anaesthesia, 1989;44:632-634.
• 28. Moore JG, Christian PE, Coleman RE - Gastric emptying of varying meal weight and composition in man. Evaluation by dual liquid and solid-phase isotopic method. Dig Dis Sci, 1981;26: 16-22.
• 29. Warde D - Fasting children for anaesthesia and surgery. Ir Med J, 1991;84:4-5.
• 30. Phillips S, Daborn AK, Hatch DJ - Preoperative fasting for paediatric anaesthesia. Br J Anaesth, 1994;73:529-536.
• 31. Moukarzel AA, Sabri MT - Gastric physiology and function: effects of fruit juices. J Am Coll Nutr, 1996;15:(Suppl5):18S-25S.
• 32. Bailey CR - Gastroesophageal reflux and aspiration of gastric contents in anesthetic practice. Survey Anesth, 2002;46:137-138.
• 33. Kahrilas PJ, Dodds WJ, Dent J et al - Effects of sleep, spontaneous gastroesophageal reflux and a meal on upper esophageal sphincter pressure in normal human volunteers. Gastroenterology; 1987;92:466-471.
• 34. 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;87:1035-1043.
• 35. Sundman E, Witt H, Olsson R et al - The incidence and mechanisms of pharyngeal and upper esophageal dysfunction in partially paralyzed humans: pharyngeal videoradiography and simultaneous manometry after atracurium, . Anesthesiology, 2000;92:977-984.
• 36. Berg H - Is residual neuromuscular block following pancuronium a risk factor for postoperative pulmonary complications? Acta Anaesthesiol Scand, 1997;110:156-158.
• 37. Coranza R, Nandwani N, Tring JP et al - Upper airway reflex sensitivity following general anaesthesia for day-case surgery. Anaesthesia, 2000;55:367-370.
• 38. Langton JA, Murphy PJ, Barker P et al - Measurement of the sensitivity of the upper airway reflexes. Br J Anaesth, 1993;70: 126-130.
• 39. Murphy PJ, Langton JA, Barker P et al - Effect of oral diazepam on the sensitivity of the upper airway reflexes. Br J Anaesth, 1993;70:131-134.
• 40. Erskine RJ, Murphy PJ, Langton JA et al - Effect of age on the sensitivity of upper airway reflexes. Br J Anaesth, 1993;70: 574-575.
• 41. Mc Intyre JWR - Evolution of 20<sup>th</sup> century attitudes to prophylaxis of pulmonary aspiration during anaesthesia. Can J Anaesth, 1998;45:1024-1030.
• 42. Sellick BA - Cricoid pressure to control regurgitation of stomach contents during induction of anesthesia . Lancet, 1961;19: 404-406.
• 43. Gallimore SC, Hoite RW, Ingram GS et al - Questionnaire in the report of the national confidential enquiry into perioperative deaths 1994-1995. London: National Confidential Enquiry into Perioperative Death, 1997.
• 44. Singh O - Effect of preoperative fasting in children and adults. Midle East J Anesthesiol, 1985;8:235-239.
• 45. Bush GH, Steward DJ - Severe hypoglycemia associated with preoperative fasting and intraoperative propranolol. A case report and discussion. Paediatr Anaesth, 1996;6:415-417.
• 46. Maekawa N, Mikawa K, Yaku H et al - Effects of 2, 4 and 12 hours fasting intervals on preoperative gastric fluid pH and volume, and plasma glucose and lipid homeostasis in children. Acta Anaesthesiol Scand, 1993;37:783-787.
• 47. Shirley DJ, Mathieu A, Gunter J - Effects of fasting interval on risk factors for pulmonary aspiration in pediatric patients: a meta-analysis. Anesth Analg, 1995;80:S440.
• 48. Guyton AC, Hall JE - Tratado de Fisiologia Médica, 10Ş Ed, Rio de Janeiro, Guanabara Koogan, 2002;64:686-701.
• 49. Manchikanti L, Colliver JA, Marrero TC et al - Assessment of age-related acid aspiration risk factors in pediatric, adult, and geriatric patients. Anesth Analg, 1985;64:11-17.
• 50. Ong BY, Palahniuk RJ, Cumming M - Gastric volume and pH in out-patients. Can Anaesth Soc J, 1978;25:36-39.
• 51. Cote CJ, Goudsouzian NG, Liu LM et al - Assessment of risk factors related to the acid aspiration syndrome in pediatric patients-gastric pH and residual volume. Anesthesiology, 1982; 56:70-72.
• 52. Sutherland AD, Maltby JR, Sale JO et al - The effect of preoperative oral fluid and ranitidine on gastric fluid volume and pH. Can J Anaesth, 1987;34:117-121.
• 53. Splinter WM, Stewart JA, Muir JG - The effect of preoperative apple juice on gastric contents, thirst and hunger in children. Can J Anaesth, 1989;36:55-58.
• 54. Goresky GV, Maltby JR - Fasting guidelines for elective surgical patients. Can J Anaesth, 1990;37:493-495.
• 55. Litman RS, Wu CL, Quinlivan JK - Gastric volume and pH in infants fed clear liquids and breast milk prior to surgery. Anesth Analg, 1994;79:482-485.
• 56. Read MS, Vaughan RS - Allowing preoperative patients to drink: effects on patients` safety and comfort of unlimited oral water until 2 hours before anesthesia. Acta Anaesthesiol Scand, 1991;35:591-595.
• 57. American Society of Anesthesiologists Task Force on Preoperative Fasting. Practice guideline for preoperative fasting. and use of pharmacology agents to reduce the risk of pulmonary aspiration: application to health patients undergoing elective procedures. Anesthesiology, 1999;90:896-905.
• 58. Ferrari LR, Rooney FM, Rockoff MA - Preoperative fasting practices in pediatrics. Anesthesiology, 1999;90:978-980.
• 59. Fasting S, Soreide S, Raeder JC - Changing preoperative fasting policies. Impact of a national consensus. Acta Anaesthesiol Scand, 1998;42:1188-1191.
• 60. Emerson BM, Wrigley SR, Newton M - Preoperative fasting for paediatric anaesthesia. A survey of current practice. Anaesthesia, 1998;53:326-330.
• 61. Green CR, Pandit SK, Schork MA - Preoperative fasting time: is the traditional policy changing? Results of a national survey. Anesth Analg, 1996;83:123-128.
• 62. Haas U, Motsch J, Schreckenberger R et al - Pramedication and preoperative fasting in pediatric anesthesia. Results e survey. Anaesthetist, 1998;47:838-843.
• 63. Dubin AS, Jense HG, Mc Crane JM et al - Sugarless gum chewing before surgery does not increase gastric volume or acidity. Can J Anaesth, 1994;41:603-606.
• 64. Wong CA, Loffredi M, Ganchiff J - Gastric emptying of water in term pregnancy. Anesthesiology, 2002;96:1395-1400.
• 65. Practice Guideline for obstetrical anesthesia: a report by the American Society of Anesthesiologists Task Force on Obstetrical Anesthesia. Anesthesiology, 1999;90:600-611.
• 66. Juvin P, Fevre G, Merouche M et al - Gastric residue is not more copious in obese patients. Anesth Analg, 2001;93:1621-1622.
• 67. Nishina K, Mikawa K, Takao Y et al - A comparison of rabeprazole, lansoprazole, and ranitidine for improving preoperative gastric fluid property in adults undergoing elective surgery. Anesth Analg, 2000;90:717-721.
• 68. Nishina K, Mikawa K, Maekawa N et al - A comparison of lanzoprazole, omeprazole, and ranitidine for reducing preoperative gastric secretion in adult patients undergoing elective surgery. Anesth Analg, 1996;82:832-836.
• 69. Escolano F, Castano J, Lopez R et al - Effects of omeprazole, ranitidine, famotidine and placebo on gastric secretion in patients undergoing elective surgery. Br J Anaesth, 1992;69: 404-406.
• 70. Manning B, Mc Greal G, Winter DC et al - Nasogastric intubation causes gastroesophageal reflux in patients undergoing elective laparotomy. Br J Surg, 2000;87:637.
• 71. Vanner RG, Pryle BJ - Regurgitation and oesophageal rupture with cricoid pressure: a cadaver study. Anaesthesia, 1992;47: 732-735.
• 72. Salem MR, Joseph NJ, Heyman HJ et al - Cricoid compression is effective in obliterating the esophageal lumen in the presence of a nasogastric tube. Anesthesiology, 1985;63:443-446.
• 73. Ferrer M, Bauer TT, Torres A et al - Effect of nasogastric tube size on gastroesophageal reflux and microaspiration in intubated patients. Ann Intern Med, 1999;130:991-994.
• 74. Roewer N - Can pulmonary aspiration of gastric contents be prevented by balloon occlusion of the cardia? A study with a new nasogastric tube. Anesth Analg, 1995;80:378-383.
• 75. Schwarzmann GF, Wurmb T, Grein CA et al - Difficult airway management: combination of the laryngeal mask airway with a new gastric balloon tube. Anesthesiology, 1998;89:1237A.
• 76. Thwaites AJ, Rice CP, Smith I - Rapid sequence induction: a questionnaire survey of its routine conduct and continued management during a failed intubation. Anaesthesia, 1999;54: 376-381.
• 77. Salem MR, Wong AY, Mani M et al - Efficacy of cricoid pressure in preventing gastric inflation during bag-mask ventilation in pediatric patients. Anesthesiology, 1974;40:96-98.
• 78. Lawes EG, Campbell I, Mercer D - Inflation pressure, gastric insufflation and rapid sequence induction. Br J Anaesth, 1987;59:315-318.
• 79. Asai T, Barclay K, McBeth C et al - Cricoid pressure applied after placement of the laryngeal mask prevents gastric insufflation but inhibits ventilation. Br J Anaesth, 1996;76:772-776.
• 80. Vanner RG, O`Dwyer JP, Pryle BJ et al - Upper oesophageal sphincter pressure and the effect of cricoid pressure. Anaesthesia, 1992;47:95-100.
• 81. Toumadre JP, Chassard D, Berrada KR et al - Cricoid cartilage pressure decreases lower esophageal sphincter tone. Anesthesiology, 1997;86:7-9.
• 82. Skinner HJ, Bedforth NM, Girling KJ et al - Effect of cricoid pressure on gastroesophageal reflux in awake subjects. Anaesthesia, 1999;54:798-808.
• 83. Palmer JH, Mac G Ball DR - The effect of cricoid pressure on the cricoid cartilage and vocal cords: an endoscopic study in anaesthetized patients. Anaesthesia, 2000;55:263-268.
• 84. Vanner RG, Clarke P, Moore WJ et al - The effect of cricoid pressure and neck support on the view at laringoscopy. Anaesthesia, 1997;52:896-900.
• 85. Asai T, Barclay K, Power I et al - Cricoid pressure impedsd placement of the laryngeal mask airway. Br J Anaesth, 1995;74:521-525.
• 86. Aoyama K, Takenaka I, Sata T et al - Cricoid pressure impedes positioning and ventilation through the laryngeal mask airway. Can J Anaesth, 1996;43:1035-1040.
• 87. Meek T, Vincent A Duggan JE - Cricoid pressure: can protective force be sustained? Br J Anaesth, 1998;80:672-674.
• 88. Young PJ, Basson C, Hamilton D et al - Prevention of tracheal aspiration using the pressure-limited tracheal tube cuff. Anaesthesia, 1999;54:559-563.
• 89. Young PJ, Ridley AS - Ventilator-associated pneumonia. Diagnosis, pathogenesis and prevention. Anaesthesia, 1999;54:1183-1197.
• 90. Young PJ, Rollinson M, Downward G et al - Leakage of fluid past the tracheal tube cuff in a benchtop model. Br J Anaesth, 1997;78:557-562.
• 91. Blunt MC, Young PJ, Patil A et al - Gel lubrification of the tracheal tube cuff reduces pulmonary aspiration. Anesthesiology, 2001;95:377-381.
• 92. Rabey PG, Murphy PJ, Langton JA et al - Effect of the laryngeal mask airway on lower oesophageal sphincter pressure in patients during general anaesthesia. Br J Anaesth, 1992;69:346-348
• 93. Valentine J, Stakes AF, Bellamy MC - Reflux during positive pressure ventilation through the laryngeal mask. Br J Anaesth, 1994;73:543-544.
• 94. Owens TM, Robertson P, Twomey C et al - The incidence of gastroesophageal reflux with the laryngeal mask: a comparison with the face mask using esophageal lumen pH electrodes. Anesth Analg, 1995;80:980-984.
• 95. Skinner HJ, Ho BY, Mahajan RP - Gastro-oesophageal reflux with the laryngeal mask during day-case gynaecological laparoscopy. Br J Anaesth, 1998;80:675-676.
• 96. Akhtar TM, Street MK - Risk of aspiration with the laryngeal mask. Br J Anaesth, 1994;72:447-450.
• 97. Cheong YP, Park SK, Son Y et al - Comparison of incidence of gastroesophageal reflux and regurgitation associated with timing of removal of the laryngeal mask airway: on appearance of signs of rejection versus after recovery consciousness. J Clin Anesth, 1999;11:657-662.
• 98. Brain AI, Verghese C, Strube PJ - The LMA 'ProSeal' - a laryngeal mask with an oesophageal vent. Br J Anaesth, 2000;84:650-654.
• 99. Keller C, Brimacombe J - Mucosal pressure and oropharyngeal leak pressure with the ProSeal versus the laryngeal mask airway in anaesthetized paralyzed patients. Br J Anaesth, 2000;85:262-266.
• 100. Brimacombe J, Keller C - The cuffed oropharyngeal airway vs the laryngeal mask airway: a randomized cross-over study of oropharyngeal leak pressure and fibreoptic view in paralyzed patients. Anaesthesia, 1999;54:683-685.
• 101. Lutke C - Abordagem à Via Aérea Difícil, em: Atualização em Anestesiologia, SAESP 2000;5:126-139.
• 102. Mallampati SR, Gatt SP, Gugino LD et al - A clinical signal to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J, 1985;32:429-434.
• 103. Benumof JL - The ASA Dificult Airway Algorithm: new thoughts/considerations. Annual Refresher Course Lectures, 1999;134:1-7.
• 104. Van Maren GA - Emergency Anaesthesia in Unprepared Patient, em: Prys-Roberts C, Brown BR - International Practice of Anesthesia. Oxford: Butterworth-Heinemann; 1996;1291-1297.
• 105. Almeida MCS - Succinilcolina 50 anos de soberania. Rev Bras de Anestesiol, 2002;52:513-516.
• 106. Kirkegaard-Nielsen H, Caldwell JE, Berry PD et al - Rapid tracheal intubation with rocuronium: a probability approach to determining dose. Anesthesiology, 1999;91:131-136.
• 107. Sparr HJ, Mitterschiffthaier G - Are only large doses of rocuronium an alternative to succinylcholine for rapid-sequence induction? Anesthesiology, 1994;80:1411-1412.
• 108. Heier T, Caldwell JE - Rapid tracheal intubation with large-dose rocuronium: a probability-based approach. Anesth Analg, 2000;90:175-179.
• 109. Engbaek J - Succinylcholine or rocuronium for rapid sequence induction. Acta Anaesthesiol Scand, 2000;44:494-495.
• 110. Irwin RS - Aspiration, em: Irwin RS, Cerra FB, Rippe JB - Irwin and Rippe`s Intensive Care Medicine. 4^th Ed, Philadelphia. Lippincott-Raven, 1999;685-692.
• 111. Caseira HA, Niederman MS - Aspiration Pneumonia, Lipoid Pneumonia and Lung Abscess, em: Baum GL, Crapo JD, Celli BR - Textbook of Pulmonary Diseases, 6^th Ed, Philadelphia. Lippincott-Raven, 1998;645-655.
• 112. Gibbs CP, Modell JH - Pulmonary Aspiration of Gastric Contents: Pathophysiology, Prevention and Management, em: Miller RD - Anesthesia, 4^th Ed, New York; Churchill Livingstone, 1994;1437-1464.
• 113. Marik PE - Aspiration pneumonitis and aspiration pneumonia. N Engl J Med, 2001;344:665-671.
• 114. Bernard GR, Luce JM, Sprung CL et al - High-doses corticosteroids in patients with tie adult respiratory distress syndrome. N Engl J Med, 1987;317:1565-1570.
• 115. Bone RC, Fisher Jr CJ, Clemmer TP et al - Early methylprednisolone treatment for septic syndrome and the adult respiratory distress syndrome. Chest, 1987;92: 1032-1036.

*

Recebido do (

Received from) Hospital Santa Lucinda, Sorocaba, SP

Publication Dates

• Publication in this collection
  29 June 2004
• Date of issue
  Apr 2004

History

• Accepted
  24 June 2003
• Received
  01 Apr 2003