Perioperative Pulmonary Aspiration in Infants and Children

Background: Pulmonary aspiration of gastric contents during the perioperative period in infants and children may be associated with postoperative mortality or pulmonary morbidity. There has not been a recent determination of the frequency of this event and its outcomes in infants and children.

Methods: The authors prospectively identified all cases of pulmonary aspiration of gastric contents during the perioperative courses of 56,138 consecutive patients younger than 18 yr of age who underwent 63,180 general anesthetics for procedures performed in all surgical specialties from July 1985 through June 1997 at the Mayo Clinic.

Results: Pulmonary aspiration occurred in 24 patients (1: 2,632 anesthetics; 0.04%). Children undergoing emergency procedures had a greater frequency of pulmonary aspiration compared to those undergoing elective procedures (1:373 vs. 1:4,544, P < 0.001). Fifteen of the 24 children who aspirated gastric contents did not develop respiratory symptoms within 2 h of aspiration, and none of these 15 developed pulmonary sequelae. Five of these nine children who aspirated and in whom respiratory symptoms developed within 2 h subsequently had pulmonary complications treated with respiratory support (P < 0.003). Three children were treated with mechanical ventilation for more than 48 h, but no child died of sequelae of pulmonary aspiration.     

Effect of Selective PEEP on Pulmonary Blood Flow following Unilateral Hydrochloric Acid Aspiration in the Dog

We investigated the effect of unilateral or bilateral positive end-expiratory pressure (PEEP) on pulmonary perfusion in 12 dogs with a hydrochloric acid aspiration injury of the left lung. The lungs were ventilated separately and PEEP was applied to the left lung at 10 cmH2O (1.0 kPa) in six and at 15 cmH2O (1.5 kPa) in six others. Measurements of the right and left pulmonary arterial blood flows (QR and QL) and venous admixture were made before, during and after PEEP. After this study, 5 and 10 cmH2O (0.5 and 1.0 kPa) PEEP were applied to both lungs in six dogs and measurements were repeated. Following the application of PEEP to the left lung, a significant decrease in QL and increase in QR were observed. However, the application of PEEP to both lungs was followed by significant decreases in both QL and QR. The cardiac output decreased slightly during unilateral PEEP and markedly during bilateral PEEP. The venous admixture decreased significantly during PEEP in all the groups. These findings indicate that selective PEEP causes a transfer of pulmonary blood flow from the injured lung to the normal lung, improving ventilation-perfusion inequality, and improves gas exchange without impeding oxygen delivery.     

Granulysin: A Novel Host Defense Molecule

Granulysin is a novel cationic molecule present in the granules of cytotoxic T lymphocytes and natural killer cells. Cytotoxic T lymphocytes have long been associated with graft destruction in transplant rejection. Recent studies implicate granulysin in cell-mediated cytotoxicity, chemoattraction, immune activation and as a potential diagnostic biomarker for transplant rejection.     

Gel Lubrication of the Tracheal Tube Cuff Reduces Pulmonary Aspiration

Background: Leakage of fluid occurs along the longitudinal folds within the wall of an inflated high-volume, low-pressure cuff. Theoretically, lubrication of the cuff with a water-soluble gel might prevent aspiration by plugging the channels in the cuff wall. Pulmonary aspiration during anesthesia has been linked with postoperative pneumonia and during critical illness causes ventilator-associated pneumonia.

Methods: Lubricated cuffs were compared with nonlubricated cuffs for leakage of dye placed in the subglottic space to the tracheobronchial tree in a benchtop model (n = 5) and in a prospective double-blinded randomized controlled trial of anesthetized patients (n = 36). The duration of the efficacy of the lubricant was determined in a prospective open observational study of critically ill patients with tracheostomies (n = 9). Dye was detected clinically by dye coloration of secretions during tracheal suctioning.

Results: In the benchtop model the incidence of leakage was 0% in the lubrication group and 100% in the nonlubrication group (P < 0.01). Dye leakage in anesthetized patients was 11% in the lubrication group and 83% in the nonlubrication group (P < 0.0001). In the critically ill patients with lubricated cuffed tracheostomy tubes, leakage first occurred after a median period of 48 h (range, 24-120 h).     

Pulmonary Aspiration of Acid: An Experimental Study on Cats

Acid aspiration is followed by a moderate to severe fall in systemic arterial blood pressure, and it has been suggested that release from the lung parenchyma of vasoactive substances may be an important causal factor. We have tested this hypothesis by twice establishing cross circulation between one cat which received hydrochloric acid (4 ml/kg b.w., pH 1.5) intratracheally and another, untreated cat. Instillation of acid caused an immediate fall in heart rate and arterial blood pressure of the aspiration animal, suggesting a reflex inhibition of the heart triggered within the lung. Cross circulation with the untreated animal did not improve the situation of the aspiration animal; nor did it cause any change in arterial blood pressure or lung mechanics in the untreated animal, although most of the blood volumes of the two animals was exchanged.
In a separate series of experiments including four cats, we investigated the relative advantages of various patterns of positive pressure ventilation in the treatment of the aspiration syndrome. Early onset of positive pressure ventilation (PPV) with a moderate positive end-expiratory pressure (PEEP) (+ 6 cmH₂O) was an effective treatment. We conclude that local lung tissue injury with a secondary fall in estimated dynamic lung compliance and arterial pH and P_o2 is the most important feature in the pathophysiology of aspiration.     

Pulmonary Aspiration: New Therapeutic Approaches in the Experimental Model

Background: Acute lung injury caused by gastric aspiration is a frequent occurrence in unconscious patients. Acute respiratory distress syndrome in association with gastric aspiration carries a mortality of up to 30% and accounts for up to 20% of deaths associated with anesthesia. Although the clinical condition is well known, knowledge about the exact inflammatory mechanisms is still incomplete. This study was performed to define the role of alveolar macrophages in this inflammatory response. In addition, potentially modifying effects of intratracheally applied nuclear factor [kappa]B inhibitor pyrrolidine dithiocarbamate were investigated.

Methods: Rat alveolar macrophages were depleted by intratracheal administration of clodronate liposomes, and lung injury was evaluated 6 h after instillation of 0.1N hydrochloric acid. In a second set of experiments, pyrrolidine dithiocarbamate was intratracheally instilled 3 h after hydrochloric acid application, and injury parameters were determined.

Results: Depletion of alveolar macrophages resulted in decreased production of inflammatory mediators in acid aspiration (23-80% reduction of messenger RNA or protein of inflammatory mediators; P < 0.05) and consequently also in diminished neutrophil recruitment (36% fewer neutrophils; P < 0.01). Treatment with pyrrolidine dithiocarbamate was highly effective in decreasing neutrophil recruitment (66%; P < 0.01) and vascular permeability (80%; P < 0.001).     

Cost-Effectiveness Analysis of Transbronchial Needle Aspiration of Pulmonary Lesions Without Endobronchial Affectation

Transbronchial needle aspiration (TBNA) of pulmonary lesions without endobronchial affectation in combination with transbronchial biopsy (TBB) has been shown to increase diagnostic perfortmance. The objective of this present study was to analyze whether the combination of TBNA with conventional TBB is a cost-effective approach.MethodologyOurs is a prospective study that included patients with lung nodules or masses with no evidence of endobronchial lesions after flexible bronchoscopy in whom both TBNA and TBB were performed. We analyzed the additional diagnostic value, the impact of TBNA on the cost of the diagnosis and the minimum level of sensitivity required in order for TBNA combined with TBB to be considered a cost-effective diagnostic approach.ResultsThirty-six patients were included in the study, 25 of whom were males. TBB reached a histologic diagnosis in 39% of the cases, and its combination with TBNA diagnosed 47%. The mean diameter of the lesions was significantly greater in the positive TBNA cases compared with the negative cases (31 mm vs 23 mm; P=.034). The cost analysis did not show the additional TBNA to be more cost-effective, despite demonstrating greater diagnostic sensitivity. The minimum sensitivity required for TBNA combined with TBB to be considered a cost-effective approach was 88%.ConclusionThe contribution of TBNA to TBB in the diagnosis of lung nodules or masses without associated endobronchial lesions does not seem to justify the additional economic cost.     

Mechanisms of Pulmonary Microvascular Dysfunction during Severe Burn Injury

Even in the absence of inhalational injury, acute lung injury is a common cause of morbidity and mortality for patients sustaining severe burns. Other than general supportive measures, there are few therapeutic options for improving survival in these critically ill patients. Numerous clinical and laboratory studies have implicated tumor necrosis factor (TNF)-a and neutrophils as important participants in the pathogenesis of burn-induced lung injury. There is, however, little information regarding the mechanism by which these and other pro-inflammatory mediators affect the movement of fluid and protein across the microvascular barrier into the interstitium of the lung. In addition to reviewing the evidence implicating TNF-a and neutrophils in the pathophysiology of burn-induced lung injury, this report summarizes current theories regarding potential mechanisms by which these mediators may alter microvascular barrier function to lead ultimately to the development of pulmonary edema.     

Reduction of the Risk of Acid Pulmonary Aspiration in Anaesthetized Patients after Cimetidine Prernedication

Forty-two patients undergoing elective general surgery received either placebo, cimetidine 300 mg, or cimetidine 600 mg orally 1.5–2 h before anaesthesia in a double-blind, randomized study. Another 13 subjects received no oral premedication and served as a control group. When compared to placebo or control patients, both doses of cimetidine significantly (P< 0.01) decreased the acidity and volume of gastric contents. None of the subjects given cimetidine were in the risk range of acid pulmonary aspiration (pH under 2.5 plus volume over 25 ml), whereas 46% of the control patients and 40% of the patients given placebo (P<0.005 vs cimetidine in both groups) were in the risk range.