Hypercapnic respiratory failure and partial upper airway obstruction during high frequency oscillatory ventilation in an adult burn patient

PURPOSE: To present a case of severe hypercapnic respiratory failure in an adult burn patient and to describe our clinical problem solving approach during support with an unconventional mode of mechanical ventilation. CLINICAL FEATURES: A 19-yr-old male with smoke inhalation and flame burns to 50% total body surface area was admitted to the Ross Tilley Burn Centre. High frequency oscillatory ventilation (HFOV) was initiated on day three for treatment of severe hypoxemia. By day four, the patient met consensus criteria for acute respiratory distress syndrome. On day nine, alveolar ventilation was severely compromised and was characterized by hypercapnea (PaCO(2) 136 mmHg) and acidosis (pH 7.10). Attempts to improve CO(2) elimination by a decrease in the HFOV oscillatory frequency and an increase in the amplitude pressure failed. An intentional orotracheal tube cuff leak was also ineffective. A 6.0-mm nasotracheal tube was inserted into the supraglottic hypopharynx to palliate presumed expiratory upper airway obstruction. After nasotracheal tube placement, an intentional cuff leak of the orotracheal tube improved ventilation (PaCO(2) 81 mmHg) and relieved the acidosis (pH 7.30). The improvement in ventilation (with normal oxygen saturation) was sustained until the patient's death from multiple organ dysfunction four days later. CONCLUSION: During HFOV in burn patients, postresuscitation edema of the supraglottic upper airway may cause expiratory upper airway obstruction. The insertion of a nasotracheal tube, combined with an intentional orotracheal cuff leak may improve alveolar ventilation during HFOV in such patients.     

Recovery of airway protection compared with ventilation in humans after paralysis with curare

d-Tubocurarine (dTc) was administered intravenously to six healthy unanesthetized volunteers to assess the sensitivity to neuromuscular blockade of those muscles involved in protecting the airway against obstruction and/or aspiration relative to the muscles of inspiration. Each subject was given an intravenous bolus of dTc followed by an infusion to allow three different levels of inspiratory muscle weakness as measured by maximum inspiratory pressure (MIP). Levels of MIP were control (-90 cm H2O), -60, -40, and -20 cm H2O. Vital capacity (VC), hand grip strength (HGS), and end-tidal CO2 (PETCO2) were obtained at each level. At each level of weakness and at intermediate values during recovery, muscles of airway protection were functionally assessed by noting the MIP at which the maneuver could be accomplished and the MIP at which they could not. The mean of these two values was calculated for each subject. The tests were: 1) ability to swallow, 2) ability to perform a valsalva maneuver, 3) prevent obstruction of the airway, and 4) ability to approximate teeth. These were compared with head lift and straight leg raising. At maximum neuromuscular blockade (MIP of -20 cm H2O), VC was 2.0 liters, HGs was 0, and PETCO2 was normal. Muscles of airway protection were still incapacitated. Swallowing returned above MIP of -43 cm H2O, approximation of teeth above -42 cm H2O, airway obstruction above -39 cm H2O, and valsalva above -33 cm H2O. Thus, although ventilation may be adequate at MIP = -25 mmHg, the muscles of airway protection are still nonfunctional.(ABSTRACT TRUNCATED AT 250 WORDS)     

Safety of transtracheal jet ventilation in upper airway obstruction

Editor—We read with interest the article by Chandradevaand colleagues,¹ who reported the use of percutaneous transtrachealjet ventilation (PTJV) in the emergency management of two patientswith severe upper airway obstruction. We agree that this isan extremely useful technique for this situation but would liketo suggest that the method they employed could be further enhancedby the use of an automated jet ventilator with end-expiratorypressure monitoring linked to a pause function. We have usedthis technique in two situations similar to those describedin their article. Case 1, a 64-yr-old man undergoing tracheostomy because of worseningepisodes of stridor secondary to a vocal cord palsy after radiotherapyfor malignant neck lymphadenopathy. He was given a     

Pulmonary edema due to upper airway obstruction after extubation

We report a patient who developed pulmonary edema due to airway obstruction after extubation. A 22-year-old man underwent removal of the nails for thoracoplasty under general anesthesia combined with epidural anesthesia. Upper airway obstruction occurred after extubation. SpO2 decreased to 70%. Insertion of an oral airway relieved the airway obstruction. However, inspiratory wheezing was heard over both lung fields. Chest X-ray taken 90 minutes after the event revealed pulmonary edema. Pulmonary edema gradually resolved after intravenous furosemide and oxygen inhalation by mask.     

Manoeuvres used to clear the airway during fibreoptic intubation

Fibreoptic orotracheal endoscopy under general anaesthesia maybe more difficult to perform if the upper airway cannot be fullycleared. We have studied the effectiveness of jaw thrust, lingualtraction and the application of both manoeuvres simultaneously,in opening up the orolaryngeal airspace in 30 ASA group 1 or2 patients aged between 16 and 70 yr undergoing elective generalsurgery requiring orotracheal intubation. Airway clearance wasassessed fibreoptically at soft palate level by observing whetheror not the uvula or soft palate was apposed to the base of thetongue, and at epiglottic level by observing whether or notthe epiglottis was apposed to the posterior pharyngeal wall.Lingual traction with Duval’s forceps cleared the tongueaway from the uvula and soft palate significantly more timesthan did jaw thrust (P<0.05). Jaw thrust cleared the epiglottisaway from the posterior pharyngeal wall more frequently thandid lingual traction (P=0.052). Applying both jaw thrust andlingual traction simultaneously cleared the airway at both softpalate and epiglottic level in every patient. When used alone,jaw thrust and lingual traction fail to produce full airwayclearance in a significant number of patients. Combined jawthrust and lingual traction clears the airway more effectivelybut requires two assistants. Br J Anaesth 2001; 87: 207–11     

Association of airway obstruction, sleep, and phasic abdominal muscle activity after upper abdominal surgery

We recorded nasal gas flow, sleep stage, and abdominal muscle EMG pattern in 11 patients throughout the night after abdominal surgery, to examine the association between phasic activity of the abdominal muscles, sleep stage, and flow disturbance. We used a miniaturized data logging system, and obtained satisfactory records in eight patients. The data were divided into 30-s epochs. Each epoch was classified as either awake or asleep. The epochs were also classified for the presence of phasic activity in the external oblique abdominal muscle, and for evidence of airway obstruction. Association between these features was tested by a quasi likelihood log linear model. Values given are median (quartiles) for the eight subjects. Sleep occurred for 62 (46-69)% of the study time. During sleep, inspiratory flow was normal for 69 (48-81)% of the time, whereas during wakefulness, the flow pattern was normal for 51 (28-77)% of the time. Phasic activity was present 16 (12-25)% of the time during sleep and 24 (19-37)% of the time during wakefulness (P<0.001). In the awake state, when breathing was normal, phasic activity was present 16 (11-30)% of the time. When breathing was obstructed, phasic activity was present 38 (25-44)% of the time (P<0.001). These surprising findings suggest that sleep may be seriously disturbed by airway obstruction, so that a stable sleep state is not reached. We could not confirm previous findings that disturbed breathing in post-operative patients only occurs during sleep.     

Pulmonary effects of expiratory‐assisted small‐lumen ventilation during upper airway obstruction in pigs

Novel devices for small‐lumen ventilation may enable effective inspiration and expiratory ventilation assistance despite airway obstruction. In this study, we investigated a porcine model of complete upper airway obstruction. After ethical approval, we randomly assigned 13 anaesthetised pigs either to small‐lumen ventilation following airway obstruction (n = 8) for 30 min, or to volume‐controlled ventilation (sham setting, n = 5). Small‐lumen ventilation enabled adequate gas exchange over 30 min. One animal died as a result of a tension pneumothorax in this setting. Redistribution of ventilation from dorsal to central compartments and significant impairment of the distribution of ventilation/perfusion occurred. Histopathology demonstrated considerable lung injury, predominantly through differences in the dorsal dependent lung regions. Small‐lumen ventilation maintained adequate gas exchange in a porcine airway obstruction model. The use of this technique for 30 min by inexperienced clinicians was associated with considerable end‐expiratory collapse leading to lung injury, and may also carry the risk of severe injury.     

Temperature distribution in the upper airway after inhalation injury

Objective

The aim of the study was to establish an animal model of laryngeal burn and to investigate the temperature distribution of heated air in the upper airway.

Methods

The animal model was established by inhalation of dry heated air at 80, 160 and 320 °C in 18 healthy, male, adult hybrid dogs. Time for inducing injury was set at 20 min. The distribution of temperatures after heated-air inhalation was examined at different locations including the epiglottis, laryngeal vestibule, vocal folds and trachea.

Results

The temperatures of the heated air decreased to 47.1, 118.4 and 193.8 °C at the laryngeal vestibule and to 39.3, 56.6 and 137.9 °C at the lower margin of vocal folds in the 80, 160 and 320 °C groups, respectively.

Conclusion

Due to its special anatomy and functions, the larynx has different responses to dry heated air at different temperatures. The air temperature decreases markedly when the air arrives at the larynx. By contrast, the larynx has a low capacity for blocking high-temperature air and retaining heat. As a result, high-temperature air often causes more severe injury to the larynx and the lower airway.     

Flumazenil antagonizes midazolam-induced airway narrowing during nasal breathing in humans

We measured nasal resistance (Rn) while awake, during midazolam-induced sedation and after antagonism with flumazenil (n = 9). Nasal and oral airflow were measured. Rn was calculated by dividing the difference between maximal nasal mask and oropharyngeal pressures by inspiratory airflow at minimum pharyngeal pressure. During sedation, two subjects developed obstructive apnoeic events and four subjects had snoring events. Each apnoea was ended by mechanisms other than a change in breathing route. After antagonism with flumazenil, apnoeic and snoring events were abolished. Rn during midazolam sedation (median 1.46 (25th percentile 1.00, 75th 2.61) kPa litre-1 s) was significantly greater than before midazolam (0.29 (0.25, 0.48) kPa litre-1 s) and after flumazenil (0.41 (0.25, 0.58) kPa litre-1 s) (P < 0.01 in each subject). We conclude that midazolam increased Rn, sometimes leading to obstruction, and flumazenil abolished this increase in Rn.      

Percutaneous transtracheal jet ventilation as a guide to tracheal intubation in severe upper airway obstruction from supraglottic oedema

We report two cases of severe upper airway obstruction causedby supraglottic oedema secondary to adult epiglottitis and Ludwig'sangina. In the former case, attempts to intubate with a directlaryngoscope failed but were successful once percutaneous transtrachealjet ventilation (PTJV) had been instituted. In the case withLudwig's angina, PTJV was employed as a pre-emptive measureand the subsequent tracheal intubation with a direct laryngoscopewas performed with unexpected ease. In both cases recognitionof the glottic aperture was made feasible with PTJV by virtueof the fact that the high intra-tracheal pressure from PTJVappeared to lift up and open the glottis. The escape of gasunder high pressure caused the oedematous edges of the glottisto flutter, which facilitated the identification of the glotticaperture. We believe that the PTJV should be considered in theemergency management of severe upper airway obstruction whenthis involves supraglottic oedema.     

Minitracheotomy in treating upper airway obstruction after anterior cervical fusion

Respiratory disturbance occurs sometimes after anterior cervical fusion. This is often a result of upper airway obstruction due to prevertebral soft tissue swelling. Therefore we used cricothyrotomy tubes (Mini-Trach) in two patients with postoperative upper airway obstruction and performed assist-ventilation via the tubes. After starting to ventilate through Mini-Trach II, respiratory disturbance disappeared soon and respiration improved markedly. Mini-Trach II is an effective device to use in patients with post-operative respiratory disturbance due to prevertebral soft tissue swelling.     

Tidal volume and airway pressure under percutaneous transtracheal ventilation without a jet ventilator: comparison of high-flow oxygen ventilation and manual ventilation in complete and incomplete upper airway obstruction models

Purpose

Percutaneous transtracheal ventilation (PTV) can be life-saving in a cannot ventilate, cannot intubate situation. The aim of this study was to investigate the efficacy of PTV by measuring tidal volumes (VTs) and airway pressure (Paw) in high-flow oxygen ventilation and manual ventilation using a model lung.

Methods

We examined 14G, 16G, 18G, and 20G intravenous catheters and minitracheotomy catheters. In high-flow oxygen ventilation, the flow was set to 10 L/min, while the inspiratory:expiratory phases (I:E) were 1?s:4?s in the complete upper airway obstruction model and 1?s:1 s in the incomplete obstruction model. In manual ventilation, I:E were 2?s:4 s in the complete obstruction model and 2?s:3 s in the incomplete obstruction model. We ventilated through each catheter for 2 min and measured VT and Paw.

Results

In high-flow ventilation, the average VTs were approximately 150 ml and <100 ml with 14G catheters in complete and incomplete upper airway obstruction, respectively. The VTs obtained were reduced when the bore size was decreased. In manual ventilation, the average VTs were over 300 ml and approximately 260 ml with 14G catheters in complete and incomplete upper airway obstruction, respectively. In high-flow ventilation, the airway pressure tended to be higher. The minitracheotomy catheters produced over 800 ml of VT and created almost no positive end-expiratory pressure.

Conclusions

High-flow ventilation tends to result in higher airway pressure despite a smaller VT, which is probably due to a PEEP effect caused by high flow.     

Chemical regulation of ventilation during isoflurane sedation and anaesthesia in humans

To assess the effects of isoflurane on chemical regulation of ventilation, we studied the ventilatory responses to (1) hyperoxic hypercarbia, (2) isocapnic hypoxaemia, and (3) a single half vital capacity breath of carbon dioxide. 20 per cent in oxygen in 12 human subjects, awake and sedated or anaesthetized with isoflurane, 0.1 or 1.1 MAC. Sedation did not alter ventilation nor the ventilatory response to hypercarbia but reduced the responses to hypoxaemia and to the half vital capacity breath of CO₂. Anaesthesia reduced ventilation and the response to hypercarbia and nearly abolished the responses to hypoxaemia and to the breath of CO₂. The results indicate that isoflurane reduces ventilatory responses to several chemical drives and that it selectively impairs those responses mediated by peripheral chemoreceptors. In these respects, isoflurane is similar to halothane and enflurane.