Major pneumothorax during pediatric cardiac MRI procedure under general anesthesia: step-by-step analysis and importance of a well-known environment and material

BACKGROUND

To perform step-by-step analysis of the different factors (material, anesthesia technique, human, and location) that led to major pneumothorax during an infrequent pediatric cardiac MRI and to prevent its occurrence in the future. Anesthesia equipment used in a remote location is often different than those in operating rooms. For magnetic resonance imaging (MRI), ventilation devices and monitors must be compatible with the magnetic fields. During cardiac MRI numerous apneas are required and, visual contact with the patient is limited for clinical evaluation. Anesthesia-related barotrauma and pneumothorax are rare in children and the first symptoms can be masked.

CASE PRESENTATION

A 3-year-old boy with atrial septal defect (ASD) and suspicious partial anomalous pulmonary venous return was anesthetized and intubated to perform a follow up with MRI. Sevoflurane maintenance and ventilation were performed using a circular CO2 absorber device, co-axial circuit, and 500 mL pediatric silicone balloon. Apneas were facilitated by Alfentanyl boluses and hyperventilation. A few moderated desaturations occurred during the imaging sequences without hemodynamic changes. At the end of the MRI, facial subcutaneous emphysema was observed by swollen eyelids and crackling snow neck palpation. A complete left pneumothorax was diagnosed by auscultation, sonography examination, and chest radiograph. Pneumo-mediastinum, -pericardium and -peritoneum were present. A chest drain was placed, and the child was extubated and transferred to the pediatric intensive care unit (PICU). Despite the anesthesiologist's belief that PEEP was minimal, critical analysis revealed that PEEP was maintained at a high level throughout anesthesia. After the initial barotrauma, repeated exposure to high pressure led to the diffusion of air from the pleura to subcutaneous tissues and mediastinal and peritoneal cavities. Equipment check revealed a functional circular circuit; however, the plastic adjustable pressure-limiting valve (APL) closed within the last 30° rotation. The balloon was found to be more rigid and demonstrated significantly reduced compliance.

CONCLUSIONS

Anesthetists require proficiency is using equipment in non-OR locations and this equipment must be properly maintained and checked for malfunctions. Controlling the human factor risks by implementing checklists, formations, and alarms allows us to reduce errors. The number of pediatric anesthesia performed routinely appeared to be essential for limiting risks and reporting our mistakes will be a benefit for all who care about patients.

Pulmonary barotrauma in SCUBA diving-related fatalities: a histological and histomorphometric analysis

Arterial gas embolism following pulmonary barotrauma occurs in 13-24% of cases of diving deaths. The study aimed to evaluate the usefulness of a histomorphometric digital analysis in the detection of air space over-distension due to pulmonary barotrauma. The study was performed on lung parenchyma specimens of 12 divers: six had died due to arterial gas embolism following pulmonary barotrauma (mean age at death of 54 years, range of 41-61 years), and six had drowned in saltwater without a diagnosis of pulmonary barotrauma (mean age at death of 54 years, range of 41-66 years) (positive controls). For negative controls, six cases of non-SCUBA divers (mean age of death of 42 years, range of 23-55 years) who died of intracerebral haemorrhage were evaluated. No significant differences were observed in the characteristics of the air spaces between control groups (positive and negative). However, differences were observed in the area occupied by air spaces and the percentage of air space area when we compared the case group to the controls (p < 0.01); and there was a slight difference in the maximum and minimum diameters of air space (p < 0.05). The mean area occupied by air spaces and the mean percentage of air space were the most useful for discriminating pulmonary barotrauma from other causes of death (100% sensitivity and 91.7% specificity). Based on our study, inclusion of an increased pattern of air spaces as a possible diagnostic criterion for pulmonary barotrauma would be useful in discerning the cause of diving death.

Hyperbaric oxygen treatment in children: experience in 329 patients

Introduction

Paediatric patients, like adults, may undergo hyperbaric oxygen treatment (HBOT) in both life-threatening situations and chronic diseases. There are particular challenges associated with managing paediatric patients for HBOT. This paper documents the indications, results, complications, and difficulties that occur during HBOT for a large cohort of paediatric patients and compares them with adult data in the literature. Methods used to reduce these difficulties and complications in children are also discussed.

Methods

This was a 15-year retrospective review of paediatric patients treated with HBOT at two hyperbaric centres. Between January 2006 and June 2021, patients under the age of 18 who received at least one session of HBOT were included.

Results

Three hundred and twenty-nine paediatric patients underwent a total of 3,164 HBOT exposures. Two-hundred and fifty-four patients (77.2%) completed treatment as planned and 218 (66.5%) achieved treatment goals without complications. Two patients treated for carbon monoxide poisoning exhibited neurological sequelae. Amputation was performed in one patient with limb ischaemia. Middle ear barotrauma events occurred in five treatments. No central nervous system oxygen toxicity was recorded during the treatments.

Conclusions

This patient series indicates that HBOT can be safely performed in pediatric patients with low complication rates by taking appropriate precautions. The cooperation of hyperbaric medicine physicians and other physicians related to paediatric healthcare is important in order for more patients to benefit from this treatment. When managing intubated patients an anaesthesiologist may need to participate in the treatment in order to perform necessary interventions.

Recurrent dysbarism presenting with amnesia and hypoaesthesia in a professional breath-hold diver

Dysbarism is a medical condition arising from change in ambient pressure which outpace the rate at which the body adapts to it. We report a case of recurrent dysbarism consistent with possible decompression illness presenting with amnesia, hypoaesthesia and other neurological manifestations in a professional breath-hold diver treated successfully with hyperbaric oxygen and fluid resuscitation.

Neuromuscular Blocking Agents for ARDS: A Systematic Review and Meta-Analysis

BACKGROUND

Studies evaluating neuromuscular blocking agents (NMBAs) in the management of ARDS have produced inconsistent results in terms of their effect on mortality. The purpose of this systematic review and meta-analysis was to evaluate differences in mortality comparing subjects with ARDS who received NMBA to those who received placebo or usual care.

METHODS

We searched Ovid, MEDLINE, Embase, CINAHL, Cochrane, Scopus, and Web of Science for randomized controlled trials evaluating administration of NMBAs in subjects with ARDS.

RESULTS

We included 6 studies (N = 1,558 subjects) from 1,814 abstracts identified by our search strategy. The use of early, continuous-infusion NMBAs reduces the risk of short-term (ie, 21-28-d) mortality (relative risk 0.71 [95% CI 0.52-0.98], P = .030, I ² = 60%) in subjects with ARDS but does not reduce the risk of long-term (ie, 90-d) mortality (relative risk 0.81 [95% CI 0.64-1.04], P = .10, I ² = 54%). NMBAs decreased the risk of barotrauma (relative risk 0.55 [95% CI 0.35-0.85], P = .008, I ² = 0%) and pneumothorax (relative risk 0.46 [95% CI 0.28-0.77], P = .003, I ² = 0%) compared to control.

CONCLUSIONS

In subjects with ARDS, early use of NMBAs improves oxygenation, reduces the incidence of ventilator-induced lung injury, and decreases 21-28-d mortality, but it does not improve 90-d mortality. NMBAs should be considered for select patients with moderate-to-severe ARDS for short durations.

An investigation into the potential for wind turbines to cause barotrauma in bats

The high rates of bat mortality caused by operating wind turbines is a concern for wind energy and wildlife stakeholders. One theory that explains the mortality is that bats are not only killed by impact trauma, but also by barotrauma that results from exposure to the pressure variations caused by rotating turbine blades. To date, no published research has calculated the pressure changes that bats may be exposed to when flying near wind turbines and then used these data to estimate the likelihood that turbines cause barotrauma in bats. To address this shortcoming, we performed computational fluid dynamics simulations of a wind turbine and analytical calculations of blade-tip vortices to estimate the characteristics of the sudden pressure changes bats may experience when flying near a utility-scale wind turbine. Because there are no data available that characterize the pressure changes that cause barotrauma in bats, we compared our results to changes in pressure levels that cause barotrauma and mortality in other mammals of similar size. This comparison shows that the magnitude of the low-pressures bats experience when flying near wind turbines is approximately 8 times smaller than the pressure that causes mortality in rats, the smallest mammal for which data are available. The magnitude of the high-pressures that bats may experience are approximately 80 times smaller than the exposure level that causes 50% mortality in mice, which have a body mass similar to several bat species that are killed by wind turbines. Further, our results show that for a bat to experience the largest possible magnitude of low- and high-pressures, they must take very specific and improbable flight paths that skim the surface of the blades. Even a small change in the flight path results in the bat being hit by the blade or experiencing a much smaller pressure change. Accordingly, if bats have a physiological response to rapid low- and high-pressure exposure that is similar to other mammals, we conclude that it is unlikely that barotrauma is responsible for a significant number of turbine-related bat fatalities, and that impact trauma is the likely cause of the majority of wind-turbine-related bat fatalities.

Rorqual whale nasal plugs: protecting the respiratory tract against water entry and barotrauma

The upper respiratory tract of rorquals, lunge-feeding baleen whales, must be protected against water incursion and the risk of barotrauma at depth, where air-filled spaces like the bony nasal cavities may experience high adverse pressure gradients. We hypothesize these two disparate tasks are accomplished by paired cylindrical nasal plugs that attach on the rostrum and deep inside the nasal cavity. Here, we present evidence that the large size and deep attachment of the plugs is a compromise, allowing them to block the nasal cavities to prevent water entry while also facilitating pressure equilibration between the nasal cavities and ambient hydrostatic pressure (Pamb) at depth. We investigated nasal plug behaviour using videos of rorquals surfacing, plug morphology from dissections, histology and MRI scans, and plug function by mathematically modelling nasal pressures at depth. We found each nasal plug has three structurally distinct regions: a muscular rostral region, a predominantly fatty mid-section and an elastic tendon that attaches the plug caudally. We propose muscle contraction while surfacing pulls the fatty sections rostrally, opening the nasal cavities to air, while the elastic tendons snap the plugs back into place, sealing the cavities after breathing. At depth, we propose Pamb pushes the fatty region deeper into the nasal cavities, decreasing air volume by about half and equilibrating nasal cavity to Pamb, preventing barotrauma. The nasal plugs are a unique innovation in rorquals, which demonstrate their importance and novelty during diving, where pressure becomes as important an issue as the danger of water entry.

Fatal air embolism in a breath-hold diver

Cerebral arterial gas embolism (CAGE) from breath-holding or inadequate exhalation during ascent is a well-recognised complication of scuba diving. It does not usually occur with breath-hold (BH) diving in those with normal lungs, as the volume of gas in the lungs on surfacing cannot exceed what it was on leaving the surface. However, a BH diver who breathes from a compressed gas supply at depth essentially becomes a scuba diver and is at risk of pulmonary barotrauma (PBt) and CAGE on ascent. In this case, a 26-year-old male experienced BH diver breathed from a scuba set at approximately 10 metres' sea water depth and ascended, sustaining massive PBt and CAGE with a fatal outcome. BH and scuba divers, especially those with less experience, need to be well-informed about this potential risk.

[The clinical research of aviatic nasal diseases with medical evaluation prevention and control intervention]

OBJECTIVE

Exploring the clinical features of aviatic nasal diseases to provide references for medical evaluation, prevention and control measures in aircrew.

METHOD

To analysis and summary 605 cases with 503 pilots of nasal diseases in aircrew during 1966 to 2013.

RESULT

(1) There were 605 cases of aviatic nasal diseases, including 550 cases of general diseases and 55 cases of specific diseases. The general nasal diseases included 140 cases of anatomical abnormalities in nasal cavity type, 290 cases of inflammation in nasal cavity, 73 cases of allergy type, 47 cases of cyst and tumor type, and the specific nasal diseases were 55 cases of sinus barotrauma (SB). (2) The, constituent ratio of SB, which was happened in frontal sinus and /or maxillary sinus, was 95.55%. (3) The constituent ratio of cyst and tumor type in nasal cavity was easier causing to SB than anatomical abnormalities, inflammation, allergy disease in nasal cavity (P < 0.05). (4) The grounded constituent ratio of secondary SB was higher than anatomical abnormalities, inflammation, allergy, cyst and tumor disease in nasal cavity (P < 0.05). (5) The ways of hypobaric chamber tests were different for the kinds of aircrew. The qualified adjustment function of sinuses for barometric pressure was an essential condition for aircrew to continue flying. (6) The key point for the treatment of aviatic nasal diseases was to remove pathological change in nasal cavity and sinus and restore sinus ostium patency. The key point for the medical evaluation was to restore normal sinus pressure balance function.

CONCLUSION

The key point of medical evaluation about aviatic nasal diseases is to assess the sinus pressure balance function in hypobaric chamber tests. Normative treatment and medical evaluation can effectively avoid flight accidents and improve the attendance rate for aircrew.

Oxygen toxicity seizures: 20 years' experience from a single hyperbaric unit

INTRODUCTION

Oxygen toxicity seizures (OTS) are a known complication of hyperbaric oxygen therapy (HBOT). The incidence of OTS has been variously reported and appears to be related to the duration and pressure of exposure in addition to individual susceptibility factors.

METHOD

All OTS occurring in patients undergoing HBOT during the first 20 years of operation of the Fremantle Hospital Hyperbaric Medicine Unit were reviewed.

RESULTS

During 41,273 HBOT in 3,737 patients, 25 OTS occurred; a rate of 0.06% (1/1,650 or 6 per 10,000) HBOT exposures. For the initial treatment of dysbarism with United States Navy Treatment Table 6, the rate was 0.56%. (4/714) and for the treatment of carbon monoxide (CO) poisoning was 0.18% overall but 0.49% for the first HBOT. There was an increasing OTS rate with increasing pressure with a statistically significant difference (P < 0.001) in OTS rate at 203 kPa or less versus > 203 kPa (OR 8.5, 95% confidence intervals (CI) 2.0 to 36.1), and for comparison of two commonly used pressures of 203 kPa versus 243 kPa (P = 0.028, OR 5.1, 95% CI 1.1 to 22.8), but not with first versus follow-up HBOT at 284 kPa for dysbarism (P = 0.061) nor CO (P = 0.142).

CONCLUSIONS

This study reports all OTS in a single hyperbaric unit over a 20-year period, the longest observational study period yet reported for OTS during HBOT for all indications. The incidence of OTS in this study compares favourably to previously reported rates, and shows an increasing OTS rate with increasing pressure.

[From barotrauma otitis to a fulminant meningitis]

OBJECTIVES

To report the case of a patient who in the follow-up of a barotrauma otitis presented a fulminant meningitis.

CLINICAL CASE

38 year old man sportsman who presented a barotrauma otitis during scuba diving. In spite of a treatment associating steroids and nasal vasoconstrictor this otitis persisted. Five weeks after the initial episode the patient went back to the clinics in emergency complaining of intense cephalgia for a few hours with impression of faintness without fever. The state of consciousness of the patient then degraded quickly during the conversation. Into the 15 minutes time, the patient slipped of a stuporous state to coma. Hospitalized in emergency in intensive care unit, the diagnosis of an otogenic meningitis with Streptococcus pneumoniae was made. The patient cured without sequelae.

CONCLUSION

An inadequate treatment accompanied by a favorable anatomical factor facilitated the diffusion of the bacterial invasive process of the ear drum through the osseous barrier until the dura mater. A banal barotrauma otitis which persists can cause serious complications. An antibiotic must be prescripted starting from stage III, i.e. when there is retrotympanic effusion. In front of a behavioral problem during an otitis, it is necessary to always think of the intracranial complications and not to delay the anti-infectious treatment which must be started as soon as possible. To obtain a complete cure without sequelae, it seems that the adapted anti-infectious treatment must be instaured within a time below 10 hours.

Middle ear pain and trauma during air travel

INTRODUCTION

Changes in air pressure during flying can cause ear-drum pain and perforation, vertigo, and hearing loss. It has been estimated that 10% of adults and 22% of children might have damage to the ear drum after a flight, although perforation is rare. Symptoms usually resolve spontaneously.

METHODS AND OUTCOMES

We conducted a systematic review and aimed to answer the following clinical question: What are the effects of interventions to prevent middle ear pain during air travel? We searched: Medline, Embase, The Cochrane Library and other important databases up to April 2007 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).

RESULTS

We found 4 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.

CONCLUSIONS

In this systematic review we present information relating to the effectiveness and safety of the following interventions: nasal balloon inflation, oral pseudoephedrine, and topical nasal decongestants.

Conventional mechanical ventilation in pediatrics

OBJECTIVE

To review the various challenges of providing mechanical ventilation to pediatric patients with diseases of increased airway resistance, diseases of abnormal lung compliance or normal lungs.

SOURCES

Original data from our pediatric intensive care unit and animal research laboratory. Relevant articles included in the MEDLINE electronic database during the last 10 years. Also included were book chapters and definitive studies, as judged by the authors, in the fields of asthma, acute respiratory distress syndrome, mechanical ventilation, ventilator-induced lung injury and permissive hypercapnia.

SUMMARY OF THE FINDINGS

Mechanical ventilation of patients with diseases of increased airway resistance should center on avoidance of dynamic hyperinflation, allowing complete exhalation prior to the initiation of a subsequent breath and permissive hypercapnia. Positive end-expiratory pressure should be used sparingly to prevent atelectasis and facilitate synchrony in spontaneously breathing patients. Mechanical ventilation of patients with diseases of abnormal lung compliance should take into consideration the inhomogeneous distribution of lung disease. Focus should be on avoidance of volutrauma and atelectrauma that could result in ventilator-associated lung injury.

CONCLUSIONS

The last decade was marked by significant advances in the management of pediatric respiratory failure. The choice of mechanical ventilation strategy can significantly influence the subsequent course of lung injury. Mechanical ventilation can no longer be viewed simply as a harmless support modality that is employed to keep patients alive while disease-specific treatments are used to ameliorate the underlying pathology.

A review of asthma and scuba diving

An increasing number of asthmatics participate in recreational scuba diving. This activity presents unique physical and physiological challenges to the respiratory system. This review addresses the susceptibility of divers with asthma to diving accidents, acute asthmatic attacks, and long-term exacerbation of their disease. Recommendations on fitness to dive with asthma and airway hyperresponsiveness are provided.

Proportional assist ventilation (PAV): a significant advance or a futile struggle between logic and practice?

Proportional assist ventilation is a promising addition to other more conventional modes of mechanical ventilation with the theoretical advantage of improving patient-ventilator interaction. It may also be of use as a diagnostic tool in the control of breathing in mechanically ventilated patients.

Inner ear damage in TORP-operated ears: experimental study on danger from environmental air pressure changes

In some cases of sudden inner ear hearing loss in ears with a total ossicular replacement prosthesis, the prosthesis has been found to be penetrating the footplate. Some authors have assumed an external pressure increase for this event. In this study I tried to estimate experimentally the pressure needed for perforating a normal footplate in a temporal bone model. From the data I concluded that "cracking" the footplate can hardly be due to 1 major event of increased pressure. On the other hand, different mechanisms making the footplate a "weak spot" must be discussed and further investigated. In those cases, secondary to thinned or even perforated footplates, environmental pressure changes may be dangerous.

Treatment of decompression illness and latrogenic gas embolism

The mainstay of treatment of gas bubble disease is therapeutic recompression while the patient is breathing oxygen. The patient should be recompressed as soon as possible; however, patients should be considered for recompression even after several days' delay. Treatments should be repeated if possible until symptoms have either resolved or stabilized. Appropriate hydration is essential. The use of HBO is generally safe, relatively nontoxic, and is possible even in neonates. Pharmacologic agents (e.g., anticoagulants, lidocaine, antiplatelet agents, corticosteroids, inhibitors of calcium flux) may be useful adjuncts to recompression therapy but they require further study. For patients who respond poorly to recompression therapy, the next advance in the treatment of DCI-induced neural injury is likely to be due to the development of agents that reduce the effects of reperfusion injury and delayed cell death.

Operational use and patient monitoring in a multiplace hyperbaric chamber

Multiplace hyperbaric chambers can be used to deliver patient care with enormous flexibility. Standard critical care techniques, such as mechanical ventilation, endotracheal suctioning, hemodynamic monitoring, blood gas measurement, and emergency therapy such as cardiopulmonary resuscitation, including defibrillation and cardioversion, can all be performed inside a multiplace chamber. The multiplace chamber can be considered an extension of the intensive care unit. This flexibility is accompanied by increased complexity of chamber operation. Careful attention must be paid to minimization of fire hazards and maintenance of a safe chamber atmosphere. Although life support apparatus can easily be taken inside the chamber and will usually work under hyperbaric conditions, care must be given to facilitate the benefits to the patient of hyperbaric oxygen treatment in the face of potential risks associated with rapid changes in environmental pressure and the partial pressures of the component gases.

Use of permissive hypercapnia in the ventilation of infants with respiratory syncytial virus infection

We wished to retrospectively evaluate the effects of permissive hypercapnia (PHY) on barotrauma, mortality and length of stay when applied to ventilated infants with respiratory syncytial virus (RSV) bronchiolitis. Nineteen control infants with RSV induced respiratory failure were treated with conventional ventilation (April 1991-January 1994), after which time PHY was adopted as unit policy. A further 28 infants were then treated with PHY (January 1994 April 1996). Demographic and physiological data were collected from admission, and outcome variables including length of stay, barotrauma and mortality were recorded. The PHY group showed a significantly higher mean pCO2 (7.6 vs 5.2 kPa), a lower mean pH (7.34 vs 7.40), and a reduction in maximal peak inspiratory pressures (25 vs 30 cmH2O). Mortality, barotrauma, use of neuromuscular blockade and nosocomial infection did not differ between groups. There was a trend towards increased length of ventilation in the PHY group (median 7 vs 5 days).

CONCLUSION

Based on this retrospective data we can show no benefit for the use of permissive hypercapnia as a ventilatory strategy in this patient group. A prospective randomised controlled trial is warranted to accurately assess the outcome variables and cost implications of this strategy.

Ventilator-induced injury: from barotrauma to biotrauma

Mechanical ventilation is an indispensable tool in the management of respiratory and ventilatory failure. However, ventilation per se may also initiate or exacerbate lung injury, contributing to patient morbidity and mortality. In this review, we examine the current mechanisms of ventilator-induced injury including those that primarily involve physical disruption of the lung, as well as those more recently described that involve cell- and inflammatory-mediator-induced injury. The latter have received attention of late because of the possible systemic sequelae such as multiple system organ failure, the primary cause of death of patients with acute respiratory distress syndrome. Although much remains to be elucidated about the mechanisms of ventilator-induced injury, it is hoped that novel approaches addressing both the physiologic as well as molecular effects of ventilation will lead to innovative therapeutic approaches that improve patient outcome.

Volume displacement of the gerbil eardrum pars flaccida as a function of middle ear pressure

The pars flaccida (PF) is a small region of the eardrum, with elasticity and histology completely different from the rest of the membrane, which has often been attributed a pressure regulating function for the middle ear (ME). In this paper, the volume displacement of the PF as a function of ME pressure is discussed. The deformation of the PF was measured in vitro in five Mongolian gerbil ears, by means of an opto-electronic moiré interferometer. Volume displacement was determined at small intervals in three sequential pressure cycles, in the range of +/- 0.4 kPa, +/- 2 kPa, and again +/- 0.4 kPa. The displacement was found to be a highly non-linear function of pressure, with a strong increase up to 0.4 kPa ME over- or underpressure and remaining nearly unchanged for pressures beyond 0.4 kPa. In all animals, maximal volume displacement was less than 0.5 microl, or 0.2% of total ME air volume. Clear hysteresis was found between the deformations at the same pressure level in the increasing and decreasing parts of the pressure cycles. Membrane behavior in the first 0.4 kPa pressure cycle was significantly different from that in the second 0.4 kPa cycle, which followed the 2 kPa pressure cycle. The results indicate that the ME pressure change regulation function of the PF is limited to very small pressure changes of a few hundred Pa around ambient pressure, and that larger ME pressures cause at least short-term changes in the membrane's behavior.

[Occurrence of eardrum pathology in a cohort of adults born 1955]

The aim of this study was to estimate the prevalence of the different types of eardrum pathology in a cohort (cohort 1955) who were children before the era of ventilation tubes, and to compare these findings with the prevalence of eardrum pathology in a previous published cohort study on 222 children followed since the age of four years (cohort 1975) in the era of ventilation tubes. All inhabitants of Hillerød county born in 1955 were invited to a screening examination including otomicroscopy, tympanometry and audiometry. All eardrum pathology was recorded. In cohort 1955, 59% of 460 possible, attended the examination. In addition 9% returned a questionnaire enquiring their otologic history. In the cohort with no grommets, retraction of Shrapnell's membrane was found in 4% of the ears compared to 20% in the cohort with grommets. Tensa pathology was found in 6% of the ears in the old cohort and in 24% in the young cohort. Despite the increased attention to the diagnosis of secretory otitis, and the increased rate of surgical treatment, the prevalence of eardrum pathology seems to have increased. The reason for this increase is discussed.

In vivo observation with magnetic resonance imaging of middle ear effusion in response to experimental underpressures

In this study, magnetic resonance imaging (MRI) was used to define, in vivo, the effect of acute middle ear (ME) underpressures on vascular permeability and the development of effusion. The MEs of four cynomolgus monkeys were unilaterally inflated with oxygen and carbon dioxide on different occasions and followed for a period of approximately 4 hours by tympanometry and MRI scanning. Carbon dioxide inflations caused the rapid development of ME underpressures of less than -600 mm H2O by 10 minutes. The MRI scans showed a progressive brightening of the ME and all associated air cells, indicative of the accumulation of effusion in three of the four experiments. An MRI contrast agent was administered to the vascular compartment during the course of the experiment and was rapidly transferred to the ME space, indicating vascular permeability to the agent. The contralateral, control side did not develop significant underpressures, effusion, or increased vascular permeability. Inflation with oxygen caused lesser underpressures and no accompanying changes in the MRI scans. These data support the hydrops ex vacuo theory and confirm the usefulness of MRI for in vivo documentation of the development of ME effusions and changes in vascular permeability of the mucosa in the experimental setting.

Therapeutic optimization including inhaled nitric oxide in adult respiratory distress syndrome in a polyvalent intensive care unit

OBJECTIVE

To investigate the effects of inhaled nitric oxide (NO) in adult respiratory distress syndrome (ARDS) associated with a therapeutic optimization strategy on oxygen parameters, barotrauma, and evolution in a medical and surgical intensive care unit.

DESIGN

Prospective study.

MATERIALS AND METHODS

Twenty consecutive patients with ARDS were studied (Murray score 3.6 +/- 0.2). Eleven were surgical patients and nine were medical patients. All fulfilled the extracorporeal membrane oxygenation entry criteria. The APACHE II score predicted mortality was 39%. All were ventilated with FiO2 1 with positive end-expiratory pressure (PEEP) of 11 +/- 1 cm H2O. Therapeutic optimization included permissive hypercapnia, tracheal gas insufflation, prone position, continuous hemofiltration, treatment of infection, and pleural drainage. We used NO continuously inhaled at a concentration ranging from 5 to 10 ppm.

MEASUREMENTS AND MAIN RESULTS

After 1 hour, inhaled NO improved PaO2 in all patients except one (78 +/- 11 to 130 +/- 25 mm Hg) (p < 0.05), allowing a reduction of FiO2 and PEEP. After 24 hours, mean pulmonary arterial pressure decreased from 31 +/- 3 to 25 +/- 2 mm Hg (p < 0.05). Systemic hemodynamics were unaffected. Oxygen delivery increased from 531 +/- 135 to 603 +/- 125 mL/minute/m-2 (p < 0.05). Barotraumatic lesions were present in only one patient. Reversal of ARDS was obtained in 16 patients, of whom 14 (70%) were discharged.

CONCLUSIONS

This study was shorter to demonstrate an improvement in the survival rate. Nevertheless, these preliminary results are encouraging. Because of its safety, effectiveness, and easy use, inhaled NO should be used as a part of a therapeutic optimization protocol before considering more invasive and expensive procedures, such as extracorporeal respiratory support or intravascular oxygenation.

Pulmonary barotrauma after a free dive--a possible mechanism

Pulmonary barotrauma during scuba diving is a life-threatening event. In a skin diver, who does not use compressed air, this complication is rare and its pathophysiology is not readily understood. We present a young, healthy skin diver who suffered pneumomediastinum and subcutaneous emphysema after a sequence of free dives to 5 m, and suggest a possible mechanism.

Fluid percussion barotrauma chamber: a new in vitro model for traumatic brain injury

Advances in the understanding of the pathophysiology of traumatic brain injury have implicated a number of cellular events as fundamental to the evolution of neurologic dysfunction in this process. Following the primary biomechanical insult, a highly complex series of biochemical changes occur, some of which are reversible. The development of fluid percussion injury as an in vivo model for traumatic brain injury has greatly improved our ability to study this disease. However, a comparable in vitro model of biomechanical injury which would enable investigators to study the response to injury in isolated cell types has not been described. We have developed a model of transient barotrauma in cell culture to examine the effects of this form of injury on cell metabolism. This model employs the same fluid percussion device commonly used in in vivo brain injury studies. The effect of this injury was evaluated in monolayers of human glial cells. Cell viability by trypan blue exclusion and the production of leukotrienes following increasing barotrauma was investigated. This model provided a reproducible method of subjecting cells in culture to forces similar to those currently used in animal experimental head injury.

Maxillary sinus barotrauma with fifth cranial nerve involvement

A case of neurapraxia of the infraorbital nerve occurring as a result of maxillary sinus barotrauma in a diver is presented. Existing reports of a similar nature are reviewed and the pathogenesis of cranial nerve involvement in barotrauma is discussed. Guidelines for treatment are suggested.

Radiologic considerations in the adult respiratory distress syndrome

ARDS is the clinical consequence of acute lung injury that results in increased-permeability edema. Distinct pathophysiologic stages are reflected in the radiographic evolution of the syndrome. Diffuse microatelectasis, proteinaceous edema fluid, and multifocal in situ pulmonary vascular occlusions characterize the acute stages of injury and result in the appearance of diffuse consolidations and occasional pleural effusions on the radiograph. In the chronic organizing stage of ARDS, the physiologic consequences of subsiding edema and tissue repair may be reflected by a transition to stable interstitial patterns. There is a high frequency of complications related to the decreased compliance of the injured lung that lead to interstitial emphysema and other barotraumatic complications. Survivors of ARDS exhibit various degrees of physiologic impairment and radiographic abnormality that may improve during the first year after survival. The relations between various indices of the severity of ARDS and the ultimate outcome are emerging. Debate continues about the specificity of the chest radiograph in distinguishing increased-permeability edema from hydrostatic edema. In fact, interstitial patterns and pleural effusions are observed in both. Nonetheless, the chest radiograph is a pivotal tool for monitoring patients at risk of serious morbidity from nosocomial lung infection, barotrauma, and the complications accompanying the use of invasive devices. It is hoped that as we develop a more uniform consensus on the clinical definition of ARDS and begin to classify patients according to specific clinical or physiologic observations, chest radiographic observation will acquire greater diagnostic and prognostic significance in these critically ill patients.

[Barodontology: current status. Dental aspects]

We present a comprehensive review of barodontalgia, with reference to the several pathogenetic hypotheses, and insisting on the consideration of barodontalgia in the differential diagnosis of toothache. The odontologists approach to this increasing clinical problem is also discussed.

The use of tympanometry in predicting otitic barotrauma

Static acoustic impedance tympanometry was used to examine 80 subjects prior to and after exposure to decreased ambient pressure in a hypobaric chamber. The predictive value of tympanometry in detecting those individuals likely to suffer from otitic barotrauma (aerotitis media) was evaluated. The results suggest that testing prior to altitude exposure is of no value in identifying those individuals who will suffer from otitic barotrauma during flight. Tympanometry however proved a useful tool in confirming the presence of barotrauma following flight, but it was no more useful than taking a history and performing an ear examination.

Physical correlates of eardrum rupture

Eardrum (tympanic membrane) rupture in humans and animals in relation to various blast pressure-time patterns was reviewed. There were few systematic studies on eardrum rupture as a consequence of blast overpressure. Most reports did not describe the area of the eardrum destroyed. The peak overpressures required to produce a 50% incidence of eardrum rupture (P50) were summarized. Most of the animal data pertained to dogs. The highest P50 for dogs, 296 kPa, was associated with smooth-rising overpressure. For complex wave patterns occurring inside open shelters subjected to nuclear blasts, the P50 was 205 kPa. For fast-rising blasts in a shock tube it was 78 kPa, and 105 kPa for statically applied pressures. The duration of the overpressure was not a factor unless it was very short. The influence of the orientation of the head to the oncoming blast was demonstrated. An ear facing the blast may receive reflected overpressures several times that for one side-on to the blast. An ear on the downstream side of the head was exposed to about the same overpressure as the side-on ear. A P50 for humans of 100 kPa and a threshold of 35 kPa has been used widely in blast criteria. A recent study suggests a threshold (P1) of about 20 kPa, and gives the overpressures required to produce minor, moderate, and major eardrum ruptures. These data were presented in the form of curves showing the overpressures as a function of duration required to inflict a P1 and a P50 of eardrum rupture of the three levels of severity.