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.