Prolonged severe hypercapnia complicating near fatal asthma in a 35-year-old woman

Hypercapnia: An Aggravating Factor in Asthma

Asthma is a common chronic respiratory disorder with relatively good outcomes in the majority of patients with appropriate maintenance therapy. However, in a small minority, patients can experience severe asthma with respiratory failure and hypercapnia, necessitating intensive care unit admission. Hypercapnia occurs due to alveolar hypoventilation and insufficient removal of carbon dioxide (CO₂) from the blood. Although mild hypercapnia is generally well tolerated in patients with asthma, there is accumulating evidence that elevated levels of CO₂ can act as a gaso-signaling molecule, triggering deleterious effects in various organs such as the lung, skeletal muscles and the innate immune system. Here, we review recent advances on pathophysiological response to hypercapnia and discuss potential detrimental effects of hypercapnia in patients with asthma.

Balancing treatments for patients with systemic hypertension and glaucoma

INTRODUCTION

Treatment of glaucoma and systemic hypertension requires careful balancing of ophthalmic and systemic medications. This report offers background on various common therapies and considerations to minimize undesirable systemic and ophthalmic outcomes.

AREAS COVERED

Key considerations relating to medical treatments for systemic hypertension and glaucoma chosen from a review of the literature are included. The historic safety of ophthalmic beta blockers and sub-types as well as combination agents are described. The potential role of ocular perfusion pressure in the pathogenesis of glaucoma is reviewed with a discussion of landmark studies, including the Barbados Eye Study and the Early Manifest Glaucoma Trial, with implications for medication choices for hypertension and glaucoma. Systemic antihypertensives are considered with regards to their potential association with glaucoma and its progression, especially in patients with low blood pressure and normal tension glaucoma. Opinions are offered with regard to therapeutic choices and considerations.

EXPERT OPINION

The medical treatment of systemic hypertension and glaucoma carries the potential for drug interactions and significant adverse effects requiring customization for each patient's particular issues. The evolution of new therapies and treatment paradigms, including laser as a first-line treatment, has expanded safe options and minimized potential dangers for high-risk patients.

Treatment of life-threatening hypercapnia with isoflurane in an infant with status asthmaticus

We encountered a 2-year-old child with life-threatening hypercapnia, with a PaCO(2) of 238 mm Hg and severe respiratory and metabolic acidosis, due to status asthmaticus that was refractory to steroid and bronchodilator therapy. Suspecting ventilatory failure and excessive ventilation-induced obstructive shock, we started respiratory physiotherapy in synchrony with her respiration, to facilitate exhalation from her over-inflated lungs. Isoflurane inhalation was commenced in preparation for extracorporeal circulation, to reduce the hypercapnia. The combination of respiratory physiotherapy and isoflurane inhalation resulted in a rapid decrease in ventilatory resistance and PaCO(2) levels within a few minutes, with recovery of consciousness within 60 min. Isoflurane inhalation was gradually discontinued and steroid and aminophylline therapy were commenced. The patient recovered completely without any recurrence of her bronchospasm and without any residual neurological deficits. In our patient with a severe asthmatic attack, decreased exhalation secondary to asthma and overventilation during artificial ventilation resulted in overinflation of the lungs, which in turn led to cerebral edema and obstructive cardiac failure. The favorable outcome in this case was due to the short duration of hypercapnia. Hence, we conclude that the duration of hypercapnia is an important determinant of the morbidity and mortality of status asthmaticus-induced severe hypercapnia.

Analytic review: management of life-threatening asthma in adults

Asthma remains a troubling health problem despite the availability of effective treatment. A small but significant number of asthmatics experience life-threatening attacks culminating in intensive care unit admission. Standard treatment includes high dose systemic corticosteroids and inhaled bronchodilators. Patients with especially severe attacks may develop respiratory failure and need endotracheal intubation and mechanical ventilation. Severe airway obstruction may lead to dynamic hyperinflation and the possibility of hemodynamic collapse and barotrauma. Fortunately, most intubated asthmatics survive if physicians adhere to key management principles intended to avoid or minimize hyperinflation. The purpose of this review is to discuss the pathogenesis of life-threatening asthma and to provide practical guidance to promote rationale, safe, and effective management.

Alteration of the piglet diaphragm contractility in vivo and its recovery after acute hypercapnia

BACKGROUND

The effects of hypercapnic acidosis on the diaphragm and its recovery to normocapnia have been poorly evaluated. The authors studied diaphragmatic contractility facing acute variations of arterial carbon dioxide tension (Paco2) and evaluated the contractile function at 60 min after normocapnia recovery.

METHODS

Thirteen piglets weighing 15-20 kg were anesthetized, ventilated, and separated into two groups: a control group (n = 5) evaluated in normocapnia (time-control experiments) and a hypercapnia group (n = 8) in which animals were acutely and shortly exposed to five consecutive ranges of Paco2 (40, 50, 70, 90, and 110 mmHg). Then carbon dioxide insufflation was stopped. Diaphragmatic contractility was assessed by measuring transdiaphragmatic pressure variations obtained after bilateral transjugular phrenic nerve pacing at increased frequencies (20-120 Hz). For each level of arterial pressure of carbon dioxide, pressure-frequency curves were obtained in vivo by phrenic nerve pacing.

RESULTS

In the hypercapnia group, mean +/- SD transdiaphragmatic pressure significantly decreased from 41 +/- 3 to 29 +/- 3 cm H2O (P < 0.05) between the first (40 mmHg) and fifth (116 mmHg) stages of capnia at the frequency of 100 Hz stimulation. The observed alteration of the contractile force was proportional to the level of Paco2 (r = 0.61, P < 0.01). Normocapnia recuperation allowed a partial recovery of the diaphragmatic contractile force (80% of the baseline value) at 60 min after carbon dioxide insufflation interruption.

CONCLUSION

A short exposure to respiratory acidosis decreased diaphragmatic contractility proportionally to the degree of hypercapnia, and this alteration was only partially reversed at 60 min after exposure.

Permissive range of hypercapnia for improved peripheral microcirculation and cardiac output in rabbits*

OBJECTIVES

Permissive hypercapnia improves outcomes in patients with respiratory failure, most likely because of a reduction in ventilator-induced lung injury. Because hypercapnia is a potent vasoactive stimulus, adequate tissue perfusion and oxygen delivery to dilated microvessels may be restored. We examined how Paco2 affects microvascular changes, hemodynamics, and cardiac output in rabbits. We evaluated the permissive range of Paco2 required for maintenance of the peripheral circulation.

DESIGN

Prospective experimental animal study.

SETTING

Animal research laboratory.

SUBJECTS

A total of 31 Japanese domestic white rabbits.

INTERVENTIONS

The animals were anesthetized with pentobarbital. An ear chamber was prepared to examine blood vessels by intravital microscopy. The rabbits were mechanically ventilated with air, oxygen, and CO2. The values of Paco2 were adjusted to about 20 (hypocapnia), 40 (normocapnia), 60, 80, 100, 125, 150, and >250 mm Hg (hypercapnia). After stabilization at each Paco2 level, microvascular changes were recorded with a microscope-closed video camera to permit analysis of arteriolar diameter and blood flow.

MEASUREMENTS AND MAIN RESULTS

The pH and heart rate decreased and mean blood pressure increased progressively as the Paco2 was increased. When Paco2 was increased from 20 to 80 mm Hg, vessel diameter, blood-flow velocity, and blood-flow rate increased markedly. Cardiac output increased slightly. When Paco2 exceeded 100 mm Hg, all of these variables decreased. When Paco2 exceeded 150 mm Hg, all variables were significantly lower than the control values (p < .01).

CONCLUSION

Intravital microscopic visualization of the rabbit ear microcirculation showed that 150 mm Hg is the permissive upper limit of acute hypercapnia with respect to maintenance of the peripheral microcirculation.

Pressure control ventilation

As mechanical ventilators become increasingly sophisticated, clinicians are faced with a variety of ventilatory modes that use volume, pressure, and time in combination to achieve the overall goal of assisted ventilation. Although much has been written about the advantages and disadvantages of these increasingly complex modalities, currently there is no convincing evidence of the superiority of one mode of ventilation over another. Pressure control ventilation may offer particular advantages in certain circumstances in which variable flow rates are preferred or when pressure and volume limitation is required. The goal of this article is to provide clinicians with a fundamental understanding of the dependent and independent variables active in pressure control ventilation and describe features of the mode that may contribute to improved gas exchange and patient-ventilator synchronization.

A 10-year-old child with status asthmaticus, hypercapnia and a unilateral dilated pupil

This article reports the case of a 10-year-old child with an exacerbation of asthma requiring mechanical ventilation. His immediate course was complicated by significantly elevated arterial CO(2) tensions and a unilateral dilated pupil. A computed tomography scan of his brain failed to demonstrate any evidence of intracranial hypertension or cerebral edema, and he went on to make an uncomplicated recovery, with no evidence of neurological sequelae. The most likely diagnosis appeared to be local contamination with ipratropium when he was receiving frequent nebulizers prior to mechanical ventilation. Similar cases reported in the literature are reviewed, with a discussion of clinical management, implications of permissive hypercapnia and neurological complications in ventilating asthmatic patients and the importance of safe drug handling by staff members.

Hypercapnia and oxygen therapy in older asthmatic patients

Excessive oxygen administration in hypercapnic chronic obstructive pulmonary disease predisposes to worsening respiratory failure during intercurrent respiratory illness. Chronic hypercapnia is thought to downregulate carbon dioxide chemoreceptor sensitivity, adversely affecting respiratory function/mechanics and worsening ventilation-perfusion inequality. These patients are dependent on hypoxic drive to maintain adequate spontaneous respiration. Whether an analogous situation occurs in asthma in older adults is unknown. These conditions may be difficult to differentiate clinically, and both may respond adversely to the administration of excessive oxygen in the presence of chronic hypercapnia. Although unrestricted oxygen is beneficial and safe in children and young adults with asthma, it may lead to progressive hypercapnia in older patients with asthma, a potential risk highlighted by this case. To avert progressive hypercapnia, oxygen therapy that is carefully adjusted to achieve adequate, but not maximal, tissue oxygenation may be a safer strategy than unrestricted oxygen use in older asthmatic patients. However, the correction of hypoxia overrides strategies to avert oxygen-related hypercapnia.

Hypercapnia: what is the limit in paediatric patients? A case of near-fatal asthma successfully treated by multipharmacological approach

We describe a case of prolonged severe hypercapnia with respiratory acidosis occurring during an episode of near-fatal asthma in an 8-year-old boy, followed by complete recovery. After admission to the intensive care unit, despite treatment with maximal conventional bronchodilatative therapy, the clinical picture deteriorated with evident signs of respiratory muscle fatigue. The child was sedated, intubated and mechanically ventilated. Magnesium sulphate, ketamine and sevoflurane were gradually introduced together with deep sedation, curarization and continuous bronchodilatative therapy. Ten hours after admission, arterial pCO2 reached 39 kPa (293 mmHg), pH was 6.77 and pO2 8.6 kPa (65 mmHg). Chest radiograph showed severe neck subcutaneous emphysema, with signs of mediastinal emphysema. No episode of haemodynamic instability was seen despite severe prolonged hypercapnia lasting more than 14 h. Oxygenation was maintained and successful recovery followed without neurological or cardiovascular sequelae. This case shows the cardiovascular and neurological tolerance of a prolonged period of supercarbia in a paediatric patient. The most important lesson to be learned is the extreme importance of maintaining adequate tissue perfusion and oxygenation during an asthma attack. The second lesson is that when conventional bronchodilators fail, the intensivist may resort to the use of drugs such as ketamine, magnesium sulphate and inhalation anaesthesia. In this context deep sedation and curarization are important not only to improve oxygenation, but also to reduce cerebral metabolic requirements.

Subarachnoid hemorrhage in a child with status asthmaticus: significance of permissive hypercapnia

OBJECTIVE

To report an 11-yr-old boy with acute status asthmaticus being managed with permissive hypercapnia who developed a subarachnoid hemorrhage during the course of his illness.

SETTING

An eight-bed pediatric intensive care unit in a community hospital.

INTERVENTIONS

The patient was intubated for respiratory failure and managed with permissive hypercapnia. After the development of changes in his pupillary exam, computerized tomography of the brain revealed diffuse subarachnoid hemorrhage. Carotid angiography was performed to rule out the possibility of underlying vascular malformation.

RESULTS

Aggressive investigation including a normal carotid angiogram failed to reveal underlying pathology that may have put the patient at risk for the event.

CONCLUSIONS

We conclude that this patient suffered subarachnoid hemorrhage in association with the use of permissive hypercapnia in the settling of severe asthma.

Severe status asthmaticus: management with permissive hypercapnia and inhalation anesthesia

OBJECTIVE

To describe the difficulties that can be encountered during mechanical ventilation of severe status asthmaticus and to discuss the safety of permissive hypercapnia as a ventilatory strategy and the role and limitations of inhalation anesthesia in the treatment of refractory cases.

DESIGN

Case series and review of literature.

SETTING

Intensive care unit of a tertiary care hospital.

PATIENTS

Two patients with severe status asthmaticus.

INTERVENTIONS

Administration of inhalational anesthetics.

MEASUREMENTS AND MAIN RESULTS

Both patients had respiratory failure secondary to status asthmaticus requiring mechanical ventilation and permissive hypercapnia. They also received inhalational anesthetics because of refractory bronchoconstriction. Levels of PaCO(2) in each case were among the highest and most prolonged elevations (>150 mm Hg for several hours) reported to date. In one case, life-threatening difficulties with ventilation were encountered related to the use of an anesthesia ventilator. Although they had complications related to the severity of their illnesses, both were treated to recovery.

CONCLUSIONS

Mechanical ventilation in severe status asthmaticus can be challenging. Permissive hypercapnia is a relatively safe strategy in the ventilatory management of asthma. High levels of hypercapnia and associated severe acidosis are well tolerated in the absence of contraindications (i.e., preexisting intracranial hypertension). Inhalation anesthesia may be useful in the treatment of refractory cases of asthma but should be used carefully because it may be hazardous owing to poor flow capabilities of most anesthesia ventilators.

Systemic adverse effects of ophthalmic beta-blockers

OBJECTIVE

To review published clinical information on the systemic adverse effects of ophthalmic beta-blockers for the purpose of developing a pilot contraindication/warning system for active prescriptions in the Veterans Affairs dispensing database.

DATA SOURCES

Articles were identified by searching MEDLINE (1966-October 2000) and International Pharmaceutical Abstracts (1970-October 2000).

STUDY SELECTION AND DATA EXTRACTION

Article relevance was determined by review of titles, abstracts, and key words.

DATA SYNTHESIS

The preponderance of the evidence suggests that ophthalmic beta-blockers may be associated with bronchospasm and adverse cardiovascular effects including bradycardia. Depression and other central nervous system effects are reported less commonly. Data are inadequate to suggest that ophthalmic beta-blocker use is routinely associated with adverse metabolic effects.

CONCLUSIONS

The strongest level of evidence (grade A1) supports a contraindication for use of ophthalmic beta-blockers for respiratory disease, with a moderate level of evidence (grade B1) for cardiovascular disease. Data are insufficient to support or refute contraindications for other disease states. The search technique and classification scheme described in this article provide a methodology for evaluating, grading, and applying evidence on potential adverse effects of drug therapy.