THE USE OF SODIUM BICARBONATE IN THE TREATMENT OF ACUTE BRONCHIAL ASTHMA

Acute sodium bicarbonate administration improves ventilatory efficiency in experimental respiratory acidosis: clinical implications

Administering sodium bicarbonate (NaHCO3) to patients with respiratory acidosis breathing spontaneously is contraindicated because it increases carbon dioxide load and depresses pulmonary ventilation. Nonetheless, several studies have reported salutary effects of NaHCO3 in patients with respiratory acidosis but the underlying mechanism remains uncertain. Considering that such reports have been ignored, we examined the ventilatory response of unanesthetized dogs with respiratory acidosis to hypertonic NaHCO3 infusion (1 N, 5 mmol/kg) and compared it with that of animals with normal acid-base status or one of the remaining acid-base disorders. Ventilatory response to NaHCO3 infusion was evaluated by examining the ensuing change in PaCO2 and the linear regression of the PaCO2 vs. pH relationship. Strikingly, PaCO2 failed to increase and the ΔPaCO2 vs. ΔpH slope was negative in respiratory acidosis, whereas PaCO2 increased consistently and the ΔPaCO2 vs. ΔpH slope was positive in the remaining study groups. These results cannot be explained by differences in buffering-induced decomposition of infused bicarbonate or baseline levels of blood pH, PaCO2, and pulmonary ventilation. We propose that NaHCO3 infusion improved the ventilatory efficiency of animals with respiratory acidosis, i.e., it decreased their ratio of total pulmonary ventilation to carbon dioxide excretion (VE/VCO2). Such exclusive effect of NaHCO3 infusion in animals with respiratory acidosis might emanate from baseline increased VD/VT (dead space/tidal volume) caused by bronchoconstriction and likely reduced pulmonary blood flow, defects that are reversed by alkali infusion. Our observations might explain the beneficial effects of NaHCO3 reported in patients with acute respiratory acidosis.

Sodium bicarbonate therapy for acute respiratory acidosis

PURPOSE OF REVIEW

Respiratory acidosis is commonly present in patients with respiratory failure. The usual treatment of hypercapnia is to increase ventilation. During the recent surge of COVID-19, respiratory acidosis unresponsive to increased mechanical ventilatory support was common. Increasing mechanical ventilation comes at the expense of barotrauma and hemodynamic compromise from increasing positive end-expiratory pressures or minute ventilation. Treating acute respiratory acidemia with sodium bicarbonate remains controversial.

RECENT FINDINGS

There are no randomized controlled trials of administration of sodium bicarbonate for respiratory acidemia. A recent review concluded that alkali therapy for mixed respiratory and metabolic acidosis might be useful but was based on the conflicting and not conclusive literature regarding metabolic acidosis. This strategy should not be extrapolated to treatment of respiratory acidemia. Low tidal volume ventilation in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) has beneficial effects associated with permissive hypercapnia. Whether the putative benefits will be negated by administration of alkali is not known. Hypercapnic acidosis is well tolerated, with few adverse effects as long as tissue perfusion and oxygenation are maintained.

SUMMARY

There is a lack of clinical evidence that administration of sodium bicarbonate for respiratory acidosis has a net benefit; in fact, there are potential risks associated with it.

Severity Stratification in Life-threatening Asthma

Severity differences may in part explain the large varia tions in asthma mortality that occur in different coun tries. This study examines the use of APACHE II for measuring asthma severity in 118 adult asthma admis sions at one intensive care unit in New Zealand during 1987-1988. Most admissions were hypercapnic (72%), and 61 % had an altered level of consciousness. Mean APACHE II score was 20 in the emergency department and 12 upon ICU admission. We summarize the extent of physiological derangement using four acute physiol ogy score (APS) ranges. Each APS range stratified admis sions into groups with differing clinical course, therapy, and outcome. These results document a high level of asthma severity among patients treated in New Zealand, the country with the world's highest asthma mortality. APACHE II provides a valid and reproducible measure of asthma severity and should be useful for describing and comparing international differences in asthma severity and as a case-mix control in studies of asthma therapy.

Life-threatening asthma in children: treatment with sodium bicarbonate reduces PCO2

OBJECTIVES

To assess the effect of administration of sodium bicarbonate on carbon dioxide levels in children with life-threatening asthma (LTA) and to evaluate the clinical effect of this treatment.

STUDY DESIGN

Retrospective study.

SETTING

A pediatric ICU (PICU) of a tertiary care university hospital.

PATIENTS

Seventeen children with LTA who received sodium bicarbonate.

MEASUREMENTS AND RESULTS

In January 1999, a new protocol for the treatment of LTA was initiated in our institution, incorporating the use of IV sodium bicarbonate in acidotic patients (pH < 7.15) with refractory status asthmaticus. Since January 1999, sodium bicarbonate was administered to 17 patients; 5 patients received two or three doses of sodium bicarbonate. In three patients, sodium bicarbonate was administered after intubation. Intubation and mechanical ventilation were performed in five patients before admission to the PICU, and in one patient during admission. There was a significant decrease of Pco(2) after sodium bicarbonate infusion (p = 0.007). An improvement of respiratory distress in all but one patient was seen as well.

CONCLUSIONS

Administration of sodium bicarbonate in 17 children with LTA was associated with a significant decrease in Pco(2) and an improvement of respiratory distress. The possible benefits of sodium bicarbonate in LTA deserve further study in a controlled, prospective design.

Pressure-controlled ventilation in children with severe status asthmaticus

OBJECTIVE

The optimum strategy for mechanical ventilation in a child with status asthmaticus is not established. Volume-controlled ventilation continues to be the traditional approach in such children. Pressure-controlled ventilation may be theoretically more advantageous in allowing for more uniform ventilation. We describe our experience with pressure-controlled ventilation in children with severe respiratory failure from status asthmaticus.

DESIGN

Retrospective review.

SETTING

Pediatric intensive care unit in a university-affiliated children's hospital.

PATIENTS

All patients who received mechanical ventilation for status asthmaticus.

INTERVENTIONS

Pressure-controlled ventilation was used as the initial ventilatory strategy. The optimum pressure control, rate, and inspiratory and expiratory time were determined based on blood gas values, flow waveform, and exhaled tidal volume.

MEASUREMENT AND MAIN RESULTS

Forty patients were admitted for 51 episodes of severe status asthmaticus requiring mechanical ventilation. Before the institution of pressure-controlled ventilation, median pH and Pco(2) were 7.21 (range, 6.65-7.39) and 65 torr (29-264 torr), respectively. Four hours after pressure-controlled ventilation, median pH increased to 7.31 (6.98-7.45, p <.005), and Pco(2) decreased to 41 torr (21-118 torr, p <.005). For patients with respiratory acidosis (Pco(2) >45 torr) within 1 hr of starting pressure-controlled ventilation, the median length of time until Pco(2) decreased to <45 torr was 5 hrs (1-51 hrs). Oxygen saturation was maintained >95% in all patients. Two patients had pneumomediastinum before pressure-controlled ventilation. One patient each developed pneumothorax and subcutaneous emphysema after initiation of pressure-controlled ventilation. All patients survived without any neurologic morbidity. Median duration of mechanical ventilation was 29 hrs (4-107 hrs), intensive care stay was 56 hrs (17-183 hrs), and hospitalization was 5 days (2-20 days).

CONCLUSIONS

Based on this retrospective study, we suggest that pressure-controlled ventilation is an effective ventilatory strategy in severe status asthmaticus in children. Pressure-controlled ventilation represents a therapeutic option in the management of such children.

Treatment of severe respiratory failure during status asthmaticus in children and adolescents using high flow oxygen and sodium bicarbonate

OBJECTIVE

Status asthmaticus with respiratory failure is a potentially fatal complication of bronchial asthma. To prevent a fatality in status asthmaticus with respiratory failure, treatment with intravenous isoproterenol or mechanical ventilation has been advocated. These interventions also have serious potential complications, however, and while continuous inhalation of beta agonists has shown promise, the optimal therapy of severe status asthmaticus remains unclear. This paper describes our experience with a treatment protocol used in status asthmaticus with respiratory failure that seeks to avoid intravenous isoproterenol or assisted ventilation.

STUDY DESIGN

Case series of pediatric intensive care patients with severe respiratory failure due to status asthmaticus. Six children and adolescents experienced a total of nine episodes of severe respiratory failure due to status asthmaticus.

RESULTS

In seven of the nine episodes the patients were managed without either intravenous isoproterenol or mechanical ventilation. Hypercarbia persisted for an average of 25 hours (range 17 to 40 hours) in these seven episodes. All subjects recovered without notable sequelae. In two episodes, clinical and blood gas deterioration led to mechanical ventilation. Ventilation was required for 112 and 42 hours, respectively, in these episodes and the patients developed either pneumothorax or pneumomediastinum during ventilation.

CONCLUSION

Using a protocol initiated in 1978 for correction of hypoxia and acidemia, many patients with severe respiratory failure from status asthmaticus can be treated without isoproterenol or mechanical ventilation. Since those treatments have significant risks, consideration should be given to this intervention before resorting to them.

Mechanical ventilation in obstructive lung disease

This article reviews selected topics relevant to the use of mechanical ventilation in patients with severe airflow obstruction. Areas discussed include the bedside assessment of respiratory system mechanics, the ventilatory determinants of dynamic pulmonary hyperinflation, the role of controlled hypoventilation with permissive hypercapnia, and the delivery of bronchodilators during mechanical ventilation.

Efficacy, results, and complications of mechanical ventilation in children with status asthmaticus

We have conducted a retrospective survey of 79 children out of a total hospital asthmatic patient population of 2,412, admitted over a 32 month period to the ICU for the management of severe status asthmaticus. All patients were in severe respiratory distress with CO2 retention; 19 required mechanical ventilation due to increasing fatigue and worsening bronchospasm, having failed to respond to either inhaled or IV bronchodilator therapy. All patients were ventilated at slow rates (less than 12 min) and their airway pressure (Paw) was deliberately kept below 45 cmH2O, while accepting a PaCO2 in the 45-60 mmHg range, as long as the pH was compensated. Although two patients developed pneumothoraces while on positive pressure ventilation, these were resolved without incidents. Five patients who had mediastinal or subcutaneous air leaks prior to intubation did not develop pneumothoraces. Following the initiation of mechanical ventilation, IV beta-agonist therapy was increased in order to reverse the bronchospasm and reduce the duration of mechanical ventilation. Mean duration of intubation was 42 hours. Fourteen of the 19 patients were weaned and extubated within 48 hours. All patients survived without sequelae. We conclude that a degree of controlled "hypoventilation" by deliberately choosing Paw less than 45 cmH2O can be successfully used to ventilate children with severe status asthmaticus with a reduced rate of pressure-related complications.

Acid-base disturbances in acute asthma

The clinical features, arterial blood gases, and acid-base profile were examined in 229 consecutive episodes of acute asthma in 170 patients who required hospitalization. A simple respiratory alkalosis was the most common acid-base disturbance, occurring in 48 percent of the episodes. Metabolic acidosis, either alone or as part of a mixed disturbance, was noted in 28 percent. Of 60 episodes presenting with respiratory acidosis, 37 (62 percent) had a coexistent metabolic acidosis. Metabolic acidosis was more likely to occur in male subjects and in patients with evidence of more severe airflow obstruction. Patients with metabolic acidosis had an average anion gap of 15.8 mEq/L; these patients were more hypoxemic than those without metabolic acidosis and there was a significant inverse correlation between the anion gap and the degree of hypoxemia. We conclude that metabolic acidosis is a common finding in acute, severe asthma and suggest that the pathogenesis of lactic acidosis is multifactorial and includes contributions from lactate production by respiratory muscles, tissue hypoxia, and intracellular alkalosis.

Face-mask CPAP and sodium bicarbonate infusion in acute, severe asthma and metabolic acidosis

A patient with a history of previous mechanical ventilation for asthma was hospitalized with acute, severe asthma; metabolic acidosis; and hyperlactatemia. In addition to standard therapy, she was successfully treated with face-mask CPAP and IV sodium bicarbonate infusion. This therapy may help prevent mechanical ventilation in some patients with acute, severe asthma and lactic acidosis.

Mechanical ventilation for status asthmaticus in children

We retrospectively reviewed the time course of recovery of pediatric patients in status asthmaticus who were undergoing mechanical ventilation for life-threatening respiratory failure to evaluate the results with current medications and technology. Ten patients between 2 and 18 years of age underwent intubation on 20 occasions. Mechanical ventilation was maintained for a mean of 2 days. Positive end-expiratory pressure was introduced in the recovery phase to prevent hypoxemia. Twelve episodes (Group 1) involved intubation less than 48 hours; in eight episodes (group 2) the patients required ventilatory support greater than 48 hours. The two groups did not differ in regard to age, pharmacologic therapy, preintubation arterial blood gas data, or initial ventilator settings, but the rise in pH and fall in Paco2 differed significantly over the first 12 hours of therapy. In the group 2 patients, peak pressures were not increased greater than 60 cm H2O despite elevated Paco2 values, and aggressive sodium bicarbonate therapy for pH correction was not pursued. Complications were few and all patients survived. We conclude that asthma patients have variable resolution of airway obstruction during mechanical ventilation and that controlled hypoventilation can be a safe therapy for the patients with more severe obstruction.

Clinical applications of mechanical ventilation

This paper reviews recent applications of mechanical ventilation such as controlled hypoventilation in acute asthma, domiciliary nocturnal ventilation in chronic respiratory failure due to neuromuscular disease and improvement of left ventricular performance by raised intrathoracic pressure. Established uses of mechanical ventilation include control of respiratory failure, intracranial pressure and pulmonary hypertension while other uses such as internal splinting of flail chest, simultaneous ventilation-compression cardiopulmonary resuscitation and prophylactic postoperative ventilation are more controversial.

Combined ventilator and bicarbonate strategy in the management of status asthmaticus

Management of intubated hypercapnic asthmatic patients requires a delicate balance between the control of pH with adequate ventilation and the risk of barotrauma associated with the high pressures that may be required. The present report documents a strategy of mechanical ventilation combined with infusion of large amounts of bicarbonate in three patients with severe status asthmaticus requiring intubation. This strategy reduced peak inflation pressure by decreasing ventilation and maintained a physiologic pH while allowing pCO2 to remain elevated.

Arterial blood gas tensions in acute severe asthma

We have studied the serial changes in arterial blood gases in fourteen patients with acute severe asthma, all of whom received a standard therapeutic regime and had similar measurements made at identical time intervals under standard conditions. Hypoxaemia on admission was a constant finding, and the arterial oxygen tension often took a week or longer to return to a normal level. Treatment with 60% inspired oxygen provided a safe means of relieving hypoxaemia, provided that blood gases were measured before and during oxygen therapy. Most patients had a normal arterial carbon dioxide tension, which indicated the severity of their illness. Acid-base disturbances, when present, were mild and needed no specific treatment. Age, duration of the acute attack, and severity of airways obstruction were all unrelated to the changes in blood gas tension, and pulse rate was found to be a poor predictor of hypoxaemia in elderly asthmatics. Serial measurements of the arterial blood gases should be made in all patients with acute severe asthma.

Arterial pH, airway caliber and response to acetylcholine and catecholamines in vivo

Direct assessment of tracheal circumference, which permits evaluation of constriction and dilatation in vivo, was made continuously in intact, pentobarbital-anesthetized, spontaneously breathing dogs. Immediate response to induction of hypercapnia included tracheal constriction and cessation of normal, vagus-dependent rhythmicity of airway tone. The characteristic constrictor response to acetylcholine was exaggerated significantly during hypercapnic acidosis and returned to normal when arterial pH, but not CSF pH, was corrected by NaHCO3 infusion. Epinephrine produced significant tracheal dilatation (infrequently followed by constriction) and isoproterenol produced only dilatation at normal pH. The catecholamine-induced dilatation was decreased significantly during hypercapnic acidosis, but improved after NaHCO3 infusion. Responses to acetylcholine and epinephrine were the the same as control during alkalemia, whereas the response to isoproterenol was unexplainedly diminished. Thus alkalemia may inhibit the action of isoproterenol; acidemia enhances parasympathomimetic constriction and reduces sympathomimetic dilatation; and correction of arterial pH returns these responses to normal, even if hypercapnia and CSF acidosis persist.

Acute respiratory failure precipitated by a carbonic anhydrase inhibitor

A 60-year-old white man with chronic bronchitis was noted to develop acute respiratory failure and metabolic acidosis four days after being started on methazolamide (Neptazane) for an ophthalmologic problem. The patient was intubated with ventilator support and improved after his metabolic acidosis resolved. Caution is emphasized in the use of carbonic anhydrase inhibitors in patients with obstructive airway disease.

Exercise-induced asthma

Tests in three patients with asthma occurring only on exertion showed that F.E.V.(1) fell progressively on exercise, to reach a minimum after 10 minutes. All patients showed a striking metabolic acidosis, with an accumulation of the products of anaerobic metabolism.

Arterial blood gas tensions and pH in acute asthma in childhood

Studies of the arterial blood gas tensions and pH in 21 children during 24 acute attacks of asthma showed that all were hypoxic on admission to hospital, and in 10 there was evidence of carbon dioxide retention. Cyanosis, invariably present when the So(2) was below 85%, and restlessness in patients breathing air were the most reliable indices of the severity of hypoxia. There were no reliable clinical guides to the Pco(2) level. Conventional oxygen therapy in tents (25-40%) did not always relieve hypoxia, and in three cases the administration of oxygen at a concentration of 40% or over failed to produce a normal arterial oxygen tension. Uncontrolled oxygen therapy may aggravate respiratory acidosis, and three of our patients developed carbon dioxide narcosis while breathing oxygen. The necessity for blood gas measurements in the management of severe acute asthma in childhood is emphasized.