Alkali Therapy for Respiratory Acidosis: A Medical Controversy

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.

Common pitfalls in the use of hypertonic sodium bicarbonate for cardiac toxic drug poisonings

BACKGROUND

Hypertonic sodium bicarbonate is advocated for the treatment of sodium channel blocker poisoning, but its efficacy varies amongst different sodium channel blockers. This Commentary addresses common pitfalls and appropriate usage of hypertonic sodium bicarbonate therapy in cardiotoxic drug poisonings.

SODIUM BICARBONATE WORKS SYNERGISTICALLY WITH HYPERVENTILATION

Serum alkalinization is best achieved by the synergistic effect of hypertonic sodium bicarbonate and hyperventilation (PCO2 ∼ 30-35 mmHg [0.47-0.6 kPa]). This reduces the dose of sodium bicarbonate required to achieve serum alkalinization (pH ∼ 7.45-7.55) and avoids adverse effects from excessive doses of hypertonic sodium bicarbonate.

VARIABILITY IN RESPONSE TO SODIUM BICARBONATE TREATMENT

Tricyclic antidepressant poisoning responds well to sodium bicarbonate therapy, but many other sodium channel blockers may not. For instance, drugs that block the intercellular gap junctions, such as bupropion, do not respond well to alkalinization. For sodium channel blocker poisonings in which the expected response is unknown, a bolus of 1-2 mmol/kg sodium bicarbonate can be used to assess the response to alkalinization.

SODIUM BICARBONATE CAN EXACERBATE TOXICITY FROM DRUGS ACTING ON MULTIPLE CARDIAC CHANNELS

Hypertonic sodium bicarbonate can cause electrolyte abnormalities such as hypokalaemia and hypocalcaemia, leading to QT interval prolongation and torsade de pointes in poisonings with drugs that have mixed sodium and potassium cardiac channel properties, such as hydroxychloroquine and flecainide.

THE GOAL FOR HYPERTONIC SODIUM BICARBONATE IS TO ACHIEVE THE ALKALINIZATION TARGET (∼PH 7.5), NOT COMPLETE CORRECTION OF QRS COMPLEX PROLONGATION

Excessive doses of hypertonic sodium bicarbonate commonly occur if it is administered until the QRS complex duration is < 100 ms. A prolonged QRS complex duration is not specific for sodium channel blocker toxicity. Some sodium channel blockers do not respond, and even when there is a response, it takes a few hours for the QRS complex duration to return completely to normal. In addition, QRS complex prolongation can be due to a rate-dependent bundle branch block. So, no further doses should be given after achieving serum alkalinization (pH ∼ 7.45-7.55).

MAXIMAL DOSING FOR HYPERTONIC SODIUM BICARBONATE

A further strategy to avoid overdosing patients with hypertonic sodium bicarbonate is to set maximum doses. Exceeding 6 mmol/kg is likely to cause hypernatremia, fluid overload, metabolic alkalosis, and cerebral oedema in many patients and potentially be lethal.

RECOMMENDATION FOR THE USE OF HYPERTONIC SODIUM BICARBONATE IN SODIUM CHANNEL BLOCKER POISONING

We propose that hypertonic sodium bicarbonate therapy be used in patients with sodium channel blocker poisoning who have clinically significant toxicities such as seizures, shock (systolic blood pressure < 90 mmHg, mean arterial pressure <65 mmHg) or ventricular dysrhythmia. We recommend initial bolus dosing of hypertonic sodium bicarbonate of 1-2 mmol/kg, which can be repeated if the patient remains unstable, up to a maximum dose of 6 mmol/kg. This is recommended to be administered in conjunction with mechanical ventilation and hyperventilation to achieve serum alkalinization (PCO2∼30-35 mmHg [4-4.7 kPa]) and a pH of ∼7.45-7.55. With repeated bolus doses of hypertonic sodium bicarbonate, it is imperative to monitor and correct potassium and sodium abnormalities and observe changes in serum pH and on the electrocardiogram.

CONCLUSIONS

Hypertonic sodium bicarbonate is an effective antidote for certain sodium channel blocker poisonings, such as tricyclic antidepressants, and when used in appropriate dosing, it works synergistically with hyperventilation to achieve serum alkalinization and to reduce sodium channel blockade. However, there are many pitfalls that can lead to excessive sodium bicarbonate therapy and severe adverse effects.

Tris-Hydroxymethyl Aminomethane in Critically Ill Adults: A Systematic Review

Tris-hydroxymethyl aminomethane (THAM) is an amino alcohol used clinically to buffer acid loads and raise pH in acidotic conditions. Unlike sodium bicarbonate, which increases plasma sodium levels with use and produces carbon dioxide (CO 2 ) as part of the buffering process, THAM does neither. Although not widely used in modern critical care and unavailable for clinical use in 2016, THAM has been available in the United States since 2020. Clinical experience and existing literature suggest that THAM may have clinical utility in acid-base management in conditions such as liver transplantation where rising sodium levels during perioperative care may be dangerous, and in managing acid-base derangements during care of patients with acute respiratory distress syndrome (ARDS). To clarify the evidence base supporting the clinical use of THAM, we conducted a systematic review to assess the efficacy and safety of THAM as a buffering agent in critically ill adults using Ovid EBM Reviews, Ovid Embase, Ovid Medline, Scopus, and Web of Science Core Collection. Randomized-, crossover-, retrospective cohort-, parallel-designed clinical trials, case series, and case reports of adult patients who received THAM in the operative or critical care setting were included. Conference abstracts of qualifying study designs were also included. Two independent reviewers extracted the data regarding the study details, demographics, treatment, and outcomes data. A third reviewer adjudicated discrepancies. A total of 21 studies including 3 randomized controlled trials, 5 observational studies, 4 case series, and 9 case reports met inclusion criteria. Eight studies (38%) were abstracts published in conference proceedings. In total, 417 critically ill patients received THAM to treat acidosis in critically ill surgical and nonsurgical patients, during liver transplantation, and in ARDS. In general, THAM corrected acidosis with an efficacy equivalent to sodium bicarbonate and did so with less hypercarbia and hypernatremia. Adverse effects of THAM included hyperkalemia, hypoglycemia, ventilator depression, and tissue damage with extravasation. We conclude that THAM may have potential advantages in some critical care settings, but that clinical evidence is limited, and high-quality evaluations are necessary.

Blood pH and COVID-19

The coronavirus disease 2019 (COVID-19) pandemic is a worldwide war. Raising the blood pH might be a crucial strategy to chase COVID-19. The human blood is slightly alkaline, which is essential for cell metabolism, normal physiology, and balanced immunity since all of these biological processes are pH-dependent. Varieties of physiologic derangements occur when the blood pH is disrupted. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) proliferates in acidic blood that magnifies the severity of COVID-19. On the other side, blood acidemia is linked to increased morbidity and mortality because of its complications on immunity, especially in the elderly and in critical diseases such as cancer, musculoskeletal degradation, renal, cardiac, and pulmonary disorders, which result in many pathological disorders such as osteomalacia, and disturbing the hematopoiesis. Additionally, acidemia of the blood facilitates viral infection and progression. Thus, correcting the acid-base balance might be a crucial strategy for the treatment of COVID-19, which might be attributed to the distraction of the viral spike protein to its cognate receptor angiotensin-converting enzyme 2 and supporting the over-taxed immunity.

Acid-Base Disorders in the Critically Ill Patient

Acid-base disorders are common in the intensive care unit. By utilizing a systematic approach to their diagnosis, it is easy to identify both simple and mixed disturbances. These disorders are divided into four major categories: metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis. Metabolic acidosis is subdivided into anion gap and non-gap acidosis. Distinguishing between these is helpful in establishing the cause of the acidosis. Anion gap acidosis, caused by the accumulation of organic anions from sepsis, diabetes, alcohol use, and numerous drugs and toxins, is usually present on admission to the intensive care unit. Lactic acidosis from decreased delivery or utilization of oxygen is associated with increased mortality. This is likely secondary to the disease process, as opposed to the degree of acidemia. Treatment of an anion gap acidosis is aimed at the underlying disease or removal of the toxin. The use of therapy to normalize the pH is controversial. Non-gap acidoses result from disorders of renal tubular H + transport, decreased renal ammonia secretion, gastrointestinal and kidney losses of bicarbonate, dilution of serum bicarbonate from excessive intravenous fluid administration, or addition of hydrochloric acid. Metabolic alkalosis is the most common acid-base disorder found in patients who are critically ill, and most often occurs after admission to the intensive care unit. Its etiology is most often secondary to the aggressive therapeutic interventions used to treat shock, acidemia, volume overload, severe coagulopathy, respiratory failure, and AKI. Treatment consists of volume resuscitation and repletion of potassium deficits. Aggressive lowering of the pH is usually not necessary. Respiratory disorders are caused by either decreased or increased minute ventilation. The use of permissive hypercapnia to prevent barotrauma has become the standard of care. The use of bicarbonate to correct the acidemia is not recommended. In patients at the extreme, the use of extracorporeal therapies to remove CO 2 can be considered.

Overview of the Medical Management of the Critically Ill Patient

The medical management of the critically ill patient focuses predominantly on treatment of the underlying condition (e g, sepsis or respiratory failure). However, in the past decade, the importance of initiating early prophylactic treatment for complications arising from care in the intensive care unit setting has become increasingly apparent. As survival from critical illness has improved, there is an increased prevalence of postintensive care syndrome-defined as a decline in physical, cognitive, or psychologic function among survivors of critical illness. The Intensive Care Unit Liberation Bundle, a major initiative of the Society of Critical Care Medicine, is centered on facilitating the return to normal function as early as possible, with the intent of minimizing iatrogenic harm during necessary critical care. These concepts are universally applicable to patients seen by nephrologists in the intensive care unit and may have particular relevance for patients with kidney failure either on dialysis or after kidney transplant. In this article, we will briefly summarize some known organ-based consequences associated with critical illness, review the components of the ABCDEF bundle (the conceptual framework for Intensive Care Unit Liberation), highlight the role nephrologists can play in implementing and complying with the ABCDEF bundle, and briefly discuss areas for additional research.

Management of Respiratory Failure: Ventilator Management 101 and Noninvasive Ventilation

Mechanical ventilation is a lifesaving therapy for critically ill patients with respiratory failure, but like all treatments, it has the potential to cause harm if not administered appropriately. This review aims to give an overview of the basic principles of invasive and noninvasive mechanical ventilation. Topics covered include modes of mechanical ventilation, respiratory mechanics and ventilator waveform interpretation, strategies for initial ventilator settings, indications and contraindications for noninvasive ventilation, and the effect of the ventilator on kidney function.

Sodium bicarbonate buffer for weaning from venovenous extracorporeal membrane oxygenation in patients with hypercapnic respiratory failure and acute renal failure

Although the routine use of alkali buffer is not recommended in patients with respiratory acidosis, some patients may benefit from its administration. A 42-year-old man was treated with venovenous extracorporeal membrane oxygenation (VV-ECMO) and continuous venovenous hemodiafiltration (CVVHDF) due to necrotizing pneumonia and emphysematous cystitis with Klebsiella pneumoniae. Although the sweep gas flow rate of the VV-ECMO was gradually reduced, he failed to wean off VV-ECMO due to respiratory acidosis, followed by tachycardia and tachypnea on the 63rd day of VV-ECMO. Therefore, we mixed sodium bicarbonate in the replacement fluid of CVVHDF for 5 days to avoid an intolerable decrease in blood pH after discontinuing the VV-ECMO sweep gas. When the serum bicarbonate concentration was >30 mmol/L and pH was maintained at >7.30 with a PCO2 of >60 mmHg, VV-ECMO was finally decannulated. Sodium bicarbonate buffer through the replacement of CVVHDF fluid facilitated VV-ECMO weaning in a patient with hypercapnic respiratory failure.

Coronary hypercontractility to acidosis owes to the greater activity of TMEM16A/ANO1 in the arterial smooth muscle cells

BACKGROUND

Severe acidosis deteriorates cardiac injury. Rat coronary arteries (RCAs) are unusually hypercontractive to extracellular (o) acidosis (EA). TMEM16A-encoded anoctamin 1 (ANO1), a Ca²⁺-activated chloride channel (CaCC), plays an important role in regulating coronary arterial tension.

PURPOSE

We tested the possibility that the activation of CaCCs in the arterial smooth muscle cell (ASMC) contributes to EA-induced RCA constriction.

METHODS

ANO1 expression was detected with immunofluorescence staining and Western blot. TMEM16A mRNA was assessed with quantitative Real-Time PCR. Cl^- currents and membrane potentials were quantified with a patch clamp. The vascular tension was recorded with a myograph. Intracellular (i) level of Cl^- and Ca²⁺ was measured with fluorescent molecular probes.

RESULTS

ANO1 was expressed in all tested arterial myocytes, but was much more abundant in RCA ASMCs as compared with ASMCs isolated from rat cerebral basilar, intrarenal and mesenteric arteries. EA reduced [Cl^-]_i levels, augmented CaCC currents exclusively in RCA ASMCs and depolarized RCA ASMCs to a greater extent. Cl^- deprivation, which depleted [Cl^-]_i by incubating the arteries or their ASMCs in Cl^--free bath solution, decreased EA-induced [Cl^-]_i reduction, diminished EA-induced CaCC augmentation and time-dependently depressed EA-induced RCA constriction. Inhibitor studies showed that these EA-induced effects including RCA constriction, CaCC current augmentation, [Cl^-]_i reduction and/or [Ca²⁺]_i elevation were depressed by various Cl^- channel blockers, [Ca²⁺]_i release inhibitors and L-type voltage-gated Ca²⁺ channel inhibitor nifedipine. ANO1 antibody attenuated all observed changes induced by EA in RCA ASMCs.

CONCLUSION

The greater activity of RCA ASMC CaCCs complicated with an enhanced Ca²⁺ mobilization from both [Ca²⁺]_i release and [Ca²⁺]_o influx plays a pivotal role in the distinctive hypercontractility of RCAs to acidosis. Translation of these findings to human beings may lead to a new conception in our understanding and treating cardiac complications in severe 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.

Acidemia subtypes in critically ill patients: An international cohort study

PURPOSE

To study the prevalence, characteristic, outcome, and acid-base biomarker predictors of outcome for different acidemia subtypes.

METHODS

We used national intensive care databases from three countries and classified acidemia subtypes as metabolic (standard base excess [SBE] < -2 mEq/L only), respiratory (PaCO₂ > 42 mmHg only), and combined (both SBE < -2 mEq/L and PaCO₂ > 42 mmHg) based on blood gas analysis in the first 24 h after ICU admission. To investigate acid-base predictors for hospital mortality, we applied the area under the receiver operating characteristic curve approach.

RESULTS

We screened 643,689 ICU patients (2014-2018) and detected acidemia in 57.8%. The most common subtype was metabolic (42.9%), followed by combined (30.3%) and respiratory (25.9%). Combined acidemia had a mortality of 12.7%, compared with 11% for metabolic and 5.5% for respiratory. For combined acidemia, the best predictor of hospital mortality was pH. However, for metabolic or respiratory acidemia, it was SBE or PaCO₂, respectively.

CONCLUSIONS

In ICU patients with acidemia, mortality differs according to subtype and is highest in the combined subtype. Best acid-base predictors of mortality also differ according to subtype with best performance for pH in combined, SBE in metabolic, and PaCO₂ in respiratory acidemia.

The therapeutic importance of acid-base balance

Baking soda and vinegar have been used as home remedies for generations and today we are only a mouse-click away from claims that baking soda, lemon juice, and apple cider vinegar are miracles cures for everything from cancer to COVID-19. Despite these specious claims, the therapeutic value of controlling acid-base balance is indisputable and is the basis of Food and Drug Administration-approved treatments for constipation, epilepsy, metabolic acidosis, and peptic ulcers. In this narrative review, we present evidence in support of the current and potential therapeutic value of countering local and systemic acid-base imbalances, several of which do in fact involve the administration of baking soda (sodium bicarbonate). Furthermore, we discuss the side effects of pharmaceuticals on acid-base balance as well as the influence of acid-base status on the pharmacokinetic properties of drugs. Our review considers all major organ systems as well as information relevant to several clinical specialties such as anesthesiology, infectious disease, oncology, dentistry, and surgery.