Hyperammonemia after heart-lung transplantation

Hyperammonemia syndrome post-lung transplantation: Case series and systematic review of literature

BACKGROUND

Hyperammonemia syndrome (HS) is a rare post-transplant complication associated with high morbidity and mortality. Its incidence appears to be higher in lung transplant recipients and its pathophysiology is not well understood. In addition to underlying metabolic abnormalities, it is postulated that HS may be associated with Ureaplasma or Mycoplasma spp. lung infections. Management of this condition is not standardized and may include preemptive antimicrobials, renal replacement, nitrogen scavenging, and bowel decontamination therapies, as well as dietary modifications.

METHODS

In this case series, we describe seven HS cases, five of whom had metabolic deficiencies ruled out. In addition, a literature review was performed by searching PubMed following PRISMA-P guidelines. Articles containing the terms "hyperammonemia" and "lung" were reviewed from 1 January 1997 to 31 October 2021.

RESULTS

All HS cases described in our center had positive airway samples for Mycoplasmataceae, neurologic abnormalities and high ammonia levels post-transplant. Mortality in our group (57%) was similar to that published in previous cases. The literature review supported that HS is an early complication post-transplant, associated with Ureaplasma spp. and Mycoplasma hominis infections and of worse prognosis in patients presenting cerebral edema and seizures.

CONCLUSION

This review highlights the need for rapid testing for Ureaplasma spp. and M. hominis after lung transplant, as well as the necessity for future studies to explore potential therapies that may improve outcomes in these patients.

Flurofamide Prevention and Treatment of Ureaplasma-Induced Hyperammonemia

Hyperammonemia (HA) syndrome caused by respiratory infection with ammonia (NH₃)-producing Ureaplasma species occurs in 4% of lung transplant recipients (LTRs) and is associated with high mortality. Although Ureaplasma-targeted antibiotic intervention is effective, the threat of antibiotic resistance development and pre-existing resistance make an alternative to antibiotics desirable. Considering that the underlying pathology of Ureaplasma-induced hyperammonemia (UIHA) is dependent upon ureaplasmal urease converting urea to NH₃, urease inhibition could represent a targeted treatment approach. Here, the ability of the urease inhibitor, flurofamide, to prevent and treat UIHA was investigated. To confirm that flurofamide is broadly active against Ureaplasma respiratory isolates, the minimum urease inhibitory concentration against 4 isolates of Ureaplasma parvum and 5 isolates of Ureaplasma urealyticum was first determined in vitro. NH₃ production by all isolates was inhibited by ≤2 μM flurofamide. To test the ability of flurofamide to prevent and treat UIHA, a mouse model of Ureaplasma respiratory infection was utilized. When animals were administered 6 mg/kg flurofamide via intraperitoneal injection 1 h prior to infection with U. parvum, flurofamide-administered animals exhibited significantly lower blood NH₃ levels than did non-prophylaxed animals (10.9 ± 4.0 μmol/L compared to 26.5 ± 17.7 μmol/L; P = 0.0146) 24 h post-treatment. When U. parvum-infected hyperammonemic mice were treated with 6 mg/kg flurofamide, treated animals had significantly greater decreases in blood-NH₃ levels 6 h post-treatment than did untreated mice (56.4 ± 17.1% compared to 9.1 ± 33.5% reduction; P = 0.0152). Together, these results indicate that flurofamide is a promising non-antibiotic treatment for UIHA in LTRs. IMPORTANCE Ureaplasma-associated hyperammonemia syndrome occurs in 4% of lung transplant recipients and has historically been almost universally fatal. While Ureaplasma-targeted antibiotics have been shown to be protective, the possibility of underlying resistance and resistance selection render non-antibiotic interventions an interesting approach.

Hyperammonemia syndrome in immunosuppressed individuals

PURPOSE OF REVIEW

Hyperammonemia syndrome is an increasingly recognized and often fatal condition that occurs in immunosuppressed individuals, most commonly lung transplant recipients. Growing evidence suggests hyperammonemia syndrome is associated with systemic infections caused by urease-producing organisms, namely Ureaplasma spp., an organism unable to grow with routine culturing techniques. This review will summarize the epidemiology and clinical manifestations of hyperammonemia syndrome, as well as diagnostic and management strategies once hyperammonemia syndrome is suspected.

RECENT FINDINGS

Hyperammonemia syndrome is being described in increasing frequency in the solid organ transplant population. Morbidity and mortality, even with treatment, is high once hyperammonemia syndrome occurs. Surveillance studies indicate the prevalence of lung donor colonization with Ureaplasma spp. is high, suggesting screening and treatment may be of benefit. Antibiotic resistance is common, and rapid diagnostics can facilitate appropriate antimicrobial therapy in the peri-transplant period.

SUMMARY

Hyperammonemia syndrome is most commonly seen in lung transplant recipients and has a high mortality rate once it occurs. Screening for Ureaplasma spp. should be considered in all lung transplant donors.

Hyperammonemia After Lung Transplantation: Systematic Review and a Mini Case Series

Background: Hyperammonemia after lung transplantation (HALT) is a rare but serious complication with high mortality. This systematic review delineates possible etiologies of HALT and highlights successful strategies used to manage this fatal complication.

Methods: Seven biomedical databases and grey literature sources were searched using keywords relevant to hyperammonemia and lung transplantation for publications between 1995 and 2020. Additionally, we retrospectively analyzed HALT cases managed at our institution between January 2016 and August 2018.

Results: The systematic review resulted in 18 studies with 40 individual cases. The mean peak ammonia level was 769 μmol/L at a mean of 14.1 days post-transplant. The mortality due to HALT was 57.5%. In our cohort of 120 lung transplants performed, four cases of HALT were identified. The mean peak ammonia level was 180.5 μmol/L at a mean of 11 days after transplantation. HALT in all four patients was successfully treated using a multimodal approach with an overall mortality of 25%.

Conclusion: The incidence of HALT (3.3%) in our institution is comparable to prior reports. Nonetheless, ammonia levels in our cohort were not as high as previously reported and peaked earlier. We attributed these significant differences to early recognition and prompt institution of multimodal treatment approach.

Contribution of Uremia to Ureaplasma-Induced Hyperammonemia

Lung transplant recipients (LTRs) are vulnerable to hyperammonemia syndrome (HS) in the early postoperative period, a condition typically unresponsive to nonantibiotic interventions. HS in LTRs is strongly correlated with Ureaplasma infection of the respiratory tract, although it is not well understood what makes LTRs preferentially susceptible to HS compared to other immunocompromised hosts. Ureaplasma species harbor highly active ureases, and postoperative LTRs commonly experience uremia. We hypothesized that uremia could be a potentiating comorbidity, providing increased substrate for ureaplasmal ureases. Using a novel dialyzed flow system, the ammonia-producing capacities of four isolates of Ureaplasma parvum and six isolates of Ureaplasma urealyticum in media formulations relating to normal and uremic host conditions were tested. For all isolates, growth under simulated uremic conditions resulted in increased ammonia production over 24 h, despite similar endpoint bacterial quantities. Further, transcripts of ureC (from the ureaplasmal urease gene cluster) from U. urealyticum IDRL-10763 and ATCC-27816 rose at similar rates under uremic and nonuremic conditions, with similar endpoint populations under the two conditions (despite markedly increased ammonia concentrations under uremic conditions), indicating that the difference in ammonia production by these isolates is due to increased urease activity, not expression. Lastly, uremic mice infected with an Escherichia coli strain harboring a U. urealyticum serovar 8 gene cluster exhibited higher blood ammonia levels compared to nonuremic mice infected with the same strain. Taken together, these data show that U. urealyticum and U. parvum produce more ammonia under uremic conditions compared to nonuremic conditions. This implies that uremia is a plausible contributing factor to Ureaplasma-induced HS in LTRs. IMPORTANCE Ureaplasma-induced hyperammonemia syndrome is a deadly complication affecting around 4% of lung transplant recipients and, to a lesser extent, other solid organ transplant patients. Understanding the underlying mechanisms will inform patient management, potentially decreasing mortality and morbidity. Here, it is shown that uremia is a plausible contributing factor to the pathophysiology of the condition.

Association between Mycoplasma and Ureaplasma airway positivity, ammonia levels, and outcomes post-lung transplantation: A prospective surveillance study

Hyperammonemia syndrome (HS) is a rare complication with high mortality described after lung transplantation. Its pathophysiology is still unclear, but previous studies, including murine models, have linked the identification of Mycoplasmataceae in airway specimens with HS occurrence. This study explores the association between Mycoplasmataceae polymerase chain reaction (PCR) positivity, ammonia levels, HS, and mortality post-lung transplant. Adults who underwent lung transplantation between July 2017 and August 2019 had prospective surveillance testing for Mycoplasma and Ureaplasma using PCR on post-operative bronchoscopy samples. One hundred and fifty-nine patients underwent lung transplantation during the study period. Mean age was 54 (±13) years; baseline diseases were predominantly pulmonary fibrosis (37.7%) and chronic obstructive pulmonary disease (35.8%). Mycoplasma and/or Ureaplasma airway positivity was found in 42 (26.4%) of tested patients, represented mostly by M. salivarium (26/43; 60.4%), U. parvum (7/43; 16.2%), and U. urealyticum (5/43; 11.6%). Median peak ammonia levels were higher in those with Ureaplasma colonization compared to uncolonized patients (p = .04), however, only three patients developed HS. Recipient airway Ureaplasma positivity was independently associated with younger (aOR 0.94, 95% CI 0.88-0.99, p = .04) and female donors (aOR 4.29; 95% CI 1.01-18.2, p = .05).

Impact of Screening and Treatment of Ureaplasma spp on Hyperammonemia Syndrome in Lung Transplant Recipients: A Single Center Experience

BACKGROUND

Infection with Ureaplasma species (spp) has been linked to fatal hyperammonemia syndrome (HS) in lung transplant recipients. We sought to characterize the epidemiology of Ureaplasma spp in candidates and donors and describe outcomes of antimicrobial therapy in preventing and treating HS.

METHODS

Candidate testing for Ureaplasma spp was performed with urine culture and PCR pre-transplant. Positive candidates were treated with levofloxacin. Donor testing was performed with bronchoalveolar lavage culture and PCR intraoperatively. From 7/2014-2/2017 patients were treated according to results; from 2/2017-10/2018 recipients received empiric levofloxacin and azithromycin at transplant until testing returned negative. HS was defined as new onset altered mental status after transplant with ammonia > 200 µmol/L.

RESULTS

60 patients who underwent lung transplant were included. 80% (n = 48) of patients had negative screening tests in donor and candidate pre-lung transplant, 8.3% (n = 5) of recipients had positive Ureaplasma spp testing in urine pre-transplant, and 13.3% (n = 8) had positive donor BAL testing at the time of lung transplant. 3 patients developed HS a median of 7 days post-transplant; 2 died of HS. Recipients of organs with Ureaplasma spp who received empiric therapy did not develop HS. Donors with Ureaplasma spp were younger and more sexually active.

CONCLUSION

Donor-derived Ureaplasma spp in lung transplant was associated with HS. Screening lung donors for Ureaplasma spp might allow for targeted therapy to reduce risk for development of HS, but future confirmatory studies are needed.

Noncirrhotic hyperammonemia after deceased donor kidney transplantation: A case report

A 72-year-old woman with end-stage kidney disease due to recurrent urinary tract infections and obstructive uropathy of a solitary kidney presented to our hospital for renal transplantation. She underwent successful transplantation of a deceased donor allograft, but developed acute mental status deterioration on the fifth postoperative day. Her serum ammonia was found to be markedly elevated to 447 μmol/L in the setting of normal hepatic function. She was treated with emergent dialysis and empiric antibiotics targeting urea-splitting organisms, and ultimately made a full neurologic recovery with stable renal allograft function. Noncirrhotic hyperammonemia (NCH) is an exceedingly rare clinical entity but seems to have a predilection for patients who have undergone solid organ transplantation. This report emphasizes the importance of rapid diagnosis and initiation of treatment for NCH, which is associated with a high rate of mortality and irreversible neurological morbidity. We outline the successful workup and management approach for this patient.

Hyperammonemia: What Urea-lly Need to Know: Case Report of Severe Noncirrhotic Hyperammonemic Encephalopathy and Review of the Literature

Purpose. A 66-year-old man who presented with coma was found to have isolated severe hyperammonemia and diagnosed with a late-onset urea-cycle disorder. He was treated successfully and had full recovery. Methods. We report a novel case of noncirrhotic hyperammonemia and review the literature on this topic. Selected literature for review included English-language articles concerning hyperammonemia using the search terms “hyperammonemic encephalopathy”, “non-cirrhotic encephalopathy”, “hepatic encephalopathy”, “urea-cycle disorders”, “ornithine transcarbamylase (OTC) deficiency”, and “fulminant hepatic failure”. Results. A unique case of isolated hyperammonemia diagnosed as late-onset OTC deficiency is presented. Existing evidence about hyperammonemia is organized to address pathophysiology, clinical presentation, diagnosis, and treatment. The case report is discussed in context of the reviewed literature. Conclusion. Late-onset OTC deficiency presenting with severe hyperammonemic encephalopathy and extensive imaging correlate can be fully reversible if recognized promptly and treated aggressively.

Noncirrhotic hyperammonaemic encephalopathy

Adult hyperammonaemia is associated with severe liver disease in 90% of cases. In the remainder, noncirrhotic causes should be considered. Measurements of serum ammonia level must be part of the basic work-up in all patients presenting with encephalopathy of unknown origin, even when liver function is normal. Clinician awareness of noncirrhotic hyperammonaemic encephalopathy can contribute to early diagnosis and the initiation of sometimes life-saving treatment. This review focuses on the physiology, aetiology and underlying mechanisms of noncirrhotic hyperammonaemic encephalopathy and discusses the available treatment modalities.