Management of hypercapnia in critically ill mechanically ventilated patients-A narrative review of literature

Effect of mixed probiotics on pulmonary flora in patients with mechanical ventilation: an exploratory randomized intervention study

OBJECTIVE

The study objective was to investigate the effect of mixed probiotics on the diversity of the pulmonary flora in critically ill patients requiring mechanical ventilation by analysing the changes in lung microbes.

METHODS

24 adult critically ill patients who needed mechanical ventilation in our hospital were randomly divided into a probiotic group and a control group. Then, the probiotic group was given Live Combined Bifidobacterium, Lactobacillus and Enterococcus Capsules, Oral (Bifico) by nasal feeding within 24 h after mechanical ventilation. Bronchoalveolar lavage fluid (BALF) and venous blood were collected within 24 h after mechanical ventilation and on the 5th day after mechanical ventilation, and the treatment status of patients (mechanical ventilation time, 28-day survival), measured cytokine levels (IL-1 β, IL-6, IL-8, IL-17A) and changes in pulmonary microorganisms were observed.

RESULTS

The microbial diversity of BALF samples decreased in the control group, and there was no significant difference in the probiotic group. Species difference analysis showed that among the three probiotics (Bifidobacterium, Lactobacillus, Enterococcus) used for intervention, Lactobacillus caused significant differences in BALF in the control group. Clinical factor association analysis displayed significant associations with IL-17A levels in both blood and BALF.

CONCLUSION

Mechanical ventilation can cause a decline in pulmonary microbial diversity, which can be improved by administering mixed probiotics.

Ultraprotective Ventilation via ECCO2R in Three Patients Presenting an Air Leak: Is ECCO2R Effective?

Extracorporeal CO₂ removal (ECCO2R) is a therapeutic approach that allows protective ventilation in acute respiratory failure by preventing hypercapnia and subsequent acidosis. The main indications for ECCO2R in acute respiratory failure are COPD (chronic obstructive pulmonary disease) exacerbation, acute respiratory distress syndrome (ARDS) and other situations of asthmatics status. However, CO₂ removal procedure is not extended to those ARDS patients presenting an air leak. Here, we report three cases of air leaks in patients with an ARDS that were successfully treated using a new ECCO2R device. Case 1 is a polytrauma patient that developed pneumothorax during the hospital stay, case 2 is a patient with a post-surgical bronchial fistula after an Ivor-Lewis esophagectomy, and case 3 is a COVID-19 patient who developed a spontaneous pneumothorax after being hospitalized for a prolonged time. ECCO2R allowed for protective ventilation mitigating VILI (ventilation-induced lung injury) and significantly improved hypercapnia and respiratory acidemia, allowing time for the native lung to heal. Although further investigation is needed, our observations seem to suggest that CO₂ removal can be a safe and effective procedure in patients connected to mechanical ventilation with ARDS-associated air leaks.

Impact of Arterial CO2 Retention in Patients With Moderate or Severe ARDS

BACKGROUND

Lung-protective ventilation (reduced tidal volume and limited plateau pressure) may lead to CO2 retention. Data about the impact of hypercapnia in patients with ARDS are scarce and conflicting.

METHODS

We performed a non-interventional cohort study with subjects with ARDS admitted from 2006 to 2021 and with PaO2 /FIO2 ≤ 150 mm Hg. We examined the association between severe hypercapnia (PaCO2 ≥ 50 mm Hg) on the first 5 days after the diagnosis of ARDS and death in ICU for 930 subjects. All the subjects received lung-protective ventilation.

RESULTS

Severe hypercapnia was noted in 552 subjects (59%) on the first day of ARDS (day 1); 323/930 (34.7%) died in the ICU. Severe hypercapnia on day 1 was associated with mortality in the unadjusted (odds ratio 1.54, 95% CI 1.16-1.63; P = .003) and adjusted (odds ratio 1.47, 95% CI 1.08-2.43; P = .004) models. In the Bayesian analysis, the posterior probability that severe hypercapnia was associated with ICU death was > 90% in 4 different priors, including a septic prior for this association. Sustained severe hypercapnia on day 5, defined as severe hypercapnia present from day 1 to day 5, was noted in 93 subjects (12%). After propensity score matching, severe hypercapnia on day 5 remained associated with ICU mortality (odds ratio 1.73, 95% CI 1.02-2.97; P = .047).

CONCLUSIONS

Severe hypercapnia was associated with mortality in subjects with ARDS who received lung-protective ventilation. Our results deserve further evaluation of the strategies and treatments that aim to control CO2 retention.

Outcomes and Prognostic Factors of Pulmonary Hypertension Patients Undergoing Emergent Endotracheal Intubation

Background: Emergent endotracheal intubations (ETI) in pulmonary hypertension (PH) patients are associated with increased mortality. Post-intubation interventions that could increase survivability in this population have not been explored. We evaluate early clinical characteristics and complications following emergent endotracheal intubation and seek predictors of adverse outcomes during this post-intubation period. Methods: Retrospective cohort analysis of adult patients with groups 1 and 3 PH who underwent emergent intubation between 2005-2021 in medical and liver transplant ICUs at a tertiary medical center. PH patients were compared to non-PH patients, matched by Charlson Comorbidity Index. Primary outcomes were 24-h post-intubation and inpatient mortalities. Various 24-h post-intubation secondary outcomes were compared between PH and control cohorts. Results: We identified 48 PH and 110 non-PH patients. Pulmonary hypertension was not associated with increased 24-h mortality (OR 1.32, 95%CI 0.35-4.94, P = .18), but was associated with inpatient mortality (OR 4.03, 95%CI 1.29-12.5, P = .016) after intubation. Within 24 h post-intubation, PH patients experienced more frequent acute kidney injury (43.5% vs. 19.8%, P = .006) and required higher norepinephrine dosing equivalents (6.90 [0.13-10.6] mcg/kg/min, vs. 0.20 [0.10-2.03] mcg/kg/min, P = .037). Additionally, the median P/F ratio (PaO₂/FiO₂) was lower in PH patients (96.3 [58.9-201] vs. 233 [146-346] in non-PH, P = .001). Finally, a post-intubation increase in PaCO₂ was associated with mortality in the PH cohort (post-intubation change in PaCO₂ +5.14 ± 16.1 in non-survivors vs. -18.7 ± 28.0 in survivors, P = .007). Conclusions: Pulmonary hypertension was associated with worse outcomes after emergent endotracheal intubation than similar patients without PH. More importantly, our data suggest that the first 24 hours following intubation in the PH group represent a particularly vulnerable period that may determine long-term outcomes. Early post-intubation interventions may be key to improving survival in this population.

Inclusion of airway pressure release ventilation in the management of respiratory failure and refractory hypercapnia in a dog

OBJECTIVE

To describe the use of airway pressure release ventilation (APRV) to relieve hypercapnia in a dog undergoing mechanical ventilation.

CASE SUMMARY

A 3-month-old male Shar-Pei mix presented to the emergency department with suspected noncardiogenic pulmonary edema. Due to severe hypercapnia, mechanical ventilation was initiated. The hypercapnia failed to improve with conventional pressure control mechanical ventilation, bronchodilator administration, suctioning, or endotracheal tube replacement. The dog was transitioned to APRV and maintained in this mode for 36 hours. A modified APRV protocol in which inverse inspiratory to expiratory ratios ranged from 4.3:1 to 6.0:1 was utilized, resulting in a drastic improvement in the patient's hypercapnia. The patient eventually was transitioned off the ventilator, and no respiratory abnormalities have been noted at subsequent recheck examinations.

NEW OR UNIQUE INFORMATION PROVIDED

This case documents the first use of APRV to relieve refractory hypercapnia in a dog undergoing mechanical ventilation and is one of the only recorded cases of using APRV for this purpose in the medical literature at large. APRV may be considered in cases of hypercapnia when traditional therapies fail, although caution is warranted as this mode of ventilation can also worsen hypercapnia.

A Case of the Use of Extracorporeal Carbon Dioxide Removal in a Patient With COVID-19 Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a severe complication of coronavirus disease 2019 (COVID-19) infection marked by increased fluid diffusely in alveolar spaces. The management of ARDS can be complicated by mechanical hyperinflation, and thus a mainstay of treatment has included low tidal volume mechanical ventilation. This, however, can lead to ventilation-associated hypercapnia, which may result in respiratory acidosis. COVID-19-associated ARDS (CARDs) has been described in the literature, and guidelines tend to mimic ARDS management. However, the heterogeneous nature of COVID-19 pulmonary disease with respect to dead space, compliance, and shunting could alter guidelines. As low tidal volume remains a cornerstone in CARDS management, hypercapnic acidosis remains a risk. An emerging technology, extracorporeal CO2 removal devices (ECCO2R), has been granted emergency use authorization by the FDA for the management of CARDS.

We present a 44-year-old male patient presenting positive for COVID-19. Following admission, the patient's oxygen status continually deteriorated and the patient went into acute respiratory distress, eventually requiring invasive mechanical ventilation. The patient became hypercapnic and acidotic due to low tidal volume ventilation. ECCO2R was used to manage the patient's hypercapnia, resulting in significant amelioration of his partial pressure of carbon dioxide (PCO2) and pH. The patient was eventually transferred to extracorporeal membrane oxygenation (ECMO) certified facility and survived after a prolonged hospital and rehabilitation course.

In the management of CARDS patients who require mechanical respiration, there are many unanswered questions as to the appropriate ventilation strategy. Current practice recommends low tidal volume ventilation, carrying, and increased risk of hypercapnic respiratory acidosis as occurred in our patient. We believe that ECCO2R may be an appropriate bridge between low tidal volume ventilation and ECMO to stabilize acid-base disturbances in ventilated patients.

Elevated PaCO2 levels increase pulmonary artery pressure

Permissive hypercapnia is commonly used in mechanically ventilated patients to avoid lung injury but its effect on pulmonary artery pressure (PAP) is still unclear, particularly in combination with tidal volume (Vt). Therefore, an in vivo study was performed on adult rabbits ventilated with low (9 ml/Kg, LVt group) or high (15 ml/Kg, HVt group) tidal volume (Vt) and alterations in PAP were estimated. Both groups of animals initially were ventilated with FiO2 0.3 (Normocapnia-1) followed by inhalation of enriched CO2 gas mixture (FiCO2 0.10) to develop hypercapnia (Hypercapnia-1). After 30 min of hypercapnia, animals were re-ventilated with FiO2 0.3 to develop normocapnia (Normocapnia-2) again and then with FiCO2 0.10 to develop hypercapnia (Hypercapnia-2). Systolic, diastolic and mean PAP were assessed with a catheter in the pulmonary artery. In HP-1 and HP-2, PaCO2 increased (p < 0.0001) in both LVt and HVt animals compared to baseline values. pH decreased to ≈7.2 in HP-1 and ≈7.1 in HP -2. In normocapnia, the rise in Vt from 9 to 15 ml/Kg induced an increase in static compliance (Cstat), plateau airway pressure (Pplat) and PAP. Hypercapnia increased PAP in either LVt or HVt animals without significant effect on Cstat or Pplat. A two-way ANOVA revealed that there was not a statistically significant interaction between the effects of hypercapnia and tidal volume on mPAP (p = 0.76). In conclusion, increased Vt per se induced an increase in Cstat, Pplat and PAP in normocapnia. Hypercapnia increased PAP in rabbits ventilated with low or high Vt but this effect was not long-lasting.

Removal of a catheter mount and heat-and-moisture exchanger improves hypercapnia in patients with acute respiratory distress syndrome: A retrospective observational study

ABSTRACT

To avoid ventilator-associated lung injury in acute respiratory distress syndrome (ARDS) treatment, respiratory management should be performed at a low tidal volume of 6 to 8 mL/kg and plateau pressure of ≤30 cmH2O. However, such lung-protective ventilation often results in hypercapnia, which is a risk factor for poor outcomes. The purpose of this study was to retrospectively evaluate the effectiveness and safety of the removal of a catheter mount (CM) and using heated humidifiers (HH) instead of a heat-and-moisture exchanger (HME) for reducing the mechanical dead space created by the CM and HME, which may improve hypercapnia in patients with ARDS.This retrospective observational study included adult patients with ARDS, who developed hypercapnia (PaCO2 > 45 mm Hg) during mechanical ventilation, with target tidal volumes between 6 and 8 mL/kg and a plateau pressure of ≤30 cmH2O, and underwent stepwise removal of CM and HME (replaced with HH). The PaCO2 values were measured at 3 points: ventilator circuit with CM and HME (CM + HME) use, with HME (HME), and with HH (HH), and the overall number of accidental extubations was evaluated. Ventilator values (tidal volume, respiratory rate, minutes volume) were evaluated at the same points.A total of 21 patients with mild-to-moderate ARDS who were treated under deep sedation were included. The values of PaCO2 at HME (52.7 ± 7.4 mm Hg, P < .0001) and HH (46.3 ± 6.8 mm Hg, P < .0001) were significantly lower than those at CM + HME (55.9 ± 7.9 mm Hg). Measured ventilator values were similar at CM + HME, HME, and HH. There were no cases of reintubation due to accidental extubation after the removal of CM.The removal of CM and HME reduced PaCO2 values without changing the ventilator settings in deeply sedated patients with mild-to-moderate ARDS on lung-protective ventilation. Caution should be exercised, as the removal of a CM may result in circuit disconnection or accidental extubation. Nevertheless, this intervention may improve hypercapnia and promote lung-protective ventilation.