A New Oxygenation Index for Reflecting Intrapulmonary Shunting in Patients Undergoing Open-Heart Surgery

doi:10.1378/chest.125.2.592

Chest

Volume 125, Issue 2, February 2004, Pages 592-596

https://doi.org/10.1378/chest.125.2.592 Get rights and content

Study objectives

To assess the reliability of new and traditional oxygenation measurements in reflecting intrapulmonary shunt.

Design

Prospective study.

Setting

Cardiac surgery unit at a university hospital.

Patients

Fifty-five patients undergoing coronary artery bypass grafting.

Measurements and results

Simultaneous blood samples were collected from an indwelling arterial line and a catheter for determination of blood gases. Standard accepted formulas were utilized to measure a new oxygenation index: Pao₂/fraction of inspired oxygen (Fio₂) × mean airway pressure (Paw). The standard formulas used were the oxygenation ratio (Pao₂/Fio₂), Pao₂/alveolar partial oxygen pressure (Pao₂), alveolar-arterial oxygen tension gradient (P[A-a]O₂), and intrapulmonary shunt (venous admixture [Qsp/Qt]). There were significant negative (p < 0.05) correlations between the Pao₂/(Fio₂ × Paw) and Qsp/Qt (r = − 0.85), between the Pao₂/Fio₂ and Qsp/Qt (r = − 0.74), and between the Pao₂/Pao₂ and Qsp/Qt (r = − 0.71). There was a significant positive (p < 0.05) correlation between the P(A-a)O₂ gradient and Qsp/Qt (r = 0.66). However, the correlation was strongest between the Pao₂/(Fio₂ × Paw) and Qsp/Qt.

Conclusion

In this group of patients, Pao₂/(Fio₂ × Paw) might be more reliable than other oxygenation measurements in reflecting intrapulmonary shunt.

Section snippets

Materials and Methods

This study was approved by the Institutional Review Board, and a consent was obtained prior to the initiation of the study. Fifty-five hemodynamically and clinically stable patients receiving mechanical ventilation in the cardiac surgery unit following coronary artery bypass graft (CABG) surgery were included in the study. These were consecutive patients in whom CABG surgery was performed with a cardiopulmonary bypass pump. All patients were monitored with continuous electrocardiography, BP,

Results

Patients characteristics are presented in Table 1. A total of 74 sets of data were obtained from 55 patients due to the fact that 1 extra set of data were obtained from 19 patients following changes in their PEEP and/or Fio₂, which were clinically indicated and under the discretion of the medical team who were blinded to the study except for the arterial blood gas values.

There was significant negative linear relationships between Qsp/Qt and Pao₂/(Fio₂ × Paw (r = −0.85, p < 0.05), between Qsp/Qt

Discussion

Our data demonstrate that the new oxygenation index (Pao₂/Fio₂ × Paw), the oxygenation ratio (Pao₂/Fio₂), Pao₂/PAo₂, and P(A-a)O₂ are reliable reflectors of intrapulmonary shunt (Qsp/Qt). However, in this group of patients, Pao₂/Fio₂ × Paw is superior to other oxygenation measurements in reflecting intrapulmonary shunt.

The intrapulmonary shunt fraction index has been considered the “gold standard” for the clinical assessment of lung oxygenation function.¹¹¹²¹³¹⁴¹⁵ This index most accurately

Conclusion

In conclusion, our data show that the currently used oxygenation measurements can be used to reflect intrapulmonary shunt in patients following open-heart surgery. However, a new and simple oxygenation index, Pao₂/Fio₂ × Paw, might be superior to most common oxygenation indexes in this group of patients. Further studies are needed to evaluate any role of Pao₂/Fio₂ × Paw in assessing and following up lung function in patients with ALI or ARDS.

ACKNOWLEDGMENT

We thank the staff of the Department of Inhalation Therapy and the nursing staff in the Cardiac Surgery Unit.

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Cited by (46)

Pulse oximetry for the diagnosis and management of acute respiratory distress syndrome
2022, The Lancet Respiratory Medicine
Citation Excerpt :
As with the PaO2/FiO2 ratio, meeting the hypoxaemia threshold with the SpO2/FiO2 ratio is not sufficient for diagnosis of ARDS; other diagnostic criteria still apply, including the presence of a likely predisposing risk factor, radiographic findings, and confirmation that pulmonary oedema is not primarily related to fluid overload or cardiac insufficiency. Because the oxygenation index (OI)—(FiO2× mean airway pressure/PaO2) × 100—incorporates mean airway pressure, some clinicians and investigators consider it to better indicate the severity of respiratory failure than does PaO2/FiO2 by accounting for features such as changes in pulmonary compliance and intrapulmonary shunt.64 In several cohorts, the OI has been shown to be superior to the PaO2/FiO2 ratio as an indicator of risk for ARDS mortality.65,66
The diagnosis of acute respiratory distress syndrome (ARDS) traditionally requires calculation of the ratio of partial pressure of arterial oxygen to fraction of inspired oxygen (PaO₂/FiO₂) using arterial blood, which can be costly and is not possible in many resource-limited settings. By contrast, pulse oximetry is continuously available, accurate, inexpensive, and non-invasive. Pulse oximetry-based indices, such as the ratio of pulse-oximetric oxygen saturation to FiO₂ (SpO₂/FiO₂), have been validated in clinical studies for the diagnosis and risk stratification of patients with ARDS. Limitations of the SpO₂/FiO₂ ratio include reduced accuracy in poor perfusion states or above oxygen saturations of 97%, and the potential for reduced accuracy in patients with darker skin pigmentation. Application of pulse oximetry to the diagnosis and management of ARDS, including formal adoption of the SpO₂/FiO₂ ratio as an alternative to PaO₂/FiO₂ to meet the diagnostic criterion for hypoxaemia in ARDS, could facilitate increased and earlier recognition of ARDS worldwide to advance both clinical practice and research.
Oxygenation Saturation Index Predicts Clinical Outcomes in ARDS
2017, Chest
Traditional measures of ARDS severity such as Pao₂/Fio₂ may not reliably predict clinical outcomes. The oxygenation index (OI [Fio₂ × mean airway pressure × 100)/Pao₂]) may more accurately reflect ARDS severity but requires arterial blood gas measurement. We hypothesized that the oxygenation saturation index (OSI [Fio₂ × mean airway pressure × 100)/oxygen saturation by pulse oximetry (Spo₂)]) is a reliable noninvasive surrogate for the OI that is associated with hospital mortality and ventilator-free days (VFDs) in patients with ARDS.
Critically ill patients enrolled in a prospective cohort study were eligible if they developed ARDS (Berlin criteria) during the first 4 ICU days and had mean airway pressure, Spo₂/Fio₂, and Pao₂/Fio₂ values recorded on the first day of ARDS (N = 329). The highest mean airway pressure and lowest Spo₂/Fio₂ and Pao₂/Fio₂ values were used to calculate OI and OSI. The association between OI or OSI and hospital mortality or VFD was analyzed by using logistic regression and linear regression, respectively. The area under the receiver-operating characteristic curve (AUC) for mortality was compared among OI, OSI, Spo₂/Fio₂, Pao₂/Fio₂, and Acute Physiology and Chronic Health Evaluation II scores.
OI and OSI were strongly correlated (rho = 0.862; P < .001). OSI was independently associated with hospital mortality (OR per 5-point increase in OSI, 1.228 [95% CI, 1.056-1.429]; P = .008). OI and OSI were each associated with a reduction in VFD (OI, P = .023; OSI, P = .005). The AUC for mortality prediction was greatest for Acute Physiology and Chronic Health Evaluation II scores (AUC, 0.695; P < .005) and OSI (AUC, 0.602; P = .007). The AUC for OSI was substantially better in patients aged < 40 years (AUC, 0.779; P < .001).
In patients with ARDS, the OSI was correlated with the OI. The OSI on the day of ARDS diagnosis was significantly associated with increased mortality and fewer VFDs. The findings suggest that OSI is a reliable surrogate for OI that can noninvasively provide prognostic information and assessment of ARDS severity.
Comparison of volume-controlled ventilation and pressure-controlled ventilation volume guaranteed during laparoscopic surgery in Trendelenburg position
2016, Journal of Clinical Anesthesia
Citation Excerpt :
Arterial blood gas analysis: arterial partial pressure of oxygen (Pao2), arterial partial pressure of carbon dioxide (Paco2), pH, and oxygen saturation (Sao2) Oxygenation index (OI) calculation; [(Fio2 × P mean)/Pao2] [8] Ratio of physiologic dead-space over tidal volume (Vd/VT) (expressed in %) was calculated with Bohr's formula [9]; Vd/VT = (Paco2 – ETCO2)/Paco2
To analyze the effects of pressure-controlled ventilation-volume guaranteed (PCV-VG) and volume controlled ventilation (VCV) on airway pressures and respiratory and circulatory indicators during laparoscopic surgery in Trendelenburg position.
Prospective randomized comparative clinical study.
Tertiary hospital.
Forty ASA physical status 1 and 2 patients who underwent elective laparoscopic surgery in Trendelenburg position.
Patients were randomly allocated to either VCV group (n = 20) or the PCV-VG group (n = 20). After induction of anesthesia, for both modes of ventilation, the target tidal volume (V_T) was 8 mL/kg and the respiratory rate was adjusted to avoid hypercarbia.
The peak and mean inspiratory pressures, dynamic compliance, exhaled V_T, oxygenation index and physiological dead space were calculated and recorded at T1, 5 minutes after induction of anesthesia in supine position, T2, 5 minutes after stabilization of pneumoperitoneum, T3 and T4, 15 and 60 minutes after 30° Trendelenburg position with pneumoperitoneum respectively.
PCV-VG group had significantly lower peak inspiratory pressure and greater dynamic compliance than VCV group (P < .001).
In patients who underwent laparoscopic surgery in Trendelenburg position, PCV-VG was superior to VCV in its ability to provide ventilation with lower peak inspiratory pressure and greater dynamic compliance.
Early prediction of extracorporeal membrane oxygenation eligibility for severe acute respiratory distress syndrome in adults
2016, Journal of Critical Care
Citation Excerpt :
The ARDS index presented here is a novel variable proposed a priori using commonly available data to measure both oxygen exchange and an approximation of dead space. In addition to the information provided by the OI (Fio2 and the mean airway pressure required to attain a specific Pao2), the ARDS index also incorporates a derivative of VE40 to approximate dead space ventilation based on easily available clinical data [42-44]. Data-driven prediction scores including OI vs the ARDS index were compared, and the prediction score including the ARDS index had a higher c-statistic (0.71 vs 0.67).
Appropriately identifying and triaging patients with newly diagnosed acute respiratory distress syndrome (ARDS) who may progress to severe ARDS is a common clinical challenge without any existing tools for assistance.
Using a retrospective cohort, a simple prediction score was developed to improve early identification of ARDS patients who were likely to progress to severe ARDS within 7 days. A broad array of comorbidities and physiologic variables were collected for the 12-hour period starting from intubation for ARDS. Extracorporeal membrane oxygenation (ECMO) eligibility was determined based on published criteria from recent ECMO guidelines and clinical trials. Separate data-driven and expert opinion approaches to prediction score creation were completed.
The study included 767 patients with moderate or severe ARDS who were admitted to the intensive care unit between January 1, 2005, and December 31, 2010. In the data-driven approach, incorporating the ARDS index (a novel variable incorporating oxygenation index and estimated dead space), aspiration, and change of Pao₂/fraction of inspired oxygen ratio into a simple prediction model yielded a c-statistic (area under the receiver operating characteristic curve) of 0.71 in the validation cohort. The expert opinion–based prediction score (including oxygenation index, change of Pao₂/fraction of inspired oxygen ratio, obesity, aspiration, and immunocompromised state) yielded a c-statistic of 0.61 in the validation cohort.
The data-driven early prediction ECMO eligibility for severe ARDS score uses commonly measured variables of ARDS patients within 12 hours of intubation and could be used to identify those patients who may merit early transfer to an ECMO-capable medical center.
Protective effect of Astragaloside IV against sepsis-induced acute lung injury in rats
2016, Saudi Pharmaceutical Journal
The study aimed to explore the protective effects of AS-IV against sepsis-induced ALI. Sepsis was induced by cecal ligation and puncture (CLP) method in Sprague Dawley rats. Rats were randomly assigned into five groups: animals undergoing a sham CLP (sham group); animals undergoing CLP (CLP group); animals undergoing CLP and treated with AS-IV at 2.5 mg/kg bw (low-dose AS-IV [L-AS] group), at 5 mg/kg bw (mid-dose AS-IV [M-AS] group), and at 10 mg/kg bw (high-dose AS-IV [H-AS] group). At 6 h, 12 h and 24 h post-CLP surgery, six rats were respectively sacrificed to collect blood and lung tissue samples. The levels of arterial blood gas index, lung water content, protein level and leukocyte counts (total amount, neutrophils and lymphocytes) in bronchoalveolar lavage fluid (BALF) and cytokines such as TNF-α and IL-6 in BALF were measured at each time point in different groups. HE-staining and optical microscopy were performed to examine the pathological changes in lungs. The 72 h-survival rate of each group was also recorded. PaO₂ was decreased significantly, while the lung water content, BALF protein level, cell numbers, BALF cytokine TNF-α and IL-6 levels were increased significantly for CLP group as compared with sham group. Moreover, pathological injury was observed in lung tissue indicating the successful sepsis-induced ALI model. Speaking of the effect of AS-IV, we founded that, compared with the CLP group, the AS-IV treatment groups could significantly alleviate all the above negative changes exited in the CLP group in a dose-dependent manner. What’s more, the pathological injury was also gradually improved by AS-IV treatment compared with the CLP rats. AS-IV exerts its protective effect against sepsis-induced ALI in rats via improving pulmonary ventilation function, decreasing the permeability of alveolar epithelium and capillary as well as repressing lung inflammation.
Lung reperfusion injury in patients after balloon angioplasty for pulmonary artery stenosis
2014, Journal of Cardiothoracic and Vascular Anesthesia
Citation Excerpt :
Currently, the PaO2/FIO2 ratio is the most commonly used measurement of oxygen exchange abnormality. The PaO2/FIO2 ratio has been used extensively in studies attempting to identify and define ARI severity.4–7 There are, however, differing opinions on its ability to do this accurately.
To determine the incidence and degree of acute lung reperfusion injury (ARI) in patients undergoing balloon angioplasty of branch pulmonary artery stenosis and to evaluate the correlation and efficacy of an oxygenation index in confirming the clinical diagnosis.
Retrospective, single-center observational study.
Cardiac catheterization laboratory at a tertiary care children’s hospital.
Patients with congenital heart disease undergoing pulmonary artery balloon angioplasty.
Review of patient medical and catheterization records.
The records of all patients with biventricular physiology undergoing balloon angioplasty of branch pulmonary artery stenosis over a period of 2 years (12/2006-12/2008) were reviewed. Data collection included demographics, details of pulmonary artery intervention, right ventricle/femoral artery systolic pressure (RV/FA) ratio, and post-procedure recovery condition. Markers of ARI, including clinical, radiographic, and blood gas analysis, were examined. Criteria for ARI were based on the International Society of Heart and Lung Transplantation (ISHLT) grading system, in which a PaO₂/F_IO₂ of 200 to 300 indicates ARI. The distribution of PaO₂/F_IO₂ after pulmonary artery intervention, the relation of clinical to laboratory manifestation of ARI, and the correlation among different oxygenation indices were examined.
During the study period, 46 patients with congenital heart disease and branch pulmonary artery stenosis were identified. Patient age ranged from 2 months to 25 years (mean 6.2±6 years) and weight ranged from 5 to 86 kg (mean 23±18 kg). ARI was identified in 10 of 46 patients (22%) using clinical criteria and correlated with ISHLT gas exchange criteria. Analysis of RV/FA ratio before (0.82±0.34) and after (0.71±0.22) balloon angioplasty revealed statistically significant decrease (p<0.004). The degree of ARI was graded using ISHLT criteria and correlated with the presence of clinical symptoms (p<0.002). As anticipated, the PaO₂/F_IO₂ ratio had a strong correlation with A-aDO₂ (r = 0.75) and SpO₂/F_IO₂ (r = 0.7) and a strong specificity (0.78) to identify patients with clinical ARI.
ARI often can occur after pulmonary artery interventions. The PaO₂/F_IO₂ is a valuable test for identifying patients at risk of developing ARI and can help guide the care of these patients in the postintervention period.

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Chest

Clinical Investigations in Critical CareA New Oxygenation Index for Reflecting Intrapulmonary Shunting in Patients Undergoing Open-Heart Surgery

Study objectives

Design

Setting

Patients

Measurements and results

Conclusion

Section snippets

Materials and Methods

Results

Discussion

Conclusion

ACKNOWLEDGMENT

Chest

Br J Anaesth

Chest

Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome

N Engl J Med

Oxygen tensions and oxyhemoglobin saturations in the assessment of pulmonary gas exchange

Crit Care Med

Indices of hypoxemia in patients with acute respiratory distress syndrome: reliability, validity, and clinical usefulness

Crit Care Med

Pulmonary response to major injury

Arch Surg

Relation of inspired oxygen fraction to hypoxemia in mechanically ventilated adults

Crit Care Med

Long-term effects of two different ventilatory modes on oxygenation in acute lung injury: comparison of airway pressure release ventilation and volume-controlled inverse ratio ventilation

Am J Respir Crit Care Med

The American-European Consensus Conference on ARDS: definitions, mechanisms, relevant outcomes, and clinical trial coordination

Am J Respir Crit Care Med

Handbook of respiratory care

Unreliability of oxygen tension-based indices in reflecting intrapulmonary shunting in critically ill patients

Crit Care Med

Applied respiratory physiology

Clinical Investigations in Critical Care
A New Oxygenation Index for Reflecting Intrapulmonary Shunting in Patients Undergoing Open-Heart Surgery