One-lung ventilation (OLV) is a technique used during thoracotomy to selectively ventilate one lung while collapsing the other. This can be achieved using a double-lumen tube (DLT), a single-lumen tube with a bronchial blocker, or an endotracheal tube positioned endobronchially ( Butterworth et al., 2013). The procedure involves both manipulation of the lungs and changes in body positioning, which can affect heart-lung interaction. Non-ventilated but perfused lungs may result in a right-to-left shunt, a condition that can be partly mitigated by hypoxic pulmonary vasoconstriction and gravity, which redistributes blood flow to the lower lung ( Marongiu et al., 2020). However, OLV also affects cardiac function. Positive pressure ventilation can decrease venous return and systemic vascular resistance, while alveolar hypoxia may induce pulmonary vasoconstriction, increasing the workload on the right ventricle ( Slinger et al., 2019). These interactions between the heart and lungs are critical, as changes in one component often affect the other. In this case, we present a patient with cardiomegaly who experienced significant changes in oxygenation during OLV. The patient exhibited desaturation when both lungs were ventilated, but oxygenation improved when only the diseased lung was ventilated.

Patient information: A 20-year-old male, weighing 45 kg with a height of 165 cm (BMI 16.5 kg/m ²), presented in March 2022 with sudden onset shortness of breath. He had no prior chronic illness until one year earlier, when he experienced moderate COVID-19 pneumonia. Since then, he reported reduced exercise tolerance and recurrent shortness of breath but had not sought medical care.

Clinical findings: On initial evaluation, he was alert, with blood pressure 100/70 mmHg, heart rate 110 bpm, respiratory rate 26–28 breaths per minute, oxygen saturation 95–96% on 2 L/min oxygen via nasal cannula, and temperature 36.7°C. Physical examination revealed decreased breath sounds on the right hemithorax with a thoracic drain in situ after recurrence.

The incidence of hypoxemia during One-Lung Ventilation (OLV) has decreased significantly over time, from 25% in the 1970s to less than 10% today ( Semedi et al., 2021). The primary advantage of OLV is that it facilitates thoracic surgery by collapsing the lung on the operative side. However, this collapse often leads to a right-to-left intrapulmonary shunt, where blood from the collapsed, non-ventilated lung mixes with oxygenated blood from the ventilated lung. This can increase the PA-a O ₂ gradient (alveolar to arterial oxygen difference), potentially causing hypoxemia. Fortunately, hypoxic pulmonary vasoconstriction (HPV) reduces blood flow to the non-ventilated lung, helping to mitigate this effect ( Marongiu et al., 2020). However, in cases where atelectasis affects the dependent lung, oxygenation is further compromised due to V/Q mismatch (ventilation-perfusion mismatch) ( Rehatta et al., 2019).

In the present case, the patient exhibited cardiomegaly with dilation of both the right atrium (RA) and right ventricle (RV), along with an increased likelihood of pulmonary hypertension. This condition, common in patients with lung damage such as post-COVID-19 patients, can lead to pulmonary hypertension type 3 ( Taha et al., 2023). Pulmonary hypertension increases the workload of the RV, causing RV dilation and subsequently RA dilation. The elevated RV afterload due to increased pulmonary vascular resistance (PVR) further affects the patient’s hemodynamics.

Positive pressure ventilation during OLV can exacerbate these hemodynamic changes by increasing intrathoracic pressure, which in turn raises RA pressure and decreases venous return. This results in reduced RV preload and output, potentially worsening the patient’s condition. Additionally, excessive lung inflation can cause alveolar distension, compressing the alveolar vessels, thus increasing pulmonary vascular resistance and reducing cardiac output ( Guia et al., 2020). The use of fentanyl and propofol in this patient could further reduce cardiac function, contributing to systemic vasodilation. To manage these issues, norepinephrine was administered to raise systemic vascular resistance (SVR), while milrinone was used as an inotropic agent and pulmonary vasodilator to decrease RV afterload.

A particularly interesting phenomenon in this case occurred when the patient was positioned in the left lateral decubitus (LLD) position for surgery. In contrast to the typical pattern of hypoxemia observed during one-lung ventilation (OLV), this patient demonstrated improved oxygenation when only the dependent left lung was ventilated. Under usual circumstances, hypoxemia during OLV improves with two-lung ventilation; however, in this case, severe cardiomegaly with a cardiothoracic ratio of 75% altered the expected physiological response. The markedly enlarged heart exerted compressive forces on the dependent left lung in the LLD position, reducing lung compliance and impairing effective ventilation. Gravitational displacement of the mediastinum further exacerbated this effect, resulting in preferential airflow toward the non-dependent right lung during two-lung ventilation. Because the right lung was diseased, this redistribution of ventilation worsened ventilation–perfusion mismatch and contributed to hypoxemia, despite on-going perfusion of the dependent lung.

However, when the patient was ventilated with only the left lung, the positive pressure ventilation was effectively directed into the left lung, despite its suboptimal compliance due to heart compression. This resulted in improved ventilation-perfusion (V/Q) matching, which led to the resolution of hypoxemia. The finding is notable because it challenges the typical response seen in most patients undergoing OLV, where ventilation of both lungs typically results in better oxygenation.

After the operation, when the patient was returned to the supine position, two-lung ventilation no longer resulted in hypoxemia and oxygenation remained stable. In the supine position, posterior displacement of the heart reduces its compressive effect on the lungs, thereby improving lung expansion and ventilation. Nevertheless, cardiomegaly may still influence regional ventilation, particularly in the lower lobes, even in the supine position, as previously reported in the literature.

This case underscores the complexity of managing OLV in patients with cardiomegaly and pulmonary hypertension. The findings suggest that patient positioning, particularly in cases of significant heart enlargement, plays a crucial role in determining oxygenation outcomes during OLV. Further studies are needed to better understand the effects of cardiomegaly and pulmonary hypertension on heart-lung interactions during thoracic surgery.

Severe cardiomegaly can affect the interaction between the heart and the lungs, particularly in the left lateral decubitus (LLD) position, where the enlarged heart can compress the left lung. This compression reduces lung compliance and disrupts the ventilation of the left lung, making it easier for positive pressure ventilation to move upward to inflate the right lung. Because there is inadequate ventilation and perfusion in the healthy left lung and the diseased right lung, a right-to-left shunt occurs, leading to hypoxemia. Surprisingly, One Lung Ventilation (OLV) in this case proves beneficial because positive pressure primarily directs air into the left lung. Despite the pressure exerted by the heart, this condition allows for ventilation along with perfusion, ultimately reducing the right-to-left shunt that causes hypoxemia.

Written informed consent for the publication of this case report and any associated images has been obtained from the patient. The patient has given permission for their medical information to be published in this case report. All identifying information has been removed to ensure confidentiality, in accordance with ethical standards and privacy regulations.