Ventilation-perfusion mismatch in anesthesia

We have investigated the elimination of inert gases in the lung during the elimination of nitrous oxide (N2 O) using a two-step mathematical model that allows the contribution from net gas volume expansion, which occurs in Step 2, to be separated from other factors. When a second inert gas is used in addition to N2 O, the effect on that gas appears as an extra volume of the gas eliminated in association with the dilution produced by N2 O washout in Step 2. We first considered the effect of elimination in a single gas-exchanging unit under steady-state conditions and then extended our analysis to a lung having a log-normal distribution of ventilation and perfusion...

BACKGROUND: Atelectasis is a common complication in neonatal anesthesia. Lung ultrasound (LUS) can be used intraoperatively to evaluate and recognize atelectatic lung areas. Hypotheses for the study are: (1) The use of LUS to guide choice of best positive end-expiratory pressure (PEEP) can lead to reduction of FiO2 to achieve same saturations of oxygen (SpO2 ). (2) In a less de-recruited lung, there will be less postoperative pulmonary complications. (3) Static respiratory system compliance could be different...

Alveolar recruitment manoeuvres may mitigate ventilation and perfusion mismatch after cardiac surgery. Monitoring the efficacy of recruitment manoeuvres should provide concurrent information on pulmonary and cardiac changes. This study in postoperative cardiac patients applied capnodynamic monitoring of changes in end-expiratory lung volume and effective pulmonary blood flow. Alveolar recruitment was performed by incremental increases in positive end-expiratory pressure (PEEP) to a maximum of 15 cmH2 O from a baseline of 5 cmH2 O over 30 min...

Anesthetists are concerned about the causes and management of hypoxia during one-lung ventilation (OLV). Here, we report a hypoxic case during OLV and video-assisted thoracic surgery (VATS) for pulmonary lobectomy. The preoperative management of hypertension with amlodipine was considered to be responsible for the hypoxia. As a calcium channel blocker, amlodipine may inhibit hypoxic pulmonary vasoconstriction (HPV) and contribute to the reduction of the ventilation/perfusion ratio (or V/Q ratio). The hypoxia efficiently was treated by atropine, where both tracheal effects and the enhancement of HPV through muscarinic receptor blocking may work...

BACKGROUND: Laparoscopic surgery and Trendelenburg position may affect the respiratory function and alter the gas exchange. Further the reduction of the lung volumes may contribute to the development of expiratory flow limitation (EFL). The latter is associated with an increased risk of postoperative pulmonary complications. Our aim was to investigate the incidence of EFL and to evaluate its effect on pulmonary function and intraoperative V/Q mismatch. METHODS: This is a prospective study on patients undergoing elective laparoscopic gynecological surgery...

Patients with achondroplasia often present with anatomical abnormalities and altered cardiopulmonary physiology that significantly increase their perioperative risk for cardiovascular and respiratory complications (e.g., worsening ventilation-perfusion mismatch, imminent desaturation, difficult airway). We describe a 34-year-old achondroplastic male presenting with altered mentation following a traumatic subdural hematoma that necessitated emergent craniotomy evacuation. Initial attempt at intubation was complicated by rapid desaturation and bradyarrhythmia...

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BACKGROUND: Inefficiency of lung gas exchange during general anesthesia is reflected in alveolar (end-tidal) to arterial (end-tidal-arterial) partial pressure gradients for inhaled gases, resulting in an increase in alveolar deadspace. Ventilation-perfusion mismatch is the main contributor to this, but it is unclear what contribution arises from diffusion limitation in the gas phase down the respiratory tree (longitudinal stratification) or at the alveolar-capillary barrier, especially for gases of high molecular weight such as volatile anesthetics...

Purpose: Monitoring end-tidal carbon dioxide partial pressure (PET CO2 ) is a noninvasive, continuous method, but its accuracy is reduced by prolonged capnoperitoneum and the steep Trendelenburg position in robot-assisted radical prostatectomy (RARP). Transcutaneous carbon dioxide partial pressure (PTC CO2 ) monitoring, which is not affected by ventilator-perfusion mismatch, has been suggested as a suitable alternative. We compared the agreement of noninvasive measurements with the arterial carbon dioxide partial pressure (PaCO2 ) over a long period of capnoperitoneum, and investigated its sensitivity and predictive power for detecting hypercapnia...

BACKGROUND: Respiratory distress is a common reason for animals to present to the emergency room. An understanding of respiratory physiology is helpful to facilitate accurate localization of the patient's source of respiratory distress. This knowledge will aid implementation of more appropriate therapies. PHYSIOLOGY/PATHOPHYSIOLOGY SUMMARY: Respiratory distress can occur secondary to lesions at any location of the respiratory system. Diseases affecting different portions of the respiratory track (eg, upper airway, lower airways, parenchymal, or the pleural space) lead to distinguishing clinical signs as the patient's respiratory physiology is affected differently...

More than 70 years after its original report, the hypoxic pulmonary vasoconstriction (HPV) response continues to spark scientific interest on its mechanisms and clinical implications, particularly for anesthesiologists involved in thoracic surgery. Selective airway intubation and one-lung ventilation (OLV) facilitates the surgical intervention on a collapsed lung while the HPV redirects blood flow from the "upper" non-ventilated hypoxic lung to the "dependent" ventilated lung. Therefore, by limiting intrapulmonary shunting and optimizing ventilation-to-perfusion (V/Q) ratio, the fall in arterial oxygen pressure (PaO2 ) is attenuated during OLV...

An elderly hypertensive lady presented with fever, respiratory symptoms, and mild abdominal discomfort and was diagnosed to have COVID-19 pneumonia. Respiratory symptoms improved with steroids, awake proning, high flow nasal cannula oxygen therapy and antibiotics. After 4 days, she developed non-occlusive superior mesenteric artery thrombosis, which initially responded to anticoagulants but was complicated on tenth day by intestinal obstruction necessitating emergency surgery. Challenges encountered perioperatively were multi systemic involvement, pneumonia, ventilation- perfusion mismatch, sepsis along with technical difficulties like fogging of goggles, stuck expiratory valve on anesthesia machine, inaudibility through stethoscope and discomfort due to personal protective equipment...

In the past, it was common practice to use a high tidal volume (VT) during intraoperative ventilation, because this reduced the need for high oxygen fractions to compensate for the ventilation-perfusion mismatches due to atelectasis in a time when it was uncommon to use positive end-expiratory pressure (PEEP) in the operating room. Convincing and increasing evidence for harm induced by ventilation with a high VT has emerged over recent decades, also in the operating room, and by now intraoperative ventilation with a low VT is a well-adopted approach...

The second gas effect occurs when high inspired concentrations of a first gas, usually nitrous oxide, enhance the uptake of other gases administered simultaneously. The second gas effect is greater in blood than in the gas phase, persists well into the period of nitrous oxide maintenance anesthesia, increases as the degree of ventilation-perfusion mismatch increases, and is most pronounced with the low soluble agents in current use. Yet, how low gas solubility and increased ventilation-perfusion mismatch can combine to improve gas transfer remains unclear, which is the focus of the present study...

RATIONALE: Chronic thromboembolic pulmonary hypertension (CTEPH) is a disease with a poor prognosis, characterized by chronic thromboembolic obstruction of the pulmonary arteries and pulmonary hypertension. Balloon pulmonary angioplasty (BPA) is a newly emergent treatment for CTEPH, which may substitute pulmonary endarterectomy, the standard but more invasive treatment for CTEPH. Here, we report the case of a CTEPH patient who underwent 2 noncardiac surgeries without complications after preoperative intervention of BPA...

The second gas effect (SGE) occurs when nitrous oxide enhances the uptake of volatile anesthetics administered simultaneously. Recent work shows that the SGE is greater in blood than in the gas phase, that this is due to ventilation-perfusion mismatch, that as mismatch increases, the SGE increases in blood but is diminished in the gas phase, and that these effects persist well into the period of nitrous oxide maintenance anesthesia. These modifications of the SGE are most pronounced with the low soluble agents in current use...

Horses are susceptible to developing large areas of pulmonary atelectasis during recumbency and anesthesia. The subsequent pulmonary shunt is responsible for significant impairment of oxygenation. Since ventilation perfusion mismatch persists into the post-operative period, hypoxemia remains an important concern in the recovery stall. This case report describes the diagnosis and supportive therapy of persistent hypoxemia in a 914 kg draft horse after isoflurane anesthesia. It highlights how challenging it can be to deal with hypoxemia after disconnection from the anesthesia machine and how life-threatening it can become if refractory to treatment...

Stenting at the flow-limiting segment can improve the ventilation-perfusion ratio in patients with central airway stenosis. However, there is no quantitative examination for assessing the perfusion status during interventional bronchoscopy. Intrabronchial capnography can estimate regional gas exchange by measuring carbon dioxide concentration. We herein report a case of bilateral bronchial stenosis where stenting was able to improve ventilation-perfusion ratio using intrabronchial capnography. A 44-year-old man was admitted to our institution with orthopnea...

BACKGROUND: Recent clinical studies suggest that the magnitude of the second gas effect is considerably greater on arterial blood partial pressures of volatile agents than on end-expired partial pressures, and a significant second gas effect on blood partial pressures of oxygen and volatile agents occurs even at relatively low rates of nitrous oxide uptake. We set out to further investigate the mechanism of this phenomenon with the help of mathematical modeling. METHODS: Log-normal distributions of ventilation and blood flow were generated representing the range of ventilation-perfusion scatter seen in patients during general anesthesia...

BACKGROUND: Arterial oxygenation is often impaired during one-lung ventilation, due to both pulmonary shunt and atelectasis. The use of low tidal volume (VT) (5 ml/kg predicted body weight) in the context of a lung-protective approach exacerbates atelectasis. This study sought to determine the combined physiologic effects of positive end-expiratory pressure and low VT during one-lung ventilation. METHODS: Data from 41 patients studied during general anesthesia for thoracic surgery were collected and analyzed...