Asymptomatic Hypoxemia as a Characteristic Symptom of Coronavirus Disease: A Narrative Review of Its Pathophysiology

Coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a pandemic and caused a huge burden to healthcare systems worldwide. One of the characteristic symptoms of COVID-19 is asymptomatic hypoxemia, also called happy hypoxia, silent hypoxemia, or asymptomatic hypoxemia. Patients with asymptomatic hypoxemia often have no subjective symptoms, such as dyspnea, even though hypoxemia is judged by objective tests, such as blood gas analysis and pulse oximetry. Asymptomatic hypoxemia can lead to acute respiratory distress syndrome, and the delay in making a diagnosis and providing initial treatment can have fatal outcomes, especially during the COVID-19 pandemic. Thus far, not many studies have covered asymptomatic hypoxemia. We present a review on the human response to hypoxemia, focusing on the respiratory response to hypoxemia rather than the pathophysiology of lung injury arising from SARS-CoV-2 infection. We have also discussed whether asymptomatic hypoxemia is specific to SARS-CoV-2 infection or a common phenomenon in lung-targeted viral infections.

The correlation between Corrected Flow Time (FTc) Based on Esophageal Doppler Monitoring and Pleth Variability Index (PVI) in the Fluid Therapy in Patients undergoing Total Abdominal Hysterectomy

Background: The occurrence of bleeding during major surgeries is common and requires timely and accurate management in the prevention and treatment of hypovolemia and hemodynamic instability during and after surgery. This study evaluated the correlation and agreement between the two protocols determining the status of the hypovolemia during hysterectomy. Methods: This study was a randomized single-blinded clinical trial. The study population included 30 patients undergoing Total Abdominal Hysterectomy in Shariati Hospital in Tehran between 2015 and 2016. The patients were randomly assigned to two groups using a randomized table of numbers, so that in the FTc group, fluid therapy was performed based on the FTc index and in the PVI group based on the PVI index. The changes in FTc and PVI values were recorded every 5 minutes and the changes in the two indicators from the beginning to the end of the treatment were evaluated. At the beginning and end of the surgery, an arterial blood gas analysis (ABG) was also performed. The amount of bleeding during operation and urinary output were recorded in two groups. Results: There was no significant difference across the two groups in total fluid intake during surgery, mean volume of blood loss, mean urine output, and duration of surgery. The arterial blood gas status was also similar in both groups at the beginning and the end of the operation. We found a strong adverse correlation between FTC and PVI indices at the different time points evaluated within the surgery. In total, there was a strong correlation between the mean FTC and the mean PVI during the first hour (r=-0.765, P < 0.001) and the second hour (r=-0.941, -P < 0.001) of operation. Considering the cut-off point of 350msec for the FTC and 13% for the PVI in predicting hypovolemia, the agreement between the two protocols in fluid therapy during the first hour after surgery was 79.8% and 76.6%. Conclusion: There is a strong and significant correlation between the two FTC (with a cut off of 350) and PVI (with a cut point of 13%) to predict need for fluid therapy.

Feasıbılıty of Transcutaneous Method for Carbon Dıoxıde Monıtorıng in an Intensive Care Unıt

Background: Transcutaneous partial pressure of carbon dioxide (PtCO2) monitorization provides a continuous and non-invasive measurement of partial pressure of carbon dioxide (pCO2). In addition, peripheral oxygen saturation (SpO2) can also be measured and followed by this method. However, data regarding the correlation between PtCO2 and arterial pCO2 (PaCO2) measurements acquired from peripheric arterial blood gas is controversial. Objective: We aimed to determine the reliability of PtCO2 with PaCO2 based on its advantages, like non-invasiveness and continuous applicability. Methods: Thirty-five adult patients with hypercapnic respiratory failure admitted to our tertiary medical intensive care unit (ICU) were included. Then we compared PtCO2 and PaCO2 and both SpO2 measurements simultaneously. Thirty measurements from the deltoid zone and 26 measurements from the cheek zone were applied. Results: PtCO2 could not be measured from the deltoid region in 5 (14%) patients. SpO2 and pulse rate could not be detected at 8 (26.7%) of the deltoid zone measurements. Correlation coefficients between PtCO2 and PaCO2 from deltoid and the cheek region were r: 0,915 and r: 0,946 (p = 0,0001). In comparison with the Bland-Altman test, difference in deltoid measurements was -1,38 ± 1,18 mmHg (p = 0.252) and in cheek measurements it was -5,12 ± 0,92 mmHg (p = 0,0001). There was no statistically significant difference between SpO2 measurements in each region. Conclusion: Our results suggest that PtCO2 and SpO2 measurements from the deltoid region are reliable compared to the arterial blood gas analysis in hypercapnic ICU patients. More randomized controlled studies investigating the effects of different measurement areas, hemodynamic parameters, and hemoglobin levels are needed.

Comparative study between ketamine-S-dexmedetomidine and ketamine-S-midazolam-methadone in the anesthesia of capuchin monkeys (Sapajus apella)

ABSTRACT: Anesthetic protocols have been developed to obtain the most effective and safe association in wildlife. This study compared the anesthetic effects and cardiorespiratory parameters of ketamine-S (+) (10 mg/kg)/dexmedetomidine (0.020 mg/kg) (KD ) and ketamine-S (+) (10 mg/kg)/midazolam (0.5 mg/kg)/methadone (1.0 mg/kg) (KMM ) in capuchin monkeys (Sapajus apella). Eight capuchin monkeys were randomly assigned to KD (n = 4) or KMM (n = 4) to evaluate induction, immobilization, and recovery scores, heart and respiratory rate parameters, besides systolic, mean, diastolic arterial pressure and arterial blood gas. There was no difference (P = 0.56) in the quality of induction, immobilization, and anesthetic recovery between the protocols. The time for anesthetic induction was 4 ± 1 min in the KD group and 5 ± 1 min in the KMM group, and these values were statistically equal (P = 0.28). The mean immobilization time in the KD and KMM groups were 35 ± 13 and 33 ± 15 min, respectively. Heart rate was lower in animals in the KD group (P < 0.001), while respiratory rate (P = 0.03), and mean blood pressure (P = 0.046) were higher than that of the animals in the KMM group. Respiratory acidosis occurred in the KMM group, with lower pH (7.25±0.047; P = 0.0055) and higher pCO2 (51 ± 6;mmHg; P = 0.008). Both protocols exhibited good induction quality, immobilization, and anesthetic recovery, despite cardiorespiratory and blood gas alterations observed, which warrants monitoring of cardiorespiratory variables during KD or KMM chemical restraint.

Presample Volume Necessary to Obtain Accurate Laboratory Parameters from Central Venous Catheters in Dogs

ABSTRACT We compared laboratory parameters from central venous catheters using multiple presample volumes (PSVs) to venipuncture values. Blood was obtained from dogs for a venous blood gas, packed red blood cell volume (PCV), total solids (TS), and a coagulation panel. Blood was drawn both by venipuncture and from the catheter (using PSVs 300%, 600%, and 1200% of the dead space volume). Twenty dogs were enrolled. Venipuncture values were significantly higher than those obtained from the catheter for PCV (300% [P = .007], 600% [P = .005], and 1200% [P = .02]), TS (300% [P = .006] and 600% [P = .04]), and lactate (600% [P = .04] and 1200% [P = .01]). Venipuncture values were significantly lower than those obtained from a catheter for pH (1200% [P = .008]) and chloride (300% [P = .04], 600% [P = .003], and 1200% [P = .03]). An increase was found in prothrombin time in samples drawn with 600% PSV compared with 1200% (P = .008). The PCV and TS are diluted when smaller PSVs are used. A 1200% PSV best approximated the PCV and TS obtained by venipuncture. A 300% PSV may be adequate to evaluate coagulation and venous blood gas values.