Effects of Hyperventilation on Venous-Arterial Bicarbonate Concentration Difference: A Possible Pitfall in Venous Blood Gas Analysis

Objectives: Recent reports on venous blood gas analysis have shown that venous bicarbonate concentration is useful in the evaluation of the body acid-base status. Most of these reports have been based on the Bland-Altman analysis comparing arterial and venous blood gas values. We intended to elucidate any factors that decrease the agreement between venous and arterial bicarbonate concentrations, which might impair the usefulness of venous blood gas analysis. Methods: Healthy volunteers and patients with various diseases (n = 141) were evaluated by simultaneous arterial and venous blood sampling and Bland-Altman analysis. The venous-arterial bicarbonate concentration difference was compared between healthy volunteers and untreated respiratory alkalosis patients. Intentional hyperventilation (30 or 60 breaths/min, for 3 min) was also performed on 6 healthy volunteers and the venous-arterial bicarbonate concentration difference was evaluated. Results: The relative average bias in bicarbonate concentration was 2.00 mEq/l with venous bicarbonate higher than arterial bicarbonate with 95% limits of agreement of ±4.15 mEq/l. Hyperventilation challenges increased the venous-arterial bicarbonate concentration difference in an intensity-dependent manner. The venous-arterial bicarbonate concentration difference was higher in untreated respiratory alkalosis patients than in healthy volunteers (P Conclusion: Although venous bicarbonate may be useful to evaluate the body acid-base status, hyperventilation increases the venous-arterial bicarbonate concentration difference. Physicians should keep this phenomenon in mind.

Central Neurogenic Hyperventilation Secondary to a Critic Thyroid Status after Aortoaortic Bypass: A Peculiar Case Report

Central neurogenic hyperventilation (CNH) is a rare condition and defined as a syndrome comprising normal or elevated arterial oxygen tension, decreased arterial carbon dioxide tension, respiratory alkalosis with hyperventilation even during sleep, and the absence of a peripheral respiratory stimulus. The diagnosis of CNH requires the exclusion of pulmonary, cardiac, metabolic-immunological disorders and some medicines that can result in hyperventilation. We detailed the case of CNH in the 4th day after vascular surgery probably secondary to acute metabolic acidosis with hyperlactatemia, due to severe hypothyroidism in the context of critically ill patient.

Effects of Moderate Hyperventilation on Jugular Bulb Gases under Propofol or Isoflurane Anesthesia during Supratentorial Craniotomy

Background：The optimal ventilated status under total intravenous or inhalation anesthesia in neurosurgical patients with a supratentorial tumor has not been ascertained.The purpose of this study was to intraoperatively compare the effects of moderate hyperventilation on the jugular bulb oxygen saturation （SjO2）,cerebral oxygen extraction ratio （O2ER）,mean arterial blood pressure （MAP）,and heart rate （HR） in patients with a supratentorial tumor under different anesthetic regimens.Methods：Twenty adult patients suffered from supratentorial tumors were randomly assigned to receive a propofol infusion followed by isoflurane anesthesia after a 30-min stabilization period or isoflurane followed by propofol.The patients were randomized to one of the following two treatment sequences：hyperventilation followed by normoventilation or normoventilation followed by hyperventilation during isoflurane or propofol anesthesia,respectively.The ventilation and end-tidal CO2 tension were maintained at a constant level for 20 min.Radial arterial and jugular bulb catheters were inserted for the blood gas sampling.At the end of each study period,we measured the change in the arterial and jugular bulb blood gases.Results：The mean value of the jugular bulb oxygen saturation （SjO2） significantly decreased,and the oxygen extraction ratio （O2ER） significantly increased under isoflurane or propofol anesthesia during hyperventilation compared with those during normoventilation （SjO2：t =-2.728,P =0.011 or t =-3.504,P =0.001;O2ER：t =2.484,P =0.020 or t =2.892,P =0.009）.The SjO2 significantly decreased,and the O2ER significantly increased under propofol anesthesia compared with those values under isoflurane anesthesia during moderate hyperventilation （SjO2：t =-2.769,P =0.012;O2ER：t =2.719,P =0.013）.In the study,no significant changes in the SjO2 and the O2ER were observed under propofol compared with those values under isoflurane during normoventilation.Conclusions：Our results suggest that the optimal ventilated status under propofol or isoflurane anesthesia in neurosurgical patients varies.Hyperventilation under propofol anesthesia should be cautiously performed in neurosurgery to maintain an improved balance between the cerebral oxygen supply and demand.

Fearful imagery induces hyperventilation and dyspnea in medically unexplained dyspnea

Background Medically unexplained dyspnea refers to a condition characterized by a sensation of dyspnea and is typically applied to patients presenting with anxiety and hyperventilation without underlying cardiopulmonary pathology. We were interested to know how anxiety triggers hyperventilation and elicits subjective symptoms in those patients. Using an imagery paradigm, we investigated the role of fearful imagery in provoking hyperventilation and in eliciting symptoms, specifically dyspnea. Methods Forty patients with medically unexplained dyspnea and 40 normal subjects matched for age and gender were exposed to scripts and asked to imagine both fearful and restful scenarios, while end-tidal PCO2 （PetCO2） and breathing frequency were recorded and subjective symptoms evaluated. The subject who had PetCO2 falling more than 5 mmHg from baseline and persisting at this low level for more than 15 seconds in the imagination was regarded as a hyperventilation responder. Results In patients with medically unexplained dyspnea, imagination of fearful scenarios, being blocked in an elevator in particular, induced anxious feelings, and provoked a significant fall in PetCO2 （P〈0.05）. Breathing frequency tended to increase. Eighteen out of 40 patients were identified as hyperventilation responders compared to 5 out of 40 normal subjects （P〈0.01）. The patients reported symptoms of dyspnea, palpitation or fast heart beat in the same fearful script imagery. Additionally, PetCO2 fall was significantly correlated with the intensity of dyspnea and palpitation experienced during the mental imagery on one hand, and with anxiety symptoms on the other. Conclusions Fearful imagery provokes hyperventilation and induces subjective symptoms of dyspnea and palpitation in patients with medically unexplained dyspnea.

Effect of hyperventilation on brain tissue oxygen pressure, carbon dioxide pressure, pH value and intracranial pressure during intracranial hypertension in pigs

To study the effect of hyperventilation on brain tissue oxygen pressure (P ti O 2) , brain tissue carbon dioxide pressure (P ti CO 2) , pH value and intracranial pressure (ICP) during intracranial hypertension in pigs. Methods: Autologous arterial blood ( 5.5 ml± 0.5 ml) was injected into the left frontal lobe by micropump to establish the model of intracerebral hematoma in pigs. After blood injection, the animals were hyperventilated for 15 minutes to decrease the pressure of carbon dioxide in arterial blood ( P aCO 2 ) to 27.35 mm*!Hg ± 11.97 mm*!Hg (1 mm*!Hg= 0.133 kPa). The mean arterial pressure (MAP), intracranial pressure (ICP), cerebral perfusion pressure (CPP), P ti O 2 , P ti CO 2 , pH value and [HCO 3 -] were continuously monitored and the blood gas was analyzed. Results: After hyperventilation, the ICP significantly decreased (P< 0.01 ), the CPP significantly increased (P< 0.05 ), while the P ti O 2 greatly decreased to the ischemic level ( 8.20 mm*!Hg± 2.50 mm*!Hg) (P< 0.01 ), the P ti CO 2 decreased (P< 0.01 ) and the pH value increased (P< 0.01 ). At the same time, blood gas analysis showed that the P aCO 2 greatly decreased and the pH value increased. Conclusions: Hyperventilation can decrease the ICP and the P ti O 2 significantly. Therefore, hyperventilation should be avoided early after brain injury. The P ti O 2 monitoring will be helpful for detecting cerebral ischemia early.

Is Acupressure Useful for Alleviating Hyperventilation Syndrome?

Case Report On April 23, 2017, a plane was flying from Hefei to Guangzhou in China. About 20 min after takeoff, a 30-year-old female passenger suddenly had on set of face redde ned all over, breathless ness, dyspnoea, palpitation and chest pain. Fortunately, two doctors came over to give help, one is Prof. Zhang, a cardiovascular specialist, the other one is Prof. Tan, a cardiovascular surgery specialist. After inquiring symptoms, two doctors believed that the woman had no organic abnormalities according to several medical examinations before, and once had a similar attack.

Effects of diabetic ketoacidosis in the respiratory system

Diabetes affects approximately 30 million persons in the United States. Diabetes ketoacidosis is one of the most serious and acute complications of diabetes. At the time of presentation and during treatment of diabetic ketoacidosis(DKA), several metabolic and electrolyte derangements can ultimately result in respiratory compromise. Most commonly, hypokalemia, hypomagnesemia and hypophosphatemia can eventually lead to respiratory muscles failure.Furthermore, tachypnea, hyperpnea and more severely, Kussmaul breathing pattern can develop. Also, hydrostatic and non-hydrostatic pulmonary edema can occur secondary to volume shifts into the extracellular space and secondary to increased permeability of the pulmonary capillaries. The presence of respiratory failure in patients with DKA is associated with higher morbidity and mortality. Being familiar with the causes of respiratory compromise in DKA, and how to treat them, may represent better outcomes for patients with DKA.

The effects of PaCO_2 on balance of cerebral oxygen supply and consumption during intravenous general anesthesia

Objective: To evaluate the effects of various degrees of hyperventilation on balance of cerebral oxygensupply and consumption during intravenous general anesthesia with jugular venous oxygen saturation monitoringMetbods: Sixty-six patients with supratentorial tumor undergoing intravenous general anesthesia for brain surgerywere randomly divided into three groups. In group Ⅰ, Ⅱ and Ⅲ, end-tidal pressure of Co2(PETCO2) were maintained at 3. 5, 4. 0 and 4. 5 kPa respectively. Radial arterial blood samples and jugular bulb blood samples weretaken synchronously at 60 min after hyperventilation to measure jugular venous oxygen saturation (SjvO2), cerebral extraction of oxygen (CEO2) and cerebral arteriovenous oxygen content difference (AVDO2) were calculatedResults: In group Ⅰ after hyperventilation, SjvO, and jugular venous oxygen content (CjvO2) were decreasedmarkedly while CEO2 was increased significantly, which was different significantly compared with the baseline andcorresponding value in group Ⅱ and Ⅲ (P<0. 05). After hyperventilation in group, and, SjvO2 CjvO2, CEO2and AVDO, remained unchanged. Conclusion: This study shows that sustained excessive hyperventilation (PETCO23.5 kPa) may account for the less favorable cerebral oxygen supply and consumption balance and maintained PETCO, at 4. 0~4. 5 kPa was optimal hyperventilation for brain surgery anesthesia.

The use of DCEEG to estimate functional and metabolic state of nervous tissue of the brain at hyper- and hypoventilation

A pilot study has been made of the simultaneous DC potential and total slow electrical activity changes during modeling various metabolic and functional states of the human brain. The multi-electrode DCEEG recordings have been performed during the hyperventilation (frequent deep one-minute long breathing motions) and the hypoventilation (voluntary breath holding). It has been shown that the ischemic state occurring in hyperventilation is accompanied by the negative shift of DC potential and increase in the EEG rhythms amplitude. A distention of brain vessels during hypoventilation (voluntary breath-hold) and an improvement of blood supply and thus improvement of vital and functional state of neurons gave rise to an increase in the EEG rhythm amplitude too, though against a background of a positive DC-potential shift. Obtained results are considered with context the generation of the qualitatively different functional states of brain cells during hyper- and hypoventilation which is reflected in their resting potential and activity. The conducted study show the prospects for DCEEG and the method we used for DCEEG data processing to understand the character of functional and metabolic changes in the nervous tissue.

Reconsideration of Augmentation Strategies in Electroconvulsive Therapy: Effects of the Concurrent Use of a Reduced Dose of Propofol with Divided Supplemental Remifentanil and Moderate Hyperventilation on Electroconvulsive Therapy-Induced Seizure Production and Adverse Events

Background: Although several treatment strategies to enhance the efficacy of electroconvulsive therapy (ECT) have been discussed, there have been no reports on the combined use of these treatments. The purpose of this study was to evaluate the efficacy and safety of concurrent use of moderate hyperventilation and a reduced dose of propofol combined with divided remifentanil in ECT practice. Methods: Sixty patients scheduled to receive a total of 300 ECT treatments were randomly assigned to have the three interventions: a standard dose (1 mg/kg) of propofol (group P/N);a standard dose of propofol and moderate hyperventilation with end-tidal pressure of carbon dioxide (ETCO2) of 30 - 35 mmHg (group P/H);and a reduced dose (0.5 mg/kg) of propofol with divided supplemental remifentanil and moderate hyperventilation (group RP/H). Patients in group RP/H received remifentanil 1 μg/kg followed by propofol 0.5 mg/kg for unconsciousness and thereafter remifentanil 1 μg/kg immediately before the ECT stimulus. Results: Patients in group RP/H showed significantly longer durations of electroencephalographic (EEG) seizures in the early phase of ECT course (P < 0.01 and 0.05) and lower electrical stimulus in the late phase of ECT course (P < 0.05 in each) than those in groups P/N and P/H, respectively. Conclusions: The use of a reduced dose of propofol combined with divided supplemental remifentanil under moderate hyperventilation during ECT can offer advantages over the use of a standard dose of propofol with or without moderate hyperventilation in terms of more seizure augmentation and/or lower electrical stimulus.

Medically unexplained dyspnea:psychophysiological characteristics and role of breathing therapy

Background Medically unexplained dyspnea occurs commonly in medical settings and remains poorly understood. This study was conducted to investigate the psychophysiological characteristics of medically unexplained dyspnea and the efficacy of breathing retraining for these patients. Methods A group of patients with medically unexplained dyspnea were compared to patients with a variety of organic lung diseases and healthy subjects. In another group of patients,the influence of breathing therapy on complaints,anxiety, and breath-holding was evaluated for an average of 1.5 years. Results Patients with medically unexplained dyspnea reported more intense dyspnea than patients with a variety of organic lung diseases. Additionally,they were anxious and presented a broad range of symptoms in daily life and under challenge,for instance voluntary hyperventilation. More than one third of them qualified for panic disorder. They had shorter breath-holding time at rest,less increase in breath-holding time and higher chances of showing a “paradoxical” decrease of breath-holding time after hyperventilation. A combination of PaO2,forced expiratory volume in one second (FEV_1),and anxiety measures distinguished them from organic dyspnea. Breathing retraining profoundly improved their symptoms and decreased the level of state and trait anxiety. Moreover,they better tolerated the voluntary hyperventilation and the symptoms induced were also markedly decreased after therapy. Breath-holding time was prolonged and PetCO2 in a representative group of patients increased. Conclusions Patients with medically unexplained dyspnea appear to have the feature of a “psychosomatic” patient: an anxious patient with a wide variety of symptoms of different organ systems that do not have an organic basis. They can be distinguished from organic dyspnea using a small set of physiological and psychological measures. Breathing retraining turns out to be an effective therapy for those “difficult to treat patients”.