Acute effects of apnea bouts on hemoglobin concentration and hematocrit: a systematic review and meta-analysis.

Objective: This study aimed to systematically analyze the existing literature and conduct a meta-analysis on the acute effects of apnea on the hematological response by assessing changes in hemoglobin (Hb) concentration and hematocrit (Hct) values. Methods: Searches in Pubmed, The Cochrane Library, and Web of Science were carried out for studies in which the main intervention was voluntary hypoventilation, and Hb and Hct values were measured. Risk of bias and quality assessments were performed. Results: Nine studies with data from 160 participants were included, involving both subjects experienced in breath-hold sports and physically active subjects unrelated to breath-holding activities. The GRADE scale showed a "high" confidence for Hb concentration, with a mean absolute effect of 0.57 g/dL over control interventions. "Moderate" confidence appeared for Hct, where the mean absolute effect was 2.45% higher over control interventions. Hb concentration increased to a greater extent in the apnea group compared to the control group (MD = 0.57 g/dL [95% CI 0.28, 0.86], Z = 3.81, p = 0.0001) as occurred with Hct (MD = 2.45% [95% CI 0.98, 3.93], Z = 3.26, p = 0.001). Conclusions: Apnea bouts lead to a significant increase in the concentration of Hb and Hct with a high and moderate quality of evidence, respectively. Further trials on apnea and its application to different settings are needed.

Selected and shared hematological responses to apnea in elite human free divers and northern elephant seals (Mirounga angustirostris).

Despite elite human free divers achieving incredible feats in competitive free diving, there has yet to be a study that compares consummate divers, (i.e. northern elephant seals) to highly conditioned free divers (i.e., elite competitive free-diving humans). Herein, we compare these two diving models and suggest that hematological traits detected in seals reflect species-specific specializations, while hematological traits shared between the two species are fundamental mammalian characteristics. Arterial blood samples were analyzed in elite human free divers (n = 14) during a single, maximal volitional apnea and in juvenile northern elephant seals (n = 3) during rest-associated apnea. Humans and elephant seals had comparable apnea durations (∼6.5 min) and end-apneic arterial Po2 [humans: 40.4 ± 3.0 mmHg (means ± SE); seals: 27.1 ± 5.9 mmHg; P = 0.2]. Despite similar increases in arterial Pco2 (humans: 33 ± 5%; seals: 16.3 ± 5%; P = 0.2), only humans experienced reductions in pH from baseline (humans: 7.45 ± 0.01; seals: 7.39 ± 0.02) to end apnea (humans: 7.37 ± 0.01; seals: 7.38 ± 0.02; P < 0.0001). Hemoglobin P50 was greater in humans compared to elephant seals (29.9 ± 1.5 and 28.7 ± 0.6 mmHg, respectively; P = 0.046). Elephant seals overall had higher carboxyhemoglobin (COHb) levels (5.9 ± 2.6%) compared to humans (0.8 ± 1.2%; P < 0.0001); however, following apnea, COHb was reduced in seals (baseline: 6.1 ± 0.3%; end apnea: 5.6 ± 0.3%) and was slightly elevated in humans (baseline: 0.7 ± 0.1%; end apnea: 0.9 ± 0.1%; P < 0.0002, both comparisons). Our data indicate that during static apnea, seals have reduced hemoglobin P50, greater pH buffering, and increased COHb levels. The differences in hemoglobin P50 are likely due to the differences in the physiological environment between the two species during apnea, whereas enhanced pH buffering and higher COHb may represent traits selected for in elephant seals.NEW & NOTEWORTHY This study uses similar methods and protocols in elite human free divers and northern elephant seals. Using highly conditioned divers (elite free-diving humans) and highly adapted divers (northern elephant seals), we explored which hematological traits are fundamentally mammalian and which may have been selected for. We found differences in P50, which may be due to different physiological environments between species, while elevated pH buffering and carbon monoxide levels might have been selected for in seals.

Effect of exercise intensity and apnea on splenic contraction and hemoglobin increase in well-trained cross-country skiers.

The human spleen acts as a reservoir for red blood cells, which is mobilized into the systemic circulation during various conditions such as hypoxia and physical exertion. Cross-country (XC) skiers, renowned for their exceptional aerobic capacity, are regularly exposed to high-intensity exercise and local oxygen deficits. We investigated a putative dose-dependent relationship between splenic contraction and concomitant hemoglobin concentration ([Hb]) elevation across four exercise intensities in well-trained XC skiers. Fourteen male XC skiers voluntarily participated in a 2-day protocol, encompassing a serial apnea test and a V ˙ O2max test (day 1), followed by three submaximal exercise intensities on a roller skiing treadmill corresponding to 55, 70, and 85% of V ˙ O2max (day 2). Spleen volume was measured via ultrasonic imaging, and venous blood samples were used to determine [Hb] levels. Baseline spleen volume was similar (266(35) mL) for all conditions (NS). Notably, all conditions induced significant splenic contractions and transient [Hb] elevations. The V ˙ O2max test exhibited the most pronounced splenic contraction (35.8%, p < 0.001) and a [Hb] increase of 8.1%, while the 85% exercise intensity led to 27.1% contraction and the greatest [Hb] increase (8.3%, < 0.001) compared to baseline. The apnea test induced relatively smaller responses (splenic contraction: 20.4%, [Hb] = 3.3%, p < 0.001), akin to the response observed at the 70% exercise intensity (splenic contraction = 23%, [Hb] = 6.4%, p < 0,001) and 55% (splenic contraction = 20.0%, [Hb] = 4.8%, p < 0.001). This study shows a discernible dose-dependent relationship between splenic contraction and [Hb] increase with levels of exercise, effectively distinguishing between submaximal and maximal exercise intensity.

Carbon Dioxide Changes during High-flow Nasal Oxygenation in Apneic Patients: A Single-center Randomized Controlled Noninferiority Trial.

BACKGROUND: Anesthesia studies using high-flow, humidified, heated oxygen delivered via nasal cannulas at flow rates of more than 50 l · min-1 postulated a ventilatory effect because carbon dioxide increased at lower levels as reported earlier. This study investigated the increase of arterial partial pressure of carbon dioxide between different flow rates of 100% oxygen in elective anesthetized and paralyzed surgical adults before intubation. METHODS: After preoxygenation and standardized anesthesia induction with nondepolarizing neuromuscular blockade, all patients received 100% oxygen (via high-flow nasal oxygenation system or circuit of the anesthesia machine), and continuous jaw thrust/laryngoscopy was applied throughout the 15-min period. In this single-center noninferiority trial, 25 patients each, were randomized to five groups: (1) minimal flow: 0.25 l · min-1, endotracheal tube; (2) low flow: 2 l · min-1, continuous jaw thrust; (3) medium flow: 10 l · min-1, continuous jaw thrust; (4) high flow: 70 l · min-1, continuous jaw thrust; and (5) control: 70 l · min-1, continuous laryngoscopy. Immediately after anesthesia induction, the 15-min apnea period started with oxygen delivered according to the randomized flow rate. Serial arterial blood gas analyses were drawn every 2 min. The study was terminated if either oxygen saturation measured by pulse oximetry was less than 92%, transcutaneous carbon dioxide was greater than 100 mmHg, pH was less than 7.1, potassium level was greater than 6 mmol · l-1, or apnea time was 15 min. The primary outcome was the linear rate of mean increase of arterial carbon dioxide during the 15-min apnea period computed from linear regressions. RESULTS: In total, 125 patients completed the study. Noninferiority with a predefined noninferiority margin of 0.3 mmHg · min-1 could be declared for all treatments with the following mean and 95% CI for the mean differences in the linear rate of arterial partial pressure of carbon dioxide with associated P values regarding noninferiority: high flow versus control, -0.0 mmHg · min-1 (-0.3, 0.3 mmHg · min-1, P = 0.030); medium flow versus control, -0.1 mmHg · min-1 (-0.4, 0.2 mmHg · min-1, P = 0.002); low flow versus control, -0.1 mmHg · min-1 (-0.4, 0.2 mmHg · min-1, P = 0.003); and minimal flow versus control, -0.1 mmHg · min-1 (-0.4, 0.2 mmHg · min-1, P = 0.004). CONCLUSIONS: Widely differing flow rates of humidified 100% oxygen during apnea resulted in comparable increases of arterial partial pressure of carbon dioxide, which does not support an additional ventilatory effect of high-flow nasal oxygenation.

Oxygen Reserve Index: Utility as an Early Warning for Desaturation in High-Risk Surgical Patients.

BACKGROUND: Perioperative pulse oximetry hemoglobin saturation (Spo2) measurement is associated with fewer desaturation and hypoxia episodes. However, the sigmoidal nature of oxygen-hemoglobin dissociation limits the accuracy of estimation of the partial pressure of oxygen (Pao2) >80 mm Hg and correspondingly limits the ability to identify when Pao2 >80 mm Hg but falling. We hypothesized that a proxy measurement for oxygen saturation (Oxygen Reserve Index [ORI]) derived from multiwavelength pulse oximetry may allow additional warning time before critical desaturation or hypoxia. To test our hypothesis, we used a Masimo multiwavelength pulse oximeter to compare ORI and Spo2 warning times during apnea in high-risk surgical patients undergoing cardiac surgery. METHODS: This institutional review board-approved prospective study (NCT03021473) enrolled American Society of Anesthesiologists physical status III or IV patients scheduled for elective surgery with planned preinduction arterial catheter placement. In addition to standard monitors, an ORI sensor was placed and patients were monitored with a pulse oximeter displaying the ORI, a nondimensional parameter that ranges from 0 to 1. Patients were then preoxygenated until ORI plateaued. Following induction of anesthesia, mask ventilation with 100% oxygen was performed until neuromuscular blockade was established. Endotracheal intubation was accomplished using videolaryngoscopy to confirm placement. The endotracheal tube was not connected to the breathing circuit, and patients were allowed to be apneic. Ventilation was resumed when Spo2 reached 94%. We defined ORI warning time as the time from when the ORI alarm registered (based on the absolute value and the rate of change) until the Spo2 decreased to 94%. We defined the Spo2 warning time as the time for Spo2 to decrease from 97% to 94%. The added warning time provided by ORI was defined as the difference between ORI warning time and Spo2 warning time. RESULTS: Forty subjects were enrolled. Complete data for analysis were available from 37 patients. The ORI alarm registered before Spo2 decreasing to 97% in all patients. Median (interquartile range [IQR]) ORI warning time was 80.4 seconds (59.7-105.9 seconds). Median (IQR) Spo2 warning time was 29.0 seconds (20.5-41.0 seconds). The added warning time provided by ORI was 48.4 seconds (95% confidence interval [CI], 40.4-62.0 seconds; P < .0001). CONCLUSIONS: In adult high-risk surgical patients, ORI provided clinically relevant added warning time of impending desaturation compared to Spo2. This additional time may allow modification of airway management, earlier calls for help, or assistance from other providers. The potential patient safety impact of such monitoring requires further study.

The Effect of High-Flow Nasal Oxygen on Carbon Dioxide Accumulation in Apneic or Spontaneously Breathing Adults During Airway Surgery: A Randomized-Controlled Trial.

BACKGROUND: High-flow nasal oxygen (HFNO) is an emerging technology that has generated interest in tubeless anesthesia for airway surgery. HFNO has been shown to maintain oxygenation and CO2 clearance in spontaneously breathing patients and is an effective approach to apneic oxygenation. Although it has been suggested that HFNO can enhance CO2 clearance during apnea, this has not been established. The true extent of CO2 accumulation and resulting acidosis using HFNO during prolonged tubeless anesthesia remains undefined. METHODS: In a single-center trial, we randomly assigned 20 adults undergoing microlaryngoscopy to apnea or spontaneous ventilation (SV) using HFNO during 30 minutes of tubeless anesthesia. Serial arterial blood gas analysis was performed during preoxygenation and general anesthesia. The primary outcome was the partial pressure of CO2 (Paco2) after 30 minutes of general anesthesia, with each group compared using a Student t test. RESULTS: Nineteen patients completed the study protocol (9 in the SV group and 10 in the apnea group). The mean (standard deviation [SD]) Paco2 was 89.0 mm Hg (16.5 mm Hg) in the apnea group and 55.2 mm Hg (7.2 mm Hg) in the SV group (difference in means, 33.8; 95% confidence interval [CI], 20.6-47.0) after 30 minutes of general anesthesia (P < .001). The average rate of Paco2 rise during 30 minutes of general anesthesia was 1.8 mm Hg/min (SD = 0.5 mm Hg/min) in the apnea group and 0.8 mm Hg/min (SD = 0.3 mm Hg/min) in the SV group. The mean (SD) pH was 7.11 (0.04) in the apnea group and 7.29 (0.06) in the SV group (P < .001) at 30 minutes. Five (55%) of the apneic patients had a pH <7.10, of which the lowest measurement was 7.057. No significant difference in partial pressure of arterial O2 (Pao2) was observed after 30 minutes of general anesthesia. CONCLUSIONS: CO2 accumulation during apnea was more than double that of SV after 30 minutes of tubeless anesthesia using HFNO. The use of robust measurement confirms that apnea with HFNO is limited by CO2 accumulation and the concomitant severe respiratory acidosis, in contrast to SV. This extends previous knowledge and has implications for the safe application of HFNO during prolonged procedures.

Changes in PUFA and eicosanoid metabolism during/after apnea diving: a prospective single-center study.

Background: The popularity of apneic diving is continually growing. As apnea diving substantially burdens the cardiovascular system, special focus is warranted. Regarding inflammation processes and associated inflammatory-related diseases (e.g., cardiovascular diseases), eicosanoids play an important role. This study aims to investigate polyunsaturated fatty acids (PUFAs) and eicosanoids in voluntary apnea divers, and so to further improve understanding of pathophysiological processes focusing on proinflammatory effects of temporarily hypercapnic hypoxia.. Methods: The concentration of PUFAs and eicosanoids were investigated in EDTA plasma in apnea divers (n=10) before and immediately after apnea, 0.5 hour and four hours later, applying liquid chromatography-tandem mass spectrometry (LC-MS/MS). Results: Mean age was 41±10 years, and divers performed a mean breath-hold time of 317±111 seconds. PUFAs, eicosanoids and related lipids could be classified in four different kinetical reaction groups following apnea. The first group (e.g., Ω-6 and Ω-3-PUFAs) showed an immediate concentration increase followed by a decrease below baseline four hours after apnea. The second group (e.g., thromboxane B2) showed a slower increase, with its maximum concentration 0.5 hour post-apnea followed by a decrease four hours post-apnea. Group 3 (9- and 13-hydroxyoctadecadienoic acid) is characterized by two concentration increase peaks directly after apnea and four hours afterward compared to baseline. Group 4 (e.g., prostaglandin D2) shows no clear response. Conclusion: Changes in the PUFA metabolism after even a single apnea revealed different kinetics of pro- and anti-inflammatory regulations and changes for oxidative stress levels. Due to the importance of these mediators, apnea diving should be evaluated carefully and be performed only with great caution against the background of cardiovascular diseases and inflammation processes.

Influence of prevention of caffeine citrate on cytokine profile and bronchopulmonary dysplasia in preterm infants with apnea.

BACKGROUND: This study aims to investigate the preventive effects of caffeine citrate on cytokine profile and bronchopulmonary dysplasia (BPD) in preterm infants with apnea. METHODS: Preterm infants with apnea who were born at less than 32 weeks of gestational age and birth weight ≤1500 g were randomly divided into caffeine citrate prevention group and caffeine citrate treatment group. Preterm infants in caffeine citrate prevention group who were at risk of developing recurrent apnea were given to caffeine citrate within 8 h after birth. Those in caffeine citrate treatment group experienced apnea after birth were given to caffeine citrate for treatment. Preterm infants in both groups were treated with the same respiratory management and other conventional therapy. After drug discontinuation, levels of cytokine profile, and incidence of BPD were compared between two groups. RESULTS: A total of 56 preterm infants were enrolled. Differences in gestational age (P=0.11) and birth weight (P=0.251) were not statistically significant. Differences in application time of caffeine citrate (P=0.356), hour of ventilator use (P=0.152), length of stay (P=0.416) and BPD morbidity (P=1.00) between two groups were not statistically significant. At birth, there were no statistically significant in levels of IL-6 (P=0.063) and IL-8 (P=0.125) between two groups. After conventional therapy, levels of IL-6 (P=0.001) and IL-8 (P=0.001) significantly decreased in caffeine citrate prevention group compared with those in caffeine citrate treatment group. CONCLUSIONS: Prevention usage of caffeine citrate in preterm infants with apnea could reduce the level of cytokine profile and the incidence of BPD.

High-Flow Nasal Oxygen Improves Safe Apnea Time in Morbidly Obese Patients Undergoing General Anesthesia: A Randomized Controlled Trial.

BACKGROUND: Morbidly obese patients undergoing general anesthesia are at risk of hypoxemia during anesthesia induction. High-flow nasal oxygenation use during anesthesia induction prolongs safe apnea time in nonobese surgical patients. The primary objective of our study was to compare safe apnea time, between patients given high-flow nasal oxygenation or conventional facemask oxygenation during anesthesia induction, in morbidly obese surgical patients. METHODS: Research ethics board approval was obtained. Elective surgical patients ≥18 years with body mass index ≥40 kg·m were included. Patients with severe comorbidity, gastric reflux disease, known difficult airway, or nasal obstruction were excluded. After obtaining informed consent patients were randomized. In the intervention (high-flow nasal oxygenation) group, preoxygenation was provided by 100% nasal oxygen for 3 minutes at 40 L·minute; in the control group, preoxygenation was delivered using a facemask with 100% oxygen, targeting end-tidal O2 >85%. Anesthesia was induced with propofol, remifentanil, and rocuronium. Bag-mask ventilation was not performed. At 2 minutes after rocuronium, videolaryngoscopy was performed. If the laryngoscopy grade was I or II, laryngoscope was left in place and the study was continued; if grade III or IV was observed, the patient was excluded from the study. During the apnea period, high-flow nasal oxygenation patients received nasal oxygen at 60 L·minute; control group patients received no supplemental oxygen. The primary outcome, safe apnea time, was reached when oxygen saturation measured by pulse oximetry (SpO2) fell to 95% or maximum 6 minutes of apnea. The patient was then intubated. T tests and χ analyses were used to compare groups. P < .05 was considered significant. RESULTS: Forty patients completed the study. Baseline parameters were comparable between groups. Safe apnea time was significantly longer (261.4 ± 77.7 vs 185.5 ± 52.9 seconds; mean difference [95% CI], 75.9 [33.3-118.5]; P = .001) and the minimum peri-intubation SpO2 was higher (91.0 ± 3.5 vs 88.0 ± 4.8; mean difference [95% CI], 3.1 [0.4-5.7]; P = .026) in the high-flow nasal oxygenation group compared to the control group. CONCLUSIONS: High-flow nasal oxygenation, compared to conventional oxygenation, provided a longer safe apnea time by 76 seconds (40%) and higher minimum SpO2 in morbidly obese patients during anesthesia induction. High-flow oxygenation use should be considered in morbidly obese surgical patients.

Erythropoietic responses to a series of repeated maximal dynamic and static apnoeas in elite and non-breath-hold divers.

PURPOSE: Serum erythropoietin (EPO) concentration is increased following static apnoea-induced hypoxia. However, the acute erythropoietic responses to a series of dynamic apnoeas in non-divers (ND) or elite breath-hold divers (EBHD) are unknown. METHODS: Participants were stratified into EBHD (n = 8), ND (n = 10) and control (n = 8) groups. On two separate occasions, EBHD and ND performed a series of five maximal dynamic apnoeas (DYN) or two sets of five maximal static apnoeas (STA). Control performed a static eupnoeic (STE) protocol to control against any effects of water immersion and diurnal variation on EPO. Peripheral oxygen saturation (SpO2) levels were monitored up to 30 s post each maximal effort. Blood samples were collected at 30, 90, and 180 min after each protocol for EPO, haemoglobin and haematocrit concentrations. RESULTS: No between group differences were observed at baseline (p > 0.05). For EBHD and ND, mean end-apnoea SpO2 was lower in DYN (EBHD, 62 ± 10%, p = 0.024; ND, 85 ± 6%; p = 0.020) than STA (EBHD, 76 ± 7%; ND, 96 ± 1%) and control (98 ± 1%) protocols. EBHD attained lower end-apnoeic SpO2 during DYN and STA than ND (p < 0.001). Serum EPO increased from baseline following the DYN protocol in EBHD only (EBHD, p < 0.001; ND, p = 0.622). EBHD EPO increased from baseline (6.85 ± 0.9mlU/mL) by 60% at 30 min (10.82 ± 2.5mlU/mL, p = 0.017) and 63% at 180 min (10.87 ± 2.1mlU/mL, p = 0.024). Serum EPO did not change after the STA (EBHD, p = 0.534; ND, p = 0.850) and STE (p = 0.056) protocols. There was a significant negative correlation (r = - 0.49, p = 0.003) between end-apnoeic SpO2 and peak post-apnoeic serum EPO concentrations. CONCLUSIONS: The novel findings demonstrate that circulating EPO is only increased after DYN in EBHD. This may relate to the greater hypoxemia achieved by EBHD during the DYN.

Severity of Desaturations Reflects OSA-Related Daytime Sleepiness Better Than AHI.

STUDY OBJECTIVES: The aim was to investigate how the severity of apneas, hypopneas, and related desaturations is associated with obstructive sleep apnea (OSA)-related daytime sleepiness. METHODS: Multiple Sleep Latency Tests and polysomnographic recordings of 362 patients with OSA were retrospectively analyzed and novel diagnostic parameters (eg, obstruction severity and desaturation severity), incorporating severity of apneas, hypopneas, and desaturations, were computed. Conventional statistical analysis and multivariate analyses were utilized to investigate connection of apnea-hypopnea index (AHI), oxygen desaturation index (ODI), conventional hypoxemia parameters, and novel diagnostic parameters with mean daytime sleep latency (MSL). RESULTS: In the whole population, 10% increase in values of desaturation severity (risk ratio = 2.01, P < .001), obstruction severity (risk ratio = 2.18, P < .001) and time below 90% saturation (t90%) (risk ratio = 2.05, P < .001) induced significantly higher risk of having mean daytime sleep latency ≤ 5 minutes compared to 10% increase in AHI (risk ratio = 1.63, P < .05). In severe OSA, desaturation severity had significantly (P < .02) stronger negative correlation (ρ = -.489, P < .001) with mean daytime sleep latency compared to AHI (ρ = -.402, P < 0.001) and ODI (ρ = -.393, P < .001). Based on general regression model, desaturation severity and male sex were the most significant factors predicting daytime sleep latency. CONCLUSIONS: Severity of sleep-related breathing cessations and desaturations is a stronger contributor to daytime sleepiness than AHI or ODI and therefore should be included in the diagnostics and severity assessment of OSA. CITATION: Kainulainen S, Töyräs J, Oksenberg A, Korkalainen H, Sefa S, Kulkas A, Leppänen T. Severity of desaturations reflects OSA-related daytime sleepiness better than AHI. J Clin Sleep Med. 2019;15(8):1135-1142.

Apneic Oxygenation During Prolonged Laryngoscopy in Obese Patients: a Randomized, Double-Blinded, Controlled Trial of Nasal Cannula Oxygen Administration.

BACKGROUND: Obese patients have a propensity to desaturate during induction of general anesthesia secondary to their reduced functional residual capacity and increased oxygen consumption. Apneic oxygenation can provide supplemental oxygen to the alveoli, even in the absence of ventilation, during attempts to secure the airway. In this study, we hypothesized that oxygen administration through a nasopharyngeal airway and standard nasal cannula during a simulated prolonged laryngoscopy would significantly prolong the safe apneic duration in obese patients. METHODS: One hundred thirty-five obese patients undergoing non-emergent surgery requiring general anesthesia were randomized to either the control group or to receive apneic oxygenation with air versus oxygen. All patients underwent a standard intravenous induction. For patients randomized to receive apneic oxygenation, a nasopharyngeal airway and standard nasal cannula were inserted. A simulated prolonged laryngoscopy was performed to determine the duration of the safe apneic period, defined as the beginning of laryngoscopy until the peripheral oxygen saturation (SpO2) reached 95%. RESULTS: The oxygen group had a median safe apneic duration that was 103 s longer than the control group. The lowest mean SpO2 value during the induction period was 3.8% higher in the oxygen group compared to the control group. Following intubation, patients in the oxygen group had a mean end tidal carbon dioxide (ETCO2) level that was 3.0 mmHg higher than patients in the control group. CONCLUSIONS: In obese patients, oxygen insufflation at 15 L/min through a nasopharyngeal airway and standard nasal cannula can significantly increase the safe apneic duration during induction of anesthesia.

Physiological stress markers during breath-hold diving and SCUBA diving.

This study investigated the sources of physiological stress in diving by comparing SCUBA dives (stressors: hydrostatic pressure, cold, and hyperoxia), apneic dives (hydrostatic pressure, cold, physical activity, hypoxia), and dry static apnea (hypoxia only). We hypothesized that despite the hypoxia induces by a long static apnea, it would be less stressful than SCUBA dive or apneic dives since the latter combined high pressure, physical activity, and cold exposure. Blood samples were collected from 12SCUBA and 12 apnea divers before and after dives. On a different occasion, samples were collected from the apneic group before and after a maximal static dry apnea. We measured changes in levels of the stress hormones cortisol and copeptin in each situation. To identify localized effects of the stress, we measured levels of the cardiac injury markers troponin (cTnI) and brain natriuretic peptide (BNP), the muscular stress markers myoglobin and lactate), and the hypoxemia marker ischemia-modified albumin (IMA). Copeptin, cortisol, and IMA levels increased for the apneic dive and the static dry apnea, whereas they decreased for the SCUBA dive. Troponin, BNP, and myoglobin levels increased for the apneic dive, but were unchanged for the SCUBA dive and the static dry apnea. We conclude that hypoxia induced by apnea is the dominant trigger for the release of stress hormones and cardiac injury markers, whereas cold or and hyperbaric exposures play a minor role. These results indicate that subjects should be screened carefully for pre-existing cardiac diseases before undertaking significant apneic maneuvers.

Use of Venous Pco2 in Determination of Death by Neurological Criteria in Children.

BACKGROUND: Compare the increase in partial pressure of carbon dioxide (Pco2) from venous blood samples with that of arterial blood samples during apnea challenge test in determination of death by neurological criteria. METHODS: Prospective nonrandomized cohort study in tertiary care pediatric intensive care unit. Patients older than 37 week's gestation admitted to PICU with irreversible brain injury at the time when attending physician will perform apnea challenge test as part of brain death examination from October 2015 till September 2017. INTERVENTIONS: None. RESULTS: The primary outcome was to measure and compare the increase in Pco2 from venous blood samples with that from arterial blood samples during apnea challenge test. A total of nine apnea challenge tests from seven patients (ages five months to 17 years) were included in the study. Pco2 in venous blood sample increased less than that in arterial blood samples (venous, 26.1 mm Hg; S.D., 10.1; 95% confidence interval, 18 to 34 mm Hg; arterial, 33.9 mm Hg; S.D., 12.0; 95% confidence interval, 24 to 43 mm Hg) (P = 0.02). CONCLUSION: Postapnea challenge test Pco2 of 60 mm Hg along with increase of 20 mm Hg in venous blood sample correlated to Pco2 greater than 60 mm Hg along with increase of greater than 20 mm Hg in arterial blood sample. Further studies are warranted to assess if current recommendations for determination of death by neurological criteria in children can be modified to allow for use of venous blood samples as an alternate to arterial blood samples.

Factors affecting the efficacy and safety of aminophylline in treatment of apnea of prematurity in neonatal intensive care unit.

BACKGROUND: The factors affecting the safety and efficacy of aminophylline use in the treatment of apnea of prematurity (AOP) in the neonatal intensive care unit (NICU) are not clear. In this study, we aimed to evaluate the potential factors affecting the efficacy and safety of aminophylline in AOP treatment at standard doses and to determine appropriate patients for this therapy. METHODS: Over a 3-year period (January 2012 to December 2014), the medical records of 206 preterm infants with apnea who were admitted to the NICU of our hospital to receive aminophylline infusions were retrospectively reviewed. These infants were subjected to routine theophylline monitoring by reversed-phase high performance liquid chromatography. The primary outcome measures were the efficacy of aminophylline treatment and adverse reactions observed upon administration. RESULTS: One-hundred and twenty-seven (61.65%) infants were considered to have undergone effective therapy and classified accordingly. Gestational age, body weight at the initiation of aminophylline, and serum theophylline concentration were identified as protective factors of therapeutic efficacy. Receiver operating characteristic (ROC) analysis indicated cutoff values of 30.36 weeks for gestational age and 1.69 kg for body weight at initiation of aminophylline administration for ensuring high efficacy of aminophylline for AOP. Fifty-three (25.73%) infants had adverse reactions. Birth weight and serum concentration of theophylline were associated with an increased risk of adverse reactions, with odds ratios of 0.167 and 1.346, respectively. The ROC curves indicated a birth weight cutoff value of 1.48 kg. CONCLUSION: Infants with apnea and gestational age >30.36 weeks, body weight at initiation of aminophylline treatment above 1.69 kg, and birth weight >1.48 kg are suitable for treatment with aminophylline. Monitoring of serum theophylline concentration should be implemented in the absence of clinical response or in case of suspected adverse reactions.

Prolonged neuromuscular block associated with cholinesterase deficiency.

RATIONALE: Hereditary genetic mutations may cause congenital cholinesterase deficiency. When succinylcholine and mivacurium are applied on cholinesterase-deficient patients during general anesthesia, prolonged postoperative asphyxia occurs, which is an uncommon but very serious complication. PATIENT CONCERNS: A previously healthy 30-year-old female presented prolonged spontaneous breathing recovery after general anesthesia. DIAGNOSES: After the patient's postoperative spontaneous breathing recovery delayed, the plasma cholinesterase was found to be 27 U/L, which was far below the normal level (4000 U/L to 13500 U/L). This patient had no disease that can cause plasma cholinesterase deficiency and was therefore diagnosed as congenital cholinesterase deficiency. INTERVENTIONS AND OUTCOMES: The patient was sent to the intensive care unit (ICU) intubated for mechanical ventilator support, and on the next day the tracheal tube was removed without any complications when her spontaneous respiration resumed. LESSONS: Cholinesterase is an enzyme secreted by the liver involved in many physiological processes in human body. Plasma cholinesterase commonly contains acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). When succinylcholine and mivacurium are applied on patients with cholinesterase-deficiency during general anesthesia, prolonged postoperative asphyxia occurs, which is an uncommon but very serious complication. Lately, new evidences have suggested that hereditary genetic mutations may be responsible for congenital cholinesterase deficiency.

Comparison of plasma propofol concentration for apnea, response to mechanical ventilation, and airway device between endotracheal tube and supraglottic airway device in Beagles.

The relationships between propofol plasma concentrations and the pharmacodynamic endpoints may differ according to a type of airway device. To clarify these relationships in different airway devices would be useful to avoid the complication such as apnea and intraoperative awareness. The aim of this study was to investigate the influence of difference of airway device on propofol requirement during maintenance of anesthesia in dogs. We compared the influence of airway devices on the plasma propofol concentrations for apnea, response to mechanical ventilation, and response to airway device between endotracheal tube (ETT) and supraglottic airway device (SGAD) in Beagles. The pharmacodynamic effects were repeatedly assessed at varying propofol concentrations. The plasma concentrations (mean ± SD) of propofol in the ETT and SGAD groups were 10.2 ± 1.8 and 10.9 ± 2.4 µg/ml for apnea (P=0.438), 7.9 ± 1.2 and 7.4 ± 1.5 µg/ml for response to mechanical ventilation (P=0.268), and 5.2 ± 0.7 and 5.4 ± 1.5 µg/ml for response to airway device (P=0.580), respectively. Required propofol concentration during maintenance of anesthesia may be similar between ETT and SGAD. Without moderate to strong stimuli such as airway device insertion or painful stimulation during surgery, the type of airway device may have little impact on required propofol concentration during maintenance of anesthesia in dogs.

Cardiovascular magnetic resonance assessment of acute cardiovascular effects of voluntary apnoea in elite divers.

BACKGROUND: Prolonged breath holding results in hypoxemia and hypercapnia. Compensatory mechanisms help maintain adequate oxygen supply to hypoxia sensitive organs, but burden the cardiovascular system. The aim was to investigate human compensatory mechanisms and their effects on the cardiovascular system with regard to cardiac function and morphology, blood flow redistribution, serum biomarkers of the adrenergic system and myocardial injury markers following prolonged apnoea. METHODS: Seventeen elite apnoea divers performed maximal breath-hold during cardiovascular magnetic resonance imaging (CMR). Two breath-hold sessions were performed to assess (1) cardiac function, myocardial tissue properties and (2) blood flow. In between CMR sessions, a head MRI was performed for the assessment of signs of silent brain ischemia. Urine and blood samples were analysed prior to and up to 4 h after the first breath-hold. RESULTS: Mean breath-hold time was 297 ± 52 s. Left ventricular (LV) end-systolic, end-diastolic, and stroke volume increased significantly (p < 0.05). Peripheral oxygen saturation, LV ejection fraction, LV fractional shortening, and heart rate decreased significantly (p < 0.05). Blood distribution was diverted to cerebral regions with no significant changes in the descending aorta. Catecholamine levels, high-sensitivity cardiac troponin, and NT-pro-BNP levels increased significantly, but did not reach pathological levels. CONCLUSION: Compensatory effects of prolonged apnoea substantially burden the cardiovascular system. CMR tissue characterisation did not reveal acute myocardial injury, indicating that the resulting cardiovascular stress does not exceed compensatory physiological limits in healthy subjects. However, these compensatory mechanisms could overly tax those limits in subjects with pre-existing cardiac disease. For divers interested in competetive apnoea diving, a comprehensive medical exam with a special focus on the cardiovascular system may be warranted. TRIAL REGISTRATION: This prospective single-centre study was approved by the institutional ethics committee review board. It was retrospectively registered under ClinicalTrials.gov (Trial registration: NCT02280226 . Registered 29 October 2014).