Yandong Jiang

Acute Reversible Stress-Induced Cardiomyopathy Associated with Cesarean Delivery under Spinal Anesthesia

Stress-induced cardiomyopathy (SIC), also known as transient left ventricular apical ballooning or Tako-tsubo cardiomyopathy, is characterized by reversible left ventricular dysfunction, chest pain or dyspnea, ST-segment elevation, and minor elevations in serum levels of cardiac enzymes, in the absence of significant coronary artery disease.1 Although its pathogenesis is incompletely understood, intense emotional or physical stress is a well-recognized precipitant.2 We present a case of SIC with severe left ventricular dysfunction but minimal ECG changes in a young, woman who received spinal anesthesia for elective cesarean delivery. A 31-year-old healthy woman was admitted at 40 weeks gestation for elective repeat cesarean delivery. Both her previous and current pregnancies were uncomplicated. Her first cesarean delivery was performed uneventfully with epidural anesthesia. She had no family history of heart disease and appeared calm on entry into the operating room. Successful spinal anesthesia was achieved …

Nasal ventilation is more effective than combined oral-nasal ventilation during induction of general anesthesia in adult subjects.

Background:The authors hypothesized that nasal mask ventilation may be more effective than combined oral–nasal mask ventilation during induction of general anesthesia. They tested this hypothesis by comparing the volume of carbon dioxide removed per breath with nasal versus combined oral–nasal mask ventilation in nonparalyzed, apneic, adult subjects during induction of general anesthesia. Methods:Fifteen adult subjects receiving general anesthesia were ventilated first with a combined oral–nasal mask and then with only a nasal mask. The patient’s head was maintained in a neutral position, without head extension or lower jaw thrust. Respiratory parameters were recorded simultaneously from both the nasal and oral masks regardless of ventilation approach. Results:The volume of carbon dioxide removed per breath during nasal mask ventilation (median, 5.0 ml; interquartile range, 3.4–8.8 ml) was significantly larger than that during combined oral–nasal mask ventilation (median, 0.0 ml; interquartile range, 0.0–0.4 ml; P = 0.001); even the peak inspiratory airway pressure during nasal ventilation (16.7 ± 2.7 cm H2O) was lower than that during combined oral–nasal ventilation (24.5 ± 4.7 cm H2O; P = 0.002). The expiratory tidal volume during nasal ventilation (259.8 ± 134.2 ml) was also larger than that during combined oral–nasal ventilation (98.9 ± 103.4 ml; P = 0.003). Conclusions:Nasal mask ventilation was more effective than combined oral–nasal mask ventilation in apneic, nonparalyzed, adult subjects during induction of general anesthesia. The authors suggest that nasal mask ventilation, rather than full facemask ventilation, be considered during induction of anesthesia.

Anosmia and hypogeusia as a complication of general anesthesia

A 57 year old woman with no previous history of any sensory deficits developed anosmia and hypogeusia after general anesthesia for laparoscopic cholecystectomy, with complete recovery over 6 months. There were no other identifiable factors that may have contributed to her anosmia and hypogeusia after general anesthesia. As anosmia and hypogeusia related to anesthesia and surgery are not frequently reported, the incidence of these events related to anesthesia may be higher than expected.

Effectiveness of Breathing through Nasal and Oral Routes in Unconscious Apneic Adult Human Subjects: A Prospective Randomized Crossover Trial

Background:The authors hypothesized that mouth ventilation by a resuscitator via the nasal route ensures a more patent airway and more effective ventilation than does ventilation via the oral route and therefore would be the optimal manner to ventilate adult patients in emergencies, such as during cardiopulmonary resuscitation. They tested the hypothesis by comparing the effectiveness of mouth-to-nose breathing (MNB) and mouth-to-mouth breathing (MMB) in anesthetized, apneic, adult subjects without muscle paralysis. Methods:Twenty subjects under general anesthesia randomly received MMB and MNB with their heads placed first in a neutral position and then an extended position. A single operator performed MNB and MMB at the target breathing rate of 10 breaths/min, inspiratory:expiratory ratio 1:2 and peak inspiratory airway pressure 24 cm H2O. A plethysmograph was used to measure the amplitude change during MMB and MNB. The inspiratory and expiratory tidal volumes during MMB and MNB were calculated retrospectively using the calibration curve. Results:All data are presented as medians (interquartile ranges). The rates of effective ventilation (expired volume > estimated anatomic dead space) during MNB and MMB were 91.1% (42.4–100%) and 43.1% (42.5–100%) (P < 0.001), and expired tidal volume with MMB 130.5 ml (44.0–372.8 ml) was significantly lower than with MNB 324.5 ml (140.8–509.0 ml), regardless of the head position (P < 0.001). Conclusions:Direct mouth ventilation delivered exclusively via the nose is significantly more effective than that delivered via the mouth in anesthetized, apneic adult subjects without muscle paralysis. Additional studies are needed to establish whether using this breathing technique during emergency situations will improve patient outcomes.

The principle of upper airway unidirectional flow facilitates breathing in humans

Upper airway unidirectional breathing, nose in and mouth out, is used by panting dogs to facilitate heat removal via water evaporation from the respiratory system. Why some humans instinctively employ the same breathing pattern during respiratory distress is still open to question. We hypothesized that 1) humans unconsciously perform unidirectional breathing because it improves breathing efficiency, 2) such an improvement is achieved by bypassing upper airway dead space, and 3) the magnitude of the improvement is inversely proportional to the tidal volume. Four breathing patterns were performed in random order in 10 healthy volunteers first with normal breathing effort, then with variable tidal volumes: mouth in and mouth out (MMB); nose in and nose out (NNB); nose in and mouth out (NMB); and mouth in and nose out (MNB). We found that unidirectional breathing bypasses anatomical dead space and improves breathing efficiency. At tidal volumes of approximately 380 ml, the functional anatomical dead space during NMB (81 +/- 31 ml) or MNB (101 +/- 20 ml) was significantly lower than that during MMB (148 +/- 15 ml) or NNB (130 +/- 13 ml) (all P < 0.001), and the breathing efficiency obtained with NMB (78 +/- 9%) or MNB (73 +/- 6%) was significantly higher than that with MMB (61 +/- 6%) or NNB (66 +/- 3%) (all P < 0.001). The improvement in breathing efficiency increased as tidal volume decreased. Unidirectional breathing results in a significant reduction in functional anatomical dead space and improvement in breathing efficiency. We suggest this may be the reason that such a breathing pattern is preferred during respiratory distress.

Continuous positive airway pressure and ventilation are more effective with a nasal mask than a full face mask in unconscious subjects: a randomized controlled trial

IntroductionUpper airway obstruction (UAO) is a major problem in unconscious subjects, making full face mask ventilation difficult. The mechanism of UAO in unconscious subjects shares many similarities with that of obstructive sleep apnea (OSA), especially the hypotonic upper airway seen during rapid eye movement sleep. Continuous positive airway pressure (CPAP) via nasal mask is more effective at maintaining airway patency than a full face mask in patients with OSA. We hypothesized that CPAP via nasal mask and ventilation (nCPAP) would be more effective than full face mask CPAP and ventilation (FmCPAP) for unconscious subjects, and we tested our hypothesis during induction of general anesthesia for elective surgery.MethodsIn total, 73 adult subjects requiring general anesthesia were randomly assigned to one of four groups: nCPAP P0, nCPAP P5, FmCPAP P0, and FmCPAP P5, where P0 and P5 represent positive end-expiratory pressure (PEEP) 0 and 5 cm H2O applied prior to induction. After apnea, ventilation was initiated with pressure control ventilation at a peak inspiratory pressure over PEEP (PIP/PEEP) of 20/0, then 20/5, and finally 20/10 cm H2O, each applied for 1 min. At each pressure setting, expired tidal volume (Vte) was calculated by using a plethysmograph device.ResultsThe rate of effective tidal volume (Vte > estimated anatomical dead space) was higher (87.9% vs. 21.9%; P<0.01) and the median Vte was larger (6.9 vs. 0 mL/kg; P<0.01) with nCPAP than with FmCPAP. Application of CPAP prior to induction of general anesthesia did not affect Vte in either approach (nCPAP pre- vs. post-; 7.9 vs. 5.8 mL/kg, P = 0.07) (FmCPAP pre- vs. post-; 0 vs. 0 mL/kg, P = 0.11).ConclusionsnCPAP produced more effective tidal volume than FmCPAP in unconscious subjects.Trial registrationClinicalTrials.gov identifier: NCT01524614.

Continuous non-invasive cardiac output monitoring during exercise: validation of electrical cardiometry with Fick and thermodilution methods

Editor—Cardiopulmonary exercise testing (CPET) is an important diagnostic procedure, and gas exchange variables along with invasive haemodynamic parameters measured during CPET provide diagnostic and prognostic information regarding patients with a variety of cardiopulmonary conditions, such as heart failure and pulmonary hypertension. 2 Measurement of cardiac output (CO) and the corresponding stroke volume in response to different levels of exercise is a critical component of CPET. TheCO during CPET has traditionally beenmeasured by the Fickmethod. Owing to its complexity, thermodilution (TD) is often used as a surrogate. However, TD is as invasive as Fick and requires pulmonary artery catheter placement. Therefore, interest has been great regarding the development of non-invasive techniques for CO measurements. 4 Electrical CardiometryTM (EC) is an advanced formof transthoracic bio-impedance for non-invasive CO measurement. It takes advantage of changes in electrical impedance associated with the change in orientation of red blood cells in the aorta. This technique has been validated against TD in critically ill, 9 preoperative, and paediatric patients. However, comparison of ECwith the Fickmethod across a large range of COs obtained during CPET has not been conducted. The aims of our study were as follows: (i) to compare COs obtained with the Fickmethod (COFick) and EC (COEC; AESCULON®; Cardiotronic, La Jolla, CA, USA) at rest and at 1 min intervals during incremental CPET; and (ii) to compare COs obtainedwith thermodilution (COTD), Fick, and EC before exercise because COTD was not obtainable during excise. We enrolled 47 patients (≥18 yr old) with dyspnoea on exertion who underwent maximal incremental upright cycle ergometry CPET with invasive haemodynamic monitoring (MedGraphics, St Paul, MN, USA). The patients exercised for 7.3 (1.8 ) min, achieving 114.6 (53.7 ) W. During exercise, we found a significant correlation between COFick and COEC (r =0.89, P<0.0001; Fig. 1). Bland–Altman analysis indicated a bias (mean difference) of 0.62 litres min and 95% limit of agreement (1.96×) of 2.77 litres min (Fig. 1). The error per cent (95% limit of agreement/mean CO) was 29.2%. Analysis of COs at rest showed bias and 95% limit of agreement 0.28 and 2.00 litres min between COEC and COFick (Fig. 1), and 0.30 and 2.20 litres min −1 between COTD and COFick (Fig. 1), respectively. The error per cent was 36.8 and 38.8% for COEC and COTD, respectively. In our study, a signal quality index of <50% was chosen as the data exclusion criterion. Using this value as cut-off, 25% (128 of 521) of data points collected during exercise were considered unreliable and excluded. Poor EC signal quality was clustered in 13 (28%) subjects, causing 82% (105 of 128) of poor-quality data points. In 10 of these patients, BMI was ≥30 kg m. An exploratory analysis indicated that morbid obesity was one of the contributing factors to low signal quality. Our results show that EC was able to track the direction of changes in COduring CPET. The precision of COEC vsCOFick during exercisewas within the criteria of acceptability, i.e. error per cent ≤30%. Considering the advantages of EC, including safety, user friendliness, and low cost, it may be clinically advantageous to use EC during CPET. The COEC at rest achieved limits of agreement very close to that of COTD, although the absolute precision of both techniques was out of the 30% limit. The potential cause of poor precision at rest is most likely to be the patients’ co-morbidities; heart failure (n=3), pulmonary hypertension (n=3), and valvular insufficiency (n=10). Previous studies have suggested that the accuracy and precision of TD and Fick methods may be compromised in such conditions. Further studies areneeded to validate the clinical significance of EC in these subgroups of patients.

Efficacy of Superimposed High-frequency Jet Ventilation Applied to Variable Degrees of Tracheal Stenosis One Step Forward to Optimized Patient Care

Anesthesiology, V 123 • No 4 747 October 2015 T he number of procedures requiring high-frequency jet ventilation (hFJV) continually increases, and the advantages of hFJV are well recognized.1,2 The majority of procedures using hFJV are performed in patients with variable degrees of tracheal stenosis. however, a comprehensive study illustrating the efficacy and safety of hFJV for ventilation of patients with tracheal stenosis is not available. Clinicians face two major challenges when using hFJV for such procedures. One is assessment of the adequacy of ventilation and gas exchange because end-tidal carbon dioxide is often not reliable with hFJV. As a result, the adequacy of ventilation must be assessed by intermittent blood gas analysis. Another challenge is the assessment for the development of autopositive end-expiratory pressure (auto-PeeP). Because a large pressure gradient may exist across the obstructed segment of the trachea, it is impossible to monitor auto-PeeP distal to the obstructed segment unless an endexpiratory pause is applied or esophageal pressure is measured. high levels of auto-PeeP often go unnoticed by clinicians until critical complications develop: pneumothorax and circulatory collapse.3–5 Therefore, understanding the dynamic interaction between hFJV settings and the severity of the tracheal stenosis is important. In this issue of AnesthesIOlOgy, sütterlin et al.6 present a systematic evaluation of the interaction of hFJV and the severity of tracheal stenosis. They compared the efficacy of hFJV and superimposed hFJV (shFJV; hFJV along with normal frequency jet ventilation) and measured auto-PeeP distal to the stenosis in an adult human sized pig model. Their novel findings include (1) shFJV produces more effective gas exchange than hFJV alone across a wide spectrum of frequencies; (2) at frequencies above 150 cycles per minute, the efficacy of hFJV alone is minimal; and (3) both hFJV and shFJV generate high auto-PeeP distal to the obstructed segment particularly with severe tracheal stenosis. Their findings are important, clinically relevant, and greatly help clinicians to understand the dynamic interaction between ventilatory settings and the severity of tracheal stenosis. Conventional hFJV is catheter based and the catheter is placed through glottis.7 however, catheter-free hFJV, as used in the study by sütterlin et al.,6 is becoming more common. Instead of a small catheter, catheter-free jet ventilation is provided directly via a cuffed endotracheal tube.8 The mechanism of gas exchange with this technique is not well understood but believed to be as a result of a combination of convection and diffusion.9 Unlike conventional mechanical ventilation, in which convection is the key component for gas exchange, gas exchange with hFJV is a result of gas diffusion and alveolar mixing generated by the small tidal volumes (often smaller than anatomic dead space) and high frequencies (>50 cycles per minute). Convection during hFJV particularly at high frequency (>300 cycles per minute) is reduced. hFJV alone can easily maintain adequate gas exchange in the absence of tracheal stenosis as demonstrated by Babinski et al.7 in patient and sütterlin et al.10 in their animal model. The presence of a stenosis, however, alters gas flow dynamics and Efficacy of Superimposed High-frequency Jet Ventilation Applied to Variable Degrees of Tracheal Stenosis

New insights into the effect of rapid transfusion of fresh frozen plasma on ionized calcium

STUDY OBJECTIVES 1) To develop an in vitro system to simulate the kinetics of ionized calcium in mixed venous blood during rapid transfusion of fresh frozen plasma (FFP) and 2) to use the in vitro data to estimate the effect of the transfusion rate relative to cardiac output (CO) on ionized calcium. DESIGN Experimental study. SETTING Research laboratory of an academic hospital. MEASUREMENTS Citrated FFP was mixed with compatible heparinized whole blood at various volume ratios in vitro to simulate the mixed venous blood obtained at various flow ratios of FFP transfusion to the recipients venous system in vivo. Ionized calcium was measured after each mixture. MAIN RESULTS Mixing FFP and whole blood at volume ratios of 0:100, 5:95, 10:90, and 15:85 yielded ionized calcium levels (mean ± SD, mmol/L) of 1.23, 0.81 ± 0.02, 0.54 ± 0.08, and 0.34 ± 0.02, respectively. The 50% reduction in ionized calcium occurred at a volume ratio of 7:93. CONCLUSIONS An instantaneous 50% reduction in ionized calcium occurs in vitro at a proportion equivalent to a transfusion rate of FFP representing 7% of CO.

Efficacy of ventilation through a customized novel cuffed airway exchange catheter: a tracheal/lung model study

Editor—Airway exchange catheters (AECs) are commonly used in difficult airways management as a guide for re-intubation or ventilation when attached to a jet ventilator. However, barotrauma resulting in pneumothorax has been a major concern when using jet ventilation with AECs. – 4 The cause of these complications is often the excessive driving pressure with jet ventilation (15–50 psi) or airway obstruction. Therefore, it has been suggested that minimizing intratracheal pressure and prolonging expiratory times can reduce the risk of barotrauma. We propose an alternative method of ventilation via an AEC with a customized cuff (Fig. 1). A cuffed AEC was created by placing a 5 cm long latex cuff over the distal side ports of a 14 and 19 Fr AEC (Cook Critical Care, Bloomington, IN, USA) and inserting a 1 cm long internal resistor (14 G i.v. catheter for 14 Fr AEC or 11 Fr Cook AEC for 19 Fr AEC) into the distal tip of each AEC (Fig. 1). Briefly, because the lumen of the cuff freely communicated through the side ports with the lumen of the AEC, the cuff inflated during inspiration due to pressure generated by the resistor and during exhalation, the cuff deflated allowing expiratory flow around the AEC (Fig. 1). We evaluate the efficacy of ventilation through novel cuffed AECs using a tracheal/lung model study. The lung model (Dual adult TTL training/test lung, Model 1600, Michigan Instruments Inc., MI, USA) was connected to the distal end of a tracheal model (Airway demonstration model, Laerdal, Stavanger, Norway). The lung model was adjusted to simulate normal lung mechanics (compliance 50 ml cm H2O , resistance 5 cm H2O litre 21 s).The proximal end wasconnected toan intensive care unit (ICU) ventilator (Puritan BennettTM 840, Covidien, Boulder, CO, USA) set to pressure control with peak pressure 40 or 70 cm H2O. Ventilation was performed at a respiratory rate of 10 bpm with inspiratory:expiratory (I:E) ratios of 1:2, and 1:1. The distal tip of the AEC was placed 3 cm above the carina of the tracheal model. A flow/pressure sensor (NICO Cardiopulmonary Management System, Model 7300, Respironics Corp., Murrysville, PA, USA) was placed between the distal end of the tracheal model and the model lung. With the cuffed AEC, ICU ventilator was able to generate reasonable tidal volume [493 (151) ml with 19 Fr, range: 328– 694 ml and 293 (103) ml with 14 Fr, range: 180–429 ml]. The mean peak inspiratory airway pressure was 11.5 (2.8) cm H2O with 19 Fr (range: 8.4–15.3 cm H2O) and 7.5 (2.2) cm H2O with 14 Fr (range: 5.0–10.4 cm H2O). Our results indicate that cuffed AEC may enable practitioners to use ordinary ICU ventilator and achieve reasonable tidal volume and provide at least partial ventilatory support at much lower driving pressure than with the jet ventilation. The ability to ventilate patients using lower pressure settings may reduce the risk of barotraumas. Because the high resistance generated by the small inner diameter of the AEC, peak inspiratory airway pressure was within a lung protective range. In addition, ICU ventilators are much more commonly available than jet ventilators. Because this study was not conducted on patients, results from our study should be cautiously extrapolated to actual patient care until clinical studies can be conducted.