Hyperventilation Group Research Articles

Small tidal volume hyperventilation relieves intraocular and intracranial pressure elevation in prone spinal surgery: a randomized controlled trial

To investigate the effects of different ventilation strategies on intraocular pressure (IOP) and intracranial pressure in patients undergoing spinal surgery in the prone position under general anesthesia. Seventy-two patients undergoing prone spinal surgery under general anesthesia between November, 2022 and June, 2023 were equally randomized into two groups to receive routine ventilation (with Vt of 8mL/kg, Fr of 12-15/min, and etCO2 maintained at 35-40 mmHg) or small tidal volume hyperventilation (Vt of 6 mL/kg, Fr of18-20/min, and etCO2 maintained at 30-35 mmHg) during the surgery. IOP of both eyes (measured with a handheld tonometer), optic nerve sheath diameter (ONSD; measured at 3 mm behind the eyeball with bedside real-time ultrasound), circulatory and respiratory parameters of the patients were recorded before anesthesia (T0), immediately after anesthesia induction (T1), immediately after prone positioning (T2), at 2 h during operation (T3), immediately after supine positioning after surgery (T4) and 30 min after the operation (T5). Compared with those at T1, IOP and ONSD in both groups increased significantly at T3 and T4(P < 0.05). IOP was significantly lower in hyperventilation group than in routine ventilation group at T3 and T4(P < 0.05), and ONSD was significantly lower in hyperventilation group at T4(P < 0.05). IOP was positively correlated with the length of operative time (r=0.779, P < 0.001) and inversely with intraoperative etCO2 at T3(r=-0.248, P < 0.001) and T4(r=-0.251, P < 0.001).ONSD was correlated only with operation time (r=0.561, P < 0.05) and not with IOP (r=0.178, P>0.05 at T3; r=0.165, P>0.05 at T4). Small tidal volume hyperventilation can relieve the increase of IOP and ONSD during prone spinal surgery under general anesthesia.

A decrease in plant gain, namely CO2 stores, characterizes dysfunctional breathing whatever its subtype in children.

Background: Whether dysfunctional breathing (DB) subtype classification is useful remains undetermined. The hyperventilation provocation test (HVPT) is used to diagnose DB. This test begins with a 3-min phase of hyperventilation during which fractional end-tidal CO2 (FETCO2) decreases that could be an assessment of plant gain, which relies on CO2 stores. Our aim was to assess 1) whether the children suffering from different subtypes of DB exhibit decreased plant gain and 2) the relationships between HVPT characteristics and plant gain. Methods: We retrospectively selected 48 children (median age 13.5years, 36 females, 12 males) who exhibited during a cardiopulmonary exercise test either alveolar hyperventilation (transcutaneous PCO2 < 30mmHg, n = 6) or inappropriate hyperventilation (increased VE'/V'CO2 slope) without hypocapnia (n = 18) or dyspnea without hyperventilation (n = 18) compared to children exhibiting physiological breathlessness (dyspnea for sports only, n = 6). These children underwent tidal-breathing recording (ventilation and FETCO2 allowing the calculation of plant gain) and a HVPT. Results: The plant gain was significantly higher in the physiological group as compared to the dyspnea without hyperventilation group, p = 0.024 and hyperventilation without hypocapnia group, p = 0.008 (trend for the hyperventilation with hypocapnia group, p = 0.078). The slope of linear decrease in FETCO2 during hyperventilation was significantly more negative in physiological breathlessness group as compared to hyperventilation without hypocapnia group (p = 0.005) and dyspnea without hyperventilation group (p = 0.049). Conclusion: The children with DB, regardless of their subtype, deplete their CO2 stores (decreased plant gain), which may be due to intermittent alveolar hyperventilation, suggesting the futility of our subtype classification.

The effect of hyperventilation versus normoventilation on cerebral oxygenation using near infrared spectroscopy in children undergoing posterior fossa tumor resection: A randomized controlled cross-over trial

BackgroundThis study aims to compare the effect of two different ventilation strategies on cerebral oxygenation in children undergoing posterior fossa tumor excision surgeries. MethodsChildren scheduled for posterior fossa tumor surgeries were enrolled in this randomized, double-blinded, controlled cross-over trial. After induction of general anesthesia and positioning, participants were randomized to have mild hyperventilation for 30 min (phase 1) followed by normal ventilation for another 30 min (phase2) (early hyperventilation group, n = 23), or normal ventilation for 30 min (phase 1) followed by hyperventilation for 30 min (phase 2) (early normoventilation group, n = 19). Our primary outcome was cerebral oxygenation, measured using near-infrared spectroscopy (NIRS). Other outcomes included the intracranial pressure (ICP), brain relaxation score at the end of phase 1, and frequency of nadir NIRS. ResultsForty-two children were available for final per protocol analysis. The cerebral oxygenation decreased after the hyperventilation phase compared to the baseline values and the corresponding phases of normoventilation. The mean difference [95% confidence intervals (CI)] in cerebral oxygen saturation between the hyperventilation and normal ventilation readings was 13.45 ± 1.14% [11.14–15.76] and 11.47 ± 0.96% [11.14–15.76] in the left and right sides, respectively (p-values <0.0001). Both carryover and period effects were not significant. The ICP at the end of phase 1 did not differ between the two groups: 22.12 ± 3.75 mmHg vs. 23.26 ± 4.33, mean difference [95%CI]: −0.78 [−3.05 to 1.5], p = 0.49. Brain relaxation score was similar in the two groups. ConclusionIn children undergoing posterior fossa craniotomy, moderate hyperventilation reduced cerebral oxygenation without significant improvement of the surgical brain relaxation or the ICP.

Use of intraoperative mild hyperventilation to decrease the incidence of postoperative shoulder pain after laparoscopic gastric sleeve surgery: A prospective randomised controlled study.

Background and Aims:Post-laparoscopic shoulder pain (PLSP) is a common problem. It is a referred type of pain resulting from irritation of phrenic nerve endings. Multiple manoeuvres were used to decrease its incidence with varying success rates. In this study, we tested the use of mild intraoperative hyperventilation to reduce PLSP in patients undergoing laparoscopic sleeve gastrectomy surgery (LSG).Methods:Consenting American Society of Anesthesiologists-I and II patients undergoing LSG under general anaesthesia were randomly assigned to two groups. Group A (53 patients) received intraoperative mild hyperventilation with target end-tidal carbon dioxide (ETCO2) of 30–32 mmHg. Group B (51 patients) received conventional ventilation (ETCO2 of 35–40 mmHg). Incidence and severity of PLSP, cumulative analgesic requirements and incidence of nausea and vomiting were recorded at 12 and 24 hours postoperatively and then followed up after discharge over the phone at 48 hours, 1 week, 1 month and 3 months. Statistical significance of differences between the two groups was defined at P < 0.05.Results:Incidence of PLSP was comparable between the two groups in the first 24 hours. The intervention group had a significantly lower incidence of PLSP throughout the remaining assessment points (56.6% vs. 80.4%, 30.2% vs. 78.4%, 15.1% vs. 70.6%, 3.8% vs. 35.3% at 36 hours, 48 hours, 1 week and 1 month, respectively, P < 0.05). The average PLSP pain score was significantly lower in the mild hyperventilation group at all assessment time points. Nausea and vomiting were non-significantly lower in the mild hyperventilation group.Conclusion:Mild intraoperative hyperventilation could be beneficial in reducing the incidence and severity of PLSP after LSG surgery.

Artificial hyperventilation normalizes haemodynamics and arterial oxygen content in hypoxic rats.

Although humans are capable of enduring critically low levels of oxygen, many hypoxaemic patients die despite aggressive therapies. Mimicking the physiological hyperventilation necessary to survive extreme hypoxic conditions could minimize the derangements caused by acute hypoxic-hypoxia. The objective of this study was to measure the haemodynamic-biochemical response to artificially induced hyperventilation in hypoxic rats. Twenty-four deeply anaesthetized and mechanically ventilated rats were allocated to 3 groups: control (n = 5, FiO2 = 1); hypoxic spontaneously hyperventilating (n = 10, FiO2 = 0.08); and hypoxic artificially induced hyperventilation (n = 9, targeting PaCO2 = 10 mm Hg, FiO2 = 0.08). We compared the spontaneously and artificially hyperventilating groups. P-values < 0.01 were considered statistically significant. Mean arterial pressure (MAP) and serum chemistry were measured for 180 minutes. The control group remained stable throughout the experiment. The hypoxic groups developed profound hypotension after the decrease in FiO2. However, the artificially induced hyperventilated rats recovered their MAP to levels higher than the spontaneously hyperventilating group (117.1 ± 17.2 vs. 68.1 ± 16.0, P = 0.0048). In regard to the biochemical derangements, even though the serum lactate and PaO2 were not different among the hypoxic groups, the artificially hyperventilated group achieved significantly higher SaO2 (94.3 ± 3.6 vs. 58.6 ± 9.6, P = 0.005), pH (7.87 ± 0.04 vs. 7.50 ± 0.13, P = 0.005), and CaO2 (17.7 ± 2.6 vs. 10.2 ± 1.3, P = 0.005) at 180 minutes. Artificially induced hyperventilation led to the correction of arterial oxygen content, severe serum chemistry, and haemodynamic derangements. These findings may represent anovel rescue manoeuvre and serve as abridge to apermanent form of support, but should be further studied before being translated to the clinical setting.

Absence seizure provocation during routine EEG: Does position of the child during hyperventilation affect the diagnostic yield?

PurposeWhen performed correctly, hyperventilation (HV) for three minutes provokes absence seizures in virtually all children, a finding suggestive of a diagnosis of childhood absence epilepsy (CAE). Interestingly, some children experience absence seizures while performing HV in the office yet do not experience absences during HV on subsequent routine EEG. In most instances, HV during routine EEG is performed in the supine position, while in the office HV is done with the child sitting-up. Therefore, we hypothesized that the position in which HV is performed may influence its yield in provoking absence seizures. MethodsWe conducted a randomized multi-center controlled trial among children (4-10 years old) with suspected CAE. During a routine EEG, children were asked to perform HV twice, in the supine and sitting positions. ResultsTwenty children (four males) diagnosed with CAE were included in the analysis. Seventeen of the 20 patients experienced absence seizures while sitting and 13 experienced seizures during supine HV (p = 0.031). All patients that had absence seizures during supine HV also had seizures during sitting HV. Among patients with absences in both positions, seizure duration was significantly shorter during sitting HV (mean 8.69 seconds) than during supine HV (mean 12 seconds) (p = 0.042).An opposite tendency was seen in the younger age group (4-7 years), with shorter seizures in the supine HV group (5.6 seconds supine, 7.57 seconds sitting, p = 0.019). ConclusionsHV in the sitting position may increase the yield of provoking absence seizures during routine EEGs, thereby improving its sensitivity in the diagnosis of CAE.

Arabization of Nijmegen questionnaire and study of the prevalence of hyperventilation in dizzy patients

Objectives: To develop and adapt the Arabic version of Nijmegen questionnaire (NQ) for assessment of hyperventilation and to determine the prevalence of hyperventilation in dizzy patients.Methods: The adapted NQ was translated following cross-cultural adaptation guidelines which includes forward and backward translation, Expert committee review, pretesting and final version of NQ. The adapted Arabic NQ was completed by 100 normal controls (control group) and 50 patients with hyperventilation symptoms (hyperventilation group) then the Arabic NQ was administered to 100 dizzy patients (dizzy group). Patients with disturbed consciousness and severe mental health disorders were excluded. Validity and reliability of the questionnaire were examined. Reliability included internal consistency and test–retest reliability. The validation of the questionnaire including content and construct validity was performed. Receiver operating characteristic (ROC) curve was used to determine the possible cutoff points. The prevalence of hyperventilation in dizzy patients was determined.Results: The Arabic NQ showed good internal consistency (Cronbach’s alpha = 0.819 for controls and Cronbach’s alpha = 0.920 for hyperventilation group). Test-retest correlation for repeatability was high (r = 0.987 among controls, and r = 0.927 among cases). Construct validity showed high negative correlations between the total score of the questionnaire and the partial pressure of carbon dioxide (PCO2) outcome (r = –0.916, p < .001). Twenty-eight percent of patients in the dizzy group give positive NQ score.Conclusion: This study showed that the adapted Arabic version of NQ is a valid and reliable questionnaire for the assessment of hyperventilation in Egyptian adults and the most sensitive cutoff point for diagnosing hyperventilation was (26.5). The prevalence of hyperventilation in dizzy patients was 28%.

Postural Hyperventilation as a Cause of Postural Tachycardia Syndrome: Increased Systemic Vascular Resistance and Decreased Cardiac Output When Upright in All Postural Tachycardia Syndrome Variants.

BackgroundPostural tachycardia syndrome (POTS) is a heterogeneous condition. We stratified patients previously evaluated for POTS on the basis of supine resting cardiac output (CO) or with the complaint of platypnea or “shortness of breath” during orthostasis. We hypothesize that postural hyperventilation is one cause of POTS and that hyperventilation‐associated POTS occurs when initial reduction in CO is sufficiently large. We also propose that circulatory abnormalities normalize with restoration of CO 2.Methods and ResultsFifty‐eight enrollees with POTS were compared with 16 healthy volunteer controls. Low CO in POTS was defined by a resting supine CO <4 L/min. Patients with shortness of breath had hyperventilation with end tidal CO 2 <30 Torr during head‐up tilt table testing. There were no differences in height or weight between control patients and patients with POTS or differences between the POTS groups. Beat‐to‐beat blood pressure was measured by photoplethysmography, and CO was measured by ModelFlow. Systemic vascular resistance was defined as mean arterial blood pressure/CO. End tidal CO 2 and cerebral blood flow velocity of the middle cerebral artery were only reduced during head‐up tilt in the hyperventilation group, whereas blood pressure was increased compared with control. We corrected the reduced end tidal CO 2 in hyperventilation by addition of exogenous CO 2 into a rebreathing apparatus. With added CO 2, heart rate, blood pressure, CO, and systemic vascular resistance in hyperventilation became similar to control.ConclusionsWe conclude that all POTS is related to decreased CO, decreased central blood volume, and increased systemic vascular resistance and that a variant of POTS is consequent to postural hyperventilation.

The Effect of Inhalation Anesthesia with Hyperventilation and Total Intravenous Anesthesia on Intracranial Pressure Control in Pediatrics with Craniosynostosis Surgery: A Randomized Clinical Trial

Background: Intracranial pressure (ICP) control is one of the anesthesiologist challenges in craniosynostosis repair surgery, especially in multiple sutures involvement. The aim of this study was comparing the effect of two anesthesia methods including inhalation with hyperventilation and total intravenous anesthesia (TIVA) on ICP control and surgeon satisfaction in pediatrics with craniosynostosis surgery. Materials and Methods: In this randomized clinical trial study, 40 pediatric patients with American society of anesthesiologists (ASA) І-ІІ, 6 months to 2 years old were included. All of the patients were scheduled for craniosynostosis repair at Mofid Children Hospital, Tehran, Iran, in May 2016 to January 2017. The patients were randomly divided into two groups. In hyperventilation group, patients received isoflurane for maintenance of anesthesia and hyperventilation (Paco2=25-30 mmHg) established during surgery. The total intravenous anesthesia (TIVA) group received propofol infusion for anesthesia maintenance and Paco2 was maintained 35 mmHg. Intra cranial pressure (ICP) was assessed by surgeon using a 4-point scale. Hemodynamic (mean arterial pressure and heart rate) changes and blood loss were compared between hyperventilation and TIVA groups. Results: The mean age of patients in hyperventilation group was 10.9±3.25 months and in TIVA group was 8.7 ± 2063 months (p=0.11). Fourteen (70%) patients in hyperventilation group and 6 (30%) patients in TIVA group were male (p=0.74). A significant difference was seen in ICP control and surgical condition between hyperventilation and TIVA groups (p=0.032). ICP was controlled better in hyperventilation group. There was no difference in hemodynamic parameters and blood loss between hyperventilation and TIVA groups (p>0.05). Conclusion: This study showed inhalation anesthesia with hyperventilation was more effective than TIVA on ICP control in craniosynostosis surgery.

Efficient Extra- and Intracellular Alkalinization Improves Cardiovascular Functions in Severe Lactic Acidosis Induced by Hemorrhagic Shock

Kimmoun, Antoine*; Ducrocq, Nicholas*†‡§; Sennoun, Nacira†§; Issa, Khodr†§; Strub, Charlène†§; Escanyé, Jean-Marie║; Leclerc, Sébastien║; Levy, Bruno*†‡§ Author Information

Efficient Extra- and Intracellular Alkalinization Improves Cardiovascular Functions in Severe Lactic Acidosis Induced by Hemorrhagic Shock

Lactic acidosis is associated with cardiovascular failure. Buffering with sodium bicarbonate is proposed in severe lactic acidosis. Bicarbonate induces carbon dioxide generation and hypocalcemia, both cardiovascular depressant factors. The authors thus investigated the cardiovascular and metabolic effects of an adapted sodium bicarbonate therapy, including prevention of carbon dioxide increase with hyperventilation and ionized calcium decrease with calcium administration. Lactic acidosis was induced by hemorrhagic shock. Twenty animals were randomized into five groups: (1) standard resuscitation with blood retransfusion and norepinephrine (2) adapted sodium bicarbonate therapy (3) nonadapted sodium bicarbonate therapy (4) standard resuscitation plus calcium administration (5) hyperventilation. Evaluation was focused in vivo on extracellular pH, on intracellular pH estimated by P nuclear magnetic resonance and on myocardial contractility by conductance catheter. Aortic rings and mesenteric arteries were isolated and mounted in a myograph, after which arterial contractility was measured. All animals in the hyperventilation group died prematurely and were not included in the statistical analysis. When compared with sham rats, shock induced extracellular (median, 7.13; interquartile range, [0.10] vs. 7.30 [0.01]; P = 0.0007) and intracellular acidosis (7.26 [0.18] vs. 7.05 [0.13]; P = 0.0001), hyperlactatemia (7.30 [0.01] vs. 7.13 [0.10]; P = 0.0008), depressed myocardial elastance (2.87 [1.31] vs. 0.5 [0.53] mmHg/μl; P = 0.0001), and vascular hyporesponsiveness to vasoconstrictors. Compared with nonadapted therapy, adapted bicarbonate therapy normalized extracellular pH (7.03 [0.12] vs. 7.36 [0.04]; P < 0.05), increased intracellular pH to supraphysiological values, improved myocardial elastance (1.68 [0.41] vs. 0.72 [0.44] mmHg/μl; P < 0.05), and improved aortic and mesenteric vasoreactivity. A therapeutic strategy based on alkalinization with sodium bicarbonate along with hyperventilation and calcium administration increases pH and improves cardiovascular function.

Hyperventilation increases the rate of the rise in arterial blood desflurane concentration during induction - a Gas Man® simulation

Lu et al. described that hyperventilation accelerated the desflurane uptake from the alveolar to the arterial blood (1). It is a very intriguing study of a direct determination of the desflurane concentration in the arterial blood (Ades). In comparison to the end-tidal volatile anesthetic concentration, the arterial concentration of a volatile anesthetic is more likely to reflect its concentration in the brain (1-3). A pharmacokinetic model for volatile anesthetics has been developed and used for over 25 years (4). Therefore, the effect of ventilation on Ades can be simulated with this model. Gas Man® (Version 4.1, Med Man Simulations, Inc., Chestnut Hill, MA, USA) is a computer simulation program which contains a five-compartment system built statistically which simulates the pharmacokinetics for volatile anesthetic uptake and distribution (4) with embedded parameters (5). This program helps users and readers understand anesthetic uptake and distribution with graphs. If the embedded parameters are adjusted prior to a simulation, simulated results can be seen in graphs individually. For the simulations, the necessary parameters and patient data were taken from the report of Lu et al. (1): an anesthesia breathing circuit volume of 6 L; a fresh gas flow of 6 L/min; a functional residual capacity of 2.4 L; 61.8, 62.0, and 58.0 kg patient (hyperventilation, normal ventilation, and hypoventilation, mean values from each group); an alveolar minute ventilation of 3.33, 2.38, and 1.80 L/min, mean values from each group; cardiac output which was derived from the cardiac index of the report of Lu et al. with Du Bois method (5.38, 5.56, and 5.36 L/min, mean values from each group). Other parameters were not manipulated. Therefore, the values for compartment volumes (vessel rich group, muscle, fat, and venous group) and the values for regional blood flow percentages (vessel rich group, muscle, and fat) showed some differences depending on the entered weight. At 0, 1, 3, 5, 10, 20, 30, and 40 minutes, the simulated Ades were recorded. In these simulations, despite having some limitations on the data used (e.g. using mean values of weight and alveolar ventilation) in the report of Lu et al, Gas Man® shows similar trends with the simulated Ades just as those of Lu et al (1). Hyperventilation seems to produce a higher Ades-over-time curve than normal ventilation and hypoventilation. Simulated Ades in the hyperventilation group also seems to increase more rapidly than those in the normal ventilation and the hypoventilation groups during the first 5 minutes (Figure 1. Figure 1 Simulated arterial concentration of desflurane (%) time curves under three different ventilatory settings, including hyperventilation, normal ventilation, and hypoventilation in Gas Man® (Version 4.1, Med Man Simulations, Inc., Chestnut Hill, ...

The effects of mitogen-activated protein kinases on the genes expression of the pulmonary surfactants from alveolar epithelial cells during ventilation induced lung injury in rats

Objective To investigate the effects of mitogen-activated protein kinases (MAPK) on the genes expression of the pulmonary surfactants from alveolar epithelial cells during ventilation induced lung injury in rats.Methods Anesthetized male SD rats were randomized into six groups:① Control group(C) received no mechanical ventilation.② Low-volume ventilation(LV) group received mechanical ventilation with Vt=6 ml/kg,RR=40 bmp,I∶E=1∶2,FiO2=21％,positive end-expiratory pressure =0.③ Hyperventilation(HV) group received mechanical ventilation with the same respiratory parameters as the LV group and the Vt was 40 ml/kg.The inhibitors of MAPK including the JNK's:SP600125,the ERK's:PD98059 and the p38's:SB203580 were pretreated 30 min before ventilation just like in the HV group.④ SP600125 group (SP600125 + HV group).⑤ PD98059 group (PD98059 + HV group).⑥ SB203580 group (SB203580 + HV group).After 4 h ventilation,the animals in each group were killed and the lungs were removed for detecting the expression of SP-A,B,C and RTI40 mRNA by RT-PCR.Results ① Compared with group C,the expression of RTI40 mRNA of lung tissue increased significantly in the LV group and the HV group (P＜0.05),but the expression of SP-A,SP-C mRNA decreased in the HV group,SP600125 group and SB203580 group (P＜0.05),while there was no significant difference in the expression of SP-A、C mRNA in LV groups and PD98059 group (P＜0.05).② Compared with the HV group,the SP-A,C gene expressions of lung tissue in SP600125 group,PD98059 group and SB203580 group increased significantly (P＜0.05),but RTI40 gene expressions decreased(P＜0.05).③ The SP-A,C gene expressions of lung tissue in PD98059 group increased significantly than those of SP600125 group and SB203580 group.④ The SP-B gene expression had no difference in all groups.Conclusions The results of our study show that mechanical ventilation inhibited the expressions of the SP-A and SP-C,but upregulated RTI40 gene expressions.The inhibitors of MAPK attenuated the changes of SP-A,C and RTI40 mRNA during the process of high volume ventilation,which indicates that MAPK,at least in part,may play a role in the functions of Ⅰ and Ⅱ alveolar epithelial cells in the lung injury induced by mechanical ventilation. Key words: Ventilation induced lung injury; Pulmonary surfactant; Genes expression; Mitogen-activated protein kinases

Hyperventilation accelerates rise in arterial blood concentrations of sevoflurane in gynecologic patients

We investigated whether ventilation volumes affected arterial blood sevoflurane concentration (A (sev)) and its uptake into the body during general anesthesia. Thirty female patients undergoing elective gynecologic surgery were randomly allocated into three groups: hyperventilation, normal ventilation, and hypoventilation. Inspiratory (CI(sev)) and end-tidal ((sev)) sevoflurane concentrations were routinely measured by infrared analysis, and A (sev) were analyzed by gas chromatography for 40 min after intubation. Cardiac index and total peripheral vascular resistance were measured with a Finometer. During the first 10 min after sevoflurane administration, A (sev) in the hyperventilation group was the highest and differed significantly from those in the normal ventilation group, followed by those in the hypoventilation group. In addition, hyperventilation significantly increased the slope of A (sev) over time in the first 5 min, but there were no differences in slopes in the 5-10, 10-20, and 20-40 min periods, which indicates no difference in sevoflurane bodily uptake among the three groups after 5 min. Hyperventilation accelerated the rate of A (sev) increase immediately after sevoflurane administration, which was time dependent with respect to different alveolar ventilation levels.

Hyperventilation accelerates the rise of arterial blood concentrations of desflurane in gynecologic patients

OBJECTIVES:Under a constant inspired concentration, the uptake of a volatile anesthetic into the arterial blood should mainly be governed by alveolar ventilation, according to the assumption that the patient's cardiac output remains stable during anesthesia. We investigated whether ventilation volume affects the rate of desflurane uptake by examining arterial blood concentrations.METHOD:Thirty female patients were randomly allocated into the following three groups: hyperventilation, normal ventilation and hypoventilation. Hemodynamic variables were measured using a Finometer, inspiratory and end-tidal concentrations of desflurane were measured by infrared analysis, and the desflurane concentration in the arterial blood (Ades) was analyzed by gas chromatography.RESULTS:During the first 10 minutes after the administration of desflurane, the Ades was highest in the hyperventilation group, and this value was significantly different from those obtained for the normal and hypoventilation groups. In addition, hyperventilation significantly increased the slope of Ades-over-time during the first 5 minutes compared with patients experiencing normal ventilation and hypoventilation, but there were no differences in these slopes during the periods from 5-10, 10-20 and 20-40 minutes after the administration of desflurane. This finding indicates that there were no differences in desflurane uptake between the three groups after the first 5 minutes within desflurane administration.CONCLUSIONS:Hyperventilation accelerated the rate of the rise in Ades following desflurane administration, which was time-dependent with respect to different alveolar ventilations levels.

Hyperventilation versus standard ventilation for infants in postoperative care for congenital heart defects with pulmonary hypertension

In infants undergoing surgery for cardiac defects with left-to-right shunt, a hyperventilation strategy has been applied to prevent pulmonary hypertensive crisis (PHC). Hyperventilation with a large tidal volume and/or higher airway pressure, however, may be detrimental to the lung. This randomized study compared the effects of hyperventilation versus standard ventilation. We enrolled 22 infants with a preoperative pulmonary-to-systemic blood pressure ratio of more than 0.7. Hyperventilation, with a tidal volume of 10-12 ml x kg(-1) to keep Pa(CO2) between 30 and 35 mmHg, was randomly applied in 11 patients for 16 h or more. The other 11 patients were randomly assigned to standard ventilation, with a 6- to 8- ml x kg(-1) tidal volume. The peak inspiratory pressure was higher (20 +/- 3 vs 18 +/- 2 cmH2O; P = 0.018), and Pa(CO2) (34 +/- 5 vs 42 +/- 7 mmHg; P = 0.003) and positive end-expiratory pressure (3 +/- 0 vs 5 +/- 0; P < 0.0001) were significantly lower in the hyperventilation than in the standard ventilation group. The Pa(CO2)/inspiratory fraction of oxygen Pa(CO2) ratio decreased from 244 +/- 160 mmHg at the onset of postoperative ventilation, to 177 +/- 96 mmHg at 24 h (P = 0.038) in the hyperventilation group, versus a decrease from 240 +/- 89 to 220 +/- 97 mmHg in the standard ventilation group not significant (NS). Serum interleukin (IL)-6 level, measured at 24 h postoperatively, was significantly lower (P = 0.02) in the standard ventilation than in the hyperventilation group, suggesting an attenuated postoperative systemic inflammatory response. A single patient in each group developed PHC. Hyperventilation may cause lung injury and systemic inflammation in infants with pulmonary hypertension undergoing corrective heart surgery.

Effects of Changes in Alveolar Ventilation on Isoflurane Arterial Blood Concentration and Its Uptake into the Human Body

We investigated whether minute alveolar ventilation affects isoflurane concentration in arterial blood and uptake of isoflurane into the body. Thirty female patients scheduled to undergo elective gynecological surgery were randomly assigned to one of three groups: i.e. hyperventilation, normal ventilation and hypoventilation. Inspiratory (CIiso) and end-tidal (CEiso) concentrations of isoflurane were measured by infrared analysis, and arterial blood isoflurane concentration (Aiso) was analyzed by gas chromatography. Cardiac index was measured by Doppler ultrasonography. The body uptake of isoflurane was determined by multiplying alveolar ventilation by the gradient of CIiso–CEiso. Aiso was highest in the hyperventilation group (significant), followed by the normal ventilation and hypoventilation groups, during the 40-min study. During the first 10 min of the study, the slope of the Aiso-over-time curve was highest in the hyperventilation group, followed by the normal ventilation group and the hypoventilation group. During the second half of the study (20–40 min), the slope Aiso-over-time curve did not differ among the three groups. Changes in ventilation affected the concentration of isoflurane in arterial blood but did not significantly alter the uptake of it during the last 20 min of the study. The change of alveolar ventilation altered the speed of functional residual capacity wash-in by isoflurane, which was the integral factor influencing Aiso and body uptake of isoflurane.

Moderate Hyperventilation Prolongs Electroencephalogram Seizure Duration of the First Electroconvulsive Therapy

Although it is controversial that seizure duration can influence the efficacy of electroconvulsive therapy (ECT), a missed or brief seizure is considered less effective ECT. Of the background in the practice of ECT, hyperventilation may augment the seizure duration. To elucidate these hypotheses, we performed double-blind randomized controlled trial for 19 patients. They were divided into 2 groups, according to the end-tidal pressure of carbon dioxide (ETCO2): The moderate hyperventilation group with ETCO2 of 30 mm Hg and the normal ventilation group with ETCO2 of 40 mm Hg. ECT was performed under general anesthesia with propofol and suxamethonium. During ECT electroencephalogram (EEG) and electromyogram were recorded. The Global Assessment of Functioning scores were also analyzed before and after 6 sequential ECT. The moderate hyperventilation group showed a significant increase in EEG seizure duration in the first treatment compared with the normal ventilation group (P < 0.05). However, EEG seizure duration in the subsequent treatments and electromyogram seizure duration in all the treatments did not differ between 2 groups. The moderate hyperventilation did not prevent the increase in seizure threshold or shortening of seizure duration. No complications or sever adverse effects were observed after ECT in any of the 6 treatments. The Global Assessment of Functioning scores were not significantly changed with moderate hyperventilation. We conclude that moderate hyperventilation is safe and may be useful for seizure augmentation before the restimulation with higher intensities.

Interaction of anxiety sensitivity and induced physiological state: Effect on behaviour and interpretation of ambiguous scenarios

The purpose of the present study was to investigate the interaction of anxiety sensitivity (AS) and induced physiological state (hyperventilation vs. relaxation) on participants' interpretation of ambiguous scenarios, and their ratings of the likelihood of participation in an anxiety-provoking, real-life behavioural task. The participants were 60 first-year female psychology students whose self-reported AS score was categorised as either high or low. Measures completed before induction of the physiological state included the Social and Avoidance Distress Scale (SADS), the State – Trait Anxiety Inventory (STAI), and a questionnaire in which participants had to make forced choice interpretations of, and generate solutions in response to, a number of hypothetical, ambiguous scenarios. Finally, participants were asked to rate the probability of them choosing to participate in a real-life behavioural task. At post-induction the participants interpreted new scenarios, completed the State Anxiety scale of the STAI, and rated the probability of completing the behavioural task. At pre-induction, participants in the high-AS group were significantly more likely than participants in the low-AS group to interpret the ambiguous scenarios in a threatening manner. Contrary to prediction, at pre-induction there was no significant difference between the high-AS and low-AS groups when rating the probability of their participation in the behavioural task. At post-induction, the high-AS – hyperventilation group reported more avoidance regarding the likelihood of participation in the behavioural task. The implications of these results are discussed.

Respiratory acidosis prolongs, while alkalosis shortens, the duration and recovery time of vecuronium in humans

Study Objective: To determine the effects of respiratory acidosis and alkalosis by mechanical ventilation on the onset, duration, and recovery times of vecuronium. Design: Randomized, prospective study. Setting: Operating rooms in the Sapporo Medical University Hospital and Kitami Red Cross Hospital. Patients: 90 ASA physical status I and II patients undergoing lower abdominal surgery. Interventions: Patients were randomly allocated to one of three groups by arterial carbon dioxide tension level ( PaCO 2 ; mmHg) after induction: hyperventilation group ( PaCO 2 = 25–35), normoventilation group ( PaCO 2 = 35–45), and hypoventilation group ( PaCO 2 = 45–55). Anesthesia was maintained by spinal block with inhalation of 50% to 66% nitrous oxide in oxygen and intermittent intravenous administration of fentanyl and midazolam with tracheal intubation. Measurements and Main Results: After vecuronium 0.08 mg/kg was given, onset, duration, and recovery time were measured by mechanomyography (Biometer Myograph 2,000, Odense, Denmark). There were significant differences in the duration and recovery time of vecuronium among the normoventilation group (12.7 ± 3.3 min and 11.8 ± 2.8 min, respectively), the hyperventilation group (10.6 ± 3.5 min and 9.2 ± 2.7 min, respectively; p < 0.01), and the hypoventilation group (14.4 ± 3.1 min and 15.0 ± 3.7 min, respectively; p < 0.01) (mean SD). The closest significant correlation in this study was observed between recovery time and arterial blood pH (r = 0.57; p < 0.05). Conclusion: In humans, duration and recovery times of vecuronium are prolonged in respiratory acidosis and shortened in respiratory alkalosis.