Pressure support ventilation vs spontaneous ventilation via ProSeal™ laryngeal mask airway in pediatric patients undergoing ambulatory surgery: a randomized controlled trial

Aim: To investigate the advantages of using pressure support ventilation (PSV) vs spontaneous ventilation via ProSeal? laryngeal mask airway in children undergoing ambulatory surgery. Background: In our ambulatory surgical unit, the use of unassisted spontaneous breathing via laryngeal mask airway is a common anesthetic technique during general anesthesia. However, this may be associated with inadequate ventilation. PSV is a ventilatory mode that is synchronized with the patient’s respiratory effort and may improve gaseous exchange under general anesthesia. Materials and methods: After the approval from the ethics committee, a randomized controlled trial involving 24 pediatric patients was conducted in our ambulatory surgical unit. They were randomized into two groups, namely Group PSV (receiving PSV) and Group SV (unassisted spontaneous ventilation). Outcome measures included intraoperative respiratory and hemodynamic parameters as well as recovery room data. Results: There were no significant differences in baseline characteristics between the two groups. Patients in Group PSV had lower ETCO₂ (42.8 ± 5.8 vs 50.4 ± 4.0, P = 0.001) and higher expiratory tidal volume per kg bodyweight (8.3 ± 1.8 ml kg^?1 vs 5.8 ± 0.8 ml kg^?1, P = 0.001) compared with patients in Group SV. There were no significant differences in other respiratory and hemodynamic parameters or recovery room data between the two groups. Conclusion: Pressure support ventilation via ProSeal? laryngeal mask airway during general anesthesia improves ventilation in pediatric patients undergoing ambulatory surgery. However, this did not translate to a difference in clinical outcome among our study patients.     

Pressure vs. volume control ventilation: effects on gastric insufflation with size-1 LMA

Background: In this randomized prospective study, peak airway pressure (PAP) and gastric insufflation were compared between volume control ventilation (VCV) and pressure control ventilation (PCV) using size‐1 laryngeal mask airway (LMA) in babies weighing 2.5–5 kg. Methods: Forty ASA I and II children, weighing 2.5–5 kg, undergoing elective infraumbilical surgeries (duration < 60 min) were randomized to two groups of 20 each to receive either PCV or VCV. Patients at risk of aspiration, difficult airway and upper respiratory tract infection, and poor lung compliance were excluded. Anesthesia technique included sevoflurane/O₂/N₂O without neuromuscular blockade. PAP in PCV and tidal volume in VCV modes were changed to achieve adequate ventilation (P_ECO₂ of 5–5.4 kPa). PAP was maintained below 20 cm H₂O. Chi‐squared test, Mann–Whitney U‐test and Wilcoxon W‐test were applied; P < 0.05 was considered significant. Results: Mean PAP (cm H₂O) was 12.2 ± 1.09 in PCV and 13.60 ± 0.94 in VCV groups (P = 0.000). The confidence interval of mean difference of PAP varied from 0.79 to 2.10. Significant increases in abdominal circumference were observed in both groups: PCV: 0.94 ± 1.04 cm and VCV: 2.2 ± 1.3 cm; (P = 0.000). The SpO₂ and hemodynamic variables did not differ between the groups. One patient in VCV group (with PAP = 14 cm H₂O) could not be ventilated to the target P_ECO₂, and the LMA had to be replaced with tracheal tube. Conclusion: In conclusion, PCV should be the preferred mode to provide positive pressure ventilatio (PPV), when using the size‐1 cLMA in babies weighing 2.5–5 kg, in view of less gastric insufflation associated with it for surgeries of brief duration. More studies are required to validate the clinical significance of these two modes of ventilation in longer procedures, in this subpopulation.     

Dexmedetomidine facilitates induction of noninvasive positive pressure ventilation for acute respiratory failure in patients with severe asthma

Noninvasive positive pressure ventilation (NPPV) has been reported to be effective for acute respiratory failure in patients with severe asthma. Although NPPV requires less sedative than invasive mechanical ventilation, agitated patients with severe asthma should be given the minimum sedation necessary to facilitate the induction of NPPV. Two asthmatic patients (a 65-year-old man and a 32-year-old woman) separately presented to the intensive care unit with exacerbating respiratory failure. We initiated NPPV using bilevel positive airway pressure (PAP) ventilation. The ventilation was initially set as an inspiratory PAP of 15 cmH₂O and an expiratory PAP of 4 cmH2O. Because they seemed too agitated to tolerate the mask ventilation, dexmedetomidine was administered intravenously, at 3 μg·kg⁻¹·min⁻¹ for 10 min, followed by a continuous infusion at 0.2–0.6 μg·kg⁻¹·min⁻¹. One hour after the institution of NPPV, the patients were well cooperative with the mask ventilation and the respiratory symptoms had markedly improved. While the Ramsay sedation scale was maintained at 2 or 3 during the continuous dexmedetomidine infusion, we successfully weaned the patients from NPPV by reducing the inspiratory PAP. Dexmedetomidine helped the agitated patients cooperate with mask ventilation without inducing respiratory depression. We conclude that dexmedetomidine may be a valuable sedative to facilitate the induction of NPPV. This case report was presented in part at the 81st clinical and scientific congress of the International Anesthesia Research Society, Orlando, Florida, March 23–27, 2007.     

Airway occlusion pressure (P0.1) — A useful predictor for the weaning outcome in patients with acute respiratory failure —

Twenty-five patients who required mechanical ventilatory support (MVS) after major surgery or severe burns were studied to determine whether airway occlusion pressure (P_0.1) is a clinically useful indicator to predict the success or failure of the weaning trial. A total of 33 weaning trials were attempted on these patients. Of the 33 trials, 24 were followed by successful weaning and 9 by failure. Although the success group, when compared with the failure group, had a lower respiratory rate (P 0.001), a lower minute ventilation (P 0.001), a higher maximal voluntary ventilation to minute ventilation ratio (P 0.01) and a higher forced vital capacity (P 0.05), no threshold values separated the success from the failure group. The alveolar-arterial P_{O 2} gradient, with an Fi _{O 2} of 1.0, in weaning success and failure showed no statistical difference. In contrast, all patients in the success group had a P_0.1 of less than 3.5cmH₂O and those in the failure group had a P_0.1 of greater than 3.5cmH₂O (P 0.001). We conclude that P_0.1 is a clinically superior indicator for discontinuing MVS in patients with acute respiratory failure.(Okamoto K, Sato T, Morioka T: Airway occlusion pressure (P_0.1)—A useful predictor for the weaning outcome in patients with acute respiratory failure—. J Anesth 4: 95–101, 1990)     

Alveolar recruitment strategy and PEEP improve oxygenation,dynamic compliance of respiratory system and end‐expiratory lung volume in pediatric patients undergoing cardiac surgery for congenital heart disease

Objective: Optimizing alveolar recruitment by alveolar recruitment strategy (ARS) and maintaining lung volume with adequate positive end‐expiratory pressure (PEEP) allow preventing ventilator‐induced lung injury (VILI). Knowing that PEEP has its most beneficial effects when dynamic compliance of respiratory system (Crs) is maximized, we hypothesize that the use of 8 cm H₂O PEEP with ARS results in an increase in Crs and end‐expiratory lung volume (EELV) compared to 8 cm H₂O PEEP without ARS and to zero PEEP in pediatric patients undergoing cardiac surgery for congenital heart disease. Methods: Twenty consecutive children were studied. Three different ventilation strategies were applied to each patient in the following order: 0 cm H₂O PEEP, 8 cm H₂O PEEP without an ARS, and 8 cm H₂O PEEP with a standardized ARS. At the end of each ventilation strategy, Crs, EELV, and arterial blood gases were measured. Results: EELV, Crs, and P_aO₂/FiO₂ ratio changed significantly (P < 0.001) with the application of 8 cm H2O + ARS. Mean P_aCO₂– PETCO₂ difference between 0 PEEP and 8 cm H2O PEEP + ARS was also significant (P < 0.05). Conclusion: An alveolar recruitment strategy with relative high PEEP significantly improves Crs, oxygenation, P_aCO₂– PETCO₂ difference, and EELV in pediatric patients undergoing cardiac surgery for congenital heart disease.     

Respiration: control of ventilation

Ventilation of the lungs is tightly regulated to maintain a P_aCO₂ that supports optimal acid-base status and an adequate PaO₂. Central and peripheral chemoreceptors feed into respiratory control centres in the brainstem. P_aO₂ exerts its influence mainly through peripheral chemoreceptors, whereas P_aCO₂ exerts its influence mainly through the central chemoreceptors and, to a much lesser extent, the peripheral chemoreceptors. The tightest physiologic control is over P_aCO₂. Indeed, a linear relationship exists between P_aCO₂ and alveolar ventilation through a broad range of P_aCO₂ values. In contrast, for P_aO₂, significant stimulation of respiration only occurs at low levels (approximately 8 kPa or less). The combination of hypoxaemia and hypercarbia exerts a synergistic effect on promoting ventilation. Acidosis, whether respiratory or metabolic, is also a potent stimulus for ventilation. Other influences on ventilatory control include airway reflexes to inhaled toxins. Various drugs used in anaesthesia and critical care medicine depress ventilation, most markedly opioids, while others notably caffeine are used to stimulate it. Evidence of disordered control of ventilation is seen in some disease states, the phenomenon of Cheyne-Stokes respiration being particularly well recognized. Measurement of respiratory drive is increasingly used in intensive care to individualize mechanical ventilation.     

Arterial to endtidal carbon dioxide gradient during pediatric laparoscopic fundoplication

Background: Discrepancies between arterial carbon dioxide (P_aCO₂) and endtidal carbon dioxide (ETCO₂) measures have been demonstrated in ventilated children with cyanotic congenital heart disease, infants with respiratory failure and during visceral and urological laparoscopic surgery. Objectives: Our objective was to assess the extent of the P_aCO₂ to ETCO₂ gradient in children during laparoscopic fundoplication. Methods: We prospectively collected data on patient characteristics, surgical conditions, pH, ETCO₂and P_aCO₂ during laparoscopic fundoplication using carbon dioxide insufflation in children age <29 months. Results: Data were collected on nine cases, four cases aged <1 year. A P_a‐ETCO₂ gradient was present during insufflation. The gradient was larger in children age less than 1 year but statistically significantly different from a value of zero, only at t = 30 min (mean = 8 mmHg, sem = 0.81, P = 0.004) and t = 60 min (mean = 5 mmHg, sem = 1, P = 0.014). Minute ventilation was increased from 20% to 100% to control ETCO₂. Conclusions: ETCO₂ may not accurately represent arterial values during laparoscopic fundoplication, especially in the infant when carbon dioxide insufflation is used. Consideration should be given to placing an arterial line for blood gas measurement in some patients.     

Elective Decompression of the Left Ventricle in Pediatric Patients May Reduce the Duration of Venoarterial Extracorporeal Membrane Oxygenation

We aimed to determine the effect of elective left heart decompression at the time of initiation of central venoarterial extracorporeal membrane oxygenation (VA ECMO) on VA ECMO duration and clinical outcomes in children in a single tertiary ECMO referral center with a large pediatric population from a national referral center for pediatric cardiac surgery. We studied 51 episodes of VA ECMO in a historical cohort of 49 pediatric patients treated between the years 1990 and 2013 in the Paediatric Intensive Care Unit (PICU) of the Royal Children's Hospital, Melbourne. The cases had a variety of diagnoses including congenital cardiac abnormalities, sepsis, myocarditis, and cardiomyopathy. Left heart decompression as an elective treatment or an emergency intervention for left heart distension was effectively achieved by a number of methods, including left atrial venting, blade atrial septostomy, and left ventricular cannulation. Elective left heart decompression was associated with a reduction in time on ECMO (128 h) when compared with emergency decompression (236 h) (P = 0.013). Subgroup analysis showed that ECMO duration was greatest in noncardiac patients (elective 138 h, emergency 295 h; P = 0.02) and in patients who died despite both emergency decompression and ECMO (elective 133 h, emergency 354 h; P = 0.002). As the emergency cases had a lower pH, a higher PaCO₂, and a lower oxygenation index and were treated with a higher mean airway pressure, positive end‐expiratory pressure, and respiratory rate prior to receiving VA ECMO, we undertook multivariate linear regression modeling to show that only PaCO₂ and the timing of left heart decompression were associated with ECMO duration. However, elective left heart decompression was not associated with a reduction in length of PICU stay, duration of mechanical ventilation, or duration of oxygen therapy. Elective left heart decompression was not associated with improved ECMO survival or survival to PICU discharge. Elective left heart decompression may reduce ECMO duration and has therefore the potential to reduce ECMO‐related complications. A prospective, randomized controlled trial is indicated to study this intervention further.     

Bi-level positive airway pressure ventilation maintains adequate ventilation in post-polio patients with respiratory failure

BACKGROUND: Patients suffering from post-polio syndrome still contribute significantly to the number of patients with chronic respiratory failure requiring home mechanical ventilation (HMV). Many of these patients are treated either with invasive (tracheostomy) or non-invasive (nasal mask) controlled mechanical ventilation i.e. volume-controlled ventilation (VCV). In this group of patients, we have previously shown that bi-level pressure support ventilation (bi-level PSV) decreases the oxygen cost of breathing. The aim of this study was to compare the effect of bi-level PSV, with special regard to the adequacy of ventilation and the oxygen cost of breathing, during the patients' ordinary VCV and spontaneous breathing. METHODS: Eight post-polio patients on nocturnal VCV were investigated. Five of them were tracheostomized and three of them used a nasal mask. Work of breathing was analysed by assessing differences in oxygen consumption (VO2) using indirect calorimetry. Blood gases were obtained regularly to assess adequacy of ventilation. RESULTS: Bi-level PSV decreases the oxygen cost of breathing in post-polio patients with respiratory failure without decreasing ventilation efficiency. Furthermore, PaCO2 decreased significantly using this mode of ventilation (P < 0.05). CONCLUSION: In this study, it was shown that bi-level PSV reduces the oxygen cost of breathing and gave a significant decrease in PaCO2 in PPS patients. These data suggest that bi-level PSV ventilation maintains adequate ventilation in patients who suffer from post-polio syndrome with respiratory failure.     

Effects of halothane and sevoflurane on the paediatric respiratory pattern

Using a respiratory inductive plethysmograph, we investigated the effects of halothane and sevoflurane on the paediatric respiratory pattern under spontaneous breathing. We measured tidal volume per weight, respiratory rate, partial pressure of end-expiratory carbon dioxide (Pet_CO2), rib cage contribution to ventilation (%RC) and phase shift between rib cage and abdominal movements at 0.5, 1.0 and 1.5 MAC of these inhalational anaesthetics in oxygen. Both of these anaesthetics increased Pet_CO2 significantly with increase in depth of anaesthesia; sevoflurane produced more profound respiratory depression than halothane at high MAC. Both agents decreased %RC significantly with increase in depth of anaesthesia; paradoxical respiration occurred in the halothane group at high MAC. The profound respiratory depression of sevoflurane is due to both decreased tidal volume and decreased respiratory rate. The paradoxical respiration under halothane may be attributed to the potent suppression of intercostal muscle function and may be partly due to compensatory sparing effect on respiratory rate, which leads to the increase in airway flow and airway resistance.     

“Open lung ventilation optimizes pulmonary function during lung surgery”

Background

We evaluated an “open lung” ventilation (OV) strategy using low tidal volumes, low respiratory rate, low FiO₂, and high continuous positive airway pressure in patients undergoing major lung resections.

Materials and methods

In this phase I pilot study, twelve consecutive patients were anesthetized using conventional ventilator settings (CV) and then OV strategy during which oxygenation and lung compliance were noted. Subsequently, a lung resection was performed. Data were collected during both modes of ventilation in each patient, with each patient acting as his own control. The postoperative course was monitored for complications.

Results

Twelve patients underwent open thoracotomies for seven lobectomies and five segmentectomies. The OV strategy provided consistent one-lung anesthesia and improved static compliance (40 ± 7 versus 25 ± 4 mL/cm H2O, P = 0.002) with airway pressures similar to CV. Postresection oxygenation (SpO₂/FiO₂) was better during OV (433 ± 11 versus 386 ± 15, P = 0.008). All postoperative chest x-rays were free of atelectasis or infiltrates. No patient required supplemental oxygen at any time postoperatively or on discharge. The mean hospital stay was 4 ± 1 d. There were no complications or mortality.

Conclusions

The OV strategy, previously shown to have benefits during mechanical ventilation of patients with respiratory failure, proved safe and effective in lung resection patients. Because postoperative pulmonary complications may be directly attributable to the anesthetic management, adopting an OV strategy that optimizes lung mechanics and gas exchange may help reduce postoperative problems and improve overall surgical results. A randomized trial is planned to ascertain whether this technique will reduce postoperative pulmonary complications.     

Full face mask for noninvasive positive-pressure ventilation in patients with acute respiratory failure

BACKGROUND: Noninvasive positive-pressure ventilation (NPPV) is commonly used to improve ventilation and oxygenation in patients with acute respiratory failure (ARF). Mask leak and intolerance due to facial discomfort or claustrophobia often occur with NPPV and are frequently cited reasons for treatment failure. METHODS: Retrospective review of patient records from a tertiary-care referral hospital. Results: We report the effectiveness of a full face mask in the application of NPPV for 10 nonambulatory patients (mean [SD], 61 [9] years) who had a combined total of 13 episodes of ARF. After these patients were unable to receive NPPV therapy via the more commonly available nasal or oronasal masks, care was provided using full face masks. Eight of 10 patients had hypercapnic respiratory failure; 2 patients, hypoxemic respiratory failure. All patients were placed on ventilation initially using a bi-level positive airway pressure device. Subsequently, patient ventilation was achieved using a Puritan Bennett 7200a ventilator for on-line respiratory monitoring. The mean (SD) duration of treatment with NPPV was 9.7 (2.7) hours per day for 3.0 (1.6) days. Following NPPV via full face mask, the patients' Paco(2) decreased (65 [20] vs 82 [27] mm Hg, P=.09) and pH increased significantly (7.36 [0.07] vs 7.26 [0.07], P<.05) in less than 2 hours. Moreover, the patients demonstrated decreased respiratory rate (18 [7] vs 32 [8] breaths/min, P<.01), heart rate (106 [13] vs 124 [16] beats/min, P=.008), and Acute Physiology and Chronic Health Evaluation II scores (12 [3] vs 17 [4], P<.005) after NPPV via full face mask. These cardiorespiratory alterations occurred as early as 1 hour after NPPV initiation and were maintained throughout treatment. Two patients required endotracheal intubation because of copious purulent secretions. CONCLUSION: For individuals with hypercapnic respiratory failure who cannot tolerate NPPV using nasal or oronasal masks, use of full face masks may improve outcomes, allowing physicians to avoid ordering endotracheal intubation and mechanical ventilation.     

Diaphragmatic dysfunction after pediatric orthotopic liver transplantation

BACKGROUND: Pediatric orthotopic liver transplantation (OLT) has a low mortality. Some children, however, have an adverse outcome defined as a prolonged ventilatory support requirement and protracted pediatric intensive care unit (PICU) stay. The aim of this study was to determine if that adverse outcome related to the child's condition pre-OLT and/or the development of a pleural effusion or diaphragmatic dysfunction. METHODS: The study included 210 children with a median age at transplantation of 45.5 months (range 0.2-252 months). Fourteen had undergone retransplantation. The duration of ventilatory support (intermittent positive pressure ventilation [IPPV]) and PICU admission and development of a pleural effusion and/or diaphragmatic dysfunction were documented for each child. The patients were divided into three groups according to whether they had acute liver failure (ALF), chronic liver disease at home (CHOM), or chronic liver failure sufficiently ill to be in the hospital awaiting transplantation (CHOSP). RESULTS: The 36 children with ALF were of similar age to the 138 CHOM and 36 CHOSP children but required longer IPPV (P<0.0001) and PICU stay (P<0.0001). Overall, 17 children developed diaphragmatic dysfunction and 138 pleural effusions; affected children required longer IPPV and PICU stay (P<0.01). Regression analysis demonstrated that diaphragmatic dysfunction, but not pleural effusion development, was associated with prolonged ventilation (P<0.01) and protracted PICU stay (P<0.05). Other risk factors were ALF (P<0.01), retransplantation (P<0.01), and young age (P<0.05). CONCLUSION: Diaphragmatic dysfunction adversely influences PICU morbidity after OLT. Early assessment of diaphragmatic function, and if necessary aggressive management, might improve outcome.     

Aide inspiratoire par masque facial dans l'insuffisance respiratoire aiguë non hypercapnique

This prospective study assessed, in 10 conscious patients without a history of chronic respiratory disease, the feasibility of mechanical pressure support ventilation with PEEP by face mask for the treatment of acute respiratory failure without hypercapnia. Pressure support level was determined to obtain a VT of 5 to 10 mL·kg⁻¹ and a decrease of respiratory rate of more than 20%. FIO₂ and PEEP levels were determined to obtain a SpO₂ > 92% and a PaO₂ > 70 mmHg. The efficiency of the technique was assessed through the time course of respiratory rate, PaO₂, PaCO₂ and SaO₂. The technique was efficient in all patients and tracheal intubation was not required. During face mask ventilation, a significant decrease in respiratory rate and an increase in PaO₂ and SaO₂ were observed. Pressure support ventilation with PEEP by face mask is an efficient technique for the treatment of acute non hypercapnic respiratory failure in conscious and cooperative patients.     

Treatment of acute respiratory failure by prolonged non-invasive ventilation in a child

Purpose

To evaluate the feasibility and the efficacy of non-invasive ventilation (NIV) by nasal mask in a paediatric patient.

Clinical features

A four-year-old girl with acute lymphocytic leukaemia (ALL L₁ pre-pre B) complicated by acute respiratory failure was treated with NIV On admission she exhibited hyperpyrexia (40C), pancytopaenia and severe hypoxia with hypocapnia (PaO₂ = 45 minHg; PaCO₂ = 28.2 mmHg; pH = 7.30; SpO₂ = 76%; ABE = ?7.3 mmol · L^?1. With NIV, PaO₂ improved (PaO₂ = 78 ± 8 mmHg; SpO₂ = 86 ± 2; PaCO₂ = 39 ± 2) throughout the first day. Treatment was continued for six days until the patient was discharged. No complications were recorded.

Conclusion

Non-invasive ventilation by nasal mask may represent a choice in the treatment of acute respiratory failure of parenchymal origin in paediatric haematological patients.     

Contribution of the nasal passage to face mask ventilation: a prospective blinded randomized crossover trial

Background

Previous studies have shown that the nasal passage plays an important role in manual face mask ventilation, but this has yet to be quantitatively assessed. We conducted a prospective randomized crossover clinical trial to compare the change in pressure-controlled face mask tidal volume with and without nasal airway occlusion.

Method

Female patients undergoing elective surgery under general anesthesia served as study subjects. Patients were randomly assigned to face mask ventilation beginning either with or without nasal passage occlusion (achieved with a swimmer’s nose clip), followed by removal or application of the nose clip, respectively. After standardized induction of general anesthesia and muscle paralysis, a tight-fitting face mask was applied to each patient, and tidal volume was measured by the anesthesia machine during pressure-controlled ventilation (10, 15, 20 cm H₂O; 8 breaths·min^?1; inspiratory:expiratory ratio 1:2).

Results

The median [interquartile range] tidal volume was lower with vs without nasal passage occlusion at 10 cm H₂O inspiratory pressure (100 [55-134] mL vs 300 [230-328] mL, respectively; median difference (MD), 200 mL; 95% confidence interval (CI), 157 to 229; P < 0.001), 15 cm H₂O inspiratory pressure (190 [120-230] mL vs 520 [420-593] mL, respectively; MD, 340 mL; 95% CI, 257 to 395; P < 0.001), and 20 cm H₂O inspiratory pressure (270 [215-390] mL vs 790 [713-823] mL, respectively; MD, 520 mL; 95% CI, 390 to 582; P < 0.001).

Conclusion

Nasal passage obstruction considerably reduces tidal volume achieved during face mask ventilation. In some patients, it may be advantageous to relieve nasal airway obstruction for effective face mask ventilation.

Trial registration

UMIN Clinical Trials Registry, number UMIN000022184. Registered 2 May 2016.

     

Role of the nasal airway in regulation of airway resistance during hypercapnia and exercise. Second-Place Resident Award at 1982 Research Forum

Posterior mask rhinomanometry was used to measure nasal resistance during exercise and hypercapnia in 10 healthy adult volunteers. Exercise was produced by peddling a stationary bicycle at three loads. Hypercapnia was produced by breathing O2 mixtures containing 5%, 6%, and 8% CO2. The results showed that nasal resistance decreases linearly as expired CO2 levels and exercise levels increase, minute ventilation increases linearly as expired CO2 levels and exercise levels increase, and nasal resistance varies inversely with minute ventilation during both hypercapnia and exercise. The constant relationship between nasal resistance and minute ventilation during hypercapnia and exercise suggests that nasal resistance is regulated by the respiratory center to match the level of respiratory demand.     

Physiological effects of a lung-recruiting strategy applied during one-lung ventilation

Background: One‐lung ventilation (OLV) affects respiratory mechanics and ventilation/perfusion matching, reducing functional residual capacity of the ventilated lung. While the application of a lung‐recruiting manoeuvre (RM) on the ventilated lung has been shown to improve oxygenation, data regarding the impact of RM on respiratory mechanics are not available. Methods: Thirteen patients undergoing lung resection in lateral decubitus were studied. During OLV, a lung‐recruiting strategy consisting in a RM lasting 1 min followed by the application of positive end‐expiratory pressure 5 cmH₂O was applied to the ventilated lung. Haemodynamics, gas exchange and respiratory mechanics parameters were recorded on two‐lung ventilation (TLV_baseline), OLV before and 20 min after the RM (OLV_pre‐RM, OLV_post‐RM, respectively) and TLV_end. Haemodynamics parameters were also recorded during the RM. Results: The PaO₂/FiO₂ ratio was 358±126 on TLV_baseline; it decreased to 235±113 on OLV_pre‐RM (P<0.01) increased to 351±120 on OLV_post‐RM (P<0.01 vs. OLV_pre‐RM), and remain stable thereafter. During the RM, CI decreased from 3.04±0.7 l/m² OLV_pre‐RM to 2.4±0.6 l/m² (P<0.05), and returned to baseline on OLV_post‐RM (3.1±0.7 l/m², NS vs. OLV_pre‐RM). The RM resulted in alveolar recruitment and caused a significant decrease in static elastance of the dependent lung (16.6±8.9 cmH₂O/ml OLV_post‐RM vs. 22.3±8.1 cmH₂O/ml OLV_pre‐RM) (P<0.01). Conclusions: During OLV in lateral decubitus for thoracic surgery, application to the dependent lung a recruiting strategy significantly recruits the dependent lung, improving arterial oxygenation and respiratory mechanics until the end of surgery. However, the transient haemodynamic derangement occurring during the RM should be taken into account.     

Nasal CPAP therapy: effects of different CPAP levels on pressure transmission into the trachea and pulmonary oxygen transfer

Background: Nasal continuous positive airway pressure (nCPAP) is considered useful for prophylaxis and treatment of respiratory complications following major thoracic surgery. It is unknown, however, which CPAP levels are required to avoid alveolar derecruitment and to consistently improve pulmonary oxygen transfer in patients following thoracotomy. We therefore studied the effects of different nCPAP levels on pressure transmission into the trachea as well as on pulmonary oxygen transfer. Methods: In 10 consecutive patients after cardiac or thoracic vascular surgery, following extubation in the ICU, nCPAP was generated by means of a high‐flow gas source and applied randomly at levels of 5 or 10 cm H₂O. Airway pressure was recorded continuously in the nasal mask and the trachea. The PaO₂/FiO₂ratio was calculated from the tracheal oxygen concentration, and PaO₂ was determined while breathing at an ambient and elevated airway pressure. Haemodynamic variables (heart rate, arterial blood pressure, central venous pressure) were also recorded. Results: Mean pressures in the nasal mask were 5.4±0.1 and 9.7±0.3 cm H₂O. Corresponding tracheal pressures were 2.8±1.0 vs. 7.2±1.1 cm H₂O (P=0.007). With higher mask pressure, the fraction of pressure transferred from the nasal mask into the trachea was larger (0.75±0.03 vs. 0.52±0.05; P=0.04), and tracheal pressures remained positive during the entire respiratory cycle in all patients. In contrast, with 5.4 cm H₂0, negative pressure changes during inspiration occurred in five out of 10 patients. The PaO₂/FiO₂ ratio increased from 183±53 (ambient pressure) to 199±74 (nCPAP 5.4 cm H₂O; P=0.25) and to 333±54 (nCPAP 9.7 cm H₂O; P=0.003). Nasal CPAP did not alter hemodynamics. Conclusion: Nasal CPAP is an effective non‐invasive means of increasing tracheal and thus intrathoracic pressure without adverse hemodynamic effects. Only mask pressures of 9–10 cm H₂O were sufficient to consistently improve pulmonary oxygen transfer in patients following thoracotomy.     

The oxygram: an unappreciated technique for assessing hypoventilation in paediatric anaesthesia

This study assessed the use of the oxygram, specifically the difference between inspired and end tidal oxygen concentrations, F₁-eto₂, to detect hypoventilation in a paediatric population. Ten healthy unpremedicated children, aged 1-5 years, scheduled for elective minor urologic surgery were studied. A Modulus® II Plus Anesthesia System was used, with Rascal® II Anesthesia Gas Monitor for analysis of anaesthetic and respiratory gases with a Wright spirometer to monitor minute ventilation. Following inhalational induction, intubation, and caudal anaesthetic administration, the children breathed end-tidal halothane concentrations of 0.5%, 2%, 1.5%, 1.0%, and again 0.5% with measurements of inspired and end-tidal oxygen and halothane concentrations, end tidal CO₂ (Petco₂), minute ventilation (VE), respiratory rate (f), pulse oximetry saturations (Spo₂), heart rate (HR), and mean blood pressure (BP). FI-ETO₂ increased proportionately with hypoventilation at 2%, 1.5%, and 1% halothane concentrations compared to the 0.5% halothane group (P < 0.0001, 0.0008, and 0.0013 respectively), associated with corresponding increases of Petco₂ and decreases of minute ventilation (VE). We conclude the oxygram was effective in monitoring hypoventilation in paediatric patients within the format of the protocol studied