The effect of caudal block on functional residual capacity and ventilation homogeneity in healthy children

Caudal block results in a motor blockade that can reduce abdominal wall tension. This could interact with the balance between chest wall and lung recoil pressure and tension of the diaphragm, which determines the static resting volume of the lung. On this rationale, we hypothesised that caudal block causes an increase in functional residual capacity and ventilation distribution in anaesthetised children. Fifty-two healthy children (15-30 kg, 3-8 years of age) undergoing elective surgery with general anaesthesia and caudal block were studied and randomly allocated to two groups: caudal block or control. Following induction of anaesthesia, the first measurement was obtained in the supine position (baseline). All children were then turned to the left lateral position and patients in the caudal block group received a caudal block with bupivacaine. No intervention took place in the control group. After 15 min in the supine position, the second assessment was performed. Functional residual capacity and parameters of ventilation distribution were calculated by a blinded reviewer. Functional residual capacity was similar at baseline in both groups. In the caudal block group, the capacity increased significantly (p < 0.0001) following caudal block, while in the control group, it remained unchanged. In both groups, parameters of ventilation distribution were consistent with the changes in functional residual capacity. Caudal block resulted in a significant increase in functional residual capacity and improvement in ventilation homogeneity in comparison with the control group. This indicates that caudal block might have a beneficial effect on gas exchange in anaesthetised, spontaneously breathing preschool-aged children with healthy lungs.     

A deeper level of ketamine anesthesia does not affect functional residual capacity and ventilation distribution in healthy preschool children

BACKGROUND: Ketamine is commonly used in children in the emergency setting and while undergoing diagnostic and therapeutic interventions because of its combination of hypnotic and analgesic properties. Although studies comparing various levels of ketamine anesthesia are lacking, previous work suggests that lung mechanics might only be minimally affected by ketamine. METHODS: After approval from the Ethics Committee, anesthesia was induced with 2 mg.kg(-1) racemic ketamine followed by a continuous infusion of ketamine 2 mg.kg(-1) h(-1) (level I) in 26 children (2-6 years of age), and after 5 min, the first set of measurements was performed. Then, a second bolus of ketamine 2 mg.kg(-1) followed by ketamine 4 mg.kg(-1) h(-1) was administered (level II) and after 5 min, the second set of measurements was performed. Functional residual capacity (FRC) and lung clearance index (LCI) were calculated using a multibreath analysis by a blinded observer. RESULTS: Functional residual capacity and LCI did not change between the two levels (FRC 25.6 [4.3] ml.kg(-1) vs 25.5 [4.2] ml.kg(-1), P=0.769, LCI 10.5 [1.2] vs 10.3 [1.1], P=0.403). The minute ventilation was similar between the two levels of anesthesia. The University of Michigan Sedation Scale increased from 3 (3) to 4 (3-4) at the second level of ketamine anesthesia. CONCLUSIONS: A deeper level of anesthesia induced by ketamine does not affect FRC, ventilation distribution or minute ventilation suggesting that the depth of ketamine anesthesia has a minimal effect on pulmonary function.     

Perioperative functional residual capacity

The literature dealing with the magnitude, mechanism and effects of reduced FRC in the perioperative period is reviewed. During general anaesthesia FRC is reduced by approximately 20%. The reduction is greater in the obese and in patients with COPD. The most likely mechanism is the loss of inspiratory muscle tone of the muscles acting on the rib cage. Gas trapping is an additional mechanism. Lung compliance decreases and airways resistance increases, in large part, due to decreased FRC. The larynx is displaced anteriorly and elongated, making laryngoscopy and intubation more difficult. The change in FRC creates or increases intrapulmonary shunt and areas of low ventilation to perfusion. This is due to the occurrence of compression atelectasis, and to regional changes in mechanics and airway closure which tend to reduce ventilation to dependent lung zones which are still well perfused. Abdominal and thoracic operations tend to increase shunting further. Large tidal volume but not PEEP will improve oxygenation, although both increase FRC. Both FRC and vital capacity are reduced following abdominal and thoracic surgery in a predictable pattern. The mechanism is the combined effect of incisional pain and reflex dysfunction of the diaphragm. Additional effects of thoracic surgery include pleural effusion, cooling of the phrenic nerve and mediastinal widening. Postoperative hypoxaemia is a function of reduced FRC and airway closure. There is no real difference among the various methods of active lung expansion in terms of the speed of restoration of lung function, or in preventing postoperative atelectasis/pneumonia. Epidural analgesia does not influence the rate of recovery of lung function, nor does it prevent atelectasis/pneumonia.     

Effect of apparatus on functional residual capacity

As the route of breathing and use of airway apparatus such as mask, mouthpiece and noseclip can alter breathing pattern, this study has used the helium dilution method to estimate the effects of mouthpiece and mask breathing on functional residual capacity (FRC) in the supine position, and the change in FRC that occurs between the sitting and supine positions while breathing by mouthpiece. In 13 normal subjects, breathing by mouthpiece, FRC was smaller, by a median of 1.07 litre (interquartile values 0.73-1.43 litre) in the supine compared with the sitting position (P < 0.01), but residual volume (RV) did not change significantly. FRC measured in the supine position was significantly greater when breathing by mask than by mouthpiece (0.25, 0.04-0.38 litre) and RV was greater by similar amounts (0.20, -0.02 to 0.49 litre). This difference may result from increased inspiratory activity while breathing via the mask.      

Impact of Trendelenburg positioning on functional residual capacity and ventilation homogeneity in anaesthetised children

Trendelenburg positioning, a head-down tilt, is routinely used in anaesthesia when inserting a central venous catheter to increase the calibre of the jugular or subclavian veins and to prevent an air embolism. We investigated the impact of Trendelenburg positioning on functional residual capacity and ventilation homogeneity as well as the potential reversibility of these changes by repositioning and/or a recruitment manoeuvre in children with congenital heart disease. Functional residual capacity and ventilation homogeneity were assessed in 20 anaesthetised children between the ages of 3 months and 8 years who required central venous catheterisation before undergoing cardiac surgery. Functional residual capacity was measured (1) in the supine position, (2) in the Trendelenburg position, (3) after repositioning supine and (4) after a recruitment manoeuvre to total lung capacity which was performed by manually elevating the airway pressure to 40 cmH(2)O for ten consecutive breaths. Adopting the Trendelenburg position led to a significant decrease in functional residual capacity (median [range]- 12 (6-21)%) and increase in lung clearance index (12 (2-19)%). Baseline values were not reached after repositioning supine in any patient until after a standardised recruitment manoeuvre was performed.     

Impact of caudal block on functional residual capacity and ventilation distribution in anaesthetized preschool children

Introduction: In children, general anaesthesia is often performed in combination with regional anaesthesia and caudal block (CB) is probably the most commonly used central neuroaxial blockade. The administration of local anaesthetics results in a motor blockade. The impact of this motor blockade induced by CB on the functional residual capacity (FRC) and ventilation distribution is unknown. The aim of this study was to determine the impact of CB versus control on FRC and ventilation distribution in preschool children. We hypothesized that an effective CB would lead to an increase of FRC and ventilation distribution while these parameters would remain unchanged in the control group. Methods: After approval from the local Ethics Committee, 52 preschool children (15–30 kg, 3–8 years) without cardiopulmonary disease who were to undergo elective surgery requiring combined general/regional anesthesia with a CB, were randomly allocated into two groups: CB (n = 26) or control (n = 26). Anesthesia was standardized using a propofol TCI for children. All children were breathing spontaneously via a laryngeal mask airway. FRC and lung clearance index (LCI), a measure of ventilation distribution, were calculated using a sulfur‐hexafluoride gas (SF₆) multibreath washout technique. A blinded reviewer performed off‐line analyses of the data. Following the first measurement in the supine position (baseline), all children were turned into the left‐lateral position. The CB group received a CB (0.2 ml·kg^‐1 bupivacaine 0.25% + epinephrine 1: 200 000 test dose and 0.8 ml·kg^‐1 bupivacaine 0.175%), while in the control group no intervention took place. After 5 min in the lateral position, all children were turned back to the supine position. After 15 min, the effectiveness of the CB was tested by pinching the skin at the L1 level with any movement being taken as a noneffective block (n = 0), and the second FRC assessment was performed in both groups. Results: At baseline, FRC and LCI were similar for the two groups. In the CB group, FRC (mean ± SD) increased from 17.0 ± 4.3 ml·kg^‐1 to 20.5 ± 5.1 ml·kg^‐1 (P < 0.0001) after an effective CB while FRC in the control group remained unchanged (17.2 ± 4.9 ml·kg^‐1 to 17.1 ± 4.8 ml·kg^‐1 (P = 0.0757). At the same time, the LCI decreased from 12.0 ± 2.5 to 9.37 ± 1.7 (P < 0.0001) in the CB group, while it remained constant in the control group (10.8 ± 2.7 vs 10.7 ± 2.6, P = 0.1515). Conclusions: CB resulted in a significantly increased FRC and ventilation distribution, whereas these parameters did not change in the control group. This indicates that a CB could have a major impact on respiratory function in anaesthetized, spontaneously breathing children. Additionally, the constant values for FRC and LCI in the control group showed that there was no ‘over‐time’ effect on these two parameters during the assessed study period. Acknowledgement: The study was funded by the Department of Anaesthesia, University of Basel, Switzerland and by the Swiss Association of Anaesthesia and Reanimation (SGAR).     

Impact of depth of propofol anaesthesia on functional residual capacity and ventilation distribution in healthy preschool children

Background: Propofol is commonly used in children undergoing diagnosticinterventions under anaesthesia or deep sedation. Because hypoxaemiais the most common cause of critical deterioration during anaesthesiaand sedation, improved understanding of the effects of anaestheticson pulmonary function is essential. The aim of this study wasto determine the effect of different levels of propofol anaesthesiaon functional residual capacity (FRC) and ventilation distribution. Methods: In 20 children without cardiopulmonary disease mean age (SD)49.75 (13.3) months and mean weight (SD) 17.5 (3.9) kg,anaesthesia was induced by a bolus of i.v. propofol 2 mg kg^–1followed by an infusion of propofol 120 µg kg^–1 min^–1(level I). Then, a bolus of propofol 1 mg kg^–1was given followed by a propofol infusion at 240 µg kg^–1 min^–1(level II). FRC and lung clearance index (LCI) were calculatedat each level of anaesthesia using multibreath analysis. Results: The FRC mean (SD) decreased from 20.7 (3.3) ml kg^–1at anaesthesia level I to 17.7 (3.9) ml kg^–1at level II (P < 0.0001). At the same time, mean (SD) LCIincreased from 10.4 (1.1) to 11.9 (2.2) (P = 0.0038), whereasbispectral index score values decreased from mean (SD) 57.5(7.2) to 35.5 (5.9) (P < 0.0001). Conclusions: Propofol elicited a deeper level of anaesthesia that led toa significant decrease of the FRC whereas at the same time theLCI, an index for ventilation distribution, increased indicatingan increased vulnerability to hypoxaemia.     

Validation and clinical feasibility of nitrogen washin/washout functional residual capacity measurements in children

Background: The functional residual capacity (FRC) is an important parameter in pediatric respiratory monitoring but it is difficult to assess in the clinical setting. We have introduced a modified N₂ washout method utilizing a change of F_IO₂ of 0.1 for FRC measurement in adult respiratory monitoring. This study validated the algorithm in a pediatric lung model and investigated the stability and feasibility in a pediatric peri‐operative and intensive care setting. Methods: The lung model was ventilated in combinations of ventilatory modes, CO₂ production, model FRC and respiratory rates. Sixteen children from 10 days to 5 years were studied peri‐operatively with controlled ventilation using a Mapleson D system and in the intensive care unit using a Servo‐i ventilator in a supported spontaneous mode. FRC was measured during stable metabolic, respiratory and circulatory periods at positive end expiratory pressure of 3–4 and 7–8 cmH₂O. Results: In the model and in the clinical setting, we found an excellent agreement between washout and washin measurements of FRC as well as acceptable coefficients of repeatability. Conclusion: FRC was satisfactorily measured by a modified N₂ algorithm and may be included as a monitoring variable in pediatric respiratory care. Pediatric FRC monitoring demands strictly stable conditions as measurements are performed close to the limits of the monitor's specifications.     

Mechanism of functional residual capacity increase in haemorrhagic shock

Shock was elicited in anaesthetized dogs by maintaining a haemorrhagic hypotension of 4 kPa until 30 per cent spontaneous refusion, followed by total reinfusion. Functional residual capacity (FRC) and minute ventilation increased considerably similarly to our previous experiments. Lactate content in both the external intercostal and the biceps femoris muscles increased significantly in advanced shock. The expiratory external abdominal oblique muscle showed electromyographic signs of fatigue. At the height of the FRC changes tonic contraction of the external intercostal muscle could be demonstrated electron microscopically. This tonic contraction is the main factor in the large FRC rise in late shock forming the basis of a hitherto unknown vicious circle.     

Decrease in functional residual capacity and ventilation homogeneity after neuromuscular blockade in anesthetized preschool children in the lateral position

BACKGROUND: While functional residual capacity (FRC) is reduced in children undergoing general anesthesia, the lateral position leads to an increase in FRC compared with the supine position. The impact of neuromuscular blockade remains unknown. We tested the hypothesis that neuromuscular blockade leads to a decrease in FRC and increase in lung clearance index (LCI) while the application of positive endexpiratory pressure (PEEP) of 6 cmH(2)O leads to a restoration in both parameters. METHODS: After approval of the local Ethics Committee, we studied 18 preschool children (2-6 years) without cardiopulmonary disease, who were scheduled for elective surgery. Anesthesia was standardized using propofol and fentanyl. FRC and LCI were calculated by a blinded observer using a SF6 multibreath washout technique with an ultrasonic transit-time airflow meter (Exhalyzer D). Measurements were taken in the left lateral position (PEEP 3 cmH2O) after 1. intubation with a cuffed tracheal tube, 2. neuromuscular blockade with rocuronium, and 3. the additional application of PEEP (6 cmH2O). RESULTS: Functional residual capacity mean (sd) decreased from 31.6 (4.4) ml.kg(-1) to 27.6 (4.2) ml.kg(-1) (P<0.001) following neuromuscular blockade while the LCI increased from 6.54 (0.6) to 7.0 (0.6) (P相似文献   

Measurement of functional residual capacity by sulfur hexafluoride washout

Measurement of functional residual capacity (FRC) by the open-circuit multiple breath tracer gas washout technique is an established method. A system based upon washout of sulfur hexafluoride (SF6) during mechanical ventilation is described. The central unit in the system is a sensitive and rapid-response infrared SF6 analyzer. SF6 is washed in until the alveolar concentration of SF6 is 0.5%, a concentration so low that the supply of other gases is hardly influenced. During washout, the flow of SF6 from the lungs is calculated by a computer every 10 ms from signals representing expiratory flow and SF6 concentration. The total volume of SF6, washed out, is calculated by integration of SF6 flow. Since the alveolar concentration at the end of washin is known, the lung volume may be obtained. The measurement procedure is highly automated and the result is presented by the computer immediately after washout. Accurate and reproducible results in model lung tests were obtained during air and N2O/O2 ventilation. Comparison with body plethysmography (FRCBOX) in eight sitting healthy subjects gave the following: FRCSF6 = 7 ml + 0.98 X FRCBOX, r = 0.99. Comparison with nitrogen washout (FRCN2) in five postoperative patients gave the following: FRCSF6 = 59 ml + 0.97 X FRCN2, r = 0.97. FRCSF6 during N2O/O2 ventilation was the same as during air/O2 ventilation in a group of paralyzed patients. The measurement system has not been tested in patients with obstructive lung disease.