Continuous positive airway pressure breathing (CPAP)

CPAP is a technique of respiratory care which was originally described in the management of the respiratory distress syndrome of the newborn and later in the post operative management of the cardiac infant following surgery. It has potential value in the respiratory management of older children and adults. Apparatus is described suitable for the application of continuous airway pressure during spontaneous ventilation via endotracheal tube in either neonates or adults. The inspired oxygen content is adjustable and the fresh gas warmed and humidified. High and low pressure alarms are not considered necessary. A head-harness is described for the application of CPAP in neonates via twin nasal or nasopharyngeal tubes. This equipment may be obtained from Messrs. Lusterlite Products Limited, 56 Devon Road, Leeds 2.     

Continuous positive airway pressure in the treatment of postoperative hypoxia

The physiopathology of postoperative hypoxia has been analysed, the cause being identified in the worsening of the V/Q ratio consequent on the reduction in CFR. By increasing CFR, CPAP reduces the superimposition of Tidal Volume and Closing Volume, thus reducing dysventilated zones and thereby improving the V/Q ratio and oxyaemia. With these premises, 18 patients undergoing cholecystectomy were examined; 8 of them were treated in the postoperative period with CPAP at pre-established intervals. The results confirm its effectiveness in terms of PaO2 improvement and the need for constant administration, considering that the benefits are lost when the patient is disconnected from the mask.     

Continuous positive airway pressure and lung separation during cardiopulmonary bypass to facilitate congenital heart surgery via the right thorax in children

We describe a fast track anesthesia technique that facilitates congenital heart surgery via right axillary thoracotomy in children. Continuous positive airway pressure on the dependent lung, before and during cardiopulmonary bypass, approximates the heart towards the chest wall incision, and significantly improves the surgeon's access to the heart.     

Beneficial effects of bilevel positive airway pressure after surgery under cardiopulmonary bypass

To support injured lungs, we have been applying bilevel positive airway pressure for adult patients undergoing surgery with cardiopulmonary bypass. Among 120 consecutive patients, 31 patients whose PaO2/FiO2 decreased to less than 180 after extubation assigned to the intermittent 15 min bilevel positive airway pressure (7.3+/-3.6 times per patient). Bilevel positive airway pressure improved oxygenation (PaO2/FiO2: 128+/-43 vs. 198+/-62, P=0.004) and allowed the patients with poor oxygenation after extubation to maintain PaO2/FiO2 levels similar to those of the patients without bilevel positive airway pressure. In conclusion, the bilevel positive airway pressure therapy after extubation was effective to improve lung oxygenation non-invasively in adult patients undergoing more invasive surgery with prolonged cardiopulmonary bypass.     

Continuous arterial and venous blood gas monitoring during cardiopulmonary bypass

A new monitoring technique, based on optical fluorescence chemistry, allows continuous monitoring of all blood gas variables during cardiopulmonary bypass. To evaluate the clinical performance of this monitor, we drew 220 arterial and 216 venous blood samples from 15 patients, and simultaneous blood gas values displayed by the monitor were compared with standard laboratory measurements. The continuous monitor predicted laboratory values with varying degrees of accuracy. (R2 values by linear regression: arterial oxygen tension 0.86, venous oxygen tension 0.36, arterial carbon dioxide tension 0.58, venous carbon dioxide tension 0.72, arterial pH 0.53, venous pH 0.58; pH 0.53, venous pH 0.58; p less than 0.0001). Monitor values of arterial oxygen tension overestimated laboratory values (bias = + 43.5 mm Hg), but the laboratory reference method likely underestimated true arterial oxygen tension in the high range achieved on bypass. Monitoring of venous oxygen tension was imprecise (precision = +/- 6.51 mmHg), regardless of whether stable conditions existed during the sampling period. Monitoring of carbon dioxide tension and pH showed small bias (carbon dioxide tension within 2 mm Hg, pH within 0.03) and good precision (carbon dioxide tension within 3 mm Hg, pH within 0.03). With the development of unstable conditions on bypass, monitor arterial oxygen tension values showed a changing relationship to corresponding laboratory values. In conclusion, arterial and venous carbon dioxide tension and pH monitoring provide acceptably accurate alternatives to laboratory measurement of these variables during cardiopulmonary bypass. Arterial oxygen tension monitoring accurately indicates changes in oxygen tension in the arterial oxygen tension range typically produced during extracorporeal circulation. Oxygen tension monitoring in the venous oxygen tension range is too imprecise for clinical decision-making purposes.     

Ventilatory support by continuous positive airway pressure breathing improves gas exchange as compared with partial ventilatory support with airway pressure release ventilation

In acute lung injury, airway pressure release ventilation (APRV) with superimposed spontaneous breathing improves gas exchange compared with controlled mechanical ventilation. However, the release of airway pressure below the continuous positive airway pressure (CPAP) level may provoke lung collapse. Therefore, we compared gas exchange and hemodynamics using a crossover design in nine pigs with oleic acid-induced lung injury during CPAP breathing and APRV with a release pressure level of 0 and 5 cm H(2)O. At an identical minute ventilation (V(E) 8 L/min) spontaneous breathing averaged 55%, 67%, and 100% of V(E) during the two APRV modes and CPAP, respectively. Because of the concept of APRV, mean airway pressure was highest during CPAP and lowest during APRV with a release pressure of 0 cm H(2)O. Shunt was reduced to almost half during CPAP (6.6% of Q(t)) compared with both APRV-modes (13.0% of Q(t)). Cardiac output and oxygen consumption, in contrast, were similar during all three ventilatory settings. Thus, in our lung injury model, CPAP was superior to partial ventilatory support using APRV with and without positive end-expiratory pressure. This may be attributable to beneficial effects of spontaneous breathing on gas exchange as well as to rapid lung collapse during the phases of airway pressure release below the CPAP level. These findings may suggest that the amount of mechanical ventilatory support using the APRV mode should be kept at the necessary minimum. IMPLICATIONS: Oxygenation is better with continuous positive airway pressure breathing than with partial mechanical ventilatory support using airway pressure release ventilation. Therefore, mechanical ventilatory support achieved by a cyclic release of airway pressure during APRV should be kept at the minimum level that enables enough ventilatory support for patients to avoid respiratory muscle fatigue.     

Inert gas exchange during pneumoperitoneum at incremental values of positive end-expiratory pressure

Laparoscopy is a surgical technique for a growing variety of abdominal operations. In patients undergoing this procedure, arterial blood oxygenation and hemodynamics are frequently depressed. This study evaluated the effect of different levels of positive end-expiratory pressure (PEEP) during intraperitoneal CO(2) insufflation on the lung's ventilation-perfusion distribution in a porcine model. We studied 13 anesthetized pigs with an intraperitoneal pressure of 15 cm H(2)O applied at either incremental values of PEEP (5-20 cm H(2)O, increments of 5 cm H(2)O) or a constant PEEP of 5 cm H(2)O. The effects of CO(2) pneumoperitoneum on inert gas exchange and hemodynamics were examined with the multiple inert gas elimination technique. During pneumoperitoneum, gas exchange was most augmented by 15 and 20 cm H(2)O of PEEP. Although the differences in hemodynamics between the individual settings were insignificant, 10 cm H(2)O of PEEP provided the smallest impairment of hemodynamics. We conclude that PEEP of 15 H(2)O during pneumoperitoneum resulted in a modest hemodynamic depression but significant gas exchange augmentation in our experiment. IMPLICATIONS: Anesthetized pigs, with a pneumoperitoneum of 15 cm H(2)O, were treated either with incremental values of positive end-expiratory pressure (5-20 cm H(2)O, increments of 5 cm H(2)O) or with a constant positive end-expiratory pressure of 5 cm H(2)O. Fifteen and 20 cm H(2)O resulted in significantly improved pulmonary gas exchange compared with 5 cm H(2)O.     

The effect of bi-level positive airway pressure mechanical ventilation on gas exchange during general anaesthesia

Background. Atelectasis may occur and ventilation–perfusionmismatch may increase during general anaesthesia with neuromuscularparalysis and mechanical ventilation, though preservation ofsome intermittent muscle contraction might mitigate this process.There is still no ideal manoeuvre to minimize such mismatchor atelectasis. Bi-level positive airway pressure (BiPAP) ventilationadjusts to extra breaths and improves gas exchange during recoveryof diaphragm function after neuromuscular paralysis. We hypothesizethat BiPAP ventilation may limit the development of pulmonaryshunt and may improve ventilation–perfusion mismatch whencompared with standard IPPV, with or without PEEP when neuromuscularparalysis has been used during surgery. Methods. Twenty ventilated patients either on BiPAP or IPPVwith or without PEEP were studied randomly using the multipleinert gas elimination technique (MIGET) at 60 and 120 min afterrocuronium at induction and after 60 min. Non-invasive cardiacoutput (NICO^®) monitoring and plasma concentrations of rocuroniumwere measured. We compared the data of MIGET, gas exchange,haemodynamic variables and pulmonary mechanics measurementsbetween the different ventilatory modes. Results. Intrapulmonary shunt (blood flow to ) did not increase at 60 min of anaesthesia in anyof the different ventilation modes compared with the shunt valuebefore anaesthesia. Log standard deviation of perfusion increasedin IPPV, with and without PEEP groups, compared with the baseline(P<0.05) but did not increase in the BiPAP group. BiPAP ventilationgenerated a higher level of Pa_O2 than IPPV with or without PEEP(P<0.05). Conclusion. BiPAP ventilation was beneficial in decreasing ventilation–perfusionmismatch and improving oxygenation when compared with conventionalIPPV (with or without PEEP). ³Present address: Department of Anaesthesia, Guangzhou MedicalCollege, Guangzhou, China     

Continuous positive airway pressure breathing in the postoperative management of the cardiac infant

Crew, A. D., Varkonyi, P. I., Gardner, L. G., Robinson, Q. L. A., Wall, E., and Deverall, P. B. (1974).Thorax, 29, 437-445. Continuous positive airway pressure breathing in the postoperative management of the cardiac infant. Continuous positive airway pressure with spontaneous ventilation was used in the postoperative period following palliative or corrective surgery for congenital heart defects in a group of children of less than 3 years of age. After stabilization of the cardiovascular state, continuous positive airway pressure breathing (CPAP) was shown to be a suitable alternative to continuous positive pressure ventilation (CPPV). A statistically significant increase in PaO₂ was observed on changing from CPPV to CPAP. A statistically significant decrease in PaO₂ and increase in pulmonary venous admixture was observed after discontinuing the positive airway pressure and allowing the patient to breathe at ambient pressure.     

Arterial pressure and deltoid muscle gas tensions during cardiopulmonary bypass in man

The results of this study demonstrate that standard techniques of conducting cardiopulmonary bypass produce low muscle oxygen and high muscle carbon dioxide tensions and, thus, little perfusion of skeletal muscle. Our findings also show that PmO2 and PmCO2 do not return to pre-bypass levels until the mean arterial blood pressure exceeds 12 kPa (90 torr) during bypass and that utilization of vasopressor drugs during bypass maintains the pressure; but at the expense of muscle blood flow. The data indicate that both high mean blood pressure and high flow are necessary during bypass to ensure skeletal muscle perfusion and suggest, when combined with preliminary animal findings, that this type of bypass perfusion may prove to be superior to standard techniques in hastening recovery after cardio-pulmonary bypass.     

Safety and efficacy of postoperative continuous positive airway pressure to prevent pulmonary complications after Roux-en-Y gastric bypass

Continuous positive airway pressure (CPAP) is used to prevent apneic arrest and/or hypoxia in patients suffering from obstructive sleep apnea. This modality has not been universally accepted for patients following upper gastrointestinal surgery because of concerns that pressurized air will inflate the stomach and proximal intestine, resulting in anastomotic disruption. This study was performed to assess the safety and efficacy of postoperative CPAP for patients undergoing a gastrojejunostomy as part of a Roux-en-Y gastric bypass (RYGB) procedure. A total of 1067 patients (837 women [78%] and 230 men [22%]) were prospectively evaluated for the risk of developing anastomotic leaks and pulmonary complications after the RYGB procedure. Of the 1067 patients undergoing gastric bypass, 420 had obstructive sleep apnea and 159 were dependent on CPAP. There were 15 major anastomotic leaks, two of which occurred in CPAP-treated patients. Contingency table analysis demonstrated that there was no correlation between CPAP utilization and the incidence of major anastomotic leakage (P = 0.6). Notably, no episodes of pneumonia were diagnosed in either group. Despite the theoretical risk of anastomotic injury from pressurized air delivered by CPAP, no anastomotic leaks occurred that were attributable to CPAP. There were no pulmonary complications in a patient population that is at risk for developing them postoperatively. CPAP is a useful modality for treating hypoventilation after RYGB without increasing the risk of developing postoperative anastomotic leaks. Presented at the Forty-Second Annual Meeting of The Society for Surgery of the Alimentary Tract, Atlanta, Georgia, May 20–23, 2001 (poster presentation).     

Five meters of H(2)O: the pressure at the urinary bladder neck during human ejaculation

BACKGROUND: There are no data in the literature on pressure changes in the prostatic urethra during ejaculation. In healthy men, it has always been postulated that there must be a pressure gradient in order to prevent retrograde ejaculation, but scientific proof for that is pending. METHODS: In five healthy male volunteers, the pressure profile in the prostatic urethra was registered during ejaculation, using a 10 French balloon catheter with 16 pressure channels. The channels were arranged in pairs at 5-mm intervals, beginning just below the balloon at the bladder neck and extending down to the external urethral sphincter. RESULTS: In the proximal part of the prostatic urethra, a pressure of up to 500 cm of H(2)O was measured in all subjects. Contrary to that, pressures did not exceed 400 cm of H(2)O distally to the verumontanum. CONCLUSIONS: A novel method to register the pressure profile in the lower urinary tract during ejaculation (ejaculomanometry) is presented. This study adds to the knowledge of the normal physiology of reproductive function and may be useful in the evaluation of male sexual and reproductive disorders.