Mohammad Maroof ( Department of Anaesthesiology and Intensive Care, King Fahad National Guard Hospital, Riyadh, Saudi Arabia. )
Rashid M. Khan ( Department of Anaesthesiology and Intensive Care, King Fahad National Guard Hospital, Riyadh, Saudi Arabia. )
Bruce G. Ryley ( Department of Anaesthesiology and Intensive Care, King Fahad National Guard Hospital, Riyadh, Saudi Arabia. )
Naveed Bad ( Department of Anaesthesiology and Intensive Care, King Fahad National Guard Hospital, Riyadh, Saudi Arabia. )
Timothy Cooper ( Department of Anaesthesiology and Intensive Care, King Fahad National Guard Hospital, Riyadh, Saudi Arabia. )
Twelve ASA I and II adult male patients (26.2SD±8.3year, range 16-45 year; 68SD±15.4 kg. range 45-95 kg) undergoing general anaesthesiaforelective surgical procedures developed acute P0 in the post-anaesthetic period 1987 to 1993. Nine of these patients had undergone surgery of the head and neck region (Table).
All patients underwent an uneventful general anaesthetic using nitrous oxide and oxygen with isoflurane or enflurane and intermittent fentanyl in appropriate dose. All patients were intubated and ventilation was controlled after relaxation with atracurium or vecuronium. At the end of the surgery, residual muscle paralysis was adequately reversed monitoring train-of-four ratio in each case. Patients were extubated after resumption of adequate spontaneous respiration. Patient # 1 to 6 (Table) were adequately breathing and saturating well (arterial oxygen saturation, Sa02>95%) prior to transfer from operation room (OR) to post-anaesthesia recovery room (PARR). However, patients # 1 to 4 were recorded to be drowsy on arrival in PARR. Patient # 1 was noted to have obstructed breathing while patient # 5 was observed to be apneic and cyanosed on arrival in PARR. Patient #6 developed laryngospasm on arrival in PARR. All these 6 patients gradually desaturated (Sa02<90%) and went on to develop signs and symptoms of acute P0 over the next 5-45 minutes despite appropriate airway management and oxygen (02) administration with face mask. Use of furosemide, morphine and appropriate respiratory management quickly resolved the pulmonary oedemain less than 24 hours in all patients. Patient # 7 (Table) underwent elective excision of a tongue lesion under general anaesthesia. A pharyngeal pack was placed by the attending anaesthesiologist. At the time of extubation the relieving anaesthesiologist, unaware of the phaiyngeal pack, extubated the patient. The patient soon developed obstructed breathing and oxygen desaturation. Laiyngoscopy within 5 minutes revealed the obstructing pack. Despite the relief of obstruction, patient developed bilateral chest crepitation 30 minutes later in the PARR. Patient responded well to conservative management without the need for intubation and positive pressure ventilation. Patient # 8 (Table) a 33 year old male with an oroniaxillary fistula underwent uneventful repair under general anaesthesia. Towards the end of the surgery, a size 18 Foley catheter was passed through his right nostril and the balloon inflated in the post-nasal space to provide tamponade to stop further bleeding. The free limb of the catheter was anchored to the right cheek with the aid of adhesive tape. Following uneventful extubation and spontaneous breathing for a few minutes, the patient was transferred to PARR. Within minutes of arrival, his oxygen saturation began to drop rapidly from the initial 100% despite oxygenation via bag mask. The patient became progressively cyanosed and bradycardic. Laryngoscopy revealed the balloon of the Foley catheter completely obstructing the larynx. Balloon was removed and the patient intubated. Florid PO was evidenced by the copious pink froth that issued from the endotracheal tube. He responded well to intra-venous morphine, diuretics and intermittent positive pressure ventilation (IPPV) with mild positive end expiratory pressure (PEEP). He was discharged from the ICU on the 2nd post-operative day. Patient #9 to 12 (Table) had uneventful intra-operative period. On extubation, each developed acute laiyngospasm. Suxamethonium 25-50 mg was administered to relieve the spasm after initial failure to ventilate them with bag mask. All these patients rapidly desatunted (Sa02<90%) and were re-intubated in the OR. Each of these 4 patients demonstrated florid pulnionaiy oedema in the form of copious pink froth issuing via the endotracheal tube. After initiation of therapy with fumsemide, morphine and IPPV they were transferred to the ICU for continuing management of acute P0. All were extubated within 24-36 hours and discharged from the ICU in less than 48 hours with complete resolution of acute P0. Increasing hypoxia, as demonstrated by the pulse oximetry, was theflrstsignofimpendingPO ineachcase. This was further confirmed by arterial blood gas analysis. The clinical diagnosis of the P0 varied from volume of fluid pouring up an endotraeheal tube to coughing blood stained sputum. All patients had crepitations on auscultation of the chest. Diagnosis of P0 was confirmed by chest x-ray in all patients. This was followed with serial chest x-rays which showed quick resolution. All patients had a final normal chest x-ray prior to discharge from the hospital.
P0 associated with UAO have been called negative pressure pulmonary oedemabecause it is largely related to the development of markedly negative intra-pleural pressure8,9. A number of conditions can produce UAO. Willms and Shure7 analyzed 26 cases of P0 due to UAO from the literature and observed that laryngospasm was the most common cause of UAO in 42.3% (11/26). 9 of these 11 patients (81.8%) had post-extubation laryngospasm. Our observations were nearly identical. UAO secondary to laryngospasm was observed in 41.6% (5/12) of our patients. Of these 80% (4/5) had post-extubation laryngospasm. Lorch and Sahn5 have identified 3 factors predisposing to UAO. These are: 1) Anatomically difficult intubation; 2) Nasal, Oral or Pharyngeal surgical site; 3) Obesity. One or more of these factors were present in 5 of our patients (41.6%). However, there are several case reports to demonstrate that this syndrome may also complicate UA0 in patients without additional identifiable risk factors3,7,10,12. The pathogenesis of P0 associated with UAO is multifactorial5. However, the principal factor leading to P0 following UAO appears to be the generation of markedly negative intra-thoracic pressure due to forceful inspiratory effort against a closed glottis. This results in a decrease in pulmonary interstitial pressure favouring transudation of oedema fluid from puhnonary capillaries13. It has been observed that markedly negative intra- thoracic pressure alone can explain the association of UAO and PO14,15. A decrease in intra-thoracic pressure may also lead to augmented venous return which theoretically increases pulmonary blood volume and pulmonary arterial pressure. This fact also may contribute to the hydrostatic transudation of fluid. In addition, increased venous return is associated with right ventricular distention and a decrease in left ventricular compliance as a result of the left ward shift of the intra-veniricular septum (ventricular inter-dependence) 16,17. This leads to an increase in the left ventricular end-diastolic pressure thereby further increasing the pulmonary vascular pressure and hydrostatic transudation of fluid. All our patients were young males and ASA I or II. It has been shown that these young healthy patients may be at increased risk for laiyngospasm-induced P0 because they can generate large negative intra-thoracic pressure18. In our series patients #2 to 5 (Table I)who were drowsy on arrival in the PARR, exhibited semi-obstructed airway possibly due to the approximation of the tongue to the posterior pharyngeal wall. Nevertheless they went on to develop clinical picture of P0 despite appropriate airway management. Nearly identical mechanism of UAO was observed by Warner et al19. We postulate that UAO need not be absolute like laryngospasm for the P0 to develop. Even mild to moderately obstructed airway can lead to negative intrathoracic pressure, hypoxia and subsequent P0. Although negative intra-thoracic pressure is the primary pathological event in the development of P0 associated with UAO, hypoxia and hyperadienergic state both contribute to its development. Hypoxia can alter capillary integrity and produce a hyperadrenergic state5,20. This hyperadrenergic state may be associated with a redistribution of blood from the periphery to the pulmonary circuit21 and to increased pulmonary vascular resistance22,23. Furthermore, hypoxia alters peri-capillary pulmonary vascular resistance ma non-uniform fashion24-26 leading to a generalized increase in pulmonary vascular pressure. Finally, hypoxia and metabolic acidosis may produce direct myocardial depression27 and may potentiate other factors known to enhance formation. Peri-operative administration of naloxone has been implicated intriggering PO28,29. However none of our patients received peri-anaesthetic nareotic antagonists. In all our patients with post-exubation laiyngospasm (Case # 9-12) and in the patient with Foley balloon obstruction, florid P0 was evidenced only after the relief of UAO by intubation. It is postulated that UAO creates more positive pressure during expiration which serves as a form of “auto-PEEP” to oppose transudation until the obstruction is removed5,7,30,31. In all these patients, the subsequent course of events was nearly identical to those previously reported6,18,32,34. Lang et al35 reviewed 77 cases of P0 associated with UA0 and observed that 85% required tracheal intubation for a short period, 50% needed mechanical ventilation and about 50% required continuous positive airway pressure or positive end-expiratory pressure. This was in contrast to 66.6% of our patients (8/12) who had to be intubated. All these patients were mechanically ventilated from 6 to 36 hours. Furosemide was administered to all our patients. Herrick, Mahenderan and Penny36 reviewing 19 cases in literature of post- obstructive P0 found diuretic administration in 13 cases (68.4%). The use of diuretic has been questioned by some. in the light of normal pulmonary capillary wedge pressure (PCWP)37. However, it is recommended by others30. Invasive haemodynamic measurements were not performed in any of our patients as data from previous studies suggests a normal haemodynamic picture (central venous pressure, pulmonary artery pressure and PCWP) in these patients3,10,38,39. This is a characteristic finding into following UA0. Invasive haemodynamic monitoring is important in situations where the diagnosis is not clear especially in patients with uncertain iatrogenic volume overload and/or cardiogenic aetiologies. In few of our cases radiological differential diagnosis suggested aspiration pneumonia/PO despite a complete lack of history of regurgitation and aspiration. However, the management of aspirationpneumonia is identical to that of P0 associated with UAO unless an infectious complication ensues40. A rapid resolution of the radiological findings in less than 36 hours in all our cases pointed more towards P0 secondary to UAO than to aspirationpneumonitis. We have observed a variety of causes of UAO which all led to a similar syndrome of rapid onset of P0 followed by quick resolution with appropriate therapy. We should be vigilant therefore not only for post-anaesthetic laryngospasm but also for the partially obstructed airway as may be seen in the drowsy patients and rare iatrogenic causes of airway obstruction. Aggressive haemodynamic monitoring, mechanical ventilation, or drug therapy are not mandatory. Maintenance of adequate oxygenation and a patent airway are the main stays of its treatment.
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