Care of the lung transplant recipient.
That said, the ideal donor has a P/F ratio of 300 or greater on 5 of PEEP, a clear chest radiograph, negative fungal cultures, and no gram negative rods in the sputum cultures. The donor must be HIV negative has no purulent secretions, no hepatitis B or C, and preferably less than 1 week on mechanical ventilation. Ideally the donor should be less than 60 years old. When matching donor to recipient the size of the thorax is the limiting factor.
The cause of death of the donor has limited influence on recipient outcomes except in the case of traumatic brain injury where outcomes may be unfavorably influenced. The donor lung resulting from Traumatic Brain Injury may predispose the recipient to acute rejection episodes and Bronchiolitis Obliterans Syndrome. Again, the procedure is defined within the parameters of organ availability and recipient needs. The ideal candidate has a disease process specific to the lung, less than 65 years old for single or under 60 for double lung transplant. Preoperatively the recipient should be within 10-20% of ideal body weight, be enrolled in a pulmonary exercise program, have completed a psychological workup and be alcohol, drug and tobacco free. If time permits cardiology workup, ventilation/perfusion scans and dental evaluations should be completed. Again, the size of the thorax has been a limiting factor however many innovative procedures are being evaluated to overcome this physical limitation.
Contraindications of recipient status include multiple disease states, the chance of a reoccurrence of a previously treated cancer, smoking within the last four months, current infection, alcohol or drug abuse, poor medical compliance and psychiatric instability. Moderate contraindications or more accurately stated, moderate exclusionary criteria include previous thoracic surgery, homodynamic instability, morbid obesity, advanced multisystem connective tissue disease and any unresolved multi-system pathology. The procedure for single lung transplant requires a posteriolateral thoracotomy and the stabilization of the uninvolved lung. It has been difficult to anticipate the need for bypass however; the personnel and equipment for bypass must always be available. The single lung transplant patient must be recognized as having dramatically disparate pulmonary mechanics which will be discussed in greater detail in this column.
A retrospective review of the literature reveals that bypass has been needed more often in patients with a history of restrictive disease than with obstructive disease. A patient with severe pulmonary hypertension will probably need bypass during the transplant surgery and bypass will be necessitated by changes in the cardiac index and determined on an individual patient basis.
A phenomena unique to the lung transplant recipient is the acute rejection syndrome. As contrasted with kidney transplants which have an acute rejection rate of lass than 40% lung transplants experience acute rejection at a rate of 54%. This is primarily due to the fact that the lung unlike other transplanted organs is in constant contact with and assault from the ambient environment. This relationship creates the potential for chronic inflammation and a persistent inflammatory response. There is enormous opportunity for Bronchiolitis Obliterans Syndrome.
The critical site for any type of complication is the bronchial anastomosis. Circulatory concerns are paramount direct vascular flow is problematic and frequently the site relies on primary flow that is retrograde in nature. Current technique favors a telescoping of the donor and recipient bronchi with an intussuscepting effect providing adequate blood flow to the donor bronchi. There is a significant psychosocial component to the lung transplant recipient. The prior level of disease is an indicator of the patient's level of anxiety and may be linked to their subjective perceptions of dyspnea. In fact the level of anxiety has no corollary in actual impairment post lung transplant. Frequently patients experience a level of anxiety that is a function of the memory of dyspnea prior to transplant and has no basis in objective measurable reality. It is indeed interesting that for these patients there was no correlation between lung function and anxiety. Indeed, it is very interesting to note tat, a vast majority of lung transplant recipients state that they would have the procedure again if they could. The quality of life for the majority of patients improves significantly.
It is not surprising that the patients self-assessment of psychological well being correlated with their social support system. The greater the social support the greater the level of well being on self assessment. Further, in some cases, the subjective self assessments of dyspnea have no corollary in objective reality. Despite improved pulmonary function tests the patients self perception of dyspnea persisted.
The prudent Respiratory Therapist should be aware of the post operative concerns when caring for the lung transplant recipient. Mechanical ventilation in the early post operative course should focus on the transplanted lung as the acutely injured lung. Indeed although the vast majority of lung transplant patients are extubated in a relatively short period of time. The uninvolved lung is ventilated independently and should be treated as an acutely injured lung.
Special consideration must be taken for the patient with pre-operative COPD who receives a single lung transplant. The prudent clinician will recognize immediately the potential for impediment to mechanical ventilation in the presence of the very non-homogenous time constants presented in this scenario. The new lung will have a dramatically dissimilar time constant than the native COPD lung. In this clinical presentation judicious use of very low PEEP should be employed as the native hyper-compliant lung will be prone to hyperinflation and over-inflation. The atypically high compliance and distorted mechanics of the native lung will exhibit tendencies towards dynamic hyperinflation which may be exaggerated with the competing dissimilar mechanical properties of the transplanted lung. Quite, one must remember that in this case the transplanted lung and the native lung are juxtaposed and the native unit will be a unilateral disease state.
In recipients without pre-existing obstructive disease and for those receiving a double lung transplant, low to mid levels of PEEP are now a standard of care. PEEP with special attention and assessment of the Plateau Pressure (PPLAT) will act as a stabilizing force for the lung. As in the orthodox use of PEEP in the transplanted lung PEEP will act to stabilize the lung, provide and enhance the FRC, increase and maintain surface area for diffusion and minimize opening and closing of recruited alveoli. PEEP will also facilitate ventilation triggering and stabilization of the conducting airways.
The transplanted lung recipient must be treated with the caution one would exercise with any patient with the significantly increased potential for acute lung injury and an ARDS-like clinical presentation. I cannot overstate the critical need for the bedside clinician to be cognizant and attentive to the fact that these patients must be weaned in as efficacious a fashion as possible. While receiving mechanical breaths caution and frequent assessment of pulmonary status must be sustained. The clinician should pay special attention to the PPLAT and the pulmonary mechanics.
Clinical goals while receiving mechanical ventilation should be both intelligent and pragmatic. The pH must remain greater than 7.30, PPLAT less than 25 cm. H2O and a Pa02 greater than 55. Additionally, the patient must be given frequent Spontaneous Breathing Trials, (SBT); with a mindful eye on weaning and liberating from mechanical ventilation. One must also be mindful to employ volume limiting strategies. It is mindful practice to utilize tidal volume strategies of 6-8 mls. / kg. ideal body weight with moderate levels of PEEP ranging from 5-15 cm. H2O. This volume limited approach assures adequate ventilation whilst minimizing the potential for excessive stretch and repetitive opening and closing of lung units with disparate time constants. This strategy when engaged by the thoughtful clinician will expedite the potential for weaning while avoiding the risk of injury to the lung.
In cases where the pulmonary graft shows evidence of dysfunction independent lung ventilation must be considered a reasonable alterative. However, this technique must be utilized with a judicious and trained hand. In most cases weaning can be facilitated with a Spontaneous Breathing Trial, (SBT). Standard parameters would include a Rapid Shallow Breathing Index, (RSBI) of 104 or less with a P/F Ratio of grater than 200. The patient who can breathe spontaneously on either a low level of pressure support or a T-Tube for 30-120 minutes should be considered a reasonable candidate for extubation. It is imperative that the post operative lung transplant patient be weaned and extubated as expeditiously as possible.
The cogent therapist will be mindful of the fact that these patients must be weaned in as rapid a fashion as possible, ( I realize I am being redundant here). The transplanted lung must be considered and injured or potentially injured lung. Indeed, in the case of a single lung transplant there is the potential for dramatically different types of acute lung injury in both the transplanted as well as the native lung unit. The patient receiving the double lung transplant may be easier to extubate as the anticipated uniformity of "new" lung units will be easier to ventilate and subsequently wean from mechanical ventilation.
I must comment briefly on the complications due to Ischemic-reperfusion injury, (IRI). IRI is an acute injury or insult to the lung that manifests with increased vascular permeability, lung water and alveolar insult. IRI may occur in as many as 15% of all patients who undergo lung transplantation. In these patients the ventilator management is that of the acutely injured ling. Higher PPLAT, decreased compliance and varying time constants require mindful ventilator management. Indeed, low volume high PEEP strategies must be utilized and a lung saving protocol should be applied. Please note that iN0 therapy has not been proven to prevent IRI.
Patients with pulmonary hypertension will experience ischernic reperfusion injury on a greater scale and to a greater degree.
Infection is probably the major cause of morbidity and mortality for the transplant recipient and I would guide the intellectually curios reader to their ID practitioner as these infections are generally managed on a case by case basis.
The post extubation care of the successfully weaned transplant recipient involves aggressive airway clearance and management. Aerosolized bronchodilators, airway clearance strategies and aggressive pulmonary toilet are the mainstays of post operative care. Anything and I do mean anything and everything that you can do to keep the lungs inflated and secretions mobilized must be clone. The most effective treatment plans involve maximum engagement by the patients and their families. The post operative recovery requires a great commitment from the patient.
The care of the lung transplant recipient can be the most rewarding aspect of any respiratory career. This end of the line therapeutic choice requires the utilization of substantial resources and the physical and psychological commitment and exertion from both the patients and their caregivers. Perhaps the greatest affirmation of the procedure lies in the fact that greater than 95% of the patients who receive lung transplantation report such a dramatic increase in the quality of their lives that they would not hesitate to go through the entire process again. This in spite of the fact that the life expectancy in time remains virtually unchanged. I find it touching that the day to clay experience of living is improved to the point where the patients all agree it was definitely worth enduring the entire process. I will explore further the care of the post transplant recipient in future columns as this topic continues to evolve almost on a daily basis.
by Dave Wheeler, RRT
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|Title Annotation:||CLINICAL RESPIRATORY CARE|
|Publication:||FOCUS: Journal for Respiratory Care & Sleep Medicine|
|Date:||Mar 22, 2012|
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