Difficult Decisions in Small Animal Fluid Therapy: Pulmonary Contusions

Dr. Philip R Judge BVSc MVS PG Cert Vet Stud MACVSc (VECC; Medicine of Dogs)

Difficult Decisions in Small Animal Fluid Therapy

Introduction

Pulmonary contusions are defined as alveolar haemorrhage and pulmonary parenchymal destruction following blunt chest trauma1,2. Pulmonary contusions result from energy transfer to the pulmonary parenchyma following trauma2. As such, the severity of contusion depends on several factors, including the location and direction of the force, velocity, weight and size of the force impulse, flexibility of the chest wall, and motion of the body when the trauma occurs2. Animal studies have demonstrated the speed of the chest compression-decompression insult to be the most significant factor in causing damage, with secondary factors such as chest wall elasticity, and even aspiration of gastric acid also influencing the extent of injury2,3

Lung contusion develops as a result of damage to the compressed lung caused by an external force, as mentioned above. Shearing force occurs between alveolar and hilar tissues within the lungs, because these tissues are of different density, and therefore accelerate and decelerate at different rates4. Additionally, compression-related damage occurs to both alveolar and vascular tissue, resulting in haemorrhage, cell damage, and subsequent activation of coagulation and inflammatory cascades2.4.

In humans, pulmonary contusions are evident in 25-35% of all blunt chest trauma patients1, with the presence of pulmonary contusions in trauma patients increasing mortality risk2.

Pulmonary contusions lead to reduced gas exchange, increased pulmonary vascular resistance and decreased pulmonary compliance2. Secondary lung injury results from an inflammatory response to tissue injury, which can lead to acute respiratory distress syndrome5,6.

Clinical manifestations of pulmonary contusions include tachypnoea, respiratory distress, and hypoxaemia1, with symptoms typically developing within 6-24 hours following injury, with severity increasing as the inflammatory response to tissue injury intensifies2. These symptoms may be superimposed on concurrent thoracic injuries, including pneumothorax, haemothorax, rib fractures, diaphragmatic hernia, and myocardial contusions, as well as injuries at distant sites, with injuries including long bone fractures, skin lacerations, and abdominal organ contusion among others2,6.

The diagnosis of pulmonary contusions is frequently made based on a history of recent acute trauma, clinical signs suggestive of contusions, and evidence of B-lines on trans-thoracic lung ultrasound2. Thoracic radiographs have low sensitivity for pulmonary contusions within the first 24 hours2. Computed tomography has high sensitivity for the diagnosis of pulmonary contusions2, but in canine and feline patients, requires general anaesthesia to safely perform, which carries some risk in the acutely traumatised patient.

The differential diagnosis of pulmonary imaging studies that mimics the appearance of pulmonary contusions includes pneumonia, pulmonary oedema of other causes (congestive heart failure, neurogenic pulmonary oedema, etc.)2.

Treatment of pulmonary contusions is largely conservative, involving oxygen supplementation, judicious use of intravenous fluid therapy, lung-protective ventilation assistance, analgesia and management of comorbidities as necessary1,2

The Issue of Fluid Therapy in the Management of Pulmonary Contusions

Fluid therapy is one of the most important aspects in the management of the post-trauma patient. Intravenous fluids are used to treat shock, correct hydration deficits, and to provide for maintenance fluid requirements in patients that are unable to drink normally6.

Fluid therapy, however, could theoretically worsen lung function, by increasing capillary hydrostatic pressure, increasing extravasation of fluids into the pulmonary interstitium, and increasing lung water volume6. In the normal patient, compensatory mechanisms including increased lymphatic drainage result in elimination of excessive lung fluid. However, this risk of increasing lung water is potentially higher in patients with pulmonary contusions, in which capillary damage, haemorrhage and lung trauma further contribute to leukocyte chemotaxis and cytokine production, causing pulmonary vasodilatation, glycocalyx damage, and movement of fluid, protein and cells into the pulmonary parenchyma6.

Administration of appropriate intravenous fluid therapy to patients with pulmonary contusions has long been an area of controversy, owing to concerns about excessive fluid administration raising pulmonary capillary pressures and contributing to worsening of pulmonary oedema6,7

No controlled studies in naturally occurring pulmonary contusions have been performed in cats or dogs to determine the optimal fluid resuscitation technique6. However, experimental animal studies, and several clinical studies in people have been performed:

  1. An experimental model of pulmonary contusions in pigs showed that pigs resuscitated with a combination of hypertonic saline and dextran had lower extravascular lung water and higher PaO2 levels than subjects resuscitated with lactated Ringer’s solution only8.
  2. In another study, pigs with experimentally-induced pulmonary contusions were resuscitated to a mean arterial pressure of 70 mm Hg using either normal saline, low-volume saline plus norepinephrine, or hypertonic saline in combination with hydroxy-ethyl starch. When compared with a control group of uninjured pigs, all the study pigs developed increased extravascular lung water. Pulmonary oedema was apparent in both the saline and the hypertonic saline-hetastarch group. All treated pigs had reduced oxygen saturation9.
  3. A study in 2009 explored the concept of biphasic (early and late) fluid management of human patients suffering septic shock complicated by acute lung injury – which has many facets similar to those observed in pulmonary contusions – including the presence of high pulmonary capillary permeability and inflammation. Their study evaluated the relationship between adequate initial fluid resuscitation (AIFR), where patients received an initial fluid bolus corresponding to a positive fluid balance, and conservative late fluid management (CLFM), defined as an even-to-negative fluid balance measurement during the first 7 days after lung injury. The results revealed both AIFR and CLFM to have lower mortality rates if used separately when compared to not being used at all; however, mortality rates were lowest if used in combination, suggesting an additive effect of both fluid strategies in reducing mortality10.
  4. Most studies demonstrate little difference in patient survival, requirement for ventilation therapy, or lung function when isotonic crystalloid fluids, colloid fluids or hypertonic crystalloid fluids are used for patient resuscitation. However, one study in humans, and one in pigs, demonstrated lower lung water volumes in patients with acute lung injury in sepsis that received synthetic colloids (hydroxy-ethyl starch) than those that did not, suggesting there may be benefit in providing colloids in some patients with severe inflammatory lung disease8,11.

Summary of Recommendations for Fluid Therapy in Pulmonary Contusions

Based on the results of these studies, and clinical reviews1,2,6,11, the following general guiding principles for fluid therapy use in patients with pulmonary contusions may be made:

  1. When establishing fluid therapy plans for patients with traumatic pulmonary contusions, clinicians must achieve a balance between limiting pulmonary vascular pressures and providing adequate fluid resuscitation to avoid hypoperfusion complications of other organ systems
  2. Administration of large volumes of isotonic crystalloids, e.g., lactated Ringer’s solution should be avoided, particularly in the post shock-resuscitation period, as they are associated with excessive lung water accumulation and a deterioration of respiratory function and gas exchange. 
  3. Given many patients with pulmonary contusions have traumatic injury to other organ systems (such as head trauma, fractures, open wounds, etc.) – all of which require positive fluid balance to ensure adequate tissue oxygen delivery for optimal healing to take place, a strategy of fluid resuscitation to restore cardiac output and tissue oxygen delivery in acute resuscitation, followed by a more conservative fluid administration protocol seems appropriate for most patients with pulmonary contusions.
  4. Practical recommendations – It is difficult to provide recommendations regarding fluid resuscitation in pulmonary contusions for all patients, as all patients are different, and require individual assessment. However, the following may be used as a guide:
    1. For acute patient resuscitation
      • Lactated Ringers’ solution 10 ml/kg IV over 10 minutes, and repeated until clinical signs of shock have resolved, systolic arterial blood pressure is 100 mm Hg, or mean arterial blood pressure is above 70 mm Hg
      • A single bolus of hydroxy-ethyl starch @ 3-5 ml/kg may be considered in some patients, (those without sepsis or kidney dysfunction), and may result in lower lung water volume. However, the influence on survival is unclear at the present time, and a firm recommendation cannot be made6.
    2. Following acute volume resuscitation
      • Lactated Ringer’s solution or other buffered poly-ionic isotonic solution should be administered at rates to provide for maintenance fluid requirements
  5. Monitoring the patient – regular assessment of cardiovascular status (heart rate, pulse quality, mucous membrane colour, blood pressure, etc.) and respiratory function (respiratory rate, effort, pulse oximetry, lung ultrasound evaluation, etc.) is essential to aid in determining the progress of the patient, and the requirement for further intervention, including mechanical ventilation. Blood gas analysis and venous blood lactate can also be used as a monitoring tool to evaluate global tissue perfusion adequacy, and the effectiveness of pulmonary gas exchange1,2,6,11.

Conclusion

Pulmonary contusions result in significant alterations to pulmonary structure and function. Fluid therapy has the potential to contribute to worsening clinical outcome in these patients – but is required to ensure normal tissue perfusion in body tissues following acute trauma.

In the short term (minutes to hours), fluid therapy is of less concern in promotion of lung injury/dysfunction than in long-term therapy, where there is potential for significant positive water balance over many hours of greater-than-maintenance fluid rates6.

Most studies have identified that a negative or neutral fluid balance after resuscitation is associated with better lung function. Consequently, conservative fluid approaches are currently preferred following initial emergency patient resuscitation, unless there is a compelling reason for higher rates of fluids6.

References

  1. Požgain, Z., Dalibor Kristek, Ivica Lovrić, Goran Kondža, Matea Jelavić, Jakub Kocur, and Mirjana Danilović. “Pulmonary contusions after blunt chest trauma: clinical significance and evaluation of patient management.” European Journal of Trauma and Emergency Surgery 44, no. 5 (2018): 773-777.
  2. Rendeki, Szilárd, and Tamás F. Molnár. “Pulmonary contusion.” Journal of Thoracic Disease 11, no. Suppl 2 (2019): S141.
  3. Viano, David C., and Ian V. Lau. “A viscous tolerance criterion for soft tissue injury assessment.” Journal of Biomechanics 21, no. 5 (1988): 387-399.
  4. Boyd, ARTHUR D. “Lung injuries.” Hood RM, Boyd AD, Culliford AT. Thoracic Trauma. Philadelphia: Saunders (1989): 153-155.
  5. Bakowitz, Magdalena, Brandon Bruns, and Maureen McCunn. “Acute lung injury and the acute respiratory distress syndrome in the injured patient.” Scandinavian journal of trauma, resuscitation and emergency medicine 20, no. 1 (2012): 1-10.
  6. Rozanski, Elizabeth, and Alex Lynch. “Fluid Therapy in Lung Disease.” Veterinary Clinics: Small Animal Practice 47, no. 2 (2017): 461-470.
  7. National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network. “Comparison of two fluid-management strategies in acute lung injury.” New England Journal of Medicine 354, no. 24 (2006): 2564-2575.
  8. Gryth, Dan, David Rocksén, Dan Drobin, Henrik Druid, Eddie Weitzberg, Jenny Bursell, Lars-Gunnar Olsson, and Ulf P. Arborelius. “Effects of fluid resuscitation with hypertonic saline dextrane or Ringer’s acetate after nonhemorrhagic shock caused by pulmonary contusion.” Journal of Trauma and Acute Care Surgery 69, no. 4 (2010): 741-748.
  9. Prunet, Bertrand, Nicolas Prat, David Couret, Pierre-Yves Cordier, Sophie De Bourmont, Dominique Lambert, Yves Asencio, Eric Meaudre, and Pierre Michelet. “Midterm effects of fluid resuscitation strategies in an experimental model of lung contusion and hemorrhagic shock.” Shock 41, no. 2 (2014): 159-165.
  10. Murphy, Claire V., Garrett E. Schramm, Joshua A. Doherty, Richard M. Reichley, Ognjen Gajic, Bekele Afessa, Scott T. Micek, and Marin H. Kollef. “The importance of fluid management in acute lung injury secondary to septic shock.” Chest 136, no. 1 (2009): 102-109.
  11. Roch A., Guervilly C. and Papazian L. (2011). Fluid management in acute lung injury and ARDS. Annals of intensive care, 19(16).

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