Survival of hypotensive cats in the ICU | VETgirl Veterinary Continuing Education Podcasts
In this VETgirl online veterinary continuing education podcast, we review the significance of lactate levels in hypotensive cats in the ICU. Can lactate be a prognostic factor for survival?
One of the major challenges we face when managing emergency cases is how to best prepare our clients with our expectations of their pet’s condition and prognosis. We aim to provide owners with our best guess of duration of hospitalization, how aggressive will we need to be with treatments, monitoring, and instrumentation, and whether we think it likely that their pet will survive his or her disease. Unfortunately, we don’t always have enough information to make these predictions at the time of triage with such limited information readily available. If we could recognize particular clinical signs, vital parameters, or blood work abnormalities that could be used as prognostic indicators, this information would benefit both our medical approach to the individual case, and our ability to portray medical expectations to clients regarding their pet’s treatment and outcome.
Lactate, or lactic acid, is a molecule that has gained much publicity in our veterinary research as a potential prognostic indicator for a variety of diseases such as GDV (1), hypotension in dogs (2), IMHA (3), babesiosis (4), and lactate clearance has been found to be of prognostic value both in humans (5) and in canines (6,7). Lactate can accumulate in the body under two general conditions. The most common condition involves tissue hypoxia with normal mitochondrial function. In this anaerobic environment, the pyruvate molecule is converted to lactate and a free hydrogen ion is released as waste. If the body’s natural lactate buffering systems are overwhelmed, the hydrogen ion production and lactate production will accumulate, creating the condition of lactic acidosis. When lactic acidosis develops from tissue hypoxia with normal mitochondrial function, such as with hypoperfusion or severe respiratory disease, this is coined “Type A lactic acidosis.” The other general condition for forming lactate is in the presence of mitochondrial dysfunction or abnormal carbohydrate metabolism, and this is coined “Type B lactic acidosis.” There are further subdivisions to Type B lactic acidosis. Type B1 is from failure to clear lactate (e.g., liver disease, renal failure, sepsis, DM). Type B2 results from drugs or toxins that interfere with oxidative phosphorylation (e.g., carbon monoxide, acetaminophen, ethylene glycol). Type B3 results from inherent mitochondrial defects.
Hypotension has already been proven to be an independent prognostic indicator in critically ill cats (8). Shea et al out of University of Pennsylvania wanted to further evaluate this; they retrospectively evaluated a population of cats with hypotension to analyze lactate as a potential prognostic indicator within all hypotensive cats in their ICU. The authors wanted to evaluate the correlation, if any, between hyperlactatemia in a population of hypotensive cats with survival to hospital discharge. The investigators hypothesized that hypotensive cats with a blood lactate higher than 2.5 mmol/L would have less favorable outcomes than hypotensive cats that did not exhibit hyperlactatemia.
Inclusion criteria included cats admitted to the ICU at the University of Pennsylvania that had documented hypotension (defined as an arterial blood pressure of less than 90 mm Hg measured via Doppler) within an hour of a lactate measurement. Exclusion criteria included a diagnosis (or high index of suspicion) of neoplasia, as neoplasia (e.g., lymphoma) can produce Type B lactic acidosis and influence the degree of hyperlactatemia. Data collected in this study included direct blood pressure, respiratory rate, creatinine, albumin, and PCV measured within the first 24 hours after admission; these data points were recorded for the purpose of calculating the survival prediction index. This index was utilized to compare the group of hypotensive cats with hyperlactatemia to the group of hypotensive cats without hyperlactatemia in regards to their disease severity. By showing that both groups did not differ in their disease severity, this study could isolate lactate for analysis. This study found a significantly lower mean blood pressure in cats with hyperlactatemia. The two groups were found to not be significantly different when comparing survival prediction index (SPI2), PCV, or median duration of hospitalization.
In total, 39 hypotensive cats were included in this study with 12 (31%) having normal lactate levels and 27 (69%) having elevated lactate levels. Diseases causing hypotension included urinary tract disease, gastrointestinal disease, respiratory disease, cardiac disease, sepsis, diabetes mellitus, asthma, seizures, anemia, and 4 cats had masses that were presumed not to be cancerous (NOTE: It should be noted that a definitive diagnosis was never made and cancer cannot be ruled out in this population of cats that were included for analysis. If these masses were neoplastic, there is the possibility that Type B lactic acidosis could have influenced this study’s results.) 17 cats had documented anemia (PCV <25%) and 2 were severely anemic (PCV<20%). Most of these cats had documentation of a pulse oximetry reading >90% to show that hypoxia was not the sole cause for the cat’s hyperlactatemia. Instead, the study assumes that hypotension was the cause for hyperlactatemia in these cats. Unfortunately, this paper does not comment whether pulse oximetry readings were performed in the cats with conditions that may have affected the pulmonary system such as the asthmatic and cardiac patients. Typically, mixed venous oxygen saturation must be significantly low to cause an elevation in lactate due to hypoxemia from pulmonary pathology. It is left assumed that none of these cats had a significantly low enough mixed venous oxygen saturation to result in a hyperlactatemia, and instead their hyperlactatemia is presumed to be the result of hypotension.
An unspecified number of study cats received intravenous isotonic crystalloid therapy to treat suspected hypovolemia based on physical examination findings. Follow up lactates were recorded in 27 cats following IV crystalloid therapy but analysis of these lactate comparisons was not reported in this paper. Of the 39 cats included in this study, only 6 survived. This report does not state how many of the survivors were from the “hyperlactatemic” category nor what diseases were represented in the cats that survived. The median lactate for survivors was 2.3 mmol/L (1.1-2.6 mmol/L) and the median lactate for non-survivors was 4.5 mmol/L (2.4-6.1 mmol/L).
So, what can we take away from this VETgirl podcast? The results from this study suggest that hyperlactatemia can be used as a negative prognostic indicator in hypotensive cats. However, there are a few limitations to this study that warrant consideration to the study’s conclusions. One limitation that plagues many of our veterinary studies is the outcome of “euthanasia.” This paper highlights the importance of owner’s decision to euthanize and the influence this outcome has on study results because we do not know if the decision was financially driven or truly a reflection of the severity of the patient’s disease.
A possible complication is that cats in this study were administered medications known to produce a Type B lactatemia that may have influenced the level of hyperlactatemia documented in these cats. The investigators did look into this possibility and found no correlation between administration of these medications and hyperlactatemia. Another factor that may have impacted the study results is that some of the cats in this study had known diseases that could produce a type B hyperlactatemia independent of hypoperfusion from hypotension. This article appropriately identifies that cats with a Type B hyperlactatemia may have influenced the survival rate in cats presenting with both hyperlactemia and hypotension. In these patients, such as the ones with kidney disease, liver disease or potentially neoplastic processes (such as lymphoma), the lactate level may not be attributed solely to hypoperfusion. It would be beneficial for a study to exclude cases with Type B hyperlactatemia, and focus only on cats with hypoperfusion. An add-on to such a study would be to focus on whether correction of hypoperfusion improved lactate levels and had any correlation to survival. Despite the study not excluding the various disease processes that can contribute to hyperlactatemia, we can still utilize this information for its intent, which is to be able to use lactate as a negative prognostic indicator in the general group of cats presenting with hypotension. Lastly, as many of our canine studies have suggested, lactate clearance may be of more prognostic value than a single lactate measurement. The retrospective nature of this study limited the investigators’ ability to make any conclusions regarding whether lactate clearance would have any correlation to survival or duration of hospitalization in hypotensive cats.
Conclusion
Cats presenting to the intensive care unit with both hypotension and hyperlactatemia may have a worse prognosis than cats presenting with hypotension without concurrent hyperlactatemia. Despite the limitations of this retrospective study, there may be useful prognostic information when looking globally at cats presenting with hypotension from any cause. Often times on an emergency basis, we do not know the patient’s underlying disease process (such as liver disease, cardiopulmonary disease vs. primary respiratory disease, sepsis, etc. ). In these cases, the finding of hypotension and hyperlactatemia may help the emergency clinician to provide prognostic information to owners before embarking treatment of their pet. This information would, at the very least, help us to inform owners that their cat will require more aggressive medical therapies and may have a poorer prognosis despite treatment.
References:
1. Beer KAS, Syring RS, Drobatz KJ. Evaluation of plasma lactate concentration and base excess at the time of hospital admission as predictors of gastric necrosis and outcome and correlation between those variables in dogs with gastric dilatation-volvulus: 78 cases (2004–2009). J Am Vet Med Assoc 2013; 242:54-58.
2. Ateca LB, Dombrowski SC, Silverstein DC. Survival analysis of critically ill dogs with hypotension with or without hyperlactatemia: 67 cases (2006–2011). J Am Vet Med Assoc 2015; 246:100-104
3. Holahan ML, Brown AJ, Drobatz KJ. Retrospective Study: The association of blood lactate concentration with outcome in dogs with idiopathic immune-mediated hemolytic anemia: 173 cases (2003–2006). J Vet Emerg Crit Care 2010; 20:413-420.
4. Nel M, Lobetti RG, Keller N, et al. Prognostic Value of Blood Lactate, Blood Glucose, and Hematocrit in Canine Babesiosis. J Vet Intern Med 2004; 18:471-476.
5. Jansen T, van Bommel J, Bakker J. Blood lactate monitoring in critically ill patients: A systematic health technology assessment*. Crit Care Med 2009; 37:2827-2839.
6. Stevenson CK, Kidney BA, Duke T, et al. Serial blood lactate concentrations in systemically ill dogs. Vet Clin Path 2007; 36:234–239.
7. Cortellini S, Seth M, Kellett-Gregory LM. Plasma lactate concentrations in septic peritonitis: A retrospective study of 83 dogs (2007–2012). J Vet Emerg Crit Care 2015; 25:388–395.
8. Silverstein DC, Wininger FA, Shofer FS, et al. Relationship between Doppler blood pressure and survival or response to treatment in critically ill cats: 83 cases (2003–2004). J Am Vet Med Assoc 2008; 232:893-897.
9. Shea EK, Dombrowski SC, Silverstein DC. Survival analysis of hypotensive cats admitted to an intensive care unit with or without hyperlactatemia: 39 cases (2005-2011). J A Vet Med Assoc 250(8):887-893.
Abbreviations:
DM – Diabetes Mellitus
SPI2 – survival prediction index
Only VETgirl members can leave comments. Sign In or Join VETgirl now!