Table 1. Summary table of included studies Articles Population Intervention Comparator Outcomes Study design Brief summary of results Significant indicators Level of evidence et al., 2003 Adult patients (n=4,535) in 8 ICUs in the US admitted with central venous catheter (CVC) Nurse-patient ratio; ICU nurse or float nurse; patient care ratios (number of PCAs per shift per 100 patients) Proportion of float nurse-days (float nurse defined as nurse who had worked in the unit < 1 year) CVC-associated bloodstream infections (BSIs) Prospective cohort study Risk for CVC-BSIs not associated with ratio or ratio but was associated with proportion of float nurse-days. Risk for CVC-BSI 2.6 times higher in patients cared for by float nurse > 60% of time; rate ratio 2.61 (1.21 to 5.59) CVC-BSIs 3e Amaravadi, et al., 2000 Adult patients (n=366) who had oesophageal resection in 32 ICUs in 32 acute care hospitals in Maryland, US time nurse patient ratio of 1 nurse to 1-2 patients Night time nurse patient ratio of 1 nurse to 3 or more patients In-hospital mortality, length of stay, pneumonia, reintubation, septicaemia, aspiration, postoperative infection, MI, cardiac arrest, surgical complications, renal failure Cohort study 39% increase in median LOS, OR 2.4 pneumonia, OR 2.6 reintubation, OR 3.6 septicaemia Hospital length of stay, pneumonia, reintubation, septicaemia 3e nurse-
Benbenbishty, et al., 2010 Adult patients physically restrained (n=669) or chemically restrained (n=566) in 34 ICUs in nine European countries ratio each shift Day and night time patient ratios of 1:1, 1:2, 1:3 or 1:4. Physical and chemical restraint use (note, results for chemical restraint use not reported in detail) Cross-sectional Physical restraint more likely to be used for patients who were in units with lower daytime ratio (χ2 = 17.17, p = 0.001). Physical restraint use 3e Blegen et al., 2011 Adult patients (approx. 1.1 million) in 54 US hospitals, staffing data from 285 ICUs, 587 general wards, outcomes measured at hospital level Total hours of care from RN/LPN/NA per patient day and skill mix (RN percent) Comparing levels between hospitals - no specific comparator In-hospital CHF mortality, decubitus ulcer, failure to rescue, infection due to medical care, postoperative sepsis, rate of LOS > expected Cross sectional Significant association between infection due to medical care and total ICU staffing and between ICU RN skill mix and postoperative sepsis in non-safety-net hospitals. Significant associations between CHF mortality and failure to rescue and ICU RN skill mix in hospitals Infection due to medical care, postoperative sepsis, in-hospital CHF mortality, failure to rescue 4b Blot et al., 2011 Adult ICU patients (n=1658) treated for pneumonia or receiving invasive mechanical ventilation ≥ 48 hours in 27 ICUs in 9 European countries. Patient-to-nurse ratio Staffing level ratios: Model I (1:1, 2:1, 2.5:2, & 3:1); Model II (1:1 & >1:1); Model III (2:1 & >2:1); Model IV (<3:1 and 3:1). pneumonia (VAP) Prospective, observational survey No significant difference in VAP rates in ICUs with patient-to-nurse ratio of 2:1 or > 2:1. A 1:1 ratio was associated with lower risk for VAP but not significant after adjustment for confounding covariates. Non-significant association between higher nurse staffing levels and reduced risk for late-onset VAP. None 3e
Bolton et al., 2007 Falls data from 65 step-down units and pressure ulcer and restraint use data from 40 units in Californian hospitals Hours of nursing care/patient day; nurse/patient ratios and skill mix pre/post introduction of mandated nurse staffing ratios Staffing changes pre/post introduction of mandated staffing ratios Falls and falls with injury; pressure ulcers; restraint use Longitudinal study pre/post mandated nurse staffing ratios Significant association between % of care by RNs & any Significant positive association between higher total hours of care per patient day & higher prevalence of stage II+ pressure ulcers - No significant results or trends in relationship between staffing variables & restraint prevalence. Falls, falls with injuries, pressure ulcers 3e Checkley et al., 2014 69 ICUs in 42 hospitals centres in the US. May include some paediatric ICUs. No information on patient numbers No intervention, Bed-to-nurse ratio of 1.5:1 Bed-to-nurse ratio of 2:1 ICU mortality Prospective observational study Significantly lower mortality, 1.8% lower when the bed-to-nurse ratio decreased from 2:1 to 1.5:1 ICU mortality 3e Chittawatanarat et al., 2014 155 ICUs in 87 hospitals in Thailand (90% of sample were adult ICUs but some paediatric). 104,046 patient admissions used for mortality calculations Average ratio (NPR) each shift Higher/lower NPR Mortality (monthly crude mortality rate), average ventilator days, ICU length of stay Retrospective observational study Increased NPR significantly associated with decreased number of ventilator days (-2.08 [-5.377 to -0.166], p = 0.037). NPR not significantly associated with crude mortality or ICU-LOS. Ventilator days 3e Cho et al., 2008 Adult patients (n=27,372) in ICUs in 236 Korean hospitals No specific intervention No specific comparator In-hospital mortality Cross sectional Significant relationship between nurse patient ratio and mortality in secondary hospitals (OR 1.43) In-hospital mortality 4b
Cho & Yun, 2009 Adult patients (n=6,957) with acute stroke admitted to ICUs in 185 Korean hospitals (No of ICUs not given as for hospitals with more than 1 ICU results were aggregated) Bed-to-nurse (RN) ratio Bed-to-nurse ratios categorised into 9 staffing grades (Grades Grade 1 (best) number of beds per nurse < 0.50, Grade 9 (worst) ratio is ≥ 2.0. (Note, for the analysis, staffing grades collapsed into four groups: 1-3, 4 & 5, 6 & 7, and 8 & 9.) In-hospital mortality & 30-day mortality, Cross sectional Worsening ICU staffing associated with stepwise decrease in the proportion of low 30-day mortality group. Hospitals with Grades 4 & 5 ICU staffing less likely to have high mortality than reference group (OR, 0.26; 95% CI, 0.09-0.80). Better ICU staffing grades (1-3 and 4 & 5) had lower probability of classification into high 30-day mortality group. In-hospital mortality and 30-day mortality 4b Dancer et al., 2006 Adult patients (n=174) in one ICU in Scotland No intervention - measured the relationship between workload and number of nurses on shift and described understaffing as weeks staffed below the line of best fit None MRSA Retrospective observational study No significant relationship between understaffing and MRSA acquisition None 4c Dang et al., 2002 patients (n=2,606) undergoing abdominal aortic surgery admitted to ICU in 38 hospitals in Maryland No specific intervention, used ratios (NPR) Compared high-intensity nurse staffing (NPR ≤ 1:2 on both day & night Low-intensity nurse staffing (NPR ≥ 1:3 on both day & night shifts); nurse staffing (NPR ≥ 1:3 on day or Cardiac complications (acute myocardial infarction, cardiac arrest, cardiac complications respiratory complications Retrospective, longitudinal study Medium-intensity nurse staffing: significant association with cardiac complications OR 1.78, (1.16-2.72); other complications OR 1.74, (1.15-2.63); cardiac complications after a procedure OR 2.10, Cardiac complications, Respiratory complications, complications 3e hospital
shifts) to two other groups night shift but not both); (aspiration, pneumonia, pulmonary insufficiency mechanical ventilation > 96 h, tracheal reintubation); Other complications (acute renal failure, septicaemia, platelet transfusion) Low-intensity nurse staffing: significant association with respiratory complications OR 2.33, (1.50-3.60); pulmonary insufficiency OR 5.11, (2.89-0.04); mechanical ventilation after 96 h OR 2.39, reintubation OR 2.09, (1.47-3.03). Dimick et al., 2001 Adult patients (n=569) who had hepatic resection in 33 non-federal acute care hospitals in Maryland, US 1 nurse for 1 or 2 patients 1 nurse for 3 or 4 patients In-hospital mortality, postoperative complications including aspiration, pulmonary insufficiency, pneumonia, reintubation, septicaemia, postoperative infection, cardiac complications, cardiac arrest, acute MI, acute renal failure, LOS Cohort study No significant difference between the two groups on in-hospital mortality, length of stay. Significant association between fewer ICU nurses at night and reintubation, no significant associations with other postoperative complications. Reintubation 3e procedure,
Dodek et al., 2014 Patients (n=42,381) in 37 ICUs in British Columbia and 20 ICUs in Ontario (n=14,165). (Sample may include paediatric patients) No specific intervention. Compared ratio ratio 1:1 vs 1:2 Hospital mortality, ICU length of stay (ICU LOS), length of stay (LOS) Cross-sectional OR 2.08 (1.45-2.97) nurse patient ratio 1:1 vs 1:2 in BC and 1.37 (0.81-2.33) in Ontario for mortality; RR 1.4 (1.09-1.79) in BC and 0.99 (0.80-1.23) in Ontario for ICU LOS; RR 1.38 in BC and 1.27 in Ontario for Hospital LOS In-hospital mortality, ICU LOS, Hospital LOS 3e Dorsey et al., 2000 Adult patients (n=52) in a surgical ICU in a general hospital in San Francisco No intervention - used the mean staffing quotient for each of the study No specific comparator Presence of Enterobacter cloacae or Serratia marcescens in the blood or CSF Retrospective cohort study Temporal relationship between infection outbreaks and lower staffing. During outbreak months, on average one less staffed empty bed each shift compared to non-outbreak months Enterobacter and Serratia presence 3e
Falk & Wallin, 2016 Patients over 15 years (n=33,032) in ICUs in 7 hospitals in Sweden Nurse to patient ratio; nurse assistant to patient ratio Compared hospitals which had 1:1, 0.6:1 and 0.5:1 ratios Length of ICU stay, ICU mortality, 30-day mortality, estimated mortality risk, unplanned extubation, time on ventilation Longitudinal Nurse to patient ratio of 0.5-0.6 per patient - patients spent longer on ventilation, higher ratios significantly longer length of stay. Higher mortality in hospitals with lowest ratios of registered staff. Other results not reported. Time on ventilation, length of stay, mortality 3e
Glance et al., 2012 Adult patients (n=70,142) admitted with trauma from 77 Level I and II hospitals in the United States (sample may include paediatric patients) Hours per Patient Day (HPPD) for registered nurses (RN), licensed practical nurses (LPN), and nurses' aides (NA) (i) Bottom & top quartiles of LPN HPPD;(ii) staffing ratio of LPN staffing to total nurse staffing In-hospital mortality, healthcare associated infections, (FTR) sectional 15 min increase in LPN HPPD associated with death OR 1.15 (1.05, 1.25) and sepsis OR 1.27 (1.11, 1.45). 1% increase in ratio of LPN to total nursing time associated with mortality OR 1.04 and sepsis OR 1.06 (1.03-1.10). 15 min increase in NA HPPD associated with pneumonia OR 0.92 (0.87, 0.98). Hospitals in highest quartile of LPN staffing had 3 excess deaths per 1000 patients and 5 more episodes of sepsis than hospitals in lowest quartile LPN staffing. In-hospital mortality; sepsis; pneumonia 4b Grundmann et al., 2002 Adult patients (n=782) in one ICU in a tertiary care hospital in the UK No intervention - used the average number of nurses per shift over a 24 hour period No specific comparator Presence of MRSA Observational study Relationship between nursing staff deficits (greater than 1:1 nurse/patient ratio) and development of MRSA - Risk ratio 1.05 (1.02, 1.08) MRSA presence 3e Halwani, et al., 2006 Adult ICU patients (n=430) with ICU stay > 48 h in one hospital in Nottingham, UK Nurse-patient ratio Understaffing defined as less than optimal staffing level (1:1 during 24-h period) Cross-contamination with nosocomial infections Prospective cohort study Relationship between cross-contamination and patients experiencing understaffing for whole ICU stay compared with patients who were not exposed to understaffing OR 3.07 (1.41-6.66) Cross-contamination with nosocomial pathogens 3e
He et al., 2012 Fall rates among adult patients in 8915 nursing units in 1171 US acute care hospitals (included 1994 critical care units & 1328 units) No intervention - used annual average nursing hours per patient day and percent of total hours of care provided by RNs No specific comparator Inpatient falls Retrospective observational study Higher HPPD and RN skill mix were significantly associated with lower fall rates (IRR: 0.95 for HPPD and 0.99 for RN skill mix) for all units together, associations consistent at unit level, results not reported Fall rate 3e Hugonnet, Chevrolet, & Pittet, 2007 Adult ICU patients (n=1,883) with ICU stay > 48 h in Geneva, Switzerland workload measured by 24-h nurse-to-patient ratio. Low staffing level Nosocomial infection Prospective cohort Significant association between nurse – patient ratio and nosocomial infections (RR 0.69 (0.50 – 0.95) Nosocomial infection 3e Hugonnet, Uçkay, & Pittet, 2007 Adult patients (n=2470) admitted to a medical ICU in Switzerland No intervention - calculated a 24 hour nurse/patient ratio and a mean ratio per shift No specific comparator pneumonia Prospective cohort study Significant association between nurse/patient ratio and late-onset VAP HR: 0.42 (0.18, 0.99) but not for early-onset VAP HR: 0.78 (0.42, 1.45) Late-onset ventilator associated pneumonia 3e Hugonnet, Villaveces & Pittet, 2007 Adult patients (n=366) admitted to a medical ICU in Geneva, Switzerland Nurse/patient ratio Lower nurse staffing (< 1.9) Nosocomial infection Case-crossover and cohort designs Relationship between nurse-patient ratio and infection. For cohort design OR 1.47 (1.03, 2.11); for case-crossover design logistic analysis OR 1.89 (1.16, 3.07) and GEE analysis OR 1.58 (1.08, 2.33) Nosocomial infection 3c & 3d
derangements, respiratory failure, pulmonary embolism, DVT relationships found. Higher non-RN HPPD related to lower O/E ratios of PE and DVT Pronovost et al., 2001 Adult patients (n=2,606) aortic surgery in ICUs in 38 Maryland hospitals Nurse-to-patient ratio during day and evening Nurse-to-patient ratio categorised as: 1:1 or 1:2 = "More ICU nurses"; ratios of 1:3 or 1:4 = "fewer ICU nurses" Pulmonary insufficiency, tracheal reintubation, cardiac complications a acute renal failure, septicaemia, acute myocardial infarction, cardiac arrest, surgical complications after a procedure, puncture, perforation or haemorrhage during surgery, reoperation for bleeding Observational study Nurse patient ratios of 1:3 or 1:4 were associated with increased risk for any complication; RR 1.7 (1.3 to 2.4), any medical complication; RR 4.5 (1.5 to 2.9), pulmonary insufficiency after procedure; RR 4.5 and reintubation; RR 1.6 (1.1 to 2.5). All other outcomes non-significant. Any complication, any medical complication, pulmonary insufficiency after procedure, and reintubation 3e Robert et al., 2000 Adult patients in a surgical ICU in one hospital in the US - 28 patients with BSI and 99 controls No intervention - looked at ratio in 3 days prior to index date as the exposure variable No specific comparator Nosocomial bloodstream infections Case-control study Significant relationship between BSI and lower nurse to patient ratios and higher pool nurse to patient ratios BSI 3d
night shifts but didn't include this as a nurse/patient ratio partial thromboplastin time Shuldham et al., 2009 (n=23,192) and paediatric (n=2,315) cardiac, cardiothoracic, and respiratory patients admitted to critical care areas (intensive care and high dependency units) of two NHS Trust hospitals in England Nursing hours per patient day (NHPPD) for permanent and temporary nursing staff (hospital staff bank or agency nurses) at ward/unit level Higher/lower NHPPD Pressure sores, patient falls, upper gastrointestinal (GI) bleed, pneumonia, sepsis, shock, deep vein thrombosis (DVT) Retrospective observational study Significant association between sepsis and the of permanent nursing staff hours. IRR 0.985 (0.972 - 0.998) and IRR 0.983 (0.972 - 0.995). No other significant associations. Sepsis 3e et al., 2007 Adult patients (n=15,902) in 51 ICUs in 31 hospitals in the US. No specific intervention - measured RN hours per patient day from monthly data and divided these into quartiles Compared the 2nd, 3rd and 4th quartiles to the 1st quartile Central line associated bloodstream infections, ventilator-associated pneumonia, catheter-associated urinary tract infections, 30-day mortality, pressure ulcer Observational study Units with higher staffing had lower incidence of CLBSI (3rd quartile OR 0.32), VAP (4th quartile OR 0.21), 30-day mortality (3rd quartile OR 0.81) and PU (3rd quartile OR 0.69). Other quartiles for these outcomes and all quartiles for CAUTI not significant CLBSI, VAP, 30-day mortality and PU 4b
Tarnow-Mordi et al., 2000 Adult medical and surgical patients (n=1,025) admitted to an ICU in a hospital in Scotland ICU workload measured by occupancy, ratio of occupied to appropriately staffed beds, and nursing requirement per shift Overall ICU workload during stay categorised as moderate, intermediate, and high (composite measure of average nursing requirement per occupied bed per shift and peak occupancy in any shift in the stay). In-hospital mortality Retrospective analysis from prospective cohort study Adjusted mortality was related to (i) ratio of occupied to appropriately staffed beds per shift and (ii) peak occupancy. In-hospital mortality 3e van den Heede et al., 2009 patients (n=9054) admitted to 28 Belgian acute care hospitals for a CABG or heart valve procedure. No specific intervention - calculated NHPPD for each nursing unit Modelled the outcome to consider the result if all units increased their staffing to the 75th percentile in-hospital mortality Observational study No significant association between ICU staffing levels and mortality None 3e van der Kooi et al. 2015 Adult patients (n=379) admitted to 25 ICUs in 25 hospitals in the Netherlands Nurse to patient ratio ≤ 1 to 1 Nurse to patient ratio >1 to 1 Restraint use Cross-sectional No significant relationship between restraint use and to patient ratio None 4b West et al., 2014 Adult patients (n=38,168) admitted to 65 ICUs in England Number of FTE permanent direct care registered nurses (RNs) and health care assistants Lower number of FTE permanent direct care RNs Mortality (in-hospital and in-ICU) Observational Significant relationship between number of direct care nurses per bed and ICU mortality; OR 0.90 (0.84, 0.97) and hospital mortality; OR 0.92 (0.87, 0.98). ICU mortality and mortality 3e
Whitman et al., 2002 NSO rates in 95 patient care units across 10 adult acute care hospitals in the US. Included 15 cardiac ICUs and 7 non-cardiac ICUs No specific intervention - calculated NHPPD No specific comparator Central line infections, pressure ulcers, falls, medication errors, restraint application duration Secondary analysis of prospective observational data No significant relationships between staffing and any outcome for non-cardiac ICUs. Significant relationship between staffing and medication error in cardiac ICUs (r = -.55), all other relationships in cardiac ICUs Medication errors 4b Levels of evidence: Joanna Briggs Institute. (2013). New JBI levels of evidence. Adelaide, SA, Joanna Briggs Institute. Retrieved from http://joannabriggs.org/assets/docs/approach/JBI-Levels-of-evidence_2014.pdf
Table 2. Quality of cohort, observational and cross-sectional studies Did the address a clearly focused issue? Did the authors use an appropriate method to answer their question? Was the cohort recruited in an appropriate way? Was the exposure accurately measured to minimise bias? Was the outcome accurately measured to minimise bias? Have the authors taken account of the potential confounding factors in the design and/or in their analysis? Was the follow up of subjects complete enough? Was the follow up of subjects long enough? Quality rating Alonso-Echanove et al., 2003 ? F Amaravadi et al., 2000 G Benbenbishty et al., 2010 X N/A N/A F Blegen et al., 2011 X X X X N/A N/A P